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Materials 2010, 3(3), 2037-2052; doi:10.3390/ma3032037

Synthesis and Properties of Octithiophene Dication Sterically Segregated by Annelation with Bicyclo[2.2.2]octene Units

Department of Chemistry, Graduate School of Science and Engineering, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan
Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
Present address: Mitsubishi Chemical Corporation, 1000, Kamoshida-cho Aoba-ku, Yokohama, Kanagawa 227-0033, Japan.
Present address: Department of Environmental and Biological Chemistry, Fukui University of Technology, Gakuen, Fukui 910-8505, Japan.
Author to whom correspondence should be addressed.
Received: 29 January 2010 / Revised: 13 February 2010 / Accepted: 16 March 2010 / Published: 19 March 2010
(This article belongs to the Special Issue Conjugated Oligomers)
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Octithiophene sterically segregated by annelation with bicyclo[2.2.2]octene (BCO) units was synthesized to study the unimolecular properties of longer oligothiophene dications. For the preparation of such longer oligomers, a new route for the synthesis of the monomer annelated with BCO unit at the 3,4-positions of thiophene ring was developed. Attempted synthesis of octithiophene 1(8T) fully annelated with BCO units was hampered by low solubility of the product, and octithiophene 2(8T) having octyl groups instead of the BCO units at the second rings from the both ends of 1(8T) was synthesized to solve the solubility problem. Neutral 2(8T) has a lower planarity due to the steric repulsion between the octyl substituents and the neighboring thiophene units. However, dication 2(8T)2+, which was obtained as a stable salt by chemical two-electron oxidation with NO+SbF6-, has a planar quinoid structure, as judged from a linear correlation between the inverse chain length and the absorption energy for 1(nT)2+ (n = 3,4,6) and 2(8T)2+. Based on the comparison with the calculated absorption spectra and the result of ESR inactive properties, 2(8T)2+ appears to have a singlet ground state with open-shell biradical character rather than a closed-shell singlet structure.
Keywords: bipolaron; dication; oligothiophene; polaron pair; singlet biradical bipolaron; dication; oligothiophene; polaron pair; singlet biradical
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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Nishinaga, T.; Yamazaki, D.; Tateno, M.; Iyoda, M.; Komatsu, K. Synthesis and Properties of Octithiophene Dication Sterically Segregated by Annelation with Bicyclo[2.2.2]octene Units. Materials 2010, 3, 2037-2052.

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