o-Carborane derivatives for probing molecular polarity effects on liquid crystal phase stability and dielectric behavior

A series of mesogenic derivatives of o-carborane was synthesized, their properties were analyzed by thermal, optical and XRD methods, and results were compared with those of isostructural p-carborane and benzene analogues. Comparative analysis revealed lower nematic phase stability and enhanced smectic behavior, including SmC, in the o-carborane derivatives relative to the isosteric p-carborane analogues. The effect of o-carborane on the electrooptical properties was assessed for biphenyl derivative 1[B]a in the 6CHBT nematic host giving the extrapolated Delta epsilon = 11.0, and a moderate increase of the elastic constants K-ii. Complete analysis of the dielectric results for o-carborane and p-carborane analogues 1[B]a and 1[A]a was performed using the Maier-Meier formalism augmented by DFT computational methods.