Zero-field-splitting and π-electron spin densities in the lowest excited triplet state of oligothiophenes

M. Bennati, K. Németh, P. R. Surján, M. Mehring

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The electronic properties of thiophene oligomers (nT, n=2-8) have been investigated in the lowest excited triplet state. Theoretical calculations of the zero field splitting parameters and of the π-electron spin density have been performed and compared with previous experimental EPR results. The calculations are based on a simple π-electron (one-electron-per-site) model including electron-electron interaction at the extended Hubbard level. Optimized bond lengths result from making them self-consistent to the corresponding bond orders via Coulson's relationship. The calculated D values decrease from D=0.0959 cm-1 for n=2 to D=0.0597 cm-1 for n=8, in agreement with EPR data. The measured as well as the calculated E values are rather small. Furthermore, we found that ZFS parameters are affected by the torsion angles between the thiophene rings. The chain length dependence of D can be rationalized comparing π-electron spin density calculations and computed bond length distortions. These clearly indicate that the triplet excitation reaches a finite extension over about four thiophene rings.

Original languageEnglish
Pages (from-to)4441-4447
Number of pages7
JournalJournal of Chemical Physics
Issue number11
Publication statusPublished - Jan 1 1996


ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

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