Theoretical studies of the electronic structure and spectroscopic properties of [Ru(Htcterpy)(NCS)₃]^3-

The ground- and excited-state structures of [Ru(Htcterpy)-(NCS) ₃]^3- (1H) (tcterpy = 4,4′,4″-tricarboxy-2, 2′:6′,2″-terpyridine) are optimized by the DFT and CIS methods, respectively. Absorption and emission spectra in the gas phase and in solution (ethanol and water) are predicted at the TD-DFT/B3LYP level. Experimental spectra are roughly reproduced by our calculated results. In ethanol solution, the HOMOs of the absorption spectra are dominated by d orbitals of the ruthenium atom and thiocyanate ligands, and the LUMOs possess π* (tcterpy) character with considerable carboxyl contribution. In the theoretically simulated absorption spectra, the first four bands are attributed to Ru/NCS→π* (tcterpy) charge-transfer (MLCT/LLCT) transitions, whereas the fifth one with the strongest intensity arises from intraligand tcterpy π→π* charge transfer (ILCT) mixed with some O(p _z)→terpy charge transfer (LLCT). Our calculations reveal that the MLCT/LLCT absorption bands in water are blue-shifted with respect to those in ethanol, agreeing with experimental observations. This can be rationalized by a decreased dipole moment in the excited state. The phosphorescent emissions are calculated to occur at 724, 711, and 691 nm in the gas phase, in ethanol, and in water, respectively, all with the same ³LMCT/³LLCT character.