A luminescent on-off probe based calix[4]arene linked through triazole with ruthenium(II) polypyridine complexes to sense copper(II) and sulfide ions

A bis-ruthenium(ii) polypyridyl complex was connected with a p-tert-butyl calix[4]arene platform (Ru2L) through 1,2,3-triazole and used as a luminescent probe to detect selected ions. Ru2L acted as a highly sensitive and selective turn off sensor towards Cu2+ ions in CH3CN/10 mM HEPES buffer (pH = 7.4) (8/2, v/v) medium. The detection limit of Cu2+ was found to be 4.11 mu M. The Cu2+ ion binding with Ru2L showed a paramagnetic signal in EPR analysis. The ensemble (Ru2L-Cu2+) was investigated with a variety of anions, but only sulfide anions enhanced the emission intensity in the presence of other anions. The ensemble works as a turn-on sensor towards S(2-)via a metal ion displacement method to form stable CuS. The detection limit of S2- was estimated from the emission intensity to be 0.35 mu M, which is an excellent result with respect to supramolecular platform based sensors in an aqueous medium. Ru2L also showed low cytotoxicity against human lung cancer cell line A549 and hence can be used in cell imaging.