A highly selective fluorescent chemosensor based on naphthalimide and Schiff base units for Cu²⁺ detection in aqueous medium

Xu, Yuling; Aderinto, Stephen Opeyemi; Wu, Huilu; Peng, Hongping; Zhang, Han; Zhang, Jiawen; Fan, Xuyang

A highly selective fluorescent chemosensor based on naphthalimide and Schiff base units for Cu²⁺ detection in aqueous medium

2017

A new Schiff base, 4-allylamine-N-(N-5-methylsalicylidene)-1,8-naphthalimide (1), has been designed and synthesized by combining a 1,8-naphthalimide moiety as a fluorophore and a Schiff base as a recognition group. Its photophysical properties were investigated by absorption and fluorescence spectroscopy, and this sensor exhibits a high fluorescence quantum yield of 0.75–0.91 inorganic solvents of different polarity. It also shows high selectivity for Cu²⁺ over other ions with fluorescence quenching in aqueous medium (pH=7.2). The reason for this phenomenon (fluorescence quenching) is attributed to the formation of a 1:1 complex between 1 and Cu²⁺ according to the Job plot and fluorescence titration. The sensor can be applied to the quantification of Cu²⁺ in a linear fashion from 0.5 to 5 μM with a detection limit of 0.23 μM. Additionally, the association constant (Kₐ) between Cu²⁺ and 1 is 1.328×10⁶ M⁻ ¹ in aqueous media.

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