A cholesteric liquid crystal guided by multi-wavelength optical tuning, its preparation and application

Abstract

The present invention discloses a cholesteric liquid crystal capable of multi-wavelength light tuning guidance. The cholesteric liquid crystal is obtained by mixing and aligning raw materials including a photo-responsive chiral dopant, a non-photo-responsive chiral dopant, and a liquid crystal matrix; and the cholesteric liquid crystal has a planar alignment in a liquid crystal cell subjected to horizontal rubbing alignment with polyvinyl alcohol. This cholesteric liquid crystal has good conditions for tunable band gaps. At the same time, this cholesteric liquid crystal can display colors under irradiation by five different wavelength light sources respectively, and can display corresponding photo-stable reflection colors under multiple cyclic alternate irradiations by five different wavelength light sources respectively. Therefore, it can be used for the preparation of complex patterns. The present invention also discloses a preparation method and an application of this cholesteric liquid crystal.

Description

Technical Field

[0001] The present invention relates to the technical field of the light response of liquid crystals. More specifically, it relates to a cholesteric liquid crystal guided by multi-wavelength light tuning, its preparation and application. Background Art

[0002] Endowing remote and dynamic control of self-organized photonic structures with unique optical properties is an emerging research field in the fabrication of intelligent stimulus-responsive soft materials and devices. For this reason, cholesteric liquid crystals have broad prospects in optics and photonics due to their self-organized periodic helical superstructures. Since cholesteric liquid crystals are anisotropic dielectric media, their morphology results in a periodic modulation of the refractive index. The reflection wavelength is expressed as λ = P·n·cosθ, where P is the helical pitch, the distance for the director field to rotate 360°, n is the average refractive index, and θ is the angle between the light propagation direction and the helical axis. In this wavelength range, since the helical superstructure can selectively reflect circularly polarized light with the same handedness as the cholesteric liquid crystal, light propagation is prohibited. External stimuli (such as magnetic fields, electric fields, light, temperature, solvents) can be used to adjust the pitch of the cholesteric liquid crystal, thereby changing the position of the photonic bandgap and the reflection color of the cholesteric liquid crystal.

[0003] Light is particularly fascinating due to its advantages of providing remote, spatial, and temporal controllability in a wide range of surrounding environments. Light-driven cholesteric liquid crystals exhibit unique selective reflection, originating from their inherent self-organized helical superstructures, as well as dynamic reflection tuning in response to light. Such a unique system is expected to be an ideal candidate for "photonic ink", capable of realizing variable information conversion in tunable color reflectors and filters, tunable lasers, and biomedical applications. Based on this, researchers have demonstrated that the light-tunable reflection of cholesteric liquid crystals in the visible spectral range is due to the different helical twisting forces of cholesteric liquid crystals after irradiation with light-converting molecules at different wavelengths. By combining light-driven cholesteric liquid crystals and photomask technology, a variety of color patterns have been prepared, including the three primary colors of red, green, and blue. However, existing cholesteric liquid crystal systems are limited to displaying static optically addressable red, green, and blue images or patterns, and need to initialize the existing images or patterns by light or heat before each subsequent image or pattern. That is to say, the red, green, and blue reflection colors only appear in the transition state of the light irradiation tuning process, rather than being "locked" in the light steady state. This indicates that precise optical control of the red, green, and blue reflection colors remains a huge challenge.

[0004] Professor Yulei Yu's research group at Fudan University fabricated a photo-driven cholesteric liquid crystal by doping a binaphthalene derivative with a high helical twisting power and o-fluoroazobenzene as a photoswitch into a nematic liquid crystal matrix. The chiral dopant can induce a helical superstructure in the cholesteric liquid crystal, and the photoswitch can undergo a conformational change during photoirradiation isomerization, resulting in a change in the liquid crystal order, thereby adjusting the pitch of the helix and the reflected color. o-Fluoroazobenzene has different trans-cis isomerization ratios in the photostable states corresponding to different wavelength light sources. Light sources with wavelengths of 365, 405, and 530 nm promoted this ratio, producing red, green, and blue reflected colors locked in the photostable states. However, the disadvantage of this method is that in this method, the photo-responsive chiral molecule consists of two separate parts, a chiral dopant and a photoswitch, and the functionality of these two parts exists independently. At the same time, only these three wavelength light sources can be used. Summary of the Invention

[0005] Based on the above problems, the first object of the present invention is to provide a cholesteric liquid crystal guided by multi-wavelength light tuning. This liquid crystal can display colors under the irradiation of five different wavelength light sources respectively, and can display the corresponding photostable reflected colors under the multiple cyclic alternate irradiations of five different wavelength light sources respectively, so it can be used for the preparation of complex patterns.

[0006] The second object of the present invention is to provide a preparation method of a cholesteric liquid crystal guided by multi-wavelength light tuning.

[0007] The third object of the present invention is to provide a method for the red, green, and blue selective reflection of a cholesteric liquid crystal guided by multi-wavelength light tuning.

[0008] The fourth object of the present invention is to provide an application of a cholesteric liquid crystal guided by multi-wavelength light tuning.

[0009] To achieve the above first object, the present invention adopts the following technical solutions:

[0010] A cholesteric liquid crystal guided by multi-wavelength light tuning, characterized in that the cholesteric liquid crystal is obtained by mixing and aligning raw materials including a photo-responsive chiral dopant, a non-photo-responsive chiral dopant, and a liquid crystal matrix;

[0011] And the cholesteric liquid crystal has a planar alignment in a liquid crystal cell with polyvinyl alcohol horizontal rubbing alignment.

[0012] Furthermore, the photo-responsive chiral dopant is selected from axially chiral azobenzene dopants. It has both chiral induction and photoswitch conversion functions, integrating the functions of a chiral dopant and a photoswitch. At the same time, it well expands the types of wavelengths of the visible light photostable state.

[0013] Further, in the raw materials, the concentration of the photo-responsive chiral dopant is 1-3 wt%.

[0014] Further, the method of orientation is to heat the mixed raw materials to their clearing point, and through capillary action, pour the raw materials in the isotropic phase into a liquid crystal cell that has been rubbed and oriented with polyvinyl alcohol, and then cool it to the cholesteric liquid crystal temperature.

[0015] Further, the starting band gap of the cholesteric liquid crystal is 420-480 nm.

[0016] Further, the non-photo-responsive chiral dopant is selected from one or more of S5011, R5011, R811, and S811.

[0017] Further, in the raw materials, the concentration of the non-photo-responsive chiral dopant is 2-5 wt%.

[0018] Further, the liquid crystal matrix is selected from one or more of the mixed crystal E7 and SLC1717.

[0019] Further, based on 100 parts by mass of the total amount of the raw materials, the raw materials include: 1-3 parts of photo-responsive chiral dopant, 2-5 parts of non-photo-responsive chiral dopant, and 92-97 parts of liquid crystal matrix.

[0020] To achieve the above second object, the present invention adopts the following technical solution:

[0021] A method for preparing a cholesteric liquid crystal, comprising the following steps:

[0022] Mix the photo-responsive chiral dopant, non-photo-responsive chiral dopant, and liquid crystal matrix to obtain a cholesteric liquid crystal mixture;

[0023] Pour the cholesteric liquid crystal mixture into a liquid crystal cell that has been rubbed and oriented with polyvinyl alcohol to obtain the cholesteric liquid crystal with planar orientation.

[0024] Further, the preparation of the cholesteric liquid crystal mixture includes the following steps:

[0025] Dissolve the photo-responsive chiral dopant, non-photo-responsive chiral dopant, and liquid crystal matrix in dichloromethane, place it on a heating table and stir evenly until the dichloromethane has completely evaporated. Thus, a cholesteric liquid crystal mixture (CLC mixture) that reflects blue can be prepared.

[0026] Further, the method of pouring the cholesteric liquid crystal mixture into the liquid crystal cell includes the following steps:

[0027] Heat the cholesteric liquid crystal mixture to its clearing point, and by capillary action, pour the cholesteric liquid crystal mixture in the isotropic phase into a liquid crystal cell that has been rubbed and oriented with polyvinyl alcohol, and then cool it to the cholesteric liquid crystal temperature to obtain a cholesteric liquid crystal with planar orientation.

[0028] Further, the preparation of the liquid crystal cell that has been rubbed and oriented with polyvinyl alcohol includes:

[0029] 1) Provide a glass substrate with a polyvinyl alcohol alignment layer on its surface;

[0030] Preferably, it specifically includes the following steps:

[0031] Prepare a PVA aqueous solution as a horizontal alignment layer: Add commercially available polyvinyl alcohol solid particles to deionized water, place it on a hot stage and stir and heat to obtain a PVA aqueous solution;

[0032] Treatment method for the glass substrate used for the PVA alignment layer: Ultrasonic cleaning (neutral detergent) - water flow cleaning (water) - ultrasonic cleaning (distilled water) - ultrasonic cleaning (isopropyl alcohol) - blow dry with nitrogen;

[0033] Prepare the PVA alignment layer: Use a KW-4A type spin coater, and spin coat the clean substrate with the PVA solution. The glass substrate covered with a thin PVA layer is placed in an oven for heat curing. And rub the PVA alignment layer with rayon cloth on a clean glass slide in the same direction.

[0034] 2) Preparation of the liquid crystal cell with horizontal rubbing and orientation of polyvinyl alcohol:

[0035] Mix silica microsphere spacers with epoxy resin adhesive and add a hardener and mix quickly. Place a small amount of the adhesive on the surfaces near the two edges of a glass substrate with a polyvinyl alcohol alignment layer prepared in step 1), and then cover it with another same glass substrate with a polyvinyl alcohol alignment layer prepared in step 1). The rubbing directions of the two glass substrates are anti-parallel. Then clamp the two ends of the liquid crystal cell with a spring clip and place it in a vacuum drying oven to dry until the adhesive cures, thus completing the preparation of the liquid crystal cell.

[0036] To achieve the above third objective, the present invention adopts the following technical solution:

[0037] A method for multi-wavelength light tuning to direct the red, green, and blue selective reflections of cholesteric liquid crystals includes the following steps:

[0038] Irradiate the cholesteric liquid crystal described in the first objective above with a 365 nm light source;

[0039] The cholesteric liquid crystal irradiated with 365 nm is irradiated again with a 645 nm or 520 nm or 460 nm or 420 nm light source to obtain a cholesteric liquid crystal with a steady state of red, green, and blue.

[0040] In the present application, five different wavelength light sources are used for irradiation to tune the bandgap. Compared with the prior art where the bandgap is only tuned during the reflection tuning process, the advantage is that the reflected color is locked in the optical steady state. For the obtained results, due to the use of different wavelength irradiations, the anti - cis isomerization rates of the photo - responsive chiral dopant axial chiral azobenzene dopants are different, and the optical steady - state reflected colors are different, achieving precise control of the three primary colors of red, green, and blue, while eliminating the step of achieving the same reflected color by controlling the irradiation time.

[0041] Further, the method further includes: alternately placing the planar - aligned cholesteric liquid crystal under irradiations of different wavelength light sources of 365 nm, 520 nm, 460 nm, and 420 nm to achieve the switching of the reflected color of the cholesteric liquid crystal among red, green, and blue.

[0042] Further, irradiate with a 365 nm light source until the optical steady state is reached. At this time, the optical steady state after 365 nm irradiation is red reflection.

[0043] Further, irradiate the liquid crystal cell with a red - reflecting optical steady state after 365 nm irradiation again with 645 nm. At this time, the optical steady state after 645 nm irradiation is blue reflection, restoring to the initial reflected color.

[0044] Further, irradiate the liquid crystal cell with a red - reflecting optical steady state after 365 nm irradiation again with 520 nm. At this time, the optical steady state after 520 nm irradiation is green reflection.

[0045] Further, irradiate the liquid crystal cell with a red - reflecting optical steady state after 365 nm irradiation again with 460 nm. At this time, the optical steady state after 460 nm irradiation is green reflection.

[0046] Further, irradiate the liquid crystal cell with a red - reflecting optical steady state after 365 nm irradiation again with 420 nm. At this time, the optical steady state after 420 nm irradiation is red reflection.

[0047] To achieve the fourth above - mentioned object, the present invention also protects the application of the cholesteric liquid crystal as described above in the field of complex patterning.

[0048] The beneficial effects of the present invention are as follows:

[0049] The cholesteric liquid crystal provided in the present invention, after being irradiated by a 365 nm light source, the photo-responsive chiral dopant axially chiral azobenzene dopant changes from the trans configuration to the cis configuration. The conversion rates of trans-cis isomerization induced by visible light of different wavelengths are different, so that the axially chiral azobenzene has different helical twisting forces in the photo-stationary states of different wavelengths, realizing that after irradiation with different specific wavelengths, it shows the photo-stationary red, green, and blue reflection colors. Moreover, after the cholesteric liquid crystal irradiated by a 365 nm light source is irradiated alternately in multiple cycles at 645 nm or 520 nm or 460 nm or 420 nm, the photo-stationary reflection color of the cholesteric liquid crystal can be switched between two colors, having more wavelength types of visible light photo-stationary states, providing an alternative light source for programmable modulation of red, green, and blue reflections. This cholesteric liquid crystal can be used in complex patterning.

[0050] The preparation method of the cholesteric liquid crystal provided by the present invention is simple, low in cost, and suitable for large-scale preparation. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The following further describes in detail the specific embodiments of the present invention with reference to the accompanying drawings.

[0052] Figure 1 Shows the results of band gap tuning of the cholesteric liquid crystal prepared in Example 13 of the present invention when irradiated with light sources of different wavelengths.

[0053] Figure 2 Shows the results of cyclic stability tests of the cholesteric liquid crystal prepared in Example 14 of the present invention when irradiated with light sources of different wavelengths.

[0054] Figure 3 Shows the patterns of the cholesteric liquid crystal prepared in Example 15 of the present invention when irradiated with light sources of different wavelengths and the same wavelength light source. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0055] To more clearly illustrate the present invention, the present invention will be further described below with reference to preferred embodiments and the accompanying drawings. Similar components in the drawings are denoted by the same reference numerals. Those skilled in the art should understand that the content specifically described below is illustrative rather than restrictive, and should not be used to limit the protection scope of the present invention.

[0056] According to a specific embodiment of the present invention, a cholesteric liquid crystal guided by multi-wavelength light tuning is provided.

[0057] The cholesteric liquid crystal is obtained by mixing and aligning raw materials including a photo-responsive chiral dopant, a non-photo-responsive chiral dopant, and a liquid crystal matrix; the band gap of the cholesteric liquid crystal can be tuned under irradiation by 5 different wavelength light sources respectively.

[0058] And the cholesteric liquid crystal is in a planar orientation in a liquid crystal cell with horizontal rubbing orientation of polyvinyl alcohol.

[0059] The helical twisting ability of a chiral dopant on liquid crystal molecules is called the helical twisting power (HTP), and this value mainly depends on the nature of the chiral dopant itself. Incorporating a chiral dopant into a nematic liquid crystal matrix and obtaining a homogeneous mixture results in a cholesteric liquid crystal. The helical pitch of a cholesteric liquid crystal depends on the helical twisting power value and concentration of the chiral dopant. The calculation method of the pitch value is:

[0060]

[0061] where P is the helical pitch, c is the concentration fraction of the chiral dopant, and HTP is the helical twisting power value.

[0062] To make the reflection band gap of the initial cholesteric liquid crystal mixture fall within the range of reflecting blue light, the total concentration of the photo-responsive chiral dopant and the non-responsive chiral dopant is selected to be 3 - 8 wt%.

[0063] Exemplarily, the photo-responsive chiral dopant includes but is not limited to axially chiral azobenzene. The photo-responsive chiral dopant needs to have two functions. One is to act as a chiral agent to induce the formation of cholesteric liquid crystals; the other is to act as a photo-responsive molecule, which can undergo cis-trans isomerization after irradiation with light sources of different wavelengths, so that the cholesteric liquid crystal has different pitches. Among them, axially chiral azobenzene refers to distinguishing left and right chirality through an axis in the molecule, and this axis is called the chiral axis. For example, introducing an axially chiral binaphthyl group into the structure of a chiral molecule with tetrahedral chirality and modifying alkyl chains with different lengths at the tail end can obtain a series of axially chiral azobenzene molecules with different helical twisting powers. Exemplarily, the axially chiral azobenzene applicable to this embodiment includes but is not limited to the compounds shown by the following structural formulas:

[0064]

[0065] In this embodiment, the initial band gap of the cholesteric liquid crystal is 420 - 480 nm. If the band gap is too small, the color cannot be seen by the naked eye. If the band gap is too large, after irradiation with a 365 nm light source, the band gap redshifts to the near-infrared region and the color cannot be seen by the naked eye either.

[0066] In this embodiment, the reflection wavelengths of the cholesteric liquid crystal after irradiation with light sources of different wavelengths are in the range of 479 - 645 nm, presenting light-stable red, green, and blue reflections. The different wavelength light sources are selected from one of 365, 645, 520, 460, and 420 nm.

[0067] Specifically, the cholesteric liquid crystal turns red after irradiation by 365 and 420 nm light sources; turns green after irradiation by 520 and 460 nm light sources; turns blue after irradiation by 645 nm light source;

[0068] In a preferred example, the non-photoresponsive chiral dopant is selected from one or more of S5011, R5011, R811, and S811. The chiral molecules are doped into the liquid crystal matrix, which can induce the liquid crystal to twist and form a cholesteric liquid crystal.

[0069] In another preferred example, the liquid crystal matrix is selected from one or more of the mixed crystal E7 and SLC1717; the liquid crystal matrix is in a liquid crystal state at room temperature, and the liquid crystal state has a relatively wide temperature range.

[0070] Doping the chiral dopant into the liquid crystal matrix can induce the liquid crystal to twist and form a cholesteric liquid crystal. When the concentration of the chiral dopant is low, the initial reflection color of the induced cholesteric liquid crystal is in the near-infrared region; when the concentration of the chiral dopant is high, the initial reflection color of the induced cholesteric liquid crystal is in the ultraviolet region. In order to make the initial reflection color of the cholesteric liquid crystal in the visible light region, an appropriate amount of chiral dopant and liquid crystal matrix are necessary. The total mass fraction of the chiral dopant in the raw materials is selected to be 3-8 wt%.

[0071] In another preferred example, the raw materials include: 1-3 parts of photoresponsive chiral dopant, 2-5 parts of non-photoresponsive chiral dopant, and 92-97 parts of liquid crystal matrix, where the total amount of the foregoing components is 100 parts by mass.

[0072] Another specific embodiment of the present invention provides a preparation method for multi-wavelength light-tuned guiding of red, green, and blue selective reflection of cholesteric liquid crystals as described above.

[0073] Mix the photoresponsive chiral dopant, non-photoresponsive chiral dopant, and liquid crystal matrix evenly to obtain a cholesteric liquid crystal mixture;

[0074] Pour the cholesteric liquid crystal mixture into a liquid crystal cell that has been rubbed and oriented with PVA to obtain the planar-oriented cholesteric liquid crystal;

[0075] In a preferred example, the method of mixing evenly is: dissolve the photoresponsive chiral dopant, non-photoresponsive chiral dopant, and liquid crystal matrix in dichloromethane, place it on a heating table at 35-50 °C and stir evenly until the dichloromethane has completely evaporated. Thus, a CLC mixture that reflects blue can be prepared.

[0076] In a preferred example, the method of planar orientation includes the following steps:

[0077] (1) Prepare an aqueous PVA solution as a horizontal alignment layer. Add 3 - 5 g of commercially available solid polyvinyl alcohol particles to 97 - 95 mL of deionized water, place it on a hot plate at 160 - 250 °C and stir and heat for 4 - 7 h to obtain a 3 - 5 wt% PVA aqueous solution;

[0078] (2) Treatment method for the glass substrate used in the PVA alignment layer:

[0079] (a) Ultrasonic cleaning (neutral detergent) - 30 min;

[0080] (b) Water flow cleaning (water) - 15 min;

[0081] (c) Ultrasonic cleaning (distilled water) - 30 min;

[0082] (d) Ultrasonic cleaning (isopropyl alcohol) - 30 min;

[0083] (e) Blow dry with nitrogen;

[0084] (3) Preparation of the PVA alignment layer

[0085] Using a KW - 4A type spin coater, a clean substrate is spin - coated with a 3 - 5 wt% PVA solution at a speed of 400 - 600 rmp / min for 10 - 30 s and then at a speed of 2500 - 4000 rmp / min for 30 - 60 s.

[0086] The glass substrate spin - coated with the PVA solution is placed in an oven at 60 - 80 °C and heated for 1 - 3 h.

[0087] The PVA alignment layer is rubbed 10 - 20 times in the same direction on a clean glass sheet with a rayon velvet cloth. Then, silica microsphere spacers are mixed with an epoxy resin adhesive, a hardener is added and quickly mixed.

[0088] A small amount of the adhesive is placed on the surface near the two edges of the glass substrate, and then another same glass substrate is covered. The rubbing directions of the two glass substrates are anti - parallel. Then, the two ends of the liquid crystal cell are clamped with a dovetail clip and placed in a vacuum drying oven at 65 - 80 °C to dry until the adhesive cures, which takes about 30 - 60 min, thus completing the preparation of the liquid crystal cell.

[0089] In a preferred example, the method for the cholesteric liquid crystal with planar alignment includes the following steps:

[0090] Heat the cholesteric liquid crystal mixture to its clearing point of 35 - 40 °C. Through capillary action, the cholesteric liquid crystal mixture in the isotropic phase is poured into the liquid crystal cell prepared above, and then cooled to the cholesteric liquid crystal temperature to obtain a cholesteric liquid crystal with planar alignment.

[0091] Another specific embodiment of the present invention provides a method for tuning the bandgap of a cholesteric liquid crystal, comprising the following steps:

[0092] First irradiate a cholesteric liquid crystal with a planar orientation and an initial color of blue with a 365 nm light source; then irradiate the cholesteric liquid crystal irradiated with the 365 nm light source again with a 645 nm or 520 nm or 460 nm or 420 nm light source to obtain a cholesteric liquid crystal with a light steady state of red, green, and blue.

[0093] In a preferred example, the 365 nm light source is irradiated to a light steady state, and at this time, the light steady state after irradiation with the 365 nm light source is red reflection. The irradiation intensity of the 365 nm light source is 10 - 90 mW / cm 2 , and the irradiation time is 0.5 - 5 s;

[0094] In a preferred example, the liquid crystal cell with a light steady state of red reflection after irradiation with the 365 nm light source is irradiated again with a 645 nm light source. At this time, the light steady state after irradiation with the 645 nm light source is blue reflection, returning to the initial reflection color. The irradiation intensity of the 645 nm light source is 100 - 200 mW / cm 2 , and the irradiation time is 100 - 500 s;

[0095] In a preferred example, the liquid crystal cell with a light steady state of red reflection after irradiation with the 365 nm light source is irradiated again with a 520 nm light source. At this time, the light steady state after irradiation with the 520 nm light source is green reflection. The irradiation intensity of the 520 nm light source is 150 - 250 mW / cm 2 , and the irradiation time is 3 - 10 s;

[0096] In a preferred example, the liquid crystal cell with a light steady state of red reflection after irradiation with the 365 nm light source is irradiated again with a 460 nm light source. At this time, the light steady state after irradiation with the 460 nm light source is green reflection. The irradiation intensity of the 460 nm light source is 3 - 10 mW / cm 2 , and the irradiation time is 15 - 60 s;

[0097] In a preferred example, the liquid crystal cell with a light steady state of red reflection after irradiation with the 365 nm light source is irradiated again with a 420 nm light source. At this time, the light steady state after irradiation with the 420 nm light source is red reflection. The irradiation intensity of the 420 nm light source is 20 - 60 mW / cm 2 , and the irradiation time is 10 - 100 s.

[0098] In another embodiment of the present invention, the application of the cholesteric liquid crystal as described above in the field of complex patterning anti-counterfeiting is provided.

[0099] Since cholesteric liquid crystals exhibit different colors after being irradiated by light sources of different wavelengths, they can be well used in the application of complex patterned anti-counterfeiting fields.

[0100] The technical solutions of the present invention will be described below in conjunction with some specific embodiments:

[0101] Example 1

[0102] 1. Preparation of PVA alignment layer

[0103] Add 3 g of commercially available polyvinyl alcohol solid particles to 97 mL of deionized water, place it on a hot plate at 250 °C and stir and heat for 7 h to obtain a 3 wt% PVA aqueous solution; use a KW-4A type spin coater, and spin coat a clean substrate with a 3 wt% PVA solution at a speed of 400 rmp / min for 10 s and at a speed of 2500 rmp / min for 30 s. The glass substrate spin-coated with a PVA thin layer is placed in an oven at 80 °C and heated for 3 h. The PVA alignment layer is rubbed 20 times in the same direction on a clean glass slide with a rayon cloth. Then, silica microsphere spacers and epoxy resin adhesive are mixed together, and a hardener is added and quickly mixed. A small amount of adhesive is placed on the surfaces near the two edges of the glass substrate, and then another same glass substrate is covered. The rubbing directions of the two glass substrates are anti-parallel, thus completing the preparation of the liquid crystal cell. Then, clamp both ends of the liquid crystal cell with a spring clip and place it in a vacuum drying oven at 65 °C to dry until the adhesive cures, which takes about 60 min.

[0104] 2. Preparation of CLC mixture that reflects blue

[0105] 1 part of the photo-responsive chiral dopant, the compound shown as C 50 H 58 N4O2, 2 parts of non-photo-responsive chiral dopant R5011, and 97 parts of liquid crystal matrix SLC1717 are dissolved in dichloromethane, placed on a hot plate at 35 °C and stirred evenly until the dichloromethane volatilizes completely. The CLC mixture that reflects blue can be prepared.

[0106] 3. Preparation of cholesteric liquid crystal with planar alignment

[0107] Heat the cholesteric liquid crystal mixture to its clearing point of 40 °C, and by capillary action, pour the cholesteric liquid crystal mixture in the isotropic phase into the liquid crystal cell prepared above, and then cool it to the cholesteric liquid crystal temperature to obtain a cholesteric liquid crystal with planar alignment.

[0108] Example 2

[0109] 1. Preparation of PVA alignment layer

[0110] Commercially available 3 g of polyvinyl alcohol solid particles were added to 97 mL of deionized water, placed on a hot plate at 160 °C and stirred and heated for 4 h to obtain a 3 wt% PVA aqueous solution; using a KW-4A type spin coater, a clean substrate was spin-coated with a 3 wt% PVA solution at a speed of 400 rmp / min for 10 s and at a speed of 2500 rmp / min for 30 s. The glass substrate spin-coated with the PVA thin layer was placed in an oven at 80 °C and heated for 2 h. The PVA alignment layer was rubbed 20 times in the same direction on a clean glass slide with a rayon cloth. Then, the silica microsphere spacer was mixed with an epoxy resin adhesive, and a hardener was added and quickly mixed. A small amount of the adhesive was placed on the surfaces near the two edges of the glass substrate, and another identical glass substrate was covered. The rubbing directions of the two glass substrates were anti-parallel, thus completing the preparation of the liquid crystal cell. Then, the two ends of the liquid crystal cell were clamped with a clip and placed in a vacuum drying oven at 65 °C to dry until the adhesive was cured, which took about 30 min.

[0111] 2. Preparation of a reflective blue CLC mixture

[0112] 3 parts of a photo-responsive chiral dopant C 50 H 58 The compound shown in N4O2, 5 parts of a non-photo-responsive chiral dopant S5011, and 92 parts of a liquid crystal matrix E7 were dissolved in dichloromethane, placed on a hot plate at 40 °C and stirred evenly until the dichloromethane evaporated completely. Thus, a reflective blue CLC mixture was prepared.

[0113] 3. Preparation of a cholesteric liquid crystal with planar alignment

[0114] The cholesteric liquid crystal mixture was heated to its clearing point of 35 °C, and by capillary action, the cholesteric liquid crystal mixture in the isotropic phase was poured into the liquid crystal cell prepared above, and then cooled to the cholesteric liquid crystal temperature to obtain a cholesteric liquid crystal with planar alignment.

[0115] Example 3

[0116] 1. Preparation of the PVA alignment layer

[0117] Commercially available 5g of polyvinyl alcohol solid particles were added to 95 mL of deionized water, placed on a hot plate at 250 °C and stirred and heated for 7 h to obtain a 5 wt% PVA aqueous solution; a KW-4A type spin coater was used, and a clean substrate was spin-coated with a 5 wt% PVA solution at a speed of 600 rmp / min for 30 s and at a speed of 4000 rmp / min for 60 s. The glass substrate spin-coated with the PVA thin layer was placed in an oven at 60 °C and heated for 2 h. The PVA alignment layer was rubbed 10 times in the same direction on a clean glass slide with a rayon cloth. Then, the silica microsphere spacer was mixed with the epoxy resin adhesive, and a hardener was added and quickly mixed. A small amount of the adhesive was placed on the surfaces near the two edges of the glass substrate, and another identical glass substrate was covered. The rubbing directions of the two glass substrates were anti-parallel, thus completing the preparation of the liquid crystal cell. Then, the two ends of the liquid crystal cell were clamped with a spring clip and placed in a vacuum drying oven at 70 °C and dried until the adhesive was cured, which took about 30 min.

[0118] 2. Preparation of a blue-reflecting CLC mixture

[0119] 3 parts of a photo-responsive chiral dopant C 50 H 58 The compound shown in N4O2, 5 parts of a non-photo-responsive chiral dopant S811, and 92 parts of a liquid crystal matrix E7 were dissolved in dichloromethane, placed on a hot plate at 50 °C and stirred evenly until the dichloromethane completely volatilized. Thus, a blue-reflecting CLC mixture was prepared.

[0120] 3. Preparation of a cholesteric liquid crystal with planar alignment

[0121] The cholesteric liquid crystal mixture was heated to its clearing point of 36 °C, and by capillary action, the cholesteric liquid crystal mixture in the isotropic phase was poured into the liquid crystal cell prepared above, and then cooled to the cholesteric liquid crystal temperature to obtain a cholesteric liquid crystal with planar alignment.

[0122] Example 4

[0123] 1. Preparation of the PVA alignment layer

[0124] Commercially available 3 g of polyvinyl alcohol solid particles were added to 97 mL of deionized water, placed on a hot plate at 250 °C and stirred and heated for 7 h to obtain a 3 wt% PVA aqueous solution; using a KW-4A type spin coater, a clean substrate was spin-coated with a 3 wt% PVA solution at a speed of 450 rmp / min for 15 s and at a speed of 3500 rmp / min for 35 s. The glass substrate spin-coated with a PVA thin layer was placed in an oven at 65 °C and heated for 3 h. The PVA alignment layer was rubbed 10 times in the same direction on a clean glass slide with a rayon cloth. Then, the silica microsphere spacer was mixed with the epoxy resin adhesive, and a hardener was added and quickly mixed. A small amount of the adhesive was placed on the surfaces near the two edges of the glass substrate, and another identical glass substrate was covered. The rubbing directions of the two glass substrates were anti-parallel, thus completing the preparation of the liquid crystal cell. Then, the two ends of the liquid crystal cell were clamped with a clip and placed in a vacuum drying oven at 70 °C and dried until the adhesive was cured, which took about 30 min.

[0125] 2. Preparation of a blue-reflecting CLC mixture

[0126] 3 parts of a photo-responsive chiral dopant C 50 H 58 The compound shown in N4O2, 5 parts of a non-photo-responsive chiral dopant R811, and 92 parts of a liquid crystal matrix SLC1717 were dissolved in dichloromethane, placed on a hot plate at 37 °C and stirred evenly until the dichloromethane evaporated completely. Thus, a blue-reflecting CLC mixture was prepared.

[0127] 3. Preparation of a cholesteric liquid crystal with planar alignment

[0128] The cholesteric liquid crystal mixture was heated to its clearing point of 37 °C, and by capillary action, the cholesteric liquid crystal mixture in the isotropic phase was poured into the liquid crystal cell prepared above, and then cooled to the cholesteric liquid crystal temperature to obtain a cholesteric liquid crystal with planar alignment.

[0129] Example 5

[0130] 1. Preparation of a PVA alignment layer

[0131] Commercially available 3 g of polyvinyl alcohol solid particles were added to 97 mL of deionized water, placed on a hot plate at 200 °C and stirred and heated for 4 h to obtain a 3 wt% PVA aqueous solution; using a KW-4A spin coater, a clean substrate was spin-coated with a 3 wt% PVA solution at a speed of 400 rmp / min for 10 s and at a speed of 2500 rmp / min for 30 s. The glass substrate spin-coated with the PVA thin layer was placed in an oven at 80 °C and heated for 1 h. The PVA alignment layer was rubbed 15 times in the same direction on a clean glass slide with a rayon cloth. Then, the silica microsphere spacer was mixed with the epoxy resin adhesive, and a hardener was added and quickly mixed. A small amount of the adhesive was placed on the surface near the two edges of the glass substrate, and another identical glass substrate was covered. The rubbing directions of the two glass substrates were anti-parallel, thus completing the preparation of the liquid crystal cell. Then, the two ends of the liquid crystal cell were clamped with a clip and placed in a vacuum drying oven at 65 °C and dried until the adhesive was cured, which took about 30 min.

[0132] 2. Preparation of the reflective blue CLC mixture

[0133] 3.5 parts of the photo-responsive chiral dopant C 50 H 58 The compound shown in N4O2, 5 parts of the non-photo-responsive chiral dopant S5011, and 91.5 parts of the liquid crystal matrix E7 were dissolved in dichloromethane, placed on a hot plate at 40 °C and stirred evenly until the dichloromethane evaporated completely. The reflective blue CLC mixture could be prepared.

[0134] 3. Preparation of the cholesteric liquid crystal with planar alignment

[0135] The cholesteric liquid crystal mixture was heated to its clearing point of 38 °C, and by capillary action, the cholesteric liquid crystal mixture in the isotropic phase was poured into the liquid crystal cell prepared above, and then cooled to the cholesteric liquid crystal temperature to obtain the cholesteric liquid crystal with planar alignment.

[0136] Example 6

[0137] 1. Preparation of the PVA alignment layer

[0138] Commercially available 3 g of solid polyvinyl alcohol particles were added to 97 mL of deionized water, placed on a hot plate at 160 °C and stirred and heated for 7 h to obtain a 3 wt% PVA aqueous solution; using a KW-4A type spin coater, a clean substrate was spin-coated with a 3 wt% PVA solution at a speed of 450 rmp / min for 15 s and at a speed of 2500 rmp / min for 35 s. The glass substrate spin-coated with the PVA thin layer was placed in an oven at 65 °C and heated for 2.5 h. The PVA alignment layer was rubbed 13 times in the same direction on a clean glass slide with a rayon cloth. Then, the silica microsphere spacer was mixed with the epoxy resin adhesive, and a hardener was added and quickly mixed. A small amount of the adhesive was placed on the surfaces near the two edges of the glass substrate, and another identical glass substrate was covered. The rubbing directions of the two glass substrates were anti-parallel, thus completing the preparation of the liquid crystal cell. Then, the two ends of the liquid crystal cell were clamped with a spring clip and placed in a vacuum drying oven at 75 °C to dry until the adhesive was cured, which took about 50 min.

[0139] 2. Preparation of a CLC mixture that reflects blue

[0140] 3.5 parts of a photo-responsive chiral dopant C 50 H 58 The compound shown in N4O2, 5 parts of a non-photo-responsive chiral dopant R5011, and 91.5 parts of a liquid crystal matrix SLC1717 were dissolved in dichloromethane, placed on a hot plate at 40 °C and stirred evenly until the dichloromethane evaporated completely. Thus, a CLC mixture that reflects blue was prepared.

[0141] 3. Preparation of a cholesteric liquid crystal with planar alignment

[0142] The cholesteric liquid crystal mixture was heated to its clearing point of 39 °C, and the cholesteric liquid crystal mixture in the isotropic phase was poured into the liquid crystal cell prepared above by capillary action, and then cooled to the cholesteric liquid crystal temperature to obtain a cholesteric liquid crystal with planar alignment.

[0143] Example 7

[0144] 1. Preparation of the PVA alignment layer

[0145] Commercially available 4 g of solid polyvinyl alcohol particles were added to 96 mL of deionized water, placed on a hot stage at 180 °C, stirred and heated for 5 h to obtain a 4 wt% PVA aqueous solution; using a KW-4A spin coater, a clean substrate was spin-coated with a 4 wt% PVA solution at a speed of 450 rmp / min for 20 s and then at a speed of 3000 rmp / min for 35 s. The glass substrate spin-coated with a thin PVA layer was placed in an oven at 70 °C and heated for 1 h. The PVA alignment layer was rubbed 18 times in the same direction on a clean glass slide with a rayon cloth. Then, the silica microsphere spacer was mixed with an epoxy resin adhesive, and a hardener was added and quickly mixed. A small amount of the adhesive was placed on the surfaces near the two edges of the glass substrate, and another identical glass substrate was covered. The rubbing directions of the two glass substrates were anti-parallel, thus completing the preparation of the liquid crystal cell. Then, the two ends of the liquid crystal cell were clamped with a spring clip and placed in a vacuum drying oven at 70 °C to dry until the adhesive was cured, which took about 35 min.

[0146] 2. Preparation of a blue-reflecting CLC mixture

[0147] 3.5 parts of a photo-responsive chiral dopant C as shown in the above C 50 H 58 The compound N4O2, 5 parts of a non-photo-responsive chiral dopant S811, and 91.5 parts of a liquid crystal matrix SLC1717 were dissolved in dichloromethane, placed on a hot stage at 50 °C, and stirred evenly until the dichloromethane completely evaporated. Thus, a blue-reflecting CLC mixture was prepared.

[0148] 3. Preparation of a cholesteric liquid crystal with planar alignment

[0149] The cholesteric liquid crystal mixture was heated to its clearing point of 40 °C, and by capillary action, the cholesteric liquid crystal mixture in the isotropic phase was poured into the liquid crystal cell prepared above, and then cooled to the cholesteric liquid crystal temperature to obtain a cholesteric liquid crystal with planar alignment.

[0150] Example 8

[0151] 1. Preparation of the PVA alignment layer

[0152] Commercially available 4 g of solid polyvinyl alcohol particles were added to 96 mL of deionized water, placed on a hot plate at 220 °C and stirred and heated for 5 h to obtain a 4 wt% PVA aqueous solution; using a KW-4A type spin coater, a clean substrate was spin-coated with a 4 wt% PVA solution at a speed of 450 rmp / min for 25 s and at a speed of 3000 rmp / min for 50 s. The glass substrate spin-coated with the PVA thin layer was placed in an oven at 75 °C and heated for 1.5 h. The PVA alignment layer was rubbed 20 times in the same direction on a clean glass slide with a rayon cloth. Then, the silica microsphere spacer was mixed with the epoxy resin adhesive, and a hardener was added and quickly mixed. A small amount of the adhesive was placed on the surfaces near the two edges of the glass substrate, and another identical glass substrate was covered. The rubbing directions of the two glass substrates were anti-parallel, thus completing the preparation of the liquid crystal cell. Then, the two ends of the liquid crystal cell were clamped with a clip and placed in a vacuum drying oven at 70 °C to dry until the adhesive was cured, which took about 55 min.

[0153] 2. Preparation of the blue-reflecting CLC mixture

[0154] 3.5 parts of the photo-responsive chiral dopant C 50 H 58 The compound shown in N4O2, 5 parts of the non-photo-responsive chiral dopant R5011, and 91.5 parts of the liquid crystal matrix E7 were dissolved in dichloromethane, placed on a hot plate at 48 °C and stirred evenly until the dichloromethane evaporated completely. The blue-reflecting CLC mixture could be prepared.

[0155] 3. Preparation of the cholesteric liquid crystal with planar alignment

[0156] The cholesteric liquid crystal mixture was heated to its clearing point of 35 °C, and the cholesteric liquid crystal mixture in the isotropic phase was poured into the liquid crystal cell prepared above by capillary action, and then cooled to the cholesteric liquid crystal temperature to obtain the cholesteric liquid crystal with planar alignment.

[0157] Example 9

[0158] 1. Preparation of the PVA alignment layer

[0159] Commercially available 4 g of polyvinyl alcohol solid particles were added to 96 mL of deionized water, placed on a hot plate at 240 °C and stirred and heated for 5 h to obtain a 4 wt% PVA aqueous solution; a KW-4A spin coater was used, and a clean substrate was spin-coated with a 4 wt% PVA solution at a speed of 450 rmp / min for 25 s and then at a speed of 3500 rmp / min for 60 s. The glass substrate spin-coated with a PVA thin layer was placed in an oven at 75 °C and heated for 2.5 h. The PVA alignment layer was rubbed 20 times in the same direction on a clean glass slide with a rayon cloth. Then, the silica microsphere spacer was mixed with an epoxy resin adhesive binder, and a hardener was added and quickly mixed. A small amount of the binder was placed on the surfaces near the two edges of the glass substrate, and another identical glass substrate was covered. The rubbing directions of the two glass substrates were anti-parallel, thus completing the preparation of the liquid crystal cell. Then, the two ends of the liquid crystal cell were clamped with a clip and placed in a vacuum drying oven at 70 °C and dried until the adhesive was cured, which took about 55 min.

[0160] 2. Preparation of a blue-reflecting CLC mixture

[0161] 2.5 parts of a photo-responsive chiral dopant, the above-mentioned C 50 H 58 The compound shown in N4O2, 5 parts of a non-photo-responsive chiral dopant R811, and 92.5 parts of a liquid crystal matrix E7 were dissolved in dichloromethane, placed on a hot plate at 47 °C and stirred evenly until the dichloromethane was completely volatilized. A blue-reflecting CLC mixture could be prepared.

[0162] 3. Preparation of a cholesteric liquid crystal with planar alignment

[0163] The cholesteric liquid crystal mixture was heated to its clearing point of 35 °C, and by capillary action, the cholesteric liquid crystal mixture in the isotropic phase was poured into the liquid crystal cell prepared above, and then cooled to the cholesteric liquid crystal temperature to obtain a cholesteric liquid crystal with planar alignment.

[0164] Example 10

[0165] 1. The preparation of the PVA alignment layer was the same as in Example 5

[0166] 2. Preparation of a blue-reflecting CLC mixture

[0167] 2.5 parts of a photo-responsive chiral dopant, the above-mentioned C 50 H 58 The compound shown in N4O2, 4 parts of a non-photo-responsive chiral dopant R5011, and 93.5 parts of a liquid crystal matrix SLC1717 were dissolved in dichloromethane, placed on a hot plate at 45 °C and stirred evenly until the dichloromethane was completely volatilized. A blue-reflecting CLC mixture could be prepared.

[0168] 3. Preparation of Cholesteric Liquid Crystal with Planar Orientation

[0169] Heat the cholesteric liquid crystal mixture to its clearing point of 40 °C. By capillary action, pour the cholesteric liquid crystal mixture in the isotropic phase into the liquid crystal cell prepared above, and then cool it to the cholesteric liquid crystal temperature to obtain cholesteric liquid crystal with planar orientation.

[0170] Example 11

[0171] 1. The preparation of the PVA alignment layer is the same as that in Example 5.

[0172] 2. Preparation of the CLC mixture that reflects blue

[0173] 2 parts of the photo-responsive chiral dopant, the compound shown as C 50 H 58 N4O2, 4.5 parts of the non-photo-responsive chiral dopant S811, and 93.5 parts of the liquid crystal matrix SLC1717 are dissolved in dichloromethane, placed on a heating table at 45 °C and stirred evenly until the dichloromethane has completely evaporated. The CLC mixture that reflects blue can be prepared.

[0174] 3. Preparation of Cholesteric Liquid Crystal with Planar Orientation

[0175] Heat the cholesteric liquid crystal mixture to its clearing point of 36 °C. By capillary action, pour the cholesteric liquid crystal mixture in the isotropic phase into the liquid crystal cell prepared above, and then cool it to the cholesteric liquid crystal temperature to obtain cholesteric liquid crystal with planar orientation.

[0176] Example 12

[0177] 1. The preparation of the PVA alignment layer is the same as that in Example 5.

[0178] 2. Preparation of the CLC mixture that reflects blue

[0179] 1.5 parts of the photo-responsive chiral dopant, the compound shown as C 50 H 58 N4O2, 4.5 parts of the non-photo-responsive chiral dopant S5011, and 94 parts of the liquid crystal matrix E7 are dissolved in dichloromethane, placed on a heating table at 35 °C and stirred evenly until the dichloromethane has completely evaporated. The CLC mixture that reflects blue can be prepared.

[0180] 3. Preparation of Cholesteric Liquid Crystal with Planar Orientation

[0181] Heat the cholesteric liquid crystal mixture to its clearing point of 38 °C. By capillary action, pour the cholesteric liquid crystal mixture in the isotropic phase into the liquid crystal cell prepared above, and then cool it to the cholesteric liquid crystal temperature to obtain cholesteric liquid crystal with planar orientation.

[0182] Example 13

[0183] 1. The preparation of the PVA alignment layer is the same as that in Example 5

[0184] 2. Preparation of a blue-reflecting CLC mixture

[0185] 1.5 parts of the photo-responsive chiral dopant C as described above 50 H 58 The compound shown as N4O2, 4.5 parts of the non-photo-responsive chiral dopant S811, and 94 parts of the liquid crystal matrix SLC1717 are dissolved in dichloromethane and placed on a heating table at 35 °C and stirred evenly until the dichloromethane has completely evaporated. Thus, a blue-reflecting CLC mixture can be prepared.

[0186] 3. Preparation of a cholesteric liquid crystal with planar alignment

[0187] The cholesteric liquid crystal mixture is heated to its clearing point of 36 °C, and by capillary action, the cholesteric liquid crystal mixture in the isotropic phase is poured into the liquid crystal cell prepared above, and then cooled to the cholesteric liquid crystal temperature, thus obtaining a cholesteric liquid crystal with planar alignment.

[0188] 4. Bandgap tuning effect of the cholesteric liquid crystal when irradiated with light sources of different wavelengths

[0189] The color change and bandgap position change of the cholesteric liquid crystal are monitored in real time using a polarized optical microscope and a fiber optic spectrometer. A blue-reflecting cholesteric liquid crystal (bandgap position of 475 nm) is selected as the starting sample for testing. The liquid crystal cell filled with the cholesteric liquid crystal is placed on a clean tabletop. Since the conversion rates of the trans-cis isomerization induced by visible light of different wavelengths are different, the axially chiral azobenzene molecules have different helical twisting forces in the photostationary states of light of different wavelengths, and ultimately the cholesteric liquid crystal appears red, green, and blue. The prepared cholesteric liquid crystal is first irradiated with a 365 nm light source, and the bandgap redshifts to 646 nm. Then, it is irradiated with a 645 nm light source, and the bandgap blueshifts to 478 nm. Or it is irradiated with a 520 nm light source, and the bandgap blueshifts to 541 nm. Or it is irradiated with a 460 nm light source, and the bandgap blueshifts to 558 nm. Or it is irradiated with a 420 nm light source, and the bandgap blueshifts to 632 nm. The bandgap tuning effect of the cholesteric liquid crystal when irradiated with light sources of different wavelengths is as Figure 1 shown.

[0190] Example 14

[0191] 1. The preparation of the PVA alignment layer is the same as that in Example 5

[0192] 2. Preparation of a blue-reflecting CLC mixture

[0193] 1.5 parts of the photo-responsive chiral dopant C as described above50 H 58 The compound shown as H N4O2, 5 parts of non-photoresponsive chiral dopant R5011, and 93.5 parts of liquid crystal matrix E7 are dissolved in dichloromethane and placed on a heating table at 40 °C and stirred evenly until the dichloromethane has completely evaporated. A CLC mixture that reflects blue can be prepared.

[0194] 3. Preparation of cholesteric liquid crystal with planar alignment

[0195] The cholesteric liquid crystal mixture is heated to its clearing point of 36 °C, and by capillary action, the cholesteric liquid crystal mixture in the isotropic phase is poured into the liquid crystal cell prepared above, and then cooled to the cholesteric liquid crystal temperature to obtain a cholesteric liquid crystal with planar alignment.

[0196] 4. Cyclic stability test of cholesteric liquid crystal when irradiated with light sources of different wavelengths

[0197] The color change and bandgap shift of cholesteric liquid crystals were monitored in real time by combining a polarized optical microscope and an optical fiber spectrometer. A cholesteric liquid crystal that reflects blue light (bandgap of 475 nm) was selected as the starting sample for testing. The liquid crystal cell filled with the cholesteric liquid crystal was placed on a clean tabletop. First, it was irradiated with 365 nm light, and the bandgap redshifted to 644 nm. Immediately afterwards, it was irradiated with 645 nm light, and the bandgap blueshifted to 481 nm. The reflection spectrum was measured cyclically in this way, and the bandgap positions were 646, 481, 645, 480, 642, 478, 641, 479, 639, 480, 645, 482 nm respectively, showing good cycle stability. A cholesteric liquid crystal with the same concentration ratio (bandgap of 475 nm) was selected as the starting sample for testing. The liquid crystal cell filled with the cholesteric liquid crystal was placed on a clean tabletop. First, it was irradiated with 365 nm light, and the bandgap redshifted to 658 nm. Immediately afterwards, it was irradiated with 520 nm light, and the bandgap blueshifted to 543 nm. The reflection spectrum was measured cyclically in this way, and the bandgap positions were 655, 540, 657, 541, 653, 544, 654, 546, 657, 542, 652, 547 nm respectively, also showing good cycle stability. A cholesteric liquid crystal with the same concentration ratio (bandgap of 475 nm) was selected as the starting sample for testing. The liquid crystal cell filled with the cholesteric liquid crystal was placed on a clean tabletop. First, it was irradiated with 365 nm light, and the bandgap redshifted to 656 nm. Immediately afterwards, it was irradiated with 460 nm light, and the bandgap blueshifted to 554 nm. The reflection spectrum was measured cyclically in this way, and the bandgap positions were 657, 555, 657, 558, 653, 550, 654, 551, 657, 558, 658, 557 nm respectively. Similarly, it showed good cycle stability. A cholesteric liquid crystal with the same concentration ratio (bandgap of 475 nm) was selected as the starting sample for testing. The liquid crystal cell filled with the cholesteric liquid crystal was placed on a clean tabletop. First, it was irradiated with 365 nm light, and the bandgap redshifted to 646 nm. Immediately afterwards, it was irradiated with 420 nm light, and the bandgap blueshifted to 632 nm. The reflection spectrum was measured cyclically in this way, and the bandgap positions were 646, 632, 646, 632, 645, 632, 646, 632, 645, 632, 645, 632 nm respectively. Similarly, it showed good cycle stability. The cycle stability test of cholesteric liquid crystals in response to irradiation with light sources of different wavelengths is as Figure 2 shown.

[0198] Example 15

[0199] 1. The preparation of the PVA alignment layer is the same as in Example 5

[0200] 2. Preparation of a CLC mixture that reflects blue light

[0201] 2 parts of the photo-responsive chiral dopant C above 50H 58 The compound shown as N4O2, 2 parts of non-photoresponsive chiral dopant S5011, and 96 parts of liquid crystal matrix SLC1717 are dissolved in dichloromethane and placed on a heating table at 40 °C and stirred evenly until the dichloromethane has completely evaporated. A CLC mixture that reflects blue can be prepared.

[0202] 3. Preparation of cholesteric liquid crystal with planar alignment

[0203] Heat the cholesteric liquid crystal mixture to its clearing point of 38 °C. Through capillary action, pour the cholesteric liquid crystal mixture in the isotropic phase into the liquid crystal cell prepared above, and then cool it to the cholesteric liquid crystal temperature to obtain cholesteric liquid crystal with planar alignment.

[0204] 4. Patterning of cholesteric liquid crystals in response to irradiation with light sources of different wavelengths and irradiation with the same wavelength light source for different times

[0205] A camera is used to monitor the color change of the cholesteric liquid crystal macroscopically in the liquid crystal cell. A cholesteric liquid crystal that reflects blue (bandgap of 475 nm) is selected as the starting sample for testing. The liquid crystal cell filled with cholesteric liquid crystal is placed on a clean tabletop. A mask plate with a "dinosaur" pattern is placed in the middle of the liquid crystal cell, and the four sides of the mask plate are fixed in position with tape. First, irradiate with a 365 nm light source for a short time, then remove the mask plate. A green "dinosaur" pattern is displayed and photographed and saved with a camera. Immediately afterwards, the mask plate is placed back in the same position, and its four sides are still fixed in position with tape. The irradiation time is extended until the "dinosaur" pattern appears red macroscopically. The red "dinosaur" pattern can be changed back to other color patterns by irradiating again with light sources of other different wavelengths. When irradiated with a 645 nm light source for a short time, the red "dinosaur" turns into a "green" dinosaur. When the irradiation time of the 645 nm light source is extended, the green "dinosaur" disappears and the entire liquid crystal cell turns blue. By irradiating with a 365 - 645 nm light source for different times, the switching between the green "dinosaur" and the red "dinosaur" can be achieved, and the appearance and disappearance of the "dinosaur" pattern can be controlled, which is realized by irradiating with light sources of different wavelengths for different times. On the other hand, the liquid crystal cell with a mask plate can also be irradiated with light sources of other different wavelengths until its photostable state, and the pattern can be fixed in the photostable state to achieve the color switching of the pattern. The "dinosaur" that has been irradiated with 365 nm for an extended time to the red stable state is irradiated with a 520 nm light source until the photostable state, and the red "dinosaur" turns into a green "dinosaur" and remains in the photostable state. That is to say, the photostable red "dinosaur" can be turned into a photostable green "dinosaur" by irradiating with light sources of other different wavelengths. Similarly, the red "dinosaur" can also be irradiated with a 460 nm light source and can ultimately also be turned into a green "dinosaur", which is also realized by irradiating the mask plate "dinosaur" with light sources of different wavelengths until its photostable state. Finally, we also irradiate the red "dinosaur" with a 420 nm light source. Due to the very low cis - trans isomer conversion rate of the photo - responsive chiral dopant axially chiral azobenzene, the red "dinosaur" still remains red, which is still realized by irradiating the mask plate "dinosaur" with light sources of different wavelengths until its photostable state. In summary, the switching between patterns of different colors can be achieved not only by controlling the irradiation time of the same wavelength light source, but also by controlling the irradiation of different wavelength light sources until their photostable states.

[0206] In addition, we can also fabricate multicolor patterns by regionally controlling the irradiation of a light source with the same wavelength on the same liquid crystal cell. Select a cholesteric liquid crystal that reflects blue light (bandgap: 475 nm) as the starting sample for testing. Place the liquid crystal cell filled with cholesteric liquid crystal on a clean tabletop, and place a mask plate with the pattern of "flowers and flowerpots" in the middle of the liquid crystal cell. Fix the position of the mask plate around its perimeter with tape. First, irradiate with a 365-nm light source for a short time, then remove the mask plate, and green "flowers" and green "flowerpots" will be shown. Immediately afterwards, place the mask plate back at the same position, still fix its position around the perimeter with tape, and at the same time cover the "flowerpot" pattern with black paper, only exposing the mask plate of the "flowers". Still irradiate with a 365-nm light source until the light-stable red color of the 365-nm light source appears. At this time, the green "flowers" turn into red "flowers". Remove the mask plate, and finally a pattern of "red flowers and green flowerpots" will be presented. The patterning of cholesteric liquid crystals in response to irradiation with different wavelength light sources and irradiation with the same wavelength light source for different times is as Figure 3 shown.

[0207] Repeatedly perform the above performance tests using the cholesteric liquid crystal microdroplets prepared in Examples 1-15, and the results are the same as above.

[0208] Obviously, the above embodiments of the present invention are merely examples for clearly explaining the present invention, rather than limitations on the implementation modes of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is impossible to enumerate all the implementation modes here. Any obvious changes or modifications derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A method for guiding the selective reflection of red, green, and blue by a multi-wavelength light-tuned cholesteric liquid crystal, characterized in that, The method includes the following steps: Irradiate the cholesteric liquid crystal guided by multi-wavelength light tuning with a 365 nm light source; Irradiate the cholesteric liquid crystal irradiated with 365 nm again with a 645 nm or 520 nm or 460 nm or 420 nm light source to obtain a cholesteric liquid crystal with a steady state of red, green, and blue; Wherein, The cholesteric liquid crystal is obtained by mixing and aligning raw materials composed of a photo-responsive chiral dopant, a non-photo-responsive chiral dopant, and a liquid crystal matrix; And the cholesteric liquid crystal is in a planar alignment in a liquid crystal cell subjected to polyvinyl alcohol horizontal rubbing alignment; The method further includes: alternately irradiating the planar-aligned cholesteric liquid crystal with light sources of different wavelengths of 365 nm, 520 nm, 460 nm, and 420 nm to realize the switching of the reflected color of the cholesteric liquid crystal among red, green, and blue; The photo-responsive chiral dopant is selected from axially chiral azobenzene dopants; The axially chiral azobenzene dopant is selected from one of the following compounds: 、 、 、 ； The non-photo-responsive chiral dopant is selected from one or more of S5011, R5011, and R811; The liquid crystal matrix is selected from one or more of the mixed crystal E7 and SLC1717; Based on 100 parts by mass of the total amount of raw materials, the composition of the raw materials is: 1-3 parts of photo-responsive chiral dopant, 2-5 parts of non-photo-responsive chiral dopant, and 92-97 parts of liquid crystal matrix; The starting band gap of the cholesteric liquid crystal is 420-480 nm; The preparation method of the cholesteric liquid crystal includes the following steps: Mix the photo-responsive chiral dopant, the non-photo-responsive chiral dopant, and the liquid crystal matrix evenly to obtain a cholesteric liquid crystal mixture; Pour the cholesteric liquid crystal mixture into a liquid crystal cell subjected to polyvinyl alcohol rubbing alignment to obtain the cholesteric liquid crystal with a planar alignment.

2. The method according to claim 1, wherein The method for pouring the cholesteric liquid crystal mixture into the liquid crystal cell includes the following steps: Heat the cholesteric liquid crystal mixture to its clearing point, and by capillary action, pour the cholesteric liquid crystal mixture in the isotropic phase into the liquid crystal cell subjected to polyvinyl alcohol rubbing alignment, and then cool it to the cholesteric liquid crystal temperature to obtain the cholesteric liquid crystal with a planar alignment.

3. Application of the method according to any one of claims 1-2 in the field of complex patterning.

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