A new class of liquid crystals: methylene-1,4-dihydropyridines

A group of liquid crystal materials which contain the novel methylene-1,4-dihydropyridine substructure were synthesized and their mesogenic properties examined. Three main classes of liquid crystal compounds which differ in the structure of the aromatic core group (phenyl, azobenzene and diphenylacetylene) attached to the nitrogen of the 1,4-dihydropyridine group were studied. The synthesis of the methylene-1,4-dihydropyridine group was accomplished in excellent yield by a Knoevenagel condensation of a 4-pyridone intermediate with an active methylene compound. The liquid crystal materials prepared thus far which contain this methylene-1,4-dihydropyridine structure all possess broad enantiotropic smectic A phases and one example also possesses a tilted smectic C phase. These mesogens may possess useful properties such as high birefringence.