Design,Synthesis And Recognition Properties Of Acridine-based Imidazole Cyclophane Fluorescent Probes

Metal cations and anions are widespread in natural environment and vivo,and play significant roles in chemical,biological,medical and environmental processes.Therefore,it is of great importance to detect and separate metal cations and anions.Fluorescence-based technique has provides a simple,sensitive,selective,relatively low-cost method for online monitoring without any pretreatment of the sample s and has become a powerful means to detect metal ions.Because imidazole has basic nitrogen as well as acidic N-H group,it is capable of binding a cation and an anion,which converts the imidazole derivatives into excellent cationic,anionic and ion pairs receptors.Acridine is a classic fluorescent group,and ether chain facilate the hydrophilicity of sensor.In this paper,we designed and synthesized six novel acridine-based imidazole cyclop ha ne receptors,and studied their recognition properties for metal ions by fluorescence spectroscopy.The main contents are as follows.1.A series of acridine-based imidazole cyclophane recep tors were synthesized and characterized by 1H NMR,13C NMR,IR,MS,HRMS and X-ray diffraction.2.The recognition behaviors of receptors la,1b,lc for Fe3+ and H2PO4-were comparatively studied by fluorescence.X-ray crystal structures demonstrated the self-assembly behavior of these cyclophanes in the solid state driven by hydrogen bond and ?-? interactions.Sensors showed excellent selectivity towards Fe3+ in aqueous solution(H2O/CH3CN=49:1,v/v)and H2PO4-in acetonitrile solution with notable color change under UV light.In fluorescence emission,the obvious turn-off was induced by Fe3+ in aqueous solution and the obvious turn-on as well as bathochromic-shift was induced by H2PO4-in acetonitrile solution3.We have designed and synthesised receptors 2a,2b and studied their recognition behaviors for Fe3+ and H2PO4 by fluorescence.A 1:1 stoichiometry of receptors 2a,2b towards H2PO4 were determined by Job's plot,a 1:1 stoichiometry of receptor 2a towards Fe3+ were determined and a 1-2 stoichiometry of receptor 2b towards Fe3+ were determined by Job's plot.The recogniton sites toward H2PO4-were studied by 1H NMR titration and the sensing mechanism were revealed to be an Excimer/Exciplex process.The PET mechanism for Fe3+ detection was further supported by the results of mass spectra studies.Receptors 2a,2b both showed low detection limit for Fe3+ and H2PO4.These results showed that the receptors 2a,2b could be used as responsive fluorescence receptor fur Fe3+ and H2PO4-.4.The recognition behaviors for Fe3+and H2PO4-of receptor 3a were studied by fluorescence.The obvious turn-off was induced by Fe3 +in aqueous solution and the obvious turn-on as well as bathochromic-shift was induced by H2PO4-in acetonitrile solution.A 1:1 stoichiometry of receptor 3a towards Fe3+ and H2PO4-were determined by Job's plot.The detection limit for Fe3+ and H2PO4 were estimated to be 1.21×10-5 M and 4.47×10-7M,respectively.