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 rheniu m(I) and copper(I) complexes with substituted dipyrido[3,2-a:2',3'-c]phenaz ine (dppz) ligands were investigated. The ligands were benzo[i]dipyrido[3,2 -a:2',3'-c]phenazine, 11,12-dimethyldipyrido[3,2-a:2',3'-c]phenazine, 10-me thyldipyrido[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 emi ssion and resonance Raman spectra of the excited states are reported, Vibra tional wavenumber calculations of the unsubstituted ligand suggest the pres ence of normal modes that are localized to various sections of the ligand s tructure; 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 n m) is metal-to-ligand charge-transfer in nature, Spectroelectrochemical res onance Raman and electronic absorption measurements revealed the spectral s ignatures 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 t he 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 (C) 2000 John Wiley & Sons, Ltd.