Defining Electronic Excited States Using Time-Resolved Infrared Spectroscopy and Density Functional Theory Calculations

Abstract

Characteristic patterns of infrared bands in the ν(CO) region have been observed in the time-resolved infrared (TRIR) spectra of fac-rhenium tricarbonyl complexes that allow for identification of transient states that result following laser flash excitation. These patterns can be interpreted by combining experimental TRIR data with density functional theory (DFT) calculations. The DFT calculations are particularly valuable as they provide vibrational energy shifts between the ground and excited states and an analysis of the electronic interactions in terms of the orbitals involved in the excitation. TRIR and DFT results for four different transient excited states, intraligand π → π*, metal-to-ligand charge transfer (MLCT), intramolecular (dπ−Οπ) → π* excited states, and a redox-separated (RS state), are presented here. A unique example of competing excited states studied by TRIR is also presented. The complexes studied include fac-[ReI(CO)3(Me2dppz)(4-Etpy)]+, fac-[ReI(CO)3(bpy)(4-Etpy)]+, fac-[ReI(CO)3(4...