Organic-inorganic hybrid metal halides with reversible thermochromic properties, their preparation methods and applications

Abstract

The present invention discloses an organic-inorganic hybrid metal halide with reversible thermochromic properties, and its chemical formula is C7H 17 Br3CuN2O, C7H 13 Br3CuFN2O, C8H 19 Br3CuN2O or C8H 18 Br3CuFN2O. The present invention also provides preparation methods and applications of these four compounds. All four compounds have fully reversible thermochromism, narrow band gaps, and near-infrared properties. The present invention provides a compound with a narrower band gap and reversible thermochromic properties by regulating organic cations, and the band gap is narrowed from 2.120 eV to 1.590 eV; the preparation method of the compound is simple, easy to operate, the raw materials are abundant, and the production cost is low; the compound with thermochromic properties proposed by the present invention can be applied as a green technology to temperature sensors, visual thermometers, and smart windows.

Description

Technical Field

[0001] The present invention belongs to thermochromic materials, their preparation methods and uses, and particularly relates to organic-inorganic hybrid metal halides with reversible thermochromic properties, their preparation methods and applications. Background Art

[0002] In recent years, the research on designing new optical, electrical, magnetic, biological and other intelligent materials and their intelligent devices using color-changing molecules has become an important branch of chemistry and materials science. Thermochromism is a phenomenon in which color changes with temperature. Thermochromic materials have great potential in the applications of devices such as smart windows, temperature sensors, and visible thermometers. Thermochromic materials can also be applied in the field of signal processing to develop a new encryption method - spectral encryption, which is of great significance to the theoretical research and practical application of spectral information security technology and is also a research hotspot in the scientific community in recent years. The discovery of the semiconductor properties of thermochromic materials provides more possibilities for the development of optoelectronic devices.

[0003] Semiconductor materials with a band gap greater than 3.0 eV at room temperature are classified as wide-bandgap semiconductors, and semiconductor materials with a band gap less than 3.0 eV are classified as narrow-bandgap semiconductors. The wider the band gap, the more difficult it is for electrons to be excited from the valence band to the conduction band. With the rapid development of optoelectronic devices, there is an urgent need to find more ways to adjust the semiconductor band gap to meet the requirements under different conditions. Thermochromic materials can change the optical band gap according to temperature changes. After repeated heating / cooling cycles, the intrinsic band gap can be negligible, showing better thermal stability and environmental stability.

[0004] The thermochromic behavior of hybrid structures is usually caused by lattice distortion, lattice expansion or ion rearrangement. Xiong Rengen et al. proposed a thermochromic molecular ferroelectric ([DMeDABCO]CuCl4), and its crystal structure presents a low-dimensional octahedron, with the advantages of flexibility and diversity, and the thermochromism shows a change from yellow to red. Fu Dawei proposed that the lead iodide hybrid [PbI4-MAPY] has a reversible thermochromic transition between lemon yellow and carmine, and the band gap of the chain [PbI4] 2- narrows from 2.72 eV to 2.33 eV under heating conditions. Hybrid metal halides provide a basis for the development of high-performance thermochromic materials.

[0005] Some typical transition metals can achieve thermochromism, such as thermochromic transition metal complexes based on Cu 2+ 、Ni 2+ 、Co 2+ and Fe 2+ ligands. However, there is relatively little work on modifying their organic cations at present, and the existing materials have a relatively wide band gap, which is severely restricted in the application in the field of narrow-bandgap semiconductors. Summary of the Invention

[0006] Object of the Invention: The first object of the present invention is to provide an organic-inorganic hybrid metal halide with a narrower bandgap and reversible thermochromic properties by regulating organic cations, so as to better realize its application in the optoelectronic field.

[0007] The second object of the present invention is to provide a preparation method of the organic-inorganic hybrid metal halide with reversible thermochromic properties.

[0008] The third object of the present invention is to provide the application of the organic-inorganic hybrid metal halide with reversible thermochromic properties in smart windows, temperature sensors, visual thermometers or signal processing.

[0009] Technical Solution: To achieve the above object, the present invention provides an organic-inorganic hybrid metal halide with reversible thermochromic properties, and the chemical general formula of the organic-inorganic hybrid metal halide with reversible thermochromic properties is as follows:

[0010]

[0011] Wherein R is Me, FMe, Et or FEt.

[0012] Preferably, the structural formula of the organic-inorganic hybrid metal halide is as follows:

[0013]

[0014] Preferably, at a temperature of 296K, compounds C7H 17 Br3CuN2O and C7H 13 Br3CuFN2O both belong to the monoclinic system, P21 / m and P21 / n centrosymmetric space groups, and compounds C8H 19 Br3CuN2O and C8H 18 Br3CuFN2O both belong to the orthorhombic system, Pnma centrosymmetric space group.

[0015] The present invention also provides a preparation method of an organic-inorganic hybrid metal halide with reversible thermochromic properties. Dissolve the soluble salt of Cu 2+ and the triethylenediamine derivative in water respectively to obtain a Cu 2+ solution and a triethylenediamine derivative solution. Mix the Cu 2+ solution and the triethylenediamine derivative solution evenly, and react at room temperature for 6-7 days. Slowly evaporate the solvent by the solution method for self-assembly to obtain light yellow transparent block crystals, which are the organic-inorganic hybrid metal halide with reversible thermochromic properties.

[0016] Preferably, the soluble salt of Cu 2+ is CuBr2.

[0017] Preferably, the general structural formula of the triethylenediamine derivative is as shown in formula (1), where R = Me, Fme, Et or FEt.

[0018]

[0019] Preferably, the molar ratio of CuBr2 to the triethylenediamine derivative is 1:1.

[0020] For the preparation method of the compound of the present invention, the following scheme is preferred:

[0021] At room temperature, dissolve 2 mmol of CuBr2 in 15 mL of distilled water, dissolve 2 mmol of 1-(bromomethyl)-1-azabicyclo[2.2.2]octane in 20 mL of distilled water, then mix the CuBr2 solution and the 1-(bromomethyl)-1-azabicyclo[2.2.2]octane solution evenly, and react at room temperature for 6 - 7 days to obtain C7H 17 Br3CuN2O with thermochromic properties.

[0022] The structural formula of 1-(bromomethyl)-1-azabicyclo[2.2.2]octane is as shown in formula (2):

[0023]

[0024] At room temperature, dissolve 2 mmol of CuBr2 in 15 mL of distilled water, dissolve 2 mmol of 2 mmol of 1-(fluorobromomethyl)-1-azabicyclo[2.2.2]octane in 20 mL of distilled water, then mix the CuBr2 solution and the 2 mmol of 1-(fluorobromomethyl)-1-azabicyclo[2.2.2]octane solution evenly, and react at room temperature for 6 - 7 days to obtain C7H 13 Br3CuFN2O with thermochromic properties.

[0025] The structural formula of 1-(fluorobromomethyl)-1-azabicyclo[2.2.2]octane is as shown in formula (3):

[0026]

[0027] At room temperature, dissolve 2 mmol of CuBr2 in 15 mL of distilled water, dissolve 2 mmol of 1-(bromoethyl)-1-azabicyclo[2.2.2]octane in 20 mL of distilled water, then mix the CuBr2 solution and the 1-(bromoethyl)-1-azabicyclo[2.2.2]octane solution evenly, and react at room temperature for 6 - 7 days to obtain C8H 19 Br3CuN2O with thermochromic properties.

[0028] The structural formula of 1-bromoethyl-1-azabicyclo[2.2.2]octane is shown in Formula (4):

[0029]

[0030] At room temperature, 2 mmol of CuBr2 was dissolved in 15 mL of distilled water, and 2 mmol of 1-fluorobromoethyl-1-azabicyclo[2.2.2]octane was dissolved in 20 mL of distilled water. Then the CuBr2 solution and the 1-fluorobromoethyl-1-azabicyclo[2.2.2]octane solution were mixed evenly and reacted at room temperature for 6 to 7 days to obtain C8H 18 Br3CuFN2O with thermochromic properties.

[0031] The structural formula of 1-fluorobromoethyl-1-azabicyclo[2.2.2]octane is shown in Formula (5):

[0032]

[0033] The present invention also provides the application of the organic-inorganic hybrid metal halide with reversible thermochromic properties in the preparation of smart windows, temperature sensors, and visual thermometers.

[0034] The present invention also provides the application of the organic-inorganic hybrid metal halide with reversible thermochromic properties in signal processing.

[0035] The present invention also provides an encryption method of the organic-inorganic hybrid metal halide with reversible thermochromic properties in signal processing, and the method is a spectral encryption method.

[0036] Beneficial effects: Compared with the prior art, the present invention has the following advantages: (1) By regulating the organic cation, an organic-inorganic hybrid metal halide with reversible thermochromic properties and a narrower bandgap is provided. The bandgap is narrowed from 2.120 eV to 1.590 eV. Compounds with tunable bandgaps are a good supplement for the transition of organic-inorganic hybrid materials to multifunctional hybrid materials; (2) The preparation method of the compound of the present invention is to synthesize by self-assembly of natural evaporation of the solvent in solution at room temperature. The material structure has high stability, does not require additional reaction conditions, and the structure of this compound has strong controllability, high yield, and good repeatability. The preparation method is simple, easy to operate, the raw materials are abundant, and the production cost is low; (3) The compound with thermochromic properties proposed by the present invention can be applied to temperature sensors, visual thermometers, and smart windows as a green technology. (4) The compound with thermochromic properties proposed by the present invention can be applied to signal processing as a spectral encryption method. Description of the Drawings

[0037] Figure 1In this, a, b, c, and d are respectively C7H of the present invention 17 Br3CuN2O, C7H 13 Br3CuFN2O, C8H 19 Br3CuN2O and C8H 18 Synthesis route diagrams of Br3CuFN2O;

[0038] Figure 2 In this, a, b, c, and d are respectively C7H of the present invention 17 Br3CuN2O, C7H 13 Br3CuFN2O, C8H 19 Br3CuN2O and C8H 18 Crystal structure packing diagram of Br3CuFN2O at 296K;

[0039] Figure 3 In this, a, b, c, and d are respectively C7H of the present invention 17 Br3CuN2O, C7H 13 Br3CuFN2O, C8H 19 Br3CuN2O and C8H 18 Crystal diagrams of Br3CuFN2O at 296K and 365K;

[0040] Figure 4 For C8H of the present invention 18 Reversible thermochromic crystal demonstration diagrams of Br3CuFN2O at 296K, 333K, and 395K;

[0041] Figure 5 In this, a, b, c, and d are respectively C7H of the present invention 17 Br3CuN2O, C7H 13 Br3CuFN2O, C8H 19 Br3CuN2O and C8H 18 Infrared spectrum diagram of Br3CuFN2O;

[0042] Figure 6 In this, a, b, c, and d are respectively C7H of the present invention 17 Br3CuN2O, C7H 13 Br3CuFN2O, C8H 19 Br3CuN2O and C8H 18 Powder XRD diffraction pattern of Br3CuFN2O;

[0043] Figure 7 In this, a, b, c, and d are respectively C7H of the present invention 17 Br3CuN2O, C7H 13Br3CuFN2O, C8H 19 Br3CuN2O and C8H 18 Experimental optical band gap diagram of Br3CuFN2O;

[0044] Figure 8 Among them, a, b, c, and d are respectively C7H of the present invention 17 Br3CuN2O, C7H 13 Br3CuFN2O, C8H 19 Br3CuN2O and C8H 18 Theoretical energy band analysis diagram and partial density of states diagram (PDOS) of Br3CuFN2O;

[0045] Figure 9 Among them, a and b are respectively C8H of the present invention 18 Experimental optical band gap diagram, theoretical energy band analysis diagram, and partial density of states diagram (PDOS) of Br3CuFN2O at 296K and 365K respectively;

[0046] Figure 10 is C7H of the present invention 17 Br3CuN2O, C7H 13 Br3CuFN2O, C8H 19 Br3CuN2O and C8H 18 UV spectra of Br3CuFN2O at 296K and 365K;

[0047] Figure 11 is C7H of the present invention 17 Br3CuN2O, C7H 13 Br3CuFN2O, C8H 19 Br3CuN2O and C8H 18 Fluorescence spectra of Br3CuFN2O at 296K and 365K;

[0048] Figure 12 Among them, a, b, c, and d are respectively C7H of the present invention 17 Br3CuN2O, C7H 13 Br3CuFN2O, C8H 19 Br3CuN2O and C8H 18 Hirshfeld surface analysis and two-dimensional fingerprint plot of Br3CuFN2O. Detailed implementation manners

[0049] Figure 1 are respectively the organic-inorganic hybrid reversible thermochromic material compound C7H of the present invention 17 Br3CuN2O, C7H 13 Br3CuFN2O, C8H19 Br3CuN2O and C8H 18 Synthesis route of Br3CuFN2O. Examples 1-4 were prepared according to this synthesis route for this thermochromic compound.

[0050] Example 1

[0051] At room temperature, 2 mmol of CuBr2 was dissolved in 15 mL of distilled water, and 2 mmol of 1-(bromomethyl)-1-azabicyclo[2.2.2]octane was dissolved in 20 mL of distilled water. Then the CuBr2 solution and the 1-(bromomethyl)-1-azabicyclo[2.2.2]octane solution were mixed evenly and reacted at room temperature for 6-7 days to obtain C7H with thermochromic properties 17 Br3CuN2O.

[0052] The synthesis method of 1-(bromomethyl)-1-azabicyclo[2.2.2]octane can be found in Jun-Yi Li, Qiu-Ling Xu, Si-Yu Ye, et al. A multiaxial molecular ferroelectric with record high TC designed by intermolecular interaction modulation[J]. Chemical Communications, 2021,57(7)-943~946. Its structural formula is as follows:

[0053]

[0054] C7H 17 The structural formula of Br3CuN2O is as follows:

[0055]

[0056] Example 2

[0057] At room temperature, 2 mmol of CuBr2 was dissolved in 15 mL of distilled water, and 2 mmol of 1-(fluorobromomethyl)-1-azabicyclo[2.2.2]octane was dissolved in 20 mL of distilled water. Then the CuBr2 solution and the 2 mmol of 1-(fluorobromomethyl)-1-azabicyclo[2.2.2]octane solution were mixed evenly and reacted at room temperature for 6-7 days to obtain C7H with thermochromic properties 13 Br3CuFN2O.

[0058] The synthesis method of 1-(fluorobromomethyl)-1-azabicyclo[2.2.2]octane is described in Jun-Yi Li, Qiu-Ling Xu, Si-Yu Ye, et al. A multiaxial molecular ferroelectric with record high TC designed by intermolecular interaction modulation [J]. Chemical Communications, 2021, 57(7)-943~946. Its structural formula is as follows:

[0059]

[0060] C7H 13 The structural formula of Br3CuFN2O is as follows:

[0061]

[0062] Example 3

[0063] At room temperature, dissolve 2 mmol of CuBr2 in 15 mL of distilled water, dissolve 2 mmol of 1-(bromoethyl)-1-azabicyclo[2.2.2]octane in 20 mL of distilled water, then mix the CuBr2 solution and the 1-(bromoethyl)-1-azabicyclo[2.2.2]octane solution evenly, and react at room temperature for 6 - 7 days to obtain C8H 19 Br3CuN2O with thermochromic properties.

[0064] The synthesis method of 1-(bromoethyl)-1-azabicyclo[2.2.2]octane is described in Jun-Yi Li, Qiu-Ling Xu, Si-Yu Ye, et al. A multiaxial molecular ferroelectric with record high TC designed by intermolecular interaction modulation [J]. Chemical Communications, 2021, 57(7)-943~946. Its structural formula is as follows:

[0065]

[0066] C8H 19 The structural formula of Br3CuN2O is as follows:

[0067]

[0068] Example 4

[0069] At room temperature, 2 mmol of CuBr2 was dissolved in 15 mL of distilled water, and 2 mmol of 1-bromo-2-fluoroethyl-1-azabicyclo[2.2.2]octane was dissolved in 20 mL of distilled water. Then the CuBr2 solution and the 1-bromo-2-fluoroethyl-1-azabicyclo[2.2.2]octane solution were mixed evenly and reacted at room temperature for 6 - 7 days to obtain C8H 18 Br3CuFN2O with thermochromic properties.

[0070] The synthesis method of 1-bromo-2-fluoroethyl-1-azabicyclo[2.2.2]octane can be found in Jun-Yi Li, Qiu-Ling Xu, Si-Yu Ye, et al. A multiaxial molecular ferroelectric with record high TC designed by intermolecular interaction modulation[J]. Chemical Communications, 2021, 57(7)-943 - 946. Its structural formula is as follows:

[0071]

[0072] C8H 18 The structural formula of Br3CuFN2O is as follows:

[0073]

[0074] The compound crystals prepared in Examples 1 - 4 were analyzed. Single crystals of appropriate size were selected under a microscope, and the X-ray diffraction structure of the single crystal was determined using graphite-monochromated Mo Kα radiation on a Bruker Apex II CCD diffractometer. The crystallographic parameter results of this phase change compound are shown in Table 1. The semi-empirical absorption correction was performed using the SADABS method, the unit cell parameters were determined by the least squares method, the data reduction and structure analysis were completed using the SAINT and SHELXL program packages respectively, and all non-hydrogen atoms were anisotropically refined using the full matrix least squares method. The single crystal structure change of the compound is as Figure 2 shown. At 296 K, the Cu atom is in a distorted trigonal bipyramidal geometric environment and is coordinated with three Br atoms respectively, and the structure is similar to that of a three-tailed phage.

[0075] Table 1 Crystallographic data of the compound

[0076]

[0077]

[0078] Figure 3 Crystal surface diagrams of the four compounds synthesized in Examples 1-4, observed under an X-ray single crystal diffractometer. As the atomic distance between the metal and the halide expands, the color of the compound changes. At room temperature of 296K, the crystal surface color is light yellow. As the temperature rises to 395K, the crystal undergoes thermochromism to purple-black.

[0079] Figure 4 For the crystal surface diagram of the compound C8H 18 Br3CuFN2O synthesized in Example 4, its thermochromism shows good reversibility. As the temperature increases, the crystal color deepens. Under heating conditions, the color gradually turns purple-black. As the temperature decreases, the color returns to the original light yellow.

[0080] Figure 5 Infrared spectrum characterization of the compounds synthesized in Examples 1-4. At 3500 cm -1 there is a strong absorption peak, which is the stretching vibration absorption peak of the C-H single bond on the triethylenediamine derivative; at 1476 cm -1 there is a strong absorption peak, which is the bending vibration absorption peak of the C-C single bond; there is an absorption peak near 1100 - 1350 cm -1 which is the stretching vibration peak of the C-F bond on the triethylenediamine derivative.

[0081] Figure 6 XRD analysis characterization of the compounds synthesized in Examples 1-4. It can be seen from the powder XRD diffraction pattern that the simulated diffraction peaks coincide with the experimentally measured diffraction peaks, indicating that the four compounds all have high phase purity.

[0082] Figure 7 Experimental optical band gap diagrams of the compounds synthesized in Examples 1-4. By extrapolating the linear region of the absorption edge to the energy axis intercept, it is determined that the optical band gaps of compounds a-d have semiconductor characteristics. According to the Tauc plot, the band gaps of compounds a-d are approximately 2.120 eV, 1.940 eV, 2.060 eV, and 1.910 eV respectively.

[0083] Figure 8Theoretical band analysis diagrams and partial density of states diagrams (PDOS) of the compounds synthesized in Examples 1-4. Based on density functional theory (DFT), the theoretical band structures and partial density of states (PDOS) of compounds a-d were calculated. Compounds a, b, and c have direct bandgap characteristics because the minimum of the conduction band (CB) and the maximum of the valence band (VB) are distributed at the same point in the Brillouin zone; while compound 4 is distributed at different points and has indirect bandgap characteristics. Due to the limitations of the density functional theory method, the bandgaps calculated by this method are slightly different from the experimental values. The calculated bandgaps of compounds a-d are 2.334 eV, 2.157 eV, 2.227 eV, and 1.996 eV, respectively.

[0084] Figure 9 Experimental optical bandgap diagrams, theoretical band analysis diagrams, and partial density of states diagrams (PDOS) of the compound C8H 18 Br3CuFN2O at 296 K and 365 K, respectively. When the temperature changes from 296 K to 365 K, the bandgap narrows from 2.120 eV to 1.590 eV, and the narrowing of the bandgap is consistent with the color change.

[0085] Figure 10 Analysis of the ultraviolet spectra of the compounds synthesized in Examples 1-4. At different temperatures, thermochromic changes from yellow to purple-black were exhibited. At room temperature (298 K), the light absorbed by compound a is less than 530 nm, which is consistent with its yellow appearance. When the temperature exceeds and reaches 365 K, compared with the spectrum under room temperature (298 K) conditions, the absorption edge moves to 670 nm. The experimental results show that the ultraviolet absorption spectrum has a red shift. C7H 13 Br3CuFN2O, C8H 19 Br3CuN2O, and C8H 18 The absorption edge of Br3CuFN2O gradually increases at around 600 nm, and when the temperature rises, the absorption band also shows a red shift trend.

[0086] Figure 11 Analysis of the fluorescence spectra of the compounds synthesized in Examples 1-4. The fluorescence characteristics are shown in the figure. The emission spectrum at 298 K has obvious sharp absorption peaks. Under the excitation wavelength of 338 nm, there is a strong dominant emission band centered at 570 nm monitored by the PLE spectrum. When the temperature rises to 365 K, there are obvious sharp absorption peaks in the fluorescence intensity range of 650 - 800 nm, presenting a near-infrared (NIR) spectrum (>650 nm), and the brightness reaches a peak at 730 nm. The copper(II) complex exhibits a sharp and strong d-d band centered at 730 nm, which is due to 2 B 1g - 2 A 1g transition.

[0087] Figure 12 Hirshfeld surface analysis and two-dimensional fingerprint analysis of the compounds synthesized in Examples 1-4. The relatively strong interactions between different asymmetric units are represented by the large dark red circular depressions on the Hirshfeld surface. In the two-dimensional fingerprint plot, each point represents a single (d i , d e ) coordinate, reflecting the distances from the interior (d i ) and exterior (d e ) of the Hirshfeld surface to the nearest atom, and the H···Br contacts and Coulomb interactions related to the surface area make significant contributions to the attractive cation-anion.

Claims

1. An organic-inorganic hybrid metal halide with reversible thermochromic properties, characterized in that, The structural formula of the organic-inorganic hybrid metal halide is as follows: At a temperature of 296 K, the compounds C7H 17 Br3CuN2O and C7H 13 Br3CuFN2O both belong to the monoclinic system, P21 / m and P21 / n centrosymmetric space groups. The compounds C8H 19 Br3CuN2O and C8H 18 Br3CuFN2O both belong to the orthorhombic system, Pnma centrosymmetric space group. Compound C7H 17 Crystallographic parameters of Br3CuN2O is 7.9966(7), is 9.7125(9), is 8.2988(8), α / deg is 90, β / deg is 97.549(7), γ / deg is 90, Compound C7H 13 Crystallographic parameters of Br3CuFN2O is 10.6622(2), is 9.6800(2), is 12.4370(3), α / deg is 90, β / deg is 92.2210(10), γ / deg is 90, Compound C8H 19 Crystallographic parameters of 19 is 18.4636(6), is 9.1753(3), is 8.0380(3), α / deg is 90, β / deg is 90, γ / deg is 90, C8H 18 Crystallographic parameters of Br3CuFN2O is 18.5303(7), is 9.1847(3), is 7.9755(3), α / deg is 90, β / deg is 90, γ / deg is 90.

2. The preparation method of an organic-inorganic hybrid metal halide with reversible thermochromic properties according to claim 1, characterized in that, Cu 2+ The soluble salt of Cu and triethylenediamine derivatives were dissolved in water to obtain Cu 2+ solution and triethylenediamine derivative solution, Cu 2+ The solution is mixed evenly with the triethylenediamine derivative solution, reacted at room temperature for 6 to 7 days, and the light yellow transparent fast-shaped crystals are prepared by self-assembly through slow evaporation of the solvent by a solution method, which is an organic-inorganic hybrid metal halide with reversible thermochromic properties; the triethylenediamine derivative has the following general structural formula: Wherein R = Me, CH2F, Et or CH2CH2F.

3. The preparation method of an organic-inorganic hybrid metal halide with reversible thermochromic properties according to claim 2, characterized in that, The described Cu 2+ soluble salt is copper bromide.

4. The preparation method of an organic-inorganic hybrid metal halide with reversible thermochromic properties according to claim 3, characterized in that, The molar ratio of copper bromide to the triethylenediamine derivative is 1:

1.

5. Use of the organic-inorganic hybrid metal halide with reversible thermochromic properties according to claim 1 in the preparation of smart windows, temperature sensors, and visual thermometers.

6. Use of the organic-inorganic hybrid metal halide with reversible thermochromic properties according to claim 1 in signal processing.

7. The application according to claim 6, characterized in that, The application includes spectral encryption in signal processing.

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