Electronic structure in pyridinium-based metal-to-ligand charge-transfer excited states by step-scan FTIR time-resolved spectroscopy

Step-scan FTIR time-resolved spectroscopy (S2FTIR TRS) has been applied to a series of ReI and OsII polypyridyl complexes that contain N-methyl-4,4′-bipyridinium (MQ+) cation as an electron acceptor. Changes in vν(CO) and ring-stretching vibrations of the acceptor ligands in the fingerprint region provide direct insight into electronic structure both in metal-to-ligand charge transfer (MLCT) excited states and 1-electron reduced complexes. The measurements reveal: (1) changes in metal-ligand back-bonding between the ground and excited state, (2) special characteristics of MQ+ as an acceptor ligand, including the appearance of an intense ΔA band at ∼1610 cm-1, which appears to be vibronically coupled to the internal charge distribution of the reduced ligand, and (3) elucidation of a competition that exists between MQ+ and 4,4′-(CO2Et)2bpy as acceptor ligands fac-[Re(4,4′-(CO2Et)2bpy)(CO)3(MQ +)]n+ (n = 1, 2).

Duke Scholars

Author Richard A. Palmer Chemistry