Devices emitting multiple light wavelengths based on chiral band-edge enhanced organic light-emitting diodes

Abstract

A light-emitting device is described. The light-emitting device includes a single-emitting photonic crystal having an electroluminescent material disposed therein. The single-emitting photonic crystal includes successive layers of chiral liquid crystal polymer. The electroluminescent material is localized in one of the layers of chiral liquid crystal polymer. At least one of the successive layers of chiral liquid crystal polymer includes a chiral liquid crystalline charge carrier transport polymer. The single-emitting photonic crystal further includes a second light-emitting material, where energy emitted from the electroluminescent material induces the second light-emitting material to emit light, and where light emitted from the light-emitting device is a mixture of light emitted from the electroluminescent material and light emitted from the second light-emitting material.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Patent Application No. 63 / 313,794, filed February 25, 2022, the entire contents of which are incorporated herein by reference. [Background technology]

[0002] US Patent 10,727,421 discloses a light-emitting photonic crystal device (referred to as C-OLED) in which an organic light-emitting diode (OLED) is embedded as a single region or layer in a single one-dimensional photonic crystal. Thus, the OLED and other organic material layers that constitute the one-dimensional photonic crystal all contain chiral liquid crystal polymer materials. It is an essential property of chiral liquid crystals that they function as one-dimensional photonic crystals that are fluorescent dyes when they are uniformly aligned. US Patent 10,727,421 explains this as follows: The alignment structure of chiral liquid crystals is shown in Figure 1. Rod-like liquid crystal molecules 110 in layer 120 tend to align with their long axes pointing in one direction parallel to an axis called director 130. In aligned nematic liquid crystals, the director always points in the same direction. However, due to the asymmetric shape of some of the molecular components, in chiral liquid crystals, as light passes downward through the material along axis 140, as shown in FIG. 1, the direction of director 130 rotates in a swept-out helical fashion. Thus, the individual liquid crystal molecules bond together into a helical structure. Due to the anisotropic electronic polarization within the individual molecules, light of the proper circular polarization passing through the liquid crystal material will have a much higher refractive index when its corresponding electric vector is parallel to the long axis of the molecule than when the electric vector is perpendicular to the long axis of the molecule. For the proper wavelength of light, the corresponding electric vector of light of the opposite circular polarization (e.g., dextrorotatory vs. levorotatory) will rotate to follow the helical structure of the liquid crystal, so no change in refractive index will be seen as the light passes upward through the chiral liquid crystal structure. Thus, circularly polarized light of the proper handedness propagating parallel to axis 140 will experience a periodic variation in refractive index as the long axis of the light varies between parallel and antiparallel to the electric vector of the light as it passes through the molecules. In this manner, the ensemble of chiral liquid crystal molecules acts as a one-dimensional photonic crystal material for one circular polarization of light along axis 140 . The functioning of C-OLED devices relies on the formation of a "stop band" within the photonic crystal. A stop band is a range of light wavelengths for which there is no solution to the wave equation for the propagation of light. In other words, luminescent molecules embedded in a photonic crystal cannot emit light in the direction of the refractive index change within the photonic crystal structure. For this type of photonic crystal, the central wavelength of the stop band is given by: λ c =(n e -n o )P / 2 In the formula, λ c is the central wavelength of the stopband, and n e is the extraordinary refractive index of the nematic liquid crystal polymer, n0 is the ordinary refractive index of the nematic liquid crystal polymer, and P is the pitch of the helical structure of the chiral liquid crystal polymer.

[0003] The light emission function of band-edge enhanced OLED devices relies on the fact that in these devices, the edge of the stop band 210 (usually the short wavelength edge 220 at this time) illustrated in FIG. 2 overlaps with the emission spectrum band of the electroluminescent material in the OLED structure. As explained in U.S. Pat. No. 10,727,421 and shown in FIG. 2, it is a property of photonic crystals that the density of states at the band edge wavelength of the stop band associated with the photonic crystal is significantly higher than the density of states for the same wavelength in air or vacuum. As a result, the emission of the electroluminescent material is significantly enhanced over other media. Also, a large portion of the light emitted in the band edge states or modes is retained within the photonic crystal structure, which exposes the photoluminescent molecules to high luminous flux light at the band edge wavelength. This retained intense light induces further emission from other electroluminescent material molecules in an excited state due to electrical excitation. Because the light emitted in the band-edge modes of propagation is restricted to emitting in a narrow band at an angle nearly normal to the surface of the C-OLED, and because stimulated emission replicates the propagation modes of stimulated optical emission, light is emitted from the C-OLED in a narrow cone at an angle nearly normal to the C-OLED surface, allowing for nearly complete fluorescent extraction of light from the C-OLED, making it significantly more energy efficient than conventional OLEDs.

[0004] The very high energy efficiency and collimated light emission of C-OLEDs are highly desirable for many applications. The narrow spectral emission band of these devices can also be highly desirable when highly saturated colors are required in the emission. However, the narrow spectral emission band is problematic when C-OLEDs are intended to be used in applications requiring white light. Several solutions to this problem have already been explored. The first is to place multiple C-OLEDs emitting different colors adjacent to each other on the same substrate. The problem with this approach is that it is complex to manufacture and very difficult to produce illumination optics that blend multiple colors so that the chromaticity of the light is uniform over the entire range of emission angles. US Patent No. 10,680,185 describes a C-OLED-based device in which the emitting surface of a C-OLED that emits short wavelength light (e.g., blue or violet) is coated with a luminescent material. The light from the C-OLED is absorbed by the photoluminescent material, which produces the photoluminescent emission. The photoluminescent material used can emit white light. In this case, the emission is in a wide angle cone, which may not be desirable for some applications. In addition, if some of the short-wavelength light from the C-OLED leaks into the white photoluminescent top layer, the emission uniformity with respect to the emission angle may be compromised. If the white photoluminescent material is coated thick enough to prevent the C-OLED emission from leaking out, the light absorption in the photoluminescent material may impair the energy efficiency of the device. It is necessary for C-OLED-based devices to emit light at multiple wavelengths (eg, white light) over a narrow angle cone and with uniform chromaticity over that range of emission angles. Summary of the Invention

[0005] The embodiment includes a light-emitting device including a single-emitting photonic crystal having a photoluminescent material disposed therein. The single-emitting photonic crystal includes successive layers of chiral liquid crystal polymer. The electroluminescent material is localized in one of the layers of chiral liquid crystal polymer. At least one of the successive layers of chiral liquid crystal polymer includes a chiral liquid crystalline charge carrier transport polymer. The single-emitting photonic crystal further includes a second light-emitting material, where the energy emitted from the electroluminescent material induces the second light-emitting material to emit light, and the light emitted from the light-emitting device is a mixture of the light emitted from the electroluminescent material and the light emitted from the second light-emitting material.

[0006] In order that the above-mentioned features of the present disclosure may be understood in detail, the present disclosure briefly summarized above may be described in more detail by reference to some embodiments illustrated in the accompanying drawings. However, it should be noted that the accompanying drawings are illustrative of typical embodiments and should not be construed as limiting; other effective embodiments are also contemplated. [Brief description of the drawings]

[0007] [Figure 1] 1 illustrates an alignment structure of a chiral liquid crystal according to one embodiment. [Diagram 2] 1 shows the emission of a band-edge enhanced OLED device according to one embodiment. [Diagram 3] 1 illustrates an exemplary light emitting element according to one embodiment. [Figure 4] 1 illustrates a further exemplary light emitting element according to an embodiment. [Diagram 5] 2 illustrates another exemplary light emitting element according to one embodiment. [Figure 6] 1 illustrates a chiral light-emitting electrochemical cell (C-LEC) according to one embodiment. [Figure 7] 1 shows the chemical structure of a light-emitting material according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] To facilitate understanding, the same reference numbers have been used whenever possible to designate identical elements common to the figures, it being understood that elements disclosed in one embodiment may be used to advantage on other embodiments without specific reference. FIG. 3 illustrates a series of embodiments 300 of the present invention. The device 300 includes a C-OLED similar to that described in US Pat. No. 10,727,421, but with the addition of an additional layer 307. The device is formed layer by layer on a transparent substrate 301 made of any suitable material, such as glass or transparent plastic. First, a transparent and conductive anode layer 302 is coated on the substrate, often by vacuum deposition. This anode layer may include a transparent semiconductor material such as indium zinc oxide or indium tin oxide. Next, a hole-transporting liquid crystal photoalignment layer 303 is coated on the substrate surface. US Pat. No. 7,118,787 and US Patent Application Publication No. 2011 / 0020566 disclose various materials that can be used as such a hole-transporting layer in various embodiments of chiral liquid crystal light-emitting devices. Details of the layers used for this purpose are described in US Pat. No. 10,727,421. The alignment layer 303 generates an anisotropic surface energy at the surface of the alignment layer, which aligns the liquid crystal molecules coated thereon.

[0009] The next layer that may be optionally fabricated as shown in Figure 3 is a p-type doped hole transport layer 304. The goal in fabricating this layer is to produce a relatively highly conductive film that minimizes the voltage drop between the anode and the emitter layer 306. This is accomplished by doping a monomeric chiral nematic liquid crystal hole transport material with a strong electron accepting monomeric p-type dopant. To obtain a complete photonic stopband in a relatively thin layer of chiral material, the chiral nematic monomers used to produce layer 304 shown in Figure 3, and other chiral liquid crystal materials used to form layers in the device, need to have a very high ratio of their extraordinary to ordinary refractive index, which therefore means that the long axis of the molecule is much longer than the molecule. Examples of chiral nematic mixtures containing such materials are described in U.S. Patent No. 10,727,421.

[0010] Since all chiral liquid crystal polymer layers in a device need to have matching ordinary and extraordinary indices of refraction, it may be necessary to adjust the refractive index by introducing low birefringent liquid crystal monomer materials into the mixture of materials for this layer. To produce a chiral liquid crystal polymer of the desired pitch, the monomer mixture used in producing layer 74 in Figure 7 must be doped with a chiral dopant. Examples of chiral dopants are described in U.S. Patent No. 10,727,421. Referring back to FIG. 3, the mixture of nematic liquid crystal monomers and p-type dopant(s) used to form layer 304 is cast onto photo-alignment layer 303 and the solvent is evaporated off at room temperature or elevated temperature. Once the solvent is removed, the material becomes a layer of chiral nematic liquid crystal fluid or possibly chiral nematic liquid crystal glass. The anisotropic surface energy at the top surface of layer 303 causes the molecules of the chiral nematic material at the interface between layers 303 and 304 to align where their long axes are parallel to the surface and all of the long axes of the molecules are in approximately the same direction, thereby forming the desired helical structure in layer 304. The chiral liquid crystal monomer mixture is then photopolymerized, typically with UV light, to fix the helical liquid crystal structure in place within the polymer matrix.

[0011] The next layer fabricated in a layer-by-layer process is the hole transport layer 305. The function of this layer is to transport conductive holes from the p-type doped layer 304 to the second emitter layer 306. In this way, an energy transition of the holes occurs from the highest occupied molecular orbital (HOMO) level of the conductive dopant of layer 304 to the HOMO energy level of the emitter layer 306. This layer is fabricated by casting a solution of a mixture of chiral nematic liquid crystal monomers in a manner similar to that used to fabricate layer 304, but without the p-type dopant in the mixture. After evaporating off the solvent used to inject the monomer mixture, the mixture material forms a layer of chiral nematic liquid crystal fluid or chiral nematic glass on the top surface of layer 304. The liquid crystal ordering of layer 304 provides a template such that the long axes of the molecules at the bottom surface of layer 305 are aligned parallel to the long axes of the nematic molecular cores of the polymeric material at the top surface of layer 304. In this way, the helical structure induced by the chiral properties of the materials in layers 304 and 305 continues across the interface between the two layers. Once the materials of layer 305 are properly aligned in place, they are polymerized by exposure to ultraviolet light. The chiral nematic monomeric materials used to form layer 305 may be the same materials used to fabricate layer 304, except for the p-dopant. The exact chemical structure of the molecules used and their length are determined by the requirements that the ordinary and extraordinary refractive index components of the mixtures in the two layers must match each other, and that the helical pitch must also be the same for the chiral nematic structures in the two layers. Examples of chiral nematic mixtures containing such materials are described in U.S. Pat. No. 10,727,421.

[0012] The next layer fabricated in a layer-by-layer process is the second emitter layer 306. The second emitter layer 306 of this device may consist solely of monomeric nematic emissive materials doped with chiral additives to produce a helical structure of appropriate pitch. Suitable emissive nematic materials may be electroluminescent materials as disclosed in U.S. Pat. No. 10,727,421 and U.S. Patent Application Serial No. 16 / 490,146. Preferably, these materials are inherently hole transporting. However, the material formulation in this layer more preferably utilizes an emissive dopant doped into a host consisting of a mixture of monomeric chiral nematic materials. This approach has the advantage that the dopant concentration may be selected to minimize self-absorption of light by the dopant. Non-liquid crystal emitter materials such as highly quantum efficient phosphorescent emitters and laser dyes may be utilized as dopants while maintaining the desired helical structure of the chiral host. The emissive dopant is preferably derivatized with one or more crosslinking groups. Some suitable dopants are described in U.S. Patent No. 10,727,421. As with layer 305, the nematic molecular order of the underlying nematic polymer layer (in this case layer 305) serves to properly align the molecules of layer 306 before they are photopolymerized. Light coupled into the helical photonic crystal structure has its electric vectors all oriented parallel to the plane of the device layers. As a result, this light interacts only with excited molecules whose transition moments are also approximately in the plane of the device. Thus, luminescent material in layer 306 preferentially oriented with their molecular transition moments in the device plane maximizes device energy efficiency (external quantum efficiency) when used in the emitter layers of devices according to embodiments of the present invention.

[0013] In various embodiments, the second emitter layer 306 formed on the hole transport layer 305 comprises an emissive material having an emission spectrum and an absorption spectrum. The stop band of the photonic crystal comprising layers 304-309 is tuned by varying the pitch of the chiral nematic structure so that the long wavelength band edge of the photonic crystal stop band overlaps with the emission spectrum of the emissive material comprising layer 306. When device 300 is electrically activated, the peak radiance wavelength of the long wavelength band edge emission measured perpendicular to the device surface is at a wavelength where the free space emission of the emissive material in layer 306 is preferably greater than ¼, and most preferably greater than ½, of the peak emission radiance of the emissive material. Also, when device 300 is electrically activated, the peak radiance wavelength of the long wavelength band edge emission occurs at a wavelength where the light absorption in a single pass through the second emitter layer is less than 1%, and preferably less than 0.5%. The luminescent material doped chiral nematic monomer mixture used to prepare the second emitter layer 306 is preferably a blend of various chiral liquid crystal components, so that the chiral liquid crystal polymer comprising layer 307 has ordinary refractive index, extraordinary refractive index and chiral pitch which vary by less than 5% from the values ​​corresponding to the same parameters in the chiral liquid crystal polymer layers 304, 305, 307, 308 and 309, and preferentially, the values ​​of these three parameters are the same in all of the layers 304-309. The materials used to prepare layer 306 may be the same as those of layer 305, except for the addition of the luminescent material.

[0014] The next layer fabricated in a layer-by-layer process is the first emitter layer 307. The first emitter layer 307 of this device may consist solely of a monomeric nematic electroluminescent material doped with a chiral additive to produce a helical structure of the appropriate pitch. Suitable electroluminescent nematic materials are disclosed in U.S. Pat. No. 10,727,421. However, the material formulation in this layer more preferably utilizes an electroluminescent dopant doped into a host consisting of a mixture of monomeric chiral nematic materials. This approach has a number of advantages, including: the dopant concentration may be selected to minimize self-absorption of light by the dopant; multiple monomeric host chiral nematic materials may be blended to produce ambipolar mixtures, i.e. mixtures with approximately equal electron and hole mobilities; and non-liquid crystal emitter materials, such as highly quantum efficient phosphorescent emitters, may be utilized as dopants while maintaining the desired helical structure of the chiral host. Suitable dopants are described in U.S. Patent No. 10,727,421 and U.S. Patent Application Serial No. 16 / 490,146. As with layer 306, the nematic molecular order of the underlying nematic polymer layer (in this case layer 306) serves to properly align the molecules of layer 307 before they are photopolymerized. The electric vectors of the light beams coupled into the helical photonic crystal structure are all oriented parallel to the plane of the device layers. As a result, the light interacts only with excited molecules whose transition moments are also approximately in the plane of the device. Thus, electroluminescent material in layer 307 preferentially oriented with their molecular transition moments in the device plane maximizes device energy efficiency (external quantum efficiency) when used in the emitter layer of a device according to an embodiment of the invention.

[0015] In various embodiments, the first phosphor layer 307 formed on top of the second phosphor layer 306 comprises a phosphor material having an emission spectrum and an absorption spectrum. The stop band of the photonic crystal comprising layers 304-309 is tuned by varying the pitch of the chiral nematic structure so that the short wavelength band edge of the photonic crystal stop band overlaps with the emission spectrum of the phosphor material comprising layer 307. When device 300 is electrically activated, the peak radiance wavelength of the short wavelength band edge emission measured perpendicular to the device surface is at a wavelength where the free space emission of the phosphor material is preferably greater than ¼, and most preferably greater than ½, of the peak emission radiance of the phosphor. Also, when device 300 is electrically activated, the peak radiance wavelength of the band edge emission occurs at a wavelength where the light absorption in a single pass through the first phosphor layer is less than 1%, and preferably less than 0.5%. The phosphor-doped chiral nematic monomer mixture used to prepare the first phosphor layer 307 is preferably a blend of various chiral liquid crystal components, so that the chiral liquid crystal polymer of which layer 307 is composed has ordinary refractive index, extraordinary refractive index and chiral pitch which vary by less than 5% from the values ​​corresponding to the same parameters in the chiral liquid crystal polymer layers 304, 305, 306, 308 and 309, and preferentially the values ​​of these three parameters are the same in all of the layers 304-309. The thickness of the first phosphor layer 307 is less than 10% of the total thickness of the layers 304-309.

[0016] The next device layer to be fabricated is the electron transport layer 308. The function of this layer is to transport electrons from the n-type doped electron transport layer 309 to the first emitter layer 307. In this way, an energy transition of electrons occurs from the electronic energy level in the conductive dopant of layer 309 to the HOMO energy level of the first emitter layer 307. This layer is fabricated by casting a solution of a mixture of chiral nematic liquid crystal monomers in a manner similar to that used to fabricate the layers described above. After evaporating off the solvent used to inject the monomer mixture, the material of the mixture forms an aligned layer of chiral nematic liquid crystal fluid or chiral nematic glass due to the template effect from the layer below. In this way, the helical structure induced by the chiral properties of the materials in layer 308 and all the layers described above in the device spans the interface between the two layers continuously. The helical structure is polymerized and fixed in place by exposure to UV light. Chiral nematic monomers that may be used to fabricate layer 308 are disclosed in US Pat. No. 10,727,421.

[0017] The next device layer to be fabricated is an n-doped electron transport layer 309. The function of this layer is to transport electrons from the cathode 312 or possibly the optional electron injection layer 311 to the electron transport layer 308. In this way, an energy transfer of electrons occurs from the electron energy level of the cathode work function to the lowest unoccupied molecular orbital (LUMO) energy level of the electron transport layer 308. This layer is fabricated by casting a solution of a mixture of chiral nematic liquid crystal monomers in a manner similar to that used to fabricate the layers described above. This layer also incorporates an n-type dopant, for example the dopant (4-(1,3-dimethyl-2,3-dihydro-1H-benzimidazol-2-yl)phenyl)dimethylamine (N-DBMI), which is activated by heating after the film is cast. Layer 309 may be made using the same mixture of monomeric nematic materials used for layer 308 doped with n-type dopants. After evaporating off the solvent used to inject the monomer mixture, the materials of the mixture form an aligned layer of chiral nematic liquid crystal fluid or chiral nematic glass due to the template effect from the layer below. Thus, a helical structure 310 induced by the chiral properties of the materials in layer 309 and all the layers mentioned above in the device spans the interface between the two layers continuously. Exposure to UV light polymerizes the helical structure and fixes it in place.

[0018] Optionally, layer 309 may be capped with an electron injection layer 311. Layer 311 may comprise, for example, lithium fluoride or cesium carbonate. Layer 312 is the cathode and may be made from a low work function metal such as, for example, aluminum, a magnesium / silver alloy, samarium, or calcium. When device 300 is energized, holes flow from anode 302 through hole injection layer 303 and layers 304, 305, and 306 to first emitter layer 307. At the same time, electrons flow from cathode layer 312 through layers 311, 309, and 308 to first emitter layer 307. Electrons and holes recombine on the electroluminescent material molecules of first emitter layer 307 to create excitons. Because first emitter layer 307 is within a photonic crystal structure, excitons formed in that layer cannot emit light at wavelengths in the stopband of the photonic crystal. However, if the emission band of the electroluminescent material of layer 307 overlaps with the short wavelength bandedge wavelengths of the stopband, emission will occur and, due to the high density of states at these wavelengths, extremely high levels of emission will occur. The photonic crystal traps the light of the bandedge emission within its structure and increases the photon density to a point where there are enough photons to interact with excitons such that nearly all of the emission in layer 306 is stimulated emission. However, the stimulated emission may be at an insufficient level to produce laser oscillation. Because the stimulated emission light propagates almost perfectly vertically within the device, losses due to internal reflection and light trapping are very low.

[0019] A portion of the excited state energy of the electroluminescent material molecules in layer 307 is transferred to the luminescent material molecules in the second emitter layer 306. This energy transfer may be mediated by Forster or Dexter exciton energy transfer mechanisms, or light emitted from the electroluminescent material in layer 307 may be absorbed by the luminescent material in layer 306. This energy transfer results in the formation of excitons in the luminescent material of layer 306. Because second emitter layer 306 is within a photonic crystal structure, the excitons formed in that layer cannot emit light at wavelengths in the stop band of the photonic crystal. However, if the emission band of the luminescent material in layer 306 overlaps with the long wavelength band edge wavelengths of the stop band, emission will occur and due to the high density of states at these wavelengths, extremely high levels of emission will occur. The photonic crystal traps the light of the band edge emission within its structure and increases the photon density to a point where there are enough photons to interact with excitons such that nearly all of the emission in layer 306 is stimulated emission. However, the stimulated emission may be at an insufficient level to cause laser oscillation. The stimulated emission light propagates almost perfectly vertically within the device, so there is very little loss due to internal reflection and light trapping. The emission mechanisms of layers 306 and 307 are similar, so the angular distributions of emission at the short and long band edge wavelengths are the same or nearly the same. If the energy transfer mechanism from the electroluminescent material of layer 307 to the luminescent material of layer 306 is the Forster or Dexter mechanism, then the emission from the second phosphor layer 306 is due to electroluminescence and the luminescent material of layer 306 is an electroluminescent material. If the energy transfer mechanism is emission from layer 307 and subsequent light absorption by layer 306, then the emission of the second phosphor layer 306 is due to photoluminescence and the luminescent material of layer 306 is a photoluminescent material. The energy transfer between layers 307 and 306 may be due to two or all three of the above energy transfer mechanisms, or may be due to all three.

[0020] Forster and Dexter energy transfer mechanisms are in the relatively short wavelength range. Therefore, if these mechanisms are important in contributing to the energy transfer, the second emitter layer 306 should be directly adjacent to the first emitter layer 307, and layer 306 should be fairly thin, e.g., less than 10 nanometers thick. If the energy transfer is via emission and subsequent reabsorption, the second emitter layer 306 may be further away from layer 307, as long as it is close enough to the center of the photonic crystal to be exposed to sufficient sustained photon levels to promote stimulated emission. It may also be advantageous, considering Forster or Dexter energy transfer, to omit the second emitter layer 306 and place the luminescent material that would otherwise be present in this layer as a component in the first emitter layer 307 in addition to the electroluminescent material already present. Light from emitter layers 306 and 307 that passes through layers 308, 309, and optionally 311 is reflected by reflective metal cathode 312 back into the photonic crystal structure. Light from emitter layers 306 and 307 passes through layers 305 and 304 and exits device 300 through layers 303, 302, and transparent substrate 301.

[0021] Another embodiment of the invention is shown in FIG. 4. Device 400 is similar to, but different from, device 300. Substrate 401 and layers 402, 403, 404, 405, 406, 407, and 408 (anode layer; hole transport layer; liquid crystal photoalignment layer; p-doped hole transport layer, hole transport layer, second emitter layer, first emitter layer, and electron transport layer, respectively) all perform the same functions as corresponding layers 302-308 of device 300. Also, cathode layer 412, which is a reflective metal layer, and optional electron injection layer 411 perform the same functions as corresponding layers 312 and 311 of device 300. However, an n-doped electron transport layer similar to layer 309 of device 300 is not present in device 400.

[0022] A cursory inspection of FIG. 4 would suggest that device 400 would not perform as well as device 300 because emitter layers 406 and 407 appear to be at the ends of helix structure 410, and because the thickness of the helix structure may not be sufficient to form a stop band. However, this is not the case. This can be explained by examining the path of light ray 413, of a wavelength at the short wavelength band edge of the stop band, which is emitted at layer 407, travels towards transparent substrate 401, but is reflected back by helix structure 410. The light ray then travels through layers 405, 406, 407, 408, and optionally 411, before being reflected back by metal reflector (cathode) 412. At reflector 412, the light ray reflects and travels back through helix structure 410, which comprises layers 408, 407, 406, 405, and 404. What the light ray "sees" along this path is a structure corresponding to photonic crystal structure 310 of FIG. 3. Thus, the helix structure 410 in combination with the reflector 412 acts as a photonic crystal to generate the device bands. A similar analysis is performed on the light emitted from layer 406.

[0023] As in device 300, energy transfer from layer 407 to layer 406 can occur via three different mechanisms: Forster or Dexter exciton energy transfer mechanism, or light emitted from the electroluminescent material of layer 407 can be absorbed by the luminescent material of layer 406. If Forster or Dexter energy transfer is relied upon, layer 406 should be directly adjacent to layer 407 and layer 406 should be fairly thin, e.g., less than 10 nanometers thick. If the energy transfer is via emission and subsequent reabsorption, the second emitter layer 406 may be further away from layer 407, as long as it is close enough to the center of the photonic crystal to be exposed to sufficient sustained photon levels to promote stimulated emission. It may also be advantageous, considering Forster or Dexter energy transfer, to omit the second emitter layer 306 and place the luminescent material that would otherwise be present in this layer as a component in the first emitter layer 307 in addition to the electroluminescent material already present. In both devices 300 and 400, the electroluminescent material in the first emitter layer (307 or 407) may emit exciton complexes. In this case, the emissive material will be a mixture of electron rich and electron deficient materials. In this case, it may be advantageous to have the emissive material in layer 306 or 406 contained in layer 307 or 407 rather than in layer 306 or 406, and to omit layer 306 or 406.

[0024] The device emits light at two wavelengths, the wavelengths being determined by the location and width of the stop band in the electromagnetic spectrum. The great advantage of using chiral nematic helical structures to generate the device band is that the width of the device band can be adjusted over a wide wavelength range, and therefore the chromaticity of the light generated by mixing the two wavelengths can be adjusted over many positions in the CIE color space. The width of the device band is given by: Δλ=P(n e -n o ) where Δλ is the width of the element band, P is the chiral pitch, and n c is the extraordinary refractive index of the liquid crystal, and n0 is the ordinary refractive index of the liquid crystal.

[0025] As a first example, P = 300 nm, n e = 1.75, and n o For P = 1.5, the emission wavelengths are 450 nm and 525 nm. e = 1.8, and n o= 1.5, the emission wavelengths are 450 nm and 540 nm. In the second example, two wavelengths are obtained that can be mixed to produce white light. In the first example, a blue wavelength and a green wavelength are obtained. A device with the parameters used in the first example can be used in the form of device 500 shown in FIG. 5, which is yet another embodiment of the invention, to emit RGB white light. In device 500, layers 503, 504, 505, 506, 507, 508, 509, 511, and 512 perform the same functions as layers 303, 304, 305, 306, 307, 308, 309, 31, and 312 in device 300. Anode 502 functions similarly to anode 302 in device 300, except that anode 502 extends outward from stack 513 to allow interconnection with a current source. The connecting means 501a and 501b connect the cathode 512 and the anode 502 and allow current to flow into the stack 513. The helical structure 510 has a pitch (e.g. 300 nm) and the electroluminescent material of the first phosphor layer 507 and the luminescent material of the second phosphor layer 506 emit light at optical wavelengths in free space, such that when these materials and layers are incorporated into the layer stack 513 and the stack is energized via the cathode 512 and the anode 502, the stack emits light at blue and green wavelengths. The light generated in the stack 513 exits the transparent anode 502 and enters the stack 519.

[0026] The stack 519 includes three layers: a first transparent chiral nematic liquid crystal polymer layer 514, a chiral nematic liquid crystal polymer layer doped with a photoluminescent material 515, and a second transparent chiral nematic liquid crystal polymer layer 516. All three layers include helical structures 517 made of chiral nematic material. The layers are formed sequentially, layer by layer, on a substrate 518 by depositing layers of chiral nematic monomers followed by photocrosslinking. The molecules of each subsequent layer are aligned due to the anisotropic surface energy of the previous layer. Once stack 519 is placed on substrate 518, stack 513 is formed thereon. The helical structure 517 causes the stack 519 to act as a one-dimensional photonic crystal. The pitch of the helical structure 517 and the refractive index of the materials used to create the layers 514, 515, and 516 are selected to provide a photonic crystal stop band with a short wavelength band edge in the red portion of the visible light spectrum, e.g., at 650 nm. The photoluminescent material doped in layer 515 is selected such that its emission spectrum overlaps with the short wavelength band edge of the photonic crystal stop band. A portion of the blue and green light leaving the stack 513 is absorbed by the photoluminescent material in the layer, causing red light to be emitted. In this way, the device 500 emits red, green, and blue light. By adjusting the concentration ratio of the luminescent materials present in layers 506, 507, and 515, the chromaticity of the light emitted by the device 500 can be tuned over most hues in the CIE 1931 color space. The nematic liquid crystal monomer materials and chiral dopants used to prepare the liquid crystal mixtures used to fabricate layers 514, 515, and 516 are selected to ensure that the helical pitch of structure 517 and the ordinary and extraordinary refractive indices of the liquid crystal materials in layers 514, 515, and 516 are all within 10% of the values ​​required to produce the desired photonic crystal stopbands. Because light of all three emitted wavelengths is generated in a similar manner by stimulated emission and they are all emitted vertically in narrow angle cones, there is little angular variation in the chromaticity of the light emitted by element 500.

[0027] Another embodiment of the present invention can be fabricated by replacing layer stack 513 in device 500 with the layer stack of device 400 excluding substrate 401 . The photoluminescent dopant in stack 519 is preferably confined to layer 515, although layers 514, 515, and 516 may be replaced by a single thick layer of polymerized chiral nematic material uniformly doped with the photoluminescent material. In another embodiment of the invention, two photoluminescent materials are doped into layer 515 of device 500. The emission spectrum of one of these materials overlaps with the short wavelength band edge of the stop band corresponding to helix 517, and the emission spectrum of the second overlaps with the long wavelength band edge of the same stop band. For example, if the pitch of helix 517 is 4009 nm and the ordinary and extraordinary refractive indices of the liquid crystal polymer in stack 519 are 1.5 and 1.76, the band edges of the stop band are at wavelengths of 554 nm and 651 nm. Since the human eye is most sensitive to light at 555 nm, devices with these emission wavelengths would be advantageous. In the above description of the various embodiments, when the emission spectrum of the luminescent material is considered to overlap with the short or long wavelength band edge of the photonic crystal stop band, the band edge is preferably located at a wavelength where the emission intensity from the luminescent material is at least half of the emission intensity at the wavelength of maximum intensity emission. Also, the band edge wavelength is preferably on the long wavelength side of the luminescent material emission band relative to the wavelength of maximum intensity emission. This would not be the case if the emission is due to exciton aggregate species formed by the transient combination of two molecular species, respectively.

[0028] The nematic monomer molecules used to form the various chiral nematic liquid crystal polymers used in the layers constructed according to the above embodiments may have a structure represented by the formula: B-S-A-S-B In the formula, B is a crosslinking group, preferably a crosslinkable group crosslinkable upon exposure to ultraviolet radiation, S is a flexible spacer, and A is a rigid or semi-rigid molecular core, preferably a chain of multiple aromatic diradicals linked in a linear fashion. In some embodiments, the core group A may be represented by the formula: [ka] wherein X is an aromatic diradical or a single bond, and Y is, independently for each unit, an aromatic diradical that may be represented by the formula: [ka] JPEG2025508468000004.jpg3777 JPEG2025508468000005.jpg3875 or Y may be a single bond as long as at least one Y is not a single bond, n is an integer from 1 to 5, and * represents a point attachment to the remainder of the molecule.

[0029] In the formula: [ka] Each X in each unit may independently represent one of the following: 1,4-phenylene, biphenyl-4,4'-diyl, terphen-4,4"-diyl, naphthalene-1,4-diyl, naphthalene-2,5-diyl, thiophene-2,5-diyl, pyrimidine-2,5-diyl, perylene-3,10-diyl, pyrene-2,7-diyl, 2,2'-dithiophene-5,5'-diyl, oxazole-2,5-diyl, oxazole-2,4-diyl, 1,3,4-oxadiazole-2,5-diyl, 1,2,4-oxadiazole-2,5-diyl, Diazole-3,5-diyl, thiazole-2,5-diyl, thiazole-2,4-diyl, 1,3,4-thiadiazole-2,5-diyl, 1,2,4-thiadiazole-3,5-diyl, thieno[3,2-b]thiophene-2,5-diyl, dithieno[3,2-b:2',3'-d]thiophene-2,6-diyl, thiazolo[5,4-d]thiazole-2,5-diyl, oxazolo[5,4-d]oxazole-2,5-diyl, thiazolo[5,4-d]oxazole-2,5-diyl, thiazolo[4,5-d]thiazole-2,5-diyl, oxazolo[5,4-d]oxazole-2,5-diyl, thiazolo[4,5-d]oxazole-2,5-diyl, thiazolo[4,5-d]oxazole-2,5-diyl, 2,1,3-benzothiadiazole-4,7-diyl, imidazo[4,5-d]imidazole-2,5-diyl, 9-alkyl(9H-carbazole)-2,7-diyl, carbazole-4,9-diyl, 9,9'-dialkyl-2,2'-bi(9H-carbazole-7,7'-diyl, 5,11-dialkyl(5,11H-indolo[3,2-b]carbazole)-3,9-diyl, dibenzo[b,d]thiophene-3,7-diyl, 5,11-dialkyl(5,11H-indolo[3,2-b]carbazole)-3,9-diyl, ,5-dioxodibenzo[b,d]thiophene-3,7-diyl, benzo[b]naphtho[1,2-d]thiophene-3,9-diyl, 7,7-dioxobenzo[b]naphtho[1,2-d]thiophene-3,9-diyl, dinaphtho[1,2-b:2',1'-d]thiophene-3,10-diyl, 13,13-dioxodinaphtho[l,2-b:2',1'-d]thiophene-3,10-diyl, dinaphtho[1,2-b:2',3'-d]thiophene-3,10-diyl, benzo[b]thieno[3,2-b]benzo[b]thiophene-3,8-diyl, 5,5-dioxobenzo[b]thieno[3,2-b]benzo[b]thiophene-3,8-diyl, bisbenzo[b]thieno[2,3-a:2,3-d]benzene-3,9-diyl, 5,5-dioxobisbenzo[b]thieno[2,3-a:2,3-d]benzene-3,9-diyl, 5,5,11,11-tetraoxobisbenzo[b]thieno[2,3-a:2,3-d]benzene-3,9-diyl, bisthieno[2,3-a:2,3-d]benzene-2,6-diyl, bisthieno[2,3-b:2,3-g]naphthalene-2,7-diyl, or other diradicals or single bonds.

[0030] More specifically, the finished molecules of the nematic monomers used to produce the various chiral nematic liquid crystal polymers used in the layers constructed according to the above embodiments may have structures represented by the formula: [ka] In the formula, the symbols B, X, Y, and n have the same meanings as those described above. m H 2m - represents an alkanediyl diradical, preferably an n-alkanediyl diradical, such as n-pentane-1.5-diyl or n-decane-1,10-diyl. The value of m is an integer between 3 and 12, selected independently for each unit. Ax represents a linking unit that connects a flexible spacer to a more rigid molecular core. Examples of Ax units include -O-, -S-, carboxyl, and carbonate, selected independently for each unit. The bridging group B may be a methacrylate, maleimide, or vinyl ether.

[0031] The chiral nematic monomer dopants used to prepare the chiral nematic mixtures used to produce the various chiral nematic liquid crystal polymers used in the layers constructed according to the above embodiments may have molecules having the formula: [ka] wherein B, X, Y, and n have the meanings given above, R is independently selected from methyl, ethyl, n-propyl, and isopropyl groups, m+n is equal to an integer from 3 to 12, and * indicates a chiral center (i.e., an asymmetric center).

[0032] Another embodiment of this patent is shown in Figure 6. This device 600 appears to be identical to the device described in US Patent Publication No. 2021 / 0119151, a chiral light-emitting electrochemical cell. However, there are important differences between the devices described herein. The chiral light-emitting electrochemical cell (C-LEC) 600 comprises a first electrode 602, which may be formed from either a light-transmitting or light-reflective material. If the first electrode 602 is light-transmitting, the first electrode 602 may be formed from indium-tin oxide, tin oxide, graphene, or other suitable light-transmitting material. If the first electrode 602 is light-reflective, the first electrode 602 may be formed from aluminum, magnesium / silver alloy, or some other suitable light-reflective material. The C-LEC 200 of the present invention further comprises a conductive liquid crystal alignment layer 604 formed on the surface of the first electrode 602. This layer 604 conducts charge carriers from the first electrode to the chiral liquid crystal organic material layer 608. A further property of this layer 604 is that when a layer of liquid crystal fluid material is formed on the top surface 606, the rod-like molecules of the liquid crystal fluid material adjacent the surface of the layer 604 are uniformly aligned, with all of their long axes oriented in the same direction (within the limits permitted by random thermal fluctuations in the liquid crystal phase) and parallel to the surface 606 of the liquid crystal alignment layer 604. The conductive liquid crystal alignment layer 604 may be a rubbed layer of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), a conductive liquid crystal photoalignment layer as described in U.S. Pat. No. 9,508,942, or other conductive liquid crystal alignment layers known in the art.

[0033] The C-LEC 600 of the present invention further comprises a layer 208 of chiral liquid crystal organic material. The chiral liquid crystal structure of this layer has rod-like molecules oriented within the layer with their long axes parallel to the surface 606 and twisting in a helical fashion as they pass upward through the layer 608. This arrangement is depicted diagrammatically (but at a greatly enlarged scale) by the arrangement of rods 612. Preferably, this arrangement results from the material of layer 608 having a chiral nematic (also called cholesteric) liquid crystal order. The material of layer 608 may be a liquid crystal fluid, but is preferably a solid. If the material is a solid, it may be a chiral liquid crystal glass, but more preferably the material is a polymer formed by polymerizing a layer containing chiral liquid crystal fluid precursor monomer material into a polymer with a chiral liquid crystal structure fixed in place by molecular crosslinks. The precursor monomers are preferably polymerized by exposure to radiation, more preferably ultraviolet light. The material of layer 608 includes an electroluminescent component material and a second light emitting component material. The C-LEC 600 further comprises a second electrode 610. The second electrode 610 may be formed from either an optically transparent or an optically reflective material. However, if the first electrode 604 is formed from an optically reflective material, the second electrode 610 should be formed from an optically transparent material. If the second electrode 610 is optically transparent, the second electrode 610 may be formed from indium-tin oxide, tin oxide, graphene, or some other suitable optically transparent material. If the second electrode 610 is optically reflective, the second electrode 610 may be formed from aluminum, magnesium / aluminum alloy, or some other suitable optically reflective material.

[0034] When a potential is established across the LEC 600 by voltage biasing one of the electrodes 602 and 610 relative to the other, the other of the two electrodes acts as an anode and the other as a cathode. Either the first or second electrode may act as an anode or a cathode. (In the example shown in FIG. 6, electrode 602 is the anode and electrode 610 is the cathode.) The component materials of the chiral liquid crystal organic material layer 608 act as an electrolyte. Molecular species in the layer 608 are oxidized to cations at the anode 602 and reduced to anions at the cathode 610. The material in the region 618 adjacent the cathode 610 behaves as if it were negatively doped. The material in the region 614 adjacent the anode behaves as if it were positively doped. As the potential difference across the layer 608 increases, the "doped" layer grows inward from the electrodes toward the center of the layer 608. The doped regions act like electrodes in an OLED, injecting holes (from the "doped" material region 618 near the cathode 610) and electrons (from the "doped" material region 614 near the anode 602) into the "undoped" material in region 616 in the center of the chiral liquid crystal organic material layer 608.

[0035] When electrons and holes are injected from regions 618 and 614, respectively, into region 616, they recombine and form excitons on the electroluminescent component molecules of the chiral liquid crystalline organic material of layer 608 in the center of region 616. These excitons decay and emit light. As explained above, the organic material of layer 608 having a chiral liquid crystal structure contains rod-like molecular cores that spontaneously align into a helical structure due to the chiral liquid crystal order. The optical anisotropy of the liquid crystal material of layer 608 is determined by the refractive index (n e ) is the refractive index (n o ) Light emitted from the electroluminescent component material of layer 608 in the center of region 616 strikes the helix structure 612 of layer 608. As described in the above embodiments, the helix structure 612 functions as a photonic crystal.

[0036] The helical pitch of the material of layer 608 having a chiral liquid crystal structure is designed such that the short wavelength stop band edge of the photonic crystal overlaps with the emission band of the electroluminescent component in the layer. When the device 600 is energized with a current passing between the anode 602 and the cathode 610, a portion of the excitation energy generated on the electroluminescent component molecules in layer 608 is transferred to the second luminescent material in layer 608, causing the second luminescent material to emit light. The helical pitch of the material of layer 608 and the ordinary and extraordinary refractive indices of the material of layer 608 are selected according to the following formula: λ c =(n e -n o )P / 2, and Δλ=P(n e -n o ) This causes the long wavelength stopband edge of the photonic crystal to overlap with the emission band of the second luminescent material. In this manner, the C-LEC device may be configured to emit light at two wavelengths by stimulated emission at the two band edges. If the parameters of the material of layer 608 are appropriately selected, blue and yellow light will be emitted, causing the emission from the device to appear yellow.

[0037] From the above, it can be seen that the material of layer 608 performs multiple functions as an electrolyte, a chiral liquid crystal material, an electroluminescent material, and a second light-emitting material. Some of these functions may be combined in a single material component. Examples include compounds whose molecular structures are symbolized in FIG. 7. These are ruthenium II containing electrolytes and light-emitting materials with the general structure 700, where A is a rigid rod- or lath-like aromatic moiety, S is a flexible spacer, C is a crosslinking group (preferably a photocrosslinking group), and X- is a negatively charged counterion. This type of ionic material can act as both an electrolyte and a triplet emitter in an LEC device. The inclusion of the rod-like molecular structure A and the flexible spacer S in the overall structure of material 300 means that a high percentage of material 700 can be incorporated into a chiral liquid crystal polymer material formulation for use in layer 608 without unnecessarily reducing the stability of the chiral liquid crystal phase of the material formulation. A second chiral liquid crystal polymer photonic crystal similar to stack 519 of element 500 may be added to element 700 to produce an element that generates light at three or four different wavelengths.

Claims

1. 1. A light emitting device comprising a single emitting photonic crystal having an electroluminescent material disposed therein, the single-emitting photonic crystal comprises a series of layers of a chiral liquid crystal polymer; the electroluminescent material is localized in one of the layers of the chiral liquid crystal polymer; At least one layer of the series of chiral liquid crystalline polymer layers comprises a chiral liquid crystalline charge carrier transport polymer; the single-emitting photonic crystal further comprises a second emitting material; The energy emitted from the electroluminescent material excites the second luminescent material to emit light; The light emitted by the light emitting element is a mixture of the light emitted by the electroluminescent material and the light emitted by the second luminescent material. Light emitting element.

2. 10. The light-emitting device of claim 1, wherein at least one of the layers of chiral liquid crystal polymer comprises a chiral nematic liquid crystal polymer.

3. 2. The light-emitting element of claim 1, wherein energy release from the electroluminescent material and emission in the second luminescent material due to the excitation of the electroluminescent material are mediated by emission from the electroluminescent material and reabsorption of light by the second luminescent material.

4. 4. The light-emitting device of claim 3, wherein the second emissive material is localized in a second layer of chiral liquid crystal polymer that is different from a first layer of chiral liquid crystal polymer in which the second emissive material is localized.

5. 5. The light-emitting device of claim 4, wherein the second layer of chiral liquid crystal polymer is adjacent to the first layer of chiral liquid crystal polymer in which the electroluminescent material is localized.

6. 5. The light-emitting device of claim 4, wherein said second layer of chiral liquid crystal polymer is separated from said first layer of chiral liquid crystal polymer in which said electroluminescent material is localized by one or more intermediate layers of chiral liquid crystal polymer.

7. The light-emitting device of claim 3 , wherein said second luminescent material is located in the same chiral liquid crystal polymer layer as said electroluminescent material.

8. 4. The light-emitting device of claim 3, wherein the second light-emitting material is disposed in multiple layers of the chiral liquid crystal polymer.

9. 10. The light-emitting device of claim 1, wherein energy emission from the electroluminescent material and emission in the second luminescent material upon excitation thereof are mediated by Forster excitation energy transfer.

10. 10. The light-emitting device of claim 9, wherein the second light-emitting material is localized in a second layer of chiral liquid crystal polymer distinct from a first layer of chiral liquid crystal polymer in which the electroluminescent material is localized, and the second layer of chiral liquid crystal polymer is adjacent to the first layer of chiral liquid crystal polymer.

11. 10. The light-emitting device of claim 1, wherein energy emission from the electroluminescent material and subsequent emission in the second luminescent material are mediated by Dexter excitation energy transfer.

12. 12. The light-emitting device of claim 11, wherein the second light-emitting material is localized in a second layer of chiral liquid crystal polymer that is different from a first layer of chiral liquid crystal polymer in which the electroluminescent material is localized, and the second layer of chiral liquid crystal polymer is adjacent to the first layer of chiral liquid crystal polymer.

13. 10. The light-emitting device of claim 1, wherein the series of layers of chiral liquid crystal polymer all have a helical structure.

14. The light-emitting device of claim 13 , wherein the structure of the single photonic crystal comprises a helical structure of the series of layers of the chiral liquid crystal polymer.

15. 14. The light-emitting device of claim 13, wherein the helical pitches of two or more of the layers of the series of chiral liquid crystal polymers are identical to within 10%.

16. 10. The light-emitting device of claim 1, wherein the series of layers of chiral liquid crystal polymer have ordinary and extraordinary refractive indices.

17. 17. The light-emitting device of claim 16, wherein the ordinary refractive indices of two or more of the layers of the series of chiral liquid crystal polymer are identical to within 10%.

18. 17. The light-emitting device of claim 16, wherein the extraordinary refractive indices of two or more of the layers of the series of chiral liquid crystal polymers are identical to within 10%.

19. 17. The light-emitting device of claim 16, wherein the difference between the ordinary and extraordinary refractive indices of two or more of the layers of the series of chiral liquid crystal polymers is identical to within 10%.

20. 10. The light-emitting device of claim 1, wherein the chiral liquid crystal polymer in each of the layers is formed by polymerization of a mixture comprising a nematic monomeric material and a chiral nematic monomeric dopant.

21. The light-emitting device according to claim 20 , wherein the polymerization is photopolymerization.

22. The light-emitting device according to claim 21 , wherein the photopolymerization is ultraviolet photopolymerization.

23. 21. The light-emitting device of claim 20, wherein nematic monomeric materials having different thermodynamic and optical properties are blended with chiral nematic monomeric dopants to obtain a desired helical pitch in each chiral liquid crystal polymer layer.

24. 21. The light-emitting device of claim 20, wherein nematic monomeric materials having different thermodynamic and optical properties are blended with chiral nematic monomeric dopants to obtain a desired ordinary refractive index in each chiral liquid crystal polymer layer.

25. 21. The light-emitting device of claim 20, wherein nematic monomeric materials having different thermodynamic and optical properties are blended with chiral nematic monomeric dopants to obtain a desired extraordinary refractive index in each chiral liquid crystal polymer layer.

26. At least one of the nematic material and the chiral nematic dopant in each of the layers is formed from a molecule that may be represented by the formula: B-S-A-S-B In the formula, A represents a molecular core comprising a linear chain of aromatic chemical diradicals, S represents a flexible spacer, and B represents a bridging group. The light-emitting device according to claim 20.

27. 27. The light-emitting device of claim 26, wherein nematic materials having molecular cores A with different chain lengths of linearly linked aromatic chemical diradicals are blended in a mixture to be polymerized to obtain a chiral nematic polymer with the desired ordinary refractive index.

28. 27. The light-emitting device of claim 26, wherein nematic materials having molecular cores A with different chain lengths of linearly linked aromatic chemical diradicals are blended in a mixture to be polymerized to obtain a chiral nematic polymer with the desired extraordinary refractive index.

29. The structure of the aromatic molecular core A may be represented by the formula: 【Chemistry 1】 In the formula, X is an aromatic diradical or a single bond, and Y is, independently in each unit, an aromatic diradical that may be represented by the formula: 【Chemistry 2】 【change】 【change】 or Y may be a single bond as long as at least one Y is not a single bond, n is an integer from 1 to 5, and * represents a point attachment to the remainder of the molecule. The light-emitting device of claim 26.

30. X is an aromatic diradical which may be independently selected from the following in each unit: 1,4-phenylene, biphenyl-4,4'-diyl, terphene-4,4"-diyl, naphthalene-1,4-diyl, naphthalene-2,5-diyl, thiophene-2,5-diyl, pyrimidine-2,5-diyl, perylene-3,10-diyl, pyrene-2,7-diyl, 2,2'-dithiophene-5,5'-diyl, oxazole-2,5-diyl, oxazole-2,4-diyl, 1,3,4-oxadiazole-2,5-diyl, 1,2 ... thiadiazole-3,5-diyl, thiazole-2,5-diyl, thiazole-2,4-diyl, 1,3,4-thiadiazole-2,5-diyl, 1,2,4-thiadiazole-3,5-diyl, thieno[3,2-b]thiophene-2,5-diyl, dithieno[3,2-b:2',3'-d]thiophene-2,6-diyl, thiazolo[5,4-d]thiazole-2,5-diyl, oxazolo[5,4-d]oxazole-2,5-diyl, thiazolo[5,4-d]oxazole-2,5-diyl, thiazolo[4,5-d]thiazole-2,5-diyl, o xazolo[4,5-d]oxazole-2,5-diyl, thiazolo[4,5-d]oxazole-2,5-diyl, 2,1,3-benzothiadiazole-4,7-diyl, imidazo[4,5-d]imidazole-2,5-diyl, 9-alkyl(9H-carbazole)-2,7-diyl, carbazole-4,9-diyl, 9,9'-dialkyl-2,2'-bi(9H-carbazole-7,7'-diyl, 5,11-dialkyl(5,11H-indolo[3,2-b]carbazole)-3,9-diyl, dibenzo[b,d]thiophene-3,7-diyl, 5,5-dioxodibenzo[b,d]thiophene-3,7-diyl, benzo[b]naphtho[1,2-d]thiophene-3,9-diyl, 7,7-dioxobenzo[b]naphtho[1,2-d]thiophene-3,9-diyl, dinaphtho[1,2-b:2',1'-d]thiophene-3,10-diyl, 13,13-dioxodinaphtho[1,2-b:2',1'-d]thiophene-3,10-diyl, dinaphtho[1,2-b:2',3'-d]thiophene-3,10-diyl, benzo[b]thieno[3,2-b]benzo[b]thiophene-3,8-diyl, 5,30. The light-emitting device of claim 29, which may be selected from 5-dioxobenzo[b]thieno[3,2-b]benzo[b]thiophene-3,8-diyl, bisbenzo[b]thieno[2,3-a:2,3-d]benzene-3,9-diyl, 5,5-dioxobisbenzo[b]thieno[2,3-a:2,3-d]benzene-3,9-diyl, 5,5,11,11-tetraoxobisbenzo[b]thieno[2,3-a:2,3-d]benzene-3,9-diyl, bisthieno[2,3-a:2,3-d]benzene-2,6-diyl, bisthieno[2,3-b:2,3-g]naphthalene-2,7-diyl, or other diradicals or single bonds.

31. At least one of the nematic materials in each of the layers is formed from a molecule that may be represented by the formula: 【Chemistry 3】 In the formula, X is an aromatic diradical or a single bond, and Y is, independently in each unit, an aromatic diradical that may be represented by the formula: 【Chemistry 4】 【change】 【change】 or Y may be a single bond as long as at least one Y is not a single bond, n is an integer from 1 to 5, * represents a point attachment to the remainder of the molecule; B is a bridging group, -C m H 2m - represents an alkanediyl diradical, preferably an n-alkanediyl diradical; the value of m is an integer from 3 to 12, selected independently for each unit; and Ax represents a linking unit that connects a flexible spacer to a more rigid molecular core. The light-emitting device according to claim 20.

32. 32. The light-emitting device of claim 31, wherein the Ax units are -O-, -S-, a carboxyl group, and a carbonate group, each independently selected for each unit.

33. 32. The light-emitting device of claim 31, wherein the bridging group B may be selected from a methacrylate, a maleimide, or a vinyl ether.

34. At least one of said chiral nematic monomeric dopants in each of said layers is formed from a molecule that may be represented by the formula: 【Chemistry 5】 In the formula, X is an aromatic diradical or a single bond, and Y is, independently in each unit, an aromatic diradical which may be represented by the formula: 【Chemistry 6】 【change】 【change】 or Y may be a single bond as long as at least one Y is not a single bond, n is an integer from 1 to 5, * represents a point attachment to the remainder of the molecule; B is a bridging group, -R is independently selected from methyl, ethyl, n-propyl, and isopropyl, m+n is equal to an integer from 3 to 12, the carbon atom directly attached to the alkyl group R acts as a chiral center, and Ax represents a linking unit that attaches a flexible spacer to a more rigid molecular core. The light-emitting device according to claim 20.

35. 35. The light-emitting device of claim 34, wherein the Ax units are -O-, -S-, a carboxyl group, and a carbonate group, each of which is independently selected for each unit.

36. 35. The light-emitting device of claim 34, wherein the bridging group B may be selected from a methacrylate, a maleimide, or a vinyl ether.

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