Tailoring Liquid Crystalline Self-Assembly in Dialkoxybenzimidazoles: The Role of Charge and Shape

Liquid crystalline self-assembly in neutral and ionic dialkoxybenzimidazoles can be precisely tuned or suppressed by controlling molecular symmetry and charge, revealing key structure-property relationships for mesophase design. To elucidate these effects, a series of neutral (L-Bi(n), U-Bi(n)) and ionic (L-Me₂Bi(n)I, U-Me₂Bi(n)I) derivatives differing in the substitution pattern of the side chains (n = chain length) at the benzimidazole was synthesized and characterized by POM, DSC, and X-ray diffraction. Nonionic systems exhibit mesomorphism only for rod-like linear homologues (n = 9-14), forming nematic phases, whereas the neutral bent U-shaped derivatives remain non-mesomorphic. In contrast, ionic U-shaped derivatives form smectic phases, including a cubic phase for n = 12, while linear derivatives do not form mesophases. The solid-state structures demonstrate that both the capacity for hydrogen bonding in the neutral derivatives and the presence of π-stacking interactions in the ionic derivatives significantly influence the molecular packing. Furthermore, distinct differences in the packing arrangements are observed depending on the specific substitution patterns.