TIME-RESOLVED RESONANCE RAMAN-SPECTROSCOPY OF [CU(DMP)2]+ IN SOLUTION

Pulsed and CW-laser-excited resonance Raman (RR) spectra are reported at a number of excitation wavelengths for the ground state and lowest energy metal-to-ligand charge-transfer (MLCT) excited state of [Cu(dmp)2]+ (1) (dmp = bis(2,9-dimethyl-1,10-phenanthroline). From analysis of the ground-state RR spectra, evidence has been obtained that three distinct transitions contribute to the MLCT absorption profile over the wavelength range 340-550 nm. The conclusions are in agreement with a recent independent analysis of the low-temperature UV-visible absorption spectrum of 1. The time-resolved RR spectra which are reported provide convincing evidence that the lowest MLCT excited state is localized, [(L)Cu(II)(L.-)]+, corroborating earlier, less extensive RR spectral data. The consequence of this assignment, that the effective symmetry of the thermally equilibrated MLCT excited state is C2-upsilon or possibly C2, is considered in relation to a recent spectroscopic analysis or the MLCT excited states of related Cu(I) complexes.