New Red Phosphorescent Heteroleptic Tris-Cyclometalated Iridium Complex with 1-phenylisoquinoline and 2,4-diphenylquinoline

The synthesis and photophysical study of efficient phosphorescent iridium(III) complexes having two different (C^N) ligands are reported. In order to improve luminescence efficiency by avoiding triplet–triplet (T-T) annihilation, a heteroleptic iridium complex, Ir(dpq)2(piq), is designed and prepared, where dpq and piq represent 2,4-diphenylquinoline and 1-phenylquinoline, respectively. Dpq and piq ligands can act as a source of energy. When Ir(dpq)2(piq) is placed in the lowest excited state, the excitation energy is neither quenched nor deactivated but quickly transferred intermolecularly from two dpq ligands to one luminescent piq ligand. Such transfer can occur because the triplet energy level of dpq is higher than that of piq and light is emitted mainly from the piq ligand in the end. Thus, Ir(dpq)2(piq) shows strong photoluminescence from piq ligands. To analyze this luminescent mechanism, we calculated these complexes theoretically using a computational method.