Triptycene-based discontinuously-conjugated covalent organic polymer photocatalysts for visible-light-driven hydrogen evolution from water

Effective photocatalytic systems that are capable of converting solar energy into chemical fuels have recently attracted significant attention. Covalent organic polymers (COPs) have been explored as promising photocatalysts for visible-light-driven hydrogen evolution from water. Herein, a series of triptycene (TP)-based discontinuously conjugated COP photocatalysts are described for the first-time using TP with monothiophene (MT), trithiophene (TT), dithiophene benzothiadiazole (DTBT), and diphenyl benzothiadiazole (DPBT), denoted as MT-TP, TT-TP, DTBT-TP, and DPBT-TP, respectively. Difference photophysical, morphological, and photocatalytic properties can be tuned by introducing different types of linkers of the TP-based COPs. DPBT-TP shows a significant enhancement of the hydrogen evolution rate (HER) in comparison to those using other polymer photocatalysts at identical conditions. The transmission electron microscopy/scanning electron microscopy data show that the tube-like polymer photocatalysts afford higher HERs than those observed with the particle-like polymer photocatalysts. This report describes the first demonstration that the polymer photocatalysts constructed by the disconuiously conjugated system (conjugation length: less than 5 aromatic rings) is sufficient for an efficient visible-light-driven hydrogen evolution. It provides an alternative material design strategy for polymer photocatalysts to achieve efficient visible light hydrogen evolution.