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(CO₂Et-dppz)]⁺ (R = py (1), 4-Me₂N-py (2); CO₂Et-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 (2100–1800 cm⁻¹) and organic ester (1800–1600 cm⁻¹) regions. For 1, the picosecond TRIR spectra in the metal carbonyl region provided evidence for the formation of an intra-ligand IL (π–π*) 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 (π–π*) and MLCT excited states are formed within 2 ps of excitation. The magnitude of the ν(CO) shift in the metal carbonyl region following excitation allows the MLCT excited states to be described more precisely as a dπ(Re) → π*(phenazine) ³MLCT state for 1 and as a dπ(Re) → π*(phenanthroline) ³MLCT state for 2.