Theoretical studies on the structural and optical properties of a series of Os(II) diimine complexes [Os(N ∧N)(CO) 2I 2] (N ∧N = 2,2′-bipyridine(bpy), 4,4′-di- tert-butyl-2,2′-bipyridine(dbubpy), 4,4′-dichlorine-2,2′-bipyridine(dclbpy))

Abstract

The ground- and excited-state structures for a series of Os(II) diimine complexes [Os(N ∧N)(CO) 2I 2] (N ∧N = 2,2′-bipyridine (bpy) ( 1), 4,4′-di- tert-butyl-2,2′-bipyridine (dbubpy) ( 2), and 4,4′-dichlorine-2,2′-bipyridine (dclbpy) ( 3)) were optimized by the MP2 and CIS methods, respectively. The spectroscopic properties in dichloromethane solution were predicted at the time-dependent density functional theory (TD-DFT, B3LYP) level associated with the PCM solvent effect model. It was shown that the lowest-energy absorptions at 488, 469 and 539 nm for 1– 3, respectively, were attributed to the admixture of the [d xy (Os) → π ∗(bpy)] (metal-to-ligand charge transfer, MLCT) and [p(I) → π ∗(bpy)] (interligand charge transfer, LLCT) transitions; their lowest-energy phosphorescent emissions at 610, 537 and 687 nm also have the 3MLCT/ 3LLCT transition characters. These results agree well with the experimental reports. The present investigation revealed that the variation of the substituents from H → t-Bu → Cl on the bipyridine ligand changes the emission energies by altering the energy level of HOMO and LUMO but does not change the transition natures.