Quaternized Side Chain: A Hydrophilic Strategy for Boosting the Visible-Light Catalytic Hydrogen Evolution of Linear Conjugated Polymers

Conjugated polymers are emerging as promising organic photocatalysts for visible-light catalytic hydrogen evolution from water. Herein, a hydrophilic strategy enabled by quaternized side chains is demonstrated to boost the photocatalytic hydrogen evolution rate from water. Three linear conjugated polymers with side chains of alkylation, tertiary amine, and quaternary ammonium were designed and synthesized based on phthalimide and thiophene–pyridine–thiophene. Compared to conjugated polymers with alkylated and tertiary aminated side chains, the quaternized side chain polymer exhibited a significantly smaller intact angle, which endowed the photocatalyst with improved hydrophilicity, better dispersity, and reduced charge transport resistance. Consequently, an 8-fold enhancement in the photocatalytic performance was achieved compared to the conjugated polymer with an alkylated side chain. Furthermore, the photocatalytic performances were further optimized, achieving a hydrogen evolution rate as high as 11608 μmol g–1 h–1 when Pt (1 wt %) was used as the cocatalyst. This work indicated that incorporating a quaternized side chain is an effective strategy to boost the photocatalytic performances of organic photocatalysts.