Method for inducing circular polarization luminescence based on cholesteric liquid crystal elastomer

Abstract

The invention relates to a method for inducing circular polarization luminescence based on a cholesteric liquid crystal elastomer, and belongs to the technical field of optical materials. Comprising the following steps: (1) dissolving a liquid crystal monomer, micromolecular liquid crystal, a chiral agent, a chain extender, a photoinitiator and a catalyst in a solvent dichloromethane to obtain a red cholesteric liquid crystal elastomer prepolymer; (2) coating on a TPU substrate, placing at a constant temperature, and carrying out ultraviolet polymerization to obtain a cholesteric liquid crystal elastomer polymer film; washing out small molecule liquid crystals, and recording the obtained thin film as a W-CLCE thin film; and (3) spraying red quantum dots on the surface of the W-CLCE film to obtain the cholesteric liquid crystal elastomer polymer film W-CLCE-R which has a high asymmetric factor and can dynamically regulate and control circular polarization luminescence. According to two mechanisms that cholesteric liquid crystal induces circular polarization luminescence, right-handed and left-handed circular polarization luminescence is induced on the front side and the back side respectively, and dynamic regulation and control of asymmetry factors of circular polarization luminescence between-0.074 and-0.01 and 0.086 and 0.016 by applying pulling force are realized respectively.

Description

Technical Field

[0001] The present invention relates to a method for inducing circularly polarized luminescence based on cholesteric liquid crystal elastomers, belonging to the technical field of optical materials. Background Art

[0002] Circularly Polarized Luminescence (CPL) refers to the phenomenon that a luminescent substance emits left-handed or right-handed circularly polarized light when excited, reflecting the excited state structure information of a chiral system. Due to its rich optical properties and high sensitivity, it has wide applications in fields such as 3D display, asymmetric catalysis, optical sensors, information storage, and polarization information encryption.

[0003] In the template-directed self-assembly method, the asymmetry factor is usually only between 10 -5 ~10 -2 . Using a cholesteric liquid crystal thin film as a template can effectively increase the asymmetry factor.

[0004] However, the existing reported methods have the following disadvantages: when encapsulating a fluorescent substance on one side of the cholesteric liquid crystal thin film, the induced circularly polarized luminescence is observation-dependent; directly mixing quantum dots into the liquid crystal material will cause spontaneous aggregation and phase separation, which is not conducive to the stability and reversibility of CPL and will seriously damage the emission intensity of the original quantum dots.

[0005] Therefore, providing a method for inducing circularly polarized luminescence based on cholesteric liquid crystal elastomers, which can induce both left-handed and right-handed circularly polarized luminescence. By constructing a composite system of cholesteric liquid crystal elastomers and quantum dots, while inducing left-handed and right-handed circularly polarized luminescence, realizing the change of the helical structure of cholesteric liquid crystal elastomers under the action of external force, and then changing the photonic band gap, and finally realizing the dynamic regulation of the high circularly polarized luminescence asymmetry factor, has become a technical problem urgently to be solved in this technical field. Summary of the Invention

[0006] The present invention aims to overcome the deficiencies in the prior art and provides a method for inducing circularly polarized luminescence based on cholesteric liquid crystal elastomers, which can induce both left-handed and right-handed circularly polarized luminescence. By constructing a composite system of cholesteric liquid crystal elastomers and quantum dots, while inducing left-handed and right-handed circularly polarized luminescence, realizing the change of the helical structure of cholesteric liquid crystal elastomers under the action of external force, and then changing the photonic band gap, and finally realizing the dynamic regulation of the high circularly polarized luminescence asymmetry factor.

[0007] The above object of the present invention is achieved by the following technical solutions:

[0008] A method for inducing circularly polarized luminescence based on cholesteric liquid crystal elastomers, comprising the following steps:

[0009] Step 1: Dissolve liquid crystal monomers, small molecule liquid crystals, chiral agents, chain extenders, photoinitiators, and catalysts in the solvent dichloromethane, mix evenly, and evaporate the solvent to obtain a red cholesteric liquid crystal elastomer prepolymer;

[0010] Step 2: Coat the cholesteric liquid crystal elastomer oligomer on a TPU (thermoplastic polyurethane, an elastomer between rubber and plastic, a polymer material) substrate, place it at a constant temperature for 24 h, and polymerize it with ultraviolet light to obtain a cholesteric liquid crystal elastomer polymer film; Immerse the cholesteric liquid crystal elastomer polymer film in cyclohexane to wash out the small molecule liquid crystal, and the obtained film is denoted as the W-CLCE film;

[0011] Step 3: Spray red quantum dots on the surface of the W-CLCE film to obtain a cholesteric liquid crystal elastomer polymer film with a high dissymmetry factor and dynamically tunable circularly polarized luminescence.

[0012] Further, in Step 1, the liquid crystal monomer is C6M, the small molecule liquid crystal is HCM-717200, the chiral agent is HCM-006, the chain extender is EDDET (2,2′-(1,2-ethylenedioxy)bis(ethanethiol), 95%), the photoinitiator is I-651 (2,2-dimethoxy-2-phenylacetophenone, 99%), the catalyst is DPA (dipropylamine, 99%), and the solvent is dichloromethane.

[0013] Further, in Step 1, the content of the liquid crystal monomer in the sum of the liquid crystal monomer, chain extender, and small molecule liquid crystal is 75.60 wt%, the content of the chain extender in the sum of the liquid crystal monomer, chain extender, and small molecule liquid crystal is 16.40 wt%, the small molecule liquid crystal in the sum of the liquid crystal monomer, chain extender, and small molecule liquid crystal is 8 wt%, and the chiral agent is 4.4% of the sum of the liquid crystal monomer, chain extender, and small molecule liquid crystal; the photoinitiator is 0.5% of the sum of the liquid crystal monomer, chain extender, and small molecule liquid crystal; the diluted catalyst is 21.4% of the sum of the liquid crystal monomer, chain extender, and small molecule liquid crystal;

[0014] Further, in Step 1, the chiral agent HCM-006 is a dextrorotatory chiral agent.

[0015] Further, in Step 1, the catalyst is a solution obtained by diluting dichloromethane and DPA at a ratio of 50:1.

[0016] Further, in Step 1, the method of evaporating the solvent is: put the mixed solution into an oil bath at 110 °C and evaporate the solvent for 3 min to obtain the cholesteric liquid crystal elastomer prepolymer.

[0017] Further, in Step 2, the coating temperature is 40°C, the coating thickness is 30 microns, and the placement temperature is 40°C.

[0018] Further, the specific operation of Step 2 is: polymerize the cholesteric liquid crystal elastomer prepolymer with ultraviolet light of wavelength 365 nm for 30 - 60 minutes, and the power of the ultraviolet light is 5 - 10 mW / cm 2 ; soak the film in cyclohexane for ten days to wash out small molecule liquid crystals, and the obtained film is denoted as the W-CLCE film.

[0019] Further, in Step 3, the emission wavelength of the red quantum dots is 625 nm, the solvent is n-hexane, and the concentration is 0.1 mg / mL.

[0020] Further, the specific operation of Step 3 is: use an airbrush to spray 100 μL of red quantum dots on the front side of the film W-CLCE, and after the n-hexane volatilizes, a cholesteric liquid crystal elastomer polymer film W-CLCE-R with a high dissymmetry factor and capable of dynamically regulating circularly polarized luminescence is obtained.

[0021] Further, apply a tensile force to both ends of the film W-CLCE-R, and the increased length of the stretch is 0 - 300% of the film W-CLCE-R; as the stretch length increases, the photonic band gap undergoes a blue shift, and the structural color of the film continuously transitions from red to blue-violet; at the same time, the g lum value (circularly polarized luminescence dissymmetry factor) also gradually decreases as the stretch length increases.

[0022] Further, the front side of the W-CLCE-R film can achieve dynamic reversible regulation of the right-handed circularly polarized luminescence dissymmetry factor g lum between -0.074 and -0.01.

[0023] Further, the back side of the W-CLCE-R film can achieve dynamic reversible regulation of the left-handed circularly polarized luminescence dissymmetry factor g lum between 0.086 and 0.016.

[0024] Beneficial effects:

[0025] (1) In the present invention, quantum dots are sprayed into the holes left after washing out small molecule liquid crystals on the front side of the cholesteric liquid crystal elastomer. Based on the optical activity of the cholesteric liquid crystal, fluorescence is transmitted along the helical axis, inducing right-handed circularly polarized light with the same helicity as the cholesteric liquid crystal elastomer on the front side. Utilizing the flexibility and stretchability of the elastomer, under an external force, by controlling the change in the pitch of the W-CLCE-R film, the movement of the photonic band gap is controlled, and the dynamic regulation of g lum is achieved.

[0026] (2) In the present invention, quantum dots are sprayed into the holes left by washing out small molecule liquid crystals on the front side of the cholesteric liquid crystal elastomer. Based on the selective reflection of the cholesteric liquid crystal, left-handed circularly polarized light with a helicity opposite to that of the cholesteric liquid crystal elastomer is induced on the back side. Utilizing the flexibility and stretchability of the elastomer, under the action of an external force, by controlling the change in the pitch of the W-CLCE-R film, the movement of the photonic bandgap is controlled to achieve the dynamic regulation of g lum .

[0027] (3) The present invention uses the coating method, which is easy to prepare on a large scale. The substrate used is TPU, and it has good stretchability.

[0028] To make the objectives, technical solutions, and advantages of the present invention clearer, the following further elaborates on the present invention in detail with reference to the accompanying drawings and specific embodiments, but it does not mean any limitation to the protection scope of the present invention. Description of the Drawings

[0029] Figure 1 Chemical structural formulas of liquid crystal monomer (C6M), chiral agent (HCM-006), chain extender (EDDET), photoinitiator (I-651), and catalyst (DPA) in Example 1 of the present invention;

[0030] Figure 2 Stress-strain curve and picture of the W-CLCE film after washing out small molecule liquid crystals and stretched to the maximum elongation rate in Example 1 of the present invention;

[0031] Figure 3 Structural color change and reflection spectrum diagram of the W-CLCE film under tensile deformation in Example 1 of the present invention;

[0032] Figure 4 Front-side CPL and g lum value variation trend with stretching of the W-CLCE-R film in Example 1 of the present invention;

[0033] Figure 5 Back-side CPL and g lum value variation trend with stretching of the W-CLCE-R film in Example 1 of the present invention;

[0034] Figure 6 Schematic diagram of the W-CLCE-R film in Example 1 of the present invention inducing right-handed circularly polarized luminescence on the front side and left-handed circularly polarized luminescence on the back side. Detailed Embodiments

[0035] To better illustrate the technical solution of the present invention, the following describes in detail a method for inducing circularly polarized luminescence based on cholesteric liquid crystal elastomer of the present invention with reference to specific embodiments. The materials and equipment used in the implementation process are all conventional experimental materials and equipment.

[0036] The present invention discloses a method for simultaneously inducing left- and right-handed circularly polarized luminescence based on cholesteric liquid crystal elastomers and quantum dots (W-CLCE-R); based on two principles of cholesteric liquid crystal-induced circularly polarized luminescence, left- and right-handed circularly polarized luminescence is simultaneously induced. At the same time, the helical structure of the cholesteric liquid crystal elastomer caused by stress changes. By controlling the stretching length, the photonic bandgap of the W-CLCE-R film is changed to achieve dynamic regulation of the circular polarization luminescence asymmetry factor.

[0037] In Example 1 of the present invention, the molecular structural formulas of HCM-006, C6M, EDDET, I-651, and DPA are as Figure 1 shown; HCM-006 and HCM-717200 are from Jiangsu HeCheng Display Technology Co., Ltd., EDDET and DPA are from Macklin; C6M is from Nanjing Xinyao Technology Co., Ltd.; I-651 is from J&K Scientific; the quantum dots are from Wuhan Jiayuan Quantum Dot Technology Development Co., Ltd.

[0038] Example 1

[0039] The quantum dots used are red quantum dots (emission wavelength 625 nm). The method for inducing circularly polarized luminescence based on cholesteric liquid crystal elastomers is as follows:

[0040] (1) Dissolve 300 mg of liquid crystal monomer (C6M), 17.5 mg of chiral agent (HCM-006), which is 4.4% of the total of liquid crystal monomer, chain extender, and small molecule liquid crystal, 65.1 mg of chain extender (EDDET), 1.83 mg of photoinitiator (I-651), 31.8 mg of small molecule liquid crystal (HCM-717200), and 85 mg of DPA diluted with dichloromethane at a ratio of 50:1 in dichloromethane (CH2Cl2), and fully dissolve and shake evenly;

[0041] (2) Put the solution obtained in step (1) into an oil bath at 110 °C, evaporate the solvent for 3 min to obtain a cholesteric liquid crystal elastomer prepolymer. Coating the cholesteric liquid crystal elastomer prepolymer on a TPU substrate, the coating temperature is 40 °C, the coating thickness is 30 microns, and place it on a hot stage at 40 °C for 24 h;

[0042] (3) Irradiate the oligomer obtained in step (2) with ultraviolet light with a wavelength of 365 nm (power 10 mW / cm 2 ) for 30 minutes, soak the film in cyclohexane for 10 days to wash out the small molecule liquid crystal to obtain a W-CLCE film. Cut the film into a rectangle with a width of 1 cm and a length of 5 cm;

[0043] (4) Using n-hexane, dilute the red quantum dots to 0.1 mg / mL. Then, using an airbrush, spray 100 μL of the red quantum dots onto the front side of the W-CLCE film to obtain a cholesteric liquid crystal elastomer polymer film W-CLCE-R with a high dissymmetry factor for dynamically tunable circularly polarized luminescence. Apply a tensile force to both ends of this film and stretch the W-CLCE-R film to even 280%; as the stretching length increases, the photonic bandgap undergoes a blue shift, and the structural color of the film continuously transitions from red to blue-violet; the specific results are as Figure 2 and Figure 3 shown. At the same time, the dissymmetry factor g lum of the circularly polarized luminescence also gradually decreases as the stretching length increases;

[0044] Figure 2 is the stress-strain curve of the W-CLCE film, and the maximum elongation rate exceeds 300%. Due to the excellent stretchability of the TPU substrate, when the maximum elongation rate of the liquid crystal elastomer is reached, the liquid crystal film breaks first, while the TPU substrate remains intact. The specific results are as Figure 2 shown;

[0045] Figure 3 in which a is the reflection spectrum diagram of the W-CLCE film at different stretching lengths; Figure 3 in which b is the W-CLCE film with an initial structural color of red. Through stretching deformation, the structural color of the W-CLCE film continuously changes from red to blue-violet. As can be seen from Figure 2 b, as the stretching length increases, the structural color of the cholesteric liquid crystal elastomer undergoes a blue shift, changing from red to green and finally to blue-violet, and the corresponding central wavelength of the reflection spectrum ranges from 692 nm to 426 nm, as Figure 3 shown in a;

[0046] Figure 4 in which a is the front side of the W-CLCE-R film, and the right-handed CPL and the g lum value decrease as the stretching rate increases; b is the dynamic change of the g lum value: when the stretching rate is 0, the front side of the W-CLCE-R film can achieve a right-handed circularly polarized luminescence dissymmetry factor g lum of -0.074; when the stretching rate reaches 40%, the right-handed circularly polarized luminescence dissymmetry factor g lum is close to 0;

[0047] Figure 5 in which a is the back side of the W-CLCE-R film, and the left-handed CPL and the g lum value decrease as the stretching rate increases; b is the dynamic change of the g lum value: when the stretching rate is 0, the back side of the W-CLCE-R film can achieve a left-handed circularly polarized luminescence dissymmetry factor g lumis 0.086; when the elongation rate reaches 50%, the right-handed circularly polarized luminescence asymmetry factor g lum is close to 0.016;

[0048] Due to the uniaxial tensile force applied to the liquid crystal elastomer, the liquid crystal helix unwinds along the direction of the applied force, forming a structure similar to the nematic phase. The CPL intensity gradually decreases, and at the same time, g lum value, as a numerical value measuring the circularly polarized luminescence intensity, also gradually approaches 0.

[0049] The contents of each component in the above-mentioned Example 1 are shown in Table 1 below.

[0050] Table 1

[0051]

[0052] The present invention proposes a method for simultaneously inducing left- and right-handed circularly polarized luminescence based on cholesteric liquid crystal elastomers. Using red quantum dots, according to two mechanisms of cholesteric liquid crystal-induced circularly polarized luminescence, right-handed and left-handed circularly polarized luminescence are induced on the front and back respectively, realizing the dynamic regulation of the circularly polarized luminescence asymmetry factor between -0.074 and -0.01, and 0.086 and 0.016 under the application of tensile force.

[0053] The asymmetry factor g of the circularly polarized luminescence lum :

[0054]

[0055] wherein, I left , I right represent the intensities of left-handed and right-handed circularly polarized light respectively, |gl um | ≤2 .

[0056] g lum can be used to measure the polarization degree and rotation direction of light. Its value range is from -2 to 2, where 2 represents pure left-handed circularly polarized light, -2 represents pure right-handed circularly polarized light, and 0 represents linearly polarized light or unpolarized light. When the absolute value of the circularly polarized luminescence asymmetry factor is closer to 2, the circular polarization degree of the light is higher.

[0057] As Figure 6 shown, it is a schematic diagram of inducing right-handed circularly polarized luminescence on the front and left-handed circularly polarized luminescence on the back of the W-CLCE-R film in Example 1 of the present invention.

[0058] As described above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as a limitation to the present invention itself. Various changes can be made in its form and details without departing from the spirit and scope of the present invention defined by the appended claims.

[0059] In the above - described specific embodiments, the purpose, technical solution, and beneficial effects of the present invention have been further described in detail, but the present invention is not limited thereby. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for inducing circularly polarized luminescence based on cholesteric liquid crystal elastomer, comprising the following steps: (1) dissolving a liquid crystal monomer, a small molecule liquid crystal, a chiral agent, a chain extender, a photoinitiator, and a catalyst in a solvent of dichloromethane, mixing them evenly, and evaporating the solvent to obtain a red cholesteric liquid crystal elastomer prepolymer; (2) coating the red cholesteric liquid crystal elastomer oligomer prepared in step (1) on a TPU substrate, placing it at a constant temperature, and polymerizing it with ultraviolet light with a wavelength of 365 nanometers for 30-60 minutes, and the power of the ultraviolet light is 5-10 mW / cm 2 , obtaining a cholesteric liquid crystal elastomer polymer film; immersing the cholesteric liquid crystal elastomer polymer film in cyclohexane to wash out the small molecule liquid crystal, and the obtained film is recorded as W-CLCE film; (3) spraying red quantum dots on the surface of the W-CLCE film to obtain a cholesteric liquid crystal elastomer polymer film W-CLCE-R with a high asymmetry factor and dynamically controllable circularly polarized luminescence.

2. The method for inducing circularly polarized luminescence based on cholesteric liquid crystal elastomer according to claim 1, characterized in that: In step (1), the liquid crystal monomer is C6M, the small molecule liquid crystal is HCM-717200, the chiral agent is HCM-006, the chain extender is EDDET, the photoinitiator is I-651, and the catalyst is DPA.

3. The method for inducing circularly polarized luminescence based on cholesteric liquid crystal elastomer according to claim 1, characterized in that: In step (1), the content of the liquid crystal monomer in the total of the liquid crystal monomer, the chain extender and the small molecule liquid crystal is 75.60wt%, the content of the chain extender in the total of the liquid crystal monomer, the chain extender and the small molecule liquid crystal is 16.40wt%, the small molecule liquid crystal in the total of the liquid crystal monomer, the chain extender and the small molecule liquid crystal is 8wt%, the chiral agent is 4.4% of the total of the liquid crystal monomer, the chain extender and the small molecule liquid crystal; the photoinitiator is 0.5% of the total of the liquid crystal monomer, the chain extender and the small molecule liquid crystal; the catalyst is 21.4% of the total of the liquid crystal monomer, the chain extender and the small molecule liquid crystal.

4. The method for inducing circularly polarized luminescence based on cholesteric liquid crystal elastomer according to claim 1, characterized in that: In step (1), the red quantum dots have an emission wavelength of 625 nm, the solvent is n-hexane, the concentration is 0.1 mg / mL, and the dosage is 100 μL.

5. The method for inducing circularly polarized luminescence based on cholesteric liquid crystal elastomer according to claim 1, characterized in that: In step (1), the chiral agent HCM-006 is a right-handed chiral agent; the method of evaporating the solvent is: placing the mixed solution in an oil bath at 110° C. to evaporate the solvent for 3 minutes to obtain a cholesteric liquid crystal elastomer prepolymer.

6. The method for inducing circularly polarized luminescence based on cholesteric liquid crystal elastomer according to claim 1, characterized in that: In step (2), the coating temperature is 40° C., the placement temperature is 40° C., and the film is immersed in cyclohexane for ten days.

7. The method for inducing circularly polarized luminescence based on cholesteric liquid crystal elastomer according to claim 1, characterized in that: The specific operation of step (3) is: dilute the quantum dots to 0.1 mg / mL using n-hexane, spray 100 μL of quantum dots on the front of the film using a spray pen, apply tension to both ends of the film, and the length increased by stretching is 0-300% of the W-CLCE-R film.

8. The method for inducing circularly polarized luminescence based on cholesteric liquid crystal elastomer according to claim 7, characterized in that: As the stretching length increases, the photonic band gap blueshifts, and the structural color of the film continuously transitions from red to blue-purple. At the same time, the circularly polarized luminescence asymmetry factor g lum It also gradually becomes lower as the stretching length increases.

9. The method for inducing circularly polarized luminescence based on cholesteric liquid crystal elastomer according to claim 1, characterized in that: The W-CLCE-R film can achieve a right-handed circularly polarized luminescence asymmetry factor g on the front side. lum Dynamically reversible regulation between -0.074 and -0.

01.

10. The method for inducing circularly polarized luminescence based on cholesteric liquid crystal elastomer according to claim 1, characterized in that: The reverse side of the W-CLCE-R film can realize the left-handed circularly polarized luminescence asymmetry factor g lum Dynamically reversible regulation between 0.086 and 0.016.

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