A Hole-Transporting Material with Controllable Morphology Containing Binaphthyl and Triphenylamine Chromophores

An organic compound with two triphenylamine moieties linked with binaphthyl at the 3,3'-positions (2,2'-dimethoxyl-3,3'-di(phenyl-4-yl-diphenyl-amine)-[1,1']-binaphthyl, TPA-BN-TPA) can be synthesized by Suzuki coupling. Amorphous and homogeneous films are obtained by either vacuum deposition or spin-coating from solution in good solvents, while single crystals are grown in an appropriate polar solvent. X-ray crystallography showed that a TPA-BN-TPA crystal is a multichannel structure containing solvent molecules in the channels. The intramolecular charge-transfer state resulting from amino conjugation effects is observed by solvatochromic experiments. The high glass-transition temperature (130 °C) and decomposition temperature (439 °C) of this material, in combination with its reversible oxidation property, make it a promising candidate as a hole-transport material for light-emitting diodes. With TPA-BN-TPA as the hole-transporting layer in an indium tin oxide/ TPA-BN-TPA/aluminum tris(8-hydroxyquinoline)/Mg:Ag device, a brightness of about 10100 cd m -2 at 15.6 V with a maximum efficiency of 3.85 cd A -1 is achieved, which is superior to a device with N,N'-di(1-naphthyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine as the hole-transporting layer under the same conditions. Other devices with TPA-BN-TPA as the blue-light-emitting layer or host for a blue dye emitter are also studied.