Phenothiazine- and carbazole-based compounds: syntheses and using the same for electrochemical energy storage

Abstract

Described herein are phenothiazine-based compounds and carbazole-based compounds and methods of making and using the same for electrochemical energy storage. The phenothiazine- based compounds can include perfluorination and a charge-bearing side chain, that may be permanent. The phenothiazine-based compounds and carbazole-based compounds have enhanced solubility and oxidation potential.

Description

Atty Docket No.395 / 45 PCT PHENOTHIAZINE- AND CARBAZOLE-BASED COMPOUNDS: SYNTHESES AND USING THE SAME FOR ELECTROCHEMICAL ENERGY STORAGE CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the priority of U.S. Provisional Patent Application No. 63 / 669,280, filed on July 10, 2024, which is incorporated by reference herein. TECHNICAL FIELD

[0002] The disclosed technology relates to phenothiazine-based compounds and carbazole- based compounds and their use for electrochemical energy storage for various battery technologies including Li-ion batteries, Na-ion batteries, polymer batteries, and redox-flow batteries, such as organic non-aqueous redox-flow batteries. BACKGROUND

[0003] Grid-scale energy storage refers to technologies connected to the power grid that can store energy and then supply it back to the energy grid at a more advantageous time – for example, at night, when no solar power is available, or during a weather event that disrupts electricity generation. A widely used technology is pumped-storage hydropower, where water is pumped into a reservoir and then released to generate electricity at a different time, but this can only be done in certain locations. Another grid-scale energy storage technology includes using thermal, compressed air. In this method, off-peak or renewably generated electricity is used to compress air, which is stored, and then when electricity demand is high, the compressed air is heated with a small amount of natural gas and then goes through turboexpanders to generate electricity and electrochemical systems. Additionally, batteries are now playing a growing role as they can be installed anywhere in a wide range of capacities. Battery technology can be one of the most powerful sources of energy for grid-energy storage devices.

[0004] The state-of-the-art battery technology relies on metals from natural resources that are constantly being depleted and are expensive. Organic electrolytes made up of earth- abundant elements such as C, H, N, O, and S, are desirable alternatives to metal-based electrolytes but are still in their developmental infancy.Atty Docket No.395 / 45 PCT SUMMARY OF THE DISCLOSURE

[0005] In an aspect of the invention, a phenothiazine-based compound is represented by Formula 2: (Formula 2).

[0006] In a secondbased compound is represented by Formula 3: R R22R N1F F

[0007] wherein:

[0008] R2 = H or CH3;

[0009] R3 = H, CH3, or CF3; and R ,

[0012] X- = I-, Br-, Cl-, TFSI-, PF6-, or BF4-, and

[0013] R5= Et, Me, Pr, iPr, -CH2CH2OCH2CH2OCH3, orAtty Docket No.395 / 45 PCT R O2R O N2X ,

[0016] In a third aspect of the invention, a carbazole-based compound is represented by Formula 4: (Formula 4),

[0017] wherein:

[0018] R2and R3= H, CF3, CH2CF3, OCH3, -COCF3, -COCH3, or NO2;

[0019] R6= H, CF3, and F; and FFR5X

[0020] R1 = ,

[0021]

[0022] R4= CF3, CF2CF3, or CH2CF3;

[0023] X- = I-, Br-, Cl-, TFSI-, PF6-, or BF4-; and

[0024] R5= Et, Me, Pr, iPr, -CH2CH2OCH2CH2OCH3, or R3

[0025] ,Atty Docket No.395 / 45 PCT

[0026] wherein R2 and R3 = H, CF3, CH2CF3, OCH3, -COCF3, -COCH3, or NO2.

[0027] In an embodiment of the third aspect, a carbazole-based compound is represented by Formula 5: (Formula 5).

[0028] In a fourthflow battery electrolyte comprises a polar solvent and one or more of the phenothiazine-based compounds of claim 1 or claim 2 or the carbazole-based compound of claim 3. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The foregoing aspects and other features of the disclosure are explained in the following description, taken in connection with the accompanying drawings, wherein:

[0030] FIG.1 is a schematic representation of the synthesis of N-(4- trifluoromethylphenyl)-3,6-bis-(trifluoromethyl)carbazole.

[0031] FIG.2A shows NMR spectral data for N-(4-trifluoromethylphenyl)-3,6-bis- (trifluoromethyl)carbazole.

[0032] FIG.2B shows NMR spectral data for N-(4-trifluoromethylphenyl)-3,6-bis- (trifluoromethyl)carbazole.

[0033] FIG.2C shows NMR spectral data for N-(4-trifluoromethylphenyl)-3,6-bis- (trifluoromethyl)carbazole.

[0034] FIG.3 is a schematic representation of the synthesis of OFPT.

[0035] FIG.4 is a schematic representation of the synthesis of MEEOFPRT-TFSI salt.

[0036] FIG.5A shows NMR spectral data for OFPTK.

[0037] FIG.5B shows NMR spectral data for OFPTK.

[0038] FIG.5C shows NMR spectral data for OFPTK.

[0039] FIG.6A shows NMR spectral data for OFPRT.Atty Docket No.395 / 45 PCT

[0040] FIG.6B shows NMR spectral data for OFPRT.

[0041] FIG.6C shows NMR spectral data for OFPRT.

[0042] FIG.7A shows NMR spectral data for OFEPRT-I salt.

[0043] FIG.7B shows NMR spectral data for OFEPRT-I salt.

[0044] FIG.7C shows NMR spectral data for OFEPRT-I salt.

[0045] FIG.8A shows NMR spectral data for OFEPRT-TFSI salt.

[0046] FIG.8B shows NMR spectral data for OFEPRT-TFSI salt.

[0047] FIG.8C shows NMR spectral data for OFEPRT-TFSI salt.

[0048] FIG.9 shows cyclic voltammetry results for a 1 mM solution of N-(4- trifluoromethylphenyl)-3,6-bis-(trifluoromethyl)carbazole in 0.1 M TEABF4 in acetonitrile.

[0049] FIG.10 shows cyclic voltammetry results for a 1 mM solution of OFPTK in 0.1 M TEABF4 in acetonitrile.

[0050] FIG.11 shows cyclic voltammetry results for 1 mM solution of MEEOFPRT-TFSI salt in acetonitrile. DETAILED DESCRIPTION

[0051] To promote an understanding of the principles of the present disclosure, reference will now be made to preferred embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended, such alteration and further modifications of the disclosure as illustrated herein, being contemplated as would normally occur to one skilled in the art to which the disclosure relates.

[0052] Described herein are phenothiazine-based compounds and carbazole-based compounds and electrolytes therewith for use in electrochemical energy storage in various battery technologies including Li-ion batteries, Na-ion batteries, polymer batteries, and organic non-aqueous redox-flow batteries. The compounds can be useful in Li-ion batteries, for example as an additive for overcharge protection or as a redox shuttle, and in polymer batteries, for example as a monomer for polymer synthesis.

[0053] There are a limited number of redox-active molecules with high oxidation potential, good solubility, and electrochemical stability. The phenothiazine-based compounds andAtty Docket No.395 / 45 PCT carbazole-based compounds described herein have a high oxidation potential with moderate solubility and very good chemical and electrochemical stability. The phenothiazine-based compounds and carbazole-based compounds can enable the commercialization of all organic redox-flow batteries and can also be used for overcharge protection in lithium ion-batteries above 5 V. In embodiments, the phenothiazine and carbazole-based electrolytes have moderate solubility and high oxidation potential of up to 1.47 V referenced to Fc / Fc+.

[0054] Phenothiazine is a tricyclic organic compound with the formula S(C₆H₄)₂NH. It has two phenyl rings bound by sulfur and nitrogen atoms.

[0055] Phenothiazine has athe N-atom in the central ring of the phenothiazine core. A phenothiazine derivative with enhanced solubility and oxidation potential and its synthesis is described herein. The phenothiazine derivative includes perfluorination and a charge-bearing side chain. In embodiments, the charge-bearing side chain is permanent. Synthesis can take place via an SNAr chemical transformation.

[0056] The perfluorinated phenothiazine compound (OFPT) can be represented in the pure form by the Formula 1:Formula 1

[0057] In an embodiment, the perfluorinated phenothiazine compound with a charge-bearing side chain is octafluoro phenothiazine ketone (OFPTK), which can be represented by theAtty Docket No.395 / 45 PCT Formula 2:

[0058] In a different embodiment, the perfluorinated phenothiazine compound with a charge- bearing side chain can be represented by the Formula 3 R R22R N1F FX- = I-, Br-, Cl-, TFSI-, PF6-, or BF4-, and R5 = Et, Me, Pr, iPr, -CH2CH2OCH2CH2OCH3, orAtty Docket No.395 / 45 PCT R O2R O N2X F F ,

[0059] Carbazole is a polycyclic aromatic hydrocarbon consisting of two six-membered benzene rings fused on either side of a five-membered nitrogen-containing ring. Carbazole is used in different battery applications and energy storage devices.

[0060] However,solubility and relatively low oxidation potential. The carbazole derivatives reported to date are found to be less than 0.6 V referenced to Fc / Fc+. Carbazole derivatives with enhanced solubility and oxidation potential and their synthesis are described herein. Carbazole derivatives can be represented by the Formula 4: ,wherein: R2 and R3 = H, CF3, CH2CF3, OCH3, -COCF3, -COCH3, or NO2; R6 = H, CF3, F, andAtty Docket No.395 / 45 PCT FFR N5FR1 = ,R4 = CF3, CF2CF3, or CH2CF3; X- = I-, Br-, Cl-, TFSI-, PF6-, or BF4-; and R5 = Et, Me, Pr, iPr, -CH2CH2OCH2CH2OCH3, or R3,OCH3, -COCF3, -COCH3, or NO2.

[0061] In embodiments, the carbazole derivative incorporates inductively electron- withdrawing CF3 groups in each para-position from the nitrogen atom, and, in testing, had an oxidation potential of 1.45V referenced to Fc / Fc+. Synthesis can take place via an SNAr chemical transformation.

[0062] This embodiment of the carbazole derivative is referred to as N-(4- trifluoromethylphenyl)-3,6-bis-(trifluoromethyl)carbazole and can be represented by the Formula 5:Formula 5.

[0063] The phenothiazine derivative and carbazole derivative described herein can be usedAtty Docket No.395 / 45 PCT in electrolytes for organic batteries and as redox-shuttles for metal ion-based batteries.

[0064] The electrolyte useful in organic batteries or redox flow batteries (“RFB”) includes A) a polar solvent, and B) the aforementioned phenothiazine derivatives or carbazole derivatives.

[0065] The polar solvent can be any solvent in which the phenothiazine derivatives or carbazole derivatives are soluble in both oxidized and reduced states. The solvent should also remain inert within the working conditions of the RFB. It is expected that those of ordinary skill can readily determine the solubility and inertness of, and therefore choose, the appropriate solvent. The solvent could be water.

[0066] The polar solvent could also be, for example, an alcohol, such as C1 to C10 alcohol or glycol, including, for example, methanol, ethanol, 1-propanol, 2-propanol, ethylene glycol, propylene glycol. Ethers may also be employed as the solvent, including, for example, dimethoxymethane, methoxybenzene (anisole), tetrahydrofuran (THF), 2- methyltetrahydrofuran, 1,4-dioxane, 1,3-dioxolane (DOL), 4-methyl-1,3-dioxolane, 1,2- dimethoxyethane (DME), and bis(2-methoxyethyl) ether (diglyme). The polar solvent can also be a ketone, such as acetone or acetylacetone. Nitriles, such as, for example, acetonitrile (ACN), methoxyacetonitrile, propionitrile, butyronitrile, isobutyronitril, benzonitrile, and 3- methoxypropionitrile can be employed as the solvent, as can amines, such as ethylenediamine and pyridines, or amides such as formamide, n-methylacetamide, N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), and N-methyl-2-pyrrolidinone (NMP). The solvent can also be a carbonate. Non-limiting examples of carbonates include propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and 1,2-butylene carbonate. The solvent can also be a cyclic ester such as γ- butyrolactone (γ-BL) or γ-valerolactone (γ-VL). Other organic based solvents are also contemplated, such as, for example, hexane, benzene, toluene, nitromethane, nitrobenzene, 1,2- dichloroethane, dimethyl sulfoxide (DMSO), ethyl acetate, and nitroethane to name a few. The solvent may also employ a combination of any of the foregoing solvents.

[0067] The phenothiazine derivatives or carbazole derivatives can be included in the polar solvent at about 1 to about 50 wt. %, or in some instances, from about 2.5 to about 30 wt. %, or even from about 5 to about 25 wt. % or about 10 to about 20 wt. %.Atty Docket No.395 / 45 PCT

[0068] The electrolyte may also include a supporting redox active species. Supporting redox active species currently envisaged include, but are not limited to, lithium salts, sodium salts, potassium salts, ammonium salts, and mixtures thereof. Examples of supporting redox active species include, but are not limited to, for example, sodium phosphate, sodium chloride, potassium phosphate, potassium chloride, potassium hexafluorophosphate, lithium hexafluorophosphate, tetrabutylammonium fluorophosphate, ammonium chloride, tetrabutylammonium chloride, lithium perchlorate, lithium nitrate, lithium chloride, and the like.

[0069] The electrolyte may further include acids, bases, supporting electrolytes additives, including redox mediators such as metallocenes and viologens, co-solvents, emulsifiers, other redox active compounds, ionic liquids, viscosity-controlling agents, wetting agents, stabilizers, salts, or combinations thereof.

[0070] The electrolyte may include buffering agents. In an embodiment, the electrolyte can have a pH of between 6 to 8. In some instances, the electrolyte can have a pH of between 6.25 and 7.75. The electrolyte can also have a pH of between 6.5 and 7.5. In some embodiments, the electrolyte can have a pH of between 6.75 and 7.25. In further embodiments, the electrolyte can have a pH of between 6.8 and 7.2, or 6.9 and 7.1, or even 6.95 and 7.05. The pH can be adjusted by adding buffering agents, such as, for example, potassium phosphate, dipotassium phosphate, tripotassium phosphate, and other typical buffers, such as sulfamic acids / sulfamates, formic acids / formates, acetic acids / acetates, ammoniums, bicarbonates / carbonates, fumaric acids / hydrogen fumarates, benzoic acids / benzoates, and the like.

[0071] Also described is a redox flow battery system including the above-discussed electrolyte. A typical RFB comprises a positive half-cell and a negative half-cell. The positive half-cell comprises an electrode tank containing a catholyte and the negative half-cell comprises an electrode tank containing an anolyte. The anolyte and catholyte are solutions comprising electrochemically active components in different oxidation states. The anolyte and catholyte are often referred to as the negative electrolyte and positive electrolyte, respectively, and these terms can be used interchangeably. As used herein, the terms anolyte and catholyteAtty Docket No.395 / 45 PCT refer to electrolytes composed of electrochemically active components and an aqueous supporting solution.

[0072] During charging and discharging of the RFB, the catholyte and anolyte are continuously circulating via pumps through the positive and negative electrodes respectively, where redox reactions proceed, providing the conversion between chemical energy and electrical energy or vice-versa. To complete the circuit during use, positive and negative electrodes (including a current collector at each side) of the RFB system are electrically connected through current collectors with an external load.

[0073] The presently-disclosed subject matter also includes derivatives of any of the compounds described herein. As used herein, the term “derivative” refers to a compound having a structure derived from the structure of a parent compound (e.g., a compounds disclosed herein) and whose structure is sufficiently similar to those disclosed herein and based upon that similarity, would be expected by one skilled in the art to exhibit the same or similar activities and utilities as the claimed compounds, or to induce, as a precursor, the same or similar activities and utilities as the claimed compounds.

[0074] The compounds described herein can contain one or more double bonds and, thus, potentially can give rise to cis / trans (E / Z) isomers, as well as other conformational isomers. Unless stated to the contrary, the invention includes all such possible isomers, as well as mixtures of such isomers. Unless stated to the contrary, a formula with chemical bonds shown only as solid lines and not as wedges or dashed lines contemplates each possible isomer, e.g., each enantiomer and diastereomer, and a mixture of isomers, such as a racemic or scalemic mixture. Compounds described herein can contain one or more asymmetric centers and, thus, potentially give rise to diastereomers and optical isomers. Unless stated to the contrary, the present invention includes all such possible diastereomers as well as their racemic mixtures, their substantially pure resolved enantiomers, all possible geometric isomers, and pharmaceutically acceptable salts thereof. Mixtures of stereoisomers, as well as isolated specific stereoisomers, are also included. During the synthetic procedures used to prepare such compounds, or in using racemization or epimerization procedures known to those skilled in the art, the products of such procedures can be a mixture of stereoisomers.

[0075] Articles “a” and “an” are used herein to refer to one or to more than one (i.e. at leastAtty Docket No.395 / 45 PCT one) of the grammatical object of the article. By way of example, “a nanostructured silicon carbon composition material” means at least one nanostructured silicon carbon composition material and can include more than one nanostructured silicon carbon composition material.

[0076] Throughout the specification, the terms "about" and / or "approximately" may be used in conjunction with numerical values and / or ranges. The term "about" is understood to mean those values near to a recited value. For example, "about 40 [units]" may mean within + / - 25% of 40 (e.g., from 30 to 50), within + / - 20%, + / - 15%, + / - 10%, + / - 9%, + / -8 %, + / - 7%, + / - 6%, + / - 5%, + / - 4%, + / - 3%, + / -2 %, + / - 1%, less than + / - 1%, or any other value or range of values therein or there below. Furthermore, the phrases "less than about [a value]" or "greater than about [a value]" should be understood in view of the definition of the term "about" provided herein. The terms "about" and "approximately" may be used interchangeably.

[0077] Throughout the specification, numerical ranges are provided for certain quantities. It is to be understood that these ranges comprise all subranges therein. Thus, the range "from 50 to 80" includes all possible ranges therein (e.g., 51-79, 52-78, 53-77, 54-76, 55-75, 60-70, etc.). Furthermore, all values within a given range may be an endpoint for the range encompassed thereby (e.g., the range 50-80 includes the ranges with endpoints such as 55-80, 50-75, etc.).

[0078] As used herein, the verb "comprise" as is used in this description and in the claims and its conjugations are used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded.

[0079] Throughout the specification the word "comprising," or variations such as "comprises" or "comprising," will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. The present disclosure may suitably "comprise", "consist of", or "consist essentially of", the steps, elements, and / or reagents described in the claims.

[0080] It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as "solely", "only" and the like in connection with the recitation of claim elements, or the use of a "negative" limitation.

[0081] Unless defined otherwise, all technical and scientific terms used herein have the sameAtty Docket No.395 / 45 PCT meanings as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Preferred methods, devices, and materials are described, although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present disclosure. All references cited herein are incorporated by reference in their entirety.

[0082] The following Examples further illustrate the disclosure and are not intended to limit the scope. In particular, it is to be understood that this disclosure is not limited to particular embodiments described, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present disclosure will be limited only by the appended claims. EXAMPLES Example 1. Synthesis of N-(4-trifluoromethylphenyl)-3,6-bis-(trifluoromethyl)carbazole

[0083] In a 100 mL oven-dried round bottom flask fitted with a magnetic stirrer, 3,6-bis- (trifluoromethyl)carbazole (0.4 g, 1.32 mmol, 1 equiv.) was dissolved in dry dimethyl sulfoxide (DMSO) at room temperature under nitrogen environment. Then, CuI (26 mg, 0.13 mmol, 0.1 equiv.), L-proline (16 mg, o.13 mmol, 0.1 equiv.), and K2CO3(365 mg, 2.64 mmol, 2 equiv.) were added and the reaction mixture was stirred for five minutes. After this, 4-iodo- trifluoromethylbenzene (0.51 g, 1.85 mmol, 1.4 equiv.) was added to the reaction mixture and then the reaction was heated to 195 ⁰C for 20 h. After the reaction was complete, the reaction mixture was diluted with water and extracted in ethyl acetate three times. The combined organic layer was washed with brine, dried over sodium sulfate, concentrated under reduced pressure, and purified through column chromatography (silica gel, 5% ethylacetate in hexane as eluent) to obtain the product as a brown crystalline solid. FIG. 1 provides a schematic representation of the synthesis scheme for N-(4-trifluoromethylphenyl)-3,6-bis- (trifluoromethyl)carbazole.

[0084] NMR Spectroscopy was performed on the product. The NMR spectral data for N- (4-trifluoromethylphenyl)-3,6-bis-(trifluoromethyl)carbazole is shown in FIGs. 2A, 2B, andAtty Docket No.395 / 45 PCT 2C. The spectral data was as follows:1H NMR (400 MHz, CHCl3) δ 8.49 (s, 2H), 7.98-7.96 (m, 2H), 7.76-7.71 (m, 4H), 7.51-7.49 (m, 2H) ppm. See, FIG.2A.19F NMR (400 MHz, CdCl3) δ -60.48, -62.46 ppm. See, FIG. 2B.13C NMR (500 MHz, CDCl3) δ 142.7, 139.7, 131.3, 130.9, 130.8, 130.3, 128.9, 127.8 (m), 127.4, 126.2, 125.1, 124.3, 124.2 (m), 124.0, 123.7, 123.5, 123.3, 123.0, 122.4, 118.5 (q, J= 4.2 Hz), 110.3 ppm. See, FIG.2C. Example 2. Synthesis of octafluoro phenothiazine ketone (OFPTK)

[0085] In a 100 mL oven-dried round bottom flask fitted with a magnetic stirrer, octafluoro phenothiazine (OFPT) (200 mg, 0.58 mmol, 1 equiv.) was dissolved in 15 mL of acetonitrile. To this solution was added NaI (173.1 mg, 1.16 mmol, 2 equiv.), NaHCO3 (97.5 mg, 1.16 mmol, 2 equiv.), and 2-chloroacetone (60 mg, 0.65 mmol, 1.1 equiv.). The reaction mixture was heated to 80 ⁰C for 48 h after which an additional 2 mL of 2-chloroacetone was added. Stirring continued overnight at the same temperature. The reaction was allowed to cool to room temperature, and the reaction product diluted with ethyl acetate. The product was washed with water, extracted with ethyl acetate, and concentrated under reduced pressure to obtain a crude product, which was purified by flash chromatography (silica gel, hexane as an eluent). FIG. 4 provides a schematic representation of the synthesis scheme for OFPTK. The first step of the reaction in FIG.4 schematically illustrates the synthesis of OFPTK.

[0086] The NMR spectral data for OFPTK is shown in FIGs.5A, 5B, and 5C. The spectral data is as follows:1H NMR (400 MHz, CHCl3) δ 4.7 (s, 2 H), 2.2 (s, 3 H). See, FIG.5A.19F NMR (400 MHz, CdCl3) δ -138.25 to -138.34 (m), -149.05 to -149.12 (m), -155.97 to -156.08 (m), -160.03 to -160.14 (m) ppm. See, FIG. 5B.13C NMR (500 MHz, CDCl3) δ 201.8, 144.2 (m), 141.9 (m), 139.6 (m), 136.8 (m), 128.6 (m), 113.5 (m), 62.5, 26.7 ppm. See, FIG.5C. Example 3. Synthesis of OFPRT

[0087] In a 100 mL oven-dried round bottom flask fitted with a magnetic stirrer, OFPTK (120 mg, 0.3 mmol, 1 equiv.) was dissolved in 10 mL of anhydrous methanol under atmosphere of nitrogen. After the complete dissolution, ammonium acetate (NH4OAc) (231.2 mg, 3 mmol, 10 equiv.) was added followed by sodium cyanoborohydride (NaBH3CN) (66 mg, 1.05 mmol, 1.05 equiv.). The reaction was stirred overnight and monitored by thin-layer chromatographyAtty Docket No.395 / 45 PCT (TLC) and liquid chromatography–mass spectrometry (LCMS). After the reaction was complete, methanol was evaporated under reduced pressure, and the organic part was extracted with ethyl acetate and concentrated. The crude product was dissolved in methanol followed by the addition of 364 mg of 37% formaldehyde in water and stirred for 1 hour. Then 63 mg of NaBH3CN was added and the reaction was stirred for another 2 hours. The reaction mixture was extracted in ethyl acetate, dried on Na2SO4, and concentrated under reduced pressure. The desired product was extracted from impurities with a small amount of diethyl ether to obtain 90 mg of the OFPRT as a low-melting solid. FIG.4 provides a schematic representation of the synthesis scheme for OFPRT. The first three steps of the reaction in FIG. 4 schematically illustrate the synthesis of OFPRT.

[0088] The NMR spectral data for OFPRT is shown in FIGS. 6A, 6B, and 6C. The NMR spectral data for the product was as follows:1H NMR (400 MHz, CHCl3) δ 3.92-3.86 (m, 1H), 3.59-3.54 (m, 1H), 2.79-2.71 (m, 1H), 2.11 (s, 6H), 0.93 (d, J = 6.6 Hz, 3H) ppm. See, FIG. 6A.19F NMR (400 MHz, CdCl3) multiple peaks δ -136.8 to -160.1 ppm. See, FIG. 6B.13C NMR (500 MHz, CDCl3) δ 144.0, 142.1, 141.6, 139.8, 139.6, 136.4, 129.8, 129.4, 113.8, 113.6, 113.4, 58.2, 57.2, 57.1, 40.3, 10.4 ppm. See, FIG.6C. Example 4: Synthesis of OFEPRT-I salt

[0089] In an oven-dried round bottom flask equipped with a magnetic stirrer, OFPRT (250 mg, 0.58 mmol, 1 equiv.) was dissolved in an anhydrous acetonitrile (10 mL) under nitrogen environment. To this solution was added ethyl iodide (137 mg, 0.87 mmol, 1.5 equiv.) The reaction was allowed to stir for 24 h under dark conditions (reaction flask wrapped with aluminum foil). The reaction was monitored by TLC and LCMS. After the consumption of the starting material, the solvent was removed under reduced pressure, and the impurities were removed by dissolving in ether. The remaining solid precipitate was dried in a vacuum oven overnight at 35 °C to get 221 mg (yield = 86%) of the OFEPRT-I salt. FIG. 4 provides a schematic representation of the synthesis scheme for OFEPRT-I salt.

[0090] The NMR spectral data for OFEPRT-I salt is shown in FIGS.7A, 7B, and 7C. The NMR spectral data for the product was as follows:1H NMR (400 MHz, DMSO-d6) δ 4.60 (d, J = 14.2 Hz, 1H), 3.90-3.84 (m, 1H), 3.61-3.57 (m, 1H), 3.40-3.35 (m, 1H), 2.94 (m, 6H), 1.40Atty Docket No.395 / 45 PCT (d, J = 6.4 Hz, 3H), 1.17 (t, J = 7.1 Hz, 3 H) ppm. See, FIG.7A.19F NMR (400 MHz, DMSO- d6) δ -138.8to -138.9 ppm (m), -146.1 to -146.2 (m), -154.9 to -155.0 (m), -155.4 to -155.5 (m), -160.1 to -160.3 (m) ppm. See, FIG.7B.13C NMR (500 MHz, DMSO-d6) δ 144.3, 142.4, 139.9, 130.2, 127.3, 114.3, 113.3, 66.7, 57.4, 52.7, 47.8, 47.7, 13.2, 8.3 ppm. See, FIG.7C. Example 5: Synthesis of OFEPRT-TFSI salt

[0091] In an oven-dried round bottom flask equipped with a magnetic stirrer, OFPRT-I (200 mg, 0.45 mmol, 1 equiv.) was dissolved in DI water and acetonitrile (1:1 v / v, 20 mL). To this solution was added lithium bis(trifluoromethane)sulfonimide (LiTFSI) (155.75 mg, 0.54 mmol, 1.2 equiv.) at 60 °C. The reaction was stirred at 90 °C overnight and allowed to cool. The organic part was extracted in ethyl acetate, dried on sodium sulfate, and concentrated under reduced pressure. The crude product was purified by collecting ether wash (OFEPRT-I is insoluble in ether while OFEPRT-TFSI is soluble in ether) followed by concentrating under reduced pressure. The crude product was dried in a vacuum oven at 30 °C to yield OFEPRT- TFSI salt (448.3 mg, yield = 88%) as a product. FIG.4 provides a schematic representation of the synthesis scheme for OFEPRT-TFSI salt.

[0092] The NMR spectral data for OFEPRT-TFSI salt is shown in FIGS.8A, 8B, and 8C. The NMR spectral data for the product was as follows:1H NMR (400 MHz, DMSO-d6) δ 4.65 (d, J = 14.4 Hz, 1H), 3.9-3.8 (m, 1 H), 3.58-3.55 (m, 1H), 3.39-3.34 (m, 2H), 2.93 (m, 6H), 1.40 (d, J = 6.4 Hz, 3H), 1.16 (t, J = 7.0 Hz, 3H) ppm. See, FIG. 8A.19F NMR (400 MHz, DMSO-d6) δ -78.7, -138.9, -155.0, -155.5, -160.3 ppm. See, FIG. 8B.13C NMR (500 MHz, DMSO-d6) δ -144.4 (m), 143.0 (m), 142.4 (m), 140.5, 139.9 (m), 139.6(m), 137.1 (br, m), 130.3 (br, m), 127.3 (br, m), 124.8, 121.6, 118.4, 115.2, 114.3, 114.1, 113.5, 113.3, 66.7, 57.4, 47.8, 47.7, 13.1, 8.2 ppm. See, FIG.8C. Example 6: Solubility measurement

[0093] The solubilities of the newly synthesized redox-active species were measured in anhydrous acetonitrile and 0.1 M tetraethylammonium tetrafluoroborate (TEABF4) in acetonitrile (Table 1) through an NMR method using 1,4-bis-(trifluoromethyl)benzene as an internal standard. In the NMR spectroscopic method, the solubility was determined byAtty Docket No.395 / 45 PCT comparing the resonance signals from the solute and standard to obtain mole fractions of the solution components. Additional details about the method of measuring solubility can be found in Perera, Anton S., et al., Large Variability and Complexity of Isothermal Solubility for a Series of Redox-Active Phenothiazines, Mater. Adv., 2022, 3, 8705.

[0094] The newly synthesized compounds were found to have better solubilities than their parent carbazole and phenothiazine molecules. Table 1: Solubility study of redoxomers S.N. Redoxmers Solubility in Solubility in 0.1 M acetonitrile TEABF4 inExample 7: Electrochemical Characterization

[0095] The oxidation potentials of the newly synthesized electrolytes were measured using cyclic voltammetry. N-(4-trifluoromethylphenyl)-3,6-bis-(trifluoromethyl)carbazole and OFPTK are neutral organic compounds and required supporting salts given their poor electrical conductivities. The cyclic voltammetry experiments were carried out using their 1 mM solutions in 0.1 M TEABF4 / acetonitrile, which exhibited reversible redox phenomenon at 1.48 V for N-(4-trifluoromethylphenyl)-3,6-bis-(trifluoromethyl)carbazole and 1.39 V for OFPTK, referenced to Fc / Fc+. FIG. 9 shows cyclic voltammetry results for a 1 mM solution of N-(4- trifluoromethylphenyl)-3,6-bis-(trifluoromethyl)carbazole in 0.1 M TEABF4 in acetonitrile. FIG.10 shows cyclic voltammetry results for a 1 mM solution of OFPTK in 0.1 M TEABF4 in acetonitrile.

[0096] OFPRT-TFSI is an ion pair and had enough conductivity in the absence of an external supporting salt. Cyclic voltammetry was carried out in anhydrous acetone, which exhibited a reversible redox phenomenon at 1.19 V referenced to Fc / Fc+ system. FIG.11 showsAtty Docket No.395 / 45 PCT cyclic voltammetry results for 1 mM solution of MEEOFPRT-TFSI salt in acetonitrile.

[0097] The oxidation potentials for N-(4-trifluoromethylphenyl)-3,6-bis- (trifluoromethyl)carbazole, OFPTK, and OFPRT-TFSI were higher than those reported in the literature for phenothiazine and carbazole derivatives that have been electrochemically characterized, making them a promising electrolyte candidate for the future organic battery technology.

[0098] Below is a list of phenothiazine derivatives that have been reported in the literature with their oxidation potentials.

[0099] Any patents or publications mentioned in this specification are indicative of the levels of those skilled in the art to which the invention pertains. These patents and publications are herein incorporated by reference to the same extent as if each individual publication was specifically and individually indicated to be incorporated by reference.

Claims

Atty Docket No.395 / 45 PCT CLAIMS The invention claimed is:

1. A phenothiazine-based compound of Formula 2:

2. A phenothiazine-based compound of Formula 3: R R22R N1F FX- = I-, Br-, Cl-, TFSI-, PF6-, or BF4-, and R5 = Et, Me, Pr, iPr, -CH2CH2OCH2CH2OCH3, orAtty Docket No.395 / 45 PCT R O2R O N2X X ,Atty Docket No.395 / 45 PCT 4. A carbazole-based compound of Formula 5:

5. A battery comprising one or more of the phenothiazine-based compounds of claim 1 or claim 2 or the carbazole-based compound of claim 3 for electrochemical energy storage.

6. The battery of claim 5, wherein the battery comprises a Li-ion battery, a Na-ion battery, a redox-flow battery, or a polymer battery.

7. A redox flow battery electrolyte comprising a polar solvent and one or more of the phenothiazine-based compounds of claim 1 or claim 2 or the carbazole-based compound of claim 3.

8. The redox flow battery electrolyte of claim 7, wherein the polar solvent comprises one or more of a C1 to C10 alcohol or glycol, ethers, ketones, nitriles, amines, amides, carbonates, cyclic esters, or other organic-based solvents.

9. The redox flow battery electrolyte of claim 7, wherein the polar solvent comprises one or more of methanol, ethanol, 1-propanol, 2-propanol, ethylene glycol, propylene glycol, dimethoxymethane, methoxybenzene (anisole), tetrahydrofuran (THF), 2- methyltetrahydrofuran, 1,4-dioxane, 1,3-dioxolane (DOL), 4-methyl-1,3-dioxolane, 1,2-dimethoxyethane (DME), and bis(2-methoxyethyl) ether (diglyme), acetone or acetylacetone, acetonitrile (ACN), methoxyacetonitrile, propionitrile, butyronitrile, isobutyronitril, benzonitrile, and 3-methoxypropionitrile, ethylenediamine and pyridines, formamide, n-methylacetamide, N,N-dimethylformamide (DMF), N,N- dimethylacetamide (DMA), and N-methyl-2-pyrrolidinone (NMP), propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonateAtty Docket No.395 / 45 PCT (DEC), ethyl methyl carbonate (EMC), and 1,2-butylene carbonate, γ-butyrolactone (γ- BL) or γ-valerolactone (γ-VL), hexane, benzene, toluene, nitromethane, nitrobenzene, 1,2-dichloroethane, dimethyl sulfoxide (DMSO), ethyl acetate, or nitroethane.

10. The redox flow battery electrolyte of claim 7, wherein the one or more phenothiazine compounds or carbazole compound is included in the polar solvent at about 1 to about 50 wt. %, or, from about 2.5 to about 30 wt. %, or from about 5 to about 25 wt. % or about 10 to about 20 wt. %.

11. The redox flow battery electrolyte of claim 7, wherein the electrolyte further comprises a supporting redox active species.

12. The redox flow battery electrolyte of claim 11, wherein the supporting redox active species comprises lithium salts, sodium salts, potassium salts, ammonium salts, and mixtures thereof.

13. The redox flow battery electrolyte of claim 7, further comprising acids, bases, supporting electrolyte additives, including redox mediators such as metallocenes and viologens, co-solvents, emulsifiers, other redox active compounds, ionic liquids, viscosity-controlling agents, wetting agents, stabilizers, salts, or combinations thereof.

14. The redox flow battery electrolyte of claim 7, further comprising buffering agents.

15. The redox flow battery electrolyte of claim 7, having a pH of between 6 and 8.

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