Diarylethene Crystals Research Articles

Morphological control for hollow rod crystals of a photochromic diarylethene on spherulites by surface properties of substrates.

Sublimation methods utilizing the surface properties of substrates can address the challenge of controlling hollow morphologies in rod crystals. Spherulites were formed on the hydrophilic surface of the (0001) planes of α-quartz and sapphire substrates by sublimation of 1,2-bis(3,5-dimethyl-2-thienyl)perfluorocyclopentene (1a). Various types of hollow morphologies, distinguished by the size and shape of their cross sections and by the presence or absence of branching structures, were formed separately on α-quartz and sapphire substrates. Such precise control of the hollow morphologies was attributed to the wettability of each substrate, leading to the formation of spherulites of 1a. In addition, it was indicated that the formation process of the surface morphologies of spherulites was associated with the hollow morphologies of rod crystals of 1a.

Mechanically Induced Transient Fluorescence of Photochromic Diarylethene Crystals for Sensing and Security Material

AbstractLuminescent materials responding to mechanical stimulation can visualize the strain and mechanical damage applied to objects. Mechanofluorochromism is a well‐known phenomenon induced by the mechanical force on fluorescent crystalline materials. However, simple application of the mechanofluorochromism is unsuitable for temporally and spatially detecting stress in detail because the fluorescent state is kept for rather long period. Here, the dynamic stress‐sensing luminescent solid material of a photochromic diarylethene with a fluorescent moiety is reported. Under the stress applied to the crystalline state, this material emitted cyan‐colored transient fluorescence that is rapidly diminished within a few second. This dynamic fluorescence phenomenon is well controlled by the combination of light irradiation and other external stimuli (organic solvent vapor and/or heat). In addition, the luminescence period is regulated by the excitation wavelength and magnitude of applied force. By utilizing these responses, the rewritable dynamic information encryption is successfully demonstrated. This material with transient fluorescence overcomes the persistence of fluorescence color of mechanochromism and present results provide a new principle for multifunctional light‐emitting materials responding to mechanical stimulation.

History-dependent nano-photoisomerization by optical near-field in photochromic single crystals

The history dependence of physical systems is promising for solving complex problems. To exploit spontaneous nanometre-scale optical memory for computation, the history dependence must be elucidated. Here, we demonstrate history-dependent or dynamic nano-photoisomerization through the sequential formation of multiple memory pathways in photochromic crystals via optical near-field interactions. Incident photons passing through photoisomerization memory pathways are observed using a double-probe optical near-field microscope, with one probe located on the front surface for local excitation and the other on the rear surface for near-field observations. By performing localised near-field excitation twice but at spatially different positions, negatively correlated near-field output patterns are observed between the first and second memory pathways. We also confirm that the first memory pathway is preserved after the formation of the second memory pathway. This result indicates that photoisomerization using an optical near field in diarylethene crystals has a history dependence, leading to brain-like dynamic information memorisation.

Efficient Surface Peeling, a Photoinduced Result of Photochromic Diarylethene Crystal by Multistep Light Irradiation

Efficient Surface Peeling, a Photoinduced Result of Photochromic Diarylethene Crystal by Multistep Light Irradiation

Multicolor Photochromism of Two-Component Diarylethene Crystals Containing Oxidized and Unoxidized Benzothiophene Groups

Preparing mixed crystals composed of two or more components is one of the useful approaches to not only modifying the physical properties and chemical reactivity of molecular crystals but also creating their novel functionality. Here we report preparation and photoresponsive properties of two-component mixed crystals containing photochromic bis(benzothienyl)ethene derivatives that show different colors in the closed-ring forms depending on the oxidation state of the benzothiophene groups. The similarity in the molecular structures of the two diarylethenes, which are different from each other only in the oxidation state of the benzothiophene groups, allowed the formation of two-component mixed crystals by recrystallization from mixed solutions containing the two compounds. Irradiating the mixed crystals with light of appropriate wavelengths induced the selective photoisomerizaion of the two diarylethenes, leading to multicolor photochromic performance, such as colorless, orange, yellow, and red. Such molecular crystals with multiresponsive functions can find potential applications in multistate optical recording and multicolor displays. The present results demonstrate that combining differently oxidized diarylethene derivatives is an effective strategy for preparing multicomponent mixed crystals with finely tuned composition and desired photoresponsive properties.

Patterning submicron photomechanical features into single diarylethene crystals using electron beam lithography.

Lithography methods are commonly used to create structures in inorganic semiconductors like silicon but have not been widely applied to organic crystals. In this work, electron beam lithography (EBL) is used to pattern structures into single organic photomechanical crystals composed of 1,2-bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentene. The electron beam creates amorphous regions of decomposed molecules, while the reactivity of the unexposed crystal regions is preserved under a removable Au coating. Exposure of the patterned crystal to 365 nm light causes ridges of amorphous material to increase in height by 30-70%. This height increase can be reversed by visible light exposure and undergo multiple cycles. The reversible surface morphology changes are strong enough to rupture a sheet of graphene placed on top of the patterned crystal. Surprisingly, the change in dimensions of the EBL features is an order of magnitude larger than the changes in overall crystal dimensions as deduced from X-ray diffraction experiments and microscopy observations. A dynamic extrusion model is presented to explain how nanoscale features imprinted into single crystals can amplify molecular-level photomechanical changes. This work demonstrates the capability of EBL methods to produce sub-micron structural features on single photomechanical crystals, providing a new route to monolithic light-powered actuator devices.

Boundary formation in photochromic diarylethene single crystals and its catastrophe theory modeling

Photochromic diarylethenes that are reversibly isomerized by visible and ultraviolet light irradiation could be had the potential to be utilized in a variety of functional devices and systems. In this study, we observed the autonomous formation of a sharp, nanometer-scale boundary between two different surface morphology of photochromic diarylethene crystals when both visible and ultraviolet light were irradiated. We developed a theoretical model using catastrophe theory, which agrees with our experimental observations. This study not only reveals a fundamental experimental finding regarding photochromic crystals but also provides interesting resources to be utilized for future natural intelligent devices and systems.

Light-Driven Rapid Peeling of Photochromic Diarylethene Single Crystals

Macroscopic transformation such as the molecular motors of biology is brought by transforming the protein using the chemical reaction of molecules by external stimuli. If it is possible to achieve it as machine-like in nanometer to micrometer size in photomechanical phenomena, there is a possibility of the application as driving devices of micro- or nanomachineries that drive without any electrical contact. Since light is useful to operate it without any direct contact as external stimuli and leads to rapid photochemical reactions, the operation at high speed can be expected. Here we newly found that crystals of a photochromic diarylethene exhibit a peeling behavior with astonishingly rapid velocity by photoirradiation to a lateral face in addition to separation behaviors such as jumping and cracking by photoirradiation to a well-developed face. The detail of the rapid photoresponsive peeling was discussed based on the molecular packings and the dependence on crystal size and photoirradiation conditions. These crystals can be potentially applied to macroscopic photomechanical actuators rapidly driven based on molecular machinery.

Stepwise Assembly of Ultrathin Poly(vinyl alcohol) Films on Photoresponsive Diarylethene Crystals

Abstract Rodlike two-component mixed crystals composed of 1-(5-methyl-2-phenyl-4-thiazolyl)-2-(5-methyl-2-p-tolyl-4-thiazolyl)perfluorocyclopentene (1a) and 1,2-bis(5-methyl-2-p-tolyl-4-thiazolyl)perfluorocyclopentene (2a) undergo light-driven bending upon alternate irradiation with ultraviolet (UV) and visible light. To provide stability of the crystals in organic solvents, the crystal surface was coated with ultrathin poly(vinyl alcohol) (PVA) films using a stepwise assembly method. The crystals coated with 15 ultrathin PVA layers were stable in n-hexane and no appreciable suppression in the bending performance was observed by the PVA coating. The light-driven bending could be repeated more than 1000 times.

Object Transportation System Mimicking the Cilia of Paramecium aurelia Making Use of the Light‐Controllable Crystal Bending Behavior of a Photochromic Diarylethene

AbstractThe 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.

Object Transportation System Mimicking the Cilia of Paramecium aurelia Making Use of the Light-Controllable Crystal Bending Behavior of a Photochromic Diarylethene.

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.

Photosalient Effect of Diarylethene Crystals of Thiazoyl and Thienyl Derivatives.

The photoresponse of diarylethene crystals is found to depend on the intensity of UV light, that is, photoinduced bending is switched to photosalient phenomena by increasing the light intensity. The change in the size of the crystal unit cell upon UV irradiation is larger for asymmetric diarylethenes with thiazole and thiophene rings than that for the corresponding symmetric diarylethenes. As a result, the crystals of an asymmetric diarylethene show much more drastic photosalient effects than those of the corresponding symmetric diarylethene crystals upon UV irradiation. It is also found that the crystals of diarylethene, which have not previously been reported to exhibit a photosalient effect, show photosalient phenomena upon irradiation with strong UV light. Furthermore, the dependence of photosalient phenomena on the size and shape of the crystals is reported.

Photomechanical bending behavior of photochromic diarylethene crystals induced under polarized light

The photoinduced bending velocity of photochromic diarylethene crystals depends on the polarization angle of UV light.

Nanometre-scale pattern formation on the surface of a photochromic crystal by optical near-field induced photoisomerization

We observed nanometre-scale optical near-field induced photoisomerization on the surface of a photochromic diarylethene crystal via molecular structural changes using an optical near-field assisted atomic force microscope. A nanometre-scale concavity was formed on the sample surface due to locally induced photoisomerization. By using this optical near-field induced local photoisomerization, we succeeded in generating a pattern of alphabet characters on the surface of the diarylethene crystal below the optical wavelength scale. Further, by exploiting the photochromism of the investigated material, erasure of the generated pattern was also confirmed, where the evolution of the pattern during erasure depended on the local spatial characteristics of the crystal. These experimental findings demonstrate the fundamental abilities of photochromic crystals in dynamic memorization in nanometre-scale light–matter interactions.

Photochromic Crystalline Systems Mimicking Bio-Functions.

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.

Study on the Mechanism of Diarylethene Crystal Growth by In Situ Microscopy and the Crystal Growth Controlled by an Aluminum Plasmonic Chip.

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 needle-shaped 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.

Photosalient Phenomena that Mimic Impatiens Are Observed in Hollow Crystals of Diarylethene with a Perfluorocyclohexene Ring

AbstractA 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‐μm 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.

Photosalient Phenomena that Mimic Impatiens Are Observed in Hollow Crystals of Diarylethene with a Perfluorocyclohexene Ring.

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-μm 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.

Mechanical Behavior of Molecular Crystals Induced by Combination of Photochromic Reaction and Reversible Single-Crystal-to-Single-Crystal Phase Transition

We herein report a unique mechanical behavior of a molecular crystal induced by combination of a photochromic reaction and a reversible single-crystal-to-single-crystal (SCSC) phase transition. A crystal of a diarylethene having octyl group at both sides (1a) was found to undergo a reversible thermodynamic SCSC phase transition accompanying a change in crystal length, which was clarified by differential scanning calorimetry measurement, X-ray crystallographic analysis, and direct microscopic observation of the crystal length. Furthermore, upon irradiation with ultraviolet light, the diarylethene crystal exhibited an unusual photomechanical behavior. The mechanism of the behavior was proposed based on photoisomerization of the diarylethene from the open-ring isomer to the closed-ring isomer and a reversible thermodynamic SCSC phase transition, which was well-supported by thermal bending behavior of a photoirradiated crystal.

Dependence of Photoinduced Bending Behavior of Diarylethene Crystals on Ultraviolet Irradiation Power

The photoinduced bending behavior of diarylethene crystals upon irradiation with various ultraviolet (UV) light intensities was investigated. The bending velocity of the photoinduced bending crystals was estimated from the curvature of the bending crystal. The initial velocity of curvature change (Vinit) increased in proportion to the power of the incident UV light even when the crystal thickness was different, which suggests that the local strain caused by photoisomerization makes a cumulative contribution to the bending behavior. Moreover, for all UV light intensities, the relationship between Vinit and the crystal thickness was well explained by the easily handled Timoshenko bimetal model. This result provides a validated method for the quantitative evaluation of the photoinduced bending velocity in various molecular crystals.