Evidence of Counterion Size Effect on the Stability of Columnar Phase of Ionic Liquid Crystals Based on Pyridinium Salts Derived from N-3,4,5-Tri(alkyloxy)-benzyl-4-pyridones

Abstract

The synthesis and characterization of novel ionic liquid crystals based on pyridinium salts with Br− and PF6− counterions are described in this work. These pyridinium salts were derived from 4-hydroxypyridine, both by N- and O-alkylation. The 3,4,5-tri(alkyloxy)-benzyl mesogenic unit was attached to the nitrogen atom of the pyridinium ring. Alkyl chains with a different number of carbon atoms (6, 8, 10, 12 and 14) were employed in order to show the effect on the stability of mesophase. The POM (polarizing optical microscopy) and XRD (powder X-ray diffraction) studies indicated that bromide salts with shorter chains C6, C8 and C10 do not show mesomorphic properties, while longer chain analogues with C12 and C14 exhibit two enantiotropic columnar phases. Surprisingly, the pyridinium salts with the larger size PF6− counterion do not exhibit liquid crystal properties.

Counterion effects on the mesomorphic and electrochemical properties of guanidinium salts

“…On the other hand, counterions also play an important role in both the mesomorphic and electrochemical properties 1,2,53,65–71 of ILCs as well as hydrophilicity, viscosity, and electrochemical window. 27,72–74…”

“…[47][48][49][50][51][52][53] However, electrochemical studies of guanidinium-based compounds are quite rare and there are no reports on the electrochemical properties of guanidinium-based ILCs. 27,29,[54][55][56][57][58][59][60][61][62][63] On the other hand, counterions also play an important role in both the mesomorphic and electrochemical properties 1,2,53,[65][66][67][68][69][70][71] of ILCs as well as hydrophilicity, viscosity, and electrochemical window. 27,[72][73][74] Thus, in order to understand their liquid crystalline selfassembly in the bulk phase and their electrochemical behavior in solution, we investigated a series of wedge-shaped 3,4,5-trisalkoxy-phenyl-guanidinium salts Gua( 14)X with different counterions X = Cl, Br, I, BF 4 , PF 6 , OMs, SCN, N(CN) 2 , NO 3 , NTf 2 , OTf, OTs, N 3 , CN, OCN, OAc.…”

Editorial: Special Issue “Liquid Crystals 2020”

“…Two interesting contributions, one by Bruce et al [12] in the field of ionic liquid crystals (ILCs), and a second by Rieth et al [13] in the field of discotic liquid crystals (DLCs) based on star-shaped compounds, were included in the present collection. ILCs are now being widely investigated due to their great characteristics that come from the combination of LC and ionic liquid (IL) properties [14,15]. The application of ILCs in solar cells, membranes, battery materials, electrochemical sensors, electroluminescent switches, etc.…”