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Chapter 6. Summary and perspective
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6-1 Summary
The author employed TR-PL and TAS to investigate the energy transfer
mechanisms in Eu(III) complexes. The goal was to gain a better understanding of the
emission mechanism and facilitate materials development.
In Chapter 1 and 2, the author explained the background and experimental
methods in this thesis, respectively.
In Chapter 3, the author conducted an investigation into the energy transfer
processes in the Eu(hfa)3(DPPTO)2 complex using TR-PL. In addition to the conventional
energy transfer pathway through the T1 state of the ligands, a fast energy transfer pathway
from the singlet excited states of the ligands to the 5D1 state of Eu(III) was discovered.
This dual energy transfer mechanism contributes to the high photoluminescence quantum
yield observed in the complex, offering important insights for the design strategies of
luminescent complexes.
In Chapter 4, the author explores the energy transfer mechanism in the
Eu(hfa)3(TPPO)2 complex, utilizing TR-PL and fs-TAS. The experimental results
demonstrate nearly unity efficiency of energy transfer from the T1 state of β-diketonate
ligands to the Eu(III) ions, unveiling a novel pathway to the 5D2 state of the Eu(III) ion.
These findings have important implications for designing efficient luminescent Eu(III)
complexes and advancing the development of lanthanide-based light-emitting materials.
In Chapter 5, the author investigates the enhancement of photoluminescence
intensity through sensitization using a host-guest system. Specifically, they explore a
system composed of triazine-based host molecules and Eu(hfa)3(TPPO)2. By conducting
TR-PL and fs-TAS measurements, the author reveals an energy transfer mechanism from
the host molecules to the Eu(III) ions, occurring via triplet states over several molecules
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with an impressive efficiency of nearly 100%. This discovery enables efficient light
harvesting in Eu(III) complexes and provides a simple solution-based fabrication process,
promising advancements in light-emitting applications.
In these studies, TR-PL and fs-TAS were employed to investigate the energy
transfer mechanisms in Eu(III) complexes. This research not only enhanced our
understanding of the emission mechanism but also played a crucial role in advancing
materials development in this field.
6-2 Future perspective
Based on the findings of this research, there are several potential directions for
future work in the field of Eu(III) complexes and their energy transfer mechanisms. One
promising avenue is the application of these complexes in organic light-emitting diodes
(OLEDs). By utilizing the knowledge gained about the energy transfer pathways and
efficiency, it becomes possible to design and optimize Eu(III)-based OLEDs with
enhanced performance and efficiency. This could lead to the development of more
efficient and vibrant displays, lighting, and other optoelectronic devices.
Additionally, further investigations can be conducted to explore the potential of
other antenna ligands and coordination structures for Eu(III) complexes. By studying
different ligand systems and their energy transfer mechanisms, it is possible to discover
novel pathways and improve the overall efficiency of energy transfer in these complexes.
This would open up new possibilities for the design and synthesis of luminescent Eu(III)
complexes with tailored properties for various applications.
Moreover, the study of host-guest systems, as demonstrated in Chapter 5, holds
promise for enhancing the photoluminescence intensity in Eu(III) complexes. Future
114
research can focus on developing new host molecules and optimizing their interaction
with Eu(III) ions to achieve even higher energy transfer efficiencies. This could lead to
the creation of highly efficient light-harvesting systems that can be utilized in a wide
range of applications.
Overall, the investigations presented in this thesis provide a solid foundation for
future research in the field of Eu(III) complexes. By further exploring their energy transfer
mechanisms and applying the gained knowledge to practical applications such as OLEDs,
significant advancements can be made in the development of luminescent materials and
optoelectronic devices.
115
Publication lists
Original papers
1. “Dual Energy Transfer Pathways from an Antenna Ligand to Lanthanide Ion in
Trivalent Europium Complexes with Phosphine-Oxide Bridges”
Shiori Miyazaki, Kiyoshi Miyata, Haruna Sakamoto, Fumiya Suzue, Yuichi
Kitagawa, Yasuchika Hasegawa, and Ken Onda
The Journal of Physical Chemistry A 2020, 124, 33, 6601–6606.
2. “Novel Energy Transfer Pathway in Trivalent Europium Complexes with βDiketonate Ligands”
Shiori Miyazaki, Kiyoshi Miyata, Yuichi Kitagawa, Yasuchika Hasegawa and Ken
Onda
(Manuscript in preparation)
3. “Highly Efficient Light Harvesting of a Eu(III) Complex in a Host–guest Film by
Triplet Sensitization”
Shiori Miyazaki, Kenichi Goushi, Yuichi Kitagawa, Yasuchika Hasegawa,
Chihaya Adachi, Kiyoshi Miyata and Ken Onda
Chemical Science 2023, 14, 6867–6875.
Joint papers
1. “Coordination Geometrical Effect on Ligand-to-Metal Charge Transfer-Dependent
Energy Transfer Processes of Luminescent Eu(III) Complexes”
Pedro Paulo Ferreira da Rosa, Shiori Miyazaki, Haruna Sakamoto, Yuichi
Kitagawa, Kiyoshi Miyata, Tomoko Akama, Masato Kobayashi, Koji Fushimi, Ken
Onda, Tetsuya Taketsugu, and Yasuchika Hasegawa
The Journal of Physical Chemistry A 2021, 125, 1, 209–217.
116
Acknowledgments
This doctoral thesis is the summary of the author’s studies conducted under the
supervision of Professor Ken Onda at the Department of Chemistry, Graduated School of
Science, Kyushu University, from April 2018 to August 2023.
The author would like to express my deepest gratitude to Professor Ken Onda
for supervising this thesis, providing an excellent research environment, helpful
discussion, and supporting all my works. The author would also like to express my deep
appreciation to Associate Professor Kiyoshi Miyata for his insightful comments and
guidance for my work and life.
The author would like to appreciate Professor Yasuchika Hasegawa and
Associate Professor Yuichi Kitagawa at Hokkaido University for providing the samples
and valuable discussions.
The author would like to appreciate Professor Chihaya Adachi and Assistant
Professor Kenichi Goushi at Center for Organic Photonics and Electronics Research
(OPERA), Kyushu University, for valuable discussions.
The author would like to thank all the members of Onda laboratory for their kind
support not only for my work but also for his daily life. The author also would like to
thank all the collaborators.
The author also thanks Japan Society for the Promotion of Science for the
financial support of the Research Fellowship for Young Scientists.
Finally, the author would like to express his gratitude to his family for always
supporting her during her long student life.
Shiori Miyazaki
August 2023
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