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A theoretical study of the lowest electronic states of azobenzene: the role of torsion coordinate in the cis-trans photoisomerization

Published inTheoretical Chemistry accounts, vol. 111, no. 2-6, p. 363-372
Publication date2004
Abstract

In the present paper we report the results of a multiconfigurational computational study on potentialenergy curves of azobenzene along the NN twisting to clarify the role of this coordinate in the decay of the S2(ππ*) and S1(nπ*) states. We have found that there is a singlet state, S3 at the trans geometry, on the basis of the doubly excited configuration n2π*2, that has a deep minimum at about 90°of twisting, where it is the lowest excited singlet state. The existence of this state provides an explanation for the short lifetime of S2(ππ*) and for the wavelength-dependence of azobenzene photochemistry. We have characterized the S1(nπ*) state by calculating its vibrational frequencies, which are found to correspond to the recently observed transient Raman spectrum. We have also computed the potential-energy curve for the triplet T1(nπ*) at the density functional theory B3LYP level, which indicates that in this state the isomerization occurs along the twisting coordinate.

Keywords
  • Azobenzene
  • Excited electronic states
  • Photoisomerization
  • Multiconfigurational wave function methods
Research group
Citation (ISO format)
GAGLIARDI, Laura et al. A theoretical study of the lowest electronic states of azobenzene: the role of torsion coordinate in the cis-trans photoisomerization. In: Theoretical Chemistry accounts, 2004, vol. 111, n° 2-6, p. 363–372. doi: 10.1007/s00214-003-0528-1
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ISSN of the journal1432-2234
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