Theoretical studies on the optical properties and substituent effects of osmium (II) complexes Os(N^N)(C [tbnd]N) 2(PH 3) 2

Abstract

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^N)(C N)2(PH3)2 [N^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)] → [π*(N^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)] [π*(N^N)]} excited state. The spectra are blue-shifted by adding electron-donating substituents of t−butyl and OCH3 on the N^N ligands, but red-shifted by adding electron-withdrawing group Cl.