Theoretical studies of ground and excited electronic states of OLED material bis(2-methyl-8-quinolinolato)gallium(iii) chlorine

By means of ab initio HF and DFT B3LYP methods, the structure of bis(2-methyl-8-quinolinolato)gallium(III) chlorine complex(GaMq2Cl) was optimized and the electronic transition mechanism was studied in the complex. The lowest singlet excited state (S1) of GaMq2Cl has been studied by the singles configuration interaction (CIS) method and time-dependent density functional theory (TD-DFT). The lowest singlet electronic transition (S0→S1) of GaMq2Cl is π-π* electronic transitions and primarily localized on the phenol and pyridyl ligands. The emission of GaMq2Cl is due to the electron transitions from the phenol donor to the pyridyl acceptor including C→C and O→N transference. Two possible electron transfer pathways are presented, one by carbon, oxygen and nitrogen atoms, and the other via metal cation Ga3+. The comparison between the CIS optimized excited-state structure and the Hartree-Fock ground-state structure indicates that the geometric shift is mainly confined to the one quinoline and these changes can be easily understood in terms of the nodal patterns of the highest occupied and lowest unoccupied molecular orbitals. TD-B3-LYP calculations predict an emission wavelength of 504.57 nm. This is comparable to GaMq2Cl 492 nm observed experimentally for photoluminescence. Lending theoretical corroboration to recent experimental observations and supposition, the nature of the electron transition mechanism was revealed.