Takuji Kato

Organic Vapor Triggered Repeatable On–Off Crystalline-State Luminescence Switching

A nonporous crystalline solid consisting of an organoarsenic platinum(II) complex, i.e., a mononuclear diiodoplatinum(II) complex trans-PtI(2)(cis-DHDAtBu)(2) (1) with cis-1,4-dihydro-1,4-dimethyl-2,3,5,6-tetrakis(tert-butoxycarbonyl)-1,4-diarsinine (cis-DHDAtBu), shows on-off solid-state luminescence switching through reversible solvent vapor uptake and escape. The on-off switching of solid-state luminescence was achieved without changing the structure or electronic state of the organoarsenic platinum(II) complex.

Practical Synthesis and Properties of 2,5-Diarylarsoles

2,5-Diarylarsoles were easily synthesized from nonvolatile arsenic precursors. Diiodoarsine was generated in situ and reacted with titanacyclopentadienes to give 2,5-diarylarsoles. The structures and optical properties were studied in comparison with those of 2,5-diarylphosphole. It was found that the arsoles were much more stable in the air than the phosphole. Single crystal X-ray diffraction revealed the arsenic atoms adopted a trigonal pyramidal structure, reflecting on the s-character of the lone pair. The obtained 2,5-diarylarsoles and 2,5-diarylphosphole showed intense emission in solutions and solid state. In addition, the optical properties were controlled by transition-metal coordination.

Polymorph control of luminescence properties in molecular crystals of a platinum and organoarsenic complex and formation of stable one-dimensional nanochannel.

The mononuclear diiodoplatinum(II) complex (trans-PtI2(cis-DHDAMe)2), where cis-DHDAMe = cis-1,4-dihydro-1,4-dimethyl-2,3,5,6-tetrakis(methoxycarbonyl)-1,4-diarsinine, forms three different crystalline polymorphs that can be either concomitantly or separately obtained on varying the recrystallization conditions. Cubic red crystals (α-phase) and red-orange needles (β-phase) exhibit solid-state red emissions at room temperature. Cubic red crystals of the γ-phase show no solid-state emission at room temperature. All crystalline structures were confirmed by X-ray crystallography. Room-temperature strongly luminescent crystals (α-phase) (λem = 657 nm, Φ = 0.52) have a triclinic P1 (No. 2) structure and no voids in the crystal structure. Red-orange needle-shaped crystals of the β-phase exhibit moderate red luminescence (λem = 695 nm, Φ = 0.09) at room temperature and have a trigonal, R3 (No. 148), structure. In the needlelike crystals of the β-phase, stable hexagonal arrays of nanoporous channels, 5.0 Å in diameter, are formed. Room-temperature nonluminescent crystals (γ-phase) have an orthorhombic, Pbca (No. 61), structure with a void volume that is 4.9% of the total crystal volume. After heating the α-phase crystals at 150 °C for 2 min, a powder XRD pattern different from the original crystal is obtained, and its solid-state emission at room temperature decreased. After heating the β-phase crystals at 150 °C for 2 min, the emission wavelength and the quantum yield of the solid-state emission at room temperature and the powder XRD pattern are the same as those of the α-phase after heating at 150 °C. A crystal-to-crystal transition triggered by the thermal stimulus produces a different stable polymorph of the mononuclear diiodoplatinum(II) complex. The one-dimensional nanoporous crystals encapsulated iodine without distorting the crystal packing.

High Carrier Mobility of 3.8 cm2 V-1 s-1 in Polydiacetylene Thin Films Polymerized by Electron Beam Irradiation

The highest carrier mobility of polydiacetylene (PDA) thin films in field-effect transistors has been limited to less than 0.8 cm2 V-1 s-1, although the main chain conduction should show higher carrier mobility potentially. We revealed that the cause of the low carrier mobility is due to the presence of local upheaval regions generated by the volume change through the polymerization process of diacetylene monomers. In order to suppress the occurrence of the upheaval regions, we found that electron beam (EB) irradiation is effective, resulted in the highest carrier mobility of µmax = 3.8 cm2 V-1 s-1.

Organic Electrodes Consisting of Dianthratetrathiafulvalene and Fullerene and Their Application in Organic Field Effect Transistors

A double layer of dianthratetrathiafulvalene (DATTF) and fullerene (C60) on an n++-Si wafer pretreated with n-octyltrichlorosilane exhibited a high electrical conductivity of σ= 0.12 S/cm and was used as source–drain electrodes in organic field effect transistors (OFETs). A simplified OFET device architecture composed of an organic semiconducting active layer and an organic electrode layer was easily fabricated by successive vacuum deposition of organic donor and acceptor layers. It was confirmed that this device configuration is applicable for both p- and n-type FET operation.

Fabrication of One-Dimensionally Oriented Fluorene–Thiophene Copolymer Thin Films and Anisotropic Transistor Characteristics

One-dimensionally oriented poly(9,9-dioctylfluorene-co-bithiophene) (F8T2) thin films with the thickness of approximately 50 nm were deposited by friction-transfer technique. Films were investigated using polarized optical spectroscopy. The dichroic ratio of absorption was estimated to be approximately eight. By means of transmission electron microscope (TEM), we revealed that the main-chains of F8T2 were aligned along the friction direction. Atomic force microscope (AFM) images of as-prepared films showed a roughened surface, whereas the film after subsequent thermal treatment showed remarkably smooth surface. Field-effect transistors utilizing the friction-transferred F8T2 films exhibited a field-effect mobility of 1.88×10-4 cm2 V-1 s-1 along the friction direction, which is about six times higher than that perpendicular to the friction direction.