JP7523390B2 - Boron chelate compound, near-infrared light absorbing material, thin film, photoelectric conversion element, and image pickup element - Google Patents

Description

The present invention relates to a novel compound having a boron chelate structure, a photoelectric conversion element, an optical sensor, and an imaging element. In particular, the present invention relates to a photoelectric conversion element having a main absorption band in the near-infrared region and the use thereof.

Near-infrared light absorbing materials having an absorption band in the wavelength region of 700 to 2,500 nm are used in various applications, such as optical information recording media such as CD-R (Compact Disk-Recordable); printing applications such as thermal CTP (Computer To Plate), flash toner fixing, and laser thermal recording; and heat shielding films. In addition, by utilizing the property of selectively absorbing light in a specific wavelength range, they are also used in near-infrared light cut filters used in PDPs (Plasma Display Panels) and films for regulating plant growth. Furthermore, printed matter using near-infrared light absorbing ink in which a near-infrared light absorbing pigment is dissolved or dispersed in a solvent is difficult to recognize visually and can only be read with a near-infrared light detector, etc., and is therefore used, for example, in printed matter for the purpose of preventing counterfeiting.

Unlike ultraviolet light or X-rays, near-infrared light is safe light that has almost no adverse effects on the human body, and in particular in the wavelength range of 700 to 1,400 nm, known as the "biological window" through which it passes through living organisms, it can image invisible information within the body without being affected by hemoglobin or water. Furthermore, by using near-infrared light with a wavelength of over 1,000 nm, it can be used to diagnose foreign objects in the food and agricultural fields and to observe defects in silicon wafers.

Known near-infrared light absorbing materials for forming such invisible images include inorganic and organic materials. Silicon, a representative inorganic near-infrared light absorbing material, has an absorption band not only for visible light but also in the near-infrared light region of about 780 to 950 nm, and sensors utilizing this material are in widespread use.
On the other hand, silicon does not have a light absorption band at wavelengths of 1,000 nm or more, so in the development of sensors that utilize near-infrared light with wavelengths of more than 1,000 nm, compound semiconductors such as indium gallium arsenide (InGaAs) are used as near-infrared absorbing materials. However, these inorganic materials generally have low light absorption ability in the near-infrared region, and a large amount of infrared absorbing material per unit area is required to form an invisible image. Therefore, when a visible image is further formed on an invisible image formed using an inorganic infrared absorbing material, there is a problem in that the unevenness of the invisible image surface affects the surface shape of the visible image.

In contrast, organic near-infrared light absorbing materials have a high absorption capacity for light in the near-infrared region, and invisible images can be formed with a small amount of near-infrared light absorbing material per unit area, so there are no inconveniences that arise when inorganic near-infrared light absorbing materials are used. In addition, the molecular structure of organic near-infrared light absorbing materials can be flexibly designed, making it possible to create materials that have an absorption band at the target light wavelength, thereby suppressing interference from light of unnecessary wavelengths. For this reason, many organic near-infrared light absorbing materials have been investigated to date.

If an organic material that efficiently absorbs near-infrared light could be developed, the range of applications for electronic devices that utilize near-infrared light as described above would be expanded. For this reason, organic near-infrared light absorbing materials must have a sufficient absorption band in the near-infrared region, and must also be sufficiently robust to withstand the temperatures (usually 120 to 180°C) required for processes such as electrode formation and introduction of semiconductor encapsulation layers during the manufacture of organic electronic devices. However, cyanine dyes, squarylium dyes, and diimmonium dyes that exhibit absorption bands in the near-infrared region all have poor robustness, and their applications are limited.

In this situation, in recent years, research has been actively conducted on boron-dipyrromethene (BODIPY) compounds that exhibit an absorption band in the near-infrared wavelength region. Non-Patent Documents 1 and 2 describe that dibenzoBODIPY compounds, in which a benzene ring is fused to the pyrrole ring of the BODIPY skeleton, exhibit an absorption band that is shifted to longer wavelengths than non-fused BODIPY compounds, and that a further longer wavelength shift can be achieved by forming a fused ring structure through B-O chelation. Patent Document 1 describes that the compound can be used as a near-infrared light absorbing material in optical recording media. Patent Documents 2 to 4 also report on organic thin films using compounds with such fused ring structures.

Furthermore, Patent Document 5 describes a near-infrared light absorbing dye that exhibits photoelectric conversion properties in light with wavelengths of 900 nm or more and is capable of sublimation deposition. However, the dye has low photoelectric conversion properties in light with wavelengths of over 1,000 nm, and the absorption wavelengths of near-infrared light are limited, so its use as a photoelectric conversion material for imaging elements and optical sensors is limited. Therefore, there is a demand for the development of a near-infrared photoelectric conversion material that exhibits high light absorption and photoelectric conversion properties even at wavelengths of over 1,000 nm.

JP 1999-255774 A JP 2012-199541 A JP 2016-166284 A International Publication No. 2013/035303 International Publication No. 2020/162345

Chem. Soc. Rev. , 2014, 43, 4778-4823 Chem. Rev. , 2007, 107, 4891-4932

The object of the present invention is to provide a compound, an organic thin film, and a photoelectric conversion element that have high thermal stability, have a main absorption band in the near-infrared light region of 900 nm or more that can be easily used in organic electronics devices, and exhibit high photoelectric conversion properties even in the wavelength region exceeding 1,000 nm.

As a result of investigations aimed at solving the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by using a BODIPY compound having a specific structure, and have thus completed the present invention.
That is, the present invention provides:
[1] The following general formula (1)

(in formula (1), R ¹ to R ⁴ each independently represent a hydrogen atom, an alkyl group, an aromatic hydrocarbon group, a heterocyclic group, or a halogen atom; m represents an integer of 1 to 3; and A represents a benzene ring or a naphthalene ring),
[2] The compound according to the above item [1], wherein at least one of R ¹ to R ⁴ is an alkyl group, an aromatic hydrocarbon group, a heterocyclic group, or a halogen atom.
[3] The compound according to the above item [2], wherein at least one of R ¹ to R ⁴ is a halogen atom.
[4] The compound according to the above item [2], wherein at least two of R ¹ to R ⁴ are an aromatic hydrocarbon group or a halogen atom.
[5] The compound according to any one of the above items [1] to [4], wherein A is a benzene ring.
[6] A near-infrared light absorbing material comprising the compound according to any one of the preceding items [1] to [5].
[7] An organic thin film comprising the compound according to any one of the preceding items [1] to [5].
[8] A photoelectric conversion element comprising the organic thin film according to the preceding item [7].
[9] An optical sensor including the photoelectric conversion element according to the preceding item [8]; and [10] an imaging element including the photoelectric conversion element according to the preceding item [8].
Regarding.

An organic thin film containing the novel compound of the present invention has a main absorption band in the near-infrared light region. Furthermore, by using the compound and/or the thin film, a near-infrared photoelectric conversion element can be realized. The compound can be used in various organic electronic devices.

FIG. 1 is a cross-sectional view illustrating an embodiment of the photoelectric conversion element of the present invention. FIG. 2 shows the results of measuring the absorption spectrum of an organic thin film obtained using the compound of the present invention.

The present invention will be described in detail below. The description of the constituent elements described herein is based on representative embodiments and specific examples of the present invention, but the present invention is not limited to such embodiments and specific examples. In this specification, the near-infrared region means a wavelength region of light within the range of 750 to 2500 nm, and the near-infrared light absorbing material means a material that has a main absorption band in the near-infrared light region.

The compound of the present invention is represented by the following formula (1):

In formula (1), R ¹ to R ⁴ each independently represent a hydrogen atom, an alkyl group, an aromatic hydrocarbon group, a heterocyclic group, or a halogen atom.

The alkyl group represented by R ¹ to R ⁴ in formula (1) is not limited to any of linear, branched, and cyclic alkyl groups, and preferably has 1 to 20 carbon atoms, and more preferably has 1 to 10 carbon atoms.
Specific examples of the alkyl group represented by R ¹ to R ⁴ in formula (1) include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an iso-butyl group, a t-butyl group, an n-pentyl group, an n-hexyl group, an n-octyl group, an n-decyl group, an n-dodecyl group, an n-tridecyl group, an n-tetradecyl group, an n-cetyl group, an n-heptadecyl group, a 2-ethylhexyl group, a 3-ethylheptyl group, a 4-ethyloctyl group, a 2-butyloctyl group, a 3-butylnonyl group, a 4-butyldecyl group, a 2-hexyldecyl group, a 3-octylundecyl group, a 4-octyldodecyl group, a 2-octyldodecyl group, a 2-decyltetradecyl group, a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. The alkyl groups represented by R ¹ to R ⁴ in formula (1) may have a substituent, and the substituent that may be had is not particularly limited.
The alkyl group represented by R ¹ to R ⁵ in formula (1) is preferably a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, an n-pentyl group, an n-hexyl group, a 2-ethylhexyl group, or a cyclohexyl group, and more preferably a methyl group, an ethyl group, a t-butyl group, or a cyclohexyl group.

The aromatic hydrocarbon group represented by R ¹ to R ⁴ in formula (1) is a residue in which one hydrogen atom has been removed from the aromatic ring of an aromatic hydrocarbon compound, and specific examples thereof include a phenyl group, a biphenyl group, a tolyl group, an indenyl group, a naphthyl group, an anthryl group, a fluorenyl group, a pyrenyl group, a phenanthenyl group, and a mestyl group, etc. The aromatic hydrocarbon group represented by R ¹ to R ⁴ in formula (1) may have a substituent, and the substituent that may be had is not particularly limited.
The aromatic hydrocarbon group represented by R ¹ to R ⁴ in formula (1) is preferably a phenyl group, a biphenyl group, a naphthyl group, a tolyl group or a mestyl group, more preferably a phenyl group or a tolyl group.

The heterocyclic group represented by ^R1 to ^R4 in formula (1) is a residue obtained by removing one hydrogen atom from a heterocyclic ring of a heterocyclic compound, and specific examples thereof include a furanyl group, a thienyl group, a thienothienyl group, a pyrrolyl group, an imidazolyl group, a thiazolyl group, an oxazolyl group, a pyridyl group, a pyrazyl group, a pyrimidyl group, an indolyl group, a benzopyrazyl group, a benzopyrimidyl group, a benzothienyl group, a benzothiazolyl group, a pyridinothiazolyl group, a benzimidazolyl group, a pyridinoimidazolyl group, a benzoxazolyl group, a pyridinooxazolyl group, a benzothiadiazolyl group, a pyridinothiadiazolyl group, a benzoxadiazolyl group, a pyridinooxadiazolyl group, a carbazolyl group, a phenoxazinyl group, and a phenothiazinyl group. The heterocyclic group represented by R ¹ to R ⁴ in formula (1) may have a substituent, and the substituent that may be had is not particularly limited.
The heterocyclic group represented by R ¹ to R ⁴ in formula (1) is preferably a thienyl group, a thienothienyl group, a pyrrolyl group, a pyridyl group, a pyrazyl group or a benzothienyl group, more preferably a thienyl group, a pyridyl group or a benzothienyl group.

Examples of the halogen atom represented by R ¹ to R ⁴ in formula (1) include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom or a chlorine atom is preferable.
It is preferable that ^R1 to ^R4 in formula (1) are all hydrogen atoms, or that ^R1 and ^R4 are hydrogen atoms, one of ^R2 and ^R3 is a hydrogen atom, an alkyl group, an aromatic hydrocarbon group, a heterocyclic group or a halogen atom, and the other is an alkyl group, an aromatic hydrocarbon group, a heterocyclic group or a halogen atom, and it is more preferable that ^R1 to R4 are all hydrogen atoms, or that R1 and ^R4 are hydrogen atoms, one of ^R2 and ^R3 is a hydrogen atom, an aromatic hydrocarbon group or a halogen atom, and the other is an aromatic hydrocarbon group or a halogen atom.

In formula (1), m represents an integer of 1 to 3, preferably 1 or 2.

In formula (1), A represents a benzene ring or a naphthalene ring. The benzene ring or the naphthalene ring represented by A may have a substituent, and the substituent is not particularly limited, but the substituent is preferably an aromatic hydrocarbon group, a heterocyclic group, or a halogen atom, and more preferably a halogen atom.
In formula (1), A is preferably a benzene ring, and more preferably an unsubstituted benzene ring.

Next, a method for synthesizing the compound of the present invention will be described. The compound represented by formula (1) can be synthesized, for example, by the synthesis method shown in the following scheme. First, a hydroxythiophene compound represented by formula (S-1) is methylated using methyl iodide to obtain a methoxythiophene intermediate represented by formula (M-1). Then, a hydrazide intermediate represented by formula (M-2) is obtained by reaction with hydrazine monohydrate. The intermediate represented by formula (M-2) and an acetophenone derivative represented by formula (S-2) are dehydrated and condensed to obtain a hydrazone intermediate represented by formula (M-3). Then, a diketone intermediate represented by formula (M-4) is obtained by a denitrogenation rearrangement reaction using iodobenzene diacetate, and the intermediate (M-4) is treated with ammonium acetate to obtain a dipyrromethene intermediate represented by formula (M-5). Finally, an intramolecular B-O bond is formed by deprotecting the methyl group on the hydroxyl group, and the compound represented by formula (1) can be synthesized. The starting compounds represented by formula (S-1) and formula (S-2) can be synthesized by using known methods.
In the following synthesis scheme, R ¹ to R ⁴ , m and A have the same meanings as R ¹ to R ⁴ , m and A in formula (1).

Specific examples of compounds represented by formula (1) are shown below, but the present invention is not limited to these. Note that the structural formulas shown as specific examples merely represent one of the resonance structures, and are not limited to the resonance structures shown.

The near-infrared light absorbing material of the present invention contains the compound represented by the above formula (1).
The content of the compound represented by formula (1) in the near-infrared light absorbing material of the present invention is not particularly limited as long as the near-infrared light absorbing ability required for the application of the near-infrared light absorbing material is exhibited, but is usually 50 mass % or more, preferably 80 mass % or more, more preferably 90 mass % or more, and even more preferably 95 mass % or more.
The near-infrared light absorbing material of the present invention may be used in combination with a compound other than the compound represented by formula (1) (e.g., a near-infrared light absorbing material (dye) other than the compound represented by formula (1)), an additive, etc. The compound, additive, etc. that can be used in combination are not particularly limited as long as they exhibit the near-infrared light absorbing ability required for the application in which the near-infrared light absorbing material is used.

The organic thin film of the present invention contains the compound represented by the above formula (1).
The organic thin film of the present invention can be prepared by a general dry film formation method or wet film formation method, specifically, a vacuum process such as resistance heating deposition, electron beam deposition, sputtering, and molecular lamination method, a solution process such as casting, spin coating, dip coating, blade coating, wire bar coating, and spray coating, a printing method such as inkjet printing, screen printing, offset printing, and letterpress printing, and a soft lithography method such as microcontact printing method can be mentioned.
In order to form organic thin films of general near-infrared absorbing materials, a process in which the compound is applied in a solution state is desirable from the viewpoint of ease of processing. From this viewpoint, it is desirable to develop organic materials with high solubility that can be adapted to solution processing.

On the other hand, in the case of organic electronic devices in which organic films are laminated, it is often difficult to select solvent conditions in which the coating solution does not attack the underlying organic film. In order to realize such a laminated structure, it is appropriate to use a material that can be evaporated and can be used in a dry film formation method, such as resistance heating evaporation. Therefore, near-infrared light absorbing materials that have a main absorption wavelength in the near-infrared region and can be evaporated are preferable for use as organic electronic materials.

When stacking organic films, a combination of the above techniques may be used to form each layer. The thickness of each layer cannot be limited because it depends on the resistance and charge mobility of each material, but it is usually in the range of 0.5 to 5,000 nm, preferably in the range of 1 to 1,000 nm, and more preferably in the range of 5 to 500 nm.

When it is intended to use an organic layer containing the compound represented by formula (1) formed by deposition, the molecular weight of the compound represented by formula (1) is preferably 1,500 or less, more preferably 1,200 or less, and even more preferably 1,000 or less. The lower limit of the molecular weight is the minimum molecular weight that formula (1) can have.
The compound represented by formula (1) may be formed into a film by a coating method regardless of the molecular weight. If a coating method is used, even a compound having a relatively large molecular weight can be formed into a film.
In this specification, the molecular weight refers to a value calculated by EI-GCMS method.

[Photoelectric conversion element]
The compound represented by the above formula (1) is a compound having near-infrared light absorption properties, and therefore is suitable for use in near-infrared photoelectric conversion elements. In particular, the compound represented by the above formula (1) can be used in the photoelectric conversion layer in the photoelectric conversion element of the present invention. In the element, it is preferable that the material has sufficient light absorption properties and photoelectric conversion properties for the light wavelength of the light source. The wavelength region of the irradiation light used as the light source is preferably 800 to 1,400 nm, more preferably 900 to 1,400 nm, and even more preferably 1,000 to 1,400 nm. Here, examples of near-infrared photoelectric conversion elements include near-infrared light sensors, organic imaging elements, and near-infrared light image sensors.
In this specification, the maximum absorption of an absorption band means a wavelength value at which the absorbance is maximum in an absorbance spectrum measured by absorption spectrometry, and the maximum absorption wavelength (λmax) means the maximum absorption on the longest wavelength side among the maximum absorptions.

A photoelectric conversion element is an element in which a photoelectric conversion section (film) is arranged between a pair of opposing electrode films, and light is incident on the photoelectric conversion section from above the electrode film. The photoelectric conversion section generates electrons and holes in response to the incident light, and a signal corresponding to the charge is read out by a semiconductor, indicating the amount of incident light corresponding to the absorption wavelength of the photoelectric conversion film section. A transistor for reading may be connected to the electrode film on the side where light is not incident. In addition, if a photoelectric conversion element arranged closer to the light source does not block (transmits) the absorption wavelength of a photoelectric conversion element arranged behind it when viewed from the light source side, multiple photoelectric conversion elements may be stacked and used.

The photoelectric conversion element of the present invention uses the compound represented by the formula (1) as a constituent material of the photoelectric conversion section.
The photoelectric conversion part is often composed of a photoelectric conversion layer and one or more organic thin film layers other than the photoelectric conversion layer selected from the group consisting of an electron transport layer, a hole transport layer, an electron blocking layer, a hole blocking layer, a crystallization prevention layer, and an interlayer contact improving layer. The compound represented by formula (1) of the present invention can be used for other purposes than the photoelectric conversion layer, but is preferably used as an organic thin film layer of the photoelectric conversion layer. The photoelectric conversion layer may be composed only of the compound represented by formula (1), but may also contain a known near-infrared light absorbing material or other materials in addition to the compound represented by formula (1).

The electrode film used in the photoelectric conversion element of the present invention plays a role of extracting holes from the photoelectric conversion layer and other organic thin film layers and collecting them when the photoelectric conversion layer contained in the photoelectric conversion unit described later has hole transport properties or when an organic thin film layer other than the photoelectric conversion layer is a hole transport layer having hole transport properties, and plays a role of extracting electrons from the photoelectric conversion layer and other organic thin film layers and discharging them when the photoelectric conversion layer contained in the photoelectric conversion unit has electron transport properties or when the organic thin film layer is an electron transport layer having electron transport properties. Therefore, the material that can be used as the electrode film is not particularly limited as long as it has a certain degree of conductivity, but it is preferable to select it in consideration of the adhesion to the adjacent photoelectric conversion layer and other organic thin film layers, electron affinity, ionization potential, stability, etc. Examples of materials that can be used as the electrode film include conductive metal oxides such as tin oxide (NESA), indium oxide, indium tin oxide (ITO) and indium zinc oxide (IZO); metals such as gold, silver, platinum, chromium, aluminum, iron, cobalt, nickel and tungsten; inorganic conductive substances such as copper iodide and copper sulfide; conductive polymers such as polythiophene, polypyrrole and polyaniline; and carbon. These materials may be used in combination as necessary, or electrode films made of different materials may be stacked in two or more layers. The conductivity of the material used for the electrode film is not particularly limited as long as it does not unnecessarily hinder the light reception of the photoelectric conversion element, but it is preferable that it is as high as possible from the viewpoint of the signal strength and power consumption of the photoelectric conversion element. For example, an ITO film having a sheet resistance value of 300 Ω/□ or less functions sufficiently as an electrode film, but since commercially available products with an ITO film having a conductivity of about several Ω/□ are also available, it is desirable to use a substrate having such a high conductivity. The thickness of the ITO film (electrode film) can be selected as desired, taking into account electrical conductivity, but is usually about 5 to 500 nm, and preferably about 10 to 300 nm. Methods for forming films such as ITO include conventionally known deposition methods, electron beam methods, sputtering methods, chemical reaction methods, and coating methods. The ITO film provided on the substrate may be subjected to UV-ozone treatment, plasma treatment, etc., as necessary.

Examples of materials for the transparent electrode film used on at least one of the sides where light is incident include ITO, IZO, _SnO2 , ATO (antimony-doped tin oxide), ZnO, AZO (Al-doped zinc oxide), GZO (gallium-doped zinc oxide), _TiO2 , FTO (fluorine-doped tin oxide), etc. The transmittance of light incident through the transparent electrode film at the absorption peak wavelength of the photoelectric conversion layer is preferably 60% or more, more preferably 80% or more, and particularly preferably 95% or more.

When multiple photoelectric conversion layers with different wavelengths to be detected are stacked, the electrode film (other than the pair of electrode films described above) used between each photoelectric conversion layer must transmit light other than the light having the wavelength detected by each photoelectric conversion layer, and it is preferable to use a material for the electrode film that transmits 90% or more of the incident light, and it is more preferable to use a material that transmits 95% or more of the light.

The electrode film is preferably produced in a plasma-free manner. By producing these electrode films in a plasma-free manner, the effect of plasma on the substrate on which the electrode film is provided is reduced, and the photoelectric conversion characteristics of the photoelectric conversion element can be improved. Here, plasma-free means a state in which no plasma is used when forming the electrode film, or the distance from the plasma generation source to the substrate is 2 cm or more, preferably 10 cm or more, and more preferably 20 cm or more, thereby reducing the amount of plasma that reaches the substrate.

Examples of devices that do not use plasma when forming an electrode film include electron beam deposition devices (EB deposition devices) and pulsed laser deposition devices. The method of forming a transparent electrode film using an EB deposition device is called the EB deposition method, and the method of forming a transparent electrode film using a pulsed laser deposition device is called the pulsed laser deposition method.

Examples of devices that can achieve a state in which plasma can be reduced during film formation include a facing target sputtering device and an arc plasma deposition device.

When a transparent conductive film is used as an electrode film (for example, a first conductive film), DC shorts or an increase in leakage current may occur. One of the reasons for this is thought to be that fine cracks that occur in the photoelectric conversion layer are covered by a dense film such as TCO (Transparent Conductive Oxide), which increases the conductivity between the electrode film (second conductive film) on the opposite side of the first conductive film. Therefore, when a material with inferior film quality such as Al is used for the electrode, the increase in leakage current is unlikely to occur. The increase in leakage current can be suppressed by controlling the film thickness of the electrode film according to the film thickness (depth of the crack) of the photoelectric conversion layer.

Normally, when the conductive film is made thinner than a predetermined thickness, a sudden increase in resistance occurs. The sheet resistance of the conductive film in the photoelectric conversion element for photosensors, which is one of the present embodiments, is usually 100 to 10,000 Ω/□, and the film thickness can be set appropriately. Furthermore, the thinner the transparent conductive film, the less light it absorbs, and generally the higher the light transmittance. Higher light transmittance is highly preferable because it increases the amount of light absorbed by the photoelectric conversion layer and improves the photoelectric conversion ability.

The photoelectric conversion section of the photoelectric conversion element of the present invention may include a photoelectric conversion layer and an organic thin film layer other than the photoelectric conversion layer. An organic semiconductor film is generally used for the photoelectric conversion layer constituting the photoelectric conversion section, but the organic semiconductor film may be one layer or multiple layers. In the case of a single layer, a p-type organic semiconductor film, an n-type organic semiconductor film, or a mixed film thereof (bulk heterostructure) is used. On the other hand, in the case of multiple layers, the number of layers is about 2 to 10, and it is a structure in which either a p-type organic semiconductor film, an n-type organic semiconductor film, or a mixed film thereof (bulk heterostructure) is laminated, and a buffer layer may be inserted between the layers. In addition, when the photoelectric conversion layer is formed from the above-mentioned mixed film, it is preferable to use the compound represented by formula (1) of the present invention as a p-type semiconductor material and a general fullerene or its derivative as an n-type semiconductor material.

In the photoelectric conversion element of the present invention, the organic thin film layer other than the photoelectric conversion layer constituting the photoelectric conversion section is used as a layer other than the photoelectric conversion layer, for example, an electron transport layer, a hole transport layer, an electron blocking layer, a hole blocking layer (hereinafter, the electron blocking layer and the hole blocking layer are also collectively referred to as "carrier blocking layers"), a crystallization prevention layer, or an interlayer contact improvement layer. In particular, by using it as one or more thin film layers selected from the group consisting of an electron transport layer and a hole transport layer, it is preferable to obtain an element that efficiently converts even weak light energy into an electrical signal.

In addition, in imaging devices, it is generally thought that the aim is to improve performance by reducing dark current in order to achieve high contrast and power saving, so a method of inserting a carrier block layer into the layer structure is preferable. These carrier block layers are commonly used in the field of organic electronics devices, and each has the function of controlling the reverse movement of holes or electrons in the constituent films of the device.

The electron transport layer transports electrons generated in the photoelectric conversion layer to the electrode film and blocks the movement of holes from the electrode film to which the electrons are transported to the photoelectric conversion layer. The hole transport layer transports generated holes from the photoelectric conversion layer to the electrode film and blocks the movement of electrons from the electrode film to which the holes are transported to the photoelectric conversion layer. The electron blocking layer prevents the movement of electrons from the electrode film to the photoelectric conversion layer, prevents recombination within the photoelectric conversion layer, and reduces dark current. The hole blocking layer prevents the movement of holes from the electrode film to the photoelectric conversion layer, prevents recombination within the photoelectric conversion layer, and reduces dark current.

Figure 1 shows a typical element structure of the photoelectric conversion element of the present invention, but the present invention is not limited to this structure. In the embodiment example of Figure 1, 1 represents an insulating part, 2 represents one electrode film (upper electrode film), 3 represents an electron blocking layer, 4 represents a photoelectric conversion layer, 5 represents a hole blocking layer, 6 represents the other electrode film (lower electrode film), and 7 represents an insulating substrate or another organic photoelectric conversion element. Although a readout transistor is not shown in the figure, it is sufficient that it is connected to the electrode film of 2 or 6, and further, if the photoelectric conversion layer 4 is transparent, it may be formed on the outside of the electrode film on the side opposite to the side where light is incident. The incidence of light on the organic photoelectric conversion element may be from either the top or bottom, as long as the components other than the photoelectric conversion layer 4 do not excessively inhibit the incidence of light of the main absorption wavelength of the photoelectric conversion layer.

A photoelectric conversion element equipped with such a photoelectric conversion unit can be used as an optical sensor because it can read out, as a signal, an electric charge that corresponds to the amount of light absorbed by the wavelength irradiated from the light source of the photoelectric conversion unit. In particular, an example of its use as a near-infrared optical sensor is the observation of in vivo information using fluorescent substances.

In addition, in the above optical sensor, when a large number of photoelectric conversion elements are arranged in an array, it is possible to obtain information on the incident position in addition to the amount of incident light, and therefore it can be used as an imaging element. The reflected light of light irradiated onto the detection body from a light source arranged on the same side as the photoelectric conversion element, or the transmitted light of light irradiated onto the detection body from a light source arranged on the opposite side to the photoelectric conversion element, is simultaneously read out as an electrical signal by a light receiving section including the photoelectric conversion element to obtain the amount of received light and the position information, thereby becoming an imaging element. An imaging element that uses near-infrared light as a light source can be used for observing veins in living organisms and diagnosing foreign bodies in the food and agricultural fields.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The structures of the compounds described in the synthesis examples were determined by mass spectrometry and nuclear magnetic resonance spectrometry (NMR) as necessary. The molecular weights in the examples were measured using an ISQ LT GC-MS (Thermo Fisher Scientific), and the absorption spectra were measured using a UV-1700 (Shimadzu Corporation). The applied current and voltage measurements of the organic photoelectric conversion element were performed using a PVL-3300 (Asahi Spectroscopy) under irradiation conditions of an irradiation light intensity of 130 μW and a half-width of 20 nm, in the range of 350 to 1100 nm using a semiconductor parameter analyzer 4200-SCS (Keithley Instruments). In addition, the raw materials for the synthesis, compounds (S-1) and (S-2), were synthesized according to the method described in "Organic Letters (2016), 18 (4), 804-807."

Example 1 (Synthesis of the compound of the present invention represented by the following formula (1-1))
(Step 1) Synthesis of intermediate compound represented by the following formula (M-1) In a flask, the compound represented by formula (S-1) (15.0 g, 56.8 mmol) was dissolved in DMF (300 mL), and potassium carbonate (15.7 g, 114 mmol), sodium iodide (4.26 g, 28.5 mmol), and methyl iodide (12.1 g, 85.2 mmol) were added at room temperature, and the mixture was heated to 80° C. with stirring and further stirred for 3 hours. The reaction solution obtained above was cooled to room temperature, poured into 1N hydrochloric acid (1 L) and stirred, and the resulting solid was collected by suction filtration. The obtained solid was washed with water and methanol to obtain an intermediate compound represented by formula (M-1) (14.5 g, 52.1 mmol, yield 91.7%).
The results of mass spectrometry of the compound represented by formula (M-1) are shown below.
DI-MS: m/z = 278 [M] ⁺

(Step 2) Synthesis of intermediate compound represented by the following formula (M-2) In a flask, the intermediate compound represented by formula (M-1) (14.5 g, 52.1 mmol) synthesized in step 1 was suspended in ethanol (260 mL), and hydrazine hydrate (25.3 mL, 521 mmol) was added at room temperature, and the mixture was heated to 78°C with stirring and refluxed for 6 hours. The reaction solution obtained above was cooled to room temperature, diluted with water (500 mL), and ethanol was distilled off by vacuum concentration. The precipitated solid was then collected by suction filtration and washed with water and methanol to obtain an intermediate compound represented by formula (M-2) (12.9 g, 46.4 mmol, yield 89.1%).
The results of mass spectrometry of the compound represented by formula (M-2) are shown below.
DI-MS: m/z = 278 [M] ⁺

(Step 3) Synthesis of intermediate compound represented by the following formula (M-3) In a flask, the intermediate compound represented by formula (M-2) (12.0 g, 43.0 mmol) synthesized in step 2 and 4'-fluoro-2'-hydroxy-5'-phenylacetophenone (11.9 g, 51.6 mmol) were suspended in ethanol (215 mL), and the temperature was raised to 78°C with stirring and refluxed for 6 hours. The reaction solution obtained above was cooled to room temperature, diluted with ethanol (300 mL), and the resulting solid was collected by filtration under reduced pressure and washed with water, methanol and a small amount of acetone to obtain the intermediate compound represented by formula (M-3) (20.3 g, 41.5 mmol, yield 96.5%).
The results of mass spectrometry of the compound represented by formula (M-3) are shown below.
DI-MS: m/z = 490 [M] ⁺

(Step 4) Synthesis of intermediate compound represented by the following formula (M-4) In a flask, the intermediate compound represented by formula (M-3) (19.7 g, 40.2 mmol) synthesized in step 3 was suspended in toluene (400 mL) and heated to 95°C, and then iodobenzene diacetate (19.4 g, 60.3 mmol) was added little by little over 10 minutes while stirring, and the reaction was carried out for 1 hour. After cooling the reaction solution obtained above to room temperature, the organic solvent was distilled off under reduced pressure, and the resulting residual liquid was purified by column chromatography (mobile phase: chloroform) using silica gel as the stationary phase to obtain the intermediate compound represented by formula (M-4) (13.1 g, 28.5 mmol, yield 70.9%).
The results of mass spectrometry of the compound represented by formula (M-4) are shown below.
DI-MS: m/z = 460 [M] ⁺

(Step 5) Synthesis of intermediate compound represented by the following formula (M-5) In a flask, the intermediate compound represented by formula (M-4) (4.88 g, 10.6 mmol) synthesized in step 4 was added to toluene (90 mL), and the temperature was raised to 60 ° C. while stirring to dissolve it, and then ammonium acetate (81.6 g, 1.06 mol) and water (10 mL) were added and the temperature was raised to the reflux temperature and the reaction was carried out for another 2 hours. The reaction solution obtained above was cooled to room temperature, and then water (500 mL) was added to separate the liquid, and the aqueous layer was extracted twice with toluene (300 mL). Anhydrous magnesium sulfate was added to the mixture of the organic layer obtained by separation and the extract obtained above, and the mixture was dried, and the solid content was removed by suction filtration, and the organic solvent was distilled off under reduced pressure. The resulting residual solid was purified by column chromatography using silica gel as a stationary phase to obtain an intermediate compound represented by formula (M-5) (2.25 g, 2.59 mmol, yield 48.9%).
The results of mass spectrometry of the compound represented by formula (M-5) are shown below.
DI-MS: m/z = 868 [M] ⁺

(Step 6) Synthesis of a compound represented by the following formula (1-1) In a flask, the intermediate compound represented by formula (M-5) (2.09 g, 2.41 mmol) synthesized in step 5 was dissolved in dichloroethane (340 mL), and 1 M boron tribromide dichloromethane solution (48.1 mL, 48.1 mmol) was added dropwise, followed by stirring for 12 hours under heating and reflux. The reaction solution obtained above was poured into saturated sodium bicarbonate water (1 L) and stirred for 1 hour, after which the precipitated solid was collected by suction filtration and washed with water, methanol and DMF. The obtained solid was purified by vacuum sublimation to obtain a compound represented by formula (1-1) (1.03 g, 1.22 mmol, yield 50.6%).
The results of mass spectrometry of the compound represented by formula (1-1) are shown below.
DI-MS: m/z = 848 [M] ⁺

Example 2 (Synthesis of the compound of the present invention represented by the following formula (1-2))
(Step 7) Synthesis of intermediate compound represented by the following formula (M-6) In a flask, the compound represented by formula (S-2) (12.0 g, 37.5 mmol) was dissolved in DMF (300 mL), and potassium carbonate (10.4 g, 75.0 mmol), sodium iodide (2.82 g, 18.8 mmol) and methyl iodide (8.00 g, 56.3 mmol) were added at room temperature, and the mixture was heated to 80° C. with stirring and further stirred for 3 hours. The reaction solution obtained above was cooled to room temperature, poured into 1N hydrochloric acid (1 L) and stirred, and the resulting solid was collected by suction filtration. The obtained solid was washed with water and methanol to obtain an intermediate compound represented by formula (M-6) (11.2 g, 33.5 mmol, yield 89.2%).
The results of mass spectrometry of the compound represented by formula (M-6) are shown below.
DI-MS: m/z = 334 [M] ⁺

(Step 8) Synthesis of intermediate compound represented by the following formula (M-7) In a flask, the intermediate compound represented by formula (M-6) (9.89 g, 29.6 mmol) synthesized in step 7 was suspended in ethanol (300 mL), and hydrazine hydrate (28.8 mL, 593 mmol) was added at room temperature, and the mixture was heated to 78°C with stirring and refluxed for 6 hours. The reaction solution obtained above was cooled to room temperature, diluted with water (500 mL), and ethanol was distilled off by vacuum concentration. The precipitated solid was then collected by suction filtration and washed with water and methanol to obtain the intermediate compound represented by formula (M-7) (8.73 g, 26.1 mmol, yield 88.3%).
The results of mass spectrometry of the compound represented by formula (M-7) are shown below.
DI-MS: m/z = 334 [M] ⁺

(Step 9) Synthesis of intermediate compound represented by the following formula (M-8) In a flask, the intermediate compound represented by formula (M-7) (7.85 g, 23.5 mmol) synthesized in step 8 and 4'-fluoro-2'-hydroxy-5'-phenylacetophenone (5.96 g, 25.9 mmol) were suspended in ethanol (400 mL) and stirred, and then the temperature was raised to 78°C while stirring and refluxed for 6 hours. After cooling the reaction solution obtained above to room temperature, the reaction solution was diluted with ethanol (150 mL), and the resulting solid was collected by filtration under reduced pressure and washed with water, methanol and a small amount of acetone to obtain the intermediate compound represented by formula (M-8) (12.2 g, 22.4 mmol, yield 95.5%).
The results of mass spectrometry of the compound represented by formula (M-8) are shown below.
DI-MS: m/z = 546 [M] ⁺

(Step 10) Synthesis of intermediate compound represented by the following formula (M-9) In a flask, the intermediate compound represented by formula (M-8) (12.2 g, 22.4 mmol) synthesized in step 9 was suspended in toluene (500 mL) and heated to 95°C, and then iodobenzene diacetate (10.8 g, 33.6 mmol) was added little by little over 10 minutes to react for 1 hour. After cooling the reaction solution obtained above to room temperature, the organic solvent was distilled off under reduced pressure, and the resulting residual liquid was purified by column chromatography (mobile phase: chloroform) using silica gel as the stationary phase to obtain the intermediate compound represented by formula (M-9) (7.64 g, 14.8 mmol, yield 66.2%).
The results of mass spectrometry of the compound represented by formula (M-9) are shown below.
DI-MS: m/z = 516 [M] ⁺

(Step 11) Synthesis of intermediate compound represented by the following formula (M-10) In a flask, the intermediate compound represented by formula (M-9) (3.23 g, 6.26 mmol) synthesized in step 10 was added to toluene (50 mL), and the temperature was raised to 60 ° C. to dissolve it, and then ammonium acetate (96.3 g, 1.25 mol) and water (5 mL) were added and the temperature was raised to the reflux temperature and the reaction was continued for another 2 hours. The reaction solution obtained above was cooled to room temperature, and then water (100 mL) was added to separate the liquid, and the aqueous layer was extracted twice with toluene (200 mL). Anhydrous magnesium sulfate was added to the mixture of the organic layer obtained by separation and the extract obtained above, and the mixture was dried, and the solid content was removed by suction filtration, and the organic solvent was distilled off under reduced pressure. The resulting residual solid was purified by column chromatography using silica gel as a stationary phase to obtain an intermediate compound represented by formula (M-10) (1.44 g, 1.47 mmol, yield 47.0%).
The results of mass spectrometry of the compound represented by formula (M-10) are shown below.
DI-MS: m/z = 980 [M] ⁺

(Step 12) Synthesis of a compound represented by the following formula (1-2) In a flask, the intermediate compound represented by formula (M-10) (1.15 g, 1.17 mmol) synthesized in step 11 was dissolved in dichloroethane (100 mL), and 1 M boron tribromide dichloromethane solution (23.4 mL, 23.4 mmol) was added dropwise, and the mixture was stirred for 12 hours under heating and reflux. The reaction solution obtained above was poured into saturated sodium bicarbonate water (500 mL), and after stirring for 1 hour, the precipitated solid was collected by suction filtration and washed with water, methanol and DMF. The obtained solid was purified by vacuum sublimation to obtain a compound represented by formula (1-2) (0.32 g, 0.334 mmol, yield 28.5%).
The results of mass spectrometry of the compound represented by formula (1-2) are shown below.
DI-MS: m/z = 960 [M] ⁺

Examples 3 and 4 (Preparation of organic thin film)
The compounds obtained in Examples 1 and 2 were subjected to resistance heating vacuum deposition on a pre-cleaned glass substrate to prepare organic thin films of the respective compounds. The organic thin film obtained using the compound represented by formula (1-1) (Example 3) had a thickness of 120 nm, and the organic thin film obtained using the compound represented by formula (1-2) (Example 4) had a thickness of 100 nm.

(Absorption spectrum measurement of organic thin films)
The absorption spectrum of each of the organic thin films obtained in Examples 3 and 4 was measured. The results are shown in Figure 2. The measurement results in Figure 2 were converted per unit film thickness (nm). The maximum absorption wavelengths (λmax) of the organic thin films obtained in Examples 3 and 4 were 921 nm and 961 nm, respectively.

The organic thin films of the present invention obtained in Examples 3 and 4 have a maximum absorption wavelength in the long wavelength region of 900 nm or more, and it is clear that they can efficiently absorb near-infrared light in the range of 800 to 1,000 nm.

Example 5 (Preparation of a photoelectric conversion element using a compound represented by formula (1-1) and its evaluation)
A 120 nm thick organic thin film of the compound represented by formula (1-1) was formed on an ITO transparent conductive glass (Geomatec Co., Ltd., ITO film thickness 150 nm) by resistance heating vacuum deposition to form a photoelectric conversion layer. An aluminum film was formed thereon by resistance heating vacuum deposition to form a photoelectric conversion element of the present invention. When ITO and aluminum were used as electrodes and a voltage of 1 V was applied in a state in which light irradiation of 1,000 nm and half-value width 20 nm could be performed, the photocurrent response was measured. The current in a dark place was 1.01×10 ^-10 A/cm ² and the current in a bright place was 1.82×10 ^-7 A/cm ² , and the bright/dark ratio (bright current/dark current) calculated from the above measurement results was 1.80×10 ³ .

Example 6 (Preparation of a photoelectric conversion element using a compound represented by formula (1-2) and its evaluation)
A photoelectric conversion element of the present invention was produced in a manner similar to that of Example 5, except that the compound represented by formula (1-2) was used instead of the compound represented by formula (1-1) and the thickness of the photoelectric conversion layer was 100 nm. When ITO and aluminum were used as electrodes and a voltage of 1 V was applied in a state in which light irradiation of 1,000 nm and half-value width of 20 nm could be performed, the current in a dark place was 2.41×10 ⁻¹⁰ A/cm ² and the current in a bright place was 3.18×10 ⁻⁷ A/cm ² , and the bright/dark ratio (bright current/dark current) calculated from the above measurement results was 1.32×10 ³ .

Comparative Example 1 (Preparation of a photoelectric conversion element using a comparative compound and its evaluation)
A comparative photoelectric conversion element was produced in the same manner as in Example 5 except that a compound represented by the following formula (R-1) synthesized in accordance with the method described in International Publication No. 2020/162345 was used instead of the compound represented by formula (1-1), and the thickness of the photoelectric conversion layer was 100 nm. The light-dark ratio (light current/dark current) calculated from the measurement results of the photocurrent response when a voltage of 1 V was applied in a state in which ITO and aluminum were used as electrodes and light irradiation with a wavelength of 1,000 nm and a half-width of 20 nm could be performed was 1.5 × 10 ⁰ .

Comparative Example 2 (Preparation of a photoelectric conversion element using a comparative compound and its evaluation)
A comparative photoelectric conversion element was produced in the same manner as in Example 5 except that a compound represented by the following formula (R-2) synthesized in accordance with the method described in International Publication No. 2020/162345 was used instead of the compound represented by formula (1-1), and the thickness of the photoelectric conversion layer was 100 nm. The light-dark ratio (light current/dark current) calculated from the measurement results of the photocurrent response when a voltage of 1 V was applied in a state in which ITO and aluminum were used as electrodes and light irradiation with a wavelength of 1,000 nm and a half-width of 20 nm could be performed was 8.6 × 10 ¹ .

Comparative Example 3 (Preparation of a photoelectric conversion element using a comparative compound and evaluation of the same)
A comparative photoelectric conversion element was produced in the same manner as in Example 5 except that a compound represented by the following formula (R-3) synthesized in accordance with the method described in International Publication No. 2020/162345 was used instead of the compound represented by formula (1-1), and the thickness of the photoelectric conversion layer was 100 nm. The light-dark ratio (light current/dark current) calculated from the measurement results of the photocurrent response when a voltage of 1 V was applied in a state in which light irradiation with ITO and aluminum was possible with a wavelength of 1,000 nm and a half-width of 20 nm could be performed was 2.0 × 10 ¹ .

The above results show that an organic photoelectric conversion element containing an organic thin film using the compound of the present invention exhibits a higher light-to-dark ratio in near-infrared light with a wavelength of 1,000 nm than a comparative organic photoelectric conversion element, and is useful as a near-infrared light absorbing material for image sensors and optical sensors.

The compound of the present invention exhibits good absorption characteristics in the near-infrared light region, high heat resistance sufficient to withstand device fabrication processes, and good near-infrared photoelectric conversion characteristics, and is therefore useful as an organic electronics device material.

Claims (10)

The following formula (1)

(In formula (1), R ¹ to R ⁴ each independently represent a hydrogen atom, an alkyl group, an aromatic hydrocarbon group, a heterocyclic group, or a halogen atom; m represents an integer of 1 to 3; and A represents a benzene ring or a naphthalene ring.) The compound according to claim 1, wherein at least one of R ¹ to R ⁴ is an alkyl group, an aromatic hydrocarbon group, a heterocyclic group, or a halogen atom. The compound according to claim 2, wherein at least one of R ¹ to R ⁴ is a halogen atom. The compound according to claim 2, wherein at least two of R ¹ to R ⁴ are an aromatic hydrocarbon group or a halogen atom. The compound according to any one of claims 1 to 4, wherein A is a benzene ring. A near-infrared light absorbing material comprising a compound according to any one of claims 1 to 5. An organic thin film comprising a compound according to any one of claims 1 to 5. A photoelectric conversion element comprising the organic thin film according to claim 7. An optical sensor comprising the photoelectric conversion element according to claim 8. An imaging device comprising the photoelectric conversion element according to claim 8 .

Images