| Conductive polymeric electrochromic materials with high coloring efficiencies,fast response times,rich color changes,easy molecular design,low cost,and the ease of band gap control with structure modification towards generating different colors,etc.,have drawn a great attention since they are potentially useful materials for a broad range of applications like smart windows,glare-free mirrors,electronic paper and electrochromic devices.Donor-acceptor type（D-A）conjugated polymers as an important part of these materials usually have high conductivity and low energy band-gap due to the intramolecular charge transfer between the donor and acceptor units.Through molecular structure design and modification,we can effectively adjust the color of electrochromic materials,so as to achieve an extension of electrochromic material change in color and make up for deficiencies in the field of electrochromic display.Therefore,in this paper,we focus on the design,synthesis and characterization of D-A type conjugated conductive polymers,and we devote continuously to improve the electrochromic properties and prepare for multi-colored electrochromic materials.Factors affecting the materials properties,such as the type of the molecular main chain structure,the strength of the side chain electron-donating or electron-accepting groups,the polymerization methods and the electrolyte of different kinds,are investigated systematically.This study mainly focused on the following five parts.(2,6-bis（trimethylstannane）-4,8-bis（2-octyldecyloxy）benzo[1,2-b:4,5-b’]dithiophe ne coupled with 2,5-didecyloxy-1,4-dibromobenzene and 4,7-dibromo-5,6-dioctyloxy-2,1,3-benzothiadiazole using Stille coupling polymerization to afford the non D-A type polymer P1 and D-A type polymer P2,respectively.Then,series of chemical instrumental analysis were carried out to prove their structures and spectral absorption properties of the polymers were also investigated.Compared with P1,the introduction of the strong electron-withdrawing group benzothiadiazole improved conjugate effect along the polymer backbone of P2,which caused the redshift of ultraviolet-visible absorption spectrum and significant reduction in energy band-gap.In addition,electrochromic performance test results showed that the P1 film can switch between orange and gray,while P2 film changed from blue neutral state to light yellow oxidation state.Moreover,the optical contrasts and response times of the polymer films also showed great differences due to the different molecular structure types.Higher optical contrast and less sensitivity to the step interval on optical contrast indicated the fast switching speed and the well cycle stability of P2 film.A novel donor-acceptor copolymer PTBTB was successfully synthesized through chemical copolymerization between 4,7-bis（4-hexyl-5-（trimethylstannane）-2-thienyl）-2,1,3-benzothiadiazole and 2,5-didecyloxy-1,4-dibromobenzene.Meanwhile the fluorinated benzothiadiazole was used as the stronger electron-withdrawing group to give the other soluble polymer PTBTB-F with similar molecular structure to the former.The electrochemical performance test showed that the electron-withdrawing ability of the side chain groups had great influence on the n-doping characteristic and the redox stability of the polymer films.In addition,the electrochromic properties of the polymers（such as changes in the color and optical absorption under different voltages,optical contrasts and response times,etc.）also varied from each other due to the difference of the side chain substituent groups.The optoelectronic material monomer 2,3-bis（5-methyl-2-furanyl）-5,8-bis（2-（3,4-ethylenedioxythiophene））quinoxaline（MFEQ）with good conjugated structure was designed and successfully synthesized by Stille coupling reaction,and the corresponding D-A type conjugated conductive polymer（PMFEQ）were synthesized using electrochemical polymerization.The influences of the kinds of electrolyte solution on the redox properties of the material,indicated that TBAPF6/ACN/DCM solution system was more appropriate for performance testing.The electrochemical and spectro-electrochemical properties showed that the PMFEQ film had low initial oxidation potential（-0.40 V）,narrow optical band gap（1.27 eV）,high optical contrast（76%）,and the film could also switch quickly between the green neutral state and the lightgray oxidation state,with the response time about 0.8 s.Three different conjugated D-A type monomers with various optical properties were synthesized using strong electron-withdrawing 2,3-bis（2-furyl）quinoxaline as acceptor unit and three different thiophene groups（thiophene,3-methoxythiophene and 3,4-ethylenedioxythiophene）as donor units.The corresponding polymer films were obtained by electrochemical polymerization.The presence of the strong electron-donating ethylenedioxy and methoxy groups on the thiophene donor unit increased the electron density in polymer backbone.Thus,the oxidation potential of PFETQ and PFMTQ shifted to a lower value than that of PFTQ.The optical analyses showed that the strength of electron donor unit had a significant impact on the optical absorption properties of the polymer films.The stronger electron-donating unit could enhance the conjugation effect in the polymer backbone,which would cause the bathochromic shift in the maximum absorption wavelength and reduction in the energy band-gap.In addition,the color of the polymer films,the optical contrasts and the response times also showed significant differences because of the different electron-donating groups.A series of chemical synthesis approaches in this chapter were taken to provide twonovelD-Atypemonomers:4,7-bis（3,4-ethylenedioxythiophene）-2-dodecyl-[1,2,3]benzotriazole（EDBT）and2,3-bis（4-methoxyphenyl）-5,7-di（2-thienyl）thieno[3,4-b]pyrazine（MTTP）.The corresponding polymer films were blue and green in the neutral state,respectively.By examining the influence of mixing ratio of the two monomers on the optical absorption and color variation of the copolymer films,we found that when M1:M2 is 1:3,the absorption spectrum of the electrochemical deposited copolymer film could cover the entire visible region and the copolymer film was black.The film changed into a transparent light gray color under the oxidation voltage,while it became dark blue in the reduced state.Therefore,electrochemical copolymerization method can adjust the optical absorption properties and the color of the polymer film,make up for the deficiencies in color display,and broaden the direction for the development and application of new polymer electrochromic materials. |
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