Chemosensing ability of hydroxynaphthylidene derivatives of hydrazine towards Cu²⁺: experimental and computational studies

Abstract

2-Hydroxynaphthylidene derivatives of hydrazine, namely L₁, L₂ and L₃, were synthesized by going through two-step reactions and the products were characterized. The ion recognition properties of these receptors were studied using fluorescence and absorption spectroscopy. The receptors were found to be sensitive and selective towards Cu²⁺ in methanol solution among the 13 metal ions studied, namely Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺, Pb²⁺, Na⁺, K⁺, Ca²⁺ and Mg²⁺, by exhibiting switch off fluorescence. The stoichiometry of the complexed species was found to be 2:1. The fluorescence quenching with Cu²⁺ is in the order of L₁ > L₂ > L₃. These conjugates were also found to act as colorimetric sensors for Cu²⁺ in solution by exhibiting visual colour change. The 2:1 complex shows a centrosymmetric structure based on DFT computations.