Yuko Takeoka

Scintillation properties of (C6H13NH3)2PbI4: Exciton luminescence of an organic/inorganic multiple quantum well structure compound induced by 2.0 MeV protons

Abstract We report a new type of scintillator especially suitable for pulse-radiation detection. Thin films of organic/inorganic perovskite compound (n-C6H13NH3)2PbI4, which is characterized by a multiple quantum well structure, were bombarded by 2.0 MeV protons, and their radiation-induced emission spectra were obtained. A single and sharp emission peak due to an exciton was observed at the wavelength of 524 nm. This emission was clearly detected even at room temperature, and its quantum efficiency was very high. The line shape of this emission did not change, retaining its sharpness, and no other emissions appeared throughout the irradiation. The optical response of (n-C6H13NH3)2PbI4 is very fast. (n-C6H13NH3)2PbI4 is a promising scintillator material, meeting requirements not satisfied by conventional scintillators.

Synthesis and properties of hydrophilic–hydrophobic diblock copolymer ionomers based on poly(p-phenylene)s

Diblock copolymer ionomers SP1-P2(m-n) with ion exchange capacity (IEC) of 0.96–2.42 meq g−1 were prepared. The parent diblock copolymers P1-P2(m-n) having various block lengths (m, n) were synthesized via successive catalyst-transfer polymerization of 1,4-dibromo-2,5-di[4-(2,2-dimethylpropoxysulfonyl)phenyl]butoxybenzene (1) and 1,4-dibromo-2,5-hexyloxybenzene (2). The molecular weights were successfully controlled by the feed ratio of the monomer and catalyst, and the molecular weight distribution values were less than 1.32, irrespective of the polymerization degree or polymerization order. Preliminary morphological studies showed that the diblock copolymer ionomers SP1-P2(m-n) had a clear phase separation that could be controlled by the ratios and lengths of the hydrophilic and hydrophobic units. The ionomers showed high proton conductivities with a small humidity dependence, indicating that the clear phase separation formed by the precisely controlled molecular weight and polydispersity index (PDI) of the diblock copolymers enhanced the ionic connectivity and proton conductivity.

Fabrication of two-dimensional layered perovskite [NH3(CH2)12NH3]PbX4 thin films using a self-assembly method

Ultra-thin films of the two-dimensional layered perovskites [NH3(CH2)12NH3]PbX4 (X = Br, I) with the quantum confinement effect have been fabricated by a convenient self-assembly method.

Synthesis of optically active regioregular polythiophenes and their self-organization at the air-water interface.

Regioregular polythiophenes containing an optically active substituent in the third position of the thiophene ring, head-to-tail poly(3-[2-((S)-1-methyloctyloxy)ethyl]thiophene)s (HT-P(S)MOETs), were synthesized using highly reactive zinc. For comparison, HT-P(R)MOET and achiral HT-P(±)MOET also were synthesized from R-type monomers and racemic monomers, respectively. The HT-PMOET possessed greater than 95% head-to-tail coupling with a weight-average molecular weight (Mw) between 1.96 × 10(4) and 2.94 × 10(4). The polymers were characterized using (1)H and (13)C NMR, optical rotatory power measurements, circular dichroism (CD), and UV-vis spectroscopy. X-ray diffraction patterns of the cast films demonstrated that regioregular HT-PMOET possessed a strong tendency to self-assemble into highly ordered, crystalline structures. The HT-P(S)MOET and HT-P(R)MOET showed strong Cotton effects, while HT-P(±)MOET showed very weak Cotton effects. The presence of a circular dichroism effect indicated that the side chain chirality induced optical activity in poly(thiophene) main chains. The monolayer formation of HT-PMOET spread on the water surface was characterized using a pressure-area (π-A) isotherm. The molecular areas of HT-P(S)MOET and HT-P(R)MOET molecules on the water surface were 33.5 and 32.9 Å(2), respectively, at 10 °C, which were larger than that of HT-P(±)MOET (27.9 Å(2)), suggesting that optically active HT-PMOET expanded because of the chiral repulsion between side chains. Multilayer films of HT-PMOET were prepared by repeating horizontal deposition of the monolayer on the water surface. The multilayer films of optically active HT-PMOET obtained showed stronger Cotton effects than did the cast films. In addition, electrical conductivities of HT-PMOET multilayer films were superior to those of spin-coated films. Head-to-tail poly(3-[2-((S)-1-methylpropyloxy)ethyl]thiophene) (HT-P(S)MPET), which contained shorter side chain lengths compared to HT-P(S)MOET, also was synthesized. The CD intensities of HT-P(S)MPET multilayer films were smaller than those of HT-P(S)MOET multilayer films, suggesting that the optically active side-chain length is critically important to the optically active self-assembly.

Synthesis of novel proton conducting polymer electrolytes containing phosphoric acid

Copolymers of acid phosphoxyethyl methacrylate (PHM) and 2,2,2-trifluoroethylacrylate (TFEA) were synthesized in order to construct hydrophilic and hydrophobic domains as well as Nafion membrane. Thermal decomposition temperatures of PHM-TFEA copolymers were about 250 °C, which showed sufficient thermal stability for polymer electrolyte fuel cells (PEFC). Water uptake of these copolymers was higher than that of Nafion 115 under low relative humidity, and proton conductivity of these polymers exhibited about 10 -3 S cm -1 under 90 % relative humidity at 80 °C.

Exciton–exciton scattering in perovskite CH3NH3PbBr3 single crystal

We have measured photoluminescence spectra in CH3NH3PbBr3 at low temperatures and found a nonlinear emission at the lower energy side of the exciton resonance. Considering that this signal shows a rapid decay, we have assigned it as originating from the exciton–exciton inelastic scattering process called P-emission. The energy difference between this P-emission and the free exciton resonance is 20–30 meV, which is consistent with recent studies of the exciton binding energy.

Incorporation of conjugated polydiacetylene systems into organic–inorganic quantum-well structures

A new type of organic–inorganic semiconductor heterostructure has been successfully fabricated by incorporating a polydiacetylene backbone into layered perovskite compounds by solid-state polymerization.

Use of a High-Performance Poly(p-phenylene)-Based Aromatic Hydrocarbon Ionomer with Superacid Groups in Fuel Cells under Low Humidity Conditions

Aromatic ionomers with perfluoroalkyl sulfonic acid groups for fuel cell applications have been prepared mostly by the post-functionalization method. Herein, we present a direct polymerization method using a novel monomer with a perfluorosulfonic acid group to control the amount and position of the sulfonic acid groups. A poly(p-phenylene)-based aromatic hydrocarbon ionomer bearing a pendant perfluorosulfonic acid group in a substituent at the 2-position is synthesized by Ni(0)-catalyzed coupling polymerization. The direct polymerization provides Mn values of up to 169 000 with a highly controlled molecular structure and allows the formation of thin membranes. These ionomers were found to combine the positive features of perfluorinated and aromatic hydrocarbon ionomers, and these thin membranes with a relatively high ion exchange capacity showed high proton conductivity and excellent fuel cell performance (907 mW cm–2 even at 80 °C and 30% RH) under low humidity conditions compared with other reported aromatic hydrocarbon ionomers.

Regiocontrolled synthesis of poly(thiophene) derivatives with fluoroalkyl side chains

Poly(3-(perfluorohexyl)thiophene) (PFHT) was synthesized from 2, 5-dibromo-3-(perfluorohexyl)thiophene via Grignard metathesis method. Obtained polymer was dissolved in a wide variety of organic solvents such as chloroform, tetrahydrofuran, and o-dichlorobenzene. Transition temperatures of PFHT were observed at 54 °C due to melting of perfluorohexyl groups. Electron-withdrawing effect of C-F bonds and weak interaction among the side chains were observed as shorter maximum absorption wavelengths. Stable monolayers of PFHT were formed on a water subphase due to strong hydrophobicity and the weak interactions of the perfluorohexyl groups.

Cellulose-dissolving protic ionic liquids as low cost catalysts for direct transesterification reactions of cellulose

Cellulose acetate (CA) is a resin derived from biomass. In addition to its various superior properties, CA is preferable to existing petroleum-derived resins from the viewpoint of green chemistry. Therefore, the acetylation of cellulose is one of the most important subjects in cellulose research. In this study, we found that the acetylation of cellulose could proceed in some protic ionic liquids (PILs) composed of amidine and acetic acid with ΔpKa = ca. 8.4–8.7 under mild conditions without any catalyst. The degree of substitution (DS) of the produced CA was above 1.84, and the maximum DS was 2.87 when the ΔpKa of the PIL was about 8.5. In propionate-based PILs, cellulose was not only acetylated but also propionated; however, the cellulose acetylation did not occur in formate-based PILs. It was revealed that the esterification of cellulose proceeded through the anion exchange between carboxylic anhydride and anion species of the PIL.