Torsional potentials and full-dimensional simulation of electronic absorption spectra of para-Phenylenevinylene oligomers using semiempirical hamiltonians

Vladimír LukeŠ, Roland Šolc, Mario Barbatti, Hans Lischka, Harald Friedrich Kauffmann

Research output: Contribution to journalArticle

10 Scopus citations

Abstract

A systematic study of torsional potential curves in electronic ground state based on second-order MøllerPlesset energy (MP2), density functional theory (DFT), and Austin mode 1 (AM1) methods is presented for para-phenylenevinylene oligomers constructed from two to four aromatic rings. The semiempirical AM1 approach gives the correct location of potential energy minima in comparison with the reference MP2 calculations and literature data. However, the semiempirical AM1 energy barriers at perpendicular orientation are ca. 30% smaller than the MP2 ones. The DFT calculations indicate optimal planar structures and the barriers are three times higher than MP2 values. Excited-state potential energy curves evaluated from vertical excitations at the time-dependent density functional theory (TD-DFT) and ab initio CI levels exhibit much steeper increase of values in the vicinity of perpendicular orientation than in the semiempirical Zerner's intermediate neglect of differential overlap (ZINDO) and ab initio RI-CC2 cases. The effects of vibrational motion of phenylene rings on the torsional broadening of absorption spectra were estimated from semi-classical molecular dynamics simulations and harmonic oscillator sampling. The simulated spectra agree well with the experiment and allow estimating the conformer distribution of the molecules.

Original languageEnglish
Pages (from-to)249-263
Number of pages15
JournalJournal of Theoretical and Computational Chemistry
Volume9
Issue number1
DOIs
StatePublished - Feb 2010

Keywords

  • Ab initio
  • PPV
  • Potential energy surface
  • RI-CC2
  • Stilbene

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