Twist-Promoted Photoredox Catalysis in Metal-Organic Framework for Defluorination Reactions

The relatively short excited-state lifetime is one main drawback of organic photosensitizers, resulting in their restricted catalytic capability and high catalyst loadings. We herein report the design of a twisted ligand N⁹,N⁹,N¹⁰,N¹⁰-tetrakis[(1,1'-biphenyl)-4-carboxylic acid]-9,10-anthracene diamine (H₄TCPDA). Its twisted geometry significantly elongates the lifetime of charge-transfer state as substantiated by detailed ultrafast transient absorption (TA) spectroscopic and electrochemical studies. Moreover, its rigid structure benefits the formation of highly crystalline Y-TCPDA metal-organic frameworks (MOFs) with excellent stability toward F^- solutions. Therefore, Y-TCPDA competently catalyzes chemoselective defluorinative modifications, a challenge remained in MOF catalysis, and olefin reductive cross-coupling with high turnover numbers of up to 9000. Control experiments underscore the protection of organic photocatalytic centers by the MOF platform, while similar organic catalysts are found to be decomposed in a homogeneous catalytic system.