Synthesis and properties of hole-transporting triphenylamine-derived dendritic compounds

•Wittig reaction yielded triphenylamine derivatives possessing alkoxyphenyl groups.•Different peripheral alkyl substitutions largely influenced their properties.•Liquid crystalline-like phase transition was observed for compound with flexible chains.•Fluorescence quantum yields in thin-films largely influenced by peripheral alkyl chains.•Hole mobility of compound with ethyl chains exceeded 1.3 × 10−3 cm2 V−1 s−1 at high field.

Materials based on triphenylamino core linked with different alkoxyphenyl-substituents through olefinic spacers were synthesised, and their thermal, photophysical and photoelectrical properties were investigated. The synthesized compounds showed relatively good thermal stability. Derivatives containing shorter alkyl chains displayed glass-forming ability, while the compounds containing flexible alkyl termini demonstrated liquid-crystalline behaviour. Flexible alkyl substituents at the periphery of triphenylamine derivatives prevented the close packing of chromophores and hence, they showed relatively similar absorption and fluorescence in thin-films and solutions. Reduction in fluorescence quantum yield in thin-films upon decreasing the size of peripheral alkyl substituents confirmed enhanced intermolecular interactions and in turn, suggested migration-induced exciton quenching at nonradiative decay sites. Ionization potentials of thin solid layers estimated by photoelectron emission spectroscopy ranged from 5.21 to 5.47 eV. Hole-drift mobility of ethyl substituted triphenylamine measured using xerographic time-of-flight (XTOF) method was 1.3 × 10−3 cm2 V−1 s−1 at an electric field of 106 Vcm−1.

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