Post-side chain engineering of difluorinated benzothiadiazole-based conjugated microporous polymer for enhanced photocatalytic H_2 evolution

摘要

Recently, donor-acceptor (D-A) conjugated polymers are regarded as promising photocatalysts for water splitting, however, direct polymerization of conjugated polymers bearing various functional groups is still limited. Herein, we have developed a post-functionalization strategy for difluorinated-benzothiadiazole based conjugated polymers (BBT-FF), and one of the two electron-withdrawing fluorine (F) could be replaced by electron-donating alkoxyl group (RO-) via nucleophilic aromatic substitution (SNAr) reaction. For the as-prepared BBT-FCO in which the methoxyl group (CH3O-) was incorporated, it exhibited comparable photocatalytic H-2 evolution rate (HER) to the same polymer which was synthesized by direct polymerization. While the aliphatic chain of alkoxyl groups was extended, increased surface hydrophobicity impair the photocatalytic performance. In order to promote hydrophilicity of the polymers, BBT-FF was further functionalized by different kinds of oligo (ethylene glycol) (OEG), and optimized BBT-FC8O5 exhibited the highest HER, reaching 311 mu mol h(-1) which is 2.46 times higher than BBT-FF. Density functional density calculations suggested that OEG side chain is beneficial to the nitrogen active sites of BT units via proton-coupled electron transfer (PCET) mechanism. Our research provides a facile method to investigate structure-property interrelationship of D-A conjugated polymers for photocatalytic hydrogen evolution.