Organic nonlinear crystal material for thermally enhancing frequency doubling signal as well as preparation method and application of organic nonlinear crystal material

Abstract

The invention relates to an organic nonlinear crystal material of a thermally enhanced frequency multiplication signal, a preparation method and application thereof, when the temperature of the organic nonlinear crystal material of the thermally enhanced frequency multiplication signal rises to 373K, the organic nonlinear crystal material of the thermally enhanced frequency multiplication signal is a polar monoclinic system P21 space group, the cell parameters are # imgabs0 # # imgabs1 # beta = 92.651 + / -0.006 DEG C, Z = 2, and Z = 1. The organic nonlinear crystal material disclosed by the invention can enhance a nonlinear signal by heating, is simple in synthesis method, low in cost, mild in reaction condition and relatively high in stability, and is a thermally induced nonlinear signal enhanced organic molecular compound with relatively high nonlinear optical strength. The material has good application prospects in the fields of second-order nonlinear frequency doubling switches, THz radiation source devices, birefringent crystal devices and scintillation imaging devices.

Description

Technical Field

[0001] The invention belongs to the field of functional materials, and in particular relates to an organic nonlinear crystal material of a thermally enhanced frequency-doubled signal, a preparation method and an application thereof. Background Art

[0002] Second harmonic generation (SHG) is a nonlinear optical (NLO) process. When a strong laser beam is irradiated into a nonlinear optical medium, a new light wave with a frequency twice that of the original laser frequency is generated, that is, a laser with a higher frequency (i.e., a shorter wavelength). Therefore, it has important applications in optoelectronic switches, laser technology, information processing, and communications. In recent years, NLO switch materials have attracted more and more attention. Their inherent SHG signals can be switched under the action of external stimuli (such as heat, pressure, electric field, and magnetic field). Among them, the most effective strategy is to adjust the conformation or orientation of NLO chromophore molecules in the crystal structure through thermal stimulation. Its mechanism is related to structural phase transition. By rearranging the NLO active groups, the SHG signal is changed, especially between the centrosymmetric structure (SHG-OFF) and the non-centrosymmetric structure (SHG-ON) to achieve a significant switching response. At present, molecular compounds are considered as potential candidates for constructing NLO switch materials due to their inherent structural adjustability and designability. The displacement or orientation movement of the molecules locally or as a whole may lead to the appearance or disappearance of the symmetry center. For example, hydrogen-bonded ionic crystals (DABCO)ClO4 (DABCO = 1,4-diazabicyclo[2.2.2]octane) exhibit switchable NLO activity. + The strong hydrogen bonding interaction between cations makes the molecules crystallize in a relatively ordered polar space group with low symmetry. When the temperature rises above the phase transition point, the organic DABCO + Cations and Inorganic ClO4 - The anions become relatively disordered, corresponding to a centrosymmetric crystal structure. However, most molecular SHG switch materials only show conventional single-step "ON-OFF" switching behavior, which usually increases with increasing temperature due to their structural symmetry. Therefore, it remains challenging to design new molecular NLO materials with thermally induced SHG signal enhancement and expand their practical applications. Summary of the invention

[0003] The present invention provides an organic nonlinear crystal material for thermally enhancing a frequency doubling signal, a preparation method and an application thereof. The organic nonlinear crystal material of the present invention can enhance the nonlinear signal by heating, and the synthesis method is simple, the cost is low, the reaction conditions are mild, and the stability is high. The organic molecular compound for thermally enhancing a nonlinear signal has a large nonlinear optical intensity. The organic nonlinear crystal material has good application prospects in the fields of second-order nonlinear frequency doubling switches, THz radiation source devices, birefringent crystal devices and scintillation imaging devices.

[0004] The present invention is achieved through the following technical solutions:

[0005] Solution 1)

[0006] An organic nonlinear crystal material for thermally enhanced frequency doubling signals, wherein the chemical formula of the organic nonlinear crystal material for thermally enhanced frequency doubling signals is C 23 H 25 N3, molecular structure diagram is:

[0007]

[0008] At room temperature 298K, the organic nonlinear crystal material of the thermally enhanced frequency-doubled signal is a polar monoclinic P21 space group, and the unit cell parameters are β=97.223±0.005°, Z=2,

[0009] It is characterized in that: when the temperature rises to 373K, the organic nonlinear crystal material of the thermally enhanced frequency-doubled signal is a polar monoclinic P21 space group, and the unit cell parameter is β=92.651±0.006°, Z=2,

[0010] Option 2)

[0011] A method for preparing an organic nonlinear crystal material for thermally enhancing a frequency-doubled signal comprises the following steps:

[0012] (1) at room temperature, dissolving malononitrile and isophorone in a molar ratio of 1-1.5:1 in anhydrous ethanol, then heating to 60-80° C., then adding piperidine for reflux reaction, adding 18-25 g of piperidine per 1 mol of isophorone, reflux reaction for 24-48 hours, until the color of the solution gradually changes from light yellow to dark yellow, then cooling for crystallization, filtering, and drying to obtain yellow 3,5,5-trimethyl(cyclohexyl-2-vinyl) malononitrile;

[0013] (2) Then, 4-(1-pyrrolidinyl)benzaldehyde and 3,5,5-trimethyl(cyclohexyl-2-vinyl)malononitrile obtained in step (1) are dissolved in anhydrous methanol at a molar ratio of 1-1.5:1, and then reacted at 80-85°C for 24-48h, followed by cooling, crystallization, filtering, and drying to obtain the organic nonlinear crystal material with thermally enhanced frequency-doubled signal.

[0014] Option 3)

[0015] The invention discloses an application of an organic nonlinear crystal material for thermally enhancing a frequency-doubled signal in a second-order nonlinear frequency-doubled switch. The second-order nonlinear frequency-doubled switch comprises the organic nonlinear crystal material for thermally enhancing a frequency-doubled signal.

[0016] Option 4)

[0017] The invention discloses an application of an organic nonlinear crystal material for thermally enhancing a frequency-doubled signal in a THz radiation source device. The THz radiation source device comprises the organic nonlinear crystal material for thermally enhancing a frequency-doubled signal.

[0018] Option 5)

[0019] The invention discloses an application of an organic nonlinear crystal material for thermally enhancing a frequency-doubled signal in a birefringent crystal device. The birefringent crystal device comprises the organic nonlinear crystal material for thermally enhancing a frequency-doubled signal.

[0020] Option 6)

[0021] The invention discloses an application of an organic nonlinear crystal material for thermally enhancing a frequency-doubled signal in a scintillation imaging device. The scintillation imaging device comprises the organic nonlinear crystal material for thermally enhancing a frequency-doubled signal.

[0022] Compared with the prior art, the present invention has the following beneficial effects: an organic nonlinear crystal material with thermally enhanced frequency doubling signal is creatively proposed. The synthesis method of the organic nonlinear crystal material with thermally enhanced frequency doubling signal is simple, low in cost, mild in reaction conditions, and high in stability. The organic molecular compound with thermally enhanced frequency doubling signal has good application prospects in the fields of second-order nonlinear frequency doubling switch, THz radiation source device, birefringent crystal device and scintillation imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a crystal photograph of the organic nonlinear crystal material of the thermally enhanced frequency-doubled signal of Example 1.

[0024] Figure 2 It is a molecular schematic diagram of the organic nonlinear crystal material of the thermally enhanced frequency-doubled signal of the present invention.

[0025] Figure 3This is a crystal structure stacking diagram of the organic nonlinear crystal material of the thermally enhanced frequency-doubled signal of Example 1.

[0026] Figure 4 This is a differential scanning calorimetry test curve of the organic nonlinear crystal material of the thermally enhanced frequency-doubled signal of Example 1.

[0027] Figure 5 This is the temperature-dependent dielectric curve of the organic nonlinear crystal material of the thermally enhanced frequency-doubled signal of Example 1.

[0028] Figure 6 This is the temperature-dependent nonlinear signal intensity curve of the organic nonlinear crystal material of the thermally enhanced frequency-doubled signal of Example 1. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0030] Example 1

[0031] The method for preparing an organic nonlinear crystal material with a thermally enhanced frequency doubling signal comprises the following steps: (1) dissolving 1 mmol of malononitrile and 1 mmol of isophorone in anhydrous ethanol at room temperature, then heating to 60°C, adding 20 mg of piperidine, and reflux reacting for 48 hours until the color of the solution gradually changes from light yellow to dark yellow, then cooling and crystallizing, filtering, and drying to obtain yellow 3,5,5-trimethyl(cyclohexyl-2-vinyl) malononitrile;

[0032] (2) Then 4-(1-pyrrolidinyl)benzaldehyde and 3,5,5-trimethyl(cyclohexyl-2-vinyl)malononitrile obtained in step (1) were dissolved in anhydrous methanol at a molar ratio of 1:1, followed by reaction at 80°C for 48 hours, followed by cooling, crystallization, filtration, and drying to obtain the organic nonlinear crystal material with thermally enhanced frequency-doubled signal, with a yield of 50%. The obtained crystal photo is shown in FIG. Figure 1 shown.

[0033] Example 2

[0034] (1) At room temperature, 1.2 mmol of malononitrile and 1 mmol of isophorone were dissolved in anhydrous ethanol, then the temperature was raised to 65° C., and then 25 mg of piperidine was added, and the reaction was refluxed for 44 hours until the color of the solution gradually changed from light yellow to dark yellow, and then cooled for crystallization, filtered, and dried to obtain yellow 3,5,5-trimethyl(cyclohexyl-2-vinyl) malononitrile;

[0035] (2) Then 4-(1-pyrrolidinyl)benzaldehyde and 3,5,5-trimethyl(cyclohexyl-2-vinyl)malononitrile obtained in step (1) were dissolved in anhydrous methanol at a molar ratio of 1.2:1, followed by reaction at 82°C for 40h, followed by cooling, crystallization, filtration, and drying to obtain the organic nonlinear crystal material with thermally enhanced frequency-doubled signals. This embodiment also obtained the following Figure 1 The same crystals as shown are not repeated here.

[0036] Example 3

[0037] (1) At room temperature, 1.5 mmol of malononitrile and 1 mmol of isophorone were dissolved in anhydrous ethanol, and then the temperature was raised to 80° C., and then 18 mg of piperidine was added, and the reaction was refluxed for 45 hours until the color of the solution gradually changed from light yellow to dark yellow, and then cooled for crystallization, filtered, and dried to obtain yellow 3,5,5-trimethyl(cyclohexyl-2-vinyl)malononitrile;

[0038] (2) Then 4-(1-pyrrolidinyl)benzaldehyde and 3,5,5-trimethyl(cyclohexyl-2-vinyl)malononitrile obtained in step (1) were dissolved in anhydrous methanol at a molar ratio of 1.5:1, followed by reaction at 85°C for 48h, followed by cooling, crystallization, filtration, and drying to obtain the organic nonlinear crystal material with thermally enhanced frequency-doubled signals. This embodiment also obtained the following Figure 1 The same crystals as shown are not repeated here.

[0039] The structure of the organic nonlinear crystal material with thermally enhanced frequency doubling signal obtained in the above examples is characterized, and the results are as follows Figure 2 and 3 As shown, at 298K, it is a polar monoclinic system P21 space group, and the unit cell parameters are β=97.223(5)°,Z=2, When the temperature rises to 373K, the organic nonlinear crystal material of the thermally enhanced SHG signal is a polar monoclinic P21 space group with a unit cell parameter of β=92.651(6)°,Z=2, Single crystal structural analysis shows that the organic nonlinear crystal material with thermally enhanced SHG signal is mainly composed of a configuration-locked p-conjugated phenylhexatriene bridge connecting the pyrrolidine electron donor and the dicyanomethyl electron acceptor. The benzene ring group is almost in the same plane as the π-conjugated bridge, which can promote effective π-electron delocalization and thus achieve a strong SHG response. It is worth noting that there are weak intermolecular hydrogen bonding interactions between adjacent organic molecules, and the pyrrolidine group and the cyanide group are aligned along the crystallographic b-axis, inducing spontaneous polarization in this direction.

[0040] The organic nonlinear crystal material with the thermally enhanced frequency-doubled signal obtained in Example 1 was subjected to differential scanning calorimetry test. Figure 4 As shown, during the heating / cooling process, at 358.1 / 333.6K (phase transition temperature T c ) with a reversible thermal anomaly peak, a thermal hysteresis of about 24.5 K, and a phase change enthalpy (ΔH) and entropy change (ΔS) of about 0.5 kJ·mol -1 and 1.4 J mol -1 K -1 Based on the Boltzmann equation ΔS=R ln N, the molecular orientation number N is calculated to be about 0.5, which is much smaller than 2.0, indicating its secondary phase transition characteristics. The differential scanning calorimetry test results of the organic nonlinear crystal materials with thermally enhanced double frequency signals of other embodiments are consistent with those of embodiment 1.

[0041] The temperature-dependent dielectric test of the organic nonlinear crystal material with the thermally enhanced frequency-doubled signal obtained in Example 1 is performed. Figure 5 As shown, the temperature-dependent dielectric constant was measured at a frequency of 300 kHz in the temperature range of 310-390 K. c A steep dielectric abnormal "platform" appears at the position of , which is very consistent with the differential scanning calorimetry test result. The temperature-dependent dielectric test results of the organic nonlinear crystal materials with thermally enhanced frequency-doubled signals of other embodiments are consistent with those of embodiment 1.

[0042] The temperature-dependent SHG signal intensity of the organic nonlinear crystal material of the thermally enhanced double frequency signal obtained in Example 1 was tested. Figure 6 As shown in Figure 1, the SHG intensity of the organic molecular crystal material was first measured at room temperature, which was 1.2 times that of the benchmark NLO material KH2PO4 with the same particle size. As the temperature increases, the SHG signal increases at the phase transition temperature T c The results of the temperature-dependent SHG signal intensity test of the organic nonlinear crystal material with thermally enhanced frequency doubling signal in other embodiments are consistent with those in the first embodiment.

[0043] In summary, the organic nonlinear crystal material for thermally enhanced frequency doubling signals of the present invention has excellent temperature-induced nonlinear signal switching performance and has outstanding application potential in the fields of second-order nonlinear frequency doubling switches, THz radiation source devices, birefringent crystal devices, and scintillation imaging. In the organic nonlinear crystal material for thermally enhanced frequency doubling signals of the present invention, the plane where the benzene ring group and the π-conjugated bridge are located is only slightly deflected, which can promote effective π-electron delocalization, thereby generating a strong second-order nonlinear response. As the temperature rises to the phase transition temperature T cThe above structures maintain the same polar space group and highly ordered arrangement, but the lattice parameters change significantly, and the crystal symmetry is further reduced. Specifically, the twist angle between the benzene ring group and the plane where the π-conjugated bridge is located is reduced, and they are almost in the same plane, thereby achieving the enhancement of the second-order nonlinear signal. Therefore, the organic nonlinear crystal material of the thermally enhanced frequency-doubled signal of the present invention has a broad chemical space and bright prospects, and is expected to become an ideal material system for the development of high-performance second-order nonlinear frequency-doubled switching devices, and stimulate the interest of researchers, thereby having a lasting impact at the basic and application levels.

[0044] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. An organic nonlinear crystal material for thermally enhanced frequency doubling signal, wherein the chemical formula of the organic nonlinear crystal material for thermally enhanced frequency doubling signal is C 23 H 25 N3, molecular structure diagram is: At room temperature 298K, the organic nonlinear crystal material of the thermally enhanced frequency-doubled signal is a polar monoclinic P21 space group, and the unit cell parameters are β=97.223±0.005°, Z=2, Features: When the temperature rises to 373K, the organic nonlinear crystal material of the thermally enhanced SHG signal is a polar monoclinic P21 space group with a unit cell parameter of β=92.651±0.006°, Z=2, 2. The method for preparing an organic nonlinear crystal material with thermally enhanced frequency-doubled signal according to claim 1, characterized in that: The steps include: (1) at room temperature, dissolving malononitrile and isophorone in a molar ratio of 1-1.5:1 in anhydrous ethanol, then heating to 60-80° C., then adding piperidine for reflux reaction, adding 18-25 g of piperidine per 1 mol of isophorone, reflux reaction for 24-48 hours, until the color of the solution gradually changes from light yellow to dark yellow, then cooling for crystallization, filtering, and drying to obtain yellow 3,5,5-trimethyl(cyclohexyl-2-vinyl) malononitrile; (2) Then, 4-(1-pyrrolidinyl)benzaldehyde and 3,5,5-trimethyl(cyclohexyl-2-vinyl)malononitrile obtained in step (1) are dissolved in anhydrous methanol at a molar ratio of 1-1.5:1, and then reacted at 80-85°C for 24-48h, followed by cooling, crystallization, filtering, and drying to obtain the organic nonlinear crystal material with thermally enhanced frequency-doubled signal.

3. Application of an organic nonlinear crystal material for thermally enhancing a frequency-doubled signal in a second-order nonlinear frequency-doubled switch, characterized in that: The second-order nonlinear frequency doubling switch comprises the organic nonlinear crystal material for thermally enhancing the frequency doubling signal as claimed in claim 1.

4. Application of an organic nonlinear crystal material for thermally enhancing frequency-doubled signals in a THz radiation source device, characterized in that: The THz radiation source device comprises the organic nonlinear crystal material of the thermally enhanced frequency-doubled signal according to claim 1.

5. Application of an organic nonlinear crystal material for thermally enhancing frequency-doubled signals in a birefringent crystal device, characterized in that: The birefringent crystal device comprises the organic nonlinear crystal material of the thermally enhanced frequency-doubled signal according to claim 1.

6. Application of an organic nonlinear crystal material with thermally enhanced frequency-doubled signals in a scintillation imaging device, characterized in that: The scintillation imaging comprises the organic nonlinear crystal material of the thermally enhanced frequency-doubled signal according to claim 1.

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