ASYMMETRIC TRIARYLDIAMINES AS THERMALLY STABLE HOLE TRANSPORTING LAYERS FOR ORGANIC LIGHT-EMITTING DEVICES

The synthesis of a series of asymmetric triaryldiamines has provided a number of materials with a wide range of thermal, electrochemical, an d spectroscopic properties, The asymmetric materials described herein have two different diarylamine groups bound to a 1,4-phenylene or 4,4' -biphenylene core, i.e., Ar1Ar2N-C6H4-NAr1'Ar-3 or Ar1Ar2N-biphenyl-NA r1'Ar-3, respectively, The diarylamines studied include diphenylamine, phenyl-m-tolylamine, naphthylphenylamine, iminostilbene, iminodibenzy l, and carbazole, These materials were prepared by copper- and palladi um-catalyzed coupling of aryl halides and diarylamines, The asymmetry inherent in these compounds prevents these low molecular mass compound s from crystallizing, thus yielding higher thermal stability over that of the symmetric derivatives. In all cases, the asymmetric diamines f orm stable glasses, with glass transition temperatures up to 125 degre es C. HOMO levels for these materials, estimated by cyclic voltammetry , show a broad range of values, with oxidation potentials both lower a nd higher than those of common hole transport materials used in organi c light emitting devices.