Modulating Charge Transfer Dynamics in Titanium Metal–Organic Frameworks via Conjugated Linker Engineering for Enhanced Photocatalytic Hydrogen Evolution

This study synthesized three isostructural 2D Ti-based MOFs (Ti–C═C, Ti–C═N, and Ti–N═N) to investigate how conjugated bridge engineering affects their electronic structure, carrier dynamics, and photocatalytic performance. DFT calculations and spectroscopic analyses revealed that the bridging bond systematically modulates frontier orbital localization, from delocalized ligand π states in Ti–C═C to localized N-lone-pair states in Ti–N═N. Ti–C═C exhibited the short-lived nature of its excited-state population with efficient nonradiative electron transfer, which accounted for its exceptional H2 evolution rate. In contrast, Ti–C═N featured a long-lived charge-separated state with a larger binding energy (Eb), resulting in dominated radiative recombination of charge carriers and an activity only one-sixth that of Ti–C═C. Ti–N═N was photocatalytically inactive owing to its narrowed bandgap and insufficient reducing power. This work elucidates the intrinsic regulation of charge carrier dynamics through linkage engineering, providing a universal strategy for the rational design of high-performance Ti-MOF-based photocatalysts.