A comparison of mesogenic properties for one- and two-ring dipentyl derivatives of p-carboranes, bicyclo[2.2.2]octane, and benzene

Abstract

A series of nonpolar single- and two-ring dipentyl derivatives of p-carboranes, bicyclo[2.2.2]-octane and benzene was investigated in the pure state and in binary mixtures with a nematic host. The resulting virtual nematic-isotropic transition temperatures [T _NI] for single ring compounds were compared with those for two ring compounds. All [T _NI] were compared with the molecular aspect ratios X and filling fractions F obtained from MNDO calculations. The highest effectiveness in promotion of the nematic phase was found for bicyclo[2.2.2]octane and 12-vertex p-carborane and ascribed to exceptional molecular rigidity and electronic properties, respectively. Results show that a high filling fraction F and molecular stiffness are the necessary factors for a highly stable nematic phase.

Notes

V _B was calculated for MNDO-optimized molecular models in a Cerius2 suite of programs using keywords volume=TOTAL, probe radius=3.0 and grid=FINE.