A series of polarity- and viscosity-sensitive AIE fluorescent sprobes with large stokes shifts for cell and zebrafish imaging.

Lipid droplets (LDs) are dynamic organelles whose microenvironmental polarity and viscosity are closely linked to metabolic diseases. In this study, we developed three D-π-A structured AIE fluorescent probes-T-EDOT-C, T-EDOT-D, and T-EDOT-N-for dynamic imaging of LDs. With triphenylamine (TPA) as the electron donor and EDOT as the π-bridge, highly efficient intramolecular charge transfer (ICT) is achieved by modulating the electron acceptor. T-EDOT-C exhibits a Stokes shift of 184 nm in DMSO and displays a polarity-dependent red shift from 566 nm to 646 nm. Viscosity testing indicates that fluorescence intensity increases with rising viscosity, demonstrating excellent viscosity sensitivity. Colocalization experiments using commercial probes yielded a Pearson's correlation coefficient of 0.96, indicating excellent targeting ability. T-EDOT-D also performed well, with a Stokes shift of 159 nm and a red shift of 70 nm, and exhibited viscosity-enhanced fluorescence. In contrast, T-EDOT-N, despite a Stokes shift of 165 nm, showed poor responsiveness to polarity and viscosity. Both T-EDOT-C and T-EDOT-D enable real-time monitoring of viscosity changes in HepG2 cells and zebrafish under starvation or oleic acid stimulation. In summary, owing to its excellent photostability, sensitivity to viscosity and polarity, and biocompatibility, T-EDOT-C emerges as the most promising probe for studying the LD microenvironment and related diseases.