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Quinoidal Oligothiophenes: Towards Biradical Ground‐State Species
Author(s) -
Ponce Ortiz Rocío,
Casado Juan,
Rodríguez González Sandra,
Hernández Víctor,
López Navarrete Juan T.,
Viruela Pedro M.,
Ortí Enrique,
Takimiya Kazuo,
Otsubo Tetsuo
Publication year - 2010
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200902037
Subject(s) - ground state , singlet state , triplet state , chemistry , excited state , dimer , raman spectroscopy , density functional theory , conjugated system , diradical , delocalized electron , oligomer , singlet fission , electronic structure , photochemistry , crystallography , chemical physics , computational chemistry , atomic physics , molecule , polymer , polymer chemistry , organic chemistry , physics , optics
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.