Electronic absorption, resonance Raman and excited-state resonance Raman spectroscopy of rhenium(I) and copper(I) complexes, with substituted dipyrido[3,2-a : 2′,3′-c]phenazine ligands, and their electron reduced products

The electronic absorption and resonance Raman spectra of a series of rhenium(I) and copper(I) complexes with substituted dipyrido[3,2-a : 2′,3′-c]phenazine (dppz) ligands were investigated. The ligands were ben[i]dipyrido[3,2-a : 2′,3′-c]phenazine, 11,12-dimethyldipyrido[3,2-a : 2′,3′-c]phenazine, 10-methyldipy- rido[3,2-a : 2′,3′-c]phenazine and 11-methyoxydipyrido[3,2-a : 2′,3′-c]phenazine. The spectroelectrochemistry of the reduced complexes and the emission and resonance Raman spectra of the excited states are reported. Vibrational wavenumber calculations of the unsubstituted ligand suggest the presence of normal modes that are localized to various sections of the ligand structure; the resonance Raman spectra of the complexes are interpreted with reference to these calculations. The analysis of the spectra revealed that the Franck–Condon state initially formed by visible photoexcitation (450 nm) is metal-to-ligand charge-transfer in nature. Spectroelectrochemical resonance Raman and electronic absorption measurements revealed the spectral signatures for the radical anions of each of the ligands used in this study. These spectral features were used to assign the excited states formed by the complexes. Most of the complexes studied show spectral features in their excited-states that suggest that the predominant state formed within 5 ns of excitation is ligand-centred. Copyright © 2000 John Wiley & Sons, Ltd.