Order parameters of some nematic p, p′ substituted tolanes as determined by polarized Raman scattering

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Abstract
The order parameters 〈P2〉 and 〈P4〉 of three nematic compounds have been determined by polarized Raman scattering. Results obtained with p‐pentyl‐p′‐cyanobiphenyl (5CB) agree well with published data. Next the influence of a strongly polar cyano end group on the order parameters was investigated. This was done by comparing two nematic liquid crystals of the tolane class, namely p‐heptyl‐p′‐cyanotolane and p‐heptyl‐p′‐methoxytolane, which have an almost identical geometrical shape. In spite of the difference in polarity hardly any difference in the order parameters 〈P2〉 and 〈P4〉 of both compounds could be observed. 〈P2〉 and 〈P4〉 of both tolanes show approximately mean field behavior in contrast to the low 〈P4〉 of 5CB.