|dc.description.abstract||Several series of aromatic and quinoidal compounds, such as oligothiophenes (Scheme 1), oligophenylene-vinylenes, oligoperylenes (oligophenyls) and graphene nanoribbon derivatives, are studied in the common context of the capability to stabilize diradical structures. [1,2,3,4]. In this work, we try to clarify how several driving forces (i.e., thermodynamic and entropic) are responsible for the generation of diradical and diradicaloid structures. A combination of different types of molecular spectroscopies (i.e., electronic absorption, electronic emission, excited state absorption, vibrational Raman, vibrational infrared, etc.) as well as hybridized with thermal and pressure-dependent techniques are shown to provide important information about the origin of the formation and stabilization of diradicals. From a conceptual point of view, we analyze these properties in the context of the oligomer approach which is the study of the evolution of these spectroscopic quantities as a function of the oligomer size.
 P. Mayorga Burrezo, J.L. Zafra, J. Casado. Angew. Chem. Int. Ed., 2017, 56, 2250.
 J. Casado, R. Ponce Ortiz, J. T. Lopez Navarrete, Chem. Soc. Rev. 2012, 41, 5672.
 P. Mayorga Burrezo, X. Zhu, S. F. Zhu, Q. Yan, J. T. Lopez Navarrete, H. Tsuji, E. Nakamura, J. Casado, J. Am. Chem. Soc. 2015, 137, 3834-3843.
 J. Casado, Para-quinodimethanes: A unified review of the quinoidal-versus-aromatic competition and its implications. Top. Curr. Chem. 2017, 375, 73.||en_US