Molecular Engineering of Fully Conjugated sp2 Carbon-Linked Polymers for High-Efficiency Photocatalytic Hydrogen Evolution.

The diverse nature of organic precursors offers a versatile platform for precisely tailoring the electronic properties of semiconducting polymers. In this study, three fully conjugated sp2 carbon-linked polymers have been designed and synthesized for photocatalytic hydrogen evolution under visible-light illumination, by copolymerizing different C3 -symmetric aromatic aldehydes as knots with the 1,4-phenylene diacetonitrile (PDAN) linker through a C=C condensation reaction. The hydrogen evolution (HER) is achieved at a maximum rate of 30.2 mmol g-1  h-1 over a polymer based on 2,4,6-triphenyl-1,3,5-triazine units linked by cyano-substituted phenylene, with an apparent quantum yield (AQY) of 7.20 % at 420 nm. Increasing the degree of conjugation and planarity not only extends visible-light absorption, but also stabilizes the fully conjugated sp2 -carbon-linked donor-acceptor (D-A) polymer. Incorporating additional electron-withdrawing triazine units into the D-A polymer to form multiple electron donors and acceptors can greatly promote exciton separation and charge transfer, thus significantly enhancing the photocatalytic activity.