Extended Single-Electron Transfer Model and Dynamically Associated Energy Transfer Event in a Dual-Functional Catalyst System

Abstract

Organic photocatalysis has been developed flourishingly to rely on bimolecular energy transfer (EnT) or oxidative/ reductive electron transfer (ET), promoting a variety of synthetic transformations. However, there are rare examples to merge EnT and ET processes rationally within one chemical system, of which the mechanistic investigation still remains in its infancy. Herein, the first mechanistic illustration and kinetic assessments of the dynamically associated EnT and ET paths were conducted for realizing the C−H functionalization in a cascade photochemical transformation of isomerization and cyclization by using the dualfunctional organic photocatalyst of riboflavin. An extended singleelectron transfer model of transition-state-coupled dual-nonadiabatic crossings was explored to analyze the dynamic behaviors in the proton transfer-coupled cyclization. This can also be used to clarify the dynamic correlation with the EnT-driven E → Z photoisomerization that has been kinetically evaluated by using Fermi's golden rule with the Dexter model. The present computational results of electron structures and kinetic data contribute to a fundamental basis for understanding the photocatalytic mechanism of the combined operation of EnT and ET strategies, which will guide the design and manipulation for the implementation of multiple activation modes based on a single photosensitizer.

Unveiling Mechanistic Insights and Photocatalytic Advancements in Intramolecular Photo-(3 + 2)-Cycloaddition: A Comparative Assessment of Two Paradigmatic Single-Electron-Transfer Models

“…These models are also further enrichment and improvement of Marcus electron-transfer theory and the transition-state theory, which facilitate our enhanced comprehension of electron-transfer phenomena. Our research group will always be devoted to developing more SET models . In general, these theoretical advancements hold promising prospects for the mechanism-guided molecular design of photocatalysts and the photochemical synthetic method design of new building blocks, especially saturated blocks suitable for pharmaceutical chemistry.…”

“…Our research group will always be devoted to developing more SET models. 47 In general, these theoretical advancements hold promising prospects for the mechanism-guided molecular design of photocatalysts and the photochemical synthetic method design of new building blocks, especially saturated blocks suitable for pharmaceutical chemistry.…”

Photocatalytic systems: reactions, mechanism, and applications

“…To support a range of synthetic reactions, organic photocatalysis has flourishingly grown to rely on bimolecular energy transfer (EnT) or oxidative/reductive electron transfer (ET). 189 Utilizing electron transfer (ET) vacancies as a coexisting strategy, EnT photo-organocatalysis has been able to get beyond the ET path's present restrictions on substrate redox potentials that are incompatible with those of excited photocatalysts. 190 Over the last ten years, two distinct catalytic cycles have been united by the use of the combined EnT and ET methods in a unique photo-organocatalysis, enabling different activation modes using a single photocatalyst.…”

“… 190 Over the last ten years, two distinct catalytic cycles have been united by the use of the combined EnT and ET methods in a unique photo-organocatalysis, enabling different activation modes using a single photocatalyst. 189–191 By using visible light to drive organocatalysis, different aromatic C–H functionalizations imposed by photosensitized EnT and ET may be easily accessed along the energetically least expensive pathways. 192,193 The issue is how to make up for the energy deficit between the input energies of visible light irradiation (about 400 nm) and the energy consumption of aromatic C–H bond dissociation.…”

“… 192,193 The issue is how to make up for the energy deficit between the input energies of visible light irradiation (about 400 nm) and the energy consumption of aromatic C–H bond dissociation. 189 Consequently, mechanistic investigation efforts are desperately needed to give the structural and energetic foundation for comprehending the dynamic pathways of excitation-energy relaxation connected to structure evolution. However, in particular for dynamically coupled EnT and ET photocatalysis, the kinetic and thermodynamic assessments should be taken into account to reveal important parameters for managing photo-sensitized area C–H bond functionalization.…”