Thermotropic liquid-crystalline properties of extended viologen bis(triflimide) salts

Abstract

A series of extended, symmetric viologen triflimides were synthesized by the metathesis reaction of lithium triflimide with the respective viologen tosyalates in methanol. Their chemical structures were characterized by Fourier Transform Infrared, 1 H and 13 C Nuclear Magnetic Resonance spectroscopy and elemental analysis. Their thermotropic liquid-crystalline (LC) properties were examined by a number of experimental techniques including differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy and variable temperature X-ray diffraction. The viologen salts containing alkyl chain of two carbon and three carbon atoms were relatively low melting salts. Those of alkyl chains of four carbon and five carbon atoms formed ionic liquids at 88 and 42 °C, respectively. Those of alkyl chain of nine, ten and eleven carbon atoms were high melting salts as high as 166 °C. Those of higher alkyl chains of sixteen, eighteen and twenty carbon atoms showed thermotropic LC phases forming SmC, SmA and an unidentified smectic (Sm) phases, and showed SmA to isotropic transitions at high temperatures. As expected, all the viologen triflimides had excellent stabilities in the temperature range of 338-365 °C.

Thermotropic Liquid-Crystalline and Light-Emitting Properties of Bis(4-aalkoxyphenyl) Viologen Bis(triflimide) Salts

“…They can be dicationic, tricationic, and multicationic in their makeups [18][19][20][21][22][23][24][25][26][27][28][29][30]. For example, viologens are examples of dicationic salts that are symmetric (alkyl groups similar) and exhibit LC phases (n = 6, 7, 8, 14-20) even at room temperature [31][32][33]. Asymmetric (alkyl groups dissimilar) types with triflimides as counterions exhibit smectic LC phases with a wide range of stability that range from as low as 0 • C to as high as 146…”

“…The LC properties of these salts with these triflimide anions enable one to establish the structure-property relationship of this important class of ILCs. Additionally, in contrast to other anions, the reports of ILCs on triflimide anions are relatively less studied [24,[31][32][33][34][38][39][40] which give the impetus for this study. As a continuation of our research efforts on ILCs, herein, we describe the synthesis of a series of extended viologen salts with bis(triflimide) (n = 1, 6, 8, 10, 12, 14, 16, 18, and 20), where n denotes the carbon atoms in the alkoxy chain.…”

Recent synthetic advances in pyridine-based thermotropic mesogens

“…Goossens and co-workers 80 published a review article on the design, synthesis, and characterization of certain pyridinium and 4,4 0 -bipyridinium (viologen)-based thermotropic ionic liquid crystals and also highlighted their applications. Further, Bhowmik et al 81 prepared a series of symmetric viologen tri-imides obtained by reacting viologen tosyalates with lithium triimide through metathesis reactions. Furthermore, they noted relatively low melting points of viologen salts that bear two or three carbon atoms in their alkyl chains.…”

Thermotropic Liquid-Crystalline Properties of Viologens Containing 4-n-alkylbenzenesulfonates

“…These applications, to name a few, include electrochromic devices, molecular machines, organic batteries, and carbohydrate oxidation catalysts in alkaline fuel cells [2,3]. In addition, they were studied not only for the preparation of the ever-increasing class of ionic liquids with proper chemical modifications of cations and anions [4][5][6][7][8][9][10][11][12], but also for the preparation of ionic liquid crystals (ILCs) [7,[13][14][15][16][17][18][19][20][21][22][23][24]. To mention several their chemical structures (I-VI) are given in Figure 1 as representative examples.…”

“…To mention several their chemical structures (I-VI) are given in Figure 1 as representative examples. Their LC phases are found to be dependent on both the chemical architecture of viologen moieties including dialkyl [13,[17][18][19]23], asymmetric dialkyl [7], di(oligooxyethylene) [14,15], di(3,4,5-tri-n-alkoxybenbenzyl) [22], diphenyl [16,24], and 4-n-alkoxyldiphenyl [24], and the chemical architecture of the anions are of varying sizes. The anions to date include bromide, iodide [14,15], − BF 4 , − PF 6 [22,24], − OTf, − SCN, − NTf 2 , 4-n-alkylsulfonates [24], 4-n-alkylbenzenesulfonates [16], and 3,4,5-tri-n-dodecyloxybenzenesulfonate [23].…”