Photoinduced Processes in Rhenium(I) Terpyridine Complexes Bearing Remote Amine Groups: New Insights from Transient Absorption Spectroscopy.

Photophysical properties of two Re(I) complexes [ReCl(CO) 3 (R-C 6 H 4 -terpy-κ 2 N)] with remote amine groups, N -methyl-piperazinyl ( 1 ) and (2-cyanoethyl)methylamine ( 2 ), were investigated. The complexes show strong absorption in the visible region corresponding to metal-to-ligand charge transfer ( 1 MLCT) and intraligand-charge-transfer ( 1 ILCT) transitions. The energy levels of 3 MLCT and 3 ILCT excited-states, and thus photoluminescence properties of 1 and 2 , were found to be strongly affected by the solvent polarity. Compared to the parent chromophore [ReCl(CO) 3 (C 6 H 5 -terpy-κ 2 N)] ( 3 ), both designed complexes show significantly prolonged (by 1-2 orders of magnitude) phosphorescence lifetimes in acetonitrile and dimethylformamide, contrary to their lifetimes in less polar chloroform and tetrahydrofuran, which are comparable to those for 3 . The femtosecond transient absorption (fsTA) measurements confirmed the interconversion between the 3 MLCT and 3 ILCT excited-states in polar solvents. In contrast, the emissive state of 1 and 2 in less polar environments is of predominant 3 MLCT nature.