An electron transfer type photochromic crystal material, a preparation method and application thereof

Abstract

The application discloses an electron transfer type photochromic crystal material and a preparation method and application thereof. The electron transfer type photochromic crystal material [(CBbpy)Zn3(TBC)2(H2O)]·NO3 is prepared by taking 1-(4-cyanobenzyl)-4,4-bipyridinium salt as a single viologen ligand and taking benzenetricarboxylic acid as a strong electron donor. The crystal has a large second harmonic generation effect, and also has a very large nonlinear optical switching ratio, and the switching ratio is up to about 25 times, which is three times of the highest nonlinear optical switchable ratio record (8 times) of the electron transfer type switch material. Therefore, the electron transfer type photochromic crystal material can be applied as a nonlinear optical switch material.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical materials, in particular to an electron transfer type photochromic crystal material and a preparation method and application thereof. BACKGROUND

[0002] In recent years, molecular switches have attracted extensive attention of researchers, mainly due to their potential application value in information storage, photonic devices and optical communication. Second-order nonlinear optical (NLO) switch material is a very important molecular switch. NLO switch is actually a molecular material capable of realizing reversible NLO response. Most NLO switch materials have donor-acceptor bridging structure or structure transformation characteristics, which will change the NLO performance of the molecule when it is stimulated by external stimuli (such as light, electricity, magnetism and pH, etc.), so as to realize the “on” and “off” states of nonlinear optics. The two states can be realized by chemical and physical methods. Chemical methods such as ion exchange and gas adsorption and desorption are limited to materials with available pores; physical methods such as light and heating can very conveniently change the nonlinear optical properties and have a wider range of applications. Most of the previous studies on nonlinear optical switches have focused on liquid materials, but they are often unstable, while solid-state nonlinear switch materials can overcome the shortcomings of structural instability and performance difficult to control, so solid-state nonlinear optical switch materials have gradually become a hot research material.

[0003] Solid-state nonlinear switches include pure inorganic materials, pure organic materials and organic-inorganic hybrid materials, and the types are relatively complete, but the number is still very scarce, and the switching ratio of the optical switch is still relatively low. The main reason is that the structural unit of the material must contain a strong response nonlinear active group, and the reversible transformation of the structure needs to be completed under relatively harsh conditions. For example, many reported nonlinear optical switches need to complete structure phase transition at different temperatures to realize optical switching. In the structure phase transition process, the material framework may collapse due to insufficient harshness of external conditions, which greatly limits the application prospect of such nonlinear optical switches. Electron transfer is an effective way to change the polarity of the material, and the switching of nonlinear optical performance can be realized through a small structural change, therefore, electron transfer type material will be a shining star in the second-order nonlinear optical switch.

[0004] For nonlinear optical (NLO) switching material, SHG switching contrast is the most important standard to measure the optical switching material, and people pay more and more attention to design NLO crystal with higher SHG switching contrast. There are only three articles reported for electron transfer type materials, Guo Guocong group synthesized the first electron transfer type nonlinear switching crystal [ZnBr2(CEbpy)]·3H2O (CEbpy=N-carboxyl-ethyl-4,4'-bipyridine), the second harmonic generation effect is 0.8 times of KH2PO4 (KDP), and the nonlinear optical switching ratio is 3.3 times; Zang Shuangquan group then reported a viologen functionalized chiral Eu-MOF which can also be used as a multifunctional switchable material, and the second harmonic generation effect is only 6.1 times of KDP, and the nonlinear optical switching ratio is 3.3 times; Guo Guocong group then reported a light and heat driven nonlinear optical switching material Zn-MOF, and the second harmonic generation effect is 0.1 times of KDP, and the nonlinear optical switching ratio is as high as 8 times. However, the synthesis of the above-mentioned electron transfer type materials is complex, the cost is high, the material structure is unstable, and the nonlinear optical signal switching can be realized only under relatively harsh conditions, and the nonlinear optical switchable ratio is not high enough.

[0005] Therefore, it is still a great challenge to design and synthesize a material with high second harmonic generation effect and high nonlinear optical switching ratio. SUMMARY

[0006] The purpose of the present application is to solve the problems existing in the prior art, and provide an electron transfer type photochromic crystal material and a preparation method and application thereof.

[0007] In order to achieve the above-mentioned purpose, the present application is implemented according to the following technical scheme:

[0008] A preparation method of an electron transfer type photochromic crystal material, comprising the following steps:

[0009] S1, synthesizing 1-(4-cyanobenzyl)-4,4-bipyridinium salt;

[0010] S2, dissolving 0.2 mmol, 0.59 g of Zn(NO3)2·6H2O, 0.1 mmol, 22 mg of H3TBC, 0.1 mmol, 37 mg of 1-(4-cyanobenzyl)-4,4-bipyridinium salt CBbpy·Cl in 3 ml of dimethylacetamide DMA and 3 ml of H2O, placing in a 15 ml reaction kettle, and then stirring the mixture on a magnetic stirrer for 30 min, heating the reaction kettle at 90℃ for 5 days, and cooling to room temperature at a cooling rate of 5℃ / min;

[0011] S3, the reaction product is washed with ethanol and water, filtered and dried to obtain colorless block crystal, namely the electron transfer type photochromic crystal material.

[0012] Further, the S1 specifically comprises:

[0013] 10 mmol, 1.562 g of 4,4'-dipyridyl, 10 mmol, 1.515 g of 4-cyanobenzyl chloride and 60 mL of acetonitrile were weighed into a 250 mL dry round-bottom flask, stirred at room temperature for 45 min to fully dissolve, stirred at 80℃ for 36 h, and the reaction product was filtered, washed and dried to obtain 1.697 g of light yellow powder, namely 1-(4-cyanobenzyl)-4,4-dipyridyl onium salt.

[0014] In addition, the present application also relates to an electron transfer type photochromic crystal material prepared by the above method.

[0015] Further, the molecular formula of the electron transfer type photochromic crystal material is C 36 H 20 Zn3N4O 16 .

[0016] Further, the crystal structure of the electron transfer type photochromic crystal material comprises: in the non-centrosymmetric space group Cc, three Zn 2+ , one end-coordinated CBbpy ligand, two TBC ligands, one coordinated water molecule and one free NO3 - anion, wherein CBbpy is 1-(4-cyanobenzyl)-4,4-dipyridyl.

[0017] Furthermore, the present application also provides an application of the electron transfer type photochromic crystal material as a nonlinear optical switching material.

[0018] Compared with the prior art, the present application has the following beneficial effects:

[0019] 1. The electron transfer type photochromic crystal material is a solid material, has stable structure, good recycling property, simple synthesis and low cost;

[0020] 2. No special external conditions are required, and the nonlinear optical "on" and "off" can be realized by applying ultraviolet light and low-temperature heating, respectively;

[0021] 3. Only electron transfer is required inside the material to realize the switching of nonlinear optical signals, and the structure does not change greatly;

[0022] 4. The nonlinear optical switching ratio of the electron transfer type photochromic crystal material prepared by the method is up to 24 times under 1064 laser irradiation, which is higher than the maximum of 8 times of the reported electron transfer type photochromic crystal materials. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 Figure 1 is a crystal structure diagram of the electron transfer type photochromic crystal material of the present application, (a) coordination environment diagram of [(CBbpy)Zn3(TBC)2(H2O)]·NO3, (b) [Zn3O 11 N] cluster polyhedral diagram, (c) 2D layered structure along the ab plane, (d) 3D framework constructed by the BTC ligand Zn3SBU, (e) 3D framework containing terminal CBbpy ligand, the arrow indicates the direction of the dipole moment, (f) 10-connected (3 12 .4 26 .5 7 ) topology structure.

[0024] Figure 2 Figure 2 is a diagram of the color deepening of the electron transfer type photochromic crystal material of the present application with the extension of light irradiation time.

[0025] Figure 3 (a) is the infrared spectrum diagram of the electron transfer type photochromic crystal material of the present application before and after light irradiation.

[0026] Figure 3 (b) is the X-ray powder diffraction diagram of the electron transfer type photochromic crystal material of the present application before and after light irradiation.

[0027] Figure 4 (a) is the time-dependent ultraviolet-visible absorption spectrum of the electron transfer type photochromic crystal material of the present application after xenon lamp irradiation.

[0028] Figure 4 (b) is the electron paramagnetic resonance spectrum diagram of the electron transfer type photochromic crystal material of the present application before and after coloring.

[0029] Figure 5 Figure 3 is a diagram of the shortest distance between the electron-deficient dipyridinium ion and the electron-rich electron donor.

[0030] Figure 6The second-order nonlinear optical test results of the electron transfer type photochromic crystal material of the present application as a nonlinear optical switch material under 1064 nm laser light: (a) SHG phase matching diagram of electron transfer type photochromic crystal materials of different sizes, (b) SHG signal of the electron transfer type photochromic crystal material (125-150 μm) with KDP as a reference, (c) SHG signal gradually weakens with the extension of xenon lamp illumination time, (d) reversible cycle diagram of nonlinear optical switch.

[0031] Figure 7 The second-order nonlinear optical test results of the electron transfer type photochromic crystal material of the present application as a nonlinear optical switch material under 532 nm laser light: (a) SHG phase matching diagram of electron transfer type photochromic crystal materials of different sizes, (b) SHG signal of the electron transfer type photochromic crystal material (125-150 μm) with BBO as a reference, (c) SHG signal gradually weakens with the extension of xenon lamp illumination time, (d) reversible cycle diagram of nonlinear optical switch. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical scheme and advantages of the present application clearer and more apparent, the present application will be further described in detail below in combination with examples. The specific examples described herein are only used to explain the present application and do not limit the present application.

[0033] Example 1

[0034] The preparation method of an electron transfer type photochromic crystal material of the present embodiment is as follows:

[0035] Take 10 mmol, 1.562 g of 4,4'-dipyridyl, 10 mmol, 1.515 g of 4-cyanobenzyl chloride and 60 mL of acetonitrile into a 250 mL dry round-bottom flask, stir at room temperature for 45 minutes to fully dissolve, reflux and stir at 80°C for 36 hours, filter, wash and dry the reaction product to obtain 1.697 g of light yellow powder with a yield of 55.15%, and the specific synthesis route is as follows:

[0036]

[0037] Then, 0.2 mmol, 0.59 g of Zn(NO3)2·6H2O, 0.1 mmol, 22 mg of H3TBC, 0.1 mmol, 37 mg of 1-(4-cyanobenzyl)-4,4-bipyridinium salt CBbpy·Cl were mixed and dissolved in 3 ml of dimethylacetamide DMA and 3 ml of H2O, and placed in a 15 ml reaction kettle, and then the mixture was stirred on a magnetic stirrer for 30 min, and the reaction kettle was heated at 90°C for 5 days, and cooled to room temperature at a cooling rate of 5°C / min;

[0038] Finally, the reaction product was washed with ethanol and water, filtered and dried to obtain colorless block-shaped crystals, i.e. electron transfer type photochromic crystal material (([CBbpy)Zn3(TBC)2(H2O)]·NO3), and the yield was about 53% according to the amount of CBbpy put.

[0039] The molecular formula of the electron transfer type photochromic crystal material prepared in this example is C 36 H 20 Zn3N4O 16 Elemental analysis calculated value (%): C, 45.01; H, 2.10; N, 5.83; measured value: C, 45.09; H, 2.17; N, 5.75. IR analysis (KBr, cm -1 ): 3462 (m), 3103 (w), 3045 (w), 2920 (w), 2223 (m), 1641 (s), 1447 (s), 1367 (s), 1207 (w), 1167 (w), 1092 (w), 1007 (w), 819 (m), 762 (s), 710 (s), 567 (m).

[0040] Specifically, the crystallographic parameters of [(CBbpy)Zn3(TBC)2(H2O)]·NO3 are shown in Table 1.

[0041] Table 1

[0042]

[0043]

[0044] a R1=∑||F o |-|F c || / ∑|F o |. b wR2= [∑[w(F o 2 -F c 2 ) 2 ] / ∑[w(Fo 2 ) 2 ]] 1 / 2 .

[0045] Furthermore, the crystal structure analysis of [(CBbpy)Zn3(TBC)2(H2O)]·NO3 is as follows: This material crystallizes in the non-central space group Cc, and the asymmetric unit contains three Zn atoms. 2+ One terminal-coordinated CBbpy ligand, two TBC ligands, one coordinated water molecule, and one free NO3. - Anions (reference) Figure 1 a) Zn 2+ It has two coordination modes. Zn(1) ions adopt a slightly distorted octahedral coordination mode, coordinating with five oxygen atoms and one nitrogen atom, with four oxygen atoms coming from four BTC ligands and the other from the μ3-H2O molecule. Zn(2) and Zn(3) ions both adopt a tetrahedral coordination mode, with each Zn(2) ion coordinating with four oxygen atoms, with three oxygen atoms coming from three BTC ligands and the other from the μ3-H2O molecule. The ZnO5N octahedrons are connected to two ZnO4 tetrahedra at their respective vertices to form [Zn3O]. 11 N] cluster (refer to) Figure 1 b), [Zn3O 11 The N clusters, acting as secondary structural units (Zn3SBUs), are arranged along the ab plane. Each Zn3SBU is connected to six adjacent Zn3SBUs via BTC ligands, thus forming a two-dimensional plane (see reference). Figure 1 c) Adjacent planes are also connected by BTC ligands to form a three-dimensional framework (see reference). Figure 1 d), while CBbpy ligands are only terminal group coordinated (see reference). Figure 1 e). The framework of this compound can also be simplified in another way, with each Zn3SBU forming a 10-connected (3) group with 10 adjacent Zn3SBUs. 12 0.4 26 0.5 7 Topology (refer to) Figure 1 f).

[0046] like Figure 2 As shown, when the colorless electron-transfer photochromic crystal material prepared in this embodiment is irradiated with a xenon lamp at room temperature and in an air atmosphere, the sample undergoes a visible color change, changing from colorless to blue. After 25 minutes of irradiation, the color change of the material approaches saturation. The colored crystal can completely fade at 120°C in an air atmosphere. This reversible color change can be repeated many times, confirming that the colorless electron-transfer photochromic crystal material prepared in this embodiment has good cyclic reversibility.

[0047] As Figure 3 shown, the infrared spectrum (IR) (refer to Figure 3 a) and the X-ray powder diffraction pattern (PXRD) (refer to Figure 3 b) of the electron transfer type photochromic crystal prepared in this example do not show obvious difference before and after light irradiation, indicating that the electron transfer type photochromic crystal prepared in this example does not undergo photolysis reaction or photo-induced isomerization phenomenon upon light irradiation. In order to clarify the photochromic mechanism of the electron transfer type photochromic crystal prepared in this example, the entire photochromic process of the crystal was monitored by UV-Vis spectrum, and with the deepening of the color of the electron transfer type photochromic crystal prepared in this example, the absorption peak at 630 nm in the UV-Vis spectrum became stronger (refer to Figure 4 a), which is likely to be the characteristic absorption peak of the viologen radical. In order to further explore the characteristic peak, we tested the electron paramagnetic resonance spectrum (EPR) of the samples before and after coloring, as shown in Figure 4 b, it was found that the sample before coloring did not have an EPR signal, while after coloring, a strong electron paramagnetic resonance signal appeared at g = 2.0045, which is very close to the standard radical signal (g = 2.0023), thus confirming that the photochromic behavior of the sample is due to the photo-induced electron transfer to form the viologen radical.

[0048] The charge transfer between the pyridinium ion and the nitrate is very weak, which to some extent is conducive to the photo-induced electron transfer from the oxygen atom of the nitrate to the electron-deficient pyridinium cation. According to the structural information of the electron transfer type photochromic crystal prepared in this example, the distance between the N + atom of the bipyridine and the nearest carboxyl oxygen atom is which is too long to be suitable for photo-induced electron transfer, but the distance between the oxygen atom of the electron donor nitrate and the N + atom of the bipyridine is only which may be one of the ways of photo-induced electron transfer, in addition, the cyano group is also a weak electron donor, and the distance between the cyano group and the center of the bipyridine ring in the structure is (refer to Figure 5 ), which may be another way of photo-induced electron transfer.

[0049] The electron transfer type photochromic crystal prepared in this example crystallizes in the non-centrosymmetric Cc space group, and the electron-deficient single-end alkylated CBbpy ligand has electron-withdrawing properties. The N atom of the single-end alkylated CBbpy ligand and the oxygen atom of the trimesic acid coordinate with the metal Zn 2+ together, and this combination forms a non-centrosymmetric push-pull system, which improves the polarity of the framework. As Figure 1The polar direction of the whole framework material is the direction from the Zn3cluster to the CBbpy ligand, as shown in FIG. 1. The material has macroscopic polarity and can exhibit second-order nonlinear optical properties. Therefore, the electron transfer type photochromic crystal prepared in this embodiment can be used as a nonlinear optical switch material to prepare a nonlinear optical switch.

[0050] Example 2

[0051] The electron transfer type photochromic crystal prepared in Example 1 was used as a nonlinear optical material and subjected to second-order nonlinear optical testing. The crystal [(CBbpy)Zn3(TBC)2(H2O)]·NO3 (crystal size: 125 μm-150 μm) exhibited a very strong second-order nonlinear optical (SHG) response under 1064 nm laser irradiation, and the signal was about 1.5 times that of the obvious nonlinear optical material KDP, while having good phase matching properties (see FIG. 2). Figure 6 a and 6b). After irradiation by a xenon lamp, the second-order nonlinear optical (SHG) signal of the colored crystal [(CBbpy)Zn3(TBC)2(H2O)]·NO3 was significantly smaller, which means that the light-induced electron transfer caused the polarity of the material to decrease, and also means that the material has second-order nonlinear optical switching properties. The second-order nonlinear optical signal of the colored crystal [(CBbpy)Zn3(TBC)2(H2O)]·NO3 was about 4.2% of that of the crystal [(CBbpy)Zn3(TBC)2(H2O)]·NO3 before coloring, that is, the nonlinear switching ratio was about 24 times (see FIG. 6c), which is three times the switching ratio of the largest electron transfer type nonlinear optical switch reported to date. Figure 6 c), which is three times the switching ratio of the largest electron transfer type nonlinear optical switch reported to date. There can be two reasons for the material having such a large nonlinear optical switching ratio: 1) during the light-induced electron transfer process, the macroscopic polarity of the material significantly decreases, thereby causing the nonlinear optical signal to change significantly during the coloring process of the material; and 2) during the coloring process, the self-absorption ability of the crystal [(CBbpy)Zn3(TBC)2(H2O)]·NO3 at 532 nm is significantly enhanced, and the light absorption intensity of the colored crystal [(CBbpy)Zn3(TBC)2(H2O)]·NO3 at 532 nm is about three times that of the crystal [(CBbpy)Zn3(TBC)2(H2O)]·NO3 before coloring, thereby enhancing the second-order nonlinear optical switching ability. These two factors together cause the super-large nonlinear optical switching ratio for 1064 nm laser light. Figure 6As shown in Fig. d, the second-order nonlinear switching performance of the crystal [(CBbpy)Zn3(TBC)2(H2O)]·NO3 can be sustained for more than four cycles, which indicates that the crystal [(CBbpy)Zn3(TBC)2(H2O)]·NO3 is an excellent second-order nonlinear switching material. The nonlinear signal is about 1.5 times the signal generated by the classic KDP, and after the (TTBPY)Zn3(TBC)2·H2O is irradiated by a xenon lamp for 50 min, the generated nonlinear signal is about 4.2% of the original, and the nonlinear optical switching ratio is as high as 24 times, which is about 3 times the largest nonlinear optical switching ratio of the reported electron transfer type materials, thereby enhancing the second-order nonlinear optical switching capability. The two factors together cause the electron transfer type photochromic crystal prepared in Example 1 to have a super-large nonlinear optical switching ratio for 1064 nm laser.

[0052] Example 3

[0053] The electron transfer type photochromic crystal prepared in Example 1 can also exhibit good nonlinear optical switching effects for other waveband lasers, for example, the nonlinear optical switching ratio of the crystal [(CBbpy)Zn3(TBC)2(H2O)]·NO3 (crystal size: 125 μm-150 μm) under 532 nm laser irradiation is about 7 times (as shown in Fig. d), which is smaller than the switching ratio for 1064 nm laser, which is likely due to the small change in the absorbance intensity of the material at 256 nm before and after coloring. Figure 7

[0054] In summary, the application of ultraviolet light and low-temperature heating to the electron transfer type photochromic crystal prepared in the application can realize the “on” and “off” of the nonlinear optics; and the nonlinear optical switching ratio of the electron transfer type photochromic crystal material prepared in the application under 1064 laser irradiation is as high as 24 times.

[0055] The technical scheme of the application is not limited to the above specific examples, and any technical modification made according to the technical scheme of the application falls within the protection scope of the application.​

Claims

1. A method for preparing an electron transfer type photochromic crystal material, characterized by, The method comprises the following steps: S1, synthesizing 1-(4-cyanobenzyl)-4,4-bipyridinium salt; S2, dissolving 0.2 mmol, 0.59 g of Zn(NO3)2·6H2O, 0.1 mmol, 22 mg of H3TBC, and 0.1 mmol, 37 mg of 1-(4-cyanobenzyl)-4,4-bipyridinium salt CBbpy·Cl in 3 ml of dimethylacetamide DMA and 3 ml of H2O, placing them in a 15 ml reaction kettle, then stirring the mixture on a magnetic stirrer for 30 min, heating the reaction kettle at 90 °C for 5 days, and cooling to room temperature at a cooling rate of 5 °C / min; S3, the reaction product is washed with ethanol and water, filtered and dried to obtain colorless block crystal, i.e. electron transfer type photochromic crystal material, the molecular formula of the electron transfer type photochromic crystal material is C 36 H 20 Zn3N4O 16 ; the crystal structure of the electron transfer type photochromic crystal material comprises: in non-center space group Cc , three Zn 2+ , one end group coordinated CBbpy ligand, two TBC ligands, one coordinated water molecule and one free NO3 − anion, wherein CBbpy is 1-(4-cyanobenzyl)-4,4-bipyridine.

2. The method for preparing the electron-transfer type photochromic crystal material according to claim 1, characterized in that, The S1 specifically comprises: Weigh 10 mmol, 1.562 g of 4,4'-bipyridine, 10 mmol, 1.515 g of 4-cyanobenzyl chloride and 60 mL of acetonitrile into a 250 mL dry round-bottom flask, stir them at room temperature for 45 min to make them fully dissolved, reflux and stir them at 80 °C for 36 h, and then filter, wash and dry the reaction product to obtain 1.697 g of light yellow powder, i.e. 1-(4-cyanobenzyl)-4,4-bipyridinium salt.

3. An electron transfer type photochromic crystalline material, characterized in that, The method is prepared by using the method of claim 1 or 2.

4. Use of the electron transfer type photochromic crystal material according to claim 3 as a nonlinear optical switch material.

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