Takahiro Kojima

Organic field-effect transistors based on heterocyclic co-oligomers containing a pyrazine ring

New oligomers containing a pyrazine unit have been prepared: the bithienyl derivatives afforded p-type FET devices whereas the trifluoromethylphenyl derivatives showed n-type FET behavior.

Organic field-effect transistors based on novel organic semiconductors containing diazaboroles

New π-conjugated systems containing a diazaborole unit have been prepared by the reaction of the corresponding boronic acids with diamines. They are nearly colorless compounds with electron-donating properties. Single crystal X-ray structure analysis of two compounds revealed their nearly planar structures and unique crystal structures. The OFET devices using the transparent organic semiconductors as an active layer have been successfully fabricated and showed good p-type FET behaviour. The FET device based on the derivative showed high air stability in spite of its high HOMO level. The film structures were investigated with XRD and AFM measurements.

Amphiphilic ferrocenylated alkylpyridinium: the formation of micelles and hydrogels and their disaggregation induced by an external stimulus

Ferrocene-containing amphiphiles [py-N-(CH2)nOCH2Fc]Cl (n = 6 (1a), 8 (1b), 10 (1c); py = C5H5N, Fc = Fe(C5H4)(C5H5)) were synthesized. The absorption spectra of 1a-1c in the presence of a small amount of dye (Nile red and pyrene) in aqueous media suggested the formation of micelles which encapsulated the dye molecules. Two critical micelle concentrations were observed at 1.1 mM and 2.3 mM at 20 °C. Compounds 1a and 1c showed a single CMC for each, while the formation of two kinds of micelles, the spherical and rod-like ones, depended on the concentrations. The addition of an oxidant, NaOCl, to the aqueous solution of the micelles of 1b turned ferrocene to ferrocenium and caused the disaggregation of the micelles. The addition of α-cyclodextrin (α-CD) to 2b caused the disaggregation of the micelle and the formation of water-soluble [2]- and [3]pseudorotaxane [{py-N-(CH2)8OCH2Fc}(α-CD)m]Cl (1b(α-CD)m) (m = 1, 2), while mixing 1c and α-CD in water formed the rotaxane gel. The addition of NaOCl to the hydrogel of 1c and α-CD changed the gel to sol.

Orientation and Electronic Structures of Multilayered Graphene Nanoribbons Produced by Two-Zone Chemical Vapor Deposition

The orientation and electronic structure of multilayered graphene nanoribbons with an armchair-edge (AGNRs) were determined by low-temperature scanning tunneling microscopy in this study. The orientation of AGNRs was found to be an edge-on structure when positioned as a top layer, while previous reports showed a face-on structure for monolayered AGNRs on Au(111). According to density functional theory calculations, AGNRs in a top layer preferentially form as edge-on structures rather than face-on structures due to the balance of CH-π and π-π interactions between AGNRs. Scanning tunneling spectroscopy and density functional theory calculations revealed that the electronic structures of multilayered AGNRs are similar to those in a gas-phase due to the lack of interaction between AGNRs and the Au(111) substrate. The observation of AGNRs in mutilayers might suggest the conformation-assisted mechanism of dehydrogenation when there is no contact with the Au(111) substrate.