Vitrified Liquid Crystalline Films: Material Synthesis and Optical Properties

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ABSTRACTCTS-9818234S. H. ChenU. of RochesterLiquid crystalline mesomorphism is characterized by a unaxial (i.e. nematic), lamellar (i.e. smectic), helical (i.e. cholesteric), or columnar (i. e. discotic) arrangement of molecular through self-assembly. Because of their unique optical properties, liquid crystals (LCs) have found various established and potential applications to electro-optics and optoelectronics. In the now almost mature LC display technology, LC materials function in the fluid state where an applied field induces molecular orientation with a response time on order of milliseconds. With judiciously designed structural moieties, LCs may also function in the solid state via a photonic or electronic stimulus with a response time on the order of pico- or femtoseconds. In addition to these switching devices, LCs in thin films can be employed as nonswitching devices (e.g. for polarization optics). With the exception of applications where the dynamics of molecular orientation are involved, vitrified LC films with an above-ambient glass transition temperature are uniquely suited for the fabrication of environmentally robust devices. The main theme of the proposed research is on vitrified LCs following two complementary approaches: glass-foaming liquid crystals (GLCs) and crosslinked LC polymers (XLCPs), with the objective of facilitating material processing into macroscopically ordered solid films.Capable of vitrification into well-ordered films with superior morphological stability, high optical birefringence GLCs have been successfully developed under a current NSF project. To take advantage of this new emerging class of organic materials, GLCs transparent down to 300 nm will be designed and synthesized for uniaxially and helically orienting luminophores to generate polarized light. As a complementary material concept, XLCPs of similar characteristics will be pursued for a comparative study. In this approach, the high degree of molecular order achieved in the fluid state will be preserved via photoinduced polymerization and crosslinking. In addition to nematic materials, novel approaches to gradient-pitch chiral-nematic GLCs and XLCPs will be explored for an extensive investigation of polarized photoluminescence, including the resonance region where no prior attempts have been made. A comprehensive theory will be constructed for circularly polarized photoluminescence by considering light absorption, emission, and propagation in periodically structured films. The general theory will be reduced to linearly polarized photoluminescence (from uniaxially aligned luminophores in vitrified nematic films and circular dichrosim/circular polarization (from light adsorption and propagation in vitrified chiral-nematic films) as two limiting cases. Experiments will be conducted to quantify the degrees of polarization for a validation of theoretical predictions. Potential applications to high-efficiency polarization, polarized light emission, color projection, stereoscopic display, and distributed feedback laser ill also be explored. In summary, polarized light is essential to optical information processing, display, and storage. The proposed research aims at the generation of polarized light using light-emitting and nonemitting films. Under the proposed program, a new generation of scientists and engineers will be educated in a multidisciplinary setting. New principles will be established for delineating optical processes in macroscopically ordered films and for developing superior materials instrumental to the advancement of optical information technologies.