Discotic liquid crystal compensation film

Discotic liquid crystals (DEC) consist of molecules with a rigid core from aromatic rings and flexible branches from hydrocarbon chains as discussed in Chapter 1. The molecules can be regarded as discs [45]. On average, the normal axes of the discs are aligned along a common 

When a discotic liquid crystal is sandwiched between two substrates (or exposed to air), the direction of the uniaxial axis can be controlled by alignment layers, external electric fields, and chiral dopants [46,47]. It is therefore possible to develop discotic compensation films with spatially varied uniaxial axis orientations. For example, Fuji Photo Film Co. developed discotic compensation films for TN LCDs. In both the TN display and discotic compensation film, the liquid crystal directors vary in the vertical direction. Each layer of nematic liquid crystal with a certain director orientation is compensated by a layer of discotic liquid crystal with the same director orientation. 

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Also, the chemistry and polymerization of discotic monomers has been reviewed [10]. Their current and emerging uses are in optical compensation films for liquid crystal displays, carbon nanostructures, organic electronics, solar cells, light-emitting diodes, and field-effect transistors. 

There are as yet ho accepted standard materials for discotic nematic liquid crystals. It is expected that the birefringence of these materials will be negative, and they have already found application as optical compensation films for liquid crystal displays [23]. In order to illustrate an example of the optical properties of discotic nematic liquid crystals, we give in TABLE 10 measurements of the ordinary and extraordinary refractive indices of hexakis[(4-octylphenyl)ethinyl]benzene (Tm = 100 C). These are taken from [24] and were measured for a wavelength of 589 nm. 

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