Thousandfold Enhancement of Photoreduction Lifetime in Re(bpy)(CO)₃ via Spin-Dependent Electron Transfer from a Perylenediimide Radical Anion Donor

Abstract

Spin-dependent intramolecular electron transfer is revealed in the Re^I(CO)₃(py)(bpy-Ph)-perylenediimide radical anion (Re^I-bpy-PDI^-•) dyad, a prototype model system for artificial photosynthesis. Quantum chemical calculations and ultrafast transient absorption spectroscopy experiments demonstrate that selective photoexcitation of Re^I-bpy results in electron transfer from PDI^-• to Re^I-bpy, forming two distinct charge-shifted states. One is an overall doublet whose return to the ground state is spin-allowed. The other, high-spin quartet state, persists for 67 ns due to spin-forbidden back-electron transfer, constituting a more than thousandfold lifetime improvement compared to the low-spin state. Exploiting this spin dependency holds promise for artificial photosynthetic systems requiring long-lived reduced states to perform multi-electron chemistry.