Conformation-driven exciton transfer in pyrene-sulfone covalent organic frameworks for bifunctional photocatalysis

Abstract

Conformation is crucial for exciton transfer and charge separation, but remains largely unexplored in covalent organic frameworks (COFs). Herein, a new D–A COF integrated with pyrene and sulfone moieties is synthesized, which undergoes a reversible conformational transition from twisted to planar with lattice expansion in polar media due to hydrogen bonding and dipolar interactions. Femtosecond transient absorption (fs-TA) spectra and time-dependent density functional theory (TD-DFT) calculations reveal a conformation-dependent exciton transfer behavior. In contrast to the twisted configuration, the planar one exhibits more charge-transfer (CT) excitons and accelerated exciton transfer (0.28 ps) and prolonged carrier lifetime (988.21 ps) with a reduced Coulomb barrier. When used as a photocatalyst, it achieves a hydrogen evolution rate of 23.46 mmol h⁻¹ g⁻¹, higher than most reported counterparts, and an independent oxygen evolution rate of 261.55 μmol h⁻¹ g⁻¹. This work demonstrates the conformation-driven exciton transfer kinetics in COFs and contributes to the understanding and rational design of efficient photocatalysts.