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Your search keyword '"Takayuki Hirai"' showing total 29 results
Start Over Author "Takayuki Hirai" Publisher american chemical society
29 results on '"Takayuki Hirai"'

4. Spontaneous Isomerization of a Hydroxynaphthalene-Containing Spiropyran in Polar Solvents Enhanced by Hydrogen Bonding Interactions

Author

Shunsuke Takagi, Takayuki Hirai, Yasuhiro Shiraishi, and Keiichiro Yomo

Subjects
Spiropyran, genetic structures, Chemistry, Hydrogen bond, General Chemical Engineering, General Chemistry, Photochemistry, Article, chemistry.chemical_compound, Optical materials, Polar, sense organs, Isomerization, QD1-999
Abstract

The synthesis of spiropyran dyes exhibiting solvent-driven isomerization even in the dark condition is an important subject for the design of optical materials. A conventional synthesis strategy involves the conjugation of indoline moieties with electron-deficient aromatic moieties. Herein, we report that a spiropyran conjugated with a hydroxynaphthalene moiety (1) is a new member exhibiting solvent-driven isomerization, even bearing an electron-donating −OH moiety. The dye exists as a colorless spirocyclic (SP) form in nonpolar media. It, however, shows a blue color in polar media, especially in aqueous media, due to the formation of ring-opened merocyanine (MC) forms, where the isomerization terminates in 10 s even at room temperature. The spontaneous SP → MC isomerization originates from the MC forms stabilized by the highly delocalized π-electrons on the hydroxynaphthalene moiety. The solvation in polar media and the hydrogen bonding interaction with water molecules decrease the ground-state energy of the MC forms, triggering spontaneous isomerization. The dye exhibits two MC absorption bands assigned to the trans–trans–cis (TTC) and cis–trans–cis (CTC) isomers. The absorbance of the CTC band increases more significantly with an increase in the water content, and the increase exhibits a linear relationship with a hydrogen-bond donor acidity of solvents. The phenolate oxygen of the CTC form has larger hydrogen-bond acceptor basicity, resulting in stronger stabilization by the water molecule.

Published
2021

6. Preparation of Sr2CeO4 blue phosphor particles and rare earth (Eu, Ho, Tm, or Er)-doped Sr2CeO4 phosphor particles, using an emulsion liquid membrane system

Author

Takayuki Hirai and Yusuke Kawamura

Subjects
Oxalates -- Research, Phosphors -- Research, Cerium -- Research, Strontium -- Research, Chemicals, plastics and rubber industries
Abstract

Sr2CeO4 blue phosphor particles were prepared with an emulsion liquid membrane system, which could be utilized as a micro reactor for the preparation of size- and morphology-controlled fine particles. The composite oxalate particles obtained were sub micrometer size and much smaller than those prepared in the homogeneous aqueous solutions.

Published
2004

17. Temperature-Controlled Photosensitization Properties of Benzophenone-Conjugated Thermoresponsive Copolymers.

Author

Hisao Koizumi, Takayuki Hirai, and Yasuhiro Shiraishi

Subjects
*POLYMERS, *MACROMOLECULES, *CONDUCTING polymers, *ELASTOMERS
Abstract

We previously found that a copolymer, poly(NIPAM- co-BP), consisting of N-isopropylacrylamide (NIPAM) and benzophenone (BP) units, behaves as a photosensitizer showing temperature-controlled oxygenation activity by singlet oxygen ( 1O 2) in water ( J. Am. Chem. Soc.2006, 128, 8751−8753 ). This polymer shows a heat-induced oxygenation enhancement at <20 °C, while showing suppression at >20 °C. This is driven by a heat-induced phase transition of the polymer from coilto micelleand then to globulestate, controlling the stability and diffusion of 1O 2and the location of substrate. In the present work, effects of polymer concentration and BP content of the polymer on the oxygenation activity were studied at 5−35 °C. Increase in the polymer concentration leads to activity decrease at >20 °C due to strong polymer aggregation, suppressing incident light absorption of the BP units. With a decrease in BP content of the polymer, heat-induced oxygenation enhancement at <20 °C is more pronounced because formation of small size micelles accelerates 1O 2oxygenation. The obtained findings reveal that the polymer with low BP content, when used at high concentration, shows clear-cut off- on- offactivity change against the temperature window: very low activity at <5 °C and >25 °C, and very high activity at middle temperature range. [ABSTRACT FROM AUTHOR]

Published
2008
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