Atsushi Kakuta

A Novel Preparation Method of Organic Microcrystals

Organic microcrystals ranging from several tens nm to µm in size of several chromophores were successfully prepared by simply dispersing ethanol solutions of compounds into stirred water, i.e. by a reprecipitation method. The size of microcrystals was found to depend on concentration of ethanol solutions, dispersing conditions, temperature and so on.

Organic photo‐ and electroluminescent devices with double mirrors

Luminescent spectra of organic thin films sandwiched with two mirrors were measured in an effort to detect optical microcavity effects. Narrowing and enhancement of photoluminescent spectra were observed from the tri‐(8‐hydroxyquinolinol)aluminum monolayer with the mirrors at both sides. Furthermore, the narrowing of spectra was also observed from electroluminescent devices fabricated with two mirrors.

Third-order non-linear optical properties of donor- and acceptor-substituted metallophthalocyanines

Several types of metallophthalocyanines have been synthesized to establish the relationship between molecular structure and third-order optical non-linearity. Third-order non-linear optical susceptibilities χ(3) of phthalocyanine (Pc) containing central metal atoms oxovanadium, copper, nickel, iron and cobalt, and peripheral substitutes were measured by the third-harmonic generation technique. The χ(3)(−3ω; ω, ω, ω) values of VOPc(NH2)4, CuPc(NH2)4, NiPc(NH2)4 and FePc(COOH)4 were found to be 6.3 × 10−12, 2.0 × 10−12, 1.63 × 10−12 and 1.18 × 10−12 e.s.u. respectively at 2.1 μm. Although the donor and acceptor substituents have a dilution effect, χ(3) was still larger than that of the corresponding unsubstituted phthalocyanines, with the exception of metallophthalocyanines with an axial group where the peripheral substituents required for processability or otherwise are not beneficial for optical non-linearity. In addition, the magnitude of χ(3)(−3ω; ω, ω, ω) was found to be influenced by different functional groups substituted in cobalt phthalocyanine. The effect of various peripheral substituents on the magnitude of the third-order non-linear optical susceptibility is discussed.

Third-order optical nonlinearities of tetrakis-n-pentoxy carbonyl metallo-naphthalocyanines

Abstract Third-order nonlinear optical susceptibilities χ (3) of tetrakis- n -pentoxy-carbonyl (COO-C 5 H 11 ) naphthalocyanines containing central metal atom oxovanadium (VO), copper (Cu), zinc (Zn), palladium (Pd), and nickel (Ni) were measured by the third-harmonic generation (THG) technique. The metal atom substitution influences the third-order nonlinear optical susceptibility but the variation is less dramatic; oxovanadium cation was found to be the most effective. The order of χ (3) (−3ω; ω, ω, ω) at 2.1 μm wavelength was VONc > CuNc > ZnNc > NiNc > PdNc. The χ (3) (−3ω; ω, ω, ω) for VONc is 8.6 × 10 −11 esu, more than an order of magnitude larger than those of CuNc, ZnNc, PdNc, and NiNc compounds. A comparative study of optical and non-linear optical properties of processable metallo-naphthalocyanines is presented.

Solid-state Polymerization of Diacetylene Microcrystals

Abstract Microcrystals of two different types of diacetylene monomers, i.e. 4BCMU known for giving a soluble polydiacetylene and 14-8 ADA known as an amphiphilic diacetylene, were prepared and in their solid-state polymerization behaviors were investigated. The polymerization of 4BCMU proceeded quantitatively in the perfect crystalline lattice to give blue-colored polymer crystals. Averaged molecular weight of poly-4BCMU was found to be. proportional to microcrystal size, implying that the solid-state polymerization proceeds from one end to the other end of microcrystals. 14-8 ADA microcrystals gave very stable water dispersion even after polymerization, so that the detailed analysis of polymerization behaviors was possible. Size-dependent spectral change and final conversion found for 14-8 ADA were discussed in terms of strain and thermal motion of the crystal lattice.

Memory effect of chromophore orientation in merocyanine Langmuir-Blodgett films☆

Abstract The changes in the in-plane spectral anisotropy caused by heat, acidic vapour and basic vapour treatments after deposition are studied for Langmuir-Blodgett (LB) films of merocyanine dye containing a benzoselenazole nuclei mixed with arachidic acid. The as-deposited films exhibit a J-like aggregate band at 597 nm which is strongly polarized along the dipping direction of the substrate. After heat treatment or HCl vapour treatment, the J-like band disappears and the in-plane spectral anisotropy is reduced. NH3 vapour treatment causes the J-like band to be restored in the wavelength region 620–627 nm. The restored J-like band is polarized along the same direction as the original J-like band. This memory effect of chromophore orientation suggests that there is a highly anisotropic structure of J-like aggregates in LB films.

Third‐order nonlinear optical properties of processable polyazine thin films

The third‐order nonlinear optical susceptibility χ(3)(−3ω;ω,ω,ω) of propylmethylpolyazine thin films as measured by the third harmonic generation is reported. The χ(3)(−3ω;ω,ω,ω) values of propylmethylpolyazine that possess statistically alternating methyl and propyl substituents on the carbon atoms along the conjugated chain were found to be 8.0×10−12 esu off resonance at 1.5 μm fundamental radiation. The interesting third‐order nonlinear properties presumably originate from the unique periodicity of the main π‐electron‐conjugated polyazine backbone.

Blue light emission from a laser diode pumped ring resonator with an organic second‐harmonic generation crystal of 8‐(4’‐acetylphenyl)‐1,4‐dioxa‐8‐azaspirol[4.5]decane

A laser diode pumped ring resonator was built with a new organic second‐order nonlinear optical crystal, 8‐(4’‐acetylphenyl)‐1,4‐dioxa‐8‐azaspiro[4.5] decane. Ultraprecision diamond polishing was used for the crystal and optically flat surfaces and roughnesses of less than λ/10 were achieved. The surfaces were dip coated with a perfluorinated polymer thin film to suppress surface reflection loss. Under resonant conditions, fundamental power was enhanced and a blue second‐harmonic emission with wavelength of 405.5 nm was observed.

Molecular Design for New Second-Order Nonlinear Optical Materials

Abstract A molecular design method of second-order nonlinear optical materials for SHG device applications of diode lasers is proposed. The method consists of a semi-empirical MO calculation (CNDO/S3-CI) to evaluate molecular nonlinear optical properties of a molecule and an intermolecular interaction energy calculation to evaluate its crystallization property, in particular whether it crystallizes in a centrosymmetric structure or not. Using this method we design novel second-order nonlinear optical materials for our target applications: xanthone and benzophenone derivatives which have relatively large optical nonlinearity and short absorption cut-off wavelength.

Effect of Molecular Orbital Distributions on Charge Transport Properties of Polymers Doped with Triphenylamine Derivatives

The hole drift mobilities of polymers doped with triphenylamine derivatives including heterocyclic groups have been measured and the effect of molecular orbital distributions of triphenylamine derivatives on the charge transport properties has been studied. The temperature dependence of the mobilities of polymers doped with two kinds of triphenylamine derivatives has been analyzed using the disorder formalism presented by Bassler and co-workers[H. Bassler, Phys. Status Solidi B 175(1993) 15.] and it has been found that highest occupied molecular orbital (HOMO) distribution of the triphenylamine derivatives has little effect on the diagonal and off-diagonal disorder but has a large effect on the disorder-free mobility in this formalism.