The Effect of SiMe3 and SiEt3 Para Substituents for High Activity and Introduction of a Hydroxy Group in Ethylene Copolymerization Catalyzed by Phenoxide-Modified Half-Titanocenes

Remarkable effects of SiMe₃ and SiEt₃ para-substituents in the phenoxide-modified half-titanocenes, Cp*TiCl₂(O-2,6-ⁱPr₂-4-R-C₆H₂) [R=SiMe₃ ( 6 ), SiEt₃ ( 7 )], toward the catalytic activities in ethylene copolymerizations with 2-methyl-1-pentene, 1-decene, 1-dodecene and with 9-decen-1-ol (DC-OH) have been demonstrated. The activities by 6 , 7 at 50 °C showed higher than those conducted at 25 °C in all cases in the presence of MAO cocatalyst. Efficient synthesis of high-molecular-weight (HMW) ethylene copolymers incorporating DC-OH (or 5-hexen-1-ol, HX-OH) has been attained in the copolymerization by 7 , which showed better DC-OH (HX-OH) incorporation at 50 °C to afford the HMW copolymers, poly(ethylene-co-DC-OH)s, with high activities (activity 1.21–3.81×10⁵ kg-polymer mol⁻¹-Ti h, M_n=6.55–10.0×10⁴, DC-OH 2.3–3.6 mol %).     

Rare direct imidation of aromatic metallacycle by reaction of CpCo(dithiolene) complex with N-halosuccinimide

The aromatic [CpCo(S₂C₂(R)(H))] (R = Ph, Me, 9-phenanthryl, H) complexes reacted with N-halosuccinimides (NXS; X = Cl, Br, I) in carbon tetrachloride at room temperature to undergo the N-succinimide substitution reaction on the dithiolene ring, but no halogenated dithiolene complex was obtained. The imidation products [CpCo(S₂C₂(R)(N-sccinimide))] were yielded up to 64% where X = I and R = 9-phenanthryl. The reaction of [CpCo(S₂C₂(Ph)(H))] with N-bromophthalimide (NBP) also gave the imidation product [CpCo(S₂C₂(Ph)(N-phthalimide))]. This is the rare direct imidation reaction to an aromatic metallacycle by NXS. The reaction of [CpCo(S₂C₂H₂)] (R = H) with NIS afforded the double imidation product. One by-product in this reaction was the dithiolene-dithiolene homo-coupling product [CpCo(S₂C₂(R))]₂ (R = Ph, Me, 9-phenanthryl). The microwave-enhanced (MW) reactions were attempted in the carbon tetrachloride solution. Although the solution temperature increased up to only 43 °C by MW irradiation, the imidation reaction worked with short reaction time.     

Olefin polymerization by (cyclopentadienyl)(ketimide)titanium(IV) complexes of the type, Cp′TiCl2(N=CBu2)-methylaluminoxane (MAO) catalyst systems

Effects of substituents on cyclopentadienyl group for homopolymerization of ethylene, 1-hexene, and for ethylene/1-hexene copolymerization using a series of nonbridged (cyclopentadienyl)(ketimide)titanium complexes of the type, Cp′TiCl₂(N=C^tBu₂) [Cp′ = Cp (1), ^tBuC₅H₄ (2), C₅Me₅ (Cp^*, 3), and indenyl (4)] have been explored in the presence of methylaluminoxane (MAO) cocatalyst. Complexes 1–3 showed the similar catalytic activities for ethylene polymerization although the activity by 4 was somewhat low, whereas the activity for 1-hexene polymerization increased in the order 1 > 4 2 > 3. These complexes showed significant activities for ethylene/1-hexene copolymerization affording high molecular weight poly(ethylene-co-1-hexene)s with unimodal molecular weight distributions, and the activity increased in the order: 4 > 1 2, 3. The r_Er_H values in the polymerization by 1–3 at 40 °C were 0.35–0.52 which clearly indicate that the 1-hexene incorporation in the copolymerization did not proceed in a random manner. The r_E values by 1–3 were 6.0–6.4 and the values were independent upon the cyclopentadienyl fragment employed; the r_E values by 4 at 40 °C were 10.2–10.9 which were close to those by ansa-metallocene complex catalysts. These values were influenced by the polymerization temperature, and the 1-hexene incorporation by 1–4 became inefficient at higher temperature, although the observed activities especially by 1, 4 were highly remarkable.     

Structural dependency of optical excitation transfer via optical near-field interactions between semiconductor quantum dots

The distribution dependency of quantum dots was theoretically and experimentally investigated with respect to the basic properties optical excitation transfer via optical near-field interactions between quantum dots. The effects of three-dimensional structure and arraying precision of quantum dots on the signal transfer performance were analyzed. In addition, the quantum dot distribution dependency of the signal transfer performance was experimentally evaluated by using stacked CdSe quantum dots and an optical near-field fiber probe tip laminated with quantum dots serving as an output terminal, showing good agreement with theory. These results demonstrate the basic properties of signal transfer via optical near-field interactions and serve as guidelines for a nanostructure design optimized to attain the desired signal transfer performances.     

Selective photocurrent generation in the transparent wavelength range of a semiconductor photovoltaic device using a phonon-assisted optical near-field process

In this paper, we propose a novel photovoltaic device using P3HT and ZnO as test materials for the p-type and n-type semiconductors, respectively. To fabricate an electrode of this device, Ag was deposited on a P3HT film by RF-sputtering under light illumination (wavelength λ ₀=660 nm) while reversely biasing the P3HT/ZnO pn-junction. As a result, a unique granular Ag film was formed, which originated from a phonon-assisted process induced by an optical near-field in a self-organized manner. The fabricated device generated a photocurrent even though the incident light wavelength was as long as 670 nm, which is longer than the long-wavelength cutoff λ _c (=570 nm) of the P3HT. The photocurrent was generated in a wavelength-selective manner, showing a maximum at the incident light wavelength of 620 nm, which was shorter than λ ₀ because of the Stark effect brought about by the reverse bias DC electric field applied during the Ag deposition.     

Benzimidazobenzothiazole‐Based Bipolar Hosts to Harvest Nearly All of the Excitons from Blue Delayed Fluorescence and Phosphorescent Organic Light‐Emitting Diodes

Much effort has been devoted to developing highly efficient organic light‐emitting diodes (OLEDs) that function through phosphorescence or thermally activated delayed fluorescence (TADF). However, efficient host materials for blue TADF and phosphorescent guest emitters are limited because of their requirement of high triplet energy levels. Herein, we report the rigid acceptor unit benzimidazobenzothiazole (BID‐BT), which is suitable for use in bipolar hosts in blue OLEDs. The designed host materials, based on BID‐BT, possess high triplet energy and bipolar carrier transport ability. Both blue TADF and phosphorescent OLEDs containing BID‐BT‐based derivatives exhibit external quantum efficiencies as high as 20 %, indicating that these hosts allow efficient triplet exciton confinement appropriate for blue TADF and phosphorescent guest emitters.     

Synthesis and Disassembly/Reassembly of Giant Ring‐Shaped Polyoxotungstate Oligomers

The disassembly and reassembly of giant molecules are essential processes in controlling the structure and function of biological and artificial systems. In this work, the disassembly and reassembly of a giant ring‐shaped polyoxometalate (POM) without isomerization of the monomeric units is reported. The reaction of a hexavacant lacunary POM that is soluble in organic solvents, [P₂W₁₂O₄₈]^14?, with manganese cations gave the giant ring‐shaped POM [{γ‐P₂W₁₂O₄₈Mn₄(C₅H₇O₂)₂(CH₃CO₂)}₆]^42?. This POM is a hexamer of manganese‐substituted {P₂W₁₂O₄₈Mn₄} units, and its inner cavity was larger than any of those previously reported for ring‐shaped polyoxotungstates. It was disassembled into monomeric units in acetonitrile, and the removal of the capping organic ligands on the manganese cations led to reassembly into a tetrameric ring‐shaped POM, [{γ‐P₂W₁₂O₄₈Mn₄(H₂O)₆}₄(H₂O)₄]^24?.     

Behavior of mercury(II) salts in electrothermal atomic absorption spectrometry : Application to the Determination of Thiosulfate

Mercury(II) salts have different decomposition temperatures in a graphite tube or tantalum coil used for electrothermal atomic absorption spectrometry. The nitrate, perchlorate and acetate were spontaneously reduced to mercury vapor at room temperature, but the thiosulfate, sulfide, cyanide and bromide were reduced only on heating. Chloride and thiocyanate in a graphite furnace and iodide in a tantalum coil did not give mercury absorbance on heating. Thiosulfate (1–10 × 10^?6 M) was determined by addition to mercury(II) nitrate in acetate buffer, removing the response from the excess mercury(II) nitrate by drying below 100° C in the graphite furnace, and measuring the mercury absorbance on heating, which was proportional to the thiosulfate concentration.