1991 Volume 49 Issue 5 Pages 383-391
A new type of photoresponsive liquid crystalline cells has been developed. The cells were constructed by putting a nematic liquid crystal between two glass plates modified with azobenzene monolayers, the photoisomerization of which induces reversible alignment change between the homeotropic and parallel modes. Detailed studies revealed that the factors affecting the photoregulation of the alignment involve the molecular structure and occupied area of the azobenzene unit and the coexistence of long alkyl chain. Derivatives of stilbene and α-hydrazono-β-ketoester were found to be also effective for the photoregulation. This suggests that the reversible structural alteration between the rodlike and L-shaped photochromic units plays an essential role in the photoregulation. Discussion was made on the mechanism of the regulation, based on the relationship between the regulation efficiency and the surface energy change and on the spectroscopic alteration of photochromic units upon the contact with liquid crystalline molecules.
