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)(R-CH-terpy-κN)] with remote amine groups, -methyl-piperazinyl () and (2-cyanoethyl)methylamine (), were investigated. The complexes show strong absorption in the visible region corresponding to metal-to-ligand charge transfer (MLCT) and intraligand-charge-transfer (ILCT) transitions. The energy levels of MLCT and ILCT excited-states, and thus photoluminescence properties of and , were found to be strongly affected by the solvent polarity. Compared to the parent chromophore [ReCl(CO)(CH-terpy-κN)] (), 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 . The femtosecond transient absorption (fsTA) measurements confirmed the interconversion between the MLCT and ILCT excited-states in polar solvents. In contrast, the emissive state of and in less polar environments is of predominant MLCT nature.