Electrochromism

Addressed herein, novel poly(3,4 ethylenedioxythiophene) PEDOT/Nanocarbon Materials (NCMs) composite films have been produced by electropolymerization of EDOT monomers onto NCMs coated indium tin oxide (ITO) glass slides. In this study NCMs/ITO working electrodes were prepared by drop casting method which is simpler, quicker, cheaper and easier than other methods. Then PEDOT/NCMs composite films have been produced and investigated by comparing the electrochemical properties with each other in this study. These novel materials significantly improved conductivity and electrochemical performance of PEDOT such as stability of electrochromic characteristics, coloration efficiency, switching time due to an important role in the electron transfer between NCMs and PEDOT films. The prepared novel PEDOT/NCMs composites exhibit excellent optical contrast that is 2 times higher than that of others. These nanocomposite films can be used for electrochromic and energy storage devices applications in near future.

Herein, we report the synthesis of two donor-acceptor-donor polymers (P1 and P2) based on thiophene (M1) and thieno [3,2-b]thiophene (M2) as the donor and 2,5-bis(dodecyloxy)benzene as the acceptor unit. The effects of different donor units on the polymers' electrochemical and optical properties were examined by cyclic voltammetry and spectroelectrochemical analysis. Introducing thieno[3,2-b]thiophene unit as the donor unit enhances π-stacking and consequently lowering the bandgap of the resulting polymer. The electronic band gaps, defined as the onset of the π-π * transition, were found to be 2.0 eV for P1 and 1.7 eV for P2. Both P1 and P2 films revealed multi-colored electrochromism. A dual-type complementary colored electrochromic device (ECD) using P2/PEDOT in sandwich configuration was constructed. Spectroelectrochemistry, switching ability and open circuit memory of the ECD were investigated. During the past decade, the field of organic electronics has progressed enormously as a result of growing interest in materials chemistry. The first generation of conducting organic materials were composed of predominantly carbon-based molecular structures such as linear acenes, poly acetylene, and poly(p-phenylene viny-lene) derivatives (PPV). 1-3 The following generation involved the widespread incorporation of heterocycles into the conjugated backbone such as thiophene, pyrrole and their derivatives. 4-6 Currently, conjugated polymers and small organic molecules have been designed using "donor-acceptor" strategy. 7-10 This method involves synthesizing monomers and polymers with a delocalized π-electron system that consists of alternating electron-rich (donor) and electron-deficient (acceptor) units. The combination of high-lying HOMO levels (residing on the donor units) and low-lying LUMO levels (residing on the acceptor units) results in a local electron density gradient along the backbone, creating a lower energy charge-transfer transition. 11,12 The presence of this lower energy transition leads to smaller optical band gaps. A low bandgap leads to absorption in the visible region. Low bandgap, stability, solubility (which is crucial for their processability), planarity (which is important for obtaining good π-orbital overlap and effective electron delocalization) are the main requirements for organic electronic materials. In an attempt to manipulate relevant parameters to fulfill these requirements through synthetic expertise, numerous organic heterocyclic and pendant groups have been incorporated into the backbones of donor-acceptor conjugated polymers and small molecules. Thiophene based materials have demonstrated great potential as donor units due to their desirable properties such as stability , ease of synthesis, and modification. In recent years, thiophene moiety was coupled with benzoselenadiazole, 13 benzotriazole, 14,15 carbazole, 16 benzothiadiazole, 17,18 ethylenedioxythiophene, 19 diketopyrrolopyrrole, 20 3-alkylthiophene, 21 quinoxaline, 22 and benzimidazole. 23 The study of the opto-electronic properties of conjugated polymers and small organic molecules designed based on D-A approach provides valuable information for understanding the structure-property relationship. And also it allows designing materials with an enhanced opto-electronic property. These materials have been used in organic light-emitting diodes, 24-27 organic solar cells, 28-31 field effect transistors, 32-34 sensors, 35-37 and electrochromic devices (ECDs). 38-43 Conjugated polymers have gained great attention for ECDs due to the z fact that they are more processable than inorganic electrochromic materials and offer the advantage of a high degree of color tailorability. Electrochromism is defined as the reversible change in transmittance and/ or reflectance of the material upon applied voltage. The color changes between a transparent state and a colored state or between the two colored states are associated with electrochemically induced oxidation-reduction reactions. In this paper, we report two new donor-acceptor-donor conjugated polymers which were synthesized by combining electron-accepting 2,5-bis(dodecyloxy)benzene with electron-donating thiophene and thieno[3,2-b]thiophene. The influence of the structural differences of the electron-donating units on the electrochemical and optical properties of the resulting polymers was investigated. Experimental General.-All reagents and chemicals were obtained from commercial sources and used without further purification unless otherwise mentioned. 1,4-Bis(dodecyloxy)benzene, 44 1,4-dibromo-2,5-bis(dodecyloxy)benzene, 44 tributyl(thiophen-2-yl)stannane, 45 tributyl(thieno[3,2-b]thiophen-2-yl)stannane 46 were synthesized according to previously published procedures. Tetrahydrofuran (THF) was dried over sodium and benzophenone. Bruker Spectrospin Avance DPX-400 Spectrometer was used to record 1 H NMR and 13 C NMR spectra of synthesized materials in CDCl 3. Chemical shifts were recorded in ppm downfield from tetramethylsilane. Elec-tropolymerization of monomers were achieved in a three-electrode electrochemical cell. Indium Tin Oxide doped glass slide (ITO) as the working electrode, platinum wire as the counter electrode, and Ag wire as the pseudo reference electrode were used under ambient conditions using a Gamry potentiostat. Spectroelectrochemical studies of polymers were performed on a Varian Cary 5000 UV-Vis-NIR spectrophotometer. Minolta CS-100 colorimeter was used to perform colorimetry studies. Synthesis.-1,4-bis(dodecyloxy)benzene (2).-To a solution of hy-droquinone (4.00 g, 36.3 mmol) in dry DMF (50.0 ml), K 2 CO 3 (20.8 g, 83.6 mmol) was added and the solution was stirred under inert atmosphere at 100 • C for 1 hour. Then 1-bromododecane (15.1 g, 109 mmol) was added to the mixture. After 42 hours, the mixture was cooled to room temperature and poured onto distilled water. The product was extracted with CH 2 Cl 2 , and dried over anhydrous MgSO 4. After) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. 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