DUGi

A valence bond description of the prefulvene extended conical intersection seam of benzene

http://dugi.udg.edu/item/http:@@@@hdl.handle.net@@10256@@11478

The permutational isomers of the prefulvene-like minimum energy conical intersection lie on an extended conical intersection seam, where they are connected by higher symmetry structures. Here, we present a VB analysis of the electronic states involved along this extended seam. The VB method produces a spin-exchange density (ie. a bonding pattern) that provides the basis to assign resonance structures to the states. The results show that in the high symmetry region of the seam, the character of the states is dominated by the positive and negative combination of the Kekulé structures, (A+B) and (A-B). The low energy parts of the seam, comprised of lower symmetry conical intersection structures, are stabilized by mixing with the Dewar resonance structures. This feature is responsible for the stability of the benzvalene-like conical intersections. The validity of the VB model is confirmed by calculating the branching space vectors at this level of theory, which are in good agreement with the CASSCF calculated vectors. The VB analysis has also allowed us to complete our picture of the global seam, since it has provided the clue to locate a conical intersection saddle point that interconverts two minima of the prefulvene conical intersection where the carbon bent out of the plane is inverted and rotated by 60°. This saddle point has a benzvalene-like geometry, in agreement with the VB picture

We thank Q. Li for help with the CASSCF computations. This work has been supported by grants CTQ2011-26573 from the Spanish Ministerio de Economia y Competividad, SGR0528 from the Catalan Agencia de Gestio d’Ajuts Universitaris i de Recerca (AGAUR), UNGI08-4E-003 from the Spanish Ministerio de Ciencia e Innovacion and the FEDER fund (European Fund for Regional Development), and the Xarxa de Referencia en Quimica Teorica i Computacional de Catalunya from AGAUR. M.A.R. acknowledges a travel grant from AGAUR (2010PIV00086)

info:eu-repo/grantAgreement/MICINN//CTQ2011-26573/ES/MODELIZACION QUIMICO CUANTICA DE FOTOQUIMICA Y TRANSFERENCIA ELECTRONICA: SISTEMAS GRANDES, EFECTOS COLECTIVOS Y CONTROL OPTICO/

American Chemical Society (ACS)