Selective recognition of Zn²⁺ by salicylaldimine appended triazole-linked di-derivatives of calix[4]arene by enhanced fluorescence emission in aqueous-organic solutions: role of terminal - CH₂OH moietieefs in conjunction with the imine in recognition

Abstract

A series of lower rim 1,3-di-derivatives possessing Schiff's base cores were synthesized using triazole unit as linker moiety by further introducing butyl (L₂), one -CH₂OH (L₃) and two -CH₂OH (L₄)-containing moieties, respectively, in order to bring additional support for ion binding. Based on fluorescence and absorption spectroscopies it has been shown that Zn²⁺ could be selectively recognized by the Schiff's base core and not by the triazole core among the ten metal ions studied both in methanol and in aqueous solutions of methanol and acetonitrile, wherein the -CH₂OH moieties augment the fluorescence response by providing additional coordinations to the Zn²⁺. Thus L₄ exhibited a fluorescence enhancement of ~65, ~48 and ~25-fold in methanol, aqueous solutions of methanol and acetonitrile, with minimum detection limits of 174, 313 and 320 ppb, respectively. Both the excitation and emission wavelengths fall in visible region.