Twisted Molecular Core Conjugated Oxo-Ether as a Fluorescent Probe for Lipid-Droplets Bioimaging and Live Cancer Cell Discrimination

In quest of a new working design for a photostable lipid-droplets (LDs) bioimaging probe, we herein unveil and demonstrate a twisted donor(naphthalene)-π-acceptor(dicyano) architecture linked with oxo/thioether functionality, where the probes' emission, hydrophobicity, cytotoxicity, and cell permeability are altered by replacing the present chalcogen/s. In this class of molecules, an "oxanthrene"-based compound, "OXNCN", was realized as the noncytotoxic and cell-permeable probe, displaying intense fluorescence in a nonpolar solvent, aggregates, and viscous medium. Time-dependent density functional theory (TD-DFT) investigations revealed that OXNCN holds a favorable extent of excited-state planarity to bring out considerable emission only in a nonpolar solvent, resulting in polarity-dependent emission. Outcomes of the concentration- and time-dependent colocalization investigations, cholesterol depletion/repletion studies, and oleic acid treatment-based experiments validated its LD specificity. Strong twisted intramolecular charge transfer (TICT) culminated in weak emission in the polar medium, which helped the probe reduce the cytoplasmic signal. Moreover, the results of time-dependent kinetic acquisitional photophysical studies, fluorescence recovery after photobleaching (FRAP), and intracellular emission investigations testified to the probe's photostability. Assiduous analysis and quantification of confocal laser scanning microscopy (CLSM) images by two-way analysis of variance (ANOVA), followed by Sidak's multiple comparison statistics, could provide insights into the probe's better performance in robust cancer cells (FaDu) than in normal ones (HEK-293). A precise discrimination between oral and normal cancer cells could be established by quantifying the deposited lipid droplets from the CLSM-captured cellular images and applying Student's t test with the quantified values.