Cholesteric liquid crystal film

Abstract

The present invention generally relates to the field of materials with anisotropic optical properties useful for optic, electronic and optoelectronic application, and provides a cholesteric liquid crystal film, as well as a multilayer projection film comprising the cholesteric liquid film. The present invention further provides methods for preparing the cholesteric liquid crystal film and the multilayer projection film. The present invention also provides transparent substrates comprising the cholesteric liquid crystal film or the multilayer projection film. Particular liquid crystal monomers for preparing the cholesteric liquid crystal film and / or the multilayer projection film are furthermore provided by the present invention.

Description

[0001] CHOLESTERIC LIQUID CRYSTAL FILM

[0002] FIELD OF THE INVENTION

[0003] The present invention generally relates to the field of materials with anisotropic optical properties useful for optic, electronic and optoelectronic application, and provides a cholesteric liquid crystal film, as well as a multilayer projection film comprising the cholesteric liquid film. The present invention further provides methods for preparing the cholesteric liquid crystal film and the multilayer projection film. The present invention also provides transparent substrates comprising the cholesteric liquid crystal film or the multilayer projection film. Particular liquid crystal monomers for preparing the cholesteric liquid crystal film and / or the multilayer projection film are furthermore provided by the present invention.

[0004] BACKGROUND TO THE INVENTION

[0005] T ransparent projection screens are innovative display surfaces that allow images to be projected while maintaining a degree of transparency. These screens are typically made from materials like acrylic or glass, and are coated with materials that enhance image clarity and brightness, and are capable of partially scattering or reflecting light at particular wavelengths. They allow light to pass through, enabling viewers to see both the projected image and the background. Transparent projection screens provide clear visibility from various angles, making them suitable for diverse settings, such as retail displays, exhibitions, and interactive installations where maintaining visibility of the background is important.

[0006] Another particular example of a transparent projection screen are smart glasses, which utilize transparent materials, such as advanced polymers or glass, integrated with electronic components to display information directly in the user's line of sight. Smart glasses allow users to see digital information overlaid on the real world without obstructing their view.

[0007] A known concern of smart glasses is that images projected on the inside of the glasses may be visible by individuals other than the wearer for whom the image is intended, which may lead to sensitive information being inadvertently disclosed, especially in low-light environments and / or crowded public areas. Privacy filters could be used to enhance confidentiality by limiting the viewing angle of displayed content. However, the use of privacy filters has several disadvantages, such as narrowing the effective viewing angle, thereby limiting the wearer's ability to see the full display clearly, especially if they move their head or eyes or reducing the brightness and clarity of the projected images, making it harder for the wearer to see the content in certain lighting conditions.

[0008] It is therefore an object of the present invention to provide a novel liquid crystal film, in particular a multilayer projection film, that can be applied onto a transparent substrate, which at least partly resolves the problems known in the prior art, or provides one or more useful alternatives.

[0009] SUMMARY OF THE INVENTION

[0010] In a first aspect, the present invention provides a liquid crystal film, in particular a cholesteric liquid crystal (CLC) film, comprising cholesteric liquid crystals having a helical twist in its molecular structure in a clockwise or counterclockwise direction when moving along a longitudinal direction x of the helical twist, having a birefringence (Δn) of at most 0.10, at a wavelength of between 380 and 750 nm.

[0011] Cholesteric liquid crystal (CLC) films as defined herein can advantageously be used in various optical applications, as they reflect specific wavelengths of light, while transmitting others. The reflected colour can furthermore be tuned by adjusting the pitch of the helical structure. The reflected light is circularly polarized, which is a further advantage for their use in optical devices and displays. As they allow transmission of a substantial part of the visible light spectrum, they are sufficiently transparent for the desired applications.

[0012] Light is selectively reflected from a CLC film when the wavelength Ao matches the pitch p of the helix such that Ao=n p cos0, wherein n is the effective refractive index, 0 is the angle between the light propagation direction and the helix axis. The reflected light is circularly polarized with the same handedness as the helix. Outside the reflection band, both polarization states are transmitted through the CLC film. The color of the reflected light can change with temperature, the angle of incidence of the light, by stretching the CLC film, or by the applied electric field. This tunability is due to changes in the pitch of the helical structure.

[0013] It was found that when the cholesteric liquid crystal (CLC) film is constructed from liquid crystal materials with a low birefringence (Δn), such as a birefringence of at most 0.10, at a wavelength of between 380 and 750 nm, it provides for several advantages Low birefringence results in a smaller band of wavelengths being reflected by the CLC film, and thus more transmittance of light with other wavelengths. Low birefringence reduces the distortion and blurring of images projected on the CLC film, making these films particularly suitable for applications requiring high optical clarity, such as displays and lenses. The images are generated by an external projection system, which comprises a light source that emits light, preferably with a narrow bandwidth, such as an LED or a laser. With reduced birefringence, the colour reflected by the CLC film may be more uniform across different viewing angles, improving the consistency of colour displays. Low birefringence minimizes light scattering, which may enhance the brightness and contrast of displays, making them more efficient in reflecting ambient light. Low birefringence may provide more precise control over the polarization of reflected light, which is beneficial in optical devices like polarizers and filters.

[0014] CLC films constructed from liquid crystal materials with low birefringence may be tailored to reflect light with particular narrow wavelength bands, while transmitting other wavelengths. When a light beam with a wavelength matching the wavelength of the CLC film is projected on one side of a transparent substrate with a CLC film on its surface, for instance the inside of smart glasses (also known as private side), that light beam will be reflected and can be perceived by a person placed on that side of the transparent substrate, for instance the wearer of the smart glasses. A person placed on the other side of the transparent substrate, for instance a person standing in front of the wearer of the smart glasses (also known as public side), is not able to perceive the image projected on the private side of the CLC film. Other sources of light, such as sunlight, are transmitted through the transparent substrate, except for the wavelengths reflected by the CLC film, and are thus perceived from both the private and the public side. In other words, objects on the public side are still perceivable by the person on the private side, and vice versa. The lower the birefringence, the more narrow the reflected wavelength band, and the more other wavelengths are transmitted through the transparent substrate.

[0015] In an embodiment, the present invention provides the cholesteric liquid crystal film as defined herein, having a birefringence (Δn) of at most 0.08, at a wavelength of between 380 and 750 nm, preferably at most 0.06, more preferably at most 0.05, even more preferably from 0.01 to 0.04.

[0016] In a further embodiment, the present invention provides the cholesteric liquid crystal film as defined herein, wherein the cholesteric liquid crystal film is obtained by polymerizing a mixture comprising liquid crystal monomers and a chiral dopant; wherein at least part of the liquid crystal monomers has a H-shape structure, in particular wherein the mixture comprises from 1 to 80 wt.% of liquid crystal monomers having a H-shape structure.

[0017] It is a further advantage that the cholesteric liquid crystal film, as defined herein, can be adhered onto any transparent surface without the need for any special facility, and may therefore be performed easily at any desired location.

[0018] In a second aspect, the present invention provides a method for preparing the cholesteric liquid crystal film as defined herein, the method comprising the steps of: a) preparing a mixture of liquid crystal monomers, a solvent, a chiral dopant, a photoinitiator, and optionally a polymerization inhibitor; b) forming a layer of the mixture obtained in step a); and c) polymerizing the layer formed in step b) under UV light, thereby obtaining the cholesteric liquid crystal film; wherein at least part of the liquid crystal monomers in step a) has a H-shape structure, in particular wherein the mixture in step a) comprises from 1 to 80 wt.% of liquid crystal monomers having a H-shape structure.

[0019] It was found that the method according to the second aspect provides the cholesteric liquid crystal film as defined herein, and therefore also provides the advantages associated with said CLC film, as described hereinbefore.

[0020] In a further aspect, the present invention provides a cholesteric liquid crystal film obtained by the method as defined herein.

[0021] In yet a further aspect, the present invention provides a multilayer projection film comprising two or more cholesteric liquid crystal films as defined herein. The multilayer projection film as defined herein preferably comprises a stack of at least three layers of cholesteric liquid crystal films.

[0022] It was further found that a multilayer projection film as defined herein also provides the advantages associated with said CLC films, as described hereinbefore. The multilayer projection film, as defined herein, can also be adhered onto any transparent surface without the need for any special facility. When a stack of three CLC films as defined herein is provided, wherein each CLC film reflects a specific colour, in particular red, green or blue (RGB), the stack may reflect up to 100% of circularly polarized light of the same handedness as the CLC films emitted by a projector comprising an RGB light source projected on the private side of a transparent substrate with a multilayer projection film on its surface, which allows projecting full colour images / videos on the private side of the transparent substrate. Similar as for a single CLC film, the full colour images / videos are not perceivable by a person on the public side.

[0023] In an embodiment, the present invention provides the multilayer projection film as defined herein, comprising three layers of right-handed cholesteric liquid crystal films.

[0024] In an embodiment, the present invention provides the multilayer projection film as defined herein, comprising three layers of left-handed cholesteric liquid crystal films.

[0025] In an embodiment, the present invention provides the multilayer projection film as defined herein, comprising three layers of right-handed cholesteric liquid crystal films, and three layers of lefthanded cholesteric liquid crystal films.

[0026] In yet a further aspect, the present invention provides a method for preparing the multilayer projection film as defined herein. The method comprises the steps for preparing the cholesteric liquid crystal film as defined herein, and repeating those steps an appropriate numbers of times for each individual layer of CLC film, wherein each subsequent layer of CLC film is formed on top of the previous layer of CLC film. For each layer of right-handed CLC film, a right-handed chiral dopant is used. For each layer of left-handed CLC film, a left-handed chiral dopant is used.

[0027] In yet a further aspect, the present invention provides a transparent substrate comprising the cholesteric liquid crystal film as defined herein, or the multilayer projection film as defined herein.

[0028] In yet a further aspect, the present invention provides a liquid crystal monomer, in particular a liquid crystal monomer having a H-shape structure, for preparing a cholesteric liquid crystal film as defined herein, or a multilayer projection film as defined herein, wherein the liquid crystal monomer is represented by formula (I) wherein

[0029] A represents a bridging moiety, and comprises at least one -C2alkynylene- group, and optionally comprises further -C2alkynylene- groups and / or -Ar1- groups; each instance of R1, and each instance of R1'is independently selected from -H, -C1-12alkyl, -C1-12cycloalkyl, -C2-12alkenyl, -C2-12alkynyl, -halo, and -CN;

[0030] Cy1, Cy1 ', Cy2, and Cy2'are each independently selected from -C1-12cycloalkylene-, and -Ar2- ; wherein each of said -C1-12cycloalkylene- optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents, independently selected from -halo, and -C1-12alkyl ; L1, L1', L2, and L2'are each independently selected from a direct bond, -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, -C2-12alkynylene-, -Ar3-, -O-, -C(O)O-, -OC(O)-, - OC(O)O-, -N=N-, and any combination of two or more thereof; wherein each of said -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, and -C2-12alkynylene- optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents, independently selected from -halo, and -C1-12alkyl ; Ar1, Ar2, and Ar3are each independently aryl; in particular Ar1, Ar2, and Ar3are each independently a 5- to 10-membered aromatic group having a single ring or multiple aromatic rings fused together, wherein said 5- to 10-membered aromatic group optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents, independently selected from -halo, -CN, and -C1-12alkyl; S1, S1', S2, and S2'are each independently selected from a direct bond, -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, -C2-12alkynylene-, -C(O)O-, -OC(O)- , -OC(O)O-, and any combination of two or more thereof; wherein each of said -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, and -C2-12alkynylene- optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents, independently selected from -halo, and -C1-12alkyl ; and

[0031] X1, X1', X2, and X2'are each independently -H, or a polymerizable end group selected from - OH=OH2, -OC(O)CH=CH2, and -OC(O)C(CH3)=CH2; wherein X1and / or X1'is a polymerizable end group; and wherein X2and / or X2'is a polymerizable end group.

[0032] BRIEF DESCRIPTION OF THE DRAWINGS

[0033] With specific reference now to the figures, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the different embodiments of the present invention only. They are presented in the cause of providing what is believed to be the most useful and readily description of the principles and conceptual aspects of the invention. In this regard no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention. The description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

[0034] Figure 1 , also abbreviated as FIG. 1 , provides a representation of the UV-Vis spectrum of a cholesteric liquid crystal film prepared according to Example 2.

[0035] Figure 2, also abbreviated as FIG. 2, provides a representation of the UV-Vis spectrum of a cholesteric liquid crystal film prepared according to Example 3.

[0036] Figure 3, also abbreviated as FIG. 3, provides a representation of the UV-Vis spectrum of a cholesteric liquid crystal film prepared according to Example 4.

[0037] Figure 4a, also abbreviated as FIG. 4a, provides a representation of the UV-Vis spectrum of a cholesteric liquid crystal film prepared according to Example 5. Figure 4b, also abbreviated as FIG. 4b, provides a representation of the UV-Vis spectrum, measured with right-handed circular polarized light, of a cholesteric liquid crystal film prepared according to Example 5.

[0038] Figure 5, also abbreviated as FIG. 5, provides a representation of the UV-Vis spectrum of a cholesteric liquid crystal film prepared according to Example 6.

[0039] Figure 6, also abbreviated as FIG. 6, provides a representation of the UV-Vis spectrum of a cholesteric liquid crystal film prepared according to Example 7.

[0040] Figure 7, also abbreviated as FIG. 7, provides a representation of the UV-Vis spectrum of a cholesteric liquid crystal film prepared according to Comparative example A.

[0041] Figure 8, also abbreviated as FIG. 8, provides a representation of the UV-Vis spectrum of a cholesteric liquid crystal film prepared according to Comparative example B.

[0042] Figure 9, also abbreviated as FIG. 9, provides a representation of the UV-Vis spectrum of a cholesteric liquid crystal film prepared according to Comparative example C.

[0043] Figure 10, also abbreviated as FIG. 10, shows illustrative examples of a helical structure having a left-handed twist (L) and a helical structure having a right-handed twist (R).

[0044] Figures 11 and 12, also abbreviated as FIG. 11 and FIG. 12, provide a representation of reflection spectra of the six layers of a CLC multilayer film.

[0045] Figure 13, also abbreviated as FIG. 13, provides a representation of transmission spectra of of combined two CLC layers with similar reflected wavelengths and the opposite handedness.

[0046] Figure 14, also abbreviated as FIG. 14, shows a grey-scale diagram showing a reflection spectrum of CLC films with the combination of right-handedness and left-handedness.

[0047] Figure 15, also abbreviated as FIG. 15, provides a screenshot of a full-color time lapse-video showing the blooming process of flowers is projected on a multilayer projection film.

[0048] DETAILED DESCRIPTION OF THE INVENTION

[0049] The present invention will now be further described. In the following passages, different aspects of the invention are defined in more detail. Each aspect so defined may be combined with any other aspect or aspects unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous.

[0050] When describing the compounds of the present invention, the terms used are to be construed in accordance with the following definitions, unless a context dictates otherwise:

[0051] The term "alkyl" by itself or as part of another substituent refers to a fully saturated hydrocarbon of Formula CXH2X+I wherein x is a number greater than or equal to 1 . Generally, alkyl groups of this invention comprise from 1 to 20 carbon atoms. Alkyl groups may be linear or branched and may be substituted as indicated herein. When a subscript is used herein following a carbon atom, the subscript refers to the number of carbon atoms that the named group may contain. Thus, for example, C1-4alkyl means an alkyl of one to four carbon atoms. Examples of alkyl groups are methyl, ethyl, n-propyl, i-propyl, butyl, and its isomers (e.g. n-butyl, i-butyl and t- butyl); pentyl and its isomers, hexyl and its isomers, heptyl and its isomers, octyl and its isomers, nonyl and its isomers; decyl and its isomers, undecyl and its isomers, dodecyl and its isomers, tridecyl and its isomers, tetradecyl and its isomers, pentadecyl and its isomers, hexadecyl and its isomers, heptadecyl and its isomers, octadecyl and its isomers, nonadecyl and its isomers, eicosanyl and its isomers. The term "optionally substituted alkyl" refers to an alkyl group optionally substituted with one or more substituents (for example 1 to 4 substituents, for example 1 , 2, 3, or 4 substituents) at any available point of attachment.

[0052] Whenever the term “substituted” is used in the present invention, it is meant to indicate that one or more hydrogens on the atom indicated in the expression using “substituted” is replaced with a selection from the indicated group, provided that the indicated atom’s normal valency is not exceeded, and that the substitution results in a chemically stable compound, i.e. a compound that is sufficiently robust to survive isolation to a useful degree of purity from a reaction mixture, and formulation into a therapeutic agent.

[0053] Where groups may be optionally substituted, such groups may be substituted once or more, and preferably once, twice or thrice. Non-limiting examples of such substituents are selected from halogen (-halo), hydroxy (-OH), oxo (=O), nitro (-NO2), amino (-NR’R”), cyano (-CN), alkyl, cycloalkyl, alkenyl, alkynyl, alkoxy or aryloxy (-OR’”), aryl, heteroaryl, carbonyl (-C(O)Riv), carboxyl (-COOH), ester or alkoxycarbonyl (-C(O)ORV), ester or alkylcarbonyloxy (-OC(O)Rvi), amido or aminocarbonyl (-NR’C(O)), amido or carbonylamino (-C(O)NR’), heterocyclyl, carbonyl, acyl, arylcarbonyl, thio (-SH), alkylthio (-SRvi), and the like.

[0054] The term "alkenyl" or “alkene”, as used herein, unless otherwise indicated, means straight-chain, cyclic, or branched-chain hydrocarbon radicals containing at least one carbon-carbon double bond. Examples of alkenyl radicals include ethenyl, E- and Z-propenyl, isopropenyl, E- and Z- butenyl, E- and Z-isobutenyl, E- and Z-pentenyl, E- and Z-hexenyl, E,E-, E,Z-, Z,E-, Z,Z- hexadienyl, be it in the terminal or internal positions, and the like. Generally alkenyl or alkene moieties of the present invention comprise from 2 to 20 C atoms. An optionally substituted alkenyl refers to an alkenyl having optionally one or more substituents (for example 1 , 2, 3 or 4), selected from those defined above for substituted alkyl. Unless stated otherwise, when a reference to "alkenyl" or “alkene”, it refers to all possible isomers of each of the carbon-carbon double bonds present.

[0055] The term "alkynyl", as used herein, unless otherwise indicated, means straight-chain or branched-chain hydrocarbon radicals containing at least one carbon-carbon triple bond. Examples of alkynyl radicals include ethynyl, propynyl, butynyl, pentynyl, hexynyl, hexadiynyl, be it in the terminal or internal positions, and the like. An optionally substituted alkynyl refers to an alkynyl having optionally one or more substituents (for example 1 , 2, 3 or 4), selected from those defined above for substituted alkyl.

[0056] The term “cycloalkyl” by itself or as part of another substituent is a cyclic alkyl group, that is to say, a monovalent, saturated, or unsaturated hydrocarbyl group having 1 , 2, or 3 cyclic structure. Cycloalkyl includes all saturated or partially saturated (containing 1 or 2 double bonds) hydrocarbon groups containing 1 to 3 rings, including monocyclic, bicyclic, or polycyclic alkyl groups. Cycloalkyl groups may comprise 3 or more carbon atoms in the ring and generally, according to this invention comprise from 3 to 15 atoms. Examples of cycloalkyl groups include but are not limited to cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, adamantanyl and cyclodecyl. An “optionally substituted cycloalkyl” refers to a cycloalkyl having optionally one or more substituents (for example 1 to 3 substituents, for example 1 , 2, 3 or 4 substituents), selected from those defined above for substituted alkyl.

[0057] The alkyl, cycloalkyl, alkenyl and alkynyl moieties as defined herein may also further comprise one or more heteroatoms, such as selected from N, S or O, in that for example a carbon atom in an alkyl, alkene or alkyne chain is replaced by a heteroatom. When two or more C atoms are replaced by heteroatoms, the heteroatoms may be adjacent or separated, as long as it results in a chemically stable compound, i.e. a compound that is sufficiently robust to survive isolation to a useful degree of purity from a reaction mixture, and formulation into a therapeutic agent. An example of a stable combination of two adjacent heteroatoms is a disulfide (-S-S-) group. Where a carbon atom in an alkyl, alkenyl or alkynyl chain is replaced by an N atom, the N atom may be N or NH depending on the number of bonds connected to said C atom.

[0058] Where alkyl groups as defined are divalent, i.e., with two single bonds for attachment to two other groups, they are termed "alkylene" groups. Non-limiting examples of alkylene groups includes methylene, ethylene, methylmethylene, trimethylene, propylene, tetramethylene, ethylethylene, 1 ,2-dimethylethylene, pentamethylene and hexamethylene. Similarly, where alkenyl groups as defined above, alkynyl groups as defined above, and cycloalkyl groups as defined above, respectively, are divalent radicals having single bonds for attachment to two other groups, they are termed "alkenylene", "alkynylene" and “cycloalkylene” respectively.

[0059] The term “alkoxy" or “alkyloxy” as used herein refers to a radical having the Formula -OR’” wherein R’” is alkyl, alkenyl, or alkynyl. Non-limiting examples of suitable alkoxy include methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, sec-butoxy, tert-butoxy, pentyloxy and hexyloxy. The term “aryloxy" as used herein refers to a radical having the Formula -OR’” wherein R’” is aryl.

[0060] Where the oxygen atom in an alkoxy group is substituted with sulfur, the resultant radical is referred to as alkylthio or arylthio, such as methylthio, ethylthio, phenylthio, and the like.

[0061] The term “oxo” as used herein refers to the group =O.

[0062] The term "carbonyl" by itself or as part of another substituent refers to the group -C(O)Riv, wherein Rivis a hydrogen atom (i.e. an aldehyde), or alkyl, alkenyl, alkynyl or aryl (i.e. a ketone).

[0063] The term "carboxy" or “carboxyl” or “hydroxycarbonyl” by itself or as part of another substituent refers to the group -COOH, -C(O)OH, or -CO2H.

[0064] The term "alkoxycarbonyl" by itself or as part of another substituent refers to a carboxy group linked to an alkyl radical i.e. to form -C(O)ORV, wherein Rvis alkyl, alkenyl, alkynyl or aryl.

[0065] The term “alkylcarbonyloxy” by itself or as part of another substituent refers to a -OC(O)Rviwherein Rviis alkyl, alkenyl, alkynyl or aryl.

[0066] The term "heterocycle" as used herein by itself or as part of another group refers to nonaromatic, fully saturated or partially unsaturated cyclic groups (for example, 3 to 13 member monocyclic, 7 to 17 member bicyclic, or 10 to 20 member tricyclic ring systems, or containing a total of 3 to 10 ring atoms) which have at least one heteroatom in at least one carbon atomcontaining ring. Each ring of the heterocyclic group containing a heteroatom may have 1 , 2, 3 or 4 heteroatoms selected from nitrogen atoms, oxygen atoms and / or sulfur atoms, where the nitrogen and sulfur heteroatoms may optionally be oxidized and the nitrogen heteroatoms may optionally be quaternized. The heterocyclic group may be attached at any heteroatom or carbon atom of the ring or ring system, where valence allows. The rings of multi-ring heterocycles may be fused, bridged and / or joined through one or more spiro atoms. An optionally substituted heterocyclic refers to a heterocyclic having optionally one or more substituents (for example 1 to 4 substituents, or for example 1 , 2, 3 or 4), selected from those defined above for substituted alkyl. Non-limiting examples of heterocycle comprise: piperidinyl, azepanyl, morpholinyl.

[0067] The term “aryl" as used herein refers to a polyunsaturated, aromatic hydrocarbyl group having a single ring (i.e. phenyl) or multiple aromatic rings fused together (e.g. naphthalene or anthracene) or linked covalently, typically containing 6 to 10 atoms; wherein at least one ring is aromatic. The aromatic ring may optionally include one to three additional rings (either cycloalkyl, heterocyclyl, or heteroaryl) fused thereto. Aryl is also intended to include the partially hydrogenated derivatives of the carbocyclic systems enumerated herein. Non-limiting examples of aryl comprise phenyl, napthyl, and the like. The aryl group or heterocycle as defined herein can optionally be substituted by one or more substituents (for example 1 to 5 substituents, for example 1 , 2, 3, 4 or 5) at any available point of attachment. Non-limiting examples of such substituents are selected from halogen, hydroxyl, oxo, nitro, amino, hydrazine, aminocarbonyl, azido, cyano, alkyl, cycloalkyl, alkenyl, alkynyl, cycloalkylalkyl, alkylamino, alkoxy, -SO2-NH2, aryl, heteroaryl, aralkyl, haloalkyl, haloalkoxy, alkoxycarbonyl, alkylaminocarbonyl, heteroarylalkyl, alkylsulfonamide, heterocyclyl, alkylcarbonylaminoalkyl, aryloxy, alkylcarbonyl, acyl, arylcarbonyl, aminocarbonyl, alkylsulfoxide, -SO2Rx, alkylthio, carboxyl, and the like, wherein Rxis alkyl or cycloalkyl.

[0068] Where aryl groups as defined are divalent, i.e., with two single bonds for attachment to two other groups, they may be termed "arylene" groups.

[0069] The term “heteroaryl” as used herein by itself or as part of another group refers but is not limited to 5 to 12 carbon-atom aromatic rings or ring systems containing 1 to 3 rings which are fused together or linked covalently, typically containing 5 to 8 atoms; at least one of which is aromatic in which one or more carbon atoms in one or more of these rings can be replaced by oxygen, nitrogen or sulfur atoms where the nitrogen and sulfur heteroatoms may optionally be oxidized and the nitrogen heteroatoms may optionally be quaternized. Such rings may be fused to an aryl, cycloalkyl, heteroaryl or heterocyclyl ring. Non-limiting examples of such heteroaryl, include piridinyl, azepinyl.

[0070] An “optionally substituted heteroaryl” refers to a heteroaryl having optionally one or more substituents (for example 1 to 4 substituents, for example 1 , 2, 3 or 4), selected from those defined above for substituted aryl.

[0071] As used herein the terms such as “alkyl, aryl, or cycloalkyl, each being optionally substituted with” or “alkyl, aryl, or cycloalkyl, optionally substituted with” refers to optionally substituted alkyl, optionally substituted aryl and optionally substituted cycloalkyl. The term “halo” or “halogen” as a group or part of a group is generic for fluoro, chloro, bromo, or iodo.

[0072] The term "direct bond" as used herein, refers to a chemical linkage directly connecting two or more specified moieties, without the presence of any intervening elements or groups.

[0073] As used herein, when a compound has one or more stereocenters, each stereocenter may have the R or S configuration, unless stated otherwise. The compound may therefore be a racemic mixture of enantiomers and / or diastereoisomers, or it may have an excess of one or more of the enantiomers and / or diastereoisomers, such as more than 60 %, more than 70 %, more than 80 %, more than 85 %, more than 90 %, more than 95 %, more than 98 %, more than 99 %.

[0074] As mentioned hereinbefore, in a first aspect, the present invention provides a liquid crystal film, in particular a cholesteric liquid crystal (CLC) film, comprising cholesteric liquid crystals having a helical twist in its molecular structure in a clockwise or counterclockwise direction when moving along a longitudinal direction x of the helical twist.

[0075] In the context of the present invention, the terms “birefringence”, “Δn”, or “refractive index anisotropy” refer to the optical property of a material having a refractive index that depends on the polarization and propagation direction of light. It is described as the difference between the extraordinary and ordinary refractive indices (Δn = ne- no), wherein neis the extraordinary refractive index (the refractive index for light polarized parallel to the director) and nois the ordinary refractive index (the refractive index for light polarized perpendicular to the director).

[0076] A liquid crystal material is often a combination of various molecules, each having their own contribution to the net birefringence, wherein the net birefringence is the sum of all contributions of each molecule. The birefringence can be measured when the material is aligned uniaxially as the difference between the extraordinary refractive index and the ordinary refractive index. By adding a chiral molecule, the cholesteric liquid crystal film is formed in the net uniaxial orientation changes into a molecular organization where the molecules organize into a helix with a periodicity defined as pitch p. The pitch p is then the length over which the molecules make a net rotation of 2π. The CLC can now be considered as a stack of ultra-thin uniaxial layers in which each next layer is rotated with respect to its former layer.

[0077] In an embodiment, the present invention provides the cholesteric liquid crystal film as defined herein, having a birefringence (Δn) of at most 0.10, at a wavelength of between 380 and 750 nm, preferably at most 0.08, more preferably at most 0.06, even more preferably at most 0.05, yet even more preferably from 0.01 to 0.04. It was further found that a cholesteric liquid crystal (CLC) film with a low birefringence (Δn) can be obtained by polymerizing a mixture comprising liquid crystal monomers and a chiral dopant; wherein at least part of the liquid crystal monomers has a H-shape structure.

[0078] In the context of the present invention, the term “H-shape structure” refers to a structure comprising, or consisting of, one or more moieties on a first axis of the H-shape structure, connected by one or more moieties on a second axis of the H-shape structure, perpendicular to the first axis. The terms “liquid crystal monomers having a H-shape structure”, or “H-shape monomers”, may in particular refer to liquid crystal monomers comprising two promesogenic moieties connected by a bridging moiety; wherein each promesogenic moiety comprises one or more aromatic groups and at least one polymerizable end group; and wherein the birefringence of the bridging moiety counteracts the birefringence of the promesogenic moieties.

[0079] In the context of the present invention, the term “promesogenic moiety” refers to a moiety with the ability to induce liquid crystal (LC) phase behaviour. The compounds comprising promesogenic groups do not necessarily have to exhibit a liquid crystal phase themselves. It is also possible that they show liquid crystal phase behaviour only in mixtures with other compounds, or when the mesogenic compounds or materials, or the mixtures thereof, are polymerized.

[0080] In the context of the present invention, the terms “at least part of” or “at least partially” refer to a definite, non-zero, portion of the item it refers to. The terms “at least part of” or “at least partially” may therefore refer to about 1 %, 2 %, 3 %, 5 %, 10 %, 20 %, 25 %, 30 %, 40 %, 50 %, 60 %, 70 %, 75 %, 80 %, or substantially all, such as about 90 %, 95 %, 99 %, and even about 100 %, of the item it refers to.

[0081] In an embodiment, the present invention provides the cholesteric liquid crystal film as defined herein, wherein the cholesteric liquid crystal film is obtained by polymerizing a mixture comprising liquid crystal monomers and a chiral dopant; wherein at least part of the liquid crystal monomers has a H-shape structure.

[0082] The mixture used for obtaining the CLC film comprises at least 1 wt.% of liquid crystal monomers having a H-shape structure, more preferably at least 2 wt.%, even more preferably at least 5 wt.%, yet even more preferably at least 8 wt.%. It was found that a high amount of H-shape monomers in the mixture in step a) may lead to misalignment of the liquid crystals, which in turn may lead to a broader reflection band. Therefore, the mixture used for obtaining the CLC film preferably comprises at most 80 wt.% of liquid crystal monomers having a H-shape structure, such as at most 70 wt.%, at most 60 wt.%, at most 50 wt.%, at most 40 wt.%, at most 30 wt.%, at most 25 wt.%, at most 20 wt.%, at most 15 wt.%, or at most 12 wt.%. In a particular embodiment, the present invention provides the cholesteric liquid crystal film as defined herein, wherein the mixture used for obtaining the CLC film comprises from 1 to 30 wt.% of liquid crystal monomers having a H-shape structure, preferably from 2 to 25 wt.%, more preferably from 3 to 20 wt.%, even more preferably from 5 to 15 wt.%, yet even more preferably from 8 to 12 wt.%.

[0083] It was moreover found that particular liquid crystal monomers having a H-shape structure may lead to a cholesteric liquid crystal film with a more narrow reflected wavelength band.

[0084] In an embodiment, the present invention provides the cholesteric liquid crystal film as defined herein, wherein the liquid crystal monomers having a H-shape structure are represented by formula (l) wherein

[0085] A represents a bridging moiety, and comprises at least one -C2alkynylene- group, and optionally comprises further -C2alkynylene- groups and / or -Ar1- groups; each instance of R1, and each instance of R1'is independently selected from -H, -C1-12alkyl, -C1-12cycloalkyl, -C2-12alkenyl, -C2-12alkynyl, -halo, and -CN;

[0086] Cy1, Cy1 ', Cy2, and Cy2'are each independently selected from -C1-12cycloalkylene-, and -Ar2- ; wherein each of said -C1-12cycloalkylene- optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents, independently selected from -halo, and -C1-12alkyl ; L1, L1', L2, and L2'are each independently selected from a direct bond, -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, -C2-12alkynylene-, -Ar3-, -O-, -C(O)O-, -OC(O)-, - OC(O)O-, -N=N-, and any combination of two or more thereof; wherein each of said -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, and -C2-12alkynylene- optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents, independently selected from -halo, and -C1-12alkyl ; Ar1, Ar2, and Ar3are each independently aryl; in particular Ar1, Ar2, and Ar3are each independently a 5- to 10-membered aromatic group having a single ring or multiple aromatic rings fused together, wherein said 5- to 10-membered aromatic group optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents, independently selected from -halo, -CN, and -C1-12alkyl ; S1, S1', S2, and S2'are each independently selected from a direct bond, -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, -C2-12alkynylene-, -C(O)O-, -OC(O)- , -OC(O)O-, and any combination of two or more thereof; wherein each of said -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, and -C2-12alkynylene- optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents, independently selected from -halo, and -C1-12alkyl ; and

[0087] X1, X1', X2, and X2'are each independently -H, or a polymerizable end group selected from -OH=OH2, -OC(O)CH=CH2, and -OC(O)C(CH3)=CH2; wherein X1and / or X1'is a polymerizable end group; and wherein X2and / or X2'is a polymerizable end group.

[0088] In an embodiment, the present invention provides the cholesteric liquid crystal film as defined herein, having a reflection band with a bandwidth (Δλ) of at most 60 nm, at a wavelength of between 380 and 750 nm, preferably at most 50 nm, more preferably at most 40 nm, even more preferably at most 30 nm, yet even more preferably at most 25 nm, yet even more preferably from 1 to 20 nm.

[0089] As mentioned hereinbefore, in a second aspect, the present invention provides a method for preparing the cholesteric liquid crystal film as defined herein, the method comprising the steps of: a) preparing a mixture of liquid crystal monomers, a solvent, a chiral dopant, and a photoinitiator; b) forming a layer of the mixture obtained in step a); and c) polymerizing the layer formed in step b) under UV light, thereby obtaining the cholesteric liquid crystal film; wherein at least part of the liquid crystal monomers has a H-shape structure.

[0090] Preferably, the mixture in step a) further comprises a polymerization inhibitor.

[0091] As mentioned hereinbefore, in a further aspect, the present invention provides a cholesteric liquid crystal film obtained by the method as defined herein.

[0092] As mentioned hereinbefore, in yet a further aspect, the present invention provides a multilayer projection film comprising two or more cholesteric liquid crystal films as defined herein. The two or more cholesteric liquid crystal films may be provided as layers and / or may be stacked on top of each other. When two or more cholesteric liquid crystal films are provided as layers stacked on top of each other, it may also be referred to as a stack of layers of cholesteric liquid crystal films.

[0093] In a preferred embodiment, the present invention provides the multilayer projection film as defined herein, comprising a stack of at least three layers of cholesteric liquid crystal films. In a particular embodiment, the present invention provides the multilayer projection film as defined herein, consisting of a stack of three layers of cholesteric liquid crystal films.

[0094] In an embodiment, the present invention provides the multilayer projection film as defined herein, wherein the stack comprises three layers of right-handed cholesteric liquid crystal films. In a particular embodiment, the present invention provides the multilayer projection film as defined herein, consisting of a stack of three layers of right-handed cholesteric liquid crystal films.

[0095] In the context of the present invention, the term “right-handed cholesteric liquid crystal film” refers to a cholesteric liquid crystal film comprising cholesteric liquid crystals having a helical twist in a clockwise direction when moving along a longitudinal direction x of the helical twist.

[0096] In an embodiment, the present invention provides the multilayer projection film as defined herein, wherein the stack comprises three layers of left-handed cholesteric liquid crystal films. In a particular embodiment, the present invention provides the multilayer projection film as defined herein, consisting of a stack of three layers of left-handed cholesteric liquid crystal films.

[0097] In the context of the present invention, the term “left-handed cholesteric liquid crystal film” refers to a cholesteric liquid crystal film comprising cholesteric liquid crystals having a helical twist in a counterclockwise direction when moving along a longitudinal direction x of the helical twist.

[0098] As mentioned hereinbefore, when a stack of three CLC films as defined herein is provided, wherein each CLC film reflects a specific colour, in particular red, green or blue (RGB), the stack may reflect up to 100% of circularly polarized light of the same handedness as the CLC films emitted by a projector comprising a RGB light source. Circularly polarized light can be emitted from the projector by placing a linear polarizer / quarterwave plate before or after the projector lens.

[0099] In a particular embodiment, the present invention provides the multilayer projection film as defined herein, wherein the stack comprises three layers of right-handed cholesteric liquid, and three layers of left-handed cholesteric liquid crystal films. When a multilayer projection film comprising three layers of CLC films (left-handed or right- handed) is used in combination with a projector that emits circularly polarized light, the film has the same properties as a multilayer projection film comprising three layers of left-handed and three layers of right-handed CLC film used in combination with a projector that emits nonpolarized light.

[0100] In an embodiment, the present invention provides the multilayer projection film as defined herein, having a reflection band with a bandwidth (Δλ) of at most 60 nm, at a wavelength of between 380 and 750 nm, preferably at most 50 nm, more preferably at most 40 nm, even more preferably at most 30 nm, yet even more preferably at most 25 nm, yet even more preferably from 1 to 20 nm.

[0101] In an embodiment, the present invention provides the multilayer projection film as defined herein, wherein the stack comprises three layers of cholesteric liquid crystal films: a red cholesteric liquid crystal film; a green cholesteric liquid crystal film; and a blue cholesteric liquid crystal film.

[0102] In the context of the present invention, the term “red cholesteric liquid crystal film” refers to a cholesteric liquid crystal film comprising cholesteric liquid crystals having a helical twist in a clockwise of counterclockwise direction when moving along a longitudinal direction x of the helical twist, wherein the film reflects red light, in particular light with a wavelength of 620 to 680 nanometer.

[0103] In the context of the present invention, the term “green cholesteric liquid crystal film” refers to a cholesteric liquid crystal film comprising cholesteric liquid crystals having a helical twist in a clockwise or counterclockwise direction when moving along a longitudinal direction x of the helical twist, wherein the film reflects green light, in particular light with a wavelength of 495 to 555 nanometer.

[0104] In the context of the present invention, the term “blue cholesteric liquid crystal film” refers to a cholesteric liquid crystal film comprising cholesteric liquid crystals having a helical twist in a clockwise or counterclockwise direction when moving along a longitudinal direction x of the helical twist, wherein the film reflects blue light, in particular light with a wavelength of 425 to 485 nanometer.

[0105] In an embodiment, the present invention provides the multilayer projection film as defined herein, having a transmittance of light at wavelengths from 425 to 485 nm, from 495 to 555 nm, and from 620 to 680 nm, of less than 10%, preferably less than 5%, more preferably less than 1 %, even more preferably less than 0.1 %.

[0106] In an embodiment, the present invention provides the multilayer projection film as defined herein, wherein the layers are contiguous. In other words, the layer of CLC films are stacked upon each other without any gap being present between each of the layers.

[0107] In an embodiment, the present invention provides the multilayer projection film as defined herein, wherein each of the layers, preferably all of the layers, has a thickness of 2 to 10 μm.

[0108] In an embodiment, the present invention provides the multilayer projection film as defined herein, wherein all the layers have the same thickness.

[0109] In an embodiment, the present invention provides the multilayer projection film as defined herein, wherein the multilayer projection film further comprises a quarter-wave (λ / 4) plate arranged for converting linearly polarized light, such as emitted by a projector, into right-handed or lefthanded circularly polarized light.

[0110] In the context of the present invention, the terms “quarter-wave plate” or “λ / 4 plate” refer to an optical device that is used to alter the polarization state of light. It can be a thin quartz plate, a thin stretched polymer film or a coating of birefringent monomers on a non-birefringent substrate. The plate (or film or coating) introduces a phase shift of a quarter of the wavelength of the light between two orthogonal polarization components of the light passing through it. A quarter-wave plate is typically made from a birefringent material, such as quarts or mica, which has different refractive indices for light polarized along different axes. When linearly polarized light is incident at a 45° angle (for right-handed CLC films) or at a 135°C angle (for left-handed CLC films) to the fast and slow axes of a quarter-wave plate, the phase shift between the orthogonal components converts the light into circularly polarized light. The quarter-wave plate has the property that the product of the thickness (d) and birefringence (Δn) is equal to a quarter of the wavelength (λ / 4), i.e. , d·Δn = λ / 4. In particular cases, this can be made wavelength independent, for instance by stacking of birefringent layers or films.

[0111] In an embodiment, the present invention provides the multilayer projection film as defined herein, wherein the multilayer projection film further comprises a linear polarizer arranged for converting unpolarized light waves into linearly polarized light.

[0112] In the context of the present invention, the term “linear polarizer” refers to an optical filter that selectively filters light waves, only allowing waves vibrating in a particular direction (the direction of polarization) to pass through. It blocks or absorbs waves vibrating perpendicular to this direction. A linear polarizer is typically a thin film or a glass plate treated to create the polarizing effect.

[0113] As mentioned hereinbefore, in yet a further aspect, the present invention provides a method for preparing the multilayer projection film as defined herein. The method comprises the steps for preparing the cholesteric liquid crystal film as defined herein, and repeating those steps an appropriate numbers of times for each individual layer of CLC film, wherein each subsequent layer of CLC film is formed on top of the previous layer of CLC film. For each layer of right- handed CLC film, a right-handed chiral dopant is used. For each layer of left-handed CLC film, a left-handed chiral dopant is used.

[0114] In a preferred embodiment, the present invention provides the method for preparing the multilayer projection film as defined herein, the method comprising the steps of: a) preparing a mixture of liquid crystal monomers, a solvent, a chiral dopant, and a photoinitiator; b) forming a layer of the mixture obtained in step a); c) polymerizing the layer formed in step b) under UV light, thereby providing a layer of CLC film; and d) repeating steps a) to c) an appropriate number of times for each individual layer of CLC film to obtain the multilayer projection film, wherein each subsequent layer of CLC film is formed on top of the previous layer of CLC film; wherein for each layer of right-handed CLC film, a right-handed chiral dopant is used; wherein for each layer of left-handed CLC film, a left-handed chiral dopant is used; and wherein at least part of the liquid crystal monomers has a H-shape structure.

[0115] In embodiments, the present invention provides the method for preparing the CLC film, or the method for preparing the multilayer projection film, as defined herein, wherein the mixture in step a) further comprises a polymerization inhibitor.

[0116] The mixture in step a) preferably comprises at least 1 wt.% of liquid crystal monomers having a H-shape structure, more preferably at least 2 wt.%, even more preferably at least 5 wt.%, yet even more preferably at least 8 wt.%. It was found that a high amount of H-shape monomers in the mixture in step a) may lead to misalignment of the liquid crystals, which in turn may lead to a broader reflection band. Therefore, the mixture in step a) preferably comprises at most 80 wt.% of liquid crystal monomers having a H-shape structure, such as at most 70 wt.%, at most 60 wt.%, at most 50 wt.%, at most 40 wt.%, at most 30 wt.%, at most 25 wt.%, at most 20 wt.%, at most 15 wt.%, or at most 12 wt.%.

[0117] In particular embodiments, the present invention provides the method for preparing the CLC film, or the method for preparing the multilayer projection film, as defined herein, wherein the mixture in step a) comprises from 1 to 30 wt.% of liquid crystal monomers having a H-shape structure, preferably from 2 to 25 wt.%, more preferably from 3 to 20 wt.%, even more preferably from 5 to 15 wt.%, yet even more preferably from 8 to 12 wt.%.

[0118] In embodiments, the present invention provides the method for preparing the CLC film, or the method for preparing the multilayer projection film, as defined herein, wherein the liquid crystal monomers having a H-shape structure are represented by formula (I) wherein

[0119] A represents the bridging moiety, and comprises at least one -C2alkynylene- group, and optionally comprises further -C2alkynylene- groups and / or -Ar1- groups; each instance of R1, and each instance of R1'is independently selected from -H, -C1-12alkyl, -C1-12cycloalkyl, -C2-12alkenyl, -C2-12alkynyl, -halo, and -CN;

[0120] Cy1, Cy1 ', Cy2, and Cy2'are each independently selected from -C1-12cycloalkylene-, and -Ar2- ; wherein each of said -C1-12cycloalkylene- optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents, independently selected from -halo, and -C1-12alkyl ; L1, L1', L2, and L2'are each independently selected from a direct bond, -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, -C2-12alkynylene-, -Ar3-, -O-, -C(O)O-, -OC(O)-, - OC(O)O-, -N=N-, and any combination of two or more thereof; wherein each of said -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, and -C2-12alkynylene- optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents, independently selected from -halo, and -C1-12alkyl ; Ar1, Ar2, and Ar3are each independently aryl; in particular Ar1, Ar2, and Ar3are each independently a 5- to 10-membered aromatic group having a single ring or multiple aromatic rings fused together, wherein said 5- to 10-membered aromatic group optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents, independently selected from -halo, -CN, and -C1-12alkyl; S1, S1', S2, and S2'are each independently selected from a direct bond, -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, -C2-12alkynylene-, -C(O)O-, -OC(O)- , -OC(O)O-, and any combination of two or more thereof; wherein each of said -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, and -C2-12alkynylene- optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents, independently selected from -halo, and -C1-12alkyl ; and

[0121] X1, X1', X2, and X2'are each independently -H, or a polymerizable end group selected from - CH=CH2, -OC(O)CH=CH2, and -OC(O)C(CH3)=CH2; wherein X1and / or X1'is a polymerizable end group; and wherein X2and / or X2'is a polymerizable end group.

[0122] In embodiments, the present invention provides the method for preparing the CLC film, or the method for preparing the multilayer projection film, wherein the chiral dopant, in particular the right-handed and / or left-handed chiral dopant, is selected from the group consisting of: 1 ,4-bis[4- (6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene, 4-cyanophenyl-4-((6-(acryloyloxy)- hexyl)oxy)benzoate, 4-methoxyphenyl-4-((6-(acryloyloxy)hexyl) oxyjbenzoate, bis[4-[4-[4- (acryloyloxy)butoxycarbonyloxy]benzoyloxy]benzoic acid]- (3S,3aS,6R,6aS)hexahydrofuro[3,2- b]furan-3,6-diyl ester, and (S)-1 -phenylethane-1 ,2-diyl bis(4-((1 s,4S)-4-pentylcyclohexyl)- benzoate).

[0123] In embodiments, the present invention provides the method for preparing the CLC film, or the method for preparing the multilayer projection film, wherein the photoinitiator is selected from the group consisting of: phenyl-bis(2,4,6-trimethylbenzoyl)phosphine oxide, 2-benzyl-2- dimethylamino-1 -(4-morpholinophenyl)-butanone-1 , 1 ,2-diphenyl-2,2-dimethoxyethanone, 1 - hydroxy-cyclohexyl-phenyl-ketone, and any combination of two or more thereof.

[0124] In embodiments, the present invention provides the method for preparing the CLC film, or the method for preparing the multilayer projection film, comprising the further step of homogenizing the mixture obtained in step a), such as by heating and or stirring, before forming the layer of the mixture in step b).

[0125] In embodiments, the present invention provides the method for preparing the CLC film, or the method for preparing the multilayer projection film, comprising the further steps of: allowing or forcing the solvent of the mixture obtained in step a) to evaporate, thereby obtaining a solid mixture; and melting the solid mixture, before forming the layer of the mixture in step b). In embodiments, the present invention provides the method for preparing the CLC film, or the method for preparing the multilayer projection film, wherein forming the layer of the mixture in step b) is performed by bar coating.

[0126] In yet a further aspect, the present invention provides a transparent substrate comprising the cholesteric liquid crystal film as defined herein, or the multilayer projection film as defined herein.

[0127] In an embodiment, the present invention provides the transparent substrate as defined herein, wherein the CLC film is provided on a surface of the transparent substrate.

[0128] In an embodiment, the present invention provides the transparent substrate as defined herein, wherein the multilayer projection film is provided on a surface of the transparent substrate, in particular wherein the layers of the multilayer projection film are stacked on the transparent substrate.

[0129] In embodiments, the present invention provides the transparent substrate as defined herein, wherein the transparent substrate is a lens, a window, or a wall panel.

[0130] In embodiments, the present invention provides the transparent substrate as defined herein, wherein the transparent substrate is a silicon-based substrate, such as glass.

[0131] In embodiments, the present invention provides the transparent substrate as defined herein, wherein the transparent substrate is a polymeric material selected from the group consisting of: polyethylene terephthalate (PET), poly(methyl methacrylate) (PMMA), polycarbonate (PC), polystyrene (PS), cyclic olefin copolymer (COC), polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyvinylchloride (PVC), polypropylene (PP), cellulose triacetate (CTA), and any combination of two or more thereof.

[0132] In embodiments, the present invention provides the transparent substrate as defined herein, wherein the transparent substrate has a transmittance of light at wavelengths from 380 to 750 nm of at least 90%, preferably at least 95%.

[0133] In embodiments, the present invention provides the transparent substrate as defined herein, wherein the transparent substrate has a thickness from 50 μm to 3 mm.

[0134] As mentioned hereinbefore, in yet a further aspect, the present invention provides a liquid crystal monomer, in particular a liquid crystal monomer having a H-shape structure, for preparing a cholesteric liquid crystal film as defined herein, or a multilayer projection film as defined herein, wherein the liquid crystal monomer is represented by formula (I)

[0135] wherein

[0136] A represents the bridging moiety, and comprises at least one -C2alkynylene- group, and optionally comprises further -C2alkynylene- groups and / or -Ar1- groups; each instance of R1, and each instance of R1'is independently selected from -H, -C1-12alkyl, -C1-12cycloalkyl, -C2-12alkenyl, -C2-12alkynyl, -halo, and -CN;

[0137] Cy1, Cy1 ', Cy2, and Cy2'are each independently selected from -C1-12cycloalkylene-, and -Ar2- ; wherein each of said -C1-12cycloalkylene- optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents, independently selected from -halo, and -C1-12alkyl ; L1, L1', L2, and L2'are each independently selected from a direct bond, -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, -C2-12alkynylene-, -Ar3-, -O-, -C(O)O-, -OC(O)-, - OC(O)O-, -N=N-, and any combination of two or more thereof; wherein each of said -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, and -C2-12alkynylene- optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents, independently selected from -halo, and -C1-12alkyl ; Ar1, Ar2, and Ar3are each independently aryl; in particular Ar1, Ar2, and Ar3are each independently a 5- to 10-membered aromatic group having a single ring or multiple aromatic rings fused together, wherein said 5- to 10-membered aromatic group optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents, independently selected from -halo, -CN, and -C1-12alkyl ; S1, S1', S2, and S2'are each independently selected from a direct bond, -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, -C2-12alkynylene-, -C(O)O-, -OC(O)- , -OC(O)O-, and any combination of two or more thereof; wherein each of said -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, and -C2-12alkynylene- optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents, independently selected from -halo, and -C1-12alkyl; and

[0138] X1, X1', X2, and X2'are each independently -H, or a polymerizable end group selected from - CH=CH2, -OC(O)CH=CH2, and -OC(O)C(CH3)=CH2; wherein X1and / or X1'is a polymerizable end group; and wherein X2and / or X2'is a polymerizable end group.

[0139] In an embodiment, the present invention provides a liquid crystal monomer as defined herein, and represented by any of formula (II), (II’), (II”), or (II’”)

[0140] wherein

[0141] A, R1, L1, L1', L2, L2', S1, S1', S2, S2', X1, X1', X2, and X2'are as defined herein.

[0142] In an embodiment, the present invention provides a liquid crystal monomer as defined herein, and represented by any of formula (Ila), (llb), (lle), (lld), (lle), (Ilf), or (llg)

[0143] wherein

[0144] A, R1, S1, S1', S2, S2', X1, X1', X2, and X2'are as defined herein.

[0145] In an embodiment, the present invention provides a liquid crystal monomer as defined herein, and represented by any of formula (ll’a), (ll’b), or (II’c)

[0146] wherein

[0147] A, R1, S1, S1', S2, S2', X1, X1', X2, and X2'are as defined herein.

[0148] In an embodiment, the present invention provides a liquid crystal monomer as defined herein, and represented by any of formula (ll”a), (ll”b), or (ll”c)

[0149] wherein

[0150] A, R1, S1, S1', S2, S2', X1, X1', X2, and X2'are as defined herein.

[0151] In an embodiment, the present invention provides a liquid crystal monomer as defined herein, and represented by formula (ll’”a)

[0152] wherein

[0153] A, R1, S1, S1', S2, S2', X1, X1', X2, and X2'are as defined herein.

[0154] In embodiments, the present invention provides a liquid crystal monomer as defined herein, wherein A is represented by any one of the following formulae:

[0155] wherein Ar1is as defined herein.

[0156] One or more aspects and / or embodiments of the present invention may also be defined by the following clauses:

[0157] 1 . A multilayer projection film comprising: - three layers of cholesteric liquid crystal (CLC) films stacked upon each other and comprising: three layers of right-handed CLC films, wherein the right-handed CLC films are defined as films containing right-handed CLC having a helical twist in its molecular structure that is in a clockwise direction when moving along a longitudinal direction x of the helical twist. A multilayer projection film comprising: three layers of cholesteric liquid crystal (CLC) films stacked upon each other and comprising: three layers of left-handed CLC films, wherein the left-handed CLC films are defined as films containing left-handed CLC having a helical twist in its molecular structure that is in a counterclockwise direction when moving along a longitudinal direction x of the helical twist. A multilayer projection film comprising: six layers of cholesteric liquid crystal (CLC) films stacked upon each other and comprising: three layers of right-handed CLC films, wherein the right-handed CLC films are defined as films containing right-handed CLC having a helical twist in its molecular structure that is in a clockwise direction when moving along a longitudinal direction x of the helical twist, and three layers of left-handed CLC films, wherein the left-handed CLC films are defined as films containing left-handed CLC having a helical twist in its molecular structure that is in a counterclockwise direction when moving along the longitudinal direction x of the helical twist. The multilayer projection film according to any of the preceding clauses, wherein all layers of CLC films are stacked upon each other without any gap being present between each of the layers. The multilayer projection film according to any of the preceding clauses, wherein each of the layers has a thickness, preferably all of the layers have the same thickness, of between 2 and 10 μm. The multilayer projection film according to any of the preceding clauses, wherein the multilayer projection film further comprises a quarter-wave (λ / 4) plate arranged for converting linearly polarized light as emitted by a projector into right-handed or lefthanded circularly polarized light. The multilayer projection film according to any of the preceding clauses, wherein the multilayer projection film further comprises a linear polarizer arranged for converting unpolarized light waves into linearly polarized light. 8. The multilayer projection film according to any of the preceding clauses, wherein the multilayer projection film further comprises a transparent substrate onto which the layers of CLC films are stacked.

[0158] 9. The multilayer projection film according to clause 8, wherein the transparent substrate is a lens.

[0159] 10. The multilayer projection film according to clause 8 or 9, wherein the transparent substrate is a silicon-based substrate, such as glass, or a polymeric material selected from the group consisting of polyethylene terephthalate (PET), poly(methyl methacrylate) (PMMA), polycarbonate (PC), polystyrene (PS), cyclic olefin copolymer (COC), polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyvinylchloride (PVC), polypropylene (PP), and a combination of two or more thereof.

[0160] 1 1 . The multilayer projection film according to any of the clauses 8 to 10, wherein the transparent substrate has a transmittance of light at wavelengths of from 380 nm to 750 nm of at least 90%, preferably at least 95%.

[0161] 12. The multilayer projection film according to any of the clauses 8 to 1 1 , wherein the transparent substrate has a thickness of from 50 μm to 3 mm.

[0162] 13. The multilayer projection film according to any of the preceding clauses, wherein the right- handed CLC and / or left-handed CLC are a mixture of liquid crystal reactive mesogens, which are RM82 (1 ,4-bis[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene), RM23 (4-cyanophenyl 4-((6-(acryloyloxy)hexyl)oxy)benzoate), RM105 (4-methoxyphenyl 4-((6- (acryloyloxy)hexyl)oxy)benzoate), and right-handed chiral dopants and / or left-handed chiral dopants, a photoinitiator and a polymerizable inhibitor.

[0163] 14. The multilayer projection film according to any of the preceding clauses, wherein each of the right-handed CLC and / or left-handed CLC has a birefringence (Δn) of at most 0.10, preferably at most 0.08, at a wavelength of between 380 and 750 nm.

[0164] 15. The multilayer projection film according to any of the preceding clauses, wherein each of the right-handed CLC and / or left-handed CLC has a reflection band with a bandwidth (Δλ) of at most 60 nm, preferably at most 30 nm, at a wavelength of between 380 and 750 nm.

[0165] 16. The multilayer projection film according to any of the preceding clauses, wherein the multilayer projection film has a transmittance of light at wavelengths of from 425 to 485 nm, from 495 to 555 nm, and from 620 to 680 nm of less than 10%, preferably less than 5%, more preferably less than 1%, most preferably less than 0.1%.

[0166] 17. A method of preparing a transparent projection film according to any of the preceding clauses, comprising the steps of: a) providing a liquid crystal mixture comprising a liquid crystal monomer and a solvent, preferably the mixture comprises liquid crystal monomer in an amount of from 5.0 to 10 wt.% based on the weight of the liquid crystal mixture of step a); b) mixing the liquid crystal mixture provided in step a) with a right-handed chiral dopant or a left-handed chiral dopant, a photoinitiator, and a polymerization inhibitor, preferably the mixture comprises right-handed chiral dopant in an amount up to 10 wt.%, lefthanded chiral dopant in an amount up to 10 wt.%, photoinitiator in an amount up to 1 .5 wt.%, and / or polymerization inhibitor in an amount up to 1 .0 wt.%, based on the weight of the mixture obtained in step b); c) heating the mixture obtained in step b) at approximately 50 °C while stirring said mixture to homogenize; d) loading the heated mixture obtained in step c) on a barcoater at 50-100 °C to form a layer of CLC film; e) polymerizing the CLC layer formed in step d) under UV light with an intensity of 130 J / cm2; f) repeating the steps a) to e) for each individual layer of CLC film of the respective three or six layers of CLC films to obtain the transparent projection film, wherein each subsequent film is loaded on top of the previous film.

[0167] 18. The method according to clause 17, wherein the right-handed chiral dopant and / or lefthanded chiral dopant is / are selected from the group consisting of 1 ,4-bis[4-(6- acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene, 4-cyanophenyl-4-((6-(acryloyloxy)- hexyl)oxy)benzoate, 4-methoxyphenyl-4-((6-(acryloyloxy)hexyl)oxy)benzoate, bis[4-[4-[4- (acryloyloxy)butoxycarbonyloxy]benzoyloxy]benzoic acid](3S,3aS,6R,6aS)-hexahydro- furo[3,2-b]furan-3,6-diyl ester, and (S)-1 -phenylethane-1 ,2-diyl bis(4-((1s,4S)-4- pentylcyclohexyljbenzoate).

[0168] 19. The method according to clause 17 or 18, wherein the photoinitiator is selected from the group consisting of phenyl-bis(2,4,6-trimethylbenzoyl)phosphine oxide, 2-benzyl-2- dimethylamino-1 -(4-morpholinophenyl)-butanone-1 , 1 ,2-diphenyl-2,2-dimethoxyethanone, 1 -hydroxy-cyclohexyl-phenyl-ketone, or combinations thereof.

[0169] 20. The method according to any of the clauses 17 to 19, wherein the polymerizable inhibitor is 2,6-di-tert-butyl-4-methylphenol. 21 . A transparent surface, such as a glass wall, comprising a multilayer projection film according to any of the clauses 1 to 16 or prepared according to a method according to any of the clauses 17 to 20.

[0170] 22. The transparent surface according to clause 21 , wherein the transparent surface is part of an optical glasses comprising an integrated projector system.

[0171] 23. The transparent surface according to clause 21 , wherein the transparent surface is part of a front window of an automobile on which images are projected 5 of an in the automobile integrated projector system.

[0172] The compounds of the present invention can be prepared according to the reaction schemes provided in the examples hereinafter, but those skilled in the art will appreciate that these are only illustrative for the invention and that the compounds of this invention can be prepared by any of several standard synthetic processes commonly used by those skilled in the art of organic chemistry.

[0173] EXAMPLES

[0174] Materials

[0175] Unless otherwise stated, all glassware was oven dried before use and all reactions were carried out under an argon atmosphere using standard Schlenk techniques. All reagents were used without further purification unless otherwise stated. H-shape monomer 1 (H1 ), RM82, LC756 and Irgacure 819 were purchased from Merck. General procedure A

[0176] Cholesteric liquid crystal films are prepared by dissolving the compounds as indicated in dichloromethane. The mixture is then slowly evaporated to obtain a homogeneous solid. These solids are melted between polyimide coated glasses with spacers of 10 μm and polymerized with UV light for 30 minutes.

[0177] After polymerization, the top glass plate is removed and the optical properties are analyzed by a UV-Vis spectrometer.

[0178] Example 1

[0179] H-shape monomer 2 (H2) was prepared according to the synthesis scheme below.

[0180] Synthesis of (1)

[0181] In a two-neck flask were dissolved methyl 4-hydroxybenzoate (1 .15 g, 7.60 mmol), potassium carbonate (3.14 g, 22.80 mmol) and tip of spatula of KI in 100 ml of acetone. After 30 minutes 10-bromo-1 -decene was added (2.00 g, 9.12 mmol) and the mixture was stirred overnight at reflux. Then the salts were filtered over celite and the solvent evaporated, the crude was purified by column chromatography in an eluent mixture of dichloromethane 1 :1 heptane obtaining the product with a yield of 78%.

[0182] 1H-NMR (CDCI3, 298K, 400 MHz, δ, ppm): 7.97 (d, J=8.9 Hz, 2H), 6.89 (d, J=8.9 Hz, 2H), 5.78 (m, 1 H), 4.95 (m, 2H), 3.99 (t, J=6.5 Hz, 2H), 3.88 (s, 3H), 2.04 (m, 2H), 1 .80 (m, 2H), 1 .38 (m, 10H);13C-NMR (CDCl3, 298K, 400 MHz, δ, ppm): 167.08, 163.10, 139.31 , 131 .71 , 122.47, 1 14.32, 1 14.21 , 68.33, 51 .97, 33.93, 29.52, 29.44, 29.25, 29.18, 29.04, 26.1 1 . Synthesis of (2)

[0183] To a solution of (1) (2.00 g, 6.88 mmol) in THF (40 ml) at 60°C, was added a solution of LiOH (0.49 g, 20.66 mmol) in methanol / water (5 / 20 ml), and the mixture was stirred overnight. The crude was precipitated in a solution of HCI / H2O 4M, obtaining a white solid with a yield of 99%.

[0184] 1H-NMR (CDCl3, 298K, 400 MHz, δ, ppm): 8.05 (d, J=8.8 Hz, 2H), 6.93 (d, J=8.8 Hz, 2H), 5.80 (m, 1 H), 4.95 (m, 2H), 4.02 (t, J=6.5 Hz, 2H), 2.04 (m, 2H), 1 .80 (m, 2H), 1 .38 (m, 10H);13C- NMR (CDCl3, 298K, 400 MHz, δ, ppm): 169.35, 164.61 , 139.32, 132.47, 122.47, 1 14.36, 1 14.33, 68.33, 33.93, 29.53, 29.44, 29.23, 29.19, 29.04, 26.1 1 .

[0185] Synthesis of (3)

[0186] In a two-neck flask was dissolved 4-bromo-2,5-dimethoxytoluene (1 .00 g, 4.32 mmol) in 50 ml of dichloromethane at 0°C under argon atmosphere. Then boron tribromide (2.60 g, 10.37 mmol) was slowly added and stirred overnight at room temperature. The crude was precipitated in 150 ml of water and extracted with DCM (3x150 ml), dried with MgSO4, filtered and the solvent evaporated. The product was characterized by NMR obtaining 700 mg with a yield of 98%.

[0187] 1H-NMR (DMSO-d6, 298K, 400 MHz, δ, ppm): 9.31 (s, 1 H), 8.85 (s, 1 H), 7.02 (s, 1 H), 6.60 (s, 1 H), 2.01 (s, 3H);13C-NMR (DMSO-d6, 298K, 400 MHz, δ, ppm): 150.30, 148.48, 124.62, 123.71 , 1 17.70, 82.72, 15.48.

[0188] Synthesis of (4)

[0189] In a two-neck flask were dissolved the compounds (2) (1 .00 g, 3.64 mmol), (3) (0.35 g, 1 .39 mmol) and DMAP (0.10 g, 0.83 mmol) in 10 ml of THF at 0°C under argon atmosphere. Then DCC (1 .01 g, 4.86 mmol) was slowly added and stirred overnight at room temperature. The crude was filtered over celite and the solvent evaporated. The crude was purified by column chromatography in an eluent mixture of heptane 6:4 dichloromethane 650 mg with a yield of 58%.

[0190] 1H-NMR (CDCl3, 298K, 400 MHz, δ, ppm): 8.22 (d, J=8.7 Hz, 2H), 8.13 (d, J=8.7 Hz, 2H), 7.62 (s, 1 H), 7.17 (s, 1 H), 7.00 (m, 4H), 5.82 (m, 2H), 4.95 (m, 4H), 4.05 (m, 8H), 2.27 (s, 6H), 2.04 (m, 8H), 1 .80 (m, 8H), 1 .38 (m, 20H);13C-NMR (CDCl3, 298K, 400 MHz, δ, ppm): 164.28, 164.1 1 , 149.00, 147.51 , 139.19, 132.63, 132.37, 132.29, 129.84, 121 .07, 120.85, 1 14.42, 1 14.22, 86.18, 68.36, 33.82, 30.99, 29.41 , 29.32, 29.09, 29.07, 28.92, 25.64, 16.38.

[0191] Synthesis of (5)

[0192] A Schlenk flask was charged with 4,4-diiodobiphenyl (1 .30 g, 3.20 mmol), Cul (60 mg. 0.32 mmol) and PdCl2(PPh3)2(180 mg, 0.32 mmol) then three cycles of vacuum-argon were carried out. The solids were dissolved in a mixture of dry THF / triethylamine (15 / 7 ml) . The crude was purified by column chromatography in an eluent mixture of heptane 7:1 dichloromethane 700 mg with a yield of 60%.

[0193] 1H-NMR (CDCl3, 298K, 400 MHz, δ, ppm): 7.53 (s, 8H), 0.26 (s, 18H);13C-NMR (CDCl3, 298K, 400 MHz, δ, ppm): 140.34, 132.60, 126.87, 122.57, 104.97, 95.37, 0.13.

[0194] Synthesis of (6)

[0195] In a flask with two necks was dissolved the compound (5) (0.70 g, 2.02 mmol) in THF (60 ml) under argon atmosphere at room temperature, over that was added TBAF (2.09 g, 8.08 mmol) and let react overnight. The crude was dissolved in DCM (100 ml) and extracted with water (3x100ml), dried with MgSO4, filtered and the solvent evaporated. The crude was purified by column chromatography in an eluent mixture of heptane 7:1 dichloromethane obtaining 300 mg with a yield of 74%.

[0196] 1H-NMR (CDCl3, 298K, 400 MHz, δ, ppm): 7.56 (m, 8H), 3.14 (s, 2H);13C-NMR (CDCl3, 298K, 400 MHz, δ, ppm): 140.69, 132.79, 127.06, 121 .63, 83.52, 78.23.

[0197] Synthesis of H-shape monomer 2 (H2)

[0198] A Schlenk flask was charged with the compounds (4) (400 mg, 0.52 mmol), Cul (8 mg, 0.022 mmol) and PdCl2(PPh3)2(16 mg, 0.022 mmol), then 10 ml of dry THF was added to the flask and three cycles of vacuum-argon were carried out. In another Schlenk flask, the compound (6) (44 mg, 0.22 mmol) was dissolved in 5 ml of dry triethylamine under argon. Finally, the contents of the second Schlenk flask was added to the first and the mixture was stirred at 60°C for 16 hours. After that time the solvent was removed, the crude was dissolved in 100 ml of dichloromethane and washed with water (3x100ml), dry with MgSO4, filtered and evaporated. The crude was purified by column chromatography in an eluent mixture of heptane 1 :1 dichloromethane 198 mg with a yield of 63%.

[0199] 1H-NMR (CDCl3, 298K, 400 MHz, δ, ppm): 8.24 (d, J=8.7 Hz, 4H), 8.17 (d, J=8.7 Hz, 4H), 7.40 (m, 6H), 7.23 (m, 6H), 6.99 (m, 8H), 5.81 (m, 4H), 4.95 (m, 8H), 4.05 (t, J=6.5 Hz, 4H), 2.21 (s, 3H), 2.04 (m, 4H), 1 .80 (m, 4H), 1 .38 (m, 56H);13C-NMR (CDCl3, 298K, 400 MHz, δ, ppm): 164.64, 164.51 , 163.83, 163.77, 149.51 , 146.97, 140.16, 139.31 , 139.29, 132.63, 132.49, 132.03, 129.84, 126.84, 126.50, 125.00, 121 .54, 121 .24, 1 14.54, 1 14.34, 94.22, 84.22, 68.49, 33.94, 32.03, 29.54, 29.45, 29.25, 29.18, 29.05, 22.85, 14.27.

[0200] MS (MALDI+, dithranol, m / z): found 1502.78 [M+Na+] calculated with sodium 1502.78 (1479.91 +22.87).

[0201] FTIR (v: cm-1): 3081 (=C-H), 2921 (C-C-H), 2128 (-C≡C-), 1729 (C=O), 1608 (C=C), 1491 (C=C), 1249 (C-O), 1 149 (C-O). Example 2

[0202] A cholesteric liquid crystal film with a red reflection band was prepared according to General procedure A using 9.72 wt.% of H-shape monomer 1 (H1 ), 85.98 wt.% of RM82, 3.2 wt.% of LC756 and 1 wt.% of Irgacure 819.

[0203] The film reflects light at 660 nm with a bandwidth of 45 nm, as shown in Figure 1 .

[0204] Example 3

[0205] A cholesteric liquid crystal film with a green reflection band was prepared according to General procedure A using 9.63 wt.% of H-shape monomer 1 (H1 ), 84.17 wt.% of RM82, 4.2 wt.% of LC756 and 1 wt.% of Irgacure 819 to prepare the mixture in dichloromethane.

[0206] The film reflects light at 506 nm with a bandwidth of 27 nm, as shown in Figure 2.

[0207] Example 4

[0208] A cholesteric liquid crystal film with a blue reflection band was prepared according to example 2, using 9.3 wt.% of H-shape monomer 1 (H1 ), 83.7 wt.% of RM82, 6.0 wt.% of LC756 and 1 wt.% of Irgacure 819.

[0209] The optical properties were analyzed by a UV-Vis spectrometer. The film reflects light at 389 nm with a bandwidth of 23 nm, as shown in Figure 3.

[0210] Example 5

[0211] A cholesteric liquid crystal film with a red reflection band was prepared according to General procedure A using 9.72 wt.% of H-shape monomer 2 (H2), 85.98 wt.% of RM82, 3.2 wt.% of LC756 and 1 wt.% of Irgacure 819.

[0212] The film reflects light at 61 1 nm with a bandwidth of 22 nm, as shown in Figure 4a.

[0213] The same film was measured with right handed circular polarized light, demonstrating an enhanced reflection, as shown in Figure 4b.

[0214] Example 6

[0215] A cholesteric liquid crystal film with a green reflection band was prepared according to General procedure A using 9.63 wt.% of H-shape monomer 2 (H2), 84.17 wt.% of RM82, 4.2 wt.% of LC756 and 1 wt.% of Irgacure 819.

[0216] The film reflects light at 490 nm with a bandwidth of 31 nm, as shown in Figure 5. Example 7

[0217] A cholesteric liquid crystal film with a blue reflection band was prepared according to General procedure A using 9.3 wt.% of H-shape monomer 2 (H2), 83.7 wt.% of RM82, 6.0 wt.% of LC756 and 1 wt.% of Irgacure 819.

[0218] The film reflects light at 402 nm with a bandwidth of 22 nm, as shown in Figure 6

[0219] Comparative example A

[0220] A cholesteric liquid crystal film with a red reflection band was prepared according to General procedure A using 95.8 wt.% of RM82, 3.2 wt.% of LC756 and 1 wt.% of Irgacure 819. Hence, no H-shape monomer was used.

[0221] The film reflects light at 601 nm with a bandwidth of 73 nm, as shown in Figure 7.

[0222] Comparative example B

[0223] A cholesteric liquid crystal film with a green reflection band was prepared according to General procedure A using 94.8 wt.% of RM82, 4.2 wt.% of LC756 and 1 wt.% of Irgacure 819. Hence, no H-shape monomer was used.

[0224] The film reflects light at 498 nm with a bandwidth of 57 nm, as shown in Figure 8.

[0225] Comparative example C

[0226] A cholesteric liquid crystal film with a blue reflection band was prepared according to General procedure A using 93.0 wt.% of RM82, 6.0 wt.% of LC756 and 1 wt.% of Irgacure 819. Hence, no H-shape monomer was used.

[0227] The film reflects light at 406 nm with a bandwidth of 53 nm, as shown in Figure 9.

[0228] Table 1 provides an overview of the optical properties of the different examples.

[0229] Table 1

[0230] Example 8

[0231] 5.0-10 wt.% of liquid crystal having the structure of Molecule 1 with Δn= 0.06-0.07 at 589 nm (purchased from Jiangsu Creative Electronic Chemicals Co., Ltd, 3CCUF) is mixed with liquid crystal reactive mesogens containing RM82, RM105, and RM23 to obtain a liquid crystal mixture. A left-handed chiral dopant with three concentrations between 1 .0 - 9.0 wt.% is added to obtain “l-R”, “l-G” and “l-B” layers. A right-handed chiral dopant with three concentrations between 1 .0 - 9.0 wt.% is added to obtain "r-R", "r-G" and "r-B" layers. The six composites are heated to approximately 50 °C with stirring to promote mixing. One of the six mixtures is loaded on a barcoater to form the first layer of CLC film at 50-100 °C. A flexible PET film or a glass slide is used as substrate. The coated film is polymerized under UV light with a intensity of 130 J / cm2. The second mixture is loaded on top of the polymerized first layer to form the second layer of CLC film, followed by UV polymerization. The rest of the CLC layers use the same method to fabricate and at the end, a six-layer CLC film is obtained for testing. Every CLC layer has the same thickness of between 5-10 μm. A RGB light source is adopted for one side of the CLC multilayer film, acting as indoor space, while an sunlight or fluorescent tubes are for another side, acting as outdoor space.

[0232] Example 9

[0233] 5.0-10 wt.% of liquid crystal having the structure of Molecule 2 with Δn= 0.06 at 589 nm (purchased from Daken, DK8014) is mixed with liquid crystal reactive mesogens containing RM82, RM105, and RM23 to obtain a liquid crystal mixture. A left-handed chiral dopant with three concentrations between 1 .0 - 9.0 wt.% is added to obtain “l-R”, “l-G” and “l-B” layers. A right-handed chiral dopant with three concentrations between 1 .0 - 9.0 wt.% is added to obtain "r-R", "r-G" and "r-B" layers. The six composites are heated to approximately 50 °C with stirring to promote mixing. One of the six mixtures is loaded on a barcoater to form the first layer of CLC film at 50-100 °C. A flexible PET film or a glass slide is used as substrate. The coated film is polymerized under UV light with a intensity of 130 J / cm2. The second mixture is loaded on top of the polymerized first layer to form the second layer of CLC film, followed by UV polymerization. The rest of the CLC layers use the same method to fabricate and at the end, a six-layer CLC film is obtained for testing. A RGB light source is adopted for one side of the CLC multilayer film, acting as indoor space, while an sunlight or fluorescent tubes are for another side, acting as outdoor space.

[0234] Molecule 2

[0235] Example 10

[0236] A liquid crystal mixture with Δn= 0.039 at 589 nm (purchased from HCCH, HNG717200-000) is used as host system. A left-handed chiral dopant with three concentrations between 1 .0 - 9.0 wt.% is added to obtain “l-R”, “l-G” and “l-B” layers. A right-handed chiral dopant with three concentrations between 1 .0 - 9.0 wt.% is added to obtain "r-R", "r-G" and "r-B" layers. The six composites are heated to approximately 50 °C with stirring to promote mixing. One of the six mixtures is loaded on a barcoater to form the first layer of CLC film at 50-100 °C. A flexible PET film or a glass slide is used as substrate. The coated film is polymerized under UV light with a intensity of 130 J / cm2. The second mixture is loaded on top of the polymerized first layer to form the second layer of CLC film, followed by UV polymerization. The rest of the CLC layers use the same method to fabricate and at the end, a six-layer CLC film is obtained for testing. A RGB light source is adopted for one side of the CLC multilayer film, acting as indoor space, while an sunlight or fluorescent tubes are for another side, acting as outdoor space.

[0237] Example 11

[0238] A multilayer projection film comprising a three-layer CLC film, a linear polarizer and a λ / 4 plate is prepared by adhering the various layers together with a polyethylene terephthalate (PET) adhesive. The angle between the transmission axis of the linear polarizer and the optical axis of the λ / 4 plate is 45°. The order of these three components are right-handed CLC films, λ / 4 plate and linear polarizer, sequentially. Every CLC layer has a thickness of between 5-10 μm. The CLC film includes a polymerizable liquid crystal mixture (Δn= 0.10-0.13 at 450-650 nm wavelength), a chiral dopant that indues left-handed helix or right-handed helix, a photoinitator and a polymerization inhibitor. Three liquid crystal compositions are prepared for three CLC layers, namely, "r-R", "r-G" and "r-B. A right-handed chiral dopant with three concentrations between 3.8 and 5.3 wt.% is added to obtain "r-R", "r-G" and "r-B" layers. The photoinitiator and polymerization inhibitor account for 1 .0 wt.% and 0.50 wt.%, respectively. Three layer of CLC films are formed one by one on a flexible PET film or a glass slide as substrate, with the use of a barcoater and UV light. The fabricated multilayer CLC film enables a full-color projection with the visibility of the behind environment. The viewer behind the film cannot perceive the projected contents or view the scene on the film’s front side, especially when an RGB light source is used at the front side of the film.

[0239] Figure 10, shows illustrative examples of a helical structure having a left-handed twist (L) and a helical structure having a right-handed twist (R). The L helix has a twist in the counterclockwise direction when moving along the longitudinal direction x of the helical twist. The R helix has a twist in the clockwise direction when moving along the longitudinal direction x of the helical twist.

[0240] Figures 1 1 and 12 are reflection spectra of the six layers of a CLC multilayer film provided by an example of the present disclosure. Herein, the CLC films with right-handedness and red light reflection, with right-handedness and green light reflection, with right-handedness and blue light reflection are denoted as “r-R”, “r-G” and “r-B”, respectively. The CLC films with left-handedness and red light reflection, with left-handedness and green light reflection, with left-handedness and blue light reflection are denoted as “l-R”, “l-G” and “l-B”, respectively.

[0241] As shown in Figure 1 1 , the reflection peaks of the three right-handed CLC layers are centrally located at wavelengths (A) of 456 nm, 510 nm and 610 nm, respectively. These reflected wavelengths correspond to the colors blue, green, and red, respectively. The reflection bandwidths are around 45-55 nm.

[0242] As shown in Fig. 12, the reflection peaks of the three left-handed CLC layers are centrally located at wavelengths (A) of 464 nm, 532 nm, and 642 nm, respectively. These reflected wavelengths correspond to the colors blue, green, and red, respectively. The reflection bandwidths are around 42-63 nm.

[0243] Figure 13 shows transmittance spectra of combined two CLC layers with similar reflected wavelengths and the opposite handedness (thus, both left- and right-handedness), indicated as “r-R + l-R”, “r-G + l-G”, and “r-B + l-B”, respectively. These two CLC layers have similar pitches to allow the full reflection of both left-handed and right-handed circularly polarized lights. For example, “r-B” layer has a similar pitch with “l-R” layer to reflect circularly polarized red light with both right-handedness and left-handedness. Therefore, at the wavelength of approx. 465 nm, 520 nm and 640 nm, respectively, the transmittance of the films are close to 0, which means the blue, green and red lights are hindered to pass through the CLC films. This provides the basic proof for the privacy protection function of the multilayer films. Figure 14 shows a grey-scale diagram showing a reflection spectrum of CLC films with the combination of right-handedness and left-handedness provided by an example of the present disclosure. Figure 16 shows the projection performances of the multilayer projection film. When used in conjunction with a front projector, the generated light source is selectively reflected to an observer in front of the created invention, allowing the observer to be able to see the projected images or videos.

[0244] A mixture of red, green and blue (RGB) monochromic light is able to produce almost all colors perceived by a human. Therefore, the present disclosure provides a full-color projection screen with high gain and brightness (square 1 : red color, square 2: blue, square 3: yellow, square 4: red, square 5: white, and square 6: white), as shown in Figure 14. At the same time, the light out of the red, green and blue wavelengths are transmitted, hence, the TU / e logo positioned behind the multilayer projection film remains visible to the observer, as shown in Figure 14.

[0245] In the multilayer projection film as shown in Figure 14, every CLC layer has a thickness between 5-10 μm. The CLC film includes a polymerizable liquid crystal mixture (Δn =0.10-0.13 at 450- 650 nm wavelength), a chiral dopant that indues left-handed helix or right-handed helix, a photoinitator and a polymerization inhibitor. Six liquid crystal compositions are prepared for six layers, namely, “l-R”, “l-G”, “l-B” and "r-R", "r-G" and "r-B". A left-handed chiral dopant was used in concentrations between 5.7 and 8.1 wt.% to obtain “l-R”, “l-G” and “l-B” layers. A right-handed chiral dopant was used in concentrations between 3.8 and 5.3 wt.% to obtain "r-R", "r-G" and "r- B" layers. The photoiniator and polymerization inhibitor account for 1 .0 wt.% and 0.50 wt.%, respectively. Six layer of CLC films are formed one by one on a flexible PET film or a glass slide as substrate, with the use of a barcoater and UV light. The fabricated multilayer CLC film enables a full-color projection, as shown in Fig 14. The TU / e logo behind the film is clearly visible. The created transparent projection multilayer film exhibits a transparency (within the visible light wavelength) of 60-90%. Notably, the viewer behind the film cannot perceive the projected contents or view the scene on the film’s front side, especially when an RGB light source is used at the front side of the film. This protects the privacy space of the front side of the film while serving as an efficient transparent projection screen.

[0246] In Figure 15, a screenshot is shown of a full-color time lapse-video showing the blooming process of flowers is projected on a multilayer projection film according to the present disclosure. It demonstrates that the present disclosure enables the full-color display of the displayed video while the TU / e logo positioned behind the multilayer projection film remains visible.

Claims

CLAIMS1 . A cholesteric liquid crystal (CLC) film comprising cholesteric liquid crystals having a helical twist in its molecular structure in a clockwise or counterclockwise direction when moving along a longitudinal direction x of the helical twist, having a birefringence (Δn) of at most 0.10, at a wavelength of between 380 and 750 nm.

2. Cholesteric liquid crystal film as claimed in claim 1 , having a birefringence (Δn) of at most 0.08, at a wavelength of between 380 and 750 nm, preferably at most 0.06, more preferably at most 0.05, even more preferably from 0.01 to 0.04.

3. Cholesteric liquid crystal film as claimed in claim 1 or 2, wherein the cholesteric liquid crystal film is obtained by polymerizing a mixture comprising liquid crystal monomers and a chiral dopant; wherein at least part of the liquid crystal monomers has a H-shape structure, in particular wherein the mixture comprises from 1 to 80 wt.% of liquid crystal monomers having a H-shape structure.

4. Cholesteric liquid crystal film as claimed in claim 3, wherein the liquid crystal monomers having a H-shape structure are represented by formula (I)whereinA represents the bridging moiety, and comprises at least one -C2alkynylene- group, and optionally comprises further -C2alkynylene- groups and / or -Ar1- groups; each instance of R1, and each instance of R1'is independently selected from -H, -C1-12alkyl, -C1-12cycloalkyl, -C2-12alkenyl, -C2-12alkynyl, -halo, and -CN;Cy1, Cy1 ', Cy2, and Cy2'are each independently selected from -C1-12cycloalkylene-, and -Ar2- ; wherein each of said -C1-12cycloalkylene- optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents, independently selected from -halo, and -C1-12alkyl ; L1, L1', L2, and L2'are each independently selected from a direct bond, -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, -C2-12alkynylene-, -Ar3-, -O-, -C(O)O-, -OC(O)-, -OC(O)O-, -N=N-, and any combination of two or more thereof; wherein each of said -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, and -C2-12alkynylene- optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents, independently selected from -halo, and -C1-12alkyl ; Ar1, Ar2, and Ar3are each independently aryl; in particular Ar1, Ar2, and Ar3are each independently a 5- to 10-membered aromatic group having a single ring or multiple aromatic rings fused together, wherein said 5- to 10-membered aromatic group optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents, independently selected from -halo, -CN, and -C1-12alkyl ; S1, S1', S2, and S2'are each independently selected from a direct bond, -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, -C2-12alkynylene-, -C(O)O-, -OC(O)- , -OC(O)O-, and any combination of two or more thereof; wherein each of said -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, and -C2-12alkynylene- optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents, independently selected from -halo, and -C1-12alkyl ; andX1, X1', X2, and X2'are each independently -H, or a polymerizable end group selected from -OH=OH2, -OC(O)CH=CH2, and -OC(O)C(CH3)=CH2; wherein X1and / or X1'is a polymerizable end group; and wherein X2and / or X2'is a polymerizable end group.

5. Cholesteric liquid crystal film as claimed in any of claims 1 to 4, having a reflection band with a bandwidth (Δλ) of at most 60 nm, at a wavelength of between 380 and 750 nm, preferably at most 50 nm, more preferably at most 40 nm, even more preferably at most 30 nm, yet even more preferably at most 25 nm, yet even more preferably from 1 to 20 nm.

6. A method for preparing the cholesteric liquid crystal film as defined in any of claims 1 to 5, the method comprising the steps of: a) preparing a mixture of liquid crystal monomers, a solvent, a chiral dopant, a photoinitiator, and optionally a polymerization inhibitor; b) forming a layer of the mixture obtained in step a); and c) polymerizing the layer formed in step b) under UV light, thereby obtaining the cholesteric liquid crystal film; wherein at least part of the liquid crystal monomers in step a) has a H-shape structure, in particular wherein the mixture in step a) comprises from 1 to 80 wt.% of liquid crystal monomers having a H-shape structure.

7. Method as claimed in claim 6, wherein the liquid crystal monomers having a H-shapestructure are represented by formula (I)whereinA represents the bridging moiety, and comprises at least one -C2alkynylene- group, and optionally comprises further -C2alkynylene- groups and / or -Ar1- groups; each instance of R1, and each instance of R1'is independently selected from -H, -C1-12alkyl, -C1-12cycloalkyl, -C2-12alkenyl, -C2-12alkynyl, -halo, and -CN;Cy1, Cy1 ', Cy2, and Cy2'are each independently selected from -C1-12cycloalkylene-, and -Ar2- ; wherein each of said -C1-12cycloalkylene- optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents, independently selected from -halo, and -C1-12alkyl ; L1, L1', L2, and L2'are each independently selected from a direct bond, -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, -C2-12alkynylene-, -Ar3-, -O-, -C(O)O-, -OC(O)-, - OC(O)O-, -N=N-, and any combination of two or more thereof; wherein each of said -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, and -C2-12alkynylene- optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents, independently selected from -halo, and -C1-12alkyl ; Ar1, Ar2, and Ar3are each independently aryl; in particular Ar1, Ar2, and Ar3are each independently a 5- to 10-membered aromatic group having a single ring or multiple aromatic rings fused together, wherein said 5- to 10-membered aromatic group optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents, independently selected from -halo, -CN, and -C1-12alkyl ; S1, S1', S2, and S2'are each independently selected from a direct bond, -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, -C2-12alkynylene-, -C(O)O-, -OC(O)- , -OC(O)O-, and any combination of two or more thereof; wherein each of said -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, and -C2-12alkynylene- optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents,independently selected from -halo, and -C1-12alkyl; andX1, X1', X2, and X2'are each independently -H, or a polymerizable end group selected from -OH=OH2, -OC(O)CH=CH2, and -OC(O)C(CH3)=CH2; wherein X1and / or X1'is a polymerizable end group; and wherein X2and / or X2'is a polymerizable end group.

8. Method as claimed in claim 6 or 7, comprising the further step of homogenizing the mixture obtained in step a), such as by heating and or stirring, before forming the layer of the mixture in step b).

9. Method as claimed in any of claims 6 to 8, wherein forming the layer of the mixture in step b) is performed by bar coating.

10. A multilayer projection film comprising a stack of at least three layers of cholesteric liquid crystal films as defined in any of claims 1 to 9.1 1 . Multilayer projection film as claimed in claim 10, wherein the stack comprises three layers of right-handed cholesteric liquid crystal films.

12. Multilayer projection film as claimed in claim 10, wherein the stack comprises three layers of left-handed cholesteric liquid crystal films.

13. Multilayer projection film as claimed in claim 1 1 , wherein the stack further comprises three layers of left-handed cholesteric liquid crystal films.

14. Multilayer projection film as claimed in any of claims 10 to 13, wherein the stacked layers are contiguous.

15. Multilayer projection film as claimed in any of claims 10 to 14, wherein each layer of CLC film has a reflection band with a bandwidth (Δλ) of at most 60 nm, at a wavelength of between 380 and 750 nm, preferably at most 50 nm, more preferably at most 40 nm, even more preferably at most 30 nm, yet even more preferably at most 25 nm, yet even more preferably from 1 to 20 nm.

16. Multilayer projection film as claimed in any of claims 10 to 15, having a transmittance of light at wavelengths from 425 to 485 nm, from 495 to 555 nm, and from 620 to 680 nm, of less than 10%, preferably less than 5%, more preferably less than 1 %, even more preferably less than 0.1 %.

17. Multilayer projection film as claimed in any of claims 10 to 16, further comprising a quarter-wave (λ / 4) plate arranged for converting linearly polarized light, such as emitted by a projector, into right-handed or left-handed circularly polarized light.

18. Multilayer projection film as claimed in any of claims 10 to 17, further comprising a linear polarizer arranged for converting unpolarized light waves into linearly polarized light.

19. A method for preparing the multilayer projection film as defined in any of claims 10 to 18, the method comprising the steps of: a) preparing a mixture of liquid crystal monomers, a solvent, a chiral dopant, a photoinitiator, and optionally a polymerization inhibitor; b) forming a layer of the mixture obtained in step a); c) polymerizing the layer formed in step b) under UV light, thereby providing a layer of CLC film; and d) repeating steps a) to c) an appropriate number of times for each individual layer of CLC film to obtain the multilayer projection film, wherein each subsequent layer of CLC film is formed on top of the previous layer of CLC film; wherein for each layer of right-handed CLC film, a right-handed chiral dopant is used; wherein for each layer of left-handed CLC film, a left-handed chiral dopant is used; and wherein at least part of the liquid crystal monomers in step a) has a H-shape structure, in particular wherein the mixture in step a) comprises from 1 to 80 wt.% of liquid crystal monomers having a H-shape structure.

20. Method as claimed in claim 19, wherein the liquid crystal monomers having a H-shape structure, are represented by formula (I)whereinA represents the bridging moiety, and comprises at least one -C2alkynylene- group, and optionally comprises further -C2alkynylene- groups and / or -Ar1- groups; each instance of R1, and each instance of R1'is independently selected from -H, -C1-12alkyl, -C1-12cycloalkyl, -C2-12alkenyl, -C2-12alkynyl, -halo, and -CN;Cy1, Cy1 ', Cy2, and Cy2'are each independently selected from -C1-12cycloalkylene-, and -Ar2-; wherein each of said -C1-12cycloalkylene- optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents, independently selected from -halo, and -C1-12alkyl; L1, L1', L2, and L2'are each independently selected from a direct bond, -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, -C2-12alkynylene-, -Ar3-, -O-, -C(O)O-, -OC(O)-, - OC(O)O-, -N=N-, and any combination of two or more thereof; wherein each of said -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, and -C2-12alkynylene- optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents, independently selected from -halo, and -C1-12alkyl ; Ar1, Ar2, and Ar3are each independently aryl; in particular Ar1, Ar2, and Ar3are each independently a 5- to 10-membered aromatic group having a single ring or multiple aromatic rings fused together, wherein said 5- to 10-membered aromatic group optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents, independently selected from -halo, -CN, and -C1-12alkyl ; S1, S1', S2, and S2'are each independently selected from a direct bond, -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, -C2-12alkynylene-, -C(O)O-, -OC(O)- , -OC(O)O-, and any combination of two or more thereof; wherein each of said -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, and -C2-12alkynylene- optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents, independently selected from -halo, and -C1-12alkyl ; andX1, X1', X2, and X2'are each independently -H, or a polymerizable end group selected from -OH=OH2, -OC(O)CH=CH2, and -OC(O)C(CH3)=CH2; wherein X1and / or X1'is a polymerizable end group; and wherein X2and / or X2'is a polymerizable end group.21 . A transparent substrate comprising the cholesteric liquid crystal film as defined in any of claims 1 to 5, or as prepared by the method as defined in claims 6 to 9.

22. A transparent substrate comprising the multilayer projection film as defined in any of claims 10 to 18, or as prepared by the method as defined in claim 19 or 20.

23. Transparent substrate as claimed in claim 22, wherein the layers of the multilayer projection film are stacked on the surface of the transparent substrate.

24. Transparent substrate as claimed in any of claims 21 to 23, wherein the transparent substrate has a transmittance of light at wavelengths from 380 to 750 nm of at least 90%,preferably at least 95%.

25. Liquid crystal monomer for preparing a cholesteric liquid films as defined in any of claims 1 to 5, or a multilayer projection film as defined in any of claims 10 to 18, wherein the liquid crystal monomer is represented by formula (I)whereinA represents the bridging moiety, and comprises at least one -C2alkynylene- group, and optionally comprises further -C2alkynylene- groups and / or -Ar1- groups; each instance of R1, and each instance of R1'is independently selected from -H, -C1-12alkyl, -C1-12cycloalkyl, -C2-12alkenyl, -C2-12alkynyl, -halo, and -CN;Cy1, Cy1 ', Cy2, and Cy2'are each independently selected from -C1-12cycloalkylene-, and -Ar2- ; wherein each of said -C1-12cycloalkylene- optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents, independently selected from -halo, and -C1-12alkyl ; L1, L1', L2, and L2'are each independently selected from a direct bond, -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, -C2-12alkynylene-, -Ar3-, -O-, -C(O)O-, -OC(O)-, - OC(O)O-, -N=N-, and any combination of two or more thereof; wherein each of said -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, and -C2-12alkynylene- optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents, independently selected from -halo, and -C1-12alkyl ; Ar1, Ar2, and Ar3are each independently aryl; in particular Ar1, Ar2, and Ar3are each independently a 5- to 10-membered aromatic group having a single ring or multiple aromatic rings fused together, wherein said 5- to 10-membered aromatic group optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents, independently selected from -halo, -CN, and -C1-12alkyl ; S1, S1', S2, and S2'are each independently selected from a direct bond, -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, -C2-12alkynylene-, -C(O)O-, -OC(O)- , -OC(O)O-, andany combination of two or more thereof; wherein each of said -C1-12alkylene-, -C1-12cycloalkylene-, -C2-12alkenylene-, and -C2-12alkynylene- optionally comprises one or more heteroatoms selected from N, O and S and / or is optionally and independently substituted with one or more substituents, such as from 1 to 3 substituents, independently selected from -halo, and -C1-12alkyl ; andX1, X1', X2, and X2'are each independently -H, or a polymerizable end group selected from -OH=OH2, -OC(O)CH=CH2, and -OC(O)C(CH3)=CH2; wherein X1and / or X1'is a polymerizable end group; and wherein X2and / or X2'is a polymerizable end group.

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