Synthesis, crystal structure, and luminescent properties of a binuclear gallium complex with mixed ligands

By introducing tridentate Schiff base ligands, a binuclear gallium complex with mixed ligands, bis(salicylidene-o-aminophenolato)-bis(8-quinolinolato)-bis-gallium(III) [Ga-2(saph)(2)q(2)], has been synthesized and structurally characterized by single-crystal X-ray crystallography. Crystal data for C44H30Ga2N4O6 are as follows: space group, triclinic, P1; a = 11.357(3) Angstrom, b = 12.945(3) Angstrom, c = 12.947(3) Angstrom, alpha = 103.461(15)degrees, beta = 100.070(7)degrees, gamma = 96.107(18)degrees, Z = 2. This complex was identified as a dimeric complex of hexacoordinated gallium with strong intermolecular and intramolecular pi-pi stacking interactions between the pyridyl/pyridyl rings. The thermal analysis showed that Ga-2(saph)(2)q(2) can readily form a stable amorphous glass with a high glass transition temperature (T-g = 204 degreesC), which is 27 degreesC higher than that of tris(8-hydroxyquinolinolate)aluminum (Alq(3)). In addition, a high photoluminescence efficiency (phi(PL)) of 0.318 in DMF has been demonstrated, although the central gallium atom can result in heavy-atom quenching. Organic light-emitting diodes (OLEDs) based on this complex displayed a turn-on voltage as low as 2.5 V and a high efficiency. Even at a low doping concentration of 1%, the doped Ga-2(saph)(2)q(2) devices with 4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) as the dopant exhibited excellent red emission centered at 628 nm with improved durability, compared with the case of Alq(3) as the host. These distinguishing properties of Ga-2(saph)(2)q(2) make it a good candidate as a novel electron-transporting and emitting material for OLEDs.