Regulating the exciton binding energy of covalent triazine frameworks for enhancing photocatalysis

Abstract

Strong excitonic effects are the major constraints hindering free charge carrier generation for conducting photocatalysis in polymeric semiconductors, which is usually inhibited by Frenkel excitons with intrinsically strong Coulomb interactions, severely limiting the photocatalytic activity of organic semiconductors. Minimizing the potential Coulomb interaction of Frenkel excitons is ideal for reducing energy loss and thus boosting the generation of charge carriers. Nonetheless, this has been long neglected and its development is still in its infancy in covalent triazine frameworks (CTFs). Herein, a series of CTFs were developed to promote exciton dissociation via a built-in dipole control strategy. Thiophene-rich CTFs deliver a reduction of exciton binding energy down to 97.5 meV to enable exciton dissociation. Thus, the facilitated generation and separation of photogenerated charge carriers over CTFs of thiophene-rich structures enabled the Ugi reaction and functionalization of thiophenols with higher yields than the benzyl analogue Ph-CTF, where boosting superoxide radical (O₂˙⁻) and singlet oxygen (¹O₂) photogeneration via electron and energy transfer processes was facilitated, respectively. This architecture not only establishes a comprehensive understanding of regulating the exciton effect of polymeric semiconductors but also furnishes a feasible avenue for the rational design of polymer-based photocatalysts with highly efficient electron–hole separation from the exciton aspect.