Triplet-Sensitized Irradiation of a Main-Chain Liquid Crystalline Poly(aryl Cinnamate) in Three Different Phases

Document Type

Article

Publication Date

1-1-2001

Department

Chemistry and Biochemistry

School

Mathematics and Natural Sciences

Abstract

Visible light irradiation of thin films of a main‐chain liquid crystalline poly(aryl cinnamate) using ketocoumarins as triplet sensitizers leads to photochemical crosslinking and UV‐vis and FTIR spectroscopic changes associated with saturation of the cinnamate double bond, most likely by 2 + 2 photocycloaddition. The triplet sensitizers are themselves photolabile and are lost by photochemical reactions during the sensitization process. A new ketocoumarin sensitizer with decyloxy substituents and a reduced tendency to phase separate from the polymer is reported. A simple calculation of the sensitization stoichiometry shows that a single molecule of this ketocoumarin sensitizes the destruction of approximately 90 cinnamate chromophores in the “as cast” films below Tg and about 300 chromophores in the more‐ordered glassy nematic films and in “as cast” films of poly(vinyl cinnamate). Triplet sensitization of fluid nematic films leads, upon initial irradiation, to UV‐vis hyperchromism that is attributed to disruption of chromophore aggregation and, possibly, to disruption of the nematic mesophase as photoproducts begin to form. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 134–144, 2001

Publication Title

Journal of Polymer Science Part A - Polymer Chemistry

Volume

39

Issue

1

First Page

134

Last Page

144

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