Theoretical studies on the optical properties and substituent effects of osmium (II) complexes Os(N∧N)(CN)2(PH3)2

The ground and the excited state geometries, electronic structures, absorption and emission spectra as well as the substituent effects of a series of osmium (II) diimine complexes Os(N boolean AND N)(C N)2(PH3)2 [N boolean AND N = 2,2'-bipyridine (bpy) 1; 4,4-di-tert-butyl-2,2'-bipyridine (dbubpy) 2; 4,4-di-methoxy-2,2'-bipyridine (dmobpy) 3; 4,4-di-chloro-2,2'-bipyridine (dcbpy) 4] were investigated by DFT and ab initio methods. At the TD-DFT and PCM level, the lowest-lying absorptions of 1-4 at 483, 467, 463, and 522 nm are dominantly assigned to a {[d(xy)(Os)] -> [pi*(N boolean AND N)]} transition with MLCT character. The calculated phosphorescence of 1-4 at 635, 605, 598, and 683 nm can be described as originating from 3{[d(xy)(Os)] [pi*(N boolean AND N)]} excited state. The spectra are blue-shifted by adding electron-donating substituents of t-butyl and -OCH3 on the N boolean AND N ligands, but red-shifted by adding electron-withdrawing group -Cl. (C) 2008 Elsevier B.V. All rights reserved