Carbazole-Based Donor-Acceptor Conjugated Microporous Polymers for Efficient Visible-Light-Driven Photocatalytic H2 Evolution

Conjugated microporous polymers (CMPs) featuring extended p-structures, large specific surface area and tailor-made functionalities are a class of promising organic photocatalysts for hydrogen evolution reaction (HER) from water. However, the photocatalytic activities of most CMPs are severely hindered by slow charge transfer rate and fast charge recombination process. Herein, we develop a strategy for the synthesis of donor-acceptor CMPs through nickel(0)-catalyzed Yamamoto cross-coupling of 3,6-dibromo-9-(4-bromophenyl)carbazole (CZ) with 5,5 '-dibromo-2,2 '-bipyridine (DBPy) for efficient HER from water. The PCZN-4 prepared with a 2 : 3 stoichiometric ratio of CZ to DBPy exhibited the highest photocatalytic hydrogen evolution rate of 7160 mu mol center dot g(-1)center dot h(-1), which was nearly equal to 179 times and 143 times that of PCZN-1 (40 mu mol center dot g(-1)center dot h(-1)) and PCZN-6 (50 mu mol center dot g(-1)center dot h(-1)) obtained by Yamamoto homocoupling of CZ and DBPy, respectively. Compared to the homocoupling counterparts, the enhanced photocatalytic activity of PCZN-4 results from improved separation efficiency of charge carriers. Interestingly, the photocatalytic H-2 evolution performance of PCZN-4 could be further improved up to 17080 mu mol center dot g(-1)center dot h(-1) by adjusting pH of the aqueous solution. This work offers a novel approach for improving photocatalytic efficiency by tuning the chemical structures and surrounding microenvironment of the polymer backbone.