Polarized photoluminescence and order parameters of “in situ” photopolymerized liquid crystal films

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Abstract
Oriented liquid crystal polymer films with different degrees of cross-linking have been obtained by “in situ” photopolymerization of different mesogenic samples at various temperatures. These samples are mixtures of a naphthalene based monoacrylate and a crosslinking agent (diacrylate). Photoluminescence has been obtained by adding a cyanoterphenyl chromophore. The order parameters of the polymer films have been derived from dichroic measurements. An increase of the dichroism has been found when the diacrylate content and/or the polymerization temperature decrease. The dichroism is also bigger if the chromophore is in a “guest-host” configuration than if it is covalently attached to the polymer backbone. The dichroic ratios do not change under annealing up to 200 °C but some photodegradation of the luminescence is observed in the naphthalene containing films.