1. Catalight Young Scientist Symposium: Light Driven Catalysis

Europe/Berlin
Online Conference

Online Conference

CYSS2020 will be hosted online using Zoom. The poster session will follow a dual-format approach using a chat-platform and videoconference rooms.
Carolin Müller (Leibniz Institute of Photonic Technology), Elisabeth Hofmeister (Leibniz Institute of Photonic Technology), Julian Hniopek (Leibniz Insitute of Photonic Technology), Ludwig Schwiedrzik (University of Vienna), Mathias Micheel (Leibniz Institute of Photonic Technology), Miftahussurur Putra (Ulm University), Pascal Wintergerst (Ulm University)
Description

The CataLight Young Scientist Symposium (CYSS) is a newly established conference organized by PhD students and junior PostDocs of SFB/TRR 234 CataLight aimed at researchers in an early career stage in the field of light-driven catalysis and related fields. By employing an online format, we want to allow for the participation of young scientists, in particular PhD students, from all over the globe and offer them an opportunity to share their work, which have been especially sparse this year due to the cancellation of on-site conferences. Therefore the event will emphasize on talks from young scientists accompanied by selected invited talks by junior groupleaders.

In line with the research area of CataLight the symposium aims to cover all facets of the highly interdisciplinary field of light-driven catalysis. We therefore welcome contributions from the fields of synthesis over (spectroscopic) characterization and theory to application-related aspects such as reactor design. For an in-depth explanation on our goals, see our Scientific Programme.

The symposium will be held every tuesday and thursday afternoon over 3 weeks from 10.11.2020 to 26.11.2020. Every day will contain an invited talk by a senior researcher and 5 slots for contributed talks, each 15 minutes + 5 minutes of discussion. Additionally we want to provide the opportunity for presenting a poster by offering a poster session in the evening on the 19.11.2020 and 24.11.2020.

To facilitate in-depth discussion discussion or even collaboration between participants of CYSS, we're accompanying the symposium with an instant messaging service that can be used to contact the speakers or any other participants with more in-depth questions or exchange contact information for further discussion.

CYSS is supported by the SFB/TRR 234 CataLight. We gratefully acknowledge the funding by the Deutsche Forschungsgemeinschaft (German Research Foundation - DFG).

 

    • 15:00 15:15
      Conference Opening 15m
    • 15:15 15:45
      Between the Hammer and the Anvil – Crafting Electron Transfer Chains by Computational Methods 30m
      Speaker: Stephan Kupfer (Friedrich Schiller University Jena)
    • 15:50 16:35
      Theoretical Studies
      Convener: Ludwig Schwiedrzik (University of Vienna)
      • 15:50
        Electronic Structure Analysis of Thermal and Photochemical Nitrogen Splitting 20m
        Speaker: Severine Rupp (Technical University of Darmstadt)

        Nitrogen makes up 78% of the Earth’s atmosphere. Ammonia derived from N2 and fossil H2 in the Haber-Bosch process represents the main source of nitrogen compounds used in fertilizers as well as a base chemical for the synthesis of value-added products. In order to access a more diverse range of N-containing chemicals without relying on NH3 as an intermediate, it is of high interest to develop tailored nitrogen-activating catalysts.

        The complete splitting of the dinitrogen triple bond can be achieved thermally, photochemically, or electrochemically. While a few transition metal complexes are capable of photochemical dinitrogen activation, the mechanistic understanding of the underlying processes is still in its early stages. All known complexes for N2 photoactivation have a linear core of the form M-N-N-M which undergoes geometric and electronic changes during the light excitation process, however the nature of the responsible excited state is presently ill-defined.[1]

        Here we will present our multi-tier approach to study the complex electronic structure of two types pf nitrogen photoactivation complex: The catalyst design based on pincer ligands of the Schneider group[2,3] and Sita’s series of homologous transition metal complexes[4-6]. We analyse the structures of two of Sita's molybdenum[4-6,7] and tungsten[4-6] complexes and their electronic spectra in terms of the molecular orbitals, difference densities and the charge-transfer numbers provided by the wavefunction analysis program TheoDORE[8,9]. We study in particular the charge transfer character of the individual excitations and find that the transitions of photochemically active complexes have more charge-transfer character and higher intensity.[10] While density functional theory (DFT) has proven to be a powerful tool for first insights into the differences between photochemically and thermally active N2-splitting complexes, in some cases the complexity of the electronic structure requires the use of multiconfigurational methods. For the rhenium complex of Schneider and coworkers we present a first multireference electronic structure analysis with a (16,16) active space based on density matrix renormalisation group (DMRG) that permits an appropriate treatment of spin-orbit coupling effects.

        References
        [1] V. Krewald, Dalton Trans. 2018, 47, 10320-10329, DOI: 10.1039/C8DT00418H.
        [2] B. M. Lindley, R. S. van Alten, M. Finger, F. Schendzielorz, C. Würtele, A. J. M. Miller, I. Siewert, S. Schneider, J. Am. Chem. Soc. 2018, 140, 7922-7935, DOI: 0.1021/jacs.8b03755.
        [3] F. Schendzielorz, M. Finger, J. Abbenseth, C. Würtele, V. Krewald, S. Schneider, Angew. Chem. Int. Ed. 2019, 58, 830-834, DOI:10.1002/anie.201812125.
        [4] A. J. Keane, W. S. Farrell; B. L. Yonke; P. Y. Zavalij, L. R. Sita, Angew. Chem. Int. Ed. 2015, 54, 10220-10224, DOI: 10.1002/ange.201502293.
        [5] P. P. Fontaine, B. L. Yonke, P. Y. Zavalij, L. R. Sita, J. Am. Chem. Soc. 2010, 132, 12273-12285, DOI: 10.1021/ja100469f.
        [6] J. P. Reeds, B. L. Yonke, P. Y. Zavalij, L. R. Sita, J. Am. Chem. Soc. 2011, 133, 18602-18605, DOI: 10.1021/ja208669s.
        [7] V. Krewald, Front. Chem. 2019, 7, 352, DOI: 10.3389/fchem.2019.00352.
        [8] F. Plasser, H. Lischka, J. Chem. Theory Comput. 2012, 8, 2777, DOI: 10.1021/ct300307c.
        [9] S. Mai, F. Plasser, J. Dorn, M. Fumanal, C. Daniel, L. González, Coord. Chem. Rev. 2018, 361, 74, DOI: 10.1016/j.ccr.2018.01.019.
        [10] S. Rupp, F. Plasser, V. Krewald, Eur. J. Inorg. Chem. 2020, 1506-1518, DOI: 10.1002/ejic.201901304.

      • 16:15
        Structure and Dynamics of Cyclohexenone-Lewis-Acid Complexes after Photoexcitation 20m
        Speaker: Martin T. Peschel (Ludwig-Maximilians-Universität München)

        The photocatalytic [2+2] cycloaddition of cyclic enones has recently received renewed attention. It was discovered that it can be catalyzed by chiral Lewis acids (1,3,2-oxazaborolidines) to yield a variety of bicyclic products with high enantioselectivity [1,2]. The key to this reaction is a redshift of the bright UV absorption band of the enone caused by the Lewis acid, which allows for a selective excitation of the chiral complex [3]. To better understand this process, the absorption spectra of basic cyclohexenone-Lewis-acid complexes were calculated using XMS-CASPT2. Both, a bright ππ singlet state and a darker nπ singlet state were found to contribute to the absorption significantly. Furthermore, their spectral shifts differ depending on the Lewis acid.
        It is known that the [2+2] photocycloaddition proceeds via a triplet state [4]. Hence, we also elucidated the reaction path from the Frank-Condon point to the triplet minima by calculating critical points and by non-adiabatic molecular dynamics simulations. Based on these results, we devised an experiment that should allow us to directly observe the triplet formation using UV transient absorption spectroscopy.


        [1]: Saner Poplata and Thorsten Bach, J. Am. Chem. Soc., 2018, 140, 3228-3231.
        [2]: Daniel P. Schwinger and Thorsten Bach, Acc. Chem. Res., 2020, 53, 9, 1933-1943.
        [3]: Christoph Brenninger, John D. Jollife and Thorsten Bach, Angew. Chem. Int. Ed. 2018, 57, 14338-14349.
        [4]: Hongjuan Wang, Xiaoyan Cao, Xuebo Chen, Weihai Fang and Michael Dolg, Angew. Chem. Int. Ed., 2015, 54, 14295-14298.

    • 16:35 16:55
      Break 20m
    • 16:55 18:05
      Theoretical Studies
      Convener: Ludwig Schwiedrzik (University of Vienna)
      • 16:55
        Two-photon excitation in wavelength-dependent photoconversion of GFP 20m
        Speaker: Ms Dilara Farkhutdinova (Lomonosov Moscow State University)

        Green Fluorescent Protein (GFP) is widely used in bioimaging due to its remarkable fluorescent properties. GFP is also found to undergo oxidative photoconversion, which is accompanied by electron transfer from the excited state of the GFP chromophore anion to oxidants of various origin. Recently, we have shown that light-induced electron transfer from GFP is mediated by a single vibrational mode. The high-frequency in-plane C=C stretching mode facilitates energy exchange between nuclei and electrons on the (sub)picosecond timescale, which is faster than vibrational relaxation. This mode is also active upon photoexcitation, thus resulting in a wavelength-dependent quantum yield of the GFP photoconversion. Here, we aim at enhancing the efficiency of the GFP photoconversion by changing the intensity of the specific vibrational mode, which is coupled to excited-state electron transfer, upon photoexcitation.
        We simulate and explore vibronic structures of one-photon (OPA) and two-photon (TPA) absorption profiles of the GFP chromophore anion in the gas phase and inside the protein. The equilibrium geometry parameters, vibrational frequencies, excited-state gradients, and two-photon absorption tensor elements of the GFP chromophore are calculated using time-dependent density functional theory (TDDFT) with the hybrid PBE0/(aug)-cc-pVDZ functional. The ground-state protein calculations are performed using the combined PBE0/CHARMM approach. The parameters used in the TPA two-level model are obtained using the extended multiconfiguration quasi-degenerate perturbation theory (XMCQDPT2), coupled to the effective fragment potential method for treating the protein environment in the excited-state protein calculations. The OPA and TPA vibrational profiles are obtained using a linear coupling scheme, within the double harmonic parallel-mode approximation, accounting for both Franck-Condon and Herzberg-Teller couplings.
        We show that the TPA and OPA spectral profiles are markedly different. The TPA maximum is blue shifted compared to that observed in the OPA spectrum, coinciding with the 0-1 excitation of the C=C stretching mode. Furthermore, by using a two-level model we show that the TPA cross-section and the contribution from each vibrational mode can be estimated using simple parameters, such as a difference between permanent dipole moments in the ground and excited states and a transition dipole moment, as well as their derivatives with respect to normal mode coordinates. These parameters can be readily evaluated at a high level of theory. Importantly, we find that the major contribution to the TPA cross-section comes from those vibrational modes that modulate permanent dipole moments. These are the infrared active modes. We therefore conclude that the intensity of the IR-active modes, including the specific mode coupled to light-induced electron transfer from GFP, can be significantly enhanced when switching from conventional one-photon excitation to a non-linear two-photon absorption regime. Our findings pave the way for TPA-enhanced wavelength-dependent photoconversion of GFP.
        This work is supported by The Russian Science Foundation (grant no. 17-13-01276). The research is carried out using the equipment of the shared research facilities of HPC computing resources at Lomonosov Moscow State University as well as the local resources provided through the Lomonosov Moscow State University Program of Development.

      • 17:20
        Elucidating the structural, spectroscopic and energetic features of the MoS3 amorphous phase by DFT simulation 20m
        Speaker: Amit Sahu (ENS Lyon and IFP Energy Nouvelles)

        In spite of the attractive interest of α-MoS3 based nanomaterials for numerous applications in catalysis and energy, the amorphous nature of the MoS3 phase makes it challenging to control and understand its chemical reactivity[1]. In particular, the type of the structural building unit such as Mo3 triangular[2,3] vs. Mo chain[4,5] is still debated[6], while the ambivalent interpretation of the nature of sulfur species (S2, S22) and MoMo bonds leads to ambiguous interpretations of spectroscopic data and reactivity[2]. By density functional theory (DFT), we simulate the energetic, structural, and spectroscopic features of relevant 0D-, 1D- and 2D-MoS3 triangular, chain-like polymorphs, including unprecedented ones (ring, wave and helix) and revisit the interpretation of EXAFS, IR-RAMAN, and XPS experimental data.
        To optimize the geometries, we use DFT as implemented in VASP relying on the Perdew-Burke-Ernzerhof (PBE)[7] functional within the framework of generalized gradient approximation (GGA). The long-range interactions were included through a density-dependent dispersion correction (dDsC)[8]. The projector augmented-wave (PAW)[9] method was chosen to describe the electron-ion interaction. Spin-polarized calculations were performed to obtain the electronic ground state of the clusters.
        The exploration of some complex structures has been refined by ab initio molecular dynamics (AIMD) with the scaled velocity Verlet algorithm to solve Newton's equations of motions.
        For frequency calculations, the structures have been optimized with tighter convergence criteria. To calculate the frequencies and corresponding infra-red intensities, the linear response method with density functional perturbation theory (DFPT) has been used as implemented in VASP.
        The thermodynamic stability (including zero-point energy and entropy corrections), of the various oligomers have been calculated w.r.t. Mo3S9 unit of triangular oligomer as reference.
        We analyze how MokS3k clusters of a few k atoms may grow up to infinite MoS3 polymorphs (figure 1(g)). The evolution of the growth energy and the computed IR spectra level suggest the coexistence of various polymorphs in the MoS3 phase as a function of sizes (figure 1(f)). Molecular dynamics simulations reveal how the small triangular MokS3k oligomers may transform into a more condensed MoS3 patches resembling embryos of the 2D 1T’-MoS2 phase (figure 1(c)). Finally, we discuss some plausible transformation pathways from one polymorph to another.[10]
        As a perspective of this works, we are currently investigating the effect of an oxide support (alumina, used in many catalysts, on the transformation of MoO3 precursor into MoS3.

        References
        1. C. G. Morales-Guio, X. Hu, Acc. Chem. Res. 2014, 47, 8, 2671-2681.
        2. Th. Weber et al., J. Phys. Chem. 1995, 99, 22, 9194-9200.
        3. H. Jiao and Y-W. Li, et al., J. Am. Chem. Soc. 2001, 123, 7334-7339.
        4. K. S. Liang, S. P. Cramer et al., J. Non-Cryst. Solids, 1980, 42, 345-356.
        5. S. J. Hibble, G. B. Wood, J. Am. Chem. Soc. 2004, 126, 3, 959-965.
        6. P. D. Tran et al. Nature Materials, 2016, 15, 640-647.
        7. J. P. Pperdew et al. Phys. Rev. Lett. 1996, 77, 3865-3868.
        8. S. N. Steinmann, C. Corminboeuf, J. Chem. Theory Comput. 2010, 7, 1990-2001.
        9. G. Kresse et al. Phys. Rev. B 1999, 59 , 1758-1775.
        10. A. Sahu, S. Steinmann, P. Raybaud. Cryst. Growth Des. (in press)

         

      • 17:45
        Computational Protocol To Predict Anti-Kasha Emissions: The Case of Azulene Derivatives 20m
        Speaker: Mr Koen Veys (KU Leuven)

        Most photochemical reactions obey Kasha's rule, i.e., they take place from the lowest excited state of a given multiplicity. This implies that the excess of energy after light excitation is lost in the course of relaxation to the lowest excited state. Therefore, molecules that are able to use higher excited states for anti-Kasha photochemistry can lead to more efficient light-energy conversions, for instance in the context of photocatalysis.[1] Finding those anti-Kasha molecular systems is usually accomplished in an experimental trial-and-error manner. Instead, computational tools capable to understand and predict these anti-Kasha properties would give the opportunity for the in silico design of more efficient anti-Kasha molecular systems. This work is one step in that direction. Specifically we demonstrate that quantitative predictions of anti-Kasha photoluminescence properties can be derived exclusively from electronic structure calculations, excited state decay rate theories and excited state kinetic modelling.[2] More in detail, the different (non-) radiative rates between all relevant states were evaluated with the thermal vibration correlation function formalism.[3] Our protocol is validated for a series of azulene derivatives, for which we have correctly predicted the exclusive emission from the second excited singlet state. We foresee that the herein developed computational protocol can be used to pre-screen dyes with the desired anomalous photoluminescence properties and eventually design tailored photocatalysts.

        [1] Demchenko A. P., Tomin V. I. and Chou P., Chem. Rev. 2017, 117, 21, 13353–13381, https://doi.org/10.1021/acs.chemrev.7b00110.
        [2] Veys K. and Escudero D., J. Phys. Chem. A 2020, 124, 36, 7228–7237, https://doi.org/10.1021/acs.jpca.0c05205.
        [3] Niu Y., Peng Q., Deng C., Gao X. and Shuai Z., J. Phys. Chem. A 2010, 114, 30, 7817–7831, https://doi.org/10.1021/jp101568f

    • 15:00 15:30
      Photochemical Reaction Engineering 30m
      Speaker: Dirk Ziegenbalg (Ulm University)
    • 15:35 16:20
      Application
      Convener: Miftahussurur Putra (Ulm University)
      • 15:35
        Plasmonic Photoreactors for Field-Enhanced Photocatalysis of Urea Oxidation and Visible Light Fuel Cells 20m
        Speaker: Mr Xingda An (Boston University)

        The localized surface plasmon resonances (LSPR) of noble metal nanostructures provide appealing strategies to enhance photocatalytic reactivity. Plasmonic hot charge carrier production for direct catalysis by plasmonic metals or heterostructures, and plasmonic Electric (E-) field enhancement of resonant intramolecular transition processes represent two major mechanisms of plasmonic photocatalysis. Harnessing plasmonic E-fields for photocatalysis, however, is fundamentally challenged by a trade-off between distance-dependent local field intensity enhancement and excited state quenching through the metal surface. Here, we explore quantitative optimization of photocatalysis mediated by an E-field enhanced metal-to-ligand charge transfer (MLCT) process. We present a hierarchical photoreactor architecture that localizes a transition metal photocatalyst, [Ru(bpy)3]2+, in an electromagnetic “sweet spot” around Ag nanoantennas for efficient plasmonic enhancement of photocatalysis. A phospholipid membrane self-assembled around the Ag nanoparticle (NP) binds [Ru(bpy)3]2+ as well as serves as a spacer between the transition metal complex and the NP, whose LSPR overlaps with the [Ru(bpy)3]2+ MLCT. The photoreactor allows for substantial absorption enhancement, but avoids quenching of photoexcited Ru*(II) state. We demonstrate direct photocatalytic urea oxidation with the Ag-[Ru(bpy)3]2+ photoreactors, and implement a visible light-driven Direct Urea Fuel Cell (LDUFC) to achieve simultaneous solar energy harvesting and waste water treatment. Our approach provides great promise as an effective and broadly applicable strategy to enhance intramolecular charge or energy transfer processes with metal plasmon resonances. It also depicts a blueprint for the designs of bio-mimetic, efficient and selective nanoreactors.

      • 16:00
        Electrochemically assisted photocatalysis for the disinfection of rainwater under solar irradiation 20m
        Speaker: Stuart McMichael (Ulster University)

        In this work a photo electrochemical reactor (PEC) with a compound parabolic collector (CPC) has been designed and tested for the electrochemically assisted photocatalytic (EAP) disinfection of rainwater under real sun conditions in South Africa. The reactor consisted of a Ti mesh coated with aligned titania nanotubes with a carbon counter electrode in a concentric tubular configuration, within a borosilicate glass tube with a CPC. Environmental strains of Escherichia coli and Pseudomonas aeruginosa were used. The viability of the microorganisms was analysed by culture-based and by EMA-qPCR methods. The reactor was tested under real sun during the winter in South Africa with a relatively low UV irradiance (max: 13 Wm-2). Under real sun irradiation, EAP yielded a 5.5-log10 reduction for E. coli and a 5.8-log10 reduction for P. aeruginosa for culture-based analysis. The EAP treatment also showed improved results by EMA-qPCR analysis with a 2.4-log10 reduction in gene copies for E. coli and 3.0-log10 for P. aeruginosa.

    • 16:20 16:40
      Break 20m
    • 16:40 17:10
      Workshop: Research Data Management 30m
      Speaker: Thomas Bocklitz (Leibniz Institute of Photonic Technology)
    • 17:15 18:00
      Application
      Convener: Miftahussurur Putra (Ulm University)
      • 17:15
        Charge Carrier Dynamics of Cu2O and its Application as Photocathode for the Photoelectrochemical Reduction of CO2 20m
        Speaker: Dr Yamen AlSalka (Institut für Technische Chemie, Leibniz Universität, Callinstr. 5, 30167 Hannover, Germany)

        Photoelectrochemical devices can be used to convert CO2 into valuable chemical compounds, which can serve as energy storage and can be used to compensate for energy fluctuations from renewable energy sources. This promising strategy relies on the development of p-type photocathodes. Cu2O is a p-type semiconductor, which has a conduction band edge thermodynamically suitable for the reduction of CO2. Therefore, Cu2O could be a promising photocathode but commonly suffers from photocorrosion and chemical instability. For this purpose, commercial Cu2O powders have been investigated in detail using different techniques.
        DRS measurement revealed that Cu2O absorbs light in the visible range, starting below 750 nm with a band gap value of 1.95 eV. On the other hand, the Mott-Schottky plot of Cu2O deposited on FTO reveals its p-type character with a value of 0.97 V vs. NHE being obtained for the valence band edge. The charge carrier dynamics have been studied by means of transient absorption spectroscopy. The transient absorption spectra of Cu2O in N2 atmosphere shows a peak at around 615 nm, which decreases in CO2 atmosphere and exhibits a faster decay than under N2 atmosphere.
        Cyclo-voltammetry of Cu2O deposited on FTO measured in 0.5 M Na2SO4 in the dark and during illumination with a solar simulator exhibit two main peaks related to the oxidation of Cu+ to Cu2+ and the reduction of Cu2+ to Cu+. However, three main peaks are present with 0.1 M NaHCO3 used as electrolyte, related to the oxidation of Cu and Cu+ to Cu2+, the reduction of Cu2+ to Cu+, and the reduction of Cu+ to Cu. For both measurements, a decrease of the currents is noticed with an increasing number of cycles.
        Following the PEC measurements, Raman spectra reveal a non-stability of the material as evinced by the appearance of Cu and Cu2+. Therefore, Cu2O electrodes have been prepared over self-prepared Cu-covered FTO substrates aiming to increase the stability. While the photocurrent of these prepared electrodes increases in the cathodic range, however, the increase of the dark current in the cathodic range is found to be significantly lower. The chrono-amperometric measurement of Cu2O deposited on Cu-covered FTO under chopped light conditions at an applied potential of -100 mV vs. NHE in 0.5 M NaHCO3 saturated with CO2 reveals that the electrode is able to generate a stable photocurrent.

      • 17:40
        Overcoming Limitations in Dual Photoredox/Nickel catalyzed C–N Cross-Couplings due to Catalyst Deactivation 20m
        Speaker: Mr Sebastian Gisbertz (a Department of Biomolecular Systems, Max-Planck-Institute of Colloids and Interfaces)

        Dual photoreodox/nickel catalyzed C–N cross-couplings are an attractive alternative to the palladium catalyzed Buchwald-Hartwig reaction, [1] but are limited to aryl halides containing electron-withdrawing groups. Here we show that the formation of catalytically inactive nickel-black is responsible for this limitation and causes severe reproducibility issues. We demonstrate that catalyst deactivation can be avoided by the combination of nickel catalysis and a carbon nitride semiconductor. [2] The broad absorption range of the organic, heterogeneous photocatalyst enables a wavelength dependent reactivity control to prevent nickel-black formation. A second approach, that is applicable to a broader set of substrates, is to run the reactions at high concentrations to increase the formation of nickel-amine complexes that reduce nickel-black formation. This allows reproducible, highly selective C–N cross-couplings of electron rich aryl bromides and enables efficient reactions of aryl chlorides. By combining an oscillatory pump with a microstructured plug flow photoreactor this semi-heterogeneous dual photoreodox/nickel catalyzed C–N cross-coupling was demonstrated in a multi-gram scale. [3]

        References:
        [1] J. Twilton, C. Le, P. Zhang, M. H. Shaw, R. W. Evans, D. W. C. MacMillan, Nat.Rev. Chem. 2017, 1, 0052. doi.org/10.1038/s41570-017-0052
        [2] S. Gisbertz, S. Reischauer, B.Pieber, Nature Catal. 2020, 3, 611-620. doi.org/10.1038/s41929-020-0473-6
        [3] C.Rosso, S.Gisbertz, J. D. Williams, H. P. L. Gemoets, W. Debrouwer, B. Pieber, C. O. Kappe, React. Chem. Eng. 2020, 5, 597-604. doi.org/10.1039/D0RE00036A

    • 15:00 15:30
      Energy and Electron Transfer in Phospholipid Bilayers 30m
      Speaker: Andrea Pannwitz (Ulm University)
    • 15:35 16:20
      Synthesis I
      Convener: Elisabeth Hofmeister (Leibniz Institute of Photonic Technology)
      • 15:35
        Metal complexes as effective photocatalysts for organic synthesis under batch and flow conditions 20m
        Speaker: Mr Daniel González-Muñoz (Universidad Autónoma de Madrid)

        Developing less polluting and more selective processes has become one of the most important objectives in the field of organic synthesis. For this reason, photocatalysis has grown exponentially as one of the most promising tools to achieve such a task.[1] In this work, two different photocatalytic approaches have been carried out. The development of new platinum(II) complexes as photocatalysts in different organic transformations and the discovery of a new process to synthesize tetrahydroquinolines.
        On one hand, the synthesis of different photocatalytic platinum(II) complexes is presented and their versatility as photocatalysts in different organic synthetic reactions was demonstrated.[2] Platinum(II) complex with a sulphur donor atom ligand was found to have higher activity than the analogous with an oxygen donor atom. We studied such a Pt(II) complexes in the oxidation of boronic acids to form alcohols, the cross-dehydrogenative coupling of tetrahydroisoquinolines and the enantioselective alkylation of aldehydes. In addition, mechanistic studies were performed by theoretical calculations regarding the structure of the different platinum(II) complexes. Hence, the Pt(II) complex with the sulphur ligand presents a larger ability to couple the bright S1 state with the T1 one, which would explain its higher activity in comparison with the O-bonded Pt(II) complex.
        On the other hand, the well-known photocatalyst Ir(ppy)3 was used to develop a new photocatalytic method for the synthesis of tetrahydroquinolines by intramolecular radical cyclization.[3] We carried out the reaction synthesizing tetrahydroquinolines with different substituents at the nitrogen group and the aromatic ring, obtaining complete selectivity towards the 6-exo-trig form. Furthermore, the methodology allowed to perform the cyclization without protecting the amino group, which is a limiting factor in the five-membered cyclization reaction previously reported. In addition, this type of reactions requires low concentrations, therefore, their development on a larger batch scale in a photocatalytic fashion is complicated. For this reason, we expanded this methodology within flow conditions, which allowed shortening the reaction time and being able to synthesize the tetrahydroquinolines on a larger scale.
        References:
        1. C. K. Prier, D. A. Rankic, D. W. C. MacMillan. Chem. Rev. 2013, 113, 7, 5322-5363. 10.1021/cr300503r.
        2. A. Casado-Sánchez, M. Uygur, D. González-Muñoz, F. Aguilar-Galindo, J.L. Nova-Fernández, J. Arranz-Plaza, S. Díaz-Tendero, S. Cabrera, O. García Mancheño, J. Alemán. J. Org. Chem. 2019, 84, 6437-6447. 10.1021/acs.joc.9b00520.
        3. D. González-Muñoz, J.L. Nova-Fernández, A. Martinelli, G. Pascual-Coca, S. Cabrera, J. Alemán. Eur. J. Org. Chem. 2020, 5995-5999. 10.1002/ejoc.202001018.

      • 16:00
        Polystyrene-block-poly(acrylic acid-co-bipyridyl acrylate) block copolymer micelles – towards catalytic nanoreactors 20m
        Speakers: Mr Jonas Eichhorn, Ms Yulia D. Gordievskaya

        Herein we describe the preparation as well as experimental and theoretical investigations of block copolymer micelles based on amphiphilic, pH-responsive block copolymers featuring bipyridine ligands in the side chain. Several well-defined polystyrene-block-poly(acrylic acid) (PS-b-PAA) and polystyrene-block-poly((acrylic acid)-co-(2-(4-(4’-methyl-2,2’-bipyridyl))ethylacrylate)) (PS-b-P(AA-co-bpyEA)) block copolymers were synthesized via nitroxide mediated polymerization. Morphological investigations of different PS-b-PAA and PS-b-P(AA-co-bpyEA) block copolymer micelles in water using dynamic light scattering (DLS) and cryogenic transmission electron microscopy (cryo-TEM) revealed spherical micelles with pH-dependent corona size. To describe conformational behavior of the micellar coronae we performed combined molecular dynamics (MD) and Monte Carlo (MC) simulations of pH-sensitive brushes with comparable grafting density and with matching composition. We have studied the brush thickness, degree of dissociation of monomer units and distributions of functional groups at different solution pH. Particular emphasis has been put on distribution and average distance between bipyridyl units as model functional groups and the theoretically obtained macrocharacteristics are in good agreement with the experimental results. Afterwards, a platinum(II)-complex was immobilized covalently at the bipyridine anchoring sites of a selected polystyrene-block-poly((tert-butyl acrylate)-co-(2-(4-(4’-methyl-2,2’-bipyridyl))ethyl-acrylate)) (PS-b-P(t-BuA-co-bpyEA)) block terpolymer. After deprotecting the t-BuA groups to AA the obtained amphiphilic diblock terpolymer formed core-corona micelles with pH-dependent corona thickness in water according to DLS and TEM investigations.

    • 16:20 16:40
      Break 20m
    • 16:40 17:50
      Synthesis I
      Convener: Elisabeth Hofmeister (Leibniz Institute of Photonic Technology)
      • 16:40
        Conversion of Electrospun Layered Perovskite Nanofibers to Perovskite Oxynitrides for Visible Light Absorbtion 20m
        Speaker: Ms Anja Hofmann (University of Bayreuth, Physical Chemistry III)

        The wide bandgap layered perovskites A5M4O15 (A = Ba, Sr; M = Ta, Nb) are shown do be very active in photocatalytic water splitting under UV-light, resulting from the additional reaction sites in the crystal structure.[1] The activity can be improved either by the formation of heterojunctions such as Ba5Ta4O15-Ba3Ta5O15 or Ba5Ta4O15-Ba3Ta5O15-BaTa2O6.[2,3] Preparation of nanofibers can additionally solve the problem of the large mismatch between the small charge carrier diffusion length and the much larger light penetration depth, resulting in higher photocatalytic activity.[4,5] Visible light activity can be gained by the formation of heterojunctions such as Ba5Ta4O15-AgVO3[6] and Ba5Ta4O15-C3N4[7] and via ammonolysis[8].

        We are combining the positive effects of the nanofiber structure and the ammonolysis by preparing (111) layered perovskites nanofibers of Ba5Ta4O15 and Ba5Nb4O15 and converting them into perovskite oxynitrides (Figure 1).

        The samples were characterized with XRD and the conversion degree was determined. SEM characterization was performed, and Kr physisorption measurements were done to determine the BET surface area before and after ammonolysis. UV-Vis spectroscopy as well as hydrogen evolution measurements in water/methanol were performed.
        In first experiments, conversion degrees of nearly 100% were obtained, yielding in a decrease of the band from 4.0 eV down to 2.0 eV for the niobium compound and from 4.6 eV down to 1.9 eV for the tantalum compound; giving visible light absorption abilities. The surface area is slightly increased. Morphology changes will be discussed in detail.

      • 17:05
        Light-driven hydrogen evolution from thiomolybdate-clusters sensitized by novel perylene monoimides in confined environment 20m
        Speaker: Daniel Costabel (FSU Jena)

        Rylene-based photosensitizers are ideal metal-free candidates for visible light sensitization of different hydrogen evolution catalysts because of their excellent visible light absorption, chemical tunability and their high chemical and photostability.[1-4] We will report on the application of novel bromination techniques that allow the introduction of electron withdrawing or donating groups in both peri and bay positions and thus the optical and electrochemical properties could be tuned to the demands of different catalysts.[5] We applied advanced optical characterization techniques to identify long-lived excited states, which prolongate the time frame of potential electron transfer. In photocatalytic experiments, poly(dehydroalanine)-graft-poly(ethylene glycol) was added as solubilizing template polymer to the light-sensitive material and hydrogen evolution catalyst (NH4)2[Mo3S13]x2H2O to solubilize the two active components and to bring them into a confined geometric matrix. Customized photoreactor was utilized to ensure well-defined evenly distributed irradiation which resulted in continous light-driven hydrogen evolution over 3 days with a maximum TON of 104.

      • 17:30
        Mesoporous TiO2 thin films: creating nanocomposites for photoelectrochemical water splitting 20m
        Speaker: Ms Priscila Vensaus (Nanosystems Institute (INS-UNSAM))

        The development of sustainable materials capable of capturing and transforming solar energy into green chemical fuels has become of great interest in the last decade, following the increased risk of global warming. Hydrogen is an environmentally friendly fuel, which can be obtained by photoelectrochemical water splitting, where a water molecule is split into H2 and O2 in presence of a semiconductor and sunlight. Recently developed materials are not practical for mass industrial use due to their low efficiencies, thus the combination of different compounds is an interesting point towards the design of better performant systems.
        Titanium dioxide (TiO2) is a stable, non-toxic and abundant semiconductor, which has a suitable band gap to conduct the water splitting reaction.[1] However, improvements are still needed in terms of efficiencies, such as enhancing light absorption into the visible range and increasing the rate of redox reactions at the interface. In this work we present the synthesis of mesoporous TiO2 thin films prepared via a sol-gel approach. These films can be easily modified either with photosensitizer or cocatalysts, which makes them an ideal support for the formation of nanocomposites.
        We studied the effect of the crystallinity in the photoelectrochemical efficiency. We then modified the films with different cobalt catalysts (CoPi, Co-PBA) [2,3] and we studied the efficiency of the composite photoelectrodes. The materials were characterized by means of photoelectrochemical techniques, scanning electron microscopy, X-ray diffraction and reflectometry, and UV-visible spectroscopy. The films have high surface areas, which improves the photoelectrochemical efficiency when compared to non-porous films. Also, crystalline (anatase) films show much higher photocurrents than amorphous ones. In terms of the catalyst, we have seen that only Co-PBA gives an increase in photocurrent, while the presence of CoPi is only beneficial at high overpotentials.

        [1]: Ahmad, H., et al. Renewable and Sustainable Energy Reviews, 2015, 43, 599-610, 10.1016/j.rser.2014.10.101
        [2]: Kanan M., Nocera D., Science,2008, 321, 1072-1075, 10.1126/science.1162018
        [3]: Pintado S., Goberna-Ferrón S., Escudero-Adán E. C., Galán-Mascarós J.R., Journal of the American Chemical Society, 2013, 135, 13270-13272, 10.1021/ja406242y

    • 15:00 15:30
      Are extended pi-systems a suitable component for photocatalysis? 30m
      Speaker: Stefanie Tschierlei (Technical University Braunschweig)
    • 15:35 16:20
      Characterization I
      Convener: Carolin Müller (Leibniz Institute of Photonic Technology)
      • 15:35
        Preparation, photo- and electrochemical studies of a homoleptic iminephosphaalkene Cu(I) complex 20m
        Speaker: Simon Clausing (Ulm University)

        A new type of homoleptic copper complex using an imine-phosphaalkene based bidentate ligand framework was synthesized and characterized.[1] The ligand, a 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU)-functionalized phosphaalkene [DBU-PA], has previously been studied with regards to stabilizing Lewis acid base interactions, as well as formation of a cis-PdCl2 complex, showing its general versatility.[2]

        The reaction of a Cu(I) source and DBU-PA at room temperature results in rapid formation of a deeply red colored complex. Despite numerous attempts, crystal growth proved impossible; however, optimizing the structure in gas phase with DFT calculations showed two possible conformations with an energy difference of only 3.6 kcal/mol, suggesting that the complex exists as a mixture in solution.

        Mass spectrometry and 31P NMR measurements were performed to prove the formation of the complex. Spectroscopic analysis including a 3D emission/excitation correlation in a frozen MeCN matrix at 77 K showed a clear distinction between LC and MLCT emission states, the latter being of modest strength in the green region of the visible spectrum. Its excited state lifetime of ~ 9 ns is modest, suggesting that despite the considerable bulk of the ligand, typical deactivation of Cu(I) complexes by geometric rearrangement in the excited state can still take place.

        Electrochemical studies showed three reductive events, all almost completely chemically irreversible. DFT calculations showed the LUMO to be mostly localized on the phosphaalkene-imine antibonding orbitals, suggesting that reductions take place first on the ligand, destabilizing its bond to the metal center. On the oxidative side, the Cu(I)/Cu(II) couple is semi-reversible at higher scan rate, again showing ligand lability. Further events are fully ligand-based. Overall, ligand non-innocence is a significant contributing factor to the electrochemical properties.

        Despite this particular complex exhibiting low stability and unwanted dynamic behavior, it is a promising first entry into a new class of Cu-based dye compounds with potential photosensitizing applications. The Mes substituent of the DBU-PA ligand is on the one hand too bulky to result in a stable complex, while also not resulting in a favorable configuration to result in the spectroscopic properties desirable for a photosensitizer. However, the synthetic route to DBU-PA easily allows replacement of the Mes moiety, making the complex studied herein an excellent starting point to establish a library of related compounds with properties fine-tuned for eventual photocatalytic applications.

        [1] S. T. Clausing, D. Morales Salazar, A. Orthaber, Inorganica Chimica Acta 2020, 513, 119958. https://doi.org/10.1016/j.ica.2020.119958
        [2] D. Morales Salazar, A. K. Gupta, A. Orthaber, Dalton Trans. 2018, 47, 10404–10409. https://doi.org/10.1039/C8DT01607K

      • 16:00
        Activity and transient absorption spectroelectrochemistry of hydrogen-evolving dye-sensitized photocathodes 20m
        Speaker: Sebastian Bold (Friedrich-Schiller-University)

        Based on our previous covalent dye-catalyst assembly for hydrogen evolution in dye-sensitized photoelectrochemical cells (DSPEC)[1], a new dyad was synthesized, introducing an extended linker to improve charge transfer, light harvesting properties and stability in aqueous media.[2] Furthermore, the catalyst unit was changed to a tetraaza-macrocyclic Co catalyst with higher activity[3]. Hydrogen evolution activity of NiO films sensitized with the new dyads was significantly improved.
        Transient absorption spectroelectrochemistry (TA-SEC) was used to investigate the light-induced processes that lead to the catalytically active state in the sensitized NiO films under applied potential. Application of a potential allows to study the system under conditions close to the operando conditions in photoelectrochemical tests and in various oxidation states of the catalyst[4]. It has been shown to strongly influence the charge recombination kinetics in sensitized NiO films[5,6].
        Charge separation and charge-separated state lifetimes could be determined and showed heavy dependence on the applied potential, increasing by up to six orders of magnitude into the millisecond scale. Furthermore, electron transfer to the catalyst unit to form the long-lived (> 1 ms) catalytically active state was observed, allowing a correlation of light-induced process kinetics with the observed catalytic performance.

        [1]: Kaeffer, N., Massin, J., Lebrun, C., Renault, O., Chavarot-Kerlidou, M., & Artero, V., Journal of the American Chemical Society, 2016, 138(38), 12308–12311. https://doi.org/10.1021/jacs.6b05865
        [2]: Click, K. A., Beauchamp, D. R., Huang, Z., Chen, W., & Wu, Y., Journal of the American Chemical Society, 2016, 138(4), 1174–1179. https://doi.org/10.1021/jacs.5b07723
        [3]: Varma, S., Castillo, C. E., Stoll, T., Fortage, J., Blackman, A. G., Molton, F., Deronzier, A., & Collomb, M.-N., Physical Chemistry Chemical Physics, 2013, 15(40), 17544. https://doi.org/10.1039/c3cp52641k
        [4]: Bold, S., Zedler, L., Zhang, Y., Massin, J., Artero, V., Chavarot-Kerlidou, M., & Dietzek, B., Chemical Communications, 2018, 54(75), 10594–10597. https://doi.org/10.1039/C8CC05556D
        [5]: Dillon, R. J., Alibabaei, L., Meyer, T. J., & Papanikolas, J. M., ACS Applied Materials & Interfaces, 2017, 9(32), 26786–26796. https://doi.org/10.1021/acsami.7b05856
        [6]: D’Amario, L., Antila, L. J., Pettersson Rimgard, B., Boschloo, G., & Hammarström, L., The Journal of Physical Chemistry Letters, 2015 6(5), 779–783. https://doi.org/10.1021/acs.jpclett.5b00048

    • 16:20 16:40
      Break 20m
    • 16:40 17:50
      Characterization I
      Convener: Carolin Müller (Leibniz Institute of Photonic Technology)
      • 16:40
        In-situ discovery of C-C bonded species formed during photocatalytic CO2 reduction 20m
        Speaker: Ms Dinumol Devasia (Department of Chemistry, University of Illinois, Urbana Champaign, IL, USA)

        Catalysis plays a key role in the current chemical manufacturing and renewable energy generation sectors. The development of active, efficient and selective catalysts is an essential step in our attempts to achieve sustainability. However, our progress is hindered because of the limited molecular-level knowledge of the surface chemistry occurring when a catalyst is in action. The in-situ investigation of catalysts at the single-nanoparticle level can bridge this knowledge gap by revealing adsorbates and rare intermediates dynamically formed on the surface of the catalyst during the reaction. Additionally, the probing of catalytic activity of individual nanoparticles can discern particle-to-particle variations in catalytic activity, information otherwise masked in ensemble measurements. To this end, we have developed a surface-sensitive, in-situ nanoscale surface enhanced Raman scattering (SERS)-based chemical imaging technique that has single-nanoparticle-level spatial resolution and a 100-ms time-resolution and can be used in aqueous media. Using this technique, we studied the light-excitation-driven CO2 reduction reaction (CO2RR) on individual Ag nanoparticle (NP) catalysts in CO2-saturated water (Figure 1). We discovered a rich array of previously unknown C1 and C2+ surface species formed in the CO2RR. Many of these species are long chain C–C coupled hydrocarbons and alcohols, which are valuable liquefiable, energy-dense fuels that are otherwise kinetically challenging to be produced in electrocatalytic CO2RR on Ag. Additionally, an analysis of catalytic activity from several individual nanoscale locations revealed spatiotemporal variabilities in the species distribution. This work demonstrates the power of high-spatial-resolution operando studies for understanding complex catalytic processes at the molecular level.
        References
        • Devasia, D.; Jain, P. K. Intrinsic noise in catalysis deduced from single-nanoparticle-level studies (2020), manuscript in preparation
        • Devasia, D.; Wilson, A. J.; Jain, P. K. A rich catalog of C–C bonded species formed in CO2 reduction on a plasmonic photocatalyst (2020), ‎Nat. Commun. (under review)
        • Devasia, D.; Das, A.; Mohan, V.; Jain, P. K. Control of chemical reaction pathways by light–matter coupling (2020), invited review article, submitted to Annu. Rev. Phys. Chem.
        • Wilson, A. J.; Devasia, D.; Jain, P. K. Nanoscale optical imaging in chemistry, Chem. Soc. Rev., 2020, DOI: 10.1039/D0CS00338G
        • Kumari, G.; Zhang, X.; Devasia, D.; Heo, J.; Jain, P. K. Watching visible light-driven CO2 reduction on a plasmonic nanoparticle catalyst, ACS Nano, 2018, 12 (8), 8330-8340, DOI: 10.1021/acsnano.8b03617

      • 17:05
        SnFe2O4 as a p-type semiconductor photocatalyst for CO2 reduction 20m
        Speaker: Mr Kamil Urbanek (Jagiellonian University, Faculty of Chemistry)

        This study concerns SnFe2O4 spinel (SFO) photocatalytic CO2 reduction properties both alone and in combination with other materials, its synthesis compared to methods presented in literature, and how the products are influenced by pH in wet methods syntheses. Many well-known photocatalytic materials exhibit too wide band gaps limiting the absorption spectra to ultraviolet range which forms only a small fraction of solar radiation, or have too weak reductive power due to not sufficiently high level of the conduction band. These shortcomings can be alleviated by combining two materials, one being oxidative photocatalyst and one reductive photocatalyst forming the so called Z-Scheme. In such a system at the expense of absorption of two photons of lower energy (visible range which is the main component of solar spectrum) an electron, at high enough potentials to reduce CO2, can be obtained along with a hole which can oxidize for example water. Such a system could be realized with for example SFO which is a p-type semiconductor, and is reported to have a high energy conduction band,[1] with an n-type material. Here the analysis and deliberations of earlier mentioned systems will be presented.

        Acknowledgements: The authors would like to acknowledge the financial support of this work from the National Centre for Science through grant no. NCN 2018/30/Q/ST5/00776 (SHENG-1).

        [1] Y. Jia Et al., Chem. Eng. Jour., 2020, 383, 123172, https://doi.org/10.1016/j.cej.2019.123172

      • 17:30
        Kinetics of Dual Nickel- and Photocatalyzed Esterification Reactions 20m
        Speaker: Ms Amiera Madani (Max-Planck-Institute of Colloids and Interfaces)

        Dual photocatalysis and nickel catalysis can effect cross-coupling under mild conditions, but little is known about the in situ kinetics of this class of reactions. In this talk I will present a comprehensive kinetic examination of a model carboxylate O-arylation, comparing a state-of-the-art homogeneous photocatalyst (Ir(ppy)3) with a competitive heterogeneous photocatalyst (graphitic carbon nitride).[1-3] Experimental conditions were adjusted such that the nickel catalytic cycle is saturated with excited photocatalyst. This approach was designed to remove the role of the photocatalyst, by which only the intrinsic behaviors of the nickel catalytic cycles are observed. The two reactions did not display identical kinetics. Ir(ppy)3 deactivates the nickel catalytic cycle and creates more dehalogenated side product. Kinetic data for the reaction using Ir(ppy)3 supports a turnover-limiting reductive elimination. Graphitic carbon nitride gave higher selectivity, even at high photocatalyst-to-nickel ratios. The heterogeneous reaction also showed a rate dependence on aryl halide, indicating that oxidative addition plays a role in rate determination. The results argue against the current mechanistic hypothesis, which states that the photocatalyst is only involved to trigger reductive elimination.

        [1] Welin, E. R.; Le, C.; Arias-Rotondo, D. M.; McCusker, J. K.; MacMillan, D. W. C., Science 2017, 355 (6323), 380-385. DOI: 10.1126/science.aal2490

        [2] Pieber, B.; Malik, J. A.; Cavedon, C.; Gisbertz, S.; Savateev, A.; Cruz, D.; Heil, T.; Zhang, G.; Seeberger, P. H., Angewandte Chemie International Edition 2019, 58 (28), 9575-9580. DOI: 10.1002/anie.201902785

        [3] Malik, J. A.; Madani, A.; Pieber, B.; Seeberger, P. H., Journal of the American Chemical Society 2020, 142 (25), 11042-11049. DOI: 10.1021/jacs.0c02848

    • 17:50 18:00
      Break 10m
    • 18:00 19:00
      Poster Session I
      • 18:00
        A (Pt/Cu-TiO2)-rGO composite for the photocatalytic conversion of CO2 into fuel: Activity in gas and liquid states 1h
        Speaker: Samar Al Jitan (Khalifa University)

        The global emissions of greenhouse gases continue to rise by about 3% each year [1]. Rising levels of CO2 in the atmosphere can be subsided though CO2 utilization technologies such as conversion into fuels and different value-added products. Unlike other CO2 conversion techniques, photocatalysis utilizes a renewable and sustainable form of energy and doesn’t increase net CO2 emissions. A variety of different catalysts have already been tested in numerous studies for the photocatalytic reduction of gaseous CO2 [2]. However, researchers have yet to discover an efficient photocatalyst that can reduce CO2 to yield economical amounts of value-added products under the irradiation of solar light.

        Hence, in this study, an attempt in enhancing the performance of TiO2-based photocatalysts for application in CO2 conversion was made. Surface modifications to help enhance the visible light absorption and the charge separation of TiO2 photocatalysts were pursued. More specifically, a novel TiO2-based photocatalyst, incorporating copper (Cu), platinum (Pt) and reduced graphene oxide (rGO), was synthesized. To investigate the intrinsic and enhanced properties of the photocatalytic composite, several advanced material characterization tools were employed and they include XRD, Raman, DRS, PL, TEM, STEM-EDX, BET, FT-IR, etc.

        A custom-built reactor was used to test the photocatalytic activity of the catalyst in reducing CO2 under different parameters and conditions, most importantly is the photocatalytic reduction of liquid CO2 which has been rarely investigated [3]. The reactor was designed and constructed to allow for operational flexibility in terms of temperature, pressure, light source, and presence/absence of a reducing agent. Gas-phase and liquid-phase products from the different photoreactivity tests were analysed using GC-FID and HPLC, respectively. A mechanism for the CO2 photoreduction reaction was also proposed.

        Results from this study show that CO2 was successfully reduced to CO, CH4, and other products under the irradiation of UV light, with the activity being much higher for liquid CO2 than for gaseous CO2. Furthermore, the proposed catalyst rGO-(Pt/Cu-TiO2) showed higher or comparable activity results during the photocatalytic reduction of liquid CO2 when compared to other tested catalysts, specifically in the formation of aldehydes.

        [1] Al Jitan, S., Palmisano, G., & Garlisi, C., Catalysts, 2020, 10, 2, 227.
        [2] Habisreutinger, S. N., Schmidt‐Mende, L., & Stolarczyk, J. K., Angewandte Chemie International Edition, 2013, 52, 29, 7372-7408.
        [3] Kaneco, S., Kurimoto, H., Ohta, K., Mizuno, T., & Saji, A., Journal of Photochemistry and Photobiology A: Chemistry, 1997, 109, 1, 59-63.

      • 18:00
        An SO2-bridged p-terphenyl as versatile organo-photocatalyst under sustainable reaction conditions 1h
        Speaker: Ms Maria-Sophie Bertrams (University of Mainz)

        One electron oxidations or reductions of many substrates require very high redox potentials. The p-terphenyl radical anion is a highly reactive intermediate and known as photoredox catalyst for energy-demanding substrate activation reactions.[1] However, its usage requires not only hazardous UV light (<320 nm mostly from mercury-based light sources) for the direct generation, but also unsustainable solvents and high catalyst loadings.[1,2] Aiming to find more sustainable reaction conditions,[3] a novel strategy to access the radical anion of a tailor-made water-soluble p-terphenyl derivative has been investigated and exploited for photocatalytic applications.
        Double sulfonation of p-terphenyl ensured the usage of water as “green” solvent. Incorporating an SO2-bridge into the terphenyl backbone shifted the absorption spectrum towards longer wavelengths allowing direct excitation and subsequent radical anion formation with a conventional violet/UVA LED (390 nm).
        Detailed spectroscopic and photophysical investigations revealed the importance of the triplet excited state of our novel catalyst. This excited species can either undergo triplet-triplet energy transfer with suitable substrates or reductive quenching with ascorbate (vitamin C) to yield a reactive radical anion, thereby initiating different types of organo-catalyzed photoreactions[4,5] under environmentally friendly conditions.

        Literature:
        [1] H. Seo, M. H. Katcher, and T. F. Jamison, Nat. Chem., 2017, 456, 9, 453–456, DOI: 10.1038/nchem.2690
        [2] S. Yanagida et al., J. Phys. Chem., 1992, 96, 11, 4437-4442, DOI: 10.1021/j100190a057
        [3] P. Anastas and N. Eghbali, Chem. Soc. Rev., 2010, 39, 1, 301-312, DOI: 10.1039/B918763B
        [4] E. Speckmeier, T. G. Fischer, and K. Zeitler, J. Am. Chem. Soc., 2018, 140, 45, 15353–15365, DOI: 10.1021/jacs.8b08933
        [5] C. Fischer, C. Kerzig, B. Zilate, O. S. Wenger, and C. Sparr, ACS Catal., 2020, 10, 1, 210-215, DOI: 10.1021/acscatal.9b03606

      • 18:00
        Catalytic role played by the protein environment in facilitating specific retinal photoisomerization in rhodopsins 1h
        Speaker: Mr Pavel Kusochek (Lomonosov Moscow State University)

        Rhodopsins are photoactive proteins that catalyze various physicochemical reactions in microbial and animal cells that underlie different biological functions, such as vision, pumping specific ions into or out of the cell, phototaxis. The primary photochemical reaction in rhodopsins is isomerization of the chromophore, the protonated Schiff base retinal (PSBR). Microbial rhodopsins contain trans retinal, which isomerizes to the 13-cis form. In contrast, animal rhodopsins contain 11-cis retinal, which undergoes isomerization to the trans form.A high isomerization rate within hundreds of femtoseconds in various rhodopsins is provided in different ways. Based on our previous calculations [1], we conclude that the visual photoreceptors rely on the ultrafast intrinsic photoresponse of their 11-cis chromophore, whereas bacterial rhodopsins tune the photoresponse of the all-trans RPSB chromophore by particularly reducing the barrier height about the C13 = C14 double bond.The protein environment also plays an important role in providing high quantum yield and specificity of retinal isomerization.

        Here, we aim at revealing the catalytic role played by the protein in the primary photochemical reaction, which results in the retinal isomerization about a specific double bond in various protein environments. By using high-level extended multi-configuration quasi-degenerate perturbation theory (XMCQDPT2) combined with the effective fragment potential (EFP) method, we model photoabsorption profiles of PSBR inside the retinal-binding pockets of microbial rhodopsin KR2 and visual rhodopsin and compare them with those obtained for the chromophore in the gas phase. By analyzing vibronic band shapes, we explore the early-time excited-state dynamics of PSBR and show that the protein environment alters vibrational modes that are active upon the S0-S1 transition, facilitating specific photoisomerization. Based on molecular dynamics sampling, we also study structural inhomogeneity and flexibility of the retinal-binding sites of rhodopsins. We show that through formation of a strong hydrogen bond between the retinal Schiff base and the counterion, the PSBR conformation can be changed. This results in pre-twisting of the specific double bond in the ground state, which enhances the activity of both the localized stretching and hydrogen-out-of-plane (HOOP) modes upon photoexcitation. This allows us to show, for the first time, a direct link between the structure of the retinal-binding pocket and the reaction dynamics of PSBR in the proteins.

        This work is supported by the Russian Foundation for Basic Research (grant no. 19-33-90254). The research is carried out using the equipment of the shared research facilities of HPC computing resources at Lomonosov Moscow State University as well as the local resources provided through the Lomonosov Moscow State University Program of Development.

        1. Kiefer H. V. et al. Intrinsic photoisomerization dynamics of protonated Schiff-base retinal // Nat. Commun. 2019. Vol. 10, № 1. P. 1210.
      • 18:00
        Crystal Facet Engineering for Tailoring Photoactive TiO2 Nanoparticles 1h
        Speaker: Dr Ángel Morales-García (University of Barcelona)

        Solar energy storage in the form of chemical bonds is of paramount relevance in the modern energy economy to increase the share of renewable energy utilization in moving to decarbonization. The ideal energy vector for the storage of solar energy is molecular H2 because of its high energy density and it can be produced from water splitting. However, photocatalysis has experienced five decades of hard struggle and solar-to-hydrogen conversion via photocatalysis remains very challenging due to great complexity of the catalytic processes sequentially occurring at different time scales.

        The current scope of the heterogeneous photocatalysis design is based on a low-efficiency “trial-and-error” methodology that tremendously increases the workload of the research community. To overcome this challenge, multiscale modelling can provide a clear picture for “photocatalysis by design” from the viewpoint of mechanisms and guide us to select proper parameters. On the other hand, the limited instrumental characterization cannot completely fulfill the requirements for complex charge kinetics, particularly at the atomic and electronic scale. Indeed, theoretical investigations of photocatalysis have progressed rapidly alongside experimental attempts and met with great success. Based on nanoparticle crystal facet engineering I will describe different ways for tailoring the properties of realistic TiO2 nanoparticles (Figure 1). My goal is to show fundamental insights, dominating factors and structure-property relationships that will be further used to optimize the product outcome and to design enhanced photocatalysts.

      • 18:00
        Crystal Structure Modification towards Visible Light Absorption in Defect-Pyrochlores 1h
        Speaker: Mr Morten Weiss (University of Bayreuth)

        The search for a sustainable energy source to satisfy the rising energy demand of an increas-ing world population is one of the most important tasks of contemporary research. Although solar energy has enough potential to satisfy the demand many times over, its intermittency is a serious bottleneck. Photocatalysis is a very promising way to convert solar energy into chemical fuels, which can be stored, transported and used on demand.

        However, the most commonly used metal oxide semiconductors – such as TiO2 – have large band gaps, which seriously restricts their application in solar light conversion. Herein, we have used defect-pyrochlores AMxW2-xO6 (A: K, Cs; M: transition metal) as model systems to achieve visible light absorption by changing the crystal structure composition.

        The defect-pyrochlore crystal structure consists of corner-sharing MO6 and WO6 octahedra forming hexagonal channels, in which the loosely bound A ions are located (Figure 1). Ion exchange of these ions with Sn2+ results in the formation of a new valence band with Sn 5s2 orbitals, which decreases the band gap by 1.4 eV down to 2.2 eV.[1]

        Another advantage of defect-pyrochlores is their high elemental diversity: since Mn+n+ and W6+ are located on the same site, it is possibly to incorporate Mn+ cations of different oxidation states by changing the M/W ration, thus retaining charge balance. By incorporating Mn+ cations with partially occupied d levels, it is possible to change the band structure and thus the band gap of these materials.

        [1] M. Weiss, T. Bredow, R. Marschall, Chem. Eur. J., 2018, 24, 69, 18535-18543, 10.1002/chem.201803276.

      • 18:00
        Degradation of polyphenolic contaminants using a natural polymeric dye of riboflavin-5'-phosphate cross-linked chitosan as photosensitizer 1h
        Speaker: Ms Julieta Sacchetto (Universidad Nacional de Rio Cuarto)

        Generally, water treatment plants fail to completely eliminate pollutants, thus resulting in some contaminants passing into water bodies, producing harmful effects on the environment. One of the main environmental pollutants degradation mechanisms are chemical pathway, which involve several transformations, some of them take place in the presence of solar radiation known as direct or sensitized photoreactions. The emphasis will be on a sensitized photolysis reaction, involving the presence of another chemical, a dye that absorbs light radiation and produce excited states capable of inducing a photoprocess cascade, in which highly reactive species are formed. Besides, the dyes used in the photodegradation processes have the disadvantage that these dyes remain in the environment. The main issue with these methods lies in extracting the dye once the reaction is complete. This problem may be reduced, or fully solved with the use of polymeric dyes (PD), whose water solubility varies with the pH of the solution. In this case, the photosensitized contaminant degradation occurs while the PD is dissolved in acid media.
        The PD consists of two natural compounds, specifically the sensitizer riboflavin 5'-phosphate (FMN) and chitosan (CH), which makes PD fully aquatic-friendly. 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) was used for PD synthesis as a crosslinker to create a phosphoramidate bond via EDC, which is formed by the FMN phosphate group and the CH amino group. A polymer of the same colour and similar photophysical properties of free sensitizer was obtained. Another important feature of this PD is that it is more photostable than the free dye and is readily removed by pH shift from the medium since it is soluble in solution of acetic acid and precipitates in solution of pH > 5.9.
        Polyphenols (THB) were selected to test the photocatalytic activity of the synthesized polymer. THBs are known pollutants that are reactive to singlet oxygen (1O2) in homogeneous media. Oxygen uptake and UV-Vis spectroscopy monitored the photosensitised oxidation of THBs by PD. These results are comparing with those obtained using the free sensitizer. Different scavengers were used to evaluate the reactive oxygen species (ROS) involvement in the degradation process. The participation of 1O2, H2O2 and HO• in the degradation of THBs were studied in these experiments. In addition, laser flash photolysis studies have shown that CP's electronically excited states are also involved in THB degradation.
        The use of the CP in the photosensitized process represents a great advantage over the free dye and heterogeneous sytems. The CP has a higher photostability, which allows it to be used for longer periods of times. It does not present the diffusion problems intrinsic to heterogeneous media. Finally, one of the most promising characteristics of these CP, is that it can be extracted after photosensitized reaction, leaving the aquatic environments free of pollutants or pigments. This environmental friendly CP, provides a practical solution for those who are immersed in the subject of environment remediation or water treatment technologies

      • 18:00
        Influence of the organic and inorganic matter in the photocatalytic degradation of pharmaceuticals 1h
        Speaker: Ms Maria Barros (Laboratory of Separation and Reaction Engineering - Laboratory of Catalysis and Materials (LSRE-LCM))

        The use of graphite-like carbon nitride (g-C3N4) combined with light-emitting diodes (LEDs) is a powerful tool for the degradation of organic contaminants in wastewaters and surface waters, since it provides high mineralisation rates under mild conditions, thus resulting in energy savings [1]. Most photocatalytic studies employ ultrapure (UP) water spiked with individual target micropollutants (MPs), with concentrations higher than those found in real waters [2]. However, the studies carried out with real waters, namely river and wastewaters, usually report removal rates lower than those in UP water due to the presence of organic and inorganic species that can trigger light attenuation, consumption or scavenging of oxidative free radicals and adsorption onto the catalyst surface [3].
        In the present work, g-C3N4 was applied to study the photocatalytic degradation of two pharmaceuticals widely consumed worldwide and found in large quantities in wastewaters and surface waters [3]. Specifically, we investigated the abatement of nonsteroidal anti-inflammatory diclofenac (DCF) and β-blocker metoprolol (MET), individually and as a mixture. The latter case to study the possible interfering effect of each pharmaceutical on the other. Also, we evaluated the impact of the water matrix type (river and wastewater), as well as the presence of inorganic ions, such as NO2-, NO3-, PO43- and SO42-.
        g-C3N4 proved to be efficient for the degradation of both MPs under visible light irradiation, even when using real water matrices. When real waters were spiked with both pharmaceuticals, some photochemical instability was detected. The organic matter might be the main responsible for indirect photolysis for both MPs since for the inorganic species we observed a negligible effect. It was also possible to verify a competitive effect between these two pharmaceuticals, due to the decrease of the degradation kinetic constants of MET when co-occurring with DCF. In contrast, the presence of MET did not significantly affect the degradation rates of DCF. Lastly, the photocatalytic degradation mechanism of g-C3N4 was studied, and we concluded that both radicals and photogenerated holes play essential roles in the degradation of these MPs with different pKa. In sum, we concluded that the degradation rate of a particular MP might depend on other co-existing MPs.

        Acknowledgements: This work was financially supported by projects POCI-01-0145-FEDER-030674 and POCI-01-0145-FEDER-029600 funded by European Regional Development Fund (ERDF) through COMPETE2020 - Programa Operacional Competitividade e Internacionalização (POCI) - and by national funds (PIDDAC) through FCT/MCTES. We would also like to thank the scientific collaboration under Base Funding - UIDB/50020/2020 of the Associate Laboratory LSRE-LCM - funded by national funds through FCT/MCTES (PIDDAC). MAB acknowledges the research grant from FCT (Ref. SFRH/BD/145014/2019).

        References:
        1. Carbajo J, Jiménez M, Miralles S, Malato S, Faraldos M, Bahamonde A. Chem Eng J. 2016;291:64-73. doi:10.1016/j.cej.2016.01.092
        2. Rioja N, Zorita S, Peñas FJ. Appl Catal B Environ. 2016;180:330-335. doi:10.1016/j.apcatb.2015.06.038
        3. Lado Ribeiro AR, Moreira NFF, Li Puma G, Silva AMT. Chem Eng J. 2019;363:155-173. doi:10.1016/j.cej.2019.01.080

      • 18:00
        Insights on the mechanism of surface grafted hexaniobate for H2 evolution 1h
        Speaker: Ms Barbara Nascimento Nunes (Leibniz Universität Hannover)

        Niobates are layered compounds formed by [NbO6] octahedral units with an extended 2D arrangement. It provides not only electronic and structural advantages due to the high surface area and electron mobility but also an easy modification by intercalation, superficial modification, or exfoliation. Nevertheless, its photoactivity is ruled by the wide bandgap energy close to 3.5 eV and the high affinity for the photogenerated H2O2. Therefore, some strategies are required to increase the photocatalytic potential and to unveil the redox processes of this material. In this sense, surface grafting is a soft and simple method that has gain attention for inducing new electronic process on the catalyst surface without changing crystallinity and electronic structure in the bulk. In our work, the surface grafting with metallic ions such as Co(II) and Fe(III) could be applied to increase the performance of the exfoliated hexaniobate. In comparison to the bare niobate, 0.1 % of the metallic cation was able to improve the evolution of H2 from water in the applied conditions. The properties and dynamics of the photocatalysts will be discussed based on steady-state and time-resolved spectroscopies.

      • 18:00
        Metal-Free Visible Light-Promoted Synthesis of Isothiazoles: a Catalytic Approach for N−S Bond Formation from Iminyl Radicals 1h
        Speaker: Dr Sara Cembellin (Universidad Autónoma de Madrid)

        Isothiazoles are important scaffolds in medicinal chemistry and agriculture industry. This prominent moiety occurs in various antipsychotic drugs, some inhibitors of biological targets and different pesticides.[1] Traditional methods for the preparation of these heterocycles often require harsh conditions, high temperatures or the use of transitions metals.[2] Therefore, a simple, direct and sustainable approach towards the synthesis of isothiazoles would be of significant interest.
        Photoredox catalysis mediated by visible light has received much attention in the past decade.[3] Its mild and green conditions have made it a suitable option to develop new efficient, economical and environmentally friendly transformations. In particular, in the last years iminyl radicals, versatile synthetic intermediates in the construction of more complex molecules, have been successfully generated from oxime derivatives through a photoredox approach, avoiding the UV irradiation or high temperatures previously required.[4]
        On this basis, and taking advantage of our experience in sulphur chemistry, we envisioned that iminyl radicals generated by oxidative SET could be appropriate for the formation of S−N bonds, although to the best of our knowledge it has not been reported to date. Herein, we describe the efficiently realization of this approach and we apply it in the development of a new synthesis of isothiazoles from α-imino-oxy acids using mild conditions and promoted by visible light.[5]

        [1] a) C. Prakash, Drug Metab. Dispos. 1997, 25, 897; b) A. Genokaki, P. Eleftheuriou, P. Vicini, I. Alam, A. Dixit, A. K. Saxena, J. Med. Chem., 2008, 51, 5221;
        [2] a) A.-S. S. Hamad Elgazwy, Tetrahedron, 2003, 59, 7445; b) A. De Oliveira Silva, J. McQuade, M. Szostaka, Adv. Synth. Catal. 2019, 361, 3050.
        [3] a) K. L. Skubi, T. R. Blum, T. P. Yoon, Chem. Rev. 2016, 116, 10035; b) N. A. Romero, D. A. Nicewicz, Chem. Rev. 2016, 116, 10075.
        [4] a) H. Jiang, A. Studer, Angew. Chem. Int. Ed. 2017, 56, 12273; b) J. Davies, N. S. Sheikh, D. Leonori, Angew. Chem. Int. Ed. 2017, 56, 13361; c) J. Davies, S. P. Morcillo, J. J. Douglas, D. Leonori, Chem. Eur. J. 2018, 24, 12154.
        [5] M. J. Cabrera, S. Cembellín, A. Halima-Salem, L. Marzo, M. Berton, C. Maestro, J. Alemán, Green Chem. 2020, in revision.

      • 18:00
        Novel Hybrid Organic-Inorganic Photoelectrodes for Hydrogen Evolution Reaction 1h
        Speaker: Elena Alfonso González (Fundación IMDEA Energía)

        Artificial photosynthesis by photoelectrocatalysis is one of the most promising ways to store solar energy in the form of fuels, thus constituting a sustainable alternative to fossil fuels.[1,2] Conjugated polymers (CPs) are used as part of some photoelectrodes due to their good conductivity and the possibility to tailor their optoelectronic properties at the molecular level. Some of the most used CPs, such as PEDOT, have a linear structure; which makes them easy to process as thin films, but also unstable under UV illumination if they are in contact with water.[3] Conjugated Porous Polymers (CPP)[3–5] show higher stability due to their 3D structure. However, it is difficult to produce thin films with them by conventional methods such as drop casting or spin coating because of their morphology.
        Thanks to the electropolymerization process, we are able to prepare homogeneous, transparent and light-absorbing CPP films both on conducting glass substrates and on inorganic semiconductors. One of these CPPs, IEP-19 (Imdea Energy Polymer-19), has been synthesized for the first time and it shows promising photocurrents, which are significantly higher than those of a previously known CPP with a similar structure: CPP-3TB. Moreover, hybrid photoanodes where the CPP is electropolymerized on top of the inorganic semiconductor present higher photocurrents than the semiconductors alone, showing a synergistic effect between the organic and inorganic semiconductors. These results will be explained according to the optical, photoelectrochemical and morphological properties of the photoanodes.

        [1]: Michael G. Walter, Emily L. Warren, James R. McKone, Shannon W. Boettcher, Qixi Mi, Elizabeth A. Santori and Nathan S. Lewis, Chemical Reviews, 2010, 110, 6446–6473, DOI: 10.1021/cr1002326
        [2]: Roel van de Krol and Michael Grätzel, Photoelectrochemical Hydrogen Production, 2012, DOI: 10.1007/978-1-4614-1380-6
        [3]: Marta Liras, Mariam Barawi and Víctor A. de la Peña O’Shea, Chemical Society Reviews, 2019, 48, 5454–5487, DOI: 10.1039/c9cs00377k
        [4]: Carmen G. López-Calixto, Silvia Cabrera, Raúl Pérez-Ruiz, Mariam Barawi, José Alemán, Víctor A. de la Peña O’Shea and Marta Liras, Applied Catalysis B Environmental, 2019, 258, 117933, DOI: 10.1016/j.apcatb.2019.117933
        [5]: Cheng Gu, Ning Huang,Youchun Chen, Leiqiang Qin, Hong Xu, Shitong Zhang,Fenghong Li, Yuguang Ma and Donglin Jiang, Angewandte Chemie International Edition, 2015, 54, 13594-13598, DOI: 10.1002/anie.201506570

      • 18:00
        Order, please: How to Create Vertically Oriented Assemblies of CdSe@CdS Nanorods on Conductive Surfaces 1h
        Speaker: Dr Mathias Micheel (Leibniz-Institute of Photonic Technology)

        Semiconductor nanostructures such as CdSe@CdS nanorods have already proved to be ideal photosensitizers for photocatalytic applications. Not only do their high absorption coefficients allow for efficient harvesting of solar light, but also their structure promotes efficient and long-lived charge separation: Upon photon excitation, an electron-hole pair is generated with the hole quickly localizing in the CdSe core and the electron, which is delocalized over the entire rod, can be transferred to a catalyst coupled to the nanorod tip. There, proton reduction can occur. [1,2]
        We are currently focusing our efforts on aligning CdSe@CdS nanorods on a transparent, conductive surface, i.e., ITO glass, for the construction of a photoelectrode in a full watersplitting cell: While the electron is transferred to the catalytic center located at the nanorod tip and used for hydrogen reduction, the hole could be transferred to a counter electrode, where it may oxidize water to generate molecular oxygen. To this end, the nanorods have to be aligned on the surface under retention of their anisotropic properties. Two different approaches, namely electrophoretic deposition and interfacial self-assembly, are discussed and compared.

        Financial support is acknowledged by the German Research Foundation (DFG) – project number 364549901 - TRR234 [CataLight, B4)] and the Fonds der Chemischen Industrie (FCI).

        [1] M. Wächtler, P. Kalisman, L. Amirav, J. Phys. Chem. C 2016, 120, 24491–24497.
        [2] Y. Nakibli, Y. Mazal, Y. Dubi, M. Wächtler, L. Amirav, Nano Lett. 2018, 18, 357–364.

      • 18:00
        Photocontrolled isomerization of azobenzenes-based platinum complexes, which can be used in PACT 1h
        Speaker: Jorge M Herrero

        Cisplatin is an antitumor metal complex known for its high activity and clinical use. However, its serious side effects have conducted research into new complex designs with less toxicity and greater antitumor efficacy. Currently, there are antitumor therapies that use irradiation as a method of activating chemical compounds to increase their activity and thus control them within the system. Photochemical therapy (PACT) is of particular interest, since it allows this control in drugs temporarily and spatially
        An alternative in the development of metal antitumor complexes is the formation of complexes containing ligands with "cis/trans" photochemical isomerization capacity due to the presence of the azo group (-N=N-). This fact offers the possibility of a photochemical control in the antitumor activity of these types of compounds.
        Within this frame, we have synthetized and characterized ligands which carry an azo group in their structures. We have also tested and studied the reactions of these ligands with platinum(II) salts to give the corresponding platinum complexes. The photochemical properties and the effect of the solvents on the structure of the azo compounds and the complexes have been studied by Nuclear Magnetic Resonance and UV-vis spectroscopy. The preliminary results evidence that the platinum complexes undergo trans-cis isomerization upon irradiation, and the cis isomers then undergo slow thermal isomerization back to the more stable trans isomers. Thus, this synthetic route and design could be a promising strategy to obtain photoactivable prodrugs to use in Phototherapy for cancer treatment.

      • 18:00
        Small Molecule Reactions Using Earth Abundant Metal Complex Photoredox Catalysts 1h
        Speaker: Bryony Hockin (University of St Andrews)

        Photoredox catalysis has become an extremely valuable process in organic synthesis. The most popular photocatalysts are based on ruthenium(II) and iridium(III) complexes such as [Ru(bpy)3]2+ and fac-Ir(ppy)3. The detracting feature of these catalysts is that the metals are both expensive and toxic.[1,2] Copper(I) complexes present an inexpensive and versatile alternative for use in photoredox catalysis, which has enticing potential for small molecule transformations.[2]

        We present the design, computational modelling, synthesis and optoelectronic characterisation of a series of photoactive Cu(I)-NHC complexes,[3] which are designed to negatively shift the excited state oxidation potential and so be better photoreductants. We also show preliminary efforts of their use in a range of photocatalytic organic transformations including C-H activation, C-C bond forming, ATRA and energy transfer reactions.[4,5]

        [1]: B. M. Hockin, C. Li, N. Robertson and E. Zysman-Colman, Catal. Sci. Technol., 2019, 9, 889, 10.1039/C8CY02336K.
        [2]: C. K. Prier, D. A. Rankic, and D. W. C. MacMillan, Chem. Rev., 2013, 113, 5322, 10.1021/cr300503r.
        [3]: R. Marion, F. Sguerra, F. Di Meo, E. Sauvageot, J.-F. Lohier, R. Daniellou, J.-L. Renaud, M. Linares, M. Hamel, and S. Gaillard, Inorg. Chem., 2014, 53, 9181, 10.1021/ic501230m.
        [4]: S. Parisien-Collette, A. C. Hernandez-Perez, and S.K. Collins, Org. Lett., 2016, 18, 4994, 10.1021/acs.orglett.6b02456.
        [5]: M. Pirtsch, S. Paria, T. Matsuno, H. Isobe, and O. Reiser, Chem. Eur. J., 2012, 18, 7336, 10.1002/chem.201200967.

      • 18:00
        Transforming bimetal zinc nickel oxide to oxysulfide photocatalyst with its exceptional performance to evolve hydrogen 1h
        Speaker: Noto Susanto Gultom (National Taiwan University of Science and Technology)

        Photocatalytic hydrogen production with semiconductor catalyst is one of the best techniques to produce green hydrogen gas. This research investigated the effect of sulfur content on phase transformation of bimetal zinc nickel oxide to oxysulfide, which simultaneously affected the performance on photocatalytic hydrogen production. Different amounts of sulfur precursor (0, 0.25, 0.5, 0.75 and 1 mmol) were added to the bimetal oxide during the hydrothermal synthesis. The as-prepared catalysts were carefully characterized with necessary analyses such as X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV–vis spectrophotometer, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, Brunauer-Emmett-Teller (BET) and transient photo current analyses. The sulfur content significantly affected not only the morphology and phase structure but also greatly improved the hydrogen production rate. The maximum hydrogen production rate of 15,000 μmol/g.h was achieved by using S-0.75 catalyst, which was 333-fold as compared to that with the catalyst before phase transformation. Our design of ZnNiOS had an exceptionally high photocatalytic activity as compared to single-phase oxide and sulfide. Herein, we demonstrated an important insight and material design about the effects of sulfur content on phase transformation, catalyst morphology, and photocatalytic activity.

      • 18:00
        Unconventional photophysical behaviour of Ruthenium(II) complexes for the localization of Catalysts in complicated polymer matrices 1h
        Speaker: Mr Benedikt Bagemihl (Institute for Inorganic Chemistry 1, Ulm University)

        Integrating homogeneous photocatalysts into soft matter scaffolds represents an attractive option for the production of solar fuels. However, analysis of the involved and catalytically active states in the catalytic cycle of the catalyst is challenging because of the photochemical background of the scaffold.
        In this study, we present a method involving combined efforts in theory and experiment that might help to overcome this issue. We modeled the optical behavior of the well-known photocatalyst (R2bpy)2Ru(tpphz)PtI2 using TDDFT calculation provided by Gaussian 16 package[1,2]. For the gas phase model, the Pt-to-tpphz transition is remarkably shifted into the low-energy region[3]. This optical transition could be used as a marker to identify the localization of the photocatalyst within a less polar polymer environment, thus providing an excellent tool for in situ characterization[4].
        Respective experimental efforts in solvating the photocatalyst will aim for solubility in low polarity solvents such as toluene, which model gaseous environment.

        We gratefully acknowledge support from DFG, TRR 234 Catalight Projects C5 and B2. Computer time on the JUSTUS cluster at Ulm University provided by the bwHPC initiative and the bwHPC-C5 project funded by the Baden-Württemberg government (MWK) and the German Research Foundation (DFG) is gratefully acknowledged.

        References:

        [1] [M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, G. A. Petersson, H. Nakatsuji, X. Li, M. Caricato, A. V. Marenich, J. Bloino, B. G. Janesko, R. Gomperts, B. Mennucci, H. P. Hratchian, J. V. Ortiz, A. F. Izmaylov, J. L. Sonnenberg, D. Williams-Young, F. Ding, F. Lipparini, F. Egidi, J. Goings, B. Peng, A. Petrone, T. Henderson, D. Ranasinghe, V. G. Zakrzewski, J. Gao, N. Rega, G. Zheng, W. Liang, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, K. Throssell, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. J. Bearpark, J. J. Heyd, E. N. Brothers, K. N. Kudin, V. N. Staroverov, T. A. Keith, R. Kobayashi, J. Normand, K. Raghavachari, A. P. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, J. M. Millam, M. Klene, C. Adamo, R. Cammi, J. W. Ochterski, R. L. Martin, K. Morokuma, O. Farkas, J. B. Foresman, and D. J. Fox, “Gaussian~16 Revision C.01,” (2016), Gaussian Inc. Wallingford CT.
        [2] M. G. Pfeffer, T. Kowacs, M. Wächtler, J. Guthmuller, B. Dietzek, J. G. Vos, S. Rau, Angew. Chemie Int. Ed. 2015, 54, 6627–6631.
        [3] J. Habermehl, D. Sorsche, P. Murszat, S. Rau, Eur. J. Inorg. Chem. 2016, 2016, 3423–3428.
        [4] L. Zedler, A. K. Mengele, K.-M. Ziems, Y. Zhang, M. Wächtler, S. Gräfe, T. Pascher, S. Kupfer, S. Rau, B. Dietzek, Angew. Chemie Int. Ed. 2019, 13140–13148.

      • 18:00
        Unraveling the Reactivity of a Tetramanganese-Polyoxovanadate Water Oxidation Catalyst 1h
        Speaker: Mr Ludwig Schwiedrzik (Institute of Theoretical Chemistry, University of Vienna)

        In nature, photosystem II carries out water splitting as part of photosynthesis to fuel cell growth and produce the oxygen all aerobic life depends on. Within photosystem II, the rate-limiting water oxidation reaction is catalyzed by the oxygen-evolving complex, a highly efficient tetramanganese enzyme that has inspired many attempts to develop synthetic catalysts of similar structure.[1] Schwarz et al. have proposed a tetramanganese-polyoxovanadate water oxidation catalyst, [Mn4V4O17(OAc3)3- (Mn4V4), that shows considerable activity (TON≈12000, TOF≈3,6s-1 under photocatalytic conditions.[2,3] However, Mn4V4 still falls short of the activity of the oxygen evolving complex by orders of magnitude.[4] Detailed mechanistic understanding of the reactivity of Mn4V4 is required to design improved water oxidation catalysts. To this end, we have carried out a comprehensive theoretical investigation of the water oxidation mechanism on Mn4V4 using density functional theory. Having optimized and compared intermediates across various catalyst oxidation and protonation states, we propose a direct coupling mechanism for the formation of O2 consisting of a series of (proton-coupled) electron transfer steps. Furthermore, we have studied the effects of Jahn-Teller distortions on the catalytic activity of Mn4V4. Using the insights gained through our theoretical simulations, we hope to unravel the reactivity of Mn4V4 and thereby open the way for the rational design of improved water oxidation catalysts.

        References:
        [1]: Umena, Y.; Kawakami, K.; Shen, J.-R.; Kamiya, N. Nature 2011, 473 (7345), 55–60, http://doi.org/10.1038/nature09913
        [2]: Schwarz, B.; Forster, J.; Goetz, M. K.; Yücel, D.; Berger, C.; Jacob, T.; Streb, C. Angew. Chem. Int. Ed. 2016, 55 (21), 6329–6333, https://doi.org/10.1002/anie.201601799
        [3]: Huber, L.; Amthor, S.; Schwarz, B.; Mizaikoff, B.; Streb, C.; Rau, S. Sustainable Energy Fuels 2018, 2 (9), 1974–1978, https://doi.org/10.1039/C8SE00328A
        [4]: Dau, H.; Limberg, C.; Reier, T.; Risch, M.; Roggan, S.; Strasser, P. ChemCatChem 2010, 2 (7), 724–761, https://doi.org/10.1002/cctc.201000126

      • 18:00
        Visible light driven water treatment through graphitic carbon nitride nanomaterials 1h
        Speaker: Mr André Torres-Pinto (LSRE-LCM/U.Porto)

        The global water crisis is hindering healthy human endurance and societal development. Water treatment is crucial for a sustainable balance between society and the environment. The industry must treat its wastewaters adequately as they are particularly rich in potentially hazardous compounds. The United Nations recognised the crisis and led to the establishment of the Sustainable Development Goals (SDGs) in 2015 [1]. A significant cause of water pollution is the inadequate release of organic contaminants to the environment. In particular, olive mill wastewaters (OMWW) are considered as hazard to environmental sustainability in the Mediterranean region.
        Advanced oxidation processes (AOPs) represent an efficient, low cost and safe solution for the removal of recalcitrant compounds present in OMWW. In particular, heterogeneous photocatalysis with graphitic carbon nitride (GCN) activated by visible light using LEDs has been proven to be efficient in the degradation of several organic pollutants [2]. In this study, we investigated the use of GCN, prepared by a thermal treatment method, in the photocatalytic degradation of phenolic compounds often present in OMWW [3]. We explored the simultaneous in situ evolution of hydrogen peroxide (H2O2) as a mean to enhance pollutant degradation. Moreover, the improvement of the mineralisation process was sought with the addition of iron to mimic photo-Fenton-like conditions [4]. An impact superior than 20% in mineralisation was observed with relatively low dosages of iron ions (according to Portugal’s legislation) and under natural pH, which could enable a greater ease on the discharge of treated liquid effluents.

        [1] Transforming Our World: The 2030 Agenda for Sustainable Development, UN General Assembly, 2015.
        [2] Wee-Jun Ong, Lling-Lling Tan, Yun Hau Ng, Siek-Ting Yong, Siang-Piao Chai, Chem. Rev., 2016, 116, 12, 7159 7329, 10.1021/acs.chemrev.6b00075.
        [3] André Torres-Pinto, Maria J. Sampaio, Cláudia G. Silva, Joaquim L. Faria, Adrián M.T. Silva, Appl. Catal. B Environ. , 2019, 252, 128-137, 10.1016/j.apcatb.2019.03.040.
        [4] André Torres-Pinto, Maria J. Sampaio, Jessica Teixo, Cláudia G. Silva, Joaquim L. Faria, Adrián M.T. Silva, J. Water Process. Eng. , 2020, 37, 101467, 10.1016/j.jwpe.2020.101467.

    • 15:00 15:30
      Charge Carrier Dynamics in Semiconductor Nanostructures for Light-Driven Catalysis 30m
      Speaker: Maria Wächtler (Leibniz Institute of Photonic Technology)
    • 15:35 16:20
      Characterization II
      Convener: Mathias Micheel (Leibniz Institute of Photonic Technology)
      • 15:35
        Time-Resolved Spectroscopy of new Fe-Based Photosensitizers 20m
        Speaker: Ms Linnea Lindh (Chemical Physics/Theoretical Chemistry Lund University)

        It has been widely recognized in the scientific community that scarce elements such as ruthenium are not ideal for sustainable technology. During the past 10 years, progress has been made in exploring first-row transition metals as replacements for scarce metals in many solar cell and photocatalysis applications.[1] Iron analogues to well-performing ruthenium-complexes were early found to not yield nearly the same solar cell performance, despite Ru and Fe being congeners.[2] Prior to our efforts, by means of ultrafast spectroscopy it was found that the relevant excited state deactivates in less than a ps, a timescale not accessible for most electron-transfer reactions.[3]

        In the work described here, a class of complexes called the iron-carbenes has by clever ligand design been able to enter a much wider range of timescales. Since the first iron-carbene published in 2013 (with a lifetime of 9 ps), excited state lifetimes are now reaching up to 2 ns with potential applications going towards the photocatalysis field.[4,5,6] Fe-carbenes was for the first time successfully used in photocatalysis in 2017,[7] and since then a bi-metallic dyad connecting an iron photosensitizer with a cobalt catalytic centre has been synthesized.[8] Also, the record efficiency for iron-based dye-sensitized solar cells is held by an Fe(II)-carbene complex.[9]

        In the study from 2017, the lifetime of the photochemically relevant 3MLCT is still a big limiting factor.[7] To further prolong the lifetime, a key strategy is to facilitate the charge-separation by using sensitizers made as push-pull complexes. In this work, a new set of push-pull iron-carbenes have been characterized by ultrafast transient absorption spectroscopy both in solution and after sensitization of titania nanoparticles. In this way it is possible to study also interfacial electron-transfer processes. In particular, our results show how the newest set of push-pull molecules, with novel ligand design, yields better photochemical properties promising for solar cell applications and heterogeneous catalysis.

        [1] O.S. Wenger, Photoactive Complexes with Earth-Abundant Metals, J. Am. Chem. Soc. 140 (2018) 13522–13533. https://doi.org/10.1021/jacs.8b08822.
        [2] S. Ferrere, B.A. Gregg, Photosensitization of TiO2 by [FeII(2,2‘-bipyridine-4,4‘-dicarboxylic acid)2(CN)2]: Band Selective Electron Injection from Ultra-Short-Lived Excited States, J. Am. Chem. Soc. 120 (1998) 843-844. https://doi.org/10.1021/ja973504e
        [3] J. E. Monat, J. K. McCusker, Femtosecond Excited-State Dynamics of an Iron(II) Polypyridyl Solar Cell Sensitizer Model, J. Am. Chem. Soc. 122 (2000) 4092–4097. https://doi.org/10.1021/ja992436o
        [4] Y. Liu et al., Towards longer-lived metal-to-ligand charge transfer states of iron(II) complexes: an N-heterocyclic carbene approach, Chem. Commun. 49 (2013) 6412–6414. https://doi.org/10.1039/c3cc43833c.
        [5] K.S. Kjær et al., Luminescence and reactivity of a charge-transfer excited iron complex with nanosecond lifetime, Science (80-. ). 363 (2019) 249–253. https://doi.org/10.1126/science.aau7160.
        [6] L. Lindh et al., Photophysics and Photochemistry of Iron Carbene Complexes for Solar Energy Conversion and Photocatalysis, Catalysts 10(3) (2020) 315. https://doi.org/10.3390/catal10030315
        [7] P. Zimmer et al., N-Heterocyclic Carbene Complexes of Iron as Photosensitizers for Light-Induced Water Reduction, European Journal of Inorganic Chemistry 11 (2017) 1504-1509 https://doi.org/10.1002/ejic.201700064
        [8] P. Zimmer et al., Towards Noble-Metal-Free Dyads: Ground and Excited State Tuning by a Cobalt Dimethylglyoxime Motif Connected to an Iron N-Heterocyclic Carbene Photosensitizer, European Journal of Inorganic Chemistry 48 (2018) 5203-5214 https://doi.org/ 10.1002/ejic.201800946
        [9] E. Marchini et al., Recombination and regeneration dynamics in FeNHC(II)-sensitized solar cells, Chem. Commun. (Camb). 56 (2020) 543–546. https://doi.org/10.1039/c9cc07794d.

      • 16:00
        Photocatalytic Water Splitting, Chemical characterization of Strontium titanate (SrTiO3) Water-Solid interface 20m
        Speaker: Martin BUESSLER (Institut für Physikalische Chemie, university of Vienna (Wien))

        The direct conversion of solar energy to hydrogen is considered as a promising method to produce carbon neutral hydrogen fuel. The mechanism of water splitting involves the chemical breakdown of water into hydrogen and oxygen by photonic energy. In 1972 Fujishima and Honda described a first photo electrochemical system capable of generating H2 and O2 using thin-films of TiO2[1].

        Nowadays, the major goal is to improve the solar to hydrogen conversion efficiency by doping, coupling and modifying the catalysts. The selection rules of a suitable material are well established and the major challenges are now to maximize the quantum yield, to improve the electrons-holes mobility and to understand the interfacial reactions driving the water oxidation reduction[2].

        Our research focuses on the mechanistic understanding of the water splitting at the interface between the catalyst and water. Using the surface specific vibrational spectroscopy sum frequency generation (SFG)[3], our final goal is to describe the water splitting process by observing the oxygen-hydrogen bonds conformation along the reaction. In this spectroscopic method an infrared beam in resonance with a molecular vibration and a visible laser beam are combined at the interface from where the sum frequency is generated. As no SFG signal is generated in centrosymmetric media like bulk water, this method provides information about the water alignment at the interface. Moreover, the frequency of the resonance reports on the hydrogen bonding strength.

        We have over the last month intensively studied the interface of the water splitting active photocatalyst Strontium titanate (SrTiO3). By studying the conformation of the water molecules at the strontium-water interface we have been able to describe the water orientation at the interface, the point of zero charge of the catalyst and to observe changes of the hydrogen bonding strength as a function of pH. This study shows a first chemical characterization of the Strontium-water interface by SFG spectroscopy and it is a first stepping stone to dynamically study the water splitting mechanism.

        [1]: Akira Fujishima and Kenichi Honda, Nature, 1972, vol 238, 7 July 1972, p. 37, 10.1038/238037a0
        [2]: Si Yin Tee, Khin Yin Win, Wee Siang Teo, Leng-Duei Koh, Shuhua Liu, Choon Peng Teng and Ming-Yong Han, Advanced Science, 2017, vol 4, 13 January 2017, p. 1600337, 10.1002/advs.201600337
        [3]: Alex G. Lambert, Paul B. Davies & David J. Neivandt, Applied Spectroscopy Reviews, 2007, vol 40, 2 February 2007, p. 103, 10.1081/ASR-200038326

    • 16:20 16:40
      Break 20m
    • 16:40 17:50
      Characterization II
      Convener: Mathias Micheel (Leibniz Institute of Photonic Technology)
      • 16:40
        From charge generation to hydrogen evolution using conjugated polymer photocatalysts 20m
        Speaker: Dr Michael Sachs (Imperial College London)

        While the field of sunlight-driven fuel generation has traditionally been dominated by inorganic materials, organic semiconductors are currently gaining substantial momentum for application as photocatalysts - particularly due to their much higher synthetic flexibility. For instance, their optical band gap can be tuned continuously throughout large parts of the solar spectrum by copolymerizing selected monomers in defined ratios. This tunability has sparked intense research interest in organic photocatalysts,[1] however, the fundamental understanding of photoinduced processes in these systems and the characterisation of their catalytically active sites have stayed behind the rapid development of new materials.

        In this presentation, I will demonstrate how transient and operando optical spectroscopic techniques can be used to track the evolution of photogenerated reaction intermediates in polymer photocatalysts on timescales of femtoseconds to seconds after light absorption. To this end, short laser pulses are used to study these photocatalysts under transient conditions whereas long LED pulses are employed to establish operando catalytic conditions, and photogenerated reaction intermediates are then probed optically. Firstly, these techniques reveal insights into the yield of photogenerated charges, which enables an understanding of differences in hydrogen evolution activity between different materials.[2] Secondly, these techniques allow to monitor the transfer of photogenerated electrons to catalytically active sites as well as their accumulation under operando photocatalytic conditions, where differences in electron transfer time translate into different kinetic bottlenecks of the hydrogen evolution reaction for different polymers.[3] To illustrate these points, I will draw direct comparisons between nanoparticle photocatalysts made from the polymers F8BT, P3HT, and the dibenzo[b,d]thiophene sulfone homopolymer, P10, which is one of the most performant polymer photocatalysts reported to date.[2]

        References:

        [1] Wang, Y.; Vogel, A.; Sachs, M.; Sprick, R. S.; Wilbraham, L.; Moniz, S. J. A.; Godin, R.; Zwijnenburg, M. A.; Durrant, J. R.; Cooper, A. I.; et al. Current Understanding and Challenges of Solar-Driven Hydrogen Generation Using Polymeric Photocatalysts. Nat. Energy 2019, 4 (9), 746–760. https://doi.org/10.1038/s41560-019-0456-5.
        [2] Sachs, M.; Sprick, R. S.; Pearce, D.; Hillman, S. A. J.; Monti, A.; Guilbert, A. A. Y.; Brownbill, N. J.; Dimitrov, S.; Shi, X.; Blanc, F.; et al. Understanding Structure-Activity Relationships in Linear Polymer Photocatalysts for Hydrogen Evolution. Nat. Commun. 2018, 9 (1), 4968. https://doi.org/10.1038/s41467-018-07420-6.
        [3] Sachs, M.; Cha, H.; Kosco, J.; Aitchison, C. M.; Francàs, L.; Corby, S.; Chiang, C.-L.; Wilson, A. A.; Godin, R.; Fahey-Williams, A.; Cooper, A. I.; Sprick, R. S.; McCulloch, I.; Durrant, J. R. Tracking Charge Transfer to Residual Metal Clusters in Conjugated Polymers for Photocatalytic Hydrogen Evolution. J. Am. Chem. Soc. 2020, 142 (34), 14574–14587. https://doi.org/10.1021/jacs.0c06104.

      • 17:05
        Mechanistic Insights into Triplet Energy Transfer Catalysis for Applications in Light-Driven Organic Synthesis of Sulfur-Containing Compounds 20m
        Speaker: Mr Christian Henkel (Friedrich-Alexander University Erlangen-Nuremberg)

        A large number of natural and/or artificial compounds – biomolecules, drugs, agrochemicals or functional materials – contain heteroatomic sulfur in their backbones.[1–3] Consequently, targeted strategies under preferably mild synthetic conditions are crucial in the context of synthesizing novel compounds with either unprecedented or fine-tailored properties. To this end, photochemistry constitutes a unique platform for precise synthetic tools. But, many (organic) substrates lack sufficient absorption throughout the visible range of the solar spectrum. Thus, a crucial bottleneck of light-driven chemical transformations is the need for substrate activation by means of harsh UV-light. The yields of transformations, which are induced by UV-light, are low and impacted by the formation of unwanted side-products including polymers etc. Here, radical intermediates produced by UV-light initiation are detrimental. An additional concern is the rather poor functional group tolerance throughout these reactions.[4] A promising approach to optimize the photon energy, which is necessary for substrate activation, is based on photocatalysis. Not only transition metal complexes, but also organic molecules stand out as suitable photocatalysts.[5] A common pathway by which the photocatalysts engage in the substrate activation is electron donation or acceptance.[5] In the present work, the focus is on a much less explored and understood pathway of photocatalysis, that is, triplet energy transfer catalysis.[1,6] In essence, upon photoexcitation the high-energy and long-lived triplet excited state of the photocatalysts are transferred in a Dexter-type fashion to the substrates of choice. We highlight recent progress in understanding the modus operandi of substrate photoactivation. This knowledge is used as starting point to design appropriate metal-complexes with optimized catalytic activity to visible-light activate organic substrates.[1,6]

        [1] M. Teders, C. Henkel, L. Anhäuser, F. Strieth-Kalthoff, A. Gómez-Suárez, R. Kleinmans, A. Kahnt, A. Rentmeister, D. Guldi, F. Glorius, Nat. Chem. 2018, 10, 981–988.
        [2] P. Devendar, G.-F. Yang, Top. Curr. Chem. 2017, 375, 82.
        [3] H. Mutlu, E. B. Ceper, X. Li, J. Yang, W. Dong, M. M. Ozmen, P. Theato, Macromol. Rapid Commun. 2019, 40, 1800650.
        [4] T. Gensch, M. Teders, F. Glorius, J. Org. Chem. 2017, 82, 9154–9159.
        [5] B. König, European J. Org. Chem. 2017, 2017, 1979–1981.
        [6] F. Strieth-Kalthoff, C. Henkel, M. Teders, A. Kahnt, W. Knolle, A. Gómez-Suárez, K. Dirian, W. Alex, K. Bergander, C. G. Daniliuc, B. Abel, D. M. Guldi, F. Glorius, Chem 2019, 5, 2183–2194.

      • 17:30
        Ruthenium(II) 2,4-di(pyridin-2-yl)-pyrimidine complexes as photosensitizers in photocatalytic hydrogen evolution under red light 20m
        Speaker: Mrs Mira Rupp (Julius-Maximilians-Universität Würzburg)

        The photocatalytic reduction of water to form hydrogen gas is a promising approach to collect, convert, and store solar energy. Typically, ruthenium tris-bipyridine and its numerous derivatives are used as photosensitizers (PSs) in a variety of photocatalytic conditions. The bis-terpyridine analogs, however, have only recently gained attention for this application due to their poor photophysical properties. Yet, by introducing electron donating or withdrawing groups on the terpyridine ligands, the photophysical and electrochemical properties can be improved significantly.
        In this study, a series of 2,6-di(pyridin-2-yl)-pyrimidine ligands with peripheral pyridine substituents has been prepared and used to prepare ruthenium(II) complexes. The presence of the pyrimidine ring stabilizes the lowest unoccupied molecular orbital (LUMO), leading to a red-shifted absorption and emission and prolonged excited-state lifetimes as well as higher luminescence quantum yields compared to analogous terpyridine complexes. Furthermore, all complexes are easier to reduce than previously reported bis-terpyridine complexes used as PS. An interesting correlation between substitution pattern and properties of the complexes was observed and further investigated using TD-DFT. In hydrogen evolution experiments under blue and red light irradiation, all investigated complexes exhibit a much higher activity compared to previously reported ruthenium(II) bis-terpyridine complexes but none of the complexes is as stable as the literature compounds, presumably due to an additional decomposition pathway of the reduced PS competing with the electron transfer from the reduced PS to the catalyst.

    • 17:50 18:00
      Break 10m
    • 18:00 19:00
      Poster Session II
      • 18:00
        A modular, self-assembling metallaphotocatalyst for cross couplings using the full visible-light spectrum 1h
        Speaker: Mrs Susanne Reischauer (Department of Biomolecular Systems, Max-Planck-Institute of Colloids and Interfaces)

        The combination of photo- and nickel catalysis (metallaphotocatalysis) has emerged as a powerful strategy for carbon–carbon and carbon–heteroatom cross couplings (1). Key to the success are redox or photosensitization events between a nickel- and a photocatalyst (PC). These protocols rely on a few photocatalysts that can only convert a small portion of visible light (<500 nm) into chemical energy. The high-energy photons that excite the photocatalyst can result in unwanted side reactions. Dyes that absorb a much broader spectrum of light are not applicable due to their short-lived excited states. We demonstrate a self-assembling catalyst system that overcomes this limitation. Immobilization of a nickel catalyst on dye-sensitized titanium dioxide results in a material that catalyzes carbon-heteroatom and carbon-carbon bond formations. The modular approach of dye-sensitized metallaphotocatalysts (DSMPs) accesses the entire visible light spectrum and allows tackling selectivity issues resulting from low-wavelengths strategically. The concept overcomes current limitations of metallaphotocatalysis by unlocking the potential of dyes that were previously unsuitable (2).

        References:
        [1] J. Twilton, C. Le, P. Zhang, M. H. Shaw, R. W. Evans, D. W. C. MacMillan, Nat.Rev. Chem. 2017, 1, 0052.
        [2] S.Reischauer, V. Strauss, B. Pieber, ChemRxiv. Preprint https://doi.org/10.26434/chemrxiv.12444908

      • 18:00
        Biipo - The Only Constant is the Life of pi 1h
        Speaker: Jannik Brückmann (Ulm University, Institute for Inorganic Chemistry I)

        Transition metal complexes of Ru(II), Os(II) or Ir(III) exhibit exeptional properties and enable various light-driven processes. But they suffer from limited photophysical activity due to decreased extinction coefficients at higher wavelengths (after 500 nm) and relatively small excited-state (ES) lifetimes. The multichromophoric approach is one possibility to overcome those drawbacks. Usage of additional, organic chromophores should enable us to use a wide range of the solar spectrum and extend the ES lifetimes. As a novel rylene type dye a diimine ligand with a fully rigid and extended π-system in its backbone was prepared by directly fusing a 1,10-phenanthroline building block with 1,8-naphthalimide. The corresponding heteroleptic ruthenium photosensitizer was synthesized and extensively analyzed by a combination of NMR, single crystal X-ray diffraction, steady-state absorption and emission, time-resolved spectroscopy and different electrochemical measurements supported by time-dependent density functional theory calculations.

        [1] A. Juris, V. Balzani, F: Barigeletti, S. Campagna, P. Belser, A. von Zelewsky Coord. Chem. Rev. 1988, 84, 85-277; [2] A. Lavie-Cambot, C. Lincheneau, M. Cantuel, Y. Leydet, N. D. McClenaghan Chem. Soc. Rev. 2010, 39 (2), 506–515; [3] H. Langhals Heterocycles 1995, 40 (1), 477–500; [4] Y. Yang, J. Brückmann, W. Frey, S. Rau, M. Karnahl, S. Tschierlei Chemistry - A European Journal 2020, accepted.

      • 18:00
        Copper(I) based photosensitizers with additional donor atoms in the proximity of the metal center 1h
        Speaker: Martin Rentschler (University of Stuttgart)

        Light-driven chemical reactions have several advantages over thermal reactions, e.g. the potential use of sunlight as an energy source or the access to certain reaction pathways that are thermally forbidden. Efficient photosensitizers that are not based on rare noble metals like ruthenium or iridium are a major subject of our current research.[1-5] In this respect, we are especially focused on heteroleptic Cu(I) photosensitizers of the type [(P^P)Cu(N^N)]+ consisting of one diphosphine (P^P) and one diimine ligand (N^N). These photosensitizers have to fulfil some basic requirements, i.e. reversible redox processes, a high (photo)stability and long-lived excited states.[1-5]
        An important de-excitation pathway for such Cu(I) photosensitizers is the so-called exciplex quenching, where a solvent molecules coordinates to the metal center in the excited complex (exciplex). Preventing this pathway by proper ligand design is a promising approach towards enhancing the excited state lifetimes of the resulting photosensitizers.[6,7] Therefore, we developed multidentate diimine ligands with different additional donor atoms in proximity of the metal center to understand and possibly overcome this quenching mechanism.[6,7]
        A multi-method approach was used to study the impact of these additional donor atoms on the coordination behavior in the ground and the excited state as well as on the complexes' photophysical and electrochemical properties.[6,7] The related complexes with no additional donor atoms were investigated for comparison.[6,7]

        [1] Y. Zhang, M. Schulz, M. Wächtler, M. Karnahl, B. Dietzek, Coord. Chem. Rev., 2018, 356, 127 146, DOI: 10.1016/j.ccr.2017.10.016.
        [2] M. Heberle, S. Tschierlei, N. Rockstroh, M. Ringenberg, W. Frey, H. Junge, M. Beller, S. Lochbrunner, M. Karnahl, Chem. Eur. J., 2017, 23, 312-319, DOI : 10.1002/chem.201604005.
        [3] R. Giereth, I. Reim, W. Frey, H. Junge, S. Tschierlei, M. Karnahl, Sustainable Energy Fuels, 2019, 3, 692-700, DOI: 10.1039/c8se00521d.
        [4] M.-A. Schmid, M. Rentschler, W. Frey, S. Tschierlei, M. Karnahl, Inorganics, 2018, 6, 134, DOI: 10.3390/inorganics6040134.
        [5] R. Giereth, A. K. Mengele, W. Frey, M. Kloß, A. Steffen, M. Karnahl, S. Tschierlei, Chem. Eur. J., 2020, 26, 2675-2684, DOI: 10.1002/chem.201904379.
        [6] M. Rentschler, S. Iglesias, M.-A. Schmid, C. Liu, S. Tschierlei, W. Frey, X. Zhang, M. Karnahl, D. Moonshiram, Chem. Eur. J., 2020, 26, 9527-9536, DOI: 10.1002/chem.201905601.
        [7] M. Rentschler, M.-A. Schmid, W. Frey, S. Tschierlei, M. Karnahl, Inorg. Chem., 2020, DOI: 10.1021/acs.inorgchem.9b03687.

      • 18:00
        Development of a Novel and Improved UVA-Photoelectrochemical Reactor for Wastewater Treatment 1h
        Speaker: Mr Salem Alkharabsheh (Ulster university)

        Photoelectrocatalysis (PEC), combining Photocatalysis (PC) and electrochemistry, is an environmentally friendly technology widely studied for the removal of organic and micropollutants in wastewater. PEC overcomes the high electron/hole recombination in PC process PEC is based on the use of a semiconductor photoelectrode and counter electrode connected by an external circuit in an electrolytic cell, the photoelectrode activated by irradiation and at the same time biased by a potential gradient. Several PEC reactors based on TiO2 photocatalyst and UV-A irradiation have been designed with different geometries and configurations for the removal of organic pollutants 1. However, these different designs are still under study at a lab-scale due to the various limitations, including high energy consumption and cost, energy loss during irradiation, low mass-transfer rate, electrode preparation difficulties, maintenance and high thickness of the immobilized film in the photoanode. This work presents a novel Photoelectrocatalytic cell based on channels sandwich configuration for the removal of organic pollutants from wastewater with improvement in the mass transfer, energy loss during irradiation, and cost (Fig.1). Further, COMSOL Multiphysics software (CFD) has been used to evaluate the effect of inlet pipe diameter (6.5 ,10 , and 17 mm) and the sandwich reactor channels width (10, and 17mm) on the flow velocity and regime inside the reactor, but no difference has been found with changing the inlet pipe diameter. Though, decreasing the channel width resulted in increasing the velocity from 0.15 m/s to 0.25 m/s, leading to higher pollutant mass transfer. Also, a particle tracing experiment was performed using COMSOL to evaluate the mean residence time inside the reactor. The mean residence time estimated from the simulation was 8.2s while the theoretical mean residence time was 7.5 s.

      • 18:00
        Impact of the Platinum-loading method on the reductive and oxidative photocatalytic half-reactions over TiO2 1h
        Speaker: Mr Osama Al-Madanat (Institut für Technische Chemie, Gottfried Wilhelm Leibniz Universität Hannover.; Chemistry Department, Mutah University, Mutah, Jordan.)

        Environmental pollution and shortage of energy resources are considered the most serious threats faced by mankind. Heterogeneous photocatalysis has become one of the most investigated technologies, thanks to its dual ability to store solar energy and perform environmental remediation. However, the low quantum efficiencies achieved so far over TiO2 photocatalysts represent a big challenge that needs to be overcome before their potential is fully realized. Among other possibilities, the loading of noble metals (e.g. platinum) is a proven strategy to enhance the activity toward both the photooxidation of organic pollutants and molecular hydrogen evolution via water reduction. However, the method, in which Pt/TiO2 is prepared has a crucial role in tuning the photocatalytic activity.
        In this work, platinum-loaded anatase TiO2 photocatalysts were prepared using two alternative methods: photodeposition by reduction of PtCl62- (PtPD-TiO2), and physical mixing of TiO2 with Pt nanoparticles synthesized by laser ablation (PtLA-TiO2). The influence of Pt and its deposition method was evaluated in the photoreforming reaction of two organic substrates: naphthalene, and methanol. To explain the different activities, a full physicochemical characterization was performed on these samples, applying inductively coupled plasma - optical emission spectrometry (ICP-OES), X-ray diffraction (XRD), high resolution-transmission electron microscopy (HR-TEM), diffuse reflectance (DR) UV-vis spectroscopy, and Brunauer, Emmett and Teller adsorption (BET) methods. Moreover, the charge-carrier dynamics in pristine and platinized TiO2 were investigated by transient absorption spectroscopy (TAS) in complement with the electron paramagnetic resonance (EPR) technique.
        The deposition of Pt evinced a significant decrease in the charge carrier recombination rates, which in turn led to increased performances in the photocatalytic reactions. This effect was mainly attributed to the strong metal-support interaction resulting from the photodeposition process, aided by the preferential deposition on crystalline facets with strong reducing properties.

      • 18:00
        Infrared-assisted direct arylation of thieno[3,4-c]pyrrole-4,6-dione in solvent-free conditions 1h
        Speaker: Mr Gianfranco Decandia

        The biaryl structure is a common feature in many compounds of technological and pharmaceutical relevance, and it has been studied comprehensively in recent years to find innovative and more cost-effective methods for the formation of aryl-aryl bonds.
        Generally aryl C-C bond formation is facilitated by a transition metal catalyst, typically Palladium, which couples two aryl groups functionalized respectively with a leaving group (I, Br) and an organometallic moiety (-B(OR)2, -SnR3, -ZnR, -MgX). However, functionalization with the latter groups requires extra synthetic steps and the compounds are often unstable or toxic [1].
        Direct heteroarylation, instead, does not need an organometallic moiety, but it involves the coupling of an arene with a leaving group with an arene C-H bond. The main drawback is represented by the use of harmful solvents (e.g. DMA, DMF). Recently, new and more environmentally friendly protocols for direct arylation have been explored, they include use of more sustainable solvents such as water [2], ionic liquids[3], or even in absence of solvent [4,5].
        The use of an IR lamp as a heating source has proved to be a good alternative to conventional ones: it has been employed to reduce reaction time and improve product yields [6].
        This study fits into this frame and shows the first example of infrared assisted solvent-free direct arylation is presented: this protocol makes it possible to achieve high yields in a short time, avoiding the formation of unwanted by products and making workup easier. In particular, the coupling of thieno[3,4-c]pyrrole-4,6-dione with electron-rich and electron-poor aryl iodides has been successfully carried on, affording yields as high as 77% in just one hour reaction.

        1. Kimbrough, R.D. Toxicity and health effects of selected organotin compounds: a review. Environ. Health Perspect. 1976, 14, 51–56, doi:10.1289/ehp.761451.
        2. Chen, F.; Min, Q.Q.; Zhang, X. Pd-catalyzed direct arylation of polyfluoroarenes on water under mild conditions using PPh 3 ligand. J. Org. Chem. 2012, 77, 2992–2998, doi:10.1021/jo300036d.
        3. Vakuliuk, O.; Gryko, D.T. Direct arylation of pyrrole derivatives in ionic liquids. European J. Org. Chem. 2011, 2854–2859, doi:10.1002/ejoc.201100004.
        4. Punzi, A.; Zappimbulso, N.; Farinola, G.M. Direct arylations via C−H bond functionalization of 1,2,3-triazoles by reusable Pd/C catalyst in solvent-free conditions. European J. Org. Chem. 2019, 1–7, doi:10.1002/ejoc.201901305.
        5. Punzi, A.; Capozzi, M.A.M.; Di Noja, S.; Ragni, R.; Zappimbulso, N.; Farinola, G.M. Solvent-Free Pd-Catalyzed Heteroaryl-Aryl Coupling via C-H Bond Activation for the Synthesis of Extended Heteroaromatic Conjugated Molecules. J. Org. Chem. 2018, 83, 9312–9321, doi:10.1021/acs.joc.8b01284.
        6. Escobedo, R.; Miranda, R.; Martínez, J. Infrared irradiation: Toward green chemistry, a review. Int. J. Mol. Sci. 2016, 17, doi:10.3390/ijms17040453.
      • 18:00
        Light-Assisted Thermocatalysis On Supported Ru-Based Photothermal Catalysts for the Formic Acid Dehydrogenation into Hydrogen. 1h
        Speaker: Mr Javier Ivañez (University of Strasbourg)

        Catalysis is playing a pivotal role in the efficient implementation of chemical reactions and in the establishment of a modern chemical industry. However, most industrial heterogeneous catalysts work in extreme conditions of temperature and pressure far removed from thermodynamic equilibrium.[1] Consequently, achieving high activity and selectivity remains still highly challenging for many catalytic conversion processes with undesirable side-reactions, which in addition to selectivity issues lead often to deactivation on-stream that requires (costly) process downtime for catalyst regeneration.

        The primary motivation for coupling thermal and photo-excitation in a one-pot operation – and giving rise to the photothermal catalysis field – is driven by the imperative of reducing those drawbacks, and more globally of improving the chemical process sustainability, ie. with a reduction in environmental and energetic footprint.[2]

        Indeed, solar energy is considered as one of the ideal (abundant) sources of renewable energy for the future to be linked with chemical processing, with the potential to meet the projected energy demand, as well as the global needs of the society. Its harnessing and integration into catalytic processing will undoubtedly play a major role in the development of more sustainable chemical processes, and in the establishment of a low carbon energy economy. The so-called solar-driven catalysis – and more precisely the photothermal catalytic strategy – is consequently an emerging area being pivotal to industrial renewal, that arouses a lot of hope for realizing the difficult transition from fossil-based resources towards an environmentally benign, CO2-neutral 'renewable-based chemicals' industry. This strategy aims at accelerating reaction rates and globally enabling higher performances – under fixed conditions, and/or at orientating the reaction selectivities enabling similar performances to be achieving under milder conditions, such as eg. at a lower temperature.

        The gas phase decomposition of formic acid into hydrogen was taken as model reaction. It is also a reaction of high interest, as formic acid is a promising hydrogen carrier for hydrogen storage and can be used as internal hydrogen source (hydrogen donor) for performing catalytic transfer hydrogenation reactions. This hydrogen donor-mediated approach instead of using external pressurized hydrogen is a step forward in the design of sustainable hydrogenation processes enabling the production of high value-added chemicals. Formic acid, a glucose derivative issued from the lignocellulosic biomass hydrolytic conversion chain, can decompose into hydrogen and carbon dioxide via dehydrogenation (1) or generate carbon monoxide and water via dehydration (2).

        HCOOH → CO2 + H2  (1)
        HCOOH → CO + H2O (2)

        Ru/TiO2 catalysts have been recently reported as very promising systems capable of meeting the challenge of catalyzing both the dehydrogenation of formic acid to hydrogen and the hydrogenation of valuable substrates under similar reaction conditions.[3] Therefore, this communication aims at reporting on the behavior of TiO2 and g-C3N4 supported Ru photothermal catalysts in the formic acid decomposition.

        In addition, the use of semiconductor materials as catalyst support – namely medium surface area g-C3N4 and TiO2 – allows the catalyst preparation to be achieved via a photo-assisted method that avoids the use of external reducing agents or harsh temperature conditions, and that further allows a fine control of the Ru nanoparticle size distribution till the sub-nanometric level.

        Combining UV-A light and heat as excitation source increased considerably the hydrogen production rate of the catalysts studied. The main findings are that Ru/g-C3N4 catalysts with highly dispersed Ru nanoparticles appear for the first time to be remarkable photo-thermal-catalysts, that clearly outperform the Ru/TiO2 reference catalyst in terms of hydrogen production as well as of selectivity to H2 and CO2, with the ability to produce larger amounts of CO-free hydrogen flows. The influence of the light irradiance on the catalytic behaviour and performances will be detailed, and the results will be discussed in terms of H2 and CO production rates, as well as of apparent activation energy of the reaction. This open the door to the implementation of hydrogenation reactions in a more sustainable way at softer/milder conditions.

        The IdEx Program of the University of Strasbourg is thanked for funding the PhD
        fellowship of Javier Ivanez.

        [1] Imbihl, R.; Behm, R. J.; Schlögl, R. Phys. Chem. Chem. Phys. 2007, 9 (27), 3459. https://doi.org/10.1039/b706675a.
        [2] Tang, S.; Sun, J.; Hong, H.; Liu, Q. Front. Energy 2017, 11 (4), 437–451. https://doi.org/10.1007/s11708-017-0509-z.
        [3] Ruppert, A. M.; Grams, J.; Jȩdrzejczyk, M.; Matras-Michalska, J.; Keller, N.; Ostojska, K.; Sautet, P. ChemSusChem 2015, 8 (9), 1538–1547. https://doi.org/10.1002/cssc.201403332.

      • 18:00
        Modeling multiphoton ionization of the solvated GFP chromophore 1h
        Speaker: Anton Boichenko (MSU)

        Green fluorescent protein (GFP), the most widely used fluorescent protein for in vivo monitoring of biological processes, is known to undergo photooxidation reactions. However, the most fundamental property underpinning photooxidation, the electron detachment energy, has only been determined for the deprotonated GFP chromophore in the gas phase. Here, we develop a methodology for calculating the electron detachment energy (VDE) of the GFP chromophore in aqueous solution and, for the first time, determine the first four VDEs, which are consistent with the experimental data.
        The first VDE are calculated using two developed approaches - the hybrid DFT/EFP/MD and XMCQDPT2/SA(10)-CASSCF(14,14)/EFP//DFT/EFP/MD methods. The vertical excitation energies (VEEs) of the first seven excited states of the GFP chromophore in aqueous solution are obtained using XMCQDPT2/SA(10)-CASSCF(16,14)/(aug)-cc-pVDZ/EFP calculations.
        We show that the first VDE strongly depends on the system size as it relies on the accuracy of the absolute energy estimation of long-range interactions between the negatively charged chromophore and polar water molecules. It converges for a system with 12500 water molecules (R = 40 Å). The calculated VDE is 6.9 eV. Notably, the first VDE is more than double that of the deprotonated chromophore in vacuo (2.7 eV) as a result of solvent stabilization of the anion. At the same time, the VDE of the GFP protein is similar to that in aqueous solution and equals 7.1 eV. Although the VEE of the first electronically excited singlet state of the protein in its anionic form is very similar to that of the deprotonated chromophore in vacuo, the VDE and the pattern of higher lying electronically excited states in the protein are very similar to those of the deprotonated chromophore in aqueous solution. We also show that higher-lying excited states of the solvated GFP chromophore may act as a gateway for electron transfer processes in the condensed phase, in particular those that are excited shape resonances with respect to the quasi-continuum of the solvated electron.
        This work is supported by the Russian Foundation for Basic Research (grant no. 20-33-90183). The research is carried out using the equipment of the shared research facilities of HPC computing resources at Lomonosov Moscow State University as well as the local resources provided through the Lomonosov Moscow State University Program of Development.

      • 18:00
        Of Anatase and Rutile: How Does the Photoactivity Depend on the Phase Composition and the Nature of Photocatalytic Reaction? 1h
        Speaker: Mr Kasidid Yaemsunthorn (Faculty of Chemistry, Jagiellonian University)

        Crystal structure is one of the most influential features of an individual TiO2 compound on photocatalytic activity, especially the composition between the most two abundant phases – anatase and rutile. Although anatase structure is considerably acceptable as the highest photoactive phase, many reactions have been facilitated much better with the rutile form, and occasionally mixed phases with the certain composition shows the highest performance on particular reactions. [1] However, the principle on the synergistic effect of anatase/rutile is still unclear and debatable. The solid experimental evidences are therefore urgently required in order to clarify the question ‘which phenomena do govern the overall observed improved photoactivity of anatase/rutile composites?’.

        In this research, two series of mesoporous TiO2 nanoparticles with tunable anatase-rutile percentage has been hydrothermally synthesized by a simple approach based on novel Ti(III)-peroxide system at relatively low temperature (≤ 200°C). Phase-tuned materials (anatase/rutile) were carefully characterized, compared, and discussed based on several photocatalytic tests, including water oxidation and reduction, hydrogen peroxide reduction. [2] It appeared, that the optimal, ‘universal’ phase composition does not exists, but strongly depends on the reaction type – high contents of rutile or anatase should be considered for H2O2 reduction and water oxidation, respectively, while methanol-assisted water reduction requires moderate contents of both polymorphs. Presented data show that a synergistic effect observed usually for anatase/rutile composites can result from both, intrinsic and extrinsic factors, which are related to its physicochemical properties and performed redox reactions, respectively.

      • 18:00
        Photocatalytic synthesis of aromatic aldehydes using immobilized graphite-like carbon nitride 1h
        Speaker: Mrs Joana Carvalho Lopes (Laboratory of Separation and Reaction Engineering – Laboratory of Catalysis and Materials (LSRE-LCM), Faculdade de Engenharia, Universidade do Porto)

        The implementation of energy-efficient and sustainable technologies for organic synthesis to reduce the ecological impact of important industrial routes has been a hot-topic in worldwide research. Traditional chemical industry requires the use of hazardous oxidants/reductants and harsh operation conditions, such as high temperature and pressure. In this scenario, photocatalytic synthesis processes have appeared as a promising route for the synthesis of fine chemicals by operating under mild conditions. Moreover, the possibility of being activated by natural energy sources, such as sunlight, or by low-energy consumption radiation sources such Light Emitting Diodes (LEDs) may contribute for reducing the energy costs of the process.
        Selective conversion of aromatic alcohols to the corresponding aldehydes is considered an essential chemical transformation from the industrial point of view. The main challenges dealing with the photocatalytic synthesis of aromatic aldehydes are related to the development of efficient catalysts and appropriate reaction systems, seeking for maximized yield and selectivity [1].
        In the present work, graphite-like carbon nitride (GCN) based materials were applied for the photocatalytic synthesis of several aromatic aldehydes namely, benzaldehyde (BAD), anisaldehyde (AAD), vanillin (VAD), piperonal (PAD) and 4-tolualdehyde (TAD). Due to several practical problems arising from the use of catalyst suspensions, C3N4 nanosheets were successfully immobilized in glass Raschig rings and polyester fabrics, avoiding the costs related to catalysts separation and enabling continuous operation. A comparison between conventional batch and continuous flow photocatalytic reactors was evaluated.

        Acknowledgements. This work was financially supported by Associate Laboratory LSRE-LCM - UIDB/50020/2020 of the Associate Laboratory LSRE-LCM - funded by national funds through FCT/MCTES (PIDDAC) and by projects POCI-01-0145-FEDER-031268 and POCI-01-0145-FEDER-030674, funded by European Regional Development Fund (ERDF) through COMPETE2020 - Programa Operacional Competitividade e Internacionalização (POCI) – and by national funds through FCT - Fundação para a Ciência e a Tecnologia.

        References.
        [1] J.C. Lopes, M.J. Sampaio, R.A. Fernandes, M.J. Lima, J.L. Faria, C.G. Silva, Catalysis Today, (2019), DOI: 10.1016/j.cattod.2019.03.050 , in press.

      • 18:00
        Photoelectrochemical activity of screen-printed multilayer TiO2 electrodes under monochromatic illumination 1h
        Speaker: Mr Carsten Günnemann (Institut für Technische Chemie, Gottfried Wilhelm Leibniz Universität Hannover)

        Screen-printing is a commonly used method for the preparation of photoelectrodes. Although previous studies have explored the effect of the number of printed layers on the efficiency of dye-sensitized solar cells, its interplay with the photoelectrocatalytic properties of the electrodes has rarely been examined. This study focuses on this issue by studying the photoelectrocatalytic oxidation of methanol over TiO2 electrodes. The number of layers was varied between one and four and the activity was determined at four different wavelengths (327, 338, 370, and 385 nm) at an applied potential of 0.5 V vs. NHE. A strong dependency on the illumination wavelength was observed. While the one-layer electrode is the most efficient one during the illumination with 327 and 338 nm, it shows the lowest activity under illumination with 385 nm. Modelling and quantification of the electron diffusion length helped explain why the two-layer electrode showed the most consistent efficiencies across all conditions. Our work shows that the optimization of photoelectrocatalytic processes should include the number of layers as a key variable.

      • 18:00
        Photoelectrochemical oxidation of nitrogen compounds in wastewater and hydrogen production. 1h
        Speaker: Ms Adriana Rioja Cabanillas (Ulster University)

        Nutrient pollution has a detrimental effect for the ecosystems, caused by the excessive loss of nutrients to the air, soil and water. Nitrogen-based compounds are one of the pollution contributors. When found in excess, nitrogen-based compounds provoke adverse effects in water bodies, known as eutrophication. These effects include the algal bloom, depletion of dissolved oxygen and ecosystem unbalance, which could cause the death of animals living in it.[1]
        Nitrogen excess is usually removed in wastewater treatment plants by several biological treatment steps. However, space and economic constrains prevent the full implementation of these processes for the required discharge limits in some plants. Due to the need of managing nitrogen pollution in a more sustainable and efficient way, this project aimed to reduce nitrogen excess and recover energy in the form of hydrogen using an alternative non-biological process. A photoelectrochemical process was studied for the oxidation of nitrogen compounds. These compounds are oxidized by the photoexcited holes generated by the incoming irradiation at the photo-anode. Consequently, the photoexcited electrons are driven to the cathode by the external circuit that connects the two electrodes to produce hydrogen. This study is focused on the oxidation of two of the nitrogen species commonly found in wastewater: ammonia and urea. A photoelectrochemical cell was used with an immobilized TiO2 semiconductor as photo-anode and a Pt metal cathode. Due to the pH-controlled equilibrium that exits between ammonia and its ionic form ammonium in water, the ammonia oxidation study was carried out over a range of different pH.
        Keywords: Photoelectrochemical oxidation, Urea, Ammonia, Hydrogen
        Acknowledgement: The authors would like to acknowledge the funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement N ͦ 812574.
        [1] EPA. Aquatic Life Ambient Water Quality Criteria for Ammonia – Freshwater. United States Environmental Protection Agency (2013).

      • 18:00
        Structural and Electronic Properties of (Zn-N) Codoped Anatase TiO2: A DFT Investigations 1h
        Speaker: Mr Muhammad Shofiyullah (Walisongo state islamic university)

        Titanium dioxide (TiO2) is one promising material that meets the requirements of photocatalysts. This research studies the effect of Zn and N doping on the geometric and electronic structure of anatase TiO2. To determine the structure and process of photocatalytic performance, density functional theory (DFT) calculations are used with the generalized gradient approximation (GGA) approach with Perdew-Burke-Ernzerhof (PBEsol) parameterization. The calculation of the electronic structure used Hubbard U parameters. After optimization, the volume distortion of Zn doping was 1.154 Å, doping N 1.352 Å and Zn-N co-doping 1.884 Å. Based on these data, the presence of doping can affect structural changes. The calculation of the electronic structure yields a pure TiO2 bandgap of 3.18 eV. Then there is narrowing of the bandgap caused by dopants. bandgap for Zn doping 3.9 eV, N doping 3.78 eV and Zn-N co-doping 3.74 eV. The introduction of a new doped electronic structure not only causes a narrowing of the band gap but can also inhibit the recombination of electron-hole pairs, significantly increasing the photocatalytic activity of TiO2 in the visible light region.

      • 18:00
        Sustainable Biohydrogen Production via Biomass Photoreforming Using Bimetallic Doped TiO2 Photocatalysts 1h
        Speaker: Wirda Udaibah (UIN Walisongo)

        Energy crisis, depletion of fossil fuel and environmental quality are major global issue that must be solve. Hydrogen will be alternative clean energy source and carrier. Nevertheless, hydrogen does not exist in nature in its molecular H2 form but combined to other elements; thus, it requires dedicated methods for its production. And the H2 production must be sustainable in source /feedstrock and production process. Biomass contain of cellulose [(C5H10O5)n] is most abundant source of H2 that fullfil sustainable and renewable requirement. It can be convert to hydrogen gas via clean process i.e photoreforming use photocatalyst. One of the keys to the success of this satisfy technology is the development of suitable catalysts which are able to maximize light harvesting from solar and therefore the hydrogen production. TiO2 is the most widely used material becauce of its high photocatalytic activity not toxic and biologically and chemically inert. Its main drawback is its band gap value (ca. 3.2 eV), which means that only ca. 5% of solar irradiation is absorbed. Furthermore, it also exhibits a high electron–hole recombination rate, which is detrimental to the photocatalytic activity. One alternative to overcome these problems is the incorporation of metals to the semiconductor. Doped metal on TiO2 can shift the absorption to the visible light (40% of solar radiastion) and also act as electron traps, thus preventing electron–hole recombination. Yield of H2 will increase significantly by doped bimetal on surface of TiO2

      • 18:00
        Theoretical study of the -Cl/-H2O ligand exchange reaction and water oxidation catalysis in two Ruthenium catalysts 1h
        Speaker: Mr David Hernández Castillo (Institute of Theoretical Chemistry, Faculty of Chemistry, University of Vienna )

        During the last years, artificial photosynthesis research has been in the spotlight due to the increasing need for clean and sustainable energy sources. A long-standing challenge has been the study and understanding of light-driven water splitting and the development of efficient catalysts for this process. Water oxidation steps are the bottleneck in this machinery, due to the large energy penalties involved. Because of their catalytic performance, Ruthenium (Ru) complexes are model systems to gain insights into the water oxidation mechanism. Experimental studies recently showed that extension of the π-system from [RuII(tpy)(bpy)(Cl)]1+ to [RuII(tpy)(dppz)(Cl)]1+, strongly and unexpectedly stabilizes the chloro-ligand towards water ligand exchange. Experiments also showed significantly different TON for the respective Ru-H2O catalysts in the water oxidation reaction. Herein, we present a theoretical study of these complexes. Computed reaction barriers for the ligand exchange reaction, after conformational searches over the transition states, are in line with experimental trends of the half-life time of the respective reactants. The analysis of the reaction barriers across the catalytic cycle indicates that the observed differences in TOF are a consequence of the Ru-Cl bond stability. According to our results, the water-nucleophilic attack (WNA) is rate-limiting and the theoretical kinetic rates showed unprecedented agreement with previously published experimental data. On this basis, we suggest that the oxygen release should no longer be considered the slowest step during catalysis, and efforts to improve catalyst performance should focus on decreasing the WNA reaction barrier. Catalyst deactivation has been related to the weakening of the axial Ru-N bond when increasing the Ru oxidation state. We propose the Wiberg bond indices as a descriptor for the rational design of substitution patterns that can increase catalyst stability and hence, the TON. Our results constitute a step forward to the understanding of the water oxidation mechanism and our computational protocol is suggested for future studies to obtain theoretical reaction rates comparable to those from experiments.

      • 18:00
        Ultrafast Spectroscopy of Excited-States of Novel Ru and Cu Photosensitizers 1h
        Speaker: Mr Miguel Andre Argüello Cordero (Universität Rostock)

        Newly synthesized ruthenium based photosensitizers with an extended π-system were found to exhibit long lived excited states with lifetimes of 1.7 and 24.7 µs after optical excitation. The applied biipo ligand coordinates via a 1,10 phenanthroline moiety, which is extended with a 1,8 naphthalimide unit.[1] In order to replace the rare noble metal, two copper based analogues were developed, see figure. Nanosecond transient absorption measurements revealed, that in the Cu complexes, non-emissive excited states are populated which exhibit even much longer lifetimes.

        In the present work, we investigate these complexes and the plain ligands by femtosecond transient absorption spectroscopy and observe rich intramolecular relaxation dynamics. The decay associated spectra of the Cu complexes are comparable to other compounds that were previously investigated.[2][3] The shortest lifetime of ≈0.3 ps can be assigned to a flattening of the geometrical structure of the complex after optical excitation. The second exponential component of ≈3.3 ps reflects probably intersystem crossing to a triplet metal-to-ligand charge transfer state (MLCT). However, the associated spectral signatures decay again with a time constant of about 10 ps. This may point to a transfer of the excited electron from the MLCT-state to a plain ligand-centered state. A remaining long-lived absorption has the same spectral shape as the signals observed by the nanosecond experiments indicating that this state is the finally populated electronically excited state.

        [1]: Yang et al., Chem. Eur. J., 2020, 10.1002/chem.202001564.
        [2]: S. Tschierlei, et al., Chem. Phys. Chem., 2014, 15, 17, 3709-3713, 10.1002/cphc.201402585.
        [3]: M. Heberle, et al., Chem. Eur. J., 2017, 23, 2, 312-319, 10.1002/chem.201604005.

    • 15:00 15:30
      Light-driven charge accumulation on Cu(I) 4H-imidazolate complexes for conversion and storage of solar energy 30m
      Speaker: Martin Schulz (Friedrich Schiller University Jena)
    • 15:35 16:20
      Synthesis II
      Convener: Pascal Wintergerst (Ulm University)
      • 15:35
        Versatile photocatalytic methods for functionalisation of electron-deficient alkenes. 20m
        Speaker: Natalia Larionova (Queen Mary University of London)

        Olefins are among the most abundant and widely available chemical feedstock, indispensable for both the synthetic and biological communities due to their unique reactivity profile. Thus, hydrogenation and hydrofunctionalisation of C-C double bonds are important transformations to access pharmaceutical and chemical compounds that are produced at an industrial scale. We have developed wide-scope, efficient protocols using Ir-based photocatalysts for the reduction and regioselective hydroaminoalkylation of electron-deficient alkenes.
        The photocatalytic reduction opens a path for the development of greener and safer hydrogenation methodologies, avoiding the use of high-energy, strong reductants as well as the use of pressure equipment.
        Radical addition to α,β-unsaturated carbonyl compounds has been widely investigated as a useful method for functionalisation at the β-position. The α-aminoalkyl radicals formed by photocatalytic oxidation are highly nucleophilic and consequently prone to attack electron-deficient alkenes at β-position via Giese-type reaction. There are examples of stereoselectivity control for this reaction, but regioselectivity is completely predetermined by the nature of the substrate. As a result of our research, we were able to direct radical addition to the α-position of α,β-unsaturated esters to produce potentially valuable β-amino acids. Importantly, our method overcomes relevant scope limitations of alternative approaches to these products, such as Mannich-type reactions.

      • 16:00
        Visible light-mediated oxidative debenzylation strategy 20m
        Speaker: Cristian Cavedon (Max Planck Institute of Colloids and Interfaces)

        Protection and deprotection protocols that enable orthogonal strategies are of utmost importance in the total synthesis of complex molecular scaffolds. This concept is emphasized in the chemical synthesis of oligosaccharides, where selective coupling is achieved by the appropriate choice of orthogonally protected building blocks that carry temporary (tPG) and permanent protecting groups (pPG).[1]
        The limited availability of non-participating, temporary PGs represents a bottleneck in carbohydrate synthesis.[2] Benzyl ethers are suitable non-participating PGs, but they are regarded as pPG due to their harsh and non-orthogonal deprotection conditions (Catalytic hydrogenolysis, Birch reduction).
        We developed a mild, visible light-mediated debenzylation protocol using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as photo-oxidant that can be either used in stoichiometric or catalytic amounts. A high functional group tolerance was achieved using 525 nm irradiation as demonstrated for several carbohydrate building blocks equipped with multiple protecting groups. A flow approach can be used to significantly enhance this protocol, reducing the reaction times from hours to minutes. Benzyl ether can be cleaved in presence of, for example, azides, alkenes and alkynes, that are not stable using common deprotection strategies. This protocol enables use of benzyl ether as orthogonal, temporary PG in synthetic chemistry.

        [1]: P. H. Seeberger, Acc. Chem. Res. 2015, 48, 1450-1463, 10.1021/ar5004362.
        [2]: M. Guberman, P. H. Seeberger, J. Am. Chem. Soc. 2019, 141, 5581-5592, 10.1021/jacs.9b00638.

    • 16:20 16:40
      Break 20m
    • 16:40 17:50
      Synthesis II
      Convener: Pascal Wintergerst (Ulm University)
      • 16:40
        Porphyrins thiol-conjugated on 2D-MoSe2 for the positive and negative regulation of light-driven electrochemical HER 20m
        Speaker: Dr Matías Blanco (Universidad Autónoma de Madrid)

        A proper design of organic dyes may own the archetypical light-harvesting characteristic while conferring at the same time anchoring groups to be bonded to specific surfaces.[1] In this way, controversial topics such as the thiol conjugation of 2D transition metal dichalcogenides (TMDCs) with organic molecules [2] shall be rationally tackled for the development of ground-breaking photocatalytic systems. We have synthesized thiolated tetraphenyl porphyrins, with and without hydroxyl groups in the phenyl substituents, which have been covalently attached to chemically exfoliated two-dimensional MoSe2 (ce-MoSe2) nanosheets. [3] We detected the formation of sulfo-selenide bridges, specifically on the edges of the ce-MoSe2, as confirmed by first principle calculations, and we investigated the modified TMDCs’ electrocatalytic activity in the hydrogen evolution reaction (HER) after conjugation with the dyes. The HER activity is suppressed or enhanced according to the presence of mildly acid hydroxyls groups in the attached molecules, since they provide a local proton relay boosting the production of H2, especially in mildly acidic conditions (pH=4.3). Moreover, the well-known light-harvesting properties of porphyrins have been exploited to improve significantly the light-assisted HER activity. Due to the formation of a type II heterojunction or Schottky contact between the molecules and the 2H and 1T MoSe2 nanosheets respectively, [4] the hybrid materials showed an improvement of the HER onset potential under illumination compared to the pristine material or dark conditions, without activity loss for more than 16 h.
        References:
        [1] Y. Zeng et al. Angew. Chem. Int. Ed. 2015, 54, 52.
        [2] X. Chen, A. R. McDonald, Adv. Mater. 2016, 28, 5738.
        [3] M. Blanco et al. J. Mater. Chem. A, 2020, 8, 11019.
        [4] Y. Zang et al. Nat. Nanotechnology, 2014, 9, 111.

      • 17:05
        Palladium-catalyzed direct C-H bond arylation of (hetero)arenes assisted by infrared (IR) light 20m
        Speaker: Dr Gianluigi Albano (Dipartimento di Chimica, Università degli Studi di Bari “Aldo Moro”)

        Organic molecules based on (hetero)aryl structural units have been extensively investigated in recent years, ranging from compounds of biological or pharmaceutical interest to highly π-conjugated materials for organic optoelectronics. The development of efficient methods for the generation of aryl-aryl bonds is a key step for the synthesis of these systems. In this context, direct C-H bond arylation of (hetero)arenes has opened new approaches for the generation of aryl-aryl bonds, replacing the more traditional transition metal-promoted cross-coupling reactions with organometallic derivatives.[1] Although significant efforts have been recently made towards more sustainable conditions, including the use of recoverable catalysts and green solvents,[2] some issues still remain, such as the need of high temperatures and long reaction times.
        The use of non-conventional heating sources has earned increasing attention, due to the possibility of minimizing reaction time, improving product yield and avoiding undesired byproducts.[3] In this context, infrared (IR) light represents a very promising tool for fast, cheap and green organic synthesis.[4] However, the true potential of IR-assisted reactions is still almost unexplored, especially for Palladium-catalyzed coupling chemistry.
        Here we report the first IR light-assisted Palladium-catalyzed direct C-H bond arylation protocol, performed in solvent-free and non-anhydrous conditions. The reaction was successfully applied to several heteroarenes (benzothiophene, thieno[3,4-c]pyrrole-4,6-dione, 1,2,3-triazole, and pentafluorobenzene) with functionalized aryl iodides, giving the corresponding direct C-H bond arylation products in good yields after very short times.

        References:
        [1]: D. Alberico, M. E. Scott, M. Lautens, Chemical Reviews, 2007, 107, 174-238, DOI: 10.1021/cr0509760.
        [2]: S. Mao, H. Li, X. Shi, J.-F. Soulé, H. Doucet, ChemCatChem, 2019, 11, 269-286, DOI: 10.1002/cctc.201801448.
        [3]: R. B. N. Baig, R. S. Varma, Chemical Society Reviews, 2012, 41, 1559-1584, DOI: 10.1039/C1CS15204A.
        [4]: R. Escobedo, R. Miranda, J. Martínez, International Journal of Molecular Sciences, 2016, 17, 453, DOI: 10.3390/ijms17040453.

      • 17:30
        Homoleptic bis-4H-Imidazolate-Cu(I) complexes as panchromatic photosensitizers 20m
        Speaker: Mr Jens Tran (Friedrich-Schiller-Universität)

        An ever-growing energy demand is the result of the constant progress of our society. The sun as unlimited and free energy source might provide the energy necessary to satisfy the energy demand. One approach to harness sunlight relies on light-harvesting molecules, like it is done in green plants via photosynthesis.
        Following the nature’s example, contemporary research efforts are devoted to mimic photosynthesis. In this effort solar energy is used to drive chemical reactions, such as in photoredox reactions. Therefore, we have developed homoleptic bis-4H-imidazolate-Cu(I) complexes with superb light absorption properties throughout the whole visible and into the NIR spectrum. Additionally, the title compounds exhibit three ligand-based reductions and one Cu(I) based oxidation, as has been revealed by cyclic voltammetry. The oxidation occurs at very low potentials reflecting the low energy metal to ligand charge transfer transition, which has been assumed from the UV/Vis data and has been supported by TD-DFT calculations. Through modification of the 4H-imidazoles electronically and sterically the properties of the resulting complexes can be modified, in terms of electrochemistry as well as UV/Vis absorption.
        The exceptional redox activity as well as well as the intense absorption render these complexes promising candidates for photoredox reactions.

    • 17:50 18:00
      Conference Closing 10m