Soichiro Nakatsuka

Ultrapure Blue Thermally Activated Delayed Fluorescence Molecules: Efficient HOMO–LUMO Separation by the Multiple Resonance Effect

Ultrapure blue-fluorescent molecules based on thermally activated delayed fluorescence are developed. Organic light-emitting diode (OLED) devices employing the new emitters exhibit a deep blue emission at 467 nm with a full-width at half-maximum of 28 nm, CIE coordinates of (0.12, 0.13), and an internal quantum efficiency of ≈100%, which represent record-setting performance for blue OLED devices.

One‐Step Borylation of 1,3‐Diaryloxybenzenes Towards Efficient Materials for Organic Light‐Emitting Diodes

The development of a one-step borylation of 1,3-diaryloxybenzenes, yielding novel boron-containing polycyclic aromatic compounds, is reported. The resulting boron-containing compounds possess high singlet-triplet excitation energies as a result of localized frontier molecular orbitals induced by boron and oxygen. Using these compounds as a host material, we successfully prepared phosphorescent organic light-emitting diodes exhibiting high efficiency and adequate lifetimes. Moreover, using the present one-step borylation, we succeeded in the synthesis of an efficient, thermally activated delayed fluorescence emitter and boron-fused benzo[6]helicene.

Construction of a Highly Distorted Benzene Ring in a Double Helicene

A P-fused double helicene consisting of a highly distorted benzene ring, with a bending angle of 23°, has been synthesized by a tandem intramolecular phospha-Friedel-Crafts reaction. Despite the distortion and reduced aromaticity, the double helicene shows thermal and chemical stability. These are important features that make these compounds attractive for applications as a new C2-symmetric bisphosphine ligand. The simple strategy proposed in this work can be used to prepare a diverse range of distorted molecules.

Synthesis of Boron-Doped Polycyclic Aromatic Hydrocarbons by Tandem Intramolecular Electrophilic Arene Borylation

Tandem intramolecular electrophilic arene borylation was developed to facilitate access to B-doped polycyclic aromatic hydrocarbons (PAHs). DFT calculations revealed that electrophilic arene borylation occurred via a four-membered ring transition state, in which C-B and H-Br bonds formed in a concerted manner. An organic light-emitting diode employing the B-doped PAH as an emitter and a B-doped PAH-based field-effect transistor were successfully fabricated, demonstrating the potential of B-doped PAHs in materials science.

Synthesis of Boronate-Based Benzo[fg]tetracene and Benzo[hi]hexacene via Demethylative Direct Borylation.

A demethylative direct borylation is reported, which was applied to the synthesis of benzo[fg]tetracenes containing boronate ester, amide, and thioester substructures. Depending on the heteroatom adjacent to boron, the molecules showed characteristic photophysical properties, molecular arrangements, and chemical stabilities. The key to the successful synthesis is the appropriate choice of the boron source and Brønsted base. The versatility of the direct borylation was demonstrated by the synthesis of a boronate-based benzo[hi]hexacene.

Divergent Synthesis of Heteroatom-Centered 4,8,12-Triazatriangulenes

The increasing attention devoted to triangulenes and their heteroatom derivatives inspired us to explore a divergent synthesis of heteroatom-centered 4,8,12-triazatriangulenes, which involved the preparation of a nitrogen-containing macrocyclic precursor and subsequent central heteroatom introduction by electrophilic C-Li and C-H substitution. The boron-centered triangulene has a planar structure unlike the bowl-shaped phosphorus- and silicon-centered triangulenes. The described synthetic procedure can be used to fabricate a broad range of attractive functional materials, for example, for organic light-emitting diodes, based on heteroatom-centered triangulenes.

Multiple heteroatom substitution to graphene nanoribbon

High-resolution atomic force microscopy can resolve the difference among B, C, and N atoms. Substituting heteroatoms into nanostructured graphene elements, such as graphene nanoribbons, offers the possibility for atomic engineering of electronic properties. To characterize these substitutions, functionalized atomic force microscopy (AFM)—a tool to directly resolve chemical structures—is one of the most promising tools, yet the chemical analysis of heteroatoms has been rarely performed. We synthesized multiple heteroatom-substituted graphene nanoribbons and showed that AFM can directly resolve elemental differences and can be correlated to the van der Waals radii, as well as the modulated local electron density caused by the substitution. This elemental-sensitive measurement takes an important step in the analysis of functionalized two-dimensional carbon materials.

Four-Step Synthesis of B2N2-Embedded Corannulene

A corannulene possessing two B-N units on the spoke, 10b1,18b1-diaza-10b,18b-diboratetrabenzo [ a, g, j, m]corannulene, was synthesized on a multigram scale in four steps from commercially available compounds. Its shallow bowl-shaped structure was confirmed by X-ray crystallography. The B2N2-embedded corannulene showed strong blue fluorescence and was employed as an efficient emitter for an organic light-emitting diode.