Synthesis And Study Of Chemical Sensors For Hg²⁺ And F^-

In this dissertation,four organic functional molecules A,B,C and D were designed and synthesized.These molecules could change in fluorescence and UV signals upon encounter of mercury ion(Hg²⁺),fluoride ion(F^-) or both mercury ion and fluoride ion.Therefore,the four molecules were developed to be chromophore or fluorescent sensors for Hg²⁺,F^- or both Hg²⁺ and F^-.It was also found that m-Methyl red could also achieve good sensing for Hg²⁺ as an existed compound.The main results obtained are as follows:The simply structured compound A was synthesized through one-step reaction of Schiff base.The structure of A was confirmed by ¹H-NMR and elemental analysis.The fluorescent spectrum and color changes as well as the mechanism of these changes when A acted with Hg²⁺ were studied.The red shift in fluorescence of the solution contain A and Hg²⁺ occurd about 115nm,and the fluorescence intensity increased with the increasing concentration of Hg²⁺.Moreover,addition of other metal ions to the solution of compound A didn't inherently cause fluorescent change,indicating a unique selectivity of A for Hg²⁺.By the comparison with the model compound a,it was found that it was the nitrogen on the aniline group of compound A that complexed with Hg²⁺,so that inducing intramolecular electron transfer, which led to changes of UV and fluorescence spectra.That meant,compound A achieved the sensing for Hg²⁺ through metal-induced charge transfer mechanism with a low detection limit and visible colour change.For that,complicated synthesis could be avoided using the strategy of simple structure designed, electron-rich system and metal-induced effect,which could help conceive sensors for the selective detection of other ions.As with the same functional group as A,m-Methyl red could also be a good chromogenic sensor for Hg²⁺ in terms of its UV features.We found that the color of solution of A changed exclusively from yellow to orange upon addition of Hg²⁺,while other ions did not interfere.Compound B was synthesized by introducing fluorene as the report moiety,and thiourea group as the recognizing moiety.¹H-NMR and elemental analysis confirmed the structure in line with expected one.UV absorption spectra proved that B and F^- formed a 1:1 complexation with a constant of 1.49×10⁴M^-1;the color change of the solution could be observed with the naked eye when B and F^-coordinated.Other ions except SO₄H^- did not change the color at all,SO₄H^- brought slight influence with no effect on judgement.On the other hand,the coordination of F^- and B produced a significant fluorescent enhancement.So compound B could be developed into a fluorescent sensor for F^-.We obtained compound C by introducing anthracene as the report moiety,which could also combine with F^-,with a constant of 2.79×10⁴M^-1.Significant fluorescent enhancement and a certain degree of red shift occurred as soon as the coordination of C and F^- took place.At the same time, fluorescent color transferred from blue to green which was visible;while addition of other ions,not only did the fluorescent wavelength not change,but also the fluorescence intensity was very low.It showed that compound C was a fluorescent sensor for F^- with high selectivity and sensitivity.Through the "building block combination" of functional groups,compound D was synthesized. ¹H-NMR and elemental analysis confirmed the structure of D.The UV absorption spectra proved that D formed a 1:1 complexation,and the constant was 4.62×10⁴M^-1.A certain degree of fluorescent quenching happened in the situation when D and Hg²⁺ combined.Simultaneously the solution color changed with the naked eye visible.These changes were not disturbed in the presence of other ions, showing that D could detect Hg²⁺ selectively and sensitively.Similar changes occurred when compound D encountered with F^- with a complexation constant of 2.24×10⁴M^-1.So compound D was able to detect F^- by present fluorescent quenching upon coordination of D and F^-.The detection of Hg²⁺ was considered based on metal induced intramolecular electron charge transfer occurred in the system,thus changing the optical properties of the receptor;while the sensing of F^- was through the formation of inter-molecule hydrogen bonds between -OH in compound D and F^-. Therefore,the compound D achieved the performance of detecting Hg²⁺ and F^- simultaneously.