Yasuhiko Sawaki

New 9-fluorene-type trispirocyclic compounds for thermally stable hole transport materials in OLEDs

A novel trispirocyclic hydrocarbon having three 9-fluorene moieties around the core of truxene (5) was prepared readily via coupling of truxenone with 2-bromobiphenyl; 5 was a high melting (>500 °C) solid. For the application of 5 to an effective hole transport material (HTM) in the OLED, a triphenylamine derivative carrying six diphenylamino groups at the 2- and 7-positions of each 9-fluorene moiety (6) was designed in order to get high thermal stability as an improved material of the TPD type HTM. The synthesis of 6 was easily achieved using 4,4′-bis(diphenylamino)-2-bromobiphenyl (9). The trispirocyclic 6 was found to show a glass transition temperature as high as 170 °C. It effects the formation of its stable cation radical upon electrooxidation in solution, and amorphous thin films in solid. A multi-layered EL device for 6 as an HTM using Alq3 as an electron transporting emitter showed good EL characteristics such as the maximum luminance of 37 000 cd m−2 at 14 V. Thus, the hexakis(diphenylamino)substituted trispirocycle 6 (TX-F6S) can be used as an efficient and thermally stable HTM in OLEDs.

Intercalation and photochromism of spiropyrans on clay interlayers

1′,3′,3′-Trimethylspiro[2H-1-benzopyran-2,2′-indoline](abbreviated to H–SP) and its derivatives, 6-nitro (NO2–SP) and 6-nitro-8-(pyridinium)methyl spiropyrans (Py+–SP), have been intercalated in the interlayers of Montmorillonite. The intercalation was highly dependent on the substituent groups on the SPs. Charged Py+–SP was quantitatively adsorbed on the clay as an equilibrium mixture with the corresponding merocyanine (Py+–MC) in aqueous colloidal solution, the ratio Py+–SP:Py+–MC being 35:65 and exhibiting reversed photochromism. In contrast, a preferential adsorption as Py+–SP was observed for the hydrophobic clay layers coadsorbing cetyltrimethylammonium bromide (CTAB), which displays normal photochromism. The thermal isomerization of Py+–SP intercalated in aqueous colloidal clay exhibited a linear combination of two components of the first-order reactions, while that of the Py+–SP–CTAB coadsorbed system satisfied a single first-order kinetics. The two-component kinetics are explicable in terms of the intervention of at least two different kinds of microscopic environment, e.g. non-polar and polar phases, in the clay interlayers. We also show that the photochemical decoloration of Py+–MC was significantly retarded by the intercalation. All of these results are discussed on the basis of the polarity of the intercalation.

The formation of peracids by the perhydrolysis with alkaline hydrogen peroxide

Abstract A high yield ( ca. 90%) of perbenzoic acid has been obtained in the alkaline perhydrolysis of benzoyl peroxide by suppressing the decomposition of the peracid with excess alkali and a little magnesium sulfate in aqueous organic solvents. This perhydrolysis method has been applied to other substrates, e.g. benzoyl chloride, phthalic anhydride and acetyl chloride giving 85–90% yields. The perhydrolysis of benzoyl chloride has been shown to proceed, partially at least, through the intermediary formation of benzoyl peroxide.

Clay-inclusion photocyclodimerization : intercalation and migration of stilbazolium ions

Photocyclodimerization and the emissive properties of 4-[2-(p-substituted phenyl)ethenyl]pyridinium ions (stilbazolium ions)(1) intercalated between clay interlayer have been studied in order to clarify the intercalation and mobility of the ions. A statistical product ratio of homo- and cross-bred cyclodimers was observed in the irradiation of an equimolar co-intercalated mixture of 4-[2-(p-tolyl)ethenyl](1b) and 4-[2-(p-cyanophenyl)ethenyl]-pyridinium chlorides (1c). In contrast, when 1b and 1c were intercalated separately, the homodimers were formed predominantly, and the cross : homo ratios increased with increasing adsorption. This indicates that the molecular diffusion of stilbazolium ions between clay particles is much slower, as was also shown by a quenching study of the excimer fluorescence of 1b by 1c.

The alkali phosphate-catalyzed epoxidation and oxidation by a mixture of nitrile and hydrogen peroxide

Abstract The reaction of nitrile with alkaline hydrogen peroxide is inhibited almost completely by the presence of phosphate; therefore, the epoxidation of styrene in this mixture gives nearly a quantitative yield of epoxide on the basis of consumed peroxide. This oxidizing agent was used to epoxidize styrene and cyclohexene in the yield of 74–95% and to oxidize dimethylaniline to its N-oxide (73–78%) and aniline to azoxybenzene (71%).

Highly efficient blue-green emission from organic light-emitting diodes using dibenzochrysene derivatives

We have fabricated highly efficient organic light-emitting diodes (OLEDs) using new hole-transporting emissive materials based on dibenzochrysene. Hole drift mobilities of the dibenzochrysene derivatives were measured in the vacuum-deposited films and found to be 5×10−4–2×10−3 cm2/V s (at 5×105 V/cm). The OLEDs consist of an emitting layer of the dibenzochrysene derivative and an electron-transport layer of tris(8-quinolinolato) aluminum. Emission colors of the OLEDs were blue-green and their spectra were consistent with the photoluminescence spectra with a peak wavelength of 490 nm. High external quantum efficiency of 2% was obtained at a luminance of 300 cd/m2, and good durability in a continuous operation at room temperature and high temperatures was achieved.

Kinetics of the addition of benzenesulufinic acid to p-benzoquinone☆

Abstract Addition of benzenesulfinic acid to p -benzoquinone-h 4 and -d 4 has been studied kinetically in aqueous solutions by means of UV spectrophotometry. Reactions at pHs below 5·7 give 2,5-dihydroxydiphenyl sulfone (II) and follow the kinetics of ν = k [quinone] [sulfinic acid]. The reactions at pHs below ca. 3·1 are subject to general acid catalysis and no kinetic isotope effect is observed, while the reactions at pHs ca. 4·0–5·7 are catalyzed by general base and exhibit increasing ratios of k H / k D from 1·15 to 1·87 with increasing pH. A mechanism is postulated which includes nucleophilic addition of the sulfinate ion followed by deprotonation of the adduct. The rate-determining stop shifts from addition to deprotonation with increasing pH. A similar mechanism may be applied to the reaction of p -benzoquinone with thiosulfate. 1

Novel aspects of carbonyl oxide chemistry

The structural and chemical properties of 1,3-dipolar peroxidic species (X—O—O) such as ozone (X=O) and carbonyl oxides (X=R2C) depend significantly on the nature of X. Although cyclic O3 is thermodynamically unstable, dioxiranes, cyclic isomers of carbonyl oxides, are isolable and have been fully characterized. In contrast to the well known electrophilic nature of ozone, carbonyl oxides usually act as a nucleophilic oxygen transfer agent, but their reactivity could be altered by substituents. It is expected that the chemistry of R2C—O2 species will provide a good starting point for a better understanding of dioxygen complexes (X—O2) with various Xs. Interesting aspects of carbonyl oxide chemistry are discussed, including methods of generation, cyclization to dioxiranes and the nature of their oxygen transfer activities.

Kinetics of the nitric acid oxidation of benzyl alcohols to benzaldehydes

Abstract The oxidation of benzyl alcohols to benzaldehydes by dilute nitric acid (≈10%) was studied kinetically in 10 vol% aqueous dioxan. The oxidation is initiated most effectively by nitrous acid, and the rate is proportional to the product of the concentrations of benzyl alcohol and nitric acid, being independent of that of nitrous acid. The rate of oxidation increases with increasing acidity of the media, the plot of logarithm of the rate constant vs . acidity function H o being a line with a slope of ca. −2. the apparent energy and entropy of activation were 28·3 kcal mole −1 and +1·85 eu, respectively. The subtituent effect satisfied Hammets equation, affording a ϱ-value of −2·25. A probable mechanism is discussed, which involves a rapid and reversible coupling of α-hydroxybenzyl radical with nitrogen dioxide followed by the hydrolysis of α-hydroxybenzyl nitrite (I).

Spatially controlled photocycloaddition of a clay-intercalated stilbazolium cation

A stilbazolium cation included in clay interlayers undergoes an efficient and regioselective photocycloaddition to afford a syn head-to-tail dimer with suppression of the cis–trans isomerization.