title: Quinoidal oligothiophenes: towards biradical ground-state species.
abstract: 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 oligomer 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.
authors: Departamento de Química Física, Universidad de Málaga, Campus de Teatinos s/n, Málaga 29071, Spain.
authors: Rocío
authors: R
authors: Ponce Ortiz
authors: Juan
authors: J
authors: Casado
authors: Sandra
authors: S
authors: Rodríguez González
authors: Víctor
authors: V
authors: Hernández
authors: Juan T
authors: JT
authors: López Navarrete
authors: Pedro M
authors: PM
authors: Viruela
authors: Enrique
authors: E
authors: Ortí
authors: Kazuo
authors: K
authors: Takimiya
authors: Tetsuo
authors: T
authors: Otsubo