Patent Application
20250037897
This application claims the benefit of priority of Poland Patent Application No. P445711 filed on Jul. 30, 2023, the contents of which are incorporated by reference as if fully set forth herein in their entirety.
The subject of the invention is a method of controlling domains of organic compounds exhibiting conformational chirality by controlling the fronts of their phase transformations. The control enables obtaining arbitrarily large areas with a selected helicity, as well as arbitrary patterns composed of domains with opposite helicities, which allows recording information in two-dimensional space.
Mesogenic compounds (i.e. those that form liquid crystalline phases, LC) are widely used in many new technologies such as displays [1], temperature sensors, [2], etc.
From a practical point of view, liquid crystalline phases that exhibit chirality are of particular interest [3,4]. Chirality is a property of three-dimensional macroscopic objects, molecules and supramolecular aggregates, which lack planes of symmetry or a centre of symmetry and are therefore not identical to their mirror image. In the case of organic molecules, chirality is of great importance when it comes to the properties of compounds, with particular emphasis on optical properties, i.e. interactions with electromagnetic waves, which are also chiral and can be left- or right-handedly polarised.
Most often chirality is defined at the stage of compound synthesis by the spatial arrangement of atoms and covalent bonds and cannot be changed later, and is associated, for example, with the presence of an asymmetric carbon atom, i.e. carbon bonded to four different substituents. However, there are such liquid crystals that even if the mesogenic compound does not have asymmetric carbon atoms, at the stage of crystallisation (at the stage of sample cooling, during phase transition) the shape of the molecule adopts a chiral conformation. A similar phenomenon is observed for quartz crystals [5] composed of achiral tetrahedral SiO4 units. Very often, the proximity of a molecule with a specific conformation forces the next ones to adopt the same conformation. This phenomenon is called chirality synchronisation and is particularly important for the technique developed here [5]. This phenomenon leads to the formation of morphologically chiral supramolecular systems in the shape of helical nanofilaments, helical microfilaments or nanotubes composed of right- or left-handed coiled layers [4]. These morphologically chiral entities have cross-sections with diameters of the order of tens or hundreds of nanometres [4,6]. There are many mesogenic compounds that exhibit such properties, e.g. 1,3-phenylene bis(4-(4-nonyloxyphenyliminomethyl) benzoate) (and analogues of this compound), α,ω-bis(4-alkoxy-azobenzene-40-carbonyloxy)alkene, or N, N′-bis [2-hydroxy-5-(4′-n-tetradecylphenylazo)benzylidene]-4-nitro-1,3-phenylenediamine [4].
In typical self-assembly conditions of this type of mesogenic compounds (i.e. without adding any external chiral factors), a statistically equal number of right-handed and left-handed helices are formed, but they are not distributed completely randomly—micrometric-sized areas are formed in which all helices adopt one handedness—these are the so-called chiral domains. The size and shape of chiral domains depend largely on the type of mesogenic compound used, as well as on the rate and conditions of the crystallisation process. Such samples are conglomerate in nature or, for two-dimensional systems, a mosaic, composed of randomly arranged domains, containing supramolecular systems with a given sense of handedness.
Due to the different properties of chiral LC structures with opposite handedness, methods for controlling the chirality of morphologically chiral liquid crystal phases are sought, leading to obtaining materials with a dominant sense of one of the handednesses in the entire sample volume. So far, the following methods have been developed to obtain the enantiomeric excess of one of the handednesses:
Due to the different properties of chiral LC structures with different orientation in space, ways are sought to control the orientation of chiral individuals in morphologically chiral LC phases, e.g. by:
Due to the different properties of chiral LC structures with different morphology, ways are sought to control it:
Examples have long been known in which the addition of a chiral compound to a non-chiral liquid crystal phase causes the formation of a chiral phase [13]. A good example of this is the research conducted by Prof. Smalyukh, whose group focuses on the study of defects that imitate the configuration of fields in particle physics, optics or cosmology with their topology [14]. The source of these defects in the liquid crystal forming the nematic phase may be chiral particles such as helices or springs [15]. Moreover, such defects in the chiral liquid crystal phase may show interesting interactions with light and be used to control it [16].
The use of light in the production of chiral liquid crystal phases is not limited to the induction of chirality using circularly polarised light—the use of photoalignment patterns allows for the control of the helical pitch of mesogenic compounds for the production of materials that selectively reflect chiral light [17]. The use of a substrate with a specific pattern, on which a chiral liquid crystal is then placed, also allows for the control of the arrangement of the mesogenic compound molecules [18].
From the point of view of the state of the art, it is worth mentioning that by controlling the organisation or polymerisation process, it is possible to obtain thin films of organic materials with a controlled, arbitrary distribution of chiral domains:
The disadvantage of these methods is the use of a chiral inducer (materials of constitutional chirality) or circularly polarised light, which imposes the requirement to work with enantiomerically pure organic compounds, causing an increase in the cost of this type of methods. The increase in costs is related to the requirement to synthesise two enantiomers or to separate them from a mixture of two enantiomers if the synthetic methods did not lead to a product with the selected chirality. In addition, selective spatial deposition of both enantiomers on the substrate is required. In the case of circularly polarised light, it is necessary to use spatial masks to selectively illuminate selected fragments of the material.
Control over the chirality of mesogenic compounds is important due to the different properties of interaction with the light of chiral systems, which is of particular importance in optics, where manipulation of light polarisation plays an irreplaceable role in many technological implementations of mesogenic compounds and is the basis of key technologies of the 19th century such as displays. Morphologically chiral liquid crystal phases are intensively studied due to their possible use as:
A particularly interesting application is the recording of information, e.g. patterns aimed at preventing forgery. Below, we discuss in detail the materials used for these purposes, which were based on morphologically chiral LC phases, and more broadly, chiral LC phases [31]. Control over the chirality of mesogenic compounds is important due to the different properties of chiral systems interacting with light, which is of particular importance in optics, where manipulation of light polarisation plays an irreplaceable role in many technological implementations of mesogenic compounds and is the basis of key technologies of the 19th century, such as displays. The use of helical, oriented liquid crystal phases with controlled parameters for manipulating light polarisation, allows the production of materials capable of 100% reflection of light with a given circular polarisation [32]. Moreover, liquid crystal compounds forming chiral phases such as helices, when the helix pitch is matched to the wavelength of light, can form three-dimensional photonic crystals exhibiting a photonic energy gap [33].
Due to their application potential, 2D thin films are a frequently used form in which liquid crystal materials are used. This is the most optimal form in terms of maximizing the surface area while maintaining a constant thickness and therefore finds a number of applications, e.g. in optics.
There is a great need in the field for new methods of recording information.
The aim of the present invention was therefore to develop a new method of recording information using the spatial arrangement of chiral domains of organic compounds through controlled synchronisation of conformational chirality.
Therefore, the subject of the present invention is a method for controlling the spatial arrangement of domains of mesogenic compounds exhibiting the ability to synchronise chirality by controlled synchronisation of conformational chirality, characterised in that the area of a thin film of a compound forming a conglomerate of domains, is heated above the isotropisation temperature of a given compound, to obtain a specific chirality in a given area, and the shape of the heated area corresponds to a selected pattern, allowing control of the crystallisation front, wherein the heating is carried out by means of area illumination with laser light of a wavelength corresponding to the high absorbance of the melted compound and/or area heating of a substrate on which the thin film of the compound is placed and/or by area illumination with laser light of a wavelength corresponding to the high absorbance of a dye added to the film.
Preferably, the laser light absorption causes the temperature of the thin organic film to be raised from the temperature to which the film is preheated to at least the temperature of the phase transition of the organic compound to the isotropic phase (TISO).
Preferably, the substrate is a transparent substrate, such as a glass plate, quartz glass, sapphire, polymer foil.
Preferably, the heating is carried out linearly to obtain a crystallisation wave which starts from the selected domain with the desired handedness, then passes to the area with domains with undesired or mixed handedness, which as a result of chirality synchronisation initiates crystallisation of the domain with handedness in accordance with the selected, adjacent domain.
Preferably, the heating is carried out pointwise to obtain a crystallisation wave which starts its travel pointwise, without contact with the crystallized area, in the centre of the area and moves radially outward.
Preferably, the heating of a given area is repeated until the desired chirality is obtained.
Preferably, for areas with a size exceeding the maximum illuminated area at one time of a thin film of an organic compound exhibiting the ability to synchronise chirality, said method is controlled by applying the following steps, in which:
The subject of the invention is illustrated in the drawings, where:
One of the proposed applications of the method according to the invention is the creation of difficult to counterfeit and at the same time easy to verify patterns aimed at preventing forgery. Mesogenic compounds are often proposed for this purpose due to their optical properties, which are relatively easy to modify and the fact that optical verification is relatively convenient and widely used. Usually, in the methods proposed in the literature, it is assumed to create a specific pattern (characteristic image, barcode or QR code) on the surface of a thin liquid crystal film in such a way that this pattern is visible only under strictly defined optical conditions, for example:
In the method according to the present invention, the obtained pattern consists of the same phase as the rest of the area but with the opposite handedness, which is the first such security feature. Due to the fact that the areas within the pattern differ only in handedness, it is not possible to see this pattern without using polarisers. Moreover, to verify the authenticity of the pattern, two linear polarisers are sufficient (which are relatively cheap, what is more, most currently used computer monitors emit linearly polarised light): when placing the sample between crossed polarisers, the pattern will be revealed when the polarizers are slightly uncrossed—i.e. one of the areas with a specific handedness will become darker and the other, with the opposite handedness, will become brighter. When changing the direction of the uncrossing of the polarisers, the change in brightness will be of exactly the same intensity, but in the opposite direction, which is very easy to verify with the naked eye.
The present inventors have unexpectedly found that the mechanism of chirality synchronisation using a laser system illuminating the LC material enables control over the handedness of chiral domains on a micrometre scale. The proposed approach allows for an area-wise change of the helicity of chiral domains of a thin film of the material. An arbitrarily selected area of a thin film of a morphologically chiral liquid crystal, forming a conglomerate of domains, is heated above the isotropisation temperature of a given mesogenic compound (e.g. 172° C. for the P9OPIMB compound) by means of area illumination with laser light at a wavelength corresponding to the high absorbance of the melted mesogenic compound (usually the optimal values are in the intermediate and near ultraviolet range, 200-400 nm as organic compounds usually absorb this wavelength range well, however, it can also be the visible range, 400-800 nm; the wavelength is determined by the structure of the compound and its organisation in the films). In order to enable the illumination of an area of any shape using a laser built into the microscope, a spatial modulator—a system of miniature mirrors (digital micromirror device, DMD) was used.
This approach is characterised by a high degree of versatility—the beam reflected from the DMD can illuminate any area in a dynamic manner, i.e. the shape of the illuminated area can change depending on time. This is particularly important, as it allows for controlling the melted area in real-time, by controlling the shape of the illuminated area and the intensity of light incident on the sample. Thanks to these dynamic changes in the beam shape, we can melt the organic compound in a controlled manner, and consequently control the local melting of the material and its crystallisation. Controlling crystallisation here means the possibility of arbitrarily shifting the crystallisation front of the organic compound. Due to the phenomenon of chirality synchronisation, the unmelted material will give the sense of chirality to the molecules crystallising in its immediate vicinity. We therefore have the freedom to choose the melted area and the area that we leave unmelted, which gives the possibility of imposing handedness on the areas subjected to illumination. By melting subsequent domains, it is possible to obtain arbitrarily (freely) designed patterns.
The subject of the invention is therefore a method of recording information in the form of patterns built from chiral domains of an organic compound by using the phenomenon of chirality synchronisation. Preferably, in cases where the isotropisation temperature (TISO) of the mesogenic compound is relatively high (>70° C.), a heated substrate should be used to bring the sample temperature closer to the isotropisation temperature. Preferably, when the substrate temperature is around (TISO)−20° C. Despite the applied heating of the sample, the possibility of observing the material in transmission mode must be maintained over the entire area where the heating process is currently being carried out. For this purpose, a commercially available heating stage in the form of a metal heating block with a small hole in the middle, enabling the observation of the sample in transmission mode can be used.
For a given liquid crystal compound to be remelted using the method of the present invention, the following conditions must be met:
There are two types of approaches to forcing a specific handedness of helices in a selected area:
To better understand the process, attention should be paid to the crystallisation wave running along with the changing illumination area, i.e. the shifting isothermal area being a closed linear shape, for which the temperature corresponds to the phase transition temperature of the mesogenic compound (
To understand the ongoing process more easily, it is necessary to pay attention to the crystallisation wave along with the changing lighting area, i.e., the sliding isothermal area being a closed linear shape, for which the temperature corresponds to the phase transition temperature of the mesogenic compound (
In the first approach, we allow the crystallisation wave to start its course from a selected, neighbouring domain with the desired handedness, then passing through the entire melted area, and, as a result of the chirality synchronisation effect, the crystallisation of the domain with handedness in accordance with the selected, neighbouring domain is initiated. In the second approach, the evolution of the illuminated area proceeds in such a way that the crystallisation wave starts its course without contacting the crystallised area, i.e. it starts pointwise in the centre and starts running radially outward. This action forces the creation of a new chiral domain with a random handedness. In the case when the randomly selected domain has an undesirable handedness, the process can be repeated. The third approach involves moving the illuminated area through the majority of the sample in such a way that the crystallisation line moves perpendicularly to the movement direction of the heated area.
The top row (A1, A2, and A3, respectively) shows remelting using nucleation from an adjacent domain with the desired handedness (here marked with an “x”). The middle row (B1, B2, and B3, respectively) shows remelting with the formation of a new domain without contact with adjacent domains. The bottom row (C1, C2, and C3, respectively) shows the method of remelting by continuously moving the heated area through the sample. In each of the three cases, it often happens that more than one domain nucleates during remelting. To minimise this phenomenon, the speed of the crystallisation wave during remelting should be reduced, but it may not be possible to completely eliminate this phenomenon. If this phenomenon occurs, remelting in a given area should be repeated until a single domain with the desired handedness is obtained.
A key element of the invention is the ability to determine the rotation, shape and position of chiral domains in real-time. For this purpose, the microscopic system (
Since the area that can be remelted at one time is limited by the size of the DMD, in order to take control over the handedness of the domains over a larger area, zone remelting is performed in the sense of area by area. The maximum size of the area remelted at a given moment depends on the laser power, the magnification of the microscope objective used and the absorbance value of the laser light by the liquid crystal material. In typical conditions, a 20× objective was used and the selected area was uniformly illuminated. The sample is placed on a motorised translation stage, capable of precise change of position in the XY axis, thanks to which moving between subsequent areas of the sample can be performed automatically, allowing control over chirality over an arbitrarily large area (limited only by the capabilities of the translation stage used). For this purpose, a map of areas is entered into the program memory, according to which the remelting of each area is then performed. Such a map can be, for example, an image with a specific resolution, in which one pixel corresponds to one area and the pixel colour (black or white) determines the handedness of the domains. In order to ensure the continuity of the area with a controlled handedness of the domains when melting large areas of the sample, the second type of melting (B1-B3) was used to a large extent, with the shape of the laser spot being a square that completely filled the maximum area melted at once.
Thanks to this, the successive melted areas connect with each other to form an uninterrupted, large area. If the percentage of the surface covered with domains of the desired handedness is large in the given area, i.e. exceeds a certain set value (this value was usually in the range >50% & <70%, most often 60%), the first type of melting is performed, where the shape of the projected laser was a circle with a diameter smaller than half of the side of the entire melted area. If the desired domains constitute at least 90% of the surface of the entire area (values in the range >85% & <95% were used), it is assumed that it is possible to proceed to melting the next area. The decision scheme used when melting larger areas is shown in
1. The possibility of recording an arbitrary pattern built of chiral domains of opposite handedness. 2. Simplification of the pattern recording process associated with the use of only achiral compounds.
The above and other advantages and benefits of the present invention will become more apparent based on the examples of embodiments of the invention presented below.
In order to prepare a thin film sample of liquid crystal material, 1,3-phenylenebis [4-(4-oleyloxyphenyliminoethyl)benzoate] was coated onto a glass plate of size 10×10 mm and thickness <400 μm. Then, in order to maintain a specific sample thickness, glass beads of diameter 10.1 μm were placed on the sample and the whole was covered with another glass plate. Then, such a system was heated to the isotropisation temperature, which is selected for a specific mesogenic compound and here it was 140° C. and it was cooled to room temperature (heating time and cooling time are selected to enable the formation of a domain conglomerate, in this case it was about 2 minutes), while during cooling the sample was pressed against the substrate to ensure a uniform thickness of the thin LC film between the glass plates. The sample obtained in this way has randomly distributed domains of small size. Analogous results are obtained for glass plates of any size larger than the later melted area, for glass plates with a thickness in the range of 400-10000 μm, and using beads (separators) with sizes in the range of 100 nm-50 μm.
The following elements were added to the existing Zeiss microscope: a motorised translation stage in the XY axis, placed at the imaging location of the microscope; a rotating linear polariser based on the ELL14 from Elliptec, just above the light source under the translation stage, as well as in front of the digital camera; a heatable heating plate based on a glass plate with an ITO layer, placed on the translation stage; an automatically removable dichroic mirror located on the optical path at the point where the light beam is collimated; the DMD from the projector, located in such a place that the DMD image can be placed in a parallel beam of light in the microscope using a dichroic mirror; a laser whose parameters (power and wavelength) are selected for a specific mesogenic compound undergoing the melting process, so as to ensure its isotropisation; in this case, a 16 W laser with a wavelength of 450 nm was used. The laser was positioned so as to illuminate the DMD.
In order to perform domain remelting to obtain a given pattern consisting of domains with the opposite sense of chirality (chiral domains pattern), a sample consisting of an organic material meeting the process conditions is placed in a microscopic system on a transparent heating plate. It is then thermostated to a temperature selected for a given type of material, so that it is below the isotropisation temperature, so that it allows for obtaining a chirality map, as well as for a local increase in temperature during laser illumination (so that isotropisation occurs locally). For the compound 1,3-phenylenebis [4-(4-oleyloxy-phenyliminonetyl)benzoate] used, this was a temperature of 104° C. Using an optical system, the arrangement of chiral domains on the sample is examined and a chirality map is created. Then, the algorithm, based on the obtained chirality map, selects the type and location of laser illumination in order to perform domain remelting. The final effect of remelting is to obtain a previously assumed pattern of chiral domains, loaded into the program memory. In this particular example, the goal was to obtain a checkerboard pattern, composed of domains with opposite handednesses (
In order to perform the melting of domains exhibiting plasmonic chirality, a sample consisting of an organic material meeting the process conditions and plasmonic nanoparticles (any that can be mixed with the organic matrix used, in this case metallic, spherical gold nanoparticles with a diameter of 15 nm) is placed in a microscopic system on a transparent heating plate and then thermostated to a temperature selected for a given type of material, so that it is below the isotropisation temperature, so that it allows for obtaining a chirality map, as well as for a local increase in temperature during laser illumination (so that isotropisation occurs locally). For the mixture of 1,3-phenylenebis [4-(4-oleyloxy-phenyliminonetyl)benzoate] and spherical gold nanoparticles used, it was 104° C. Using an optical system, the arrangement of chiral domains on the sample is examined and a chirality map is created. Then, based on the obtained chirality map, the algorithm selects the type and location of laser illumination in order to perform domain remelting. The final effect of remelting is obtaining a previously assumed pattern of chiral domains, uploaded to the program memory. In this particular example, the goal was to obtain a pattern composed of domains with one selected handedness. Each domain exhibits chiral properties in the range of electromagnetic wavelengths with lengths characteristic of the organic compound and nanoparticles used.
In order to perform the melting of domains exhibiting plasmonic chirality, a sample consisting of an organic material meeting the process conditions and an additive of an organic compound that exhibits photoluminescent properties (e.g. 2% by weight 1,1,2,2-tetraphenylethene) is placed in a microscopic system on a transparent heating plate and then thermostated to a temperature selected for a given type of material, so that it is below the isotropisation temperature so that it allows for obtaining a chirality map, as well as for a local increase in temperature during laser illumination (so that isotropisation occurs locally). For the mixture of 1,3-phenylenebis [4-(4-oleyloxy-phenyliminonetyl)benzoate] and 2% by weight 1,1,2,2-tetraphenylethene, this was 104° C. Using an optical system, the arrangement of chiral domains on the sample is examined and a chirality map is created. Then, the algorithm, based on the obtained chirality map, selects the type and location of laser illumination in order to perform domain remelting. The final effect of remelting is obtaining a previously assumed pattern of chiral domains, uploaded into the program memory. Each domain exhibits the emission of circularly polarised light.
| Number | Date | Country | Kind |
|---|---|---|---|
| P445711 | Jul 2023 | PL | national |
