New Coumarin Polymers as Non-Contact Alignment Layers for Liquid Crystals

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Abstract
The synthesis of polymethacrylate derivatives of 6- and 7-hydroxycoumarin is described and their use as photoinduced alignment layers for liquid crystals is discussed. Strong anchoring is found with azimuthal anchoring energies > 6.9 × 1 (10−5 J m−2. The liquid crystal alignment direction is parallel to the polarisation direction of the incident UV light when low fluences are incident. At a critical fluence threshold, a sharp change to perpendicular alignment is found. The incorporation of a flexible spacer into the coumarin sidechain results in stronger anchoring at low fluences. These results are discussed in terms of a molecular model.