Theoretical Studies of Quantum Amplified Isomerizations for Imaging Systems Involving Hexamethyl Dewar Benzene and Related Systems.
The ring-opening reactions of the radical cations of hexamethyl Dewar benzene (1) and Dewar benzene have been studied using density functional theory (DFT) and complete active-space self-consistent field (CASSCF) calculations. Compound 1 is known to undergo photoinitiated ring opening by a radical c...
| Publicado en: | Journal of the American Chemical Society Vol. 128; no. 24; pp. 7835 - 7846 |
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| Autores principales: | , , |
| Formato: | Artículo |
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American Chemical Society
6/21/2006
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| Acceso en línea: | Ver este registro en EBSCOhost |
| fields | @attributes: recordID: 1 pdfLink: plink: https://search.ebscohost.com/login.aspx?direct=true&db=hlh&AN=21461121&site=ehost-live header: @attributes: shortDbName: hlh uiTerm: 21461121 longDbName: Humanities International Complete uiTag: AN controlInfo: bkinfo: jinfo: jid: 00027863 ACS jtl: Journal of the American Chemical Society issn: 00027863 maglogo: N pubinfo: dt: 6/21/2006 vid: 128 iid: 24 pid: 997 pub: American Chemical Society artinfo: ui: 21461121 10.1021/ja060182i ppf: 7835 ppct: 11 formats: tig: atl: Theoretical Studies of Quantum Amplified Isomerizations for Imaging Systems Involving Hexamethyl Dewar Benzene and Related Systems. aug: au: Norton, Joseph E. Olson, Leif P. Houk, K. N. affil: Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569 Research & Development, Eastman Kodak Company, Rochester, New York 14650-2109 su: Ring-opening polymerization Isomerization Benzene Imaging systems Density functionals Cations Quantum chemistry sug: subj: Ring-opening polymerization Isomerization Benzene Imaging systems Density functionals Cations Quantum chemistry ab: The ring-opening reactions of the radical cations of hexamethyl Dewar benzene (1) and Dewar benzene have been studied using density functional theory (DFT) and complete active-space self-consistent field (CASSCF) calculations. Compound 1 is known to undergo photoinitiated ring opening by a radical cation chain mechanism, termed ‘quantum amplified isomerization’ (QAI), which is due to the high quantum yield. Why QAI is efficient for 1 but not other reactions is explained computationally. Two radical cation minima of 1 and transition states located near avoided crossings are identified. The state crossings are characterized by conical intersections corresponding to degeneracy between doublet surfaces. Ring opening occurs by formation of the radical cation followed by a decrease in the flap dihedral angle. A rate-limiting C transition state leads to a second stable radical cation with an elongated transannular CC bond and an increased flap dihedral. This structure proceeds through a conrotatory-like pathway of C symmetry to give the benzene radical cation. The role of electron transfer was investigated by evaluating oxidation of various systems using adiabatic ionization energies and electron affinities calculated from neutral and cation geometries. Electron-transfer theory was applied to 1 to investigate the limiting effects of back-electron transfer as it is related to the unusual stability of the two radical cations. Expected changes in optical properties between reactants and products of Dewar benzene compounds and other systems known to undergo QAI were characterized by computing frequency-dependent indices of refraction from isotropic polarizabilities. In particular, the reaction of 1 shows greater contrast in index of refraction than that of the Dewar benzene parent system. pubtype: Academic Journal doctype: Article src: R language: English refInfo: copyright: @attributes: flag: Y dt: @attributes: year: 2006 holdings: @attributes: islocal: N |
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