Design,Synthesis And Anion Recognition Of 2,2-diferrocenylpropane-based Imidazole Receptor Molecules

Metal cations and anions exist in the natural environment and vivo widespread,play an important role in biological systems.It has been found that imidazole is capable of binding a cation and an anion because it has basic nitrogen as well as acidic N-H group,which converts the imidazole derivatives into excellent cationic,anionic and ion pairs receptors.2,2-diferrocenylpropane?DFP?was added into the imidazole ring as a signal group for its deformed tetrahedral structure,two-component redox system,easy modification,etc.In addition,the binding properties of 2,2-diferrocenylpropane-based imidazole receptors may be modulated by linear or angular annulation to aza-heterocycles such as pyridine or phenanthroline,leading to expanded imidazole derivatives bearing several binding sites.In this paper,we designed and synthesized six novel 2,2-diferrocenylpropane-based imidazole receptor molecules,and studied the recognition properties for metal cations and anions by UV absorption spectroscopy,fluorescence spectroscopy and electrochemistry.The main contents are as follows.1.A series of 2,2-diferrocenylpropane-based imidazole receptors were synthesized and structurally characterized by IR,1H NMR,13C NMR,HRMS,element analysis and X-ray diffraction.2.Receptor 2a,2b,2c were comparative studied by UV absorption,fluorescence and electrochemical for their recognition behavior for Cu²⁺.Addition of Cu²⁺disturbed most remarkable on the spectral properties of the receptor 2b:UV absorption redshift 49 nm,fluorescence enhancement more than 179-fold,quantum yield increased 22-fold,oxidation peak potential of Fc2 unit anodic shift 404 mV.A 1:1 stoichiometry of receptor 2b,2c towards Cu²⁺ were determined by Job's plot,while a 2:1 complex was observed for receptor 2a and Cu²⁺.These results showed that the receptor 2a,2b,2c could be used as a naked-eyes-detectable Cu²⁺ responsive fluorescence receptor.3.The ion pair receptor 3 showed excellent selectivity and sensitivity towards Pb²⁺ and HSO4-with multi-channel?chromogenic,fluorogenic and electrochemical?responses.When Pb²⁺ were bounded to the cation binding-site of receptor 3,fluorescence enhancement more than 42-fold,the maximum wavelength in UV absorption redshift 38 nm,redox of Fc2 unit anodic shift 151 mV,addition of HSO4-promoted the fluorescence enhancement?F/F0 = 67?.A 1:1 stoichiometry of the receptor 3 towards Pb²⁺ and HSO4-were proposed based on Job's plot.Furthermore,]H NMR titration and density functional theory were carried out to reveal the recogniton sites as well as the sensing mechanism based on photo-induced electron transfer?PET?.4.Receptor 4a and 4b were studied by electrochemical,UV absorption spectra and 'H NMR for selective recognition of F-and H₂PO₄^-.Studies showed that F-induced cathodic shifts of 110-140 mV for redox peaks of receptor 4a and 4b,obvious redshift?10-21 nm?occured in UV absorption spectra.Results showed different mechanisms of receptor 4a towards F-and H₂PO₄^-:F-induced hydrogen bond and deprotonation at the same time,while H₂PO₄^-was hydrogen bonding.