Theoretical investigation of excited states of oligothiophene anions


Creative Commons License

Alkan F. , Salzner U.

JOURNAL OF PHYSICAL CHEMISTRY A, vol.112, no.27, pp.6053-6058, 2008 (Journal Indexed in SCI) identifier identifier identifier

  • Publication Type: Article / Article
  • Volume: 112 Issue: 27
  • Publication Date: 2008
  • Doi Number: 10.1021/jp711135e
  • Title of Journal : JOURNAL OF PHYSICAL CHEMISTRY A
  • Page Numbers: pp.6053-6058

Abstract

Electron-hole symmetry upon p- and n-doping of conducting organic polymers is rationalized with Mickel theory by the presence of symmetrically located intragap states. Since density functional theory (DFT) predicts very different geometries and energy level diagrams for conjugated pi-systems than seiniernpirical methods, it is an interesting question whether DFT confirms the existence of electron-hole symmetry predicted at the Mickel level. To answer this question, geometries of oligothiophene anions with 5-19 rings were optimized and their UV/vis spectra were calculated with time-dependent DFT. Although DFT does not produce symmetrically placed sub-band energy levels, spectra of cations and anions are almost identical. The similarity in transition energies and oscillator strengths of anions and cations can be explained by the fact that the single sub-band energy level of cations lies above the valence band by the same amount of energy as the single sub-band level of anions lies below the conduction band. This and the resemblance of the energy level spacings in valence bands of cations to those in conduction bands of anions give rise to peaks with equal energies and oscillator strengths.