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[Display omitted] • Tetraphenylimidazole (TPI)-based styryl dyes TPI-In , TPI-Bt , and TPI-Qu exhibited polarity sensitivity. • TPI-Qu and TPI-Bt were viscosity-sensitive with extremely high fluorescence quantum yields in a dense environment. • The hues of TPI-In , TPI-Qu , and TPI-Bt solutions changed in response to their acidic and basic nature. • Only TPI-Qu and TPI-Bt fluoresced more brightly in high-viscosity cellular environments. Fluorescence probes have grown to be incredibly popular tools for measuring viscosity because of their high sensitivity, ease of use, and capacity to detect a microscopic scale. In this study, we developed a new line of excited-state intramolecular proton transfer (ESIPT)-based styryl fluorescent dyes based on tetraphenylimidazole (TPI) for measuring cellular viscosity. These dyes have good photophysical properties, including significantly large Stokes shifts and sensitivity to the hydrogen-bonding donor/acceptor solvent, according to the ESIPT characteristic. By observing variations in fluorescence, TPI-Bt , and TPI-Qu demonstrated exceptional sensitivity to viscosity in a water/glycerol system and substantial sensitivity to pH in a buffered water system. Furthermore, first-principles computations, crystallography, and application in living cells all supported the behaviors of the dyes in viscous environments. [ABSTRACT FROM AUTHOR]

β-Galactosidase (β-gal) has captured the attention of biologists, chemists, and medical researchers as an important biomarker for cell senescence and primary ovarian cancer. Therefore, many fluorescent probes with visible light emission have been developed for the detection and imaging of β-gal in living cells. However, near-infrared (NIR) ratiometric probes are more suitable for bioimaging because near-infrared light can effectively avoid the interference of autofluorescence and the ratiometric approach can improve sensitivity and accuracy of the detection. In this work, we designed an NIR ratiometric probe (TMG) for the highly sensitive detection of β-gal. Using a spontaneous degradation mechanism based on the ICT effect, the change in ratio (F650/F580) exhibited a prominent β-gal-dependent performance and proved a strong linear response to the activity of β-gal at an enzyme concentration between 0 and 200 U L−1, with a limit of detection as low as 0.86 U L−1, and the response speed is much faster than the same type of probes previously reported. The probe also revealed an excellent biocompatibility and a large Stokes shift. Moreover, fluorescence microscopy imaging experiments confirmed that this probe could be successfully used for the detection of endogenous β-gal in living cells. [ABSTRACT FROM AUTHOR]