Journal of The Electrochemical Society, 164 (2) H11-H20 (2017) H11 0013-4651/2017/164(2)/H11/10/$33.00©The Electrochemical Society
High Contrast Electrochromic Polymer and Copolymer Materials
Based on Amide-Substituted Poly(Dithienyl Pyrrole)
Tugba Soganci,aSevil Soyleyici,aHakan Can Soyleyici,b,zand Metin Aka,z
aFaculty of Art and Science, Chemistry Department, Pamukkale University, Denizli, Turkey
bDepartment of Electricity and Energy, Adnan Menderes University Buharkent Vocational School, Buharkent, Aydın, Turkey
Conducting polymers have attracted attention as active materials for low power consuming, flexible devices with vivid colors and simple, room temperature processing methods. However, the conductive polymers with high-contrast electrochromic properties are limited in the literature. Here we achieve high-contrast electrochromic switching by copolymerization of newly synthesized an amide substituted dithienyl pyrrole (PBA) and 3,4-ethylenedioxythiophene (EDOT). In order to obtain the best optical properties of copolymer, spectral characteristics of the synthesized copolymers with different monomer feed ratios were investigated. Both homopolymer and copolymer films exhibit well defined redox and satisfied coloration efficiency. Spectroelectrochemistry studies indicate that the P(PBA-co-EDOT) has a lower bandgap (1.67 eV) and shows the excellent optical contrast (77% of 1000 nm) and coloration efficiency (697.01 cm2 C−1). The copolymer method provides a novel way to fabricate a freestanding organic electrochromic device. Additionally, the fluorescence properties of both monomer and polymer were investigated. P(PBA) having strong emission and good solubility and also P(PBA) has the potential to be used in OLEDs.
© 2016 The Electrochemical Society. [DOI:10.1149/2.0111702jes] All rights reserved.
Manuscript submitted October 13, 2016; revised manuscript received November 18, 2016. Published December 2, 2016.
In the last decade, polythiophene (PT) and polypyrrole (PP) have been commonly used because of their electrochemical properties. However, polypyrrole, although highly conducting, is not stable in the dedoped state toward oxygen. On the other hand, polythiophene, al-though stable, requires high potentials to be cycled between the doped and dedoped states. Considering of all these, a tailoring of the elec-troactive properties could be provided by the preparation of diversified monomer including pyrrole and thiophene units.1Formed from these monomers, namely, 2,5-di(2-thienyl)pyrroles (SNS) monomer have interesting optical and electronic properties. Although, the oxidation potentials of PT and PP are ca. 1.5 V and 0.9 vs. Ag/AgCl,2,3oxidation potentials of Poly(2,5-dithienylpyrrole) derivatives are about 0.7 V vs. Ag/AgCl4–6indicating the incorporation of a pyrrole ring between two thiophene units in SNS monomer decreases the oxidation potentials of polymer films markedly. Due to their low oxidation potential and effortless electrochemical polymerization, PSNS derivatives are one of the most promising conducting polymers.
Additionally, the incorporation of a substituent into SNS backbone can ensure the bandgap tunability and valuable properties, making possible further modifications to properties.7 In recent years, in or-der to explore the effect of substitution through the pyrrole units of PSNS, a number of SNS derivatives have been synthesized with sub-stituted phenyl derivatives,8,9aryl derivatives,10ferrocene,11azide,12 anthraquinone,13 carbazole group.14,15 However, to the best of our knowledge, there is no study on amide substituted PSNS in literatures except our study.16–18
Other than the modification of monomer structure, copolymer-ization is a method to tune electrochromic properties of polymers. Usually novel copolymers are synthesized using multifunctional monomers via electrochemical polymerization.19This method offers the possibility of obtaining materials with characteristic properties of their individual components, and thus expands the scope of ap-plication of a given polymer in various fields. In the last years, the excellent properties of poly(3,4-ethylenedioxythiophene) (PEDOT)20 have been combined with those of other typical conducting poly-mers. So far, copolymers of 3,4-ethylenedioxythiophene (EDOT) with thiophene,21naphthalene22or pyrene23has been successfully obtained and studied. In the literature of recent years are also described inter-esting properties of polypyrrole (PPy)24and polymers of substituted pyrrole (Py)8,25–27and Ref.28. In this way copolymerization can lead to an interesting combination of the properties such as fune tuning of the color for electrochromic applications.
In this work, the copolymerization of amide substituted (PBA) and EDOT have been achieved and expected to combine their advantages
zE-mail:metinak@pau.edu.tr;hcsoyleyici@gmail.com
to produce a high quality film with good electrochromic property. Electrochemical copolymerization of amide substituted PBA with EDOT was chosen due to its low oxidation potential and effortless electrochemical polymerization. Beside these, the influences of dif-ferent feed ratios of the comonomer on the spectroelectrochemical and electrochemical properties of the resulting copolymer films were investigated. Therefore, this study is novel and significant for deter-mination of copolymer reactivity ratios in the conducting polymers.
Experimental
General.—All chemicals, reagents and solvents are available as commercial products and used in highest purity. Indium tin oxide (ITO) coated glass was used as a transparent working electrode. Melt-ing points were determined on an electrothermal capillary meltMelt-ing point apparatus.1H and13C NMR spectra were recorded on Varian 400 NMR spectrophotometers. Electrochemical polymerizations and characterizations were performed by Ivium Compactstat electrochem-ical potentiostat/galvanostat. A three electrode electrochemelectrochem-ical cell was used for electrodeposition of monomers. The reference electrode was Ag/Ag+ reference electrode and Pt wire as counter electrode. Spectroelectrochemical measurements were made using an Agilent 8453 UV-visible spectrophotometer and all of the characterizations were performed in monomer free 0.1 M LiClO4/acetonitrile elec-trolyte solution.
Synthesis of N-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)benzamide (PBA).—The synthetic route of the monomer PBA is depicted in Scheme 1. The reagents 1,4-di(2-thienyl)-1,4-butanedione and benzohydrazide were prepared according to previously published literature.29,30All experiments were carried out under dry argon by using Standard Schlenk techniques.
The monomer (PBA) was synthesized from 1,4-di(2-thienyl)-1,4-butanedione and benzohydrazide in the presence of catalytically amount of p-toluenesulfonic acid (PTSA). A round-bottomed flask equipped with an argon inlet and magnetic stirrer was charged with 2.5 g (10 mmol) 1,4-di(2-thienyl)-1,4- butanedione, 1.36 g (10 mmol) benzohydrazide, 0.2 g (1.2 mmol) PTSA, 1 ml DMSO and 50 ml toluene. The resultant mixture was stirred and refluxed for 24 h under argon. Darkened solution was filtered hot to remove oily decompo-sition products. Then, the mixture was cooled to room temperature and the solid product was filtered off to give a green powder that was washed with pentane (3× 15 ml) and air-dried, yield 3.2 g %91 (mp 111–112◦C). The structure of the monomer was confirmed by 1H-NMR and13C-NMR spectral analyses (Figures1aand1b).
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