Synthesis of novel chiral ionic liquids and their phase behavior in mixtures with smectic and nematic liquid crystals

Alkylation of 1-alkyl-1H-imidazoles 2a-f with citronellyl bromide 1b opens access to chiral 1H-imidazolium bromides 3a-f (Scheme 1). A similar strategy yielded the chiral pyridinium ionic liquid 6 (Scheme 2). Dialkylation of 1H-imidazole (7) gave the C-2-symmetric 1,3-dicitronellyl-1H-imidazolium bromide (8) (Scheme 3). Differential scanning calorimetry and optical polarizing microscopy revealed smectic mesophases for 1-citronellyl-3-tetradecy-1H-limidazolium bromide (3e) and 1-citronellylpyridinium bromide (6) (Table). In binary mixtures with smectic and nematic liquid crystals 9 and 10, 1-citronellyl-3-methyl-1H-imidazolium bromide (3a) behaved differently. Increasing quantities of 3a cause a decrease of the smectic-phase width for the mixture 3a/9 (Fig. 3), whereas the phase width of the nematic phase for 3a/10 remained nearly constant (Fig. 4).