5-Amino-2-aryl-2H-1,2,3-triazole-4-carboxamides: Unique AIEE-gens and selective Hg²⁺ fluorosensors

A series of fluorescent sensors based on small molecule were designed and fully characterised, demonstrating AIEE effect and revealing an outstanding ability to selectively detect Hg2+ ions. The structural and electronic properties were studied through quantum chemical calculations at (Time-Dependent) Density Functional Theory ((TD)-DFT) level. Carboxamides of 2-Aryl-1,2,3-Triazoles (CATs) showed significant differences in their photophysical properties depending on the structure of the substituent at amino function on the C5-atom in the heterocycle. When the tert-cycloalkylamino group (pyrrolidine, piperidine, azepane) was attached, the triazoles exhibited highly intensive blue fluorescence, with quantum yields (QYs) up to 95 % and lifetime up to 6.9 ns in different solvents, whereas the QYs of congeners bearing secondary alkylaminogroups (viz., NHMe, NHC6H11-cyclo) indicate low QYs (1-10 %). Nevertheless, all types of the obtained fluorophores demonstrated excellent AIEE effect and formed fluorescent nanoparticles in a binary mixtures of organic solvents and water. The introduction of the carboxamide function enhances the sensing properties of 2-aryl-1,2,3-triazoles, providing a selective fluorescence quenching reaction in the presence of Hg2+. The fluorescence intensity of the CATs declines with the addition of 1.0 eq. of Hg2+ into DMSO-water (v/v, 1:9). The other cations used did not induce any appreciable changes in fluorescence intensity. The CATs form a complex with Hg2+ with highly specific detection for Hg2+ over other competitive metal ions: the detection limits were determined to be 0.23 and 0.15 μM for the CATs 1b and 2c. The reverse effect was registered with the addition of ethylene diamine sodium salt; meanwhile, the CATs demonstrated more effective coordination with Hg2+ in comparison with cysteine. This last finding, as well as the ability to detect Hg2+, is very valuable for application within biology and medicine.