| Summary: | 碩士 === 國立成功大學 === 化學工程學系碩博士班 === 97 === 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) to electron-acceptor (stilbene unit). CN-Crown shows high selectivity toward Li+, while H-Crown is quenched not only by Li+ but also by Fe3+. The sensitivity of CN-Crown toward Li+ (Ksv = 6.39×104 M-1) is about one order higher than that of H-Crown (Ksv = 6.13×103 M-1). Clearly, e-withdrawing cyano group promotes ICT process in CN-Crown that results in its enhanced selectivity and sensitivity. In addition, incorporation of cyano group not only causes red-shift in fluorescence spectra but also leads to lower band gap in electrochemical property.
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