Synthesis And Application Of Conjugated Polymers Containing Perylene Building Blocks

Compared with fluorescent small molecules,fluorescent conjugated polymers have been widely used in sensing and biological fields because of their many advantages,such as structural modifiability,processability and high sensitivity.Over the past several decades,different fluorescent conjugated polymers have been successfully synthesized with different emission colors.Fluorescent conjugated polymers with longer emission wavelength have many advantages in biological field,such as the ability to eliminate the interference from their own fluorescent substances,the lower energy required for excitation light source and less damage to biological samples.Moreover,the water-soluble conjugated polymers have many advantages for sensing application in aqueous enviroment,thus the design and synthesis of these conjugated polymers are of practical significance.In this paper,a series of orange-yellow fluorescent conjugated polymers containing perylene building blocks with side chains in different lengths were designed and synthesized;their structures and photophysical properties were characterized.Then,these polymers were selectively hydrolyzed and the polymers with various carboxylic acid groups were obtained.Finally,the sensing applications of these polymers were studied.1.Five new conjugated polymers,poly?perylene-alt-phenyleneethynylene?s?PPPEs?with the same backbone and multi similar ester-group-containing side chains in various lengths,were synthesized via Sonogashira coupling reaction.These polymers were characterized by ¹H NMR,FTIR,GPC,elemental analysis,UV spectra and fluorescence spectra,and the results confirmed that we successfully synthesized these polymers with different side chain lengths.These polymers have good solubility in common organic solvents.These polymers are slightly different in the degree of polymerization and the fluorescence quantum yield,likely due to the subtle impacts of the different length of the side chains on the polymerization process and solubility.Two comonomers with different ester groups?aromatic esters and aliphatic esters?were designed.After optimization of the hydrolysis conditions,we successfully realized the selective hydrolysis of the ester groups on the different building units;we obtained conjugated polymers containing carboxyl groups in different density.The resultant polymers were characterized by FTIR and elemental analysis.The partially hydrolyzed polymer are insoluble in common solvents,only the completely hydrolyzed polymer?PPPECOOH?can be dissolved in an alkaline aqueous solution.In future,we may take advantage of the solublity of the polymers before hydrolysis to fabricate them into solid materials in various forms;after hydrolysis,the polymers in solid materials will have good stability.2.The PPPECOOH/CPVA fibrous membrane was prepared by elecrospinning of the blend of polyvinyl alcohol?PVA?and PPPECOONa followed by crosslinking and acidification;then it was treated with NaOH aqueous solution,resulting in PPPECOONa/CPVA fibrous membrane.The PPPECOOH/CPVA and PPPECOONa/CPVA fibrous membranes can be converted each other by treated with acidic or basic solutions;and the PPPECOOH/CPVA and PPPECOONa/CPVA membranes have very different colors under both natural light and UV light.0.2%PPPECOONa/CPVA fibrous membranes and 1%PPPECOONa/CPVA fibrous membranes were prepared with PPPECOONa contents of 0.2 wt%and 1 wt%,respectively.The above two fibrous membranes were used to sensing the H₂SO₄ aqueous solutions,by comparing the colors under natural light and UV light before and after contacting with H₂SO₄ solutions with different pH values.First,the 0.2%PPPECOONa/CPVA fibrous membrane was immersed in H₂SO₄ aqueous solutions with different pH value for 3 min.The results showed that H₂SO₄ solution with pH lower than 3.0 could make the fluorescence of this fibrous membranecompletelyquenched.Then,underthesameconditions,1%PPPECOONa/CPVA fibrous membrane was used for the same purpose.The results showed that the H₂SO₄ solutions with pH lower than 4.0 could make the fluorescence of the fibrous membranes completely quenched.We anticipate that,by varying the percentage of PPPECOONa in the fibrous membrane,the sensing range of pH value of H₂SO₄ aqueous solutions could be enlarged.In addition,the membranes can be reused for a certain times.Therefore,we believe these fibrous membrane can be used for the sensing the pH of acidic rain in the future.3.Based on the characteristics of PPPEs,one of PPPEs was used to detect nitrobenzene?NB?and 2,4-dinitrotoluene?DNT?with visible light?516 nm?excitation.However,the result was unexpected that the fluorescence of this polymer almost had no response to NB and DNT.Then the excitation wavelength range?such as the excitation wavelength of 350 nm?commonly used in the literature was used to excite PPPEs for detection NB and DNT.The results showed that five PPPEs all had good response to NB and DNT with the excitation wavelength of 350 nm,with negligible difference.After that,several other conjugated polymers previously synthesized by our group were used to detect NB and DNT with the excitation wavelength of 330 nm or visible light wavelength,and the results were basically the same as those of PPPEs.In order to study the influence of the excitation wavelength on the response upon NB and DNT,several conjugated polymers above used and one fluorescent small molecule were selected to detect DNT,and the excitation wavelengths were set at 270 nm,290 nm,310 nm,330 nm,350 nm,370 nm,390 nm,410 nm,430 nm and 450 nm,respectively.The results showed that the sensitivity toward DNT had a strong dependence on the excitation wavelength;and the shorter the excitation wavelength,the higher the sensitivity.Finally,the sensing mechanism was studied.The results showed that these polymers had a fluorescence inner filter effect on the detection process of NB and DNT;and the shorter the excitation wavelength,the stronger the absorption of NB and DNT,and the stronger the fluorescence inner filter effect.