A new strategy for fabrication of water dispersible and biodegradable fluorescent organic nanoparticles with AIE and ESIPT characteristics and their utilization for bioimaging.

Fluorescence probes play a crucial role in optical imaging for visualization of complex biological processes. As compared with conventional organic fluorogens, the probes with aggregation-induced emission (AIE) and excited-state intramolecular proton transfer (ESIPT) characteristics show significant advantages in high quantum yield at concentrated and aggregated state, large Stokes shift and low cytotoxicity. However, the synthesis of AIE-active fluorescent probes through the ESIPT mechanism has received only very limited attention. On the other hand, the preparation of biodegradable fluorescent probes through the ESIPT mechanism has not been demonstrated thus far. In this work, we reported for the first time that water dispersible and biodegradable fluorescent polymeric nanoparticles with AIE and ESIPT characteristics could be facilely obtained through conjugation of 2,4-Dihydroxybenzophenone based benzophenone azine (BPA) and polyethylene glycol (PEG) using hexamethylene diisocyanate. The final copolymers contained hydrophilic and biocompatible PEG and biodegradable urethane linkage are readily self-assembled into core-shell nanostructures. Moreover, the self-assembled BPA-PEG2000 fluorescent organic nanoparticles (FONs) displayed obvious AIE feature, high water dispersibility, superb biocompatibility, biodegradability and excellent cell dyeing performance. All of the above properties implied that BPA-PEG2000 FONs are promising candidates for a variety of biomedical applications.