Tuning the Electronic Nature of Aggregation-Induced Emission Luminogens with Enhanced Hole-Transporting Property

Triphenylamine (TPA) is a well-known hole-transporting material but suffers aggregation-caused emission quenching in the solid state. Tetraphenylethene (TPE), on the other hand, is an archetypal luminogen that shows the phenomenon of aggregation-induced emission (AIE). In this work, TPA is attached to the TPE core as peripheral group to generate new AIE luminogens with enhanced hole-transporting property. The TPA-TPE adducts, named 1-[4′-(diphenylamino)biphenyl-4-yl]-1,2,2-triphenylethene (TPATPE) and 1,2-bis[4′-(diphenylamino)biphenyl-4-yl]-1,2-diphenylethene (2TPATPE) are synthesized in satisfactory yields by Suzuki coupling of 4-(diphenylamino)phenylboronic acid with 1-(4-bromophenyl)-1,2,2-triphenylethene and 1,2-bis(4-bromophenyl)-1,2-diphenylethene, respectively. Whereas the hybrid molecules are practically nonluminescent in the solution state, their aggregates in poor solvents and thin films emit intensely with fluorescence quantum yields up to 100%. Both TPATPE and 2TPATPE are thermally and morphologically stable, showing high thermal-degradation (Td up to 430 °C) and glass transition (Tg = 119 °C) temperatures. Multilayer electroluminescence (EL) devices are constructed, which emit sky blue and green EL with maximum luminance of 32230 cd/m2 and current efficiency up to 13.0 cd/A. The devices without hole-transporting layers (HTL) show performances comparable to or better than those with HTL, presumably because of the high hole mobility of TPATPE and 2TPATPE coupled with the matching of their energy levels with the anode.