They propose to conduct a three-year study of the structure and properties of discotic liquid crystals and liquid crystal polymers. Both known and new compounds will be synthesized, purified, and characterized optically and thermodynamically. Their structures will then be studied via x-ray diffraction, with particular emphasis on single-domain, high resolution studies of the columnar phases, in a suspended strand geometry. Discotic liquid crystals are typically composed of molecules with a rigid, disk-shaped core, and 4-8 flexible alkyl tails. In addition to orientationally ordered nematic phases, these molecules can order into columnar structures, with long range two-dimensional positional order of the columns but only short range order along each column; such columnar phases can be thought of as complementing the one-dimensional smectic phases formed by many rod-like mesogens. Although discotics have been studied for over a decade, little is known about the structural order, conditions for stability, and phase transitions of these unusual materials. The materials to be studied include: a) hexa-n- alkylthiotriphenylene and related analogs, which display an unusual transition from a disordered columnar phase to a closely related helical incommensurate crystalline phase; b) phthalocyanine and related organometallic liquid crystalline compounds, which have potentially important applications as anisotropic organic conductors; and c) discotic liquid crystal polymers incorporating a variety of mesogenic units, including triphenylene, phthalocyanine, and "Tubular" cores.
