Isomerization Through Conical Intersections

Department of Chemistry, University of Illinois, Urbana-Champaign, Urbana, Illinois, United States
Annual Review of Physical Chemistry (Impact Factor: 16.84). 02/2007; 58(1):613-34. DOI: 10.1146/annurev.physchem.57.032905.104612
Source: PubMed


The standard model for photoinduced cis-trans isomerization about carbon double bonds is framed in terms of two electronic states and a one-dimensional reaction coordinate. We review recent work that suggests that a minimal picture of the reaction mechanism requires the consideration of at least two molecular coordinates and three electronic states. In this chapter, we emphasize the role of conical intersections and charge transfer in the photoisomerization mechanism.

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    • "This simple model for non-radiative decay, originally due to Jortner [55], is now widely accepted and supported by many theoretical and experimental studies [54] [56] [57], even though it is not applicable to all systems [58]. The energy gap law approximation seems here somehow justified by the fact that the conical intersection lies very close to the minimum of the excited state and to the maximum of the ground state PES, therefore it can be considered as a " minimum energy " CI, i. e. the centre of a broad region where population transfer may occur [21]. Is is worth mentioning that at least other two conical intersections with the ground state are present on the S 1 PES, but only the minimum energy one modelled here is likely to be accessible through n, π * excitation, whilst the others become important when reaching the S 1 state from higher excited states ( " hot " isomerization) [40] [41] [44] [51] [42]. "
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