Electronic states of emodin and its conjugate base: Synchrotron linear dichroism spectroscopy and quantum chemical calculations

Son Chi Nguyen, Bjarke Knud Vilster Hansen, Søren Vrønning Hoffmann, Jens Spanget-Larsen

Research output: Contribution to journalJournal articlepeer-review


The electronic transitions of emodin (1,3,8-trihydroxy-6-methyl-9,10-anthraquinone, E) and its conjugate base (3-oxido-6-methyl-1,8-dihydroxy-9,10-anthraquinone, Ecb) were investigated by UV-Vis linear dichroism (LD) spectroscopy on molecular samples aligned in stretched poly(vinylalcohol). The experiments in the UV region were performed with synchrotron radiation, thereby obtaining significantly improved signal to noise ratio compared with traditional technology. The LD spectra provided information on the polarization directions of the observed transitions, thereby leading to resolution of otherwise overlapping, differently polarized transitions. The investigation was supported by PCM-TD-DFT calculations; a mixed discrete/continuum solvation model was applied in the case of the strongly solvated Ecb anion. The calculations led to excellent agreement with the observed transitions, resulting in the assignment of at least 7 excited electronic states in the region 15000 - 50000 cm-1 for each species. A recent assignment of the absorption spectrum of E to a superposition of contributions from 9,10- and 1,10-anthraquinoid tautomeric forms was not supported by the results of the present investigation.
Original languageEnglish
JournalChemical Physics
Issue number1-3
Pages (from-to)167-174
Number of pages8
Publication statusPublished - 2008


  • Hydroxy-anthraquinones
  • Electronic transitions
  • Polarization directions
  • Transition moments
  • Time-Dependent Density Functional Theory (TD-DFT)
  • Solvation models

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