Synthesis of circularly polarized light isonitrile material with multi-stimulus response and all-light-white light regulation

Abstract

The invention relates to synthesis of a circularly polarized light isonitrile material with multi-stimulus response and all-light-white light regulation and control, and belongs to the field of intelligent high polymer materials. According to the covalent construction strategy, multi-adjustable CPL from molecular design to supramolecular assembly is achieved, and due to the fact that the azobenzene side group is subjected to reversible cis-reflective isomerization under stimulation of light, pH, metal ions and humidity, the material is endowed with various responsive CPL characteristics; the method has potential application value in multicolor dynamic display, anti-counterfeiting security, information encryption and chiral logic gate application. This work provides a basic insight for covalently constructing static helical polymers with dynamically tunable CPL.

Description

Technical Field

[0001] This invention relates to the synthesis of a multi-stimulus responsive polyisocyanate material capable of controlling circularly polarized light from both light and white light, belonging to the field of smart polymer materials. More specifically, it relates to a chiral polyisocyanate material that combines multi-stimulus responsiveness with the ability to control circularly polarized light from both light and white light, suitable for applications in optical devices, information encryption, and biosensing. Background Technology

[0002] In recent years, circularly polarized light (CPL) materials have exhibited unique photophysical properties, showing broad application prospects in fields such as optical storage devices, optoelectronic devices, and three-dimensional optical displays, and have become a research hotspot in chiral-related fields and materials science. Among various CPL materials, helical polymer CPL materials have become a new favorite in the field of CPL materials due to their chiral helical structure, rich variety, ease of manufacture, high thermal stability, tunable performance, and excellent processing properties, and are widely used in drug tracking, fluorescent probes, and biosensors. Recent studies have found that helical polyisocyanates are stable, easy-to-synthesize, and have important application prospects in the field of circularly polarized light materials. Helical polyisocyanates have great application potential in various fields due to their stable structure and diverse functions. However, to this day, researchers usually choose metal catalysts when catalyzing the polymerization of functional isonitriles. This problem leads to serious metal residues, which greatly affect the application of these polymers in different aspects. For example, metal residues affect the thermal stability of polymers and accelerate the aging of polyisocyanates. When polyisocyanates are used for ion detection, they will greatly affect the experimental results and make it impossible to accurately detect target metal ions. When polyisocyanates are used in biological experiments, they can affect the health of living organisms and the release and efficacy of drugs. Therefore, designing and synthesizing metal-free catalysts that can efficiently catalyze the polymerization of isonitriles without metal residues is particularly important. This will greatly benefit the application of isonitriles in drug release, ion detection, wound dressings, and other fields. The direct use of [Ph3C][B(C6F5)4] in catalytic polymerization has also been successfully reported, exhibiting high polymerization activity, which is instructive for exploring new metal-free cationic catalysts.

[0003] The design and synthesis of low-cost, environmentally friendly metal-free initiators for the detection of metal ions has become a current research focus. Currently, there are no reports on whether the two novel carbocation initiators, 4-methoxy-α-methylbenzyl alcohol (TMOH) and 1-chloro-1-phenylethane (PhEtCl), can be applied to isonitrile polymerization. Furthermore, the influence of metal-free carbocations on the catalytic activity of isonitrile monomer polymerization under different conditions (catalyst type, co-catalyst type, temperature, and monomer concentration, etc.) has not been investigated.

[0004] This catalytic system achieved homopolymerization of chiral aromatic isonitrile monomers and helical copolymerization of chiral aromatic isonitrile monomers with stimuli-responsive azobenzene monomers, preparing high molecular weight isonitrile polymers with varying degrees of single-chiral helical conformation and AIE properties. A chiral amplification effect was observed in the copolymerization system. This ingenious covalent construction strategy not only achieved multi-tunable CPLs from molecular design to supramolecular assembly, but also, due to the reversible cis-reflex photoisomerization of the azobenzene side groups under light, pH, metal ion, and humidity stimulation, led to helical conformational changes in the polymers, thus endowing the materials with multiple responsive CPL properties and preparing a batch of novel smart materials. These materials have potential applications in multicolor dynamic displays, anti-counterfeiting security, information encryption, and chiral logic gates. This work provides fundamental insights into the covalent construction of static helical polymers with dynamically tunable CPLs. Based on the above summary, the synthesis of a novel multi-stimuli-responsive and all-light-white-light-tunable circularly polarized isonitrile material is a very significant achievement.

[0005] Existing technical documents

[0006] Non-patent literature

[0007] Non-patent literature 1: S.Li, Y.Zong, B.Liu. Helix-induced full-color circularlypolarized luminescence films with multiple information encryption and multi-stimuli responsiveness Chem.Sci., 2025, 16, 5036.

[0008] Non-patent literature 2: Li M, Hu H, Liu B, Liu X, Zheng ZG, Tian H, Zhu WH.Light-Reconfiguring Inhomogeneous Soft Helical Pitch with Fatigue Resistance and Reversibility.J Am Chem Soc.2022 Nov 16;144(45):20773-20784.doi:10.1021 / jacs.2c08505.Epub 2022 Nov 7.PMID:36343183.

[0009] Non-Patent Document 3: Li Y, Chen Y, Li H, Liu C, Li L, Quan Y, Cheng Y. Achiral Dichroic Dyes-mediated Circularly Polarized Emission Regulated by Orientational Order Parameter through Cholesteric Liquid Crystals. Angew Chem Int Ed Engl. 2023 Nov 13; 62(46): e202312159. doi: 10.1002 / anie.202312159. Epub 2023 Oct 12. PMID: 37776155.

[0010] Non-Patent Document 4: Yang X, Zhou M, Wang Y, Duan P. Electric-Field-Regulated Energy Transfer in Chiral Liquid Crystals for Enhancing Upconverted Circularly Polarized Luminescence through Steering the Photonic Bandgap. Adv Mater. 2020 Jun; 32(24): e2000820. doi: 10.1002 / adma.202000820. Epub 2020 May 6. PMID: 32378267.

[0011] Non-Patent Document 5: Kang W, Tang Y, Meng X, Lin S, Zhang X, Guo J, Li Q. A Photo- and Thermo-Driven Azoarene-Based Circularly Polarized Luminescence Molecular Switch in a Liquid Crystal Host. Angew Chem Int Ed Engl. 2023 Nov 27; 62(48): e202311486. doi: 10.1002 / anie.202311486. Epub 2023 Sep 18. PMID: 37648676.

[0012] Non-patent literature 6: Wang Y, Nie J, Fang W, Yang L, Hu Q, Wang Z, Sun JZ, TangBZ.Sugar-Based Aggregation-Induced Emission Luminogens: Design, Structures, and Applications. Chem Rev.2020May 27;120(10):4534-4577.doi:10.1021 / acs.chemrev.9b00814.Epub 2020Apr14.PMID:32286808. Summary of the Invention

[0013] One of the objectives of this invention is, in view of the above, to provide a novel synthesis of a non-polarized isonitrile material with multi-stimulus response and all-light-white light modulated circular polarization.

[0014] The problem with this invention lies in the application of carbocationic initiators in isonitrile polymerization, wherein the carbocation acts as a cationic initiator to catalyze the polymerization reaction of isonitrile monomers, and the carbocationic initiator is readily available to obtain high molecular weight isonitrile polymers. Preferably, the carbocationic initiator is 4-methoxy-α-methylbenzyl alcohol (TMOH) or 1-chloro-1-phenylethane (PhEtCl).

[0015] To solve the above problems, the present invention adopts the following technical solution.

[0016] The steps of the homopolymerization reaction are as follows: In an anhydrous and oxygen-free glove box, 4-methoxy-α-methylbenzyl alcohol (TMOH) or 1-chloro-1-phenylethane (PhEtCl) is added to a reactor using chlorobenzene as a solvent. A co-catalyst is then added to the reactor, also using chlorobenzene as a solvent; the molar ratio of catalyst to co-catalyst is 10:1. The reactor containing the mixture is kept at room temperature and stirred for 1 minute until the color of the reaction solution completely fades. Stirring continues for another 2 minutes. A chlorobenzene solution of monomer d is added to the reaction solution, and the reaction is continued for 1–720 minutes with constant stirring. Methanol is then added to stop the reaction. The reaction solution is precipitated with methanol to obtain a solid substance. This solid substance is then vacuum dried at 40°C to remove the solvent until constant weight, yielding the target product. In this system, the molar ratio of monomer d to carbocation initiator / co-catalyst in the binary catalytic system is 100–500:1; the reaction temperature is 25–100℃; the solvent volume in the system is 3–5 mL; and monomer d is one of the isonitriles.

[0017] The copolymerization reaction steps are as follows: In an anhydrous and oxygen-free glove box, 4-methoxy-α-methylbenzyl alcohol (TMOH) or 1-chloro-1-phenylethane (PhEtCl) is added to a reactor using chlorobenzene as a solvent. A co-catalyst is then added to the reactor, also using chlorobenzene as a solvent; the molar ratio of catalyst to co-catalyst is 10:1. The reactor containing the mixture is kept at room temperature and stirred for 1 minute until the color of the reaction solution completely disappears. Stirring continues for another 2 minutes. A chlorobenzene solution of monomer e is added to the reaction solution, and the reaction is continued for 1–720 minutes with constant stirring. Methanol is then added to stop the reaction. The reaction solution is precipitated with methanol to obtain a solid substance. This solid substance is then vacuum dried at 40°C to remove the solvent until constant weight, yielding the target product. In this system, the molar ratio of monomer e to carbocation initiator / co-catalyst in the binary catalytic system is 100–500:1; the reaction temperature is 25–100℃; the solvent volume in the system is 3–5 mL; and monomer e is one of two isonitrile monomers. The preferred solvent for the catalytic system is one of tetrahydrofuran, dichloromethane, chloroform, toluene, or o-dichlorobenzene. The isonitrile is one of (E)-1-(4-isocyanophenyl)-2-phenyldiazene, 4-((1R,2S,5R)-2-isopropyl-5-methylcyclohexyl)phenylisocyanate, and 4-((1S,2R,5S)-2-isopropyl-5-methylcyclohexyl)phenylisocyanate;

[0018] The preparation method of the carbon-cationic initiator / co-catalyst binary catalytic system described in this invention is economical and efficient. The catalyst can be purchased directly without complicated synthesis steps, the catalyst is not easily poisoned, and it is simpler, more economical and efficient. It expands the application range of metal-free cationic initiators in isonitrile polymerization, has good environmental performance, and is suitable for industrial production.

[0019] The carbon-cationic initiator / co-catalyst binary catalytic system described in this invention can carry out self-polymerization and copolymerization reactions of isonitrile monomers to obtain a series of novel stimulus-responsive and all-light-white light polymerizable materials with wide application market.

[0020] A novel multi-stimulus response and all-light-white light modulated circularly polarized isonitrile material can be applied to fields such as information anti-counterfeiting and security encryption.

[0021] Figure 1 The gel permeation chromatography (GPC) spectrum of the polymer was obtained by using 1-chloro-1-phenylethane as an initiator / co-catalyst in Example 10 to catalyze the polymerization of (E)-1-(4-isocyanophenyl)-2-phenyldiazepine.

[0022] Figure 2The gel permeation chromatography (GPC) spectrum of the polymer obtained in Example 10 is catalyzed by the polymerization of 4-((1R,2S,5R)-2-isopropyl-5-methylcyclohexyl)phenylisocyanate using 1-chloro-1-phenylethane as an initiator / co-catalyst.

[0023] Figure 3 The gel permeation chromatography (GPC) spectrum of the polymer obtained in Example 10 is catalyzed by the polymerization of 4-((1S,2R,5S)-2-isopropyl-5-methylcyclohexyl)phenylisocyanate using 1-chloro-1-phenylethane as an initiator / co-catalyst.

[0024] Figure 4 The 1H NMR spectrum of the polymer was obtained by using 1-chloro-1-phenylethane as an initiator / co-catalyst in Example 10 to catalyze the polymerization of (E)-1-(4-isocyanophenyl)-2-phenyldiazepine.

[0025] Figure 5 The 1H NMR spectrum of the polymer was obtained by using 1-chloro-1-phenylethane as an initiator / co-catalyst to catalyze the polymerization of 4-((1R,2S,5R)-2-isopropyl-5-methylcyclohexyl)phenylisocyanate.

[0026] Figure 6 The change in the intensity of circularly polarized light is caused by the relevant stimulus response of the polymer.

[0027] Figure 7 This represents the wavelength variation of circularly polarized light from a panchromatic material.

[0028] Figure 8 This is a schematic diagram illustrating the application of new materials in the anti-counterfeiting market. Detailed Implementation

[0029] The embodiments of the present invention will now be described in detail.

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described below in conjunction with embodiments.

[0031] The main reagent information mentioned in the following examples is shown in Table 1, and the main instruments and equipment are shown in Table 2.

[0032] Table 1

[0033] Table 2

[0034] In an anhydrous and oxygen-free glove box, 2 mL of a chlorobenzene solution containing 100 μmol of chlorobenzene (PhEtCl) was added sequentially to a Schlenk flask, followed by 2 mL of a chlorobenzene solution containing 10 μmol of B(C6F5)3. The reactor containing the mixture was kept at room temperature and stirred for 1 min until the color of the reaction solution completely disappeared. Stirring was continued for another 2 min. Then, 2 mL of a chlorobenzene solution containing 1 mmol of (E)-1-(4-isocyanophenyl)-2-phenyldiazene was added to the reaction solution. The reaction temperature was 25 °C, and the reaction time was 5 min. The Schlenk flask was then quickly removed from the glove box, and under atmospheric conditions, a large amount of anhydrous methanol was added while stirring. After drying in a vacuum oven, poly(E)-1-(4-isocyanophenyl)-2-phenyldiazene was obtained, with a net weight of 184 mg and a yield of 60%. GPC analysis determined the number-average molecular weight M of poly(E)-1-(4-isocyanophenyl)-2-phenyldiazene. n =6.4×10 4 Molecular weight distribution M w / M n =3.04.

[0035] Including but not limited to the above implementations

[0029] , white light CPL has received widespread attention from academia and industry due to its extensive applications in optical sensing, information encryption, and optoelectronic devices. A common method to achieve white light CPL is to combine three primary colors or two complementary colors from a chiral luminescent material. By adjusting the mixing ratio of the three fluorophores, a composite film that has both white fluorescence emission and white light CPL can be prepared.

[0036] Therefore, by adding appropriate achiral fluorophores to CPL-active polyisocyanate materials with highly ordered helical superstructures, a full-color CPL spectrum covering the visible light region can be obtained. In this process, three fluorophores with different emission wavelengths were selected sequentially: styrene (TPE), coumarin 6 (Cou6), and Nile red (NR).

[0037] Selected fluorophores, including blue fluorophore TPE, green fluorophore Cou6, and red fluorophore NR, were added to superpolyisocyanates to prepare supramolecular composite films.

[0038] Furthermore, the full-color film exhibited a distinct circular dichroism (CPL) signal in the wavelength range of 400 to 800 nanometers, confirming the successful preparation of the full-color CPL active film.

[0039] By adjusting the mass ratio of blue fluorophore TPE, green fluorophore Cou6, and red fluorophore NR to 40:3:5 (denoted as T...), 40A novel white CPL composite film was successfully prepared using C3N5. This film not only exhibits white fluorescence emission (CIE coordinates (0.32, 0.33)) but also displays white CPL properties. Calculation results show that T 40 The maximum |glum| value of C3N5 is as high as -4.39×10 -3 .

[0040] In composite films composed of fluorescent pigments and polyisocyanates, the generation mechanism of CPL (circular dichroism spectroscopy) involves the transfer of chirality from the chiral source to the fluorescent pigment. When the fluorescent dye is introduced into the system, the large conjugated groups on the dye's functional groups interact with the IPPD and IMCI structures on the PI backbone through π-π interactions, participating in the self-assembly process of the PI backbone. During this process, the chiral structures transfer their chirality to the dye, prompting the dye to self-assemble into an ordered arrangement within the film, ultimately generating strong circular dichroism and circular polarization spectral signals.

[0041] Stimulus-responsive cyclohexane (CPL) materials have shown significant advantages in sensor devices and information encryption technologies. Recent studies have demonstrated that the cis-trans isomerization of azobenzene units can trigger a chiral 'on-off' switching of side-chain polymers in solution. By utilizing this mechanism, stimulus-responsive CPLs can be realized in helical supramolecular polyisocyanates, achieved through the reversible switching of the cis-trans configuration of the azobenzene side groups on the polymer chain in response to external stimuli.

[0042] Trans-azobenzene (with a linear molecular structure and high π-electron conjugation) can absorb ultraviolet light at 365 nm (its absorption peak matches this wavelength, effectively promoting the E→Z transition). The π-π* electron transition breaks the π bond of the N=N double bond, causing the molecule to rotate around the σ bond, transforming from a linear trans structure to a spatially curved cis structure. In flexible polymers, azobenzene units possess a high degree of freedom of movement and a rapid photoisomerization rate (this process typically occurs on a nanosecond to microsecond timescale). In rigid polymers or crystalline regions, molecular motion is restricted, reducing isomerization efficiency. Typically, trans-azobenzene molecules exhibit a linear structure, readily forming close-packed structures, while cis structures, due to greater steric hindrance, are difficult to stack closely. Therefore, the spatially curved structure of the cis-azophenyl group reduces conjugation, affecting the polymer's optical properties and macroscopic morphology. Conversely, the cis isomer is unstable (possessing high steric hindrance and dipole moment), and at room temperature, it accelerates the transition from cis to trans by absorbing longer wavelengths of light (such as visible light), restoring its self-assembly degree, fluorescence, and chirality. This process is reversible and controllable, and is the core mechanism for designing photoresponsive smart materials.

[0043] The protonation of azophenyl dyes promotes the formation of the cis configuration. In an acidic environment, the nitrogen atom in the azophenyl group is protonated (-N=N-H+), forming a positively charged conjugated structure. At this point, the π-electron cloud density of the N=N double bond decreases, the double bond energy weakens, and the energy barrier for cis-trans isomerization is lowered, making it easier to convert from trans to cis. Furthermore, after protonation, the polarity of the azophenyl group increases, and the electrostatic repulsion between it and adjacent groups may prompt the molecule to adopt a cis conformation (i.e., a bent structure) to mitigate this repulsion. Therefore, the cis-azophenyl group forms a bent molecular structure, which reduces its degree of conjugation. Simultaneously, the polymer chain extends due to charge repulsion. These changes lead to alterations in chiral polymer properties, such as the degree of self-assembly, fluorescence, and decreased chirality. In contrast, alkaline conditions (high pH) can enhance the stability of the trans structure of the azophenyl group. In an alkaline environment, the azo group undergoes deprotonation (i.e., reverts to -N=N-), which increases the π-electron cloud density and enhances the energy of the N=N double bond. The thermodynamic stability of the trans structure is significantly higher than that of the cis structure. Furthermore, the deprotonated azophenyl group exhibits reduced polarity, and the linear arrangement of the trans structure favors π-π stacking between aromatic rings (e.g., within the polymer chain or intermolecularly), further stabilizing the trans conformation. Therefore, the polymer may further aggregate, leading to changes in chiral polymer properties, such as increased self-assembly, fluorescence, and chirality.

[0044] Azobenzene's cis and trans structures possess different molecular shapes, dipole moments, and electron distributions, which influence their coordination ability and patterns with metal ions. Typically, the trans-structured azobenzene molecule is linear and readily coordinates with Fe. 3+ The ions form stable coordination bonds, thus transforming into a cis structure. However, due to greater steric hindrance, the cis structure interacts more readily with Fe. 3+ The coordination ability of Fe ions is relatively weak. Furthermore, Fe... 3+ Coordination of ions with azobenzene polymers reduces the rate of photoisomerization and lowers the concentration of the trans isomer under photostable conditions. Furthermore, coordination of the azophenyl group with metal ions may alter the molecular stacking and spacing, thereby weakening π-π interactions. Therefore, Fe was observed... 3+ The properties of coordinated chiral polymers have changed significantly, such as reduced self-assembly, decreased fluorescence intensity, and weakened chirality.

[0045] In favorable solvents, azobenzene side groups can rotate freely, exhibiting rapid cis-trans isomerization rates and good photoreversibility. However, poorly water-soluble solvents promote the aggregation of lipophilic azobenzene polymers. In the aggregated state, strong intermolecular interactions (such as π-π stacking and hydrogen bonding) restrict molecular movement, increase the energy barrier for isomerization, and enhance the stability of the trans isomer. Furthermore, in the aggregated state, the π-π interactions between azobenzene molecules alter their electron cloud distribution, affecting the isomerization energy barrier. In other words, due to restricted molecular motion and steric hindrance, azobenzene side groups tend to form trans structures in aggregated states (such as nanoparticles). Given the compact structure formed by the trans-azophenyl group, different degrees of π-π interactions lead to polymer self-assembly in different forms, increasing helicity and CPL value.

[0046] Including but not limited to the above embodiments, any equivalent substitutions or partial improvements made under the spirit and principles of this invention shall be considered within the protection scope of this invention.

Claims

1. The synthesis of a multi-stimulus responsive and all-light-white-light modulated circularly polarized isonitrile material, characterized in that: The catalysts are carbocation initiators 4-methoxy-α-methylbenzyl alcohol (TMOH) and 1-chloro-1-phenylethane (PhEtCl).

2. The synthesis of a multi-stimulus responsive and all-light-white light modulated circularly polarized isonitrile material according to claim 1, characterized in that: The catalyst can be purchased directly, and the polymerization reaction is carried out in an anhydrous and oxygen-free environment to obtain a high molecular weight polymer.

3. The synthesis of a multi-stimulus responsive and all-light-white light modulated circularly polarized isonitrile material according to claim 1, characterized in that: The resulting polymer is vacuum dried at 40°C.

4. The synthesis of a multi-stimulus responsive and all-light-white light modulated circularly polarized isonitrile material according to claim 1, characterized in that: The monomers are (E)-1-(4-isocyanophenyl)-2-phenyldiazepine, 4-((1R,2S,5R)-2-isopropyl-5-methylcyclohexyl)phenylisocyanate, and 4-((1S,2R,5S)-2-isopropyl-5-methylcyclohexyl)phenylisocyanate.

5. The synthesis of a multi-stimulus responsive and all-light-white light modulated circularly polarized isonitrile material according to claim 1, characterized in that: The carbocation initiator does not need to coordinate with a ligand.

6. The synthesis of a multi-stimulus responsive and all-light-white light modulated circularly polarized isonitrile material according to claim 1, characterized in that: The cocatalysts are organoborates [PhNHMe2][B(C6F5)4] and borane compounds B(C6F5)3.

7. According to claim 1, the fluorescent molecules are Nile Red, Coumarin and Tetraphenylene Alcohol, and the proportion of white light is strictly controllable.

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