Molecular Organization in the Nematic and Smectic A Mesophases of 4-n-butyloxybenzylidene-4′-acetoaniline

Fryburg, Gelerinter and Fishel have studied the structure of two smectic A phases using electron resonance spectroscopy with vanadyl acetylacetonate as the spin probe. (1) Their analysis of the electron resonance spectra shows that in 4-n-butyloxybenzylidene-4′-aceto-aniline the orientational order of the probe does not change at the nematic-smectic transition and that the temperature dependence of the order is the same in both phases. In addition the angular dependence of the vanadium coupling constant, in the smectic A phase, was found to be in poor agreement with theory. These findings are unexpected for the orientational order of spin probes dissolved in smectic A mesophases has been found(2,3) to be essentially temperature independent in contrast to the behaviour in a nematic mesophase. Further the angular dependence of the hyperfine coupling was found to be in excellent agreement with theory. (2,3) Finally earlier results indicate that there should be a discontinuity in the orientational order at the nematic-smectic transition.(3) These differences have prompted us therefore to reinvestigate the molecular organization within the nematic and smectic A mesophases of 4-n-butyloxybenzylidene-4′-acetoaniline but with (3-spiro-[2′N-oxyl-3′,3′-dimethyloxazolidine]) 5α-cholestanaes a spin probe.(4)