Enhanced photocatalytic performance of tetraphenylethylene-based porous aromatic frameworks by bandgap adjustment for the synthesis of benzimidazoles†

Porous aromatic frameworks (PAFs) as visible-light active and reusable photocatalysts provide a green and sustainable alternative to conventional metal-based photocatalysts. In this study, we design and synthesize three novel photoactive tetraphenylethylene (TPE) based PAF photocatalysts (TPE-PAFs) linked with thiophene units in an alternating donor (D)–acceptor (A) fashion. Photoelectrochemical measurements show that the introduction of different thiophene units can effectively regulate the optical band gap and energy level, which may further determine their photocatalytic performance. As a result, TPE-PAFs achieve excellent yields (up to 99%), broad substrate scope and high recyclability (up to 10 cycles) for the photosynthesis of benzimidazoles. The photocatalytic reaction is successfully monitored using in situ IR spectra. This work provides a feasible approach for designing PAFs with high photocatalytic activity and broadens the application of PAFs for photocatalytic organic transformations.