About Control: Kinetics in Molecule-based Photochemical Water Reduction Investigated by Transient IR Spectroscopy

This review aims to promote the role of transient IR spectroscopy to investigate molecular-based photocatalytic water reduction. Examples are discussed in which this method has been successfully applied to elucidate reaction mechanisms. Focus is given to kinetic changes and their consequences when a photochemical water reduction system, which is functional and well understood in solution, is brought onto a metal oxide surface

About Control: Kinetics in Molecule- based Photochemical Water Reduction Investigated by Transient IR Spectroscopy

This review aims to promote the role of transient IR spectroscopy to investigate molecular-based photocatalytic water reduction. Examples are discussed in which this method has been successfully applied to elucidate reaction mechanisms. Focus is given to kinetic changes and their consequences when a photochemical water reduction system, which is functional and well understood in solution, is brought onto a metal oxide surface

Flexible to rigid: IR spectroscopic investigation of a rhenium-tricarbonyl-complex at a buried interface

This work explores the solid–liquid interface of a rhenium-tricarbonyl complex embedded in a layer of zirconium oxide deposited by atomic layer deposition (ALD). Time-resolved and steady state infrared spectroscopy were applied to reveal the correlations between the thickness of the ALD layer and the spectroscopic response of the system. We observed a transition of the molecular environment from flexible to rigid, as well as limitations to ligand exchange and excited state quenching on the embedded complexes, when the ALD layer is roughly of the same height as the molecules

Nanosecond protein dynamics in a red/green cyanobacteriochrome revealed by transient IR spectroscopy

Over the last decades, photoreceptive proteins were extensively studied with biophysical methods to gain a fundamental understanding of their working mechanisms and further guide the development of optogenetic tools. Time-resolved infrared (IR) spectroscopy is one of the key methods to access their functional non-equilibrium processes with high temporal resolution but has the major drawback that experimental data are usually highly complex. Linking the spectral response to specific molecular events is a major obstacle. Here, we investigate a cyanobacteriochrome photoreceptor with a combined approach of transient absorption spectroscopy in the visible and IR spectral regions. We obtain kinetic information in both spectral regions by analysis with two different fitting methods: global multiexponential fitting and lifetime analysis. We investigate the ground state dynamics that follow photoexcitation in both directions of the bi-stable photocycle (Pr* and Pg*) in the nanosecond and microsecond time regimes. We find two ground state intermediates associated with the decay of Pr* and four with Pg* and report the macroscopic time constants of their interconversions. One of these processes is assigned to a structural change in the protein backbone

Biscoumarin-containing acenes as stable organic semiconductors for photocatalytic oxygen reduction to hydrogen peroxide

Conversion of solar energy into chemical energy in the form of hydrogen peroxide and other reactive oxygen species has been predicted to be an efficient strategy, yet few organic materials systems support these types of photochemical conversion reactions. Herein we report a simple synthetic route to yield biscoumarin-containing acenes, semiconducting small molecules with exceptional stability and tunable electrochemical and electrical properties. We find that these semiconductors are photo(electro) catalysts capable of reducing oxygen to hydrogen peroxide. Visible light irradiation of thin films on insulating substrates in pure water results in H2O2 photogeneration with water as the sacrificial electron donor. Thin films on conducting substrates are robust catalytic photocathodes for producing H2O2. These semiconductor photoelectrodes retain their catalytic properties in a pH range from 2-13. Photocatalytic or photoelectrocatalytic deployment of biscoumarin-containing acenes does not lead to measurable degradation. This work demonstrates a strategy to synthesize stable organic semiconductors not only suitable for thin-film electronic devices but also next-generation photocatalytic concepts.Funding Agencies|Austrian-Polish bilateral WTZ program; Austrian Science Fund FWF [TRP 294-N19]; Wittgenstein Prize [Z222-N19]; National Centre for Research and Development (Polish-Taiwanese project) [PL-TWIII/17/2016]; Polish Ministry of Science and Higher Education, "Diamond Grant" program [DI2012000742]; Knut and Alice Wallenberg Foundation</p

Photocatalytic Reduction of Artificial and Natural Nucleotide Co-factors with a Chlorophyll-Like Tin-Dihydroporphyrin Sensitizer

An efficient photocatalytic two-electron reduction and protonation of nicotine amide adenine dinucleotide (NAD⁺), as well as the synthetic nucleotide co-factor analogue <i>N</i>-benzyl-3-carbamoyl-pyridinium (BNAD⁺), powered by photons in the long-wavelength region of visible light (λ_irr > 610 nm), is demonstrated for the first time. This functional artificial photosynthetic counterpart of the complete energy-trapping and solar-to-fuel conversion primary processes occurring in natural photosystem I (PS I) is achieved with a robust water-soluble tin­(IV) complex of <i>meso</i>-tetrakis­(<i>N</i>-methylpyridinium)-chlorin acting as the light-harvesting sensitizer (threshold wavelength of λ_thr = 660 nm). In buffered aqueous solution, this chlorophyll-like compound photocatalytically recycles a rhodium hydride complex of the type [Cp*Rh­(bpy)­H]⁺, which is able to mediate regioselective hydride transfer processes. Different one- and two-electron donors are tested for the reductive quenching of the irradiated tin complex to initiate the secondary dark reactions leading to nucleotide co-factor reduction. Very promising conversion efficiencies, quantum yields, and excellent photosensitizer stabilities are observed. As an example of a catalytic dark reaction utilizing the reduction equivalents of accumulated NADH, an enzymatic process for the selective transformation of aldehydes with alcohol dehydrogenase (ADH) coupled to the primary photoreactions of the system is also demonstrated. A tentative reaction mechanism for the transfer of two electrons and one proton from the reductively quenched tin chlorin sensitizer to the rhodium co-catalyst, acting as a reversible hydride carrier, is proposed

Rhodium-Coordinated Poly(arylene-ethynylene)-<i>alt</i>-Poly(arylene-vinylene) Copolymer Acting as Photocatalyst for Visible-Light-Powered NAD⁺/NADH Reduction

A 2,2′-bipyridyl-containing poly­(arylene-ethynylene)-<i>alt</i>-poly­(arylene-vinylene) polymer, acting as a light-harvesting ligand system, was synthesized and coupled to an organometallic rhodium complex designed for photocatalytic NAD⁺/NADH reduction. The material, which absorbs over a wide spectral range, was characterized by using various analytical techniques, confirming its chemical structure and properties. The dielectric function of the material was determined from spectroscopic ellipsometry measurements. Photocatalytic reduction of nucleotide redox cofactors under visible light irradiation (390–650 nm) was performed and is discussed in detail. The new metal-containing polymer can be used to cover large surface areas (e.g. glass beads) and, due to this immobilization step, can be easily separated from the reaction solution after photolysis. Because of its high stability, the polymer-based catalyst system can be repeatedly used under different reaction conditions for (photo)­chemical reduction of NAD⁺. With this concept, enzymatic, photo-biocatalytic systems for solar energy conversion can be facilitated, and the precious metal catalyst can be recycled

Doping-Induced Polaron Formation and Solid-State Polymerization in Benzoporphyrin–Oligothiophene Conjugated Systems

Benzoporphyrins and their derivatives are of high interest in organic semiconductor technology due to their peculiar physical properties valuable for optoelectronic applications. Following our previous work successfully developing <i>meso</i>-thienyl- or <i>meso</i>-bithiophenyl-substituted zinc benzoporphyrins as efficient ternary components for bulk heterojunction solar cells, we describe herein detailed spectroscopic studies on doping of solid films of these benzoporphyrins under iodine atmosphere. Solid-state doping and oxidative polymerization are investigated by Raman and Fourier transform infrared spectroscopy. Structural and vibrational changes upon doping are explored with supporting data from density functional theory calculations. Furthermore, the optical and spectroscopic characteristics of the films of these materials are also monitored during the doping, and the polaron formation as evidenced by in situ attenuated total reflection Fourier transform infrared and UV–vis spectroscopy is observed. These results suggest that the target zinc benzoporphyrins, both in monomeric and in polymeric forms, should be good candidates in several other optoelectronic applications