Quinoidal oligothiophenes: Towards biradical ground-state species

Rocío Ponce Ortiz, Juan Casado, Sandra Rodríguez González, Víctor Hernández, Juan T. López Navarrete, Pedro M. Viruela, Enrique Ortí, Kazuo Takimiya, Tetsuo Otsubo

Research output: Contribution to journalArticlepeer-review

73 Citations (Scopus)


A family of quinoidal oligothiophenes, from the dimer to the hexamer, with fused bis(butoxymethyl)cyclopentane groups has been extensively investigated by means of electronic and vibrational spectroscopy, electrochemical measurements, and density functional calculations. The latter predict that the electronic ground state always corresponds to a singlet state and that, for the longest oligomers, this state has biradical character that increases with increasing oli-gomer length. The shortest oligomers display closed-shell quinoidal structures. Calculations also predict the existence of very low energy excited triplet states that can be populated at room temperature. Aromatization of the conjugated carbon backbone is the driving force that determines the increasing biradical character of the ground state and the appearance of low-lying triplet states. UV/Vis, Raman, IR, and electrochemical experiments support the aromatic biradical structures predicted for the ground state of the longest oligomers and reveal that population of the low-lying triplet state accounts for the magnetic activity displayed by these compounds.

Original languageEnglish
Pages (from-to)470-484
Number of pages15
JournalChemistry - A European Journal
Issue number2
Publication statusPublished - 2010 Jan 11


  • Biradicals
  • Density functional calculations
  • Electronic structure
  • Oligothiophenes
  • Vibrational spectroscopy


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