Optical anisotropies of alkylcyanobiphenyls, alkoxycyanobiphenyls and related compounds

Abstract

Mean-square optical anisotropies, γ², of cyanobenzene, anisole, cyanobiphenyl, p,p′-cyano-n-alkylbiphenyls, NC—C₆H₄—C₆H₄—C_mH_2m+1, with m= 6, 8 and 9, and p,p′-cyano-n-alkyoxybiphenyls, NC—C₆H₄—C₆H₄—O—C_mH_2m+1, with m= 6 and 9, have been determined from intensities of the depolarized Rayleigh scattering of their dilute solutions in carbon tetrachloride. Results are compared with previously reported determinations of optical anisotropies by other means. Treatment of the data according to a constitutive scheme corresponding to that applied in the preceding paper demonstrates consistency of the main results and enables calculations to be performed for homologues not included in the experiments. The difference between the polarizabilities parallel and perpendicular to the long axis of the cyanobiphenyl group is Δα= 20.6 ų in the alkyl series and 23.3₅ų in the alkoxy series; the difference is attributable to para substitution of the phenyl group by oxygen. Bonds of the randomly configured alkyl groups make a negligible contribution to the configurationally averaged anisotropy tensor, 〈â〉. Their contribution to 〈γ²〉 is small but not negligible. The relevance of the anisotropies, Δα, to the manifestation of liquid crystallinity in the alkyl and alkoxy homologues is pointed out.