Abstract: The ground- and excited-states geometries, electronic structures, absorptions and emissions of three iridium(Ⅲ) complexes, Ir(ppy)2(N^N)+ [ppy=2-phenylpyrine, N^N=bpy=2,2’-bipyridine(1); N^N=H2dcbpy=4.4’-dicarboxy-2,2’-bipyridine(2); N^N=Hcmbpy=4-carboxy-4’-methyl-2,2’-bipyridine(3)] were investigated theoretically. Their ground and excited state geometries were fully optimized at B3LYP/LANL2DZ and UB3LYP/LANL2DZ levels, respectively, and the calculated geometry of complex 3 is consistent with the X-ray results. At the Time dependent density functional theory(TD-DFT) level with PCM model, the absorption and phosphorescence properties of complexes 1—3 were calculated on the basis of the optimized ground and excited states geometries, respectively. The calculated lowest-lying absorption of complexes 1(384 nm), 2(433 nm) and 3(413 nm) are attributed to a MLCT/LLCT [dIr+π(ppy)→π*(N^N)] transition. The calculated phosphorescence of complexes 1(486 nm), 2(576 nm) and 3(567 nm) can be described as originated from a 3[dIr+π(ppy)]→[π*(N^N)] excited state with 3MLCT/3LLCT character. The calculated results show that the modulation of the lowest 3MLCT excited states can be achieved by grafting electron-withdrawing substituents on the coordinated ligands. In addition, nonlinear optical properties(NLO) calculations reveal that the static first hyperpolarizabilities(β0) are greatly enhanced through the introduction of the carboxy group into the bpy ligand.

Key words: Cyclometalated Ir(Ⅲ) complex, Time dependent density functional theory(TD-DFT), Charge transfer, Excited state