Framework Deuteration Regulates Excited-State Dynamics and H2O2 Release in Covalent Organic Framework Photocatalysis

Hydrogen/deuterium (H/D) substitution provides a unique means of perturbing nuclear motion while largely preserving electronic structure. Here, we investigate isotope-regulated photocatalysis using structurally matched H-TpPa and D-TpPa covalent organic frameworks (COFs) for H2O2 production. Deuteration preserves framework connectivity, crystallinity, porosity, and ground-state electronic structure, yet increases the H2O2 production rate by 1.80-fold in O2-saturated pure water. Spectroscopic and theoretical analyses show that D-TpPa exhibits weaker effective exciton–phonon coupling, a lower apparent exciton-dissociation energy, a longer-lived photoexcited population, and redistributed mode-resolved Huang–Rhys contributions, collectively improving charge utilization. Both isotopologues follow the same coupled two-electron oxygen reduction and four-electron water oxidation pathway. At the catalytic interface, isotope-dependent vibrational free-energy contributions reduce terminal *HOOH stabilization and lower the free-energy requirement for H2O2 release. These results establish framework isotope engineering as a generic strategy for regulating photocatalysis from excited-state evolution to interfacial product release without substantial electronic reconstruction.