Design and synthesis of triphenylphosphine-based donor-π-acceptor fluorophores with strong aggregation-induced emission and enantiomer-paired flower-like stacking

Abstract

Triphenylphosphine (TPP) shows stereo pyramidal configuration and has been considered as a poor electron-donor and fluorophore. Here, seven TPP-based compounds (o-TPPs 3a–3e and p-TPPs 3f/g) introducing simple non-aromatic electron-withdrawing (EW) groups at the ortho- and para-position of P atom have been synthesized to understand the inherent optical properties of TPP. All TPPs show aggregation-induced emission (AIE): non-emissive in solutions but emissive upon aggregation. Unexpectedly, lower conjugative o-TPPs possess much higher fluorescence quantum yields (43 and 65 %) than those (1 and 29 %) of their corresponding position isomers, p-TPPs; these achiral pyramidal TPPs in crystals exist as racemic M- and P-enantiomers, with all o-TPPs showing unique MP-paired flower-like arrangements; and the pyramidal TPP moiety could form an excellent electron delocalization system via through-space conjugation. This work proves that TPP could act as an excellent electron-donor and AIEgen by reasonable design, opens a new window to the application of pyramidal TPPs or other pyramidal compounds and affords a new strategy to design strong AIE fluorophores.