Regulating Excitonic Effects in Covalent Organic Frameworks to Promote Free Charge Carrier Generation

Strong excitonic effects, induced by the Coulombic interactions between photogenerated electrons and holes, seriously hinder the generation of free charge carriers in organic semiconductors for conducting photocatalysis. Herein, we report a built-in control of the donor-acceptor (D-A) interaction strategy to regulate excitonic effects within benzobisthiazole-bridged covalent organic frameworks (Tz-COFs). Theoretical calculation and ultrafast spectroscopy reveal that strengthening D-A interactions by this built-in control strategy in Tz-COFs can accelerate exciton dissociation, thus generating more long-lived photogenerated charge carriers for photoredox reactions. As a result, the optimized Tz-COF-3 exhibits high photocatalytic H2 evolution activity as high as 43.2 mmol g-1 h-1, with an apparent quantum yield of 6.9% at 420 nm. This work guides the development of COFs from excitonic aspects for photocatalysis.