Infrared spectra of the excited states of coordination compounds containing CO groups: Bandwidths in polar and nonpolar solvents

Time-resolved infrared spectroscopy has been used to probe the ν(CO) bandwidths of the MLCT excited states of carbonyl-containing metal complexes, in both polar and nonpolar solvents. Considerably broader excited state bands observed in the polar solvents indicate that the broadening of the ν(CO) bands is a consequence of solvent-solute interactions. ππ* excited states, with no charge-transfer character, exhibit no such broadening of the ν(CO) bands upon excitation.