The geometrical structures of a series of Os(II) diimine complexes [Os(L)2(CN)2(phen)] (phen＝1,10-phenanthroline; L＝Ph3 (1), DMSO (2)) and [Os(PH3)2(phen)Br2] (3) in the ground state and the lowest-energy triplet excited state were optimized by the restricted and unrestricted B3LYP/UB3LYP methods. The absorption and emission properties and transition characters in dichloromethane solution were predicted at the time-dependent density functional theory TD-DFT level associated with the PCM solvent effect model. The mechanism and the effects of the π-acid and π-alkali ligands on the phosphorescent spectroscopic properties for 1～3 were explored. As revealed in this paper, complex 3 is prone to break up from the bond Os—Br and the quantum chemical mechanism of potential reaction was further explained. The computed results of 1～3 phosphorescent emission in different solvents indicated that the solvent would affect the quantum efficiencies of the complexes and the solvatochromic effect was observed.

Key words: Os(II) complex, excited state, density functional theory, TD-DFT, effect of solvent