Cage escape governs photoredox reaction rates and quantum yields

Nature Chemistry, Journal Year: 2024, Volume and Issue: 16(7), P. 1151 - 1159

Published: March 18, 2024

Abstract Photoredox catalysis relies on light-induced electron transfer leading to a radical pair comprising an oxidized donor and reduced acceptor in solvent cage. For productive onward reaction occur, the must escape from that cage before they undergo spontaneous reverse transfer. Here we show decisive role plays three benchmark photocatalytic reactions, namely, aerobic hydroxylation, reductive debromination aza-Henry reaction. Using ruthenium(II)- chromium(III)-based photocatalysts, which provide inherently different quantum yields, determined quantitative correlations between rates of photoredox product formation yields. These findings can be largely rationalized within framework Marcus theory for

Language: Английский

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Factors that Impact Photochemical Cage Escape Yields

Chemical Reviews, Journal Year: 2024, Volume and Issue: 124(11), P. 7379 - 7464

Published: May 14, 2024

The utilization of visible light to mediate chemical reactions in fluid solutions has applications that range from solar fuel production medicine and organic synthesis. These are typically initiated by electron transfer between a photoexcited dye molecule (a photosensitizer) redox-active quencher yield radical pairs intimately associated within solvent cage. Many these radicals undergo rapid thermodynamically favored "geminate" recombination do not diffuse out the cage surrounds them. Those escape useful reagents may subsequent important above-mentioned applications. process factors determine yields remain poorly understood despite decades research motivated their practical fundamental importance. Herein, state-of-the-art on light-induced appeared since seminal 1972 review J. P. Lorand entitled "The Cage Effect" is reviewed. This also provides some background for those new field discusses both homolytic bond photodissociation bimolecular induced reactions. concludes with key goals directions future promise elevate this very vibrant even greater heights.

Language: Английский

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Improved transition metal photosensitizers to drive advances in photocatalysis

Chemical Science, Journal Year: 2023, Volume and Issue: 15(1), P. 77 - 94

Published: Nov. 24, 2023

To function effectively in a photocatalytic application, photosensitizer's light absorption, excited-state lifetime, and redox potentials, both the ground state excited state, are critically important. The absorption profile is particularly relevant to applications involving solar harvesting, whereas potentials lifetimes determine thermodynamics, kinetics, quantum yields of photoinduced processes. This perspective article focuses on synthetic inorganic organometallic approaches optimize these three characteristics transition-metal based photosensitizers. We include our own work areas, which has focused extensively exceptionally strong cyclometalated iridium photoreductants that enable challenging reductive photoredox transformations organic substrates, more recent led improved harvesting charge-transfer copper(i) chromophores, an emerging class earth-abundant compounds solar-energy applications. also highlight many other complementary strategies for optimizing parameters representative examples from literature. It remains significant challenge simultaneously all at once, since improvements one often come detriment others. These inherent trade-offs obviate or circumvent them discussed throughout.

Language: Английский

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Direct Observation of Triplet States in the Isomerization of Alkenylboronates by Energy Transfer Catalysis

Journal of the American Chemical Society, Journal Year: 2023, Volume and Issue: 145(39), P. 21576 - 21586

Published: Sept. 20, 2023

Alkenylboronates are versatile building blocks for stereocontrolled synthesis owing to the traceless nature of boron group that can be leveraged achieve highly selective geometric isomerization. Using thioxanthone as an inexpensive photocatalyst, photoisomerization these species continues provide expansive platform stereodivergent synthesis, particularly in construction bioactive polyenes. Although mechanistic investigations consistent with light-driven energy transfer, direct experimental evidence remains conspicuously absent. Herein, we report a rigorous investigation using two widely used alkenylboronates alongside relevant reference compounds. Through combination irradiation experiments, transient absorption spectroscopic studies, kinetic modeling, and DFT calculations all isomers model compounds, it has been possible unequivocally detect characterize perpendicular triplet generated by transfer. Our results serve not only blueprint studies challenging organic sensitizers, but guidelines delineated have also enabled development more sustainable reaction conditions: first time, efficient organocatalytic isomerization under sunlight become feasible.

Language: Английский

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Efficient Energy and Electron Transfer Photocatalysis with a Coulombic Dyad

Journal of the American Chemical Society, Journal Year: 2024, Volume and Issue: 146(37), P. 25799 - 25812

Published: Sept. 3, 2024

Photocatalysis holds great promise for changing the way value-added molecules are currently prepared. However, many photocatalytic reactions suffer from quantum yields well below 10%, hampering transition lab-scale to large-scale or even industrial applications. Molecular dyads can be designed such that beneficial properties of inorganic and organic chromophores combined, resulting in milder reaction conditions improved reactions. We have developed a novel approach obtaining advantages molecular without time- resource-consuming synthesis these tailored photocatalysts. Simply by mixing cationic ruthenium complex with an anionic pyrene derivative water salt bichromophore is produced owing electrostatic interactions. The long-lived triplet state obtained static quantitative energy transfer preorganized complex. exploited this so-called Coulombic dyad catalysis similar reactivity higher photostability compared reference photosensitizers several photooxygenations. In addition, it was shown system also used maximize yield photoredox This due intrinsically cage escape after photoinduced electron purely compounds heavy atom-containing molecules. combination laboratory-scale as mechanistic irradiation experiments detailed spectroscopic investigations provided deep insights into easy-to-use photocatalyst class.

Language: Английский

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Direct Evidence for Excited Ligand Field State-based Oxidative Photoredox Chemistry of a Cobalt(III) Polypyridyl Photosensitizer

Journal of the American Chemical Society, Journal Year: 2023, Volume and Issue: 145(38), P. 20786 - 20791

Published: Sept. 13, 2023

Increasing interest in sustainable chemistry coupled with the quest to explore new reactivity has spurred research on first-row transition metal complexes for potential applications a variety of settings. One more active areas is photoredox catalysis, where synthetically tunable nature their electronic structures provides rich palette options tailoring desired chemical transformation. Understanding mechanism excited-state critical informed development next-generation catalysts, which turn requires information concerning propensity excited states engage electron or energy transfer processes. Herein we provide direct evidence highly oxidizing lowest-energy ligand-field (LF) state d6-low-spin Co(III) photosensitizer [Co(4,4′-Br2bpy)3]3+ (where 4,4′-Br2bpy 4,4′-dibromo-2,2′-bipyridine). The redox associated LF complex was bracketed by performing bimolecular quenching studies using series simple organic donors. Time-resolved absorption spectroscopy confirmed dynamic process attributed reductive chromophore. Analysis Stern–Volmer plots each chromophore-quencher pair revealed limiting value Ered* ∼ 1.25 V vs Fc/Fc+ metal-centered state, significantly stronger than that commonly employed metal-based agents such as [Ru(bpy)3]2+ (Ered* = 0.32 Fc/Fc+) and [Ir(ppy)2(bpy)]+ 0.27 Fc/Fc+). These results suggest this class chromophores could find utility requiring activation oxidatively resistant substrates catalysis.

Language: Английский

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The photophysics and applications of molecular rubies

Advances in inorganic chemistry, Journal Year: 2024, Volume and Issue: unknown, P. 111 - 159

Published: Jan. 1, 2024

Language: Английский

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Factors Controlling Cage Escape Yields of Closed- and Open-Shell Metal Complexes in Bimolecular Photoinduced Electron Transfer

Journal of the American Chemical Society, Journal Year: 2024, Volume and Issue: 146(32), P. 22818 - 22828

Published: July 30, 2024

The cage escape yield, i.e., the separation of geminate radical pair formed immediately after bimolecular excited-state electron transfer, was studied in 11 solvents using six Fe(III), Ru(II), and Ir(III) photosensitizers tri-p-tolylamine as donor. Among all complexes, largest yields (0.67–1) were recorded for photosensitizer, showing highest potential a photocatalyst photoredox catalysis. These dropped to values around 0.65 both Ru(II) 0.38 Os(II) photosensitizer. Interestingly, open-shell Fe(III) small (<0.1) with dielectric constant greater than 20 but shown reach up 0.58 low constants. results presented herein on closed-shell suggest that rate triplet–singlet intersystem crossing within manifold states implies charge recombination toward ground state is spin-forbidden process, favoring large are not influenced by effects. Geminate metal such two herein, no longer process becomes highly sensitive solvent Altogether, this study provides general guidelines factors influencing reactivity prototypical also allows one foresee great development 2LMCT excited catalysis, providing constants used.

Language: Английский

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A protocol for determining cage-escape yields using nanosecond transient absorption spectroscopy

STAR Protocols, Journal Year: 2023, Volume and Issue: 4(2), P. 102312 - 102312

Published: May 15, 2023

Here, we present a protocol for the determination of cage-escape yields following excited-state electron transfer between photosensitizer and quencher. We describe steps determining changes in molar absorption coefficient different oxidation states via photolysis experiments percentage reacted species steady-state or time-resolved spectroscopy. then detail measurement amount formed product nanosecond transient For complete details on use execution this protocol, please refer to Ripak et al. (2023).1.

Language: Английский

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Spectroscopic Techniques to Unravel Mechanistic Details in Light‐Induced Transformations and Photoredox Catalysis

ChemCatChem, Journal Year: 2023, Volume and Issue: 16(1)

Published: Nov. 9, 2023

Abstract The rapid development of photo(redox) catalysis within the last decades is remarkable to extent that utilization light‐driven processes in organic chemistry has become a credible alternative current thermal processes. Such advances offer tremendous opportunities collaborations between scientific realms can have drastic impact on field. In this concept article, special emphasis placed spectroscopic techniques are used, or could be for light‐induced transformations and photoredox applications. These include spectroelectrochemistry, UV‐VIS, IR X‐Ray transient absorption spectroscopy, laser pulsed radiolysis (PR), photo‐induced chemically induced dynamic nuclear polarization (Photo‐CIDNP), photoacoustic time‐resolved Raman spectroscopy (TRRS), Electron Paramagnetic Resonance (TREPR) dielectric loss (TRDL). theoretical background behind each technique briefly introduced followed by selected relevant examples from literature.

Language: Английский

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