Bistriazolylpyridines as molecular sensors for multiple transition metal ions

Two click-derived bistriazolylpyridines, 2,6-bis(1-(pyridin-2-yl)-1H-1,2,3-triazol-4-yl)isonicotinate methyl ester (L1) and 2,6-bis-(1-methoxycarbonylmethyl-1H-1,2,3-triazol-4-yl)isonicotinate methyl ester (L2), were prepared, characterized and their photophysical properties as well as the capability of binding metal ions studied. The crystal structure of Zn(II) complex [Zn2(L1)4](ClO4)4.3CH3CN was determined by X-ray single crystallography. Both L1 and L2 were chemosensors with high selectivity and sensitivity for Al3+, Fe3+, Ni2+, Cu2+ and Zn2+. Based on the data from the UV-vis absorption and the luminescence spectroscopy, bistriazolylpyridines L1 and L2 were "turn-on"fluorescent probes for Al3+ and Zn2+ with enhanced emission bands at 430 nm and 380 nm, respectively. They were colorimetric and "turn-off'' probes for Fe3+ with an absorption band at 475 nm and fluorescent quenching. L1 and L2 were also "turn-off'' probes for Ni2+ and Cu2+. It was revealed that the stoichiometric ratio of chemosensor:metal ion was 2:1 or 1:1 for the metal complex species formed in the solutions during the titration. The limit of detection (LOD) values and binding constants of L1 and L2 for Al3+, Fe3+, Ni2+, Cu2+ and Zn2+ were determined in CH3CN. Furthermore, the INHIBIT and YES logic gates were constructed on the basis of the selective response of L1 and L2 to Al3+ and Zn2+. It was demonstrated that bistriazolylpyridines were excellent candidates for multi-channel chemosensors for detecting different metal ions.