桑折 道済

Melanin is a widely occurring biopolymer and has been the subject of much research, especially in dermatology. However, from a resource perspective, melanin is still an unutilized biomass because of its complex three-dimensional cross-linked structure, which makes it challenging to handle. Here, we demonstrate melanin upcycling by decomposing melanin and preparing polymeric materials from its products. A detailed study of the chemical decomposition products of artificial melanin, i.e., polydopamine, reveals that the melanin decomposition products are mainly oligomeric pyrrole derivatives containing carboxylic acids. Furthermore, decomposition experiments using natural melanin extracted from cuttlefish ink revealed that the composition of melanin decomposition products is almost identical regardless of the melanin source. We proposed a melanin decomposition mechanism and demonstrated the preparation of biobased polymer films and particles from melanin decomposition products. The use of melanin decomposition products as building blocks for material preparation is expected to lead to the development of new biodegradable polymers from biomass.

The columnar polarization direction of ferroelectric columnar liquid crystals can be switched by applying an external electric field, and the polarization direction can be maintained, even after the electric field is removed. If the polarization direction of each column in ferroelectric columnar liquid crystals can be switched and maintained, then ultrahigh-density memory devices can be generated. Recently, we found that the columnar phase of N,N′-bis(3,4,5-tri(S)-citronellyloxyphenyl)urea (Urea-(S)-cit) shows ferroelectricity, whereas that of N,N′-bis(3,4,5-tridecyloxyphenyl)urea (Urea-10) does not. However, the mechanisms by which the six chiral alkoxy groups in Urea-(S)-cit generate ferroelectricity have not been determined. In this study, we regioselectively synthesized four diphenylurea compounds containing (S)-citronellyloxy and decyloxy groups, i.e., N,N′-bis(3,5-di((S)-citronellyloxy)-4-decyloxyphenyl)urea (1), N,N′-bis(4-((S)-citronellyloxy)-3,5-didecyloxyphenyl)urea (2), N,N′-bis(3-((S)-citronellyloxy)-4,5-didecyloxyphenyl)urea (3), and N,N′-bis(3,4-di((S)-citronellyloxy)-5-decyloxyphenyl)urea (4), and investigated which chiral alkoxy group at which position is strongly responsible for the ferroelectricity. The chiral alkoxy groups at 3- and 5-positions of the phenyl groups were clarified to play a significant role in the generation of ferroelectricity. Furthermore, a comparison of these four compounds based on circular dichroism spectroscopy and second harmonic generation experiments revealed the relationship between the helical structure order and the stability of the polarized structure.

Abstract Here, an unprecedented phenomenon in which 7‐coordinate lanthanide metallomesogens, which align via hydrogen bonds mediated by coordinated H₂O molecules, form micellar cubic mesophases at room temperature, creating body‐centered cubic (BCC)‐type supramolecular spherical arrays, is reported. The results of experiments and molecular dynamics simulations reveal that spherical assemblies of three complexes surrounded by an amorphous alkyl domain spontaneously align in an energetically stable orientation to form the BCC structure. This phenomenon differs greatly from the conventional self‐assembling behavior of 6‐coordinated metallomesogens, which form columnar assemblies due to strong intermolecular interactions. Since the magnetic and luminescent properties of different lanthanides vary, adding arbitrary functions to spherical arrays is possible by selecting suitable lanthanides to be used. The method developed in this study using 7‐coordinate lanthanide metallomesogens as building blocks is expected to lead to the rational development of micellar cubic mesophases.

The realization of ferroelectric columnar liquid crystals (FCLCs) capable of axial polarization switching along the column axis at room temperature (RT) is an important breakthrough in the practical application of FCLCs. However, molecules exhibiting FCLC phases generally have low fluidity at RT, which inhibits the response of polar functional groups to an applied external electric field, making changing the direction of the column polarity difficult. Here, we report RT-FCLCs, N,N′-bis(3,4-dialkoxyphenyl)ureas, driven by a low electric field. The introduction of bulky branched alkyl chains lowered the temperature range of the columnar liquid crystal phases, resulting in a fluid-assembled state with moderate hydrogen bonding that allowed polarization switching at RT. Comparison of these synthesized ureas revealed that reductions in the bulk and length of the side chains produced longer retention times of the polarization. Our thermodynamic analyses clarified that these ureas have high enough depolarization activation energy to maintain polarization, despite a low coercive field of a few V μm-1. Furthermore, the retention time of the columnar liquid crystal phase dramatically increased as the temperature neared RT, indicating an increase in the slowness of molecular motion, reminiscent of the vitrification process. We established a methodology to achieve FCLCs with the desired performance by selecting the alkyl chain to be introduced.

In this study, we show that doping lanthanides into lamellar crystals reorganizes the lamellar structure and dramatically changes the crystal morphology. Azo-DA, a compound with azobenzene derivatives and carboxylic acids at both ends of the diacetylene moiety, formed plate-like lamellar crystals. The doping of holmium (Ho), a lanthanide, into the film obtained by stacking Azo-DA lamellar crystals, promoted a dramatic change in crystal morphology, resulting in the formation of an Azo-DA/Ho film with a radial lamellar crystal structure. A detailed investigation of the crystal growth process revealed that Azo-DA/Ho, which is slightly formed in the solution phase during Ho doping, acts as a pseudonucleating agent and dramatically changes the morphology of the lamellar crystals. Additionally, the morphological changes in the lamellar crystal films significantly changed the surface properties of the films, such as their appearance and water repellency. Similar morphological changes in lamellar crystals were induced when other lanthanide elements were used instead of Ho, and the type of lanthanide dopant can affect the magnetic properties of the films.

Metal-lustrous porphyrin foils, self-standing films of fully π-conjugated polymers composed of a glassy porphyrin unit bearing the elastic 3,4,5-tri((S)-dihydrocitronellyloxy)phenyl groups, are disclosed. A remarkable refractive index of 3.04 due to the anomalous dispersion effect of the intense resonance absorption was found for the porphyrin foil of a polymer with a meso-to-meso 1,4-diethynylphenylene-linked backbone (1). Due to the anomalous dispersion effect, the sharp contrast between the intense absorption and specular reflection at the smooth glassy porphyrin foils provides a brilliant noniridescent green metallic luster. On the other hand, the porphyrin foil of a 1,4-diethynyl-2,3,5,6-tetrafluorophenylene-linked polymer with a conformation-locked conjugated backbone via the C-F···H-C interaction between and the edge-faced porphyrin β-protons (2) results in an insignificant refractive index presumably because of the low dielectric constant of fluorine. Nevertheless, the enlarged π-conjugated domain of 2 forms a stable ground-state biradical, while the open-shell character of 1 is moderate. The study reveals that brilliant metallic luster manifests the considerably delocalized π-system in a relatively bulk and/or macroscopic context rather than the molecular-scale properties.

Films that exhibit different metallic luster on the front and back, called Janus metallic films, have broad applications ranging from design materials to optical devices. However, the fabrication of these films is often a complicated process involving multiple metal deposition steps, thermal annealing, and calcination. Herein, we report the simple preparation of a Janus metallic film by electroless deposition of silver on a poly(dopamine acrylamide) (pDOPAm) thin film. pDOPAm was successfully synthesized via the controlled reversible addition-fragmentation chain transfer polymerization of dopamine acrylamide without a protective group using dimethylformamide as the solvent. The synthesized pDOPAm was spin-coated onto a solid substrate, which was then immersed in an aqueous AgNO3 solution to achieve the electroless deposition of silver. Our preparation method will considerably simplify the fabrication of Janus metallic films, enabling their widespread application as decorative or authentication materials.

The seven-coordinate Ho(III) aqua-tris(dibenzoylmethane)(DBM) complex, referred to as Ho-(DBM)3·H2O, was first reported in the late 1960s. It has a threefold symmetric structure, with Ho at the center of three dibenzoylmethane ligands and hydrogen-bonded water to ligands. It is considered that the hydrogen bonds between the water molecule and the ligands surrounding Ho play an important role in the formation of its symmetrical structure. In this work, we developed new force-field parameters for classical molecular dynamics (CMD) simulations to theoretically elucidate the structure and dynamics of Ho-(DBM)3·H2O. To develop the force field, structural optimization and molecular dynamics were performed on the basis of ab initio calculations using the plane-wave pseudopotential method. The force-field parameters for CMD were then optimized to reproduce the data obtained from ab initio calculations. Validation of the developed force field showed good agreement with the experimental crystalline structure and ab initio data. The vibrational properties of water in Ho-(DBM)3·H2O were investigated by comparison with bulk liquid water. The vibrational motion of water was found to have a characteristic mode originating from stationary rotational motion along the c-axis of Ho(III) aqua-tris(dibenzoylmethane). Contrary to expectations, the hydrogen-bond dynamics of water in Ho-(DBM)3·H2O were found to be almost equivalent to those of bulk liquid water except for librational motion. This development route for force-field parameters for CMD and the establishment of water dynamics can advance the understanding of water-coordinated metal complexes with high coordination numbers such as Ho-(DBM)3·H2O.

Tetraalkoxylated diphenylureas U-3,4-Scit and U-3,4-raccit were synthesized from chiral and racemic citronellyl bromides as starting materials, respectively. To prepare pyroelectric crystals, these two compounds were slowly cooled from their molten states. Although the two compounds have very similar molecular structures, they exhibited quite different electric-field responsiveness. U-3,4-Scit spontaneously polarized during the crystallization process, and almost no polarization switching was observed. On the other hand, U-3,4-raccit exhibited polarization switching in its crystalline state at a high-temperature range, and the polarization direction could be fixed by cooling the crystal to room temperature while applying a direct current voltage. This flexibility occurs because the alkyl chain parts in the crystal are disordered. These pyroelectric thin films are promising materials, as they function in a polycrystalline state without poling treatment.

In fabricating structural color materials with assembled colloidal particles, there is a trade-off between the internal stresses acting on the particles and the interactions between the particles during solvent volatilization. It is crucial to fabricate crack-free materials that maintain the periodic arrangements of the particles by understanding the mechanism for crack initiation. Here, we focused on the composition and additives of melanin particle dispersions to obtain crack-free structural color materials without disturbing the particle arrangements. The use of a water/ethanol mixture as a dispersant effectively reduced the internal stresses of the particles during solvent evaporation. Furthermore, the addition of low-molecular-weight, low-volatility ionic liquids ensured that the arrangement and interactions of the particles were maintained after solvent volatilization. Optimization of the composition and additives of the dispersion made it possible to achieve crack-free melanin-based structural color materials while maintaining vivid, angular-dependent color tones.

In fabricating structural color materials with assembled colloidal particles, there is a trade-off between the internal stresses acting on the particles and the interactions between the particles during solvent volatilization. It is crucial to fabricate crack-free materials that maintain the periodic arrangements of the particles by understanding the mechanism for crack initiation. Here, we focused on the composition and additives of melanin particle dispersions to obtain crack-free structural color materials without disturbing the particle arrangements. The use of a water/ethanol mixture as a dispersant effectively reduced the internal stresses of the particles during solvent evaporation. Furthermore, the addition of low-molecular-weight, low-volatility ionic liquids ensured that the arrangement and interactions of the particles were maintained after solvent volatilization. Optimization of the composition and additives of the dispersion made it possible to achieve crack-free melanin-based structural color materials while maintaining vivid, angular-dependent color tones.

Axially polar-ferroelectric columnar liquid crystals (AP-FCLCs) consist of nanosized axially polarized columnar molecular aggregates arranged in parallel, in which their polar directions can be switched by applying an electric field and maintained after removal of the electric field. However, the problem remains that the induced polarity can be disturbed by external stimuli because liquid crystals are fluid. To solve this problem, we planned to realize a smooth phase transition system from an AP-FCLC phase to a crystal phase without disturbing the induced polar structure. Thus, we designed a urea compound with two biphenyl groups and four 2-butyloctyl groups to achieve the system. As a result, we succeeded in realizing an AP-FCLC compound that transitions from the FCLC phase to the crystal phase at room temperature while maintaining the polarization induced in the FCLC phase, which is expected to enable long-term maintenance of polarization information.

Ferroelectric columnar liquid crystals have recently been expected to be utilized as high-density memory materials. In this study, we succeeded in realizing ferroelectric columnar liquid crystals by introducing a biphenyl moiety with two CF3 groups in the molecular center. In addition, the introduction enabled the liquid crystal to have a wide temperature range and exhibit an electroresponse at room temperature. This is the first example of ferroelectric columnar liquid crystals realized by using rotational isomerization of a laterally polar biphenyl moiety.

In this study, 3,4,5-trialkoxybenzyl pentafluorbenzoates with alkyl chains of various lengths were synthesised, and the phase transition behaviours, liquid crystallinities, and molecular packing structures of their columnar phases were investigated. The results showed that discs comprising two half-discoid molecules stack up to form columns with rack-gear structures, generating columnar liquid crystal phases. From powder and single crystal X-ray diffraction investigation, the mechanism of the self-assembly of molecules into columns and their intercolumnar interdigitation was postulated. Furthermore, it was revealed that the combination of alkyl groups of the benzyl groups was closely related to the type of columnar liquid crystal phases generated and the macroscopic morphologies of the liquid crystal domains.

In this study, core-shell-hairy-type melanin particles surface modified with a polydopamine shell layer and a polymer brush hairy layer were fabricated and assembled to readily obtain bright structural color films. The hot pressing of freeze-dried samples of melanin particles decorated with a hydrophilic, low glass transition temperature polymer brush results in films that exhibit an angle-dependent structural color due to a highly periodic microstructure, with increased regularity in the arrangement of the particle array due to the fluidity of the particles. Flexible, self-supporting, and easy-to-cut and process structural color films are obtained, and their flexibility and robustness are demonstrated using compression tests. This method of obtaining highly visible structural color films using melanin particles as a single component will have a significant impact on practical materials and applications.

In this study, we developed a method for fabricating conductive particles with an insulating layer on the surface, which can be applied to anisotropic conductive films. Core-shell particles were prepared from conductive nickel-plated core particles and positively charged polystyrene (PSt) shell particles carrying phosphonium groups on their surface by the heterocoagulation technique. The effect of alkyl chain lengths (ethyl, n-butyl, and n-octyl) of (4-vinylbenzyl)trialkylphosphonium chloride on the interfacial properties was investigated by surface tension measurement. Monodisperse PSt shell particles with a controlled particle size were successfully synthesized by emulsifier-free emulsion polymerization of styrene, (4-vinylbenzyl)triethylphosphonium chloride, and n-butyl acrylate. The effects of stirring time, temperature, NaCl concentration, and PSt shell particle concentration on heterocoagulation between the nickel-plated core particles and PSt shell particles were investigated. Uniform core-shell particles with a coverage of 60% could be prepared even though the heterocoagulation temperature was below the glass transition temperature and the NaCl concentration was below the critical coagulation concentration of the PSt shell particles. When the core-shell particles obtained through the heterocoagulation process were heated above the glass transition temperature of the shell particles for 6 h, a smooth polymeric insulating layer with melted shell particles was successfully formed on the surface of the nickel-plated core particles.

We demonstrated control of structural color visibility using colloidal particles covered with a catecholic polymer shell layer. When exposed to ammonia vapor, the pellet sample obtained by assembling the particles extended the conjugated length of the shell polymer, giving the particles the ability to absorb scattered light in situ and improving the visibility of structural colors.

Replacement of stearyl groups with oleyl groups in a discoid molecule induced a rectangular columnar phase at low temperature. Although the molecule has no hydrogen bonding sites, the induced liquid crystal phase showed a highly efficient chiral amplification. The helical packing structure was postulated based on its X-ray diffraction profile and circular dichroism spectra.

Holmium (Ho) is a lanthanide element with a high magnetic moment. Here, we create an amorphous metal-organic framework (MOF) that has no long-range periodic order but retains the basic components of MOF by using isophthalic acid as an organic linker and Ho as a metal species. The resulting spherical Ho-MOF particles disperse well in a solvent and exhibit excellent magnetic properties in response to magnets. Since Ho has almost no coloring, Ho-MOF particles are a colorless magnetic material, unlike conventional iron oxide particles. Taking advantage of the colorless property, the selective adsorption of dyes on Ho-MOF particles can be easily visually confirmed by magnetically separating the particles. In addition, present versatile processes that enable adaptation of lanthanide elements other than Ho enable the development of colorless multifunctional MOF particles.

In the field of columnar liquid crystals, a new type of thermo-optical switching material that shows a birefringence inversion without changing the columnar alignment by controlling the temperature was synthesized. The urea molecules generate one-dimensional linear molecular aggregates using urea-urea intermolecular hydrogen bonding and exhibit rectangular and hexagonal columnar phases. In polarized light optical microscopy, the texture perfectly disappears during the transition between the two columnar phases because it passes through the point where birefringence becomes zero. The inversion mechanism is explained by the conformational change of each molecule in the column. In this study, we propose a new switchable optical material in columnar liquid crystal phases.

An optical vortex possesses a ring-shaped spatial profile and orbital angular momentum (OAM) owing to its helical wavefront. This form of structured light has garnered significant attention in recent years, and it has enabled new investigations in fundamental physics and applications. One such exciting application is laser-based material transfer for nano-/micro-fabrication. In this work, we demonstrate the application of a single-pulse optical vortex laser beam for direct printing of ring-shaped structures composed of hexagonal close-packed, mono-/multi-layered nanoparticles which exhibit 'structural color'. We compare and contrast the interaction of the vortex beam with both dielectric and metallic nanoparticles and offer physical insight into how the OAM of vortex beams interacts with matter. The demonstrated technique holds promise for not only photonic-based nano-/micro-fabrication, but also as a means of sorting particles on the nanoscale, a technology which we term 'optical vortex nanoparticle sorting'.

Electro-optically responsive liquid crystal (LC) nanocapsules were prepared by miniemulsion polymerization of oil-in-water emulsion monomer droplets dissolving LC compounds. As theoretically predicted based on the spreading coefficients, the choice of capsule wall-forming monomers was important for the formation of the capsule structure. The copolymerization of fluorine-containing monomers effectively suppressed the interaction between the LC compound and the capsule wall, allowing the LC molecules to repeatedly change their orientation in response to an external electric field.

An axially polar-ferroelectric columnar liquid crystal (AP-FCLC) phase that exhibits both switching and maintenance of the macro-polarity in the column axis direction has been achieved in an N,N'-bis(3,4,5-trialkoxyphenyl)urea compound (rac-1) prepared from (±)-citronellyl bromide. Although it had been thought that chirality is necessary to achieve the AP-FCLC phase from our previous study, the optically inactive compound which is a mixture of 21 stereoisomers, generated an AP-FCLC phase. We confirmed its ferroelectricity and investigated the mechanism for realizing the AP-FCLC phase using optoelectronic experiments, X-ray diffraction, and circular dichroism spectroscopy. As a result, it was suggested that chiral self-sorting occurs in the columnar liquid crystal phase, in which molecules with a similar stereochemistry form a one-handed helical column, and columns with the same helicity gather together to form a chiral domain. Accordingly, we conclude that the optically inactive compound rac-1 also indicates ferroelectricity similar to that of an optically pure urea compound because of chiral self-sorting.

We demonstrate, for the first time, the fabrication of a monolayer photonic micro-ring formed of polydopamine coated monodisperse polystyrene particles by employing optical vortex induced forward mass transfer technique. Such interesting micro-ring formation will provide a new insight for interaction between the orbital angular momentum of light and matters.

Luminescent core–shell polymer particles carrying amino groups for covalent immobilization of enzymes were synthesized for practical applications in immunoassays. The polystyrene core particles were synthesized by miniemulsion polymerization of oil-in-water emulsion styrene droplets dissolving 2-(2-chloropropionyl)ethyl methacrylate and the europium complex emulsified with 2-methacryloyloxyethyl-N,N-dimethyl-N–n-dodecylammonium bromide. The red luminescence attributed to europium complexes embedded in the core particles was observed upon UV irradiation. The PSt-g-POEGMAx-NH2 aminated core–shell particles were prepared by surface-initiated atom transfer radical polymerization of oligo(ethylene glycol) methyl ether methacrylate (OEGMAx), followed by Gabriel synthesis. The densities of grafted chains were determined by the composition, the hydrodynamic diameters, and the fluorescence labeling method. POEGMAx-grafted chains were found to affect the dispersion stability of the particles. The nonspecific adsorption of bovine serum albumin was suppressed by the POEGMAx-grafted chains. The enzymatic activity of horseradish peroxidase covalently bound to the terminal amino groups of POEGMAx-grafted chains was evaluated by colorimetric immunosorbent assay.

An N, N'-diphenylurea derivative possessing six oleyloxy groups exhibited hexagonal columnar liquid crystal phases, and the columnar molecular aggregates were cross-linked with applying an electric field to produce a highly-ordered thin film which has a polarity in the thickness direction. The resulting aromatic polyurea film showed a relatively large vertical piezoelectric constant (d33 of 6.1 pm/V).

A chiral urea compound, N,N’-bis(4-(3,4,5-trialkoxyphenylmethyl)phenyl)urea (1a), possessing a long core and six chiral alkyl chains ((S)-citronellyl groups) was designed to construct a double helix supramolecular structure in a liquid crystal phase. As a result, the urea compounds exhibited a hexagonal columnar liquid crystal phase, and the molecules were self-organised into a double helix structure by intermolecular interactions (dipole-dipole interactions, hydrogen bonds, and π-π interactions). Furthermore, the compound’s responsive behaviour to an applied external electric field was investigated, and its phase transition behaviour, column alignment, columnar structures, and electro-responsiveness were compared with those of an achiral urea compound (1b) possessing six n-decyl groups to investigate the effect on introducing the chirality. These results indicated that higher-order structures such as double helices are effective in suppressing thermal motion and delaying polarisation relaxation.

Natural melanin affects the reflection and absorption of light, and it is known as an important element in producing bright structural colors in nature. In this study, we prepared core-shell particles using a melanin precursor polymer, that is, polytyrosine (PTy), as a shell layer by the oxidative polymerization of tyrosine ethyl ester (Ty) in the presence of cerium oxide (CeO2) core particles. Inspired by skin tanning, irradiating the CeO2@PTy core-shell particles with UV or natural sunlight caused melanization by extending the π-conjugated length of PTy, producing colloidal particles with the ability to absorb light. The pellet samples consisting of CeO2@PTy particles appeared whitish because of multiple scattered light. In contrast, the light absorption capacity of CeO2@PTy UV or CeO2@PTy Sun particles after light irradiation suppressed scattered light, dramatically improving the visibility of the structural color of the pellet samples made from these particles. Thus, a new method has been developed to control the visualization of structural colors to the human eye by irradiating the melanin precursor polymer with light.

Inspired by the coloring mechanism of insects, we demonstrated the preparation of metallic luster materials by a combination of dye absorption and specular reflection from layered microcrystals. Metallic luster films were prepared by the recrystallization of diacetylene derivatives with different linker chains bearing azobenzene moieties. The lamellar structure of the molecules formed plate-like microcrystals, which were piled up to form layered films. A gold-like texture was observed due to the combination of the absorption of the azobenzene moiety and specular reflection from the surface of layered microcrystals. The film of the diacetylene derivative with a dodeca-5,7-diynedioate moiety used as a linker maintained its golden color regardless of light or thermal stimuli. In contrast, the color of the film composed of the diacetylene derivative containing the docosa-10,12-diynedioate linker turned purple due to solid-state polymerization by UV-light irradiation and maintained its metallic gloss. Additionally, the glossy color changed reversibly with changing temperature. The responsiveness of metallic luster films to stimuli was controlled by changing the linker chain length. The photo- and thermal-responsive metallic luster materials presented here can have a significant impact on decoration and ink applications.

An inverse opal structure was created using artificial melanin particles composed of a polystyrene core and a polydopamine shell as the template. The melanin-mimicking polydopamine that remained inside the inverse opal structure effectively absorbed multiple scattered light, producing bright structural color that was reversibly changed by solvent penetration.

The present report describes the preparation of lanthanide-doped colorless magnetic materials based on poly-beta-ketoester particles. Monodisperse poly(2-acetoacetoxy ethyl methacrylate) (PAAEM) particles were prepared by dispersion polymerization using AAEM as the monomer in the presence of a cross-linker. Because of the swelling characteristics of the cross-linked PAAEM particles in solvent, the lanthanide was effectively doped inside the particles, and the distribution of the lanthanides in the particles was visualized. By creating terbium (Tb)-doped PAAEM particles (PAAEM/Tb), which has luminescence properties in addition to magnetic properties, the relationship between efficient lanthanide doping conditions and magnetism was clarified. Because of the low coloration of lanthanides, the resulting PAAEM/Tb particles were colorless magnetic materials compared with conventional iron oxide magnetic nanoparticles. Magnetic force microscope measurements revealed that each particle exhibited magnetism. In addition, because of the high dispersibility of PAAEM/Tb particles and their colorless nature, the inkjet printing of particles and preparation of composites with commodity polymers have been demonstrated. The present technique has been shown to be widely applicable to other lanthanides instead of Tb. This versatile process enables the development of colorless functional polymeric materials with magnetic properties.

Here, we have demonstrated the production of colorless and full-color magnetic nanoparticles based on holmium (Ho)-doped polymers, which could not be achieved with conventional dark brown iron oxide magnetic nanoparticles. The coordination of Ho, a lanthanide with low colorability and a strong magnetic moment, with a poly(2-acetoacetoxy ethyl methacrylate) brush built on the surface of submicron-sized silica particles allowed for the formation of colorless magnetic nanoparticles. Additionally, bright and full-color magnetic nanoparticles were obtained by mixing different colored magnetic nanoparticles that were prepared by copolymerization of 2-acetoacetoxy ethyl methacrylate and dye monomers. Various colors, including transparency, were demonstrated by means of the present method, which determines the presence or absence of magnetism by Ho doping. The bright and magnetically controllable colored nanoparticles presented herein may have a significant impact on practical substances and applications, such as ink and biomedical and device applications.

Melanin influences light reflection and absorption and is known to be one of the elements producing structural color, such as that in the feathers of birds. In this study, we used polydopamine (PDA), an artificial melanin, as a light-absorbing material and examined in detail the effect of its composite method on the structural color. The following two composite methods were investigated using cerium(IV) oxide (CeO2) particles as a core particle: binary coassembly of CeO2 and PDA particles and unary assembly of CeO2@PDA core-shell particles. While both methods dramatically improved the visibility of the structural color by suppressing the scattered light due to the light absorption capability of the PDA, there was a difference in the particle arrangement, angle dependence of the structural color, and color tone change. By selecting the PDA composite method, the guidelines for providing high visibility and the desired structural color were presented.

Structural color is a color derived from optical interaction between light and a microstructure and is often seen in nature. Natural melanin plays an important role in bright structural coloration. For example, the vivid colors of peacock feathers are due to structural colors. The periodic arrangement of melanin granules inside the feathers leads to light interference, and the black granules absorb scattered light well, resulting in bright structural color. In recent years, polydopamine (PDA) has attracted attention as a melanin mimetic material. This review article summarizes recent research on structural coloration using PDA-based artificial melanin materials. It also outlines possible applications using bright structural colors realized by artificial melanin materials and future perspectives.

Axially polar ferroelectric columnar liquid crystals (AP-FCLCs) are materials in which the molecules are self-organized into axially polar columns and exhibit switching and holding of their polar directions. If the polar directions along the columnar axis can be controlled by using a nanosized electrode, AP-FCLCs have the potential to realize ultrahigh-density memory devices. Though switching polarities in columnar liquid crystal phases have been studied by many scientists, it remains difficult to realize bistable switching. In this study, it is found that replacement of the normal alkyl groups (decyl groups) with chiral groups ((S)-citronellyl groups) in an N,N’-bis(3,4,5-trialkoxyphenyl)urea realizes perfect ferroelectricity in the rectangular columnar liquid crystal phase, and it is confirmed that the phase is an AP-FCLC phase. The differences in the properties and molecular packing structures between the achiral and chiral urea compounds are investigated. Furthermore, the mechanism for achieving ferroelectricity by introduction of the chiral alkyl chains is postulated.

Electroresponsive columnar liquid crystalline urea compounds, N,N’-bis(3,4,5-trialkyloxyphenyl)ureas 1 and 2 possessing six and four terminal double bonds, were photopolymerized by UV irradiation in the liquid crystal phases to give polymerized compounds, labeled P-1-Colh and P-2-Colh, that possessed a hexagonal columnar structure. Furthermore, the photo polymerization of 1 and 2 sandwiched between two indium tin oxide-deposited glass plates with applying an electric field (20 V μm−1), produced polymerized compounds, P-1-Colh-E and P-2-Colh-E, and polarized light optical microscopy clarified that the columns polymerized were aligned in parallel to the applied electric field. In addition, by the phenomenon that polar substances absorb laser light (λ = 1064 nm) and emit second harmonic generation light (λ = 532 nm), the difference in electro-response between P-1-Colh-E and P-2-Colh-E has been revealed. The former was a polymer whose macropolarity was completely fixed, and the latter was a polymer whose macropolarity was controllable by applying an external voltage.

In vivid structural coloration in the natural world, melanin plays an important role. For example, the coloring of peacock feathers is based on the periodic microstructure formed by melanin granules. Melanin, which has the ability to absorb light, not only builds a microstructure but also absorbs scattered light to produce highly visible structural colors. We focus on polydopamine as a mimic of melanin and the production of structural color materials from a biomimetic perspective. This review paper focuses on our recent findings on structural color materials using artificial melanin particles made of polydopamine and describes the research trends.

Ferroelectric columnar liquid crystals have received much attention as energy-saving electronic materials. In this study, an N,N¤-bis(3,4,5-tris((2-ethylhexyl)oxy)phenyl)urea was synthesized and characterized. As a result, the compound exhibited a ferroelectric columnar liquid crystal phase at low-temperature (63103°C), and succeeded in significantly lowering the temperature compared to conventional ferroelectric urea compounds (>105°C). This is the first example where ferroelectricity is greatly affected by the temperature in a columnar liquid crystal phase.

© 2019 Elsevier Inc. Liquid crystal nanocapsules (LC-Nanocapsules) were prepared by miniemulsion polymerization of the oil-in-water emulsion monomer droplets dissolving the liquid crystal (LC) compounds. In order to establish the preparation conditions of LC-Nanocapsules exhibiting the liquid crystallinity, the effects of the capsule wall-forming monomers and the crosslinking agent concentration on the capsule structure were investigated in detail. The monodisperse colloidal products covered with the robust polymer shell wall was successfully prepared by the polymerization of the emulsion monomer droplets obtained through the phase inversion temperature emulsification technique using the amphiphilic block copolymer as an emulsifier. The endothermic peak was observed at the nematic-isotropic phase transition temperature (TNI) of the LC in the differential scanning calorimetry diagram of LC-Nanocapsules. The bright- and dark-field images of the dried thin films of LC-Nanocapsules spread on a glass substrate were found to appear repeatedly by the temperature change below and above TNI by polarized optical microscopic analysis. These results revealed that the LC-Nanocapsules with a complete engulfing morphology were successfully formed by the spontaneous coacervation phenomena between the crosslinked polymer and the LC with a progression of the polymerization, as theoretically predicted from the viewpoint of the spreading coefficients.

Photochromic materials have attracted considerable attention for their practical applications in optoelectronic devices. In this study, we developed the photochromic liquid core nanocapsules by polymerization of oil-in-water (O/W) nanoemulsion monomer droplets on the basis of Hansen solubility parameters. The thermoresponsive amphiphilic block copolymers (POEGMAm-b-PStn and POEGMAm-b-PMMAn) were synthesized by sequential reversible addition fragmentation chain transfer (RAFT) polymerization of hydrophilic oligo(ethylene glycol) methyl ether methacrylate and hydrophobic styrene or MMA. The O/W nanoemulsion methyl methacrylate (MMA) droplets, dissolving dipropylene glycol methyl-n-propyl ether (DPMNP) and (E)-3-(adamantan-2-ylidene)-4-[1-(2,5-dimethyl-3-furyl) ethylidene]dihydro-2,5furandione (Aberchrome 670) as a core liquid and a photochromic dye, respectively, were obtained through the phase inversion temperature emulsification technique using POEGMAm-b-PStn as a surfactant. As theoretically predicted in terms of the spreading coefficients, the DPMNP solution of Aberchrome 670 was successfully encapsulated by coacervation of the crosslinked PMMA condensed phase. Aberchrome 670 dissolved in a liquid core was found to photoisomerize twice as fast as that dispersed in the solid polymer matrices.

Inspired by the structural coloration of anisotropic materials in nature, we demonstrate the preparation of structural color materials by the assembly of anisotropic particles. Spherical artificial melanin particles consisting of a polystyrene core and polydopamine shell were stretched asymmetrically to form uniform-sized ellipsoidal particles with different aspect ratios. The aspect ratio and assembly method of the ellipsoidal particles influence the structural coloration, indicating that the particle shape is one of the important parameters for controlling the structural coloration. The discovery of a method to control the structural color using ellipsoidal particles is useful in basic research on structural colors in nature and provides flexibility in material design and extends the application range of structural color materials.

Herein, we present a method for controlling the surface properties of a substrate through exposure of the catechol group by acid stimulation. The results showed that the wettability and adhesion properties of the surface of the substrate can be controlled by acid treatment or UV irradiation in the presence of a photoacid generator. These findings will provide new insights into the development of materials with controlled surface properties.

A novel bisurea compound showed columnar liquid crystal phases possessing a new functionality, polarity-adjustability. Its molecular packing structures were analyzed by X-ray diffraction (XRD), and its polarity switching behavior and magnitude of the polarity were examined by electro-optic and second harmonic generation (SHG) experiments, respectively. As a result, it was revealed that the macroscopic polarity gradually increased with every ON/OFF cycle in SHG experiment applying an electric field. This strongly suggests that the anti-parallel hydrogen bonding network in each of the columns is reconstructed to syn-parallel by applying the electric field intermittently. Furthermore, it was confirmed that the reconstructed network mostly remained even once the temperature was raised to its isotropic state.

Inspired by the structural coloration of anisotropic materials in nature, we demonstrate the preparation of structural color materials by the assembly of anisotropic particles. Spherical artificial melanin particles consisting of a polystyrene core and polydopamine shell were stretched asymmetrically to form uniform-sized ellipsoidal particles with different aspect ratios. The aspect ratio and assembly method of the ellipsoidal particles influence the structural coloration, indicating that the particle shape is one of the important parameters for controlling the structural coloration. The discovery of a method to control the structural color using ellipsoidal particles is useful in basic research on structural colors in nature and provides flexibility in material design and extends the application range of structural color materials.

Lanthanide composites having functionalities due to lanthanide elements, such as magnetic and luminescent properties, are of interest because of their use in various applications and their scientific importance. In this study, we prepared transparent materials with both magnetic and luminescent properties by immobilizing terbium on nanogel particles. The resulting materials were optically transparent, responded quickly to a magnet, and showed green fluorescence.

By introducing an oleyl group at the end of the straight rodlike molecule, the effect of the tail shape on the liquid crystallinity, biaxiality, and lateral switching behavior of the smectic A phase was investigated. Three types of molecules possessing a fluorinated phenyl (pentafluorophenyl, 2,3,4-trifluorophenyl, or 2,3-difluorophenyl) group and a cis-octadec-9-enyl group were synthesized, and their liquid crystallinities were compared with the corresponding molecules with a straight alkyl ( trans-octadec-9-enyl or n-octadecanyl) group. In switching experiments, the molecules with a bent terminal chain showed higher spontaneous polarization ( Ps) values than those with a straight terminal chain. Further, the directional changes of the long molecular axes were suppressed for the molecules possessing a bent terminal chain. These results show that the introduction of a bent terminal chain is highly effective for stabilizing ferroelectric switching behaviors.

Nature creates beautiful structural colors, and some of these colors are produced by nanostructural arrays of melanin. Polydopamine (PDA), an artificial black polymer produced by self-oxidative polymerization of dopamine, has attracted extensive attention because of its unique properties. PDA is a melanin-like material, and recent studies have reported that photonic materials based on PDA particles showed structural colors by enhancing color saturation through the absorption of scattered light. Herein, we describe the preparation of three-dimensional (3D) colloidal photonic materials, such as structural color balls and fibers, from biomimetic core shell particles with melanin-like PDA shell layers. Structural color balls were prepared through the combined use of membrane emulsion and heating. We also demonstrated the use of microfluidic emulsification and solvent diffusion for the fabrication of structural color fibers. The obtained 3D colloidal materials, i.e., balls and fibers, exhibited angle-independent structural colors due to the amorphous assembly of PDA-containing particles. These findings provide new insight for the development of dye-free technology for the coloration of various 3D colloidal architectures.

Polydopamine (PDA) is of interest as a mimetic material of melanin to produce structural color materials. Herein, to investigate the influence of the material composition of the artificial melanin particles on structural color, we demonstrated the preparation of core-shell particles by polymerization of norepinephrine or 3,4-dihydroxyphenylalanine, which are melanin precursors similar to dopamine, in the presence of polystyrene particles. It was revealed that the arrays of the prepared particles produce high-visibility structural color because of absorption of scattering light. Although poly(3,4-dihydroxyphenylalanine) showed the same tendency as PDA which was previous studied, polynorepinephrine can easily produce a smooth and thick shell layer compared with that of PDA, and pellets consisting of the particles showed angle-dependent structural color. Therefore, the artificial melanin particles that produce angle-dependent structural color became stable than ever before. These results indicated that material compositions of artificial melanin particles have influence on structural color, and an important finding for application as a coloring material was obtained.

Holmium (Ho), one of the lanthanide elements, shows a high magnetic moment. Here we present a simple, yet highly potential approach for preparing polymer-based magnetic materials from a three-dimensional polymer network composed with poly(acrylic acid) and Ho showing trivalent nature. We have successfully prepared a magnetic polymer network that reacts directly to a magnet by three-dimensionally immobilizing Ho in the polymer matrix. The present method allowed a preparation of wide range of magnetic materials using polymeric scaffolds, e.g., polymer-grafted particles and cross-linked polymer gels. As a result of the high Ho content, these materials responded quickly to the magnet. The discovery of a method to prepare magnetic materials will provide flexibility in materials design and greatly expand the scope of application of magnetic materials.