Synthesis And Sensing Application Of Fluorescent Conjugated Polymers Containing Pendent Rhodamine B Groups

In recent years,fluorescent conjugated polymers have aroused great research interest owing to their superior characteristics and been used in various applications such as optoelectronic devices,biomedicine and sensing.It has unique advantages for fluorescence sensing due to that its "molecular wire" effect can amplify the signal to a certain extent.Rhodamine dyes have also become important starting materials in the synthesis of many fluorescent probes and molecular markers due to their good luminous properties,low cost and facile modification.Based on our previous research on fluorescent conjugated polymers,we hope to combine the fluorescent conjugated polymers with rhodamine B(RB)to synthesize new fluorescent conjugated polymer probes for sensing different metal ions.The specific content is as follows:The first part,rhodamine B spirolactam derivative(RB-NH2)with amino group was obtained by simple modification of rhodamine B(RB)and then the fluorescent conjugate polymer(PPETE-RB)containing pendent rhodamine B groups was synthesized through Sonogashira coupling.The polymer(PPETE-RB)was characterized by 1H nuclear magnetic resonance spectra(1H NMR),fourier transform infrared spectroscopy(FTIR),elemental analysis(EA),and gel permeation chromatography(GPC).The results confirmed the successful synthesis of the target polymer.The polymer has good solubility in some common organic solvents.Through the study of the photophysical properties of PPETE-RB,we found that the solution exhibits a dual-excitation selective response to Fe3+/Fe2+.The emission around 481 nm(excited at 360 nm)decreased and that around 571 nm(excited at 520 nm)emerged and increased when increasing the concentration of iron ions.After the investigation of the response mechanism,we attributed the quenching around 481 nm to the inner filter effect(IFE)between the Fe3+/Fe2+and PPETE-RB;while that enhancement around 571 nm could be attributed to the formation of fluorescent ring-open structure from nol-fluorescent spirolactan of pedant rhodamine B groups upon Fe3+/Fe2+.The second part,on the basis of the first part,we hope to synthesize a new conjugated polymer and realize the recognition of Hg2+through the thiophilicity of mercury ion.Thus,we obtained a rhodamine B spirolactam derivative(RB-NH2(S))with an amino group containing a sulfur atom,through sulfurization of the previously synthesized RB-NH2.Then we synthesized another fluorescent conjugated polymer(PPETE-RB(S))containing pendent rhodamine B groups.Various characterizations have been used to confirm the successful synthesis of the target polymer.Subsequently,PPETE-RB(S)N+Me3 was obtained through the quaternization reaction of the side chains.It has good solubility in relatively polar solvents.The photophysical properties of PPETE-RB(S)and PPETE-RB(S)N+Me3 were compared.Preliminary sensing experiments on the PPETE-RB(S)N+Me3 showed that the polymer solution exhibited selective response to Hg2+.We attributed the phenomenon to the ring-opening of rhodamine B spirolactam caused by the combination of Hg2+ and sulfur atoms.