Light upconversion composition, film, and light upconversion method

Abstract

This invention provides a light upconversion composition that can achieve higher light upconversion efficiency than conventional methods without the need for degassing, and has a low environmental impact. [Solution] The light upconversion composition of the present invention comprises fine cellulose fibers, a sensitizer, a light-emitting element, and an imidazolium compound.

Description

[Technical Field]

[0001] The present invention relates to a light upconversion composition, a film formed from this light upconversion composition, and a light upconversion method using this film. [Background technology]

[0002] Optical upconversion is a method of converting long-wavelength light into short-wavelength light. Applications of optical upconversion compositions include, for example, organic solar cells. In organic solar cells, free charge carriers are generated by ultraviolet and visible light from sunlight. Therefore, by using optical upconversion compositions in organic solar cells, it is expected that long-wavelength light such as near-infrared light can be converted into short-wavelength light such as ultraviolet and visible light, thereby increasing the photoelectric conversion efficiency of organic solar cells.

[0003] Conventional methods of optical upconversion include (1) two-photon absorption using a powerful pulsed laser, (2) second harmonic generation using a nonlinear optical crystal and a coherent light source, and (3) two-step excitation of rare earth elements. These methods require very strong coherent incident light (laser), and their optical upconversion efficiency is very low, below 0.2%. These are used as optical elements for laser wavelength conversion, but because they require very strong coherent light, they cannot be used in organic solar cells. In contrast, in recent years, a method using two types of photofunctional molecules and triplet-triplet annihilation (TTA) has attracted attention as a method that can perform optical upconversion of 1% or more even with non-coherent light of low incident light intensity. Specifically, it combines two types of elements with distinct roles: a sensitizer that absorbs long-wavelength light and efficiently generates triplets, and an emitter that generates long-lived excited triplets through triplet-triplet energy transfer (TTET) from the sensitizer, and further generates excited singlets through collisions between these excited triplets, thereby emitting fluorescence.

[0004] As a method for combining the two types of elements mentioned above, solution systems containing a mixture of these two elements have been investigated (see, for example, Patent Document 1). However, the excited triplet state is quenched and deactivated by oxygen in the air or solution, so the solution system requires degassing to remove dissolved oxygen. Therefore, film formation is essential for practical application. As an investigation into film formation, for example, Patent Document 2 investigates a method of forming a film by photopolymerization using a sensitizer, a luminescent agent, and a polymerizable liquid crystal monomer. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2014 / 136619 [Patent Document 2] Japanese Patent Publication No. 2020-26477 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, the film obtained by the method described in Patent Document 2 uses liquid crystals that are not biodegradable, resulting in a significant environmental impact. Furthermore, there was a need for a composition that could achieve higher light upconversion efficiency.

[0007] Therefore, the present invention aims to provide a light upconversion composition that can achieve higher light upconversion efficiency than conventional methods without degassing treatment and has a low environmental impact, a film using the same, and a light upconversion method using the film. [Means for solving the problem]

[0008] As a result of diligent research to achieve this objective, the inventors of the present invention found that using fine cellulose fibers and specific compounds is extremely effective, and thus completed the present invention.

[0009] The present invention provides the following: (1) A photo-upconversion composition comprising fine cellulose fibers, a sensitizer, a light-emitting element, and an imidazolium compound. (2) The photo-upconversion composition according to (1), wherein the fine cellulose fibers are anionic modified cellulose nanofibers. (3) The photo-upconversion composition according to (2), wherein the anion-modified cellulose nanofiber is a carboxylated cellulose nanofiber. (4) The photo-upconversion composition according to (1), wherein the sensitizer is a metal complex, and the metal complex is a palladium complex or a platinum complex. (5) The light upconversion composition according to (1), wherein the light-emitting element is a condensed polycyclic aromatic compound. (6) A film formed from the optical upconversion composition described in (1). (7) An optical upconversion method comprising the step of irradiating light on the film described in (6). [Effect of the Invention]

[0010] According to the present invention, it is possible to achieve a higher optical upconversion efficiency than before without performing a degassing process, and to provide an optical upconversion composition with a low environmental load, a film using the same, and an optical upconversion method using this film. [Brief Description of the Drawings]

[0011] [Figure 1] It is a figure showing the ultraviolet-visible absorption spectra of the compositions of Examples 1 to 5 and Comparative Examples 1 and 2. [Figure 2] It is an external appearance photograph of the measurement samples produced from the compositions of Comparative Example 1, Example 1, and Example 4. [Figure 3] It is a figure showing the emission spectra of the compositions of Examples 1 to 5 and Comparative Examples 1 and 2. [Figure 4] It is a figure showing the excitation laser intensity dependence of the relative quantum yield ΦUC of the compositions of Examples 1 to 5 and Comparative Examples 1 and 2. [Modes for Carrying Out the Invention] <00几千0098>

[0012] Hereinafter, the present invention will be described in detail. In the present invention, "~" includes the end values. That is, "X~Y" includes the values X and Y at both ends.

[0013] The optical upconversion composition of the present invention contains microcrystalline cellulose fibers, a sensitizer, a phosphor, and an imidazolium-based compound.

[0014] (Microcrystalline cellulose fibers) The fine cellulose fibers used in this invention are fine fibers made from cellulose, and are a general term for cellulose nanofibers (hereinafter sometimes referred to as "CNF") with an average fiber diameter of less than 500 nm and microfibrillated cellulose (hereinafter sometimes referred to as "MFC") with an average fiber diameter of 500 nm or more. The average fiber diameter is a length-weighted average fiber diameter and can be measured by observing the fine cellulose fibers using, for example, a fractionator manufactured by Valmet Corporation or an atomic force microscope (AFM). The average fiber diameter of the fine cellulose fibers is not particularly limited, but is approximately 1 nm to 60 μm. Fine cellulose fibers can be produced by defibrating cellulose.

[0015] (Cellulose nanofiber (CNF)) The average fiber diameter of the CNF that can be used in this invention is preferably 100 nm or less, more preferably 50 nm or less. The average fiber length is preferably 5 μm or less, more preferably 3 μm or less. The lower limit of the average fiber length is approximately 0.1 μm or more. The average fiber length can be measured by analyzing 200 randomly selected fibers using an atomic force microscope (AFM) if the diameter is less than 20 nm, or by using a field emission scanning electron microscope (FE-SEM) if the diameter is 20 nm or more, and calculating the average. The average aspect ratio of the CNF that can be used in this invention is preferably 50 or more. There is no particular upper limit, but it is usually 1000 or less. The average aspect ratio can be calculated by the following formula: Aspect ratio = average fiber length / average fiber diameter

[0016] The cellulose raw material is not particularly limited as long as it contains cellulose, but examples include plants (e.g., wood, bamboo, hemp, jute, kenaf, agricultural waste, cloth, pulp (unbleached coniferous kraft pulp (NUKP), bleached coniferous kraft pulp (NBKP), unbleached hardwood kraft pulp (LUKP), bleached hardwood kraft pulp (LBKP), bleached kraft pulp (BKP), unbleached coniferous sulfite pulp (NUSP), bleached coniferous sulfite pulp (NBSP), thermomechanical pulp (TMP), recycled pulp, waste paper, etc.), animals (e.g., sea squirts), algae, microorganisms (e.g., acetic acid bacteria (Acetobacter)), microbial products, etc. The cellulose raw material may be any one of these or a combination of two or more, but it is preferably a cellulose raw material derived from plants or microorganisms (e.g., cellulose fibers), and more preferably a cellulose raw material derived from plants (e.g., cellulose fibers).

[0017] The number-average fiber diameter of cellulose raw materials is not particularly limited, but for common pulps such as softwood kraft pulp, it is about 30-60 μm, and for hardwood kraft pulp, it is about 10-30 μm. For other pulps, after general refining, it is about 50 μm. For example, if the material is made from wood chips or other materials several centimeters in size, it is preferable to mechanically process it using a refiner or beater to adjust it to about 50 μm.

[0018] Cellulose has three hydroxyl groups per glucose unit, and can be subjected to various chemical modifications. In the present invention, from the viewpoint of promoting the progression of defibrillation, it is preferable to use cellulose raw material obtained by anionic modification (anionic modified cellulose) among the various chemical modifications.

[0019] Examples of anionic modification include carboxylation (oxidation), carboxymethylation, and esterification. Of these, carboxylation (oxidation) is more preferred.

[0020] (Anionic denaturation) In the present invention, anionic modification refers to the introduction of anionic groups into cellulose, specifically, the introduction of anionic groups into the pyranose ring of cellulose by carboxylation (oxidation) or substitution reaction. In the present invention, the carboxylation (oxidation) reaction refers to the reaction in which the hydroxyl group of the pyranose ring is directly oxidized to a carboxyl group. Furthermore, in the present invention, substitution reaction refers to a reaction in which anionic groups are introduced into the pyranose ring by a substitution reaction other than the carboxylation (oxidation) described above.

[0021] Examples of anionic modification include carboxylation (oxidation), carboxymethylation, and esterification. Among these, carboxylation (oxidation), carboxymethylation, and phosphorylated esterification are more preferred, with carboxylation (oxidation) being particularly preferred.

[0022] (carboxylation) In the present invention, when carboxylated (oxidized) cellulose is used as anionically modified cellulose, carboxylated cellulose (also called oxidized cellulose) can be obtained by carboxylating (oxidizing) the above-mentioned cellulose raw material using a known method. Although not particularly limited, when carboxylating, it is preferable to adjust the amount of carboxyl groups to 0.6 to 2.0 mmol / g relative to the oven-dry mass of the anionically modified cellulose nanofiber, and more preferably to adjust it to 1.0 mmol / g to 2.0 mmol / g.

[0023] One example of a carboxylation (oxidation) method is to oxidize a cellulose raw material in water using an oxidizing agent in the presence of an N-oxyl compound and a compound selected from the group consisting of bromide, iodide, or a mixture thereof. This oxidation reaction selectively oxidizes the primary hydroxyl group at the C6 position of the glucopyranose ring on the surface of the cellulose, resulting in the formation of an aldehyde group and a carboxyl group (-COOH) or carboxylate group (-COOH) on the surface. - Cellulose fibers having the following characteristics can be obtained. The concentration of cellulose during the reaction is not particularly limited, but 5% by mass or less is preferred.

[0024] An N-oxyl compound is a compound that can generate a nitroxyl radical. Any compound that promotes the desired oxidation reaction can be used as an N-oxyl compound. Examples include 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) and its derivatives (e.g., 4-hydroxyTEMPO).

[0025] The amount of N-oxyl compound used is not particularly limited, as long as it is a catalytic amount that can oxidize the raw material cellulose. For example, 0.01 to 10 mmol is preferred, 0.01 to 1 mmol is more preferred, and 0.05 to 0.5 mmol is even more preferred, per 1 g of oven-dried cellulose. Also, about 0.1 to 4 mmol / L relative to the reaction system is preferable.

[0026] Bromides are compounds containing bromine, and examples include alkali metal bromides that can dissociate and ionize in water. Iodides are compounds containing iodine, and examples include alkali metal iodides. The amount of bromide or iodide used can be selected within a range that promotes the oxidation reaction. The total amount of bromide and iodide is preferably 0.1 to 100 mmol, more preferably 0.1 to 10 mmol, and even more preferably 0.5 to 5 mmol per 1 g of oven-dried cellulose.

[0027] As an oxidizing agent, known substances can be used, such as halogens, hypohalous acids, halogenous acids, perhalous acids or their salts, halogen oxides, and peroxides. Among these, sodium hypochlorite is preferred because it is inexpensive and has a low environmental impact. The appropriate amount of oxidizing agent to use is, for example, 0.5 to 500 mmol, more preferably 0.5 to 50 mmol, even more preferably 1 to 25 mmol, and most preferably 3 to 10 mmol per 1 g of oven-dried cellulose. Also, for example, 1 to 40 mol per 1 mol of N-oxyl compound is preferred.

[0028] The cellulose oxidation process can proceed efficiently even under relatively mild conditions. Therefore, the reaction temperature is preferably 4 to 40°C, and can also be room temperature of about 15 to 30°C. As the reaction progresses, carboxyl groups are formed in the cellulose, causing a decrease in the pH of the reaction solution. To ensure the oxidation reaction proceeds efficiently, it is preferable to add an alkaline solution such as an aqueous sodium hydroxide solution to maintain the pH of the reaction solution at 8 to 12, preferably 10 to 11. Water is preferred as the reaction medium due to its ease of handling and the low likelihood of side reactions.

[0029] The reaction time in an oxidation reaction can be set appropriately according to the degree of oxidation, and is usually 0.5 to 6 hours, for example, 0.5 to 4 hours.

[0030] Furthermore, the oxidation reaction may be carried out in two stages. For example, by filtering out the oxidized cellulose after the first stage of the reaction and then oxidizing it again under the same or different reaction conditions, the oxidation can be carried out efficiently without being inhibited by the salt produced as a by-product in the first stage of the reaction.

[0031] Another example of a carboxylation (oxidation) method involves contacting a cellulose raw material with an ozone-containing gas. This oxidation reaction oxidizes at least the hydroxyl groups at positions 2 and 6 of the glucopyranose ring, and also causes decomposition of the cellulose chain. The ozone concentration in the ozone-containing gas is 50-250 g / m³. 3 Preferably, it is 50-220 g / m² 3It is more preferable that the cellulose raw material is as follows: The amount of ozone added to the cellulose raw material is preferably 0.1 to 30 parts by mass, and more preferably 5 to 30 parts by mass, when the solid content of the cellulose raw material is 100 parts by mass. The ozone treatment temperature is preferably 0 to 50°C, and more preferably 20 to 50°C. The ozone treatment time is not particularly limited, but is about 1 to 360 minutes, and is preferably about 30 to 360 minutes. When the ozone treatment conditions are within these ranges, it is possible to prevent excessive oxidation and decomposition of the cellulose, and the yield of oxidized cellulose is good. After ozone treatment, a follow-up oxidation treatment may be performed using an oxidizing agent. The oxidizing agent used for the follow-up oxidation treatment is not particularly limited, but examples include chlorine compounds such as chlorine dioxide and sodium chlorite, as well as oxygen, hydrogen peroxide, persulfuric acid, and peracetic acid. For example, these oxidizing agents can be dissolved in water or a polar organic solvent such as alcohol to create an oxidizing agent solution, and the follow-up oxidation treatment can be performed by immersing the cellulose raw material in the solution.

[0032] The amount of carboxyl groups in oxidized cellulose can be adjusted by controlling the reaction conditions, such as the amount of oxidizing agent added and the reaction time.

[0033] (carboxymethylation) In the present invention, when carboxymethylated cellulose is used as the anionically modified cellulose, the carboxymethylated cellulose may be obtained by carboxymethylating the above-mentioned cellulose raw material by a known method, or a commercially available product may be used. In either case, it is preferable that the degree of carboxymethyl group substitution per anhydrous glucose unit of cellulose is 0.01 to 0.50. An example of a method for producing such carboxymethylated cellulose is as follows: Cellulose is used as the base material, and 3 to 20 times the mass of water and / or lower alcohols, specifically water, methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol, tertiary butanol, etc., are used as the solvent, either individually or as a mixture of two or more. When lower alcohols are mixed, the mixing ratio of the lower alcohols is 60 to 95% by mass. As a mercerizing agent, 0.5 to 20 times the molar amount of alkali metal hydroxide per anhydrous glucose residue of the base material is used, specifically sodium hydroxide and potassium hydroxide. The starting material, solvent, and mercerizing agent are mixed, and the mercerizing treatment is carried out at a reaction temperature of 0 to 70°C, preferably 10 to 60°C, and for a reaction time of 15 minutes to 8 hours, preferably 30 minutes to 7 hours. After that, a carboxymethylating agent is added at a rate of 0.05 to 10.0 molars per glucose residue, and the etherification reaction is carried out at a reaction temperature of 30 to 90°C, preferably 40 to 80°C, and for a reaction time of 30 minutes to 10 hours, preferably 1 hour to 4 hours.

[0034] In this specification, "carboxymethylated cellulose," a type of anionically modified cellulose used in the preparation of anionically modified CNF, refers to cellulose that maintains at least a portion of its fibrous structure even when dispersed in water. Therefore, it is distinguished from carboxymethylcellulose, a type of water-soluble polymer. When an aqueous dispersion of "carboxymethylated cellulose" is observed with an electron microscope, fibrous material can be observed. On the other hand, when an aqueous dispersion of carboxymethylcellulose, a type of water-soluble polymer, is observed, no fibrous material is observed. Furthermore, when "carboxymethylated cellulose" is measured by X-ray diffraction, a peak of cellulose type I crystals can be observed, but cellulose type I crystals are not seen in carboxymethylcellulose, a water-soluble polymer.

[0035] (Esterification) In the present invention, when esterified cellulose is used as anionically modified cellulose, the esterified cellulose is obtained by mixing the aforementioned cellulose raw material with powder or aqueous solution of phosphate compound A, or by adding an aqueous solution of phosphate compound A to a slurry of cellulose raw material.

[0036] Examples of phosphate compounds A include phosphoric acid, polyphosphate, phosphorous acid, hypophosphorous acid, phosphonic acid, polyphosphonic acid, or esters thereof. These may also be in salt form. Among these, compounds having a phosphate group are preferred because they are low-cost, easy to handle, and can improve defibration efficiency by introducing a phosphate group into the cellulose of pulp fibers. Examples of compounds having a phosphate group include phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium phosphite, potassium phosphite, sodium hypophosphite, potassium hypophosphite, sodium pyrophosphate, sodium metaphosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, potassium metaphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, and ammonium metaphosphate. These can be used individually or in combination of two or more. Of these, phosphoric acid, sodium salts of phosphoric acid, potassium salts of phosphoric acid, and ammonium salts of phosphoric acid are more preferred from the viewpoint of high efficiency in introducing a phosphate group, ease of defibration in the defibration process described below, and ease of industrial application. Sodium dihydrogen phosphate and disodium hydrogen phosphate are particularly preferred. Furthermore, it is preferable to use the phosphate compound A as an aqueous solution because this increases the uniformity of the reaction and the efficiency of phosphate group introduction. The pH of the aqueous solution of phosphate compound A is preferably 7 or less because it increases the efficiency of phosphate group introduction, but a pH of 3 to 7 is preferable from the viewpoint of suppressing hydrolysis of pulp fibers.

[0037] The following method is an example of a method for producing phosphate-esterified cellulose. A phosphate compound A is added to a dispersion of cellulose raw material with a solid content concentration of 0.1 to 10% by mass while stirring to introduce phosphate groups into the cellulose. When the cellulose raw material is 100 parts by mass, the amount of phosphate compound A added is preferably 0.2 to 500 parts by mass, and more preferably 1 to 400 parts by mass, in terms of phosphorus element content. If the proportion of phosphate compound A is above the lower limit, the yield of fine cellulose fibers can be further improved. However, if it exceeds the upper limit, the effect of improving the yield plateaus, which is undesirable from a cost perspective.

[0038] In this process, in addition to the cellulose raw material and phosphate compound A, powder or aqueous solution of compound B other than A may be mixed. Compound B is not particularly limited, but a nitrogen-containing compound exhibiting basicity is preferred. Here, "basicity" is defined as the aqueous solution exhibiting a pink to red color in the presence of phenolphthalein indicator, or the pH of the aqueous solution being greater than 7. The nitrogen-containing compound exhibiting basicity used in this invention is not particularly limited as long as it achieves the effects of the present invention, but a compound having an amino group is preferred. Examples include, but are not particularly limited, urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, and hexamethylenediamine. Among these, urea is preferred because it is low-cost and easy to handle. The amount of compound B added is preferably 2 to 1000 parts by mass, and more preferably 100 to 700 parts by mass, per 100 parts by mass of solid content of the cellulose raw material. The reaction temperature is preferably 0 to 95°C, and more preferably 30 to 90°C. The reaction time is not particularly limited, but is approximately 1 to 600 minutes, with 30 to 480 minutes being more preferable. When the esterification reaction conditions are within this range, it is possible to prevent the cellulose from being excessively esterified and becoming easily soluble, resulting in a good yield of phosphate-esterified cellulose. After dehydrating the obtained phosphate-esterified cellulose suspension, it is preferable to heat-treat it at 100 to 170°C from the viewpoint of suppressing hydrolysis of cellulose. Furthermore, it is preferable to heat it at 130°C or lower, preferably 110°C or lower, while water is present during the heat treatment, and then heat-treat it at 100 to 170°C after removing the water.

[0039] The degree of phosphate group substitution per glucose unit in phosphate-esterified cellulose is preferably 0.001 to 0.40. By introducing phosphate group substituents to cellulose, the cellulose molecules repel each other electrically. Therefore, cellulose with introduced phosphate groups can be easily defibrillated. If the degree of phosphate group substitution per glucose unit is less than 0.001, sufficient defibrillation is not possible. On the other hand, if the degree of phosphate group substitution per glucose unit is greater than 0.40, swelling or dissolution may occur, making it impossible to obtain fine cellulose fibers. In order to efficiently defibrillate, it is preferable to boil the phosphate-esterified cellulose raw material obtained above and then wash it with cold water. These modifications by esterification are modifications by substitution reactions. The degree of substitution in esterified cellulose and the degree of substitution when the esterified cellulose is finely pulverized are usually the same.

[0040] In the present invention, the anion-modified CNF is preferably used as hydrophobized anion-modified CNF, in which a hydrophobic agent is bound to the anion-modified CNF, from the viewpoint of uniform solubility / dispersibility in a common good solvent such as tetrahydrofuran (THF) when mixed with a hydrophobic agent for composite film formation treatment. Hydrophobized anion-modified CNF can be obtained, for example, by binding a hydrophobic agent to anion-modified cellulose and then defibrating it.

[0041] (Hydrophobic agent) As a hydrophobic agent for hydrophobizing anionically modified cellulose, compounds having amines or phosphines that can bond with the anionic groups of anionically modified cellulose to form an onium salt are preferred, and any of the following may be used: primary amines, secondary amines, tertiary amines, quaternary ammonium compounds, aromatic amines, diamines, polyetheramines, phosphines, or phosphoniums.

[0042] Examples of hydrophobic agents include, but are not limited to, polyetheramines such as JEFFAMINE® M-600, JEFFAMINE® M-1000, JEFFAMINE® M-2005, and JEFFAMINE® M-2070 manufactured by HUNTSMAN, methylamine, ethylamine, oleylamine, propylamine, dodecylamine, stearylamine, tetradecylamine, 1-hexenylamine, 1-dodecenylamine, 9,12-octadecadienylamine (linoleamine), 9,12,15-octadecatrienyamine, and linoleylamine; primary amines such as dimethylamine and diethylamine; tertiary amines such as trimethylamine and triethylamine; and four types of amines such as benzalkonium chloride, benzethonium chloride, methylbenzethonium chloride, cetylpyridinium chloride, cetrimonium chloride, dophanium chloride, tetraethylammonium bromide, and didecyldimethylammonium chloride. Examples include ammonium compounds, aromatic amines such as aniline, pyridine, and benzylamine, diamines such as ethylenediamine and hexamethylenediamine, and phosphines such as triphenylphosphine and trimethylphosphine. From the viewpoint of obtaining a composite film with excellent photo-upconversion effect, due to its high compatibility with sensitizer dyes and luminescent dyes, and the ease with which sensitizer dyes and luminescent dyes can be uniformly dispersed in CNF.

[0043] It is preferable to add the hydrophobic agent so that the amount of hydrophobic agent bound to 1 g of anionic modified cellulose is 0.40 g or more. More preferably, the amount of hydrophobic agent bound is 0.50 g or more, and even more preferably 1.00 g or more. The method for calculating the amount of hydrophobic agent bound will be described later. The hydrophobic agent binds to the anionic groups of the anionic modified cellulose. When a sufficient amount of hydrophobic agent is added according to the amount of anionic groups of the anionic modified cellulose, aggregation due to hydrogen bonding between cellulose fibers during drying in the subsequent process of producing dried solids is inhibited, and defibration and nanofiber formation in the subsequent defibration process are promoted. There is no particular upper limit to the amount of hydrophobic agent bound to 1 g of anionic modified cellulose, but if the amount of hydrophobic agent bound is excessively high, the proportion of anionic modified cellulose in the hydrophobic anionic modified cellulose will decrease. Therefore, the amount of hydrophobic agent bound to 1 g of anionic modified cellulose is preferably 10.00 g or less, and more preferably 5.00 g or less.

[0044] The hydrophobic agent binds to the anionic groups of anionic-modified cellulose. Due to the reaction mechanism, all of the added hydrophobic agent reacts with the anionic groups. The inventors have found that when 1 molar equivalent or more of the hydrophobic agent is added, all of the anionic-modified cellulose, which was in the acid form (-COOH), becomes -COOH. - This change was confirmed using infrared spectroscopy. This indicates that the amine hydrophobic agent ionically bonded to all of the anionic groups of the anionically modified cellulose. Therefore, the amount of hydrophobic agent bonded to 1 g of anionically modified cellulose can be calculated using the following formula, depending on the amount of hydrophobic agent added: i) When the hydrophobic agent is added in an amount equal to or greater than the amount (in moles) of the anionic group. Amount of hydrophobic agent bound to 1g of anionic-modified cellulose [g] = Amount of anionic groups in anionic-modified cellulose [mmol / g] × Molecular weight of hydrophobic agent × 0.001 × Valence of anionic groups ii) When the amount (in moles) of hydrophobic agent added is less than the amount (in moles) of anionic groups. Amount of hydrophobic agent bound to 1 g of anionic-modified cellulose [g] = Amount of anionic groups in anionic-modified cellulose [mmol / g] × Molecular weight of hydrophobic agent × 0.001 × Moles of added hydrophobic agent [mmol / g] / Moles of anionic groups [mmol] i) In this case, the valency of the anionic group is 1 if the anionic group is a carboxyl group or a carboxyalkyl group, and if the anionic group is a phosphate group (e.g., H2PO4) - ) If this is the case, then it is 2. In ii), the number of moles of anionic groups (mmol) can be determined from the amount of anionic groups (mmol / g) and the oven-dry mass of anionically modified cellulose (g).

[0045] The hydrophobic agent may be added in an amount of 50-150% of the amount (moles) of anionic groups in the anionic-modified cellulose, preferably 70-130%, more preferably 80-120%, and even more preferably 100-120%.

[0046] The hydrophobic agent can be added to the anionic modified cellulose dispersion either as is or mixed with water or a water-soluble organic solvent. When adding the hydrophobic agent, the concentration of anionic modified cellulose in the anionic modified cellulose dispersion is preferably 0.01 to 50% by mass, preferably 1 to 45% by mass, and more preferably 2 to 40% by mass. A hydrophobic anionic modified cellulose dispersion can be produced by mixing the hydrophobic agent and the anionic modified cellulose while stirring for a certain period of time.

[0047] Water-soluble organic solvents are organic solvents that dissolve in water. Examples include methanol, ethanol, 2-propanol, butanol, glycerin, acetone, methyl ethyl ketone, 1,4-dioxane, N-methyl-2-pyrrolidone, tetrahydrofuran (THF), N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, acetonitrile, and combinations thereof.

[0048] Before defibration, it is preferable to dry the dispersion of hydrophobized anionic modified cellulose to which a hydrophobic agent has been bound, thereby removing the dispersion medium and obtaining a dry solid. In this case, it is necessary to remove the dispersion medium sufficiently so that the solid content concentration in the dry solid is higher than 90% by mass. The solid content concentration in the dry solid is preferably higher than 95% by mass, more preferably 97% by mass or higher, and even more preferably 98% by mass or higher.

[0049] The solid content concentration in a dry solid can be measured by the following procedure: The dried solid material is dried in an oven at 105°C for 12 hours, and the solid content concentration of the dried solid material is calculated from the mass before and after drying. Solid content concentration (mass%) of a dried solid = Mass after drying / Mass before drying × 100.

[0050] The means for removing the dispersion medium are not particularly limited; for example, the dispersion medium can be removed by placing the mixture at a temperature of 60 to 130°C for 1 to 24 hours. The resulting dried solid of hydrophobically modified anion cellulose or its defibrated product can be easily converted to hydrophobically modified anion cellulose fiber (CNF) by defibration in an organic solvent. The dried solid of hydrophobically modified anion cellulose can be suitably used as a raw material for producing hydrophobically modified anion cellulose.

[0051] (Fibreation) The above-mentioned dried solid can be mixed with an organic solvent, and the hydrophobically modified anion cellulose can be defibrated in the organic solvent to produce a dispersion of hydrophobically modified anion CNF using the organic solvent as the dispersion medium.

[0052] The type of organic solvent used is not particularly limited, and may be a water-soluble organic solvent as described above. However, in the present invention, organic solvents that are less polar than water-soluble organic solvents (those that separate when mixed with water) can also be used as a dispersion medium for the CNF dispersion.

[0053] Examples of low-polarity organic solvents, though not limited to these, include benzene, toluene, xylene, n-hexane, n-octane, cyclohexane, methylcyclohexane, dichloromethane, dichloroethane, chloroform, methylene chloride, carbon tetrachloride, fluorotrichloromethane, trichlorotrifluoromethane, hexafluorobenzene, ethylbenzene, xylene, cyclopentyl methyl ether, and methyl tert-butyl ether.

[0054] In the present invention, the organic solvents used are the sensitizer (sensitizer dye) and the luminescent material (luminescent dye). Since both are hydrophobic, when these are mixed and used to form a composite film, from the viewpoint of being able to uniformly dissolve / disperse in a common good solvent such as tetrahydrofuran (THF), acetone and THF are preferred among water-soluble organic solvents, and toluene and chloroform are preferred among low-polarity organic solvents.

[0055] The ratio of organic solvent to dry solid is not particularly limited, but considering the efficiency of defibration, it is preferable to add the organic solvent so that the solid content concentration of anionically modified cellulose (including the hydrophobic agent portion) is 0.01 to 10% by mass, and more preferably 0.5 to 8.0% by mass.

[0056] After mixing a dry solid with an organic solvent, the cellulose is defibrated in the organic solvent to form a dispersion of hydrophobically modified anion-type CNF using the organic solvent as the dispersion medium. The apparatus used for defibration is not particularly limited, but high-speed rotary, colloidal mill, high-pressure, roll mill, and ultrasonic devices can be used. It is preferable to apply a strong shear force to the anion-modified cellulose dispersion during defibration. In particular, to efficiently defibrate, it is preferable to use a wet high-pressure or ultra-high-pressure homogenizer capable of applying a pressure of 50 MPa or more and a strong shear force to the dispersion. The pressure is more preferably 100 MPa or higher, and even more preferably 140 MPa or higher. Furthermore, prior to defibration and dispersion in the high-pressure homogenizer, the dispersion may be pre-treated using known mixing, stirring, emulsifying, and dispersion devices such as a high-speed shear mixer, if necessary.

[0057] (Sensitizer) In the present invention, the sensitizer is not particularly limited as long as it can absorb light energy, enter an excited triplet state, and transfer light energy (triplet energy) to the light-emitting element. For example, known photosensitizers can be used. From the viewpoint of efficiently transferring light energy, it is preferable to use a metal complex as the sensitizer.

[0058] The metals that make up the metal complex are not particularly limited, but examples include Li, Mg, Al, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ru, Pd, Ag, Re, Os, Ir, Pt, and Pb. Among these, Pt (platinum) and Pd (palladium) are preferred, with Pd (palladium) being more preferred, from the viewpoint of the "heavy atom effect," where the magnitude of the spin-orbit interaction increases due to the heavier the atom, making spin reversal easier. In other words, the spin forbidden rule weakens in heavy atoms within the molecule, making it easier for electrons to undergo an energy state change from a singlet state to a triplet state within the molecule.

[0059] Examples of ligands in metal complexes include porphyrins such as octaethylporphyrin or their substituted derivatives, phthalocyanines such as tetra-tert-butylphthalocyanine or their substituted derivatives, and naphthalocyanines such as tetra-tert-butylnaphthalocyanine or their substituted derivatives.

[0060] Examples of the substituent in the replacement body include hydrocarbon groups such as chain hydrocarbon groups such as alkyl groups such as methyl group, ethyl group, t-butyl group, alkenyl groups such as vinyl group, allyl group, and alkynyl groups such as ethynyl group, propynyl group; hydrocarbon groups having acid groups such as carboxyalkyl groups such as carboxymethyl group, carboxyethyl group, and the like.

[0061] Among these, as the ligand in the metal complex, porphyrin or its substituent and phthalocyanine or its substituent are preferable, and the substituent of porphyrin is more preferable.

[0062] That is, as the metal complex, a palladium complex having porphyrin or its substituent as a ligand, a palladium complex having phthalocyanine or its substituent as a ligand, and a palladium complex having naphthalocyanine or its substituent as a ligand are more preferable, and a palladium complex having a substituent of porphyrin as a ligand is particularly preferable.

[0063] The lower limit of the content ratio of the photosensitizer in all components excluding the solvent of the photo up-conversion composition of the present invention is preferably 1×10 -5 mol / kg, more preferably 1×10 -4 mol / kg, still more preferably 1×10 -3 mol / kg, and particularly preferably 3×10 -3 mol / kg. The upper limit of the above content ratio is preferably 1×10 -1 mol / kg, more preferably 5×10 -2 mol / kg, and still more preferably 1×10 -2 mol / kg. The "all components" of the photo up-conversion composition means the sum of components other than the solvent.

[0064] (Luminescent substance) In the present invention, the light-emitting element is not particularly limited as long as it receives triplet energy transfer from a sensitizer to produce an excited triplet state and then becomes an excited singlet state through collisions between the excited triplet states. For example, a condensed polycyclic aromatic compound can be mentioned. Here, a condensed polycyclic aromatic compound refers to a compound having at least one condensed aromatic ring.

[0065] Examples of condensed aromatic rings include condensed aromatic carbocyclic rings such as naphthalene rings, anthracene rings, tetracene rings, pentacene rings, perylene rings, and fluorene rings; and condensed aromatic heterocyclic rings such as benzothiophene rings, benzofuran rings, and quinoline rings. Among these, condensed aromatic carbocyclic rings are preferred, and anthracene rings are more preferred.

[0066] The condensed aromatic ring may have substituents. Examples of substituents on the condensed aromatic ring include linear hydrocarbon groups such as alkyl groups such as methyl, ethyl, and t-butyl groups; and alicyclic hydrocarbon groups such as cycloalkyl groups such as cyclopropyl and cyclohexyl groups.

[0067] Furthermore, the fused aromatic ring may also contain alicyclic rings such as cyclobutane, cyclohexane, or norbornane rings; or aliphatic heterocyclic rings such as piperidine, tetrahydrothiophene, or tetrahydrofuran rings.

[0068] The condensed polycyclic aromatic compound is preferably one that contains 3 to 8 aromatic rings.

[0069] Examples of condensed polycyclic aromatic compounds include compounds having an anthracene skeleton, tetracene skeleton, pentacene skeleton, perylene skeleton, fluorene skeleton, benzothiophene skeleton, and the like. Among these, compounds having an anthracene skeleton are preferred.

[0070] Specific examples of condensed polycyclic aromatic compounds include 9-(3-methyl-4-allyloxyphenyl)-10-(3-methyl-4-allyloxyphenylmethyl)anthracene, 9,10-diphenylanthracene, and rubrene. Among these, 9-(3-methyl-4-allyloxyphenyl)-10-(3-methyl-4-allyloxyphenylmethyl)anthracene is preferred.

[0071] The lower limit of the content of the light-emitting material in all components of the light upconversion composition excluding the solvent is 1 × 10 -3 mol / kg is preferred, and 1 × 10 -2 mol / kg is more preferable, 5 × 10 -2 mol / kg is more preferable, 1 × 10 -1 A concentration of mol / kg is particularly preferred. The upper limit of the above content is preferably 1 mol / kg, and 7 × 10⁻⁶ -1 mol / kg is more preferable, 5 × 10 -1 mol / kg is even more preferable.

[0072] The lower limit of the ratio of moles of light-emitting material to moles of sensitizer in the light upconversion composition (light-emitting material (mol) / sensitizer (mol)) is preferably 1, more preferably 10, and still more preferably 30. The upper limit of the above ratio is preferably 1,000, more preferably 100, and still more preferably 70.

[0073] (Ionic liquid) The photo-upconversion composition of the present invention contains an ionic liquid. The ionic liquid used in the present invention contains at least an imidazolium compound in which the organic cation is an imidazolium ion. In the present invention, an ionic liquid is a room-temperature molten salt (a salt that is liquid at 100°C or below) composed of ions that combine an organic cation and anion. Ionic liquids are characterized by being non-volatile, flame-retardant, heat-resistant, and safer than organic solvents.

[0074] Examples of organic cations include imidazolium ions such as dialkylimidazolium cations and trialkylimidazolium cations, tetraalkylammonium ions, alkylpyridinium ions, dialkylpyrrolidinium ions, and dialkylpiperidinium ions. Here, imidazolium ions are used in various applications such as battery electrolytes and organic synthesis solvents. In particular, imidazolium ions are used in non-volatile electrolyte solutions for dye-sensitized solar cells and are characterized by their high miscibility with sensitizer dye molecules. In the present invention, imidazolium ions are used as organic cations from the viewpoint of miscibility between the sensitizer dye molecules and the light-emitting dye molecules that constitute the photo-UC dye system.

[0075] Examples of imidazolium ions include 1,3-dimethylimidazolium cation, 1,3-diethylimidazolium cation, 1-ethyl-3-methylimidazolium cation, 1-butyl-3-methylimidazolium cation, 1-hexyl-3-methylimidazolium cation, 1-octyl-3-methylimidazolium cation, 1-decyl-3-methylimidazolium cation, 1-dodecyl-3-methylimidazolium cation, 1-tetradecyl-3-methylimidazolium cation, 1,2-dimethyl-3-propylimidazolium cation, 1-ethyl-2,3-dimethylimidazolium cation, 1-butyl-2,3-dimethylimidazolium cation, 1-hexyl-2,3-dimethylimidazolium cation, and 1-(2-methoxyethyl)-3-methylimidazolium cation. Here, imidazolium ions have been reported to have electrochemical applications, such as being used not only as a reaction solvent but also as an electrolyte in secondary batteries. In particular, they are used in non-volatile electrolyte solutions for dye-sensitized solar cells and are characterized by their high miscibility with sensitizer dye molecules. From the viewpoint of miscibility between the sensitizer dye molecules and the light-emitting dye molecules that constitute the photo-UC dye system, the 1-ethyl-3-methylimidazolium cation is preferred.

[0076] Examples of anions that act as counters to these organic cations include PF6 anion, PF3(C2F5)3 anion, PF3(CF3)3 anion, BF4 anion, BF2(CF3)2 anion, BF3(CF3) anion, bisoxalatoborate anion, Tf (trifluoromethanesulfonyl) anion, Nf (nonafluorobutanesulfonyl) anion, bis(fluorosulfonyl)imide anion, bis(trifluoromethanesulfonyl)imide anion, bis(pentafluoroethanesulfonyl)imide anion, dicyanoamine anion, halide anions, and carboxylate anions (e.g., acetate anion, trifluoroacetate anion). From the viewpoint of miscibility between the sensitizer dye molecule and the luminescent dye molecule constituting the photo-UC dye system, it is preferable to use the bis(trifluoromethanesulfonyl)imide anion.

[0077] These ionic liquids can be used individually or in combination of two or more.

[0078] Furthermore, the amount of ionic liquid contained in 100% by mass of the photo-upconversion composition of the present invention is preferably 10 to 90% by mass, more preferably 20 to 60% by mass, and even more preferably 30 to 50% by mass, from the viewpoint of optimal concentration and immobilization of the photo-UC dye system molecules.

[0079] (Other ingredients) The light upconversion composition of the present invention may also contain other components such as a solvent, a dye such as a dichroic dye, or fine particles (including nanoparticles).

[0080] (solvent) The solvent is not particularly limited and includes, for example, organic solvents and water. However, in this specification, ionic liquids are not included as solvents.

[0081] Specific examples of organic solvents include nitrile solvents such as acetonitrile and benzonitrile; halogenated solvents such as chloroform, dichloromethane, 1,2-dichloroethane, 1,1,2-trichloroethane, chlorobenzene, and o-dichlorobenzene; ether solvents such as tetrahydrofuran, dioxane, and anisole; aromatic hydrocarbon solvents such as benzene, toluene, and xylene; aliphatic hydrocarbon solvents such as cyclohexane, methylcyclohexane, n-pentane, n-hexane, n-heptane, n-octane, n-nonane, and n-decane; ketone solvents such as acetone, methyl ethyl ketone, and cyclohexanone; and ethyl acetate, butyl acetate, and ethyl acetate. Examples of suitable solvents include ester solvents such as cellulose acetate; polyhydric alcohols and their derivatives such as ethylene glycol, ethylene glycol monobutyl ether, ethylene glycol monoethyl ether, ethylene glycol monomethyl ether, dimethoxyethane, propylene glycol, diethoxymethane, triethylene glycol monoethyl ether, glycerin, and 1,2-hexanediol; alcohol solvents such as methanol, ethanol, propanol, isopropanol, and cyclohexanol; sulfoxide solvents such as dimethyl sulfoxide; and amide solvents such as N-methyl-2-pyrrolidone and N,N-dimethylformamide. Among these, chloroform, tetrahydrofuran, toluene, and anisole are preferred, with toluene and tetrahydrofuran being more preferred.

[0082] In the photo-upconversion composition of the present invention, when the total mass of the sensitizer and the luminescent agent is 10 parts by mass, the amount of fine cellulose fibers (solid content including the hydrophobic agent portion) blended is preferably 10 to 90 parts by mass, and more preferably 40 to 60 parts by mass.

[0083] Furthermore, in the photo-upconversion composition of the present invention, when the total mass of the sensitizer and the luminescent agent is 10 parts by mass, the amount of ionic liquid to be blended is preferably 10 to 90 parts by mass, more preferably 20 to 60 parts by mass, and even more preferably 30 to 50 parts by mass, from the viewpoint of optimal concentration and immobilization of the photo-UC dye system molecules composed of the sensitizer and the luminescent agent. Note that if the amount of ionic liquid blended is too high, the ionic liquid will crystallize, reducing the miscibility between the dye molecules and the ionic liquid and causing phase separation, which is undesirable. On the other hand, if the amount of ionic liquid blended is too low, the molecular mobility of the dye molecules will decrease, making diffusion and collision difficult, which is also undesirable.

[0084] (Method for preparing a light upconversion composition) The photo-upconversion composition of the present invention can be prepared, for example, by mixing essential components such as fine cellulose fibers, a sensitizer, a light-emitting element, and an imidazolium compound as an ionic liquid, as well as other components as needed. In this preparation, the mixture may be mixed using a solvent such as tetrahydrofuran, or the solvent may be removed from the resulting mixture.

[0085] If the photo-upconversion composition contains a solvent, the solvent content is preferably 99% by mass or less, and more preferably 90% by mass or less, when the total amount of the photo-upconversion composition is considered to be 100% by mass. The solvent content may also be 0% by mass.

[0086] According to the light upconversion composition of the present invention, the degassing treatment to remove dissolved oxygen, which was performed in conventional solution systems, can be eliminated.

[0087] The photo-upconversion composition of the present invention can be used in photo-upconversion methods in various forms such as dispersions, gels, and films. Among these, when applied as an optical element for converting light energy wavelength, the solid state is more convenient from the viewpoint of processing and installation compared to the dispersion or gel state. Furthermore, since photo-upconversion is based on a mechanism that occurs via an excited triplet state of dye molecules, it is preferable to use it as a film, as it requires an environment that does not come into contact with oxygen (air), which acts as a quencher.

[0088] (film) The film of the present invention is a film formed from the above-described light upconversion composition.

[0089] The film can be produced, for example, in the above-mentioned photo-upconversion composition, if a solvent is used in mixing the photo-upconversion composition, by removing the solvent using a solvent casting method, which involves casting the mixture onto a metal band or the like and drying off the solvent to obtain a film, thereby forming a solid film.

[0090] This film utilizes the photo-upconversion composition of the present invention, and by forming a solid film, the arrangement of sensitizers, light-emitting elements, etc., is more concentrated and fixed, thereby achieving higher photo-upconversion efficiency. Furthermore, this film eliminates the need for degassing treatment to remove dissolved oxygen, which was necessary in conventional solution systems.

[0091] (Light Upconversion Method) The light upconversion method of the present invention comprises the step of irradiating the film of the present invention with light. This makes it possible to generate light with a wavelength shorter than the wavelength of the irradiated light, that is, light with an energy higher than the energy of the irradiated light.

[0092] Examples of illumination light sources include LEDs, Xe lamps, lasers, and sunlight. The wavelength of the illumination light is, for example, 800 nm to 2,500 nm for near-infrared light, 400 nm to 800 nm for visible light, and 250 nm to 400 nm for ultraviolet light. Visible light is preferred as the illumination light, more preferably visible light with a wavelength of 450 nm to 600 nm, and even more preferably visible light with a wavelength of 500 nm to 560 nm. [Examples]

[0093] The present invention will be described in detail below with reference to examples. However, the present invention is not limited to these examples.

[0094] (Manufacturing Example 1) (Preparation of CNF dispersion 1) 500 g (absolutely dry) bleached, unbeaten kraft pulp (whiteness 85%) derived from coniferous trees was added to 500 mL of an aqueous solution containing 780 mg of TEMPO (Sigma Aldrich) and 75.5 g of sodium bromide, and the mixture was stirred until the pulp was uniformly dispersed. Sodium hypochlorite aqueous solution was added to the reaction system to a level of 6.0 mmol / g to initiate the oxidation reaction. During the reaction, the pH of the system decreased, but 3M sodium hydroxide aqueous solution was added sequentially to adjust the pH to 10. The reaction was terminated when the sodium hypochlorite was consumed and the pH of the system no longer changed. The mixture after the reaction was filtered through a glass filter to separate the pulp, and the pulp was thoroughly washed with water to obtain carboxylated cellulose. The amount of carboxyl groups in this carboxylated cellulose was 1.42 mmol / g.

[0095] The solid content of carboxylated cellulose was adjusted to 5% by mass with water, and 10% hydrochloric acid was added to convert the sodium salt type carboxyl group (-COONa) in the carboxylated cellulose to the acid type (-COOH). Then, dehydration was performed by suction filtration using a glass filter. The solid content of the carboxylated cellulose was adjusted again to 5% by mass with water and then dehydrated. This process was repeated three times to obtain a dispersion of acid-type carboxylated cellulose with a solid content of 25% by mass.

[0096] To 1.5 kg of the obtained dispersion of acid-type carboxylated cellulose with a solid content concentration of 25% by mass, 1 equivalent of JEFFAMINE® M-2070 (HUNTSMAN, molecular weight 2000), a polyetheramine, was added as a hydrophobic agent relative to the amount of carboxyl groups. The mixture was mixed and stirred at 1500 rpm for 10 minutes using a Super Mixer (SMV-20B, Kawata Co., Ltd.). The temperature of the sample reached 70°C due to the heat generated by stirring. Next, the mixture was stirred at 1500 rpm for 40 minutes while blowing air from the top lid of the Super Mixer, simultaneously drying (removing the dispersion medium) and grinding the carboxylated cellulose. The temperature of the sample during drying and grinding was 60-70°C. This produced a dried solid (solid content concentration 97% by mass) of pulverized carboxylated cellulose (hydrophobized carboxylated cellulose) with the hydrophobic agent attached.

[0097] To the obtained dried solid, toluene was added so that the solid content concentration including the hydrophobic agent portion was 7.6% by mass, and the mixture was stirred at 3000 rpm for 10 minutes. Subsequently, the mixture was treated once at 80 MPa and then twice at 150 MPa using an ultra-high pressure homogenizer (defibrillation) to obtain a dispersion of hydrophobically carboxylated CNF (CNF dispersion 1) with toluene as the dispersion medium.

[0098] (Example 1) (Preparation of light upconversion composition) 0.3725 mg (4.0 × 10) of 2,3,7,8,12,13,17,18-Octaethyl-21H,23H-porphine palladium(II) (PdOEP) (sensitizer dye), represented by the following formula (X-1) -7 9.628 mg (2.0 × 10¹⁶) of anthracene compound represented by the following formula (Y-1) (9,10-Diphenylanthracene (DPA), manufactured by Sigma-Aldrich) (luminescent dye), i.e., 0.4 μmol. -5 20 μmol of ions (i.e., 20 μmol) of an imidazolium compound represented by the following formula (Z-1) (1-Ethyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide, hereinafter sometimes abbreviated as "EMI-TFSI") as an ionic liquid, and 132 mg of CNF dispersion 1 with a solid content concentration of 7.6% by mass were added and mixed with 1 mL of tetrahydrofuran. The mixture was then heated using a hot plate to remove the tetrahydrofuran and toluene, thereby preparing a photo-upconversion composition (composite film). The composition ratio of the photo-upconversion composition was such that the ratio of the total mass of the sensitizer dye and the luminescent dye (hereinafter sometimes referred to as "dye system") to the mass of the ionic liquid and the CNF solids containing the hydrophobic agent portion (dye system / ionic liquid / CNF) was 10 / 80 / 10 (by mass%).

[0099] [ka]

[0100] [ka]

[0101] [ka]

[0102] (Example 2) A photo-upconversion composition (composite film) was prepared in the same manner as in Example 1, except that the amount of ionic liquid used was changed to 70 mg and the amount of CNF dispersion 1 was changed to 263 mg. The composition ratio of the obtained photo-upconversion composition was 10 / 70 / 20 (mass%), which is the ratio of the total mass of the dye system to the mass of the ionic liquid and the CNF solids containing the hydrophobic agent portion (dye system / ionic liquid / CNF).

[0103] (Example 3) A photo-upconversion composition (composite film) was prepared in the same manner as in Example 1, except that the amount of ionic liquid used was changed to 60 mg and the amount of CNF dispersion 1 was changed to 395 mg. The composition ratio of the obtained photo-upconversion composition was 10 / 60 / 30 (mass%), which is the ratio of the total mass of the dye system to the mass of the ionic liquid and the mass of the CNF solids including the hydrophobic agent portion (dye system / ionic liquid / CNF).

[0104] (Example 4) A photo-upconversion composition (composite film) was prepared in the same manner as in Example 1, except that the amount of ionic liquid used was changed to 50 mg and the amount of CNF dispersion 1 was changed to 526 mg. The composition ratio of the obtained photo-upconversion composition was 10 / 50 / 40 (mass%), which is the ratio of the total mass of the dye system to the mass of the ionic liquid and the CNF solids including the hydrophobic agent portion (dye system / ionic liquid / CNF).

[0105] (Example 5) A photo-upconversion composition (composite film) was prepared in the same manner as in Example 1, except that the amount of ionic liquid used was changed to 40 mg and the amount of CNF dispersion 1 was changed to 658 mg. The composition ratio of the obtained photo-upconversion composition was 10 / 40 / 50 (mass%), which is the ratio of the total mass of the dye system to the mass of the ionic liquid and the mass of the CNF solids including the hydrophobic agent portion (dye system / ionic liquid / CNF).

[0106] (Comparative Example 1) Similar to Example 1, a dye system consisting of a sensitizer dye and a luminescent dye was prepared. EMI-TFSI, the same imidazolium compound as in Example 1, was used as the ionic liquid. Without adding a CNF dispersion, 1 mL of tetrahydrofuran was added and mixed. The mixture was then heated using a hot plate to remove the tetrahydrofuran, thereby preparing the composition (composite film). The composition ratio of the photo-upconversion composition was set to 10 / 90 (mass%), where the total mass of the dye system was equal to the mass of the ionic liquid (dye system / ionic liquid).

[0107] (Comparative Example 2) A photo-upconversion composition (composite film) was prepared in the same manner as in Example 1, except that the amount of CNF dispersion 1 was changed to 1,184 mg without adding an ionic liquid. The composition ratio of the obtained photo-upconversion composition was 10 / 90 (mass%), which is the ratio of the total mass of the dye system to the mass of the CNF solids including the hydrophobic agent portion (dye system / CNF).

[0108] (evaluation) (Preparation of samples for measurement) For the compositions prepared in Examples 1-5 and Comparative Examples 1 and 2, samples for measurement were prepared by sandwiching each composition between two glass slides and a PET film used as a spacer.

[0109] (Appearance evaluation) The measurement samples prepared from the compositions in Examples 1-5 and Comparative Examples 1 and 2 were visually inspected for appearance. Furthermore, the same samples were observed using a polarizing microscope. Miscibility was evaluated according to the following criteria. ○: The external appearance was transparent and optically uniform, and the optical structure observed in the polarized light microscope image was uniform. △: The external appearance was semi-transparent with some turbidity observed, and the optical structure in the polarized microscope image was partially non-uniform. ×: The appearance was cloudy, and the optical structure observed under a polarizing microscope was heterogeneous. (Phase separation was observed.)

[0110] (Spectroscopic characterization) (Ultraviolet-Visible absorption spectroscopy measurement) The ultraviolet-visible absorption spectra were measured for the measurement samples prepared as described above using the compositions of Examples 1-5 and Comparative Examples 1 and 2.

[0111] Figure 1 shows the results for the compositions of Examples 1-5 and Comparative Examples 1 and 2. In Figure 1, the horizontal axis represents wavelength, and the vertical axis represents absorbance. In Figure 1, waveform 1 represents the composition of Comparative Example 1, waveform 2 represents the composition of Example 1, waveform 3 represents the composition of Example 2, waveform 4 represents the composition of Example 3, waveform 5 represents the composition of Example 4, waveform 6 represents the composition of Example 5, and waveform 7 represents the measurement results for Comparative Example 2. Figure 2 shows photographs of the appearance of the measurement samples (cells) prepared from the compositions of Comparative Example 1, Example 1, and Example 4.

[0112] Figure 1 shows that in the absorption spectra of Examples 1-5 and Comparative Example 2, absorption peak wavelengths (λ=516nm, 548nm) attributable to the Q-band of PdOEP used as a sensitizing dye were confirmed. Furthermore, the π-π of the anthracene compound used as a luminescent dye was also observed. * An absorption peak in the ultraviolet region at λmax = 373 nm, caused by a transition, was observed. No absorption was observed at all in the composition of Comparative Example 1. This is thought to be because the composition was in a phase-separated state, resulting in light scattering. In the composition of Example 1, a higher baseline was observed. This is thought to be because the cell's appearance indicates a partially phase-separated state, which caused light scattering.

[0113] (Emission spectrum measurement) Measurement samples prepared as described above using the compositions of Examples 1-5 and Comparative Examples 1 and 2 were excited with a green laser with an excitation wavelength λexc = 532 nm and an excitation intensity of 20 mW, and the emission spectra were measured. The results for the compositions of Examples 1-5 and Comparative Examples 1 and 2 are shown in Figure 3. In Figure 3, the horizontal axis represents wavelength, and the vertical axis represents emission intensity. In Figure 3, waveform 1 represents the composition of Comparative Example 1, waveform 2 represents the composition of Example 1, waveform 3 represents the composition of Example 2, waveform 4 represents the composition of Example 3, waveform 5 represents the composition of Example 4, waveform 6 represents the composition of Example 5, and waveform 7 represents the measurement results for Comparative Example 2.

[0114] Figure 3 shows that upconversion fluorescence was observed in the wavelength range of 400-500 nm for the compositions of Examples 1-5 and Comparative Example 2. The fluorescence intensity, in descending order, was Example 5 > Example 4 > Example 3 > Comparative Example 2 > Example 1 > Example 2 > Comparative Example 1. The fluorescence intensity of the compositions of Examples 3-5 was stronger than that of the composition of Comparative Example 2. The fluorescence intensity of the compositions of Examples 1 and 2 was weaker than that of the composition of Comparative Example 2. In Examples 1-5, it was confirmed that the fluorescence intensity increased as the CNF content increased. In Comparative Example 1, the dye system and ionic liquid were in a phase-separated state, and the incident light was scattered and did not function effectively, so the optical properties could not be confirmed.

[0115] (Relative quantum yield Φ) UC ) The measurement samples prepared as described above using the compositions of Examples 1-5 and Comparative Examples 1 and 2 were excited with a green laser with an excitation wavelength λexc = 532 nm and an excitation intensity varied within a range of up to 20 mW, and the photo-upconversion fluorescence was measured. A chloroform solution of rhodamine B was used as the standard substance, and the quantum yield was calculated according to the following formula. The results are shown in Figure 4. In Figure 4, the horizontal axis represents power density, and the vertical axis represents the upconversion quantum yield (Φ). UCFigure 4 shows the following: In Figure 4, line 1 represents the composition of Comparative Example 1, line 2 represents the composition of Example 1, line 3 represents the composition of Example 2, line 4 represents the composition of Example 3, line 5 represents the composition of Example 4, line 6 represents the composition of Example 5, and line 7 represents the measurement results of Comparative Example 2.

[0116]

number

[0117] Figure 4 shows that the composition of Example 5 had the highest relative quantum yield. In Examples 1 to 5, the relative quantum yield (Φ UC It was observed that the concentration (CNF) increased as the proportion of CNF in the composition increased. This is thought to be because, as the proportion of CNF in the composite film increases, the CNF acts as an admixture, allowing the photo-UC dye system molecules to be uniformly dispersed in the ionic liquid, resulting in concentration and immobilization.

[0118] [Table 1]

[0119] As can be seen from Table 1, the photo-upconversion compositions (composite films) of Examples 1 to 5 of the present invention, which contain fine cellulose fibers, a sensitizer, a light-emitting element, and an imidazolium compound, exhibited photo-upconversion fluorescence even without degassing. In particular, the composite film of Example 5 showed a relative quantum yield (Φ UC ) achieved a relative quantum yield of approximately 30%, which is significantly higher than conventional methods. However, in Examples 1 and 2, where the CNF addition amount was low (20% by mass or less), the mixture was partially in a phase-separated state, and therefore its optical upconversion luminescence performance is not considered to be very good. In the prior art, for example, in the composition of Patent Document 2, the relative quantum yield Φ UCThe percentage was approximately 2%.

Claims

1. A light upconversion composition comprising fine cellulose fibers, a sensitizer, a light-emitting element, and an imidazolium compound.

2. The photo-upconversion composition according to claim 1, wherein the fine cellulose fibers are anion-modified cellulose nanofibers.

3. The photo-upconversion composition according to claim 2, wherein the anion-modified cellulose nanofiber is a carboxylated cellulose nanofiber.

4. The sensitizer is a metal complex, The photo-upconversion composition according to claim 1, wherein the metal complex is a palladium complex or a platinum complex.

5. The photo-upconversion composition according to claim 1, wherein the light-emitting element is a condensed polycyclic aromatic compound.

6. A film formed from the light upconversion composition described in claim 1.

7. A light upconversion method comprising the step of irradiating the film described in claim 6 with light.

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