Imidazole and oxazole containing fluorescent dyad: Cu²⁺ induced fluorescence quenching and cyanide sensing <em>“On-Off-On” via</em> copper displacement approach

Abstract

A new simple organic molecule <strong>4</strong> containing imidazole and oxazole moiety has been synthesized and utilized for Cu²⁺ and cyanide sensing <em>via</em> displacement approach and fluorescence <em>On-Off-On</em> mechanism with rapid response in either of two sequential sensing events. The photophysical behavior of probe <strong>4</strong> toward different metal ions and anions has been examined through the absorption and fluorescence spectroscopy in HEPES buffer. Probe <strong>4</strong> shows high selectivity for Cu²⁺ with fluorescence quenching (~93%; switch-<em>Off</em>). The <em>in situ</em> generated ensemble, <strong>4</strong>+Cu²⁺ upon interaction with different anions shows high selectivity for CN⁻ in which the fluorescence intensity revived (switched-<em>On</em>) due to the formation [Cu(CN)_x]^1−x species in the medium. Further, the naked eye sensitive “<em>On-Off-On</em>” sensing behavior of <strong>4</strong> has been utilized for construction of a sequential logic circuit at the molecular level. The FT-IR, ¹H NMR and ESI-MS spectroscopy and DFT support the proposed mechanism of interaction.