A dual-function probe based on naphthalene for fluorescent turn-on recognition of Cu and colorimetric detection of Fe in neat HO.

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 HO (10% 0.01 M HEPES buffer, v/v, pH = 7.4), probe NAH showed a highly selective and sensitive response towards Fe via perceptible color change and displayed "turn-on" dual-emission fluorescence response for Cu. The binding stoichiometry ratio of NAH/Cu and NAH/Fe 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 (2.0-10.0) and Cu (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 or Cu, 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, H NMR titration and HRMS. Moreover, NAH was successfully applied to the detection of Cu and Fe in tap water, ultrapure water and BSA.