Many chemists have attempted syntheses of extended π-electron network molecules because of the widespread interest in the chemistry, physics and materials science of such molecules and their potential applications. In particular, extended phenacene molecules, consisting of coplanar fused benzene rings in a repeating W-shaped pattern have attracted much attention because field-effect transistors (FETs) using phenacene molecules show promisingly high performance. Until now, the most extended phenacene molecule available for transistors was [8]phenacene, with eight benzene rings, which showed very high FET performance. Here, we report the synthesis of a more extended phenacene molecule, [9]phenacene, with nine benzene rings. Our synthesis produced enough [9]phenacene to allow the characterization of its crystal and electronic structures, as well as the fabrication of FETs using thin-film and single-crystal [9]phenacene. The latter showed a field-effect mobility as high as 18 cm2 V−1 s−1, which is the highest mobility realized so far in organic single-crystal FETs.

Field-effect transistors (FETs) were fabricated with a thin film of 3,10-ditetradecylpicene, picene-(C14H29)2, formed using either a thermal deposition or a deposition from solution (solution process). All FETs showed p-channel normally-off characteristics. The field-effect mobility, μ, in a picene-(C14H29)2 thin-film FET with PbZr0.52Ti0.48O3 (PZT) gate dielectric reached ~21 cm2 V−1 s−1, which is the highest μ value recorded for organic thin-film FETs; the average μ value (<μ>) evaluated from twelve FET devices was 14(4) cm2 V−1 s−1. The <μ> values for picene-(C14H29)2 thin-film FETs with other gate dielectrics such as SiO2, Ta2O5, ZrO2 and HfO2 were greater than 5 cm2 V−1 s−1, and the lowest absolute threshold voltage, |Vth|, (5.2 V) was recorded with a PZT gate dielectric; the average |Vth| for PZT gate dielectric is 7(1) V. The solution-processed picene-(C14H29)2 FET was also fabricated with an SiO2 gate dielectric, yielding μ = 3.4 × 10−2 cm2 V−1 s−1. These results verify the effectiveness of picene-(C14H29)2 for electronics applications.

The characteristics of field‐effect transistors (FETs) fabricated from thin films and single crystals of phenacene molecules are fully reported in this review together with the electronic and crystal structures of phenacenes. Phenacene molecules possess a low HOMO level and a wide band gap. The highest mobility observed in the phenacene thin‐film FETs is 7.4 cm2 V–1 s–1 for [6]phenacene, and in single‐crystal FETs the highest value is 6.3 cm2 V–1 s–1 for [7]phenacene. The phenacene thin‐film FETs show O2‐sensing properties unlike their single‐crystal FETs. The bias‐stress effect is fully investigated for phenacene single‐crystal FETs. Furthermore, the low‐voltage operation of phenacene single‐crystal FETs with electric‐double‐layer (EDL) capacitors is reported. The temperature dependence of phenacene single‐crystal FETs is reported to clarify the transport mechanism, which is suggestive of band‐like transport.

A new phenacene-type molecule, [8]phenacene, which is an extended zigzag chain of coplanar fused benzene rings, has been synthesised for use in an organic field-effect transistor (FET). The molecule consists of a phenacene core of eight benzene rings, which has a lengthy π-conjugated system. The structure was verified by elemental analysis, solid-state NMR, X-ray diffraction (XRD) pattern, absorption spectrum and photoelectron yield spectroscopy (PYS). This type of molecule is quite interesting, not only as pure chemistry but also for its potential electronics applications. Here we report the physical properties of [8]phenacene and its FET application. An [8]phenacene thin-film FET fabricated with an SiO2 gate dielectric showed clear p-channel characteristics. The highest μ achieved in an [8]phenacene thin-film FET with an SiO2 gate dielectric is 1.74 cm2 V−1 s−1, demonstrating excellent FET characteristics; the average μ was evaluated as 1.2(3) cm2 V−1 s−1. The μ value in the [8]phenacene electric-double-layer FET reached 16.4 cm2 V−1 s−1, which is the highest reported in EDL FETs based on phenacene-type molecules; the average μ was evaluated as 8(5) cm2 V−1 s−1. The μ values recorded in this study show that [8]phenacene is a promising molecule for transistor applications.

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