A “naked-eye” Naphthalimide based Chemosensor for CN− ion detection: Investigating its application as test-strips, Smartphone Analysis & Molecular Logic gate and its TD-DFT study

It is unanimously known that cyanide (CN⁻) is one of the most toxic ions because it can interfere with the body's physiological phenomenon causing endocrine disorders, respiratory failure, hypoxia, vascular necrosis, and even death. Therefore, it is essential to develop cost-effective, sensitive, rapid, and efficient methods for sensing CN⁻ ions. The naphthalimide-based highly selective probe 1 was successfully synthesized in a multi-step process. Probe 1 displayed high selectivity and specificity against cyanide (CN⁻) ion and exhibited naked eye changes accompanied by “turn-off” fluorescence behavior. The introduction of CN⁻ ion into the probe solution shows a visible color change from yellow to blue. Further, the optical methods were employed to determine the sensing performance of probe 1 towards CN⁻ ion. The CN⁻ ion detection limit was 5.47 μM with a binding constant of 1.52 × 10⁵ M⁻¹. The fluorescence quenching efficiency towards cyanide ion was found to be 73.21 %, with the Stern-Volmer quenching constant to be 1.22 × 10⁵ M⁻¹. Job's plot analysis revealed 1:1 stoichiometric binding between probe 1 and CN⁻ ion, further supported by FT-IR analysis, mass analysis, ¹H NMR titrations, and TD-DFT study. Probe 1 finds its practical application for detecting CN⁻ ion using the test strip method. In addition, chemically switchable fluorescent dyes provide helpful building blocks for developing intricate molecular devices that communicate via adjustments in their emission characteristics; therefore, probe 1 was also used to establish molecular logic gates.