Verdazyl-based Bent-Core Liquid Crystals

Abstract

The scope of this thesis is focused on the development and characterization of paramagnetic bent-core liquid crystals based on the verdazyl radical.

Intermediary to both crystalline and ordinary liquid states of matter exists a unique state, the liquid crystal state, which exhibits some characteristics of both, such as the fluidity of a liquid, and the long-range partial orientational and positional order of a crystal. Liquid crystalline phases manifest variations depending on molecular shape, such as rod-like, disc-like or bent-core molecules. The structure of a liquid crystal molecule typically consists of a judicious arrangement of rigid core units, linking groups and flexible carbon chains. Variations of these components give rise to divergent types and properties of the liquid crystalline phases. In this work, the verdazyl, a stable heterocyclic radical, is used as the key structural element of a series of bent-core liquid crystals.

As the first step toward this goal, fundamental chemistry of the verdazyl radical was explored and practical synthetic methodologies for functionalization and functional group transformations on the verdazyl heterocycle were established. Using these strategies, a series of paramagnetic bent-core molecules with 1,3-“di-armed” substitution pattern on the verdazyl has been prepared and investigated by thermal and optical methods. Results show that some of these new compounds exhibit smectic liquid crystalline behavior and they have lower melting point temperatures than the previously investigated 1,5-“di-armed” analogues. These materials will be further characterized for their magnetic and photoconducting properties.