Polymerization-Enhanced Photocatalysis for the Functionalization of C(sp3)-H Bonds

A series of conjugated polymetric photocatalysts (CPPs) based on 1,2,3,5-tetrakis(carbazol-9-yl)4,6-dicyanobenzene (4CzIPN) were synthesized via nucleophilic substitution reaction and Sonogashira-Hagihara coupling. Among the as-prepared CPPs (CPP1-CPP6), CPP3 was selected as the optimized heterogeneous photocatalyst for visible-light-driven functionalization of C(sp(3))-H bonds to synthesize 87 final products with yields up to 99%. The heterogeneous photocatalyst CPP3 is easily recovered from the reaction with excellent retention of photocatalytic activity, which can be reused at least for five times. Time-dependent density functional theory (TD-DFT) calculations demonstrate that the photocatalysis performance of CPP3 is superior to the corresponding monomer 4CzIPN because of the enhanced intersystem crossing (ISC) process. Spin-orbit coupling calculations prove that the rate constant of ISC outcompetes that of reverse intersystem crossing (RISC). The rapidly generated and long-lived triplet state T-1 is considered to be a more accessible excited state than the singlet-state S-1 generated from either direct excitation or RISC. The successful application of this polymerization-enhanced photocatalysis strategy should guide a metal-free approach to the rational design of CPP-type heterogeneous photocatalysts to address the dilemma of homogeneous photocatalysts in sustainability, stability, and recyclability.

Automated summary

A series of conjugated polymeric photocatalysts based on 4CzIPN were synthesized and optimized photocatalyst CPP3 showed superior visible-light-driven functionalization of C(sp(3))-H bonds with high yields; the enhanced intersystem crossing in CPP3 led to its better photocatalytic performance compared to the monomer 4CzIPN, allowing for easy recovery and reuse.