para‐Phenylene‐Bridged Spirobi(triarylamine) Dimer with Four Perpendicularly Linked Redox‐Active π Systems |
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Authors: | Dr. Akihiro Ito Kazuhira Hata Kensuke Kawamoto Dr. Yasukazu Hirao Prof. Dr. Kazuyoshi Tanaka Dr. Motoo Shiro Dr. Ko Furukawa Prof. Dr. Tatsuhisa Kato |
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Affiliation: | 1. Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Nishikyo‐ku, Kyoto 615‐8510 (Japan), Fax: (+81)?75‐383‐2556;2. Present address: Department of Chemistry, Graduate School of Science, Osaka University, 1‐1 Machikaneyamacho, Toyonaka, Osaka 560‐0043 (Japan);3. X‐ray Research Laboratory, Rigaku Corporation, Matsubaracho 3‐9‐12, Akishima, Tokyo 196‐8666 (Japan);4. Institute for Molecular Science, Myodaiji, Okazaki 444‐8585 (Japan);5. Department of Chemistry, Josai University, 1‐1 Keyakidai, Sakado, Saitama 350‐0295 (Japan);6. Present address: Institute for the Promotion of Excellence in Higher Education, Kyoto University, Yoshida‐Nihonmatsu, Sakyo‐ku, Kyoto 606‐8501 (Japan) |
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Abstract: | para‐Phenylene‐bridged spirobi(triarylamine) dimer 2 , in which π conjugation through four redox‐active triarylamine subunits is partially segregated by the unique perpendicular conformation, was prepared and characterized by structural, electrochemical, and spectroscopic methods. Quantum chemical calculations (DFT and CASSCF) predicted that the frontier molecular orbitals of 2 are virtually fourfold degenerate, so that the oxidized states of 2 can give intriguing electronic and magnetic properties. In fact, the continuous‐wave ESR spectroscopy of radical cation 2 .+ showed that the unpaired electron was trapped in the inner two redox‐active dianisylamine subunits, and moreover was fully delocalized over them. Magnetic susceptibility measurements and pulsed ESR spectroscopy of the isolated salts of 2 , which can be prepared by treatment with SbCl5, revealed that the generated tetracation 2 4+ decomposed mainly into a mixture of 1) a decomposed tetra(radical cation) consisting of a tri(radical cation) moiety and a trianisylamine radical cation moiety (≈75 %) and 2) a diamagnetic quinoid dication in a tetraanisyl‐p‐phenylendiamine moiety and two trianisylamine radical cation moieties (≈25 %). Furthermore, the spin‐quartet state of the tri(radical cation) moiety in the decomposed tetra(radical cation) was found to be in the ground state lying 30 cal mol?1 below the competing spin‐doublet state. |
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Keywords: | arylamines intervalent compounds organic radicals radical ions spiro compounds |
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