Preparation And Electrochromic Behaviors Of Conducting Polymers Based On Dithienylpyrrole Derivatives

Electrochromic materials have attracted great attention due to their excellent electronic, optoelectronic and electrochemical properties. Conducting polymers stand for a sort of important electrochromic materials that present good properties. In order to realize desirable properties for commercial applications in the construction of smart windows, electrochromic displays, electronic paper, and military camouflage, great efforts have been devoted to design and synthesize polymeric electrochromic materials by the assembly of available monomers or adopting functional groups. Recently, dithienylpyrrole(SNS) derivatives have received much attention due to their excellent electrochromic properties.In this paper, four N-substituted dithienylpyrrole derivatives were synthesized successfully with the characterization of Fourier Transform Infrared(FTIR) and Nuclear Magnetic Resonance(NMR). Conducting polymers of these dithienylpyrroles were synthesized on the ITO glass by electrochemical polymerization in boron trifluride diethyl etherate(BFEE). The four polymers were characterized by SEM, cyclic voltammetry and spectroelectrochemistry. The resultant polymer films presented multicolor electrochromic change from yellow to blue, and then to blue-violet under different potentials. The polymer 1-4-nitrophenyl-2,5-di(2-thienyl)-1H-pyrrole(PSNSNO2) exhibited more excellent electrochromic behavior with faster switching speed and higher coloration efficiency(CE) and optical density(?OD) than 1-4-methylphenyl-2,5-di(2-thienyl)-1H-pyrrole(PSNSCH3) and 1-4-chlorophenyl-2,5-di(2-thienyl)-1H-pyrrole(PSNSCl). However, unlike the other polymers, PSNSNO2 was poor adhered to the working electrode surface.In order to improve the properties of the conducting polymers based on PSNSNO2, 3,4-ethylenedioxythiophene(EDOT), thiophene and selenophene were elected as monomers to copolymerize with PSNSNO2 in this paper. The resultant copolymers were successfully synthesized by electrochemical polymerization and characterized by cyclic voltammetry, XPS, SEM, EDS and spectroelectrochemistry. It was demonstratd that the redox process of the three novel copolymers were non-diffusional, which means the good electrochemical activity and adhesion of the copolymer films.The copolymer P(SNSNO2-co-EDOT) showed tricolor electrochromism, which was brown(in the neutral state), green-yellow(in the intermediate state) and light blue(in the oxidized state). The copolymer P(SNSNO2-co-Th) presented orange-yellow in the neutral state; upon increasing the potential, the color turned to yellow and light green in the intermediate state, and light blue in the oxidized state. The copolymer P(SNSNO2-co-SE) exhibited multielectrochromic behaviors, which was orange-yellow in the neutral state and turned into dark-yellow, green-yellow, green, blue and blue-violet upon oxidation. Owning faster switching speed, higher CE and better electrochemical stability than P(SNSNO2-co-EDOT) and P(SNSNO2-co-Th), P(SNSNO2-co-SE) was an excellent candidate for the application of electrochromic materials.