Aggregation-induced emission and intermolecular charge transfer effect in triphenylamine fluorophores containing diphenylhydrazone structures

Three new chromophores incorporating acceptor-π-donor-π-acceptor structural motifs and mono-, di- and tri-branched diphenylsulfone base linked to triphenylamine through a hydrazone π-bridge were synthesized, and the photoluminescence properties of the three chromophores were studied in solutions as well as in aggregated states. All the fluorophores emitted strong blue fluorescence in THF. Mono- and di-branched triphenylamine both exhibited increasing blue fluorescence and displayed an AIEE effect in the aggregated state. Tri-branched triphenylamine emitted green fluorescence and presented the AIE effect in the aggregated state. These interesting phenomena have been interpreted by a molecular stacking mode with molecular dynamics (MD) and DFT calculations. The unique propeller shaped molecular configuration of triphenylamine prevented face to face π-π stacking and induced the hindered rotation, which resulted in the AIEE or AIE effect in the aggregated state. The enlarged coplanarity of diphenylhydrazone chains increased the conjugation of tri-branched triphenylamine, which was beneficial to the formation of ICT and AIE and resulted in emitting green ICT fluorescence in the aggregated state. Fluorescent microscope imaging and the fluorescent pictures of the powder states certified the strong AIEE effect or AIE effect in the solid.