Theoretical design study on the electronic structure and photophysical properties of a series of osmium(II) complexes with different ancillary ligands

The geometrical structures, electronic structures, absorption and phosphorescent properties of a series of osmium(II) complexes with the structure (N^N)₂Os(P^P) [where N^N = 2-pyridyl phenyl triazolate, P^P = 1,2-bis(phospholano)methylene (1); 1,2-bis(phospholano)ethane (2); 1,2-bis(phospholano)-4-methyl-benzene (3); 1,2-bis(phospholano)benzene (4); 1,2-bis(phospholano)-4-cyano-benzene (5); 1,2-bis(phospholano)naphthalene (6)] have been investigated using density functional theory (DFT) and time-dependent density functional theory (TDDFT). Ionization potential and electron affinity values indicate that complex 5 has a good charge transfer balance to enhance device performance of organic light-emitting diodes (OLEDs). The lowest energy emissions of complexes 1-6 at the PBE0 level are localized at 663, 656, 660, 659, 647 and 656 nm, respectively. From the theoretical results, it can be predicted that complex 3 has possibly a larger k_r value than the other complexes. These theoretical studies could be useful in providing valuable information on the optical and electronic properties of phosphorescent materials used in organic light-emitting diodes (OLEDs).