Charge dynamics in covalent organic framework photocatalysts.

Abstract

Covalent organic frameworks (COFs) are atomically precise, crystalline platforms for efficient solar-to-chemical energy conversion. However, their net efficiency is fundamentally limited by severe kinetic competition, in which ultra-fast exciton recombination outpaces the slower multi-electron kinetics required for surface photocatalytic reactions. This review provides a comprehensive analysis of fundamental exciton dynamics in COF photocatalysts, tracing the photophysical cascade from initial photon absorption and bound electron-hole pair generation to long-range carrier migration and interfacial transfer. We have systematically discussed the significant role of various advanced time-resolved and operational spectroscopic techniques, which serve as vital toolkits for quantifying excited-state lifetimes and mapping charge-translocation pathways. Building upon these insights, we critique state-of-the-art structural modulation strategies, highlighting different parameters such as linkage engineering, donor-acceptor architectures, polarization effects, and internal dielectric environment tuning that manipulate carrier behaviour to force efficient charge separation. Finally, we explore how matching bulk photophysics with customized interfacial active sites drives diverse, highly demanding photocatalytic applications, including hydrogen evolution, CO2 reduction, organocatalysis, H2O2 generation, nitrate reduction, and uranium extraction. Ultimately, this review underscores that maximizing quantum efficiency requires a deliberate, multi-scale synergy that balances bulk solid-state photophysics with the reaction-specific kinetics of the catalyst-substrate interface.