Metallized ring-fused tetrathiafulvalene dicarboxylic acid monolayer and its preparation method

Abstract

To provide a method for growing a needle-shaped single crystal which has a size of submillimeter scale and for which single crystal X-ray structure analysis is feasible, in order to supply a high quality organic metal alleviating contribution of grain boundary resistance and exhibiting high conductivity suitable for many applications.SOLUTION: In a production method of a single molecule organic metal single crystal, powder of an organic metal molecule which exhibits high conductivity without adding any dopant such as an oxidation / reduction reagent is pulverized. After adding a high-boiling organic solvent of which the weight 30-400 times, and a basic additive of which the weight 5-300 times that of the powder of the organic metal molecule, the addition product is left standing for several days to several months at a temperature of 0-50°C, and a brown needle-shaped single crystal of the TED is obtained.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention provides a metallized organic material suitable for applications requiring both high conductivity and transparency, such as touch panels. fused tetrathiafulvalene dicarboxylic acid The present invention relates to a single molecular single crystal (hereinafter also referred to as a "single molecular organometallic single crystal") and a method for producing the same. [Background technology]

[0002] Organic materials are inherently insulating, but it is known that they can be made conductive by adding dopants such as oxidizing and reducing agents. However, the inclusion of dopants can reduce the stability of the compound, and the dopants themselves are known to have adverse effects on other parts of the product, significantly reducing the applicability of organic electronic materials. On the other hand, single-molecule organometallic materials (see, for example, Patent Documents 1 and 2) have the advantage of their molecular structure, which allows them to achieve high conductivity without the addition of dopants such as oxidation-reduction reagents. If they can be made into thin films suitable for practical applications, the ripple effect will be enormous in many electronic devices, including transparent electrodes.

[0003] Therefore, if single crystals of single-molecule organic metals with a grain size large enough to allow X-ray structural analysis can be obtained, X-ray structural analysis can be used to effectively advance material exploration. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5943285 [Patent Document 2] Patent No. 6145660 [Non-patent literature]

[0005] [Non-Patent Document 1] Nature Mat. 2017, 16, 109 Summary of the Invention [Problem to be solved by the invention]

[0006] However, with conventional manufacturing methods, it was not possible to obtain single crystals large enough to perform single crystal structure analysis, for example, crystals with a long axis on the submillimeter scale, even when using synchrotron radiation, and X-ray single crystal structure analysis was not possible, which hindered progress in physical property analysis. Furthermore, even with single-molecule organic metals, there is a problem in that fine polycrystalline powders cannot exhibit high electrical conductivity due to high grain boundary resistance, which reduces performance in applications that require both high conductivity and transparency, such as touch panels.

[0007] The present invention solves the above-mentioned problems by providing a method for growing single crystals having submillimeter-scale dimensions that allow single crystal X-ray structural analysis, with the aim of reducing the contribution of grain boundary resistance and supplying high-quality organic metals that exhibit high conductivity suitable for many applications. [Means for solving the problem]

[0008] [1] The unimolecular organometallic single crystal of the present invention is any compound represented by the following general formula (wherein R1, R2, R3, R4 and R' may be the same or different): [ka] [ka] [ka] [ka]

[0009] [2] The single molecular organometallic single crystal [1] of the present invention is preferably a compound represented by the following formula: [ka] [3] The single molecular organometallic single crystals [1] to [2] of the present invention preferably have a needle-like crystal shape with a major axis of 50 μm or more and 5000 μm or less and a minor axis of 5 μm or more and 500 μm or less.

[0010] [4] The method for producing a single molecular organometallic single crystal of the present invention is characterized in that, without using a dopant such as an oxidizing or reducing agent, an organometallic molecular powder that exhibits high conductivity is pulverized, a high-boiling organic solvent having a boiling point of 100°C to 250°C and a basic additive having a pH of 7.5 or higher are added relative to the weight of the organometallic molecular powder, and the mixture is allowed to stand at a temperature of 0°C to 50°C to obtain a needle-shaped single crystal with metallic properties. Preferably, the needle-shaped single crystal having metallic properties is the needle-shaped single crystal described in [1] to [3].

[0011] [5] In the method [4] for producing a pure single-molecule organometallic single crystal of the present invention, preferably, the organometallic molecular powder exhibits high conductivity without using a dopant containing an oxidizing agent or a reducing agent. Here, high conductivity means that the resistivity is lower than 1 (Ωcm), which is the boundary between general organic semiconductors and organic metals, and has a value that makes it a good conductor comparable to that of a metal. [6] In the method [4] for producing a pure single molecular organometallic single crystal of the present invention, it is preferable to further filter the grown single crystal, wash it with water in large excess relative to the weight of the recovered single crystal, and then dry it to obtain the final product. Here, the grown single crystal refers to a single crystal that has grown to a major axis of 100 μm or more, and the large excess of water refers to water that is 2 to 100 times the weight of the sample. [7] In the method for producing a pure unimolecular organometallic single crystal of the present invention [4], the organometallic molecule is preferably a molecule that is chemically stabilized by electrically neutralizing a radical cation on a fused tetrathiafulvalene skeleton or a fused tetraselenafulvalene skeleton by a proton defect.

[0012] [8] In the method for producing a single molecular organometallic single crystal of the present invention [7], the organometallic molecule is preferably a fused tetrathiafulvalene-extended dicarboxylate (TED) or its selenium-substituted derivative, a fused tetraselenafulvalene-extended dicarboxylate. [9] In the method for producing a single molecular organometallic single crystal [8] of the present invention, the fused tetrathiafulvalene dicarboxylic acid and the fused tetraselenafulvalene dicarboxylic acid are preferably produced by the process shown in the following chemical formula: [ka]

[0013]

[10] In the methods [4] to [9] for producing a single molecular organometallic single crystal of the present invention, the high-boiling organic solvent preferably contains at least one of dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and N-methylpyrrolidone (NMP).

[11] In the method for producing a single molecular organometallic single crystal

[10] of the present invention, the ratio of the high-boiling organic solvent to the weight of the organometallic molecular powder is preferably 30 times or more and 400 times or less.

[12] In the methods [4] to

[11] for producing a single molecular organometallic single crystal of the present invention, the basic additive preferably contains any one of an aqueous hydroxylamine solution, an aqueous ammonia solution, and an aqueous dimethylamine solution.

[13] In the method

[12] for producing a single molecular organometallic single crystal of the present invention, the ratio of the weight of the basic additive to the weight of the organometallic molecular powder is preferably 5 to 300 times. [Effects of the Invention]

[0014] According to the method for producing a single-molecular organometallic single crystal of the present invention, the individual particles of the single-molecular organometallic single crystal are in the form of nanoscale powder immediately after synthesis, but needle-like single crystals with a single-crystal long axis of several hundred micrometers in size can be obtained, enabling X-ray structural analysis. Furthermore, the electrical properties of submillimeter-scale single crystals, which are suitable for many applications, are such that the resistivity is not affected by contributions from grain boundary resistance, and the single-molecule organometallic single crystals exhibit the maximum electrical conductivity. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a photograph showing an example of an organic metal (TED) needle-like single crystal grown by the manufacturing method of the present invention. [Figure 2] 1 is a photograph showing a comparative example in which a needle-like metal-organic (TED) single crystal was not obtained, which is outside the scope of the manufacturing method of the present invention. [Figure 3A] The unit cell structure (units are angstroms) is shown in the TED single crystal structure analysis. The numbers in parentheses indicate the least significant digit error. [Figure 3B] TED single crystal structure analysis shows a layered structure projected along the b-axis. [Figure 3C] TED single crystal structure analysis shows a layered structure projected along the a-axis. [Figure 3D] TED single crystal structure analysis shows the arrangement of intermolecular π orbitals. [Figure 4] FIG. 1 shows the temperature dependence of the electrical resistance of a TED single crystal measured by a four-terminal method using gold electrodes. [Figure 5] FIG. 1 is a diagram showing the reflectance of a TED single crystal at room temperature. [Figure 6] FIG. 1 shows powder X-ray diffraction patterns at room temperature of an organic metal (TED) needle-like single crystal (bottom) and powder (top). DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention provides a method for growing a single crystal of fused tetrathiafulvalene-extended dicarboxylate (hereinafter also abbreviated as TED) as an example of a single molecular organometallic single crystal. [Example]

[0017] Dimethyl sulfoxide (DMSO) and aqueous hydroxylamine solution were purchased from Wako Pure Chemical Industries, Ltd. and Aldrich Co., Ltd., respectively. TED was synthesized according to the following chemical scheme, which shows the synthesis method for single-molecule organometallic compounds. [ka]

[0018] Powdered TED crystals (1 mg, 21 μmol) were ground in a mortar and dissolved in DMSO (160 μL). To control the acidity of the solution, aqueous hydroxylamine solution (50 wt% solution, 50 μL) was added. The solution was placed in a sealed vial and stored at room temperature for several months. The grown single crystals were collected by filtration, washed with water in an amount approximately 10 times the weight of the TED, and then air-dried. Brown, needle-like single crystals were obtained with typical dimensions of 400 μm x 20 μm x 10 μm (see, for example, Figure 1).

[0019] TED powder is crushed, and a specific weight ratio of a high-boiling organic solvent and a basic additive is added. After that, it is left to stand for a long period of time at temperatures between 0°C and 50°C to produce a brown needle-like substance. A single crystal of this shape is obtained. The grown single crystals are filtered, washed with a suitable amount of water, and then dried to obtain the final product.

[0020] Although TED powder is a nanoscale piece, when crystals are grown using the above method, needle-like single crystals with a long axis on the submillimeter scale are obtained (Fig. 1). Table 1 shows an example of single crystal growth conditions in the present invention. The values in the table indicate the ratio of the weight of each solvent used when the substrate weight is set to 1. Here, the solvents are, from left to right, DMSO, DMF, NMP, NHOH aqueous solution, NH aqueous solution, and NH(Me) aqueous solution. [Table 1]

[0021] On the other hand, if growth is not performed under the preferred conditions (for example, Table 1) shown in the present invention, a single crystal does not grow and the material remains in powder form (FIG. 2).

[0022] X-ray crystal analysis revealed that the needle-like single crystal has a periodic structure with two molecules as an asymmetric unit, and has a layered crystal structure consisting of molecular sheets stacked in the a- and b-axis directions (Figure 4). Figure 3A shows the unit cell structure (units are angstroms) from TED single crystal structure analysis. The numbers in parentheses indicate the least significant digit error. Figure 3B shows the layered structure projected along the b-axis from TED single crystal structure analysis. Figure 3C shows the layered structure projected along the a-axis from TED single crystal structure analysis. Figure 3D shows the arrangement of intermolecular π orbitals from TED single crystal structure analysis. The crystal lattice is: P21 / m, a = 3.7464(2) Å, b = 11.8946(6) Å, c = 20.2094(11) Å, b = 93.506(2) Å, V = 898.88(8) Å, R1 = 5.38%. (X-ray structure analysis was performed at 113 K.) The numbers in parentheses indicate the least significant digit error in the X-ray structure analysis. In Figure 3A, the gray and black dotted lines indicate the intermolecular distance of S...S contacts and the intramolecular hydrogen bonds, respectively, in angstroms. In Figures 3B and 3C, the gray shaded area indicates a monolayer. In Figure 3D, the π orbitals overlap vertically along the a-axis with π···π stacking and horizontally along the b-axis with S...S contacts.

[0023] X-ray crystal analysis The crystal structure of the single crystal was determined using 1922 reflections based on high-resolution diffraction images collected at 113 K using a Rigaku Saturn CCD system. All atoms, except hydrogen atoms, were determined anisotropically.

[0024] Resistivity measurement Four gold wires (0.01 mm diameter) were attached as electrode probes along the longitudinal axis of the needle-shaped single crystal using silver paste (Dupont 4922N) at the contact points. Resistivity measurements were performed by temperature modulation in a He cryostat at 305 to 2 K, and the electrical properties were measured using a source meter (KEITHLEY 2450) and a nanovoltmeter (KEITHLEY 2182A).

[0025] The temperature dependence of resistivity is shown in Figure 5. Here, the vertical axis is resistivity (Ωcm) and the horizontal axis is temperature (K). The solid line drawn on the plot above 100K shows a fitting with a function proportional to the cube of the temperature T. The inset in Figure 4 shows the experimental setup with electrodes attached to the single crystal. The conductivity at room temperature is a maximum of 530 S / cm in the form of a pellet or a free-standing film made by pressing the powder. -1 However, the maximum conductivity of the single crystal is 2,300 S / cm, and the improvement in conductivity is clear.

[0026] optical measurement The reflectance spectra were measured at room temperature using a microscope UV-Vis-NIR spectrometer (JASCO MSV-5200) and a microscope FT-IR spectrometer (FT / IR-JASCO 6700 Type A) with P-wave. The reflectance of a standard Al mirror was used as a reference. The reflectance is shown in Figure 6. The vertical axis is reflectance (%) and the horizontal axis is wavelength range (nm).

[0027] Crystal structure TED was synthesized based on the proton-defect-induced carrier generation method via a solution process. Single crystals were slowly grown over several months from organic solvents without using electrochemical crystallization techniques, with typical dimensions of 400 μm x 20 μm x 10 μm (see Experimental Methods). Powder X-ray structural analysis showed that the obtained single crystals have similar reflection peaks to the powder, suggesting that they are of the same crystalline system (Figure 6).

[0028] The crystal structure of TED was determined by single-crystal X-ray diffraction (SXRD) at 113 K. The space group is P21 / m, and the lattice data are P21 / m, a = 3.7464(2) Å, b = 11.8946(6) Å, c = 20.2094(11) Å, b = 93.506(2) Å, V = 898.88(8) Å. 3 The R-factor, an indicator of the accuracy of the structural analysis, is 5.38%. The unit cell shown in Figure 3a consists of two planar TED molecules with their long axes aligned along the c-direction and offset in the a-direction. The intermolecular distance within the unit cell is 3.4957(13) Å. TED molecules are spaced 3.7464(2) Å apart along the a-axis and 3.6821(13) Å apart along the b-axis, forming a TED molecular layer. As shown in Figures 3b and 3c, TED layers stacked along the c-axis form a layered structure with small voids between the layers. Solvents (e.g., DMSO and / or HO) may be mixed into these voids. While the mixed solvent does not form significant intermolecular interactions with the TED, such as hydrogen bonding, it does affect the resistivity. In this example, we report only solvent-free TED crystals without solvent contamination.

[0029] The two central C=C bond distances in TED are close to each other (1.345(8) and 1.365(8) Å). The C-S bond distances are also very close to each other in the two TTF moieties. Furthermore, the symmetric intramolecular hydrogen bond between the two carboxylate oxygens is 2.420(8) Å. This intramolecular hydrogen bond is classified as a proton-centered, strong interaction energy hydrogen bond (SSHB) or low energy barrier hydrogen bond (LBHB). This covalent bond, coupled with the delocalization of π orbitals, plays an important role in delocalizing and stabilizing the radical electrons within the TED molecule. These facts support the fact that the radical electrons are not localized on only one side of the TTF moiety but are spread throughout the TED molecule via π conjugation, favoring charge transport. [Industrial Applicability]

[0030] Although conventional techniques have not been able to obtain single crystals large enough for single-crystal X-ray structural analysis, the present invention has succeeded in obtaining needle-like single crystals with long axes measuring submillimeters, which not only makes single-crystal structural analysis possible but also enables the development of electrical conductivity with reduced grain boundary resistance.

Claims

1. A fused ring tetrathiafulvalene dicarboxylic acid represented by the following chemical formula: A single crystal of a metallized ring-fused tetrathiafulvalene dicarboxylic acid, characterized in that it has a needle-like crystal shape with a major axis of 50 μm or more and 5,000 μm or less and a minor axis of 5 μm or more and 500 μm or less. 【Chemistry 5】

2. A process of adding a high-boiling organic solvent consisting of at least one of dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and N-methylpyrrolidone (NMP) in a first ratio and a basic additive consisting of at least one of an aqueous hydroxylamine solution, an aqueous ammonia solution, and an aqueous dimethylamine solution having a pH of 7.5 or higher in a second ratio relative to the weight of a pulverized powder of a fused ring-type tetrathiafulvalene dicarboxylic acid represented by the following chemical formula: A step of leaving the mixture at a temperature of 0°C to 50°C; A method for producing a single molecular crystal of a metallized ring-fused tetrathiafulvalene dicarboxylic acid, comprising a step of obtaining a needle-like single crystal having metallic properties. 【Chemistry 5】

3. The method for producing a single molecular single crystal of a metallated ring-fused tetrathiafulvalene dicarboxylic acid according to claim 2, characterized in that the single crystal grown to a major axis of 100 μm or more is filtered, washed with water having a weight of 2 to 100 times the weight of the sample, and then dried to obtain a final product.

4. 3. The method for producing a single molecular crystal of a metallated fused tetrathiafulvalene dicarboxylic acid according to claim 2, wherein the fused tetrathiafulvalene dicarboxylic acid is synthesized according to the following chemical formula: 【Chemistry 6】

5. 3. The method for producing a monomolecular single crystal of a metallated fused-ring tetrathiafulvalene dicarboxylic acid according to claim 2, wherein the first ratio of the high-boiling organic solvent to the weight of the fused-ring tetrathiafulvalene dicarboxylic acid powder is 30 times or more and 400 times or less.

6. 3. The method for producing a monomolecular single crystal of a metallated fused-ring tetrathiafulvalene dicarboxylic acid according to claim 2, wherein the second ratio of the weight of the basic additive to the weight of the fused-ring tetrathiafulvalene dicarboxylic acid powder is 5 times or more and 300 times or less.

Images