Electrochemical and optical properties of novel donor-acceptor thiophene-perylene-thiophene polymers (original) (raw)
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Journal of The Electrochemical Society, 2015
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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New low-gap thiophene-based regular copolymers are produced by anodic coupling of 3,4ethylenedioxythiophene-2,5-substituted thieno[3,4-b]pyrazine (TP), cyclopenta[2,1-b;3,4-b′]dithiophen-4-one (CO), and 4-dicyanomethylene-4H-cyclopenta[2,1-b;3,4-b′]dithiophene (CN). The copolymers are characterized by cyclic voltammetry, FTIR reflection-absorption and UV-vis spectroscopy, electrochemical quartz crystal microbalance analysis, and in situ pand n-conductivity measurement. The copolymers show low optical gaps (measured at the maximum absorption) and electrochemical gaps (measured from redox potentials) in the range 0.8-1.3 eV. The CN-based polymer displays the lowest reported electrochemical gap (0.8 V). Random copolymers of CO and 3,4-ethylenedioxythiophene (EDT) have also been produced and compared with the relevant regular copolymer. Copolymerization of CO with increasing amounts of EDT decreases the gap. From an analysis of redox potential as a function of EDT fraction, it is found that the gap is limited by the redox potentials of the individual homopolymers. Localization of n-doping carriers in the polythiophene chains is progressively increased by donor-acceptor alternation and then by copolymerization till the expected intrinsic conductivity is made completely p-type. Figure 9. Cyclic voltammograms of (a) poly(3-octylthiophene) and (b) poly(dithienylvinylene) in acetonitrile + 0.1 M Bu4NClO4. Scan rate: 0.1 V s -1 .
Polímeros, 2020
This work reports the spectroelectrochemical and electrical behavior of electropolymerized donor-acceptor like (D-A) copolymer films, based on 3,4-ethylenedioxythiophene (EDOT) and beta-substituted electron-acceptor thiophenes. Initially, the copolymer films were deposited on indium tin oxide substrates, which spectroelectrochemistry measurements were carried out with an UV-Vis spectrophotometer. Hence, it was possible to observe the electrochromic properties of these materials, visualizing the color changing towards different potentials applied. The experiments have shown that these D-A like copolymers presented good electrochromic properties, such as optical contrast, coloration efficiency, and switching times. Additionally, films prepared on a platinum working electrode were investigated by electrochemical impedance spectroscopy, which has shown the electrical behavior of those copolymers and their potential as candidates to capacitive devices building. Therefore, the combination of electron-donor EDOT with those electron-acceptor monomers is indeed a useful strategy to tailoring and fine-tuning the physicochemical properties of polythiophenes with innovative applications.
Synthetic Metals, 1986
Passive, ultra-thin dielectric films (5-7 nm) of poly(phenylene oxide), PPO, are formed by the anodic electropolymerization of tetramethylammonium phenoxide from acetonitrile onto Pt or Au electrodes. These films can have exceptionally low permeabilities to solution redox species, depending on electrcpolymerization potential, the time of deposition, and cross-linking reactions. The latter becomes evident at +0.4 V vs. SSCE and in the presence of electrogenerated mediator-oxidant. PPO blocks the cyclic voltammetry of ferrocene carboxylic acid and Cl-oxidations in acetonitrile by > 99% and 922, respectively, and reduction of [Fe(CN)JM3 and oxidation of the sodium salt of ferrocene carboxylic acid in water by > 99%. By rotating disk voltammetry, the permeability PDs.poL of the film to FeCp,* in CH,CN is as low as 8 x lo-" cm2/s. Films prepared from alkyl substituted phenolates are thicker, more hydrophobic, but also more permeable owing to less efficient cross-linking. Film thicknesses were obtained by profilometry, ellipsometry, XPS, and high frequency electrical capacitance measurements, and physical and structural information by use of contact angle measurements and attenuated total reflectance FTIR.
Electrochemical copolymerization of thiophene derivatives; a precursor to photovoltaic devices
Electrochimica Acta, 2011
This work presents an electrochemical technique for the polymerization and copolymerization of thiophene derivatives like 7,9-dithiophene-2yl-8H-cyclopenta[a]acenaphthalene-8-one and 3-hexylthiophene. The structural characterization of chemically synthesized monomers and electrochemically synthesized polymers was carried out by nuclear magnetic resonance and Fourier transform infrared spectroscopy. Thermal characterizations indicate that copolymer has increased thermal stability than that of homopolymer. Morphological studies of the polymerized films carried out by scanning electron microscopy shows network structure of copolymer. Optical properties of the homopolymers and copolymer were studied by UV–visible spectrometer and it was observed that band gap of copolymer is less than the homopolymers. HOMO and LUMO levels, band gap values of the respective polymers were also calculated from the cyclic voltammetry technique with various scan rates. By the peak current obtained from various scan rates shows that all polymerization reactions are diffusion controlled process. Charge transfer resistances of polymers were determined using Nyquist plots. Conductivity of synthesized polymers shows higher conductivity for copolymer than homopolymers.► This work presents an electrochemical technique for the polymerization and copolymerization of thiophene derivatives. ► Copolymerization of thiophene based monomers like 7,9-dithiophene-2yl-8H-cyclopenta[a]acenaphthalene-8-one and 3-hexylthiophene are synthesized. ► Study of the structural, optical, thermal, conductivity, morphological, band gap and impedance measurements of the copolymer indicates a suitable material for photovoltaic applications.
Electrochimica Acta, 2000
3-Thiophene-acetic acid and 3-methylthiophene co-polymers have been prepared with the consideration that the solvation behaviour of the film could be modified. The modification is coupled with the observed splitting of the oxidation peak on the cyclic voltammograms. The redox transformation of the films was studied by electrochemical quartz crystal microbalance (EQCM) and in situ conductance (ISC) techniques. Mass changes during the electrochemical processes showed that the cation is not involved into the charge balancing of the film. Manifestation of self-doping was excluded by analogous measurements with an aprotic co-polymer of methylthiophene. Results completed with in situ conductance and spectroelectrochemical observations confirmed the assumption of a chemical step taking place after the first oxidation. In this process desolvation of the oxidised intermediate occurs, which is a necessary step for the achievement of the quasi-metallic state.
2004
Step towards the realisation of low-cost, allpolymer, flexible OFETs. Charge carrier mobilities comparable to that of amorphous silicon have been obtained. 15 As a demonstrator functional 15-bit programmable code generators are fabricated. generate the electronically excited-state molecule as well as development of new materials with high performance and judicious choice of the combination of emitting and charge transporting materials and the combination of emitting and luminescent dopant molecules, are of vital importance. For this purpose, not only emitting materials but also charge transporting materials are also required. Both polymers and small molecules are candidates for materials in OLEDs. Considering the fact that light-emitting films of plastic materials have been realised, there is also a chance to achieve photovoltaic conversion in such materials. 39 There is no short-term ambition to replace silicon, or thin film technologies (crystalline and amorphous silicon, copper indium diselenide) 40 , but to develop a long-term technology based on organic materials with almost unlimited availability. Before these cells become practical, which at the moment still looks far away, the efficiency will have to be increased further. The long-term Over the last decade, organic polymeric thin films for photonic applications have been a rapidly growing research area. Conjugated polymers 42,54 are the classes of plastic materials, in which semiconducting characteristics can be observed as given in Figure 12. Conjugated polymers become conducting in the doped state. These are polymers that possess a meta-and para-linkages 67b. Suzuki coupling between dibromotriarylamine and phenylene-1,4-diboronic ester also resulted in a sparingly soluble poly(triarylamine) with low molecular weight possessing highly efficient blue photoluminescence 68. All synthetic methods for preparation of polymeric triarylamines described above are illustrated in Scheme 1. Polythiophenes Polythiophenes are an important representative class of conjugated polymers that form some of the most environmentally and thermally stable materials that can be used as electrodes 73 , sensors 74 , transistors 75 , polymer LEDs 76 , solar cells etc. Polythiophene and its derivatives work very well in some of the above applications and less impressively in other devices. Creative new design and development strategies of new polythiophenes has led to interesting new materials and enhanced performance in certain devices. The ability of molecular designers to begin understanding how to gain control over the structure, properties, and function in polythiophenes continue in order to make the synthesis of polythiophenes a critical subject in the development of new advanced materials. Pure polythiophene without side chains is neither soluble nor fusible. Once the polymer is prepared, it's not possible to further process the obtained film or powder. However, side chains, which give solubility and fusibility to the polymer, can be attached to the thiophene ring. The most widely used polymer is the poly(3-hexylthiophene) (P3HT). Since 3-alkylthiophene is not a symmetrical molecule, the band gap and conductivity of poly(3-alkylthiophene)s are strongly dependent on regioregularity of these polymers. There
Study of a thiophene-based polymer for optoelectronic applications
Thin Solid Films, 2006
A thiophene-based conjugated polymer bearing a cyano group (-CN) as a side chain substituent was successfully synthesized. The polymer evidences an excellent filmability from various organic solvents as well as an enhanced photoluminescence. The polymer has been characterized optically (Fourier Transformed Infrared spectroscopy, absorption and photoluminescence) in solution and in film, while X-ray diffraction measurements (XRD) of thin films were performed to investigate its bulk morphological features. From the absorption edge of the spectrum of a thin polymer film, the optical band gap of the polymer is estimated to be 2.0 eV, which corresponds to orange emission. Furthermore, a single layer light emitting diode (LED) was fabricated. The device produced bright stable electroluminescence at room temperature. All of the results indicate that this polymer is a promising emissive material for application in polymeric LEDs.