Synthesis and characterization of photoactive columnar liquid crystals containing azobenzene and quinoxaline moieties

Light Modulated Reversible "On-Off" Transformation of Arylazoheteroarene Based Discotics in Nematic Organization

Three benzene-1,3,5-tricarboxamide (BTA) core-based molecular systems appended with phenylazo-3,5-dimethylisoxazole photoswitches at the peripheral position through variable-length alkoxy chains have been designed and synthesized. The supramolecular interactions of the mesogens provided discotic nematic liquid crystalline assembly as confirmed by polarized optical microscopy (POM) and X-ray diffraction (XRD) studies. Spectroscopic studies confirmed the reversible photoswitching and excellent thermal stability of the photoswitched states in solution phase and thin film. Also, atomic force microscopic (AFM) and POM investigations demonstrated the morphological changes in the self-assembly induced by the photoirradiation as monitored by the changes in the height profiles and optical appearance of the textures, respectively. Remarkably, the liquid crystalline discotic molecules showed reversible "on and off states" controlled by light at ambient temperature.

Chiral columns forming a lattice with a giant unit cell

Mesogenic materials, quinoxaline derivatives with semi-flexible cores, are reported to form a new type of 3D columnar phase with a large crystallographic unit cell and Fddd lattice below the columnar hexagonal phase. The 3D columnar structure is a result of frustration imposed by the arrangement of helical columns of opposite chiralities into a triangular lattice. The studied materials exhibit fluorescence properties that could be easily tuned by modification of the molecular structure; for compounds with the extended π electron conjugated systems the fluorescence is quenched. For molecules with a flexible structure the fluorescence quantum yield reaches 25%. On the other hand, compounds with a more rigid mesogenic core, for which the fluorescence is suppressed, show effective photogeneration of charge carriers. For some materials bi-polar hole and electron transport was observed.

Structure-property relationships of quinoxaline-based liquid crystals

Quinoxaline derivatives with different molecular structures stabilizing liquid crystalline self-assembly are discussed in this review. This class of molecules can be systematically modified with careful molecular engineering to achieve different molecular shapes, directing them to self-assemble into various types of mesophases. The structure-property relationships of such molecules and the resultant self-assembled functional structures are of utmost importance in organic electronic devices and related applications.