Publishing type：Research paper (scientific journal)   Publisher：The Chemical Society of Japan  

DOI： 10.1246/bcsj.20220169

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Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

In this study, a new type of single-molecule white luminescence is presented. This luminescence is accomplished by dual emission from two different stacking patterns having different overlapping areas in the crystal.

DOI： 10.1039/d2ma00670g

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Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

Introduction of neopentyl substituents at reactive carbons dramatically increases the cycloreversion (switching-off) quantum yield of fluorescent diarylethenes.

DOI： 10.1039/d2cc00554a

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Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acs.jpca.1c01569

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGERNATURE  

The study concerning the physical and chemical properties of thiophene derivatives has received much attention because they are incorporated in natural products, medicines, functional materials, and photoresponsive dyes. The autopolymerization reaction is one of the synthesis methods of polythiophenes using halogenated thiophene derivatives. In this paper, we analyzed the products and reaction mechanism of the polymerization reaction of 2-bromo-3-methoxythiophene by investigating the gas, liquid, and solid states using UV-Vis, electron spin resonance (ESR), gas chromatography/mass spectrometry (GC/MS), elemental analysis, NMR, and FT-IR spectroscopy. Consequently, we found a side reaction of the autopolymerization reaction and estimated that the polymerization reaction mechanism occurred in multiple steps. When we employed the brominated alkoxythiophene as a monomer, hydrogen bromide gas was generated to act not only as a catalyst of the polymerization reaction but also as an acid to cleave the alkoxyl group. The results provide useful information for the design of monomers via autopolymerization.

DOI： 10.1038/s41428-020-00435-1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

Photochromic diarylethene (DAE) materials are expected to be applied to various organic devices, and it is important to measure the glass transition temperature (T-g) in order to evaluate their stability. Although DAEs have excellent thermal stability, their colored state has a high melting point, and either a thermal cyclo-reversion reaction or decomposition occurs during the differential scanning calorimetry (DSC) measurement. T(g)s in the colored state, therefore, are hard to measure. In this study, we succeeded in measuring T(g)s of the colored state with DSC by preparing the colored amorphous state based on a mechanochemical effect for various DAEs. In addition, the relationship between the isomerization ratio and T-g was determined by combining the amorphization and the thermal reversion reaction near the melting point. It was found that T-g changed monotonically according to the isomerization ratio.

DOI： 10.1016/j.dyepig.2020.109069

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

A novel diarylethene formed “crystalline capsules” containing liquid inclusions, and chemicals trapped in the capsules were released by photoinduced breaking. Operations by multiphoton and linear polarized light were demonstrated.

DOI： 10.1039/d1sc03394h

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

Photoinduced topographical changes, bending, and photosalient effect due to the dimerization reaction were observed on a single crystal of 7-methoxycoumarin, upon deep UV (254 nm) light irradiation.

DOI： 10.1039/d1ce00444a

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

We report a swinging motion of photochromic thin broad sword shaped crystals upon continuous irradiation with UV light. By contrast in thick crystals, photosalient phenomena were observed. The bending and swinging mechanisms are in fact due to molecular size changes as well as phase transitions. The first slight bending away from the light source is due to photocyclization-induced surface expansion, and the second dramatic bending toward UV incidence is due to single-crystal-to-single-crystal (SCSC) phase transition from the original phase I to phase IIUV. Upon visible light irradiation, the crystal returned to phase I. A similar SCSC phase transition with a similar volume decrease occurred by lowering the temperature (phase IIItemp). For both photoinduced and thermal SCSC phase transitions, the symmetry of the unit cell is lowered; in phase IIUV the twisting angle of disordered phenyl groups is different between two adjacent molecules, while in phase IIItemp, the population of the phenyl rotamer is different between adjacent molecules. In the case of phase IIUV, we found thickness dependent photosalient phenomena. The thin broad sword shaped crystals with a 3 mu m thickness showed no photosalient phenomena, whereas photoinduced SCSC phase transition occurred. In contrast, large crystals of several tens of mu m thickness showed photosalient phenomena on the irradiated surface where SCSC phase transition occurred. The results indicated that the accumulated strain, between isomerized and non-isomerized layers, gave rise to the photosalient phenomenon.

DOI： 10.1039/d0sc05388k

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Publisher：Springer Singapore  

DOI： 10.1007/978-981-15-5451-3_24

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Bio-inspired functional materials have received much attention for their potential to provide sustainable and advanced materials. The lotus effect has proven to be one of the most remarkable biomimetic effects since it was discovered by Barthlott. A superhydrophobic surface with the ability to bounce water droplets is the origin of the self-cleaning mechanism that keeps the surface clean by removing dust using water droplets moving with momentum. We have developed a crystal growth technique (CGT) of photo-chromic diarylethenes over the past decade, and from this, we fabricated a surface structure that closely resembles the natural lotus leaf's characteristic of controlling the Laplace pressure and clarified the importance of the double roughness structure of the surface. The bouncing ability is also discussed in terms of the characteristic size of the double roughness structure theoretically. Moreover, this work clarifies the exquisiteness of the double roughness structure of the leaf. We also show that the CGT is a versatile technique with the potential to fabricate desired structured surfaces.

DOI： 10.1021/acs.langmuir.9b02358

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：BEILSTEIN-INSTITUT  

Background: Diarylethenes are well-known photochromic compounds, which undergo cyclization and cycloreversion reactions between open- and closed-ring isomers. Recently, diarylethene derivatives with photoswitchable fluorescent properties were prepared. They are applicable for fluorescence imaging including bio-imaging. On the other hand, a new system called "excited state intramolecular proton transfer (ESIPT)" is reported. In the system, absorption and emission bands are largely separated due to the proton transfer, hence it showed strong fluorescence even in the crystalline state. We aimed to construct the photochromic system incorporating the ESIPT mechanism.Results: A diarylethene incorporating a fluorescent moiety that exhibit ESIPT behavior was prepared. The ESIPT is one of the examples which express the mechanisms of aggregation-induced emission (AIE). This compound emits orange fluorescence with a large Stokes shift derived from ESIPT in aprotic solvents such as THE or hexane, while it exhibits only a photochromic reaction in protic solvents such as methanol. In addition, it shows turn-off type fluorescence switching in an aprotic solvent and in crystals. The fluorescence is quenched as the content of closed-ring isomers increases upon UV light irradiation.Conclusions: A diarylethene containing an ESIPT functional group was prepared. It showed fluorescent turn-off behavior during photochromism in aprotic solvents as well as in crystalline state upon UV light irradiation. Furthermore, it showed AIE in THF/water mixtures with blue-shift of the emission.

DOI： 10.3762/bjoc.15.217

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

The design of an object transportation system exploiting the bending behavior of surface-assembled diarylethene crystals is reported. A photoactuated smart surface based on this system can transport polystyrene beads to a desired area depending on the direction of the incident light. Two main challenges were addressed to accomplish directional motion along a surface: first, the preparation of crystals whose bending behavior depends on the direction of incident light; second, the preparation of a film on which these photochromic crystal plates are aligned. Nuclei generation and nuclear growth engineering were achieved by using a roughness-controlled dotted microstructured substrate. This system demonstrates how to achieve a mechanical function as shown by remote-controlled motion along a surface.

DOI： 10.1002/anie.201907574

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Language：English   Publisher：NATURE PUBLISHING GROUP  

DOI： 10.1038/s42004-019-0209-1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TECHNICAL ASSOC PHOTOPOLYMERS,JAPAN  

Wetting in Cassie-Baxter state on multi-pillar and multi-hole surfaces is discussed in terms of Gibbs free energy. To discuss thermodynamic stability, free-energy differences before and after the wetting are formulated. However, no difference between the Cassie-Baxter states on multi pillar and multi-hole surfaces is found. Furthermore, Laplace pressure generated by pillars or by a hole is discussed to find the conditions to prevent the penetration of water into the space between the pillars and the hole. As a result, it is predicted the condition in which multi-hole surface easily generates higher Laplace pressure than multi-pillar surface and easy to prevent the penetration. In other words, it is found that the multi-hole surface is a promising way to generate the Cassie-Baxter state.

DOI： 10.2494/photopolymer.32.279

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Language：English   Publisher：WILEY-V C H VERLAG GMBH  

Photoresponsive crystalline systems mimicking bio-functions are prepared using photochromic diarylethenes. Upon UV irradiation of the diarylethene crystal, the photogenerated closed-ring isomers self-aggregate to form needle-shaped crystals on the surface. The rough surface shows the superhydrophobic lotus effect. In addition, the rose-petal effects of wetting, the anti-reflective moth-eye effect, and a double-roughness structure mimicking the surface of a lotus leaf are observed by controlling the heating procedures, UV irradiation processes, and molecular structural modification. By changing the molecular structure, a superhydrophilic surface mimicking a snail shell can be generated. We also find the crystal of a diarylethene derivative that shows a photosalient effect. The effect is observed partly due to the hollow structure of the crystal. It is demonstrated that a photo-response similar to the response of impatiens plant to stimulation is observed by packing small beads in the hollow. These photoresponsive functions are unique, and they demonstrate a macroscopic response by means of microscopic molecular movement induced by light. In the future, such a molecular assembly system will be a promising candidate for fabricating photoresponsive architectures and soft robots.

DOI： 10.1002/chem.201705427

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The microcrystalline film of an open-ring isomer (1o) of diarylethene 1 was prepared on an Al plasmonic chip with a grating structure. Photoisomerization from 1o to the closed-ring isomer (1c) and growth of needleshaped crystals in 1c were observed in situ under an upright-inverted microscope. In the center part of the film, crystal growth of needle-shaped-crystal of 1c was observed upon UV irradiation from the top side, but not upon UV irradiation from the bottom side. However, crystallization occurred at the edge of the film upon UV irradiation from the bottom side. It was suggested that crystal growth of 1c required a high mobility of 1c near the film surface. Furthermore, the existence of 1o platform is also found to be required for alignment of 1c molecules by the results under the irradiation from the bottom and top sides. With the Al plasmonic chip, the conversion rate from 1o to 1c was larger inside the grating by the plasmonic enhanced field. Therefore, when the attenuated UV light was irradiated to the film edge with high mobility of 1c from the bottom side, the conversion rate was more than 60%, and the needle-shaped crystals of 1c were observed only inside the grating area. Crystal growth was controlled by the conversion rate of 1c promoted inside the grating. From the above, the larger conversion rate of 1c more than 60%, a high mobility of 1c near the film surface or edge, and the existence of the 1o platform for alignment of 1c molecules, are considered to be required for crystal growth in 1c.

DOI： 10.1021/acs.langmuir.8b00200

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Needle-like microcrystals growing after photoisomerization from an open-ring (1o) to a closed-ring (1c) isomer in a diarylethene 1 film were studied with an optical microscope. The photoisomerization and the crystal growth in the diarylethene 1 film were not measured in situ by scanning electron microscopy but measured with an optical microscope. The film set on the stage of an upright/inverted microscope was exposed to UV and visible (yellow) light using a Xe lamp in situ to induce the reversible photochromic reactions; optical and spectroscopic images of the diarylethene I film were also observed in situ using a halogen lamp. At 1 h after the photochromic isomerization reaction to lc under the UV light, needle shaped microcrystals were observed in the inplane radial direction from the outline of island-shaped film, and they gradually grew. After incubation for 41 h in the dark at room temperature, the film was exposed to visible light for the reverse isomerization to lo. It was confirmed from absorption spectra, and the crystals simultaneously disappeared. The optical and spectroscopic imaging with a microscope was found to be a powerful tool for in situ observation of the photochromic reaction and crystallization processes. (C) 2018 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jphotochem.2018.01.022

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

A diarylethene with a perfluorocyclohexene ring formed hollow crystals by sublimation under normal pressure. Upon UV irradiation of the crystals, they showed remarkable photosalient phenomena and scattered into small pieces. The speed of the flying debris released from the crystal by UV irradiation exceeded several meters per second. To clearly show a photosalient effect resembling the scattering behavior of Impatiens on a smaller scale, small fluorescent beads (1-mu m diameter) were inserted into the hollow crystal. Consequently, scattering of the beads was observed as UV irradiation caused deformation and bursting of the hollow structure. This phenomenon is unique to hollow crystals, and the ability to effectively induce remarkable photosalient phenomena is similar to the behavior of hollow-structured Impatiens in nature.

DOI： 10.1002/anie.201706684

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：A V S AMER INST PHYSICS  

Vacuum evaporation, which is widely used to obtain a metal-film coating on substrates and/or targets, results in a large loss of evaporation materials. The authors discovered a selective metalvapor deposition phenomenon in which metal-vapor atoms can be deposited selectively without a shadow mask. The core phenomenon of selective deposition is the desorption of metal-vapor atoms from organic surfaces with a low-glass transition temperature (low-Tg). The authors investigated metal-atom desorption from low-Tg polymer [polydimethylsiloxane (PDMS)] surfaces during vacuum deposition and found that greater than 2-lm-thick PDMS film enables high desorption efficiency. The authors proposed two vacuum deposition methods: metal-vapor transportation and metal-vapor integration. The former method attained reduced substrate surface temperatures during vacuum evaporation and the latter enabled extremely high deposition efficiency and three-dimensional deposition in a one-batch process. These new methods can greatly widen applications of vacuum deposition. (C) 2016 American Vacuum Society.

DOI： 10.1116/1.4971415

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Double roughness structure, the origin of the lotus effect of natural lotus leaf, was successfully reproduced on a diarylethene microcrystalline surface. Static superwater-repellency and dynamic water drop -bouncing were observed on the surface, in the manner of natural lotus leaves. Double roughness structure was essential for water-drop bouncing. This ability was not observed on a single roughness microcrystalline surface showing the lotus effect of the same diarylethene derivative. The double roughness structure was reversibly controlled by alternating irradiation with UV and visible light.

DOI： 10.1021/jacs.6b05562

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.71.1.0_3220

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

By alternate irradiation with UV and visible light, reversible topographical changes were observed on the microcrystalline surfaces of diarylethene derivatives above the glass transition temperatures (T-g) of their open-ring isomers. For the photogenerated closed-ring isomers, the crystal growth proceeded at the surface softened by molecular movement. This is the self-aggregation of the closed-ring isomers. The photogenerated surface topographies appear depending on the crystal habits of the closed-ring isomers. Reflecting the properties (crystal habits) of diarylethene derivatives, we obtained cubic, needle, and plate-shaped crystals of the closed-ring isomers on the microcrystalline surfaces of the open-ring isomers by irradiation with UV light. Even a derivative having one isopropyl group at a reactive carbon atom, whose closed-ring isomer is thermally unstable, showed photoinduced topographical changes, because the Tg of the open-ring isomer is around ambient temperature.

DOI： 10.1039/c6ce00718j

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Authorship：Lead author   Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

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Authorship：Lead author   Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

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Authorship：Lead author   Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

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