Organic crystal with both thermal phase transition induced mechanical behavior and fluorescence enhancement and preparation method and application thereof

Abstract

This invention discloses an organic crystal exhibiting both thermal phase transition-induced mechanical behavior and fluorescence enhancement, its preparation method, and its applications. The molecular formula of the organic crystal is C0. 18 H 15 N3 belongs to the monoclinic crystal system, space group P21 / c, with cell parameters of α = 90°, β = 105.357–105.957°, γ = 90°, and Z = 8. The crystal material of this invention exhibits significant thermally induced phase transition-induced mechanical behavior and thermo-fluorescence enhancement. This crystal exhibits mechanical behavior similar to circular motion, rotating 20–25° within 25–30 minutes at an angular velocity of 0.01–0.015° / s. The organic crystal emits at a wavelength of 720–740 nm, exhibiting fluorescence thermal quenching at 300–370 K and thermo-fluorescence enhancement at 370–440 K. The thermally phase transition-induced mechanical behavior of this crystal material can be used as an actuator, crystal robot material, etc.; its fluorescence enhancement during the high-temperature phase transition can be used as a high-temperature fluorescent probe, thermo-fluorescently enhanced light-emitting diode material, etc.

Description

Technical Field

[0001] This invention belongs to the field of functional organic fluorescent materials technology, specifically relating to an organic crystal that combines thermal phase transition-induced mechanical behavior and fluorescence enhancement, its preparation method, and its application. Background Technology

[0002] Materials capable of responding to external stimuli such as light, heat, electricity, humidity, pH, and concentration gradients have attracted considerable attention in the fields of chemistry, materials science, and engineering. Many polymers and gels exhibit mechanical motion in response to external stimuli, displaying characteristics of movement. However, the movement of materials is limited. It has been reported that molecular crystals, due to repeated crystallization and melting under light irradiation, exhibit slow mechanical behaviors such as crawling. Although this mechanical behavior currently has limitations, molecular crystals still hold promise as materials for mechanical motion, particularly in the field of robotics.

[0003] Crystals exhibit mechanical behaviors such as bending, twisting, rolling, crawling, and jumping during heating. However, due to the unpredictable and erratic molecular motion within the crystal after heating, the movement direction is largely difficult to control, thus limiting crystal motion. But under heating / cooling conditions, crystal phase transitions involve continuous stretching and bending. Crystals with different width gradients can have their trajectory controlled, providing a new approach to directional crystal motion. Simultaneously, the mechanical motion generated by crystal phase transitions is accompanied by fluorescence enhancement, and most semiconductors and fluorescent molecular materials exhibit varying degrees of thermal fluorescence quenching (TQ), meaning that the photoluminescence intensity (PL) in solids decreases with increasing temperature. This is because, with increasing temperature, the nonradiative relaxation of excited electrons to the ground state increases rapidly, resulting in significant energy loss and reduced emission intensity. This TQ effect severely impacts the efficiency of light-emitting diodes (LEDs) and degrades their performance.

[0004] In some semiconductor nanostructures, the intensity of photoluminescence (PL) increases with increasing temperature; this is known as thermoluminescence enhancement of PL, and this anomaly typically occurs at very low temperatures in conventional semiconductors. Publication number CN 115246848 A discloses a zero / negative thermal quenching near-infrared photoluminescent material, its preparation method, and applications of this material (λ). ex =400nm) exhibits a fluorescent thermal quenching effect at 295K-385K and a fluorescent negative thermal quenching effect at 385K-475K. The fluorescence intensity is very stable in the high-temperature region, and it can be used as a photoluminescent material for OLEDs. However, it cannot be used as a mechanically responsive crystal, which limits its application range.

[0005] Therefore, the challenge in achieving thermoluminescence enhancement in molecular materials lies in the necessary rearrangement of the molecular or electronic structure within the crystal matrix under external thermal stimulation, so as to effectively transform thermoluminescence quenching into thermoluminescence enhancement. Summary of the Invention

[0006] To address the above problems, this invention provides an organic crystal that exhibits both thermally induced mechanical behavior and fluorescence enhancement, along with its preparation method and applications. This organic crystal demonstrates significant thermally induced phase transition behavior and readily apparent fluorescence changes, providing not only a new material for mechanically responsive organic crystals but also a new option for the application of thermo-fluorescently enhanced light-emitting diodes.

[0007] This invention is achieved through the following technical solution:

[0008] An organic crystal exhibiting both thermal phase transition-induced mechanical behavior and fluorescence enhancement, wherein the molecular formula of the organic crystal is C0. 18 H 15 N3 belongs to the monoclinic crystal system, space group P21 / c, and its unit cell parameters are as follows at 298–400 K: α=90°, β=105.357~105.957°, γ=90°, Z = 8.

[0009] Furthermore, the organic crystal exhibits mechanical behavior similar to circular motion, rotating 20-25° within 25-30 minutes at an angular velocity of 0.01-0.015° / s; the organic crystal emits light at a wavelength of 720-740 nm, exhibits a fluorescence thermal quenching effect at 300-370 K, and a thermo-fluorescence enhancement effect at 370-440 K.

[0010] A method for preparing an organic crystal exhibiting both thermal phase transition-induced mechanical behavior and fluorescence enhancement as described above includes the following steps:

[0011] (1) 6-bromo-2-naphthol, dimethylamine, sodium metabisulfite and water were mixed and subjected to hydrothermal reaction. After the reaction was completed, the mixture was cooled, the solid material was removed, and then extracted, dried, concentrated under reduced pressure and purified to obtain 6-bromo-N,N-dimethylnaphth-2-amine.

[0012] (2) Dissolve 6-bromo-N,N-dimethylnaphthyl-2-amine in N,N-dimethylformamide solution, then add acrolein diethyl acetal, tetrabutylammonium acetate, potassium carbonate, potassium chloride and tetra(triphenylphosphine)palladium and mix. Stir the resulting mixture and cool it. Add hydrochloric acid to the mixture and continue stirring. Add water and extract, dry, concentrate under reduced pressure and purify to obtain (E)-3-(6-(dimethylamino)naphthyl-2-yl)propenal.

[0013] (3) Dissolve (E)-3-(6-(dimethylamino)naphth-2-yl)propenal in methanol solution, add potassium carbonate in methanol solution, and then add malononitrile for mixing. Stir the resulting mixture, filter, wash and recrystallize to obtain (E)-2-(3-(6-(dimethylamino)naphth-2-yl)allyl)malononitrile, which is an organic crystal with both thermal phase transition induced mechanical behavior and fluorescence enhancement.

[0014] Further, in step (1), the mass ratio of 6-bromo-2-naphthol, dimethylamine and sodium metabisulfite is 1:1 to 1.2:1.5 to 2.

[0015] Further, in step (1), the hydrothermal reaction is carried out at a temperature of 130-150°C for 40-50 hours.

[0016] Further, in step (2), the mass ratio of 6-bromo-N,N-dimethylnaphthalene-2-amine to acrolein diethyl acetal, tetrabutylammonium acetate, potassium carbonate, potassium chloride, and tetra(triphenylphosphine)palladium is 2:2~3:3.5~5:0.8~1.2:0.5~1:0.05~0.08; the ratio of 6-bromo-N,N-dimethylnaphthalene-2-amine to N,N-dimethylformamide solution and hydrochloric acid is 2g:20~25mL:45~60mL.

[0017] Further, in step (2), the stirring is carried out at a temperature of 110-130°C for 45-50 hours; the stirring time is 5-15 minutes.

[0018] Further, in step (3), the mass-to-volume ratio of (E)-3-(6-(dimethylamino)naphth-2-yl)propenal to methanol solution is 1g:20-40mL; the ratio of (E)-3-(6-(dimethylamino)naphth-2-yl)propenal, methanol solution of potassium carbonate, and malononitrile is 1g:0.1-0.5mL:0.3-0.5g.

[0019] Further, in step (3), the stirring is carried out at a temperature of 60-70°C for 0.4-0.5 hours.

[0020] An application of an organic crystal that combines thermal phase transition-induced mechanical behavior and fluorescence enhancement as described above, wherein the organic crystal is used as an actuator material, a crystal robot material, a high-temperature fluorescent probe material, and a thermo-fluorescent enhanced light-emitting diode material.

[0021] The preparation principle of the organic crystal with both thermal phase transition-induced mechanical behavior and fluorescence enhancement of the present invention:

[0022] This invention involves a high-temperature hydrothermal reaction of 6-bromo-2-naphthol, dimethylamine, sodium metabisulfite, and water to generate 6-bromo-N,N-dimethylnaphthyl-2-amine. Then, 6-bromo-N,N-dimethylnaphthyl-2-amine undergoes a Heck reaction with acrolein diethyl acetal to generate (E)-3-(6-(dimethylamino)naphthyl-2-yl)propenal. Finally, (E)-3-(6-(dimethylamino)naphthyl-2-yl)propenal reacts with malononitrile via a Knoevenagel condensation reaction to generate the product of this invention, (E)-2-(3-(6-(dimethylamino)naphthyl-2-yl)allyl)malononitrile. This invention successfully constructs an organic molecular crystal with a D-π-A type donor (dimethylamino)-π-acceptor (malononitrile) structure. The electron-donating-π-electron-withdrawing structure significantly improves electron conjugation and enhances luminescence efficiency.

[0023] In this invention, (E)-2-(3-(6-(dimethylamino)naphth-2-yl)allyl)malononitrile was grown into single crystals using a solvent method of dichloromethane and methanol. The crystals were subjected to DSC, temperature-dependent fluorescence and other related tests. The crystals exhibited bending behavior at thermal phase transition temperature, which led to mechanical movement accompanied by fluorescence enhancement.

[0024] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0025] 1. The organic crystal material prepared by this invention exhibits both thermally induced phase transition-induced mechanical behavior and thermo-fluorescence enhancement. It not only demonstrates significant thermally induced phase transition-induced mechanical behavior but also exhibits thermo-fluorescence enhancement. The thermally induced phase transition-induced mechanical behavior of this crystal material during its phase transition can be used as an actuator, crystal robot material, etc.; its fluorescence enhancement during the high-temperature phase transition solves the problem of fluorescence quenching with increasing temperature in existing organic fluorescent probes of temperature sensors, and can be used as a high-temperature fluorescent probe, a thermo-fluorescently enhanced light-emitting diode material, etc.

[0026] 2. The organic crystal of this invention exhibits mechanical behavior similar to caterpillar walking and circular rotation during thermal phase transition. Repeated heating and cooling near the phase transition temperature causes the crystal to repeatedly bend and straighten. Specifically, a long, plate-shaped crystal with a width gradient in the lateral direction rotates 22° within 28 minutes at an angular velocity of 0.013° / s, resembling circular motion. This motion characteristic allows for the calculation of the crystal's approximate position over a certain period, enabling positioning. When two crystals are bonded together to form a triangular bridge, under heating conditions, the crystal moves horizontally through repeated bending and straightening, exhibiting caterpillar-like walking behavior. This intelligent material, which exhibits controllable behavior through shape change, plays a crucial role in sensors, actuators, and robotics.

[0027] 3. The organic crystal of the present invention exhibits thermo-induced fluorescence enhancement, in (λ)ex =620nm (excitation wavelength for testing) Excited at 300–370K, it exhibits a fluorescent thermal quenching effect, and at 370–440K, it exhibits a thermo-fluorescent enhancement effect. The fluorescence intensity is very stable in the high-temperature region. Its emission center is at 730nm, and it is an organic crystal capable of thermo-fluorescent enhancement in the near-infrared region. Compared with visible and ultraviolet light, near-infrared light has the advantages of being invisible, having strong penetrability, less background interference, and no side effects from short-term irradiation, making it valuable for applications in light-emitting diodes, communications, and information storage.

[0028] 4. The thermoluminescence-enhancing compound in this invention comprises a conjugated molecule with a D-π-A structure consisting of an electron-donating dimethylamino group and an electron-withdrawing malononitrile. The charge-transfer properties of this molecule significantly enhance linear optical properties. Temperature-dependent single-crystal X-ray diffraction, XRD, and fluorescence spectroscopy revealed alterations in crystal structure packing caused by thermally driven changes in the overlapping of crystal molecules. This alteration can be manipulated to modulate the temperature dependence of photoluminescence intensity, providing new clues for understanding thermoluminescence enhancement phenomena related to molecular packing in molecular materials. Attached Figure Description

[0029] Figure 1 The organic crystal in Example 1 1 H NMR spectrum.

[0030] Figure 2 The image shows the XRD pattern of the organic crystal phase transition in Example 1.

[0031] Figure 3 The image shows the DSC spectrum of the organic crystal phase transition in Example 1.

[0032] Figure 4 The images show crystallographic analysis of the organic crystal in Example 1 at different temperatures.

[0033] Figure 5 This is a conformational diagram of the relative molecular positions of the organic crystal in Example 1 at 298K and 400K.

[0034] Figure 6 The graph shows the changes in intermolecular interaction forces of the organic crystal in Example 1 at 298K and 400K.

[0035] Figure 7 A schematic diagram showing the changes in molecular arrangement of the organic crystal in Example 1 at 298K without heating and at 400K with heating.

[0036] Figure 8 This is an exploded view of the mechanical motion of the organic crystals in Example 1 during the heating process.

[0037] Figure 9This is a diagram showing the mechanical motion behavior of the organic crystal during the heating process after processing in Example 1.

[0038] Figure 10 This is a fluorescence change diagram of the organic crystal in Example 1 during the heating process.

[0039] Figure 11 This is a fluorescence change diagram of the organic crystal in Example 1 during the heating process under ultraviolet light.

[0040] Figure 12 This is a linear correlation graph between the fluorescence intensity of the organic crystal in Example 1 and temperature.

[0041] Figure 13 This is a diagram showing the degree of molecular stacking in the organic crystal of Example 1 at different temperatures.

[0042] Figure 14 The image shows the fluorescence changes of the organic crystals in Example 1 in DMF / H2O mixed solvents with different water contents.

[0043] Figure 15 The fluorescence spectra of the organic crystal in Example 1 were obtained by exciting DMF / H2O mixed solvents with different water contents at 500 nm.

[0044] Figure 16 The graph shows the maximum fluorescence emission of the organic crystal in Example 1 when excited by a DMF / H2O mixed solvent with different water contents at 500 nm. Detailed Implementation

[0045] The present invention will be further described in detail below through embodiments. These embodiments are only used to illustrate the present invention and do not limit the scope of protection of the present invention.

[0046] Example 1

[0047] Preparation of organic crystals exhibiting both thermal phase transition-induced mechanical behavior and fluorescence enhancement:

[0048] (1) Mix 5g of 6-bromo-2-naphthol, 5.05g of dimethylamine, 8.52g of sodium metabisulfite and water, seal in a high-pressure reactor, and react at 140℃ for 50h. After the reaction is completed, cool and remove the solid material. Then extract three times with 50mL of dichloromethane, collect the organic layer, and dry it with anhydrous sodium sulfate. Concentrate the organic solution under reduced pressure. The residue is purified by chromatography (silica gel; petroleum ether) to obtain a white powder of 6-bromo-N,N-dimethylnaphthyl-2-amine.

[0049] (2) Dissolve 2.000 g of 6-bromo-N,N-dimethylnaphthyl-2-amine in 20.0 mL of N,N-dimethylformamide solution, then add 2.300 g of acrolein diethyl acetal, 4.060 g of tetrabutylammonium acetate, 0.930 g of potassium carbonate, 0.745 g of potassium chloride and 0.068 g of tetra(triphenylphosphine)palladium and mix. Stir the resulting mixture at 120 °C for 48 h. After cooling, add 50 mL of hydrochloric acid (1 mol / L) to the mixture and continue stirring for 10 min. Then add 200 mL of water and extract three times with 50 mL of dichloromethane. Collect the organic layer and dry it with anhydrous sodium sulfate. Concentrate the organic solution under reduced pressure. The residue is purified by chromatography (silica gel; 50 / 1 v / v n-hexane / ethyl acetate) to obtain a yellow powder of (E)-3-(6-(dimethylamino)naphthyl-2-yl)propenal.

[0050] (3) Dissolve 1.08 g of (E)-3-(6-(dimethylamino)naphth-2-yl)propenal in 30 mL of methanol solution, add 0.3 mL of potassium carbonate in methanol solution, and then add 0.38 g of malononitrile under stirring. Stir the resulting mixture at 60 °C for 0.5 h, then filter out the red precipitate from the solution and wash it with methanol. By recrystallization from 30 mL of methanol, (E)-2-(3-(6-(dimethylamino)naphth-2-yl)allyl)malononitrile is obtained, which is an organic crystal exhibiting both thermal phase transition-induced mechanical behavior and fluorescence enhancement. 1 H NMR spectrum as shown Figure 1 As shown.

[0051] Example 2

[0052] Preparation of organic crystals exhibiting both thermal phase transition-induced mechanical behavior and fluorescence enhancement:

[0053] (1) Mix 5g of 6-bromo-2-naphthol, 5.20g of dimethylamine, 9.11g of sodium metabisulfite and water, seal in a high-pressure reactor, and react at 130℃ for 50h. After the reaction is completed, cool and remove the solid material. Then extract three times with 50mL of dichloromethane, collect the organic layer, and dry with sodium sulfate. Concentrate the organic solution under reduced pressure. The residue is purified by chromatography (silica gel; petroleum ether) to obtain a white powder of 6-bromo-N,N-dimethylnaphthyl-2-amine.

[0054] (2) Dissolve 2.005 g of 6-bromo-N,N-dimethylnaphthyl-2-amine in 22.0 mL of N,N-dimethylformamide solution, then add 2.200 g of acrolein diethyl acetal, 4.218 g of tetrabutylammonium acetate, 0.890 g of potassium carbonate, 0.805 g of potassium chloride and 0.700 g of tetra(triphenylphosphine)palladium and mix. Stir the resulting mixture at 110 °C for 50 h. After cooling, add 45 mL of hydrochloric acid (1 mol / L) to the mixture and continue stirring for 10 min. Then add 200 mL of water and extract three times with 50 mL of dichloromethane. Collect the organic layer and dry it with sodium sulfate. Concentrate the organic solution under reduced pressure. The residue is purified by chromatography (silica gel; 50 / 1 v / v n-hexane / ethyl acetate) to obtain a yellow powder of (E)-3-(6-(dimethylamino)naphthyl-2-yl)propenal.

[0055] (3) Dissolve 1.05 g of (E)-3-(6-(dimethylamino)naphth-2-yl)propenal in 25 mL of methanol solution, add 0.4 mL of potassium carbonate methanol solution, and then add 0.40 g of malononitrile under stirring. Stir the resulting mixture at 70 °C for 0.4 h, then filter out the red precipitate from the solution and wash it with methanol. By recrystallizing from 30 mL of methanol, (E)-2-(3-(6-(dimethylamino)naphth-2-yl)allyl)malononitrile is obtained, which is an organic crystal with both thermal phase transition induced mechanical behavior and fluorescence enhancement.

[0056] Example 3

[0057] Preparation of organic crystals exhibiting both thermal phase transition-induced mechanical behavior and fluorescence enhancement:

[0058] (1) Mix 5g of 6-bromo-2-naphthol, 5.10g of dimethylamine, 9.50g of sodium metabisulfite and water, seal in a high-pressure reactor, and react at 150℃ for 40h. After the reaction is completed, cool and remove the solid material. Then extract three times with 50mL of dichloromethane, collect the organic layer, and dry with sodium sulfate. Concentrate the organic solution under reduced pressure. The residue is purified by chromatography (silica gel; petroleum ether) to obtain a white powder of 6-bromo-N,N-dimethylnaphthyl-2-amine.

[0059] (2) Dissolve 2.100 g of 6-bromo-N,N-dimethylnaphthyl-2-amine in 25.0 mL of N,N-dimethylformamide solution, then add 2.300 g of acrolein diethyl acetal, 4.500 g of tetrabutylammonium acetate, 1.000 g of potassium carbonate, 0.905 g of potassium chloride and 0.070 g of tetra(triphenylphosphine)palladium and mix. Stir the resulting mixture at 130 °C for 45 h. After cooling, add 55 mL of hydrochloric acid (1 mol / L) to the mixture and continue stirring for 10 min. Then add 200 mL of water and extract three times with 50 mL of dichloromethane. Collect the organic layer and dry it with sodium sulfate. Concentrate the organic solution under reduced pressure. The residue is purified by chromatography (silica gel; 50 / 1 v / v n-hexane / ethyl acetate) to obtain a yellow powder of (E)-3-(6-(dimethylamino)naphthyl-2-yl)propenal.

[0060] (3) Dissolve 1.10 g of (E)-3-(6-(dimethylamino)naphth-2-yl)propenal in 35 mL of methanol solution, add 0.5 mL of potassium carbonate methanol solution, and then add 0.40 g of malononitrile under stirring. Stir the resulting mixture at 70 °C for 0.4 h, then filter out the red precipitate from the solution and wash it with methanol. By recrystallizing from 30 mL of methanol, (E)-2-(3-(6-(dimethylamino)naphth-2-yl)allyl)malononitrile is obtained, which is an organic crystal with both thermal phase transition induced mechanical behavior and fluorescence enhancement.

[0061] Material characterization analysis

[0062] (I) XRD Analysis

[0063] The organic crystal in Example 1 was characterized using variable-temperature X-ray diffraction (XRD), and the characterization results are as follows: Figure 2 As shown. Figure 2 The thermal cycling in the figure shows the reversible process of crystal single crystal to single crystal (SCSC). In the figure, red represents the heating process 298K-453K and blue represents the cooling process 453K-303K. Figure 2 The varying-temperature XRD patterns during heating from 298 to 453 K and during cooling back to room temperature (RT) are shown, along with the varying-temperature XRD patterns of the crystal phase transitions between 423 K and 453 K and between 453 K and 413 K during heating / cooling, indicating that the reversible phase transition occurs through a single-crystal-to-single-crystal process. The temperature dependence of the crystal XRD patterns shows a continuous shift in peak positions with temperature: during heating, the low-angle shift of the XRD peaks indicates gradual lattice expansion due to an increase in the lattice constant, consistent with the results of single-crystal diffraction characterization of the crystal constant at different temperatures; during cooling, the high-angle shift of the XRD peaks indicates gradual lattice contraction due to a decrease in the lattice constant, with the lattice gradually recovering.

[0064] (II) DSC Analysis

[0065] The organic crystals in Example 1 were characterized using differential scanning calorimetry (DSC), and the characterization results are as follows: Figure 3 As shown. By Figure 3 It is known that when organic crystals are heated, the crystal molecules undergo vibration and torsion at a certain temperature. During DSC analysis of the crystal molecules, the crystal structure before the phase transition is called Form I, and the crystal structure after the phase transition is called Form II. When the molecules are heated, an endothermic phase transition occurs between 416 and 420 K, from Form I to Form II. Upon cooling, an exothermic phase transition occurs between 407 and 412 K, from Form II to Form I, showing a thermal hysteresis of 8 K. The enthalpy values ​​of the endothermic and exothermic peaks are relatively small, at 2.44 and -2.93 kJ / mol, respectively, indicating that this phase transition from Form I to Form II is a first-order reversible phase transition. This is consistent with the gradual structural transformation observed in variable-temperature XRD analysis.

[0066] (III) Crystallographic Data Analysis

[0067] The organic crystals in Example 1 were subjected to variable-temperature X-ray diffraction crystallography analysis at -150, 298, 343, 373, and 400 K. The results are shown in Table 1 below. Figure 4 As shown.

[0068] Table 1 Crystallographic data of organic crystals

[0069]

[0070]

[0071] As shown in Table 1 above, the organic crystal in Example 1 belongs to the monoclinic crystal system, space group P21 / c. Figure 4 In the diagram, figures a, b, c, d, and e represent the lengths of the a-axis, b-axis, and c-axis, the β angle, and the volume of the organic crystal at different temperatures (-150, 298, 343, 373, and 400 K), respectively. Figure 4 It can be seen that between -150K and 400K, the lengths of the a-axis, b-axis and c-axis increased by +2.12%, +2.55% and +1.04% respectively, the volume increased by +5.79% and β increased by 1.16%. This is consistent with the results of XRD test characterization that the peak gradually shifts to a lower angle during heating, the lattice expands continuously, and the lattice constant increases.

[0072] (iv) Crystal Structure Analysis

[0073] The molecular structures of the organic crystal in Example 1 were determined at 298 and 400 K. Their molecular structures at 298 and 400 K are as follows: Figure 5 As shown. By Figure 5 It can be seen that 298K represents a type I structure (blue), and 400K represents a type II structure (orange). At 400K, the molecular pairs exhibit unidirectional slip. For clarity, hydrogen atoms are omitted. Figure 6 It can be seen that the molecular pairs are arranged at a certain angle, and weak intermolecular CH…π interactions are formed between adjacent molecular layers. Under heating conditions, after co-directional slip, the distance between each pair of molecules and the CH…π interaction of the benzene ring to the benzene ring plane increases from... and Reduce to and The intermolecular hydrogen bond distance of butadiene is from Reduce to This indicates that after a high-temperature phase transition, intermolecular interactions increase, intermolecular distances decrease, and the molecules that are heated first contract, producing... Figure 7 The schematic bending behavior causes crystals of different shapes to produce different trajectories. Thin, elongated plate-shaped crystals with width gradients produce circular motion, while uniformly shaped crystals move horizontally along their long axis through processing.

[0074] (V) Mechanical Motion Analysis

[0075] The mechanical motion of the organic crystal in Example 1 during the phase transition process was analyzed. When the thin, plate-like crystal with a width gradient was heated and cooled within a temperature range of 418–433 K (at speeds of 10 °C / min and 6 °C / min), the entire crystal slowly rotated forward along its minor axis on a glass slide, like the movement of a clock hand, undergoing circular motion and repeated slight bending and straightening. To further investigate the mechanism of this circular motion, the crystal's motion was simultaneously observed from the top using a microscope. The analysis results are as follows: Figure 8 As shown. Figure 8 In the diagram, figure a shows the displacement of the crystal after multiple heating and cooling cycles, figure b shows the decomposition of the crystal during the heating process, and figure c is a schematic diagram of the decomposition of the crystal during the heating process.

[0076] Depend on Figure 8As shown in b, during heating, the crystal remains flat until the surface temperature of the glass plate reaches 393K, at which point it significantly elongates along its long axis, reaching its maximum length. This is due to the thermal expansion of the crystal, at which point the crystal is darker in color. Continued heating causes the crystal color to lighten until the surface temperature of the glass plate reaches 418K, reaching the phase transition point. Afterward, during heating, the crystal quickly bends, reaching its maximum temperature upon further heating. Simultaneously, because the bending reaches its maximum angle, the surface temperature in the middle is lower than the temperatures on the left and right sides.

[0077] Depend on Figure 8 As shown in c, the bending is tilted, and this tilted bending disrupts the crystal's balance, causing it to tilt to one side, displace along its short axis, and return to an almost straight shape. The bending and straightening behavior of the crystal completes a process in 30–40 ms. Multiple such bending and straightening behaviors occur during a heating and cooling process. The bending abruptly ends, restoring the crystal to its original straight shape. At this point, the crystal undergoes circular motion displacement. During subsequent heating, each bending causes a rapid decrease in the surface temperature of the bent crystal's center, and the degree of curvature gradually decreases as the surface temperature decreases, eventually rotating forward along the short axis to return to its initial straight shape. This phase transition is reversible; when cooled to the temperature range of 418–433 K, the crystal can still exhibit the same behavior and undergo a certain distance displacement in the same direction. Below or above this temperature range, the crystal will not exhibit significant elongation or behavior.

[0078] Depend on Figure 8 As shown in diagram a, after repeated heating and cooling near the phase transition temperature, the crystal moves in a circle with a small circle radius of 0.37 mm, a large circle radius of 3.31 mm, and a length of 2.94 mm. Within 28 minutes, the crystal rotates 22°. Based on the circular motion formula, the wider end of the crystal rotates by 1.27 mm, with a linear velocity of 0.00074 mm / s and an angular velocity of 0.013° / s. Using this motion characteristic, the approximate position of the crystal over a certain period can be calculated for localization.

[0079] Utilizing the property that crystals undergo mechanical motion during heating phase transitions, uniformly shaped crystals are simply processed, and two crystals are bonded together with an adhesive to form a triangular bridge. Under heating conditions, the crystals move horizontally along their long axis. The motion behavior of the crystals is analyzed, and the results are as follows: Figure 9 As shown. Figure 9 In the image, Figure 9a is a top view of the processed crystal, Figure 9b is a side view of the processed crystal, and Figure 9c is a side view of the crystal before and after bending.

[0080] Depend on Figure 9 As can be seen from c, the crystal moves horizontally through repeated bending and straightening motions. Figure 9a) Similar to the movement behavior of a caterpillar, the side heating and bending process is magnified in the diagram ( Figure 9 (b) Under repeated heating and cooling conditions near the phase transition temperature, the crystal traveled 0.025 mm horizontally in 3 minutes, with an average speed of 0.00014 mm / min. The same crystal bending interpretation was applied to the processed crystal. This organic crystal smart material, which exhibits different motion trajectories (horizontal and circular) due to thermally induced phase transition, provides a new option for actuators with different motion trajectories.

[0081] (vi) Fluorescence intensity analysis

[0082] The heating process of the crystal is accompanied by a fluorescence enhancement effect, which is an anomalous phenomenon in which the fluorescence intensity increases with increasing temperature. Temperature-dependent variable-temperature fluorescence analysis was performed on the organic crystal in Example 1, and the results are as follows: Figure 10-13 As shown. In (λ) ex =620nm) Excitation wavelength is 620nm. Fluorescence exhibits thermal quenching in the 300–370K range and thermo-enhanced fluorescence in the 370–440K range. Fluorescence intensity is very stable in the high-temperature region. The emission center is at 730nm. Figure 10 The emission center is at 730nm, and it is an organic crystal that can achieve thermo-fluorescence enhancement in the near-infrared region. Figure 11 In the case of a single crystal, under a UV lamp, the light emitted by conjugated molecules transitions from one crystal to another, accompanied by a change in the color of the emitted light from dark red to bright red upon heating. Figure 12 The temperature dependence of fluorescence intensity was demonstrated: during crystal heating, fluorescence intensity decreased in the range of 300–370 K and increased in the range of 370–440 K, and a linear correlation (λ) was observed between the crystal fluorescence intensity and temperature within the temperature range of 370–440 K. max / nm=2801.24x-871452.02,R 2 =0.9642). It is well known that stronger π…π stacking interactions lead to greater molecular fluorescence quenching. Figure 13 It is known that the weakening of intermolecular π…π stacking interactions after the high-temperature phase transition triggers molecular fluorescence, and the degree of intermolecular stacking decreases to three-quarters upon increasing the temperature to 400K. This linearity and temperature response of the material's fluorescence to temperature is advantageous for its use as a high-temperature sensing medium. This effectively solves the problem of fluorescence quenching of organic fluorescent probes in existing temperature sensors with increasing temperature, providing new insights for developing advanced molecular-based thermoluminescent emitters that can operate at high temperatures in the field of organic light-emitting diodes. This phenomenon is attributed to the mechanical behavior and fluorescence enhancement resulting from a thermally induced phase transition in the molecules.

[0083] By adjusting the relative water content in different N,N-dimethylformamide (DMF) / H₂O mixed solvents, the analysis demonstrated that the accumulation of this substance itself is aggregation-induced quenching, and the enhanced thermoluminescence at high temperatures is an anomaly generated during the phase transition process. The analytical results are as follows: Figure 14-16 As shown. By Figure 14 It can be seen that in the DMF / H2O two-phase solvent, as the relative proportion of water gradually increases, the crystal molecular packing gradually strengthens. This stronger packing manifests as a gradual quenching of fluorescence, which is consistent with... Figure 15 The fluorescence spectra obtained by exciting different water contents at 500 nm showed that the fluorescence results were consistent with the observed results, that is, as the water content increased, the crystal stacking was enhanced and the fluorescence intensity decreased. Figure 16 In the diagram, the maximum fluorescence emission under 500nm excitation is plotted as a line graph, which more clearly shows that as the proportion of water in the two-phase solvent increases, the crystal molecules are more packed and the fluorescence gradually decreases.

[0084] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An application of an organic crystal, characterized in that, The organic crystal is used as an actuator material, a crystal robot material, a high-temperature fluorescent probe material, and a thermoluminescent light-emitting diode material. The structural formula of the organic crystal is: The molecular formula of the organic crystal is C0. 18 H 15 N3 belongs to the monoclinic crystal system and has the space group P21 / c. The organic crystal has the following unit cell parameters at 298 K: a = 16.0745 Å, b = 7.53573 Å, c = 25.6902 Å, α = 90°, β = 105.357°, γ = 90°, V = 3000.81 Å. 3 Z=8; The organic crystal has the following unit cell parameters at 400 K: a = 16.228 Å, b = 7.6192 Å, c = 25.840 Å, α = 90°, β = 105.957°, γ = 90°, V = 3071.7 Å. 3 Z=8; During the thermal phase transition, the organic crystal exhibits mechanical behavior similar to circular motion, rotating 20-25° within 25-30 minutes at an angular velocity of 0.01-0.015° / s. The organic crystal emits light at a wavelength of 720-740 nm, exhibits a fluorescence thermal quenching effect at 300-370 K, and a thermo-fluorescence enhancement effect at 370-440 K.

Images