A Dual-responsive Benzothiazole Based Fluorescent Probes for Viscosity Detection in Beverages, in Situ Imaging of Molecular Viscosity and Latent Fingerprints.

Viscosity plays a pivotal role in regulating diffusion, a process central to various biological functions. Its detection is crucial in diagnostics, disease detection, and food freshness identification. To probe such micro-viscosity changes in live cells, fluorescent molecular rotors (FMRs) are commonly employed. The study developed two benzothiazole-based fluorescent molecular rotors, BCN1 and BCN2, designed for viscosity sensing via the TICT mechanism. Both probes were structurally characterized by various techniques such as NMR, FTIR, HRMS, SCXRD and exhibited high sensitivity of 1.18 cP (BCN1) and 1.94 cP (BCN2) in methanol-glycerol mixtures. Photophysical studies revealed strong emission, large Stokes shifts, pH resilience, and minimal aggregation. Biocompatibility was confirmed through cytotoxicity assays, enabling successful application in live-cell imaging and food spoilage detection. Solid-state fluorescence probes enabled high-resolution latent fingerprint visualization across various substrates, revealing nine different features of three different levels of fingerprint analysis. DFT calculations supported their electronic properties. Collectively, BCN1 and BCN2 emerge as multifunctional probes with broad utility in biological, environmental, and forensic applications.