2,6-pyridinedicarbohydrazide-salicylal hydrazone-base derivative with high detection limit and binding constant for emissive ion chemosensing in aqueous solution

A new tridentate luminescent molecule, N²,N⁶-bis(salicylidene)pyridine-2,6-dicarbohydrazide (BSPDH), was introduced and facilely eco-synthesized with high yield. It was then characterized through Fourier transform infrared, Hydrogen-1 nuclear magnetic resonance, Carbon-13 nuclear magnetic resonance, mass and photo-luminescence spectroscopy, X-Ray Diffraction and Ultraviolet-visible absorption methods. BSPDH showed an enhanced aggregation-induced emission as well as highly fast-response “turn-off” selectivity and sensitivity behaviors towards Cu²⁺ ions in aqueous solutions at physiological pH. Density Functional Theory calculations confirmed the formation of strong BSPDH-Cu²⁺ complex with lower energy gap compared to BSPDH. Among PDH-base fluorescent sensors reported so far, BSPDH is the first tautomerization-base luminescence molecular chemo-sensor with the high detection limit of 3.11 × 10⁻⁵ M and binding constant of 1.978 × 10⁵ M⁻¹ at the concentration of 10 μM of BSPDH for detecting Cu²⁺ ions without any interference from other metal cations in the aqueous solution at the physiological pH.