Quantitative insights into charge-separated states from one- and two-pulse laser experiments relevant for artificial photosynthesis

Neumann, Svenja; Kerzig, Christoph; Wenger, Oliver S.

doi:10.1039/c9sc01381d

Cited by 20 publications

(31 citation statements)

References 94 publications

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“…This is due to the nature of the p-xylene spacers, as they do not significantly affect the electronic properties of covalently attached chromophores. [54][55][56][57] In line with the expected poor orbitalo verlap, our DFT calculations (Supporting Information, SectionS3) predict average equilibrium torsion angles between the p-xylene planesa nd the adjacent p-systems of the two chromophores on the order of 708.M oreover,t he computed . (c)Energy diagram for the four key stepso ft he mechanism shownin( b).…”

Section: Molecular Design and Ground State Properties Of The Dyadssupporting

confidence: 57%

Controlling Spin‐Correlated Radical Pairs with Donor–Acceptor Dyads: A New Concept to Generate Reduced Metal Complexes for More Efficient Photocatalysis

Neumann

Wenger

Kerzig

2021

Chemistry A European J

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One-electron reduced metal complexes derived from photoactive ruthenium or iridium complexes are important intermediates for substrate activation steps in photoredox catalysis and for the photocatalytic generation of solar fuels. However,o wing to the heavy atom effect, direct photochemical pathways to these key intermediates suffer from intrinsic efficiency problems resulting from rapid geminate recombination of radical pairs within the so-called solvent cage. In this study,w ep repared and investigated molecular dyads capable of producing reduced metal complexes via an indirect pathway relyingo nas equence of energy and electron transfer processes between aR uc omplex and ac ovalently connected anthracene moiety.O ur test reaction to establish the proof-of-concept is the photochem-ical reduction of ruthenium(tris)bipyridine by the ascorbate dianion as sacrificial donor in aqueous solution. The photochemicalk ey step in the Ru-anthracene dyads is the reduction of ap urely organic (anthracene) triplet exciteds tate by the ascorbate dianion, yielding as pin-correlated radical pair whose (unproductive) recombination is strongly spin-forbidden. By carrying out detailed laser flash photolysis investigations, we provide clear evidence for the indirect reduced metal complex generation mechanism and show that this pathway can outperform the conventionald irect metal complex photoreduction. The furthero ptimization of our approach involving relativelys imple molecular dyads might result in novel photocatalysts that convert substrates with unprecedented quantum yields.

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Section: Molecular Design and Ground State Properties Of The Dyadssupporting

confidence: 57%

Controlling Spin‐Correlated Radical Pairs with Donor–Acceptor Dyads: A New Concept to Generate Reduced Metal Complexes for More Efficient Photocatalysis

Neumann

Wenger

Kerzig

2021

Chemistry A European J

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“…We use a commercial transient‐absorption spectrometer equipped with beam‐expanding optics ensuring an optimal overlap between the pump and probe pulses, and two nanosecond lasers along with a delay generator to control the synchronization of the lasers and the detection system . This setup permits quantitative two‐pulse two‐color experiments (one Nd:YAG laser is equipped with an optical parametric oscillator (OPO), the other is frequency‐doubled) . When radical ions and their electronically excited states are of interest, the first laser pulse might well be replaced by pulse radiolysis …”

Section: Kinetic Aspects and Pertinent Methods In Multi‐photon Excitamentioning

confidence: 99%

Multi‐Photon Excitation in Photoredox Catalysis: Concepts, Applications, Methods

2020

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The energy of visible photons and the accessible redox potentials of common photocatalysts set thermodynamic limits to photochemical reactions that can be driven by traditional visible‐light irradiation. UV excitation can be damaging and induce side reactions, hence visible or even near‐IR light is usually preferable. Thus, photochemistry currently faces two divergent challenges, namely the desire to perform ever more thermodynamically demanding reactions with increasingly lower photon energies. The pooling of two low‐energy photons can address both challenges simultaneously, and whilst multi‐photon spectroscopy is well established, synthetic photoredox chemistry has only recently started to exploit multi‐photon processes on the preparative scale. Herein, we have a critical look at currently developed reactions and mechanistic concepts, discuss pertinent experimental methods, and provide an outlook into possible future developments of this rapidly emerging area.

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“…Further, additional electronic states might contribute to light absorption leading to new relaxation or degradation pathways compared to the original species. [152][153][154][155][156] Furthermore, the interaction with the sacrificial agent can significantly alter the electron transfer process as is observed under inert conditions. Depending on the order of events, electron transfer before rereduction of the sensitizer (oxidative quenching) or first reduction of the photoexcited sensitizer followed by electron transfer (reductive quenching) can occur, and hence the mechanism might be completely different from what is observed in inert solvent environment.…”

Section: Spectroscopic Techniquesmentioning

confidence: 99%

“…The adaption of pump-pump-probe schemes to photocatalytic systems might pave the way towards the next level of understanding in this respect. 156,193,194…”

Section: Spectroscopic Techniquesmentioning

confidence: 99%

Characterizing photocatalysts for water splitting: from atoms to bulk and from slow to ultrafast processes

2021

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Quantitative insights into charge-separated states from one- and two-pulse laser experiments relevant for artificial photosynthesis

Abstract: Quantitative laser flash photolysis experiments with several excitation wavelengths provided unprecedented insights into the charge-separated state photochemistry of molecular triads.

Cited by 20 publications

References 94 publications

Controlling Spin‐Correlated Radical Pairs with Donor–Acceptor Dyads: A New Concept to Generate Reduced Metal Complexes for More Efficient Photocatalysis

Controlling Spin‐Correlated Radical Pairs with Donor–Acceptor Dyads: A New Concept to Generate Reduced Metal Complexes for More Efficient Photocatalysis

Multi‐Photon Excitation in Photoredox Catalysis: Concepts, Applications, Methods

Characterizing photocatalysts for water splitting: from atoms to bulk and from slow to ultrafast processes

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