High Delta epsilon nematic liquid crystals: fluxional zwitterions of the [closo-1-CB9H10](-) cluster

A new class of nematics with high dielectric anisotropy (Delta) for display applications has been developed and characterized by thermal and dielectric methods in mixtures with 3 nematic hosts: ClEster, 6-CHBT, and ZLI-1132. The key structural element is the zwitterionic derivative of the [closo-1-CB9H10](-) anion substituted at the B(10) position with either pyridinium (3) or sulfonium (4) groups. The zwitterions increase the longitudinal molecular electric dipole moment by 8 D (4) or 12 D (3) and give rise to the extrapolated Delta epsilon in the range of 22 (4a)-113 (3c). The sulfonium derivatives 4 have higher solubility in nematic hosts, lower tendency to aggregate, and lower impact on host's viscosity than pyridinium 3. This, in part, is attributed to facile epimerization at the sulfur center in 4 and existence of the trans/cis equilibrium. Experimental results are augmented with DFT calculations and analyzed using the Maier-Meier relationship.