Oligothiophene quinoids containing a benzo[ c ]thiophene unit for the stabilization of the quinoidal electronic structure

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Vol. 6; no. 28; pp. 7493 - 7500
• Main Authors: Yamamoto, Keitaro, Ie, Yutaka, Nitani, Masashi, Tohnai, Norimitsu, Kakiuchi, Fumitoshi, Zhang, Ke, Pisula, Wojciech, Asadi, Kamal, Blom, Paul W. M., Aso, Yoshio
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 2018
• Subjects: Benzene; Benzothiophene; Crystal structure; Electron transport; Electronic structure; Electrons; Energy levels; Field effect transistors; Fluorination; Molecular chains; Molecular orbitals; Molecular structure; N-type semiconductors; Semiconductor devices; Single crystals; Stabilization; Thiophenes; X-ray diffraction
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/C8TC01802B

Bis(dicyanomethylene)-substituted quinoidal π-conjugated systems possess a high electron-accepting nature and thus have been extensively investigated for application as n-type semiconductors. We focus on the utilization of benzene-annelation for the stabilization of the quinoidal electronic structure against the biradicaloid structure by designing quinoidal thiophenes 3-mer ( BTQ ) and 6-mer ( BTQ-6 ) that have benzo[ c ]thiophene units. We also develop quinoidal oligothiophenes ( BTQ-F ) consisting of both benzo[ c ]thiophene and fluorinated thiophene units. The influence of benzo[ c ]thiophene on the quinoidal electronic structure is investigated by theoretical studies and property measurements. The molecular structure of BTQ-F is unambiguously confirmed through single-crystal X-ray diffraction. Analyses of cyclic voltammetry reveal that the lowest unoccupied molecular orbital energy levels of these compounds lie below −4.0 eV, leading to good electron-transporting characteristics even under ambient conditions in organic field-effect transistors (OFETs). Due to an increased highest occupied molecular orbital energy level, ambipolar transport is observed in BTQ-6 , indicating the versatility of quinoidal π-conjugated systems incorporating benzo[ c ]thiophene.