Preparation and application of oxime ester space conjugated organic molecules based on hexaphenylbenzene anchoring group

Abstract

The invention belongs to the technical field of organic electronics, and discloses a preparation method and application of spatial conjugation and photoresponse organic molecules based on a hexaphenylbenzene anchoring group. The organic molecule based on the spatial conjugation of the hexaphenylbenzene anchoring group and having the photoresponse has a structure shown in the following I-II: the unique spatial conjugation structure of the organic molecule enables electrons not only to be transmitted along a valence bond conjugation channel, but also to be transmitted along a spatial conjugation channel, and the organic molecule has a plurality of electric conduction channels. Meanwhile, imine free radicals are considered to be capable of being bonded with transition metal, so that the required catalytic reaction is generated. In view of the unique reactivity, free imino free radicals generated by homogeneous solution of an NO bond of the oxime ester precursor induced by ultraviolet light are directly coordinated with gold atoms to form a covalent AuN bond, so that single-molecule connection is formed. The preparation method is simple and applicable, and has a good application prospect in the field of organic monomolecular wires.

Description

Technical Field

[0001] The invention belongs to the technical field of organic electronics, and particularly relates to the preparation of imine radical molecules with covalent Au-N bonds based on hexaphenylbenzene anchoring groups and their application in the field of organic optoelectronics. Background Art

[0002] The preparation process of integrated circuits in the semiconductor industry has been developed in a top-down manner according to Moore's Law. The preparation of smaller components through silicon-based micromachining technology has reached a bottleneck. Molecular electronics has attracted much attention because of its potential to break through the inherent limitations of silicon-based electronics. Molecular wires, as the basic components of molecular electronics, are responsible for charge transfer and electronic communication between different components at the molecular level. They are currently a research hotspot in the field of multidisciplinary intersections, and organic molecular wires are an indispensable part of them. The conjugated structure directly affects the energy level structure, chemical stability and thermal stability of organic molecules, and also affects the photophysical properties, carrier transport properties and processing properties of optoelectronic devices, and has a decisive influence on the stability of the device. Therefore, the regulation of the conjugated structure is an indispensable and important link in the design of organic optoelectronic materials.

[0003] Molecular electronics has attracted extensive attention due to its potential to break through the inherent limitations of silicon-based electronics. Single-molecule wires are the basic elements of molecular electronics, responsible for charge transport and electronic communication between different components at the molecular level. In addition to the electrode-molecule interface, the internal electronic structure and geometry of the molecule play a decisive role in the overall performance of the molecular wire in the metal-molecule-metal junction. Therefore, exploring robust single-molecule wires with ideal conformations and unique electronic effects remains a huge challenge to achieve high and stable conductance. To date, the molecular cores of artificial single-molecule wires widely studied in the literature are mainly limited to rod-shaped organic molecules and organometallic molecules through bond π conjugation, in which a high density of delocalized π electrons facilitates charge transport through the molecular backbone. This through-bond conjugation usually refers to the direct connection of aliphatic and aromatic units with carbon-carbon single, double or triple bonds composed of sp, sp2 or sp3 carbon frameworks. Another type of interesting single-molecule wires that has just emerged is based on non-covalent spatial conjugation, in which the π electrons are spatially distributed in the interplanar regions of closely stacked aromatic rings and can be used for charge transport. When two chromophores or aromatic rings are arranged close enough and their electron density distributions overlap, through-space conjugation and long-range Coulomb (dipole-dipole) interactions are formed. This unique spatial conduction mode has attracted increasing attention and has shown important significance in various systems, including redox processes in biological complexes, electronic signaling in DNA molecules, carrier transport in organic electronics and photovoltaics, etc. However, compared with through-bond single-molecule wires, the exploration of through-space wires is far less, which may be due to the lack of suitable organic platforms with strong through-space conjugation.

[0004] Single-molecule junctions are a popular platform for studying molecular electronics. To this end, there have been numerous demonstrations of single-molecule electron transport properties. To count the molecular conductances that can occur in junctions at room temperature, one of the most widely used experimental techniques to study single-molecule junctions is the scanning tunneling microscopy-broken junction (STM-BJ) approach. In this approach, the properties of single-molecule junctions are measured while increasing the electrode separation to promote the formation, evolution, and rupture of the junction. Therefore, each measurement samples the progression of many different conformations. This approach has previously been used for the covalent binding of rigid molecules to electrodes. It provides a platform to elucidate the nature of distance-dependent electronic interactions such as van der Waals (vdW) forces. Iminium radicals are believed to be able to bond to transition metals to produce the desired catalytic reactions. Given these unique reactivities, the radicals directly react with Au electrodes to form single-molecule junctions by Au-N bonding. Summary of the invention

[0005] In order to overcome the shortcomings and deficiencies of the above-mentioned prior art, the primary purpose of the present invention is to provide an oxime ester spatial conjugated organic molecule based on a hexaphenylbenzene anchoring group and a preparation method thereof. The imino radical molecule of the covalent Au-N bond based on the hexaphenylbenzene anchoring group of the present invention has the characteristics of spatial conjugation and valence bond conjugation at the same time, has multiple conductive channels, one end of which is anchored by a coordination bond formed with a gold electrode through a mercaptomethyl group, and the other end of the hexaphenylbenzene is anchored with a gold electrode through van der Waals force, which can effectively compensate for the low conductivity phenomenon caused by insufficient valence bond conjugation. At the same time, the oxime ester conjugated organic molecule based on the hexaphenylbenzene anchoring group can be photo-responsively regulated by ultraviolet light.

[0006] Another object of the present invention is to provide the application of oxime ester spatial conjugated organic molecules based on hexaphenylbenzene anchoring groups, and the application of oxime ester spatial conjugated organic molecules based on hexaphenylbenzene anchoring groups in the field of organic molecular wires.

[0007] The purpose of the present invention is achieved based on the following technical solutions:

[0008] An oxime ester spatial conjugated organic molecule based on a hexaphenylbenzene anchoring group, the structure of which is shown in Formula I-II:

[0009]

[0010] To achieve the above object, the present invention provides the following technical solution: a preparation and application of an oxime ester spatial conjugated organic molecule based on a hexaphenylbenzene anchoring group, wherein the preparation method comprises the following steps:

[0011] The compound 4-(methylthio)benzaldehyde and hydroxylamine hydrochloride were mixed in pyridine and added to a single-necked round-bottom flask. oC for 6 hours. After the reaction, the resulting mixture was poured into water and filtered under reduced pressure to obtain a white solid product (e)-N-(4-(methylthio)phenyl)carboximidic acid. Compound 4-(phenylinyl)benzoic acid and tetraphenylcyclopentadienone were mixed in phenyl ether and added to a single-mouth round-bottom flask. The mixture was heated to 260 o C for 8 hours. After cooling to room temperature, the mixture was poured into water and extracted with dichloromethane three times. The combined organic layer was washed with saturated sodium bicarbonate and water in turn, and then dried over anhydrous magnesium sulfate. After filtration, the solvent was evaporated under reduced pressure, and the crude product was purified by silica gel column chromatography using petroleum ether: dichloromethane as eluent to obtain a white solid product 3',4',5',6'-tetraphenyl-[1,1':2',1''-terphenyl]-4-carboxylic acid. Compound (e)-N-(4-(methylthio)phenyl)carboximidic acid, 3',4',5',6'-tetraphenyl-[1,1':2',1''-terphenyl]-4-carboxylic acid, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and 4-dimethylaminopyridine were added to a double-necked round-bottom flask. The culture flask was evacuated under vacuum, flushed with dry nitrogen three times, and then dichloromethane was added. The reaction mixture was refluxed for 12 hours. After cooling to room temperature, the mixture was poured into water and extracted with dichloromethane three times. The combined organic layers were dried over anhydrous magnesium sulfate. After filtration, the solvent was evaporated under reduced pressure and the crude product was purified by silica gel column chromatography using petroleum ether: dichloromethane (3:1, v:v) as the eluent to obtain a yellow solid product ZL-05.

[0012] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0013] In addition to the electrode-molecule interface, the internal electronic structure and geometric structure of the molecule play a decisive role in the overall performance of the molecular wire in the metal-molecule-metal junction. The traditional valence bond conjugated molecular wire for through-bond transmission is affected by the reverse ring current, and the molecular conductivity is poor. The oxime ester spatial conjugated organic molecule based on the hexaphenylbenzene anchoring group synthesized by the present invention not only has the traditional valence bond conjugated structure, but also has a spatial conjugation effect. The molecular anchoring group with an intramolecular π-π stacking structure enables electrons to be transmitted not only along the valence bond conjugated channel, but also along the spatial conjugated channel. It has multiple conductivity channels, which effectively compensates for the low conductivity phenomenon caused by insufficient valence bond conjugation of the molecule. This series of molecules, one end of which is anchored to the gold electrode through the van der Waals force of hexaphenylbenzene and the gold electrode, and the other end is an oxime ester derivative, which will be cleaved under 365 NM light irradiation, providing new insights for regulating the charge transfer performance of single molecule wires. The spatial conjugated organic molecule of the present invention is easy to prepare and has excellent conductivity. It is a building unit of a molecular wire with good prospects. The preparation method of the present invention has wide universality and greatly improves the conductivity of single-molecule wires. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Steady-state photolysis of ZL-05 (A) and ZL-06 (B) in propylene carbonate (PC) under UV-LED (365 nm) irradiation.

[0015] Figure 2 Electron spin resonance spectra of covalent imine radical adducts generated by photolysis of ZL-05 (A) and ZL-06 (B) in PC solvent.

[0016] Figure 3 One-dimensional conductance histogram of ZL-05 and UV-treated ZL-05 (A) and one-dimensional conductance histogram of ZL-06 and UV-treated ZL-06 (B), two-dimensional conductance-displacement histogram of ZL-05 and UV-treated ZL-05 (C) and two-dimensional conductance-displacement histogram of ZL-06 and UV-treated ZL-06 (D).

[0017] Figure 4 The chemical structures and torsion angles of ZL-05 and ZL-06.

[0018] Figure 5 Illustration of the frontier molecular orbitals of HOMO-2, HOMO-1, HOMO, LUMO, LUMO+1 and LUMO+2 of ZL-05 determined at the M06-2X / 6-311G (d, p) theoretical level.

[0019] Figure 6 Diagram of the frontier molecular orbitals of HOMO-2, HOMO-1, HOMO, LUMO, LUMO+1 and LUMO+2 of ZL-06 determined at the M06-2X / 6-311G (d, p) theoretical level

[0020] Figure 7 This is the high-resolution MALDI-TOF spectrum of ZL-05 [MALDI-TOF, m / z: 750.24 (Na) (Calcd727.25)].

[0021] Figure 8 This is the high-resolution MALDI-TOF spectrum of ZL-06 [MALDI-TOF, m / z: 750.24 (Na) (Calcd727.25)]. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below in conjunction with examples and drawings, but the embodiments of the present invention are not limited thereto.

[0023] Example 1 Preparation of imine-based free radical single-molecule wire [ZL-05] based on covalent Au-N bond of hexaphenylbenzene anchor group

[0024]

[0025] The synthetic route is as follows:

[0026]

[0027] (1) All chemicals and reagents were purchased from commercial sources and used without further purification. All reagents and drugs were sealed and not handled before use.

[0028] (2) Mix the compound 4-(methylthio)benzaldehyde (0.76 g, 5.00 mmol) and hydroxylamine hydrochloride (0.69 g, 10.00 mmol) in 10 mL of pyridine and add it to a 25 mL single-necked round-bottom flask. o C for 6 hours. After the reaction, the resulting mixture was poured into water (50 mL) and filtered under reduced pressure to obtain 0.80 g of white solid product 2 with a yield of 96%. 1 H NMR (500 MHz, CDCl3) δ 8.10 (s, 1H), 7.49 (d, J = 8.45 Hz, 2H), 7.23 (d, J= 8.45 Hz, 2H), 2.50 (s, 3H). 13 C NMR (125 MHz, DMSO-d6) δ 147.72, 139.77, 129.56, 126.85, 125.73, 14.37.

[0029] (3) Mix 4-(phenylinyl)benzoic acid (1.00 g, 2.60 mmol) and tetraphenylcyclopentadienone (0.73 g, 2.86 mmol) in 10 mL of phenyl ether and add to a 25 mL single-necked round-bottom flask. Heat the mixture to 260 °C. o C for 8 hours. After cooling to room temperature, the mixture was poured into water and extracted with dichloromethane three times. The combined organic layer was washed with saturated sodium bicarbonate and water in turn, and then dried over anhydrous magnesium sulfate. After filtration, the solvent was evaporated under reduced pressure, and the crude product was purified by silica gel column chromatography using PE:DCM (1:1, v:v) as the eluent to obtain 1.35 g of white solid product 5 with a yield of 90%. 1H NMR (500 MHz, CDCl3) δ 12.74 (s, 1H), 7.39 (d, J = 7.70 Hz, 2H), 7.01 (d, J =7.85 Hz, 2H), 6.89–6.80 (m, 25H). 13 C NMR (125 MHz, Dimethyl Sulfoxide-d6) δ140.40, 140.09, 139.94, 139.87, 139.73, 139.69, 139.15, 130.86, 126.67,126.59, 125.62, 125.45, 118.63.

[0030] (4) Compound 2 (1.00 g, 1.70 mmol), 5 (0.30 g, 1.70 mmol), 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDCl) (0.14 g, 5.00 mmol) and 4-dimethylaminopyridine (0.02 g, 0.17 mmol) were added to a 100 mL double-necked round-bottom flask. The culture flask was evacuated under vacuum, flushed with dry nitrogen three times, and then 30 mL of dichloromethane was added. The reaction mixture was refluxed for 12 hours. After cooling to room temperature, the mixture was poured into water and extracted with dichloromethane three times. The combined organic layers were dried over anhydrous magnesium sulfate. After filtration, the solvent was evaporated under reduced pressure, and the crude product was purified by silica gel column chromatography using petroleum ether: dichloromethane (3:1, v:v) as the eluent to obtain 0.41 g of yellow solid ZL-05 with a yield of 33%. 1 H NMR (500 MHz, CDCl3) δ 8.38 (s, 1H), 7.64 (t, J = 17.60 Hz, 4H), 6.96 (d, J =8.30 Hz, 2H), 6.85–6.83 (m, 27H), 2.46 (s, 3H). 13 C NMR (125 MHz, CDCl3) δ140.63, 140.48, 140.39, 140.18, 132.32, 131.74, 131.45, 131.41, 128.80,128.29, 126.95, 126.77, 125.77, 125.59, 125.45, 15.10. MALDI-TOF, m / z: 750.24(Na) (Calcd 727.25).

[0031] Example 2 Preparation of covalent Au-N bonded imine radical [ZL-06] based on hexaphenylbenzene anchoring group

[0032]

[0033] The synthetic route is as follows:

[0034]

[0035] (1) Mix 4-(phenylethynyl)benzaldehyde (1.00 g, 2.60 mmol) and tetraphenylcyclopentadienone (0.60 g, 2.86 mmol), add to 10 mL of phenyl ether, and place in a 25 mL single-necked round-bottom flask. o C for 8 hours. After cooling to room temperature, the mixture was poured into water and extracted with dichloromethane three times. The combined organic layer was washed with saturated sodium bicarbonate and water in turn, and then dried over anhydrous magnesium sulfate. After filtration, the solvent was evaporated under reduced pressure, and the crude product was purified by silica gel column chromatography using petroleum ether and dichloromethane as eluents to obtain 1.09 g of white solid product 7 in a yield of 75%. 1 H NMR (500 MHz, CDCl3) δ 9.75 (s, 1H), 7.38 (d, J = 7.70 Hz, 2H), 7.01 (d, J= 7.85 Hz, 2H), 6.85–6.82 (m, 25H). 13 C NMR (125 MHz, CDCl3) δ 192.43, 147.99,141.17, 140.69, 140.43, 140.31, 140.14, 140.09, 139.18, 133.35, 132.19,131.44, 131.39, 129.87, 128.33, 126.98, 126.81, 126.79, 125.75, 125.50,125.48, 122.96, 122.79, 119.01.

[0036] (2) Compound 7 (1.00 g, 1.60 mmol) and hydroxylamine hydrochloride (0.20 g, 3.20 mmol) were mixed in 10 mL of pyridine and added to a 25 mL single-necked round-bottom flask. The mixture was heated at 100 o C for 6 hours. After the reaction, the resulting mixture was poured into water (50 mL) and filtered under reduced pressure to obtain 0.85 g of white solid product 8 with a yield of 92%. 1 H NMR (500 MHz, CDCl3) 7.88 (s, 1H), 7.07 (d, J = 8.00 Hz, 2H), 6.86–6.83 (m, 27H).13 C NMR(125 MHz, CDCl3) δ 150.67, 143.10, 140.77, 140.59, 140.56, 140.53, 140.41,140.29, 139.62, 131.95, 131.48, 131.46, 129.87, 128.63, 126.88, 126.74,125.261, 125.54, 123.26, 119.01.

[0037] (3) This synthesis procedure is similar to that described in ZL-05. After filtration, the solvent was evaporated under reduced pressure and the crude product was purified by silica gel column chromatography using PE:DCM (3:1, v:v) as the eluent to obtain 0.45 g of a yellow solid with a yield of 36%. 1 HNMR (500 MHz, CDCl3) δ 8.29 (s, 1H), 7.96 (d, J = 8.05 Hz, 2H), 7.30 (d, J =8.15 Hz, 4H), 6.92 (d, J = 7.80 Hz, 2H), 6.85-6.82 (m, 27H), 2.52 (s, 3H). 13 CNMR (125 MHz, CDCl3) δ 140.45, 132.07, 131.46, 130.08, 127.10, 126.94,126.77, 125.68, 125.44, 125.09. MALDI-TOF, m / z: 750.24 (Na) (Calcd 727.25).

[0038] Example 3 Ultraviolet absorption spectrum and electron spin resonance spectrum analysis

[0039] Figure 1 We measured the optical properties of the molecules in dilute propylene carbonate solution by UV-visible spectroscopy and found that low-energy absorption bonds with peak values ​​above 100 nm appeared in ZL-05 (A) and ZL-06 (B). When exposed to a 365 n UV LED, the maximum absorption peaks at 280 nm, 1140 nm, and 1386 nm gradually increased with increasing irradiation time, indicating that the oxime esters were photolyzed and imine radicals were formed. To further confirm the formation of imine radicals during the photolysis process, Figure 2 To investigate the use of 5,5-dimethyl-1-pyrroline N-oxide as a free radical trap, the electron spin resonance (EPR) spectra of ZL-05 and ZL-06 were analyzed. Figure 2As shown in A and 2B, obvious EPR signals of ZL-05 and ZL-06 were detected after irradiation at 365 nm. These results prove the formation of free imine radicals.

[0040] Example 4 Determination of molecular conductance based on scanning tunneling microscopy-broken junction (STM-BJ) technology

[0041] Figure 3 The one-dimensional conductance histograms of ZL-05 (A) and ZL-06 (B) and the two-dimensional conductance-distance histograms of ZL-05 (C) and ZL-06 (D). The peak of the one-dimensional conductance histogram indicates that the most likely conductance of the molecular connection formed with ZL-05 and ZL-06 is about 10 before irradiation. -4.20 G0 and 10 -4.12 G0. With the increase of irradiation time, the possible conductivity of ZL-05 and ZL-06 increased to 10- 2.83 G0 and 10 -3.43 G0. As expected, the on-off ratios were calculated to be 23 and 4.9 based on the molecular conductance before and after irradiation. As shown in the two-dimensional conductance-distance histograms, the conductance plateaus of ZL-05 and ZL-06 shifted toward higher conductance values ​​with decreasing stretching length upon irradiation with 365 nm UV light, indicating that the conductance increase was due to the cleavage of the N-O bond during the photolysis process under UV irradiation. Therefore, a significant reduction in the length of the conductance plateau under UV irradiation can be expected due to the photolysis process of the oxime ester. The above conductance results indicate that the robust formation of the electrode-molecule bond formed by the spatially conjugated hexaphenylbenzene and the construction of the Au-N bonding reaction between the imine radical and the Au electrode enable reliable formation of single-molecule connections.

[0042] Example 5 Optimized structures of ZL-05 and ZL-06 and molecular frontier orbital analysis

[0043] To reveal the nature of the bond conformation and charge transport of the imino radical molecule based on the covalent Au-N bond of the hexaphenylbenzene anchoring group, theoretical simulations including density functional theory using Gaussian 16 and the Transiesta function of Siesta software were employed. Figure 4 - Figure 6 As shown, the six ring-shaped phenyl groups exhibit a face-to-face configuration around the central benzene, the electron distribution between the peripheral benzene rings dominates the frontier orbitals, and the molecular orbitals are distributed throughout the molecular skeleton, indicating more efficient charge transfer via spatial conjugation.

[0044] The above data show that the present invention synthesized a series of novel spatially conjugated organic molecules based on hexaphenylbenzene anchoring groups and applied them to organic single-molecule wires. Its unique spatial conjugated structure enables electrons to be transmitted not only along the valence bond conjugated channel, but also along the spatial conjugated channel, with multiple conductance channels. At the same time, imine radicals are believed to be able to bond with transition metals to produce the desired catalytic reaction. In view of these unique reactivities, the free imine radicals generated by the UV-induced N−O bond homolysis of the oxime ester precursor directly coordinate with gold atoms and form covalent Au−N bonds to form single-molecule connections.

[0045] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that the exemplary embodiments may be modified and other arrangements may be designed without departing from the spirit and scope of the present invention as defined by the appended claims.

Claims

1. A class of oxime ester spatially conjugated organic molecules based on hexaphenylbenzene anchor groups, with characteristic structures As shown below I-II: .

2. The imino radical molecule based on the covalent Au-N bond of the hexaphenylbenzene anchoring group according to claim 1, characterized in that: The imino radical molecule of the covalent Au-N bond based on the hexaphenylbenzene anchoring group of the present invention constructs a stable multi-transmission channel single-molecule device containing an anchoring group, and has the characteristics of spatial conjugation and valence bond conjugation, and has multiple transmission channels. At the same time, the molecule directly coordinates with the gold atom and forms a covalent Au-N bond to form a single-molecule connection through the free imino radical generated by the homolysis of the N-O bond of the oxime ester precursor induced by ultraviolet light.

3. According to the application of the imino radical molecule with covalent Au-N bond based on hexaphenylbenzene anchoring group in organic single-molecule wires according to claims 1-2, Au-S-oxime ester π bridge-hexaphenylbenzene-Au single-molecule wire constructed by STM-BJ technology.

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