A dual-function probe based on naphthalene for fluorescent turn-on recognition of Cu2+ and colorimetric detection of Fe3+ in neat H2O

Abstract A simple naphthalene derivative, 6-hydroxy-2-naphthohydrazide ( NAH ), was designed and synthesized through two facile steps reactions with the 6-hydroxy-2-naphthoic acid (NCA) as the starting material. In neat H 2 O (10% 0.01 M HEPES buffer, v/v, pH = 7.4), probe NAH showed a highly selective and sensitive response towards Fe 3+ via perceptible color change and displayed “turn-on” dual-emission fluorescence response for Cu 2+ . The binding stoichiometry ratio of NAH /Cu 2+ and NAH /Fe 3+ were all confirmed as 1:1 by the method of fluorescence job's plot and UV–Vis job's plot, respectively. Probe NAH can be used over a wide pH range for the determination of Fe 3+ (2.0–10.0) and Cu 2+ (6.0–10.0) without interference from other co-existing metal ions. A possible detection mechanism was the hydrolysis of NAH upon the addition of Fe 3+ or Cu 2+ , thereby leading to the formation of 6-hydroxy-naphthalene-2-carboxylic acid ( NCA ) which was further confirmed by the various spectroscopic techniques including FT-IR, 1 H NMR titration and HRMS. Moreover, NAH was successfully applied to the detection of Cu 2+ and Fe 3+ in tap water, ultrapure water and BSA.