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Section 8-Electronic Properties1-Polyacetylene

Section 8-Electronic Properties1-Polyacetylene -...

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Unformatted text preview: Polyacetylene: The Prototype Conducting Polymer \\\ 1. Bates and Taylor, J. Am. Chem. Soc. 49, 1144 (1928). Hg lamp photopolymerization . sublimable oligomers 2, Melville, Tran. Far. Soc. 32,- 258 (1936). Hg - photosensitized polymerization 3. Natta . (1958) Ti(OBu)4/A|Et3 Ziegler-Natta Initiator . gray infusible powder 4, Ito and Shirakawa, J. Polym, §gi., thm. Eg. 12, 11 (1974) . free standing films ' serendipity #1 (catalyst concentration, stirring) A . iia. ' 1'" :17 ' -fi Fig. 3.16 Electron micrograph of an ultrathin film of trans-polyacetrlene. reciprocal lattice is approximated to be “orthorhombic.” However, the presence of (001) intensity would require certain modifications not permit— ted by the present data. The unit-cell parameters are givenin Table 3.9. As in the cis polymer, the c axis is the molecular axis oflrans‘polyacetylene, which is along the fiber axis. . Six meridional reflections were observed. These and other reflections fall on the approximated orthorhombic reciprocal lattice sites (Fig. 3.18c). Using the same procedures described in Section 3.5, the (MO) reflection intensity (Fig. 3.19) was calculated as a function of the setting angle and compared with the calculated intensities in Table 3.10. The best setting angle was found to be ~24“, according to Eq. (3.14) (Fig. 3.20). The 130 LUGLI, PEDRETTI, AND PEREGO Fig. E 'tha poi 0.1 mit‘ HO} ples 1‘ drama or per has be obserx almos X—r: of the HOP! config entati fact, i udmfi; .l_ ‘ - _ . .... - - - ‘.-'_r_‘_.....a-—— .—:-—-‘ ' _ _ ._ ., -. v .- ;' . . _ .._...._ ____-,..... - harm. Fig perpe Perk“ Fig. 1. Scanning electron microscope picture of (a) as-grown PA, (b) surface of cis-rich HOPA (a = 6.5), (c) HOPA (a = 7) isomerized at 200'C over 5 min, longitudinal section. Energy Levels: ‘11: Molecular Orbitals for Polyacetylene 1r Systems ofCH ‘ —(CH)§ _________________— ____________ ~(CH); —(CH)4— (CH); —{CH)‘-;3 Uniform Alternating 0—0 0—0 Bond Bond Order Order «2 ‘ # e g: E EGE4EV r-‘H: 4+ H e e E 4+ 4+ “4+ 3"” H 15: 2: :3; 4+ 4+ _-1-JV 4? "‘7? 4+ H I i H s a 4+ a .-_.~--_ Polyacetylene Conduction Via Solitons ENERGY (eV) Figure 5. (a) Absorption coefficient of trans-(CH); (x) before doping; (0) after doping to a fraction of a percent by exposure to Ast vapor. See ref 37. (b) In situ absorption curves for Pram-(CH), during electrochemical doping with 0104‘. The ap- plied cell voltages (relative to Li) and corresponding concentrations are as follows: curve 1, 2.2 V (y = 0); curve 2, 3.28 V (y =5 0.003); curve3, 3.37V(y~ 00065), curve4 3.46V(y~ 0.;012) curve 5, 3.57V(yz 0.027);curve6, 3.64V(y~ 0.047);curve7, 3.73 V (y a 0.078). See ref 24. Pam , Huger, awn CHMRH mes, e8, [$31200 ILOGU LOG Y IN c1-1(c104)‘Y ...
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