Turn On, Tune In, Drop Out

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Science  05 Aug 2005:
Vol. 309, Issue 5736, pp. 852
DOI: 10.1126/science.309.5736.852a

In a liquid crystal display, the brightness or color of a pixel is controlled by the orientation of the molecules and can be changed by turning on an electric field. In order to ensure uniform alignment within a domain, the glass surface is treated to make it grooved or otherwise anisotropic, which lowers the overall surface energy between the liquid crystal molecules and the glass.

Having shown previously that an oligosiloxane compound deposited onto glass covered with indium tin oxide (ITO) spontaneously forms rigid oligomers that amplify the grooves in the ITO coating, Hoogboom et al. use a pyridine-functionalized siloxane that forms an alignment layer capable of binding to the dye zinc phthalocyanine (ZnPc). The ZnPc molecules form epitaxial stacks whose height can be controlled by varying the immersion time, thus providing an opportunity to tune the sizes of domains. After liquid crystal molecules are deposited, it is generally difficult to alter the strength of the surface interactions or to correct defects. However, in this system, adding nitrogen-containing compounds partially dissolves the ZnPc stacks, which drop out and hence provide a second chance to tune the device. — MSL

J. Am. Chem. Soc. 10.1021/ja051865l (2005).

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