Azobenzene group-containing photoinduced isomerization ionic gel as well as preparation method and application thereof

Abstract

The invention discloses an azobenzene group-containing photoinduced isomerization ionic gel and a preparation method and application thereof, and the ionic gel is prepared by the following method: mixing 4, 4 '-dihydroxyazobenzene, olefine acid, a condensing agent and a catalyst, and carrying out esterification reaction to obtain a double-end double bond modified azobenzene monomer; uniformly mixing the azobenzene monomer modified by the double-end double bond, an acrylate monomer, a hydrophobic ionic liquid and a thermal initiator in a solvent, then carrying out thermal polymerization reaction, and drying to remove the solvent to obtain the azobenzene group-containing photoinduced isomerization ionic gel. Based on cis-trans isomerization transformation of azobenzene groups under ultraviolet light and visible light, the topological structure and chain segment movement capability of a polymer network are directly and efficiently regulated and controlled, so that a remarkable light control effect on an ion transmission path and a migration energy barrier is realized, and controllable regulation of ion transmission is further realized; the obtained gel has excellent adhesiveness and information storage and anti-counterfeiting capabilities.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials and flexible electronics technology, specifically relating to a photo-isomerized ion gel containing azophenyl groups, its preparation method and application, and particularly to a flexible multifunctional electronic skin based on the photo-isomerization of azophenyl groups to regulate ion transport and its application in strain sensing and ultraviolet light detection. Background Technology

[0002] With the development of science and technology, humanity is entering the intelligent era. Flexible electronic devices based on artificial intelligence technology have attracted widespread attention due to their enormous application prospects in wearable devices and electronic skin. Electronic skin can simulate the sensory functions of human skin, converting external stimuli such as stress, temperature, and humidity into electrical signals, and has important application value in human-computer interaction, health monitoring, and soft robotics.

[0003] Iongels, due to their excellent ionic conductivity, environmental stability, and softness similar to biological tissues, have become one of the ideal materials for flexible electronic skin. However, current iongel sensors mainly focus on sensing mechanical deformation, while research on multifunctional integration in response to other physical fields such as light, electricity, and magnetism is relatively limited. Among these, light, as a non-contact, high spatiotemporal resolution, and easily modulated external stimulus, has unique advantages in the field of flexible sensing and actuation. Therefore, the development of light-responsive iongel sensors is of great significance for promoting the future development of flexible electronics.

[0004] Azobenzene is a typical photoresponsive molecule whose molecular structure can undergo a reversible photoisomerization transition between trans and cis configurations. This transition is accompanied by significant changes in molecular geometry, polarity, and free volume, which can potentially affect the microstructure of the polymer matrix and its ability to confine ion transport. Introducing azophenyl groups into ionogel networks holds promise for enabling photomodulation of the gel's ionic conductivity, thereby leading to the development of novel photoresponsive sensor devices.

[0005] Currently, doping small molecule azobenzene or its derivatives (such as ionic liquids containing azobenzene) into polymer matrices is a common method for constructing photoresponsive ionic gels. However, this method has many limitations: (1) small molecule additives may become unstable due to migration, precipitation, or environmental influences (such as solvents and temperatures); (2) dispersed azobenzene molecules have relatively low isomerization efficiency and are difficult to form ordered and efficient responsive structures in polymer networks; (3) they contribute little to improving the overall mechanical properties of the gel, and may even lead to a decrease in mechanical properties due to compatibility issues.

[0006] Therefore, developing an ion gel material that firmly incorporates azophenyl groups into a polymer network via chemical bonds and possesses excellent mechanical properties, high ionic conductivity, and sensitive photoresponse characteristics is of great significance for promoting the development of multifunctional electronic skin. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing a photoisomerized ion gel containing azophenyl groups, the resulting ion gel material, and its applications. This material possesses excellent mechanical properties and high ionic conductivity, and its ion transport behavior can be reversibly modulated by ultraviolet / visible light irradiation, thereby achieving dual-modal sensing of strain and ultraviolet light.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing a photo-isomerized ionic gel containing an azophenyl group, comprising the following steps:

[0010] 4,4'-dihydroxyazobenzene, olefinic acid, condensing agent, and catalyst were mixed and esterified to obtain azobenzene monomers modified with double-terminated double bonds; the synthetic route is as follows:

[0011]

[0012] Where n = 1, 2, 3, 4, 5, 6, 7;

[0013] Azobenzene monomers modified with double-ended double bonds, acrylate monomers, hydrophobic ionic liquids and thermal initiators are mixed uniformly in a solvent, followed by thermal polymerization. After drying to remove the solvent, the photo-isomerized ionic gel containing azobenzene groups is obtained.

[0014] In the method of the present invention, the azobenzene monomer has the dual functions of reactive monomer and crosslinking agent, so that the photoresponsive azobenzene group is directly constructed on the main chain crosslinking point of the polymer network.

[0015] Preferably, the condensing agent is N,N'-dicyclohexylcarbodiimide (DCC), and the catalyst is 4-dimethylaminopyridine (DMAP).

[0016] Preferably, the molar ratio of 4,4'-dihydroxyazobenzene, olefinic acid and condensing agent is 1:2-3:2.2, more preferably 1:2:2.2.

[0017] Preferably, the acrylate monomer is selected from one of ethyl acrylate, butyl acrylate, ethyl methacrylate, and butyl methacrylate.

[0018] Preferably, the hydrophobic ionic liquid is selected from one of 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([HMIM][TFSI]), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([BMIM][TFSI]), and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([EMIM][TFSI]).

[0019] Preferably, the thermal initiator is ammonium persulfate or potassium persulfate, and its amount accounts for 0.5-1.5 wt% of the total mass of the azobenzene monomer modified with double-ended double bonds and the acrylate monomer.

[0020] Preferably, the mass ratio of the azobenzene monomer modified with double-ended double bonds to the acrylate monomer is 1:4-40, more preferably 1:10.

[0021] Preferably, the total mass ratio of the ionic liquid to the azobenzene monomer modified with double-ended double bonds to the acrylate monomer is 0.2-0.4:1.

[0022] Preferably, the temperature of the thermal polymerization reaction is 60-100 °C and the time is 8-12 hours.

[0023] Preferably, the drying temperature is 80-100 ℃ and the time is 16-48 hours.

[0024] Secondly, the present invention provides a photo-isomerized ionic gel containing azophenyl groups prepared by the above method. This ionic gel has a cross-linked network structure, with azophenyl groups acting as network nodes bonded to the polymer backbone by chemical bonds. An ionic liquid is dispersed within this polymer network, and upon irradiation, it transforms from a trans configuration to a cis configuration.

[0025] Preferably, the thickness of the ionogel is 0.5-0.85 mm.

[0026] The ionogel described in this invention utilizes the photoinduced cis-trans isomerization of azobenzene located at the cross-linking points of the main chain to achieve sensitive control over the intrinsic ionic conductivity and other electrical properties of the gel. Firstly, under unilluminated conditions, the trans-Azobenzene in the gel is linear and tightly packed, restricting ion migration. However, the cis-Azo, excited by ultraviolet light, exhibits a curved structure, significantly increasing the free volume of the polymer network and reducing the tortuosity of the ion transport path, providing physical space for ion migration. By adjusting the topology of the polymer network and the chain segment mobility using light irradiation, controllable regulation of ion transport can be further achieved. Simultaneously, the conversion from trans to cis configuration increases polarity and decreases the glass transition temperature, both of which effectively promote ion migration.

[0027] Thirdly, the present invention provides the application of the above-mentioned photoisomerized ion gel containing azophenyl groups in the preparation of flexible sensors.

[0028] Preferably, the flexible sensor is a strain sensor used to detect mechanical deformations such as tension and bending.

[0029] Preferably, the flexible sensor is a photosensitive sensor, which is particularly suitable for ultraviolet light detection.

[0030] Preferably, the flexible sensor is a multifunctional sensor that can respond to both strain and light stimulation simultaneously.

[0031] Fourthly, the present invention provides a flexible sensor whose sensing element is made of the above-mentioned photoisomerized ionogel containing azophenyl groups.

[0032] Preferably, the sensor includes a sensitive layer made of the ionogel and an electrode connected to the sensitive layer.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1. This invention introduces azophenyl groups as structural units into a polymer network through a chemical reaction, avoiding the migration and precipitation problems of small molecule additives and ensuring the stability and repeatability of the material in long-term use; at the same time, the azophenyl groups themselves can act as crosslinking agents, overcoming the defect of the prior art that requires the introduction of traditional small molecule crosslinking agents to form a network.

[0035] 2. In this invention, the rigid structure of the azophenyl group effectively enhances the tensile strength and modulus of the ion gel, while the selected flexible acrylate segments ensure the high ductility of the material, giving the gel both good toughness and flexibility, making it suitable for wearable devices.

[0036] 3. This invention achieves "regulation of ion transport" through "volume change actuation." It utilizes the changes in free volume and polarity resulting from the isomerization transition between the trans (linear, low polarity) and cis (flexible, high polarity) forms of azobenzene to reversibly regulate the migration rate and pathway of ions within the gel. Ultraviolet light irradiation induces the trans-to-cis transition, typically leading to an increase in ionic conductivity; visible light induces a cis-to-trans reversion, restoring conductivity. This characteristic can be used to construct highly sensitive ultraviolet light detectors.

[0037] 4. The photoisomerized ion gel containing azophenyl groups prepared in this invention has high ionic conductivity. When stretched, its internal ion transport path changes, resulting in a change in resistance, thereby enabling sensitive detection of mechanical deformation and making it suitable for human motion monitoring.

[0038] 5. The photo-isomerized ionogel containing azophenyl groups prepared in this invention can respond to both strain and light stimulation, providing a possibility for realizing multifunctional integrated sensing. Furthermore, based on the changes in local conductivity and transparency caused by light illumination, patterned information can be written and erased on the gel surface, showing potential applications in information encryption, optical anti-counterfeiting, and other fields.

[0039] 6. The method for preparing photoisomerized ionic gels containing azophenyl groups according to the present invention uses readily available raw materials, has mild process conditions, and is easy to scale up for production. Attached Figure Description

[0040] Figure 1 This is the 1H NMR spectrum of the azobenzene monomer modified with double-ended double bonds in an embodiment of the present invention.

[0041] Figure 2 The stress-strain curve of the ion gel prepared in Example 8 of this invention.

[0042] Figure 3 This is a schematic diagram of the assembly of the ion gel strain sensor of the present invention.

[0043] Figure 4 This is a comparison chart of the conductivity of the ion gels prepared in Examples 4, 8, and 12 of this invention.

[0044] Figure 5 The curve showing the relative resistance change of the ion gel strain sensor prepared in Example 8 of this invention under tension.

[0045] Figure 6 This is a schematic diagram of the adhesion properties of the ion gel prepared in Example 8 of the present invention.

[0046] Figure 7 This is a schematic diagram of the overlap shear test device.

[0047] Figure 8 The curve showing the relationship between the relative resistance change and ultraviolet light power density of the ion gel prepared in Example 8 of this invention.

[0048] Figure 9 This is a schematic diagram of the writing and erasing process of patterned information on the ion gel prepared in Example 8 of the present invention under ultraviolet and visible light irradiation, where a is the writing pattern, b is the erasing pattern, and c is the repetition of the above process. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of protection of this invention.

[0050] Taking 4-pentenoic acid (n=2) as an example, the synthesis process of the azobenzene monomer modified with double-terminal double bonds in the embodiments of the present invention is described in detail. 4,4'-dihydroxyazobenzene (2.14 g, 0.1 mol), 4-pentenoic acid (2 g, 0.2 mol), and 4-dimethylaminopyridine (DMAP, 0.1 g, 0.08 mol) were dissolved in 50 mL of dichloromethane. Then, N,N'-dicyclohexylcarbodiimide (DCC, 4.54 g, 0.22 mol) was added to the solution, and the mixture was heated to room temperature and stirred for 24 h. The product was filtered to remove the filter residue, dicyclohexylurea. The resulting solution was washed three times with deionized water, and the solvent was removed by vacuum distillation to obtain a brown solid. The yield was 83%.

[0051] The NMR data of this monomer are as follows Figure 1 As shown, 1 H NMR (500MHz, DMSO-d6), δ ppm: 7.95–7.92(4H, Ar-H), 7.26–7.22 (4H, Ar-H), 5.92–5.9 (2H, CH2=CH), 5.19–5.08 (4H, CH2=CH), 3.7-3.67 (4H, CH2), 2.43–2.37 (4H, CH2OCO).

[0052] Examples 1-12: Preparation of photoisomerized ionogels containing azophenyl groups

[0053] The specific feed ratios and process parameters for each of the following embodiments and comparative examples are shown in Table 1. Example 8 will be used as an example for detailed explanation:

[0054] Weigh 0.1 g of azobenzene monomers modified with double-ended double bonds (n = 2), 1.0 g of ethyl methacrylate (as an acrylate monomer) (monomer mass ratio 1:10), 0.33 g of ionic liquid [BMIM][TFSI] (total monomer mass ratio 0.3:1), and 0.011 g of thermal initiator potassium persulfate (approximately 1 wt% of the total monomer mass). Add an appropriate amount of dimethyl sulfoxide as a solvent and stir for 2 hours to fully dissolve and mix, forming a transparent precursor solution. Sonicate the precursor solution for 20 minutes to remove air bubbles, then inject it into a mold between two glass plates sealed with a 1 mm thick silicone gasket. Place the mold in an oven at 80 °C for 12 hours to complete the thermal polymerization. Subsequently, place the gel along with the mold in a vacuum drying oven at 80 °C for 16 hours to completely remove the organic solvent, obtaining a photoisomerized ionogel film containing azobenzene groups with a thickness of approximately 0.5-0.85 mm. A photoisomerized ionogel film containing azophenyl groups was cut into rectangular strips 30 mm long, 5 mm wide, and 1 mm thick. Copper sheets wound with copper wire were fixed at both ends as electrodes to study the strain response of the ionogel sensing material. The ionogel was cut to a size of 10 × 10 mm. 2 The ultraviolet-responsive sensor was fabricated using the size and interdigitated electrode assembly method.

[0055] The preparation methods of Comparative Examples 1-4 are similar to those of the Examples, but without the addition of azobenzene monomers modified with double-ended double bonds.

[0056] Table 1: Reaction parameters of Examples 1-12 and Comparative Examples 1-4 (with variations in feed ratio, heating temperature, drying solvent temperature, and polymerization time)

[0057] sample The alkyl chain length (n) of azobenzene monomers modified with double-terminal double bonds. Types of acrylate monomers Ionic liquid type Mass ratio of acrylate monomer to azobenzene monomer modified with double-terminated double bonds Mass ratio of ionic liquid to monomer Polymerization temperature (°C) Aggregation time (h) Vacuum drying temperature (°C) Vacuum drying time (h) Example 1 1 Ethyl methacrylate [BMIM][TFSI] 40：1 0.4：1 60 8 80 32 Example 2 2 Ethyl acrylate [EMIM][TFSI] 30：1 0.4：1 70 9 100 16 Example 3 3 Butyl acrylate [BMIM][TFSI] 20：1 0.4：1 80 10 80 48 Example 4 7 Ethyl acrylate [EMIM][TFSI] 10：1 0.4：1 100 12 90 16 Example 5 4 Ethyl methacrylate [BMIM][TFSI] 40：1 0.3：1 60 8 80 16 Example 6 6 Ethyl acrylate [BMIM][TFSI] 30：1 0.3：1 70 9.5 80 16 Example 7 5 Butyl acrylate [BMIM][TFSI] 20：1 0.3：1 80 10 80 16 Example 8 2 Ethyl acrylate [EMIM][TFSI] 10：1 0.3：1 80 12 80 16 Example 9 4 Ethyl acrylate [HMIM][TFSI] 40：1 0.2：1 100 12 90 16 Example 10 2 Ethyl acrylate [EMIM][TFSI] 30：1 0.25：1 75 8 80 36 Example 11 2 Ethyl acrylate [EMIM][TFSI] 5：1 0.2：1 80 9 90 24 Example 12 2 Ethyl acrylate [EMIM][TFSI] 4：1 0.2：1 60 12 80 16 Comparative Example 1 / Ethyl methacrylate [HMIM][TFSI] 1：0 0.4：1 60 8 80 16 Comparative Example 2 / Ethyl acrylate [EMIM][TFSI] 1：0 0.3：1 80 10 90 32 Comparative Example 3 / Butyl acrylate [BMIM][TFSI] 1：0 0.2：1 100 12 100 16 Comparative Example 4 / Butyl methacrylate [BMIM][TFSI] 1：0 0.2：1 100 12 80 48

[0058] The tensile properties of ionogels were tested using a universal testing machine. Figure 2 The stress-strain curves of Example 8 are shown, exhibiting high strength and high ductility. However, as shown in Table 2, Comparative Examples 1-4, which do not contain azophenyl groups, have lower mechanical strength and elongation at break than Examples 1-12, which contain azophenyl groups. This is because the rigid framework of azophenyl can significantly enhance the tensile strength of the ionomer gel.

[0059] Subsequently, the ionogel was cut into strips of 30 mm × 5 mm, and the two ends were connected with conductive copper foil and wires to serve as electrodes, and assembled into a strain sensor. Figure 3 Using formulas The conductivity of the ionogel film in this invention was calculated, where L, S, and R represent the length, cross-sectional area, and resistance value of the sample, respectively. The results are shown in Table 2. In Examples 2, 8, 10, and 11, the conductivity of the azobenzene-containing ionogel conductive film increased with increasing ion liquid content. Examples 4, 8, and 12 also showed similar results. Figure 4 ).

[0060] Tensile strain was applied using a universal testing machine, while resistance changes were monitored using a digital multimeter. Figure 5 The relative resistance change of Example 8 under different tensile strains is shown, demonstrating high sensitivity and good repeatability, and can be used to monitor human movements such as finger bending and wrist movement.

[0061] Due to hydrogen bonding, van der Waals forces, and ionic dipole interactions between the ionogel and the matrix, the prepared photoisomerized ionogel containing azophenyl groups exhibits excellent adhesion properties to various matrices. To visually demonstrate the adhesive strength of the material, Figure 6 The image shows a load test photograph after two wooden substrates were bonded together using the ionomer gel of Example 8. As shown in the figure, the two bonded wooden boards can withstand two 200g weights, indicating that the ionomer gel has excellent adhesive properties.

[0062] use Figure 7 The adhesion strength of the ionogel was tested using an overlap shearing device. As shown in Table 2, the adhesion of the photoisomerized ionogel films containing azophenyl groups decreased with decreasing ion liquid content in Examples 2, 8, 10, and 11. The adhesion performance of Comparative Example 2 was significantly lower than that of Example 8, indicating that the introduction of azophenyl groups is crucial for improving the adhesion strength of the ionogel.

[0063] An ion gel film was assembled with interdigitated electrodes and irradiated under 365 nm ultraviolet light of different power densities to monitor its resistance changes. Figure 8 The relationship between the relative resistance change and ultraviolet light power density of Example 8 is shown, indicating that its resistance change is sensitive to ultraviolet light intensity and can be used as an ultraviolet detector. After the ultraviolet light irradiation is stopped, the resistance can be restored to near the initial value when placed under visible light, showing reversible light-switching characteristics. However, when Comparative Examples 1-4 are irradiated with ultraviolet or visible light, the resistance of the ion gel does not change, which indicates that the photoisomerization transition of the azophenyl group can reversibly regulate the ion transport of the ion gel. Furthermore, the ion gel film of Example 8 is locally irradiated with ultraviolet light using a mask. Due to the isomerization of azophenyl, the transparency and electrical properties of the irradiated area change, thereby "writing" a pattern ( Figure 9 (a) Then, by illuminating the entire pattern with visible light, the pattern can be "erased" ( Figure 9 (b) This process can be repeated. Figure 9 (c) demonstrates its application potential in information storage and anti-counterfeiting.

[0064] Table 2: Performance parameters of Examples 1-12 and Comparative Examples 1-4

[0065] sample <![CDATA[Initial conductivity (S∙m -1 ).]]> Adhesion (kPa) Stress (kPa) strain(%) Does the conductivity of the gel change after UV irradiation? Does the conductivity of the gel return to its initial resistance after UV irradiation? Example 1 0.025 50 98 1015 yes yes Example 2 0.018 45 100 1022 yes yes Example 3 0.015 42 126 962 yes yes Example 4 0.012 36 133 850 yes yes Example 5 0.0035 28 125 875 yes yes Example 6 0.0025 22 130 960 yes yes Example 7 0.0028 25 127 923 yes yes Example 8 0.0043 30 122 900 yes yes Example 9 0.0023 15 113 830 yes yes Example 10 0.0038 27 87 845 yes yes Example 11 0.0032 23 140 816 yes yes Example 12 0.0030 23 147 800 yes yes Comparative Example 1 0.022 20 55 650 no No change Comparative Example 2 0.004 18 60 620 no No change Comparative Example 3 0.0035 15 65 600 no No change Comparative Example 4 0.0026 12 67 586 no No change

[0066] The above embodiments demonstrate that the present invention successfully prepared an azophenyl ionic gel possessing excellent mechanical properties, high ionic conductivity, excellent adhesion, and sensitive photoresponse characteristics. This material shows promising application prospects in fields such as flexible strain sensing, ultraviolet light detection, and intelligent patterning.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and all of these should be covered within the protection scope of the present invention.

Claims

1. A method for preparing a photoisomerized ionic gel containing an azophenyl group, characterized in that, The preparation method includes the following steps: 4,4'-dihydroxyazobenzene, olefinic acid, condensing agent, and catalyst were mixed and esterified to obtain azobenzene monomers modified with double-terminated double bonds; the synthetic route is as follows: Where n = 1, 2, 3, 4, 5, 6, 7; The azobenzene monomer modified with double-ended double bonds, acrylate monomers, hydrophobic ionic liquids and thermal initiators are mixed evenly in a solvent, followed by thermal polymerization. After drying to remove the solvent, the photo-isomerized ionic gel containing azobenzene groups is obtained.

2. The preparation method according to claim 1, characterized in that, The condensing agent is N,N'-dicyclohexylcarbodiimide, and the catalyst is 4-dimethylaminopyridine; the acrylate monomer is selected from ethyl acrylate, butyl acrylate, ethyl methacrylate, and butyl methacrylate; the hydrophobic ionic liquid is selected from 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt.

3. The preparation method according to claim 2, characterized in that, The molar ratio of 4,4'-dihydroxyazobenzene, olefinic acid, and condensing agent is 1:2-3:2.

2.

4. The preparation method according to claim 1, characterized in that, The thermal initiator is ammonium persulfate or potassium persulfate, and its amount accounts for 0.5-1.5 wt% of the total mass of the azobenzene monomer modified with double-ended double bonds and the acrylate monomer.

5. The preparation method according to claim 1, characterized in that, The thermal polymerization reaction is carried out at a temperature of 60-100 ℃ for 8-12 hours; the drying process is carried out at a temperature of 80-100 ℃ for 16-48 hours.

6. The preparation method according to claim 1, characterized in that, The mass ratio of the azobenzene monomer modified with double-ended double bonds to the acrylate monomer is 1:4-40; the total mass ratio of the ionic liquid, the azobenzene monomer modified with double-ended double bonds, and the acrylate monomer is 0.2-0.4:

1.

7. A photo-isomerized ionic gel containing an azophenyl group prepared by the method according to any one of claims 1-6, characterized in that, The ion gel changes from trans configuration to cis configuration after being irradiated with ultraviolet light, and after being irradiated with visible light, the cis configuration azobenzene changes back to trans configuration.

8. The application of the photoisomerized ionogel containing azophenyl groups as described in claim 7 in the preparation of flexible sensors.

9. The application according to claim 8, characterized in that, The flexible sensor is a strain sensor and / or a light-response sensor.

10. A flexible sensor, characterized in that, The sensing element of the flexible sensor is made of a photoisomerized ionogel containing azophenyl groups as described in claim 7.

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