Alkyl-triphenylamine end-capped triazines with AIE and large two-photon absorption cross-sections for bioimaging

In the present study, three new luminogens ATT-(1-3) based on 1,3,5-triazine and end-capped with multi-branched triphenylamine-containing alkyl chains have been synthesized and characterized. All the three dyes are nonemissive in solution but have a strong red fluorescent emission in the aggregate state. The two-photon absorption (2PA) cross sections measured by the open aperture Z-scan technique are determined to be as large as 2756, 4750 and 10003 GM for ATT-1, ATT-2 and ATT-3 in chloroform, respectively, showing a dramatic enhancement with an increasing number of donor branches. The relationship between their structures and properties on one- and two-photon absorption and aggregation-induced emission (AIE) is discussed, which can serve as a guideline for the development of a series of solid materials with larger two-photon cross sections and high fluorescence quantum yield. In addition, one- and two-photon fluorescence (2PF) microscopy images of HeLa cells incubated with these three dyes were obtained to demonstrate the potential applications of these fluorophores in biosensing and bioimaging.