title: Dithienyl Acenedithiophenediones as New π-Extended Quinoidal Cores: Synthesis and Properties.
abstract: We have synthesized two isomeric pairs of benzo- and naphthodithiophenediones with two flanking thiophenes and characterized them by single-crystal X-ray analysis, cyclic voltammetry, steady-state optical electronic absorption and emission spectroscopies, transient absorption spectroscopy, and vibrational spectroscopies with in situ spectroelectrochemistry techniques, and then compared them with the thieno[3,2-b]thiophene-2,5-dione counterpart that we previously reported. The results show that the central acenedithiophenedione cores have quinoidal conjugation with closed-shell character. The π-extension of the quinoidal core raises (lowers) the HOMO (LUMO) energy levels of the triads, resulting in the drastic reduction of their energy gaps from approximately 2.0 eV to 1.1 eV. Owing to the electron-withdrawing nature of the carbonyl terminal group at the quinoidal core, the triads have low-lying LUMO energy levels ranging from -3.9 eV to -4.3 eV, and can be regarded as strong electron-acceptor building units. Interestingly, the pairs of structural isomers have similar electronic structures in both the neutral and charged states despite the different shapes (linear and angular) and/or symmetry (C2hand C2v) of the acenedithiophenedione cores.
authors.affiliation: Emergent Molecular Function Research Group, RIKEN Center for Emergent Matter Science, Wako, Saitama, 351-0198, Japan.|Current address: Department of Chemical and Environmental Engineering, Yale University, New Haven, Connecticut, 06511, USA.
authors.forename: Kohsuke
authors.initials: K
authors.lastname: Kawabata
authors.affiliation: Emergent Molecular Function Research Group, RIKEN Center for Emergent Matter Science, Wako, Saitama, 351-0198, Japan.|Current address: Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima, 739-8527, Japan.
authors.forename: Itaru
authors.initials: I
authors.lastname: Osaka
authors.affiliation: Emergent Molecular Function Research Group, RIKEN Center for Emergent Matter Science, Wako, Saitama, 351-0198, Japan.|Program in Physics and Functional Materials Science, Graduate School of Science and Engineering, Saitama University, Saitama, 338-8570, Japan.
authors.forename: Masanori
authors.initials: M
authors.lastname: Sawamoto
authors.affiliation: Department of Physical Chemistry, Faculty of Science, University of Málaga, Campus de Teatinos, s/n, Málaga, Spain.
authors.forename: José L
authors.initials: JL
authors.lastname: Zafra
authors.affiliation: Department of Physical Chemistry, Faculty of Science, University of Málaga, Campus de Teatinos, s/n, Málaga, Spain.
authors.forename: Paula
authors.initials: P
authors.lastname: Mayorga Burrezo
authors.affiliation: Department of Physical Chemistry, Faculty of Science, University of Málaga, Campus de Teatinos, s/n, Málaga, Spain.
authors.forename: Juan
authors.initials: J
authors.lastname: Casado
authors.affiliation: Emergent Molecular Function Research Group, RIKEN Center for Emergent Matter Science, Wako, Saitama, 351-0198, Japan.
authors.forename: Kazuo
authors.initials: K
authors.lastname: Takimiya
keywords: donor-acceptor systems; electronic structure; organic electronics; spectroscopic properties; thienoquinoid