Dyes, liquid crystal

Aromatic fluorination certainly is one of the best candidate reactions for micro reactors. Fluorinated compounds are of high industrial interest. For instance, they find wide application as pharmaceuticals, dyes, liquid crystals and crop-protection agents [3,13,16, 38] about every third drug contains a fluorine moiety. The introduction of fluorine moieties in molecules has unique effects on biological activity (see original citations in [16]). 

L. Komitov, C. Rnslim, Y. Matsuzawa, and K. Ichimura, Photoinduced anchoring transitions in a nematic doped with azo dyes. Liquid Crystals 27, 1011 (2000). 

Liquid crystal polymers are also used in electrooptic displays. Side-chain polymers are quite suitable for this purpose, but usually involve much larger elastic and viscous constants, which slow the response of the device (33). The chiral smectic C phase is perhaps best suited for a polymer field effect device. The abiHty to attach dichroic or fluorescent dyes as a proportion of the side groups opens the door to appHcations not easily achieved with low molecular weight Hquid crystals. Polymers with smectic phases have also been used to create laser writable devices (30). The laser can address areas a few micrometers wide, changing a clear state to a strong scattering state or vice versa. Future uses of Hquid crystal polymers may include data storage devices. Polymers with nonlinear optical properties may also become important for device appHcations. 

Table 10. Some Examples of Liquid Crystal Dyes...

Plastics can be used to make erasable printing media by a number of different techniques. Photo changing dyes could be incorporated into the structure of the plastics. The printer could change the dye to the colored form to read, and the material can be bleached with another unit that would reverse the photo coloring process. An ionic type plastic can be incorporated into the plastics and used to color the printed area by the use of an indicator type reaction with an organic acid or base. Another method would be to use a thermal printer in conjunction with liquid crystal type materials that would alter the state of the liquid crystals in the printed areas. Applying heat and electrical fields to the printed sheet would erase the printing. 

Reliable micro-scale measurement and control of the temperature are required in developing thermal micro-devices. Available measurement techniques can be largely classified into contact and non-contact groups. While the resistance thermometer, thermocouples, thermodiodes, and thermotransistors measure temperature at specific points in contact with them, infrared thermography, thermochromic liquid crystals (TLC), and temperature-sensitive fluorescent dyes cover the whole temperature field (Yoo 2006). 

The direction of the transition moment is of practical consequence in dyes used in liquid crystal display systems. It is important for such applications that the direction of the transition moment is aligned with the molecular axis of the dye. Since this is the case with azo dye 15f, the dye would appear to be a reasonable candidate as a liquid crystal display dye (see Chapter 10 for further discussion of this application of dyes). 

Figure 10.1 Orientation of dyes in on/off states of a liquid crystal display...

Figure 10.3 Anthraquinone dyes used in liquid crystal displays...

M Voigt, M Chambers, and M Grell, Circularly polarized emission from a narrow bandwidth dye doped into a chiral nematic liquid crystal, Liq. Cryst., 29 653-656, 2002. 

HJ Coles, GA Lester, and H Owen, Fluorescent dye guest-host effects in advanced ferroelectric liquid crystals, Liq. Cryst., 14 1039-1045, 1993. 

Chromoionophores, 20 517-518 Chromonema fibers, 17 612 Chromonic liquid crystals, 15 101 Chromophore interaction, in dye molecules, 20 511-512... 

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