Mechanistic study of initial quenching process in photocatalyticα-keto acids radical acylation:A general strategy for enhancing quantum efficiency  

光催化α-酮酸自由基酰化反应初始淬灭过程的机理研究:一种提高量子效率的通用策略

作　　者：Zhicong Lin Jialu Li Chenli Chen Linan Zhou Jialong Jie Hongmei Su 林志聪;李佳璐;陈辰丽;周礼楠;节家龙;苏红梅(北京师范大学化学学院,北京100890;华南理工大学化学化工学院/自旋科技研究院,广州511442)

机构地区：[1]College of Chemistry,Beijing Normal University,Beijing 100890,China [2]School of Chemistry and Chemical Engineering,Spin-X Institute,South China University of Technology,Guangzhou 511442,China

出　　处：《Chinese Journal of Chemical Physics》2024年第6期878-892,I0044,共16页化学物理学报(英文)

基　　金：supported by the National Key R&D Program of China(No.2022YFA1505400);the National Natural Science Foundation of China(Nos.21933005,21727803,22003005 and 22273007);the Fundamental Research Funds for the Central Universities(No.2233300007).

摘　　要：The photocatalytic decarboxylation ofα-keto acids to generate acyl radicals under mild conditions represents a novel strategy in organic synthesis.However,the quantum efficiency of this process has been underexplored,limiting its practicality.To improve quantum efficiency,detailed analysis of mechanisms and kinetic data for key steps are essential.In this work,using time-resolved emission and absorption spectroscopy,we conducted a mechanistic study focusing on the excited-state properties of representative photocatalysts and their quenching efficiencies during the initial quenching process([Ir(dFCF_(3)ppy)_(2)(dtbbpy)]+(IrIII),Eosin Y(EY),Rose Bengal(RB),and 4CzPN).Our findings revealed that RB is active in its triplet states(^(3)RBH*),with lifetimes of 103 ns(in air)and 3.4µs(in anaerobic conditions),while EY and 4CzPN are active in their singlet states(^(1)EYH*and^(1)4CzPN*),with lifetimes of 2.9 ns and 5.1 ns,respectively.We measured the second-order rate constants for quenching by electron transfer fromα-keto acids:^(1)EYH*,2.3×10^(9)(mol/L)^(-1)·s^(-1);^(3)RBH*,3.2×10^(8)(mol/L)^(-1)·s^(-1)4CzPN*,2.8×10^(8)(mol/L)^(-1)·s^(-1).With our previously reported data for Mil,we established the quenching efficiency relationships for these photocatalysts withα-keto acids concentration.Our steady-state chromatography experiments determined the quantum efficiencies for consumption ofα-keto acids(IrIII>RBH>EYH>4CzPN),correlating these efficiencies with the initial quenching process.The results suggest that IrIII/RBH under anaerobic conditions could be optimal for high quantum efficiency.This study provides a foundation for designing new photocatalyticα-keto acid radical acylation systems with enhanced quantum efficiency.本研究聚焦于光催化α-酮酸脱羧生成酰基自由基的过程,提出了一种在有机合成中具有潜力的新策略.鉴于该过程量子效率的研究不足,限制了其实际应用,深入探讨了关键步骤的机制与动力学特性.通过时间分辨光谱技术,分析了代表性光催化剂(IrⅢ、EY、RB、4CzPN)的激发态性质及在初始淬灭过程中的表现.研究发现,RB在三重态下尤为活跃,而EY和4CzPN则在单重态下发挥作用,且各催化剂的淬灭效率与α-酮酸浓度密切相关.结合稳态色谱实验,确定了各催化剂的量子效率排序(IrⅢ>RBH>EYH>4CzPN),并指出在无氧条件下,IrⅢ/RBH系统可能实现最优的量子效率.本研究不仅丰富了光催化α-酮酸脱羧机制的理解,也为开发高效的光催化有机合成系统提供了理论依据和实践指导.

关 键 词：Chemical kinetics and dynamics Time-resolved spectroscopy Electron transfer quenching Photocatalytic reaction 

分 类 号：O644.1[理学—物理化学] O643.3[理学—化学]