Dopant-Mediated Modulation of Charge-Transfer Pathways in Metal-Organic Frameworks: A Quantum Dynamics Perspective

Metal substitution offers a powerful route to enhance charge separation in metal-organic framework (MOF) photocatalysts, yet the mechanism remains elusive. Using ab initio adiabatic and nonadiabatic molecular dynamics, we show that Ce- and Ti-doped UiO-66-NH₂(Zr) generate localized electron-polaron states within the midgap immediately after photoexcitation. These self-trapped polarons form on a femtosecond time scale through strong electron-lattice coupling, redirecting charge flow from ligand-to-ligand to ligand-to-metal transfer and thereby suppressing band-edge recombination. The trapped electrons can subsequently hop to neighboring Zr sites via energetically favorable metal-to-metal transfer, enabled by the lower electronegativity of the dopants and occurring faster than polaron recombination. This work establishes the microscopic mechanism by which metal substitution improves charge separation and provides design principles for high-performance MOF-based photocatalytic systems.