Discotic liquid crystals as new class of fluid and their electrical and optical properties

Abstract

Unique shctural, electrical and optical properties of discotic liquid crystals composed of disc-shaped molecules are discussed in comparison with those of calamitic liquid crystals composed of rod-like molecules, dielectric liquids and crystals.Electronic carrier is confirmed to contribute dominantly in fast photoconductivity in discotic liquid crystals. Hole mobility in discotic phases has been found to be much larger compared with ionic mobility and to be dependent on the molecular structure, phases and disorders. Photo-carrier generation process in discotic liquids is also studied and discussed in terms of Onsager model.

Electrical and optical properties of discotic liquid crystals with various core structures

“…Contrary to organic liquids in which free electrons with large mobility dependq on the molecular structure are confmed to exist [ 1.21, only ionic carrier mobility, which is related to the viscosity of the fluid by Walden's rule, has been reported in ordinary liquid crystals such as nematic, smectic and cholesteric liquid crystals [3,4]. However, recently, observations of hole mobility have been reported in discotic liquid crystals such as 2,3,6.7,10,1 I-Hexahexyloxytnphenylene (HHOTP) in which disc-shaped aromatic units stack in one direction and form a columnar structure [5][6][7][8][9], although direct evidence of hole transport is not complete. This is very important finding for the understanding of carrier transport process in fluids, because the report on direct observation of holes in dielectric liquids is highly limited so far.…”