有機エレクトロルミネッセンス材料の電荷輸送および発光特性に関する構造研究

京都大学0048新制・課程博士博士(工学)甲第20631号工博第4369号新制||工||1679(附属図書館)京都大学大学院工学研究科分子工学専攻(主査)教授 梶 弘典, 教授 白川 昌宏, 教授 佐藤 啓文学位規則第4条第1項該当Doctor of Philosophy (Engineering)Kyoto UniversityDFA

Effects of Structural and Energetic Disorders on Charge Transports in Crystal and Amorphous Organic Layers

Understanding charge transports in organic films is important for both fundamental science and practical applications. Here, contributions of off-diagonal (structural) and diagonal (energetic) disorders to charge transports were clarified using molecular-based multiscale simulation. These disorders, important for understanding charge transport in organic systems, are investigated by comparing crystal and amorphous aggregates of N, N′-diphenyl-N, N′-bis(1-naphthyl)-1, 1′-biphenyl-4, 4′-diamine (NPD). Although NPD has been used as a hole transport material, it also exhibits comparable electron mobility experimentally. The experimental mobility and its electric field dependence in amorphous layers were reasonably reproduced by the multiscale simulation, confirming the electron transport properties of NPD. We assumed that the structural disorder would lower mobilities; however, the mobilities were found to be independent of the degree of structural disorder. Energetic disorder markedly lowered charge mobility instead. Charge migration in crystals was dominated by maximum electronic coupling pairs, whereas small electronic coupling pairs significantly contributed to charge transport in amorphous aggregate

Purely organic electroluminescent material realizing 100% conversion from electricity to light.

効率100％で電気を光に変換する有機EL材料の高性能化に成功. 京都大学プレスリリース. 2015-10-21.Efficient organic light-emitting diodes have been developed using emitters containing rare metals, such as platinum and iridium complexes. However, there is an urgent need to develop emitters composed of more abundant materials. Here we show a thermally activated delayed fluorescence material for organic light-emitting diodes, which realizes both approximately 100% photoluminescence quantum yield and approximately 100% up-conversion of the triplet to singlet excited state. The material contains electron-donating diphenylaminocarbazole and electron-accepting triphenyltriazine moieties. The typical trade-off between effective emission and triplet-to-singlet up-conversion is overcome by fine-tuning the highest occupied molecular orbital and lowest unoccupied molecular orbital distributions. The nearly zero singlet-triplet energy gap, smaller than the thermal energy at room temperature, results in an organic light-emitting diode with external quantum efficiency of 29.6%. An external quantum efficiency of 41.5% is obtained when using an out-coupling sheet. The external quantum efficiency is 30.7% even at a high luminance of 3, 000 cd m(-2)

Refined Structure Determination of Blue-Emitting Tris(8-hydroxyquinoline) Aluminum(III) (Alq₃) by the Combined Use of Cross-Polarization/Magic-Angle Spinning ¹³C Solid-State NMR and First-Principles Calculation

The combined use of cross-polarization/magic-angle spinning (CP/MAS) ¹³C NMR experiments and gauge-including projector-augmented wave (GIPAW) isotropic chemical shift calculations is an easy and useful method for the structural refinement of organic aggregates. In this study, the method is applied to an important material for organic light-emitting diodes, tris­(8-hydroxyquinoline) aluminum­(III) (Alq₃). CP/MAS ¹³C NMR spectra include precise structural information of not only the conformation of the molecules but also the intermolecular packing. First, the structural refinements were performed for the Alq₃ in the γ- and δ-crystalline forms employing the combined method. Second, information on intramolecular structures and intermolecular structures was distinguished by comparing GIPAW calculations for crystals under periodic boundary conditions and those for isolated molecules extracted from the crystals. It was found from the analysis that the γ-Alq₃ and δ-Alq₃ crystals have similar intramolecular structures both in the facial isomeric state, whereas their intermolecular packing is significantly different. Both the γ-Alq₃ and δ-Alq₃ crystals exhibit unusual blue emission, which is different from conventional green emission, and the origin of the difference has been debated. This investigation shows that the origin of the blue-shifted emission is the isomeric states of Alq₃, not the intermolecular packing

Detailed analysis of charge transport in amorphous organic thin layer by multiscale simulation without any adjustable parameters

Hopping-type charge transport in an amorphous thin layer composed of organic molecules is simulated by the combined use of molecular dynamics, quantum chemical, and Monte Carlo calculations. By explicitly considering the molecular structure and the disordered intermolecular packing, we reasonably reproduce the experimental hole and electron mobilities and their applied electric field dependence (Poole-Frenkel behaviour) without using any adjustable parameters. We find that the distribution of the density-of-states originating from the amorphous nature has a significant impact on both the mobilities and Poole-Frenkel behaviour. Detailed analysis is also provided to reveal the molecular-level origin of the charge transport, including the origin of Poole-Frenkel behaviour

Refined Structure Determination of Blue-Emitting Tris(8-hydroxyquinoline) Aluminum(III) (Alq₃) by the Combined Use of Cross-Polarization/Magic-Angle Spinning ¹³C Solid-State NMR and First-Principles Calculation

The combined use of cross-polarization/magic-angle spinning (CP/MAS) ¹³C NMR experiments and gauge-including projector-augmented wave (GIPAW) isotropic chemical shift calculations is an easy and useful method for the structural refinement of organic aggregates. In this study, the method is applied to an important material for organic light-emitting diodes, tris­(8-hydroxyquinoline) aluminum­(III) (Alq₃). CP/MAS ¹³C NMR spectra include precise structural information of not only the conformation of the molecules but also the intermolecular packing. First, the structural refinements were performed for the Alq₃ in the γ- and δ-crystalline forms employing the combined method. Second, information on intramolecular structures and intermolecular structures was distinguished by comparing GIPAW calculations for crystals under periodic boundary conditions and those for isolated molecules extracted from the crystals. It was found from the analysis that the γ-Alq₃ and δ-Alq₃ crystals have similar intramolecular structures both in the facial isomeric state, whereas their intermolecular packing is significantly different. Both the γ-Alq₃ and δ-Alq₃ crystals exhibit unusual blue emission, which is different from conventional green emission, and the origin of the difference has been debated. This investigation shows that the origin of the blue-shifted emission is the isomeric states of Alq₃, not the intermolecular packing

On-top π-stacking of quasiplanar molecules in hole-transporting materials: inducing anisotropic carrier mobility in amorphous films.

Dimers of partially oxygen-bridged triarylamines were designed and synthesized as hole-transporting materials. X-ray structural analyses revealed that these compounds form on-top π-stacking aggregates in the crystalline state. TRMC measurements showed that high levels of anisotropic charge transport were induced in the direction of the π-stacking. Surprisingly, even in vacuum-deposited amorphous films, these compounds retained some of the face-on π-stacking, thus facilitating an out-of-plane carrier mobility

Determination of Accurate ¹H Positions of (Ala-Gly)n as a Sequential Peptide Model of Bombyx mori Silk Fibroin before Spinning (Silk I)

The accurate ¹H positions of alanine-glycine alternating copolypeptide, (AG)₁₅ with Silk I structure were determined. For the purpose, the geometry optimization was performed starting with the atomic coordinates of the hetero atoms reported previously (Macromolecules 2005, 38, 7397−7403) and applied only for protons under periodic boundary conditions. The agreement between the calculated and observed chemical shifts of all ¹H,¹³C and ¹⁵N nuclei was excellent, indicating strongly that the determination of all the atomic-coordinate including ¹H nuclei was performed with high accuracy. Here the ¹H chemical shift was obtained by using both 1 mm microcoil MAS NMR probe-head for mass-limited solid-state samples developed by us and ultrahigh field NMR at 920 MHz. The DQ correlations in the ¹H DQMAS NMR spectra were also used to confirm the intra- and intermolecular structures obtained here. The characteristic structure of Silk I which can be easily converted to Silk II by external forces was discussed together with the generation of Silk I structure from the aqueous solution of the silk fibroin