Novel thiophene-aryl co-oligomers for organic thin film transistors

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Abstract
A series of thiophene-aryl co-oligomers with phenyl-based central units, i.e. phenyl, biphenyl, fluorene and phenanthrene, were synthesized, and their optical properties and charge carrier transporting properties were characterized. The co-oligomers with biphenyl and phenanthrene units exhibited significantly improved thermal stability. Absorption measurements and electrochemical characterization revealed that all co-oligomers have broader band gap and lower HOMO levels than the corresponding thiophene oligomer, α,ω-dihexylsexithiophene (DHα6T). Introduction of biphenyl and phenanthrene units afforded co-oligomers with the broadest band gap and lowest HOMO levels in comparison with the counterparts of phenyl and fluorene central units. Depending on the structure of the central units, the field-effect mobility (μTFT) of the co-oligomers from top-contact thin film transistors is in the range of (1–6.7) × 10−2 cm2 V−1 s−1. The rigid and planar central unit is favorable for good device performance. Among the co-oligomers, 2,7-bis(5′-hexyl-2,2′-bithien-5-yl)phenanthrene (DH-TTPhTT) exhibits the highest μTFT of 6.7 × 10−2 cm2 V−1 s−1, comparable to that of DHα6T in the same device configuration and fabrication conditions.