Gigantic Electric Dipole Moment of Organic Microcrystals Evaluated in Dispersion Liquid with Polarized Electroabsorption Spectra

Polarized electroabsorption spectra of the 4-N,N-dimethylamino-4'-N'-methyl-stilbazolium tosylate (DAST) microcrystal, which is well-known as an organic nonlinear optical material, were measured in decalin liquid using electric-field modulation spectroscopy. On the basis of the results, the magnitude of the electric dipole moment in the ground state of DAST microcrystals whose size was about 0.35 mu m was determined to be as large as similar to 4.5 x 10(4) D, and the magnitude of the difference in the dipole moment between the ground state and excited state was estimated to be similar to 2.5 x 10(3) D, though the local field correction was not made. The transition moment of the DAST crystal was also found to be a little affected by application of electric fields.