Electron Transfer Mechanism in Organometallic Molecules Studied by Subpicosecond Extended X-ray Absorption Fine Structure Spectroscopy

Abstract

The mechanism responsible for the redox reaction of [Co(III)(en)3]Ac3 to Co(II) complex has been determined to be intramolecular electron transfer. It was measured in real time by means of subpicosecond extended X-ray absorption fine structure spectra, EXAFS, and optical experiments and supported by density functional theory calculations. The proposed mechanism is based on histograms of bond length changes of the transient structures measured as a function of time, with subpicosecond time and sub-Angstrom resolution and femtosecond transient spectra and kinetics after excitation with a 267 nm femtosecond pulse. Even though four Fe and Co complexes were excited in the charge transfer band and the photoinduced redox reaction proceeds with similar high redox quantum yield, the dominant electron operating mechanism differs: intramolecular for amine metal complexes and intermolecular for oxalate metal complexes. The ligand orientation degree of freedom and counterion effect are proposed to provide tentative explanation for the electron transfer mechanism.