Effect of size of the lateral substituent at the chiral centre on the stability of some chiral smectic liquid-crystalline phases. The ‘propyl effect’ in some chiral phenylpropiolates and benzoates

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Abstract
Two separate homologous series of chiral smectic liquid crystals have been prepared and their physical properties investigated. The materials were designed so that the size of the lateral substituent at the chiral centre could be varied. Thus, the (S)- or (R)-1-alkylheptyl 4′-(4-n-nonyloxyphenylpropioloyloxy)biphenyl-4-carboxylates, and the (S)- or (R)-1-alkylheptyl 4′-(4-n-nonyloxybenzoyloxy)biphenyl-4-carboxylates were synthesized where the length of the lateral alkyl chain at the chiral centre was varied from methyl to propyl. It was discovered that the ferroelectric phase was depressed on ascending the series and eclipsed by the antiferroelectric phase for the propyl members. Thus, the propyl substituent appears as a crossover point for the change in ferroelectric to antiferroelectric properties in liquid-crystalline systems.