Racemic and Enantiomeric Alkoxycyanobiphenyls Bearing Terminal Vicinal Fluorine Substituents: Synthesis and Mesogenic Behavior

Fascinated by the influence of fluorine atom substitution in liquid crystal mesogens and building on our previous research on the influence of fluorination in liquid crystal mesogens, a novel project was undertaken where racemates and enantiomers of alkoxycyanobiphenyls with two adjacent fluorine atoms, one on each of two terminal carbon atoms, were synthesized to study their phase properties. The compounds were synthesized via Mitsunobu reaction, alkylation, epoxidation, hydrolytic kinetic resolution, fluoride opening, and deoxyfluorination. Racemates showed a monotropic nematic phase, while enantiomers showed a monotropic cholesteric phase. The dipole moments of the final difluorinated mesogens were also evaluated. The phase behavior of all the epoxy and fluorohydrin intermediates was also measured. This article provides data on the phase behavior of a handful of racemic compounds and their enantiomers. Additionally, the phase behavior of the enantiomerically impure and enantiomerically pure compounds is compared.