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Issue 12, 2003
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Isomerization around a C[double bond, length as m-dash]N double bond and a C[double bond, length as m-dash]C double bond with a nitrogen atom attached: thermal and photochemical routes

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Abstract

The Longuet-Higgins phase change theorem is used to show that, in certain photochemical reactions, a single product is formed via a conical intersection. The cistrans isomerization around the double bond in the formaldiminium cation and vinylamine are shown to be possible examples. This situation is expected to hold when the reactant can be converted to the product via two distinct elementary ground-state reactions that differ in their phase characteristics. In one, the total electronic wavefunction preserves its phase in the reaction; in the other, the phase is inverted. Under these conditions, a conical intersection necessarily connects the first electronic excited state to the ground state, leading to rapid photochemical isomerization following optical excitation. Detailed quantum chemical calculations support the proposed model. The possibility that a similar mechanism is operative in other systems, among them the rapid photo-induced cistrans isomerization of longer protonated Schiff bases (the parent chromophores of rhodopsins), is discussed.

Graphical abstract: Isomerization around a C [[double bond, length as m-dash]] N double bond and a C [[double bond, length as m-dash]] C double bond with a nitrogen atom attached: thermal and photochemical routes

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Publication details

The article was received on 30 May 2003, accepted on 26 Jun 2003 and first published on 15 Jul 2003


Article type: Paper
DOI: 10.1039/B306137J
Citation: Photochem. Photobiol. Sci., 2003,2, 1256-1263
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    Isomerization around a C[double bond, length as m-dash]N double bond and a C[double bond, length as m-dash]C double bond with a nitrogen atom attached: thermal and photochemical routes

    S. Zilberg and Y. Haas, Photochem. Photobiol. Sci., 2003, 2, 1256
    DOI: 10.1039/B306137J

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