Electric-Field-Induced Orientation of Organic Microcrystals with Large Dipole Moment

The microcrystals of molecules with large dipole moment in a non-centrosymmetric crystal structure should possess a huge dipole moment. Therefore, such polar microcrystals dispersed in nonpolar liquid may easily respond to a weak electric field and orient to it. On the basis of this idea, dimethylaminostilbazolium tosylate (DAST) microcrystals dispersed in decahydronaphthalene have been prepared, for which a rather large dipole moment and non-centrosymmetric crystal structures was confirmed. Absorption change of DAST microcrystals was observed even under a extremly weak DC electric field of 100 V·cm-1 and the magnitude of absorption change rate at absorption maximum varied almost linearly up to 300 V·cm-1. This phenomenon may be applied to display devices.