Physical Chemistry

Vibrational Excitation Initiates Biomimetic Charge-Coupled Motions in the Electronic Ground State

Abstract

The concerted interplay between reactive nuclear and electronic motions in molecules actuates chemistry. Manipulating reaction pathways to achieve product selectivity via precise control of light-molecule interactions has allured chemists for decades. Yet it remains an elusive challenge in the electronic ground state, where conventional thermally-driven chemistry occurs. Here, we demonstrate that ground-state vibrational excitation of localised bridge modes initiates charge transfer in a donor-bridge-acceptor molecule in solution. The vibrationally-induced change in the ground-state electronic configuration is visualised by transient absorption spectroscopy, involving a mid-infrared pump and a visible probe, and detailed ab initio molecular dynamics simulations. Mapping the potential energy landscape unravels a hitherto undocumented charge-transfer-assisted double-bond isomerization channel in the electronic ground state. The reaction pathway bears remarkable parallels with the thermal isomerization process in rhodopsin, the retinal protein responsible for scotopic vision. Our results illustrate a generic protocol for activating key vibrational modes to drive photo-triggered ground-state reactions and motivate synthetic and catalytic strategies to achieving potentially new chemistry.

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