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 μm was determined to be as large as ∼4.5 × 10 ⁴ D, and the magnitude of the difference in the dipole moment between the ground state and excited state was estimated to be ∼2.5 × 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.