Orange to black electrochromic behaviour in poly(2-(2-thienyl)-1H-pyrrole) thin films

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• 作者：Pozo-Gonzalo Cristina ; José ; A. Pomposo ; Juan A. Alduncin ; Maitane Salsamendi ; Al’ ; bina I. Mikhaleva ; Leonid B. Krivdin ; Boris A. Trofimov
• 关键词：Electrochromic displays ; Conducting polymers ; Polythiophene ; Copolymers ; Spectroelectrochemistry ; Electrochemical polymerisation
• 刊名：Electrochimica Acta
• 出版年：2007
• 期刊代码：30_00134686
• 类别：ch
• 出版时间：1 April 2007
• 卷：52
• 期：14
• 页码：4784-4791
• 文件大小：1154 K

摘要

We have studied an electrochromic precursor, 2-(2-thienyl)-1H-pyrrole (<strong>1strong>), using two improved procedures of the Trofimov reaction. Optimised stereochemical calculations at the B3LYP/6-311G* level showed almost equal s-cis and s-trans conformational populations in <strong>1strong> with marked out-of-plane deviations of ca. 30°. Model calculations suggest that the predominant rotational conformation in undoped poly(<strong>1strong>) would be s-trans with the essential out-of-plane deviations around the all three interheterocyclic bonds of ca. 25–30°. Monomer <strong>1strong> exhibited two irreversible oxidation processes at +0.86 and +1.3 V corresponding to the oxidation of the pyrrole and thiophene rings, respectively. Orange to black electrochromic behaviour was found in ClO<sub>4sub><sup>−sup> doped poly(<strong>1strong>) thin films with colouring and bleaching times of 1.8 and 1.3 s, respectively. The colouration efficiency during the bleaching process was 233 cm<sup>2sup>/C. The optical contrast at 450 nm was 19%and in the near-IR was 36%. The band-gap of poly(<strong>1strong>) (1.6–1.7 eV) was found to be significantly lower than that of polypyrrole (2.85 eV) and polythiophene (2.3 eV) as a consequence of increased electron delocalisation in the system. Important differences in the morphology of doped and dedoped poly(<strong>1strong>) films were observed by atomic-force microscopy (AFM). Doped poly(<strong>1strong>) films showed a granular morphology with primary particles of 45–60 nm in size and an average surface roughness of 3.5 nm. On the other hand, dedoped poly(<strong>1strong>) films showed interconnected aggregates of 65–90 nm in size as a consequence of particle fusion, with a surface roughness of 9.2 nm. In summary, poly(<strong>1strong>) is a promising material for emerging flexible electrochromic devices such as displays and variable optical attenuators.