Regioisomeric Engineering of Covalent Organic Frameworks toward Enhanced Photocatalytic Performance

The photocatalytic performance of covalent organic frameworks (COFs) is often restricted by the inefficient utilization of photogenerated charge carriers. Achieving precise regulation of their electronic structures to facilitate charge separation and transport remains a great challenge. Herein, two regioisomeric COFs bearing pyrene units substituted at the 1,6- or 2,7-positions were rationally designed and synthesized to elucidate the influence of isomerism on electron distribution and photocatalytic behavior. Despite their comparable chemical composition and framework topology, the two regioisomeric COFs exhibited distinct photocatalytic activities. The 2,7-substituted P-COF exhibited a remarkable hydrogen evolution rate of 12.3 mmol h^-1 g^-1, whereas the 1,6-substituted D-COF displayed only negligible activity of 0.42 mmol h^-1 g^-1. Furthermore, P-COF achieved a H₂O₂ generation rate of 4.25 mmol h^-1 g^-1 using benzyl alcohol as sacrificial agent, much higher than that of D-COF (0.64 mmol h^-1 g^-1). A combination of experimental characterization and theoretical analysis revealed that regioisomerism exerts a decisive effect on the electronic structures as well as charge separation and transport dynamics, thereby substantially enhancing photocatalytic performance of pyrene-based COFs.