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Theoretica chimica acta

, Volume 33, Issue 4, pp 307–321 | Cite as

Geometries of excited states of small polyenes

  • Jacqueline Langlet
  • Jean -Paul Malrieu
Commentationes

Abstract

The behaviour under rotations around one or two double bonds of the first (π) singlet and triplet states of small conjugated molecules have been investigated using localized Molecular Orbitals. The results obtained with a (σ + π) excitonic matrix are in agreement with previous results obtained with delocalized Molecular Orbitals: 1. the rotation around one double bond is more favorable than two symmetrical rotations around two double bonds, 2. the rotation occurs around one inner double bond rather than around a terminal bond. This work shows the role played by the (σ — π) mixing in the stabilization of the twisted conformations. A further optimization of the bond lengths in the excited singlet and triplet states of butadiene shows that the preferred geometry is a non symmetrical twisted geometry with different lengths for the two C=C double bonds. This “symmetry instability” suggests to introduce a vibronic wave-function in which the various locally excited electronic wave functions are multiplied by different vibrational wave functions corresponding to local deformations of the nuclear skeleton.

Key words

Butadiene Hexatriene 

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Copyright information

© Springer-Verlag 1974

Authors and Affiliations

  • Jacqueline Langlet
    • 1
  • Jean -Paul Malrieu
    • 1
  1. 1.Institut de Biologie Physico-ChimiqueLaboratoire de Biochimie Théorique associé au C.N.R.S.Paris

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