Organic microcrystals of several tens nanometer to 1 μm in size were successfully prepared by reprecipitation method. Microcrystals of diacetylene monomers could be polymerized to give those of π-conjugated polymer by UV or γ-ray irradiation. For merocyanine and perylene microcrystals, optical properties such as absorption and emission were found to be vary depending on their crystal size. Nonlinear optical properties of those samples were also evaluated.

View full abstract

Langmuir-Blodgett films have attracted much attention from the viewpoint of organic functional ultrathin films. Long alkylacrylamide compounds have an excellent property to form stable monolayers and LB films. The copolymers of the acrylamide monomers with various photofunctional comonomers often form stable monolayer and LB films with a help of the acrylamide property. In this contribution, the LB film formation of the copolymer, the photophysical processes in the LB films, and photo energy conversion using the LB films are described.

View full abstract

Poly(aryleneethynylene) type π-conjugated polymers (PAEs) are synthesized and the third-order optical susceptibility χ^<(3)> of their thin films is evaluated. There is a red-shift in the electronic absorption of the PAE caused by an intramolecular charge transfer (CT) interaction when π-electron excessive heteroaromatic rings are introduced. The χ^<(3)> value of the PAEs is enhanced by increasing the CT interaction and reaches more than 10^<-11> esu in the near resonant region. The main factor enhancing χ^<(3)> is the increase in the π-electron delocalization caused by the CT interaction.

View full abstract

EO/passive hybridized Polymer waveguides are realized, which are vertically stacked waveguides and serially grafted waveguides. They are applied to optical modulators and an optical intensity modulation is successfully demonstrated. Serially grafted waveguides allow connections between EO waveguides and Passive waveguides with very low loss of 0.005 dB/point.

View full abstract

Organic electroluminescent(EL) diodes have been extensively investigated. In this paper, electrical and optical characteristics of some kinds of organic multiple-quantum-well (MQW) structure utilizing organic dye materials have been investigated. The organic MQW structure has been fabricated by organic molecular beam deposition technique (OMBD) . Organic EL diode with organic MQW structure has also been fabricated. We found that the PL emission peak has been shifted to shorter wavelength as the layer thickness decreases. Spectral narrowing and the shift of peak emission wavelength have been observed in the EL diode with thin multilayer structure with Alq_3/TPD system. Unique polarization characteristics of EL diode with MQW structure with both Alq_3/TPD and PPCP/TPD systems has also been clarified. Quantum size effects of the MQW structure with Alq_3/TPD and PPCP/TPD systems have been investigated.

View full abstract

White light-emitting organic LEDs (electroluminescent devices) were fabricated using dye-dispersed polymers as an emitter layer. In one example, hole-transporting poly(N-vinylcarbazole) (PVK) were used as a host polymer to be doped with fluorescent dyes. A multilayer structure combined with electron transport layers was employed to maximize carrier recombination efficiency. In the other example, electrically inert poly(methyl methacrylate) (PMMA) was used as a host polymer. PMMA was doped with 50 wt% electron-transporting 1,3,4-oxadiazole derivative and fluorescent dyes. In this case, a hole transport layer was inserted between doped PMMA layer and anode. White electroluminescence was observed from both devices and the maximum luminance exceeded 3000 cd/m^2 in case of the device with doped PVK layer.

View full abstract

Electroluminescent devices with mixed single layer of organic materials that consist of hole transport material(TPD), electron transport material(Alq_3) and dopant material(DCM) are studied. The luminance in excess of 10,000cd/m^2 as high as multi layer device could be obtained by optimizing the weight ratio TPD:Alq_3:DCM=20:80:1. Better preservation stability of single layer device is obtained compared to multi layer device.

View full abstract

We have developed an optical liquid-crystal polymer film with a twisted nematic structure, named "LC film". This film shows the excellent performance as an STN-LCD compensator by control of its twist angle, retardation and the wavelength dependence of the birefringence. Also by control of the optical parameters LC film shows the optical characteristics of cholesteric as well as twisted nematic.

View full abstract

We have defined "rubbing strength parameter" as a measure of the rubbing strength of polymer alignment layer. We have also proposed simple as well as reliable method to measure anchoring strength. By using this method we actually measured the anchoring strength and found that it was proportional to the rubbing strength parameter. On the other hand, we have calculated the anchoring strength by Berreman's theory and found that the measured value was two orders larger than the calculated value, which indicates that the liquid crystal orientation is not caused by the grooves created by the rubbing. Retardation and the anchoring strength of the surface with grooves made by stamping method were measured. From the results, it is believed that the liquid crystal alignment is caused by intermolecular interaction between liquid crystal and the polymer of the rubbed surface.

View full abstract

Liquid crystal molecules on a rubbed polymer alignment layer are oriented at some polar angle away from the surface. This so-called pretilt angle is an important parameter which determines the electro-optical properties of liquid crystal devices. Therefore, it is necessity to study generation of pretilt angle and its stability. Several researchers have been studying on this problem but the physical mechanism is not thoroughly understood. Therefore, we have investigated LC pretilt angle and polymer inclination angle and the effect of heat treatment on these angles. We also studied the pretilt changes by the heat treatment using various LC materials to clarify the reason of the heat treatment dependence of a pretilt angle. From these results we discuss the mechanism of change in LC pretilt by the heat treatment.

View full abstract

We investigated the electrical properties of Liquid crystal molecules on the basis of Physics of dielectrics. LC monolayers on a water interface were investigated in context with phase transitions by means of a Maxwell-displacement-current-measuring technique. The transition was found to be clearly detected by the technique even in the range of immeasurably low surface pressures. The dielectric dispersion of LC cells arizing from the motion of impurity ions was also investigated in the range of low-frequency, and the result was analyzed.

View full abstract