Synthesis And Electrochromic Properties Of Thiophene And Quinoxaline Conjugated Polymers

The organic ?-conjugated polymers have become a class of conductive polymers that are widely studied because of their superior photoelectric properties,which were used in many fields including energy-saving materials,displays,organic light-emitting diodes,sensors,metal antisepsis,solar cells and electrochromic materials,etc.Electrochromism refers to the phenomenon that the optical properties of a material are stimulated by an external electric field to produce appearances such as a reversible change in color and transparency,and can be widely used in automotive non-glare mirrors,smart windows,camouflage materials,and the like.The optical band gap is the key among many factors about conductive polymers properties,and the backbone of the conductive polymers is composed of alternating electron-rich and electron-poor groups(donor-acceptor),so designing and synthesizing molecules through the donor-acceptor effect theory to optimize the performance is more popular method at present.In this paper,the thiophene and quinoxaline derivatives were modified by Stille coupling reaction and dehydration condensation reaction and we obtained four novel monomers containing 2,3-bis(furan-2-yl)-5,7-Bis(4-butylthiophen-2-yl)thieno[3,4-b]pyrazine(FBTP),2,3-bis(furan-2-yl)-5,7-bis(thiophene-2)-thieno[3,4-b]pyrazine(FTTP),5,8-bis-(3,4-dimethox y-thiophen-2-yl)-2,3-di-furan-2-Methyl-quinoxaline(MTFQ)and 5,8-bis-(3,4-dimethoxythiophene-2-yl)-2,3-diphenylquinoxaline(MTPQ)finally,and we synthesized the corresponding polymer through electrochemical polymerization which were studied the optical,electrochemical and electrochromic properties by Cyclic voltammetry,UV-Vis absorption spectroscopy and kinetic testingcyclic voltammetry.The monomer FBTP and FTTP were designed and synthesized.The results showed that the surface morphology,optical,electrochemical and electrochromic properties of the polymer film were changed with the introduction of different donor groups during monomer synthesis.The butylthiophene group was introduced into FBTP,and its electron donating ability was stronger than that of PTTP without substituent.In surface morphology,FBTP showed a network structure with more dense pores,while FTTP presented an irregular root structure with channels between clusters and clusters.In comparison,the shape structure of FBTP was more conducive to the electrochemical polymerization process.The polymer properties test showed that the initial oxidation potential of PFBTP was 0.01 V,the optical band gap was 0.87 eV,and the initial oxidation potential of PFTTP was 0.33 V,the optical band gap was 0.91 eV,PFBTP has a lower oxidation potential and optical band gap,which indicating that PFBTP had a better conductivity.In the electrochromic properties test,both polymer films exhibited a color change from a neutral state to a fully oxidation state,PFBTP was changed from olive green to light brown,and PFTTP was changed green to brown,also kinetic test analysis showed that both polymers have electrochromic properties with a good stability,short response time and high coloring efficiency.In summary,both conjugated polymers had low initial oxidation potentials and optical band gaps,good electrochemical stability,and electrochromic properties which showed that they are excellent electrochromic materials so that deserved further study and developped applications.Two novel monomers MTFQ and MTPQ were designed and synthesized with 3,4-dimethoxythiophene as the donor unit and furanylquinoxaline and phenylquinoxaline as the acceptor units,respectively.In the surface structure,PMTFQ presented a honeycomb structure with more holes,while PMTPQ showed an irregular network structure with the holes were all different.Compared with the shape of PMTPQ,the structure of PMTFQ was more favorable to the electrochemical polymerization process.The polymer properties test showed that the initial oxidation potential of PMTFQ was 0.39 V,the optical band gap was 1.43 eV,and the initial oxidation potential of PMTPQ was 0.41 V,the optical band gap was 1.59 eV.PMTFQ had a lower oxidation potential and optical band gap than PMTPQ due to the difference in the ability of the acceptor groups to absorb electrons.In the electrochromic performance test,both polymers showed a change in color from a neutral state to a fully oxidation state.The PMTFQ was changed from light blue to light gray,and the PMTPQ was changed from Hu purple to smoke gray,also kinetic test analysis showed that both polymers exhibit good electrochromic properties,high coloring efficiency and short response time make them potential high-quality electrochromic materials,so that deserved further research and applied to more fields.