Lipid-Targeting Multiresponsive Benzothiadiazole Fluorophore for Live-Cell Imaging and Real-Time Liver Injury Monitoring

Abstract This work describes the multiresponsive photophysical behavior of BTD-4AS, a donor–acceptor benzothiadiazole fluorophore. BTD-4AS shows pronounced solvatochromism, viscosity- and temperature-dependent emission, and large Stokes shifts, consistent with a twisted intramolecular charge transfer state supported by Lippert-Mataga and Reichardt analyses. Its fluorescence is strongly pH-sensitive (maximum near pH ≈6–8) and markedly enhanced in micellar and viscous media. The dye’s photostability and lipophilicity support its use as a versatile probe for polarity, viscosity, pH, and lipid-rich environments. Building on these properties, BTD-4AS enables selective cellular bioimaging of lipid droplets and, in a mouse model, reports liver injury through polarity/viscosity-dependent spectral shifts─red emission in damaged regions exposed to extracellular milieu and green emission in intact lipid-rich cells.