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Conjugated Organic Materials
Nobel Prize 2000: Shirakawa, Heeger, MacDiarmid Applications: Batteries Antistatic & Electrochromic Coatings Plastic Electronics Sensors, etc Konarka Sony
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Conductivity in Polymers
Insulating Polymers / Semiconductors / Synthetic Metals Electrical conductivity / Ionic conductivity Metals Silver Copper Aluminum 102 to 1010 S /cm Graphite Polyacetylene Poly(p-phenylene vinylene) Silicon (10-4) Aqueous salt solutions (ca. 1) Semiconductors Doping 10-5 to 102 S /cm PEO / LiOTf (10-8) Glass Polyethylene Polystyrene Insulators 10-15 to 10-5 S /cm
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Band Theory CB VB Medium-sized molecule Large sized molecule Diatomic
Separate atoms Antibonding orbital CB Band gap VB Bonding orbital Effect on Optical Properties and Ability to Generate Charge Carriers (Doping)
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Band Gaps in Common Conjugated Polymers
Conducting Polymer Band Gap trans-Polyacetylene (PAc) 1.4 eV Polythiophene (PTh) 2.1 eV Poly(p-phenylene vinylene) (PPV) 2.5 eV Intrinsically non-conductive polymers !
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Synthetic Aspects Oxidative Polymerization (electrochemical / chemical) Example: Polythiophenes, polypyrrole, polyaniline Polymerization through organo- metallic coupling reactions Example: Polythiophenes, polypyrrole, PPV Polymer Modification Example: PPV derivatives Stille Coupling; Suzuki-Miyaura Coupling; etc
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GRIM Process for the Synthesis of Regioregular Poly(3-alkylthiophene)s
An Example of a Living Condensation Polymerization Process R group ends up at polymer chain end First Step: Conversion of dibromothiophene to Grignard Species Second Step: Catalytic process (Kumada coupling) Third Step: In our case hydrolysis; also possible to react with a second Grignard species
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GRIM Mechanism
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Applications h+ e - Coatings: Polypyrrole, Polythiophenes
Antistatic coatings, fibers polypyrrole, PEDOT (BaytronTM) Anticorrosive coatings polypyrrole Electrochromic Windows polythiophenes Electronic Devices: PPV, Polythiophenes Polymer Light Emitting Diodes (PLEDs) Field-Effect Transistors Photovoltaics (combination with fullerenes) Sensors: functionalized PPV, polythiophene derivatives, polyaniline Mg:Ag Cathode e - Conjugated Polymer h+ ITO Anode Transparent Cover hn Swager et al., Chem Rev. 2000, 2537.
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