A TD-DFT study on the electronic spectrum of Ru(II)L2 [L = bis(5′-methyl-2,2′-bipyridine-6-carboxylato)] in the gas phase and DMF solution

Ruthenium polypyridine and polypyridined-derivative complexes are used in dye-sensitized solar cell as a light to current conversion sensitizers, study on the electronic absorption spectroscopy of which are very important for the understanding of their photovoltaic character. A theoretical research of UV-Vis spectrum on the Ru(II)L2[L = bis(5′-methyl-2,2′-bipyridine-6-carboxylato)], a polypyridined-derivative mononuclear ruthenium complex, is presented here. Transition excited states of Ru(II)L2 in the gas phase have been studied by the time-dependent density functional theory (TD-DFT) using a hybrid functional, B3LYP, as well as the 3-21G∗ basis set. Two maximum absorptions are dominated by the metal-to-ligand-charge-transfer (MLCT) transitions, from Ru 4d orbitals to the bipyridine rings π∗. Taking account of solvent effect, the electronic absorption spectrum of Ru(II)L2 in N,N′-dimethyl formamide (DMF) solution has also been investigated on the basis of Polarized Continuum Model (PCM) in connection with TD-DFT. Calculation results indicate that the two maximum MLCT absorption peaks are blue-shifted in DMF solution with respect to those in the gas phase, which is in agreement with the observed phenomenon of other ruthenium polypyridine-type complexes.