Wataru Sotoyama

Efficient organic light-emitting diodes with phosphorescent platinum complexes containing N∧C∧N-coordinating tridentate ligand

We describe the phosphorescent characteristics of two platinum complexes containing an N∧C∧N-coordinating tridentate ligand: platinum(II) 3,5-di(2-pyridyl)toluene chloride [Pt(dpt)Cl] and a newly synthesized platinum(II) 3,5-di(2-pyridyl)toluene phenoxide [Pt(dpt)(oph)], together with the performance of organic light-emitting diodes (OLEDs) prepared with these complexes as phosphors. Films containing each one of the complexes in a 4,4’-N,N’-dicalbazolylbiphenyl (CBP) host showed highly efficient photoluminescence. The fabricated OLEDs exhibited high efficiencies; the maximum external quantum efficiency of the device with Pt(dpt)(oph) phosphor after correction of angular dependence of emission was found to be 16.5%. The luminance half decay time of the Pt(dpt)(oph) device under a constant-current operation was considerably longer than that of the Pt(dpt)Cl device.

Polymer films formed with monolayer growth steps by molecular layer deposition

Molecular layer deposition is the process in which molecules are stacked on substrates one by one in order of preference in a vacuum. We studied the possibility using two kinds of molecules: pyromellitic dianhydride (A) and 2,4‐diaminonitrobenzene or 4,4’‐diaminodiphenyl ether (B). After forming a layer consisting of A (or B), we supplied molecule B (or A). The film rapidly thickened and became saturated in 10–60 s. The change in thickness induced in this step was about 5 A, close to the size of the molecules involved. This indicates that a monomolecular layer of B (or A) grew on layer A (or B) and film growth self‐terminated automatically. 15 steps of alternately supplying A and B produced a polymer film 100 A thick.

Quantum wire and dot formation by chemical vapor deposition and molecular layer deposition of one‐dimensional conjugated polymer

Using the reaction between two types of molecules, I [terephthalaldehyde (TPA)] and II [p‐phenylenediamine (PPDA), 4,4’‐diaminodiphenyl ether (DDE), 4,4’‐diaminodiphenyl sulfide (DDS), or 1,4‐diaminodiphenylmethane (DDM)], we fabricate quantum wires and quantum dots by chemical vapor deposition. In the TPA/PPDA film, an exciton absorption peak occurs near 500 nm, indicating that long conjugated chains (quantum wire) are formed. In TPA/DDE, TPA/DDS, and TPA/DDM films, which have quantum dots consisting of three benzene rings separated by barriers of ‐O, ‐S‐, and ‐CH2‐ bonds, blue shifts of the absorption band occur due to an electron confinement. We also demonstrate molecular layer deposition of the TPA/PPDA film.

Electro‐optic side‐chain polyimide system with large optical nonlinearity and high thermal stability

We report electro‐optic (EO) efficiency and thermal stability of a poled polyimide system with nonlinear optical dyes as side chains. The side‐chain polyimide system is synthesized from a dianhydride containing azobenzene dye and a diamine. The dye in the polymer is chemically stable for temperatures below 250 °C. The polymer can be poled simultaneously with or after imidization of the polyamic acid. Our sample poled after imidization shows a large EO coefficient (r33=10.8 pm/V at λ=1.3 μm) and long‐term thermal stability at 120 °C.

45.3: Tetra‐Substituted Pyrenes: New Class of Blue Emitter for Organic Light‐Emitting Diodes

We have developed a new class of highly-fluorescent blue emitter for organic light-emitting diodes (OLEDs) consisting of tetra-substituted pyrenes. From the analysis of the excited state diagrams of pyrene and its derivatives by molecular orbital calculations, we found that the new tetra-substituted pyrenes are highly fluorescent. OLEDs fabricated using the synthesized tetra-substituted pyrenes as emitters showed high efficiency and good color purity.

Directional-Coupled Optical Switch between Stacked Waveguide Layers Using Electro-Optic Polymer

A vertical optical switch consisting of an electro-optic polymer is described. Two-layer stacked slab waveguides were fabricated with para-nitroaniline-bonded epoxy polymer as the core layer and polyvinylalcohol as the cladding layer. After poling treatment, a He-Ne laser beam was coupled to the waveguides, and guided-wave switching was observed between the two waveguide layers with application of voltage to the electrodes.

Polyazomethine conjugated polymer film with second order nonlinear optical properties fabricated by electric‐field‐assisted chemical vapor deposition

We fabricated polyazomethine head‐to‐tail conjugated polymer films with second order nonlinear optical (NLO) properties using a dry‐processing technique, electric‐field‐assisted chemical vapor deposition (E‐CVD). Molecular orbital calculations show that the polyazomethine conjugated polymer chain, to which methoxy groups are attached as donors, has second order NLO susceptibility, β, 3–5 times larger than that of paranitroaniline. During film deposition the monomers were ordered by an electric field applied between slit‐type electrodes, and simultaneously polymerized. A channel waveguide for the TE mode of a He‐Ne laser beam was formed in a polymer film between the electrode gap. An electro‐optic (EO) effect in the polymer film was observed using a Mach–Zehnder interferometer. This indicates that head‐to‐tail conjugated polymers would be promising for second order NLO materials.

Electro‐optic polymer waveguide fabricated using electric‐field‐assisted chemical vapor deposition

We describe the fabrication of an electro‐optic (EO) polymer channel waveguide using a new technique, electric‐field‐assisted chemical vapor deposition. A polymer film is deposited from epoxy and nonlinear optical (NLO) aliphatic amine using chemical vapor deposition under an electric field applied by slit electrodes on a thermally oxidized Si wafer, at room temperature. A clear propagating He‐Ne laser beam is observed along the electrode gap. The propagated beam’s near field pattern is bright for the TE mode, but very weak for the TM mode. This indicates the NLO side groups’ in‐plane alignment and the fabrication of a channel waveguide. The EO coefficient of this waveguide, measured in a Mach–Zehnder interferometer, is r11∼0.1 pm/V. The polymer channel waveguide, which is poled at room temperature after film deposition, shows no EO response. This means NLO molecules are actually aligned during polymerizing, not after.

Chemical vapour deposition of polyamic acid thin films by stacking non-linear optical molecules aligned with a strong electric field

Polyamic acid films, a precursor of polyimide, containing non-linear optical (NLO) molecules in the polymer chains, were deposited under a high electric filed in molecular alignment by co-evaporating pyromellitic dianhydride and the NLO molecule 2,4-diaminonitrobenzene in vacuum

Epoxy-amine polymer waveguide containing nonlinear optical molecules fabricated by chemical vapor deposition

Epoxy‐amine polymer thin films are fabricated by chemical vapor deposition using an aliphatic amine, which is very reactive to epoxy groups and has nonlinear optical properties. A transparent thin film is obtained by controlling the temperature and surface condition of the substrate, and the epoxy‐amine ratio during deposition. The refractive index of the film is 1.648. A slab waveguide is constructed by depositing the polymer film on SiO2 which is formed by thermal oxidation of a Si wafer. End coupling of a He‐Ne laser (632.8 nm) launches a well‐propagating beam. This is the first case in which a polymer waveguide is fabricated by dry processing.