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

Abstract

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 μM. 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 S²⁻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 μM, 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.