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The main chemical, spectroscopic and material research done in tetracyano quinoidal oligothiophenes in the last 30 years has been reviewed. Their use as semiconducting substrates in organic electronic and their versatility to act as multifunctional materials have been highlighted. This tutorial review has been paralleled by the description of the main findings provided by Raman spectroscopy, in particular, associated with the discovery of the intrinsic diradical properties inherent to the pro-aromatic character of the quinoidal arrangement. It turns out that the fascinating properties of these materials are the manifestation of the diradical fingerprint behind a rather unconventional electronic structure.
Casado et al. (2012) studied this question.