Substantial Cyano-Substituted Fully sp²-Carbon-Linked Framework: Metal-Free Approach and Visible-Light-Driven Hydrogen Evolution

Polymeric semiconductors are emerging as a kind of competitive photocatalysts for hydrogen evolution due to their well-tunable structures, versatile functionalization, and low-cost processibility. In this work, a series of conjugated porous polymers with substantial cyano-substituted fully sp²-carbon frameworks are efficiently synthesized by using electron-deficient tricyanomesitylene as a key building block to promote an organic base-catalyzed Knoevenagel condensation with various aldehyde-substituted arenes. The resulting porous polymers feature donor-acceptor structures with π-extended conjugation, rendering them with distinct semiconducting properties. They possess hierarchically porous structures, nanoscale morphologies, and intriguing wettability. These promising physical characters, finely tailorable by varying the arene units, are essentially relevant to the abundant cynao substituents over the whole frameworks. The as-prepared porous polymers exhibit excellent visible-light-driven photocatalytic activity for water-splitting hydrogen evolution with apparent quantum yield up to 2.0% at 420 nm or 1.9% at 470 nm, among the highest values yet reported for porous polymer-based photocatalysts, also representing the first example of such kinds of catalysts formed through a metal-free-catalyzed carbon–carbon coupling reaction.