title: Two-dimensional π-expanded quinoidal terthiophenes terminated with dicyanomethylenes as n-type semiconductors for high-performance organic thin-film transistors.
abstract: Quinoidal oligothiophenes (QOT), as classical n-type semiconductors, have been well-known for a long time but with non-optimal semiconducting properties. We report here the design and selective synthesis of new two-dimensional (2D) π-expanded quinoidal terthiophenes, 2DQTTs, with proximal (2DQTT-i) and distal (2DQTT-o) regiochemistry for high-performance n-channel organic thin-film transistors (n-OTFTs) featuring high electron mobility, solution processability, and ambient stability. The elegant combination of thieno[3,4-b]thiophene [TT, donor (D)] and 5-alkyl-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione [TPD, acceptor (A)] units with relatively large π-surface endows these 2DQTTs with distinctive 2D structural characteristics and flat configuration stabilized by weak intramolecular S-O/S weak interactions. Furthermore, the A-D-A-D-A electronic structure maintains an adequately low LUMO energy level. These 2DQTTs are shown to exhibit outstanding semiconducting properties with electron mobilities of up to 3.0 cm(2) V(-1) s(-1) and on/off ratios of up to 10(6) (2DQTT-o) in ambient- and solution-processed OTFTs. Investigations on thin-film morphology reveal that the microstructure of 2DQTTs is highly dependent on the orientation of the fused thiophene subunits, leading to differences in electron mobilities of 1 order of magnitude. X-ray diffraction studies in particular reveal increased crystallinity, crystalline coherence, and orientational order in 2DQTT-o compared to 2DQTT-i, which accounts for the superior electron transport property of 2DQTT-o.
authors.affiliation: Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences , Beijing 100190, P. R. China.
authors.forename: Cheng
authors.initials: C
authors.lastname: Zhang
authors.forename: Yaping
authors.initials: Y
authors.lastname: Zang
authors.forename: Eliot
authors.initials: E
authors.lastname: Gann
authors.forename: Christopher R
authors.initials: CR
authors.lastname: McNeill
authors.forename: Xiaozhang
authors.initials: X
authors.lastname: Zhu
authors.forename: Chong-An
authors.initials: CA
authors.lastname: Di
authors.forename: Daoben
authors.initials: D
authors.lastname: Zhu