The effect of the cyano-group substitution on the electronic properties of 8-hydroxyquinoline lithium studied with DFT

Electronic structures of 8-hydroxyquinoline lithium (Liq) and its derivatives substituted by cyano-group (CN) are studied by the quantum mechanics program, which is based on density functional theory (DFT). The electron properties of system after introducing CN are analyzed, which includes geometry structure, system energy, electron distribution, frontier molecular orbital, band structure and density of states (DOS). The results indicate that CN attached to 5-position of 8-hydroxyquinoline ligand, takes part in the whole π-conjugated system well, and that 5-CNLiq is the most stable. The substitution group CN weakens the conjugation effect of C(5)C(10) and C(5)C(6), the contravalency effect of Li and N, and electrostatic effect of Li and O. There is strong interaction between frontier molecular orbital and CN, and therefore the electronic properties of (5-CN8-hydroxyquinoline)lithium(5-CNLiq) are changed compared with Liq. The LUMO energy level decreases and the energy gap enlarge. The electron cloud density of phenol ring and pyridine ring reduces. The degeneracy of molecular orbital energy level is changed and the energy band is broadened. In result, the electronic spectra blue-shift and electron can easily inject and transmit for 5-CNLiq. It can be concluded that 5-CNLiq is better blue emitting material than Liq for organic electroluminescent devices (OLEDs) in theory.