Photophysical properties of Re(CO) 3L +3 (L=monoazine) complexes : Electronic delocalization effect in metal-to-ligand charge transfer excited states

Abstract

The photophysical properties of the series of the [Re(CO) 3L 3]CF 3SO 3 (L=4-phenylpyridine, 3-phenylpyridine, 4–benzylpyridine, 4-(4′-nitrobenzyl)-pyridine and 4,4′-bipyridine) have been studied. Emission spectral changes with temperature and biexponential decay of the luminescence both in dichloromethane fluid solution and frozen (77 K) media show two excited states, intraligand (IL) and metal-to-ligand charge transfer (MLCT) in character, emitting with intrinsic rates. Rates of MLCT emission badly correlate with the excited state-ground state energy gap. Departures from the energy gap law are rationalized in terms of excited state distortion and electronic delocalization.