Fluorescent scaffold integrating 2-aryl-1,2,3-triazole and thiazole rings with tuneable optical properties. Fundamental aspects and application prospects

[Display omitted] •New fluorophores with high absorption, strong ICT, and multi-colour emission were obtained.•They form highly fluorescent nanoaggregates or micelles.•Excitation wavelength dependence on concentration was found.•Intense blue fluorescence in lipid droplets and yellow fluorescence in mitochondria were detected. A fluorescent scaffold was designed and synthesised by the conjugating of the 1,2,3-triazole ring with aryl- or diarylthiazole systems. As a result, two series of thiazole-1,2,3-triazole fluorophores were prepared by the Hantzsch reaction and Suzuki-Miyaura coupling, namely 4-aryl-2-(2-aryl-2H-1,2,3-triazol-4-yl)thiazole (DATTs) and 4,5-diaryl-2-(2-aryl-2H-1,2,3-triazol-4-yl)thiazole (TATTs). Their structures were investigated by XRD and quantum mechanical calculations at DFT level. All the novel compounds were studied under different conditions by UV–vis absorption and fluorescent spectroscopy and TD-DFT calculations. Strong solvato(fluoro)chromism was registered, resulting in a two- or three colour fluorescence depending on solvent polarity, accompanied by an increase in emission intensity when solvent polarity increases. Concentration dependent emissions were found, and DATTs and TATTs exhibited red-shifted absorption and emission compared to the parent triazoles and sensitivity to polar media. Biological tests demonstrated the biocompatibility of the synthesised fluorophores and their low or null toxicity. Multicolour fluorescence of DATTs and TATTs as a function of the excitation wavelength and dye localisation was demonstrated in cell experiments.