Step-Scan Fourier Transform Infrared Absorption Difference Time-Resolved Spectroscopy Studies of Excited State Decay Kinetics and Electronic Structure of Low-Spin d⁶ Transition Metal Polypyridine Complexes With 10 Nanosecond Time Resolution

Abstract

Step-scan Fourier transform absorption difference time-resolved spectroscopy (S²FTIR ∆A TRS) has been used to collect mid-IR time-resolved infrared spectra of the transient electronic excited states of polypyridine transition metal complexes with 10 ns time resolution. The time-resolved data can be used for kinetic analysis or to generate “snapshots” of the lowest lying excited state. Shifts of vibrational bands in the excited state relative to the ground state can be used to infer significant details of the electronic structure of the excited state. The multiplex advantage of the FTIR technique allows a wide variety of vibrational bands to be analyzed for this purpose. In the example illustrated, the shift of the ester ν(CO) band in {Ru(bpy)[4,4′-(COOEt)₂bpy]₂}²⁺ compared to those in related complexes has been used to address the question of electron delocalization in the excited state.