JP7764997B2 - Fluorene compound and method for producing the same - Google Patents

Description

The present invention relates to a novel fluorene compound.

Inorganic and organic light-emitting materials are used as light sources for devices such as light-emitting diodes (LEDs). Among these light-emitting materials, inorganic light-emitting materials tend to complicate the device manufacturing process, resulting in high manufacturing equipment costs and making it difficult to achieve large-area light emission. Therefore, there is a demand for organic light-emitting materials, which can be easily and efficiently produced using methods such as coating. Compounds with a fluorene skeleton are known as such organic light-emitting materials.

JP 2020-164518 A (Patent Document 1) discloses a fluorene compound represented by the following formula (1) as a light-emitting material capable of emitting light with high luminescence quantum efficiency (quantum efficiency or quantum yield).

(In the formula, Z ^1a and Z ^1b each independently represent an arene ring, Z ^2a and Z ^2b each independently represent an arene ring, R ^1a , R ^1b , R ^2a , R ^2b , R ^3a and R ^3b each independently represent a substituent, A ^1a and A ^1b each independently represent a linear or branched alkylene group, k1 and k2 each independently represent an integer of 0 or more, m1 and m2 each independently represent an integer of 0 to 4, n1 and n2 each independently represent an integer of 0 to 4, p1 and p2 each independently represent an integer of 0 or more, m1 + n1 and m2 + n2 each independently represent an integer of 0 to 4, and at least one of m1 and m2 is an integer of 1 or more.)

Japanese Patent Application Laid-Open No. 2020-164518

In the examples of Patent Document 1, fluorene compounds such as 9,9-bis(2-phenylethyl)-2,7-diphenylfluorene (BEPF-Ph) in which Z ^1a and Z ^1b are benzene rings, 9,9-bis(2-phenylethyl)-2,7-di(4-biphenylyl)fluorene (BEPF-BPh) in which Z ^1a and Z ^1b are biphenyl rings, and 9,9-bis(2-phenylethyl)-2,7-di(2-naphthyl)fluorene (BEPF-Np) in which Z ^1a and Z ^1b are naphthalene rings are prepared as the compound represented by formula (1), and their luminescence properties are evaluated.

These fluorene compounds have been shown to be capable of emitting ultraviolet or visible light with a maximum wavelength λ _em,max of 360 to 399 nm in their emission spectra in solution, which readily reflect the pure luminescence characteristics based on their chemical structure. While these fluorene compounds exhibit high luminescence quantum efficiency, the resulting visible light with wavelengths less than 400 nm tends to be invisible (difficult to see) or perceived as dim due to the standard relative luminous efficiency of humans. To perceive blue colors with low standard relative luminous efficiency as brighter, it is preferable for the emission peak to be on the long wavelength side of 400 nm or more, and visibility improves as the wavelength increases (because the standard relative luminous efficiency increases up to 565 nm). However, if the wavelength of the emission peak is too long, the base (or end) of the emission peak extends into the light blue to blue-green wavelength range, making it impossible to perceive as pure blue. Therefore, there is a demand for bright blue-emitting materials that have an emission peak in a specific wavelength range, exhibit high quantum efficiency, and emit strong blue light.

Accordingly, the object of the present invention is to provide a fluorene compound that has an emission peak in the wavelength region of 400 to 460 nm and is capable of emitting blue light with high luminescence quantum efficiency (quantum efficiency or quantum yield), as well as a method for producing the same and uses thereof.

As a result of extensive research to achieve the above-mentioned objectives, the inventors discovered that a specific fluorene compound has an emission peak in the wavelength region of 400 to 460 nm and exhibits extremely high luminescence quantum efficiency, leading to the completion of the present invention.

That is, the novel fluorene compound of the present invention is represented by the following formula (1):

(wherein Z ^1a and Z ^1b each independently represent a polycyclic C _16-18 arene ring;
R ^1a and R ^1b each independently represent a substituent; k1 and k2 each independently represent an integer of 0 or more;
m1 and m2 each independently represent an integer of 0 to 4, and at least one of m1 and m2 is an integer of 1 or more;
R ^2a and R ^2b each independently represent a substituent; n1 and n2 each independently represent an integer of 0 to 4;
m1+n1 and m2+n2 each independently represent an integer of 0 to 4,
A ^1a and A ^1b each independently represent a linear or branched alkylene group;
^Z2a and ^Z2b each independently represent an arene ring, ^R3a and ^R3b each independently represent a substituent, and p1 and p2 each independently represent an integer of 0 or more).

In the formula (1), Z ^1a and Z ^1b are terphenylene rings or pyrene rings, m1 and m2 are integers of 0 to 2,
A ^1a and A ^1b are linear or branched C _1-6 alkylene groups;
Z ^2a and Z ^2b may be a C _6-12 arene ring.

In addition, in the formula (1), Z ^1a and Z ^1b are pyrene rings, m1 and m2 are 1,
A ^1a and A ^1b are linear or branched C _1-4 alkylene groups;
Z ^2a and Z ^2b may each be a benzene ring, a naphthalene ring or a biphenyl ring.

Furthermore, the compound represented by formula (1) may be a blue light-emitting material having an emission spectrum in a dichloromethane solution state, which includes at least one emission peak with a maximum wavelength λ _em,max of about 410 to 460 nm and a half-width of about 70 nm or less, and an emission quantum efficiency of about 40% or more. Furthermore, the compound represented by formula (1) may be in the form of a crystal.

The present invention encompasses a method for producing a compound represented by formula (1), which includes either step (i) or (ii) below:

(i) A step of coupling a compound represented by the following formula (2) with a compound represented by the following formula (3):

(In the formula, X ^1a and X ^1b each independently represent a group capable of forming a carbon-carbon bond by a coupling reaction,
^X2 represents a group capable of forming a carbon-carbon bond by a coupling reaction together with ^X1a and/or ^X1b ;
Z ¹ is the same as Z ^1a and/or Z ^1b in formula (1),
R ¹ is the same as R ^1a and/or R ^1b in formula (1), k is the same as k1 and/or k2 in formula (1),
^Z2a , ^Z2b , ^R2a , ^R2b , ^R3a , ^R3b , ^{A1a, A1b ,} m1, m2, n1, n2, m1+n1, m2+n2, p1 and p2 are the same as in formula (1).
(ii) In the step (i), when Z ¹ of the compound represented by formula (3) is a C _16-18 arene ring assembly, reacting in the presence of an ether.

The present invention also encompasses a method for exciting a compound represented by formula (1) to emit light, as well as a luminescent composition containing the compound represented by formula (1). The luminescent composition may further contain a binder component. The binder component may contain at least one resin selected from a (meth)acrylic resin, a styrene resin, a polycarbonate resin, and a silicon resin. In the luminescent composition, the ratio of the compound represented by formula (1) to the binder component (former/latter) (mass ratio) may be approximately 1/0.5 to 1/1000. The luminescent spectrum of the luminescent composition may include at least one emission peak having a maximum wavelength λ _em,max of approximately 410 to 460 nm and a half-width of approximately 70 nm or less, and may have a luminescence quantum efficiency of approximately 70% or more.

Furthermore, the present invention includes a light-emitting device containing a compound represented by formula (1).

In this specification and claims, the number of carbon atoms may be indicated as C ₁ , C ₆ , C ₁₀ , etc. For example, an alkyl group having one carbon atom is indicated as "C ₁ alkyl," and an aryl group having 6 to 10 carbon atoms is indicated as "C _6-10 aryl."

In addition, in this specification and claims, "solid state" means a solidified state in which fluidity has been lost and the substance is not dispersed in a dispersion medium (binder component or matrix) such as a resin.

The fluorene compound of the present invention has a specific chemical structure, and therefore has an emission peak (maximum wavelength λ _em,max ) in the wavelength region of 400 to 460 nm, and can emit blue light with high luminescence quantum efficiency. In particular, it can emit pure (monochromatic or highly color-pure) blue light. Furthermore, the fluorene compound can emit blue light with high luminescence quantum efficiency even in the form of a composition (or coating film) containing a polymer (resin or binder component), and therefore, by using the fluorene compound as a blue-emitting material, excellent organic electroluminescence (EL) devices [or organic light-emitting diodes (OLED)] can be easily and efficiently produced.

FIG. 1 shows the measurement results of the excitation spectrum (solid line) and emission spectrum (dashed line) of the BEPF-TPh obtained in Example 1 in a solid state. FIG. 2 shows the measurement results of the excitation spectrum (solid line) and emission spectrum (dashed line) of the BEPF-Py obtained in Example 2 in a solid state. FIG. 3 shows the measurement results of the excitation spectrum (solid line) and emission spectrum (dashed line) of BEPF-TPh obtained in Example 1 in a dichloromethane solution state. FIG. 4 shows the measurement results of the excitation spectrum (solid line) and emission spectrum (dashed line) of BEPF-Py obtained in Example 2 in a dichloromethane solution state. FIG. 5 shows the measurement results of the excitation spectrum (solid line) and the emission spectrum (dashed line) in the coating film state of BEPF-TPh/PS (mass ratio) = 1/10 obtained in Example 1. FIG. 6 shows the measurement results of the excitation spectrum (solid line) and the emission spectrum (dashed line) in the coating film state of BEPF-TPh/PC (mass ratio) = 1/10 obtained in Example 1. FIG. 7 shows the measurement results of the excitation spectrum (solid line) and emission spectrum (dashed line) in the coating film state of BEPF-TPh/PMMA (mass ratio) = 1/10 obtained in Example 1. FIG. 8 shows the measurement results of the excitation spectrum (solid line) and the emission spectrum (dashed line) in the coating film state of BEPF-TPh/PPSQ (mass ratio) = 1/10 obtained in Example 1. FIG. 9 shows the measurement results of the excitation spectrum (solid line) and the emission spectrum (dashed line) in the coating film state of BEPF-Py/PS (mass ratio) = 1/10 obtained in Example 2. FIG. 10 shows the measurement results of the excitation spectrum (solid line) and the emission spectrum (dashed line) in the coating film state of BEPF-Py/PC (mass ratio) = 1/10 obtained in Example 2. FIG. 11 shows the measurement results of the excitation spectrum (solid line) and the emission spectrum (dashed line) in the coating film state of BEPF-Py/PMMA (mass ratio) = 1/10 obtained in Example 2. FIG. 12 shows the measurement results of the excitation spectrum (solid line) and the emission spectrum (dashed line) in the coating film state of BEPF-Py/PPSQ (mass ratio) = 1/10 obtained in Example 2.

[Fluorene compounds]
The fluorene compound of the present invention is represented by the following formula (1).

(wherein Z ^1a and Z ^1b each independently represent a polycyclic C _16-18 arene ring;
R ^1a and R ^1b each independently represent a substituent; k1 and k2 each independently represent an integer of 0 or more;
m1 and m2 each independently represent an integer of 0 to 4, and at least one of m1 and m2 is an integer of 1 or more;
R ^2a and R ^2b each independently represent a substituent; n1 and n2 each independently represent an integer of 0 to 4;
m1+n1 and m2+n2 each independently represent an integer of 0 to 4,
A ^1a and A ^1b each independently represent a linear or branched alkylene group;
^Z2a and ^Z2b each independently represent an arene ring, ^R3a and ^R3b each independently represent a substituent, and p1 and p2 each independently represent an integer of 0 or more).

In the formula (1), examples of the polycyclic arene rings represented by Z ^1a and Z ^1b include fused polycyclic arene rings (fused polycyclic aromatic hydrocarbon rings) and ring-assembled arene rings (ring-assembled polycyclic aromatic hydrocarbon rings).

In this specification and claims, the term "ring assembly arene ring" refers to two or more ring systems (arene ring systems) directly linked by single or double bonds, with the number of bonds directly linking the rings being one less than the number of ring systems. For example, as will be described later, phenylnaphthalene rings are included in the category of ring assembly arene rings even though they have a fused polycyclic arene ring skeleton, and are clearly distinguished from "fused polycyclic arene rings" such as pyrene rings (non-ring assembly arene rings).

Examples of the fused polycyclic C 16-18 arene ring represented by Z ^1a and Z ^1b include fused tetracyclic C _16-18 arene rings such as a naphthacene ring, a benzo[a]anthracene ring, a chrysene ring, _{a benzo[c]phenanthrene ring, a pyrene ring, a triphenylene ring, etc. A preferred fused polycyclic C 16-18 arene} ring is a pyrene ring.

Examples of the C _16-18 arene ring assembly represented by Z ^1a and Z ^1b include phenylnaphthalene rings such as 1-phenylnaphthalene ring and 2-phenylnaphthalene ring, and terphenyl rings such as o-terphenyl ring, m-terphenyl ring and p-terphenyl ring. A preferred C _16-18 arene ring assembly is a p-terphenyl ring.

Preferred rings Z ^1a and Z ^1b are fused polycyclic C _16-18 arene rings such as a pyrene ring, and terphenyl rings such as a p-terphenyl ring. From the viewpoints of more effectively improving the quantum efficiency and facilitating an improvement in the extinction coefficient, fused polycyclic C _16-18 arene rings such as a pyrene ring are more preferred, and a pyrene ring is particularly preferred.

Generally, as the number of aromatic rings (benzene ring skeletons) in a chemical structure increases via condensation and/or single bonds, particularly via condensation, it is expected that the conjugation length will increase and the emission wavelength (wavelength at the emission peak) will become longer. However, specific emission characteristics, such as the extent to which the wavelength will become longer and the emission quantum efficiency, cannot be predicted from the chemical structure. In other words, it is extremely difficult to design a highly efficient light-emitting material having an emission peak in a predetermined wavelength region. The compound represented by formula (1) has a chemical structure in which polycyclic C _16-18 arene rings represented by Z ^1a and Z ^1b are bonded to fluorene rings, and many aromatic rings are connected via condensation or single bonds, but has an emission peak in a predetermined wavelength region without excessively long wavelength and can emit blue light with high quantum efficiency.

The types of rings Z ^1a and Z ^1b may be different from each other, but are preferably the same. When m1 and/or m2 are 2 or more, the types of the two or more rings Z ^1a and/or Z ^1b may be the same or different from each other.

Furthermore, rings Z ^1a and/or Z ^1b may be substituted at any of the 1- to 4-positions and the 5- to 8-positions of the fluorene skeleton. When m1 and m2 are 1, preferred substitution positions (or bonding positions) are those which are symmetrical on the paper in formula (1), such as the 1- and 8-positions, the 2- and 7-positions, the 3- and 6-positions, and the 4- and 5-positions, and particularly preferred are the 2- and 7-positions.

When rings Z ^1a and Z ^1b are pyrene rings, the bonding positions to the fluorene skeleton in rings Z ^1a and Z ^1b are, for example, the 1-position, 2-position, or 4-position of the pyrene ring, preferably the 1-position; when rings Z ^1a and Z ^{1b are p-terphenyl rings, the bonding positions to the fluorene skeleton in rings Z 1a and Z 1b} are, for example, the 2-position, 3-position, or 4-position of the p-terphenyl ring, preferably the 4-position.

Examples of the substituents represented by R ^1a and R ^1b include a hydrocarbon group (or group [-R ^A ]), a halogen atom, a hydroxyl group, a group [-OR ^A ] (wherein R ^A represents the hydrocarbon group), a hydroxy(poly)alkoxy group, a thiol group (mercapto group), a group [-SR ^A ] (wherein R ^A represents the hydrocarbon group), an acyl group, a carboxyl group, an alkoxycarbonyl group, an amino group, a substituted amino group, a cyano group, a nitro group, a trialkylsilyl group, a dialkylhydrosilyl group, etc. In this specification and claims, the term "(poly)alkoxy group" is used to include both an alkoxy group and a polyalkoxy group.

Examples of the hydrocarbon group (or group [—R ^A ]) include an alkyl group, a cycloalkyl group, an aryl group, and groups in which two or more of these hydrocarbon groups are combined (or bonded).

Examples of the alkyl group include linear or branched C 1-20 alkyl groups such as methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, s-butyl, t-butyl, n-hexyl, n-octyl, 2-ethylhexyl, n-decyl, and n-dodecyl groups. Linear or branched C _1-12 alkyl groups are preferred, and linear or branched C _1-6 alkyl groups are more _preferred .

Examples of the cycloalkyl group include a C _5-10 cycloalkyl group such as a cyclopentyl group and a cyclohexyl group, and a C _5-8 cycloalkyl group is preferred.

Examples of the aryl group include a phenyl group, a naphthyl group such as a 1-naphthyl group or a 2-naphthyl group, a biphenylyl group, an anthryl group, a phenanthryl group or other C _6-14 aryl group, etc. A C _6-10 aryl group is preferred.

Examples of groups in which two or more hydrocarbon groups are combined (bonded) include alkylaryl groups and aralkyl groups. Examples of alkylaryl groups include mono- or di-C _1-6 alkyl C _6-10 aryl groups such as methylphenyl group (tolyl group) and dimethylphenyl group (xylyl group). Examples of aralkyl groups include C _6-10 aryl C _1-6 alkyl groups such as phenylmethyl group (benzyl group) and 2-phenylethyl group (phenethyl group).

Examples of halogen atoms include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms.

Examples of the group [—OR ^A ] include groups corresponding to the hydrocarbon group represented by R ^A , such as an alkoxy group, a cycloalkyloxy group, an aryloxy group, and an aralkyloxy group.

Examples of the alkoxy group include alkoxy groups corresponding to the alkyl groups exemplified in the section on R 1 ^A , such as linear or branched C _1-10 alkoxy groups such as a methoxy group.

Examples of the cycloalkyloxy group include cycloalkyloxy groups corresponding to the cycloalkyl groups exemplified in the section on R 1 ^A , for example, C _5-10 cycloalkyloxy groups such as cyclohexyloxy group.

Examples of the aryloxy group include aryloxy groups corresponding to the aryl groups exemplified in the section on R ^A , such as C _6-10 aryloxy groups such as a phenoxy group.

Examples of the aralkyloxy group include aralkyloxy groups corresponding to the aralkyl groups exemplified in the section on R 1 ^A , for example, C _6-10 aryl-C _1-4 alkyloxy groups such as benzyloxy group.

Examples of the hydroxy(poly)alkoxy group include hydroxy(poly)C _2-6 alkoxy groups such as a 2-hydroxyethoxy group, a 2-hydroxypropoxy group, and a 2-(2-hydroxyethoxy)ethoxy group.

Examples of the group [—SR ^A ] include groups corresponding to the hydrocarbon group represented by R ^A , such as alkylthio groups, cycloalkylthio groups, arylthio groups, and aralkylthio groups.

Examples of the alkylthio group include alkylthio groups corresponding to the alkyl groups exemplified in the section on R 1 ^A , for example, C _1-10 alkylthio groups such as methylthio groups.

Examples of the cycloalkylthio group include cycloalkylthio groups corresponding to the cycloalkyl groups exemplified in the section on R ^A above, for example, C _5-10 cycloalkylthio groups such as cyclohexylthio group.

Examples of the arylthio group include arylthio groups corresponding to the aryl groups exemplified in the section on R ^A above, for example, C _6-10 arylthio groups such as phenylthio group (or thiophenoxy group).

Examples of the aralkylthio group include aralkylthio groups corresponding to the aralkyl groups exemplified in the section on R ^A above, for example, C _6-10 aryl-C _1-4 alkylthio groups such as benzylthio groups.

Examples of the acyl group include C _1-6 acyl groups such as an acetyl group.

Examples of the alkoxycarbonyl group include C _1-6 alkoxy-carbonyl groups such as methoxycarbonyl groups.

Examples of the substituted amino group include mono- or di-alkylamino groups, mono- or di-acylamino groups, etc. Examples of the mono- or di-alkylamino group include mono- or di-C _1-4 alkylamino groups such as dimethylamino group, etc. Examples of the mono- or di-acylamino group include mono- or di-(C _1-6 acyl)amino groups such as diacetylamino group, etc.

Examples of the trialkylsilyl group include triC _1-6 alkylsilyl groups such as trimethylsilyl group.

Examples of the dialkylhydrosilyl group include di-C _1-6 alkylhydrosilyl groups such as dimethylhydrosilyl group.

These groups R ^1a and R ^1b may be used alone or in combination of two or more. When the groups R ^1a and R ^1b are cyclic hydrocarbon groups such as aryl groups, they may form a ring assembly such as a ring assembly arene ring together with the rings Z ^1a and Z ^1b , but it is preferable that the groups R ^1a and R ^1b are not aryl groups.

When the number of substitutions k1 or k2 is 1 or more, preferred groups R ^1a and R ^1b include hydrocarbon groups such as alkyl groups, hydroxyl groups, hydroxy(poly)alkoxy groups, and carboxyl groups. The alkyl group is more preferably a linear or branched C _1-6 alkyl group such as methyl, and the hydroxy(poly)alkoxy group is more preferably a hydroxy(mono- to deca)C _2-4 alkoxy group such as 2-hydroxyethoxy. Of these groups R ^1a and R ^1b , C _1-4 alkyl groups such as methyl, hydroxyl groups, and carboxyl groups are preferred.

The substitution numbers k1 and k2 of the groups R ^1a and R ^1b may be selected depending on the types of the rings Z ^1a and Z ^1b , and can be selected, for example, from integers of about 0 to 7. Preferred ranges are, in the following stepwise order, integers of 0 to 6, integers of 0 to 5, integers of 0 to 4, integers of 0 to 3, and integers of 0 to 2, more preferably 0 or 1, and particularly preferably 0.

The two substitution numbers k1 and k2 may be different from each other, but are preferably the same. When the substitution number k1 or k2 is 2 or more, the types of the two or more groups R ^1a or R ^1b substituting on ring Z ^1a or Z ^1b may be the same or different from each other. Furthermore, the types of groups R ^1a and R ^1b may be different from each other, but are preferably the same. The substitution positions of groups R ^1a and R ^1b are not particularly limited and may be selected depending on the types of rings Z ^1a and Z ^1b .

The numbers of substitutions m1 and m2 in the group [-Z ^1a -(R ^1a ) _k1 ] and the group [-Z ^1b -(R ^1b ) _k2 ] (hereinafter also referred to as Z ^1- containing groups) are, for example, integers of about 1 to 3, preferably 1 or 2, and more preferably 1. m1 and m2 may be different from each other, but are preferably the same. At least one of m1 and m2 is an integer of 1 or more, preferably both are integers of 1 or more, and more preferably both are 1.

When m1 or m2 is 2 or more, the types of the two or more ^Z1- containing groups substituted on the same benzene ring among the two benzene rings forming the fluorene skeleton may be the same or different. Furthermore, the group [-Z ^1a -(R ^1a ) _k1 ] and the group [-Z ^1b -(R ^1b ) _k2 ] may be the same or different, and are preferably the same.

^R2a and ^R2b may be any substituent other than the ^Z1- containing group, and representative examples include hydrocarbon groups such as alkyl groups (excluding aryl groups), halogen atoms such as fluorine atoms, chlorine atoms, and bromine atoms, and cyano groups. Examples of alkyl groups include linear or branched _C1-6 alkyl groups such as methyl groups, ethyl groups, and t-butyl groups. When the number of substitutions n1 and/or n2 is 1 or more, preferred ^R2a and/or ^R2b are linear or branched _C1-4 alkyl groups such as methyl groups.

The substitution numbers n1 and n2 of R ^2a and R ^2b are, for example, integers of about 0 to 3, preferably integers of 0 to 2, more preferably 0 or 1, and particularly 0. n1 and n2 may be different from each other, but are preferably the same. When n1 or n2 is 2 or more, the types of two or more R ^2a or two or more R ^2b substituted on the same benzene ring among the two benzene rings forming the fluorene skeleton may be the same or different. The types of R ^2a and R ^2b may be the same or different from each other, but are preferably the same. The substitution positions of R ^2a and R ^2b are not particularly limited, as long as they are substituted at positions other than the substitution position of the ^Z1- containing group.

m1+n1 and m2+n2 are, for example, each an integer of about 1 to 3, preferably 1 or 2, and more preferably 1. m1+n1 and m2+n2 may be different from each other, but are preferably the same.

Examples of the linear or branched alkylene groups represented by A ^1a and A ^1b include linear or branched C _1-6 alkylene groups such as methylene, ethylene, methylmethylene (ethylidene), propylene, 1,3-propanediyl, 2,2-propanediyl, and 1,4-butanediyl. The two alkylene groups A ^1a and A ^1b may be different from each other, but are preferably the same. Preferred alkylene groups A ^1a and A ^1b are linear or branched C _1-4 alkylene groups, more preferably linear or branched C _1-3 alkylene groups, and particularly preferred are C _1-2 alkylene groups such as methylene and ethylene. An ethylene group is particularly preferred because it facilitates improving luminescence quantum efficiency.

Examples of the arene ring (aromatic hydrocarbon ring) represented by ^Z2a and ^Z2b include monocyclic arene rings such as a benzene ring, polycyclic arene rings, etc. Examples of the polycyclic arene ring include fused polycyclic arene rings (fused polycyclic aromatic hydrocarbon rings) and ring-assembled arene rings (ring-assembled polycyclic aromatic hydrocarbon rings).

Examples of fused polycyclic arene rings include fused bicyclic arene rings, fused tricyclic arene rings, and other fused bicyclic to tetracyclic arene rings. Examples of fused bicyclic arene rings include fused bicyclic _C10-16 arene rings such as naphthalene rings and indene rings. Examples of fused tricyclic arene rings include fused tricyclic _C14-20 arene rings such as anthracene rings and phenanthrene rings.

Examples of ring-assembled arene rings include biarene rings such as biphenyl rings, phenylnaphthalene rings, and binaphthyl rings; and terarene rings such as terphenyl rings.

Preferred rings Z ^2a and Z ^2b include C _6-14 arene rings, more preferably C _6-12 arene rings such as benzene ring, naphthalene ring and biphenyl ring, still more preferably C _6-10 arene rings such as benzene ring and naphthalene ring, especially benzene ring.

The rings Z ^2a and Z ^2b may be different from each other, but are preferably the same. There are no particular limitations on the bonding positions of the rings Z ^2a and Z ^2b to the alkylene groups A ^1a and A ^1b .

Examples of the substituents represented by R ^3a and R ^3b include the same groups as the substituents exemplified in the section on R ^1a and R ^1b .

When the number of substitutions p1 or p2 is 1 or more, preferred groups ^R3a and ^R3b include alkyl groups, aryl groups, hydroxyl groups, hydroxy(poly)alkoxy groups, and carboxyl groups. The alkyl group is more preferably a linear or branched _C1-6 alkyl group such as a methyl group, the aryl group is more preferably a _C6-10 aryl group such as a phenyl group, and the hydroxy(poly)alkoxy group is more preferably a hydroxy(mono- to deca) _C2-4 alkoxy group such as a 2-hydroxyethoxy group. Of these groups ^R3a and ^R3b , _C1-4 alkyl groups such as a methyl group, hydroxyl groups, and carboxyl groups are preferred.

The substitution numbers p1 and p2 of the groups ^R3a and ^R3b may be selected depending on the types of the rings ^Z2a and ^Z2b , and can be selected, for example, from integers of about 0 to 7, preferably integers of 0 to 5, integers of 0 to 4, integers of 0 to 2, and more preferably 0 or 1, and particularly preferably 0.

The two substitution numbers p1 and p2 may be different from each other, but are usually the same in many cases. When the substitution number p1 or p2 is 2 or more, the types of the two or more groups ^R3a or two or more groups ^R3b substituting the same ring ^Z2a and ^Z2b may be the same or different from each other. The types of the groups ^R3a and ^R3b may be different from each other, but are preferably the same.

The substitution positions of the groups ^R3a and ^R3b are not particularly limited and may be selected depending on the types of the rings ^Z2a and ^Z2b . When ^Z2a and ^Z2b are benzene rings, they are, for example, 3-position, 4- ^position , 3,4-position, 3,5-position, or 3,4,5-position, preferably 4-position, 3,4-position, and more preferably 4-position, relative to the phenyl groups bonded to the groups ^A1a and ^A1b . For example, when ^Z2a and ^Z2b are naphthalene rings, the substitution positions of the groups ^R3a and ^R3b are, for example, 1,5-position, ^2,6 -position, preferably 2,6-position, relative to the 1-naphthyl group or 2-naphthyl group bonded to the groups A1a and A1b.

Representative examples of the fluorene compound represented by the formula (1) include 9,9-bis(arylalkyl)-diarylfluorenes, such as 9,9-bis(arylalkyl)-2,7-di(fused _polycyclic C aryl)fluorene and 9,9-bis(arylalkyl)-2,7-di(ring-assembled _polycyclic C aryl)fluorene.

Examples of 9,9-bis(arylalkyl)-2,7-di(fused polycyclic C aryl)fluorenes include 9,9-bis(C _aryl C alkyl)-2,7-di(pyrenyl)fluorenes such as 9,9-bis(phenylmethyl)-2,7-di(1-pyrenyl)fluorene, 9,9-bis(2-phenylethyl)-2,7-di(1-pyrenyl)fluorene, 9,9-bis(2-phenylethyl)-2,7-di(2-pyrenyl)fluorene, and 9,9-bis( ₂ -phenylethyl)-2,7- _di (4-pyrenyl)fluorene.

9,9-bis(arylalkyl)-2,7-dicyclic assembled polycyclic C Examples of _16-18 arylfluorenes include 9,9-bis(C 6-10 aryl C fluorenes) such as 9,9-bis(phenylmethyl)-2,7-di(p-terphenyl-4-yl)fluorene, 9,9-bis(phenylethyl)-2,7-di(p-terphenyl-4-yl)fluorene, 9,9-bis(phenylethyl)-2,7-di(p-terphenyl-3-yl)fluorene, 9,9-bis(phenylethyl)-2,7-di(p-terphenyl-2-yl)fluorene, 9,9-bis(phenylethyl)-2,7-di(m-terphenyl-4-yl)fluorene, 9,9-bis(phenylethyl)-2,7-di(m-terphenyl-3-yl)fluorene, and 9,9-bis(phenylethyl)-2,7-di(m-terphenyl- _5′ -yl)fluorene. _1-2 alkyl)-2,7-di(terphenylyl)fluorene, and the like.

Of these fluorene compounds represented by formula (1), 9,9-bis( _{C6-10 arylC1-2} alkyl)-2,7-di(p-terphenylyl)fluorene such as 9,9-bis(phenylmethyl)-2,7-di(p-terphenyl-4-yl)fluorene, and 9,9-bis( _C6-10 arylC1-2 _alkyl )-2,7-di(fused polycyclic _C16-18 aryl)fluorene are preferred, and from the viewpoints of more effectively improving quantum efficiency and facilitating an improvement in the extinction coefficient, 9,9-bis( _{C6-10 arylC1-2 alkyl} )-2,7-di(pyrenyl)fluorene such as 9,9-bis(phenylmethyl)-2,7-di(1-pyrenyl)fluorene are even more preferred.

(Method for producing fluorene compound)
The fluorene compound represented by formula (1) may be produced by a conventional method, for example, by subjecting a compound represented by formula (2) below and a compound represented by formula (3) below to a coupling reaction (or cross-coupling reaction) according to the following reaction formula (hereinafter also referred to as method 1):

(In the formula, X ^1a and X ^1b each independently represent a group capable of forming a carbon-carbon bond by a coupling reaction,
^X2 represents a group capable of forming a carbon-carbon bond by a coupling reaction together with ^X1a and/or ^X1b ;
Z ¹ is the same as Z ^1a and/or Z ^1b in formula (1), including preferred embodiments thereof;
R ¹ is the same as R ^1a and/or R ^1b in the formula (1), including preferred embodiments thereof, and k is the same as k1 and/or k2 in the formula (1), including preferred embodiments thereof;
^Z2a , ^Z2b , ^R2a , ^R2b , ^R3a , ^R3b , ^{A1a, A1b ,} m1, m2, n1, n2, m1+n1, m2+n2, p1 and p2 are the same as those in the formula (1), including preferred embodiments.

Coupling reactions include conventional coupling reactions, such as palladium-catalyzed (or palladium(0)) coupling reactions such as the Suzuki-Miyaura coupling reaction, Migita-Kosugi-Stille coupling reaction, Negishi coupling reaction, and Hiyama coupling reaction, and nickel-catalyzed (or nickel(0)) coupling reactions such as the Kumada-Tamao-Corriu coupling reaction, with the Suzuki-Miyaura coupling reaction being preferred.

The reactive groups X ^1a , X ^1b , and X ² can be appropriately selected depending on the type of the coupling reaction. When synthesis is performed by the Suzuki-Miyaura coupling reaction, one of the reactive groups X ^1a and X ^1b can be, for example, a halogen atom or a fluorinated alkane sulfonyloxy group. Examples of halogen atoms include an iodine atom, a bromine atom, and a chlorine atom. Examples of fluorinated alkane sulfonyloxy groups include fluorinated C _1-4 alkanesulfonyloxy groups such as a trifluoromethanesulfonyloxy group (or group [-OTf]).

These one reactive groups X ^1a and X ^1b may be used alone or in combination of two or more. Of these one reactive groups, a halogen atom is preferred, an iodine atom or a bromine atom is more preferred, and a bromine atom is more preferred.

In the Suzuki-Miyaura coupling reaction, examples of the other reactive group ^X2 capable of coupling with one of the reactive groups ^X1a and ^X1b include a boronic acid group (dihydroxyboryl group or group [—B(OH) ₂ ]), a boronate ester group, etc. Examples of the boronate ester group include dialkoxyboryl groups such as dimethoxyboryl group, diisopropoxyboryl group, and dibutoxyboryl group; and cyclic boronate ester groups such as pinacolatoboryl group (or group [-Bpin]), 1,3,2-dioxaborinan-2-yl group, and 5,5-dimethyl-1,3,2-dioxaborinan-2-yl group.

These other reactive groups ^X2 may be used alone or in combination of two or more. Of the other reactive groups, the group [-B(OH) ₂ ] and the group [-Bpin] are preferred.

The groups ^X1a and ^X1b and the group ^X2 may be any reactive groups regardless of the examples given above, as long as they are a pair of reactive groups capable of undergoing a coupling reaction with each other. For example, the groups ^X1a and ^X1b may be the other reactive group such as a boronic acid group, and the group ^X2 may be one reactive group such as a halogen atom. However, it is preferable that the groups ^X1a and ^X1b are one reactive group such as a halogen atom, and the group ^X2 is the other reactive group such as a boronic acid group.

Examples of the compound represented by formula (2) include 9,9-bis(C _6-10 aryl C _1-2 alkyl)-dihalofluorenes such as 9,9-bis(phenylmethyl)-2,7-dibromofluorene and 9,9-bis(2-phenylethyl)-2,7-dibromofluorene.

The compound represented by formula (2) may be prepared, for example, by the method described in JP 2009-96782 A, i.e., by reacting a 9H-fluorene unsubstituted at the 9-position, such as 2,7-dibromofluorene, with a base catalyst such as potassium t-butoxide to generate a fluorene anion having an anion at the 9-position of the fluorene skeleton, and then reacting this fluorene anion with a haloalkylarenes such as (2-bromoethyl)benzene.

Examples of the compound represented by formula (3) include boronic acid compounds or boronic acid ester compounds corresponding to Z ^1a and/or Z ^1b in formula (1), and examples thereof include terphenyls having a cyclic boronic acid ester group such as 2-([1,1':4',1"-terphenyl]-4-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane; and pyreneboronic acids such as 1-pyreneboronic acid. As the compound represented by formula (3), commercially available products can be used.

The ratio of the compound represented by formula (2) to the compound represented by formula (3) may be, for example, the former/latter (molar ratio) of about 1/2 to 1/10, preferably 1/2.05 to 1/3, and more preferably 1/2.1 to 1/2.5.

When synthesizing by the Suzuki-Miyaura coupling reaction, the reaction is usually carried out in the presence of a palladium catalyst. Examples of palladium catalysts include conventional coupling catalysts such as palladium(0) catalysts and palladium(II) catalysts.

Examples of palladium(0) catalysts include palladium(0)-phosphine complexes such as tetrakis(triphenylphosphine)palladium(0) [or Pd(PPh ₃ ) ₄ ] and bis(tri-t-butylphosphine)palladium(0) [or Pd(P(t-Bu) ₃ ) ₂ ].

Examples of the palladium(II) catalyst include palladium(II)-phosphine complexes such as [1,2-bis(diphenylphosphino)ethane]palladium(II) dichloride [or PdCl ₂ (dppe)], [1,3-bis(diphenylphosphino)propane]palladium(II) dichloride [or PdCl ₂ (dppp)], [1,1′-bis(diphenylphosphino)ferrocene]palladium(II) dichloride [or PdCl ₂ (dppf)], bis(triphenylphosphine)palladium(II) dichloride [or PdCl ₂ (PPh ₃ ) ₂ ], and bis(tri-o-tolylphosphine)palladium(II) dichloride [or PdCl ₂ (P(o-tolyl) ₃ ) ₂ ]. When a palladium (II) catalyst is used, the reaction starts when the catalyst is reduced to a zero-valent complex by a reducing compound in the reaction system, such as a phosphine, an amine, or an organometallic reagent.

The palladium catalyst may be prepared in situ by adding a catalyst precursor such as tris(dibenzylideneacetone)dipalladium(0) chloroform complex [or Pd ₂ (dba) _{3.CHCl 3} ] and a ligand such as a phosphine or a carbene.

These catalysts can be used alone or in combination of two or more. Among these catalysts, palladium(0)-phosphine complexes such as Pd(PPh ₃ ) ₄ are preferred. The proportion of the catalyst, in terms of metal, may be, for example, about 0.005 to 0.1 moles, and preferably 0.01 to 0.03 moles, per mole of the compound represented by formula (2).

The Suzuki-Miyaura coupling reaction may be carried out in the presence of a base. Examples of bases include metal carbonates or bicarbonates, metal hydroxides, metal fluorides, metal phosphates, metal organic acid salts, and metal alkoxides.

Examples of metal carbonates or bicarbonates include alkali metal carbonates or bicarbonates such as sodium carbonate, potassium carbonate, cesium carbonate, and sodium bicarbonate, as well as thallium(I) carbonate.

Examples of metal hydroxides include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, and cesium hydroxide, alkaline earth metal hydroxides such as barium hydroxide, and thallium(I) hydroxide.

Examples of metal fluorides include alkali metal fluorides such as potassium fluoride and cesium fluoride.

Examples of metal phosphates include alkali metal phosphates such as tripotassium phosphate.

Examples of metal organic acid salts include alkali metal acetates such as potassium acetate.

Examples of metal alkoxides include alkali metal alkoxides such as sodium methoxide, sodium ethoxide, and potassium t-butoxide.

These bases can be used alone or in combination of two or more. Of these bases, metal carbonates such as potassium carbonate are preferred. The proportion of the base relative to 1 mole of the compound represented by formula (2) may be, for example, approximately 0.01 to 100 moles, preferably 1 to 80 moles, and more preferably 10 to 60 moles.

The coupling reaction may be carried out in the presence or absence of a phase transfer catalyst. Examples of phase transfer catalysts include tetraalkylammonium halides such as tetrabutylammonium bromide (TBAB) and trioctylmethylammonium chloride. These phase transfer catalysts can be used alone or in combination. Of these phase transfer catalysts, TBAB is preferred.

The coupling reaction may be carried out in the absence or presence of a reaction-inert solvent. Examples of solvents include water; alcohols such as methanol and ethanol; ethers such as cyclic ethers and chain ethers; ketones such as acetone and methyl ethyl ketone; esters such as ethyl acetate; nitriles such as acetonitrile and benzonitrile; amides such as N,N-dimethylformamide, dimethylacetamide, and N-methyl-2-pyrrolidone; sulfoxides such as dimethyl sulfoxide; and hydrocarbons such as aliphatic hydrocarbons, alicyclic hydrocarbons, and aromatic hydrocarbons.

Examples of cyclic ethers include dioxane and tetrahydrofuran (THF). Examples of chain ethers include diethyl ether and diisopropyl ether.

Aliphatic hydrocarbons include, for example, hexane and dodecane. Alicyclic hydrocarbons include, for example, cyclohexane. Aromatic hydrocarbons include, for example, toluene and xylene.

These solvents can be used alone or in combination of two or more. When using a compound of formula (3) in which Z ¹ (Z ^1a and Z ^1b ) are a C _16-18 arene ring assembly, the reaction does not proceed unless at least an ether is present, and the compound of formula (1) cannot be prepared. Therefore, when using a compound of formula (3) in which Z ¹ (Z ^1a and Z ^1b ) are a C _16-18 arene ring assembly, a mixed solvent of water and an ether, particularly water and a cyclic ether such as THF, is preferred; when using a compound of formula (3) in which Z ¹ (Z ^1a and Z ^1b ) are a fused polycyclic C _16-18 arene ring, a mixed solvent of water and an aromatic hydrocarbon such as toluene is preferred.

The coupling reaction may be carried out under an inert gas atmosphere, such as nitrogen or a rare gas such as helium or argon. The reaction temperature is, for example, 50 to 200°C, preferably 60 to 150°C, and more preferably 70 to 130°C. The reaction time may be, for example, about 1 to 48 hours, specifically about 12 to 36 hours.

After the reaction is complete, the reaction mixture may be separated and purified, if necessary, by conventional separation and purification methods, such as washing, extraction, dehydration, concentration, decantation, crystallization, recrystallization, reprecipitation, column chromatography, or a combination of these.

The fluorene compound represented by formula (1) may also be produced by a second method shown in the following reaction scheme:

(wherein ^X3 represents a halogen atom;
A ¹ is the same as A ^1a and/or A ^1b in the formula (1), including preferred embodiments thereof;
^Z2 is the same as ^Z2a and/or ^Z2b in the formula (1), including preferred embodiments thereof;
^R3 is the same as ^R3a and/or ^R3b in the formula (1), including preferred embodiments thereof, and p is the same as p1 and/or p2 in the formula (1), including preferred embodiments thereof;
Z ^1a , Z ^1b , R ^1a , R ^1b , R ^2a , R ^2b , k1, k2, m1, m2, n1, n2, m1+n1 and m2+n2 are each the same as those in formula (1) above, including preferred embodiments.

In the second method, a compound represented by the formula (4) (or a 9H-fluorene which already has a ^Z1- containing group and is unsubstituted at the 9-position) is reacted with a compound represented by the formula (5) corresponding to the group [-A ^1a -Z ^2a -(R ^3a ) _p1 ] and the group [-A ^1b -Z ^2b -(R ^3b ) _p2 ] (hereinafter, these may also be referred to as Z ^2- containing groups). In other words, the order of introduction of the Z ^1- containing group and the Z ^2- containing group is different from that in the first method.

Examples of the halogen atom represented by ^X3 include a chlorine atom, a bromine atom, and an iodine atom.

Examples of the compound represented by formula (4) include 9H-fluorenes having a ^Z1- containing group and unsubstituted at the 9-position, such as 2,7-diphenylfluorene. The compound represented by formula (4) may be prepared by a method in which a compound unsubstituted at the 9-position of the fluorene skeleton is used instead of the compound represented by formula (2) in the first method, and the method is the same as that described for the first method, including preferred embodiments such as reaction conditions.

The second method corresponds to using a compound represented by formula (4) as a 9H-fluorene unsubstituted at the 9-position in the method for preparing a compound represented by formula (2), and can be prepared in accordance with the method described in JP 2009-96782 A.

(Characteristics of fluorene compounds)
The fluorene compound represented by the formula (1) has a specific molecular structure, and therefore, when excited by external energy such as light energy or electrical energy, it has at least one emission peak in a specific wavelength region (has a maximum wavelength λ _em,max of the emission peak in a specific wavelength region), and can emit blue light with extremely high luminescence quantum efficiency. Therefore, the present invention also encompasses a method of exciting the fluorene compound represented by the formula (1) with the external energy or the like to cause the fluorene compound to emit light in a specific wavelength region.

The luminescence quantum efficiency of the fluorene compound represented by the formula (1) is, for example, about 20% or more, and preferably 25 to 50%, at a temperature of 25°C in a solid state. When Z ^1a and Z ^1b are fused polycyclic C _16-18 arene rings, the luminescence quantum efficiency is preferably 30 to 45%, and more preferably 35 to 40%. When Z ^1a and Z ^1b are ring assembly C _16-18 arene rings, the luminescence quantum efficiency is preferably 20 to 35%, and more preferably 25 to 30%.

The fluorene compound represented by formula (1) may have, in its emission (fluorescence or phosphorescence) spectrum in a solid state at a temperature of 25°C, at least one emission peak (or emission band) having a maximum wavelength λ _em,max in the range of, for example, about 400 to 460 nm, preferably 410 to 460 nm. When Z ^1a and Z ^1b are fused polycyclic C _16-18 arene rings, the fluorene compound preferably has at least one emission peak having a maximum wavelength λ _em,max in the ranges of 420 to 460 nm, 435 to 455 nm, and 445 to 455 nm, respectively, in the following stepwise order; and when Z ^1a and Z ^1b are ring assembly C _16-18 arene rings, the fluorene compound preferably has at least one emission peak having a maximum wavelength λ _em,max in the ranges of 410 to 450 nm, 410 to 435 nm, and 415 to 425 nm, respectively.

In the emission spectrum in the solid state, the half width of the emission peak (or emission band) having the maximum wavelength λ _em,max is, for example, 100 nm or less, preferably 1 to 70 nm. When Z ^1a and Z ^1b are fused polycyclic C _16-18 arene rings, it is preferably 10 to 65 nm, 40 to 60 nm, and 50 to 60 nm, in the following stepwise order; and when Z ^1a and Z ^1b are ring assembly C _16-18 arene rings, it is preferably 10 to 60 nm, 25 to 50 nm, and 35 to 45 nm, in the following stepwise order.

The fluorene compound represented by formula (1) may have, in its excitation spectrum (or absorption spectrum) in a solid state at a temperature of 25°C, at least one emission peak (or absorption peak) having a maximum wavelength λ _ex,max in the range of, for example, about 250 to 450 nm. When Z ^1a and Z ^1b are fused polycyclic C _16-18 arene rings, the fluorene compound has at least one emission (absorption) peak having a maximum wavelength λ _ex,max in the range of preferably 260 to 350 nm, more preferably 270 to 300 nm. When Z ^1a and Z ^1b are ring assembly C _16-18 arene rings, the fluorene compound has at least one emission (absorption) peak having a maximum wavelength λ _ex ,max in the range of preferably 350 to 430 nm, more preferably 380 to 420 nm.

The solid state may be, for example, a crystalline form such as a single crystal or polycrystal, or an amorphous form, with a crystalline form such as a polycrystal being preferred.

Furthermore, the fluorene compound represented by formula (1) can emit light with high quantum efficiency in a specific wavelength range, even in the emission spectrum in a solution state, which tends to reflect the pure luminescence characteristics based on the chemical structure.

The luminescence quantum efficiency of the fluorene compound represented by formula (1) may be, for example, about 30% or more, preferably 50 to 100%, in a dichloromethane solution state at a temperature of 25°C. When Z ^1a and Z ^1b are fused polycyclic C _16-18 arene rings, it is preferably 70 to 100%, 80 to 100%, and 85 to 95%, stepwise, as shown below. When Z ^1a and Z ^1b are ring assembly C _16-18 arene rings, it is preferably 50 to 60%.

The fluorene compound represented by formula (1) may have, in its emission (fluorescence or phosphorescence) spectrum in a dichloromethane solution at a temperature of 25°C, at least one emission peak (or emission band) having a maximum wavelength λ _em,max in the range of, for example, about 400 to 460 nm, preferably 410 to 460 nm, and more preferably 410 to 450 nm; when Z ^1a and Z ^1b are fused polycyclic C _16-18 arene rings, the fluorene compound may have at least one emission peak having a maximum wavelength λ _em,max in the ranges of 415 to 440 nm and 420 to 430 nm, preferably in the following stepwise order; and when Z ^1a and Z ^1b are ring assembly C _16-18 arene rings, the fluorene compound may have at least one emission peak having a maximum wavelength λ _em,max in the ranges of 410 to 435 nm and 415 to 425 nm, preferably in the following stepwise order. In the emission spectrum in the solution state, the fluorene compound may have one or more emission peaks, preferably only one emission peak, and more preferably all emission peaks (maximum wavelength λ _em,max ) are included in the wavelength range.

In the emission spectrum in a dichloromethane solution state, the half width of the emission peak (or emission band) having the maximum wavelength λ _em,max may be selected from the range of, for example, 1 to 100 nm, preferably about 30 to 70 nm, and when Z ^1a and Z ^1b are fused polycyclic C _16-18 arene rings, it is preferably 40 to 65 nm and 50 to 60 nm, in the following stepwise order, and when Z ^1a and Z ^1b are ring assembly C _16-18 arene rings, it is preferably 30 to 60 nm and 40 to 50 nm, in the following stepwise order.

The fluorene compound represented by formula (1) may have, in its excitation spectrum (or absorption spectrum) in a dichloromethane solution at a temperature of 25°C, at least one emission peak (or absorption peak) having a maximum wavelength λ _ex, max in the range of, for example, about 270 to 400 nm, preferably 300 to 380 nm; when Z ^1a and Z ^1b are fused polycyclic C _16-18 arene rings, it preferably has at least one emission (absorption) peak having a maximum wavelength λ _ex ,max in the range of 340 to 370 nm; and when Z ^1a and Z ^1b are ring assembly C _16-18 arene rings, it preferably has at least one emission (absorption) peak having a maximum wavelength λ _ex,max in the range of 320 to 350 nm.

In measuring the luminescence quantum efficiency, emission spectrum, and excitation spectrum of the dichloromethane solution, the concentration of the fluorene compound is not particularly limited as long as it is sufficiently diluted to such an extent that the effects of concentration quenching and the like are not significantly observed, and may be, for example, about 1×10 ⁻³ to 5×10 ⁻³ g/L, or about 1×10 ⁻⁶ to 10×10 ⁻⁶ mol/L.

In this specification and claims, the emission spectrum, excitation spectrum, and luminescence quantum efficiency can be measured by methods such as those described in the Examples below.

In addition, because the fluorene compound represented by formula (1) exhibits high luminescence quantum efficiency, it may act as a sensitizer that can sensitize a photosensitive substance (or sensitive substance) that is responsive to light, such as a photopolymerization initiator or a luminescent material (or luminescent compound). The luminescent material (other luminescent material) used as the photosensitive substance may be a fluorescent material or a phosphorescent material, and is not particularly limited as long as it can transfer energy from the excited sensitizer (exciton or excited species), i.e., as long as its excitation energy (band gap) is lower than the energy transferable from the exciton. Conventional luminescent materials such as green to red luminescent materials can be used.

(Light-emitting composition)
The luminescent composition (or blue luminescent composition) contains at least the fluorene compound represented by formula (1) as a luminescent material and/or a sensitizer. When the fluorene compound represented by formula (1) is contained as a sensitizer, it is preferable that another luminescent material is contained. The fluorene compound represented by formula (1) can be used alone or in combination of two or more kinds.

The luminescent composition may or may not further contain a binder component, as necessary, in addition to the fluorene compound represented by formula (1). The inclusion of a binder component dilutes the fluorene compound represented by formula (1), which tends to reduce the effects of concentration quenching compared to the solid state. Therefore, using a coating film (luminescent composition) containing a binder as the luminescent layer of an organic EL device is preferable in that it has high luminescence quantum efficiency and can be produced easily or efficiently.

As mentioned above, when the conjugation length is extended by bonding rings ^Z1a and ^Z1b to the fluorene ring, the emission wavelength is expected to become longer. On the other hand, compounds containing a large number of aromatic rings (benzene ring skeletons) in their chemical structure generally tend to have reduced dispersibility (compatibility or solubility). Therefore, even in a coating film containing a binder component, the fluorene compound represented by formula (1) aggregates and cannot be sufficiently diluted, and a decrease in emission quantum efficiency due to concentration quenching, as in a solid state, is expected. However, despite having many benzene ring skeletons, the fluorene compound can surprisingly suppress aggregation in the binder component and exhibits unexpectedly high quantum efficiency, making it particularly useful as a blue-emitting material for organic electroluminescence (OLED).

The binder component can be, for example, a conventional resin (or polymer compound), such as a thermoplastic resin or a curable resin (thermo- or photo-curable resin).

Examples of thermoplastic resins include olefin-based resins; (meth)acrylic resins; styrene-based resins; vinyl-based resins such as vinyl chloride resins and vinyl alcohol-based resins; fluororesins; polycarbonate-based resins; thermoplastic polyester-based resins such as polyalkylene arylates, polyarylates, and liquid crystal polyesters; polyamide-based resins such as aliphatic polyamides, alicyclic polyamides, semi-aromatic polyamides, and wholly aromatic polyamides (aramids); polyacetal-based resins; polyphenylene ether-based resins; polyphenylene sulfide-based resins; polysulfone-based resins such as polysulfone and polyethersulfone; polyetherketone-based resins such as polyetherketone, polyetheretherketone, and polyetherketoneetherketoneketone; thermoplastic polyimide-based resins such as polyetherimide-based resins and polyamideimide-based resins; thermoplastic elastomers; cellulose-based resins such as cellulose ester-based resins such as triacetyl cellulose and cellulose ether-based resins such as ethyl cellulose.

Examples of curable resins (thermo- or photo-curable resins) include epoxy resins; urethane-based resins; thermosetting polyester-based resins such as alkyd resins, unsaturated polyester-based resins, diallyl phthalate resins, and vinyl ester resins; phenolic resins; amino resins such as melamine resins, urea resins, and guanamine resins; furan resins; thermosetting polyimide-based resins such as bismaleimide-based resins and bismaleimide-triazine resins; and silicon-based resins such as polysilsesquioxane.

These binder components can be used alone or in combination of two or more. Of these binder components, (meth)acrylic resins, styrene resins, polycarbonate resins, and silicon resins are preferred from the viewpoint of making it easier to uniformly disperse the fluorene compound represented by formula (1).

Examples of the (meth)acrylic resin include homopolymers or copolymers of (meth)acrylic monomers such as (meth)acrylic acid, C _1-18 alkyl (meth)acrylate, hydroxy C _2-18 alkyl (meth)acrylate, glycidyl (meth)acrylate, and (meth)acrylonitrile; and copolymers of the above-mentioned (meth)acrylic monomers with other copolymerizable monomers.

Examples of homopolymers or copolymers of (meth)acrylic monomers include poly(meth)acrylic acid esters such as polymethyl(meth)acrylate, methyl methacrylate-(meth)acrylic acid copolymers, methyl methacrylate-acrylic acid ester-(meth)acrylic acid copolymers, and methyl methacrylate-(meth)acrylic acid ester copolymers.

In copolymers of (meth)acrylic monomers and other copolymerizable monomers, examples of the copolymerizable monomers include styrene, α-methylstyrene and other styrene monomers, and maleic anhydride.

Of these (meth)acrylic resins, poly(meth)acrylic acid C _1-8 alkyl esters such as polymethyl methacrylate are preferred.

Examples of styrene-based resins include homopolymers or copolymers of styrene-based monomers such as styrene, α-methylstyrene, and vinyltoluene; copolymers of the above-mentioned styrene-based monomers with copolymerizable monomers; and impact-resistant styrene-based resins (i.e., graft copolymers and/or blends (mixtures) with rubber components).

Examples of homopolymers or copolymers of styrene-based monomers include polystyrenes such as atactic polystyrene, isotactic polystyrene (IPS), and syndiotactic polystyrene (SPS), as well as styrene-vinyltoluene copolymers and styrene-α-methylstyrene copolymers.

Examples of copolymers of styrene-based monomers and copolymerizable monomers include styrene-acrylonitrile copolymers (AS resins), styrene-(meth)acrylic acid copolymers, styrene-(meth)acrylic acid ester copolymers (such as MS resins), styrene-maleic anhydride copolymers, styrene-phenylmaleimide copolymers, styrene-butadiene block copolymers, and styrene-butadiene-styrene block copolymers.

Examples of impact-resistant styrene resins include high-impact polystyrene (HIPS); acrylonitrile-butadiene-styrene copolymer (ABS resin); AXS resins, specifically AAS resin, ACS resin, AES resin, etc., in which rubber components such as acrylic rubber A, chlorinated polyethylene C, or ethylene propylene rubber (or ethylene propylene diene rubber) E are used instead of the butadiene rubber B of the ABS resin; and (meth)acrylic acid ester-butadiene-styrene copolymers, such as methyl methacrylate-butadiene-styrene copolymer (MBS resin).

Of these styrene-based resins, homopolymers or copolymers of styrene-based monomers, particularly homopolymers, are preferred.

Examples of polycarbonate resins include aromatic polycarbonate resins, specifically bisphenol-type polycarbonate resins that contain bisphenols or bisphenols as polymerization components, such as bisphenol A polycarbonate resin and bisphenol F polycarbonate resin.

Examples of the biphenols or bisphenols include bisphenols such as bis(hydroxyaryl)alkanes, bis(hydroxyaryl)-arylalkanes, bis(hydroxyaryl)cycloalkanes, bis(hydroxyaryl)ethers, bis(hydroxyaryl)ketones, bis(hydroxyaryl)sulfides, bis(hydroxyaryl)sulfoxides, and bis(hydroxyaryl)sulfones; and biphenols.

Examples of bis(hydroxyaryl)alkanes include bis(4-hydroxyphenyl)methane (bisphenol F), 1,1-bis(4-hydroxyphenyl)ethane (bisphenol AD), 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), 1,1-bis(4-hydroxyphenyl)butane, 2,2-bis(4-hydroxyphenyl)butane (bisphenol B), 2,2-bis(4-hydroxyphenyl)-3-methylbutane, 2,2-bis(4-hydroxy-3-phenylphenyl)propane, 2,2-bis(4-hydroxy-3-methylphenyl)propane (bisphenol C), and 2,2-bis(4-hydroxy-3-isopropylphenyl)propane (bisphenol G).

Examples of bis(hydroxyaryl)-arylalkanes include 1,1-bis(4-hydroxyphenyl)-1-phenylethane (bisphenol AP) and bis(4-hydroxyphenyl)-diphenylmethane (bisphenol BP).

Examples of bis(hydroxyaryl)cycloalkanes include 1,1-bis(4-hydroxyphenyl)cyclopentane, 1,1-bis(4-hydroxyphenyl)cyclohexane (bisphenol Z), and 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane (bisphenol TMC).

Examples of bis(hydroxyaryl) ethers include bis(4-hydroxyphenyl) ether.

Examples of bis(hydroxyaryl)ketones include bis(4-hydroxyphenyl)ketone.

Examples of bis(hydroxyaryl) sulfides include bis(4-hydroxyphenyl) sulfide.

Examples of bis(hydroxyaryl) sulfoxides include bis(4-hydroxyphenyl) sulfoxide.

Examples of bis(hydroxyaryl)sulfones include bis(4-hydroxyphenyl)sulfone (bisphenol S).

Examples of biphenols include o,o'-biphenol, m,m'-biphenol, and p,p'-biphenol.

These biphenols or bisphenols can be used alone or in combination.

Among these polycarbonate resins, bisphenol-type polycarbonate resins containing bis(hydroxyaryl)alkanes such as bisphenol A as polymerization components are preferred.

In the silicon-based resin, the polyorganosiloxane (silicone) skeleton may contain at least one unit selected from the group consisting of monofunctional M units (units generally represented by R ₃ SiO _1/2 ), difunctional D units (units generally represented by R ₂ SiO _2/2 ), trifunctional T units (units generally represented by RSiO _3/2 ), and tetrafunctional Q units (units generally represented by SiO _4/2 ).

The group R in the formulas representing the M unit, D unit, and T unit is a substituent. Examples of this substituent include an alkyl group, an aryl group, a cycloalkyl group, and a vinyl group.

Examples of the alkyl group include C 1-12 alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, s-butyl, t-butyl, n-hexyl, n-octyl, ₂ -ethylhexyl, and n-decyl.

Examples of the aryl group include C _6-14 aryl groups such as phenyl group, methylphenyl group (tolyl group), dimethylphenyl group (xylyl group), biphenylyl group, and naphthyl group.

Examples of the cycloalkyl group include a C _5-10 cycloalkyl group such as a cyclopentyl group, a cyclohexyl group, and a methylcyclohexyl group.

These substituents can be used alone or in combination of two or more. Among these substituents, C _1-4 alkyl groups such as methyl groups and C _6-12 aryl groups such as phenyl groups are preferred, and C _6-10 aryl groups such as phenyl groups are particularly preferred because they facilitate uniform dispersion of the fluorene compound.

Furthermore, examples of the terminal group (a group bonded to the terminal silicon (Si) atom) include a hydroxyl group, an alkoxy group, a halogen atom such as a chlorine atom, etc. Examples of the alkoxy group include a C _1-4 alkoxy group such as a methoxy group or an ethoxy group, and a C _1-2 alkoxy group is preferred.

These terminal groups can be used alone or in combination of two or more. Among these terminal groups, hydroxyl groups, _C1-2 alkoxy groups, etc. are usually used in many cases.

The silicon-based resin preferably contains at least one unit selected from the T and Q units, particularly T units, to facilitate coating formation. The proportion of T units in the entire silicon-based resin is, for example, 50 mol% or more, with preferred ranges being 60 mol% or more, 70 mol% or more, 80 mol% or more, 90 mol% or more, and 95 mol% or more, in the following stepwise order. Silsesquioxanes (or polysilsesquioxanes) are particularly preferred, with the proportion of T units in the entire silicon-based resin being essentially 100 mol%. The proportion of T units in the entire silicon-based resin can be selected from the range of approximately 60 to 100 mol%, and preferably 80 to 99.9 mol%.

The silsesquioxane (or polysilsesquioxane) may be ladder-shaped or cage-shaped, but is preferably in the form of a three-dimensional network (network or random structure) from the viewpoint of ease of forming a coating film. Examples of such silsesquioxanes include polyalkylsilsesquioxanes formed with T units (alkylsilsesquioxane units) in which the substituent R is an alkyl group, such as polyC _1-4 alkylsilsesquioxanes such as polymethylsilsesquioxane; polyarylsilsesquioxanes formed with T units (arylsilsesquioxane units) in which R is an aryl group, such as polyC _6-12 arylsilsesquioxanes such as polyphenylsilsesquioxane; and polysilsesquioxanes formed with T units in which R is an alkyl group and T units in which R is an aryl group.

These silsesquioxanes can be used alone or in combination of two or more. Among these silsesquioxanes, polyarylsilsesquioxanes formed from T units in which R is an _aryl group are preferred, and polyC arylsilsesquioxanes such as polyphenylsilsesquioxane are particularly preferred.

As a preferred binder component, when Z ^1a and Z ^1b are fused polycyclic C _16-18 arene rings, (meth)acrylic resins, styrene resins, and polycarbonate resins are preferred, and styrene resins and polycarbonate resins are more preferred, and when Z ^1a and Z ^1b are ring assembly C _16-18 arene rings, (meth)acrylic resins and polycarbonate resins are preferred, and (meth)acrylic resins are also preferred. Combining these binder components with the fluorene compound appears to facilitate effective improvement of luminescence quantum efficiency.

The proportion of the binder component may be selected from the range of, for example, approximately 1 to 99.99% by mass, approximately 10 to 99.9% by mass, based on the total solid content, and preferably in the following stepwise ranges: 20 to 90% by mass, 30 to 70% by mass, 40 to 60% by mass, and more preferably in the following stepwise ranges: 30 to 99% by mass, 50 to 95% by mass, 80 to 93% by mass. Furthermore, the ratio of the fluorene compound represented by formula (1) to the binder component may be selected, for example, from a range of approximately 1/0.5 to 1/1000 (mass ratio) of the former to the latter, preferably 1/0.7 to 1/200, 1/0.8 to 1/100, in the following stepwise manner. From the viewpoint of effectively suppressing a decrease in luminescence quantum efficiency, more preferred ranges are 1/1 to 1/50, 1/1 to 1/40, 1/2 to 1/30, 1/4 to 1/20, and 1/6 to 1/15, in the following stepwise manner. If the binder component ratio is too low, luminescence quantum efficiency may decrease due to concentration quenching, while if the binder component ratio is too high, luminescence intensity may decrease (or the luminescence may not be bright enough).

The luminescent composition (or coating agent) may further contain a solvent to adjust viscosity and improve application (or handling) properties, and this may be dried and removed from the coating film after application. Examples of solvents include hydrocarbons, halogenated hydrocarbons, alcohols, glycols, ethers, glycol ethers, glycol ether acetates, ketones, carboxylic acids, esters, carbonates, nitriles, amides, sulfoxides, water, and mixed solvents of these.

Examples of hydrocarbons include aliphatic hydrocarbons such as hexane, alicyclic hydrocarbons such as cyclohexane, and aromatic hydrocarbons such as toluene and xylene.

Examples of halogenated hydrocarbons include dichloromethane, chloroform, 1,2-dichloroethane, and chlorobenzene.

Examples of alcohols include C _1-6 alkanols such as methanol, ethanol, 1-propanol, 2-propanol, n-butanol, isobutanol, s-butanol, and t-butanol.

Examples of glycols include (poly)C _2-4 alkylene glycols such as ethylene glycol, propylene glycol, and diethylene glycol.

Examples of ethers include chain ethers such as diethyl ether, and cyclic ethers such as tetrahydrofuran and 1,4-dioxane.

Examples of glycol ethers include cellosolves, carbitols, (poly) _C2-4 alkylene glycol mono- _C1-4 alkyl ethers such as triethylene glycol monomethyl ether, propylene glycol monomethyl ether, and dipropylene glycol monomethyl ether; and (poly) _C2-4 alkylene glycol di- _C1-4 alkyl ethers such as ethylene glycol dimethyl ether, propylene glycol dimethyl ether, diethylene glycol dimethyl ether, and dipropylene glycol dimethyl ether.

Examples of the cellosolves include C _1-4 alkyl cellosolves such as methyl cellosolve and ethyl cellosolve, etc. Examples of the carbitols include C _1-4 alkyl carbitols such as methyl carbitol and ethyl carbitol, etc.

Examples of glycol ether acetates include cellosolve acetates, carbitol acetates, (poly)C _2-4 alkylene glycol monoC _1-4 alkyl ether acetates such as propylene glycol monomethyl ether acetate and dipropylene glycol monobutyl ether acetate.

Examples of the cellosolve acetates include C _1-4 alkyl cellosolve acetates such as methyl cellosolve acetate, etc. Examples of the carbitol acetates include C _1-4 alkyl carbitol acetates such as methyl carbitol acetate, etc.

Examples of ketones include chain ketones such as acetone and methyl ethyl ketone, and cyclic ketones such as cyclohexanone.

Examples of carboxylic acids include acetic acid and propionic acid.

Examples of esters include acetate esters such as methyl acetate, ethyl acetate, and butyl acetate, and lactate esters such as methyl lactate.

Examples of carbonates include chain carbonates such as dimethyl carbonate, and cyclic carbonates such as propylene carbonate.

Examples of nitriles include acetonitrile, propionitrile, and benzonitrile.

Examples of amides include N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone.

Examples of sulfoxides include dimethyl sulfoxide.

These solvents can be used alone or in combination. Of these solvents, halogenated hydrocarbons such as dichloromethane and chloroform are preferred.

The proportion of the solvent can be selected appropriately depending on the viscosity of the luminescent composition, and is not particularly limited. The solids concentration of the luminescent composition is, for example, 0.01 to 50% by mass, preferably 0.1 to 10% by mass, more preferably 0.5 to 10% by mass, and particularly preferably 0.5 to 2% by mass.

The luminescent composition may contain conventional additives. Examples of conventional additives include dyes, pigments, pigment dispersants, wetting agents, thickeners, coupling agents, antifoaming agents, anti-settling agents, anti-skinning agents, polymerization inhibitors, polymerization initiators, curing agents, leveling agents, thixotropic agents, color separation inhibitors, matting agents, flame retardants, stabilizers, plasticizers, softeners, lubricants, release agents, and antistatic agents. Examples of stabilizers include antioxidants, ultraviolet absorbers, light stabilizers, and antiozonants.

The coating agent may be substantially free of additives, as additives may absorb the excitation light used to excite the fluorene compound (light-emitting material) and the light emitted by the excited light-emitting material. Therefore, the luminescent composition preferably contains at least the fluorene compound represented by formula (1) and, as necessary, only a binder component and/or a solvent, i.e., a composition that is substantially free of additives.

The luminescent properties of a luminescent composition containing a binder component or a coating film formed using this composition may be adjusted appropriately depending on the type and concentration of the fluorene compound, binder component, etc.

The luminous quantum efficiency of a luminescent composition (or coating film) containing a binder component may be selected from a range of, for example, about 30% or more at a temperature of 25°C, and is preferably 50 to 100%, and more preferably 70 to 100%. When Z ^1a and Z ^1b are fused polycyclic C _16-18 arene rings, it is preferably 75 to 100%, 80 to 100%, and 85 to 95%, in the following stepwise manner; and when Z ^1a and Z ^1b are ring assembly C _16-18 arene rings, it is preferably 75 to 90%, and 75 to 85%, in the following stepwise manner.

The luminescent composition (or coating film) may have, in its emission (fluorescence or phosphorescence) spectrum at a temperature of 25°C, at least one emission peak (or emission band) having a maximum wavelength λ _em,max in the range of, for example, about 400 to 460 nm, preferably 410 to 460 nm, and more preferably 410 to 450 nm; when Z ^1a and Z ^1b are fused polycyclic C _16-18 arene rings, the luminescent composition (or coating film) may have at least one emission peak having a maximum wavelength λ _em,max in the ranges of 415 to 440 nm and 420 to 430 nm, preferably in the following stepwise order; and when Z ^1a and Z ^1b are ring assembly C _16-18 arene rings, the luminescent composition (or coating film) may have at least one emission peak having a maximum wavelength λ _em,max in the ranges of 415 to 440 nm and 420 to 435 nm, preferably in the following stepwise order. In the emission spectrum of the luminescent composition (or coating film) containing the binder component, the fluorene compound may have one or more emission peaks, preferably only one emission peak, and more preferably all emission peaks (maximum wavelength λ _em,max ) are included in the wavelength range.

In the emission spectrum of the luminescent composition (or coating film), the half width of the emission peak (or emission band) having the maximum wavelength λ _em,max may be selected from the range of, for example, about 1 to 100 nm, and is preferably 30 to 70 nm. When Z ^1a and Z ^1b are fused polycyclic C _16-18 arene rings, it is preferably 40 to 65 nm and 50 to 60 nm, stepwise thereafter; and when Z ^1a and Z ^1b are ring assembly C _16-18 arene rings, it is preferably 40 to 60 nm and 45 to 55 nm, stepwise thereafter.

The luminescent composition (or coating film) may have, in its excitation spectrum (or absorption spectrum) at a temperature of 25°C, at least one emission peak (or absorption peak) having a maximum wavelength λ _ex,max in the range of, for example, about 300 to 400 nm, preferably 320 to 380 nm, and more preferably 340 to 370 nm; when Z ^1a and Z ^1b are fused polycyclic C _16-18 arene rings, it preferably has at least one emission (absorption) peak having a maximum wavelength λ _ex,max in the range of 350 to 360 nm; and when Z ^1a and Z ^1b are ring assembly C _16-18 arene rings, it preferably has at least one emission (absorption) peak having a maximum wavelength λ _ex,max in the range of 345 to 360 nm.

Such luminous compositions can be used in a variety of forms or applications, for example, as coating agents such as paints and ink compositions. The luminous compositions may also be used as invisible inks, such as the security inks (or security markers) described in JP 2020-164518 A.

(Light-emitting element or photoelectric conversion element)
The light-emitting element (or photoelectric conversion element) may contain at least the fluorene compound represented by the formula (1) as a light-emitting material and/or a sensitizer, and may contain the fluorene compound in the form of the light-emitting composition, for example, a coating film, etc. Note that when the fluorene compound represented by the formula (1) is contained as a sensitizer, it is preferable that another light-emitting material is contained.

Representative examples of light-emitting elements include current-injection light-emitting elements such as inorganic light-emitting diodes (LEDs) and organic EL elements (or organic light-emitting diodes (OLEDs)), with organic EL elements being preferred. Current-injection light-emitting elements such as organic EL elements are formed from an anode (transparent electrode) and a cathode (metal electrode), with an organic layer (organic thin film) or organic-inorganic hybrid layer interposed between the electrodes. A typical configuration preferably has the layers formed in the following order: transparent substrate/anode/hole transport layer/light-emitting layer/electron transport layer/cathode. Note that if the light-emitting layer also functions as a hole transport layer or electron transport layer, the hole transport layer or electron transport layer is not necessarily required.

Transparent substrates include, for example, substrates made of inorganic materials such as glass; and substrates made of organic materials such as (meth)acrylic resins, styrene resins, polycarbonate resins, and polyester resins. Polyester resins include polyalkylene arylate resins such as polyethylene terephthalate. The substrate may be in the form of a plate, sheet, or film.

The anode may be a transparent electrode, and conductive metal oxides such as ITO (indium tin oxide), FTO (fluorine-doped tin oxide), and ZnO (zinc oxide) are preferred.

Examples of hole transport materials that form the hole transport layer include aromatic amines, phthalocyanines such as copper phthalocyanine, and conductive polymers such as polythiophenes. Specifically, the hole transport materials described in JP 2020-164518 A (Patent Document 1) may be used. These hole transport materials may be used alone or in combination of two or more. Of these, conductive polymers such as PEDOT:PSS are preferred.

The light-emitting layer may contain the fluorene compound represented by formula (1) above as the light-emitting material, or may contain other conventional light-emitting materials. These light-emitting materials may be used alone or in combination of two or more. The light-emitting layer may be composed solely of the light-emitting material, or may contain the light-emitting material as a guest material (or dopant) and a host material. Examples of host materials include the host materials described in JP 2020-164518 A (Patent Document 1), such as biphenyls; and the binder components exemplified in the above-mentioned section on the light-emitting composition, such as (meth)acrylic resins, polycarbonate resins, and silicon-based resins. These host materials may be used alone or in combination of two or more.

Examples of electron transport materials that form the electron transport layer include light metal organic complexes such as aluminum complexes and beryllium complexes, bisstyrylarene derivatives, oxadiazole derivatives, triazole derivatives, phenanthroline derivatives, and silole derivatives, and may also include the electron transport materials described in JP 2020-164518 A (Patent Document 1). These electron transport materials can be used alone or in combination of two or more.

The cathode (metal electrode) is often made of a metal such as aluminum (Al), magnesium (Mg), or silver (Ag), or an alloy of these metals.

An anode buffer layer (hole injection layer) such as a copper phthalocyanine thin film may be formed between the anode and the hole transport layer, and a cathode buffer layer (electron injection layer) such as an inorganic thin film such as a lithium fluoride (LiF) thin film or a lithium oxide (Li ₂ O) thin film, or an organic thin film doped with a metal such as lithium (Li) may be formed between the cathode and the electron transport layer.

The thickness of each layer (organic phase) interposed between the anode and cathode is, for example, 0.1 to 500 nm, preferably 1 to 200 nm, and the total thickness of the organic phase may be approximately 1 μm or less.

The present invention will be explained in more detail below based on examples, but the present invention is not limited to these examples. Evaluation methods are also described below.

[Evaluation method]
(NMR)
Measurement was carried out using BRUKER's "ULTRASHIELD300".

(HPLC)
Measurement was carried out using "LC-20A" manufactured by Shimadzu Corporation.

(Light Emitting Characteristics)
The excitation spectrum and emission (fluorescence or phosphorescence) spectrum of the sample were measured at room temperature (25°C) using a spectrofluorometer (Hitachi High-Technologies Corporation, "F-4500," light source: xenon lamp, detector: photomultiplier tube, spectroscope: diffraction grating), and the maximum wavelength λ _ex,max of the excitation spectrum, the maximum wavelength λ _em,max of the emission spectrum, and the half-width of the peak (or emission band) containing this λ _em,max were determined.

(Quantum Efficiency)
A fluorescence spectrophotometer (JASCO Corporation "FP-6500", light source: xenon lamp, detector: photomultiplier tube, spectroscope: diffraction grating) equipped with a fluorescence integrating sphere unit (JASCO Corporation "ILF-533", diameter 100 mm) was subjected to spectral correction using an instrument function obtained using the attached calibration standard light source, and the spectral area and number of photons were made proportional. The luminescence quantum efficiency was then calculated by the absolute method. The excitation light was measured without a sample in place to determine the spectral area of the irradiated excitation light, and then the excitation light was measured with a sample in place to determine the spectral area of the irradiated excitation light not absorbed by the sample. The number of photons absorbed by the sample was calculated by calculating the difference between these values. The emission spectrum of the sample was simultaneously observed, and the number of emitted photons was calculated from the spectral area. Finally, the luminescence quantum efficiency was calculated from the number of emitted photons relative to the number of absorbed photons.

[Preparation of Fluorene Compounds]
(Example 1) Preparation of BEPF-TPh

A 100 mL three-necked recovery flask was charged with 9,9-bis(2-phenylethyl)-2,7-dibromofluorene [also referred to as BEPF-Br] (0.266 g, 0.50 mmol) represented by the above formula (2-1), which was prepared in accordance with Synthesis Example 1 of JP 2020-164518 A (Patent Document 1), 2-([1,1':4',1"-terphenyl]-4-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (0.392 g, 1.1 mmol) represented by the above formula (3-1), a 2 M aqueous potassium carbonate solution (5 mL), and tetrahydrofuran (THF, 20 mL). Pd(PPh ₃ ) ₄ (0.0116 g, 0.010 mmol) was added under a nitrogen atmosphere, and the mixture was heated and stirred at 80°C for 24 hours.

After returning the mixture to room temperature, dichloromethane (10 mL) and distilled water (20 mL) were added and extracted. The organic layer was then washed with distilled water (20 mL x 2). The washed organic layer was then dehydrated over magnesium sulfate, and the solvent was removed to yield a yellow solid.

The crystals were purified by silica gel chromatography (solvent: hexane/dichloromethane = 10/1 (volume ratio)) and then recrystallized (solvent: toluene) to obtain 9,9-bis(2-phenylethyl)-2,7-di(p-terphenyl-4-yl)fluorene (also referred to as BEPF-TPh) represented by the above formula (1-2) as pale yellow crystals (0.172 g, yield: 41%). The ¹ H NMR spectrum of the obtained BEPF-TPh is shown below.

^1H NMR (600MHz, _CDCl3 ): δ (ppm) 2.07-2.10 (m, 4H), 2.46-2.48 (m, 4H), 6.96-6.97 (m, 4H), 7.07-7.17 (m, 6H), 7.36-7.39 (m, 2H), 7.46-7.49 (m, 4H), 7.66-7.79 (m, 24H), 7.89-7.90 (m, 2H).

(Reference example 1)
A coupling reaction was attempted in the same manner as in Example 1, except that 20 mL of toluene was used instead of THF as the reaction solvent. However, the reaction did not proceed, and BEPF-TPh was not obtained (yield 0% by NMR).

(Example 2) Preparation of BEPF-Py

BEPF-Br (0.106 g, 0.20 mmol) represented by the above formula (2-1), 1-pyreneboronic acid (0.108 g, 0.44 mmol) represented by the above formula (3-2), 2 M aqueous potassium carbonate solution (2 mL), and toluene (5 mL) were placed in a 100 mL three-necked recovery flask. Pd(PPh ₃ ) ₄ (0.0046 g, 0.0040 mmol) was added under a nitrogen atmosphere, and the mixture was heated and stirred at 120°C for 24 hours.

After returning the mixture to room temperature, dichloromethane (10 mL) and distilled water (20 mL) were added and extracted. The organic layer was then washed with distilled water (20 mL x 2). The washed organic layer was then dehydrated over magnesium sulfate, and the solvent was removed to yield a yellow solid.

The product was purified by silica gel chromatography (solvent: hexane/dichloromethane = 10/1 (volume ratio)) and then recrystallized (solvent: toluene) to obtain 9,9-bis(2-phenylethyl)-2,7-di(1-pyrenyl)fluorene (also referred to as BEPF-Py) represented by the above formula (1-2) as white crystals (0.102 g, yield: 66%). The ¹ H NMR spectrum of the resulting BEPF-Py is shown below.

^1H NMR (600MHz, _CDCl3 ): δ (ppm) 2.27-2.28 (m, 4H), 2.48-2.50 (m, 4H), 7.05-7.13 (m, 6H), 7.19-7.22 (m, 4H), 7.74-7.79 (m, 4H), 8.03-8.34 (m, 20H).

(Comparative Example 1) Preparation of BEPF According to Reference Example 1 of JP 2020-164518 A (Patent Document 1), 9,9-bis(2-phenylethyl)fluorene (also referred to as BEPF) represented by the following formula was prepared.

(Comparative Example 2) Preparation of BEPF-Ph According to Example 1 of JP 2020-164518 A (Patent Document 1), 9,9-bis(2-phenylethyl)-2,7-diphenylfluorene (also referred to as BEPF-Ph) represented by the following formula was prepared.

(Comparative Example 3) Preparation of BEPF-BPh According to Example 4 of JP 2020-164518 A (Patent Document 1), 9,9-bis(2-phenylethyl)-2,7-di(4-biphenylyl)fluorene (also referred to as BEPF-BPh) represented by the following formula was prepared.

(Comparative Example 4) Preparation of BEPF-Np According to Example 3 of JP 2020-164518 A (Patent Document 1), 9,9-bis(2-phenylethyl)-2,7-di(2-naphthyl)fluorene (also referred to as BEPF-Np) represented by the following formula was prepared.

[Emission properties of fluorene compounds]
(Light-emitting properties in the solid state)
The solid-state excitation and emission spectra, as well as the luminescence quantum efficiency, of the fluorene compounds prepared in the Examples and Comparative Examples were measured. Table 1 shows the correspondence between the samples and the obtained spectra, as well as the conditions for measuring the spectra, and Table 2 and Figures 1 and 2 show the measurement results. In Table 1, "emission wavelength" refers to the wavelength at which the emission intensity was monitored in the excitation spectrum, and "excitation wavelength" refers to the wavelength of the excitation light in the emission spectrum (the same applies hereinafter).

(Emission characteristics in solution state)
The fluorene compounds prepared in the Examples and Comparative Examples were dissolved in dichloromethane at the concentrations shown in Table 3, and the excitation spectrum, emission spectrum, and luminescence quantum efficiency in the solution state were measured. Table 3 shows the correspondence between the samples and the obtained spectra, as well as the spectrum measurement conditions, and Table 4 and Figures 3 and 4 show the measurement results.

In addition, when measuring the solution state, all examples and comparative examples were sufficiently diluted, and no significant effects such as concentration quenching were observed.

As is clear from Tables 2 and 4 and FIGS. 1 to 4, the Examples, unlike the Comparative Examples, emitted blue light with a maximum wavelength λ _em,max in the wavelength region of 410 to 460 nm in the emission spectrum.

As mentioned above, it is generally expected that increasing the number of aromatic rings in a chemical structure through condensation or single bonds will increase the conjugation length and lengthen the emission wavelength, but it is difficult to predict how much longer the wavelength will be. For example, pentacene, which has five benzene ring skeletons, emits green to yellow light in solution with maximum wavelengths λ _em,max at 537 nm and 582 nm, respectively. In contrast, in the Examples, terphenyl rings and pyrene rings are bonded to the 2- and 7-positions of the fluorene ring, respectively, and although the structure has more benzene ring skeletons than pentacene, it emitted blue light without extending the wavelength into the green wavelength region. Furthermore, in the Examples, not only did the compounds emit blue light in the specific wavelength region, but they also emitted light with high quantum efficiency and a relatively narrow half-width, but these emission characteristics were also difficult to predict from the chemical structure.

The luminescence characteristics based on the compound (or chemical structure) are reflected particularly in the results in the solution state (Table 4). The fluorene compounds of the Examples were found to be particularly suitable as blue-emitting materials because they were capable of emitting light in the wavelength region of 410 to 460 nm (a purer, brighter blue). In particular, the quantum efficiency of BEPF-Py of Example 2 was not only remarkably high, but also unexpectedly exhibited a single emission peak, demonstrating high monochromaticity as visible light (blue emission). In particular, pyrene, the compound corresponding to Z ^1a and Z ^1b in BEPF-Py, is known to exhibit a single emission peak on the longer wavelength side in the excimer (excited dimer) state, but to exhibit multiple emission peaks on the shorter wavelength side in the monomer state (solution state) (the peaks are split into smaller pieces). Therefore, it was unexpected that BEPF-Py exhibited a single emission peak in the wavelength region of 410 to 460 nm.

(Light-emitting properties in coated film state)
As shown in Table 6, 0.001 g of each fluorene compound prepared in the Examples or Comparative Examples and 0.01 g of each binder component described below were mixed with chloroform to a predetermined solid content concentration (Examples: 1 mass %, Comparative Examples: 5 mass %) to prepare a mixed solution (coating agent).

Each of the resulting coating agents was applied to a quartz substrate (Labo-USQ, manufactured by Taiko Seisakusho Co., Ltd.) using a spin coater (1H-D7, manufactured by Mikasa Co., Ltd., 1000 rpm) and dried on a hot plate at 90°C for 30 minutes to form a coating film. The excitation spectrum, emission spectrum, and luminescence quantum efficiency of each formed coating film were measured. Table 5 shows the correspondence between the sample and the obtained spectrum, as well as the spectral measurement conditions, and Table 6 and Figures 5 to 12 show the measurement results. The resins used as binder components are listed below.

PS: polystyrene, manufactured by PS Japan Co., Ltd. PC: polycarbonate, manufactured by Mitsubishi Engineering Plastics Corporation PMMA: polymethyl methacrylate, manufactured by Mitsubishi Rayon Co., Ltd. PPSQ: polyphenylsilsesquioxane, prepared by the method described below.

1 mmol of trimethoxyphenylsilane, 1.5 mL of tetrahydrofuran as a solvent, 60 μL of formic acid as an acid catalyst, and 60 μL of water were mixed, and the mixture was heated and stirred at 90° C. for 3 hours to carry out hydrolysis and condensation reactions, followed by drying. After cooling, the remaining acid was washed away with pure water, and 1.5 mL of tetrahydrofuran was added to reconstitute the solution. The mixture was heated and stirred at 110° C. for 2 hours, followed by drying, to synthesize PPSQ represented by the following formula:

As is clear from Table 6 and Figures 5 to 12, even in the coating film state containing the binder component, the Examples, unlike the Comparative Examples, exhibited a maximum wavelength λ _em,max in the wavelength region of 410 to 460 nm in the emission spectrum, and emitted light with a relatively narrow half-width. Furthermore, high quantum efficiency was also observed for all binder components. Note that, as in Patent Document 1, in ultraviolet-emitting organic EL applications, materials are actually used in a solid state without a binder component due to the tendency for energy transfer from the emitting material to the binder component. Therefore, the luminescence characteristics in the solid state are important. In contrast, in visible light (blue)-emitting organic EL applications, where such energy transfer is less likely to occur, the luminescence characteristics in the coating film state are important. Therefore, the fluorene compounds of the Examples, which exhibit excellent quantum efficiency in the wavelength region, can be suitably used in blue-emitting organic EL applications.

As mentioned above, while an increase in conjugation length is expected to result in a longer emission wavelength, the inclusion of many aromatic rings in the chemical structure generally reduces dispersibility, and molecules (light-emitting materials) tend to aggregate more easily, particularly in a coated film, which is expected to result in a decrease in luminescence quantum efficiency due to concentration quenching. However, despite having a considerable number of benzene ring skeletons, the fluorene compounds of the examples exhibit unexpectedly high quantum efficiency in a coated film, making them particularly useful as blue-emitting materials for organic light-emitting diodes (OLEDs). Furthermore, the quantum efficiency of BEPF-TPh in Example 1 was unexpectedly significantly improved in a coated film compared to its solution state.

Furthermore, when the luminescence characteristics of BEPF-Py in Example 2 were evaluated by setting the solids concentration of the coating agent to 5% by mass when preparing the coating film (i.e., preparing a thick coating film), the film absorbed too much light, resulting in saturated measurement results (all light was absorbed by the film, making it impossible to confirm changes in the absorption coefficient with wavelength, and the excitation spectrum became trapezoidal rather than peaked). In the comparative example (solids concentration of 5% by mass), no saturation was observed for any of the fluorene compounds, indicating that BEPF-Py has a higher absorption coefficient than conventional fluorene compounds. Since the intensity (or brightness) of luminescence increases in proportion to the absorption coefficient (ability to absorb light) and luminescence quantum efficiency (efficiency of conversion from absorbed excitation light), BEPF-Py with high absorption coefficients is thought to be able to emit light more brightly.

The fluorene compounds of the present invention can be effectively used as luminescent materials and/or sensitizers, particularly as blue luminescent materials. In particular, unlike inorganic luminescent materials formed from inorganic materials, the fluorene compounds are soluble in organic solvents, easily disperse uniformly in matrix materials such as various resins, and can easily and efficiently form coating layers or paint films on substrates with complex shapes. Therefore, they can be effectively used as luminescent materials and/or sensitizers in applications such as coating agents for invisible inks and light-emitting devices (or photoelectric conversion devices).

Examples of the light-emitting element (or photoelectric conversion element) include current injection type light-emitting elements such as organic EL elements, etc. Representative examples include light sources for displays and lighting, etc., which can be effectively used in various applications.

Claims (11)

A compound represented by the following formula (1):
(In the formula, Z ^1a and Z ^1b each independently represent a terphenylene ring or a pyrene ring ,
R ^1a and R ^1b each independently represent an alkyl group, a cycloalkyl group, a halogen atom, a hydroxyl group, a group [—OR ^A ] (wherein R ^A represents an alkyl group or a cycloalkyl group), a hydroxy(poly)alkoxy group, a thiol group, a group [—SR ^A ] (wherein R ^A represents an alkyl group or a cycloalkyl group), a carboxyl group, an alkoxycarbonyl group, an amino group, a cyano group, a trialkylsilyl group, or a dialkylhydrosilyl group; k1 and k2 each independently represent an integer of 0 to 2;
m1 and m2 represent 1;
R ^2a and R ^2b each independently represent a hydrocarbon group (excluding an aryl group), n1 and n2 each independently represent an integer of 0 to 2,
A ^1a and A ^1b each independently represent a linear or branched C _1-4 alkylene group;
^Z2a and ^Z2b each independently represent a _C6-12 arene ring, ^R3a and ^R3b each independently represent a _C1-4 alkyl group, a hydroxyl group, or a carboxyl group, and p1 and p2 each independently represent an integer of 0 to 2. In the formula (1), Z ^1a and Z ^1b are pyrene rings,
2. The compound according to claim 1 , wherein ^Z2a and ^Z2b are a benzene ring, a naphthalene ring, or a biphenyl ring. 3. The compound according to claim 1, which is a blue light-emitting material having an emission spectrum in a dichloromethane solution state, the emission spectrum having at least one emission peak with a maximum wavelength λ _em,max of 410 to 460 nm and a half-value width of 70 nm or less, and an emission quantum efficiency of 40% or more. A method for producing the compound according to any one of claims 1 to 3 , comprising either the following step (i) or (ii):
(i) a step of subjecting a compound represented by the following formula (2) to a coupling reaction with a compound represented by the following formula (3):
(In the formula, X ^1a and X ^1b each independently represent a group capable of forming a carbon-carbon bond by a coupling reaction,
^X2 represents a group capable of forming a carbon-carbon bond by a coupling reaction together with ^X1a and/or ^X1b ;
Z ¹ is the same as Z ^1a and/or Z ^1b in formula (1),
R ¹ is the same as R ^1a and/or R ^1b in formula (1), k is the same as k1 and/or k2 in formula (1),
^Z2a , ^Z2b , ^R2a , ^R2b , ^R3a , ^R3b , ^A1a , ^A1b , m1, m2, n1, n2, p1 and p2 are the same as in formula (1).
(ii) In the step (i), when Z ¹ of the compound represented by formula (3) is a terphenylene ring, a step of reacting in the presence of an ether. A method for exciting the compound according to any one of claims 1 to 3 to cause it to emit light. A luminescent composition comprising the compound according to any one of claims 1 to 3 . The luminescent composition according to claim 6 , further comprising a binder component. 8. The luminescent composition according to claim 7 , wherein the binder component contains at least one resin selected from the group consisting of (meth)acrylic resins, styrene resins, polycarbonate resins, and silicon resins. 9. The luminescent composition according to claim 7 , wherein the ratio of the compound represented by formula (1) to the binder component is the former/latter (mass ratio) = 1/0.5 to 1/1000. The luminescent composition according to any one of claims 6 to 9 , which has an emission spectrum including at least one emission peak having a maximum wavelength λ _em,max of 410 to 460 nm and a half-value width of 70 nm or less, and has a luminescence quantum efficiency of 70% or more. A light-emitting device comprising the compound according to any one of claims 1 to 3 .