Method for obtaining circularly polarized luminescence by covalently anchoring chiral liquid crystal through light-induced anthraquinone molecules

Abstract

The invention discloses a method for obtaining circularly polarized luminescence by covalently anchoring a chiral liquid crystal through light-induced anthraquinone molecules. The method comprises the following steps: S1, adding a solution of a chiral dopant into nematic liquid crystals, stirring until the solution is transparent, and obtaining a binary assembly after a solvent is volatilized; s2, adding a solution of an achiral object into the binary assembly, and volatilizing the solvent to obtain a ternary cholesteric liquid crystal assembly; the achiral guest is a polycyclic conjugated quinone derivative. Under the induction of 365nm ultraviolet light, a diaryl acetylene part and anthraquinone molecules in the ternary cholesteric liquid crystal assembly are covalently bound, so that a new luminous body with a green emission color is formed, and the luminous body generated in situ is well arranged in an original liquid crystal and is beneficial to generating nearly pure circularly polarized light; more importantly, a new method is provided for construction of the circular polarization luminescent material through the non-covalent doping-covalent anchoring mode.

Description

Technical Field

[0001] The present invention relates to a method for obtaining circularly polarized luminescence by covalently anchoring anthraquinone molecules on chiral liquid crystals through photoinduction, belonging to the field of circularly polarized luminescence materials. Background Art

[0002] In the colorful natural world, chameleons can change the color of their own skin after perceiving the external environment to achieve the effect of camouflaging themselves. In addition, the outer shells of beetles, the wings of butterflies, and the fruits of plants can also exhibit similar structural color changes. This rapid adaptive regulation was once as mysterious as the smile of the Mona Lisa. Inspired by photonic crystals in nature, people have attempted to explore the origin of life through chiral soft matter materials. Liquid crystal is an intelligent soft matter material that combines the fluidity of liquids with the orderliness of crystals. This wonderful substance is thermodynamically stable. Introducing chiral species into liquid crystals can self-assemble to form cholesteric liquid crystals with a layered helical structure. Due to the unique periodic helical structure, it can selectively reflect circularly polarized light identical to itself, providing an effective way to artificially construct photonic crystals. The synthesized or assembled cholesteric liquid crystals not only provide artificial analogs of naturally occurring photonic crystals, but also doping luminescent species including various organic small molecules, polymers, and quantum dots into the helical structure of cholesteric liquid crystals promotes the development of chiral circularly polarized materials. In recent years, circularly polarized luminescence (CPL), as a chiral feature in the excited state, has shown broad application prospects in fields such as three-dimensional display, information encryption storage and anti-counterfeiting, and bioimaging, and has been favored by more and more researchers in the chemical and materials science communities. Generally, the luminescence asymmetry factor (g lum ) is used to evaluate the properties of CPL materials. Developing circularly polarized luminescence materials with high g lum is not only a necessary condition for commercial applications, but also the direction of basic scientific research. Based on previous theoretical research and recent experimental progress, using the selective reflection of photonic band gaps has been proven to be a promising method to increase the g lum value. Through the co-assembly between achiral molecules and chiral cholesteric liquid crystals, not only can the CPL performance of photonic materials be effectively manipulated, but also it helps to understand the origin of polarization phenomena in nature.

[0003] Previous literature reports that quinone compounds with polycyclic conjugated structures can be efficiently excited by ultraviolet light to react with double bonds in unsaturated lipids, forming [2+2] cycloaddition products. Inspired by these progress and the fact that the nematic liquid crystal SLC1717 contains unsaturated carbon-carbon triple bond components, we speculate that in the absence of solvent molecules, doping guest molecules with C=O double bond polycyclic conjugation into cholesteric liquid crystals, due to the close arrangement of the assembly, makes the distance between molecules closer, providing the possibility for the occurrence of topochemical reactions. The present invention is expected to provide a new method for generating circularly polarized luminescence by inducing in-situ topochemical reactions under 365nm ultraviolet light to generate new fluorescent emitters. Summary of the Invention

[0004] The object of the present invention is to provide a method for obtaining circularly polarized luminescence by photoinduced covalent anchoring of anthraquinone molecules to chiral liquid crystals. Based on a new strategy of non-covalent doping-covalent anchoring, circularly polarized luminescence is obtained by inducing topochemical reactions using 365nm ultraviolet light.

[0005] The present invention is based on the formation of binary cholesteric liquid crystal assemblies. By co-assembling achiral guests and binary cholesteric liquid crystals into a ternary AQ / 5011 / SLC1717 system, circularly polarized luminescent materials with high g lum values are gradually prepared. The achiral guest can be a quinone molecule with a symmetric structure - anthraquinone.

[0006] Specifically, the method for preparing ternary cholesteric liquid crystal assemblies provided by the present invention includes the following steps:

[0007] S1. Add a solution of a chiral dopant to a nematic liquid crystal and stir until it becomes transparent. After the solvent evaporates, a binary assembly is obtained;

[0008] S2. Add a solution of an achiral guest to the binary assembly. After the solvent evaporates, a ternary cholesteric liquid crystal assembly is obtained;

[0009] The achiral guest is a polycyclic conjugated quinone derivative.

[0010] Preferably, the nematic liquid crystal SLC1717 is composed of the following compounds:

[0011]

[0012] Preferably, the chiral dopant is R / S5011, and its structural formula is shown as follows:

[0013]

[0014] The achiral guest is preferably anthraquinone or its derivative, more preferably the following compound:

[0015]

[0016]

[0017] In step S1, it is confirmed whether self-assembly behavior occurs in the following manner: after the solvent completely evaporates, a milky white fluid with a reflected color is formed, indicating that the chiral dopant and the nematic liquid crystal have assembled.

[0018] In step S1, the planar texture is observed through a polarized light microscope to confirm whether a cholesteric liquid crystal assembly is formed: the binary assembly is injected into the liquid crystal cell by capillary action, and a planar texture can be observed under the polarized light microscope, indicating that the molecules gradually assemble to form a cholesteric liquid crystal assembly.

[0019] In the method of the present invention, dichloromethane is used to prepare the solution of the chiral dopant;

[0020] N,N-dimethylformamide is used to prepare the solution of the achiral guest.

[0021] In the method of the present invention, the doping amount of the chiral dopant relative to the nematic liquid crystal is 2.6 - 3.2%, preferably in the range formed by any two values among 2.6%, 2.8%, 3.0% and 3.2%.

[0022] In the method of the present invention, the doping amount of the achiral guest relative to the nematic liquid crystal is 0.1 - 1.0 wt.%, preferably 0.5 wt.%.

[0023] Based on the cholesteric liquid crystal assembly provided by the present invention, the present invention also provides a method for obtaining circularly polarized luminescence by covalent anchoring induced by 365 nm ultraviolet light.

[0024] Specifically, the ternary cholesteric liquid crystal assembly of the present invention is placed under an ultraviolet lamp to induce the occurrence of a topochemical reaction.

[0025] Experimental evidence of the present invention shows that by monitoring with a fluorescence spectrum, compared with the ternary cholesteric liquid crystal assembly before illumination, different fluorescence emissions are significantly observed, and the fluorescence intensity gradually increases with the increase of the illumination time until it reaches a fluorescence steady state. A weak change in the texture of the assembly after ultraviolet illumination can be observed under a polarized light microscope. This is because the 365 nm ultraviolet illumination induces covalent anchoring between the diarylacetylene moiety in the SLC1717 liquid crystal and the anthraquinone molecule to generate a green fluorescent emitter with a wavelength range of 500 nm to 600 nm.

[0026] Among them, the ultraviolet irradiation time is 0 - 40 min, preferably 40 min.

[0027] When the ternary assembly after the above-mentioned light irradiation was subjected to CPL measurement, it showed a positive signal, and the g lum value was as high as +1.73.

[0028] As a control, the above steps were repeated, and AQ / S5011 / SLC1717 N*LC also showed the same change under ultraviolet light irradiation. The CPL signal showed a negative signal, which was opposite to the signal of the AQ / R5011 / SLC1717 N*LC assembly after light irradiation.

[0029] In the present invention, first, a binary cholesteric liquid crystal R / S5011 N*LC with different reflection bands was co-assembled by a chiral dopant R / S5011 and a nematic liquid crystal SLC1717. Further, by introducing an appropriate amount of achiral anthraquinone molecules, a ternary cholesteric liquid crystal AQ / 5011 / SLC1717 N*LC was formed. Under the induction of 365 nm ultraviolet light, a covalent bond was formed between the diarylacetylene moiety and the anthraquinone molecule in the ternary cholesteric liquid crystal assembly, thereby forming a new luminescent body with a green emission color. This in-situ generated luminescent body was well arranged in the original liquid crystal, which helped to generate nearly pure circularly polarized light. More importantly, this non-covalent doping-covalent anchoring method provided a new method for the construction of circularly polarized luminescent materials. Brief Description of the Drawings

[0030] Figure 1 It is the transmission spectrum of the assembly after mixing different weight percentages of R5011 into SLC1717 in the ultraviolet-visible spectral range.

[0031] Figure 2 It is the polarized light microscope image of 0.5 wt.% AQ / R5011 / SLC1717 N*LCs.

[0032] Figure 3 It is the fluorescence spectral diagram of 0.5 wt.% AQ / R5011 / SLC1717 N*LCs assembly changing with time under 365 nm ultraviolet light irradiation.

[0033] Figure 4 It is the absolute fluorescence quantum yield (QY) diagram of 0.5 wt.% AQ / R5011 / SLC1717 N*LCs before light irradiation (left column) and after 40 minutes of ultraviolet light irradiation (right column).

[0034] Figure 5 It is the matching diagram of the ultraviolet transmission spectrum of 3.2 wt.% R5011 in SLC1717 (blue dotted line) and the fluorescence spectrum of 0.5 wt.% AQ / R5011 / SLC1717 after ultraviolet light irradiation (red line).

[0035] Figure 6CPL spectra of 0.5 wt.% AQ / 5011 / SLC1717 N*LCs after 40 minutes of ultraviolet light irradiation.

[0036] Figure 7 Fluorescence spectra of cholesteric liquid crystal assemblies formed by three anthraquinone derivatives before and after ultraviolet light irradiation.

[0037] Figure 8 Fluorescence spectra of cholesteric liquid crystal assemblies formed by 2,6-bis(diphenylamino)anthraquinone before and after ultraviolet light irradiation. Detailed implementation mode

[0038] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods.

[0039] Unless otherwise specified, the materials, reagents, etc. used in the following examples can all be obtained from commercial channels.

[0040] The cholesteric liquid crystal (CLC) involved in the present invention is also called chiral nematic liquid crystal. Its molecular arrangement has a unique helical structure and exhibits remarkable optical properties (such as selective reflection of light, circularly polarized light regulation, etc.).

[0041] The circularly polarized luminescence (CPL) involved in the present invention refers to the phenomenon that substances emit light with circularly polarized characteristics after being excited (such as photoexcitation, electrical excitation, etc.). Its core feature is that the electric field vector of light rotates in a helical form during propagation, forming a left-handed or right-handed polarization state (corresponding to left-handed circularly polarized light LCP and right-handed circularly polarized light RCP respectively).

[0042] The chiral dopant involved in the present invention is a type of molecule or compound with a chiral structure, which can induce non-chiral materials (such as nematic liquid crystals) to form chiral superstructures (such as helical arrangements) through physical or chemical interactions, thereby endowing the materials with unique optical, electrical or mechanical properties.

[0043] The covalent anchoring involved in the present invention refers to a chemical method of fixing molecules on the surface or interface of a specific substrate (in the present invention, it refers to cholesteric liquid crystal assemblies) through covalent bonds.

[0044] Example 1: Preparation of SLC1717 / 5011N*LC binary cholesteric liquid crystal assemblies

[0045] Weigh 10 mg of R5011 molecules into a 20 mL sample vial, and add the organic solvent dichloromethane. Promote dissolution by ultrasonic treatment to form a clear solution. Add 260, 280, 300, and 320 μL of 1 mg / mL R5011 solution to 10 mg of SLC1717 nematic liquid crystal respectively, and stir well to form a homogeneous solution. Transfer the sample to a glass slide, and heat it on a hot stage to 45 °C to evaporate the solvent, obtaining a milky white fluid. Inject the assembly into a liquid crystal cell by capillary action using a 1 mL syringe to prepare a binary cholesteric liquid crystal sample.

[0046] Prepare S5011 / SLC1717 N*LC by the same method.

[0047] Carry out relevant tests and characterizations on the binary liquid crystal co-assembly obtained above.

[0048] As Figure 1 shown, the cholesteric liquid crystals formed by doping 0.26 mg, 0.28 mg, 0.30 mg, and 0.32 mg of R5011 in SLC1717 nematic liquid crystal have different reflection bands. The planar texture of the R5011 / SLC1717 N*LC binary assembly can be observed under a polarized light microscope.

[0049] Example 2: Co-assembly of anthraquinone cholesteric liquid crystal and formation of ultraviolet light-induced green emitter

[0050] Weigh 5 mg of anthraquinone molecules into a 4 mL sample vial, add 1 mL of the organic solvent N,N-dimethylformamide, and dissolve it fully to obtain a clear and transparent solution. Based on the binary cholesteric liquid crystal assembly obtained in Example 1, add 10 μL, 20 μL, and 40 μL of the solution, namely 0.05 mg, 0.1 mg, and 0.2 mg of AQ molecules respectively, to form a ternary cholesteric liquid crystal assembly AQ / SLC1717 / 5011 N*LCs.

[0051] Carry out relevant tests and characterizations on the co-assembly obtained above.

[0052] First, observe under a polarized light microscope. As Figure 2 shown, only for the ternary assembly 0.5 wt.% AQ / 5011 / SLC1717 formed by adding 0.05 mg of anthraquinone molecules, no solid precipitation occurs, and the assembly can be better coupled to show a planar texture similar to that of the binary assembly.

[0053] The ternary assembly of 0.5 wt.% AQ / 5011 / SLC1717 was placed under a 365 nm ultraviolet lamp for light irradiation (with a power of 20 W) to induce the formation of emitters. The time-dependent fluorescence spectrum recorded that the cholesteric liquid crystal assembly doped with 0.05 mg anthraquinone molecules showed a green fluorescence emission at 500 nm and reached the fluorescence steady state after 40 minutes of ultraviolet light irradiation, as Figure 3 shown.

[0054] After 40 minutes of ultraviolet light irradiation to induce the formation of green emitters, as Figure 4 the photoluminescence quantum yield could be increased from 0.69% to 27.84% and the planar texture of the ternary assembly was not affected. The assembly with green emitters was characterized by mass spectrometry. Found: [M+H] + , 485.21104, obviously the green emitter is a new fluorescent species.

[0055] The perfect match between the center of the photonic bandgap and the fluorescence emission is crucial for obtaining a large luminescence asymmetry factor. As Figure 5 shown, the center of the reflection band obtained by doping 0.32 mg of R5011 can be perfectly aligned with the emission center of the photoinduced emitter. The circularly polarized luminescence of the irradiated assembly was tested. Figure 6 The test results showed that mirror-symmetric CPL signals appeared near the fluorescence emission peak. Among them, the 0.5 wt.% AQ / R5011 / SLC1717 ternary assembly showed a positive signal, and the 0.5 wt.% AQ / S5011 / SLC1717 ternary assembly showed a negative signal, which was caused by the suppression of the signal with the same helical chirality as the existing photonic bandgap. Calculated by the formula g lum could reach 1.73.

[0056] Example 3. Co-assembly of anthraquinone derivatives and cholesteric liquid crystals and formation of photoinduced emitters To verify the universality of the method for obtaining circularly polarized luminescence of the present invention, three anthraquinone derivatives were selected for verification.

[0057] Weigh 5 mg of anthraquinone-2-carboxylic acid, 2-phenylanthraquinone, and 5,12-diketopentacene respectively. Add 1 mL of the organic solvent N,N-dimethylformamide to a 4 mL sample to form a transparent solution. Take 10 μL of the above solutions respectively and use the method for preparing ternary cholesteric liquid crystals in Example 2 to prepare three cholesteric liquid crystals of 0.5 wt.% AQCOOH / R5011 / SLC1717, 0.5 wt.% 2-PhAQ / R5011 / SLC1717, and 0.5 wt.% 5,12-TetrAQR5011 / SLC1717 respectively.

[0058] The three anthraquinone cholesteric liquid crystal assemblies in the above preparation were respectively placed under ultraviolet light at 365 nm (with a power of 20 W), and the assemblies formed with anthraquinone showed the same photoluminescence behavior. As Figure 7 shown, strong fluorescence emission signals appeared at 505 nm, 500 nm, and 518 nm respectively in the ternary anthraquinone derivative assembly after ultraviolet light irradiation.

[0059] This example shows that various anthraquinone derivatives can covalently anchor the diarylacetylene part of the liquid crystal through ultraviolet light induction to obtain new luminescent species, and at the same time obtain circularly polarized luminescence with a g lum value exceeding 1.0.

[0060] Comparative Example 1,

[0061] A 0.5 wt.% N-AQ / R5011 / SLC1717 cholesteric liquid crystal was prepared according to the method of Example 3 and placed under ultraviolet light at 365 nm (with a power of 20 W). Its photoluminescence behavior is as Figure 8 shown. It can be seen that this compound is in a stable state and cannot form free intermediates under ultraviolet excitation to covalently anchor and form new emitters.

Claims

1. A method for preparing a ternary cholesteric liquid crystal assembly, comprising the following steps: S1, adding a solution of a chiral dopant into a nematic liquid crystal, stirring until transparent, and obtaining a binary assembly after the solvent evaporates; S2, adding a solution of an achiral guest to the binary assembly, and waiting for the solvent to evaporate to obtain a ternary cholesteric liquid crystal assembly; The achiral guest is a polycyclic conjugated quinone derivative.

2. The method according to claim 1, characterized in that: The nematic liquid crystal is composed of the following compounds:

3. The method according to claim 1 or 2, characterized in that: The chiral dopant is R / S5011.

4. The method according to any one of claims 1 to 3, characterized in that: The polycyclic conjugated quinone derivatives are selected from the following compounds:

5. The method according to any one of claims 1 to 4, characterized in that: Using dichloromethane to prepare a solution of the chiral dopant; The solution of the achiral guest is prepared using N,N-dimethylformamide.

6. The method according to any one of claims 1 to 5, characterized in that: The doping amount of the chiral dopant relative to the nematic liquid crystal is 2.6-3.2%; The doping amount of the non-chiral guest relative to the nematic liquid crystal is 0.1-1.0%.

7. A ternary cholesteric liquid crystal assembly prepared by the method according to any one of claims 1 to 6.

8. Use of the ternary cholesteric liquid crystal assembly according to claim 7 in obtaining circularly polarized luminescence.

9. The use according to claim 8, characterized in that: A circularly polarized luminescence signal with a glum value greater than ±1.0 was obtained by 365nm ultraviolet light-induced covalent anchoring.

10. The use according to claim 8 or 9, characterized in that: The irradiation time of the ultraviolet light is 0-40min; The wavelength range of the fluorescent emitter induced by the ultraviolet light is 500-600nm.

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