Spectral chiral nematics

Guo, J.-X., and Gray, D. G. (1991). Spectral behavior of dye molecules oriented by chiral nematic (acetylXethyl)cellulose solutions. In Fourth Chemistry Congress of North America, Polym. Abstract 331. Am. Chem. Soc., Washington, DC. 

For chiral nematics, this relationship has been satisfactorily verified [46] over a range of An from 0.04 to 0.15 and bandwidths of -10-50 nm have been readily achieved. This is important for spectral filters and optical mirrors. 

Figure 26. Infrared helical absorption spectrum for a 1.71 1.00 chiral nematic mixture of cholesteryl chlo-ride cholesteryl myristate (redrawn from [106]). The dashed line corresponds to spectral regions of strong infrared absorption.

Woon, K.L., O NeiU, M., Richards, G.J., Aldred, M.P., Kelly, S.M., Fox, A.M. Highly circularly polarized photoluminescence over a broad spectral rtmge from a calamitic, holetransporting, chiral nematic glass and from tm indirectly excited dye. Adv. Mater. 15(18), 1555-1558 (2003). doi 10.1002/adma.200304960... 

In any case however, antipodal helices cause countercurrent spectra of the optical rotation, so that the observation of just a single Cotton effect is sufficient to discriminate the antipodes and, in case, enantiomeric solutes. For such an experiment the choice of the infrared spectral range is no longer dictated by the structure period but by the presence of suitable transition moments. The low demand for the chiral solute to be characterized (Korte, 1978) is exemplified by Fig. 4.6-14. In the 20 im wide sample cell an area of 3 mm times 3 mm was filled with approximately 200 pg solution containing circa 0.2 pg of either S-(-) or R-(-i-) Thalidomide (Contergan) in a nematic solvent. In the spectral interval shown, at least three oppositely shaped ACE are found, the pronounced one around 836 cm is related to the 7 (C- H), phenyl-H out-of-plane vibration of the... 

This section pertains to reports on oriented molecules in which phases other than the usual thermotropic nematics have been used. Studies in chiral, smectic, columnar, lyotropic and polymeric liquid crystals as well as other unusual phases have been presented. The use of carbon-proton heteronuclear selective refocusing 2D NMR experiment designed for the spectral analysis of enantiomers dissolved in weakly ordering chiral liquid crystal solvents has been proposed." The method permits the extraction of carbon-proton residual dipolar couplings for each enantiomer from a complex or unresolved proton-coupled... 

Analysis of the optical properties of liquid crystals in more complex geometries, such as the twisted nematic state, can also be used to determine the refractive indices of nematics. Generalised transmission ellipsometry [13] has been used to measure the principal refractive indices and then-dependence on wavelength over the spectral range 350 to 1700 nm for 5CB and mixtures of 5CB with its chiral isomer CB15 (4-cyano-4 -(2methyI)-butylbiphenyl). 

---