Electric field-induced orientation of organic microcrystals with large dipole moment in dispersion liquid

The reprecipitation method is a useful technique to fabricate organic microcrystals such as polydiacetylene, low-molecular weight aromatic compounds, organic functional dyes, which features are located in a mesoscopic phase between a single molecule and bulk crystals, and peculiar optical and electronic properties are expected to be exhibited in organic microcrystals. By using this technique, we succeeded in fabricating polar organic microcrystals such as 4′-dimethylamino-N-methylstilbazolium p-toluenesulfonate (DAST) dispersed in decalin with low dielectric constant. The resulting DAST microcrystals were confirmed to be second-harmonic generation (SHG)-active from the measurements with powder test and powder X-ray diffraction (XRD), which means that DAST microcrystals have dipole moment. Actually, it has become apparent from absorbance changes that DAST microcrystals in the dispersion liquid were oriented by applying remarkably lower DC electric field, in comparison with DC electric field in common LC displays. The present DAST microcrystals-dispersion liquid would serve both as crystal property and liquid one. In other words, this system can be regarded as a new concept of ‘liquid and crystals’ system, which will be expected to be applied to novel optical devices in electronics and photonics fields.