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Issue 11, 2002
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Photooxygenation of aromatic alkenes in zeolite nanocavities

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Abstract

Aromatic alkenes such as styrene (1), 1,1-diphenylethene (2), and cis- and trans-stilbenes (3), but not triphenylethene (4), formed their contact charge-transfer (CCT) complexes with O2 in solutions. In zeolite NaY, the CCT absorption band was observed only for 1 and 3. Irradiation of alkenes 1–4 included in the zeolite nanocavities under O2 produced benzaldehyde and benzophenone as the major oxygenation products. In particular, for 3 and 4, the photooxygenation competed with a photoelectrocyclic reaction, which subsequently yielded phenanthrenes as the exclusive photoproducts under O2 in solution. It is likely that the oxygenation products were produced through the alkene cation radicals and superoxide anion radical generated by excitation of the CCT complexes and/or photoinduced electron transfer from the excited alkenes to O2. YAG laser (266 nm) excitation of 1 included in the zeolite cavities under vacuum produced its alkene cation radical and the trapped electron, Na43+, both of which were quenched by O2. On the basis of the optimum structure for the guest molecules obtained by semi-empirical molecular orbital calculations (AM1), it is suggested that the photooxygenation reaction was regulated by the electrostatic interaction between the guest molecules and alkali-metal cations in the nanocavities as well as by the strong electrostatic field which stabilized the ion radical pairs generated.

Graphical abstract: Photooxygenation of aromatic alkenes in zeolite nanocavities

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Publication details

The article was received on 11 Jun 2002, accepted on 12 Aug 2002 and first published on 26 Sep 2002


Article type: Paper
DOI: 10.1039/B205672K
Citation: J. Chem. Soc., Perkin Trans. 2, 2002, 1894-1901
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    Photooxygenation of aromatic alkenes in zeolite nanocavities

    M. Kojima, M. Nakajoh, C. Matsubara and S. Hashimoto, J. Chem. Soc., Perkin Trans. 2, 2002, 1894
    DOI: 10.1039/B205672K

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