Conjugated Polymers with Sequential Fluorination for Enhanced Photocatalytic H2 Evolution via Proton-Coupled Electron Transfer

The performance of donor-acceptor (D-A) conjugated polymer-based photocatalyts for solar hydrogen production is severely limited by poor charge mobility and weak reactive sites. Here, a series of D-A conjugated polymers with electronegative fluorine atoms on the backbone is presented and the influence of fluorination on charge transfer and catalytic site activity is investigated. Theoretical calculation reveals that sequential fluorination on the A unit benzothiadiazole will activate the catalytic site, and the photocatalytic H-2 generation process could be illustrated by a proton-coupled electron-transfer mechanism. Two series of fluorinated polymers were synthesized, and accelerated charge transfer was also verified. Among them, linear B-FOBT-1,4-E and porous B-FOBT-1,3,5-E with simultaneous electron-donating CH3O- and electron-withdrawing F-substitution show a H-2 evolution rate that is 3.1 and 28.8 times higher than that of nonfluorinated counterparts, respectively, and the apparent quantum yield of 5.7% at 420 nm is obtained for B-FOBT-1,4-E. The results provide reciprocal understanding of the activation nature of substituent-regulating polymers.