Design and synthesis of new fused arene- containing conjugated polymers

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Kulkarni, Chinmay R.
Collard, David M.
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Conjugated polymer have attracted attention in the past two decades because of a range of advantages over inorganic – semiconductors. They can be solution processed, they offer flexibility, and their electronic structure can be tuned through molecular design. These characteristics make them applicable in solar cells, light-emitting diodes and transistors. There are few examples of conjugated polymers that contain simple acenes (e.g., naphthalene, anthracene, pentacene). One of the key challenges to the incorporation of acene units is the need to retain solubility of the polymers. This requires the multistep synthesis of acene monomers bearing flexible alkyl or alkoxy groups. Conjugated polymers containing aromatic units have two non-degenerate ground states that are referred to as the aromatic and quinoidal forms. The quinoidal form is higher in energy and can be stabilized by fusion of a benzene ring onto the aromatic unit of the conjugated backbone. The stabilization of the quinoidal form impacts the band gap of conjugated polymers, as demonstrated by the low band gap of polyisothianaphthalene, which is ~1 eV lower than that of polythiophene. In chapter two, the effect of the incorporation of acenes into poly(arylene ethynylene)s is explored through the preparation and characterization of a series of copolymers. It was found that the incorporation of a 9,10-anthracene unit significantly lowers the bandgap compared to analogs containing 1,4-phenylene and 1,4-naphthalene units. This can be understood in terms of the stabilization of the quinoidal form of the anthracene-containing polymers compared to the phenylene and naphthalene-containing analogs. The stabilization of quinoid form arises from the fusion of benzene rings onto the phenylene ring in the conjugated backbone. In chapter three, the impact of in the incorporation of naphthalene and anthracene units on the electronic structure of alternating donor-acceptor polymers with N,N-disubstituted naphthalenediimide (NDI) units is explored. In this series of polymers it was observed that the anthracene-containing polymer displayed a significantly red-shifted charge transfer type transition compared to phenylene and naphthalene containing polymers. This may be understood to arise from the stabilization of quinoidal form of the anthracene-containing conjugated polymer. In chapter four, approaches to the synthesis of tetraalkoxy-substituted anthracene monomers for synthesis of anthracene-containing (arylene vinylene) polymers are discussed.
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