| Among many conducting polymers, polythiophene(PTh) has drawn much attention in recent years because of its attractive applications such as conductors, electrode materials, and organic semiconductors. However, PTh is generally synthesized by electrochemical oxidation of the monomer in an organic medium. More evidences showed that trace water was harmful to the electropolymerization of thiophene and reduced the efficient conjugated chain length and conductivity of PTh films. Ionic liquids are a class of novel environmentally benign "green solvents" that have remarkable properties and promising applications in many fields. In this thesis, we report for the first time on the direct electropolymerization of thiophene and 3-methylthiophene in l-butyl-3-methylimidazolium hexafluorophosphate ionic liquid ([BMIMJPFe) used as solvent and electrolyte.The ionic liquid [BMIM]PF6 was synthesized with two steps and was characterized by FT-IR^H-NMR^V. [BMIM]PF6 took on a wide and stable electrochemical window (ca. 4.5 V);It's conductivity was 3.5*10"3 s/cm; dielectric constant is 3.1 xlO"8 F/m, and characteristic viscidity is 1.62ml/g. Although it's viscidity is rather high, [BMIMJPFg could be used as fine solvent in electrochemistry because of it's conductivity and solvation.The electrochemical polymerization of thiophene monomer with the different concentration (0.02M, 0.1M, 0.2M, 0.3M, 0.5M) in ionic liquid [BMIM]PF6 has been studied using cyclic voltammetry, potentiostatic steps and galvanostatic steps. When the monomer concentration was lower than 0.1M, it's hard to obtain polymer films. When the monomer concentration was higher thanO.lM, it was found that very homogeneous and blue-green films were obtained when the potential for electropolymerization was controlled between +1.7 V and +1.9 V or the current density was between 3.0 mA cm"2 and 8.0mA cm"2. When the monomer concentration increased, the current density also increased evidently, and the oxidation potentials of the monomer decreased (+ 1.64V at 0.1M, but + 1.54V at 0.5M), but the oxidation peak potentials of the monomer shifted to larger potentials (ca. +1.9V at 0.02M, but ca. +2.4V at 0.5M); the reduction peaks (de-doping) shifted largely to smaller potentials; but the oxidation peaks (doping)didn't change too much at a broad range.PTh films obtained electrochemically under 1.8V were characterized by IR. The band at 790cm"1 of the dedoped polymer films is attributed to the out-of-plane vibration of C-H on the p-position of 2,5-disubstituted thiophene. These results indicate that the PTh films polymerized in ionic liquid is dominantly a ?a ' linked. Four intense bands at 1030, 1120, 1200 and 1340 cm"1, are the bands of doped polythiophene from the vibration of charge transfer conjugated thiophene rings or a charged polaron.The UV-Vis spectrum of polythiophene films show that the bands at 740nm, as observed from an as-grown polythiophene film, may be assigned to a bipolaron. When the doped polythiophene films were electrochemically reduced, polythiophene films turned red from blue-green, and the bands at 740nm disappeared; however a new band appeared at 490nm, characteristic of a n ?JT transition of conjugated polymer chain. After neutral PTh films were electrochemically redoped, the band at 740nm appeared again. This is because the originally filled valence band of the polymer becomes partially empty and the Fermi level lowers to the valence band, resulting in red-shift of the most absorption band.SEM photographs of PTh films (same thickness) electrochemically prepared under different potential change from loosen meshwork to compact meshwork with increasing of potential (from 1.6V to 1.9V). PTh films obtained under 2.6V change to compact cumulate clump structure because of overoxidation. The as-grown PTh film (prepared at +1.8V) is blue-green with a metallic luster, exists as loose solid meshwork; however the dedoped film changes to a compact "cauliflower" structure. This is probably because the departure of opposite anion caused closing up of...
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