Abstract
The synthesis and characterization of a novel florescent chemosensor 1 with two different types of cationic binding sites have been reported in this work, which is a calix[4]crown derivative in 1,3-alternate conformation bearing two 2-phenyl-5-(4-dimethylaminopyenyl)-1,3,4-oxadiazole units. The recognition behaviors of 1 in dichloromethane/acetonitrile solution to alkali metal ions (Na+ and K+), alkaline earth metal ions (Mg2+ and Ca2+), and transition metal ions (Co2+, Ni2+, Zn2+, Cd2+, Cu2+, Mn2+, and Ag+) have been investigated by UV-Vis and fluorescence spectra. The fluorescence of 1 might be quenched selectively by Cu2+ due to the photo-induced electron transfer mechanism, and the quenched emission from 1 could be partly revived by the addition of Ca2+ or Mg2+; thus, the receptor 1 might be worked as an on–off switchable fluorescent chemosensor triggered by metal ion exchange.
Highlights
As the third most abundant transition metal ion after zinc and iron in the human body, copper is required by many living organisms for normal physiological processes (Turski and Thiele, 2009; Cotruvo Jr et al, 2015)
Except for the calix[4]arene 3, all of the intermediate calix[4]crowns 3–6 and the chemosensor 1 are in 1,3-alternate conformation, which were well established by 1H NMR and 13C NMR data
The nitrogen atoms of the 1,3,4-oxadiazle units can bind with Cu2+ to form the complex 1·Cu2+, and the paramagnetic nature of Cu2+ ion could strongly quench the fluorescence of the 1,3,4-oxadiazole units through the electron transfer mechanism, which is consistent to the results reported in literature (Han et al, 2012)
Summary
As the third most abundant transition metal ion after zinc and iron in the human body, copper is required by many living organisms for normal physiological processes (Turski and Thiele, 2009; Cotruvo Jr et al, 2015). The main progress in this area has been well reviewed (Cao et al, 2019; Sivaraman et al, 2018; Udhayakumari et al, 2017; Liu et al, 2017), and many fluorescent chemosensors for Cu2+ ion based on various fluorophores such as coumarin (Zhang et al, 2019), Bodipy (Ömeroğlu et al, 2021), rhodamine (Fernandes and Raimundo, 2021), Schiff base (Singh et al, 2020), pyrene (Kowser et al, 2021), and 1,3,4-oxadiazole (Wang, et al, 2018) have been reported by different research groups Among these fluorescent chemosensors, the 1,3,4-oxadiazoles have drawn special interest due to their electron-deficient nature, high photoluminescence quantum yield, and excellent chemical stability, and have found practical applications in the fields of organic light-emitting diodes (Meng et al, 2020) and liquid crystals (Han et al, 2013; Han et al, 2015; Han et al, 2018). The compound 1 might work as a new type of switchable off–on fluorescent chemosensor
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