The synthesis and liquid crystalline behaviour of 2-(4-n-alkoxyphenyl)-5-methylpyridines

We have synthesized a new series of polyphenylene compounds with a pyridine ring, 2-(4-n-alkoxyphenyl)-5-methylpyridines (CH3C5H3NC6H4OCiH2i+1) (1a-i; the carbon number, i, of the alkoxy group is 1-9), and studied their phase transitions and mesogenicity using DSC and polarizing microscopy. In the h omologous series of 1a-i, no mesomorphic phase appeared for i = 1-5 and onl y a monotropic nematic phase was observed for i = 6-9. The mesomorphic pote ntial is relatively weaker for the 1a-i than for the 2a-i and 3a-i homologu es, which are pyridine-containing three- and four-ring similar systems. Thi s lowering of the mesogenicity may be due to the lack of a phenyl ring betw een the pyridine ring and the methyl group in the 1a-i homologues.