A single molecular weight chiral azobenzene oligomer and its preparation method and application

Abstract

The present application relates to a single molecular weight chiral azobenzene oligomer and a preparation method and application thereof, and belongs to the technical field of oligomers. The molecular formula of the single molecular weight chiral azobenzene oligomer is wherein N=2, 4, 8, 12 or 16. The single molecular weight chiral azobenzene oligomer can control the aggregation mode and supramolecular chiral expression of the assembly by controlling the size of the oligomer molecular weight and the proportion of the assembly solvent, realizes the precise construction and preparation of the supramolecular chiral structure, and has good application prospects in the fields of chiral switches, molecular recognition and molecular device design.

Description

Technical Field

[0001] This invention belongs to the field of oligomer technology, and particularly relates to a single molecular weight chiral azobenzene oligomer, its preparation method and application. Background Technology

[0002] Chirality is a ubiquitous structural feature in nature. Studying chiral structures plays a crucial role in exploring the mysteries of life and serves as an important bridge connecting life sciences and chemistry. Researchers often use artificial synthesis to study the transfer processes from molecular chirality to supramolecular chirality and even macroscopic chirality (Gao, Y.; Hao, J.; Zhang, X.; Hu, J.; Ju, Y. Nanoscale 2015, 7, pp13568-13575; Karunakaran, SC; Cafferty, BJ; Weigert-Munoz, A.; Schuster, GB; Hud, NV. Angew. Chem. Int. Ed. 2019, 58, pp1453-1457). Azobenzene polymers have been widely used in the study of supramolecular chirality. Reversible photoinduced cis-trans isomerism of azobenzene can be used to construct chiral photoswitches. The supramolecular chirality of azobenzene polymers can usually be constructed by using chiral azobenzene polymers or by inducing chiral assembly of achiral azobenzene polymers under external conditions. Constructing chiral photoswitches based on this would be a very meaningful endeavor (Jiang, S.; Zhao, Y.; Wang, L.; Yin, L.; Zhang, Z.; Zhu, J.; Zhang, W.; Zhu, X. Polym. Chem. 2015, 6, pp4230-4239.; Gan, Y.; Dai, H.; Ma, Y.; Cheng, X.; Wang, Z.; Zhang, W. Macromolecules 2022, 55, pp8556-8565). Structure determines properties, and the molecular weight of a polymer has a significant impact on the morphology of its assembly and the expression of supramolecular chirality (Cheng, X.; Miao, T.; Ma, Y.; Zhu, X.; Zhang, W.; Zhu, X. Angew. Chem. Int. Ed. 2021, 60, pp. 24430-24436). However, current research still focuses on polydisperse polymer systems, and the results are based on statistical estimates, which cannot precisely explore the influence of polymer molecular weight on the morphology and supramolecular chirality of its assembly.Polymers with single molecular weights possess definite chain lengths and structures, making them ideal models for studying the structure-property relationship between material properties and polymer structure (Takizawa, K.; Tang, C.; Hawker, CJAm. Chem. Soc. 2008, 130, pp. 1718-1726; Lawrenc, J.; Goto, E.; Ren, J.; McDearmon, B.; Kim, D.; Ochiai, Yuto; Clark, P.; Laitar, D.; Higashihara, T.; Hawker, CJAm. Chem. Soc. 2017, 139, pp. 13735-13739). Therefore, preparing single molecular weight chiral azobenzene polymers and exploring their structure-property relationships can provide a theoretical basis for the development and application of chiral photoelectric switching materials. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a single-molecular-weight chiral azobenzene oligomer, its preparation method, and its applications. A series of single-molecular-weight oligomers containing an azobenzene structure and chiral carbon in their main chain were designed and synthesized. Since each oligomer chain has the same structure and molecular weight, polymer self-assembly and supramolecular chiral behavior can be precisely studied.

[0004] The first objective of this invention is to provide a single-molecular-weight chiral azobenzene oligomer with the following structure:

[0005]

[0006] Where N = 2, 4, 8, 12 or 16.

[0007] A second objective of this invention is to provide a chiral azobenzene monomer with the following structure:

[0008]

[0009]

[0010] A third objective of this invention is to provide the application of the chiral azobenzene monomer in the preparation of the single molecular weight chiral azobenzene oligomer.

[0011] The fourth objective of this invention is to provide a method for preparing the single molecular weight chiral azobenzene oligomer, comprising the following steps:

[0012] S1, chiral azobenzene monomer (R / S)-TBDPS-Azo-tBu, tetrabutylammonium fluoride and glacial acetic acid undergo a detert-butyldiphenylsilylation reaction in the presence of dichloromethane to give (R / S)-HO-Azo-tBu;

[0013] Chiral azobenzene monomer (R / S)-TBDPS-Azo-tBu and p-toluenesulfonic acid monohydrate undergo a detert-butylation reaction in the presence of silica gel and tetrahydrofuran to give (R / S)-TBDPS-Azo-COOH;

[0014] S2. The (R / S)-HO-Azo-tBu, (R / S)-TBDPS-Azo-COOH and dicyclohexylcarbodiimide described in S1 are subjected to an esterification reaction in the presence of 4-dimethylaminopyridine and dichloromethane to obtain the single molecular weight chiral azobenzene oligomer.

[0015] Alternatively, the (R / S)-HO-Azo-tBu, (R / S)-TBDPS-Azo-COOH and dicyclohexylcarbodiimide described in S1 are subjected to an esterification reaction in the presence of 4-dimethylaminopyridine and dichloromethane. The above-described detert-butyldiphenylsilylation reaction, detert-butylation reaction and esterification reaction are repeated to obtain the single molecular weight chiral azobenzene oligomer through iterative growth.

[0016] In one embodiment of the present invention, the temperature of the detert-butylation reaction is 90°C-110°C.

[0017] The fifth objective of this invention is to provide a method for preparing the chiral azobenzene monomer, comprising the following steps:

[0018] S1, 4-(BOC-amino)phenol, (R / S)-methyl lactate, triphenylphosphine and diisopropyl azodicarbonate react in the presence of tetrahydrofuran to give (R / S)-Boc-Ben-Me.

[0019] S2, (R / S)-Boc-Ben-Me and trifluoroacetic acid react in the presence of dichloromethane to give (R / S)-NH2-Ben-Me;

[0020] S3 and (R / S)-NH2-Ben-Me undergo a diazo reaction in the presence of dilute hydrochloric acid and sodium nitrite to obtain a diazonium salt, which is then coupled with phenol to obtain (R / S)-HO-Azo-Me.

[0021] S4 and (R / S)-HO-Azo-Me react in the presence of lithium aluminum hydride and tetrahydrofuran to give (R / S)-HO-Azo-OH;

[0022] Br-tBu is obtained by reacting 6-bromohexanoic acid and tert-butanol in the presence of trifluoroacetic anhydride and tetrahydrofuran.

[0023] S5, (R / S)-HO-Azo-OH and Br-tBu react at 55℃-65℃ in the presence of cesium carbonate and acetonitrile to give (R / S)-HO-Azo-tBu;

[0024] S6, (R / S)-HO-Azo-tBu, and tert-butyldiphenylchlorosilane react in the presence of imidazole and dichloromethane to give the chiral azobenzene monomer.

[0025] In one embodiment of the invention, in S3, the temperatures of the diazo reaction and the coupling reaction are independently -5°C to 5°C.

[0026] A sixth object of the present invention is to provide an assembly prepared from the aforementioned single-molecular-weight chiral azobenzene oligomer.

[0027] A seventh object of the present invention is to provide an oligomer film prepared from the aforementioned single molecular weight chiral azobenzene oligomer.

[0028] An eighth object of the present invention is to provide an application of the single molecular weight chiral azobenzene oligomer, the assembly, or the oligomer film in the field of chiral photoconversion.

[0029] The technical solution of the present invention has the following advantages compared with the prior art:

[0030] (1) The preparation method described in this invention introduces a chiral center into an azobenzene compound and successfully prepares a single molecular weight chiral azobenzene oligomer by combining orthogonal deprotection of the end groups and iterative exponential growth method.

[0031] (2) The chemical reagents used in the preparation method of the present invention are stable in air, and the reaction operation in this method is simple, easy to perform, and highly efficient.

[0032] (3) The single molecular weight chiral azobenzene oligomers of the present invention can control the aggregation mode and supramolecular chiral expression of the assembly by controlling the size of the oligomer molecular weight and the ratio of the assembly solvent, thus realizing the precise construction and preparation of supramolecular chiral structures, and has good application prospects in the fields of chiral switches, molecular recognition and molecular device design. Attached Figure Description

[0033] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein:

[0034] Figure 1 The 1H NMR spectra are R / S-Nmer (N = 2, 4, 8, 12, 16).

[0035] Figure 2GPC effluent curves for R / S-Nmer (N = 2, 4, 8, 12, 16);

[0036] Figure 3 MALDI-TOF plots for R / S-Nmer (N = 2, 4, 8, 12, 16);

[0037] Figure 4 DSC spectra of R-Nmer (N = 2, 4, 8, 12, 16);

[0038] Figure 5 POM images of R-Nmer (N = 2, 4, 8, 12, 16) at different temperatures;

[0039] Figure 6 The SAXS and WASD spectra after R-Nmer (N = 2, 4, 8, 12, 16) annealing are shown.

[0040] Figure 7 The length of a repeating element when fully extended, obtained by simulation calculation using the MM2 force field method;

[0041] Figure 8 The circular dichroism and UV / Vis absorption spectra of R / S-Nmer (N = 4, 8, 12, 16) in the dissolved state are shown.

[0042] Figure 9 The following are the CD and UV-vis absorption spectra of the R / S-Nmer (N = 16, 12, 8) assemblies in different volume ratios of the mixed solvent THF / EtOH; where ac and gi are the CD and UV-vis absorption spectra, and df and jl are the g values ​​of the assembly at the first Cotton effect. CD Trend of maximum value changes;

[0043] Figure 10 The CD and UV-vis absorption spectra of R / S-Nmer (N=2, 4) in mixed solvents with THF / EtOH volume ratios of 3.0 / 0 and 0.1 / 2.9 are shown.

[0044] Figure 11 Normalized UV-Vis and CD spectra of R-Nmer (N=16, 12) assembly solutions under different volume ratios of mixed solvents THF / EtOH;

[0045] Figure 12 The CD (AC) and normalized UV-Vis spectra (ac) of the R-16mer assembly solution before and after heating and cooling treatment under different volume ratios of the mixed solvent THF / EtOH are shown; where (A, a) represents the v THF / vEtOH＝ 0.1 / 2.9; (B, b) is v THF / v EtOH＝ 0.4 / 2.6; (C, c) represents v THF / v EtOH＝ 0.8 / 2.2;

[0046] Figure 13 TEM images of R / S-Nmer (N = 8, 12, 16) assemblies in different volume ratios of mixed solvent THF / EtOH; where (a) is R-16mer, (b) is S-16mer, (c) is R-12mer, (d) is S-12mer, (e) is R-8mer, and (f) is S-8mer.

[0047] Figure 14 For use in mixed solvents (v THF / v EtOH =1.0 / 2.0), TEM images of the R / S-12mer assembly before and after ultrasound; where (ab) is the R-12mer assembly and (cd) is the S-12mer assembly;

[0048] Figure 15 For use in mixed solvents (v THF / v EtOH =1.0 / 2.0), TEM images of the R / S-12mer assembly at different aging times; where (ac) represents R-12mer and (df) represents S-12mer;

[0049] Figure 16 For use in mixed solvents (v THF / v EtOH =1.0 / 2.0), characterization diagram and assembly diagram of R-12mer thin sheet structure, where (a) is SEM, (b) is AFM image, (c) is AFM height map, and (d) is assembly diagram;

[0050] Figure 17 The CD and UV-vis absorption spectra of the R / S-16mer assembly are shown in the mixed solvent THF / EtOH at different volume ratios; where (a) represents the mixed solvent (v) THF / v EtOH =0.8 / 2.2), the changes in CD and UV-vis absorption spectra of the R-16mer assembly after 365nm UV irradiation and HC treatment, (b) are the changes in the mixed solvent (v THF / v EtOH =0.4 / 2.6), the CD and UV-vis absorption spectra of the R-16mer assembly under 365 nm ultraviolet light irradiation, (cd) is the absorption spectrum in the mixed solvent (vTHF / v EtOH =0.4 / 2.6), the CD and UV-vis absorption spectra of the R / S-16mer assembly after alternating 365nm UV irradiation and HC treatment, and the maximum CD value at the first Cotton effect, are shown in the graph after 5 cycles. (e) shows the changes in the CD and UV-vis absorption spectra of the R / S-16mer assembly after alternating 365nm UV irradiation and HC treatment. THF / v EtOH =0.1 / 2.9), CD and UV-vis absorption spectra of the R-16mer assembly under 365 nm UV irradiation; (f) shows the absorption spectra of the R-16mer assembly in a mixed solvent (v THF / v EtOH =0.1 / 2.9), CD and UV-vis absorption spectra of the R-16mer assembly during HC treatment;

[0051] Figure 18 Thermodynamic properties of R-8mer and disp-R-8mer were tested; (a) DSC temperature curves of R-8mer and disp-R-8mer, and (b) CD and UV-vis absorption spectra of disp-R-8mer assemblies under different volume ratios of mixed solvent THF / EtOH.

[0052] Figure 19 TEM images of the disp-R-8mer assembly under different volume ratios of the mixed solvent THF / EtOH;

[0053] Figure 20 The supramolecular chirality expression of R / S-Nmer (N = 2, 4, 8, 12, 16) films is shown. (a) shows the internal packing diagram of the film before and after annealing; (b) shows the CD and UV-vis absorption spectra of the film before annealing; and (c) shows the CD and g... CD The graph shows the change in maximum value as molecular weight increases. (d) represents the changes in CD and UV-vis absorption spectra of the R-8mer film before and after annealing. Detailed Implementation

[0054] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0055] Example

[0056] A single molecular weight chiral azobenzene oligomer, taking the R-configuration oligomer as an example, includes the following steps:

[0057] S1. Synthesis of (R)-Boc-Ben-Me: 4-(BOC-amino)phenol (20.00 g, 1 eq.), (R)-methyl lactate (14.93 g, 1.5 eq.), diisopropyl azodicarbonate (29.00 g, 1.5 eq.), and 300 mL of tetrahydrofuran were added to a 1000 mL single-necked round-bottom flask and stirred in an ice-water bath. Triphenylphosphine (37.61 g, 1.5 eq.) was dissolved in 80 mL of tetrahydrofuran and then added to the flask. The reaction was carried out at room temperature for 12 h. After the reaction was completed, the solvent was removed by rotary evaporation, and most of the byproduct triphenylphosphine oxide was precipitated with ice-cold diethyl ether. Then, the product was purified by column chromatography (petroleum ether: ethyl acetate = 4:1, volume ratio), and dried under vacuum at 35 °C to obtain a pale yellow liquid (R)-Boc-Ben-Me (25.6 g, 87.0%).

[0058]

[0059] S2. Synthesis of (R)-NH2-Ben-Me: (R)-Boc-Ben-Me (15.00 g, 1 eq.) and 75 mL of dichloromethane were added to a 250 mL single-necked round-bottom flask and stirred at room temperature. 75 mL of trifluoroacetic acid was added dropwise using a constant-pressure dropping funnel. After the addition was complete, the reaction was continued for 30 min. After the reaction was completed, 5% Na2CO3 aqueous solution was added to quench the reaction solution until the pH of the reaction solution was 7. The solution was then extracted with dichloromethane. The organic layer was dried with anhydrous sodium sulfate, filtered, concentrated, and dried to obtain a brown liquid (R)-NH2-Ben-Me (8.97 g, yield: 90.5%).

[0060]

[0061] S3, Synthesis of (R)-Me-Azo-OH (including the preparation of diazonium salt and coupling reaction with phenol):

[0062] Preparation of diazonium salt: Weigh (R)-Me-Ben-NH2 (5.00 g, 1 eq.) into a 50 mL round-bottom flask, add 7.5 mL of methanol to dissolve, and stir in an ice-water bath; dilute 7.5 mL of concentrated hydrochloric acid with 7.5 mL of water, and add the diluted hydrochloric acid dropwise to the round-bottom flask; then weigh sodium nitrite (2.1 g, 1.2 eq.) and dissolve it in 20 mL of water, slowly add it dropwise to the above flask and stir for 1 h; finally, add a certain amount of urea to consume the unreacted sodium nitrite to obtain a diazonium salt solution, and keep the temperature at 0-5℃ throughout;

[0063] Coupling reaction: Phenol (4.81 g, 2 eq.) and sodium hydroxide (4.10 g, 4 eq.) were dissolved in 600 mL of water in a 1 L beaker. Sodium bicarbonate was added to maintain the pH of the solution at 9-10, and the mixture was stirred in an ice-water bath. The diazonium salt component was added dropwise, and the temperature was maintained at 0-5 °C. After the addition was complete, the reaction was continued for 5 h. After the reaction was completed, the mixture was filtered, the filter cake was washed with deionized water, and dried at 50 °C to obtain a yellow solid (R)-Me-Azo-OH (6.07 g, yield: 79.1%).

[0064]

[0065] S4. Synthesis of (R)-HO-Azo-OH: Weigh (R)-Me-Azo-OH (8.00 g, 1 eq.) and 200 mL of anhydrous tetrahydrofuran and add them to a 500 mL single-necked round-bottom flask. Stir under an ice-water bath. Dissolve lithium aluminum hydride (3.04 g, 3 eq.) in 30 mL of anhydrous tetrahydrofuran and slowly add it dropwise to the round-bottom flask. After the addition is complete, continue the reaction for 30 min. Quench the reaction by slowly adding saturated magnesium sulfate aqueous solution to the system. Remove the solvent by rotary evaporation, then dissolve in methanol, filter, concentrate, and purify by column chromatography (dichloromethane:methanol = 10:1, volume ratio). Dry under vacuum at 35 °C to obtain a yellow solid (R)-HO-Azo-OH (6.27 g, yield: 86.3%).

[0066]

[0067] S5. Synthesis of Br-tBu: 6-bromohexanoic acid (9.50 g, 1 eq.), trifluoroacetic anhydride (40.93 g, 4 eq.) and 60 mL tetrahydrofuran were weighed into a 250 mL single-necked round-bottom flask and stirred at room temperature for 1 h. Then, 30 mL of tert-butanol was added to the flask, and the reaction was continued for 16 h. After the reaction was completed, the reaction was quenched with saturated sodium bicarbonate aqueous solution until the pH of the reaction solution was 8. The solution was extracted with 150 mL of ethyl acetate, dried over anhydrous sodium sulfate, concentrated, and purified by column chromatography (petroleum ether:ethyl acetate = 30:1, volume ratio) to obtain a colorless liquid Br-tBu (11.97 g, yield: 97.9%).

[0068]

[0069] S6. Synthesis of (R)-HO-Azo-tBu: Weigh (R)-HO-Azo-OH (5.00 g, 1 eq.) and cesium carbonate (9.00 g, 2 eq.) and dissolve them in 150 mL of acetonitrile in a 250 mL single-necked round-bottom flask. Stir at 60 °C, then add Br-tBu (6.93 g, 2 eq.) to the flask and continue the reaction for 6 h. After the reaction is complete, filter, concentrate, and purify by column chromatography (petroleum ether: ethyl acetate = 1:1, volume ratio). Dry under vacuum at 35 °C to obtain a yellow solid (R)-HO-Azo-tBu (6.68 g, yield: 82.2%).

[0070]

[0071] S7. Synthesis of monomer (R)-TBDPS-Azo-tBu: Weigh (R)-HO-Azo-tBu (3.00 g, 1 eq.) and imidazole (0.94 g, 2 eq.) and dissolve them in 50 mL of dichloromethane in a 250 mL single-necked round-bottom flask. Stir at room temperature, then add tert-butyldiphenylchlorosilane (3.80 g, 2 eq.) to the flask and continue the reaction for 2 h. After the reaction is complete, filter, concentrate, and purify by column chromatography (petroleum ether: ethyl acetate = 30:1, volume ratio). Dry under vacuum at 35 °C to obtain a yellow solid, namely monomer (R)-TBDPS-Azo-tBu (4.37 g, yield: 93.1%).

[0072]

[0073] S8, Synthesis of (R)-TBDPS-Azo-COOH and R-2mer:

[0074] Synthesis of (R)-TBDPS-Azo-COOH: (R)-TBDPS-Azo-tBu (4.00 g, 1 eq.) was dissolved in 30 mL of toluene in a 100 mL single-necked round-bottom flask and stirred at 105 °C. Then, p-toluenesulfonic acid monohydrate (0.52 g, 0.2 eq.) and silica gel (4.0 g) were added to the flask, and the reaction was continued for 0.5 h. After the reaction was completed, the mixture was filtered, concentrated, purified by column chromatography (petroleum ether: ethyl acetate = 2:1, volume ratio), and dried under vacuum at 35 °C to obtain a yellow solid product (R)-TBDPS-Azo-COOH (3.43 g, yield: 93.1%).

[0075]

[0076] Synthesis of R-2mer: (R)-TBDPS-Azo-COOH (1.50 g, 1 eq.), (R)-HO-Azo-tBu (1.06 g, 1 eq.) and 4-dimethylaminopyridine (0.29 g, 1 eq.) were weighed and dissolved in dichloromethane in a 100 mL single-necked round-bottom flask. The mixture was stirred at room temperature, and then dicyclohexylcarbodiimide (0.99 g, 2 eq.) was dissolved in an appropriate amount of dichloromethane. The reaction was continued for 8 h. After the reaction was completed, the mixture was filtered, concentrated, purified by column chromatography (petroleum ether: ethyl acetate = 3:1, volume ratio), and dried under vacuum at 35 °C to obtain the yellow solid product R-2mer (2.30 g, yield: 93.1%).

[0077]

[0078] S9. Synthesis of R-2mer-COOH, R-2mer-OH and R-4mer:

[0079] Synthesis of R-2mer-COOH: R-2mer (1 eq.) was weighed and dissolved in toluene in a 100 mL single-necked round-bottom flask. The mixture was stirred at 105 °C. Then, p-toluenesulfonic acid monohydrate (0.52 g, 0.2 eq.) and an appropriate amount of silica gel were added to the flask, and the reaction was continued for 0.5 h. After the reaction was completed, the mixture was filtered, concentrated, purified by column chromatography (petroleum ether: ethyl acetate = 1:1, volume ratio), and dried under vacuum at 35 °C to obtain the yellow solid product R-2mer-COOH.

[0080] Synthesis of R-2mer-OH: Weigh R-2mer (1 eq.) and dissolve it in tetrahydrofuran in a 100 mL single-necked round-bottom flask. Stir at room temperature, add acetic acid (1 eq.) dropwise to the flask, and then add tetrabutylammonium fluoride (TBAF) (1 mol / L THF solution, 1 eq.) dropwise to the reaction solution. React for 2 h. After the reaction is completed, concentrate the solution, purify by column chromatography (petroleum ether: ethyl acetate = 3:2, volume ratio), and dry under vacuum at 35 °C to obtain the yellow solid product R-2mer-OH.

[0081] Synthesis of R-4mer: R-2mer-COOH (1 eq.), R-2mer-OH (1 eq.) and 4-dimethylaminopyridine (1 eq.) were weighed and dissolved in dichloromethane in a 100 mL single-necked round-bottom flask. The mixture was stirred at room temperature, and then dicyclohexylcarbodiimide (2 eq.) was dissolved in an appropriate amount of dichloromethane. The reaction was continued for 8 h. After the reaction was completed, the mixture was filtered, concentrated, purified by column chromatography (dichloromethane:ethyl acetate = 20:1, volume ratio), and dried under vacuum at 35 °C to obtain the yellow solid product R-4mer.

[0082] S10, synthesis of R-4mer-COOH, R-4mer-OH and R-8mer:

[0083] Synthesis of R-4mer-COOH: Weigh R-4mer (1 eq.) and dissolve it in toluene in a 100 mL single-necked round-bottom flask. Stir at 105 °C, then add p-toluenesulfonic acid monohydrate (0.52 g, 0.2 eq.) and an appropriate amount of silica gel to the flask, and continue the reaction for 0.5 h. After the reaction is completed, filter, concentrate, and purify by column chromatography (dichloromethane:ethyl acetate = 10:1, volume ratio). Dry under vacuum at 35 °C to obtain the yellow solid product R-4mer-COOH.

[0084] Synthesis of R-4mer-OH: Weigh R-4mer (1 eq.) and dissolve it in tetrahydrofuran in a 100 mL single-necked round-bottom flask. Stir at room temperature, add acetic acid (1 eq.) dropwise to the flask, and then add tetrabutylammonium fluoride (TBAF) (1 mol / L THF solution, 1 eq.) dropwise to the reaction solution. React for 2 h. After the reaction is completed, concentrate the solution, purify by column chromatography (dichloromethane:ethyl acetate = 10:1, volume ratio), and dry under vacuum at 35 °C to obtain the yellow solid product R-4mer-OH.

[0085] Synthesis of R-8mer: R-4mer-COOH (1 eq.), R-4mer-OH (1 eq.) and 4-dimethylaminopyridine (1 eq.) were weighed and dissolved in dichloromethane in a 100 mL single-necked round-bottom flask. The mixture was stirred at room temperature, and then dicyclohexylcarbodiimide (2 eq.) was dissolved in an appropriate amount of dichloromethane. The reaction was continued for 8 h. After the reaction was completed, the mixture was filtered, concentrated, purified by column chromatography (dichloromethane:ethyl acetate = 15:1, volume ratio), and dried under vacuum at 35 °C to obtain the yellow solid product R-8mer.

[0086] S11, Synthesis of R-8mer-COOH, R-8mer-OH, R-12mer and R-16mer:

[0087] Synthesis of R-8mer-COOH: R-8mer (1 eq.) was weighed and dissolved in toluene in a 100 mL single-necked round-bottom flask. The mixture was stirred at 105 °C. Then, p-toluenesulfonic acid monohydrate (0.52 g, 0.2 eq.) and an appropriate amount of silica gel were added to the flask, and the reaction was continued for 0.5 h. After the reaction was completed, the mixture was filtered, concentrated, purified by column chromatography (dichloromethane:ethyl acetate = 5:1, volume ratio), and dried under vacuum at 35 °C to obtain the yellow solid product R-8mer-COOH.

[0088] Synthesis of R-8mer-OH: Weigh R-8mer (1 eq.) and dissolve it in tetrahydrofuran in a 100 mL single-necked round-bottom flask. Stir at room temperature, add acetic acid (1 eq.) dropwise to the flask, and then add tetrabutylammonium fluoride (TBAF) (1 mol / L THF solution, 1 eq.) dropwise to the reaction solution. React for 2 h. After the reaction is completed, concentrate the solution, purify by column chromatography (dichloromethane:ethyl acetate = 5:1, volume ratio), and dry under vacuum at 35 °C to obtain the yellow solid product R-8mer-OH.

[0089] Synthesis of R-12mer: R-4mer-COOH (1 eq.), R-8mer-OH (1 eq.) and 4-dimethylaminopyridine (1 eq.) were weighed and dissolved in dichloromethane in a 100 mL single-necked round-bottom flask. The mixture was stirred at room temperature, and then dicyclohexylcarbodiimide (2 eq.) was dissolved in an appropriate amount of dichloromethane. The reaction was continued for 12 h. After the reaction was completed, the mixture was filtered, concentrated, purified by preparative GPC, and dried under vacuum at 35 °C to obtain the yellow solid product R-12mer.

[0090] Synthesis of R-16mer: R-8mer-COOH (1 eq.), R-8mer-OH (1 eq.) and 4-dimethylaminopyridine (1 eq.) were weighed and dissolved in dichloromethane in a 100 mL single-necked round-bottom flask. The mixture was stirred at room temperature, and then dicyclohexylcarbodiimide (2 eq.) was dissolved in an appropriate amount of dichloromethane. The reaction was continued for 12 h. After the reaction was completed, the mixture was filtered, concentrated, purified by preparative GPC, and dried under vacuum at 35 °C to obtain the yellow solid product R-16mer.

[0091] Test Example 1

[0092] R / S-Nmer (N = 2, 4, 8, 12, 16) were subjected to 1 Characterization by 1H NMR, GPC, and MALDI-TOF MS, the results are as follows: Figure 1-3 As shown. Figure 1 As shown, the proton chemical shifts and their integral values ​​on the benzene ring and tert-butyl group of R / S-Nmer (N = 2, 4, 8, 12, 16) are consistent with the theoretical values. Figure 2 As shown, oligomers of different molecular weights all exhibit narrowly distributed single peaks, and the molecular weight distribution M... W / M n All are less than 1.01. For example... Figure 3 As shown, the calculated molar mass of each oligomer is in agreement with the experimental measurement, indicating the successful preparation of R / S-Nmer.

[0093] Test Example 2

[0094] The physical properties of R / S-Nmer (N = 2, 4, 8, 12, 16) were investigated using DSC, POM, WAXD, and SAXS tests to elucidate the intrinsic relationship between oligomer structure and aggregation-induced chiral supramolecular structures.

[0095] The results of DSC and POM tests are as follows: Figure 4-5 As shown. By Figure 4 The thermal analysis spectra of the first cooling and second heating of R-Nmer (N = 2, 4, 8, 12, 16) are shown, with a heating / cooling rate of 5℃ / min. For R-2mer with lower molecular weight, only the glass transition temperature is observed in the heating / cooling curves, with no phase transition temperature, and no birefringence is observed in the POM (polymorphism). Figure 5 a) This indicates that lower molecular weight R-2mers lack liquid crystal properties; besides R-2mers, other R-4mers, R-8mers, R-12mers, and R-16mers with larger molecular weights all exhibited obvious phase transition peaks in both cooling and heating curves. POM tracking was used to observe the liquid crystal texture of R-Nmers (N = 2, 4, 8, 12, 16) during the slow cooling from an isotropic state to room temperature, indicating that upon cooling to the corresponding liquid crystal phase transition temperature (Tc) of each oligomer... l A clear birefringence phenomenon was observed at that time. Figure 5 b-5e). In summary, the glass transition temperature (T) of R-Nmer g ), liquid crystal phase transition temperature (T) l ) and clearing (T) i It exhibits chain length dependence, meaning that it gradually increases with increasing chain length, and the increase weakens or plateaus when the chain length exceeds R-12mer. Figure 4 c). This is because as the molecular weight increases, the non-covalent interactions between the oligomer backbones are enhanced, the steric hindrance effect between chains is strengthened, and chain segment movement becomes more difficult, resulting in an increase in the phase transition temperatures of the oligomer. However, when the molecular weight is large enough, the influence of chain length on the non-covalent interactions between molecular chains decreases, and its influence on the phase transition temperatures also gradually decreases.

[0096] The aligned polymer R-Nmer was first heated to an isotropic state and then slowly cooled to room temperature before SAXS and WAXD tests were performed. Figure 6 Meanwhile, to infer the arrangement and stacking of liquid crystal cells, simulation calculations were performed on individual cells using the MM2 force field method, yielding a length r = 2.2 nm for a repeating cell when fully extended. Figure 7 ).from Figure 6As can be seen, no scattering peaks were observed in R-2mer. With increasing oligomer molecular weight, obvious scattering peaks began to appear. When the molecular weight was greater than that of R-4mer, multi-level scattering peaks began to appear, and the ratio of the q values ​​of the first-order scattering peak to the second-order scattering peak was 1:2, indicating that the oligomer tends to be arranged in a layered manner, thus the formed liquid crystal is a smectic phase. The interlayer spacing d of each generation of smectic liquid crystals was calculated based on the first-order scattering peak q1 (Table 1), and the calculated result is approximately 50% of the extended chain length (L) of the oligomer backbone.

[0097] Table 1

[0098] sample <![CDATA[q1(nm -1 )]]> <![CDATA[q2(nm -1 )]]> <![CDATA[q3(nm -1 )]]> <![CDATA[d(nm) a ]]> <![CDATA[1 / 2L(nm) b ]]> R-2mer - - - - 2.20 R-4mer 1.41 - 2.88 4.46 4.40 R-8mer 0.66 1.28 2.88 9.52 8.80 R-12mer 0.46 0.93 2.88 13.66 13.20 R-16mer 0.36 0.73 2.88 17.45 17.60

[0099] a The interlayer spacing d of smectic liquid crystals is calculated using the formula d = 2π / q1;

[0100] b Half of the extended length (L) of the oligomer backbone is calculated using the formula 1 / 2L = N / 2 * r, where N is the oligomer algebra and r is the length of a repeating unit in the oligomer backbone when fully extended, calculated through simulation, and r = 2.2 nm.

[0101] Furthermore, a weak, broad peak appeared near the q-value of 2.88, with a calculated length l = 2.18 nm. This is consistent with the 2.2 nm length of a fully extended repeating unit calculated using the MM² force field method. The liquid crystal phase structure of the oligomer was also confirmed in the WAXD spectrum, where a distinct diffraction peak appeared at R-4mer, R-8mer, R-12mer, and R-16mer. Figure 6 b, 2θ≈22.6°, The Bragg equation (λ = 2csinθ, λ = 0.1542 nm) corresponds to the spacing of the azophenyl units in the smectic phase. Based on the above test data and calculation results, it can be seen that the smectic liquid crystal uses the folded oligomer backbone as the basic unit and is arranged in layers according to the π-π stacking method.

[0102] Test Example 3

[0103] CD and UV-vis absorption spectra were performed on solutions of R / S-Nmer (N = 2, 4, 8, 12, 16) to investigate the supramolecular chiral properties of the assemblies by focusing on the solution self-assembly of the polymers.

[0104] (1) Preparation of oligomer solution: R / S-Nmer (N=2, 4, 8, 12, 16) were dissolved in tetrahydrofuran and filtered through a 0.22 μm filter membrane to obtain an oligomer solution with a concentration of 1.0 mg / mL.

[0105] (2) Test the CD and UV-vis spectra of the oligomer solution: Take 0.1 mL of oligomer solution into an SQ-cuvette, add 2.9 mL of tetrahydrofuran into the cuvette, shake gently, and then perform CD and UV-vis absorption spectrum tests.

[0106] (3) At 25℃, take 0.05 mL of the oligomer solution into an SQ-cuvette, add a pre-set volume of tetrahydrofuran (a good solvent), and then add anhydrous ethanol (a poor solvent) to the cuvette. Adjust the volume ratio of tetrahydrofuran to anhydrous ethanol so that the total volume of solvent in the cuvette is 3 mL. After mixing the cuvette solution, a pale yellow assembly solution is obtained, which is then subjected to CD spectroscopy and transmission electron microscopy tests.

[0107] like Figure 8 As shown, when oligomers of different molecular weights are in the dissolved state, none exhibit the Cotton effect, indicating that the free azophenyl units are isolated and chirality cannot be transferred to the azobenzene. When ethanol is added to solutions of 16-mer, 12-mer, and 8-mer tetrahydrofuran, due to solvent-phobic interactions, the oligomers gradually transition from a free state to an aggregated state, leading to assembly. Figure 9 As shown, with increasing ethanol content in the mixed solvent, the intensity of the characteristic absorption peak corresponding to the trans-azobenzene π-π* electronic transition at 358 nm in the assembled solution gradually decreases, indicating that the azophenyl units undergo π-π stacking. Simultaneously, a significant Cotton effect is observed in the CD spectrum corresponding to the azobenzene absorption region, indicating that in the aggregated state, the azobenzene units, through π-π interactions, transfer chirality from the chiral carbon to the azobenzene, and further to the assembly, forming a chiral supramolecular structure. Furthermore, a mirror-symmetric CD signal is observed in the enantiomeric (S-configuration) oligomer assembly solution, further verifying that the chirality of the assembly originates from the chiral center in the main chain.

[0108] For R-16mer, such as Figure 9 As shown in Figure a, when the volume ratio of tetrahydrofuran / ethanol is v THF / v EtOH When v = 3.0 / 0 changes to 1.2 / 1.8, a negative CD signal with a triple Cotton effect appears. THF / v EtOH When v = 0.6 / 2.4, the assembly solution changes from a triple Cotton effect to a double Cotton effect while maintaining a negative signal. THF / v EtOH When the ethanol content is 0.1 / 2.9 (maximum), the CD signal flips, becoming a positive Cotton effect. For example... Figure 9As shown in diagram d, with increasing ethanol content, a negative CD signal initially appears, then the CD intensity gradually increases and then decreases, finally reversing from a negative CD signal to a positive CD signal. The chiral expression of R-12mer is similar to that of R-16mer; its CD signal undergoes a similar evolution with increasing ethanol content, changing from a negative triple Cotton effect to a negative double Cotton effect, and finally reversing to a positive double Cotton effect. Figure 9 b). Compared to R-12mer and R-16mer, R-8mer requires a higher ethanol content for chiral assembly, at v THF / v EtOH The CD signal only begins to appear at a concentration of 0.6 / 2.4. The assembly initially shows a positive CD signal, which gradually flips to a negative CD signal as the ethanol content increases, eventually reaching a negative CD signal at v. THF / v EtOH When the value is 0.05 / 2.95, it flips back to a positive CD signal. Figure 9 f). The S-Nmer (N = 16, 12, 8) assembly solutions exhibited CD signals mirror-symmetric to those of R-Nmer with changes in ethanol content, indicating that aggregation-induced chiral center transfer to oligomers leads to consistent chiral expression.

[0109] However, for R / S-2mer and R / S-4mer, even if v THF / v EtOH At 0.1 / 2.9, no CD signal was observed, and the absorption peak showed almost no change compared to the dissolved state. Figure 10 This indicates that the azophenyl group did not undergo π-π stacking, and therefore could not undergo chiral supramolecular self-assembly. This is because the increased solubility of lower molecular weight oligomers in mixed solvents leads to a weakening of solubilizing forces, thus preventing the formation of azophenyl π-π stacking to produce a chiral supramolecular structure.

[0110] The study found that the supramolecular chirality expression of single-molecular-weight chiral azobenzene oligomers is closely related to the stacking mode of the azophenyl group. For example... Figure 11As shown, two typical absorption peaks were observed in the UV-vis absorption spectrum: a strong absorption peak near 258 nm is attributed to the π-π* electronic transition of the trans-azophenyl group; and a weak absorption peak near 450 nm is attributed to the n-π* electronic transition of the cis-azophenyl group. Comparing the absorption spectra of the oligomer before and after assembly, the absorption peak near 258 nm is significantly broadened compared to the absorption peak before assembly, and two distinct shoulder peaks appear at 346 nm and 382 nm, respectively, showing a blue shift of approximately 12 nm and a red shift of approximately 24 nm compared to the maximum absorption wavelength (358 nm) before assembly. The blue shift indicates H-aggregation between azophenyl groups, while the red shift corresponds to J-aggregation between azophenyl groups. This indicates that both modes of azophenyl π-π stacking coexist in the aggregated state.

[0111] Taking R-16mer as an example, three different volume ratios (v / tOH) in the mixed solvent THF / EtOH were selected. THF / v EtOH The assemblies in the ratios (0.8 / 2.2, 0.4 / 2.6, and 0.1 / 2.9) were investigated, and the results showed that the supramolecular chirality expression and absorption peaks of the azobenzene oligomer assemblies differed among the three ratios. Figure 11 As shown in Figure a, with increasing ethanol content, the left shoulder peak (346 nm) gradually decreases, while the right shoulder peak (382 nm) gradually increases. This indicates that H-aggregates and J-aggregates coexist under all three ratios, and that increasing ethanol content favors the formation of J-aggregates. When v THF / v EtOH When the signal is 0.1 / 2.9, the assembly changes from a negative CD signal to a positive CD signal. Figure 11 (a-11b). Because the two aggregation modes induce opposite helical structures, H-aggregation induces a negative Cotton effect, while J-aggregation induces a positive Cotton effect. In this case, J-aggregates dominate in the assembly solution; while when v THF / v EtOH When v = 0.4 / 2.6, the CD signal exhibits a negative Cotton effect, at which point H-aggregates dominate; when v THF / v EtOH At 0.8 / 2.2, three Cotton effects were observed in the CD spectrum of the assembly at 330 nm, 366 nm and 418 nm. At this time, the proportions of the two aggregation modes are equal. According to the principle of the additive nature of the Cotton effect, this triple Cotton effect comes from the superposition of the Cotton effects generated by the splitting of H-aggregates and J-aggregates.

[0112] The assembly solutions of the above-mentioned R-16mer in three solvent ratios were subjected to heating-cooling (HC) treatment. Figure 12The assembly solution was first heated to 90°C at a rate of 2°C / min, and then cooled to room temperature. The chiral expression of the assembly solution exhibited a significant thermal response behavior. At v THF / v EtOH After HC treatment, the CD signal inverted in the assembly solution at a concentration of 0.1 / 2.9. The CD signal changes were tracked during the heating and cooling processes. Figure 12 A) It was found that during the heating process, the CD signal gradually changed from a positive Cotton effect to a negative Cotton effect, while the direction of the CD signal remained unchanged during the subsequent cooling process. Comparison of the absorption spectra before and after HC treatment ( Figure 12 a) A significant blue shift was observed in the UV absorption peak, indicating that HC treatment reduced J-aggregates while increasing H-aggregates. Under heating, the aggregates disassembled, and the dissociated J-aggregated azobenzene units reassembled via H-aggregation, leading to a change in chiral signal and ultimately a chiral reversal. Therefore, the chiral reversal caused by HC treatment is a result of the transformation from a kinetically controlled product to a thermodynamically controlled product. (v) THF / v EtOH In the assembly with a frequency of 0.4 / 2.6, the CD signal intensity only changes slightly during the heating and cooling process; there is no flipping, and the negative Cotton effect is still maintained. Figure 12 B), while after HC treatment, the absorption spectrum only showed a reduction in the shoulder peak corresponding to J-aggregation ( Figure 12 b), corresponding to the dissociation of a small number of J-aggregates. In v THF / v EtOH After HC processing, the triple Cotton effect in the CD signal of the assembly in =0.8 / 2.2 disappears and is transformed into a negative double Cotton effect. Figure 12 (C) This is because during heating, J-aggregates gradually dissociate and transform into H-aggregates, weakening the corresponding positive Cotton effect, while the negative Cotton effect corresponding to H-aggregates strengthens. The absorption peak after HC treatment shows a significant blue shift, consistent with the change in the CD signal. This indicates that there is a balance between thermodynamically stable H-aggregates and kinetically controlled J-aggregates within the assembly.

[0113] In summary, there are mainly two aggregation modes during the self-assembly process of single molecular weight chiral azobenzene oligomers, namely J-aggregation and H-aggregation. The increase in the ethanol content in tetrahydrofuran / ethanol helps the formation of J-aggregation; H-aggregation is a thermodynamically controlled process that forms relatively stable aggregates; while J-aggregation is a kinetically controlled process, and its aggregates are unstable metastable states. Moreover, the helical directions of the chiral supramolecular assemblies formed under the two aggregation modes are opposite. Therefore, the CD signal flips after H-C treatment. The supramolecular chirality expression of the assemblies can be regulated by changing the ratio of the mixed solvent or by the method of H-C treatment.

[0114] The morphologies of the assemblies of R / S-Nmer (N = 8, 12, 16) in tetrahydrofuran / ethanol mixed solvents with different ratios were observed by TEM and AFM. As Figure 13 shown, the morphologies of all assemblies showed a similar evolution process, that is, as ethanol was added, assemblies with an octopus-like morphology were first formed. As the ethanol content in the mixed solvent increased, the morphology of the assemblies gradually changed into an icicle flower-like, spherical network or spherical random aggregates. This is because when the ethanol content is low, the solvophobic interaction between the oligomers and the solvent is small, so the assembly occurs slowly and tends to undergo thermodynamically stable H-aggregation, thus assembling into helical fibers. As the ethanol content increases, the solvophobic interaction between the oligomers and the solvent strengthens, the aggregation speed is fast and the stacking is tighter, and the helical fibers aggregate with each other to form spherical random aggregates.

[0115] The helical direction was further confirmed by AFM. In contrast, the helical bands of the assemblies of R / S-8mer are relatively loose and thinner ( Figure 13 e-13f), and the helical direction of R-8mer is P-helix (v THF / v EtOH = 0.6 / 2.4, 0.5 / 2.5), which is opposite to the helical directions of the assemblies of R-12mer and R-16mer. When the ethanol content continues to increase, the morphology of the R-8mer assembly changes from P-helical bands to M-helical nanofibers (v THF / v EtOH = 0.3 / 2.7); as the ethanol content continues to increase, spherical random aggregates are finally formed (v THF / v EtOH = 0.05 / 2.95). This transformation process is consistent with the Figure 9 flipping process from positive to negative and then to positive in g CD It is precisely this morphological transformation that drives the unique CD signal flipping of the assemblies.

[0116] Taking R / S-12mer as an example, v THF / v EtOHThe assembly solution with a viscosity of 1.0 / 2.0 was sonicated in a water bath for 3 minutes, and the morphological changes before and after sonication were observed by TEM. Figure 14 As shown, the nanofibers before ultrasound treatment all exhibited a distinct helical structure. Ultrasonic treatment caused some of the nanofibers to unwind, forming sheet-like structures. It is speculated that the helical fibers originated from the twisting and entanglement of the sheet-like aggregates during self-assembly. Furthermore, regarding v... THF / v EtOH The morphological evolution of assemblies at different aging times during self-assembly was tracked when the morphology was 1.0 / 2.0. For example... Figure 15 As shown, random micelles were observed at the start of assembly; larger lamellar structures began to appear after 20 minutes of aging; after 30 minutes of aging, the lamellars began to break into fragments from the edges and intertwine with each other; after 60 minutes, they were twisted into helical fibers. This result is consistent with the previously speculated formation process of helical fibers.

[0117] The lamellar structure during the self-assembly process was confirmed by SEM and AFM. Figure 16 AFM showed that the average thickness of the monolayer was approximately 13.5 nm, slightly smaller than the interlayer spacing of 13.66 nm for the R-12mer smectic liquid crystal measured by SAXS. The chiral supramolecular assembly mechanism of the oligomers is as follows... Figure 16 As shown in Figure d, with the addition of ethanol, the oligomer backbone rearranges under liquid crystal drive to form a folded chain structure, and assembles into nanosheets under strong π-π interactions. With the extension of aging time, the nanosheets gradually split into nanoribbons under the influence of hydrophobic forces. The π-π asymmetric stacking of azobenzene induces the nanoribbons to twist and further entangle along the chiral center direction, eventually forming supramolecular helical fibers with tight helices.

[0118] R-16mer in three solvent ratios (v THF / v EtOH Assemblies with molecular weights (=1.2 / 1.8, 0.4 / 2.6, 0.1 / 2.9) were subjected to UV irradiation and HC treatment to investigate the supramolecular chiral photoswitching properties of the oligomers. For example... Figure 17 As shown, the assembly solution (v THF / v EtOH =1.2 / 1.8) Under 365nm UV irradiation, the originally negative triplet Cotton effect signal peak disappeared. After HC treatment, the Cotton effect signal recovered, transforming into a negative doublet Cotton effect. This is because azobenzene underwent trans-cis isomerization under UV irradiation, and after HC treatment, cis-azobenzene reverted to trans-azobenzene, thus the Cotton effect signal underwent a reversible change from disappearance to recovery. Assembly solution (v THF / v EtOH=0.4 / 2.6) also showed a reversible change in CD induced by UV / HC, from disappearance to recovery, similar to the assembly solution (v THF / v EtOH The experimental results (=1.2 / 1.8) are similar. Figure 17 b). This is because after HC treatment, cis-azobenzene gradually reverts to trans-azobenzene, leading to preferential H-aggregation of the azophenyl group, which is thermodynamically the most stable arrangement, inducing a negative Cotton effect. However, the positive Cotton effect caused by kinetically driven J-aggregation cannot be recovered. For the assembly solution (v... THF / v EtOH =0.4 / 2.6) Alternating between 365nm ultraviolet irradiation and HC treatment, the reversible change in the CD signal can be repeated at least five times. Figure 17 c-17d) indicates that the assembly exhibits good chiral optical switching behavior. When the assembly solution (v) is irradiated with 365nm ultraviolet light... THF / v EtOH When = 0.1 / 2.9), such as Figure 17 As shown in Figure e, a chiral reversal phenomenon occurred. The assembly solution initially exhibited a positive Cotton effect, which rapidly reversed to a negative Cotton effect upon UV irradiation, reaching its maximum absolute value after 60 seconds of irradiation. With prolonged irradiation time, the negative Cotton effect gradually weakened, and the CD signal completely disappeared when photosteady state was reached after 300 seconds of irradiation. Immediately following irradiation, HC treatment was performed, and the CD signal was found to revert to a negative Cotton effect, instead of the original positive Cotton effect. Figure 17 f). Both H-aggregation and J-aggregation coexist within the assembly, when v THF / v EtOH At a concentration of 0.1 / 2.9, J-aggregates dominate in the assembled solution, exhibiting a positive Cotton effect overall. However, the kinetically controlled J-aggregates have weak UV resistance; when irradiated with 365nm UV light, the J-aggregates are rapidly destroyed, while the H-aggregates are not completely destroyed, resulting in a negative Cotton effect. With continued UV irradiation, both aggregates are completely destroyed, and the CD signal disappears. After HC treatment, the cis structure of azobenzene is restored to the trans structure, and the oligomers reassemble into an ordered helical structure as H-aggregates, restoring the negative Cotton effect to the CD signal. This indicates that the oligomers show good application potential in the field of chiral photoswitches.

[0119] Using R-8mer as a typical sample, R-4mer, R-8mer, R-12mer, and R-16mer were mixed in a certain proportion to obtain the polydisperse oligomer disp-R-8mer. The thermodynamic properties of R-8mer and disp-R-8mer were compared by DSC, such as... Figure 18 As shown in Figure a, the DSC heating and cooling curves exhibit significant differences (heating and cooling rates of 5℃ / min). The phase transition peaks of disp-R-8mer are not as sharp as those of R-8mer, and both the glass transition temperature and the liquid crystal phase transition temperature are significantly lower. This is because the chain length of disp-R-8mer is non-uniform, the stacking order between molecular chains is lower, and the structure is relatively loose. Therefore, the glass transition temperature and the liquid crystal phase transition temperature are lower than those of R-8mer, and the phase transition peaks are broader.

[0120] The supramolecular chiral self-assembly behavior of disp-R-8mer was studied in a tetrahydrofuran / ethanol mixed solvent, such as... Figure 18 As shown in b, compared to R-8mer ( Figure 9 e) With increasing ethanol content, the absorption decrease of disp-R-8mer near 360 nm is relatively small. This is because the non-uniformity of chain length hinders π-π stacking between oligomers to some extent. Meanwhile, with increasing ethanol content, the CD signal first exhibits a negative Cotton effect, and finally decreases at v... THF / v EtOH At a concentration of 0.1 / 2.9, the CD signal flips to a positive Cotton effect. This phenomenon differs from that of R-8mer, but is similar to the chiral expression of larger molecular weight R-12mer and R-16mer. Figure 9 a, 9c). This indicates that the chiral expression of the disp-R-8mer supramolecular assembly follows the supramolecular chiral characteristics of the larger oligomers in the mixture more closely than its own average molecular weight. Furthermore, TEM observation of the morphological changes of the disp-R-8mer assembly with increasing ethanol content, such as... Figure 19 As shown, with the increase of ethanol content, the morphology of disp-R-8mer initially forms a network structure composed of short and thick fibers. Eventually, the fibers gradually disappear and transform into random aggregates. Furthermore, no uniform helical morphology was observed in the network structure. In contrast, the helical fibers formed by the single molecular weight oligomers are longer and more compact and ordered, indicating that the polydispersity of the oligomers hinders the orderly arrangement between molecular chains.

[0121] Test Example 4

[0122] To investigate the supramolecular chiral properties of films, R / S-Nmer (N = 2, 4, 8, 12, 16) were spin-coated. The specific procedures were as follows: R / S-Nmer (N = 2, 4, 8, 12, 16) were dissolved in chloroform and filtered through a 0.22 μm filter to obtain an oligomer solution with a concentration of 15 mg / mL. A clean quartz slide was fixed in a spin coater, and then 20 μL of the oligomer solution was slowly added dropwise to the surface of the quartz slide using a pipette. The film was then spin-coated at 2000 rpm for 30 s to obtain the film. The film was then placed in a vacuum oven for 12 h to completely remove residual solvent, followed by CD and UV-Vis absorption spectroscopy measurements.

[0123] The supramolecular chiral expression of R / S-Nmer in the thin film state was investigated using CD and UV-vis absorption spectroscopy. Except for R / S-2mer, which showed no CD signal, all oligomer films exhibited a significant Cotton effect. Figure 20 By rotating the thin film at different angles and measuring its CD spectrum, the results showed that the CD signal peaks of the films rotated at different angles were basically coincident, indicating that linear polarization (LD) has minimal influence on the CD signal, and the measured CD signal results originate from the actual supramolecular chiral structure of the thin film. Figure 20 As shown in b, the R / S-2mer film has no chiral signal, while when the chain length is greater than that of R / S-2mer, the film has a chiral signal. The R-oligomer exhibits a positive Cotton effect, and the S-oligomer exhibits a negative Cotton effect. The CD signal peaks are mirror images of each other, indicating that the helical arrangement inside the film depends on the configuration of the chiral carbon in the oligomer backbone. Figure 20 c in CD and g CD The signal increases with increasing oligomer chain length because the π-π interaction between azophenyl units is enhanced with increasing oligomer chain length. In the thin film, the non-liquid crystallizer R / S-2mer does not exhibit chiral expression; when the chain length exceeds that of the R / S-2mer, the liquid crystallization of the oligomer begins to increase, and the CD signal of the oligomer also increases accordingly.

[0124] Taking R-8mer thin films as an example, they were annealed at temperatures within the liquid crystal phase transition temperature range. After annealing for 1 hour, the Cotton effect signal of the film reversed from an initial positive Cotton effect to a negative Cotton effect. Figure 20d). Simultaneously, a significant blue shift was observed in the UV-vis absorption spectrum of the annealed film compared to the unannealed film, indicating that H-aggregation occurred in the oligomers after annealing. This is consistent with the CD and UV-vis characterization results of the assemblies before and after HC treatment. Before annealing, the π-π stacking of azobenzene units in the film was predominantly J-aggregate, thus inducing a positive Cotton effect. During annealing, the unstable J-aggregates gradually transformed into thermodynamically stable H-aggregates, thereby inducing a negative Cotton effect. This further confirms that the chiral expression of a single-molecular-weight chiral backbone azobenzene oligomers depends on two modes of π-π stacking of azobenzene units: J-aggregation and H-aggregation.

[0125] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A single-molecular-weight chiral azobenzene oligomer, characterized in that, The structure is as follows: ， R -No, ， S -Number; Where N = 2, 4, 8, 12 or 16.

2. A chiral azobenzene monomer, characterized in that, The structure is as follows: ， ( R )-TBDPS-Azo- t This, ， ( S )-TBDPS-Azo- t This.

3. The use of the chiral azobenzene monomer of claim 2 in the preparation of the single molecular weight chiral azobenzene oligomer of claim 1.

4. A method for preparing the single molecular weight chiral azobenzene oligomer according to claim 1, characterized in that, Includes the following steps, S1, the chiral azobenzene monomer of claim 2 ( R / S )-TBDPS-Azo- t Bu, tetrabutylammonium fluoride, and glacial acetic acid undergo a detert-butyldiphenylsilylation reaction in the presence of dichloromethane to give ( R / S )-HO-Azo- t Bu; Chiral azobenzene monomers ( R / S )-TBDPS-Azo- t Bu and p-toluenesulfonic acid monohydrate undergo a detert-butylation reaction in the presence of silica gel and tetrahydrofuran to give ( R / S )-TBDPS-Azo-COOH; S2, the (s1) R / S )-HO-Azo- t Bu、( R / S )-TBDPS-Azo-COOH and dicyclohexylcarbodiimide were esterified in the presence of 4-dimethylaminopyridine and dichloromethane to obtain the single molecular weight chiral azobenzene oligomer. Or, as described in S1 ( R / S )-HO-Azo- t Bu、( R / S )-TBDPS-Azo-COOH and dicyclohexylcarbodiimide were esterified in the presence of 4-dimethylaminopyridine and dichloromethane. The above-mentioned detert-butyldiphenylsilylation reaction, detert-butylation reaction and esterification reaction were repeated to obtain the single molecular weight chiral azobenzene oligomer through iterative growth.

5. The method for preparing a single molecular weight chiral azobenzene oligomer according to claim 4, characterized in that, The temperature for the detert-butylation reaction is 90℃-110℃.

6. A method for preparing the chiral azobenzene monomer according to claim 2, characterized in that, Includes the following steps, S1, 4-(BOC-amino)phenol, ( R / S )-Methyl lactate and triphenylphosphine and diisopropyl azodicarbonate react in the presence of tetrahydrofuran to give ( R / S )-Boc-Ben-Me; in,( R The structural formula of )-Boc-Ben-Me is ; S2、( R / S )-Boc-Ben-Me and trifluoroacetic acid react in the presence of dichloromethane to give ( R / S )-NH2-Ben-Me; where, ( R The structural formula of )-NH2-Ben-Me is ; S3、( R / S )-NH2-Ben-Me undergoes a diazotization reaction in the presence of dilute hydrochloric acid and sodium nitrite to yield a diazonium salt, which is then coupled with phenol to obtain ( R / S )-HO-Azo-Me; where, ( R The structural formula of )-HO-Azo-Me is ; S4、( R / S )-HO-Azo-Me reacts in the presence of lithium aluminum hydride and tetrahydrofuran to give ( R / S )-HO-Azo-OH; where, ( R The structural formula of )-HO-Azo-OH is ; The reaction of 6-bromohexanoic acid and tert-butanol in the presence of trifluoroacetic anhydride and tetrahydrofuran yields Br- t Bu; where Br- t The structural formula of Bu is: ; S5、( R / S )-HO-Azo-OH and Br- t Bu reacts with cesium carbonate and acetonitrile at 55℃-65℃ to obtain ( R / S )-HO-Azo- t Bu; among which, ( R )-HO-Azo- t The structural formula of Bu is: ; S6、( R / S )-HO-Azo- t Bu and tert-butyldiphenylchlorosilane react in the presence of imidazole and dichloromethane to give the chiral azobenzene monomer.

7. The method for preparing chiral azobenzene monomer according to claim 6, characterized in that, In S3, the temperatures for the diazo reaction and the coupling reaction are independently -5°C to 5°C.

8. An assembly, characterized in that, The assembly was prepared from the single molecular weight chiral azobenzene oligomer according to claim 1, and the preparation of the assembly is as follows: The numbers N=2, 4, 8, 12, and 16 are respectively... R / S -Nmer was dissolved in tetrahydrofuran and passed through a 0.22µm filter membrane to obtain an oligomer solution with a concentration of 1.0 mg / mL; At 25°C, take 0.05 mL of oligomer solution into an SQ-cuvette, add a pre-set volume of tetrahydrofuran, then add anhydrous ethanol to the cuvette, adjust the volume ratio of tetrahydrofuran to anhydrous ethanol so that the total volume of solvent in the cuvette is 3 mL, and mix the cuvette solution to obtain a pale yellow assembly solution.

9. An oligomer film, characterized in that, It is prepared from the single molecular weight chiral azobenzene oligomer described in claim 1.

10. The application of a single molecular weight chiral azobenzene oligomer of claim 1, the assembly of claim 8, or the oligomer film of claim 9 in the field of chiral photodiodes.

Images