Dual roles of alkyl alcohols as syndiotactic‐specificity inducers and accelerators in the radical polymerization of N‐isopropylacrylamide and some properties of syndiotactic poly(N‐isopropylacrylamide)

The effects of simple alkyl alcohols on the radical polymerization of N‐isopropylacrylamide in toluene at low temperatures were investigated. We succeeded in the induction of syndiotactic specificity and the acceleration of polymerization reactions at the same time by adding simple alkyl alcohols such as 3‐methyl‐3‐pentanol (3Me3PenOH) to N‐isopropylacrylamide polymerizations. The dyad syndiotacticity increased with a decrease in the temperature and an increase in the bulkiness of the added alcohol and reached up to 71% at ?60 °C in the presence of 3Me3PenOH. With the assistance of NMR analysis, it was revealed that the alcohol compounds played dual roles in this polymerization system; an alcohol compound coordinating to the N? H proton induced syndiotactic specificity, and that hydrogen‐bonded to the C?O oxygen accelerated the polymerization reaction. The effect of syndiotacticity on the properties of poly(N‐isopropylacrylamide)s was also examined in some detail. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4450–4460, 2006     

Shape optimization of a body located in low Reynolds number flow

The purpose of this study is to perform a numerical application of the shape optimization formulation of a body located in an incompressible viscous flow field. The formulation is based on an optimal control theory in which a performance function of the fluid force is introduced. The performance function should be minimized satisfying the state equation. This problem can be transformed into the minimization problem without constraint condition by the Lagrange multiplier method and the adjoint equations using adjoint variables corresponding to the state equations. As a numerical study, the drag force minimization problem in the steady Stokes flow, which means approximated equation of the low Reynolds number Navier–Stokes equation is carried out. After that, the unsteady Navier–Stokes flow is analysed. As the minimization algorithm, the steepest descent method is successfully applied. Copyright © 2005 John Wiley & Sons, Ltd.     

Pyrene‐Containing Twistarene: Twelve Benzene Rings Fused in a Row

Success in obtaining higher‐order twistarenes with precise structures is very important for fundamentally understanding the relationship between the structures and physical properties/optoelectronic applications. In this research, by using the advantages from a retro‐Diels–Alder process (clean reaction) and the cross‐conjugated nature of the pyrene unit, a novel dodeca‐twistarene was prepared for the first time. Its structure, confirmed by single‐crystal XRD analysis, indicates that it possesses a twisted angle (≈30°), and two neighboring molecules in the crystal lattice are perpendicular to each other because of the twisted character and the strong intermolecular CH–π interactions. However, its basic physicochemical properties suggest its instability in air derives from its elevated HOMO energy level, although NICS calculations confirm that the pyrene units contribution poorly to the π conjugation of the overall molecule.     

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.     

Correlation between the O 2p Orbital and Redox Reaction in LiMn0.6Fe0.4PO4 Nanowires Studied by Soft X‐ray Absorption

The changes in the electronic structure of LiMn_0.6Fe_0.4PO₄ nanowires during discharge processes were investigated by using ex situ soft X‐ray absorption spectroscopy. The Fe L ‐edge X‐ray absorption spectrum attributes the potential plateau at 3.45 V versus Li/Li⁺ of the discharge curve to a reduction of Fe³⁺ to Fe²⁺. The Mn L ‐edge X‐ray absorption spectra exhibit the Mn²⁺ multiplet structure throughout the discharge process, and the crystal‐field splitting was slightly enhanced upon full discharge. The configuration‐interaction full‐multiplet calculation for the X‐ray absorption spectra reveals that the charge‐transfer effect from O 2p to Mn 3d orbitals should be considerably small, unlike that from the O 2p to Fe 3d orbitals. Instead, the O K‐edge X‐ray absorption spectrum shows a clear spectral change during the discharge process, suggesting that the hybridization of O 2p orbitals with Fe 3d orbitals contributes essentially to the reduction.     

Dynamics of Photoelectrons and Structural Changes of Tungsten Trioxide Observed by Femtosecond Transient XAFS

The dynamics of the local electronic and geometric structures of WO₃ following photoexcitation were studied by femtosecond time‐resolved X‐ray absorption fine structure (XAFS) spectroscopy using an X‐ray free electron laser (XFEL). We found that the electronic state was the first to change followed by the local structure, which was affected within 200 ps of photoexcitation.     

A Diradical Approach towards BODIPY‐Based Dyes with Intense Near‐Infrared Absorption around λ=1100 nm

A diradical approach to obtain stable organic dyes with intense absorption around λ=1100 nm is reported. The para‐ and meta‐quinodimethane‐bridged BODIPY dimers BD‐1 and BD‐2 were synthesized and were found to have a small amount of diradical character. These molecules exhibited very intense absorption at λ=1088 nm (?=6.65×10⁵ M ^?1 cm^?1) and 1136 nm (?=6.44×10⁵ M ^?1 cm^?1), respectively, together with large two‐photon‐absorption cross‐sections. Structural isomerization induced little variation in their diradical character but distinctive differences in their physical properties. Moreover, the compounds showed a selective fluorescence turn‐on response in the presence of the hydroxyl radical but not with other reactive oxygen species.     

Problems on the Evaluation of the Critical Wavelength of Sunscreens for “Broad Spectrum” Approval Brought on by Viscous Fingering During Sunscreen Application

When a viscous liquid is applied to a solid substrate, a patterned liquid layer is usually formed by the phenomenon called viscous fingering, since the moving liquid surface is in far‐from‐equilibrium conditions to let the morphological fluctuation to grow. Pseudosunscreen solutions were prepared and applied on a flat quartz plate. A spatially periodic stripe pattern was formed on the pseudosunscreen layer when a block applicator was used, whereas a flat surface layer was formed when a four‐sided applicator was used. UV absorbance of the patterned layer was lower than that of the flat layer having the same average thickness. In addition, a larger decrease in the UV absorbance by the pattern formation was observed at wavelengths at which the UV absorbance of the flat layer was large, which was consistent with theoretical simulations. In 2011, US FDA introduced a new rule using the term “Broad Spectrum” for labeling the sunscreens. The different decrease in the UV absorbance at each wavelength was found to change the critical wavelength, which is a criterion for sunscreens to be labeled as “Broad Spectrum” protection. The result of this study makes the problem on the evaluation of the critical wavelength come to the surface.     

Redox Reaction in Ti−Mn Redox Flow Battery Studied by X-ray Absorption Spectroscopy

We performed X-ray absorption studies for the electrolytes of a Ti−Mn redox flow battery (RFB) to understand the redox reaction of the Ti/Mn ions and formation of precipitates in charged catholyte, because suppression of the disproportionation reaction is a key to improve the cyclability of Ti−Mn RFB and enhance the energy density. Hard X-ray absorption spectroscopy with a high transmittance and soft X-ray absorption spectroscopy to directly observe the 3d orbitals were complementarily employed. Moreover, the Ti/Mn 3d electronic structure for each precipitate and solution in the charged catholyte was investigated by using scanning transmission X-ray microscopy: the valence of Mn in the precipitate is mostly attributed to 4+, and the solution includes only Mn²⁺. This charge disproportionation reaction should occur after the Mn ions in the catholyte should be oxidized from Mn²⁺ to Mn³⁺ by charge.     

Direct observation of the unstable intermediates in radical addition reaction by using an interfacing microchip combined with an NMR

Direct observation of the unstable intermediate in the radical addition reaction of the oxime ether 1 mediated by triethylborane (Et(3)B) is described using (1)H and (11)B micro channeled cell for synthesis monitoring (MICCS), which was recently developed as an interfacing microchip for NMR. It was possible that the signal of the intermediate was observed as a result of using MICCS technique with a standard NMR instrument. This result supports the structure of the intermediate analyzed by diffusion-ordered spectroscopy (DOSY) NMR method in a previous paper. The procedure of micro channeled cell for synthesis monitoring-nuclear magnetic resonance (MICCS-NMR) was much easier than that of DOSY method. It was proven that it could be applied to the reaction in an anhydrous condition.