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For changing environmental circumstances, interactive structural color (SC) observation is a promising strategy to store and express external information. SCs based on self-assembled block copolymer (BCP) photonic crystals have been a research focus due to their facile and diverse nanostructures relying on the volume ratio of blocks. Their unique nano-architectonics can reflect incident light due to constructive interference of the two different dielectric constituents. Their excellent ability to change nano-architectonics in response to external stimuli (i.e. humidity, temperature, pH, and mechanical force) allows for a programmable and stimuli-interactive BCP SC display. In this review, recent advances in programmable and stimuli-interactive SC displays with the 1-dimensional self-assembled BCP nano-architectonics are comprehensively discussed. First, this review focuses on the development of programmable BCP SCs that can store various information. Second, stimuli-interactive BCP SCs capable of responding reversibly to external stimuli are also addressed. Particularly, reversible BCP SC changes are suitable for rewritable displays and emerging human-interactive BCP SC displays that detect various human information through changes in electric signals with the simultaneous alteration of the BCP SCs. Based on previously reported literature, the current challenges in this research field are further discussed, and the perspective for future development is presented in terms of material, nano-architectonics, and process.

Background: This study aimed to evaluate the color matching, light transmittance, and reflectance characteristics of the novel flowable resin composite OCF-001 (OCF). Methods: Fifty-four resin composite molds were made with simulated class I cavities of A2, A3, and A4 shades by filling the rubber mold interspace with Estelite Sigma Quick (ESQ), Gracefil Putty (GP) and Filtek Supremme Ultra (FSU). After applying the adhesive, three different flowable resin composites (n = 6), OCF, Gracefil LoFlo (GLF), and Supreme Ultra Flowable (SUF), were used to fill the cavities. A colorimeter was used to measure the color parameters (CIEDE2000). The color measurements were taken immediately and after 28 days. Data were analyzed using the nonparametric Kruskal–Wallis (α = 0.05) and Wilcoxon tests. The light transmittance and reflection characteristics were measured with a black background using a spectrophotometer under D65 illumination. Results: The ΔE00, and ΔC of OCF was lower than other tested materials in A2 and A3 shades both immediately and after 28 days. OCF showed the highest transmittance characteristic, and a relatively stable reflectance curve in all the wavelengths. Conclusions: OCF showed better shade matching with the surrounding shades of A2 and A3, a relative uniform reflectance and higher light transmission properties.

For changing environmental circumstances, interactive structural color (SC) observation is a promising strategy to store and express external information. SCs based on self-assembled block copolymer (BCP) photonic crystals have been a research focus due to their facile and diverse nanostructures relying on the volume ratio of blocks. Their unique nano-architectonics can reflect incident light due to constructive interference of the two different dielectric constituents. Their excellent ability to change nano-architectonics in response to external stimuli (i.e. humidity, temperature, pH, and mechanical force) allows for a programmable and stimuli-interactive BCP SC display. In this review, recent advances in programmable and stimuli-interactive SC displays with the 1-dimensional self-assembled BCP nano-architectonics are comprehensively discussed. First, this review focuses on the development of programmable BCP SCs that can store various information. Second, stimuli-interactive BCP SCs capable of responding reversibly to external stimuli are also addressed. Particularly, reversible BCP SC changes are suitable for rewritable displays and emerging human-interactive BCP SC displays that detect various human information through changes in electric signals with the simultaneous alteration of the BCP SCs. Based on previously reported literature, the current challenges in this research field are further discussed, and the perspective for future development is presented in terms of material, nano-architectonics, and process.

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.

Bioinspired Structurally Colored Materials The striking coloration in the natural world is typically caused by light interference at nanostructured materials and the broadband light absorption of melanin pigments. In article 2300986, Nico Nees, Nicolas Vogel, and co‐workers use colloidal photonic crystals containing polydopamine as synthetic mimics of this structural coloration and investigate the total amount of absorber and the way of its incorporation to create the most saturated structural coloration.

Nanoparticles The cover art depicts a novel mechanically responsive optical device that modulates light transmission and generates iridescent structural colors under reflection. The optical transition arises from the exposure of nanoparticles upon stretching, which are initially embedded beneath the surface. This design is inspired by natural structural coloration found in species such as butterflies and flowers. More details can be found in the Research Article by Jae Sung Yoon and co‐workers (DOI: 10.1002/admi.202500640).

Living organisms have developed a wide range of appearances from iridescent to matte textures. Interestingly, angular-independent structural colors, where isotropy in the scattering structure is present, only produce coloration in the blue wavelength region of the visible spectrum. One might, therefore, wonder if such observation is a limitation of the architecture of the palette of materials available in nature. Here, by exploiting numerical modeling, we discuss the origin of isotropic structural colors without restriction to a specific light scattering regime. We show that high color purity and color saturation cannot be reached in isotropic short-range order structures for red hues. This conclusion holds even in the case of advanced scatterer morphologies, such as core-shell particles or inverse photonic glasses—explaining recent experimental findings reporting very poor performances of visual appearance for such systems.

Materials in nature are characterized by structural order over multiple length scales have evolved for maximum performance and multifunctionality, and are often produced by self-assembly processes. A striking example of this design principle is structural coloration, where interference, diffraction, and absorption effects result in vivid colors. Mimicking this emergence of complex effects from simple building blocks is a key challenge for manmade materials. Here, we show that a simple confined selfassembly process leads to a complex hierarchical geometry that displays a variety of optical effects. Colloidal crystallization in an emulsion droplet creates micron-sized superstructures, termed photonic balls. The curvature imposed by the emulsion droplet leads to frustrated crystallization. We observe spherical colloidal crystals with ordered, crystalline layers and a disordered core. This geometry produces multiple optical effects. The ordered layers give rise to structural color from Bragg diffraction with limited angular dependence and unusual transmission due to the curved nature of the individual crystals. The disordered core contributes nonresonant scattering that induces a macroscopically whitish appearance, which we mitigate by incorporating absorbing gold nanoparticles that suppress scattering and macroscopically purify the color. With increasing size of the constituent colloidal particles, grating diffraction effects dominate, which result from order along the crystal’s curved surface and induce a vivid polychromatic appearance. The control of multiple optical effects induced by the hierarchical morphology in photonic balls paves the way to use them as building blocks for complex optical assemblies—potentially as more efficient mimics of structural color as it occurs in nature.

Color reproduction is an important aspect of three-dimensional (3D) printing in terms of creating a colored visual appearance with high fidelity and stability. To this end, structural color is an ideal coloring mechanism, which processes unique nonfading ability and tunable optical features. In this study, we propose a printable structural color ink composed of cholesteric cellulose liquid crystals together with gelatin and a thermal-responsive hydrogel. The ink maintains a cholesteric liquid crystalline state that gives rise to the structural color, and the rheology properties of the ink are optimized by gelatin, which allows the ink to flow during printing and form self-supporting structures after printing. The incorporation of the hydrogel further enables shape maintenance of the ink after printing via in situ ultraviolet-crosslinking. Based on this, we print a series of graphics and 3D objects with angle-independent color appearances and demonstrate the versatility of the printing system in different substrates. Moreover, the printed objects possess dual thermal responsiveness, which results in visible color changes around body temperature. These performances, together with the biocompatibility of the constituents, indicate that the present ink represents a leap forward to the next-generation 3D printing and would unlock a wide range of real-life applications.

Disordered nanostructures with correlations on the scale of visible wavelengths can show angle-independent structural colors. These materials could replace dyes in some applications because the color is tunable and resists photobleaching. However, designing nanostructures with a prescribed color is difficult, especially when the application—cosmetics or displays, for example—requires specific component materials. A general approach to solving this constrained design problem is modeling and optimization: Using a model that predicts the color of a given system, one optimizes the model parameters under constraints to achieve a target color. For this approach to work, the model must make accurate predictions, which is challenging because disordered nanostructures have multiple scattering. To address this challenge, we develop a Monte Carlo model that simulates multiple scattering of light in disordered arrangements of spherical particles or voids. The model produces quantitative agreement with measurements when we account for roughness on the surface of the film, particle polydispersity, and wavelength-dependent absorption in the components. Unlike discrete numerical simulations, our model is parameterized in terms of experimental variables, simplifying the connection between simulation and fabrication. To demonstrate this approach, we reproduce the color of the male mountain bluebird (Sialia currucoides) in an experimental system, using prescribed components and a microstructure that is easy to fabricate. Finally, we use the model to find the limits of angle-independent structural colors for a given system. These results enable an engineering design approach to structural color for many different applications.