Molecular structure and the occurrence of smectic A and smectic c phases

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Abstract
The mesomorphic properties of various terminally alkyl and/or alkoxy substituted azobenzenes are investigated. The non-polar dialkylazobenzenes have nematic and smectic A phases. For each alkyl group that is replaced by an alkoxy group (thus introducing an outboard dipole moment) the tendency to form a smectic C phase is increased. These results can be rationalized in terms of a dipole model of the smectic C phase, and do not support the idea that this phase occurs mainly because of steric interactions between zig-zag shaped molecules. In the case of only one outboard dipole moment there are two possibilities for a model with dipole interaction, one of which has ferroelectric smectic layers. This situation could possibly provide a model for the smectic F phase