Fullerene derivative, production method for fullerene derivative, thin film, photoelectric conversion element, and solid-state imaging device

Abstract

To provide a fullerene derivative that can be synthesized without using a special synthesis device and can be vapor-deposited at a low temperature without thermal decomposition.SOLUTION: A fullerene derivative according to the present invention has a partial structure represented by formula (1). (In the formula, the respective moieties represented by C* are adjacent carbon atoms constituting the fullerene skeleton, and n is 1 or 2.)SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a fullerene derivative that can be vapor-deposited at low temperatures, a method for producing a fullerene derivative, a thin film, a photoelectric conversion element, and a solid-state imaging device. [Background technology]

[0002] Fullerenes are molecules with a closed-shell structure made of carbon, and are used in a variety of fields due to their stable structure, high light absorption properties, and good electrical properties. In recent years, various fullerene derivatives in which substituents are bonded to fullerenes have also been developed. Meanwhile, photoelectric conversion elements are elements that convert light into an electrical signal using the photoelectric effect, and include photodiodes and phototransistors, and can be applied to electronic devices such as solid-state imaging devices. Therefore, in the development of photoelectric conversion elements, technologies using fullerenes or their derivatives that have high light absorption properties and good electrical properties have attracted attention, and the development of such elements has become a challenge.

[0003] For example, Patent Document 1 discloses a fullerene derivative that exhibits sublimation properties, in which a substituted or unsubstituted C3 to C20 branched alkyl group or a substituted or unsubstituted C1 to C20 alkyl group is bonded to a fullerene.

[0004] Patent Document 2 discloses a fullerene derivative having a structure in which any aromatic ring to which O, S, Se, Te or the like is bonded is bonded to a fullerene core.

[0005] Non-Patent Document 1 describes fullerene derivatives (C 60 CF2) and fullerene derivatives with multiple trifluoromethyl groups (C 60 (CF3)2, etc.) have been described. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-99570 [Patent Document 2] International Publication No. WO2021 / 149801 [Non-patent literature]

[0007] [Non-Patent Document 1] Brian J. Reeves et al., "Fluorous Fullerene Acceptors in Vacuum-Deposited Photovoltaic Cells" Solar RRL, 3,1900070, 2019 Summary of the Invention [Problem to be solved by the invention]

[0008] The fullerene derivative has a structure in which a pentagonal ring and an aromatic ring are substituted with each other, thereby increasing steric hindrance and reducing the pi-conjugated system compared to unsubstituted fullerenes.Compared to unsubstituted fullerenes, the fullerene derivative can reduce aggregation during deposition and improve film formation properties, thereby effectively reducing deformation of optical properties, such as deformation of the absorption wavelength range, which may occur due to aggregation.

[0009] However, many fullerene derivatives have the problem of thermal decomposition when heated for vapor deposition, and even those that are sublimable have problems such as the sublimation temperature being too high or being difficult to synthesize.

[0010] For example, the fullerene derivatives listed in Patent Document 1 have a relatively high sublimation temperature of 400° C. or higher, which is close to the decomposition temperature of the fullerene derivatives, making it difficult to stably vapor-deposit them.

[0011] The fullerene derivative having a trifluoromethyl group described in Non-Patent Document 1 has a low sublimation temperature of less than 400°C, but is not suitable for mass production because a special reaction apparatus is required for synthesis. Furthermore, the fullerene derivative having a difluoromethano structure disclosed in Non-Patent Document 1 has a high sublimation temperature and is therefore not practical.

[0012] One aspect of the present invention has been made in view of the above circumstances, and aims to provide a fullerene derivative that can be synthesized without using a special synthesis device and can be vapor-deposited at a low temperature without thermal decomposition. [Means for solving the problem]

[0013] In order to solve the above problems, the present invention has the following configuration. [1] A fullerene derivative having a partial structure represented by the following formula (1): [ka] (In the formula, C * are adjacent carbon atoms that form the fullerene skeleton, and n is 1 or 2. [2] The fullerene skeleton is C 60 , C 70 , C 74 , C 76 or C 78 The fullerene derivative according to [1], [3] The fullerene derivative according to [1] or [2], wherein n is 1. [4] The fullerene derivative according to any one of [1] to [3], wherein one partial structure represented by the formula (1) is present per fullerene skeleton. [5] Equation (2): [ka] (In the formula, C * are adjacent carbon atoms that form the fullerene skeleton, and n is 1 or 2. via an intermediate fullerene derivative having a partial structure represented by formula (1): [ka] (In the formula, C *are adjacent carbon atoms that form the fullerene skeleton, and n is 1 or 2. A method for producing a fullerene derivative, comprising producing a fullerene derivative having a partial structure represented by the formula: [6] A thin film comprising the fullerene derivative according to any one of the above items [1] to [3]. [7] The thin film according to [6], wherein the thin film is a vapor-deposited film. [8] A first electrode and a second electrode facing each other; an organic layer disposed between the first electrode and the second electrode; and The organic layer of the photoelectric conversion element comprises the fullerene derivative according to any one of [1] to [3]. [9] A solid-state imaging device having the photoelectric conversion element according to [8]. [Effects of the Invention]

[0014] The fullerene derivative according to one embodiment of the present invention can be synthesized without using a special synthesis device, and can be vapor-deposited at a low temperature at which thermal decomposition does not occur. DETAILED DESCRIPTION OF THE INVENTION

[0015] The following describes the configuration of an embodiment of the present invention. The present invention can be implemented by appropriately modifying it as long as the gist of the invention is not changed. In this specification, unless otherwise specified, the symbol "to" indicating a numerical range means that the numerical values ​​before and after it are included as the lower and upper limits.

[0016] [Fullerene derivatives] The fullerene derivative according to this embodiment is a compound having a partial structure represented by formula (1) in the fullerene skeleton.

[0017] [ka] (In the formula, C* represents adjacent carbon atoms forming a fullerene skeleton, and n is 1 or 2.)

[0018] In this embodiment, the term "fullerene derivative" refers to a compound having a structure in which a specific group is added to a fullerene skeleton, and the term "fullerene skeleton" refers to a carbon skeleton that constitutes a closed-shell structure derived from fullerene.

[0019] The fullerene skeleton in the fullerene derivative according to this embodiment is preferably one or more fullerene skeletons having a carbon number of 60 to 200. Specific examples of the fullerene skeleton include C 60 , C 70 , C 76 , C 78 , C 82 , C 84 , C 90 , C 94 , C 96 , C 120 , C 200 Among these, C 60 , C 70 , C 76 or C 78 is more preferred, and C 60 or C 70 It is more preferable that C 60 This is because the fullerene used as the raw material has a smaller number of carbon atoms, which makes it easier to obtain a product with a higher purity, and in particular, 60 This is because it is easier to obtain a higher purity fullerene than other fullerenes.

[0020] In the above formula (1), n ​​represents the number of trifluoromethyl groups, and is preferably 2 from the viewpoint of lowering the sublimation temperature, and is preferably 1 from the viewpoint of avoiding the complexity of synthesis and purification.

[0021] The fullerene derivative according to this embodiment has the above-described structure, which allows for a lower sublimation temperature. Therefore, deposition by sublimation is possible without decomposing the fullerene derivative. It is preferable that there are multiple partial structures represented by the above formula (1) per fullerene skeleton, from the viewpoint of lowering the sublimation temperature. However, it is preferable that there is only one partial structure per fullerene skeleton, from the viewpoint of avoiding the complexity of synthesis and purification.

[0022] Whether deposition by sublimation is possible can be confirmed simply by thermogravimetric analysis under vacuum. The results of thermogravimetric analysis of a fullerene derivative are compared with the results of thermogravimetric analysis of a fullerene corresponding to the fullerene skeleton of the fullerene derivative. If the temperature at which the fullerene derivative loses 10% of its initial weight before heating in thermogravimetric analysis is 400°C or lower, deposition is generally possible. If the temperature at which the fullerene derivative loses 50% of its initial weight is 400°C or lower, deposition is more reliably possible.

[0023] [Method of producing fullerene derivatives] The method for producing the fullerene derivative according to this embodiment is not particularly limited, and known production methods can be applied. The method for producing the fullerene derivative according to this embodiment may be a method for producing a fullerene derivative having a partial structure represented by the above formula (1) via a fullerene derivative having a desired partial structure as an intermediate. Examples of the method for producing the fullerene derivative according to this embodiment include the following methods.

[0024] That is, a fullerene and a compound represented by the following formula (3) are reacted with a nitrite ester in the presence of a base to obtain a fullerene derivative having a partial structure represented by the following formula (2) as an intermediate (first reaction).

[0025] [ka] (In formula (3), n is 1 or 2.)

[0026] Thereafter, a fullerene derivative having a partial structure represented by the following formula (2) is further reacted in the presence of an acid or an acid anhydride to obtain a fullerene derivative having a partial structure represented by the above formula (1) (second reaction).

[0027] [ka] (In formula (2), C *are adjacent carbon atoms that form the fullerene skeleton, and n is 1 or 2.

[0028] Here, the fullerene used in the first reaction preferably has a carbon number of 60 to 200. Specific examples include C 60 , C 70 , C 76 , C 78 , C 82 , C 84 , C 90 , C 94 , C 96 , C 120 , C 200 Among these, C 60 , C 70 , C 76 or C 78 is more preferred, and C 60 or C 70 It is more preferable that C 60 It is particularly preferred that:

[0029] A solvent may be used in the first reaction. The solvent is not particularly limited, but a liquid in which fullerene, the compound of formula (3) above, and the fullerene derivative of formula (2) above are dissolved is preferred. Examples of solvents include benzene, toluene, xylene, trimethylbenzene, chlorobenzene, and 1,2-dichlorobenzene. Among these, 1,2-dichlorobenzene is preferred because of its high solubility in fullerene and the compound of formula (3).

[0030] The base used in the first reaction is not particularly limited, but examples thereof include pyridine, quinoline, isoquinoline, 1,4-diazabicyclo[2.2.2]octane (DABCO), 4-dimethylaminopyridine (DMAP), triethylamine, triisopropylamine, 1,8-diazabicyclo[5.4.0]-7-undecene (DBU), 4-methylmorpholine (NMM), N,N,N',N'-tetramethylethylenediamine (TMEDA), sodium carbonate, sodium acetate, potassium hydroxide, disodium hydrogen phosphate, etc. Among these, DABCO, DMAP, triethylamine, triisopropylamine, DBU, NMM, and TMEDA are preferred, and triethylamine is more preferred, in terms of excellent reaction yield.

[0031] Examples of nitrites used in the first reaction include n-propyl nitrite, isopropyl nitrite, n-butyl nitrite, isobutyl nitrite, t-butyl nitrite, isoamyl nitrite, etc. Among these, isoamyl nitrite is preferred.

[0032] The higher the reaction temperature of the first reaction, the easier the reaction will proceed, while the lower the reaction temperature, the higher the reaction selectivity and the higher the yield of the target product. From this perspective, the reaction temperature of the first reaction may be selected depending on the purpose, but is usually selected between room temperature and the boiling point of the solvent used. If the reaction temperature is too low, the reaction will proceed slowly, and if the reaction temperature is too high, the reaction selectivity will decrease and the yield of the target product will decrease, so it is preferable to select a temperature between room temperature and 160°C.

[0033] Regarding the reaction time of the first reaction, in order to obtain a high yield, it is better to carry out the reaction for a long time until the reaction has progressed sufficiently, and in order to increase the production amount, it is better to complete one reaction in a short time before the reaction rate slows down and to repeat this one reaction multiple times. From this perspective, the reaction time of the first reaction may be selected depending on the purpose, but is usually selected between 1 minute and 120 hours. If the reaction time of the first reaction is too short, the reaction will not proceed sufficiently, and if the reaction time of the first reaction is too long, productivity will be poor. Therefore, it is more preferable to select between 5 minutes and 24 hours, and even more preferable to select between 30 minutes and 12 hours.

[0034] A solvent may also be used in the second reaction. The solvent is not particularly limited, but is preferably one that dissolves fullerene, the compound of formula (3) above, and the fullerene derivative of formula (2) above. Examples of solvents include benzene, toluene, xylene, trimethylbenzene, chlorobenzene, and 1,2-dichlorobenzene. Among these, 1,2-dichlorobenzene is preferred because of its high solubility in fullerene and the compound of formula (3).

[0035] The acid or acid anhydride in the second reaction is not particularly limited, and examples thereof include toluenesulfonic acid, methanesulfonic acid, trifluoromethanesulfonic acid, trifluoroacetic acid, toluenesulfonic anhydride, methanesulfonic anhydride, trifluoromethanesulfonic anhydride, trifluoroacetic anhydride, etc. Among these, trifluoromethanesulfonic acid and trifluoromethanesulfonic anhydride are preferred, and trifluoromethanesulfonic anhydride is more preferred, from the viewpoint of excellent reaction yield.

[0036] The higher the reaction temperature of the second reaction, the easier the reaction will proceed, while the lower the reaction temperature, the higher the reaction selectivity and the higher the yield of the target product. From this perspective, the reaction temperature of the second reaction may be selected depending on the purpose, but is usually selected between room temperature and the boiling point of the solvent used. If the reaction temperature is too low, the reaction will proceed slowly, and if the reaction temperature is too high, the reaction selectivity will decrease and the yield of the target product will decrease, so it is more preferable to select a temperature between 50°C and 160°C.

[0037] Regarding the reaction time of the second reaction, in order to obtain a high yield, it is better to carry out the reaction for a long time until the reaction has progressed sufficiently, and in order to increase the production amount, it is better to complete one reaction in a short time before the reaction rate slows down and to repeat this one reaction multiple times. From this perspective, the reaction time of the second reaction may be selected depending on the purpose, but is usually selected between 1 minute and 120 hours. If the reaction time of the second reaction is too short, the reaction will not proceed sufficiently, and if the reaction time of the second reaction is too long, productivity will be poor. Therefore, it is more preferable to select between 5 minutes and 24 hours, and even more preferable to select between 30 minutes and 12 hours.

[0038] The pressure during the reaction is not particularly limited, but the reaction can be carried out under pressure, for example, when the reaction is to be carried out at a temperature near or above the boiling point of the solvent. When pressurizing, the pressure is preferably between atmospheric pressure and 10 atmospheres. From the viewpoint of not requiring special equipment such as pressurizing equipment and being able to keep costs low, the reaction at atmospheric pressure is preferred.

[0039] As described above, the fullerene derivative according to this embodiment has a partial structure represented by the above formula (1) in the fullerene skeleton, which lowers the sublimation temperature, allowing it to be sublimated at a lower temperature and making it less susceptible to thermal decomposition, so that the fullerene derivative can be sublimated without decomposition. Furthermore, the fullerene derivative according to this embodiment can be synthesized without using a special reaction apparatus. Therefore, the fullerene derivative according to this embodiment can be synthesized without using a special reaction apparatus and can be vapor-deposited at a low temperature that does not cause thermal decomposition.

[0040] The fullerene derivative according to this embodiment can be synthesized without requiring a special synthesis device and can be sublimated at a low temperature without thermal decomposition, and therefore is useful as a fullerene derivative to be used when forming a film using a vapor deposition method.

[0041] [Thin Film] The thin film according to the present embodiment includes the fullerene derivative according to the present embodiment described above. The thin film may be formed by any method, such as a wet film formation method such as spin coating or slit coating, or a dry film formation method such as vapor deposition, but is preferably a vapor deposition film formed by vapor deposition.

[0042] The thin film may be composed solely of the fullerene derivative according to this embodiment, or may be composed in a state where it is mixed with other compounds, such as compounds generally used in organic layers of photoelectric conversion elements described later.

[0043] Since the decomposition of the fullerene derivative is suppressed during the film formation, the thin film is likely to maintain the inherent properties of the fullerene derivative. This prevents the aggregation of unsubstituted fullerenes (e.g., C 60 ) thin film, the optical properties can be improved, and further the properties of the photoelectric conversion element and solid-state imaging device described later can also be improved.

[0044] The light absorption characteristics of the thin film are particularly reduced in the visible light region of about 400 nm to 500 nm compared to the light absorption characteristics of a thin film containing unsubstituted fullerene. For example, the absorption coefficient of the thin film at a wavelength of 450 nm is smaller than the absorption coefficient of the thin film containing unsubstituted fullerene at a wavelength of 450 nm, for example, the absorption coefficient of the thin film at a wavelength of 450 nm is about half or less of the absorption coefficient of the thin film containing unsubstituted fullerene at a wavelength of 450 nm.

[0045] [Photoelectric conversion element] The photoelectric conversion element according to this embodiment has a first electrode and a second electrode facing each other, and an organic layer disposed between the two electrodes. The organic layer contains the fullerene derivative according to this embodiment, represented by the above formula (1). The organic layer may also contain other compounds in addition to the above fullerene derivative. The first electrode and the second electrode are not particularly limited, and known materials can be used. The photoelectric conversion element according to this embodiment is not particularly limited in structure, and may have a general element structure, as long as it has the above characteristics.

[0046] [Solid-state imaging device] The solid-state imaging device (image sensor) according to this embodiment includes one or more photoelectric conversion elements according to this embodiment. The solid-state imaging device is applicable to various electronic devices, such as, but not limited to, mobile phones and digital cameras.

[0047] Although each embodiment has been described above, the above embodiments are presented as examples, and the present invention is not limited to the above embodiments. The above embodiments can be embodied in various other forms, and various combinations, omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as set forth in the claims. [Example]

[0048] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples.

[0049] (Synthesis Example 1) Synthesis of Compound 1a Under a nitrogen atmosphere, 60Compound 2a (360 mg, 0.5 mmol) was dissolved in 1,2-dichlorobenzene (30 mL), and 2-amino-4-trifluoromethylbenzoic acid (513 mg, 2.5 mmol), triethylamine (304 mg, 3 mmol), and isoamyl nitrite (351 mg, 3 mmol) were added to the 1,2-dichlorobenzene solution. The mixture was then reacted at 60 °C for 4 hours. After the reaction, the reaction mixture was purified using a silica gel column (eluent: 1,2-dichlorobenzene). The solvent was removed by distillation, and the resulting solid was washed with methanol and dried to obtain compound 2a (140 mg) as a brown powder. Compound 2a (45 mg, 0.05 mmol) was then placed in a pressure-resistant glass sealed vessel and dissolved in 1,2-dichlorobenzene (5 mL). Trifluoromethanesulfonic acid (42 mg, 0.15 mmol) was added, and the vessel was sealed and reacted at 120 °C for 5 hours. After the reaction, the reaction mixture was purified by preparative HPLC (column: COSMOSIL PBB (inner diameter 20 mm, length 250 mm) manufactured by Nacalai Tesque, eluent: toluene), the solvent was distilled off, and the resulting solid was washed with methanol and dried to obtain compound 1a (15 mg) as a brown powder.

[0050] [ka]

[0051] [ka]

[0052] (Synthesis Example 2) Synthesis of Compound 1b The same procedure as in Synthesis Example 1 was carried out except that 2-amino-5-trifluoromethylbenzoic acid was used instead of 2-amino-4-trifluoromethylbenzoic acid, to obtain compound 2b (127 mg) as an intermediate product in the form of a brown powder, and further obtain compound 1b (17 mg) as the target product in the form of a brown powder.

[0053] [ka]

[0054] [ka]

[0055] (Example 1-1) Thermogravimetric analysis was performed in a vacuum to confirm whether compound 1a could be deposited by sublimation and to determine the sublimation temperature. A sample (approximately 5 mg) was placed in a thermogravimetric analyzer (TG-DTA8122, manufactured by Rigaku Corporation). The sample was heated from room temperature to 1000°C at a rate of 10°C / min in a vacuum of 1 Pa or less. The temperature at which the sample's weight decreased by 10% of the initial weight was defined as Ts (°C) (-10 wt%), and the temperature at which the sample's weight decreased by 50% was defined as Ts (°C) (-50 wt%). The measurement results are shown in Table 1.

[0056] (Example 1-2 and Comparative Examples 1-1 to 1-2) Thermogravimetric analysis was carried out in the same manner as in Example 1, except that the compounds shown in Table 1 were used instead of compound 1a. Comparative compound 1 used in Comparative Example 1-1 was produced by the production method disclosed in the above-mentioned Patent Document 2. The measurement results are shown in Table 1.

[0057] [ka]

[0058] [Table 1]

[0059] As can be seen from Table 1, Examples 1-1 and 1-2 had lower Ts (°C) (-10 wt%) and Ts (°C) (-50 wt%) than Comparative Examples 1-1 and 1-2. Therefore, the fullerene derivative according to this embodiment has a lower Ts (°C) (-10 wt%) and Ts (°C) (-50 wt%) than unsubstituted fullerene C 60 It was found that it can be sublimated at a lower temperature and is less likely to be decomposed by heat compared to the fullerene derivative (Comparative Example 1-1) and the fullerene derivative (Comparative Example 1-2) that has been known to sublimate. [Industrial Applicability]

[0060] The fullerene derivative according to this embodiment can be preferably used for film formation by vapor deposition.

Claims

1. A fullerene derivative having a partial structure represented by the following formula (1): 【Chemical 1】 (In the formula, C ＊ are adjacent carbon atoms forming a fullerene skeleton, and n is 1 or 2.

2. The fullerene skeleton is C ６０ , C ７０ , C ７４ , C ７６ or C ７８ 2. The fullerene derivative according to claim 1, wherein

3. 3. The fullerene derivative according to claim 1, wherein n is 1.

4. 2. The fullerene derivative according to claim 1, wherein the partial structure represented by formula (1) is present in one per fullerene skeleton.

5. Formula (2): 【Chemistry 2】 (In the formula, C ＊ are adjacent carbon atoms forming a fullerene skeleton, and n is 1 or 2. via an intermediate fullerene derivative having a partial structure represented by formula (1): 【Chemistry 3】 (In the formula, C ＊ are adjacent carbon atoms forming a fullerene skeleton, and n is 1 or 2. A method for producing a fullerene derivative, comprising producing a fullerene derivative having a partial structure represented by the formula:

6. A thin film comprising the fullerene derivative according to claim 1 .

7. The thin film according to claim 6, wherein the thin film is a vapor-deposited film.

8. a first electrode and a second electrode facing each other; an organic layer disposed between the first electrode and the second electrode; and The photoelectric conversion element, wherein the organic layer comprises the fullerene derivative according to claim 1 .

9. A solid-state imaging device comprising the photoelectric conversion element according to claim 8.

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