Synthesis and characteristics of bis(2,4-dimethyl-8-quinolinolato)(triphenylsilanolato)aluminum (III): A potential hole-blocking material for the organic light-emitting diodes

A new five-coordinated bis(2,4-dimethyl-8-quinolinolato)(triphenylsilanolato)aluminum (III) (24MeSAlq) material, having bulky substituents, was prepared in one-step reaction and was characterized. The photoluminescent (PL) spectrum of 24MeSAlq shows the largest hypsochromic shift exhibiting the maximum wavelength at the peak of 461 nm among the blue-emitting q2AlOR-type complexes (q = 8-quinolinolato ligand and OR = aryloxy or alkoxy ligand) reported. The deep blue device composed of ITO/2-TNATA (60 nm)/NPB (15 nm)/24MeSAlq (20 nm)/Alq3 (45 nm)/LiF (1 nm)/Al (100 nm), which uses 24MeSAlq as a hole-blocking layer and applies a principle efficiently confining an exciton recombination zone into a hole transporting layer, shows the maximum electroluminescent (EL) at the peak of 446 nm originating from the NPB emissive layer. This is attributed to an excellent hole-blocking property due to the high HOMO (highest occupied molecular orbital) energy level (6.14 eV).