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Keywords:

  • Charge transfer;
  • Hole transport;
  • Light-emitting diodes, organic

Abstract

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 10 100 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.