Application of Time-Resolved, Step-Scan Fourier Transform Infrared Spectroscopy to Excited-State Electronic Structure in Polypyridyl Complexes of Rhenium(I)

Abstract

Time-resolved infrared difference spectra have been acquired for a series of Re(I) complexes by step-scan Fourier transform infrared spectroscopy, the first application of the step-scan technique to transient inorganic photochemistry. Shifts in ν(CO) following laser flash excitation at 354.7 nm in CH3CN at room temperature show that the lowest-lying excited state in fac-[Re(phen)(CO)3(4-Mepy)]+ (1) is a metal-to-ligand charge transfer (MLCT) state, in fac-[Re(dppz)(CO)3(PPh3)]+ (2) a 3ππ* state, and in fac-[Re(4,4‘-(NH2)2bpy)(CO)3(4-Etpy)]+ (3) a mixture of ligand-based and MLCT states.