Insulated Polyacetylene Chains in an Inclusion Complex by Photopolymerization
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Insulated Polyacetylene Chains in an Inclusion Complex by Photopolymerization Steluţa A. Dincă, Damian G. Allis, Amanda F. Lashua, Michael B. Sponsler, and Bruce S. Hudson Department of Chemistry, Syracuse University, Syracuse, NY 13244-4100, U.S.A ABSTRACT: The properties of a material often depend on the degree of order of their atomic, molecular, or crystalline domain components. This is expected to be especially true for the case of polyacetylene, whose properties are highly anisotropic. For many applications, it may be necessary to have macroscopic order but not necessarily crystalline order. Having polyacetyelene chains fully extended and aligned parallel to each other may be sufficient for these applications even without order of the chains around their long axis. We report here progress in the use of an inclusion crystal containing a photo-reactive precursor to prepare high molecular weight polyacetylene. Raman spectroscopy was performed to probe the resulting conjugated polyene chains. Ultraviolet irradiation of a 1,4-diiodo-1,3-butadiene/urea inclusion complex results in the appearance of new resonance-enhanced Raman modes at 1125 and 1509 cm-1. The Raman spectra of the resulting confined polyene chains are very similar to freestanding isolated transpolyacetylene prepared by solution methods. INTRODUCTION Conducting polymers can be thought of as molecular materials that are comprised of many individual polymer chains.[1,2] Their unique properties - chemical, physical, and mechanical - make conjugated polyenes an appealing alternative to conventional inorganic semiconductor materials. All of these properties have paved the way for flexible, ultra-thin, and less expensive electronics. The effectiveness of π-conjugated devices depends significantly on the way the polyene chains pack together in a material, on the chemical structure of the material, and on the extent to which the conjugated chains are orientationally ordered. These polymer structures are complicated and not precisely defined. Macroscopically long polyacetylene, (CH)x, is the simplest conjugated polymer. The analyses of previously synthesized (CH)x have led to its characterization as an extended backbone structure, despite evidence that (CH)x samples are heterogeneous mixtures of relatively short conjugated chains with considerable defects.[2,3] The undesirable physical properties and reactivity of (CH)x make it impossible to process this material using standard methods. Although remarkable improvement in structure and morphological order has been achieved, preparing high molecular weight polymer single-crystals remains a general challenge.[1] In this paper, we report a novel method for the preparation of parallel, extended chains of polyacetylene by photochemical conversion of a reactive molecule (1,4-diiodo-1,3butadiene, DIBD) constrained within the parallel tunnels of a urea inclusion complex (UIC). The method used to synthesize this composite/hybrid conjugated material is photochemical elimination of iodine and formation of carbon-carbon bo
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