Order Parameters of Guest/Host Systems from UV Spectra – A Test of a New Method and its Application to Rigid Guest Molecules –

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Abstract
For a determination of the order parametersS*,D* of nematic guest/host phases from polarized UV and sometimes IR spectroscopy, the experimental information is often not sufficient because of overlapping absorption bands. For molecules with only one purely polarized band, the temperature dependence of the degree of anisotropy and a theoretical relationD* =f(S*) can be used to overcome this lack of information. A method introduced earlier [7] is examined with respect to its range of applicability. It can be shown that in the region of overlapping bands an amount of about 30% of the band with the proper polarization direction is sufficient to determineS* andD* with an error of at most 2 to 5% and 5 to 10%, respectively. The temperature dependence ofS*,D* for the rigid molecules azulene, phenanthrene, anthracene, 9,10‐dichloro‐, 9,10‐dibromo‐, 9,10‐dimethylanthracene, phenazine, and acridine in ZLI 1695 has been determined. Three different types of structural dependence can be derived from the experimental data.