Photoinduced step-growth polymerization of N-ethylcarbazole

Conjugated polymers have been an interesting research area due to their applicability in varied electronic and electrooptic devices. Organic photovoltaics, batteries, electrochomic devices, light emmiting diodes and sensors can be based on conjugated polymers, therefore there is a growing interest in this area. Some known strategies for the synthesis of these polymers are electropolymerization, oxidative polymerization, coupling reactions (e.g. Suzuki and Yamamoto). In 1862, polyaniline, which was the first conducting polymer, had been synthesized by Letheby, but features of this polymer were not totally understood, so it was not applied in industrial way. Then, polyacetylene, the first known conjugated polymer, was synthesized by Natta, in 1958. In the next decade, Hideki Shirakawa, accidently synthesized polyacetylene as silvery thin film, the conductivity of this film was much more conductive than previously synthesized polyacetylene. This was the milestone for these research area and made a great impact on researchers. Although polyacetylene has many superior characteristics, their applicability is restricted because of its structure can be disrupted easily when exposing water or oxygen in air. Therefore, this drawback leads the researches to create new stable conjugated polymers such as polythiophene, polypryrrole, polyphenylene and polycarbazole for overcoming these limitions. These polymers, which are synthesized with heterocyclic organic monomers, are used in the industrial applications. Though there are many methods for synthesizing the conjugated polymers, electrochemical and oxidative polymerization are frequently used. The conductivity of these polymers depend on the synthetic method, substances, doping agents and surface morphology. Photopolymerization; a general method of polymerization by photoinitiators and photosensitizers in which the reaction is initiated by the action of light, the functional monomers, oligomers and polymers being converted into higher molecular weight polymers. Photopolymerization is the most common method in terms of usage area and much faster than other polymerization methods, and therefore, leads to an economical and efficient process. According to the thermal polymerization methods, photopolymerization, which is an environmentally friendly method due to its low energy requirement, with high product yields and short reaction times. In the 21st century, photopolymerization has receieved prominence in the industrial sense and has been introduced in a wide range of the fields. In the industrial fields, photopolymerization method is used in the synthesis of adhesives, polishers, coatings, electronic device designs, tooth fillers, optical waveguides and paints. The photopolymerization method consists of four main stages. The photoinitiators interacts with the light in the "initiation" stage, using the energy from the light to initiate the reaction by interacting with the monomer. In the "growth" step, chain growth occurs using monomers. The chains that grow in the "chain transfer" phase continue their reactivity through a dehydrogenated molecule while the reactants terminate their hydrogen by removing hydrogen from other molecules present in the medium. In the "termination" stage, the reagents in the medium interact with each other and terminate the reaction by losing their activity. Although photopolymerization is studied under many headings, free radical and cationic photopolymerization are more widely used methods. There are two types of initiators in free radical photopolymerization: Type I, where the reaction begins with a single molecule, and Type II, including the photoinitiator as well as the coinitiator. Cationic photopolymerization can be examined under two main headings: direct and indirect photolysis. In this thesis, A noval method for photochemical step-growth systhesis of poly(N-ethylcarbazole) (PCE) via consecutive diphenyliodonium hexafluorophosphate (Ph2I+PF6-) mediated electron transfer and coupling reaction of the excited N-ethylcarbazole (EC) in the presence of Ph2I+PF6- as oxidizing salt proceeded efficiently giving EC radical cations. Subsequently, the protons released concomitantly with coupling of two EC radicals cantions. The successive reactions involving excitation, electron transfer, proton release, and coupling lead to the formation of PEC. The electrochemical properties and surface morphology of the thin films of the formed polymers before and after dedoping were investigated by cyclic voltammetry, differential pulse voltammetry, and atomic force microscopy techniques, respectively.