Extinction dichroic dyes

Dyes that dissolve in the liquid crystal and have high extinction coefficients at the laser emission wavelength are required. If the device is for projection applications, the dye should not absorb at the wavelengths that may be used to project the final image-infrared dyes and lasers are well suited for this. The dye will experienee very high temperatures for very short time periods when addressed by the laser and should therefore be stable to heat and light. Dichroic dyes appear to give smaller spot widths than isotropic dyes, and so dyes with a modest order parameter (5=0.5-0.6) are desirable [23]. 

The butyl derivative of these nickel complexes was investigated as a dye in a guest-host system using 4-pentyl-4 -cyanobiphenyl (5CB) as the host. The complex was found to have a large extinction coefficient of absorption (e = 28,000 moC dm cm at 860 nm) and dissolved in 5CB at concentrations up to 10% (w/w). At 20 °C, such solutions showed a dichroic ratio (Rd. defined as + /+x = absorbance) of 4.97 and a dye order parameter of 0.57. 

Dye Sign of dichroism Wavelength of maximum absorption A (nm) Extinction coefficient (10 ) Dichroic ratio Maximmn solubility at room temp. (wt. %)... 

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