Characterization of Micrometer-Sized Thin Films of Electrocoated Carbazole with p-Tolylsulfonyl Pyrrole on Carbon Fiber Microelectrodes

Abstract

Carbazole ͑Cz͒ monomers with p-tolylsulfonyl pyrrole ͑pTsp͒ ͑used as self-dopant͒ were electrochemically coated onto micrometer-sized carbon fiber by potentiodynamic method. The resulting micrometer-sized thin films of homopolymer and copolymers were characterized by using electrochemical methods ͑i.e., cyclic voltammetry͒, solid-state conductivity measurements ͑four-point probe͒, spectrophotometric methods ͑in situ spectroelectrochemistry͒, Fourier transform infrared reflectance spectroscopy, and scanning electron microscopy. Cyclic voltammetric results indicate that an increase of pTsp concentration in copolymer formation ͑while the Cz concentration was kept constant͒ current density increases randomly. The maximum anodic current density was obtained as 0.49 A cm −2 by the initial feed ratio of ͓pTsp͔ 0 /͓Cz͔ 0 = 5. This is three times higher than the anodic current density of polycarbazole ͑PCz͒ ͑0.15 A cm −2 ͒. The electrocoated copolymer corresponding to an initial feed ratio of ͓pTsp͔ 0 /͓Cz͔ 0 = 5 was observed as polaron and bipolaron on indium tin oxide ͑ITO͒ by UV-vis spectrophotometry. The solid-state conductivity was measured with a four-point probe apparatus. Results show that a tenfold increase in Cz concentration leads to an increase in conductivity from 0.08 to 6.36 mS cm −1 , and also raises yields from 13.69% to 97.72%. In contrast, a 10 times increase in pTsp concentration leads to a decrease in conductivity from 0.39 to 0.02 mS cm −1 , and also decreases yields from 21.72% to 2.82% which is due to the polymer's bulky structure. The efficiency of the electropolymerization process on the carbon fiber surfaces by cyclic voltammetry, depending on the experimental conditions, was evaluated to ascertain the effects of copolymer thickness, dopant, optical bandgap ͑E g ͒, and the redox parameters ͑anodic and cathodic potentials, E a ,E c ͒, oxidation peak potentials, E ox , and stability test of electrodes.Carbazole is an organic molecule that has shown great potential for technological applications. Polymers based on this molecule display good electron donor 1 and photoactive properties because of their high hole transporting mobility and strong absorption capacity in the UV spectral region. 2-4 Polycarbazole ͑PCz͒ is one of many relatively new conducting polymer groups with good electrochemical characteristics, and its conductive form can easily be obtained by the electrochemical method. 5 Polycarbazole is also a functional polymer material suitable for electrografting applications on carbon fibers. Polycarbazoles have a fused planar structure and are insoluble and infusible, making them essentially impossible to process into flexible films or shaped objects. 6 Investigations related to chemical modification or copolymerization of carbazole with other monomers have led to the use of PCz and its derivatives as redox catalysts, sensors, electrochromic displays, electroluminescent devices, and biosensors. 7-11 Chemical and electrochemical homo-and copolymerization of Cz were separately investigated. 12-...

Electrochemical formation of polycarbazole films in air- and water-stable room-temperature ionic liquids

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