A pyrrolopyrrole organic small molecule photothermal material with high photothermal conversion efficiency, its preparation method and application

Abstract

This invention relates to a pyrrolopyrrole organic small molecule photothermal material with high photothermal conversion efficiency, its preparation method, and its application. The invention belongs to the field of organic small molecule photothermal materials. It aims to solve the problems of poor thermal stability and low photothermal conversion efficiency in existing photothermal materials. Preparation method: BrDPPBr, R-boronate, potassium carbonate, and a high-boiling-point solvent are mixed, then heated, and a phosphine compound is added. The mixture is heated and stirred continuously. After the reaction, it is cooled to room temperature, and then pure water is added to precipitate the solid. The solid is then recrystallized and purified to obtain the pyrrolopyrrole organic small molecule photothermal material. Application: It is used for water evaporation. This invention relates to pyrrolopyrrole organic small molecule photothermal materials with high photothermal conversion efficiency, their preparation, and their applications.

Description

Technical Field

[0001] This invention belongs to the field of organic small molecule photothermal materials. Background Technology

[0002] Although Earth's water resources are relatively abundant, the amount of freshwater directly usable by humans is very limited. Moreover, with the continuous expansion of the industrial economy and the increasing population, freshwater resources are becoming increasingly scarce due to pollution and overuse, seriously threatening sustainable socio-economic development. Therefore, seawater desalination is an essential means to alleviate freshwater shortages. To address these issues, various traditional seawater desalination strategies have emerged in recent years, including multi-stage flash evaporation, vacuum distillation, reverse osmosis, and nanofiltration. However, these methods are costly, cause severe secondary pollution, and consume enormous amounts of energy, seriously hindering their large-scale commercial application. Therefore, developing efficient, low-cost, and eco-friendly freshwater production technologies remains a significant challenge. Among the many seawater desalination technologies, solar energy is the most promising renewable energy source. Solar interface evaporation technology uses clean, renewable solar energy as energy input, converting solar energy into heat energy. It has higher evaporation efficiency and heating rate, where solar heat conversion and heating are confined to the air-water interface, effectively utilizing absorbed sunlight and avoiding heat transfer to the surrounding environment, thus resulting in higher photothermal conversion efficiency. Therefore, solar interfacial evaporation technology is a promising freshwater acquisition technology due to its high conversion efficiency, great potential for industrial applications, and environmental sustainability. However, this evaporation system is a complex coupled process, influenced by many factors such as photothermal conversion materials, thermal management, and structural design.

[0003] Among these factors, photothermal conversion materials play a crucial role in the system. To date, three popular photothermal conversion mechanisms have been identified: localized plasma heating, electron-hole generation and relaxation, and molecular thermal vibration. Currently, the most reported photothermal materials mainly focus on plasma-enhanced metal nanoparticles, semiconductor materials, carbon materials, and polymer materials. However, due to their poor thermal stability, the photothermal conversion efficiency is relatively low, and there are few reports on the use of organic dye molecules for solar-interface seawater evaporation. Therefore, in order to obtain excellent photothermal conversion performance and study its working mechanism, it is necessary to develop photothermal conversion systems based on novel organic dye molecules. Summary of the Invention

[0004] This invention aims to address the problems of poor thermal stability and low photothermal conversion efficiency of existing photothermal materials, and further provides a pyrrolopyrrole organic small molecule photothermal material with high photothermal conversion efficiency, its preparation method, and its application.

[0005] A pyrrolopyrrole organic small molecule photothermal material with high photothermal conversion efficiency has the following general chemical formula:

[0006] The R mentioned is

[0007] A method for preparing a pyrrolopyrrole organic small molecule photothermal material with high photothermal conversion efficiency, comprising the following steps:

[0008] BrDPPBr, R-boronic acid ester, potassium carbonate and high-boiling-point solvent were mixed, and then heated to 70℃~90℃ under nitrogen atmosphere and stirring. Phosphine compound was then added, and the mixture was heated and stirred for 7h~9h under nitrogen atmosphere and temperature of 70℃~90℃. After the reaction, the mixture was cooled to room temperature, and then pure water was added to precipitate the solid. The solid was then recrystallized and purified to obtain a pyrrolopyrrole organic small molecule photothermal material with high photothermal conversion efficiency.

[0009] The structural formula of the BrDPPBr is as follows: The R-boronic ester is 4-(9H-carbazole-9-yl)phenylboronic acid pinacol ester or 4-(diphenylamino)phenylboronic acid pinacol ester.

[0010] An application of a pyrrolopyrrole organic small molecule photothermal material with high photothermal conversion efficiency, used for water evaporation.

[0011] The beneficial effects of this invention are:

[0012] This invention provides a pyrrolopyrrole organic small molecule photothermal material with high photothermal conversion efficiency, its preparation method, and its applications. First, the desired target organic small molecule-electron donor-acceptor (DA) type pyrrolopyrrole organic small molecule photothermal material is synthesized through a simple one-step organic reaction. This type of organic small molecule photothermal material exhibits unique properties and strong solid-state π-π packing. Through intramolecular charge transfer transitions and broad π-π* and n-π* absorption spectra, the highly conjugated structure is beneficial for improving the molar extinction coefficient. Furthermore, strong intermolecular interactions and polyphenyl rotor units enhance non-radiative transition efficiency, which is beneficial for photothermal conversion. The pyrrolopyrrole organic small molecule photothermal material of this invention features a high molar extinction coefficient and broad spectral absorption.

[0013] A porous photothermal conversion composite material was formed by loading pyrrolopyrrole organic small molecule photothermal materials onto polyurethane foam (PU). The synthesized organic small molecules possess strong light absorption capabilities, while PU is porous. This composite material can better improve the evaporation rate and light absorption rate, thereby effectively promoting multiple absorption of sunlight and increasing light capture. Under single-illumination conditions, the water evaporation rate was 1.08 kg·m³. -2 ·h -1The photothermal conversion efficiency is 71.23%, and the performance remains stable after multiple cycles, demonstrating excellent thermal stability. The molecular design concept proposed in this invention can be applied to solar interfacial evaporation, providing more ideas for the research of small molecule organic photothermal conversion materials and promoting the rapid development of seawater desalination.

[0014] This invention relates to a pyrrolopyrrole organic small molecule photothermal material with high photothermal conversion efficiency, its preparation method, and its application. Attached Figure Description

[0015] Figure 1 The 1H NMR spectrum of CzDPPCz prepared in Example 1;

[0016] Figure 2 The carbon NMR spectrum of CzDPPCz prepared in Example 1;

[0017] Figure 3 The mass spectrometry analysis chromatogram of CzDPPCz prepared in Example 1;

[0018] Figure 4 The UV-Vis absorption spectra of CzDPPCz prepared in Example 1 under different solvents;

[0019] Figure 5 The fluorescence emission spectra of CzDPPCz prepared in Example 1 under different solvents;

[0020] Figure 6 The images show CzDPPCz prepared in Example 1 under 365nm UV light irradiation in different solvents.

[0021] Figure 7 The solid-state fluorescence emission spectrum and solution fluorescence emission spectrum of CzDPPCz prepared in Example 1 are shown.

[0022] Figure 8 The images are scanning electron microscope (SEM) images of CzDPPCz, polyurethane foam prepared in Example 1, and CzDPPCz@PU (40 mg) prepared in Example 3. a and b are CzDPPCz, c and d are polyurethane foam, and e and f are CzDPPCz@PU (40 mg).

[0023] Figure 9 The image shows the solid-state UV diffuse reflectance test results of CzDPPCz@PU with different loadings prepared in Example 3;

[0024] Figure 10 The simulated seawater circulation test diagram shows the CzDPPCz@PU (40mg) prepared in Example 3;

[0025] Figure 11The graph shows a comparison of the photothermal conversion efficiency of CzDPPCz@PU with different loadings prepared in Example 3. Detailed Implementation

[0026] The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any combination of the specific embodiments.

[0027] Specific Implementation Method 1: This implementation method describes a pyrrolopyrrole organic small molecule photothermal material with high photothermal conversion efficiency, whose general chemical formula is:

[0028] The R mentioned is

[0029] In this specific embodiment, R is a triphenylamine unit or an N-phenylcarbazole unit.

[0030] The beneficial effects of this embodiment are:

[0031] This specific embodiment provides a pyrrolopyrrole organic small molecule photothermal material with high photothermal conversion efficiency, its preparation method, and its application. Firstly, the desired target organic small molecule-electron donor-acceptor (DA) type pyrrolopyrrole organic small molecule photothermal material is synthesized through a simple one-step organic reaction. This type of organic small molecule photothermal material exhibits unique properties and strong solid-state π-π packing. Through intramolecular charge transfer transitions and broad π-π* and n-π* absorption spectra, the highly conjugated structure is beneficial for increasing the molar extinction coefficient. Furthermore, strong intermolecular interactions and polyphenyl rotor units enhance non-radiative transition efficiency, which is beneficial for photothermal conversion. The pyrrolopyrrole organic small molecule photothermal material of this specific embodiment features a high molar extinction coefficient and broad spectral absorption.

[0032] A porous photothermal conversion composite material was formed by loading pyrrolopyrrole organic small molecule photothermal materials onto polyurethane foam (PU). The synthesized organic small molecules possess strong light absorption capabilities, while PU is porous. This composite material can better improve the evaporation rate and light absorption rate, thereby effectively promoting multiple absorption of sunlight and increasing light capture. Under single-illumination conditions, the water evaporation rate was 1.08 kg·m³. -2 ·h -1 The photothermal conversion efficiency is 71.23%, and the performance remains stable after multiple cycles, demonstrating excellent thermal stability. The molecular design concept proposed in this specific embodiment can be applied to solar interfacial evaporation, providing more ideas for the research of small molecule materials for organic photothermal conversion and promoting the rapid development of seawater desalination.

[0033] Specific Implementation Method Two: This implementation method provides a method for preparing a pyrrolopyrrole organic small molecule photothermal material with high photothermal conversion efficiency, which is carried out according to the following steps:

[0034] BrDPPBr, R-boronic acid ester, potassium carbonate and high-boiling-point solvent were mixed, and then heated to 70℃~90℃ under nitrogen atmosphere and stirring. Phosphine compound was then added, and the mixture was heated and stirred for 7h~9h under nitrogen atmosphere and temperature of 70℃~90℃. After the reaction, the mixture was cooled to room temperature, and then pure water was added to precipitate the solid. The solid was then recrystallized and purified to obtain a pyrrolopyrrole organic small molecule photothermal material with high photothermal conversion efficiency.

[0035] The structural formula of the BrDPPBr is as follows: The R-boronic ester is 4-(9H-carbazole-9-yl)phenylboronic acid pinacol ester or 4-(diphenylamino)phenylboronic acid pinacol ester.

[0036] The specific embodiment of the preparation reaction equation for pyrrolopyrrole organic small molecule photothermal material with high photothermal conversion efficiency is as follows:

[0037] The R mentioned is

[0038] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 2 in that the high-boiling-point solvent is a mixture of toluene, tetrahydrofuran, or methanol and water. Everything else is the same as in Specific Implementation Method 2.

[0039] Specific Implementation Method Four: This implementation method differs from Specific Implementation Method Two or Three in that the phosphine compound is PCl2, PCl3, PCl5, POCl3, or tetrakis(triphenylphosphine)palladium. Everything else is the same as in Specific Implementation Method Two or Three.

[0040] Specific Embodiment Five: This embodiment differs from Specific Embodiments Two to Four in that the molar ratio of BrDPPBr to R-boronate is 1:(2.5-3). Everything else is the same as in Specific Embodiments Two to Four.

[0041] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods Two to Five in that the molar ratio of BrDPPBr to potassium carbonate is 1:(2.5-3). Everything else is the same as in Specific Implementation Methods Two to Five.

[0042] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods Two to Five or Six in that the molar ratio of BrDPPBr to the volume ratio of the high-boiling-point solvent is 1 mol:(20-30) mL. Everything else is the same as in Specific Implementation Methods Two to Five or Six.

[0043] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods Two to Five-Seven in that the molar ratio of BrDPPBr to the phosphine compound is 1:(0.005~0.015). Everything else is the same as in Specific Implementation Methods Two to Five-Seven.

[0044] Specific Implementation Method Nine: This implementation method describes the application of a pyrrolopyrrole organic small molecule photothermal material with high photothermal conversion efficiency, which is used for water evaporation.

[0045] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Method Nine in that it is used for water evaporation. Specifically, it involves loading a pyrrolopyrrole organic small molecule photothermal material with high photothermal conversion efficiency into polyurethane foam. Everything else is the same as in Specific Implementation Method Nine.

[0046] The beneficial effects of the present invention are verified using the following embodiments:

[0047] Example 1:

[0048] A pyrrolopyrrole organic small molecule photothermal material with high photothermal conversion efficiency has the following chemical formula:

[0049] The R mentioned is

[0050] The preparation method of the above-mentioned pyrrolopyrrole organic small molecule photothermal material with high photothermal conversion efficiency is carried out according to the following steps:

[0051] BrDPPBr, R-boronic acid ester, potassium carbonate and high-boiling-point solvent were mixed and then heated to 85°C under nitrogen atmosphere and stirring. Phosphine compound was then added and the mixture was heated and stirred for 8 hours under nitrogen atmosphere and 85°C. After the reaction, the mixture was cooled to room temperature and then pure water was added to precipitate the solid. The solid was then recrystallized and purified to obtain a pyrrolopyrrole organic small molecule photothermal material with high photothermal conversion efficiency, named CzDPPCz.

[0052] The structural formula of the BrDPPBr is as follows: The R-boronic ester is 4-(9H-carbazole-9-yl)phenylboronic acid pinacol ester;

[0053] The high-boiling-point solvent is toluene.

[0054] The phosphine compound is tetra(triphenylphosphine)palladium.

[0055] The molar ratio of BrDPPBr to R-boronic acid ester is 1:3.

[0056] The molar ratio of BrDPPBr to potassium carbonate is 1:3.

[0057] The molar ratio of BrDPPBr to the volume ratio of the high-boiling-point solvent is 1 mol: 20 mL.

[0058] The molar ratio of BrDPPBr to the phosphine compound is 1:0.01.

[0059] The preparation reaction equation for the pyrrolopyrrole organic small molecule photothermal material with high photothermal conversion efficiency in this embodiment is as follows:

[0060]

[0061] Example 2:

[0062] A pyrrolopyrrole organic small molecule photothermal material with high photothermal conversion efficiency has the following chemical formula:

[0063] The R mentioned is

[0064] The preparation method of the above-mentioned pyrrolopyrrole organic small molecule photothermal material with high photothermal conversion efficiency is carried out according to the following steps:

[0065] BrDPPBr, R-boronic acid ester, potassium carbonate and high-boiling-point solvent were mixed and then heated to 85°C under nitrogen atmosphere and stirring. Phosphine compound was then added and the mixture was heated and stirred for 8 hours under nitrogen atmosphere and 85°C. After the reaction, the mixture was cooled to room temperature and then pure water was added to precipitate the solid. The solid was then recrystallized and purified to obtain a pyrrolopyrrole organic small molecule photothermal material with high photothermal conversion efficiency, named TPADPPTPA.

[0066] The structural formula of the BrDPPBr is as follows: The R-boronic acid ester mentioned is 4-(diphenylamino)phenylboronic acid pinacol ester;

[0067] The high-boiling-point solvent is toluene.

[0068] The phosphine compound is tetra(triphenylphosphine)palladium.

[0069] The molar ratio of BrDPPBr to R-boronic acid ester is 1:3.

[0070] The molar ratio of BrDPPBr to potassium carbonate is 1:3.

[0071] The molar ratio of BrDPPBr to the volume ratio of the high-boiling-point solvent is 1 mol: 25 mL.

[0072] The molar ratio of BrDPPBr to the phosphine compound is 1:0.01.

[0073] The preparation reaction equation for the pyrrolopyrrole organic small molecule photothermal material with high photothermal conversion efficiency in this embodiment is as follows:

[0074]

[0075] Example 3: The pyrrolopyrrole organic small molecule photothermal material with high photothermal conversion efficiency prepared in Example 1 was used for water evaporation. Specifically, the pyrrolopyrrole organic small molecule photothermal material with high photothermal conversion efficiency was loaded into polyurethane foam. The preparation method is as follows:

[0076] 1. Place a cylindrical polyurethane foam with a diameter of 2.6 cm and a thickness of 1 cm in a petri dish;

[0077] 2. Dissolve 10mg, 20mg, 30mg, 40mg and 50mg of CzDPPCz in 1mL of dichloromethane to obtain CzDPPCz solutions;

[0078] 3. The CzDPPCz solution was dripped onto the surface of a cylindrical polyurethane foam, and then dried at 60°C for 3 hours to obtain CzDPPCz@PU (10mg, 20mg, 30mg, 40mg and 50mg).

[0079] Figure 1 The image shows the 1H NMR spectrum of CzDPPCz prepared in Example 1; its structure was identified by 1H NMR spectroscopy. 1 H NMR (400MHz, CDCl3) δ9.04 (d, J=4.2Hz, 2H), 8.16 (dd, J=7.6, 1.1Hz, 4H), 7.94-7.8 9(m,4H),7.69-7.65(m,4H),7.58(d,J=4.1Hz,2H),7.50-7.43(m,8H),7.34-7.30(m ,4H),4.12(d,J=7.2Hz,5H),3.72(q,J=7.0Hz,2H),2.96-2.73(m,2H),2.71-2.50( m, 2H), 2.34 (q, J = 8.6, 8.0Hz, 2H), 1.33 (s, 5H), 0.96 (s, 7H), 0.89 (d, J = 6.5Hz, 7H).

[0080] Figure 2 The image shows the carbon NMR spectrum of CzDPPCz prepared in Example 1; its structure was identified by carbon NMR spectroscopy. 13C NMR (101MHz, CDCl3) δ155.53,141.41,130.03,128.76,125.88,123.10,120.28,1 19.65,116.68,109.76,53.50,49.99,31.69,30.90,30.02,29.77,29.73,17.62.

[0081] Figure 3 The mass spectrometry analysis chromatogram of CzDPPCz prepared in Example 1 is shown; its relative molecular weight was determined by mass spectrometry analysis, and C was obtained. 66 H 62 The relative molecular weight of N4O2S2 is 1007.43956.

[0082] Select a double-sided transparent UV quartz cuvette and add 3 mL of a 1×10⁻⁶ solution. -5 M was prepared in CzDPPCz solution with solvents including dichloromethane (DCM), tetrahydrofuran (THF), chloroform (CHCl3), dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), acetone (ACE), ethyl acetate (EA), and toluene, and the UV-Vis absorption spectra of the different solvents were measured. Figure 4 The UV-Vis absorption spectra of CzDPPCz prepared in Example 1 under different solvents are shown in the figure. As can be seen from the figure, this type of fluorescent dye has a broader emission range, which allows it to absorb light energy better, providing a prerequisite for achieving materials with high photothermal conversion efficiency.

[0083] Select a four-sided transparent fluorescent quartz cuvette and add 3 mL of a 1×10⁻⁶ solution. -5 M was used to prepare CzDPPCz solutions in solvents including dichloromethane (DCM), tetrahydrofuran (THF), chloroform (CHCl3), dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), acetone, ethyl acetate (EtOAc), and toluene, and the fluorescence emission spectra under different solvents were measured. Figure 5 The figures show the fluorescence emission spectra of CzDPPCz prepared in Example 1 in different solvents. As can be seen from the figures, this compound exhibits strong fluorescence emission in different solvents, making it a good fluorescent dye.

[0084] In a dark environment, images were taken under 365nm UV light at a concentration of 1×10⁻⁶. -5The CzDPPCz solution of M contains dichloromethane (DCM), tetrahydrofuran (THF), chloroform (CHCl3), dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), acetone, ethyl acetate (EtOAc), and toluene. Figure 6 The image shows CzDPPCz prepared in Example 1 under 365nm UV light irradiation in different solvents. As can be seen from the image, the fluorescence intensity initially increases with increasing solvent polarity, then decreases, but the overall fluorescence intensity does not decrease significantly.

[0085] The fluorescence emission spectra of the CzDPPCz solid-state solution prepared in Example 1 (solvent: tetrahydrofuran, concentration: 1×10⁻⁶) were measured using a fluorescence emission spectrometer. -5 The fluorescence emission spectrum of M). Figure 7 The solid-state fluorescence emission spectrum and solution fluorescence emission spectrum of CzDPPCz prepared in Example 1 are shown in the figure. As can be seen from the figure, the quantum yield in solution is 29.9%, and the solid state hardly emits any light. The weaker fluorescence in the solid state indicates that it has better light absorption ability.

[0086] SEM was used to observe the organic small molecules, polyurethane foam (PU), and their loading (40 mg). Figure 8 The images show scanning electron microscope (SEM) images of CzDPPCz, polyurethane foam prepared in Example 1, and CzDPPCz@PU (40 mg) prepared in Example 3. a and b are CzDPPCz, c and d are polyurethane foam, and e and f are CzDPPCz@PU (40 mg). As can be seen from the images, the prepared organic small molecules were successfully doped with polyurethane foam to form the desired composite material.

[0087] Solid-state UV diffuse reflectance tests were performed on CzDPPCz@PU prepared in Example 3 with different loading amounts; Figure 9 The figures show solid UV diffuse reflectance test results for CzDPPCz@PU with different loadings prepared in Example 3; as can be seen from the figures, the composite material of the two also has a wider absorption range.

[0088] Simulated seawater circulation tests were conducted on CzDPPCz@PU prepared in Example 3 with different loading amounts. The test process is as follows:

[0089] Step 1: Prepare two identical evaporation dishes and fill them with the same volume of seawater. Add an appropriate amount of CzDPPCz@PU (10mg, 20mg, 30mg, 40mg or 50mg) to one of the dishes.

[0090] Step 2: Irradiate the two samples using a simulated sunlight source with a light intensity of 1000 W / m². 2 Each light exposure lasts for 60 minutes;

[0091] Step 3: Use a thermometer to periodically measure and record the surface temperature of the two groups of samples and the amount of water evaporation over a certain period of time;

[0092] Step 4: Compare the temperature difference and evaporation rate of seawater with added photothermal conversion materials with the control group.

[0093] Figure 10 The simulated seawater circulation test diagram shows the CzDPPCz@PU (40mg) prepared in Example 3; Figure 11 The graph shows a comparison of the photothermal conversion efficiency of CzDPPCz@PU with different loadings prepared in Example 3. As can be seen from the graph, after one light irradiation, the water evaporation rate of CzDPPCz@PU (40 mg) is 1.08 kg·m³. -2 ·h -1 The photothermal conversion efficiency can reach 71.23%, and the performance remains stable after multiple cycles, demonstrating excellent thermal stability.

Claims

1. A method for preparing a porphyro-pyrrolo organic small-molecule photothermal material with high light-to-heat conversion efficiency, characterized in that It is done in the following steps: BrDPPBr, R-boronic acid ester, potassium carbonate and high-boiling-point solvent were mixed, and then heated to 85°C under nitrogen atmosphere and stirring. Phosphine compound was added, and the mixture was heated and stirred for 8 hours under nitrogen atmosphere and 85°C. After the reaction, the mixture was cooled to room temperature, and then pure water was added to precipitate the solid. The solid was then recrystallized and purified to obtain a pyrrolopyrrole organic small molecule photothermal material with high photothermal conversion efficiency. The structural formula of the BrDPPBr is as follows: The R-boronic ester is 4-(9H-carbazole-9-yl)phenylboronic acid pinacol ester; The high-boiling-point solvent is toluene; The phosphine compound is tetra(triphenylphosphine)palladium; The molar ratio of BrDPPBr to R-boronic acid ester is 1:3; The molar ratio of BrDPPBr to potassium carbonate is 1:3; The molar ratio of BrDPPBr to the volume ratio of the high-boiling-point solvent is 1 mol: 20 mL. The molar ratio of BrDPPBr to the phosphine compound is 1:0.01; The solution quantum yield of the pyrrolopyrrole organic small molecule photothermal material with high photothermal conversion efficiency is 29.9%. The pyrrolopyrrole organic small molecule photothermal material with high photothermal conversion efficiency is loaded in polyurethane foam, under 1 time of light irradiation condition, the water evaporation rate is 1.08 kg·m -2 ·h -1 , the photothermal conversion efficiency is 71.23%, and has cycle stability.

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