cis peak as probe to investigate the molecular structure. Application to the rotational isomerism of 2,5-diphenylethenyl(hetero)arenes

Ivan Baraldi, Enrico Benassi, Anna Spalletti

Research output: Contribution to journalArticle

9 Citations (Scopus)

Abstract

A combined theoretical and experimental study on rotational isomerism, excited electronic states structure and cis peak effect is presented for flexible conjugated molecules containing two styryl groups coupled by an unsaturated pentatomic ring (furan, thiophene, pyrrole, cyclopentadiene). The several conformers of the ground electronic state have been investigated by means of Hartree-Fock ab initio methods and density functional theory. The electronic spectra have been calculated with the CS INDO CI approach in the singly-excited scheme and in that involving multiple excitations. By means of the theoretical findings and of the analysis of the cis peak of UV-vis absorption spectra, it is shown that the stable rotamer of these molecules is the trans-trans conformer. The trans-cis conformer may have also a relative presence at room temperature, mainly in 2,5-(PhE)2P. The cis-cis form is the most destabilized. The importance of the doubly excited electronic configurations in the theoretical treatments of the excited electronic states, in particular of the one responsible for the cis peak, the 21A1 state, is shown. Some useful considerations on the S1 → Sn transient spectra are reported.

Original languageEnglish
Pages (from-to)543-549
Number of pages7
JournalSpectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy
Volume71
Issue number2
DOIs
Publication statusPublished - 15 Nov 2008
Externally publishedYes

Fingerprint

Electronic states
Molecular structure
molecular structure
probes
electronics
Cyclopentanes
Thiophenes
Pyrroles
Molecules
Thiophene
Density functional theory
Absorption spectra
furans
pyrroles
thiophenes
electronic spectra
molecules
density functional theory
absorption spectra
rings

Keywords

  • Ab initio calculations
  • cis peak
  • Conjugated molecules
  • CS INDO CI
  • Rotational isomerism

ASJC Scopus subject areas

  • Analytical Chemistry
  • Spectroscopy
  • Instrumentation
  • Atomic and Molecular Physics, and Optics

Cite this

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AU - Baraldi, Ivan

AU - Benassi, Enrico

AU - Spalletti, Anna

PY - 2008/11/15

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N2 - A combined theoretical and experimental study on rotational isomerism, excited electronic states structure and cis peak effect is presented for flexible conjugated molecules containing two styryl groups coupled by an unsaturated pentatomic ring (furan, thiophene, pyrrole, cyclopentadiene). The several conformers of the ground electronic state have been investigated by means of Hartree-Fock ab initio methods and density functional theory. The electronic spectra have been calculated with the CS INDO CI approach in the singly-excited scheme and in that involving multiple excitations. By means of the theoretical findings and of the analysis of the cis peak of UV-vis absorption spectra, it is shown that the stable rotamer of these molecules is the trans-trans conformer. The trans-cis conformer may have also a relative presence at room temperature, mainly in 2,5-(PhE)2P. The cis-cis form is the most destabilized. The importance of the doubly excited electronic configurations in the theoretical treatments of the excited electronic states, in particular of the one responsible for the cis peak, the 21A1 state, is shown. Some useful considerations on the S1 → Sn transient spectra are reported.

AB - A combined theoretical and experimental study on rotational isomerism, excited electronic states structure and cis peak effect is presented for flexible conjugated molecules containing two styryl groups coupled by an unsaturated pentatomic ring (furan, thiophene, pyrrole, cyclopentadiene). The several conformers of the ground electronic state have been investigated by means of Hartree-Fock ab initio methods and density functional theory. The electronic spectra have been calculated with the CS INDO CI approach in the singly-excited scheme and in that involving multiple excitations. By means of the theoretical findings and of the analysis of the cis peak of UV-vis absorption spectra, it is shown that the stable rotamer of these molecules is the trans-trans conformer. The trans-cis conformer may have also a relative presence at room temperature, mainly in 2,5-(PhE)2P. The cis-cis form is the most destabilized. The importance of the doubly excited electronic configurations in the theoretical treatments of the excited electronic states, in particular of the one responsible for the cis peak, the 21A1 state, is shown. Some useful considerations on the S1 → Sn transient spectra are reported.

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