JP2009292746A - THIAZOLE DERIVATIVE HAVING EXTENDED pi-CONJUGATED SYSTEM - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a π-conjugate system organic compound useful as a luminescent layer material of organic EL, or the like. <P>SOLUTION: The thiazole derivative is represented by general formula (I) (wherein n is an integer of 2-4; R<SP>11</SP>s are the same or different and each a hydrogen atom, a lower alkyl group or a lower alkoxycarbonyl group; Ar<SP>11</SP>s are the same or different and each a hydrogen atom or an aromatic group exhibiting electron withdrawing property with the proviso that at least one Ar<SP>11</SP>is an aromatic group exhibiting electron withdrawing property; and Ar<SP>12</SP>is an electron-donating group having an aromatic ring directly bonded to a thiazole backbone). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a thiazole derivative useful for organic EL and the like.

  π-conjugated organic materials are attracting attention as materials for “light thin and short” conductors (semiconductors) or EL elements. As such a π-conjugated organic material, the present inventor has been paying attention to thiazole derivatives for many years.

  In the non-patent document 1, the present inventors have a donor-acceptor of the following formula having an electron-donating group (donor) at the 2-position of the thiazole ring and an electron-withdrawing group (acceptor) at the 5-position of the thiazole ring. It has been reported that type thiazole derivatives exhibit strong fluorescence and stable liquid crystallinity.

Shikuma, J .; Mori, A .; Masui, K .; Matsuura, R .; Sekiguchi, A .; Ikegami, H .; Kawamoto, M .; Ikeda, T. Chem. Asian J., 2007, 2, 301 .

  An object of the present invention is to provide a π-conjugated organic compound (particularly a thiazole derivative having an expanded π-conjugated system) useful as a light emitting layer material for organic EL.

  The thiazole derivative of the present invention that has achieved the above object is represented by the following formula (I).

In the formula (I), n represents an integer of 2 to 4.
R ¹¹ are the same or different and each represents a hydrogen atom, a lower alkyl group or a lower alkoxycarbonyl group.
Ar ¹¹ is the same or different and represents a hydrogen atom or an aromatic group exhibiting electron withdrawing properties. However, at least one Ar ¹¹ is an aromatic group exhibiting electron withdrawing properties.
Ar ¹² represents an electron donating group having an aromatic ring directly bonded to the thiazole skeleton.

  Hereinafter, the thiazole derivative represented by the formula (I) may be abbreviated as a thiazole derivative (I) or a compound (I). Similarly, thiazole derivatives and compounds represented by other chemical formulas may be abbreviated as well.

  Among the thiazole derivatives (I), thiazole derivatives represented by the following formula (II) are preferable.

In the formula (II), R ²¹ represents a lower alkyl group or a lower alkanoyl group.
R ^{22 to} R ²⁵ are the same or different and each represents a hydrogen atom or a lower alkyl group.
R ²⁶ and R ²⁷ are the same or different and each represents a hydrogen atom, a lower alkyl group or a lower alkoxycarbonyl group.
Ar ²¹ and Ar ²² are the same or different and each represents a hydrogen atom or an aromatic group exhibiting electron withdrawing properties. However, at least one of Ar ²¹ and Ar ²² is an aromatic group exhibiting electron withdrawing properties.

  Of the thiazole derivatives (I), a thiazole derivative represented by the following formula (III) is preferable.

In formula (III), R ³¹ and R ³² are the same or different and each represents a hydrogen atom, a lower alkyl group or an acyl group.
R ³³ and R ³⁴ are the same or different and each represents a hydrogen atom, a lower alkyl group or a lower alkoxycarbonyl group.
Ar ³¹ and Ar ³² are the same or different and each represents a hydrogen atom or an aromatic group exhibiting electron withdrawing properties. However, at least one of Ar ³¹ and Ar ³² is an aromatic group exhibiting electron withdrawing properties.

  Of the thiazole derivatives (I), a thiazole derivative represented by the following formula (IV) is preferable.

In formula (IV), R ^{401 to} R ⁴¹² are the same or different and each represents a hydrogen atom or a lower alkyl group.
R ^{413 to} R ⁴¹⁵ are the same or different and each represents a hydrogen atom, a lower alkyl group or a lower alkoxycarbonyl group.
Ar ^{41 to} Ar ⁴³ are the same or different and each represents a hydrogen atom or an aromatic group exhibiting electron withdrawing properties. However, at least one of Ar ^{41 to} Ar ⁴³ is an aromatic group exhibiting electron withdrawing properties.

The thiazole derivative of the present invention has a donor-acceptor type structure in which the thiazole skeleton has an electron-donating group Ar ¹² (donor) and an electron-withdrawing group Ar ¹¹ (acceptor), and exhibits strong fluorescence. it can. In addition, the thiazole derivative of the present invention has a further expanded π-conjugated system as compared with the thiazole derivative shown in Non-Patent Document 1, and can realize better light absorption and fluorescence. Furthermore, the maximum fluorescence wavelength of the thiazole derivative of the present invention is red-shifted to a longer wavelength side (more visible light region side) than a thiazole derivative that is not a donor / acceptor type. The thiazole derivative of the present invention, which exhibits good light absorption and fluorescence, and whose maximum fluorescence wavelength is red-shifted to the visible light region, is useful as, for example, a light emitting layer material for an organic EL device.

As represented by the formula (I), the thiazole derivative of the present invention has a donor-acceptor type structure in which an electron-donating group Ar ¹² (donor) → thiazole skeleton → an electron-withdrawing group Ar ¹¹ (acceptor) is bonded. And the movement of electrons is likely to occur, so that strong fluorescence can be exhibited. Furthermore, since the thiazole derivative of the present invention has a π-conjugated system expanded by bonding Ar ¹¹ and Ar ¹² so as to sandwich the thiazole skeleton, the thiazole derivative exhibits strong light absorptivity, and fluorescence emission more toward the visible light region side. Demonstrates the effect of red shift. As described above, the thiazole derivative of the present invention has a feature that it has an extended π-conjugated system in addition to taking a donor-acceptor type structure, and has strong light absorption and fluorescence, and to the visible light side. The effect of red shift can be achieved.

  First, the thiazole derivative (I) of the present invention will be described. In addition, as the definition of “group” described below, “Organic Compound” described in “Chemical Dictionary” (Tokyo Chemical Co., Ltd., 1st edition, 1st edition, published on October 20, 1989), p. 520 In the present invention, an atomic group in which hydrogen is formally removed from is adopted. The concept of “group” used in the present invention includes an atomic group such as a carbazole skeleton, a fluorene skeleton, or a triphenylamine skeleton.

R ¹¹ are the same or different and each represents a hydrogen atom, a lower alkyl group or a lower alkoxycarbonyl group. It is preferred that all R ¹¹ are the same. The lower alkyl group is preferably a C _1-6 alkyl group, more preferably a methyl group. In the present invention, “Ca-b” means “having a carbon number of a to b”. The lower alkoxycarbonyl group (—COOR, R: lower alkyl group) is preferably a carbonyl group to which a C _1-6 alkoxy group is bonded, more preferably a methoxycarbonyl group (—COOMe), an ethoxycarbonyl group (—COOEt) or t— It is a butoxycarbonyl group (—COO (t-Bu)). The thiazole derivative (I) in which R ¹¹ is a hydrogen atom has high crystallinity and exhibits good fluorescence. On the other hand, thiazole derivative (I) in which R ¹¹ is a lower alkyl group or a lower alkoxycarbonyl group has good solubility in a solvent. It is preferable that all R ¹¹ is a hydrogen atom or a methyl group.

Ar ¹¹ is the same or different and represents a hydrogen atom or an aromatic group exhibiting electron withdrawing properties. It is preferred that all Ar ¹¹ are the same. The thiazole derivative (I) is characterized in that it has a donor-acceptor type structure of electron donating group → thiazole skeleton → electron withdrawing group, so that at least one Ar ¹¹ is an aromatic group exhibiting electron withdrawing property. It is necessary to be. It is preferable that all Ar ¹¹ is an aromatic group exhibiting electron withdrawing properties.

Ar ¹¹ includes an aromatic ring having an electron-withdrawing substituent bonded thereto. Examples of the aromatic ring of Ar ¹¹ include a phenyl group, a biphenyl group, a naphthyl group, an anthryl group, and a pyridyl group. Among these, a phenyl group, a biphenyl group, and a naphthyl group are preferable, and a phenyl group is more preferable.

Examples of the electron-withdrawing substituent for Ar ¹¹ include a halogen atom (preferably a chlorine atom and a fluorine atom, more preferably a fluorine atom), a carboxy group (—COOH), a lower alkoxycarbonyl group (—COOR, preferably R ═C _1-4 alkyl group), lower alkanoyl group (—C (═O) R, preferably _{R═C 1-4} alkyl group), perfluoro (lower) alkyl group (—C _n F _{2n + 1} , preferably Is n = 1 to 4, more preferably n = 1), a cyano group (—CN), a sulfo group (—SO ₃ H), a lower alkoxysulfonyl group (—SO ₃ R, preferably R═C _1-4 alkyl). Group) and a lower alkylsulfonyl group (—SO ₂ R, preferably R═C _1-4 alkyl group). In addition, the alkyl group contained in the electron-withdrawing substituent may have a halogen atom (particularly a fluorine atom). A nitro group (—NO ₂ ) can also be used as an electron-withdrawing substituent. However, when a nitro group is used, there is a merit that the maximum absorption wavelength of the thiazole derivative is red-shifted to a longer wavelength side, but there is a demerit that the fluorescence of the thiazole derivative disappears. Therefore, when using the fluorescence of the thiazole derivative of the present invention (for example, when the thiazole derivative is used as a material for a fluorescent paint or a light emitting layer of an organic EL layer), it is recommended not to use a nitro group as an electron-attracting substituent. Is done.

The aromatic group Ar ¹¹ exhibiting electron withdrawing property is preferably 4-ethoxycarbonylphenyl group, 4-cyanophenyl group, 4-trifluoromethylphenyl group, 3,5-bistrifluoromethylphenyl group, pentafluorophenyl group. Or a 3,5-di (phenylsulfonyl) phenyl group, more preferably a 4-ethoxycarbonylphenyl group, a 4-cyanophenyl group, or a 4-trifluoromethylphenyl group, still more preferably 4-ethoxycarbonyl. It is a phenyl group.

Ar ¹² represents an electron donating group having an aromatic ring directly bonded to the thiazole skeleton.
Examples of Ar ¹² where n = 2 include a carbazole skeleton or a fluorene skeleton represented by the following formula (A) or (B). The hydrogen atom in these skeletons may be substituted with a substituent such as a lower alkyl group (in the following formula, the wavy line indicates the bonding position with the thiazole skeleton).

Examples of Ar ¹² where n = 3 include a triphenylamine skeleton represented by the following formula (C). The hydrogen atom in this skeleton may be substituted with a substituent such as a lower alkyl group (in the following formula, the wavy line indicates the bonding position with the thiazole skeleton).

Examples of Ar ¹² where n = 4 include a carbazole dimer skeleton represented by the following formula (D). The hydrogen atom in this skeleton may be substituted with a substituent such as a lower alkyl group (in the following formula, the wavy line indicates the bonding position with the thiazole skeleton).

  Next, the thiazole derivative (II) of the present invention will be described.

R ²¹ represents a lower alkyl group (preferably a C _1-6 alkyl group, more preferably a C _1-3 alkyl group, particularly an ethyl group) or a lower alkanoyl group (—C (═O) R, preferably _{R═C 1— 4} alkyl group; especially acetyl group). R ²¹ is preferably an ethyl group.

R ^{22 to} R ²⁵ are the same or different and each represents a hydrogen atom or a lower alkyl group (preferably a C _1-3 alkyl group, more preferably a methyl group). R ^{22 to} R ²⁵ are preferably hydrogen atoms.

R ²⁶ and R ²⁷ are the same or different and each represents a hydrogen atom, a lower alkyl group or a lower alkoxycarbonyl group. R ²⁶ and R ²⁷ are preferably the same. The detailed description (preferred examples) of R ²⁶ and R ²⁷ is the same as that described for R ¹¹ of the thiazole derivative (I).

Ar ²¹ and Ar ²² are the same or different and each represents a hydrogen atom or an aromatic group exhibiting electron withdrawing properties. Ar ²¹ and Ar ²² are preferably the same. At least one of Ar ²¹ and Ar ²² needs to be an aromatic group exhibiting electron withdrawing properties, and it is preferable that both of these are aromatic groups exhibiting electron withdrawing properties. The detailed description (preferred examples) of Ar ²¹ and Ar ²² is the same as that described for Ar ¹¹ of the thiazole derivative (I).

  Next, the thiazole derivative (III) of the present invention will be described.

R ³¹ and R ³² are the same or different and each represents a hydrogen atom, a lower alkyl group or an acyl group. Preferred lower alkyl groups are C _1-6 alkyl groups. This lower alkyl group may have a C _1-3 alkyl group as a side chain. Examples of the acyl group include a lower alkanoyl group (—C (═O) R, preferably R═C _1-4 alkyl group; particularly acetyl group) and an aryloyl group (particularly benzoyl group). R ³¹ and R ³² are preferably a hexyl group or a 2-ethylhexyl group, and more preferably a hexyl group.

R ³³ and R ³⁴ are the same or different and each represents a hydrogen atom, a lower alkyl group or a lower alkoxycarbonyl group. R ³³ and R ³⁴ are preferably the same. The detailed description (preferred examples) of R ³³ and R ³⁴ is the same as that described for R ¹¹ of the thiazole derivative (I).

Ar ³¹ and Ar ³² are the same or different and each represents a hydrogen atom or an aromatic group exhibiting electron withdrawing properties. Ar ³¹ and Ar ³² are preferably the same. At least one of Ar ³¹ and Ar ³² needs to be an aromatic group exhibiting electron withdrawing properties, and it is preferable that both of these are aromatic groups exhibiting electron withdrawing properties. The detailed description (preferred examples) of Ar ³¹ and Ar ³² is the same as that described for Ar ¹¹ of the thiazole derivative (I).

  Next, the thiazole derivative (IV) of the present invention will be described.

R ^{401 to} R ⁴¹² are the same or different and each represents a hydrogen atom or a lower alkyl group (preferably a C _1-3 alkyl group, more preferably a methyl group). R ^{401 to} R ⁴¹² are preferably hydrogen atoms.

R ^{413 to} R ⁴¹⁵ are the same or different and each represents a hydrogen atom, a lower alkyl group or a lower alkoxycarbonyl group. R ^{413 to} R ⁴¹⁵ are preferably the same. The detailed description (preferred examples) of R ^{413 to} R ⁴¹⁵ is the same as that described for R ¹¹ of the thiazole derivative (I).

Ar ^{41 to} Ar ⁴³ are the same or different and each represents a hydrogen atom or an aromatic group exhibiting electron withdrawing properties. All of Ar ^{41 to} Ar ⁴³ are preferably the same. At least one of Ar ^{41 to} Ar ⁴³ needs to be an aromatic group exhibiting electron withdrawing properties. Preferably two of Ar ^{41 to} Ar ⁴³ , more preferably all of Ar ^{41 to} Ar ⁴³ are aromatic groups exhibiting electron withdrawing properties. The detailed description (preferred examples) of Ar ³¹ and Ar ³² is the same as that described for Ar ¹¹ of the thiazole derivative (I).

  The thiazole derivatives of the present invention can be produced by methods known in the field of synthetic organic chemistry. Hereinafter, the manufacturing method will be described based on the formula (I).

First, an iodine-containing compound corresponding to the central skeleton Ar ¹² is prepared. For example, iodine-containing carbazole or iodine-containing fluorene can be synthesized by introducing iodine into carbazole or fluorene by a known method. The carbazole, fluorene, and iodides thereof can be obtained from Tokyo Kasei. Carbazoles having a substituent can be produced by a known method. For example, carbazoles having a methyl group can be produced by synthesizing biphenyl by coupling m-cresol or o-cresol and converting it to carbazole.

Tri (4-iodophenyl) amine can be obtained from Tokyo Kasei. In addition, tri (4-iodophenyl) amines having a substituent can be produced from iodobenzenes represented by the following formula (E) or anilines represented by the formula (F) (in the following formula, R ^{41 to} R ⁴⁸ are the same or different and each represents a hydrogen atom or a substituent such as an alkyl group, provided that at least one of R ^{41 to} R ⁴⁸ is a substituent such as an alkyl group.

Next, the thiazole skeleton and Ar ¹² were bonded by reacting the iodine compound with thiazole or thiazole (for example, 4-methylthiazole) in the presence of a palladium catalyst, a copper catalyst, and an additive (such as NaOH). Compounds can be synthesized. Thiazole or thiazoles can be obtained from Tokyo Kasei. As shown in the following synthesis example, in this reaction, a compound in which all iodine of an iodine compound is substituted with a thiazole skeleton and a compound having iodine and a thiazole skeleton are synthesized depending on reaction conditions. A compound having different R ¹¹ can be produced by reacting another compound having an iodine and a thiazole skeleton with another thiazole.

Next, the thiazole derivative (I) of the present invention can be produced by reacting the above compound in which Ar ¹² and a thiazole skeleton are bonded to the Ar ¹¹ -I compound. For example, an Ar ¹¹ -I compound in which iodine and a perfluoro (lower) alkyl group which is an electron-withdrawing substituent are bonded to an aromatic ring can be obtained from Asahi Glass or Central Glass, for example. Note that it is difficult to directly react a compound in which iodine and a carboxy group (electron-withdrawing substituent) are bonded to an aromatic ring. Therefore, the thiazole derivative (I) having a carboxy group may be synthesized by synthesizing the thiazole derivative (I) having a lower alkoxycarbonyl group (so-called ester group) and then hydrolyzing it.

  Detailed conditions in each of the above reactions can be appropriately set by those skilled in the art by referring to the conditions described in the following synthesis examples and general knowledge of organic synthetic chemistry.

  EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited by the following examples, and appropriate modifications are made within a range that can meet the above and the following purposes. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

<Synthesis example>
Each compound was synthesize | combined by the method shown to the following synthesis examples 1-8. The identification data of the synthesized compound was measured with the following equipment and conditions.
(1) ¹ H-NMR (500 MHz) and ¹³ C-NMR (125 MHz) spectra Equipment used: Bruker Avance 500 spectrometer
Unless otherwise specified, ¹ H-NMR and ¹³ C-NMR data of CDCl ₃ solution are shown. Chemical shifts are expressed in ppm relative to CHCl ₃ ( ¹ H, 7.26 ppm) or CDCl ₃ ( ¹³ C, 77.0 ppm) as internal standards.
(2) IR spectrum Equipment used: Perkin-Elmer FT-IR Spectrometer SPECTRUM 1000 Equipment Absorption spectrum by KBr method (3) HRMS
Equipment used: JEOL MStation JMS-700 (EI +)
(4) Elemental analysis Equipment used: Yanaco MTCHN coder

  Synthesis Example 1: Synthesis of compound (III-a)

In a 25 mL Schlenk tube under an argon atmosphere, compound (iii) (293.2 mg, 0.5 mmol), PdCl ₂ (PPh ₃ ) ₂ (10.5 mg, 0.015 mmol), CuI (1.9 mg, .0. 01 mmol) and 3 mL of DMSO were added. To this mixture was added thiazole (0.11 mL, 1.25 mmol) and NaOH (50.0 mg, 1.25 mmol) successively. After stirring for 21 hours, more NaOH (24.0 mg, 0.6 mmol) was added. The resulting mixture was heated in an oil bath (60 ° C.) and stirred for 48 hours. The mixture was cooled to room temperature and 10 mL of dichloromethane was added. The solution added with dichloromethane was poured into a separatory funnel containing 20 mL of water, the aqueous layer and the organic layer were separated, and the separated aqueous layer was extracted with dichloromethane (10 mL × 3). The extracts were combined, washed with brine, dried over anhydrous sodium sulfate and concentrated in vacuo. The residue was purified by silica gel column chromatography to obtain 123.8 mg (yield: 49%) of compound (III-a). As a by-product, compound (III-b) was obtained with 53.7 mg (yield: 23%).

Identification data of compound (III-a)
¹ H-NMR (500 MHz, CDCl ₃ , ppm) δ 0.59-0.68 (m, 4H), 0.72 (t, J = 7.1 Hz, 6H), 0.95-1.14 (m, 12H), 2.06-2.12 (m, 4H), 7.36 (d, J = 3.2 Hz, 2H), 7.78 (d, J = 8.0 Hz, 2H), 7.91 ( d, J = 3.2 Hz, 2H), 7.95 (dd, J = 1.3, 8.0 Hz, 2H), 8.03 (d, J = 1.3 Hz, 2H).
¹³ C-NMR (125 MHz, CDCl ₃ , ppm) δ 13.8, 22.4, 23.7, 29.5, 31.4, 40.2, 55.6, 118.6, 120.4, 120. 6, 126.0, 132.8, 142.2, 143.5, 152.1, 168.8.
IR (KBr, cm ⁻¹ ) 3115, 3074, 2948, 2926, 2858, 1493, 1466, 1392, 1241, 1139, 1131.
HRMS (m / z) measured value 500.2315, calculated value 500.2320.

Identification data of compound (III-b)
¹ H-NMR (500 MHz, CDCl ₃ , ppm) δ 0.63-0.76 (m, 20H), 0.99-1.13 (m, 24H), 2.06-2.13 (m, 8H) 7.35 (d, J = 3.2 Hz, 1H), 7.36 (d, J = 3.2 Hz, 1H), 7.58 (d, J = 1.4 Hz, 1H), 7.65 ( dd, J = 1.4, 8.0 Hz, 1H), 7.77 (d, J = 7.9 Hz, 1H), 7.78 (d, J = 7.9 Hz, 1H), 7.79 (d , J = 8.0 Hz, 1H), 7.86 (d, J = 7.9 Hz, 1H), 7.91 (d, J = 3.2 Hz, 1H), 7.92 (d, J = 3. 2Hz, 1H), 7.95 (dd, J = 1.4, 7.9Hz, 1H), 7.96 (dd, J = 1.4, 7.9Hz, 1H), 8.00 (dd, J = 1.4,7. 9 Hz, 1H), 8.03 (d, J = 1.4 Hz, 2H), 8.04 (d, J = 1.4 Hz, 1H), 8.13 (s, 1H).
¹³ C-NMR (125 MHz, CDCl ₃ , ppm) δ 13.94, 13.96, 22.53, 22.55, 23.76, 23.80, 29.60, 29.62, 31.45, 31. 49, 40.4, 55.6, 55.7, 118.6, 118.7, 120.3, 120.45, 120.53, 120.59, 120.6, 120.66, 120.74, 121.0, 125.7, 125.9, 126.1, 130.7, 132.7, 132.9, 133.0, 139.1, 139.8, 140.7, 142.29, 142. 34, 142.4, 143.61, 143.64, 151.8, 152.21, 152.23, 152.4, 167.4.

  Synthesis Example 2: Synthesis of compounds (III-a) and (III-c)

  Compounds (III-a) and (III-c) were synthesized in the same manner as in Synthesis Example 1 under the conditions shown in the above reaction formula and Table 1 below. Table 1 shows the yield under each condition. In addition, the mol% and equivalent shown in the above reaction formula and the following Table 1 are values based on the compound (iii).

Identification data of compound (III-c)
¹ H-NMR (500 MHz, CDCl ₃ , ppm) δ 0.45-0.57 (m, 4H), 0.61 (t, J = 7.0 Hz, 6H), 0.82-1.01 (m, 12H), 1.80-1.99 (m, 4H), 7.13 (d, J = 3.2 Hz, 1H), 7.31 (d, J = 8.0 Hz, 1H), 7.53 ( d, J = 8.0 Hz, 1H), 7.55 (d, J = 8.0 Hz, 1H), 7.60 (s, 1H), 7.90 (d, J = 3.2 Hz, 1H), 7.92 (d, J = 8.0 Hz, 1H), 7.99 (s, 1H).
¹³ C-NMR (125 MHz, CDCl ₃ , ppm) δ 13.8, 22.4, 23.6, 29.4, 31.3, 40.0, 55.4, 93.4, 118.4, 120. 1, 120.4, 121.6, 125.9, 132.0, 135.9, 139.7, 141.9, 143.4, 150.8, 153.4, 168.6.
HRMS (m / z) measured value 5433.1458, calculated value 5433.1457.

  Synthesis Example 3: Synthesis of compounds (II-a), (II-b) and (II-c)

  Compounds (II-a), (II-b) and (II-c) were synthesized in the same manner as in Synthesis Example 1 under the conditions shown in the above reaction formula and Table 2 below. Table 2 shows the yield under each condition. The mol% shown in the above reaction formula is a value based on the compound (ii). In addition, Table 2 No. Under the condition 2, 2.5 equivalents of NaOH were added to carry out the reaction for 48 hours, and then 1.2 equivalents of NaOH were added to carry out the reaction for another 9 hours. Similarly, the following Table 2 No. Under the condition 3, 1.2 equivalent of NaOH was added and the reaction was carried out for 27 hours, then 0.5 equivalent of NaOH was added and the reaction was further carried out for 21 hours.

  Identification data of compound (II-a)

¹ H-NMR (500 MHz, CDCl ₃ , ppm) δ 1.45 (t, J = 7.3 Hz, 3H), 4.35 (q, J = 7.3 Hz, 2H), 7.29 (d, J = 3.2 Hz, 2H), 7.41 (d, J = 8.5 Hz, 2H), 7.86 (d, J = 3.2 Hz, 2H), 8.11 (d, J = 8.5 Hz, 2H) ), 8.73 (s, 2H).
¹³ C-NMR (125 MHz, CDCl ₃ , ppm) δ 13.8, 37.9, 109.0, 117.7, 119.2, 123.2, 125.0, 125.5, 141.4, 143. 3, 169.4.
IR (KBr, cm ⁻¹ ) 3074, 2976, 1626, 1596, 1475, 1407, 1348, 1320, 1299, 1249, 1158, 1138, 1125.
Elemental analysis _{(C 20 H 15 N 3 S} 2) Calculated C: 66.45%, H: 4.18 %, N: 11.62%, S: 17.74%. Found C: 66.28%, H: 4.19%, N: 11.62%, S: 17.66%.

  Identification data of compound (II-b)

¹ H-NMR (500 MHz, CDCl ₃ , ppm) δ 1.47 (t, J = 7.3 Hz, 3H), 2.55 (s, 6H), 4.38 (q, J = 7.3 Hz, 2H) 6.85 (s, 2H), 7.42 (d, J = 8.5 Hz, 2H), 8.09 (dd, J = 1.6, 8.5 Hz, 2H), 8.73 (d, J = 1.6 Hz, 2H).
¹³ C-NMR (125 MHz, CDCl ₃ , ppm) δ 13.8, 17.3, 37.9, 108.9, 112.3, 119.1, 123.3, 124.9, 125.7, 141. 3, 153.4, 168.6.
IR (KBr, cm ⁻¹ ) 2978, 2919, 1629, 1599, 1505, 1444, 1422, 1333, 1293, 1238.
HRMS (m / z) measured value 389.1101, calculated value 389.1020.

  Identification data of compound (II-c)

¹ H-NMR (500 MHz, CDCl ₃ , ppm) δ 1.42 (t, J = 7.5 Hz, 3H), 2.54 (s, 3H), 4.31 (q, J = 7.5 Hz, 2H) 6.84 (s, 1H), 7.18 (d, J = 8.5 Hz, 1H), 7.38 (d, J = 8.5 Hz, 1H), 7.71 (d, J = 8. 5 Hz, 1 H), 8.06 (d, J = 8.5 Hz, 1 H), 8.46 (s, 1 H), 8.60 (s, 1 H).
¹³ C-NMR (125 MHz, CDCl ₃ , ppm) δ 13.6, 17.3, 37.5, 81.8, 108.6, 110.6, 112.2, 118.6, 121.7, 124. 9, 125.2, 125.4, 129.3, 134.1, 139.3, 140.5, 153.3, 168.3.
IR (KBr, cm ⁻¹ ) 2977, 2918, 1625, 1591, 1479, 1455, 1292, 1231.
Elemental analysis _{(C 18 H 15 IN 2 S} ) Calculated C: 51.68%, H: 3.61 %, N: 6.70%, S: 7.67%. Found C: 51.50%, H: 3.54%, N: 6.63%, S: 7.50%.

  Synthesis Example 4: Synthesis of compound (IV-a)

  Compound (IV-a) was synthesized in the same manner as in Synthesis Example 1 under the conditions shown in the above reaction formula (yield: 95%). The mol% and equivalent shown in the above reaction formula are values based on the compound (iv). In this reaction, 4 equivalents, 2.5 equivalents, 1.5 equivalents and 1 equivalent of NaOH were added, and after each addition, the reaction was performed for 24 hours, 25 hours, 23 hours and 24 hours.

Identification data of compound (IV-a)
¹ H-NMR (500 MHz, CDCl ₃ , ppm) δ 2.50 (s, 9H), 6.83 (s, 3H), 7.17 (d, J = 8.6 Hz, 6H), 7.84 (d J = 8.6 Hz, 6H).
¹³ C-NMR (125 MHz, CDCl ₃ , ppm) δ 20.6, 116.3, 127.6, 131.0, 132.4, 151.3, 157.1, 170.2.
IR (KBr, cm ⁻¹ ) 2977, 2918, 1625, 1591, 1479, 1455, 1292, 1231.
HRMS (m / z) measured value 536.1163, calculated value 536.1177.

  Synthesis Example 5: Synthesis of compound (III-1)

In a 25 mL Schlenk tube, under argon atmosphere, compound (III-a) (50.5 mg, 0.1 mmol), PdCl ₂ (PPh ₃ ) ₂ (3.5 mg, 0.005 mmol) and DMSO (0.5 mL) Was added. To this mixture was added ethyl 4-iodobenzoate (0.068 mL, 0.4 mmol) and KF (14.5 mg, 0.25 mmol) successively. The resulting mixture was heated in an oil bath (60 ° C.) and stirred for 53 hours. AgNO ₃ (42.5 mg, 0.25 mmol) was then added in 5 portions at 1 hour intervals. The mixture was cooled to room temperature and filtered through a celite pad followed by washing with chloroform. The filtrate was washed with brine and the aqueous layer was extracted with chloroform. The organic phases were combined, washed with anhydrous sodium sulfate, and concentrated under reduced pressure to obtain a crude oil. This oil was purified by silica gel column chromatography (eluent: hexane / ethyl acetate) to obtain 63.8 mg (yield: 80%) of compound (14a).

Identification data of compound (III-1)
¹ H-NMR (500 MHz, CDCl ₃ , ppm) δ 0.62-0.71 (m, 4H), 0.73 (t, J = 7.2 Hz, 6H), 0.98-1.12 (m, 12H), 1.43 (t, J = 7.1 Hz, 6H), 2.09-2.15 (m, 4H), 4.42 (q, J = 7.1 Hz, 4H), 7.70 ( d, J = 8.4 Hz, 4H), 7.82 (d, J = 8.0 Hz, 2H), 7.98 (dd, J = 1.6, 8.0 Hz, 2H), 8.04 (d , J = 1.6 Hz, 2H), 8.11 (d, J = 8.4 Hz, 4H), 8.16 (s, 2H).
¹³ C-NMR (125 MHz, CDCl ₃ , ppm) δ 13.9, 14.3, 22.5, 23.8, 29.6, 31.5, 40.3, 55.8, 61.2, 120. 6, 120.7, 126.1, 126.3, 130.1, 130.4, 132.7, 135.6, 138.0, 140.2, 142.6, 152.4, 166.0, 168.8.
IR (KBr, cm ⁻¹ ) 2954, 2925, 2855, 1717, 1606, 1421, 1406, 1366, 1274, 1236, 1125, 1108.
Elemental analysis _{(C 49 H 52 N 2 O} 4 S 2) Calculated C: 73.84%, H: 6.58 %, N: 3.51%, S: 8.05%. Found C: 73.78%, H: 6.46%, N: 3.64%, S: 7.90%.

  Synthesis Example 6: Synthesis of compounds (III-2) and (III-3)

  Compounds (III-2) and (III-3) were synthesized in the same manner as in Synthesis Example 5 under the conditions shown in the above reaction formula (yield of compound (III-2): 94%, compound (III-3) Yield: 85%). The mol% and equivalent shown in the above reaction formula are values based on the compound (III-a).

  Identification data of compound (III-2)

¹ H-NMR (500 MHz, CDCl ₃ , ppm) δ 0.63 to 0.69 (m, 4H), 0.73 (t, J = 7.1 Hz, 6H), 0.99-1.11 (m, 12H), 2.09-2.13 (m, 4H), 7.73 (s, 8H), 7.82 (d, J = 8.0 Hz, 2H), 7.96 (dd, J = 1. 3, 8.0 Hz, 2H), 8.03 (d, J = 1.3 Hz, 2H), 8.16 (s, 2H).
¹³ C-NMR (125 MHz, CDCl ₃ , ppm) δ 13.9, 22.5, 23.8, 29.6, 31.4, 40.2, 55.7, 111.5, 118.4, 120. 6, 120.8, 126.2, 126.8, 132.5, 132.9, 135.7, 136.9, 140.8, 142.7, 152.4, 169.4.

  Identification data of compound (III-3)

¹ H-NMR (500 MHz, CDCl ₃ , ppm) δ 0.65-0.71 (m, 4H), 0.74 (t, J = 7.2 Hz, 6H), 1.00-1.11 (m, 12H), 2.11-2.14 (m, 4H), 7.67 (d, J = 8.2 Hz, 2H), 7.72-7.77 (m, 12H), 7.79 (d, J = 7.9 Hz, 2H), 7.95 (d, J = 7.9 Hz, 2H), 8.05 (s, 2H), 8.14 (s, 2H).
¹³ C-NMR (125 MHz, CDCl ₃ , ppm) δ 13.9, 22.5, 23.8, 29.6, 31.5, 40.3, 55.7, 111.2, 118.8, 120. 5, 120.7, 126.0, 127.2, 127.5, 127.9, 131.6, 132.6, 132.7, 138.2, 128.9, 142.5, 144.5, 152.3, 168.1.

  Synthesis Example 7: Synthesis of compounds (II-1) to (II-9)

  Compounds (II-1) to (II-9) were synthesized in the same manner as in Synthesis Example 5 under the conditions shown in the above reaction formula and Table 3 below. Table 3 shows the yield under each condition. The mol% and equivalent shown in the above reaction formula are values based on the compound (II-a) or (II-b).

  Identification data of compound (II-1)

¹ H-NMR (500 MHz, CDCl ₃ , ppm) δ 1.52 (t, J = 7.3 Hz, 3H), 4.44 (q, J = 7.3 Hz, 2H), 7.50 (d, J = 8.6 Hz, 2H), 7.69 (d, J = 8.4 Hz, 4H), 7.75 (d, J = 8.4 Hz, 4H), 8.11 (s, 2H), 8.16 ( dd, J = 1.6, 8.6 Hz, 2H), 8.79 (d, J = 1.6 Hz, 2H).
¹³ C-NMR (125 MHz, CDCl ₃ , ppm) δ 13.9, 38.1, 109.3, 119.3, 124.0 (q, J = 272.2 Hz), 123.4, 125.1, 125 .5, 126.1 (q, J = 3.9 Hz), 126.6, 129.8 (q, J = 33.0 Hz), 135.2, 136.5, 140.2, 141.8, 169 .4.

  Identification data of compound (II-2)

¹ H-NMR (500 MHz, CDCl ₃ , ppm) δ 1.49 (t, J = 7.2 Hz, 3H), 2.62 (s, 6H), 4.40 (q, J = 7.2 Hz, 2H) 7.45 (d, J = 8.5 Hz, 2H), 7.64 (d, J = 8.1 Hz, 4H), 7.71 (d, J = 8.1 Hz, 4H), 8.10 ( d, J = 8.5 Hz, 2H), 8.75 (s, 2H).
¹³ C-NMR (125 MHz, CDCl ₃ , ppm) δ 13.9, 16.6, 38.0, 109.1, 119.0, 123.3, 124.1 (q, J = 272.2 Hz), 124 .9, 125.4, 125.6 (q, J = 3.7 Hz), 129.2, 129.39 (q, J = 32.5 Hz), 129.41, 136.2, 141.6, 149 .6, 166.9.
IR (KBr, cm ⁻¹ ) 2921, 2979, 1615, 1600, 1441, 1323, 1240, 1167, 1121, 1070.
HRMS (m / z) measured value 677.1394, calculated value 677.1137.

  Identification data of compound (II-3)

¹ H-NMR (500 MHz, CDCl ₃ , ppm) δ 1.43 (t, J = 7.2 Hz, 6H), 1.51 (t, J = 7.3 Hz, 3H), 2.67 (s, 6H) 4.40-4.44 (m, 6H), 7.49 (d, J = 8.7 Hz, 2H), 7.60 (d, J = 8.3 Hz, 4H), 8.14 (d, J = 8.3 Hz, 4H), 8.19 (d, J = 8.7 Hz, 2H), 8.79 (s, 2H).
¹³ C-NMR (125 MHz, CDCl ₃ , ppm) δ 13.8, 14.2, 16.7, 37.7, 60.9, 108.8, 118.7, 123.0, 124.6, 125. 0, 128.4, 129.0, 129.7, 129.8, 136.8, 141.2, 149.2, 166.0, 166.6.
HRMS (m / z) measured value 685.2084, calculated value 685.2069.

  Identification data of compound (II-4)

¹ H-NMR (500 MHz, CDCl ₃ , ppm) δ 1.51 (t, J = 7.1 Hz, 3H), 2.64 (s, 6H), 4.43 (q, J = 7.1 Hz, 2H) 7.48 (d, J = 8.5 Hz, 2H), 7.64 (d, J = 8.2 Hz, 4H), 7.75 (d, J = 8.2 Hz, 4H), 8.11 ( d, J = 8.5 Hz, 2H), 8.78 (s, 2H).

  Identification data of compound (II-5)

¹ H-NMR (500 MHz, CDCl ₃ , ppm) δ 1.52 (t, J = 7.3 Hz, 3H), 2.67 (s, 6H), 4.44 (q, J = 7.3 Hz, 2H) 7.49 (d, J = 8.4 Hz, 2H), 7.70 (d, J = 8.6 Hz, 4H), 8.12 (d, J = 8.4 Hz, 4H), 8.32 ( d, J = 8.6 Hz, 4H), 8.79 (s, 2H).
¹³ C-NMR (125 MHz, CDCl ₃ , ppm) δ 13.9, 17.0, 38.1, 61.1, 109.3, 119.3, 123.4, 124.1, 125.2, 125. 3, 128.8, 129.4, 139.4, 141.8, 146.7, 150.7, 167.8.
HRMS (m / z) measured value 631.1362, calculated value 631.1348.

  Identification data of compound (II-6)

¹ H-NMR (500 MHz, CDCl ₃ , ppm) δ 1.50 (t, J = 7.3 Hz, 3H), 4.41 (q, J = 7.3 Hz, 2H), 7.32 (d, J = 3.2 Hz, 2H), 7.47 (d, J = 8.5 Hz, 1H), 7.68 (d, J = 8.2 Hz, 2H), 7.73 (d, J = 8.2 Hz, 2H) ), 7.89 (d, J = 3.2 Hz, 1H), 8.10 (s, 1H), 8.13-8.17 (m, 2H), 8.76 (s, 2H).
¹³ C-NMR (125 MHz, CDCl ₃ , ppm) δ 13.9, 38.1, 109.2, 117.9, 119.25, 119.29, 123.3, 123.4, 124.2 (q, J = 228.0 Hz), 124.9, 125.2, 125.3, 125.8, 126.1 (q, J = 4.1 Hz), 126.5, 136.5 (q, J = 35. 7 Hz), 140.2, 141.5, 141.7, 143.4, 169.4, 169.5.

  Identification data of compound (II-7)

¹ H-NMR (500 MHz, CDCl ₃ , ppm) δ 1.43 (t, J = 7.1 Hz, 6H), 1.49 (t, J = 7.2 Hz, 3H), 2.56 (s, 3H) 2.64 (s, 3H), 4.38-4.44 (m, 4H), 6.86 (s, 1H), 7.44 (d, J = 8.6 Hz, 1H), 7.45 (D, J = 8.6 Hz, 1H), 7.60 (d, J = 8.3 Hz, 4H), 8.10-8.14 (m, 4H), 8.75 (d, J = 1. 6 Hz, 1 H), 8.76 (d, J = 1.6 Hz, 1 H).
¹³ C-NMR (125 MHz, CDCl ₃ , ppm) δ 13.9, 14.3, 16.8, 17.3, 38.0, 61.1, 109.01, 109.03, 112.4, 119. 06, 119.13, 123.3, 123.4, 124.8, 125.1, 125.3, 125.8, 128.7, 129.2, 129.9, 130.0, 137.1, 141.4, 141.6, 149.5, 153.4, 166.2, 166.9, 168.6.
HRMS (m / z) measured value 537.1543, calculated value 537.1545.

  Identification data of compound (II-8)

¹ H-NMR (500 MHz, CDCl ₃ , ppm) δ 1.48 (t, J = 7.2 Hz, 3H), 2.56 (s, 3H), 2.63 (s, 3H), 4.40 (q , J = 7.2 Hz, 2H), 6.86 (s, 1H), 7.44 (d, J = 8.5 Hz, 2H), 7.61 (d, J = 8.4 Hz, 2H), 7 .73 (d, J = 8.4 Hz, 2H), 8.09 (dd, J = 1.6, 8.4 Hz, 1H), 8.12 (dd, J = 1.4, 8.4 Hz, 1H) ), 8.74 (d, J = 1.6 Hz, 1H), 8.75 (d, J = 1.4 Hz, 1H).

  Identification data of compound (II-9)

¹ H-NMR (500 MHz, CDCl ₃ , ppm) δ 1.50 (t, J = 7.2 Hz, 3H), 2.56 (s, 3H), 2.66 (s, 3H), 4.41 (q , J = 7.2 Hz, 2H), 6.86 (s, 1H), 7.45 (d, J = 8.6 Hz, 1H), 7.46 (d, J = 8.5 Hz, 1H), 7 .68 (d, J = 8.7 Hz, 2H), 8.09-8.12 (m, 2H), 8.31 (d, J = 8.7 Hz, 2H), 8.76 (s, 2H) .

  Synthesis Example 8: Synthesis of compound (IV-1)

Compound (IV-1) was synthesized in the same manner as in Synthesis Example 5 under the conditions shown in the above reaction formula (yield: 77%). Specifically, at 60 ° C., AgNO ₃ was added in 0.8 equivalents in 5 portions every 12 hours (reaction time 12 × 5 = 60 hours), and AgNO ₃ and KF were further added one equivalent at a time. The reaction was continued for 48 hours, and then the reaction was continued for 36 hours by adding 5 mol% of palladium catalyst. Thereafter, the reaction temperature was raised to 100 ° C. and the reaction was carried out for 12 hours. In addition, the mol% and the equivalent shown in the above reaction formula are values based on the compound (IV-a).

Identification data of compound (IV-1)
¹ H-NMR (500 MHz, CDCl ₃ , ppm) δ 2.59 (s, 9H), 7.22 (d, J = 8.8 Hz, 6H), 7.61 (d, J = 8.2 Hz, 6H) 7.70 (d, J = 8.2 Hz, 6H), 7.88 (d, J = 8.8 Hz, 6H).
¹³ C-NMR (125 MHz, CDCl ₃ , ppm) δ 16.4, 124.4, 124.0 (q, J = 272.2 Hz), 125.7 (q, J = 3.7 Hz), 127.7, 128.7, 129.2, 129.7 (q, J = 33.0 Hz), 130.1, 135.9, 148.2, 149.8, 165.3.
HRMS (m / z) measured value 968.174, calculated value 9688.1724.

<Evaluation of the physical properties>
The ultraviolet-visible absorption spectrum (device used: JASCO V530) and fluorescence spectrum (device used: JASCO FP6300) of a chloroform solution (0.01 mM) of each compound synthesized in the above synthesis example were measured. The maximum absorption wavelength (λ _max ) and molar extinction coefficient (ε) of the UV-visible absorption spectrum, and the maximum excitation wavelength (λ _max ) and maximum emission wavelength (λ _max ) in the fluorescence spectrum are shown in Table 4 below.

Moreover, the fluorescence quantum yield of each compound was computed from the following formula. The results are also shown in Table 4 below.
Φ _x = Φ _std × (I _x / I _std ) × (A _std / A _x ) × (n _x / n _std ) ²

In the above formula, Φ represents the quantum yield, I represents the peak area of the fluorescence spectrum, A represents the absorbance at the excitation wavelength, and n represents the refractive index of the solvent. The subscript x indicates a sample of each compound, and std indicates a standard substance. As a standard substance for calculating the fluorescence quantum yield, a 0.01 mM ethyl acetate solution of 7-diethylamino-4-methylcoumarin was used (Φ _std = 0.99, I _std = 1.84 × 10 ⁴ , A _std = 0.312, n _std = 1.37).

  From the results of Table 4, the thiazole derivative of the present invention having a donor-acceptor type structure has a maximum absorption wavelength and fluorescence spectrum of the UV-visible absorption spectrum as compared with the thiazole derivative of the comparative example not having such a structure. The maximum emission wavelength is red-shifted to the long wavelength side. Further, except for the compound (IV-1), the thiazole derivative of the present invention example has a higher molar extinction coefficient value than the corresponding thiazole derivative of the comparative example.

  Compounds (II-1) to (II-7) (thiazole derivatives having a carbazole skeleton) of the inventive examples are compared to the compounds (II-a) to (II-c) of the comparative examples and the compounds of the inventive examples The fluorescence quantum yield of (IV-1) (thiazole derivative having a triphenylamine skeleton) is improved as compared with the corresponding compound (IV-a) of Comparative Example. In addition, almost no fluorescence was observed in the compound (II-5) of the present invention having a nitro group. This applies to the rule of thumb that a compound having a nitro group loses fluorescence.

  Compounds (II-2) to (II-4) and (II-7) having a methyl group at the 4-position of the thiazole ring are the compounds (II-1) and (II-) wherein the 4-position of the thiazole ring is a hydrogen atom. Compared with 6), the fluorescence quantum yield is lowered. This is thought to be due to the fact that the introduction of the methyl group increases the steric hindrance and lowers the molecular flatness. Thus, introduction of a substituent such as a methyl group is disadvantageous in terms of fluorescence, but has an advantage of improving solubility in a solvent.

  Compounds (III-1) to (III-3) (thiazole derivatives having a fluorene skeleton) of the inventive examples have lower fluorescence quantum yields than the corresponding compound (III-a) of the comparative example. This is because the fluorescence quantum yield (0.55) of the compound (III-a) of the comparative example was specifically high, and the fluorescence quantum yields of the compounds (III-1) to (III-3) of the examples of the present invention. The rate (0.20 to 0.35) is not so low.

  The thiazole derivative of the present invention exhibits good light absorption and fluorescence, and its maximum fluorescence wavelength is red-shifted to the visible light region side. Therefore, it is useful as a material for a fluorescent paint or a light emitting layer of an organic EL device. is there.

Claims (4)

A thiazole derivative represented by the following formula (I).

[In formula (I), n shows the integer of 2-4.
R ¹¹ are the same or different and each represents a hydrogen atom, a lower alkyl group or a lower alkoxycarbonyl group.
Ar ¹¹ is the same or different and represents a hydrogen atom or an aromatic group exhibiting electron withdrawing properties. However, at least one Ar ¹¹ is an aromatic group exhibiting electron withdrawing properties.
Ar ¹² represents an electron donating group having an aromatic ring directly bonded to the thiazole skeleton. ] A thiazole derivative represented by the following formula (II).

[In the formula (II), R ²¹ represents a lower alkyl group or a lower alkanoyl group.
R ^{22 to} R ²⁵ are the same or different and each represents a hydrogen atom or a lower alkyl group.
R ²⁶ and R ²⁷ are the same or different and each represents a hydrogen atom, a lower alkyl group or a lower alkoxycarbonyl group.
Ar ²¹ and Ar ²² are the same or different and each represents a hydrogen atom or an aromatic group exhibiting electron withdrawing properties. However, at least one of Ar ²¹ and Ar ²² is an aromatic group exhibiting electron withdrawing properties. ] A thiazole derivative represented by the following formula (III).

[In formula (III), R ³¹ and R ³² are the same or different and each represents a hydrogen atom, a lower alkyl group or an acyl group.
R ³³ and R ³⁴ are the same or different and each represents a hydrogen atom, a lower alkyl group or a lower alkoxycarbonyl group.
Ar ³¹ and Ar ³² are the same or different and each represents a hydrogen atom or an aromatic group exhibiting electron withdrawing properties. However, at least one of Ar ³¹ and Ar ³² is an aromatic group exhibiting electron withdrawing properties. ] A thiazole derivative represented by the following formula (IV).

[In Formula (IV), R ^{401 to} R ⁴¹² are the same or different and each represents a hydrogen atom or a lower alkyl group.
R ^{413 to} R ⁴¹⁵ are the same or different and each represents a hydrogen atom, a lower alkyl group or a lower alkoxycarbonyl group.
Ar ^{41 to} Ar ⁴³ are the same or different and each represents a hydrogen atom or an aromatic group exhibiting electron withdrawing properties. However, at least one of Ar ^{41 to} Ar ⁴³ is an aromatic group exhibiting electron withdrawing properties. ]