Probing intraligand and charge transfer excited states of fac-[Re(R)(CO)3(CO2Et-dppz)]+ (R = py, 4-Me2N-py; CO2Et-dppz = dipyrido[3,2a:2′,3′c]phenazine-11-carboxylic ethyl ester) using time-resolved infrared spectroscopy

Abstract

The photophysics of fac-[Re(R)(CO)(3)(CO(2)Et-dppz)](+) (R = py (), 4-Me(2)N-py (); CO(2)Et-dppz = dipyrido[3,2a:2',3'c]phenazine-11-carboxylic ethyl ester) was studied with luminescence spectroscopy and time-resolved infrared (TRIR) spectroscopy in the metal carbonyl (2,100-1,800 cm(-1)) and organic ester (1,800-1,600 cm(-1)) regions. For 1, the picosecond TRIR spectra in the metal carbonyl region provided evidence for the formation of an intra-ligand IL (pi-pi) excited state, which partially decays to an equilibrium with the metal-to-ligand charge transfer (MLCT) excited state. For 2 it is evident that both IL (pi-pi) and MLCT excited states are formed within 2 ps of excitation. The magnitude of the nu(CO) shift in the metal carbonyl region following excitation allows the MLCT excited states to be described more precisely as a dpi(Re) -->pi (phenazine) (3)MLCT state for 1 and as a dpi(Re) -->pi (phenanthroline) (3)MLCT state for 2.