A highly Selective Fluorescent Sensor for Monitoring Cu2+ Ion: Synthesis, Characterization and Photophysical Properties

Abstract

A new fluorescent sensor, 4-allylamine-N-(N-salicylidene)-1,8-naphthalimide (1), anchoring a naphthalimide moiety as fluorophore and a Schiff base group as receptor, was synthesized and characterized. The photophysical properties of sensor 1 were conducted in organic solvents of different polarities. Our study revealed that, depending on the solvent polarity, the fluorescence quantum yields varied from 0.59 to 0.89. The fluorescent activity of the sensor was monitored and the sensor was consequently applied for the detection of Cu with high selectivity over various metal ions by fluorescence quenching in Tris-HCl (pH = 7.2) buffer/DMF (1:1, v/v) solution. From the binding stoichiometry, it was indicated that a 1:1 complex was formed between Cu and the sensor 1. The fluorescence intensity was linear with Cu in the concentration range 0.5-5 μM. Moreso, the detection limit was calculated to be 0.32 μM, which is sufficiently low for good sensitivity of Cu ion. The binding mode was due to the intramolecular charge transfer (ICT) and the coordination of Cu with C = N and hydroxyl oxygen groups of the sensor 1. The sensor proved effective for Cu monitoring in real water samples with recovery rates of 95-112.6 % obtained.

Sensitive and selective detection of Cu(II) ion: A new effective 1,8‐naphthalimide‐based fluorescence ‘turn off’ sensor

“…In the absence of various metal ions, the sensor exhibited a high fluorescence peak at 532 nm. When the metal ions Na(I), K(I), Ca(II), Mg(II), Al(III), Fe(III), Ni(II), Zn(II), Hg(II), Ag(I), Co(II), Cr(II), Mn(II), Cd(II) or Cu(II) were introduced into a 0.5 μM DMSO–HEPES buffer solution (v/v, 1:1; pH 7.4) of the sensor, Cu(II) ion was able to quench the fluorescence of the sensor by up to 79.79%, possibly due to the powerful paramagnetic nature of the Cu(II) ion . In contrast, other metal ions investigated under the same conditions had negligible effects on the fluorescence intensity of the sensor.…”

“…Cu 2+ is paramagnetic with an unfilled d shell and could strongly quench the emission of a nearby fluorophore via electron transfer. The quenching response of V towards Cu 2+ could be ascribed to a reverse‐PET mechanism, that is electron transfer from the 1,8‐naphthalimide moiety to an electron‐deficient carboxyl group occurs by metal ion complexation …”

A selective fluorescence probe for copper(II) ion in aqueous solution based on a 1,8-naphthalimide Schiff base derivative

“…Nowadays, there is still an intense demand for Cu 2+ fluorescent probes, especially those that can function in actual water samples. Derivatives of 1,8-naphthalimide are widely employed as fluorophores of choice due to their advantageous features of excellent photophysical fluorescent properties, strong absorption bands in the visible region, and large Stokes shifts, which allow this method to overshadow the merits of other conventional analytical methods [40][41][42][43][44][45][46][47][48][49]. Herein, we describe the synthesis of a new fluorescent probe HL for Cu 2+ detection that satisfies the prerequisite for the proposition of an efficient fluorescent probe.…”

A new Schiff base as a turn‐off fluorescent sensor for Cu2+ and its photophysical properties

“…By using the fluorescent quantum yield, the ability of receptor 1 to emit absorbed light energy is characterized. The results acquired in solvents of different polarity indicated that the photoinduced energy transfer (PET) process was speed up in polar solvents, which led to a moderate fluorescence quantum yield …”

“…The results acquired in solvents of different polarity indicated that the photoinduced energy transfer (PET) process was speed up in polar solvents, which led to a moderate fluorescence quantum yield. [35][36][37][38] The sensing ability of receptor [39,40] Under similar situations, receptor 1 did not shows any selectivity and sensitivity towards the tested anions ( Figure S6).…”