The effects of terminal groups on the structure and photocatalytic performance of imine-linked conjugated polymers

Abstract

The metal-free conjugated polymers have shown great potential application in various photocatalytic and energy fields in recent years, due to their unique properties. Here, a series of imine-linked conjugated polymers (ICPs) with different terminal functional groups were synthesized by Schiff base reactions using low-cost green solvents at low temperatures. The changes of their structures and photoelectric properties resulted by various terminal groups were investigated. By changing the substitution position (o-, m- or p-) of the amine group of the copolymer monomer and different end groups (–CHO, –NH2), a series of CPs with tunable bandgap in the range of 1.82–2.50 eV and various charge separation efficiency were obtained, indicating the ability to structurally tune the photocatalytic activity. The results show that the OT-CHO whose end group is an aldehyde group in the OT series materials has the highest hydrogen production rate of 22.6 μmol/h among the six materials. OT-CHO has good photocatalytic performance owing to its good crystallinity and enhanced conjugation, which promotes charge separation and light absorption. For the binary imine-linked copolymer with various morphologies from one-dimension to three-dimension, the terminal groups with amine electron donating or aldehyde electron withdrawing groups will bring different effects on the aggregate state, crystallinity, conjugation, photoelectric properties and specific surface area of the final synthesized polymer, thereby affecting its photocatalytic hydrogen production performance.