A series of triphenylamine-based two-photon absorbing materials with AIE property for biological imaging.

A specific series of D-π-A (1A-3A) and D-π-A (1B-3B) structural chromophores with various electron donors and π-conjugated bridges were designed, synthesized, and fully characterized. Their crystal structures were determined by single crystal X-ray diffraction analysis. The one/two-photon absorption properties of the chromophores have been successfully tuned by using different electron donors and π-bridges. Interestingly, it was found that chromophore 3B shows quite weak fluorescence in pure DMSO, while a significant AIE (aggregation-induced emission) effect is observed in water-DMSO (v/v 90%) mixtures with a sharp increase in fluorescence intensity of about 11 times. Furthermore, chromophore 3B shows strong two-photon excited fluorescence (TPEF) and has a large 2PA action cross-section (394 GM). The results of live-cell imaging experiments show that 3B can be effectively used as a bio-imaging probe in two-photon fluorescence microscopy towards HepG2 cells in vitro. The TPEF images of 3B not only exhibit cellular cytosol uptake but also exhibit actin regulatory protein uptake which are different from OPEF images.