We have prepared an dispersion of 4'-dimethylamino-N-methylstilbazolium p-toluenesulfonate (DAST)
nanocrystals using the reprecipitation method and have spectroscopically measured their orientation in an electric or
magnetic field. As a result, we could observe reversible and efficient contrast change that depends on the on-off of
applied field. In addition, with controlling the orientation of DAST nanocrystals by the external field, the immobilization
was performed using light-cured polymer and the light irradiation. These materials may be applied to the display device
or polarized light filter.
We report the study of the dynamics of the third-order nonlinear optical response of polydiacetylene micro-crystals. The material employed is the polydiacetylene know as poly-DCHD, and the micro-crystals were 100 nm in diameter contained in an aqueous suspension. Experimental results for transient changes in transmission measured by a time-resolved excite-probe technique, conducted with 100 fs pulses at 850 nm from a mode-locked Ti:sapphire laser are presented. A discussion of the role of the excitonic origin of the nonlinear response is also presented. (Abstract only available)
In order to improve third-order nonlinear optical properties of polydiacetylenes (PDAs), we have been investigating modification of PDA structures. From the point of view of PDA molecular design, three series of monomers for ladder- type PDAs were prepared. Oligoyne monomers having more than five conjugated acetylenes gave polymers which showed broad bands at longer wavelength than their excitonic absorption bands. This implies production of (pi) -conjugated ladder polymer having two PDA backbones linked by acetylenic groups in each repeating unit. From monomers with two butadiynes connected by an alkylene group, ladder-type PDAs were obtained when the carbon number of the alkylene group is more than four. However, monomers with two butadiynes connected by an arylene group gave only single-chain PDAs. From the point of view of PDA morphological engineering, PDA microcrystal water dispersions were applied to evaluate nonlinear optical susceptibilities by z-scan method together with PDA thin films. High-density microcrystal deposited film prepared by layer-by-layer deposition technique showed more than three orders of magnitude enhanced (chi) (3) than the dispersion state. Polycrystalline thin films compose of ladder-type PDAs were also found to have large (chi) (3). The quite large nonlinear refractive index of -41 cm2/GW was attained just near excitonic absorption maximum for one of the polymers.
Polydiacetylene microcrystals in a water suspension or a polymer matrix were prepared by a simple precipitation procedure in order to obtain a thin samples with good optical quality maintaining the characteristics of crystalline materials. The nonlinear refraction, n2, and nonlinear absorption, (beta) , around the exciton peak were measured by z-scan method using a tunable picosecond laser. The signs of the n2 are positive/negative at wavelengths shorter/longer than the exciton peak and strong saturable absorption, which (beta) is negative, are observed around the peak. The largest n2 was obtained to be plus 0.024 cm2/GW (Re(chi(3) equals plus 1.4 multiplied by 10-9 esu) at 640 nm for a gelatin composite film containing 24 wt percent of polydiacetylene microcrystals.