Ayataka Endo

Efficient up-conversion of triplet excitons into a singlet state and its application for organic light emitting diodes

A material possessing a very small energy gap between its singlet and triplet excited states, ΔE1−3, which allows efficient up-conversion of triplet excitons into a singlet state and leads to efficient thermally activated delayed fluorescence (TADF), is reported. The compound, 2-biphenyl-4,6-bis(12-phenylindolo[2,3-a] carbazole-11-yl)-1,3,5-triazine, breaks the restriction of a large energy gap, with a ΔE1−3 of just 0.11 eV, while maintaining a high fluorescent radiative decay rate (kr∼107). The intense TADF provides a pathway for highly efficient electroluminescence.

Thermally Activated Delayed Fluorescence from Sn4+–Porphyrin Complexes and Their Application to Organic Light Emitting Diodes — A Novel Mechanism for Electroluminescence

[*] Prof. C. Adachi, A. Endo, Dr. D. Yokoyama Center for Future Chemistry Kyushu University 744 Motooka Nishi, Fukuoka 819-0395 (Japan) E-mail: adachi@cstf.kyushu-u.ac.jp M. Ogasawara, Prof. Y. Kato Department of Materials Science and Engineering Kyushu University 744 Motooka Nishi, Fukuoka 819-0395 (Japan) Dr. A. Takahashi Sogo Pharmaceutical Co., Ltd. Hebinami 28-3, Johban Shimofunao Iwaki, Fukushima 972-8312 (Japan) [+] Present address: Mitsubishi Chemical Group Science and Technology Research Center, Inc., Display Project, Research and Development Division, 1000 Kamoshida-cho, Aoba-ku, Yokohama 227-8502, Japan.

Nanoparticles of Adaptive Supramolecular Networks Self-Assembled from Nucleotides and Lanthanide Ions

Amorphous nanoparticles of supramolecular coordination polymer networks are spontaneously self-assembled from nucleotides and lanthanide ions in water. They show intrinsic functions such as energy transfer from nucleobase to lanthanide ions and excellent performance as contrast enhancing agents for magnetic resonance imaging (MRI). Furthermore, adaptive inclusion properties are observed in the self-assembly process: functional materials such as fluorescent dyes, metal nanoparticles, and proteins are facilely encapsulated. Dyes in these nanoparticles fluoresce in high quantum yields with a single exponential decay, indicating that guest molecules are monomerically wrapped in the network. Gold nanoparticles and ferritin were also wrapped by the supramolecular shells. In addition, these nucleotide/lanthanide nanoparticles also serve as scaffolds for immobilizing enzymes. The adaptive nature of present supramolecular nanoparticles provides a versatile platform that can be utilized in a variety of applications ranging from material to biomedical sciences. As examples, biocompatibility and liver-directing characteristics in in vivo tissue localization experiments are demonstrated.

Highly efficient and stable red phosphorescent organic light-emitting device using bis[2-(2-benzothiazoyl)phenolato]zinc(II) as host material

The red-emitting phosphorescent organic light-emitting device employing Bis[2-(2-benzothiazoyl)phenolato]zinc(II) (Zn(BTP)2) as a host material has been demonstrated. The device generates saturated red emission with Commission Internationale de l’Eclairage coordinates of (0.67, 0.33), characterized by a low driving voltage of 3.2V and high external quantum efficiency of 10.3% at 10mA∕cm2. Moreover, the efficiency and lifetime are improved by using 30% NPB-doped Zn(BTP)2 host in the emitting layer, where NPB is 4,4′-bis(N-phenyl-1-naphthyl-amino)biphenyl. The maximum external quantum efficiency of the device reaches 12.6% at 1.7mA∕cm2. The device has exhibited excellent stability. The half-luminance lifetime is 240h at 80mA∕cm2 (initial luminance of 6070cd∕m2). The relationship between the employed host material and device performance is discussed.

Photophysical and photosensitizing properties of brominated porphycenes.

A heavy atom, bromine, was directly substituted into the porphycene macrocycle to promote intersystem crossing by way of spin-orbit coupling. The singlet oxygen production ability of the porphycene is dramatically enhanced, and the highest value of 0.95 for the quantum yield of singlet oxygen generation (PhiDelta) was obtained for the dibrominated porphycene by visible light excitation.

Novel Electron-Transporting Carbazolylphenylquinolines for Phosphorescent Organic Light-Emitting Diodes

We developed four types of novel electron-transporting carbazolylphenyl-quinoline (CQ) derivatives. The photophysical and thermal properties of these materials were studied. Moreover, these materials were applied for an electron-transport layer and for a host material in phosphorescent organic light-emitting diodes, and a high electroluminescence (EL) efficiency was obtained in these devices. With 2-(3-(3,6-diphenylcarbazole-9-yl)phenyl)lepidine (DPCLP) as a host and tris(2-phenylpyridine)iridium(III) [Ir(ppy)3] as a guest, the highest EL efficiency of ηext=11.2% was obtained.

Preparation of Micropatterned Organic Light Emitting Diodes by Self-Organization

A dewetting process of an evaporating solution is used to form micrometer-sized amorphous droplets, or domes, of the low molar mass solute on substrates such as silicon, mica, glass, and indium-tin-oxide. Using dewetting, the organic hole transporting material of organic light emitting diodes was patterened into micrometer-sized domes on an indium-tin-oxide electrode. Annealing led to a structural change of the domes, which was investigated by optical and electron microscopes. The dewetted dome samples were then coated with electron transport material and top electrode to give functioning organic light emitting diodes devices.

Photoluminescence Characteristics of Organic Host Materials with Wide Energy Gaps for Organic Electrophosphorescent Devices

The photoluminescence, i.e., fluorescence and phosphorescence, characteristics of host materials with wide energy gaps suitable for phosphorescence-based organic light-emitting diodes (OLEDs) are summarized. In the vacuum deposited films, the host materials show phosphorescent emission in the blue to green region and triplet energy levels of ET = 2.6–3.1 eV because of the presence of steric hindrance. An OLED containing 1,2,3,4-tetraphenyl-5-(3-pyridyl)benzene as a host and iridium(III) bis[(4,6-difluorophenyl)-pyridinato-N,C2]picolinate as a blue emissive phosphorescent dopant exhibits an external electroluminescence efficiency of ~12%.

Dewetting-induced self-organization of nano- and microstructures for optoelectronic applications

A dewetting process of an evaporating solution is used to form micrometer-sized amorphous droplets, or domes, of the low molar mass solute on substrates such as silicon, mica, glass, and indium-tin-oxide. Using dewetting, the organic hole transporting material of organic light emitting diodes was patterened into micrometer-sized domes on an indium-tin-oxide electrode. Annealing led to a structural change of the domes, which was investigated by optical and electron microscopies. The dewetted dome samples were then coated with electron transport material and top electrode to give functioning organic light emitting diodes. Microscope imaging reveals a strong luminescence from the micrometer-sized domes.