Optical Properties of Distyrylbenzene Chromophores and their Segmented Copolymers
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Jayant
Center for Advanced Materials, Department of Chemistry, University of Massachusetts Lowell, Lowell, MA 01854 **Center for Advanced Materials, Department of Physics, University of Massachusetts Lowell, Lowell, MA 01854 ***Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139. Abstract A new segmented polymer (_) consisting of a distyrylbenzene chromophore separated by polyethylene glycol segments has been prepared by two independent methods: a novel, polymer analogous Mitsunobu reaction and conventional double displacement reaction. The polymer is soluble in a variety of organic solvents, forms excellent, optically clear films and exhibits strong fluorescence. The properties of the chromophore and the polymer, as well as the scope and limitations of the novel Mitsonobu polymerization are presented. Attempts to use polymer (3) in electroluminescent devices are also discussed. Introduction In recent years, poly(p-phenylenevinylene) (PPV) has been extensively investigated because it exhibits efficient photoluminescence and potentially useful electroluminescent properties.I Numerous phenylene vinylene oligomers have been synthesized in order to improve the solubility and stability of these materials as well as to tune their S . 2,3,4,5,6,7,8,9 Innalih-mtngecroeialel a light-emitting electrochemical cell emission frequencies.'.... (LEC), emission occurs because of hole-electron combination, from electrochemically generated p-type and n-type materials. In this case, good counterion mobility is required. This concept has been used to fabricate numerous devices using poly(ethylene glycol), as the ion transporting medium blended with a photoluminescent material.10 A potential problem with this approach has been phase separation of a hydrophobic chromophore and the oligo(ethylene glycol).11 Only one other electroluminescent polymer, in which diethylene glycol units are attached as side chains on a oligo(p-phenlyene) backbone, has so far been 12 reported. Here we report the first synthesis of a polymer containing a photoluminescent distyrlbenzene chromophore separated by poly(ethylene 533 Mat. Res. Soc. Symp. Proc. Vol. 488 0 1998 Materials Research Society
glycol) spacers. This polymer exhibits efficient solution fluorescence and was characterized by IH NMR, t3C NMR, IR, elemental analysis, X-ray powder diffraction, TGA and DSC. EXPERIMENTAL SECTION Materials. All solvents and materials were used as received unless otherwise noted. a, a'-Para xylylene dichloride and polyethylene glycol were purchased from Aldrich. Poly(ethylene glycols) were dried at 45°C under vacuum over P205 for a minimum of three days. Tetrahydrofuran (THF) was distilled from sodium under inert atmosphere. All reactions were performed under a dry argon atmosphere. Chromophore. The distyrylbenzene chromophore (2) was synthesized by direct condensation of the bis phosphonate (I_) with phydroxybenzaldehyde using excess sodium hydride in DMF (Scheme 1).1 3 The expected all trans configuration was
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