WO2025029628A1 - Ionic liquid crystals of bis(4-oligoethyleneoxyphenyl) viologen salts - Google Patents

Abstract

Described herein are bis(4-oligoethyleneoxyphenyl) viologen salts and the synthesis thereof. The electrolytes exhibit extremely high ionic-conductivities >1 × 10⁻⁵ S·cm⁻¹. Also described are the use of bis(4-oligoethyleneoxyphenyl) viologen salts in various energy storage devices such as lithium-ion batteries, rechargeable batteries, fuel cells, super capacitors, or solar cells.

Description

IONIC LIQUID CRYSTALS OF B/S( 4-OLIGOETHYLENEOXYPHENYL) VIOLOGEN SALTS

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application No. 63/516,431 , filed on July 28, 2023, which is incorporated by reference herein in its entirety.

BACKGROUND

Thermotropic ionic liquid crystals (ILCs) are an important class of functional materials that combine the properties of ionic liquids and liquid crystals (LCs). The LC phases endow many advantages over isotropic melts; for example, ion conduction can be significantly enhanced in smectic A (SmA) and columnar phases (Col) when compared to the isotropic liquid phases. The unique properties of ILCs enable them for many technological applications, including display technology, solar cells, ion conductors in batteries, and templates for the synthesis of nanomaterials, among others. ILCs are even touted as organized reaction media in which many organic reactions including Diels-Alder reactions with highly regio- and chemo-selectivity may take place and have the potential to be recycled.

The properties of ILCs can be tailored by a combination of organic cations and organic/inorganic anions. Notable common cations include quaternary ammonium, quaternary phosphonium, pyrrolidinium, piperidinium, guanidinium, imidazolium, pyridinium, pyrazolium and triazolium, among other cations; notable common anions comprise Br, NOr, BF4’, CFsSOs", PFe", CIO4", OTs“, N(SO₂CF₃)2’, and ReC ", among other anions.

While previous are examples of monocations and monoanions predominantly employed for the synthesis of ILCs, the preparation of dicationic, tricationic and multicationic materials broadens the structural combinations that result in advanced properties, including enhanced conductivity and thermal stability. For example, symmetric viologens (made up of similar alkyl chains) are examples of dicationic salts, which have exhibited SmA, smectic C (SmC) and unidentified smectic (SmX) phases (n = 6, 7, 8, 14-20), even at room temperature. Asymmetric viologens (containing alkyl groups of dissimilar carbon chain lengths) with triflimides as counterions develop smectic LC phases in a wider range of temperatures, from as low as 0 °C to as high as 146 °C. A series of asymmetric viologens was described with triflimides as counterions (6BPn, where BP = 4,4'-bipyridinium ion and n = 5, 7, 10, 11 , 12, 14, 16, 18, 20 that melt into highly-ordered smectic T phases (SmT) at relatively low temperatures (lowest transition at -12 °C) and maintain liquid crystallinity in a wide range of temperatures (8-132 °C), with excellent thermal stabilities up to 320 °C. See Bhowmik et al., J. Mol. Liquids 365: 120126 (2022), and Int. Pat. App. No. PCT/US23/13284, each of which is incorporated by reference herein for such teachings.

What is needed are symmetric viologen salts with improved properties.

SUMMARY

One embodiment described herein is an ionic liquid crystal comprising a viologen salt of formula (I):

wherein:

. _D2 . . . . .. i-(OCH₂CH₂)_nOCH₂CH₃ . . _

R¹ and R² are each independently ? where n is 3-10; m and p are each independently 1-3;

R^a, at each occurrence, is independently Ci-4alkyl , Ci-2haloalkyl, -OCi-4alkyl, -OCi_₂haloalkyl, halogen, -NO₂, -CN, or -(OCH₂CH₂)i_₃OCH₂CH₃;

R^b, at each occurrence, is independently Ci-4alkyl, Ci-₂haloalkyl, -OCi-4alkyl, -OCi_₂haloalkyl, halogen, -NO₂, -CN,

^QX¹ and °X² are each independently

In one aspect, m is 1. In another aspect, p is 1. In another aspect, m is 2. In another aspect, p is 2. In another aspect, m is 3. In another aspect, p is 3. In another aspect, m is 1 and p is 1. In another aspect, m is 2 and p is 2. In another aspect m is 3 and p is 3. In another aspect, the viologen salt of formula (I) is a symmetric viologen salt.

In another aspect, °X¹ and °X² are each

In another aspect, °X¹ and °X² are each

In another aspect, the viologen salt of formula (I) is a viologen salt of formula (l-a):

In another aspect, the viologen salt of formula (I) is:

In another aspect, n is 1-3.

In another aspect, the viologen salt of formula (I) has a conductivity of at least about 1 x 10’³⁵ S cm’¹. In another aspect, the viologen salt of formula (I) has a conductivity of at least about 1 x 10^-5 S cm^-1. In another aspect, the viologen salt of formula (I) has a conductivity of at least about 4 x 10^-5 S- cm^-1.

Another embodiment described herein is a solid-state battery, supercapacitor, solar cell, or perovskite photovoltaic cell comprising an ionic liquid crystal comprising a viologen salt as described herein.

DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

FIG. 1 shows chemical structures of extended viologen salts (I— VI) that exhibit smectic A (SmA) phases.

FIG. 2 show thermogravimetric analysis (TGA) thermograms of Salts 1-3 obtained a heating rate of 10 °C/min in nitrogen.

FIG. 3A-B show differential scanning calorimetry (DSC) data of Salt 1. FIG. 3A shows DSC thermograms of Salt 1 obtained at both heating and cooling rates of 10 “C min^-1 in nitrogen (Exo up). FIG. 3B shows the d-spacings of Salt 1 plotted as a function of temperature around the crystal to isotropic transition (7cr .i = 212 °C) measured in the cooling cycle.

FIG. 4A-C show differential scanning calorimetry (DSC) data of Salt 2. (a) DSC thermograms of Salt 2 obtained at both heating and cooling rates of 10 °C- min^-1 in nitrogen (Exo up). FIG. 4B shows a photomicrograph of Salt 2 taken by Proof of Mechanism (POM) studies at 220 °C after melting at 212 °C revealing LC texture. FIG. 4A-C shows the d-spacings of Salt 2 plotted as a function of temperatures measured in the cooling cycle.

FIG. 5A-B show differential scanning calorimetry (DSC) data of Salt 3. FIG. 5A shows DSC thermograms of Salt 3 obtained at both heating and cooling rates of 10 °C min^-1 in nitrogen (Exo up). FIG. 5B shows a photomicrograph of Salt 3 taken at 200 °C on heating after its melting transition revealing fan-shaped texture of SmA. FIG. 5C shows the d-spacings of Salt 3 plotted as a function of temperatures (different colors correspond to different diffracted line) measured in the cooling cycle.

FIG. 6 shows a comparison of real conductivity o' of Salts 1-3 at 30 °C.

FIG. 7A-B show isothermal Bode plots of the complex permittivity (E^A*= s^A'-j E^A") for Salt 3, showing the real (lower) and imaginary (upper) components. FIG. 7Bshows the temperature dependence of E^A' measured at 3 kHz.

FIG. 8 shows the temperature variation of the complex conductivity, o*, for Salt 3 showing the real component, o' (lower) and the imaginary component, o" (upper).

FIG. 9 shows the temperature variation of the complex conductivity, o*, for Salt 1 showing the real component, o' (lower) and the imaginary component, o" (upper).

FIG. 10 shows the temperature variation of the complex conductivity, o*, for Salt 2 showing the real component, o' (lower) and the imaginary component, o" (upper).

FIG. 11A-C show the fluorescent spectra of Salt 1 (FIG. 11 A), Salt 2 (FIG. 11 B) or Salt 3 (FIG. 11C) in the solid state for the measurements of absolute quantum yields.

FIG. 12 shows thermal activation of conductivity in an Arrhenius plot for Salts 1-3.

FIG. 13A shows a molecular model and lengths for Salt 3, estimated with Advanced Chemistry Development (ACD) Software. FIG. 13B shows schematics of a potential smectic nanostructure based on the X-ray diffraction results from FIG. 5, indicating aromatic and ethylene oxide regions.

DETAILED DESCRIPTION

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. For example, any nomenclatures used in connection with, and techniques of chemistry, molecular biology, immunology, microbiology, genetics, cell and tissue culture, and protein and nucleic acid chemistry described herein are well known and commonly used in the art. In case of conflict, the present disclosure, including definitions, will control. Exemplary methods and materials are described below, although methods and materials similar or equivalent to those described herein can be used in practice or testing of the embodiments and aspects described herein.

As used herein, the terms such as “include,” “including,” “contain,” “containing,” “having,” and the like mean “comprising.” The present disclosure also contemplates other embodiments “comprising,” “consisting essentially of,” and “consisting of’ the embodiments or elements presented herein, whether explicitly set forth or not.

As used herein, the term “a,” “an,” “the” and similar terms used in the context of the disclosure (especially in the context of the claims) are to be construed to cover both the singular and plural unless otherwise indicated herein or clearly contradicted by the context. In addition, “a,” “an,” or “the” means “one or more” unless otherwise specified.

As used herein, the term “or” can be conjunctive or disjunctive.

As used herein, the term “and/or” refers to both the conjuctive and disjunctive.

As used herein, the term “substantially” means to a great or significant extent, but not completely.

As used herein, the term “about” or “approximately” as applied to one or more values of interest, refers to a value that is similar to a stated reference value, or within an acceptable error range for the particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, such as the limitations of the measurement system. In one aspect, the term “about” refers to any values, including both integers and fractional components that are within a variation of up to ± 10% of the value modified by the term “about.” Alternatively, “about” can mean within 3 or more standard deviations, per the practice in the art. Alternatively, such as with respect to biological systems or processes, the term “about” can mean within an order of magnitude, in some embodiments within 5-fold, and in some embodiments within 2-fold, of a value. As used herein, the symbol means “about” or “approximately.”

All ranges disclosed herein include both end points as discrete values as well as all integers and fractions specified within the range. For example, a range of 0.1-2.0 includes 0.1 , 0.2, 0.3, 0.4 . . . 2.0. If the end points are modified by the term “about,” the range specified is expanded by a variation of up to ±10% of any value within the range or within 3 or more standard deviations, including the end points.

As used herein, the terms “control,” or “reference” are used herein interchangeably. A “reference” or “control” level may be a predetermined value or range, which is employed as a baseline or benchmark against which to assess a measured result. “Control” also refers to control experiments or control cells. Definitions of specific functional groups and chemical terms are described in more detail below. For purposes of this disclosure, the chemical elements are identified in accordance with the Periodic Table of the Elements, CAS version, Handbook of Chemistry and Physics, 75^th Ed., inside cover, and specific functional groups are generally defined as described therein. Additionally, general principles of organic chemistry, as well as specific functional moieties and reactivity, are described in Organic Chemistry, Thomas Sorrell, University Science Books, Sausalito, 1999; Smith and March March’s Advanced Organic Chemistry, 5^th Edition, John Wiley & Sons, Inc., New York, 2001 ; Larock, Comprehensive Organic Transformations, VCH Publishers, Inc., New York, 1989; Carruthers, Some Modern Methods of Organic Synthesis, 3^rd Edition, Cambridge University Press, Cambridge, 1987; the entire contents of each of which are incorporated herein by reference.

The term “alkoxy,” as used herein, refers to a group -O-alkyl. Representative examples of alkoxy include, but are not limited to, methoxy, ethoxy, propoxy, 2-propoxy, butoxy and tertbutoxy.

The term “alkyl,” as used herein, means a straight or branched, saturated hydrocarbon chain. The term “lower alkyl” or “Ci-ealkyl” means a straight or branched chain hydrocarbon containing from 1 to 6 carbon atoms. The term “Ci-4alkyl” means a straight or branched chain hydrocarbon containing from 1 to 4 carbon atoms. Representative examples of alkyl include, but are not limited to, methyl, ethyl, n-propyl, /so-propyl, n-butyl, sec-butyl, /so-butyl, tert-butyl, n- pentyl, isopentyl, neopentyl, n-hexyl, 3-methylhexyl, 2,2-dimethylpentyl, 2,3-dimethylpentyl, n- heptyl, n-octyl, n-nonyl, and n-decyl.

The term “alkenyl,” as used herein, means a straight or branched, hydrocarbon chain containing at least one carbon-carbon double bond.

The term “alkoxyalkyl,” as used herein, refers to an alkoxy group, as defined herein, appended to the parent molecular moiety through an alkyl group, as defined herein.

The term “alkoxyfluoroalkyl,” as used herein, refers to an alkoxy group, as defined herein, appended to the parent molecular moiety through a fluoroalkyl group, as defined herein.

The term “alkylene,” as used herein, refers to a divalent group derived from a straight or branched chain hydrocarbon of 1 to 10 carbon atoms, for example, of 2 to 5 carbon atoms. Representative examples of alkylene include, but are not limited to, -CH2-, -CD2-, -CH2CH2-, -CH2CH2CH2-, -CH2CH2CH2CH2-, and -CH2CH2CH2CH2CH2-.

The term “alkylamino,” as used herein, means at least one alkyl group, as defined herein, is appended to the parent molecular moiety through an amino group, as defined herein. The term “amide,” as used herein, means -C(O)NR- or -NRC(O)-, wherein R may be hydrogen, alkyl, cycloalkyl, aryl, heteroaryl, heterocycle, alkenyl, or heteroalkyl.

The term “aminoalkyl,” as used herein, means at least one amino group, as defined herein, is appended to the parent molecular moiety through an alkylene group, as defined herein.

The term “amino,” as used herein, means -NR_xR_y, wherein R_x and R_y may be hydrogen, alkyl, cycloalkyl, aryl, heteroaryl, heterocycle, alkenyl, or heteroalkyl. In the case of an aminoalkyl group or any other moiety where amino appends together two other moieties, amino may be -NR_X- wherein R_x may be hydrogen, alkyl, cycloalkyl, aryl, heteroaryl, heterocycle, alkenyl, or heteroalkyl.

The term “aryl,” as used herein, refers to a phenyl or a phenyl appended to the parent molecular moiety and fused to a cycloalkane group (e.g., the aryl may be indan-4-yl), fused to a 6-membered arene group (i.e., the aryl is naphthyl), or fused to a non-aromatic heterocycle (e.g., the aryl may be benzo[d][1,3]dioxol-5-yl). The term “phenyl” is used when referring to a substituent and the term 6-membered arene is used when referring to a fused ring. The 6- membered arene is monocyclic (e.g., benzene or benzo). The aryl may be monocyclic (phenyl) or bicyclic (e.g., a 9- to 12-membered fused bicyclic system).

The term “cyanoalkyl,” as used herein, means at least one -CN group, is appended to the parent molecular moiety through an alkylene group, as defined herein.

The term “cyanofluoroalkyl,” as used herein, means at least one -CN group, is appended to the parent molecular moiety through a fluoroalkyl group, as defined herein.

The term “cycloalkoxy,” as used herein, refers to a cycloalkyl group, as defined herein, appended to the parent molecular moiety through an oxygen atom.

The term “cycloalkyl” or “cycloalkane,” as used herein, refers to a saturated ring system containing all carbon atoms as ring members and zero double bonds. The term “cycloalkyl” is used herein to refer to a cycloalkane when present as a substituent. A cycloalkyl may be a monocyclic cycloalkyl (e.g., cyclopropyl), a fused bicyclic cycloalkyl (e.g., decahydronaphthalenyl), or a bridged cycloalkyl in which two non-adjacent atoms of a ring are linked by an alkylene bridge of 1 , 2, 3, or 4 carbon atoms (e.g., bicyclo[2.2.1]heptanyl).

Representative examples of cycloalkyl include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl, adamantyl, and bicyclo[1.1.1]pentanyl.

The term “cycloalkenyl” or “cycloalkene,” as used herein, means a non-aromatic monocyclic or multicyclic ring system containing all carbon atoms as ring members and at least one carbon-carbon double bond and preferably having from 5-10 carbon atoms per ring. The term “cycloalkenyl” is used herein to refer to a cycloalkene when present as a substituent. A cycloalkenyl may be a monocyclic cycloalkenyl (e.g., cyclopentenyl), a fused bicyclic cycloalkenyl (e.g., octahydronaphthalenyl), or a bridged cycloalkenyl in which two non-adjacent atoms of a ring are linked by an alkylene bridge of 1 , 2, 3, or 4 carbon atoms (e.g., bicyclo[2.2.1]heptenyl).

Exemplary monocyclic cycloalkenyl rings include cyclopentenyl, cyclohexenyl or cycloheptenyl. Exemplary monocyclic cycloalkenyl rings include cyclopentenyl, cyclohexenyl or cycloheptenyl.

The term “carbocyclyl” means a “cycloalkyl” or a “cycloalkenyl.” The term “carbocycle” means a “cycloalkane” or a “cycloalkene.” The term “carbocyclyl” refers to a “carbocycle” when present as a substituent.

The terms cycloalkylene and heterocyclylene refer to divalent groups derived from the base ring, i.e. , cycloalkane, heterocycle. For purposes of illustration, examples of cycloalkylene and heterocyclylene include, respectively,

Cycloalkylene and heterocyclylene include a geminal divalent groups such as 1 ,1-C3-6cycloalkylene (i.e.,

A further example is 1,1 -cyclopropylene (i.e.,

The term “fluoroalkyl,” as used herein, means an alkyl group, as defined herein, in which one, two, three, four, five, six, seven or eight hydrogen atoms are replaced by fluorine. Representative examples of fluoroalkyl include, but are not limited to, 2-fluoroethyl, 2,2,2- trifluoroethyl, trifluoromethyl, difluoromethyl, pentafluoroethyl, and trifluoropropyl such as 3,3,3- trifluoropropyl.

The term “fluoroalkylene,” as used herein, means an alkylene group, as defined herein, in which one, two, three, four, five, six, seven or eight hydrogen atoms are replaced by fluorine. Representative examples of fluoroalkyl include, but are not limited to -CF₂-, -CH₂CF₂-, 1 ,2- difluoroethylene, 1 ,1 ,2,2-tetrafluoroethylene, 1,3,3,3-tetrafluoropropylene, 1 , 1 ,2, 3,3- pentafluoropropylene, and perfluoropropylene such as 1 ,1,2,2,3,3-hexafluoropropylene.

The term “halogen” or “halo,” as used herein, means Cl, Br, I, or F.

The term “haloalkyl,” as used herein, means an alkyl group, as defined herein, in which one, two, three, four, five, six, seven or eight hydrogen atoms are replaced by a halogen.

The term “haloalkoxy,” as used herein, means at least one haloalkyl group, as defined herein, is appended to the parent molecular moiety through an oxygen atom. The term “halocycloalkyl,” as used herein, means a cycloalkyl group, as defined herein, in which one or more hydrogen atoms are replaced by a halogen.

The term “heteroalkyl,” as used herein, means an alkyl group, as defined herein, in which one or more of the carbon atoms has been replaced by a heteroatom selected from S, O, P and N. Representative examples of heteroalkyls include, but are not limited to, alkyl ethers, secondary and tertiary alkyl amines, amides, and alkyl sulfides.

The term “heteroaryl,” as used herein, refers to an aromatic monocyclic heteroatomcontaining ring (monocyclic heteroaryl) or a bicyclic ring system containing at least one monocyclic heteroaromatic ring (bicyclic heteroaryl). The term “heteroaryl” is used herein to refer to a heteroarene when present as a substituent. The monocyclic heteroaryl are five or six membered rings containing at least one heteroatom independently selected from the group consisting of N, O and S (e.g., 1, 2, 3, or 4 heteroatoms independently selected from O, S, and N). The five membered aromatic monocyclic rings have two double bonds, and the six membered aromatic monocyclic rings have three double bonds. The bicyclic heteroaryl is an 8- to 12- membered ring system and includes a fused bicyclic heteroaromatic ring system (i.e., 10 electron system) such as a monocyclic heteroaryl ring fused to a 6-membered arene (e.g., quinolin-4-yl, indol-1-yl), a monocyclic heteroaryl ring fused to a monocyclic heteroarene (e.g., naphthyridinyl), and a phenyl fused to a monocyclic heteroarene (e.g., quinolin-5-yl, indol-4-yl). A bicyclic heteroaryl/heteroarene group includes a 9-membered fused bicyclic heteroaromatic ring system having four double bonds and at least one heteroatom contributing a lone electron pair to a fully aromatic 10K electron system, such as ring systems with a nitrogen atom at the ring junction (e.g., imidazopyridine) or a benzoxadiazolyl. A bicyclic heteroaryl also includes a fused bicyclic ring system composed of one heteroaromatic ring and one non-aromatic ring such as a monocyclic heteroaryl ring fused to a monocyclic carbocyclic ring (e.g., 6,7-dihydro-5H- cyclopenta[b]pyridinyl), or a monocyclic heteroaryl ring fused to a monocyclic heterocycle (e.g., 2,3-dihydrofuro[3,2-b]pyridinyl). The bicyclic heteroaryl is attached to the parent molecular moiety at an aromatic ring atom. Other representative examples of heteroaryl include, but are not limited to, indolyl (e.g., indol-1-yl, indol-2-yl, indol-4-yl), pyridinyl (including pyridin-2-yl, pyridin-3-yl, pyridin-4-yl), pyrimidinyl, pyrazinyl, pyridazinyl, pyrazolyl (e.g., pyrazol-4-yl), pyrrolyl, benzopyrazolyl, 1 ,2,3-triazolyl (e.g., triazol-4-yl), 1 ,3,4-thiadiazolyl, 1 ,2,4-thiadiazolyl, 1 ,3,4- oxadiazolyl, 1 ,2,4-oxadiazolyl, imidazolyl, thiazolyl (e.g., thiazol-4-yl), isothiazolyl, thienyl, benzimidazolyl (e.g., benzimidazol-5-yl), benzothiazolyl, benzoxazolyl, benzoxadiazolyl, benzothienyl, benzofuranyl, isobenzofuranyl, furanyl, oxazolyl, isoxazolyl, purinyl, isoindolyl, quinoxalinyl, indazolyl (e.g., indazol-4-yl, indazol-5-yl), quinazolinyl, 1 ,2,4-triazinyl, 1 ,3,5-triazinyl, isoquinolinyl, quinolinyl, imidazo[1 ,2-a]pyridinyl (e.g., imidazo[1 ,2-a]pyridin-6-yl), naphthyridinyl, pyridoimidazolyl, thiazolo[5,4-b]pyridin-2-yl, and thiazolo[5,4-d]pyrimidin-2-yl.

The term “heterocycle” or “heterocyclic,” as used herein, means a monocyclic heterocycle, a bicyclic heterocycle, or a tricyclic heterocycle. The term “heterocyclyl” is used herein to refer to a heterocycle when present as a substituent. The monocyclic heterocycle is a three-, four-, five- , six-, seven-, or eight-membered ring containing at least one heteroatom independently selected from the group consisting of O, N, and S. The three- or four-membered ring contains zero or one double bond, and one heteroatom selected from the group consisting of O, N, and S. The fivemembered ring contains zero or one double bond and one, two or three heteroatoms selected from the group consisting of O, N and S. The six-membered ring contains zero, one or two double bonds and one, two, or three heteroatoms selected from the group consisting of O, N, and S. The seven- and eight-membered rings contains zero, one, two, or three double bonds and one, two, or three heteroatoms selected from the group consisting of O, N, and S. Representative examples of monocyclic heterocyclyls include, but are not limited to, azetidinyl, azepanyl, aziridinyl, diazepanyl, 1,3-dioxanyl, 1 ,3-dioxolanyl, 1 ,3-dithiolanyl, 1 ,3-dithianyl, imidazolinyl, imidazolidinyl, isothiazolinyl, isothiazolidinyl, isoxazolinyl, isoxazolidinyl, morpholinyl, 2-oxo-3-piperidinyl, 2- oxoazepan-3-yl, oxadiazolinyl, oxadiazolidinyl, oxazolinyl, oxazolidinyl, oxetanyl, oxepanyl, oxocanyl, piperazinyl, piperidinyl, pyranyl, pyrazolinyl, pyrazolidinyl, pyrrolinyl, pyrrolidinyl, tetrahydrofuranyl, tetrahydropyranyl, tetrahydropyridinyl, tetrahydrothienyl, thiadiazolinyl, thiadiazolidinyl, 1 ,2-thiazinanyl, 1 ,3-thiazinanyl, thiazolinyl, thiazolidinyl, thiomorpholinyl, 1 ,1- dioxidothiomorpholinyl (thiomorpholine sulfone), thiopyranyl, and trithianyl. The bicyclic heterocycle is a monocyclic heterocycle fused to a 6-membered arene, or a monocyclic heterocycle fused to a monocyclic cycloalkane, or a monocyclic heterocycle fused to a monocyclic cycloalkene, or a monocyclic heterocycle fused to a monocyclic heterocycle, or a monocyclic heterocycle fused to a monocyclic heteroarene, or a spiro heterocycle group, or a bridged monocyclic heterocycle ring system in which two non-adjacent atoms of the ring are linked by an alkylene bridge of 1 , 2, 3, or 4 carbon atoms, or an alkenylene bridge of two, three, or four carbon atoms. The bicyclic heterocyclyl is attached to the parent molecular moiety at a non-aromatic ring atom (e.g., indolin-1-yl). Representative examples of bicyclic heterocyclyls include, but are not limited to, chroman-4-yl, 2,3-dihydrobenzofuran-2-yl, 2,3-dihydrobenzothien-2-yl, 1 , 2,3,4- tetrahydroisoquinolin-2-yl, 2-azaspiro[3.3]heptan-2-yl, 2-oxa-6-azaspiro[3.3]heptan-6-yl, azabicyclo[2.2.1]heptyl (including 2-azabicyclo[2.2.1]hept-2-yl), azabicyclo[3.1.0]hexanyl (including 3-azabicyclo[3.1.0]hexan-3-yl), 2,3-dihydro-1 H-indol-1 -yl, isoindolin-2-yl, octahydrocyclopenta[c]pyrrolyl, octahydropyrrolopyridinyl, tetrahydroisoquinolinyl, 7- oxabicyclo[2.2.1]heptanyl, hexahydro-2H-cyclopenta[b]furanyl, 2-oxaspiro[3.3]heptanyl, 3- oxaspiro[5.5]undecanyl, 6-oxaspiro[2.5]octan-1-yl, and 3-oxabicyclo[3.1.0]hexan-6-yl. Tricyclic heterocycles are exemplified by a bicyclic heterocycle fused to a 6-membered arene, or a bicyclic heterocycle fused to a monocyclic cycloalkane, or a bicyclic heterocycle fused to a monocyclic cycloalkene, or a bicyclic heterocycle fused to a monocyclic heterocycle, or a bicyclic heterocycle in which two non-adjacent atoms of the bicyclic ring are linked by an alkylene bridge of 1 , 2, 3, or 4 carbon atoms, or an alkenylene bridge of two, three, or four carbon atoms. Examples of tricyclic heterocycles include, but are not limited to, octahydro-2, 5-epoxypentalene, hexahydro-2H-2,5- methanocyclopenta[b]furan, hexahydro-1 H-1 ,4-methanocyclopenta[c]furan, aza-adamantane (1- azatricyclo[3.3.1.13,7]decane), and oxa-adamantane (2-oxatricyclo[3.3.1.13,7]decane). The monocyclic, bicyclic, and tricyclic heterocyclyls are connected to the parent molecular moiety at a non-aromatic ring atom.

The term “hydroxyl” or “hydroxy,” as used herein, means an -OH group.

The term “hydroxyalkyl,” as used herein, means at least one -OH group, is appended to the parent molecular moiety through an alkylene group, as defined herein.

The term “hydroxyfluoroalkyl,” as used herein, means at least one -OH group, is appended to the parent molecular moiety through a fluoroalkyl group, as defined herein.

Terms such as “alkyl,” “cycloalkyl,” “alkylene,” etc. may be preceded by a designation indicating the number of atoms present in the group in a particular instance (e.g., “Ci-4alkyl,” “Cs-ecycloalkyl,” “Ci-4alkylene”). These designations are used as generally understood by those skilled in the art. For example, the representation “C” followed by a subscripted number indicates the number of carbon atoms present in the group that follows. Thus, “Csalkyl” is an alkyl group with three carbon atoms (i.e., n-propyl, isopropyl). Where a range is given, as in “C1-4,” the members of the group that follows may have any number of carbon atoms falling within the recited range. A “Ci_₄alkyl,” for example, is an alkyl group having from 1 to 4 carbon atoms, however arranged (i.e., straight chain or branched).

The term “substituted” refers to a group that may be further substituted with one or more non-hydrogen substituent groups. Substituent groups include, but are not limited to, halogen, =0 (oxo), =S (thioxo), cyano, nitro, fluoroalkyl, alkoxyfluoroalkyl, fluoroalkoxy, alkyl, alkenyl, alkynyl, haloalkyl, haloalkoxy, heteroalkyl, cycloalkyl, cycloalkenyl, aryl, heteroaryl, heterocycle, cycloalkylalkyl, heteroarylalkyl, arylalkyl, hydroxy, hydroxyalkyl, alkoxy, alkoxyalkyl, alkylene, aryloxy, phenoxy, benzyloxy, amino, alkylamino, acylamino, aminoalkyl, arylamino, sulfonylamino, sulfinylamino, sulfonyl, alkylsulfonyl, arylsulfonyl, aminosulfonyl, sulfinyl, -COOH, ketone, amide, carbamate, and acyl. Three b/s(4-oligoethyleneoxyphenyl) viologen bistosylate salts were prepared via Zincke reaction followed by metathesis reaction of silver tosylate and characterized for their chemical structures by spectroscopic techniques and elemental analysis. Their thermotropic liquid crystalline phase behavior and related physical properties were determined by differential scanning calorimetry, polarizing optical microscopy, and variable temperature X-ray diffraction techniques. The salt containing two oxyethylene units at both ends of extended viologen moiety had a high T_m at 212 °C. Those containing three and four oxyethylene units showed crystal-to- smectic A transitions at 184 and 153 °C, and smectic A-to-isotropic liquid transitions at 216 and 170 °C resulting in a range of liquid crystal phases of 32 and 17 °C, respectively. All salts had excellent thermal stabilities up to 288 °C, assessed by thermogravimetric analysis. The salts exhibited weak emission in dichloromethane and no emission in acetonitrile but exhibited light emission in the solid state. Their absolute quantum yields ranged between 3 and 12%. Conductivity increases with the length of the oxyethylene units in the extended viologen moiety, with the sample containing four oxyethylene units reaching ~ 10^-2 S-cnr¹, attributed to its larger molecular flexibility and improved ionic liquid mobility.

Extending the viologen moiety with phenyl residues can be a good strategy to promote anisotropy through increasing the molecular length to width ratio, there are limited examples in the literature (I— VI), FIG. 1. The properties of extended viologen salts were examined (not showing liquid crystalline behaviour) containing oxyethylene groups, obtaining promising results in terms of conductivity. In this work, tosylate was used as an alternative counterion to bistriflimide, which could be more compatible to the extended phenyl core. The location of the tosylate ions in the viologen can help promote micro-phase segregation and ultimately smectic phases. Interestingly, while many ionic liquids are reported based on tosylate counterions, materials showing liquid crystallinity (ionic liquid crystals) are still limited.

Described herein is the synthesis of three phenyl-extended viologen salts with bistosylate counterions, having different chain lengths. Their chemical structures have been correlated with their dielectric and ionic conductivity responses and studied their potential as components in electrolytes for future applications.

Schemes 1-2 below show methods for the synthesis of example ionic liquid crystals (ILCs) disclosed and contemplated herein. Other ILCs may be prepared using similar methods. Scheme 1. Steps for the synthesis of ionic liquid crystal Salts 1-3.

Scheme 2. Synthetic route for symmetric oligoethyleneoxy extended viologen salts containing 4- n-alkylbenzenesulfonates.

One embodiment described herein is an ionic liquid crystal comprising a viologen salt of formula (I):

wherein:

, „2 K ■ i-(OCH₂CH₂)_nOCH₂CH₃ . . >

R¹ and R² are each independently ? where n is 3-10; m and p are each independently 1-3; R^a, at each occurrence, is independently Ci-4alkyl, Ci-zhaloalkyl, -OCi-4alkyl,

-OCi_₂haloalkyl, halogen, -NO₂, -CN, or -(OCH₂CH₂)i ₃OCH₂CH₃:

R^b, at each occurrence, is independently Ci-4alkyl, Ci-₂haloalkyl, -OCi-4alkyl,

-OCi_₂haloalkyl, halogen, -NO₂, -CN,

°X¹ and °X² are each independently

In one aspect, m is 1. In another aspect, p is 1. In another aspect, m is 2. In another aspect, p is 2. In another aspect, m is 3. In another aspect, p is 3. In another aspect, m is 1 and p is 1. In another aspect m is 2 and p is 2. In another aspect, m is 3 and p is 3. In another aspect, the viologen salt of formula (I) is a symmetric viologen salt.

O ® CO In another aspect, °X¹ and °X² are each

In another aspect, In another aspect, °X¹ and °X² are each

In another aspect, the viologen salt of formula (I) is a viologen salt of formula (l-a):

In another aspect, the viologen salt of formula (I) is:

In another aspect, n is 1-3. In another aspect, the viologen salt of formula (I) has a conductivity of at least about 1 x 10’^{3 5} S cm^-1. In another aspect, the viologen salt of formula (I) has a conductivity of at least about 1 x 10^-5 S cm^-1. In another aspect, the viologen salt of formula (I) has a conductivity of at least about 4 x 10^-5 S cm^-1. Another embodiment described herein is a solid-state battery, supercapacitor, solar cell, or perovskite photovoltaic cell comprising an ionic liquid crystal comprising a viologen salt as described herein.

The class of ionic liquid crystals (ILCs) described herein are based on Zincke salts which allow efficiently to build up dicationic or multicationic ILCs with high yields. These methods are unique compared to other methods including quaternization reactions typically used for the preparation of ILCs (monocationic and multicationic). ILCs containing bistosylates are a unique class of ionic liquid crystals for two reasons. Tosylates are non-toxic, cheap, and easily available counterions that provide the thermotropic liquid-crystalline properties in combination of dicationic extended viologen moieties. Tosylate counterions have been used for the preparation of relatively low-cost ionic liquids including phosphonium ions, but ILCs are relatively scarce with these counterions. Monocationic ILCs including pyridinium and imidazolium cations have been prepared based on fluorinated anions such as tetrafluoroborate and hexafluorophosphate. Unfortunately, these fluorinated anions undergo hydrolysis, producing hydrogen fluoride, which limits their applications. Tosylates are stable ions and these ILCs are superior to fluorinated ILCs. In addition to tosylates, other ILCs containing fluorinated anions such as triflates and nonaflates are alternatives to tetrafluoroborate and hexafluorophosphate. They have hydrolytic stability and liquid crystalline phases that are conducive. ILCs can be used as electrolytes in battery applications and as additives for modification of perovskites solar cells for better performance.

It will be apparent to one of ordinary skill in the relevant art that suitable modifications and adaptations to the compositions, formulations, methods, processes, and applications described herein can be made without departing from the scope of any embodiments or aspects thereof. The compositions and methods provided are exemplary and are not intended to limit the scope of any of the specified embodiments. All of the various embodiments, aspects, and options disclosed herein can be combined in any variations or iterations. The scope of the compositions, formulations, methods, and processes described herein include all actual or potential combinations of embodiments, aspects, options, examples, and preferences herein described. The exemplary compositions and formulations described herein may omit any component, substitute any component disclosed herein, or include any component disclosed elsewhere herein. The ratios of the mass of any component of any of the compositions or formulations disclosed herein to the mass of any other component in the formulation or to the total mass of the other components in the formulation are hereby disclosed as if they were expressly disclosed. Should the meaning of any terms in any of the patents or publications incorporated by reference conflict with the meaning of the terms used in this disclosure, the meanings of the terms or phrases in this disclosure are controlling. Furthermore, the foregoing discussion discloses and describes merely exemplary embodiments. All patents and publications cited herein are incorporated by reference herein for the specific teachings thereof.

Various embodiments and aspects of the inventions described herein are summarized by the following clauses:

Clause 1 . An ionic liquid crystal comprising a viologen salt of formula (I):

wherein:

. _D2 . . . . .. f— (OCH₂CH₂)_nOCH₂CH₃ . . _

R¹ and R² are each independently ? where n is 3-10; m and p are each independently 1-3;

R^a, at each occurrence, is independently Ci_4alkyl, Ci_2haloalkyl, -OCi-4alkyl,

-OCi_₂haloalkyl, halogen, -NO₂, -CN, or -(OCH₂CH₂)i_₃OCH₂CH₃;

R^b, at each occurrence, is independently Ci_₄alkyl, Ci_₂haloalkyl, - OCi_₄alkyl,

-OCi-2haloalkyl, halogen, -NO

°X¹ and °X² are each independently

Clause 2. The ionic liquid crystal of clause 1 , wherein m is 1 .

Clause 3. The ionic liquid crystal of clause 1 , wherein p is 1.

Clause 4. The ionic liquid crystal of clause 1 , wherein m is 2.

Clause 5. The ionic liquid crystal of clause 1 , wherein p is 2.

Clause 6. The ionic liquid crystal of clause 1 , wherein m is 3.

Clause 7. The ionic liquid crystal of clause 1 , wherein p is 3.

Clause 8. The ionic liquid crystal of clause 1 , wherein m is 1 and p is 1.

Clause 9. The ionic liquid crystal of clause 1 , wherein m is 2 and p is 2.

Clause 10. The ionic liquid crystal of clause 1 , wherein m is 3 and p is 3.

Clause 11. The ionic liquid crystal of clause 1 , wherein the viologen salt of formula (I) is a symmetric viologen salt. Clause 12. The ionic liquid crystal of clause 1 , wherein °X¹ and °X² are each

Clause 13. The ionic liquid crystal of clause 1, wherein °X¹ and °X² are each

Clause 14. The ionic liquid crystal of clause 1 , wherein the viologen salt of formula (I) is a viologen salt of formula (l-a):

Clause 15. The ionic liquid crystal of clause 1 , wherein the viologen salt of formula (I) is:

Clause 16. The ionic liquid crystal of clause 1 , wherein n is 1-3.

Clause 17. The ionic liquid crystal of clause 1 , wherein the viologen salt of formula (I) has a conductivity of at least about 1 x 10’³⁵ S cm’¹.

Clause 18. The ionic liquid crystal of clause 1 , wherein the viologen salt of formula (I) has a conductivity of at least about 1 x 10^-5 S cm^-1.

Clause 19. The ionic liquid crystal of clause 1, wherein the viologen salt of formula (I) has a conductivity of at least about 4 x 10^-5 S cm^-1.

Clause 20. A solid-state battery, supercapacitor, solar cell, or perovskite photovoltaic cell comprising the ionic liquid crystal of clause 1.

EXAMPLES

Materials and Methods

The general structures and designations for the extended viologen compounds and their synthetic routes are shown in Scheme 1. Their chemical structures were determined using ¹H and ¹³C NMR (in CD3OD) as well as elemental analysis. All chemicals and solvents were reagent grade and purchased from commercial vendors (Acros Organics, Alfa-Aesar, Sigma-Aldrich, and TCI America) and were used as received. The FTIR spectra were recorded with a Shimadzu infrared spectrometer. The salts were prepared in thin films casting from chloroform on NaCI plates and subsequently vacuum dried at 70 °C overnight. The ¹H, and ¹³C nuclear magnetic resonance (NMR) salt solutions of extended viologen salts 1-3 were prepared by dissolving 10 mg of each of the salts in 1 ml_ CD₃OD, and the spectra were recorded by using VNMR 400 spectrometer operating at 400 and 100 MHz, respectively, at room temperature and chemical shifts were referenced to tetramethylsilane (TMS) for ¹H and ¹³C nuclei. Elemental analyses were performed by Atlantic Microlab Inc., Norcross, GA.

Synthesis

Synthetic procedure for 4-oligoethylenoxy anilines (OEA1-OEA3)

The 4-(2-ethoxyethoxy) aniline (OEA1) and 4-(2-(2-ethoxyethoxy) ethoxy] aniline (OEA2) and 4-(2-(2-(2-ethoxyethoxy) ethoxy)ethoxy]ethoxy] aniline (OEA3) were prepared according to the slightly modified literature procedure. See Sudhakar et al., Liq. Cryst. 27: 1525-1532 (2000). The modification was the use of acetone instead of ethanol and oligoethylene bromides instead of oligoethylene tosylates in the alkylation of 4-hydroxyacetanilide. The oligoethylene bromides were prepared via Appel reaction (Step 1). See Kim et al., J. Med. Chem. 50: 5217-5226 (2007). The synthesis of 4-[2-[2-(2-ethoxyethoxy) ethoxy) ethoxy] ethoxy] aniline (OEA3) is described below in detail; the other two 4-oligoethyleneoxy anilines were prepared in the identical manner. It was prepared in a three-step reaction starting with the bromination of 4-[2-(2-ethoxyethoxy) ethoxy] ethanol via Appel reaction. The synthesis of 4-[2-(2-ethoxyethoxy) ethoxy] bromide (OEB3) is as follows. An amount of 4-[2-(2-ethoxyethoxy) ethoxy] ethanol (1.000 g, 5.61 mmol) and an excess of triphenylphosphine (2.458 g, 9.37 mmol) were added to an Erlenmeyer flask and dissolved in 10 mL of dichloromethane (DCM). When the mixture was stirred and cooled to 0 °C, carbon tetrabromide (2.326 g, 7.01 mmol) dissolved in 10 mL of DCM was added to the mixture dropwise. Once all the carbon tetrabromide solution was added, the reaction mixture was let stir at room temperature for 30 min. After 30 min., the DCM was removed using a rotary evaporator. Upon removal of the DCM, 30 mL of hexane was added to the reaction mixture to precipitate out the excess starting material and byproducts. The reaction mixture in hexane was cooled down to -77 °C by keeping the flask in an isopropyl alcohol and dry ice bath. The contents of the flask were filtered through Celite, and the hexane was evaporated leaving a pure product of 4-[2-(2-ethoxyethoxy) ethoxy] ethyl bromide (OEB3) (0.700 g, 2.90 mmol, Yield = 52%). In Step 2, the alkylation of 4-hydroxyacetanilide was performed as follows. The 4-[2-(2- ethoxyethoxy) ethoxy] bromide (0.700 g, 2.90 mmol) was added to a round-bottomed flask containing 4-hydroxyacetanilide (0.483 g, 3.19 mmol) dissolved in 50 mL of acetone. Potassium carbonate (0.401 mg, 2.90 mmol) was added to the flask and the reaction mixture was heated to reflux on stirring for 24 h. At the end of the reaction, the mixture was brought to room temperature and filtered. The acetone was removed using a rotary evaporator and the product was purified by extraction with DCM and warm deionized water. The DCM was then evaporated to yield a pure product of 4-[2-[2-(2-ethoxyethoxy)ethoxy)ethoxy]ethoxy] acetanilide (0.800 g, 2.57 mmol, Yield = 88%).

Finally, a hydrolysis reaction (Step 3) was performed by adding 4-[2-[2-(2- ethoxyethoxy)ethoxy)ethoxy]ethoxy] acetanilide (0.800 g, 2.57 mmol) to a three-necked flask with sodium hydroxide (2.000 g, 50.0 mmol) dissolved in 25 mL of deionized water. The reaction flask was heated under nitrogen atmosphere for 12 h. At the end of the reaction, the flask was cooled down to room temperature and the desired product was purified by extraction with DCM and deionized water. The DCM was removed using a rotary evaporator to yield a pure product of 4- [2-[2-(2-ethoxyethoxy)ethoxy)ethoxy]ethoxy] aniline (OEA3) (0.576 g, 2.14 mmol, Yield = 83%).

Synthetic Procedure for Zincke Salts (ZS)

The salts were prepared according to the literature, from the reaction of 1-chloro-2,4- dinitrobenzene (2.5 equivalents) with 4,4'-bipyridine (1 equiv.) on heating in acetonitrile (Step 3). See Sharma et al., Synth. Met. 106: 97-105 (1999); Cheng and Kurth, Org. Prep. Proced. Int. 34: 585-608 (2002).

Synthetic Procedure for b/s-(4-oligoethyleneoxyphenyl)-4,4'-bipyridinium dichloride (P1-P3)

The synthesis of P2 is described as an example (Step 4); P1 and P3 were prepared in an identical manner. P2 was prepared by adding the 4-(2-(2-ethoxyethoxy) ethoxy] aniline (0.192 g, 0.85 mmol) to a round-bottomed flask containing Zincke salt (0.217 g, 0.39 mmol) and 15 mL of A/,A/-dimethylacetamide (DMAc). The reaction mixture was stirred at room temperature for 3 h. At the end of the reaction, the crude product was collected by simple gravity filtration and washed with acetone to give a pure product (0.162 g, 0.25 mmol).

P2

Data for P1 : Yield 93%. 6_H (CD₃0D, 400 MHz, ppm): 9.50 (4H, d, J = 6.8), 8.89 (4H, d, J = 6.8), 7.89 (4H, d, J = 9.2), 7.34 (4H, d, J = 9.2), 4.30 (4H, t, J = 4.4), 3.87 (4H, t, J = 2.8), 3.65 (4H, t, J= 6.8) 1.25 (6H, t, J = 7.2). 0_c (CD₃0D, 100 MHz, ppm): 163.18, 151.17, 146.82, 137.02, 128.30, 126.94, 117.44, 69.95, 69.53, 67.85, 15.47.

Data for P3: Yield 70%. 5_H (CD₃0D, 400 MHz, ppm): 9.50 (4H, d, J = 6.4), 8.88 (4H, d, J = 6.4), 7.88 (4H, d, J = 8.8), 7.34 (4H, d, J = 9.2), 4.31 (4H, t, J = 4.8), 3.93 (4H, t, J = 3.2), 3.75 (4H, t, J = 4.0), 3.51-3.69 (16H, m), 1.20 (6H, t, J = 6.8). be (CD3OD, 100 MHz, ppm): 163.19, 151.18, 146.83, 137.01 , 128.28, 126.94, 117.46, 71.84, 71.64, 70.94, 70.62, 69.55, 67.59, 15.48.

Synthetic Procedure for b/s-(4-oligoethyleneoxyphenyl)-4,4'-bipyridinium bistosylate Salts 1-3 by Metathesis Reaction

Salts 1-3 were synthesized from the metathesis reaction of the dichloride salts with silver (I) tosylate. The synthesis of 2 is described as an example (Step 5); 1 and 3 were prepared in an identical manner. In a red-light environment, the silver salt (0.380 g, 1.36 mmol) dissolved in 10 mL of warm deionized water and was added to a reaction flask containing a clear solution of P2 (0.352 g, 0.55 mmol) dissolved in 30 mL of ethanol. The flask was covered to avoid light exposure and heated to reflux for 72 h. At the end of the reaction, the solvent was removed by using a rotary evaporator. The reaction mixture was dried overnight in a vacuum oven at 60 °C. After drying, the reaction mixture was dissolved in methanol and filtered through 0.2 pm PTFE membrane. The methanol was removed by a rotary evaporator and once again dried in a vacuum oven at 60 °C overnight. After drying a second time, the reaction mixture was washed with cold acetonitrile and filtered to give a pure yellow product (0.426 g, 0.46 mmol, yield = 85%).

Salt 2

Data for Salt 2: FTIR (NaCI, Vmax CRT¹): 3115, 3041 , 2975, 2867, 1632, 1508, 1497, 1458, 1375, 1347, 1306, 1250, 1178, 1157, 1063, 1040, 1032, 1010, 963, 921, 829, 815, 798, 728, 712, 677, 667, 634, 614, 545, 532, 415, 393, 369, 356, 339. 5_H (CD₃0D, 400 MHz, ppm): 9.44 (4H, d, J = 6.8), 8.83 (4H, d, J = 6.8), 7.85 (4H, d, J = 9.2), 7.66 (4H, d, J = 8.0), 7.32 (4H, d, J = 8.8), 7.21 (4H, d, J = 8.0), 4.30 (4H, t, J = 4.4), 3.92 (4H, t, J = 4.8), 3.73 (4H, t, J = 4.0), 3.64 (4H, t, J = 5.2), 3.58 (4H, t, J = 7.2), 2.34 (6H, s), 1.21 (6H, t, J = 6.8). 6_C (CD3OD, 400 MHz, ppm): 163.16, 151.17, 146.73, 143.62, 141.68, 136.98, 129.84, 128.27, 126.94, 126.89, 117.43, 71.84, 70.95, 70.61 , 69.51 , 67.63, 21.33, 15.47. Anal. Calc for C48H56N2O12S2 (917.09): C, 62.86; H, 6.15; N, 3.05; S, 6.99%. Found C, 62.81 ; H, 6.03; N, 3.15; S, 6.96%.

Salt 1

Data for Salt 1: Yield 84%. FTIR (NaCI, v_max cm’¹): 3035, 2973, 2921 , 2870, 1629, 1591 , 1541 , 1508, 1494, 1442, 1425, 1375, 1356, 1307, 1254, 1188, 1118, 1061 , 1032, 1010, 943, 920, 851 , 822, 713, 677, 669, 633, 611 , 565, 527, 392, 370, 360, 350, 346. 5_H (CD₃OD, 400 MHz, ppm): 9.41 (4H, d, J = 6.8), 8.82 (4H, d, J = 6.8), 7.84 (4H, d, J = 9.2), 7.65 (4H, d, J = 8.4), 7.31 (4H, d, J = 9.2), 7.19 (4H, d, J = 8.0), 4.28 (4H, t, J = 4.4), 3.86 (4H, t, J = 2.8), 3.65 (4H, t, J = 6.8), 2.33 (6H, s), 1.25 (6H, t, J = 6.8). 6_C (CD3OD, 400 MHz, ppm): 163.13, 151.14, 146.69, 143.64, 141.70, 136.98, 129.86, 128.30, 126.94, 126.90, 117.41 , 69.95, 69.51 , 67.84, 21.33, 15.47. Anal. Calc for C44H48N2O10S2 (828.99): C, 63.75; H, 5.84; N, 3.38; S, 7.74%. Found C, 63.47; H, 5.67; N, 3.55; S, 7.60%.

Salt 3

Data for Salt 3: Yield 57%. FTIR (NaCI, v_max cm-¹): 3114, 3033, 2926, 2874, 1632, 1591 , 1544, 1512, 1498, 1471, 1446, 1425, 1385, 1326, 1310, 1256, 1035, 1012, 956, 871 , 852, 825, 713, 680, 667, 633, 610, 555, 547, 509, 426, 395, 367, 352, 344. 6_H (CD₃OD, 400 MHz, ppm): 9.44 (4H, d, J = 6.8), 8.83 (4H, d, J = 6.8), 7.85 (4H, d, J = 8.8), 7.66 (4H, d, J = 8.0), 7.32 (4H, d, J = 8.8), 7.21 (4H, d, J = 8.0), 4.30 (4H, t, J = 4.0), 3.93 (4H, t, J = 4.8), 3.74 (4H, t, J = 2.8), 3.51- 3.69 (16H, m), 2.34 (6H, s), 1.20 (6H, t, J = 7.2). 5_C (CD3OD, 400 MHz, ppm): 163.16, 151.17, 146.74, 143.64, 141.72, 136.99, 129.87, 128.29, 126.95, 126.92, 117.45, 71.84, 71.65, 70.94, 70.63, 69.54, 67.60, 21.34, 15.48. Anal. Calc for C52H64N2O14S2 (1005.20): C, 62.13; H, 6.42; N, 2.79; S, 6.38%. Found C, 61.70; H, 6.43; N, 2.89; S, 6.06%.

Characterization Techniques

The phase transition temperatures of the salts were determined using a TA module differential scanning calorimetry (DSC) Q200 series in nitrogen, at heating and cooling rates of ± 10 °C- min^-1. The temperature axis of the DSC thermograms was calibrated with reference standards of high purity indium and tin. The thermal stability properties of the compounds were assessed using a TGA Q50 instrument at a heating rate of 10 °C- min^-1 in nitrogen. Proof of Mechanism (POM) studies were carried out by sandwiching them between standard glass coverslips. The samples were heated and cooled on a Mettler hot-stage (FP82HT) and (FP90) controller and had their phase transitions observed between cross polarizers of an Olympus BX51 microscope.

Variable-temperature X-ray diffraction (VTXRD) studies of the salts contained in flame sealed 1 mm quartz capillaries were carried out using a Rigaku Screen Machine. The ILCs were placed inside the Linkam HFS350X-Cap capillary hot stage 72 mm away from the 2D detector, with temperature controlled to the accuracy of ± 0.1°C. A magnetic field of ~2.5 kG was applied to the samples using a pair of samarium cobalt permanent magnets (with B nearly parallel to the beamstop visible as a vertical line in diffraction images). Scattering patterns were collected using a Mercury 3 CCD detector with resolution 1024 x 1024 pixels (size: 73.2 pm x 73.2 pm) and copper K_a radiation generated by a microfocus sealed X-ray tube with copper anode (A = 1.542 A). The data were analyzed using publicly available Fit-2D software to correct for background scattering and generate intensity vs scattering vector, l-q curves.

The UV-Vis absorption spectra of the Salts 1-3 in dichloromethane (DCM) and acetonitrile were recorded by using the pertinent accessory attached to PerkinElmer Fluorescence Spectrometer FL 6500. The room-temperature fluorescence spectra, excitation spectra and absolute quantum yields were measured with the FL 6500 spectrometer, with the use of integrating sphere protocol of the salts in solutions. Absolute quantum yields of the as- synthesized Salts 1-3 solid state were measured with a Horiba Fluorolog fluorimeter (HORIBA Instruments Inc.) also equipped with an integrating sphere.

For the dielectric and conductivity analyses, the tosylate salts were placed between two stainless steel electrodes. The top and bottom electrodes had diameters of 10 mm and 20 mm, respectively. A fused silica fiber spacer with a diameter of 120 pm was used to separate the electrodes. The sample's temperature was precisely controlled using a Lakeshore temperature controller. Dielectric measurements were performed using an Impedance Analyzer (Agilent 4294) within a frequency range of 40-10⁶ Hz. The samples were heated from 30 °C to above 100 °C. Prior to each measurement, the samples were allowed to stabilize at the specified temperature for approximately two minutes.

Thermal and Transitional Properties

Thermal Stability - TGA

The thermal stability for Salts 1-3 was assessed by th erm ogravi metric analysis (TGA) and is defined as the temperature (°C) at which a 5% weight loss occurred at a heating rate of 10 °C- min^-1 in nitrogen. Despite the presence of flexible oxyethylene groups, the TGA thermograms display relatively high thermal stabilities, which are in the 283-288 °C temperature range (see FIG. 2 and Table 1). These temperatures gradually decrease with the increase in the number of oxyethylene groups in the terminal chains. As expected, the tosylate salts showed lower thermal stabilities than those of the homologous series containing bistriflimide as counterions (311-334 °C range), due to the absence of fluorine atoms, and the reactivity of the p-tolyl group.

Phase Behavior: DSC, POM, and VTXRD Studies FIG. 3A shows the DSC thermograms of Salt 1 obtained at both heating and cooling rates of 10 “C min^-1 rates. In the first heating cycle, there are several endotherms prior to melting at 212 °C, associated to its thermal history, and the second heating cycle only shows a broad endotherm at 197 °C. In the cooling cycles, the presence of broad exotherms accompanied by shoulder peaks at 170 and 155 °C, respectively, are indicative of crystallization occurring from the melt. POM and VTXRD studies further confirm the crystal-to-isotropic liquid transition at T_Cr = 212 °C, based on the diffractograms patterns. The endotherms prior to the crystal-to-liquid were related to several crystal-to-crystal transitions, which reflect polymorphism, and FIG. 3B depicts the d-spacings of Salt 1 as a function of temperatures measures in heating cycle.

FIG. 4A shows the DSC thermograms of Salt 2 obtained at heating and cooling rates of ± 10 °C- min^-1. The first heating cycle is dominated by a large endotherm with a shoulder visible at 184 °C (92.2 kJ-rnol^-1), and a small endotherm is also visible at 216 °C (2.6 kJ-rnol^-1, absent in the second heating scan) In the first cooling cycle, only a single exotherm is visible at 170 °C, whilst in the subsequent heating cycle, a cold crystallization exotherm appears at 117 °C, followed by an endotherm at 182 °C. In the subsequent cooling cycle, there was only an exotherm at 154 °C. In conjunction with POM studies, it was determined that the large endotherm corresponded to crystal-to-LC phase transition (FIG. 4B) and small endotherm corresponded to LC-to-isotropic liquid transition, TLCI = 216 °C. In the cooling cycles, the exotherms correspond to LC-to-crystalline transitions, but no exotherm of liquid-to-LC transition was detected in the thermogram. Thus, based on the first heating scan, the range of the LC phase was 32 °C. These results are consistent with the corresponding equilibrium VTXRD measurements, which allowed us to identify the liquid crystal phase as a smectic phase, SmA, in comparable temperature ranges, see FIG. 4C and Table 1 . Its diffractograms contained one inner sharp ring and one outer diffuse ring above the crystal-to-LC transition and isotropic liquid pattern above the LC-to-liquid transition. Its d-spacings in the crystalline, SmA and liquid phases were plotted as a function of temperatures are displayed in FIG. 7. It is worth mentioning that the diffractograms also indicated the existence of biphasic temperature ranges, where smectic and isotropic regions coexisted.

FIG. 5A shows the DSC thermograms of Salt 3 obtained at both heating and cooling rates of 10 °C min^-1. Its thermal properties are comparable with those of 2 including polymorphism and the formation of a fan-shaped texture typical of SmA phases, FIG. 5B. The SmA range, determined by DSC, was smaller than 2 and found to be 17 °C. Phase assignment and stability was further verified with VTXRD studies, which showed diffractograms containing one inner sharp ring and one outer diffuse ring pattern above the crystal-to-SmA transition and isotropic liquid pattern above the SmA-to-liquid transition. The d-spacings for Salt 3 in the crystalline, SmA and liquid phases, are displayed in FIG. 5C suggesting its layer spacings were increased on increasing chain length. Thermal properties obtained from DSC measurements and decomposition temperatures obtained from TGA measurements are compiled in Table 1.

Table 1. Thermodynamic Properties of Phase Transition Temperatures of Salts 1-3

(2.3)

2C 105 (12.9)

³ T_m c >L = The temperature recorded by DSC when the salt has a melting transition from crystal to liquid. b T_m c— *LC = The temperature recorded by DSC when the salt has a melting transition from crystal to liquid crystal. c T = The temperature recorded by DSC when the salt has a transition from liquid crystal to isotropic liquid. d AT = (T - T_m), that is, the LC phase range. e Td = The temperature recorded by TGA when 5% weight loss for the salt with the tosylate counterions occurred. f All other transitions prior to the T_m are related to the crystal-to-crystal transitions of the respective salts.

⁹ Cold crystallization exotherm.

Optical Properties of Salts 1-3

The presence of the extended viologen moieties prompts optical response in Salts 1-3, which were examined by UV-Vis and photoluminescence spectroscopies, both in DCM solution and acetonitrile (ACN), as well, as in the solid state. In DCM, they showed a broad absorption peak having A_max at 390, 389, and 389 nm, whilst in ACN they showed a broad absorption peak having A_max at 377, 378, and 399 nm. The measured molar absorption coefficients of the salts both in DCM and in ACN calculated from the respective Beer-Lambert plots are large, in the 19668-20057 M’¹ cm’¹ range. Their light emissions in both DCM and CAN were too weak to be measured or detected. For example, Salt 3 in DCM showed A_em at 606 nm when excited at 412 nm wavelength of light. These results prompted the measurement of the light emission (546, 508, and 533 nm, respectively, FIG. 11A-C) of the salts in the solid state, and the absolute quantum yields were determined. Interestingly, their light emissions in the solid state were quite respectable and found to be 7, 12 and 3%, respectively. Generally, quantum yields are low in solid state because of aggregation-caused quenching (ACQ), while the quantum yields are high in solutions because aggregation phenomena do not occur. These results suggest that these salts undergo aggregation-induced emission (AIE) in the solid state, which has been studied for many organic luminophores for the last two decades or so and pinpoint the interest of the viologens as promising materials for potential applications in optoelectronic technologies.

Conductivity and Dielectric Response

The variation of the real component of the complex conductivity, o', with frequency fin loglog scale for the three samples at 30 °C is shown in FIG. 6. Conductivity increases with the length of the oxyethylene units located at both ends of the extended viologen moiety, and the salt containing four oxyethylene units exhibits the highest conductivity which is ~4 10^-5 S COT¹. Longer oxyethylene units in the salt’s structure may increase the flexibility of the molecule promoting the movement of ions within the ionic liquid and leading to lower conductivity. This is consistent with the decrease in the melting points reported in Table 1. Interestingly, longer oxyethylene may also increase the relative concentration of sites available for solvation of ions. , and also reduce ion-ion interactions. However, while extending the end-chains could be seen as an opportunity to yield higher conductivities, this may also result in strong ionic complexation, and result in mobility hindrance.

FIG. 7 illustrates the effect of temperature on the complex permittivity for Salt 3, obtained on heating from 30 to 190 °C, and subsequently cooling back to 30 °C at a rate of ± 1 °C- min^-1. The high E' values (see FIG. 7A) are indicative of a strong dielectric response, associated to the existence of polarizable groups in the molecule, and the increase of E" at low frequencies, FIG. 7B, is consistent with the high conductivity displayed in FIG. 6 (even at low temperatures), and may mask the existence of dielectric relaxations. As expected, the dielectric response increases on heating, and the temperature-frequency relationships will be explained in more detail later section. Focusing on the E' values obtained at 3 kHz, two peaks were observed at 49 °C and 92 °C, followed by a plateau and further drop above 170 °C. This later value fits well to the clearing temperature of this sample reported in Table 1 and suggests that the crystal to smectic transition is: either not clearly visible in FIG. 70 or takes place at lower temperatures within the cells (T > 92 °C), due to strong alignment effects between electrodes and the ionic liquid that promote smectic organizations. On cooling, the real permittivity remained approximately constant at E'~10⁴, above 160 °C, subsequently dropping to e'~10² at 158 °C. This drop could indicate sudden crystallization of the salt inside the cell, and the smectic phase would then be supercooled below the crystallization temperature.

Due to its higher conductivity, the temperature response of the complex conductivity of Salt 3 was investigated (shown in FIG. 8), and the temperature dependent behavior of Salt 1 and Salt 2 are shown in FIG. 9-10, respectively. The real component of the conductivity (o') plot exhibits distinct three regions, see FIG. 8-10. At high frequencies, the conductivity is governed by strong dispersion effects. At intermediate frequencies, the ions have enough time to hop between electrodes and the appearance of plateaus in o' demonstrates the occurrence of de conductivity, which can be estimated by extrapolation to f—>0. Lastly, at low-frequencies, the o' values decrease due to electrode polarization effects caused by accumulation of charges at the electrode surfaces. The existence of significant polarization is consistent with the appearance of a maximum in the conductivity's imaginary part, o", shown in FIG. 8. At higher frequencies, the conductivity of the ionic liquid shows an upward trend, with the o" relaxation peak occurring at increasing frequency. Increase in conductivity can be attributed to a two-fold effect. On the one hand, temperature may activate more ionic sites due to an increase in the molecular mobility of the salt, and larger free volume available for ion hopping. On the other hand, ions will have further thermal energy and hence diffusion will be promoted. These two effects also reflect the shift of the de conductivity region towards higher frequencies on heating in FIG. 8 since the ions require less time to completely relax into their equilibrium positions between successive cycles of the applied electric field.

The thermal activation of conductivity was studied and plotted in the Arrhenius plots in FIG. 12. The de conductivity values o_dc are estimated by extrapolating the constant o' ranges to f— >0 at various temperature. At low temperatures, the ac conductivity follows a linear behavior, and the activation energies E_a can be calculated using Arrhenius equation,

where R is the gas constant, 8.31 J mol^-1 K^-1, T is the absolute temperature and o_o is a preexponential term. Salt 1 and 2 have activation energies of 39 kJ mol^-1 and 49 kJ mol^-1 while Salt 3 exhibits 57 kJ mol^-1, respectively. The sample with the highest conductivity (4 oxyethylene units; Salt 3) also has the highest activation energy. Even though a higher conductivity would be expected to be associated with a lower activation energy, it is important to note that activation energy alone does not solely determine conductivity. Other factors, such as the number of charge carriers and their mobility, can significantly influence conductivity.

Indeed, the highest conductivities exhibited for Salt 3 (despite its high E_a values) can be explained by the flexibility of the longer oxyethylene units. This increased mobility may offset for the higher activation energy, resulting in a higher conductivity compared to the other samples. The formation of more defined microphase separated smectic domains may be promoted by longer ethylene oxy chains. In FIG. 13A the molecular lengths associated with Salt 3 are shown and a representation of the smectic phase is shown in FIG. 13B, consistent with the diffractions calculated by X-ray in FIG. 5. The formation of such a bilayer nanostructure would allow for sufficient free volume to promote molecular and ionic mobility. Determining which region is responsible of the direct conductivity, and how to promote it via layer alignment, remain some intriguing questions that will be further explored.

The three extended viologens containing bistosylate as counterions were successfully synthesized using Zincke reactions, followed by metathesis reactions, and display high thermal stabilities (283-288 °C) assessed by TGA. The first member in the series (with the shortest oxyethylene terminal chain) was a high melting salt (212 °C), and the second and third members showed SmA above their T_ms at 184 and 153°C, and exhibited Ts at216 and 170 °C, respectively. These salts showed liquid crystalline ranges of 32 and 17 °C, respectively. While the salts showed weak (or non-existing) light emission in relatively non-polar solvents, they exhibited light emission in the solid state promoted by aggregation induced emission, with moderate absolute quantum yields between 3 and 12 %. Conductivity increases with the length of the oxyethylene units in the extended viologen moiety, reaching o_dc ~10^-2 S-cnr¹, close to those values exhibited by commercial electrolytes used in fuel cells or batteries, and higher than other liquid crystalline materials. The presence of longer oxyethylene units enhances the flexibility of the molecules, promoting ion movement within the ionic liquid and resulting in higher conductivity. Both permittivity and conductivity increase with temperature, which can be beneficial to yield controllable electrolytes in their liquid crystalline mesophases. The combination of light emission and conductivity will prompt new developments to further improve conductivities of new ionic liquids and their inclusion in self-standing films for application in optical and energy devices.

Claims

CLAIMS What is claimed:

1. An ionic liquid crystal comprising a viologen salt of formula (I):

wherein:

. _D7 . . . . .. I- (OCH₂CH₂)_nOCH₂CH₃ . . _

R¹ and R² are each independently ? where n is 3-10; m and p are each independently 1-3;

R^a, at each occurrence, is independently Ci-4alkyl, Ci-2haloalkyl, -OCi-4alkyl,

-OCi_₂haloalkyl, halogen, -NO₂, -CN, or -(OCH₂CH₂)i_₃OCH₂CH₃;

R^b, at each occurrence, is independently Ci_4alkyl, Ci_₂haloalkyl, -OCi-4alkyl,

-OCi_₂haloalkyl, halogen, -NO₂,

°X¹ and °X² are each independently ^c

2. The ionic liquid crystal of claim 1, wherein m is 1.

3. The ionic liquid crystal of claim 1 , wherein p is 1.

4. The ionic liquid crystal of claim 1, wherein m is 2.

5. The ionic liquid crystal of claim 1 , wherein p is 2.

6. The ionic liquid crystal of claim 1, wherein m is 3.

7. The ionic liquid crystal of claim 1 , wherein p is 3.

8. The ionic liquid crystal of claim 1, wherein m is 1 and p is 1.

9. The ionic liquid crystal of claim 1, wherein m is 2 and p is 2.

10. The ionic liquid crystal of claim 1, wherein m is 3 and p is 3.

11. The ionic liquid crystal of claim 1 , wherein the viologen salt of formula (I) is a symmetric viologen salt.

The ionic liquid crystal of claim 1, wherein °X¹ and °X² are each

13. The ionic liquid crystal of claim 1, wherein °X¹ and °X² are each

14. The ionic liquid crystal of claim 1 , wherein the viologen salt of formula (I) is a viologen salt of formula (l-a):

The ionic liquid crystal of claim 1, wherein the viologen salt of formula (I) is:

16. The ionic liquid crystal of claim 1 , wherein n is 1-3.

17. The ionic liquid crystal of claim 1 , wherein the viologen salt of formula (I) has a conductivity of at least about 1 * 10’³⁵ S cm^-1.

18. The ionic liquid crystal of claim 1 , wherein the viologen salt of formula (I) has a conductivity of at least about 1 x 1O^-5 S cm^-1.

19. The ionic liquid crystal of claim 1 , wherein the viologen salt of formula (I) has a conductivity of at least about 4 * 10’⁵ S cm’¹.

20. A solid-state battery, supercapacitor, solar cell, or perovskite photovoltaic cell comprising the ionic liquid crystal of claim 1.