title: Alternating covalent bonding interactions in a one-dimensional chain of a phenalenyl-based singlet biradical molecule having Kekulé structures.
abstract: A novel naphthoquinoid singlet biradical (2a) stabilized by phenalenyl rings is prepared by a multistep procedure and is investigated in terms of covalent bonding interactions. The molecule 2a gives single crystals, in which a 1D chain is formed with a very short π-π contact at the overlapping phenalenyl rings. The unpaired electrons in 2a are involved in covalent bonding interactions not only within the molecule but also between the molecules in the 1D chain, and a linear conjugation is made of the alternating intra- and intermolecular covalent bonding interactions through conventional π-conjugation and multicenter bonding, respectively. The linear conjugation causes a lower-energy shift of the optical transition band in the crystal, but the transition energy is higher than that of the benzoquinoid singlet biradical (1a). This optical behavior and the magnetic susceptibility measurements reveal that the intermolecular covalent bonding interaction in the 1D chain of 2a is greater in strength than the intramolecular one, despite the fact that a fully conjugated Kekulé structure can be drawn for 2a.
authors.affiliation: Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan.
authors.forename: Akihiro
authors.initials: A
authors.lastname: Shimizu
authors.forename: Takashi
authors.initials: T
authors.lastname: Kubo
authors.forename: Mikio
authors.initials: M
authors.lastname: Uruichi
authors.forename: Kyuya
authors.initials: K
authors.lastname: Yakushi
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Nakano
authors.forename: Daisuke
authors.initials: D
authors.lastname: Shiomi
authors.forename: Kazunobu
authors.initials: K
authors.lastname: Sato
authors.forename: Takeji
authors.initials: T
authors.lastname: Takui
authors.forename: Yasukazu
authors.initials: Y
authors.lastname: Hirao
authors.forename: Kouzou
authors.initials: K
authors.lastname: Matsumoto
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kurata
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Morita
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Nakasuji