Oxadiazolyl-Pyridinium as Cationic Scaffold for Fluorinated Ionic Liquid Crystals

Abstract

The synthesis and characterization of a new class of 1,2,4-oxadiazolylpyridinium as a cationic scaffold for fluorinated ionic liquid crystals is herein described. A series of 12 fluorinated heterocyclic salts based on a 1,2,4-oxadiazole moiety, connected through its C(5) or C(3) to an N-alkylpyridinium unit and a perfluoroheptyl chain, differing in the length of the alkyl chain and counterions, has been synthesized. As counterions iodide, bromide and bis(trifluoromethane)sulfonimide have been considered. The synthesis, structure, and liquid crystalline properties of these compounds are discussed on the basis of the tuned structural variables. The thermotropic properties of this series of salts have been investigated by differential scanning calorimetry and polarized optical microscopy. The results showed the existence of an enantiotropic mesomorphic smectic liquid crystalline phase for six bis(trifluoromethane)sulfonimide salts.

Synthesis and Antibacterial Activity of Mono- and Bi-Cationic Pyridinium 1,2,4-Oxadiazoles and Triazoles

“…Column chromatography on silica gel, technical grade, pore size 60 Å, 230-400 mesh, and particle size 40-63 µm and TLC silica gel 60 F 254 on aluminium support were used. Compounds 3a-c, 4, 5, 6a-c, 9, 10, 11a-b, 12a-b, 14a-b, 15a-b, 16a-b, 17a-b, 18a-b, 19a-b, 20a-b, 21, 22, 23a-c, 24, 25, 27, 28a-b, 29a-b, and 30a-b synthesis and characterization are in agreement with the previously reported data (see Supplementary Material) [26][27][28][29][30][31][32]36,37].…”

“…In this work, the antibacterial activity of different mono- and bi-pyridinium salts with different lengths of the alkyl chain, fluorinated or not, and with different counter ions, was evaluated. Some of the N -alkylpyridinium salts and N -perfluoroalkylpiridinium salts taken into consideration have been previously reported for different applications, such as ILs or ionic liquid crystals (ILCs) [ 26 , 27 , 28 , 29 , 30 , 31 , 32 ]. These organic salts have an azole ring as a spacer (specifically, 1,2,4-oxadiazole or 1,2,4-triazole).…”

Shaping 1,2,4-Triazolium Fluorinated Ionic Liquid Crystals

“…However, [Ph-Tri-( 14) 2 ][OTf] showed a deviation from the above trend as a decrease in T c value was recorded for this salt. The observed increase in clearing points with an increasing chain length are in agreement with what was previously reported as longer hydrocarbon chains increase the van der Waals forces among the alkoxy moieties, inducing micro-segregation between the hydrophobic alkyl chains and charged ionic regions [10]. Interestingly, passing from 14 hydrocarbon chains to longer alkyloxy chains (16), more than one transition can be recognized and, moreover, the transitions to mesophases are observable both in cooling and heating ramps.…”

“…These combined properties allow ILCs to be exploited in a variety of fields, such as acting as electrolytes for batteries, [3] in dye-sensitized solar cells, [4] in sensors, [5,6] and as water desalination membranes, [7] to cite a few. Aside from the widely explored cationic cores such as imidazolium and pyridinium, [8][9][10] other heterocyclic core ionic structures, such as oxadiazoles and triazoles, which have been mainly investigated for their biological activity, [11][12][13][14] are interesting for their predictable tuning of mesophase behavior [1,15] when segregations between polar charged regions and non-polar aliphatic chains are expected to drive self-assembly. Moreover, the presence of fluorocarbon chains would additionally stress self-organisation [9,16,17] and allow for the formation of ordered, smectic lamellar phases [18][19][20][21] with the appealing property of gas sorption [22].…”

“…In this context, we recently studied a set of 1,2,4-triazolium salts with a variable fluoroalkyl chain length (3,7,9), a variable alkyl chain length (10,12,14), and different anions that showed predominantly smectic A (SmA) phases [23,24]. Their liquid crystalline behaviour was dependent on the counterion and on the length of the perfluoroalkyl chain linked to the triazolium core of the salts [23,24].…”