Azacrown ether linked with 1,4-dihydropyridine as new fluorescence chemosensors

Abstract

Water soluble fluorescent sensors are of interest for sensing the metal ion in aqueous media. The target molecules possessing a DHP moiety as fluorophore and azacrown ring as a receptor and water soluble moiety were synthesized. The synthetic preparation of the series of 1,4-dihydropyridine (DHP) derivatives linked with various sizes of azacrown ring involves 3 steps of reaction. Firstly, Et-DHP-OH can be obtained from the cyclotrimerization of β-amino acrylates. Then, the hydroxyl group of Et-DHP-OH was tosylated followed by the substitution with the azacrown ether (n=1.3) to afford the corresponding Et-DHP-AC(1-3). According to the investigation results of photophysical property in milliQ water, these Et-DHP-AC(1-3) exhibited the absorption maxima at 367, 369, and 362 nm and the similar emission peak at 439 nm with the florescence quantum efficiencies (ɸf) of 0.41, 0.45, and 0.46, respectively. The Et-DHP-AC(3) showed selective fluorescence quenching by gold(III) with the the lowest detectable concentration of 50 µM. The florescence quenching occurred through the oxidation reaction of the DHP into a pyridinium, ring also confirmed by the 1H NMR results. Moreover, when Et-DHP-AC(1-3) were used as sensors in THF or result, Et-DHP-AC(2) was found to demonstrate the best selective enhancement with chromium(III) that formed complexation with the ratio of Et-DHP-AC(2):Cr3+ equal to 3:1 in THF/milliQ water (v/v=1:1).