Synthesis and sensing properties of 1,1′-disubstituted unsymmetrical ferrocene-triazole derivatives: a multichannel probe for Hg(ii) ion

Abstract

Triazole-based unsymmetrically 1,1′-disubstituted ferrocene derivatives 4 and 5 have been synthesized using “click chemistry” with sequential functionalization at the cyclopentadienyl rings. The cation complexation properties of these ferrocene derivatives have been studied using electrochemical and spectroscopic techniques. The exceptional structural features present in these ligands are the presence of one cholesterol moiety, connected to the 1-position of the ferrocene center through a 1,2,3-triazole ring, and a fluorescent moiety, linked to the 1′-position of such a core through another triazole-ether linkage. Both the receptors experience perturbation of the CV in the presence of Hg2+ with a change of electrochemical potential (the large anodic shift ΔE_1/2 = 129 mV for 4 and ΔE_1/2 = 140 mV for 5). The changes in the absorption spectra are accompanied by the appearance of a new high energy (HE) peak at ca. 206 nm for 4 and 202 nm for 5 (4: ε = 3123 × 10² M⁻¹ cm⁻¹, 5: ε = 3140 × 10² M⁻¹ cm⁻¹) in the presence of Hg²⁺ ion. In addition, receptors 4 and 5 show colorimetric response and act as a selective “turn off” fluorescent receptor for Hg²⁺ and Cu²⁺ ions. On the basis of the ¹H NMR titration, ESI-MS and DFT study, probable binding modes of 1,1′-disubstituted ferrocene derivatives 4 and 5 with Hg²⁺ have been proposed.