Liquid crystalline properties of dissymmetric molecules part 5: the effects of alkyl chain length and linkages on thermal properties of smectic A and C phases in three aromatic ring systems

This paper describes the effect or alkyl and alkoxy chain lengths on the thermal properties of four isomeric systems; 4-R-phenyl 4-(4-octyloxybenzoyloxy)benzoates (1). 4-octyloxyphenyl 4-(4-R-benzoyloxy)benzoates (2), 4-(4-R-benzoyloxy)phenyl 4-octyloxybenzoates (3), and 4-R-phenyl 4-octyloxyphenyl terephthalates (4) (R=alkoxy, alkyl). The smectic properties for 1 and 2 are fairly different when both terminal alkyl and alkoxyl groups are short. while both have the same liquid crystalline core. The homologs of 3 exhibit only a smectic C phase even in the higher homologs. The homologs of 4 preferentially exhibit smectic A and C phases from the earlier homologs. The difference in the smectic properties will be discussed in terms of their molecular characteristics.