Pyrene- and 1,3,5-triazine-based D-A two-dimensional polymers for sunlight-driven hydrogen evolution: the influence of the linking pattern

Conjugated microporous polymers (CMPs) have been widely used as photocatalysts for water splitting to produce hydrogen. Appropriate design of the CMP structure is a key factor for enhancing the efficiency of photocatalytic hydrogen evolution. Herein, we report two pyrene and 2,4,6-triphenyl-1,3,5-triazine-based conjugated microporous polymers (CMPs), TzSPy and TzPy , which were synthesized via Pd-catalyzed Suzuki-Miyaura polymerization. The integration of pyrene with triazine resulted in continuous electron donor-acceptor systems with high photocatalytic hydrogen evolution activity. Although the 1,6-linked TzSPy skeleton possesses a larger torsional angle compared to the 2,7-linked TzPy , it has a higher degree of conjugation and, consequently, can absorb visible light across a broader wavelength range. TzSPy and TzPy exhibited surprising hydrogen evolution rates (HER) of 10.3 mmol g −1 h −1 and 6.93 mmol g −1 h −1 , respectively, under simulated sunlight (AM1.5G). DFT calculations and the experimental results of additional four groups of pyrene-based CMPs supported our conclusions that the 1,6-substituted pyrene-based CMPs possess a greater degree of conjugation compared to 2,7-substituted pyrene-based CMPs and thus demonstrate a higher photocatalytic activity. Two conjugated organic polymers constructed from electron-rich pyrenes and electron-deficient 2,4,6-triphenyl-1,3,5-triazine demonstrated good photocatalytic hydrogen evolution activity.