Liquid-crystalline and thermochromic behaviour of 4-substituted 1-methylpyridinium iodide surfactants

Ionic Liquid Crystals

“…4-Alkylpyridinium hydrochlorides, hydrobromides, or hydroiodides are not mesomorphic (70), but methylation of the N-atom induces mesomorphism (71). 166 The thermotropic mesomorphism of 4-substituted 1-alkylpyridinium iodides was investigated by Nusselder et al 167 The authors noticed that a mesophase is present when the substituent in the 1-position of 4-n-dodecyl-1-alkylpyridinium iodide is a methyl group but not when the methyl was changed into hydrogen, ethyl, n-propyl, i-propyl, n-butyl, n-hexyl, 3-hydroxypropyl, or 2-methoxyethyl. Given the fact that the N-alkylpyridinium (1-alkylpyridinium) compounds exhibit a mesophase for very long chain lengths (see further), it can be predicted that the 4-substituted 1-alkylpyridinium iodides can be made liquid-crystalline by inserting a long alkyl chain in the 1-position.…”

Thermotropic Ionic Liquid Crystals

“…Among organic cations, mesomorphism of pyridinium salts has been known since 1938 [ 81 ]. Later, it has been demonstrated that N -methylation (or more generally N -alkylation) is necessary for these salts to show mesomorphic behavior [ 82 , 83 ]. Recently, new imidazolium 51 and pyridinium salts 52 ( Scheme 14 ), bearing N -alkyl substituents with a chiral center in the position four to the nitrogen atom, have been synthesized and investigated [ 84 ].…”

Ionic Liquid Crystals Based on Pyridinium Salts

“…Moreover, it was observed that the 1-methyl-4-alkoxycarbonylpyridinium iodides salts have thermochromic properties. Color changes were observed on heating at both crystal to crystal and crystal to mesophase transitions, while such an observation could not be made for the 1-methyl-4-alkylpyridinium iodides salts [4,12,13].…”