title: Terazulene Isomers: Polarity Change of OFETs through Molecular Orbital Distribution Contrast.
abstract: Intermolecular orbital coupling is fundamentally important to organic semiconductor performance. Recently, we reported that 2,6':2',6″-terazulene (TAz1) exhibited excellent performance as an n-type organic field-effect transistor (OFET) via molecular orbital distribution control. To validate and develop this concept, here we present three other terazulene regioisomers, which have three azulene molecules connected at the 2- or 6-position along the long axis of the azulene, thus constructing a linear expanded π-conjugation system: 2,2':6',2″-terazulene (TAz2), 2,2':6',6″-terazulene (TAz3), and 6,2':6',6″-terazulene (TAz4). TAz2 and TAz3 exhibit ambipolar characteristics; TAz4 exhibits clear n-type transistor behavior as an OFET. The lowest unoccupied molecular orbitals (LUMOs) of all terazulenes are fully delocalized over the entire molecule. In contrast, the highest occupied molecular orbitals (HOMOs) of TAz2 and TAz3 are delocalized over the 2,2'-biazulene units; the HOMOs of TAz4 are localized at one end of the azulene unit. These findings confirm that terazulene isomers which are simple hydrocarbon compounds are versatile materials with a tunable-polarity FET characteristic that depends on the direction of the azulene unit and the related contrast of the molecular orbital distribution in the terazulene backbone.
authors: Graduate School of Science and Engineering, Yamagata University , 4-3-16 Jonan, Yonezawa, Yamagata 992-8510, Japan.
authors: Yuji
authors: Y
authors: Yamaguchi
authors: Graduate School of Science and Engineering, Yamagata University , 4-3-16 Jonan, Yonezawa, Yamagata 992-8510, Japan.
authors: Maki
authors: M
authors: Takubo
authors: Graduate School of Science and Engineering, Yamagata University , 4-3-16 Jonan, Yonezawa, Yamagata 992-8510, Japan.
authors: Keisuke
authors: K
authors: Ogawa
authors: Graduate School of Science and Engineering, Yamagata University , 4-3-16 Jonan, Yonezawa, Yamagata 992-8510, Japan.
authors: Ken-Ichi
authors: K
authors: Nakayama
authors: Japan Synchrotron Radiation Research Institute (JASRI), SPring-8 , 1-1-1 Kouto, Sayo, Hyogo 679-5198, Japan.
authors: Tomoyuki
authors: T
authors: Koganezawa
authors: Graduate School of Science and Engineering, Yamagata University , 4-3-16 Jonan, Yonezawa, Yamagata 992-8510, Japan.
authors: Hiroshi
authors: H
authors: Katagiri