Hideo Taka

Disilanyl double-pillared bisanthracene: a bipolar carrier transport material for organic light-emitting diode devices.

The first direct-current electroluminescent material, anthracene, has been the cornerstone molecule for organic electronics. However anthracene derivatives have been rarely utilized for electron or hole transport layers (ETL or HTL) of organic light-emitting diodes (OLEDs), and only a few derivatives importing established structural motifs have been reported. We designed an anthracene derivative, disilanyl double-pillared bisanthracene (DPBA) as a new structural motif for carrier transport material for OLEDs. We synthesized DPBA in a one-step operation from 1,8-diiodoanthracene in 50% yield without recourse to column chromatography. The anti-geometry of the anthracene units in DPBA was revealed by X-ray crystallographic analysis. The device performance of DPBA as a carrier transport material was evaluated by employing a standard green phosphorescent OLED. The standard device with Alq3 in ETL and α-NPD in HTL showed external quantum efficiency (EQE) of 3.4% at the constant current of 2.5 mA/cm, whereas the device with DPBA in ETL showed superior performance of EQE = 11.0%. Notably, DPBA functioned not only as an electron transporting material but also as a hole transporting material, and the device with DPBA both in ETL and HTL effectively operated at EQE of 8.7%. In the presentation, theoretical investigation that reveals favorable structural features for organic semiconducting materials will be presented.

Cyclo-meta-phenylene Revisited: Nickel-Mediated Synthesis, Molecular Structures, and Device Applications

From a one-pot nickel-mediated Yamamoto-type coupling reaction of m-dibromobenzene, five congeners of [n]cyclo-meta-phenylenes were synthesized and fully characterized. The [n]cyclo-meta-phenylenes possessed a commonly shared arylene unit and intermolecular contacts but varied in packing structures in the crystalline solid state. Columnar assembly of larger congeners yielded nanoporous crystals with carbonaceous walls to capture minor protic or aliphatic solvent molecules. The concise and scalable synthesis allowed exploration of the macrocyclic hydrocarbons as bipolar charge carrier transport materials in organic light-emitting diode devices.

Luminescent alternating boron quinolate–fluorene copolymers exhibiting high electron mobility

π-Conjugated copolymers composed of 9,9-didodecylfluorene and boron quinolate were synthesized by an efficient chelating reaction of quinolinol-based polyfluorene derivative, as a polymeric ligand, with arylborane compounds such as triphenylborane (BPh3) or fluorobis(pentafluorophenyl)borane diethyl etherate ((C6F5)BF·OEt2). The polymeric ligand was prepared from the deprotection reaction of boron tribromide and benzyloxyquinoline-based polyfluorene, which was produced via the efficient Suzuki cross-coupling reaction of 5,7-dibromo-8-benzylquinoline and 9,9-didodecylfluorene-2,7-diboronic acid in the presence of 2-(2′,6′-dimethoxybiphenyl)dicyclohexylphosphine (S-Phos) and palladium(II) acetate. Their optical properties were studied by UV-vis absorption and photoluminescence spectroscopies. The absorption and PL spectra of the obtained polymers were red-shifted in comparison with those of the polymeric ligand due to the decrease of the LUMO level by the formation of boron complexes, explained by theoretical calculations of the model compounds using the density-functional theory (DFT) method. The molar extinction coefficients and emission maxima of boron-chelating polymers were analogous values to those of (κ2-(N,O)-5,7-bis(9,9-dihexylfluoren-2-yl)-8-quinolinolate)diphenylborane (BFluorene2q). Furthermore, the electron mobilities of the polymers were determined from the space-charge limited current (SCLC) with electron-only device structure of ITO/Ca/polymer/LiF/Al. As a result, the mobilities for the polymers (3.9 or 2.0 × 10−5 cm2 V−1 s−1) were reasonably close to the value (7.9 × 10−5 cm2 V−1 s−1) calculated from the Alq3-fabricated device.

Modular Synthesis of Aromatic Hydrocarbon Macrocycles for Simplified, Single-Layer Organic Light-Emitting Devices

A method for the modular synthesis of aromatic hydrocarbon macrocycles has been developed for base materials in single-layer organic light-emitting devices. The method with Ir-catalyzed direct C-H borylation and Suzuki-Miyaura coupling was concise and scalable, which allowed for a gram-scale preparation of aromatic hydrocarbon macrocycles that have bulky substituents at the periphery. The new arylated hydrocarbon macrocycles enabled a quantitative electro-optical conversion in organic light-emitting devices with a phosphorescent emitter, which is, notably, in a single-layer architecture consisting of two regions of doped and undoped materials. The highest external quantum efficiencies reached 24.8%, surpassing those of previous hydrocarbon base materials.

ISOLATION AND STEREOCHEMISTRY OF OPTICALLY ACTIVE SELENONIUM IMIDES

Optical resolution of racemic diaryl selenonium-N-toluene-4‘-sulfonimides (rac-1a−d) by liquid chromatography using an optically active column yielded optically pure selenonium imides. The absolute configuration around the selenium atom of (−)-2,4,6-tri-tert-butyldiphenylselenonium N-toluene-4‘-sulfonimide [(−)-1a] was determined to be S by X-ray crystallographic analysis, and those of the other optically active selenonium imides were determined on the basis of their specific rotations and CD spectra. The kinetics of racemization by pyramidal inversion of the optically active selenonium imides (+)- and (−)-1b and 1d were studied. The results indicated that the activation energy for the racemization of optically active selenonium imides was greater than those for sulfonium imides.

Synthesis of Disilanyl Double-Pillared Bisdibenzofuran with a High Triplet Energy

A double-pillaring strategy for the synthesis of silacyclophanes has been applied to dibenzofuran to create a new cyclophane molecule that links two dibenzofuran molecules through σ(SiSi)-π conjugation. The performance of disilanyl double-pillared dibenzofuran [(Si)DPBD(O)] in green phosphorescent organic light-emitting diode (OLED) devices was evaluated as both a carrier-transport material and a host material for an Ir-based phosphorescent emitter.

Synthesis and stereochemistry of optically active selenonium imides

Diastereoisomeric mixtures of 4-[(–)-menthyloxycarbonyl]phenyl(methyl)selenonium-N-toluene-4′sulfonimides (dia.-1) and 4-[(–)-menthyloxycarbonyl]phenyl(2′, 4′, 6′-triisopropylphenyl)selenonium N-toluene-4″-sulfonimides (dia.-7) were synthesized. Optical resolution by the fractional recrystallization of dia.-7 from methanol gave the optically pure (–)-selenonium imide as stable crystals. The absolute configuration around the selenium atom was determined to be S based on the CD spectra. The kinetics for the epimerization by pyramidal inversion of the optically active selenonium imide were studied.

Efficient Blue Electroluminescence from a Single-layer Organic Device Composed Solely of Hydrocarbons

An interesting physical phenomenon, electroluminescence, that was originally observed with a hydrocarbon molecule has recently been developed into highly efficient organic light-emitting devices. These modern devices have evolved through the development of multi-element molecular materials for specific roles, and hydrocarbon devices have been left unexplored. In this study, we report an efficient organic light-emitting device composed solely of hydrocarbon materials. The electroluminescence was achieved in the blue region by efficient fluorescence and charge recombination within a simple single-layer architecture of macrocyclic aromatic hydrocarbons. This study may stimulate further studies on hydrocarbons to uncover their full potential as electronic materials.

Room temperature magnetoresistance in an organic spin valve with an aromatic hydrocarbon macrocycle

Aromatic hydrocarbon macrocycles, which have a conjugated π-electron system, are potentially useful for various organic device applications, although there have been no attempts to apply them to organic spin valves (OSVs). Here, we studied OSVs with [6]cyclo-2,7-naphthylene (CNAP), a type of aromatic hydrocarbon macrocycle. OSV stacking structures of Co/AlOx/CNAP/Ni80Fe20 with different CNAP thicknesses were fabricated, and the transport properties of the OSVs were measured from 300 to 5 K. A magnetoresistance of approximately 1%-2% at 300 K (4%-6% at 5 K) was observed for 15-nm-thick OSVs, showing the potential for organic spintronics based on aromatic hydrocarbon macrocycles.

First Isolation and Stereochemistry of Optically Active Telluroxides

Optically active telluroxides 1 and 2 were isolated for the first time by means of medium-pressure liquid chromatography using an optically active column. Absolute configuration of the telluroxides (+)-1 and (+)-2 was determined to be R based on their specific rotations and circular dichroism spectra. The configurational lability and mechanism for racemization via an achiral hydrate were clarified by kinetic study and isotope tracer experiment.