Theoretical investigation of the chemical bonds in metal chelates as emitting material for OLED

Geometries of ground (S0) states of mer-tris(8-hydroxyquinolinato)metal (Mq3, M = Al3+, Ga3+, In3+, Tl3+) are optimized by B3LYP/6-31G(d) methods. In order to investigate the distribution for unequal individual ligands in mer-Mq3 as key materials for OLED, the bonding interactions either between the metal fragment Mq2 and a single ligand q have been analyzed with the energy decomposition scheme. The bonding analysis has been carried out at the BP86 level using TZ2P quality basis functions with small core. All the calculated results suggest that the HOMOs for Mq3 are mainly localized on A-quinolate ligand, which are responsible to the optical characteristics. The calculated phenomena about optical and structural properties of mer-Mq3 can be simply traced back to the lowest electrostatic attractive interaction energy between fragments A-quinolate ligand and the Mq2 due to the special arrangement, resulting in the easy of geometry relaxation for excited state or interaction with metal atoms.