Synthesis of the extended phenacene molecules, [10]phenacene and [11]phenacene, and their performance in a field-effect transistor

The [10]phenacene and [11]phenacene molecules have been synthesized using a simple repetition of Wittig reactions followed by photocyclization. Sufficient amounts of [10]phenacene and [11]phenacene were obtained, and thin-film FETs using these molecules have been fabricated with SiO₂ and ionic liquid gate dielectrics. These FETs operated in p-channel. The averaged measurements of field-effect mobility, <μ>, were 3.1(7) × 10⁻² and 1.11(4) × 10⁻¹ cm² V⁻¹ s⁻¹, respectively, for [10]phenacene and [11]phenacene thin-film FETs with SiO₂ gate dielectrics. Furthermore, [10]phenacene and [11]phenacene thin-film electric-double-layer (EDL) FETs with ionic liquid showed low-voltage p-channel FET properties, with <μ> values of 3(1) and 1(1) cm² V⁻¹ s⁻¹, respectively. This study also discusses the future utility of the extremely extended π-network molecules [10]phenacene and [11]phenacene as the active layer of FET devices, based on the experimental results obtained.

Convenient Phenacene Synthesis by Sequentially Performed Wittig­ Reaction and Mallory Photocyclization Using Continuous-Flow Techniques

Various phenacenes possessing chrysene, picene, and fulminene frameworks were prepared by using a continuous-flow synthetic protocol in which Wittig reaction affording diarylethenes and their Mallory­ photocyclization producing phenacene skeletons were sequentially performed. The Wittig reaction solution, containing the diaryl­ethene obtained from an arylaldehyde and an arylmethyltriphenylphosphonium salt, was mixed with an iodine solution in the flow system and, subsequently, the solution was subjected to the photoreaction. Desired phenacenes were obtained with high to moderate chemical yield. For the present protocol, isolation of the intermediary diarylethene, which is the key precursor of the phenacene, is unnecessary. The approach provides a convenient method to supply a variety of phenacene samples, which are needed for initial systematic surveys in material science.

Chemical analysis of superconducting phase in K-doped picene

Potassium-doped picene (K3.0picene) with a superconducting transition temperature (T C) as high as 14 K at ambient pressure has been prepared using an annealing technique. The shielding fraction of this sample was 5.4% at 0 GPa. The T C showed a positive pressure-dependence and reached 19 K at 1.13 GPa. The shielding fraction also reached 18.5%. To investigate the chemical composition and the state of the picene skeleton in the superconducting sample, we used energy-dispersive x-ray (EDX) spectroscopy, MALDI-time-of-flight (MALDI-TOF) mass spectroscopy and x-ray diffraction (XRD). Both EDX and MALDI-TOF indicated no contamination with materials other than K-doped picene or K-doped picene fragments, and supported the preservation of the picene skeleton. However, it was also found that a magnetic K-doped picene sample consisted mainly of picene fragments or K-doped picene fragments. Thus, removal of the component contributing the magnetic quality to a superconducting sample should enhance the volume fraction.

Transistor application of alkyl-substituted picene

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 PbZr_0.52Ti_0.48O₃ (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, |V_th|, (5.2 V) was recorded with a PZT gate dielectric; the average |V_th| 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 crystal structure of a Dcp-containing peptide

We have investigated the conformational preferences of a newly synthesized C(alpha,alpha) symmetrically disubstituted glycine, namely alpha,alpha-dicyclopropylglycine (Dcp). We report here the crystal structure of a fully protected dipeptide containing Dcp, namely Z-Dcp(1)-Dcp(2)-OCH(3). Both Dcp residues are in a folded conformation. The overall peptide structural organization corresponds to an alpha-pleated sheet conformation, similar to that observed in linear peptides made up of alternating D- and L-residues and in Z-Aib-Aib-OCH(3) (Aib: alpha,alpha-dimethylglycine). These preliminary data suggest that the Dcp could represent an alternative as molecular tool to stabilize folded conformations.

The superreactive disulfide bonds in alpha-lactalbumin and lysozyme

The disulfide reduction kinetics in equine lysozyme (ELZ), which is a Ca(2+)-binding lysozyme, and human (HLA) and equine alpha-lactalbumin (ELA) at pH 8.5 and 25 degrees C by excess dithiothreitol were studied, and it was found that in ELZ there is no superreactive disulfide bond, while one of the disulfides is reduced very quickly by the reducing agent in HLA and ELA, as in bovine alpha-lactalbumin. The local conformation around the surface disulfide in ELZ seems to be more similar to that in hen egg-white lysozyme than in alpha-lactalbumin. The four disulfides in ELZ were reduced slowly in an apparently single-exponential form, and the bound Ca2+ lowered the reduction rate. The torsion energy on each of the disulfides in three alpha-lactalbumin and eight c-type lysozymes whose native conformations have been experimentally or theoretically analyzed was calculated, and it was found that torsion imposed on the surface disulfide between Cys 6 and Cys 120 in alpha-lactalbumin is a main cause of the superreactivity and all of lysozymes, including the Ca(2+)-binding ones, have no such strained surface bond.