氏 名 カンムルール
カ ン ム ル ー ルハサン
ハ サ ン所 属 理工学研究科 分子物質化学専攻 学 位 の 種 類 博士（理学）
学 位 記 番 号 理工博 第
210号 学位授与の日付 平成
28年
9月
30日 課程・論文の別 学位規則第４条第
1項該当
学 位 論 文 題 名
Synthetic and Photophysical Studies on Axially Chiral Ligands Based onπ-Expanded Aromatic Hydrocarbons and Their Metal Complexes.π電子が拡張した軸不斉配位子の合成と分光学的挙動、及びそれら の金属錯体の合成に関する研究 （英文）
論 文 審 査 委 員 主査 教 授 杉浦 健一 委員 教 授 清水 敏夫 委員 准教授 久冨木 志郎
委員
准教授 今井 喜胤
(近畿大学
)【論文の内容の要旨】
Summary
Circularly polarized luminescence (CPL) is the luminescence emitted from a chiral molecule.
CPL is regarded as one of the most important chiroptical property along with CD and optical rotation.
Because of the high sensitivity of fluorescence, it was proposed that the naturally occurring chiral chromophore, such as chlorophyll are detected by CPL. Furthermore, the application of CPL have switched from the analytical chemistry of biological chiral molecules to the advanced material science, such as three-dimensional displays and quantum computing using polarized light.
This science was promoted using classical chiral chromophores such as 1,1'-binaphthalene-2,2'-diol (BINOL) and its derivatives. Unfortunately the CPL parameters of BINOLs, i.e., quantum yield (Φfl) and dimensionless Kuhn's anisotropy factor (|gem|) are not so high.
Therefore it is always challenging to find new molecule having large Φfl and |gem|. The lack of new CPL materials prevent the development of science in this field. This thesis aims at obtaining a CPL active molecule having large CPL parameters. I planned to expand the π-electronic system of BINOL because π-expanded polycyclic aromatic hydrocarbons usually have higher Φfl. Pyrene was
focused as PAH because this molecule shows strong emission, long life time and high quantum yield and these properties should definitely be interesting for CPL spectroscopy.
Chapter Two describes molecular design, synthesis, and circularly polarized luminescence properties of 1,1'-bipyrene-2,2'-diol. As described in the introduction section the axial chirality of BINOL and its related derivatives are widely used in photochemistry but their lower CPL intensities and quantum yields prevented the progress of this research field. I replaced the π-system of BINOL with pyrene because π-expanded compounds are good luminescent materials. Therefore, I designed 1,1'-bipyrene-2,2'-diol. The synthesis was designed according to the synthesis of BINOL, that is, the oxidative coupling reaction of the corresponding hydroxy pyrene by the treatment of FeCl3. Firstly tert-butyl group was introduced on pyrene to increase the solubility. Then boronic acid ester was
introduced by iridium catalyzed reaction. Finally oxidation reaction was carried out by hydrogen peroxide which afforded hydroxy pyrene and was treated with FeCl3 in boiling EtOH, thus giving the desired product. The obtained 1,1'-bipyrene-2,2'-diol is a racemic mixture. Therefore optical resolution was examined by the transformation of the corresponding menthol ester i.e.,formation and separation of the diastereomers. Surprisingly the obtained diastereomixture was successfully separated by normal SiO2 cromatography. The separated diastereomer was then hydrolyzed by KOH to give optically pure (R)- and (S)- 1,1'-bipyrene-2,2'-diol, respectively. The absolute configuration was determined by diffraction studies.
CD spectra of 1,1'-bipyrene-2,2'-diol show mirror image relationship with strong Cotton effect attributable due to the axial chirality. The λmax was found at 354 nm and the anisotropy factor |gCD| was 3.7X10-3. The CPL spectra also show the mirror image relationship for opposite enantiomer with emission λmax at 438 nm. The |gem| for 1,1'-bipyrene-2,2'-diol was found to be 3.6X10-4 which is a large value for a simple organic chiral molecule. Finally, the quantum yield (Φfl = 0.57) shows a significant improvement compared with that of BINOL (Φfl = 0.04) which makes 1,1’-bipyrene-2,2'-diol a new exciting candidate for CPL chemistry.
Chapter Three describes the synthesis and chiroptical property studies on bridged bipyrenols.
The chiroptical properties could be controlled by the nature of the substituents and the geometrical structure of the molecule, however, the lack of suitable model prevented these understandings.
1,1'-bipyrene-2,2'-diol should be a very good candidate to evaluate the relationship between the structure and chiroptical properties because of its high sensitivity. A series of O-alkylated bipyrenol were designed and synthesized with the hope to control the dihedral angles between the two pyrenes.
The synthesis was carried out by Williamson ether synthesis on optically pure bipyrenol and
tosylates in the presence of K2CO3 in DMF which afforded the desired bridged and open ethers derivatives of bipyrenol. The ring size of the bridged bipyrenol depends on the bridging ether unit’s size, i.e., ethylene, propylene and butylene. The open bipyrenol have ethyl ether derivatives.
The estimated structure from DFT calculation shows that the dihedral angle was increased as the ring size of the bridiging unit increased. This structural change have significant effect on photophysical and chiroptical properties. As for example, the gCD and gem value increased or decreased depending on the conformational flexibility. Moreover, quantum yields also significantly depend on the dihedral angle of the compound. As for example, the smallest dihedral angled compound i.e., ethylene bridged bipyrenol has a very high quantum yield (88%) which is one of the highest quantum yield for simple organic chiral molecules. Therefore, conformational flexibility have severe effect on the photophysical and chiroptical properties of bipyrenol derivatives.
Chapter four illustrates the synthesis, optical rsolution and chiroptical properties of 5,5'-bipyrene-4,4'-diol : an isomer of bipyrenol. Pyrene has nodal plane passing through the 2- and 7- positions. Therefore, previously synthesized compound 1,1′-bipyrenol have small electronic perturbation between oxygen and pyrene. To increase the electronic perturbation between oxygen and pyrene, new compound 5,5'-bipyrenol was designed where the hydroxyl group was in the high atomic coefficient 4 position of pyrene. Such electronic perturbation will be reflected in both the photophysical and chiroptical properties. The synthesis was a little modified compared to that of the previous bipyrenol. In this case two tert-butyl groups were introduced at 2- and 7- position of pyrene to achieve subsequent borylation at 4-position by their steric hindrance. Oxidation reaction was then successfully carried out by the treatment of hydrogen peroxide which affords 4-hydroxy pyrene.
Finally the dimer was synthesized by the solid state reaction between 4-hydroxy pyrene and FeCl3.6H2O, as the oxidative coupling reaction by FeCl3 and EtOH were not successful. For optical resolution similar strategy was applied, to synthesize corresponding menthol ester and diastereomers were obtained which were also separated by the normal SiO2 column chromatography. Pure enantiomer was obtained after removal of ester group under basic medium. The stereochemistry was determined by the single crystal diffraction studies of the menthol ester diastereomer. Finally optically pure 5,5'-bipyrene-4,4'-diol was protected again by the acetate ester because the free hydroxyl group was not stable under ambient condition. The separated menthol ester and acetate ester showed strong cotton effect on CD spectra and also showed intense CPL signal with mirror image relationship, however quantum yield decrease significantly due to the electronic interaction between oxygen and pyrene’s 4-position.
Chapter five mainly represents the application of bipyrenol as a ligand. The coordination site is
oxygen, a hard base. Therefore, metal complexes with hard acid seems to be suitable for bipyrenol. I prepared its complexes with B3+ and P5+ however difficult purification prevented the future investigation. High valent tungsten hard acid could be stabilized by hard base such as phenolate anion. Such metal complexes are not popular, I firstly reveled the general chemistry of W6+ with phenolate ligand, i.e., the synthesis of the W6+ complexes with 2-pyrenol, 2-naphthol and 1-naphthol.
The synthesis was designed by the transesterification reaction. For that purpose firstly tungsten ethylene glycol complex and acetate ester of naphthalene and pyrene were synthesized. Then the reaction between tungsten ethylene glycol complex and aromatic acetate ester affords the hexavalent tungsten complex. All the complexes were characterized by spectroscopically and molecular structure was confirmed by diffraction studies. Electrochemical properties were observed and found to be as expected, that is, two reversible reduction potential for W(V/VI) and W(IV/V) state.
In conclusion pyrene based axial chiral ligands, i.e., bipyrenol and its derivatives tremendously improved chiroptical properties and quantum yields. Therefore, such compounds could be considered as a new standard CPL materials. The hexavalent tungsten complexes have octahedral structure which were slightly depends on ligands size and in future can be used as a catalyst.
