FORMULATIONS OF BIOREACHABLE DOPANTS FOR LIQUID CRYSTALS
20230203378 · 2023-06-29
Inventors
- Shilpa Naresh Raja (Emeryville, CA, US)
- Arjan Zoombelt (Emeryville, CA, US)
- Adam Safir (Berkeley, CA)
- Peter Palffy-Muhoray (Kent, OH, US)
- Robert J. Twieg (Kent, OH, US)
- Hiroshi Yokoyama (Kent, OH, US)
- Tianyi Guo (Kent, OH, US)
- Pawan Nepal (Kent, OH, US)
Cpc classification
G02F1/13
PHYSICS
C09K19/0208
CHEMISTRY; METALLURGY
International classification
C09K19/02
CHEMISTRY; METALLURGY
Abstract
The present disclosure relates to formulations having one, two, or more chiral dopants, as well as materials and methods including such formulations. In particular instances, the formulation can include an achiral host, such as a nematic substance.
Claims
1. A formulation comprising: about 0.5 wt. % to about 30 wt. % of a first chiral dopant derived from betulin or glycyrrhetinic acid; and about 50 wt. % to about 99.5 wt. % of an achiral host.
2. The formulation of claim 1, wherein the first chiral dopant comprises a structure having formula (IA) or (IB): ##STR00027## or a salt thereof, wherein: each of R.sup.1 and R.sup.2 is, independently, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted aralkyl, optionally substituted aryl, optionally substituted alkaryl, optionally substituted alkanoyl, optionally substituted aryloyl, or optionally substituted heterocyclyloyl.
3. The formulation of claims 1-2, wherein the first chiral dopant comprises a structure having formula (IAa), (IBa), (IAb), or (IBb): ##STR00028## wherein: each of R.sup.1a, R.sup.2a, R.sup.1b, and R.sup.2b is, independently, optionally substituted alkyl, optionally substituted haloalkyl, optionally substituted alkenyl, optionally substituted aralkyl, optionally substituted aryl, or optionally substituted alkaryl.
4. The formulation of claims 1-3, wherein the first chiral dopant is selected from the group consisting of: ##STR00029## ##STR00030##
5. The formulation of claims 1-4, further comprising at least one polymerizable mesogenic compound having at least one polymerizable functional group or wherein the achiral host comprises at least one polymerizable mesogenic compound having at least one polymerizable functional group.
6. The formulation of claim 5, wherein the polymerizable functional group includes an epoxy group, a vinyl group, an allyl group, an acrylate, a methacrylate, an isoprene group, an alpha-amino carboxylate, or any combination thereof.
7. The formulations of claims 1-6, wherein the achiral host further comprises a nematic or a nematogenic substance.
8. The formulation of claim 7, wherein the nematic or the nematogenic substance is selected from azoxybenzenes, benzylideneanilines, biphenyls, terphenyls, phenyl benzoates, cyclohexyl benzoates, phenyl esters of cyclohehexanecarboxylic acid, cyclohexyl esters of cyclohehexanecarboxylic acid, phenyl esters of cyclohexylbenzoic acid, cyclohexyl esters of cyclohexylbenzoic acid, phenyl esters of cyclohexylcyclohexanecarboxylic acid, cyclohexyl esters of cyclohexylcyclohexanecarboxylic acid, cyclohexylphenyl esters of benzoic acid, cyclohexylphenyl esters of cyclohexanecarboxylic acid, cyclohexylphenyl esters of cyclohexylcyclohexanecarboxylic acid, phenylcyclohexanes, cyclohexylbiphenyls, phenylcyclohexylcyclohexanes, cyclohexylcyclohexanes, cyclohexylcyclohexenes, cyclohexylcyclohexylcyclohexenes, 1,4-bis-cyclohexylbenzenes, 4,4′-bis-cyclohexylbiphenyls, phenylpyrimidines, cyclohexylpyrimidines, phenylpyridines, cyclohexylpyridines, phenylpyridazines, cyclohexylpyridazines, phenyldioxanes, cyclohexyldioxanes, phenyl-1,3-dithianes, cyclohexyl-1,3-dithianes, 1,2-diphenylethanes, 1,2-dicyclohexylethanes, 1-phenyl-2-cyclohexylethanes, 1-cyclohexyl-2-(4-phenylcyclohexyl) ethanes, 1-cyclohexyl-2-biphenylethanes, 1-phenyl2-cyclohexylphenylethanes, halogenated stilbenes, benzyl phenyl ether, tolanes, substituted cinnamic acids, or any combination thereof.
9. A formulation comprising: a first chiral dopant derived from betulin or glycyrrhetinic acid; and a second chiral dopant derived from betulin or glycyrrhetinic acid, wherein the first and second chiral dopants are different.
10. The formulation of claim 9, wherein the first chiral dopant comprises a structure having formula (IA) or (IB): ##STR00031## or a salt thereof, wherein: each of R.sup.1 and R.sup.2 is, independently, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted aralkyl, optionally substituted aryl, optionally substituted alkaryl, optionally substituted alkanoyl, optionally substituted aryloyl, or optionally substituted heterocyclyloyl.
11. The formulation of claims 9-10, wherein the second chiral dopant comprises a structure having formula (IIA) or (IIB): ##STR00032## wherein: each of R.sup.3 and R.sup.4 is, independently, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted aralkyl, optionally substituted aryl, optionally substituted alkaryl, optionally substituted alkanoyl, optionally substituted aryloyl, or optionally substituted heterocyclyloyl.
12. The formulation of claims 9-11, wherein the first or second chiral dopant comprises a structure having formula (IAa), (IBa), (IAb), or (IBb): ##STR00033## wherein: each of R.sup.1, R.sup.2a, R.sup.1b, and R.sup.2b is, independently, optionally substituted alkyl, optionally substituted haloalkyl, optionally substituted alkenyl, optionally substituted aralkyl, optionally substituted aryl, or optionally substituted alkaryl.
13. The formulation of claims 9-12, further comprising: a third chiral dopant derived from betulin, wherein the first, second, and third chiral dopants are different.
14. The formulation of claim 13, wherein the third chiral dopant comprises a structure having formula (IA) or (IB).
15. The formulation of claims 9-14, wherein each of the first chiral dopant, the second chiral dopant, and the third chiral dopant, if present, is selected from the group consisting of: ##STR00034## ##STR00035##
16. A liquid crystalline material comprising: about 0.5 wt. % to about 20 wt. % of a first chiral dopant derived from betulin; and about 0.5 wt. % to about 20 wt. % of a second chiral dopant derived from betulin, wherein the first and second chiral dopants are different.
17. The material of claim 16, further comprising: a third chiral dopant derived from betulin, wherein the first, second, and third chiral dopants are different.
18. The material of claims 16-17, wherein the first chiral dopant comprises a structure having formula (IA) or (IB): ##STR00036## or a salt thereof, wherein: each of R.sup.1 and R.sup.2 is, independently, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted aralkyl, optionally substituted aryl, optionally substituted alkaryl, optionally substituted alkanoyl, optionally substituted aryloyl, or optionally substituted heterocyclyloyl.
19. The material of claims 16-18, the second chiral dopant comprises a structure having formula (IIA) or (IIB): ##STR00037## wherein: each of R.sup.3 and R.sup.4 is, independently, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted aralkyl, optionally substituted aryl, optionally substituted alkaryl, optionally substituted alkanoyl, optionally substituted aryloyl, or optionally substituted heterocyclyloyl.
20. The material of claims 16-19, further comprising at least one polymerizable mesogenic compound having at least one polymerizable functional group.
21. The material of claim 20, wherein the polymerizable functional group includes an epoxy group, a vinyl group, an allyl group, an acrylate, a methacrylate, an isoprene group, an alpha-amino carboxylate, or any combination thereof.
22. The material of claims 16-19, further comprising a nematic or a nematogenic substance.
23. The material of claim 22, wherein the nematic or the nematogenic substance is selected from azoxybenzenes, benzylideneanilines, biphenyls, terphenyls, phenyl benzoates, cyclohexyl benzoates, phenyl esters of cyclohehexanecarboxylic acid, cyclohexyl esters of cyclohehexanecarboxylic acid, phenyl esters of cyclohexylbenzoic acid, cyclohexyl esters of cyclohexylbenzoic acid, phenyl esters of cyclohexylcyclohexanecarboxylic acid, cyclohexyl esters of cyclohexylcyclohexanecarboxylic acid, cyclohexylphenyl esters of benzoic acid, cyclohexylphenyl esters of cyclohexanecarboxylic acid, cyclohexylphenyl esters of cyclohexylcyclohexanecarboxylic acid, phenylcyclohexanes, cyclohexylbiphenyls, phenylcyclohexylcyclohexanes, cyclohexylcyclohexanes, cyclohexylcyclohexenes, cyclohexylcyclohexylcyclohexenes, 1,4-bis-cyclohexylbenzenes, 4,4′-bis-cyclohexylbiphenyls, phenylpyrimidines, cyclohexylpyrimidines, phenylpyridines, cyclohexylpyridines, phenylpyridazines, cyclohexylpyridazines, phenyldioxanes, cyclohexyldioxanes, phenyl-1,3-dithianes, cyclohexyl-1,3-dithianes, 1,2-diphenylethanes, 1,2-dicyclohexylethanes, 1-phenyl-2-cyclohexylethanes, 1-cyclohexyl-2-(4-phenylcyclohexyl) ethanes, 1-cyclohexyl-2-biphenylethanes, 1-phenyl2-cyclohexylphenylethanes, halogenated stilbenes, benzyl phenyl ether, tolanes, substituted cinnamic acids, or any combination thereof.
24. The material of claims 16-23, wherein the material comprises a helical twisting power of from about 1 μm.sup.−1 to about 100 μm.sup.−1.
25. A liquid crystal display, optical element, or color filter comprising a formulation of any of claims 9-15.
26. A display comprising a layer of liquid crystalline material of any of claims 16-24, the liquid crystalline material having a cholesteric pitch (P) and a thickness (d), wherein a ratio of d/P is at least 0.01, at least 0.02, at least 0.05, at least 0.1, or at least 0.15.
27. The display of claim 26, wherein the ratio of d/P is not greater than 1, not greater than 0.8, not greater than 0.6, not greater than 0.4, not greater than 0.3, or not greater than 0.25.
28. A method of making a formulation, the method comprising: reacting a first biomolecule with a first derivatizing agent to provide a first chiral dopant comprising a structure having formula (I), (III), or a salt thereof, wherein first biomolecule comprises betulin or glycyrrhetinic acid; and combining the first chiral dopant with an achiral host to provide the formulation comprising about 0.5 wt. % to about 30 wt. % of the first chiral dopant and about 50 wt. % to about 99.5 wt. % of the achiral host.
29. The method of claim 28, wherein said combining provides the formulation of claims 1-8.
30. A method of making a formulation, the method comprising: reacting a first biomolecule with a first derivatizing agent to provide a first chiral dopant comprising a structure having formula (I), (III), or a salt thereof, wherein first biomolecule comprises betulin or glycyrrhetinic acid; reacting a second biomolecule with a second derivatizing agent to provide a second chiral dopant comprising a structure having formula (I), (III), or a salt thereof, wherein second biomolecule comprises betulin or glycyrrhetinic acid and wherein the first and second chiral dopants are different; and combining the first and second chiral dopants to provide the formulation.
31. The method of claim 30, wherein said combining provides the formulation of claims 9-15.
32. The method of claim 30, wherein said combining further includes combining the first and second chiral dopants with an achiral host to provide a further formulation.
33. The method of claim 32, wherein said combining provides the further formulation comprising about 0.5 wt. % to about 30 wt. % of the first chiral dopant, about 0.5 wt. % to about 30 wt. % of the second chiral dopant, and about 40 wt. % to about 99 wt. % of the achiral host.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0061]
[0062]
[0063]
[0064]
[0065]
[0066]
[0067]
[0068]
[0069]
[0070]
[0071]
[0072]
[0073]
[0074]
[0075]
[0076]
[0077]
[0078]
[0079]
[0080]
[0081]
DETAILED DESCRIPTION
[0082] The present disclosure relates to stable formulations including one or more chiral dopants in various hosts. In particular embodiments, enhanced stability was observed by including smaller percentages of different dopants rather than using mono-dopant formulations. Illustrative enhanced stability metrics can include enhanced thermal cycling stability, enhanced phase stability, enhanced voltage cycling stability, long term phase stability (e.g., for over 6 months, 7 months, or more), UV stability, among others (e.g., described herein). In another embodiment, enhanced stability was observed by dopants having extended aliphatic groups (e.g., linear or branched C.sub.3-12 alkyl groups), as compared to those lacking such aliphatic groups.
[0083] In use, the dopant(s) act as a twist agent. When combined with a host, the resultant material forms a twisted cholesteric structure in a self-assembled layer, which can then act as an interference filter. Light can be regarded as being composed of right- and left-handed circularly polarized modes, where the electric field of light rotates in space clockwise and counterclockwise. The cholesteric structure gives rise to destructive interference of forward-propagating light and constructive interference of backward-propagating light of one handedness, resulting in essentially total reflection of one mode.
[0084] In addition, the periodicity of cholesteric structure provides a material that behaves like a perfect mirror in a selected range of wavelengths—the photonic bandgap. The location and the width of the bandgap can be determined by the refractive indices of the nematic host and the pitch of the cholesteric structure. The contrast can be determined by the film or layer thickness. Furthermore, an applied field can modify the underlying liquid crystal structure, thereby providing a material in which the bandgap location and bandwidth can be tuned. Such optical and physical properties can depend on the stability of the liquid crystalline material.
[0085] Accordingly, also described herein are methodologies for mitigating crystallization or phase segregation instabilities within such liquid crystalline materials. Illustrative methodologies include using a robust mixing protocol to provide uniform mixtures and formulations; enhancing solubility of a single dopant by chemical modification or derivatization (e.g., including aryl groups and/or longer alkyl groups); and developing multicomponent formulations including a host and two or more dopants. These methodologies can be used alone in combination. In one non-limiting instance, the methodologies provide a ternary formulation having a first dopant, a second dopant that is different than the first dopant, and a host.
[0086] Additional details follow.
[0087] Dopants
[0088] The present disclosure relates to the use of one or more chiral dopants. In particular embodiments, the dopant is derived from a biomolecule (e.g., a molecule produced by biology, such as an organism). Without wishing to be limited by mechanism, biomolecules are generally enantiomerically pure chiral compounds. If chemistry with such biomolecules is controlled to retain stereochemistry, then the resultant dopants can also be of high optical purity. Thus, biomolecules are excellent candidates as twist agents for application in cholesteric liquid crystal technology.
[0089] In some embodiments, the chiral dopant (or precursor thereof) is obtained from a bioreachable source that employs engineered microbes to overexpress desired biomolecules (e.g., through fermentation). In some embodiments, the dopant is derived from betulin or glycyrrhetinic acid (e.g., 18α glycyrrhetinic acid or 180 glycyrrhetinic acid, such as 3β,18β glycyrrhetinic acid). In certain embodiments, salts are avoided in the formulation when used with otherwise non-ionic hosts or liquid crystal media. As described herein, one, two, three, four, or more dopants can be included within a mixture or formulation.
[0090] Such biomolecules may be further modified or derivatized, e.g., as described herein. Such derivatization can include, e.g., modification of polar functional groups in the original biotarget materials to enhance physically compatibility (e.g., miscibility or solubility) with the host nematic materials (e.g., enhancing their interaction with the nematic components instead of themselves); enhancement of chemical stability, e.g., by including one or more aryl, alkaryl, or aralkyl groups; or enhancement of solubility, e.g., within a host, such as by including one or more extended alkyl moieties.
[0091] Chemical modification can result in ethers or esters having small or large moieties of a saturated aliphatic, unsaturated aliphatic, saturated alicyclic, unsaturated alicyclic, aromatic, or a combination thereof. Likewise, hydroxyl groups or keto groups can be converted into amines or imines by ways of substitution reactions or conjugation reactions followed by reduction. Acids can be converted into amides.
[0092] Further modifications include oxidation or reduction reactions. For example, a primary alcohol can be converted into an aldehyde or carboxylic acid group, or a secondary alcohol can be converted into a keto group. As for reduction, a carboxy group can be converted into a C—OH group or ether group; a carbon-carbon double bond can be reduced to a single bond.
[0093] In one aspect, a chiral dopant (e.g., a first dopant) can include a structure having formula (I), (IA), (IB), or (III):
##STR00009##
or a salt thereof, wherein each of R.sup.1, R.sup.2, and R.sup.6 is, independently, H, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted aralkyl, optionally substituted aryl, optionally substituted alkaryl, optionally substituted alkanoyl, optionally substituted aryloyl, or optionally substituted heterocyclyloyl; R.sup.5 is H, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted aralkyl, optionally substituted aryl, or optionally substituted alkaryl; and letter “a” represents a pi-bond, in which the pi-bond “a” may be present or absent. In particular embodiments of formulas (I), (IA), or (IB), R.sup.1 and R.sup.2 are the same. In other embodiments, R.sup.1 and R.sup.2 are different. In some embodiments of formula (III), R.sup.5 and R.sup.6 are the same. In other embodiments, R.sup.5 and R.sup.6 are different. In yet other embodiments, at least one R.sup.1, R.sup.2, R.sup.5, and R.sup.6 is not H. In some embodiments, each of R.sup.1, R.sup.2, R.sup.5, and R.sup.6 is not H.
[0094] As can be seen, formula (III) includes the hydrogen at C18 that is in a β-conformation, thereby providing a 18β-glycyrrhetinic acid derivative. In other embodiments, formula (III) can include the hydrogen at C18 that is in an α-conformation, thereby providing a 18α-glycyrrhetinic acid derivative.
[0095] A formulation of chiral dopants can include a first dopant (e.g., including a structure having formula (I), (IA), (IB), or (III)) in combination with a second dopant including a structure having the formula (II), (IIA), or (IIB):
##STR00010##
or a salt thereof, wherein each of R.sup.3 and R.sup.4 is, independently, H, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted aralkyl, optionally substituted aryl, optionally substituted alkaryl, optionally substituted alkanoyl, optionally substituted aryloyl, or optionally substituted heterocyclyloyl; and letter “a” represents a pi-bond, in which the pi-bond “a” may be present or absent. In some embodiments of formula (II), R.sup.3 and R.sup.4 are the same. In other embodiments, R.sup.3 and R.sup.4 are different. In yet other embodiments, at least one R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, and R.sup.6 is not H. In some embodiments, each of R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, and R.sup.6 is not H.
[0096] In particular embodiments, the first and second chiral dopants are different. For example and without limitation, R.sup.1 can be different from R.sup.3; R.sup.2 can be different from R.sup.4; or both of R.sup.1 and R.sup.2 can be different from R.sup.3 and R.sup.4. In other embodiments, R.sup.1 and R.sup.2 are the same; R.sup.3 and R.sup.4 are the same; but R.sup.1 and R.sup.3 are different. In yet other embodiments, each of R.sup.1, R.sup.2, R.sup.3, and R.sup.4 can be the same but the pi-bond “a” is present in one of formula (I) and (II) and absent in the other formula.
[0097] In some embodiments, the first and second chiral dopants are present in any useful ratio. A representative ratio includes a 1:1 ratio of the first chiral dopant to the second chiral dopant. Yet other illustrative ratios of the first and second chiral dopants include from about 90:10 (w/w) to about 10:90 (w/w) ratio, as well as ratios therebetween (e.g., 90:10 to 20:80, 90:10 to 30:70, 90:10 to 40:60, 90:10 to 50:50, 90:10 to 60:40, 90:10 to 70:30, 90:10 to 80:20, 80:20 to 10:90, 80:20 to 20:80, 80:20 to 30:70, 80:20 to 40:60, 80:20 to 50:50, 80:20 to 60:40, 80:20 to 70:30, 70:30 to 10:90, 70:30 to 20:80, 70:30 to 30:70, 70:30 to 40:60, 70:30 to 50:50, 70:30 to 60:40, 60:40 to 10:90, 60:40 to 20:80, 60:40 to 30:70, 60:40 to 40:60, 60:40 to 50:50, 50:50 to 10:90, 50:50 to 20:80, 50:50 to 30:70, 50:50 to 40:60, 40:60 to 10:90, 40:60 to 20:80, 40:60 to 30:70, 30:70 to 10:90, 30:70 to 20:80, or 20:80 to 10:90). In particular embodiments, the ratio of two or more chiral dopants are determined by compensating for the temperature dependence of the cholesteric pitch and thus the selective reflection wavelength, for example.
[0098] In particular embodiments, R.sup.1, R.sup.2, R.sup.3, R.sup.4, and/or R.sup.6 includes one of optionally substituted alkyl, aryl, alkaryl, or aralkyl groups that is attached to the parent molecular group through a carbonyl group. In some embodiments, R.sup.1 is —C(O)R.sup.1a or —C(O)—Ar—R.sup.1a, in which R.sup.1a is H, optionally substituted alkyl, optionally substituted haloalkyl, optionally substituted alkenyl, optionally substituted aralkyl, optionally substituted aryl, or optionally substituted alkaryl; and in which Ar is optionally substituted arylene. In other embodiments, R.sup.2 is —C(O)R.sup.2a or —C(O)—Ar—R.sup.2a; R.sup.3 is —C(O)R.sup.3a or —C(O)—Ar—R.sup.3a; R.sup.4 is —C(O)R.sup.4a or —C(O)—Ar—R.sup.4a; and R.sup.6 is —C(O)R.sup.6a or —C(O)—Ar—R.sup.6a; and in which each of R.sup.2a, R.sup.3a, R.sup.4a, and R.sup.6a is H, optionally substituted alkyl, optionally substituted haloalkyl, optionally substituted alkenyl, optionally substituted aralkyl, optionally substituted aryl, or optionally substituted alkaryl; and in which Ar is optionally substituted arylene.
[0099] In any of formulas (I), (IA), (IB), (II), (IIA), (IIB), and (III), any of R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, or R.sup.6 can be selected independently for each occasion from the group consisting of hydrogen, an aliphatic moiety, an aryl moiety, an aryl alkylene (or aralkyl) moiety, an alkyl arylene (or alkaryl) moiety, an alkanoyl moiety, an arylalkanoyl (or aralkanoyl) moiety, and any halogenated derivative of the foregoing moieties.
[0100] In any of formulas (I), (IA), (IB), (II), (IIA), (IIB), and (III), any of R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, or R.sup.6 can be selected independently for each occasion from the group consisting of hydrogen, a methyl, an ethyl, a propyl, a butyl, a pentyl, a hexyl, a heptyl, an octyl, a nonyl, a decyl, a phenyl, a benzyl, a p-tolyl, a p-halophenyl, a p-biphenyl, a p-(4-halophenyl)phenylene, a p-(4-cyanophenyl) phenylene, an o-biphenyl, a 3,5-dimethoxyphenyl, an acetyl, a propionyl, a butanoyl, a pentanoyl, a hexanoyl, a heptanoyl, an octanoyl, a nonanoyl, a decanoyl, an undecanoyl, a dodecanoyl, a 1-naphthyl, and a 2-naphthyl.
[0101] Further non-limiting dopants are provided in Table 1.
TABLE-US-00001 TABLE 1 Non-limiting dopants Melting Compound point/phase No. Structure Transition [° C.] PN02063 CD13
[0102] The dopants herein can be prepared by processes analogous to those established in the art, for example, by the reaction sequences shown in Scheme 1 and Scheme 2.
##STR00020##
[0103] As seen in Scheme 1, a betulin compound (1) can be provided. In non-limiting instances, betulin is provided from a biological resource as a highly optically pure compound. Betulin can be provided in any useful stereoisomer.
[0104] Compounds 2a, 2b can be provided under standard etherification or esterification conditions by treating compound 1 with a compound (e.g. a derivatizing agent) of formula R.sup.1-L or R.sup.1a—C(O)-L, in which R.sup.1 and R.sup.1a can be any described herein and L is a leaving group, such as chloro, bromo, iodo, sulfonate (e.g., mesylate, tosylate, or triflate), or carboxylate (e.g., —OC(O)—R.sup.1a, in which R.sup.1a is any described herein). Based on experimental conditions, compounds 2a and/or 2b can be formed in this reaction. Whereas both hydroxyl moieties at C.sub.3 and C.sub.28 are modified in compound 2a, only the hydroxyl moiety at C.sub.28 is modified in compound 2b. In some instances, the hydroxyl group at C.sub.3 can be further modified by treating compound 2b with a compound (e.g. a derivatizing agent) of formula R.sup.2-L or R.sup.2a—C(O)-L, thereby providing compound 3. R.sup.2 and R.sup.2a can be any described herein; and L is a leaving group, such as chloro, bromo, iodo, sulfonate (e.g., mesylate, tosylate, or triflate), or carboxylate (e.g., —OC(O)—R.sup.1a or —OC(O)—R.sup.2a, in which R.sup.1a and R.sup.2a are any described herein).
[0105] Conditions to provide compounds 2a, 2b may include heating compound 1 and R.sup.1-L with or without a solvent, preferably with a suitable solvent such as THF, optionally in the presence of a suitable base, such as potassium carbonate, sodium carbonate, potassium hydride, or sodium hydride. Other conditions to provide compounds 2a, 2b may include heating compound 1 and R.sup.1a—C(O)-L with or without a solvent, preferably with a suitable solvent such as DCM, optionally in the presence of a suitable base, such as pyridine or DMAP.
[0106] Similarly, these conditions can be applied to provide compound 3, which may include heating compound 2b and R.sup.2-L with or without a solvent (e.g., THF) and optionally in the presence of a suitable base (e.g., any herein). Other conditions to provide compound 3 may include heating a compound of formula 2b and R.sup.2a—C(O)-L with or without a solvent (e.g., any herein) and optionally in the presence of a suitable base (e.g., any herein).
[0107] Betulin (1) can be further treated prior to derivatization. For instance, betulin (1) can be treated under standard reduction conditions to provide, e.g., dihydrobetulin (4) with a single bond between C20 and C29. Illustrative reduction conditions can include use of hydrogen in the presence of nickel, platinum, or palladium. In another instance, betulin (1) can be treated under standard oxidation conditions to provide, e.g., betulone having a carbonyl at C3. Illustrative oxidation conditions can include use of pyridinium chlorochromate or Jones reagent. Such compounds can then be further derivatized (e.g., similar to conditions provided above with respect to compounds 2a, 2b).
[0108] Compound 5a and/or 5b can be provided under standard etherification or esterification conditions by treating compound 4 with a compound (e.g. a derivatizing agent) of formula R.sup.1-L or R.sup.1a—C(O)-L, as described herein. Reaction conditions may include heating compound 4 with R.sup.1-L or R.sup.1a—C(O)-L with or without a solvent (e.g., any herein), optionally in the presence of a suitable base (e.g., any herein). Compound 5b, if present, can be heated in the presence of R.sup.2-L or R.sup.2a—C(O)-L (e.g. a derivatizing agent), either with or without a solvent (e.g., any herein), and optionally in the presence of a suitable base (e.g., any herein) to provide compound 6.
##STR00021##
[0109] As seen in Scheme 2, an 18β-glycyrrhetinic acid compound (10) can be provided. In non-limiting instances, glycyrrhetinic acid is provided from a biological resource as a highly optically pure compound. Glycyrrhetinic acid can be provided in any useful stereoisomer, such as 18α-glycyrrhetinic acid and 18β-glycyrrhetinic acid in which the hydrogen at C18 is in the a or R conformation, respectively. In particular embodiments, glycyrrhetinic acid is 18β-glycyrrhetinic acid.
[0110] Compound 11 can be provided under standard esterification conditions by treating compound 10 with a compound (e.g. a derivatizing agent) of formula R.sup.5-L or R.sup.5—OH, in which R.sup.5 can be any described herein and L is a leaving group, such as chloro, bromo, iodo, sulfonate (e.g., mesylate, tosylate, or triflate), or carboxylate). Conditions to provide compound 11 can include optional use of a solvent (e.g., DMF) in the presence of a suitable agent (e.g., a base, such as potassium carbonate, sodium carbonate, potassium hydride, or sodium hydride; a coupling reagent, such as N,N′-dicyclohexylcarbodiimide; or an acid, such as sulfuric acid).
[0111] Compound 12 can be provided under standard etherification or esterification conditions by treating compound 11 with a compound (e.g. a derivatizing agent) of formula R.sup.6-L or R.sup.6a—C(O)-L, in which R.sup.6 and R.sup.6a can be any described herein and L is a leaving group, such as chloro, bromo, iodo, sulfonate (e.g., mesylate, tosylate, or triflate), or carboxylate (e.g., —OC(O)—R.sup.6a, as described herein). Conditions to provide compound 12 can include use of a solvent (e.g., THF or DCM), and optionally in the presence of a suitable base (e.g., potassium carbonate, sodium carbonate, potassium hydride, sodium hydride, pyridine, DMAP, etc.).
[0112] Glycyrrhetinic acid (10) can be further treated prior to derivatization. For instance, glycyrrhetinic acid (10) can be treated under standard oxidation conditions to provide, e.g., compound 13 having a carbonyl at C3. Illustrative oxidation conditions can include use of pyridinium chlorochromate or Jones reagent. Compound 13 can be further derivatized under standard esterification conditions to provide compound 14 by treating with a compound of formula R.sup.5-L or R.sup.5—OH, in which R.sup.5 can be any described herein and L can be any leaving group described herein. Reaction conditions to provide compound 14 can include optional use of a solvent (e.g., DMF) in the presence of a suitable agent (e.g., a base, such as potassium carbonate, sodium carbonate, potassium hydride, or sodium hydride; a coupling reagent, such as N,N′-dicyclohexylcarbodiimide; or an acid, such as sulfuric acid).
[0113] In some cases, the chemistries outlined above may have to be modified, for instance, by the use of protective groups to prevent side reactions due to reactive groups, e.g., attached as substituents. Further, desired compound salts and solvates may be formed, e.g., by treating with an acid or an appropriate solvent; and by isolating with filtration, extraction, additional of an antisolvent, drying, azeotroping, or any other suitable method. Additional modifications can include purification (e.g., by separation, recrystallization, or other suitable method) and preparation of an optical isomer (e.g., by reaction of the appropriate optically active starting materials under reaction conditions which will not cause racemization; or by separation of a racemic mixture using standard techniques, such as fractional crystallization or chiral HPLC).
[0114] Generally, the dopant (or twist agent) is a chiral molecule (often a pure enantiomer or diastereomer), which can be added to the achiral nematic to provide an increase in twist in the average molecular orientation of the bulk material. The amount of twist can be in proportion to the concentration, and the dopant can be employed at any useful concentration. However, in some instances, the proportion of dopant that can be added is limited by solubility or loss or cholesteric temperature range of the formulation.
[0115] The dopant can have any useful characteristic or property (e.g., any described herein). For instance, the helical twisting power (HTP) indicates a dopant's ability to induce twist, which is a property for light control. In some embodiments, the dopant has an HTP from about 1 μm.sup.−1 to about 100 μm.sup.−1 (e.g., from 1 μm.sup.−1 to 10 μm.sup.−1, 1 μm.sup.−1 to 20 μm.sup.−1, 1 μm.sup.−1 to 30 μm.sup.−1, 1 μm.sup.−1 to 40 μm.sup.−1, 1 μm.sup.−1 to 50 μm.sup.−1, 1 μm.sup.−1 to 60 μm.sup.−1, 1 μm.sup.−1 to 70 μm.sup.−1, 1 μm.sup.−1 to 80 μm.sup.−1, 1 μm.sup.−1 to 90 μm.sup.−1, 5 μm.sup.−1 to 10 μm.sup.−1, 5 μm.sup.−1 to 20 μm.sup.−1, 5 μm.sup.−1 to 30 μm.sup.−1, 5 μm.sup.−1 to 40 μm.sup.−1, 5 μm.sup.−1 to 50 μm.sup.−1, 5 μm.sup.−1 to 60 μm.sup.−1, 5 μm.sup.−1 to 70 μm.sup.−1, 5 μm.sup.−1 to 80 μm.sup.−1, 5 μm.sup.−1 to 90 μm.sup.−1, 5 μm.sup.−1 to 100 μm.sup.−1, 10 μm.sup.−1 to 20 μm.sup.−1, 10 μm.sup.−1 to 30 μm.sup.−1, 10 μm.sup.−1 to 40 μm.sup.−1, 10 μm.sup.−1 to 50 μm.sup.−1, 10 μm.sup.−1 to 60 μm.sup.−1, 10 μm.sup.−1 to 70 μm.sup.−1, 10 μm.sup.−1 to 80 μm.sup.−1, 10 μm.sup.−1 to 90 μm.sup.−1, 10 μm.sup.−1 to 100 μm.sup.−1, 20 μm.sup.−1 to 30 μm.sup.1, 20 m.sup.−1 to 40 μm.sup.−1, 20 μm.sup.−1 to 50 μm.sup.−1, 20 μm.sup.−1 to 60 μm.sup.−1, 20 μm.sup.−1 to 70 μm.sup.−1, 20 μm.sup.−1 to 80 μm.sup.−1, 20 μm.sup.−1 to 90 μm.sup.−1, 20 μm.sup.−1 to 100 μm.sup.−1, 25 μm.sup.−1 to 30 μm.sup.−1, 25 μm.sup.−1 to 35 μm.sup.−1, 25 μm.sup.−1 to 40 μm.sup.−1, 25 μm.sup.−1 to 50 μm.sup.−1, 25 μm.sup.−1 to 60 μm.sup.−1, 25 μm.sup.−1 to 70 μm.sup.−1, 25 μm.sup.−1 to 80 μm.sup.−1, 25 μm.sup.−1 to 90 μm.sup.−1, 25 μm.sup.−1 to 100 μm.sup.−1, 30 μm.sup.−1 to 35 μm.sup.−1, 30 μm.sup.−1 to 40 μm.sup.−1, 30 μm.sup.−1 to 50 μm.sup.−1, 30 μm.sup.−1 to 60 μm.sup.−1, 30 μm.sup.−1 to 70 μm.sup.−1, 30 μm.sup.−1 to 80 μm.sup.−1, 30 μm.sup.−1 to 90 μm.sup.−1, 30 μm.sup.−1 to 100 μm.sup.−1, 40 μm.sup.−1 to 50 μm.sup.−1, 40 μm.sup.−1 to 60 μm.sup.−1, 40 μm.sup.−1 to 70 μm.sup.−1, 40 μm.sup.−1 to 80 μm.sup.−1, 40 μm.sup.−1 to 90 μm.sup.−1, 40 μm.sup.−1 to 100 μm.sup.−1, 50 μm.sup.−1 to 60 μm.sup.−1, 50 μm.sup.−1 to 70 μm.sup.−1, 50 μm.sup.−1 to 80 μm.sup.−1, 50 μm.sup.−1 to 90 μm.sup.−1, 50 μm.sup.−1 to 100 μm.sup.−1, 60 μm.sup.−1 to 70 μm.sup.−1, 60 μm.sup.−1 to 80 μm.sup.−1, 60 μm.sup.−1 to 90 μm.sup.−1, 60 μm.sup.−1 to 100 μm.sup.−1, 70 μm.sup.−1 to 80 μm.sup.−1, 70 μm.sup.−1 to 90 μm.sup.−1, 70 μm.sup.−1 to 100 μm.sup.−1, 80 μm.sup.−1 to 90 μm.sup.−1, 80 μm.sup.−1 to 100 μm.sup.−1, or 90 μm.sup.−1 to 100 μm.sup.−1).
[0116] In another instance, the dopant can be characterized by a high solubility value that provide a stable formulation, in which exemplary values include from about 0.1 wt. % to about 60 wt. % of the dopant(s) in a formulation or a material (e.g., 0.1 wt. % to 5 wt. %, 0.1 wt. % to 10 wt. %, 0.1 wt. % to 15 wt. %, 0.1 wt. % to 20 wt. %, 0.1 wt. % to 25 wt. %, 0.1 wt. % to 30 wt. %, 0.1 wt. % to 35 wt. %, 0.1 wt. % to 40 wt. %, 0.1 wt. % to 45 wt. %, 0.1 wt. % to 50 wt. %, 0.1 wt. % to 55 wt. %, 0.5 wt. % to 5 wt. %, 0.5 wt. % to 10 wt. %, 0.5 wt. % to 15 wt. %, 0.5 wt. % to 20 wt. %, 0.5 wt. % to 30 wt. %, 0.5 wt. % to 40 wt. %, 0.5 wt. % to 50 wt. %, 0.5 wt. % to 60 wt. %, 1 wt. % to 5 wt. %, 1 wt. % to 10 wt. %, 1 wt. % to 15 wt. %, 1 wt. % to 20 wt. %, 1 wt. % to 30 wt. %, 1 wt. % to 40 wt. %, 1 wt. % to 50 wt. %, 1 wt. % to 60 wt. %, 3 wt. % to 5 wt. %, 3 wt. % to 10 wt. %, 3 wt. % to 15 wt. %, 3 wt. % to 20 wt. %, 3 wt. % to 30 wt. %, 3 wt. % to 40 wt. %, 3 wt. % to 50 wt. %, 3 wt. % to 60 wt. %, 5 wt. % to 10 wt. %, 5 wt. % to 15 wt. %, 5 wt. % to 20 wt. %, 5 wt. % to 30 wt. %, 5 wt. % to 40 wt. %, 5 wt. % to 50 wt. %, 5 wt. % to 60 wt. %, 8 wt. % to 10 wt. %, 8 wt. % to 15 wt. %, 8 wt. % to 20 wt. %, 8 wt. % to 30 wt. %, 8 wt. % to 40 wt. %, 8 wt. % to 50 wt. %, 8 wt. % to 60 wt. %, 10 wt. % to 15 wt. %, 10 wt. % to 20 wt. %, 10 wt. % to 30 wt. %, 10 wt. % to 40 wt. %, 10 wt. % to 50 wt. %, 10 wt. % to 60 wt. %, 12 wt. % to 15 wt. %, 12 wt. % to 20 wt. %, 12 wt. % to 30 wt. %, 12 wt. % to 40 wt. %, 12 wt. % to 50 wt. %, 12 wt. % to 60 wt. %, 15 wt. % to 20 wt. %, 15 wt. % to 30 wt. %, 15 wt. % to 40 wt. %, 15 wt. % to 50 wt. %, 15 wt. % to 60 wt. %, 20 wt. % to 30 wt. %, 20 wt. % to 40 wt. %, 20 wt. % to 50 wt. %, 20 wt. % to 60 wt. %, 30 wt. % to 40 wt. %, 30 wt. % to 50 wt. %, 30 wt. % to 60 wt. %, 40 wt. % to 50 wt. %, 40 wt. % to 60 wt. %, or 50 wt. % to 60 wt. %, based on the weight of the formulation or the material).
[0117] In yet another instance, the dopant or combination of dopants is characterized by an HTP from about 1 μm.sup.−1 to about 100 μm.sup.−1 and a solubility from about 5 wt. % to about 60 wt. % (e.g., an HTP of about 20 μm.sup.−1 to about 40 μm.sup.−1 with a solubility of about 10 wt. % to about 30 wt. %).
[0118] Formulations and Liquid Crystalline Materials
[0119] The present disclosure encompasses a formulation having at least one host and at least one dopant. In particular embodiments, the formulation includes a plurality of dopants. The formulation can provide any useful material, such as a chiral nematic material, a cholesteric liquid crystalline material, among others. As used herein, the terms “formulation” and “liquid crystalline material” can be used interchangeably.
[0120] The simplest form of a liquid crystalline material is the nematic phase. Organic molecules of rod-like shape are oriented on average along one direction, called the director n (see
[0121] Most of the physical properties of a liquid crystalline material depend on the direction relative to the average orientation of the molecules. The dielectric constant for an electric field parallel to the average orientation is ε.sub.1, and the dielectric constant for an electric field perpendicular to the average orientation is ε.sub.2. Some liquid crystals have ε.sub.1>ε.sub.2, and others have ε.sub.1<ε.sub.2. The former property, ε.sub.1, is called the positive dielectric anisotropy; and the latter, ε.sub.2, is called negative dielectric anisotropy. Under electric fields, the larger the difference between ε.sub.1 and ε.sub.2, the more easily the orientation of the liquid crystal can be controlled by an electric field. Liquid crystals with positive dielectric anisotropy are oriented parallel to the electric field, while the negative ones are perpendicularly oriented. Since the magnitude of the dielectric constants determine the responsiveness and the mode of response, their control is a desirable target of materials design for liquid crystals.
[0122] Cholesteric liquid crystals or chiral nematic liquid crystals can possess a one-dimensional periodic structure based on the natural helical twisting power of these materials (see
[0123] The formulation can exhibit strong helical twist by, e.g., using a higher amount of dopant(s) and/or by using one or more dopants having a higher helical twisting power (HTP), thus a shorter pitch length. However, using chiral dopants in too high amounts can negatively affect the properties of the liquid crystalline host mixture, for example, the dielectric anisotropy, the viscosity, and the driving voltage or the switching times among others. Thus, the amount of dopant can be optimized to provide a desired combination of properties. In non-limiting liquid crystalline formulations that are used in selectively reflecting cholesteric displays, the pitch can be selected such that the maximum of the wavelength reflected by the cholesteric helix is in the range of required for the desired application.
[0124] Illustrative formulations include a binary formulation including one dopant and a host; a ternary formulation including two different dopants and a host; and a quaternary formulation including three different dopants and a host. Such formulations can have reflection bands in the visible range (e.g., from about 380 nm to about 780 nm) or any other range (e.g., in the ultraviolet region, such as from about 200 nm to about 380 nm; in the infrared region, such as from about 780 nm to about 1 mm; or in the near infrared region, such as about 740 nm to about 1000 nm).
[0125] Formulations can be selected to reflect various wavelengths of incident electromagnetic radiation. In one instance, the formulation can include an enantiomer of a particular dopant. As the chirality of the dopant influences the helical rotation of the host, a corresponding formulation can include an opposite enantiomer of that particular dopants. In yet other embodiments, enantiomeric pairs of dopants can be prepared, and formulations including one of the pair can be used to prepare separate light modulating layers.
[0126] Formulations and materials can possess any useful property that can be measured in any useful manner. For instance, stability can be determined by assessing the reflection band of the material in an absorption spectrum, conducting phase boundary and phase transition studies of the material as a function of dopant concentration, and/or measuring light transmittance of the material as a function of temperature. Evidences of instability include observing changes in the reflection band over time (e.g., red-shifting of the band, such as by about 100 nm), characterizing nematic-isotropic phase transitions, and/or determining the presence of crystallization or coexistence of one or more phases within the material. In addition to stability against phase segregation, formulations can be assessed for stability after UVA irradiation, stability after thermal cycling, lifetime stability, sample pitch, dopant HTP, and host NI transition temperature.
[0127] Any useful host can be employed within a formulation. The host can include a single compound or a combination of different compounds. Such compounds can include one or more mesogens, cholesteric compounds, nematic compounds, as well as combinations thereof. In particular embodiments, the host can include one or more achiral cholesteric nematic mesogens. In another embodiment, the host can include one or more nematic or nematogenic compounds.
[0128] In some embodiments, the formulation or liquid crystalline material includes 3 to 25 components, such as 3 to 15 compounds, or 4 to 10 compounds, of which at least two is a chiral dopant originating from the herein discussed bioreachables. The other compounds can be low molecular weight liquid crystalline compounds selected from nematic or nematogenic substances.
[0129] Exemplary host compounds (e.g., nematic or nematogenic substances) can be selected from azoxybenzenes, benzylideneanilines, biphenyls, terphenyls, phenyl benzoates, cyclohexyl benzoates, phenyl esters of cyclohexanecarboxylic acid, cyclohexyl esters of cyclohexanecarboxylic acid, phenyl esters of cyclohexylbenzoic acid, cyclohexyl esters of cyclohexylbenzoic acid, phenyl esters of cyclohexylcyclohexanecarboxylic acid, cyclohexyl esters of cyclohexylcyclohexanecarboxylic acid, cyclohexylphenyl esters of benzoic acid, cyclohexylphenyl esters of cyclohexanecarboxylic acid, cyclohexylphenyl esters of cyclohexylcyclohexanecarboxylic acid, phenylcyclohexanes, cyclohexylbiphenyls, phenylcyclohexylcyclohexanes, cyclohexylcyclohexanes, cyclohexylcyclohexenes, cyclohexylcyclohexylcyclohexenes, 1,4-bis-cyclohexylbenzenes, 4,4′-bis-cyclohexylbiphenyls, phenylpyrimidines, cyclohexylpyrimidines, phenylpyridines, cyclohexylpyridines, phenylpyridazines, cyclohexylpyridazines, phenyldioxanes, cyclohexyldioxanes, phenyl-1,3-dithianes, cyclohexyl-1,3-dithianes, 1,2-diphenylethanes, 1,2-dicyclohexylethanes, 1-phenyl-2-cyclohexylethanes, 1-cyclohexyl-2-(4-phenylcyclohexyl) ethanes, 1-cyclohexyl-2-biphenylethanes, 1-phenyl-2-cyclohexylphenylethanes, halogenated stilbenes, benzyl phenyl ether, tolanes, substituted cinnamic acids, or any combination thereof. The 1,4-phenylene groups in these compounds may also be fluorinated.
[0130] Yet other host compounds include R′—[O].sub.h1-[A.sup.1].sub.h2-L.sup.1-[A.sup.2].sub.h3-L.sup.2-[O].sub.h4—R″ or R′—[O].sub.h1-[A.sup.1].sub.h2-L.sup.1-[A.sup.2].sub.h3-L.sup.2-R″ or R′—[O]-[A.sup.1]-L.sup.1-[A.sup.2]-L.sup.2-R″ or R′-[A.sup.1]-L.sup.1-[A.sup.2]-L.sup.2-R″, where each of A.sup.1 and A.sup.2 is, independently, -Phe-, -Cyc-, -Phe-Phe-, -Phe-Phe-Phe-, -Phe-Cyc-, -Cyc-Phe-, -Cyc-Cyc-, -Het-, —B-Phe-, and —B-Cyc-; Phe is unsubstituted or halo-substituted 1,4-phenylene, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl, or 1,2,3,4-tetrahydronaphthalene-2,6-diyl; Cyc is trans-1,4-cyclohexylene or 1,4-cyclohexenylene or bicyclo [2.2.2]octane; Het is pyrimidine-2,5-diyl, pyridine-2,5-diyl, 1,3-dioxane-2,5-diyl, or tetrahydropyran-2,5-diyl; B is 2-(trans-1,4-cyclohexyl)ethyl, pyrimidine-2,5-diyl, pyridine-2,5-diyl 1,3-dioxane-2,5-diyl, or tetrahydropyran-2,5-diyl; each of L.sup.1 and L.sup.2 is, independently, —CH═CY′—, —CH═CH—, —C≡C—, —N═N(O)—, —CH═N(O)—, —CY′═N—, —CH═N—, —CY′.sub.2—, —(CY′.sub.2).sub.2—, —CY′.sub.2O—, —OCY′.sub.2—, —COO—, —O—, —C(O)—, —OCO—, —CY′.sub.2—O—, —O—CY′.sub.2—, —CO—S—, —CY′.sub.2—S—, —COO-Phe-COO—, or a single bond; each Y′ is, independently, hydrogen, halo, or —CN; and each of R′ and R″ is, independently, alkyl (e.g., linear or branched C.sub.1-12 or C.sub.1-24 alkyl), alkenyl, alkoxy, alkenyloxy, alkanoyloxy, alkoxycarbonyl, alkoxycarbonyloxy, halo, —CF.sub.3, —OCF.sub.3, —NCS, —CN, —OR′″, —OC(O)R′″, —C(O)OR′″, —C(O)OH, or —OC(O)OR′″, in which R′″ is H, optionally substituted C.sub.1-10 alkyl, or optionally substituted C.sub.2-10 alkenyl; h1 is 0 or 1; h2 is 0, 1, 2, 3, 4, or 5; h3 is 0, 1, 2, 3, 4, or 5; and h4 is 0 or 1.
[0131] In some embodiments, the host can include one or more polymerizable compounds (e.g., a polymerizable mesogenic compound). Such polymerizable compounds can be configured to (co)polymerize with the dopant(s) in order to provide a polymer film. Accordingly, the polymerizable compound can have at least one polymerizable functional group. In one embodiment, the polymerizable functional group includes an epoxy group, a vinyl group, an allyl group, an acrylate, a methacrylate, an isoprene group, an alpha-amino carboxylate, or any combination thereof. In particular embodiments, the polymerizable compound provides a polymer network, which stabilizes the material, reduces scattering, and increases speed.
[0132] The host can have any useful property, such as beneficial viscosity, birefringence, electrical anisotropy, and magnetic anisotropy, among others. Any properties may be tailored to the desired usage by altering the chemical composition of the host (e.g., by including a mixture of mesogens or nematic compounds). Then, chiral dopant(s) can be incorporated to induce helical twisting so as to provide the desired chiral nematic pitch. For instance, as seen in
[0133] The liquid crystalline material can include any useful dopant(s) in any useful amount, e.g., of at least 0.001 wt. %, such as at least 0.002 wt. %, at least 0.005 wt. %, at least 0.01 wt. %, at least 0.02 wt. %, at least 0.05 wt. %, at least 0.1 wt. %, at least 0.2 wt. %, at least 0.5 wt. %, at least 1 wt. %, at least 1.2 wt. %, at least 1.5 wt. %, at least 2 wt. %, at least 2.5 wt. %, at least 3 wt. %, at least 3.5 wt. %, at least 4 wt. %, at least 4.5 wt. %, at least 5 wt. %, at least 6 wt. %, at least 7 wt. %, at least 8 wt. %, at least 9 wt. %, or at least 10 wt. %, based on the weight of the liquid crystalline material.
[0134] In another embodiment, the liquid crystalline material includes at least one chiral dopant present in an amount of not greater than 20 wt. %, such as not greater than 18 wt. %, not greater than 16 wt. %, not greater than 14 wt. %, not greater than 12 wt. %, not greater than 10 wt. %, or not greater than 8 wt. % based on the weight of the liquid crystalline material. Further, in one embodiment, the chiral dopant can be present in an amount ranging from 0.0015 wt. % to 17 wt. %, such as from 0.01 wt. % to 15 wt. %, from 0.05 wt. % to 13 wt. %, or from 0.1 wt. % to 11 wt. % based on the weight of the liquid crystalline material.
[0135] Multicomponent formulations (e.g., having two or more dopants with a host) can be formulated in any useful manner. In particular embodiments, the method includes initially forming a mixture having two or more dopants. Then, the stability of that mixture can be tested prior to adding a host. Stability can be tested in any useful manner, e.g., as described herein, such as by comparing the reflection band of a transmission or absorption spectrum over time.
[0136] Mixing of formulations can include providing a uniform combination of host and chiral dopant(s). In some embodiments, such mixing reduces the extent of metastable crystals that can be formed due to inhomogeneous concentration or temperature fields. In non-limiting embodiments, the protocol includes providing a host and dopant(s) within a vessel; mixing and heating the combination above a first temperature T.sub.1 (e.g., in which T.sub.1 is above the isotropic phase, such as from about 80° C. to about 120° C.) for a first time duration t.sub.1 (e.g., in which t.sub.1 is from about 30 minutes to 1.5 hours); placing in a centrifuge (e.g., at a first rate from about 3000 rpm to 7000 rpm) for a second time duration t.sub.2 (e.g., in which t.sub.2 is from about 5 minutes to 1 hour); reheating the combination above a second temperature T.sub.2 (e.g., in which T.sub.2 is above the isotropic phase, such as from about 80° C. to about 120° C.) for a third time duration t.sub.3 (e.g., in which t.sub.3 is from about 5 minutes to 1 hour); optionally repeating the placing and reheating steps in cycles for any useful n number of times (e.g., n is 1, 2, 3, 4, 5, or more); and optionally repeating the placing step one last time.
[0137] Applications
[0138] The mixtures, formulations, and materials herein can find use in a variety of optical or photonic applications. Non-limiting embodiments of applications include filters (e.g., color filters), polarizers, other optical elements, devices (e.g., an agile optical filter device), displays, smart windows, sensor protection materials, photoactive materials, cosmetics, paints, coatings, chemical sensors, laser cavities, and other photonic devices. Other non-limiting applications include electronic writers or tablets, electronic skins, inks, among others.
[0139] In one instance, the present disclosure encompasses use of dopants for an optical element (e.g., a filter). Generally, optical filters are of two types: (i) absorptive filters, which absorb the unwanted radiation, and (ii) interference filters, which reflect rather than absorb. Interference filters are preferable in many applications, since absorbing the radiation can lead to damage and failure. Interference filters are typically layered structures, reflecting light from each interface in such a way that the propagating waves interfere destructively and cancel, while the reflected waves interfere constructively, and essentially all incident light is reflected, without damage to the filter. Such optical elements can include absorption or reflection of radiation (e.g., in the visible range), as well as protection of underlying components from such radiation. In some instances, the optical element can include tunable (or agile) filters, in which the amount and type of radiation to be adsorbed or reflected can be actively switched (e.g., on or off) or tuned (e.g., to different wavelengths of radiation). In other instances, the optical element is a polarizer (e.g., a cholesteric broadband polarizer), a liquid crystalline retardation film, an active optical element, a passive optical element, a color filter, a reflective film, among others.
[0140] A layer or a component of an optical element can include the mixtures, formulations, or materials described herein. In a particular embodiment, an optical element includes a pair of enantiomers of a dopant, in which a first layer includes one enantiomer and the second layer includes the other enantiomer.
[0141] An agile optical filter may include one or more of the dopants herein. In particular embodiments, the agile optical filter device has the ability to change wavelengths. For instance, a change in temperature can change the location of the reflection banc, and applying a voltage can do the same. In addition, if the K3 elastic constant is reduced by the addition of one or more dimers, the voltage tunability expands dramatically due to formation of heliconical structure.
[0142] In other embodiments, the agile optical filter is characterized by a broad temperature cholesteric range (usually including ambient temperature), a higher response speed, a twist with minimal temperature dependence, and/or enhanced rejection efficiency. The agile optical filter device can include a cholesteric (twisted nematic) media. In one case, the medium is comprised of a molecule that is both mesogenic and intrinsically chiral. The individual molecules comprising the media can contain one (pure enantiomer) or more (pure diastereomer) sites. It is also possible to mix different chiral nematic mesogens to create a medium with improved properties (attention must be paid to the relationship between the chiral centers and the resulting twist sense for each component). If an enantiomer of a molecule is mixed with its mirror image, the twist will be reduced (a racemic mixture contains equal amounts of the two enantiomers and will behave as an achiral nematic). In another case, the medium is comprised of a molecule that is mesogenic (nematic), but the molecule is not intrinsically chiral. Here again, it is possible to mix different achiral nematic mesogens to create a medium (or host) with improved properties (but it will never be cholesteric). An achiral nematic host can be converted into a cholesteric media by the addition of a twist agent. Alternatively, a cholesteric liquid crystal can serve as a twist agent when mixed into an achiral nematic mesogen.
[0143] Further applications include smart windows, sensor protection, photoactive materials, optical filters, liquid crystal displays, for example STN, TN, AMD-TN, temperature compensation, guest-host or phase change displays, or polymer free or polymer stabilized cholesteric texture (PFCT, PSCT) displays. Such liquid crystal displays can include a chiral dopant in a liquid crystalline medium and a polymer film with a chiral liquid crystalline phase obtainable by (co)polymerizing a liquid crystalline material containing a chiral dopant and a polymerizable mesogenic compound.
[0144] The liquid crystal display can include a layer of liquid crystalline material. In some embodiments, the layer of a liquid crystalline material is characterized by a cholesteric pitch (P) and a thickness (d). In one embodiment, a ratio of d/P is at least 0.01, at least 0.02, at least 0.05, at least 0.1, or at least 0.15. In another embodiment, the layer includes a ratio of d/P that is not greater than 1, not greater than 0.8, not greater than 0.6, not greater than 0.4, not greater than 0.3, or not greater than 0.25. In yet another embodiment, the ratio of d/P can range from 0.01 to 0.9, such as from 0.02 to 0.7, from 0.03 to 0.5, or from 0.04 to 0.4.
EXAMPLES
Example 1: Scaled-Up Synthesis of Dibutanoyl Ester of Betulin (CD13)
[0145] ##STR00022##
[0146] In a 2000 ml round bottom flask with stir bar was placed betulin (1, 44.300 gm, 100.0 mmol), dry dichloromethane (DCM, 500 ml), butyric anhydride (63.200 gm, 400.0 mmol), pyridine (200 ml), and 4-dimethylaminopyridine (DMAP, 24.400 gm, 200.0 mmol). The mixture was protected under nitrogen atmosphere and warmed at 55° C. for six hours. After this time, the reaction was monitored by thin layer chromatography (TLC), which indicated the complete consumption of betulin to give single less polar product. Then, 200 ml of cold water was added dropwise with stirring, and the solution was made acidic by adding 10% HCl (200 ml). Organic layer was separated, and the aqueous layer was extracted with ethyl acetate (EtOAc, 3×250 ml). The organic fractions were combined, washed with brine, and dried over anhydrous MgSO.sub.4. Solvent was evaporated, and the liquid obtained was absorbed on 300 cc of silica gel with 500 ml of ethyl acetate. After concentration to dryness, the absorbed material was placed at the top of the silica gel column made up with EtOAc:Hexane 1:9 to elute (solvent:EtOAc:Hexane 1:9). Concentration of the fraction provided white solid, which was recrystallized from MeOH (yield=51.833 gm, 89%).
[0147] Melting Point: 102-104° C.
[0148] .sup.1H NMR (CDCl.sub.3, 400 MHz): δ=4.68 (d, 1H), 4.58-4.59 (m, 1H), 4.26 (dd, 1H), 3.85 (d, 1H), 3.16-3.20 (m, 1H), 2.41-2.49 (m, 1H), 2.31 (t, 2H), 1.91-2.05 (m, 1H), 1.50-1.87 (m, 16H), 1.34-1.45 (m, 5H), 1.15-1.33 (m, 8H), 1.05-1.15 (m, 1H), 1.03 (s, 3H), 0.93-0.99 (m, 8H), 0.85-0.89 (m, 5H), 0.82 (s, 3H), 0.76 (s, 3H), 0.76 (s, 3H), 0.67-0.69 (m, 1H).
[0149] .sup.13C NMR (CDCl.sub.3, 100 MHz): δ=13.7, 14.7, 16.0, 16.1, 16.6, 18.1, 18.5, 18.6, 19.1, 20.8, 23.7, 25.2, 27.0, 28.0, 29.6, 29.8, 34.1, 34.6, 36.4, 36.7, 37.1, 37.6, 37.8, 24 38.4, 40.9, 42.7, 46.4, 47.7, 48.8, 50.3, 55.4, 62.5, 80.6, 109.8, 150.2, 173.4, 174.2.
Example 2: Scaled-Up Synthesis of Di-p-Toluyl Ester of Betulin (CD29)
[0150] ##STR00023##
[0151] In a 2000 ml recovery flask with stir bar was placed betulin (1, 44.300 gm, 100.0 mmol), dry DCM (450 ml), p-toluoyl chloride (61.800 gm, 400.0 mmol), pyridine (250 ml), and 4-dimethylaminopyridine (19.874 gm, 162.6 mmol). The mixture was protected under nitrogen atmosphere and warmed at 55° C. for five hours. After this time, TLC indicated the complete consumption of the starting material and formation of two new less polar products. The mixture was left stirring at 55° C. overnight and monitored by TLC, which indicated the complete consumption the starting material to give single less polar product. Then, cold water (200 ml) and 10% HCl (200 ml) was added dropwise with stirring. The product was extracted with EtOAc (3×250 ml), washed with water, and dried over anhydrous MgSO.sub.4. Solvent was evaporated, and the liquid obtained was absorbed on 300 cc of silica gel with 500 ml of ethyl acetate. The absorbed material was placed at the top of the silica gel column made up with EtOAc:Hexane 1:9 to elute (solvent:EtOAc:Hexane 1:9). Concentration of the fractions provided a solid product, which was recrystallized from 1-PrOH (yield=57.682 gm, 85%)
[0152] Melting Point: 207-209° C.
[0153] .sup.1H NMR (CDCl.sub.3, 400 MHz): δ=7.91-7.95 (m, 4H), 7.22-7.25 (m, 4H), 4.68-4.73 (m, 2H), 4.61-4.62 (m, 1H), 4.51 (d, 1H), 4.07 (d, 1H), 2.49-2.57 (m, 1H), 2.39-2.43 (m, 6H), 1.72 (s, 3H), 1.57 (s, 6H), 1.06 (s, 3H), 1.02 (s, 3H), 0.99 (s, 3H), 0.91 (s, 3H).
[0154] .sup.13C NMR (CDCl.sub.3, 100 MHz): δ=14.1, 14.8, 16.1, 16.2, 16.8 (x2C), 18.2, 19.2, 20.9, 21.6, 21.7, 22.7, 23.8, 25.2, 27.2, 28.1, 29.7, 30.0, 34.1, 34.7, 37.1, 37.7, 38.2, 38.4, 40.9, 42.8, 46.7, 47.8, 48.9, 50.3, 55.5, 63.1, 81.3, 109.9, 127.8, 128.3, 129.0, 129.1, 129.5, 129.6 (x2C), 143.3, 143.5, 150.2, 166.4, 167.1.
Example 3: Synthesis of Di-p-Toluyl Ester of Dihydrobetulin (PN02082)
[0155] ##STR00024##
[0156] In a 100 ml recovery flask with stir bar was placed dihydrobetulin (4, 0.210 gm, 0.5 mmol), dry DCM (10 ml), p-toluoyl chloride (0.308 gm, 2.0 mmol), pyridine (5 ml), and 4-dimethylaminopyridine (0.122 gm, 1.0 mmol). The mixture was protected under nitrogen atmosphere and warmed at 55° C. overnight. After this time, TLC indicated the complete consumption of the starting material to give a single less polar product. Then, cold water (50 ml) and 10% HCl (5 ml) were added dropwise with stirring. The product was extracted with EtOAc (3×25 ml), washed with water, and dried over anhydrous MgSO.sub.4. Solvent was evaporated, and the liquid obtained was absorbed on 25 cc of silica gel with 50 ml of ethyl acetate. The absorbed material was placed at the top of the silica gel column made up with EtOAc:Hexane 1:9 to elute (solvent:EtOAc:Hexane 1:9). Concentration of fractions provided a solid product, which was recrystallized from 1-PrOH (yield=0.262 gm, 77%).
[0157] Melting point: 210.5° C.
[0158] .sup.1H NMR (400 MHz, CDCl.sub.3): δ=7.29-7.95 (m, 4H), 7.22-7.26 (m, 4H), 4.69-4.73 (m, 1H), 4.71 (dd, J.sub.1=5.1 Hz, J.sub.2=10.7 Hz, 1H), 4.51 (d, J=10.8 Hz, 1H), 4.04 (d, J=11.1 Hz, 1H), 2.41 (s, 6H), 1.09 (s, 3H), 1.00 (s, 6H), 0.92 (s, 6H), 0.86 (d, J=6.7 Hz, 3H), 0.79 (d, J=6.7 Hz, 3H).
[0159] .sup.13C NMR (CDCl.sub.3, 100 MHz): δ=167.07, 166.4, 143.5, 143.3, 129.6, 129.1, 129.0, 128.3, 127.8, 81.3, 63.1, 55.4, 50.0, 48.2, 46.9, 44.6, 43.0, 41.0, 38.4, 38.2, 37.2, 37.1, 34.9, 34.2, 30.1, 29.5, 28.1, 27.0, 26.9, 23.8, 23.0, 21.7, 20.8, 18.2, 16.8, 16.1, 16.1, 14.9, 14.7.
Example 4: Synthesis of di-4-butylbenzoic acid ester of betulin (CD46)
[0160] ##STR00025##
[0161] In a 100 ml recovery flask with stir bar was placed betulin (1, 0.443 gm, 1.0 mmol), dry DCM (10 ml), p-n-butylbenzoyl chloride (0.558 gm, 3.0 mmol), pyridine (10 ml), and 4-dimethylaminopyridine (0.366 gm, 3.0 mmol). The mixture was protected under nitrogen atmosphere and warmed at 55° C. for five hours. After this time, TLC indicated the formation of two new products. Additional pyridine (3.0 ml), DMAP (0.122 gm, 1.0 mmol), and p-n-butylbenzoyl chloride (0.392 gm, 2.0 mmol) were added, and the mixture was left stirring at 55° C. overnight. After this time, TLC indicated the complete consumption of the starting material to give single less polar product. Then, cold water (50 ml) and 10% HCl (5 ml) were added dropwise with stirring. The product was extracted with EtOAc (3×25 ml), washed with water, and dried over anhydrous MgSO.sub.4. Solvent was evaporated, and the liquid obtained was absorbed on 20 cc of silica gel with 50 ml of ethyl acetate. After concentration to dryness, the absorbed material was placed at the top of the silica gel column made up with EtOAc:Hexane 1:9 to elute (solvent:EtOAc:Hexane 1:9). Concentration of the fractions provided a solid product, which was recrystallized from 1-PrOH/H.sub.2O (yield=0.410 gm, 54%).
[0162] Melting Point: 164.8° C.
[0163] .sup.1H NMR (CDCl.sub.3, 400 MHz): δ=7.93-7.97 (m, 4H), 7.23-7.26 (m, 4H), 2.68-4.72 (m, 2H), 4.61-4.62 (m, 1H), 4.51 (d, J=10.8 Hz, 1H), 4.07 (d, J=11.0 Hz, 1H), 2.63-2.68 (m, 4H), 2.50-2.57 (m, 1H), 1.72 (s, 3H), 1.08 (s, 3H), 1.02 (s, 3H), 0.99 (s, 3H).
[0164] .sup.13C NMR (CDCl.sub.3, 100 MHz): δ=167.1, 166.4, 150.2, 148.5, 148.3, 129.6, 129.6, 128.5, 128.4, 128.4, 127.9, 109.9, 81.3, 63.1, 55.5, 50.3, 48.9, 47.8, 46.7, 42.8, 40.9, 16 38.4, 38.2, 37.7, 37.1, 35.7, 34.8, 34.1, 33.3, 30.0, 29.7, 29.7, 29.6, 28.1, 27.1, 25.2, 23.8, 22.3, 20.8, 19.2, 18.2, 16.8, 16.2, 16.1, 14.8, 13.9.
[0165] IR (cm.sup.−1): 2926, 2868, 1714, 1610, 1455, 1269, 1176, 1105, 971.
Example 5: Synthesis of di-4-heptylbenzoic acid ester of betulin (CD47)
[0166] ##STR00026##
[0167] In a 100 ml recovery flask with stir bar was placed betulin (1, 0.443 gm, 1.0 mmol), dry DCM (10 ml), p-n-heptylbenzoyl chloride (0.956 gm, 4.0 mmol), pyridine (10 ml), and 4-dimethylaminopyridine (0.366 gm, 3.0 mmol). The mixture was protected under nitrogen atmosphere and warmed at 55° C. for four hours. After this time, TLC indicated the formation of two new products. Additional pyridine (3.0 ml), DMAP (0.122 gm, 1.0 mmol) and p-n-heptylbenzoyl chloride (0.478 gm, 2.0 mmol) were added, and the mixture was left stirring at 55° C. overnight. After this time, TLC indicated the complete consumption of the starting material to give single less polar product. Then, cold water (50 ml) and 10% HCl (5 ml) were added dropwise with stirring. The product was extracted with EtOAc (3×25 ml), washed with water, and dried over anhydrous MgSO.sub.4. Solvent was evaporated, and the liquid obtained was absorbed on 20 cc of silica gel with 50 ml of ethyl acetate. After concentration to dryness, the absorbed material was placed at the top of the silica gel column made up with EtOAc:Hexane 1:9 to elute (solvent:EtOAc:Hexane 1:9). Concentration of the fractions provided a viscous liquid product.
[0168] The crude product was suspected to contain acid chloride impurities from .sup.1H NMR, and so it was attempted to selectively hydrolyze into carboxylic acid to remove from the mixture. The crude product was transferred into a 200 ml recovery flask with stir bar and dissolved in THF (20 ml). Aqueous sodium bicarbonate solution (20 ml, 20% w/v) was added, and the mixture with two layers was stirred for 48 hours at room temperature. After this time, TLC indicated no change in the mixture (acid chloride persisted in the mixture), and so the reaction was forced to stop by adding 100 ml water. The product was extracted with EtOAc (3×25 ml), dried over anhydrous MgSO.sub.4 and filtered through the sintered funnel. Solvent was removed, and the product was transferred into a 200 ml recovery flask with 1,4-dioxane (20 ml). Aqueous hydrazine solution (10% v/v, 5 ml) was added dropwise with stirring, and the mixture was stirred at room temperature for 25 minutes. After this time, only a single spot was observed on TLC indicating all the acid chloride disappeared from the mixture. Cold water (100 ml) was added dropwise, and the product was extracted with EtOAc (3×25 ml). Organic phase was dried over anhydrous MgSO.sub.4, filtered through sintered funnel, and concentrated under reduced pressure. The liquid residue was absorbed on silica gel (15 cc) with 50 ml EtOAc. After concentration to dryness, the absorbed material was placed at the top of the silica gel column made up with EtOAc:Hexane 1:9 to elute (solvent:EtOAc :Hexane 1:9). Concentration of the fractions provided a viscous liquid as a product which was shown to be pure by .sup.1H NMR (yield=0.733 gm, 53%).
[0169] .sup.1H NMR (CDCl.sub.3, 400 MHz): δ=7.93-7.97 (m, 4H), 7.22-7.26 (m, 4H), 4.61-4.70 (m, 2H), 4.51 (d, J=10.8 Hz, 1H), 4.31 (t, J=6.6 Hz, 1H), 4.07 (d, J=11.2 Hz, 1H), 2.63-2.68 (m, 4H), 2.49-2.56 (m, 1H), 1.56 (s, 3H), 1.08 (s, 3H), 1.02 (s, 3H), 0.99 (s, 3H).
[0170] .sup.13C NMR (CDCl.sub.3, 100 MHz): δ=167.1, 166.4, 150.2, 148.5, 148.3, 129.6, 129.6, 128.4, 128.3, 127.9, 109.9, 81.3, 64.6, 63.1, 55.5, 50.3, 48.9, 47.8, 46.7, 42.8, 41.0, 38.4, 37.7, 37.1, 36.0, 34.8, 34.2, 31.8, 31.2, 30.8, 30.3, 30.0, 29.7, 29.2, 29.1, 28.1, 27.1, 25.2, 23.8, 22.6, 20.9, 19.3, 19.2, 18.2, 16.8, 16.2, 16.1, 14.8, 14.1, 13.8.
[0171] IR (cm.sup.−1): 2924, 2854, 1713, 1456, 1269, 1175, 1105, 1018, 970.
Example 6: Potential Strategies to Mitigate Crystallization/Phase Segregation Instabilities
[0172] Three strategies can be adopted to eliminate phase separation instability, which include the following: [0173] Utilizing the mixing protocol in Example 7, below, to ensure uniform mixture of host and chiral dopant. This eliminated metastable crystals formed during past history due to homogeneous concentration or temperature fields. [0174] Increasing the solubility of chiral dopants by structural modifications. Three chiral dopants, CD46, CD47 and CD48, were synthesized with modified structure to enhance solubility. [0175] Formulating multicomponent mixtures. Typically, binary mixtures including a nematic host and one chiral dopant with a given concentration have been used in previous studies. However, crystallization can be avoided if two chiral dopants, with reduced concentrations, are used instead. The stability of ternary mixtures is discussed below.
[0176] In subsequent work, all three of the above strategies were implemented. The developed mixing protocol was used with success, and using the protocol appeared to eliminate unwanted long-lived metastable crystals. Various chiral dopants were synthesized and characterized; their properties are reported below. Multicomponent mixtures were formulated and studied; various stable ternary mixtures with reflection bands in the visible are reported below.
Example 7: Non-Limiting Mixing Protocol
[0177] One aspect of the phase behavior of liquid crystals is the existence of long-lived metastable states. These metastable states can persist despite changes in temperature or other experimental conditions, thus providing anomalous phase behavior (e.g., crystallization or phase segregation) that depends on the prior history of the material.
[0178] In order to minimize spurious history—dependent phenomena (e.g., such as crystallization due to concentration inhomogeneities), we have implemented a nematic—chiral dopant mixture preparation protocol. This protocol can enhance reliable formation and comparison of mixtures, as well as contributes to stability against phase separation.
[0179] An illustrative protocol is provided below: [0180] 1. host nematic and chiral dopant(s) are weighed and put into a vial [0181] 2. mixture with magnetic stirrer is heated above isotropic phase (e.g., about 90° C.) for a first time duration (e.g., about 60 minutes) [0182] 3. mixture is placed in centrifuge (e.g., 6000 rpm) for a second time duration (e.g., about 10 minutes) [0183] 4. mixture with magnetic stirrer is heated above isotropic phase for a third time duration (e.g., about 5 minutes) [0184] 5. steps 3 and 4 can be optionally repeated for any useful n number of times (e.g., n is 1, 2, 3, 4, 5, or more) [0185] 6. optionally, the mixture is placed in centrifuge (e.g., 6000 rpm) for a fourth time duration (e.g., about 10 minutes)
[0186] The resulting mixture can be used to form a material (e.g., by filling a sample cell).
[0187] Furthermore, the protocol can optionally include an initial assessment regarding the stability of a mixture of dopants without the host. For instance, when stability is observed within a dopant mixture, then such stability will likely contribute to the stability of multi-component formulation having a host.
Example 8: Characterization of Dopants from Small-Scale and Scaled-Up Synthesis
[0188] Physical properties of CD13 and CD29 from scaled-up synthesis were compared to prior small-scale results. Of note, there were no significant differences in the product properties based on chemical and spectroscopic analysis, as well as functional/performance analysis. Any differences were within experimental accuracy.
[0189] In brief, samples were prepared with various concentrations (0.5, 2, 4, 6, 8, and 10 wt. %) of CD29 in E7. The pitch of each sample was measured using the cylindrical Cano wedge method (
[0190] When using CD29 in E7, measured HTP included 27.2 μm.sup.−1 for small scale synthesis of CD29, as compared to 26.7 μm.sup.−1 for scale-up synthesis of CD29. This difference is less than 2%, which is within experimental accuracy. Similar measurements of CD13 in E7 provided HTP of 16.5 μm.sup.−1 for both small scale and scaled-up synthesis. Although less sensitive than pitch measurements, low voltage measurements of the dielectric constant ε.sub.⊥ gave similar agreement. We conclude therefore that there appears to be minimal difference in the relevant physical properties of CD13 and CD29 from small scale and scaled up synthesis.
[0191] Accordingly, these results indicate the feasibility of optimizing chemical transformations (and molecule purification as needed) to produce a desired bioreachable chiral dopant with scaled-up synthetic processes. Further derivatives can include hydrogenated derivatives of any chiral dopant described herein, as well as structurally modified derivatives having aliphatic ester or alkaryl ester modifications. In addition, physical and optical properties of the scaled-up material can be compared to prior small-scale results in order to verify the process.
Example 9: Further Characterization of Phase-Stable Dopants CD13 and CD29
[0192] CD13 and CD29 were assessed in two different hosts: E7 or MAT12-978 (available as Licristal®, from Merck Advanced Technologies Ltd., Pyongtaek, Korea, having a clearing point of 80° C. and a twist angle of 90°). Table 2 summarizes these results.
[0193] As can be seen, CD13 was stable at some concentrations, e.g., 10 wt. % in E7 or 5 wt. % in MAT12-978. Characterization of 10 wt. % CD13 in E7 is provided in
TABLE-US-00002 TABLE 2 Phase stability of binary doped materials with CD13 or CD29 Dopant and concentration [wt. %] E7 host MAT 12-978 host 5% CD13 — Yes 10% CD13 Yes No 5% CD29 No Yes 10% CD29 No No
Example 10: Characterization of Phase-Stable Dopants CD46, CD47, and CD48
[0194] Other phase-stable dopants provided herein have extended aliphatic groups (e.g., linear or branched C.sub.3-12 alkyl groups). Illustrative dopants include CD46 and CD47, which are benzoate esters having pendant C.sub.4-7 alkyl groups. CD48 is an aliphatic ester having branched C.sub.7 alkyl groups.
[0195] CD46 showed enhanced miscibility in E7 at concentrations up to 10 wt. %, in which no crystallization was observed (
TABLE-US-00003 TABLE 3 Pitch of CD46 and E7 formulations CD46 concentration [wt. %] Pitch [μm] 2.1 1.529 4.2 0.766 6 0.531 8.2 0.398 10 0.322 12 0.261
[0196] CD47 also showed suitable miscibility in E7 at all tested concentrations (
TABLE-US-00004 TABLE 4 Summary of helical twisting power and phase of CD46, CD47, and CD48 Dopant Host Phase at 20° C. HTP [μm.sup.−1] CD46 E7 crystalline powder 31.3 CD47 E7 liquid 24.5 CD48 E7 liquid 13.8
Example 11: Multicomponent Formulations
[0197] Multicomponent nematic formulations could allow for fine tuning of the physical and optical properties of the material. Another advantage of multicomponent formulations is the suppression of crystallization. Rather than using a single chiral component with a given HTP at 10% concentration to realize a bandgap in the visible, two chiral dopants with similar HTPs can be employed at a lower concentration (e.g., about 5 wt. % for each dopant). Without wishing to be limited by mechanism, the lower concentration could reduce the crystallization temperature, resulting in a formulation with desired optical properties and stability against crystallization/phase segregation.
[0198] To demonstrate this approach, four ternary formulations were formulated and tested. Each ternary formulation included two chiral dopants that were simultaneously present in the host. Table 5 summarizes these results.
TABLE-US-00005 TABLE 5 Composition and stability of non-limiting ternary materials Stable against Formulation No. Composition phase segregation 10-1 5 wt. % CD13 + 5 wt. % No CD29 + MAT 12-978 10-2 5 wt. % CD13 + 5 wt. % Yes CD29 + E7 10-3 5 wt. % CD29 + 5 wt. % Yes CD46 + E7 10-4 5 wt. % CD29 + 5 wt. % Yes CD47 + E7
[0199] Stability was determined by obtaining absorption spectra of the formulations and then assessing any temporal changes in the reflection band (e.g., changes such as red-shifting). As seen in
[0200] Ternary formulations 10-2, 10-3, and 10-4 were stable against crystallization/phase segregation (to date from the time of mixing). Further characterization data are provided for formulation 10-3 (5 wt. % CD29+5 wt. % CD46+E7,
Example 12: UV Stability
[0201] For certain device application, chemical stability of the formulations under UV illumination may be beneficial. UV stability studies were conducted for a nematic host (E7), binary formulations (host and one chiral dopant), and ternary formulations (host and two chiral dopants). In each case, sample responses were measured and compared prior to and after UV exposure (e.g., at wavelength of about 310 nm to about 400 nm).
[0202] Dopant UV stability can be measured in any useful manner. Illustrative testing methods include dielectric measurements (e.g., measurement of one or more of capacitance or permittivity), pitch measurements, and/or relative band measurements (e.g., using absorption or transmission spectra in the visible range) of formulations before and after UV exposure. Examples of pitch measurements and relative band measurements are described in
Example 13: Thermal Cycling
[0203] Another property of a cholesteric bandgap material is its stability against thermal degradation. We studied the optical response of ternary formulations before and after thermal cycling to look for evidence of thermal degradation. In an example, a 5 wt. % CD29+5 wt. % CD46+E7 formulation exhibited thermally stability after 24 hours of thermocycling (
TABLE-US-00006 TABLE 6 Capacitance measurements before and after thermocycling Empty Before After cell thermocycling thermocycling Capacitance (pF) 42.5 232.0 232.0 Loss 0.0200 0.0600 0.0600
Example 14: Voltage Cycling
[0204] When comparing samples before and after stimulus (e.g., such as exposure to UV or thermal cycling), the samples can possess defects with differing defect densities. Such defects can be ubiquitous in cholesterics, due to the high energy barrier that must be overcome to anneal defects.
[0205] One non-limiting strategy to reduce the number of defects is to apply a high AC voltage (e.g., about 100 V at 1 kHz across a 50 μm cell) and then suddenly reduce the voltage to zero. The high voltage creates a uniform homeotropic alignment, with the director normal to the cell windows everywhere, and when this voltage is suddenly removed, the director assumes the helical cholesteric structure with relatively few defects. This strategy can be applied to produce nearly uniform defect densities in cells needed for comparisons.
[0206] To determine the voltage required to produce homeotropic alignment, we devised a procedure where initially a small voltage is applied, followed by 0 volts, and the intensity of light transmitted through the cell between crossed polarizers is measured (see
[0207] Although the voltage cycling method described above can be employed for confirming stability results obtained by other means, such methods also reduce the defect density in cholesteric cells to a nearly uniform low value to facilitate comparisons. In addition to this, however, the process serves as a voltage cycling stimulus. Subsequent dielectric and optical measurements, together with critical voltage results, such as in
Example 15: Long-Term Phase Stability
[0208] To assess long-term phase stability, studies were conducted after maintaining materials for more than seven months. Planar LC cells with a thickness of 20 μm were filled with formulations; and transmission spectra and polarization microscopy (PM) images were obtained and assessed.
[0209] Results are provided for a binary formulation: 8 wt. % CD46+E7 (
[0210] Further results are provided for a ternary formulation: 5 wt. % CD29+5 wt. % CD46+E7 (
Example 16: Illustrative Agile Optical Filter Device
[0211] In order to make an “agile optical filter device,” a cholesteric (twisted nematic) media is required. This media can possess a variety of physical properties including a broad temperature cholesteric range (usually including ambient temperature) and a twist with minimal temperature dependence. The required cholesteric media can be created by mixing achiral nematic hosts with one or more bioreachable chiral dopants (e.g., any described herein).
[0212] Regarding achiral nematic mesogens (hosts), the medium can include molecules that are mesogenic (nematic), but the molecule is not intrinsically chiral. Typical commercial mixtures include a number of distinct molecular species, such that their combination results in the required physical and optical properties.
[0213] Regarding chiral twisting agents (dopants), the twist agent is a chiral molecule; often a pure enantiomer. The twist agent is added to the achiral nematic, producing a twist in the average molecular orientation of the bulk material. The twist increases in proportion to the dopant concentration. In many cases, the proportion of twist agent that can be added is limited by solubility or loss or cholesteric temperature range of the mixture.
[0214] The twisted cholesteric structure formed by the twisting agent can be a self-assembled layered structure, which, because of its periodicity, is a photonic band-gap material. Location and the width of the band-gap can be determined by the refractive indices of the nematic, and the pitch of the cholesteric structure. The contrast can be determined by the film thickness. Since the liquid crystal structure can be modified by applied fields, the filter can be switched on and off, and its location and bandwidth can be tuned.
[0215] The accessibility of enantiomerically pure chiral compounds through biology makes a bioreachable excellent candidates as twist agents for application in cholesteric liquid crystal technology. Chemical modification of the bioreachables can be performed in order to achieve new molecules with anticipated utility in liquid crystal technology. In particular, as described herein, betulin derivates show considerable promise as chiral dopants in cholesteric liquid crystal systems.
Other Embodiments
[0216] While the disclosure has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modifications and this application is intended to cover any variations, uses, or adaptations of the disclosure following, in general, the principles of the disclosure and including such departures from the present disclosure that come within known or customary practice within the art to which the disclosure pertains and may be applied to the essential features hereinbefore set forth, and follows in the scope of the claims.
[0217] Other embodiments are within the claims.