Photophysical investigations of rhenium(I)Cl(CO)3(phenanthroline) complexes

The electronic states of three complexes with the generic formula Re(I)Cl(CO)(3)(s-phen) [s-phen = 4,7-dimethyl-1,10-phenanthroline, 5,6-dimethyl-1,10-phenanthroline, and 3,4,7,8-tetramethyl-1,10-phenanthroline] have been characterized by absorption and luminescence spectroscopy and the T-dependence of the decay times in rigid glasses in the range 4-77 K. Methyl substitution leads to composite phosphorescence bands that arise from (MLCT)-M-3 and (3)pi pi* terms that are separated by Franck-Condon barriers. Evidence is also presented for the existence of FC barriers in singlet manifolds. Criteria are defined for the occurrence of FC barriers and slow rates of radiationless transitions between terms arising from disparate electronic configurations. The energy splittings and the decay constants of the individual sublevels of the (MLCT)-M-3 manifolds have been determined. (C) 2001 Elsevier Science B.V. All rights reserved.