A chiral nitrogen heterocyclic organic crystalline piezoelectric material and its preparation method

Abstract

This invention relates to the field of piezoelectric materials technology, specifically to a chiral nitrogen-containing heterocyclic organic crystalline piezoelectric material and its preparation method. The organic crystalline piezoelectric material is N-cyanoethyl-( S )-2-methylpiperazine hydrochloride, whose core is a one-dimensional hydrogen-bonded chain construction strategy of unilaterally protonated chiral piperazine, with protonated N-cyanoethyl-( S Using 2-methylpiperazine cations as structural building blocks and chloride ions as charge balancers, a highly oriented one-dimensional hydrogen bond chain is constructed by regulating intermolecular hydrogen bonding. This enhances the ordered arrangement of molecular dipoles and optimizes the synergistic mode of lattice strain-polarization response, achieving a breakthrough in piezoelectric properties. The material exhibits a piezoelectric coefficient as high as ±80 pC / N and an electromechanical coupling coefficient as high as 0.35, far exceeding known chiral organic piezoelectric materials. Furthermore, it demonstrates excellent thermal stability and can be widely applied in demanding applications such as micro-pressure sensors, low-frequency vibration detectors, and micro energy harvesters.

Description

Technical Field

[0001] This invention relates to the field of piezoelectric materials technology, specifically to a chiral nitrogen heterocyclic organic crystalline piezoelectric material and its preparation method. Background Technology

[0002] Piezoelectric materials, with their bidirectional electromechanical energy conversion capability based on the direct / inverse piezoelectric effect, play a central role in smart sensing, precision actuation, and new energy devices. The direct piezoelectric effect can convert mechanical stress into detectable electrical signals (such as...). d 33 , d 31 The inverse piezoelectric effect, which allows for displacement of materials through external electric fields, makes it an indispensable functional material in flexible electronics and biomedicine. Traditional inorganic piezoelectric materials (such as lead zirconate titanate (PZT) and barium titanate (BTO)) have high piezoelectric coefficients, but suffer from high density, brittleness, high acoustic impedance, and potential heavy metal ion leakage risks. These limitations severely restrict their application prospects in flexible, biodegradable, and implantable biomedical devices. In contrast, organic piezoelectric materials exhibit significant comprehensive advantages: they possess excellent flexibility, low toxicity, low acoustic impedance, and good biocompatibility. They can also be prepared using simple solution methods and their chemical structures can be flexibly designed based on application requirements. These characteristics make them a key factor in replacing traditional inorganic piezoelectric materials and open up broad prospects for applications in flexible electronics, biodegradable devices, and implantable medical devices in the biomedical field.

[0003] Of the 32 point groups covered in crystallography, 20 lacking a center of symmetry exhibit piezoelectric effects. Ten of these belong to chiral point groups, a characteristic that lays the theoretical foundation for the precise construction of piezoelectrically active organic crystalline materials based on the structural design of chiral molecules. However, current chiral organic crystalline piezoelectric materials generally still face the challenge of relatively low piezoelectric coefficients. d 33 <20pC / N) and insufficient electromechanical coupling coefficient ( k 33 The problem of piezoelectricity (<0.2) restricts its practical application in energy harvesting and sensitive sensing. Furthermore, the complex synthetic routes and poor controllability of crystallization processes of some chiral molecules further limit the large-scale preparation and application expansion of these materials. Therefore, developing a chiral organic crystalline piezoelectric material that combines high piezoelectric properties, excellent stability, and a simple preparation process has become a key direction for advancing this field. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] To address the shortcomings of existing technologies, this invention provides a method for achieving a breakthrough improvement in piezoelectric performance based on N-cyanoethyl-( S Organic heterocyclic crystalline piezoelectric materials of 2-methylpiperazine hydrochloride and their preparation method are disclosed. This material has a high piezoelectric coefficient and electromechanical coupling coefficient that far exceed those of existing chiral organic piezoelectric materials, excellent thermal stability and good deliquescence resistance, and the preparation process is simple. It is expected to promote the application upgrade of organic crystalline piezoelectric materials in flexible electronics, biomedicine, Internet of Things and other fields.

[0006] (II) Technical Solution

[0007] In a first aspect, the present invention provides a chiral nitrogen heterocyclic organic crystalline piezoelectric material, which is based on chloride ions Cl... - As an anion, with protonated N-cyanoethyl-( S N-cyanoethyl-( )-2-methylpiperazine is composed of cations. S 2-Methylpiperazine hydrochloride, in which the molar ratio of anion to cation is 1:1, has the following structural formula:

[0008] .

[0009] Preferably, the organic crystalline piezoelectric material crystallizes at room temperature in space group P21, with cell parameters of... a =7.9245(18) Å、 b =7.985(2) Å、 c =8.565(2) Å, α= 90°、 β =112.46(3)°、 γ =90°, cell volume V=500.9(3)Å 3 The piezoelectric coefficient of the organic crystalline piezoelectric material d 33 The electromechanical coupling coefficient is ±80 pC / N. k 33 It is 0.35.

[0010] Secondly, the present invention provides a method for preparing the above-mentioned chiral nitrogen heterocyclic organic crystalline piezoelectric material, the preparation process of which is as follows:

[0011] S1. Weigh out ( ) according to a molar ratio of 2~2.1:1 (preferably 2.1:1) S 2-methylpiperazine and bromoacetonitrile were placed in a reaction vessel, and an acid-binding agent and acetonitrile were added to dissolve and dilute the mixture. The mixture was stirred in an ice-water bath for 20-40 minutes, and then allowed to react at room temperature for 20-28 hours. After the reaction was completed, N-cyanoethyl-( SThe crude product of 2-methylpiperazine was separated by column chromatography to obtain purified N-cyanoethyl-( S )-2-methylpiperazine;

[0012] S2, the N-cyanoethyl-( S )-2-methylpiperazine was dissolved in methanol, ethanol, or isopropanol until clear, and N-cyanoethyl-( S A solution of N-2-methylpiperazine was placed in an ice-water bath, and concentrated hydrochloric acid was added dropwise to it to make N-cyanoethyl-( S The molar ratio of 2-methylpiperazine to HCl in concentrated hydrochloric acid is 1~1.05:1;

[0013] S3. After the addition is complete, stir the reaction (preferably for 1 hour) to complete the reaction of N-cyanoethyl-( S The reaction system was protonated, and then filtered. The filtrate was slowly evaporated at a constant temperature of 24-28°C until transparent, colorless, centimeter-sized bulk single crystals were obtained, which is the organic crystalline piezoelectric material. The structural formula of the material is as follows:

[0014] .

[0015] Preferably, in S1, ( S The molar ratio of 2-methylpiperazine to bromoacetonitrile is 2.1:1.

[0016] ( S 2-Methylpiperazine is a chiral isomer of 2-methylpiperazine. The parent structure is piperazine, with a methyl group (-CH3) substituted at the second carbon atom of the piperazine ring. This carbon atom is chiral because it is attached to four different groups (the two adjacent groups on the ring, the methyl group, and a hydrogen atom), resulting in two mirror-image stereoisomers of 2-methylpiperazine. S )-configuration and ( R (-configuration). Prioritize the four groups attached to the chiral carbon, placing the lowest priority group (-H) away from the observer. If the remaining three groups are arranged counter-clockwise from highest to lowest priority, they are labeled as... S - Configuration (Latin Sinister, meaning "left").

[0017] Preferably, in S1, the acid-binding agent is potassium carbonate, sodium carbonate, sodium bicarbonate, triethylamine, or diisopropylethylamine.

[0018] Preferably, in S1, the column eluent is a composition of dichloromethane:methanol in a volume ratio of 15:1, and the column chromatography is used to remove methylpiperazine and bilateral N-cyanoethyl-( S )-2-methylpiperazine was used to obtain purified N-cyanoethyl-( S )-2-methylpiperazine.

[0019] Preferably, in S1, the reaction is stirred in an ice-water bath for 30 minutes, and then the reaction is carried out at room temperature for 24 hours.

[0020] Preferably, the concentration of concentrated hydrochloric acid in S2 is 33-36 wt%, and the dropping rate is 1 drop / second to avoid local uneven concentration caused by violent exothermic reaction.

[0021] Preferably, in step S3, the filtrate is slowly evaporated at a constant temperature of 25°C for one week to obtain the organic crystalline piezoelectric material.

[0022] Preferably, in S2, the ice-water bath temperature is 273K (0℃) to maintain the temperature stability of the reaction system and ensure that the protonation reaction proceeds uniformly.

[0023] The methanol, ethanol, or isopropanol used in S2 is a reaction solvent that can dissolve N-cyanoethyl-( S )-2-methylpiperazine until clear, ensuring uniform contact of reactants, compatibility with concentrated hydrochloric acid (no side reactions, no layering) and without affecting N-cyanoethyl-( S The protonation process of 2-methylpiperazine.

[0024] (III) Beneficial Effects

[0025] This invention proposes a one-dimensional hydrogen bond chain construction strategy for unilaterally protonated chiral piperazines, using protonated N-cyanoethyl-( S Using 2-methylpiperazine cations as structural units and chloride ions as charge balancers, a highly oriented one-dimensional hydrogen bond chain is constructed by precisely controlling intermolecular hydrogen bond interactions. By enhancing the ordered arrangement of molecular dipoles and optimizing the synergistic mode of lattice strain-polarization response, a breakthrough improvement in piezoelectric properties is achieved, providing a new paradigm for the development of high-performance organic piezoelectric materials.

[0026] This invention uses N-cyanoethyl-( S Using N-2-methylpiperazine and hydrochloric acid as raw materials, a novel organic heterocyclic crystalline piezoelectric material was synthesized by precisely controlling the stoichiometric ratio and crystallization conditions. This material exhibits excellent properties: ① Breakthrough piezoelectric performance: The N-cyanoethyl-( S The ordered stacking of 2-methylpiperazine cations in the crystal lattice induces stable polarization; the strong hydrogen bonds formed between them and chloride ions in a one-dimensional chain enhance the lattice's sensitivity to external stress, making the material prone to dipole rotation and lattice strain under external forces, and the material exhibits a piezoelectric coefficient as high as ±80 pC / N. d 33 ) and the electromechanical coupling coefficient of 0.35 ( k 33 This far exceeds that of known chiral organic piezoelectric materials (traditional materials). d33 <20pC / N, k 33 <0.2). ② Excellent stability: The construction of strong hydrogen-bonded one-dimensional chains not only optimizes piezoelectric properties, but also endows the material with excellent thermal stability.

[0027] The chiral nitrogen heterocyclic organic crystalline piezoelectric material provided by this invention is suitable for scenarios with stringent sensitivity requirements, specifically as follows: ① Micro-pressure sensor: It can accurately capture weak physiological signals such as human pulse and respiration, and is compatible with wearable health monitoring devices. ② Low-frequency vibration detector: It can efficiently identify weak vibrations in the environment (such as abnormal noises from equipment operation and minor deformations of buildings), and is applied in industrial inspection and security fields. ③ Miniature energy harvester: It can efficiently convert low-intensity mechanical energy such as human movement and environmental vibration into electrical energy to power IoT micro-devices.

[0028] In summary, the chiral nitrogen heterocyclic organic crystalline piezoelectric material provided by this invention combines high piezoelectric performance with stability, and is expected to promote the application upgrade of organic crystalline piezoelectric materials in fields such as flexible electronics, biomedicine, and the Internet of Things. Attached Figure Description

[0029] Figure 1 This is the N-cyanoethyl-( S Centimeter-scale crystal photographs of 2-methylpiperazine hydrochloride, an organic crystalline piezoelectric material.

[0030] Figure 2 It is N-cyanoethyl-( S A schematic diagram of the smallest asymmetric unit of 2-methylpiperazine hydrochloride.

[0031] Figure 3 It is N-cyanoethyl-( S Packing morphology of 2-methylpiperazine hydrochloride along the b-axis.

[0032] Figure 4 It is N-cyanoethyl-( S Diagram of a testing apparatus for the piezoelectric properties of 2-methylpiperazine hydrochloride, an organic heterocyclic crystalline piezoelectric material.

[0033] Figure 5 It is N-cyanoethyl-( S A comparison of room temperature powder diffraction data and simulated data for 2-methylpiperazine hydrochloride.

[0034] Figure 6 It is N-cyanoethyl-( S Thermogravimetric diagram of 2-methylpiperazine hydrochloride.

[0035] Figure 7 It is N-cyanoethyl-( SElectromechanical coupling coefficient of 2-methylpiperazine hydrochloride organic heterocyclic crystalline piezoelectric material determined by dynamic resonance method at 293 K. Detailed Implementation

[0036] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] Example 1

[0038] This embodiment prepares N-cyanoethyl-( S The crystalline piezoelectric material of 2-methylpiperazine hydrochloride is prepared by the following steps:

[0039] (1) 157.5 mmol ( S 2-Methylpiperazine, 81.15 mmol of bromoacetonitrile, and 82.5 mmol of potassium carbonate (acid-binding agent) were placed in a 2500 mL beaker, and 870 mL of acetonitrile was added to dissolve and dilute the solution. The mixture was first stirred in an ice-water bath (0 °C) for 30 min, and then reacted at room temperature for 24 h. After the reaction was completed, N-cyanoethyl-( S The crude product of 2-methylpiperazine was purified by column chromatography to obtain pure N-cyanoethyl-( S )-2-methylpiperazine. The eluent for column chromatography was a combination of dichloromethane and methanol in a volume ratio of 15:1. The column chromatography process removed (…). S )-2-methylpiperazine and bilateral N-cyanoethyl-( S )-2-methylpiperazine.

[0040] Potassium carbonate acts as an acid-binding agent, primarily used to neutralize the byproduct HBr, thus promoting the reaction to proceed to the right. The acid-binding agent is a weakly basic inorganic or organic base; besides potassium carbonate, it can also be sodium carbonate, sodium bicarbonate, triethylamine, or diisopropylethylamine.

[0041] (2) Take 20g of the N-cyanoethyl-( S 2-Methylpiperazine solid was placed in a 500 mL beaker, and 350 mL of methanol was added. The mixture was magnetically stirred until the solid was completely dissolved, forming a clear solution. Then, 12 mL of 36% concentrated hydrochloric acid was slowly added dropwise in an ice-water bath (0 °C) at a rate of 1 drop / second to avoid vigorous exothermic reactions that could lead to uneven concentrations. After the addition was complete, stirring was continued for 1 hour to ensure the N-cyanoethyl-( S )-2-methylpiperazine is fully protonated. Among them, N-cyanoethyl-( S The molar ratio of 2-methylpiperazine to concentrated hydrochloric acid (HCl) is 1.02:1.

[0042] Methanol is used as the solvent, and this solvent can dissolve N-cyanoethyl-(S )-2-methylpiperazine until clear, ensuring uniform contact of reactants, compatibility with concentrated hydrochloric acid (no side reactions, no layering) and without affecting N-cyanoethyl-( S The protonation process of 2-methylpiperazine. In addition to methanol, ethanol or isopropanol can also be selected.

[0043] (3) Filter the solution into another clean beaker and slowly evaporate the solvent in a constant temperature room at 25°C.

[0044] After one week, transparent, colorless, centimeter-sized blocky single crystals were observed to precipitate at the bottom of the beaker, which is the N-cyanoethyl-( S 2-methylpiperazine hydrochloride crystalline piezoelectric material.

[0045] Example 2

[0046] This embodiment is based on Example 1, except that potassium carbonate in step (1) is replaced with an equimolar amount of sodium carbonate, and methanol in step (2) is replaced with an equal volume of ethanol. The mass concentration of concentrated hydrochloric acid is 33%, and the total volume added is 13.1 ml. The temperature of the constant temperature chamber in step (3) is adjusted to 26°C. After one week of evaporation, transparent and colorless centimeter-sized blocky single crystals can be collected at the bottom of the beaker.

[0047] Material property characterization:

[0048] like Figure 1 As shown, the N-cyanoethyl-( S Centimeter-scale crystal photographs of 2-methylpiperazine hydrochloride, revealing a transparent, thin-film-like material.

[0049] like Figure 2 As shown, it is N-cyanoethyl-( S A schematic diagram of the smallest asymmetric unit of 2-methylpiperazine hydrochloride. Figure 3 It is N-cyanoethyl-( S Packing morphology of 2-methylpiperazine hydrochloride along the b-axis. Figure 2 It can be seen that N-cyanoethyl-( S The smallest asymmetric unit structure of 2-methylpiperazine hydrochloride consists of a protonated N-cyanoethyl-( S It consists of a 2-methylpiperazine cation and a chloride ion. The chloride ion interacts with the hydrogen atom of the protonated nitrogen atom on the piperazine ring through an NH…Cl hydrogen bond. Figure 3 It can be seen that N-cyanoethyl-( S The 2-methylpiperazine cation forms one-dimensional hydrogen bonds with chloride ions and is arranged in an orderly manner along the a-axis and forms an orderly stack in the b-axis, thereby generating spontaneous polarization in the b-axis direction.

[0050] like Figure 4 As shown, the N-cyanoethyl-( S The piezoelectric properties of crystalline piezoelectric materials containing 2-methylpiperazine hydrochloride were tested, and the test results represent the piezoelectric coefficient of the material. d 33 The value is ±80 pC / N.

[0051] like Figure 5 The image shows the N-cyanoethyl-( S A comparison of room-temperature powder diffraction data and simulated data for 2-methylpiperazine hydrochloride is shown in the figure. As can be observed, the diffraction data of the sample and the simulated data are completely consistent, indicating that the sample has extremely high purity. Using an X-ray single-crystal diffractometer (X-ray source, molybdenum target (Mo Kα, λ=0.71073 Å)), the organic crystalline piezoelectric material was found to crystallize in space group P21 at room temperature, with cell parameters of [missing information]. a =7.9245(18) Å、 b =7.985(2)Å、 c =8.565(2) Å, α= 90°、 β =112.46(3)°、 γ =90°, cell volume V=500.9(3)Å 3 .

[0052] like Figure 6 As shown, it is N-cyanoethyl-( S The thermogravimetric analysis of the 2-methylpiperazine hydrochloride sample shows that the sample only begins to lose thermal weight at 467 K (approximately 194 °C), indicating its good thermal stability.

[0053] like Figure 7 As shown, it is N-cyanoethyl-( S The electromechanical coupling coefficient of the organic heterocyclic crystalline piezoelectric material 2-methylpiperazine hydrochloride was determined by the dynamic resonance method at 293 K. The electromechanical coupling coefficient was then calculated. k 33 It reached 0.35, far exceeding the value of the classic molecular piezoelectric triglycine sulfate (TGS). k 33 Approximately 0.11) and commercially available piezoelectric polymer polyvinylidene fluoride (PVDF). k 33 (Approximately 0.2). This excellent electromechanical coupling performance indicates that the organic piezoelectric material has high sensitivity and is very suitable for electromechanical devices with high requirements for image resolution and penetration depth, such as medical imaging ultrasound probes.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features. These modifications or substitutions, or combinations of technical features in the above embodiments that do not conflict with each other, can be made in accordance with the manner described in the embodiments. These modifications, substitutions or combinations do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A chiral nitrogen heterocyclic organic crystalline piezoelectric material, characterized in that, This material is based on chloride ions (Cl). - As an anion, with protonated N-cyanoethyl-( S N-cyanoethyl-( )-2-methylpiperazine is composed of cations. S 2-Methylpiperazine hydrochloride, in which the molar ratio of anion to cation is 1:1, has the following structural formula: ； The piezoelectric coefficient of the organic crystalline piezoelectric material d 33 The electromechanical coupling coefficient is ±80 pC / N. k 33 It is 0.

35.

2. The chiral nitrogen heterocyclic organic crystalline piezoelectric material according to claim 1, characterized in that: The organic crystalline piezoelectric material crystallizes at room temperature in space group P21, with cell parameters of [missing information]. a =7.9245(18) Å、 b =7.985(2) Å、 c =8.565(2) Å, α= 90°、 β =112.46(3)°、 γ =90°, cell volume V=500.9(3)Å 3 .

3. A method for preparing a chiral nitrogen heterocyclic organic crystalline piezoelectric material, characterized in that, Its preparation process is as follows: S1. Weigh out according to a molar ratio of 2~2.1:1 ( S 2-methylpiperazine and bromoacetonitrile were placed in a reaction vessel, and an acid-binding agent and acetonitrile were added to dissolve and dilute the mixture. The mixture was stirred in an ice-water bath for 20-40 minutes, and then allowed to react at room temperature for 20-28 hours. After the reaction was completed, N-cyanoethyl-( S The crude product of 2-methylpiperazine was separated by column chromatography to obtain purified N-cyanoethyl-( S )-2-methylpiperazine; S2, the N-cyanoethyl-( S )-2-methylpiperazine was dissolved in methanol, ethanol, or isopropanol until clear, and N-cyanoethyl-( S A solution of N-2-methylpiperazine was placed in an ice-water bath, and concentrated hydrochloric acid was added dropwise to it to make N-cyanoethyl-( S The molar ratio of 2-methylpiperazine to HCl in concentrated hydrochloric acid is 1~1.05:1; S3. After the addition is complete, stir the reaction to complete the N-cyanoethyl-( S The reaction system was protonated, and then filtered. The filtrate was allowed to evaporate the solvent slowly at a constant temperature of 24-28°C until transparent, colorless, centimeter-sized bulk single crystals were obtained, which is the organic crystalline piezoelectric material, and its structural formula is as follows: 。 4. The preparation method according to claim 3, characterized in that: In S1, ( S The molar ratio of 2-methylpiperazine to bromoacetonitrile is 2.1:

1.

5. The preparation method according to claim 3, characterized in that: In S1, the acid-binding agent is potassium carbonate, sodium carbonate, sodium bicarbonate, triethylamine, or diisopropylethylamine.

6. The preparation method according to claim 3, characterized in that: In S1, the column eluent is a combination of dichloromethane and methanol in a volume ratio of 15:

1. Column chromatography is used to remove methylpiperazine and bilateral N-cyanoethyl-( S )-2-methylpiperazine was used to obtain purified N-cyanoethyl-( S )-2-methylpiperazine.

7. The preparation method according to claim 3, characterized in that: In S1, the reaction was stirred in an ice-water bath for 30 minutes, and then the reaction was carried out at room temperature for 24 hours.

8. The preparation method according to claim 3, characterized in that: The concentration of concentrated hydrochloric acid in S2 is 33-36 wt%, and the dropping rate is 1 drop / second.

9. The preparation method according to claim 3, characterized in that: In step S3, the filtrate is slowly evaporated at a constant temperature of 25°C for one week to obtain the organic crystalline piezoelectric material.

10. The preparation method according to claim 3, characterized in that: In S1 and S2, the temperature of the ice water bath is 273K.

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