Syntheses, electrochemical and spectroelectrochemical characterizations of benzothiadiazole and benzoselenadiazole containing random copolymers

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2016
Kutkan, Seda
Donor-acceptor-donor type conjugated polymers have drawn a tremendous attention in the synthetic modification of optical and electronic properties. Low redox potentials, low band gaps, broad absorption spectrum, processability and durability are some of the crucial parameters for conjugated polymers according to the application areas. Efficient combination of strong electron-accepting units with strong electron-donor species can produce polymers with low oxidation potentials and low band gaps. Besides, introducing alkyl chains onto these donoracceptor units can solve the solubility problem and provide processability and stability. 2,1,3-Benzothiadiazole (BTh) and 2,1,3-benzoselenadiazole (BSe) are the most commonly preferred acceptor moieties in the donor-acceptor type polymer designs. When their literature examples are considered, it is seen that they are capable of producing low oxidation potential polymers with high efficiencies in optical applications like polymer solar cells when coupled with strong donor units. In this study, strong donor units like carbazole, fluorene and silafluorene were used to achieve an efficient donor-acceptor coupling and intramolecular charge transfer through the backbone. Three conjugated random copolymers were synthesized via Suzuki polycondensation reaction in the presence of Pd (0) catalyst. Characterizations of the synthesized monomers were done by 1H and 13C-NMR spectroscopy. Electrochemical and spectroelectrochemical properties of the corresponding polymers were studied successfully. Cyclic Voltammetry (CV) was carried out in order observe the redox behavior of polymers. Corresponding HOMO/LUMO energy levels and band gaps were calculated from the CV results. Absorption characteristics were observed via spectroelectrochemical studies and comparable maximum absorption wavelengths, polaron and bipolaron band formations and color changes upon oxidation were reported from the results of absorption spectra of the polymers. Percent transmittance changes and switching times were recorded via kinetic studies. Weight-average (Mw) and number-average (Mn) molecular weights were measured using Gel Permeation Chromatography (GPC) method. For the further characterization, colorimetric studies were done and the scientific color values were reported according to the CIE coordinates. When the electronic and optical results of three copolymers were regarded, they showed enhanced properties such as low oxidation potentials, low band gaps, high solubility in common solvents and chemical stability compared to their counterparts in the literature. Hence they can be promising candidates for optoelectronic applications.

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Citation Formats
S. Kutkan, “Syntheses, electrochemical and spectroelectrochemical characterizations of benzothiadiazole and benzoselenadiazole containing random copolymers,” M.S. - Master of Science, Middle East Technical University, 2016.