Synthesis and fluorescent sensory properties of a 5-cyanostilbene derivative linked to monoaza-15-crown-5

Abstract

To study the effect of electron-withdrawing group upon sensory characteristics of fluorescent chemosensors containing crown ether moiety (monoaza-15-crown-5), two stilbene derivatives CN-Crown and H-Crown were synthesized to compare their selectivity and sensitivity toward metal ions. CN-Crown contains two e-withdrawing groups (bromine and cyano) in stilbene unit, whereas H-Crown possesses bromine only. Fluorescence spectral variations in the presence of different metal ions or concentrations were used to elucidate the selectivity and sensitivity, respectively. CN-Crown displays dual fluorescence, where the short-wavelength emission (locally excited state) mainly results from the stilbene group and the long-wavelength emission is attributed to the intramolecular charge transfer (ICT) process between electron-donor (amino) and electron-acceptor (stilbene unit). CN-Crown shows high selectivity toward Li +, while H-Crown is quenched not only by Li + but also by Fe 3+. The sensitivity of CN-Crown toward Li + ( K sv = 6.39 × 10 4 M −1) is about one order higher than that of H-Crown ( K sv = 6.13 × 10 3 M −1). Clearly, e-withdrawing cyan group promotes ICT process in CN-Crown that leads to enhanced selectivity and sensitivity. Combination of high selectivity and sensitivity in CN-Crown promises its potential application as chemosensory materials.