Dynamic Color Change Research Articles

Dynamic color change in the grouper Variola louti during interspecific interactions and swimming

Abstract Animals can change their body color for various ecological functions. In fish, rapid dynamic color change is primarily known in contexts of intraspecific communication and camouflage, while examples in interspecific contexts are rare. We studied dynamic color changes and their associated behaviors in the grouper Variola louti in its native coral reef environment in the Red Sea. Using underwater videos to record natural behaviors and color-calibrated still images to measure body colors, we quantified color displays as the brightness of the body and the contrast of three distinct patterns: body patches, head stripe, and side bars. V. louti exhibited a diverse range of pattern displays, which rapidly transformed according to its behavioral shifts. A high-contrast head stripe pattern was observed when V. louti engaged in agonistic interspecific interactions, but was interestingly absent when hunting alone or in cooperation with moray eels. The brightness of V. louti’s body color and the contrasts of the body patches and side bars were associated with its swimming behavior. Darker body colors and high contrast body patches and side bars were expressed when the fish rested on the bottom, whereas bright and uniform body colors were displayed when swimming higher above the reef. Our results suggest that V. louti utilizes dynamic color displays for camouflage and interspecific communication in agonistic and competitive interspecific interactions. These findings highlight the importance of dynamic color changes for communication and provide valuable insights into the behavioral ecology of animals.

A Streamlined Approach to Anticounterfeiting Technologies: Patterned AAO Membranes Based on Photonic Crystal Effects with Tunable Color Shifts and pH Responsiveness.

Anticounterfeiting technologies have become increasingly crucial due to the growing issue of counterfeit goods, particularly in high-value industries. Traditional methods such as barcodes and holograms are prone to replication, prompting the need for advanced, cost-effective, and efficient solutions. In this work, a practical application of anodic aluminum oxide (AAO) membranes are presented for anticounterfeiting, which addresses the challenges of high production costs and complex fabrication processes. Unlike previous approaches requiring metal coatings for color generation, this method uses commercial aluminum foils to produce colorful AAO membranes without metal layers. Elemental mapping suggests that impurities on the aluminum surface contribute to enhanced reflectivity, aiding photonic crystal formation. A two-step anodization process that creates patterned AAO membranes is further introduced, with the pattern clarity controlled by anodization time. Additionally, a pH-responsive film composed of 2-anilino-6-dibutylaminofluoran (ODB-2) and thermoplastic polyurethane (TPU) is integrated, enabling dynamic color changes under varying pH conditions, further enhancing the anticounterfeiting functionality. This streamlined approach provides a scalable and cost-effective solution for developing versatile AAO membranes for industrial anticounterfeiting applications.

Dynamic colour change in zebrafish (Danio rerio) across multiple contexts.

Many animals are capable of rapid dynamic colour change, which is particularly well represented in fishes. The proximate mechanisms of dynamic colour change in fishes are well understood; however, less attention has been given to understanding its ecological relevance. In this study, we investigate dynamic colour change in zebrafish (Danio rerio) across multiple contexts, using a protocol to image the colouration of live fish without anaesthesia under standardized conditions. We show that zebrafish respond to different visual environments by darkening their overall colouration in a dark environment and lightening in a light environment. This is consistent with crypsis through background matching as a function of dynamic colour change. Additionally, we find that zebrafish use dynamic colour change to increase the internal contrast of their striped patterning in the presence of conspecifics. We speculate that this may function in social signalling and/or dazzle colouration. We find no effect of a predator stimulus on dynamic colour change. Finally, we discuss the potential for zebrafish to use multiple colouration strategies simultaneously as distance-dependent effects, considering the typical viewing distances of zebrafish and their predators.

Cephalopod‐Inspired MXene‐Integrated Mechanochromic Cholesteric Liquid Crystal Elastomers for Visible‐Infrared‐Radar Multispectral Camouflage

Multispectral camouflage materials play a vital role in sophisticated multi‐band electromagnetic (EM) applications. However, conventional single‐band stealth is difficult to align with the growing demand for multi‐band compatibility and intelligent adaptation. Herein, we report the design and synthesis of cephalopod‐inspired MXene‐integrated cholesteric liquid crystal elastomers (MXene‐CLCEs) with multispectral camouflage capability, which was fabricated through in situ thiol‐acrylate Michael addition and free‐radical photopolymerization of CLCE precursor and isocyanate‐mediated robust covalent chemical bonding of MXene nanocoating at the interface. The resulting MXene‐CLCE exhibits dynamic structural color changes, tunable infrared radiation, and switchable microwave shielding across wide ranges upon mechanical stretching, with its infrared stealth and microwave shielding properties being realized through the reconfiguration of surface morphology from planar to cracked states via mechanical actuation. A visible‐to‐infrared camouflage octopus‐patterned MXene‐CLCE is demonstrated to achieve a stealth effect across the visible‐infrared spectrum upon mechanical stretching. As an illustration, proof‐of‐concept pneumatic‐driven octopus‐inspired soft models are demonstrated, which enables dynamic visible‐infrared camouflage and microwave shielding switching between two compatible states. The research herein can offer new perspectives on the development of bioinspired smart camouflage materials and their application in smart optical stealth, dynamic thermal management, and switchable electromagnetic devices.

Cephalopod-Inspired MXene-Integrated Mechanochromic Cholesteric Liquid Crystal Elastomers for Visible-Infrared-Radar Multispectral Camouflage.

Multispectral camouflage materialsplay a vital role in sophisticated multi-band electromagnetic (EM) applications. However, conventional single-band stealth is difficult to align with the growing demand for multi-band compatibility and intelligent adaptation. Herein, we report the design and synthesis of cephalopod-inspired MXene-integrated cholesteric liquid crystal elastomers (MXene-CLCEs) with multispectral camouflage capability, which was fabricated through in situ thiol-acrylate Michael addition and free-radical photopolymerization of CLCE precursor and isocyanate-mediated robust covalent chemical bonding of MXene nanocoating at the interface. The resulting MXene-CLCE exhibits dynamic structural color changes, tunable infrared radiation, and switchable microwave shielding across wide ranges upon mechanical stretching, with its infrared stealth and microwave shielding properties being realized through the reconfiguration of surface morphology from planar to cracked states via mechanical actuation. A visible-to-infrared camouflage octopus-patterned MXene-CLCE is demonstrated to achieve a stealth effect across the visible-infrared spectrum upon mechanical stretching. As an illustration, proof-of-concept pneumatic-driven octopus-inspired soft models are demonstrated, which enables dynamic visible-infrared camouflage and microwave shielding switching between two compatible states. The research herein can offer new perspectives on the development of bioinspired smart camouflage materials and their application in smart optical stealth, dynamic thermal management, and switchable electromagnetic devices.

Chromatic Resonance: Investigating the Effects of Dynamic Color Changes on Human Emotional Responses

This study investigates the impact of dynamic color changes on human emotional responses by exploring variations in color saturation and transition modes. Previous research has established that static colors evoke specific emotional associations; for example, red is linked with vitality and enthusiasm, blue with sadness and tranquility, and green with nature and freshness. To expand on this understanding, an experiment was designed utilizing the Berkeley Color Project 32 (BCP-32), where participants were grouped to observe three types of video stimuli: discrete high-saturation transitions between red and blue, continuous high-saturation transitions between yellow and violet, and continuous low-saturation transitions between the same colors. Following the viewing, participants completed a questionnaire to assess their emotional reactions. The findings indicate that while the mode of color transitiondiscrete or continuousdid not significantly alter emotional responses, changes in color saturation produced noticeable effects on participants' emotions. This suggests that the intensity of a color, rather than the manner of its change, plays a more pivotal role in influencing human emotional states.

Retroreflective Multichrome Microdome Arrays Created by Single-Step Reflow.

Structural colors are known for their tunability, fade resistance, and eco-friendliness. Recent advancements have shown that such colors can be efficiently produced using total internal reflection (TIR) on high-refractive-index convex microstructures without the need for periodic nanostructures. However, a reproducible, fast, and programmable production strategy for these microstructures is essential for commercial applications. Here, a single-step method is reported for creating multicolor patterns by transforming photolithographically-patterned micropillars into microdomes through thermal reflow. These micropillars, uniform in height but varying in diameter, are converted into microdomes that differ in diameter and height, which display a full spectrum of structural colors, creating a versatile color palette. This process enables the production of high-resolution multicolor graphics using a rainbow color set, with high reproducibility. Additionally, by mixing distinct microdomes and adjusting their densities, a rich variety of color presentations can be achieved, enabling the recreation of arbitrary color images with microdome arrays. The variable heights of the microdomes also allow for dynamic discoloration or color changes through mechanical compression. The high reproducibility and scalability of this method hold significant commercial promise for various optical applications.

Multiomics analysis reveals the involvement of OnDIVARICATA 3 in controlling dynamic flower coloring of Oncidium hybridum

Flower color is one of the main quality and economic traits of ornamental plants, and a large amount of research on flower color mainly focuses on the differences between varieties, while there were few reports on the change of flower color at different developmental stages. In this study, the metabolome and transcriptome of a new strain ‘XM-1’ with dynamic color changes of Oncidium were analyzed. The results showed that rutin, quercetin and carotenoids metabolism decreased significantly during the change of color from yellow to white. Analyzing the correlation network between metabolites and differential expressed genes, 25 key structural genes were detected and regulated by multiple MYB-related transcription factors. The MYB-related transcription factor Cluster-100966.1_OnDIVARICATA 3 was selected for further analysis. The phylogenetic tree of DIVARICATA in different species of Orchidaceae and Arabidopsis thaliana was constructed and the most closely related members were selected for sequence comparison. The results showed that OnDIVARICATA 3 contained MYB-like conserved domains. Subcellular localization results showed that OnDIVARICATA 3 was located in the nucleus. In overexpressing OnDIVARICATA 3 transgenic hairy roots, the expression of flower color related genes FLS, ZEP, and CHYB were significantly up-regulated. In summary, this study characterized the key metabolic pathways in the formation of the dynamic flower color of Oncidium hybridum, and constructed the regulatory network of the MYB-related. These results laid a theoretical foundation for the subsequent research on flower color and genetic engineering technology breeding of Oncidium hybridum.

Vapor Absorption and Liquefication Triggered Dynamic Color Changes and Pattern Conversions on Photonic Crystal Films for Anticounterfeiting.

The widespread use of counterfeit goods caused significant damage to economy, personal data security, and public health. There is an urgent need to develop innovative anticounterfeiting materials to enhance their performance. Anticounterfeiting labels based on responsive photonic crystals have been widely researched for the inherent difficulty in replicating the delicate structures and structure colors. By integrating various distinct nanoparticles (NPs), it is expected to produce photonic crystal patterns that offer more intricate color effects and improved anticounterfeiting capabilities. In this work, we reported a photonic crystal anticounterfeiting label with dynamic color variations in solvent vapors and pattern conversions upon vapor liquefication by utilizing three different nanoparticles including d-SiO2, h-SiO2, and m-SiO2 NPs as building blocks. This anticounterfeiting label exhibits a wealth of dynamic color changes associated with the absorption time, absorption rate, absorption medium, and microstructure of the nanoparticles, offering diverse visual effects and showcasing interesting anticounterfeiting performances. The dynamic color change or pattern conversion effect of this photonic crystal (PC) pattern is realized through refractive index changes induced by vapor absorption or solvent filling, which involves no volume changes and shows exceptional durability for repeated applications. This label shows promising broad applications in anticounterfeiting areas.

Ultra-Fast Fabrication of Mechanical-Water-Responsive Color-Changing Photonic Crystals Elastomers and 3D Complex Devices.

The traditional fabrication of opal-structured photonic crystals is constrained by the rate of solvent evaporation, a process that is not only time-consuming but also labor-intensive. This study introduces a paradigm shift by incorporating silica nanoparticles (SiNPs) with high zeta potentials and hydrogen bonding capabilities into an elastomeric matrix, resulting in a novel non-close-packed structure. This innovation circumvents the limitations of conventional methods by enabling the rapid formation of photonic inks (PI) into vibrant and luminous photonic elastomers (PEs) within seconds. These PEs demonstrate remarkable mechanochromic properties, exhibiting dynamic color changes across the visible spectrum in response to tensile and compressive deformations. Furthermore, the presence of hydroxyl groups endows the PEs with superior water-responsiveness, which can be finely tuned through the ink formulation. The elimination of solvent evaporation dependency facilitates the fabrication of macroscopic photonic crystal devices with complex geometries using digital light processing (DLP)-based 3D printing. This approach ensures exceptional optical performance and high customization potential. The resulting PEs hold significant promise for applications in smart wearables, soft robotics, and advanced human-machine interface technologies.

Selective colorimetric sensors and diagnostic microfiber yarn for carbonyl groups via ion-pairing dyes with plural chromatic behaviors

An ideal chemo-responsive dye requires several essential features, including a facile preparation method, a broad range of dynamic color changes, and colorimetric responses to multiple stimuli. Herein, we present a simple and reliable procedure for synthesis of chemo-responsive dye from ion-pair formation of oppositely charged dyes. The ion-pairing dye exhibits various colorimetric responses to pH levels and amine concentrations, indicating that the dye has plural chromatic behaviors and wide visible spectrum: ‘halochromism’ and ‘solvatochromism’. Due to this, our colorimetric sensors can selectively identify various carbonyl groups such as ketone, aldehyde, and carboxylic acid, in which the detection limits range from a minimum of 0.019 to maximum of 2.506 ppm. Furthermore, the sensing array composed of a single ion-pairing dye enables the generation of easily identifiable color-patterns as unique fingerprints for each carbonyl groups across a range of gas levels. Based on these colorimetric responses to carbonyl groups, we develop dye-loaded microfiber yarn for biomarker diagnosis, which can check for the presence of acetone gas in the exhaled breaths and confirm whether an individual is in the optimal ketosis state or not.

Thermochromic pastes for reversible dynamic simulation of colors and visible reflection spectra of green leaf and soil

In the field of camouflage, smart color-changing devices that can accurately adapt to different outdoor environments are a current research hotspot. However, traditional color-changing devices can be indistinguishable from the naked eye but cannot deceive advanced hyperspectral detectors, due to the visible reflectance spectrum difference between color-changing devices and the environmental background. Herein, a novel thermochromic paste is developed to achieve an accurate simulation of colors and reflection spectra of green leaves and soils. The paste displays a green color at < 30 °C and a soil-yellow color at > 30 °C, respectively. By further optimizing the dye ratio, the pastes can accurately simulate the reflection spectra of green leaves and soil. The spectral similarity between the pastes and green leaves and soils can be as high as 0.9674 and 0.9886, respectively. Moreover, the paste realizes reversible dynamic color change in 6 s and still possesses stable simulation after 100 times of cooling down and warming up. The thermochromic paste provides new insights for the development of multi-scene, multi-climate, and multi-band camouflage materials.

Carbon Dots-Inked Paper with Single/Two-Photon Excited Dual-Mode Thermochromic Afterglow for Advanced Dynamic Information Encryption.

Achieving thermochromic afterglow (TCAG) in a single material for advanced information encryption remains a significant challenge. Herein, TCAG in carbon dots (CDs)-inked paper (CDs@Paper) is achieved by tuning the temperature-dependent dual-mode afterglow of room temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF). The CDs are synthesized through thermal treatment of levofloxacin in melting boric acid with postpurification via dialysis. CDs@Paper exhibit both TCAG and excitation-dependent afterglow color properties. The TCAG of CDs@Paper exhibits dynamic color changes from blue at high temperatures to yellow at low temperatures by adjusting the proportion of the temperature-dependent TADF and phosphorescence. Notably, two-photon afterglow in CDs-based afterglow materials and time-dependent two-photon afterglow colors are achieved for the first time. Moreover, leveraging the opposite emission responses of phosphorescence and TADF to temperature, CDs@Paper demonstrate TCAG with temperature-sensing capabilities across a wide temperature range. Furthermore, a CDs@Paper-based 3D code containing color and temperature information is successfully developed for advanced dynamic information encryption.

Dynamic Photonic Janus Colloids with Axially Stacked Structural Layers.

Diblock copolymer (dBCP) particles capable of dynamic shape and color changes have gained significant attention due to their versatility in programmable shapes and intricate nanostructures. However, their application in photonic systems remains limited due to challenges in achieving a sufficient number of defect-free photonic layers over a tens-of-micrometer scale. In this study, we present a pioneering demonstration of photonic dBCP particles featuring over 300 axially stacked photonic layers with responsive color- and shape-transforming capabilities. Our approach leverages the complex interplay between the macrophase separation of multiple incompatible components and the microphase separation of dBCP from solvent-evaporative microemulsions. Specifically, continuous phase separation of silicone oil from polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP), triggered by solvent evaporation, promotes the anisotropic growth of PS-b-P2VP layers. This results in the formation of Janus colloids, where an oil droplet merges with a nanostructured polymer cone and lamellar structures align along the long axis of the cone. We highlight the capability to precisely adjust the particle morphology and the corresponding orientation, dispersion, and structural color window by modulating both the molecular weight of PS-b-P2VP and the volume ratio between PS-b-P2VP and silicone oil. Furthermore, reversible swelling/deswelling of photonic colloids is visualized and correlated with their structural colors. Finally, we demonstrate the potential of this study by presenting a multicolor-patterned array of photonic colloids, highlighting the possibilities for applications in smart photonic ink and devices.

UV-induced feather color change reflects its porphyrin content.

Pigmentary coloration is widespread in animals. Its evolutionary and ecological features are often attributed to the property of predominant pigments; therefore, most research has focused on predominant pigments such as carotenoids in carotenoid-based coloration. However, coloration results from predominant pigments and many other minority pigments, and the importance of the latter is overlooked. Here, we focused on porphyrin, an "uncommon" pigment found in bird feathers, and investigated its importance in the context of feather color changes in the barn swallow Hirundo rustica. We found that the "pheomelanin-based coloration" of the barn swallow faded after the irradiation of UV light, and this effect was particularly strong in the feathers of young swallows (nestlings and fledglings, here). We also found that it is not the predominant pigment, pheomelanin, but protoporphyrin IX pigment that showed the same pattern of depigmentation after the irradiation of UV light, particularly in the feathers of young swallows. In fact, the abovementioned age-dependent feather color change was statistically explained by the amount of porphyrin in the feathers. The current study demonstrates that a minority pigment, porphyrin, explains within-season dynamic color change, an ecological feature of feather coloration. The porphyrin-mediated rapid color change would benefit young birds, in which feather coloration affects the parental food allocation during a few weeks before independence, but not later. Future studies should not ignore these minor but essential pigments and their evolutionary and ecological functions.

Topologically Engineered Strain Redistribution in Elastomeric Substrates for Dually Tunable Anisotropic Plasmomechanical Responses.

The prompt visual response is considered to be a highly intuitive tenet among sensors. Therefore, plasmomechanical strain sensors, which exhibit dynamic structural color changes, have recently been developed by using mechanical stimulus-based elastomeric substrates for wearable sensors. However, the reported plasmomechanical strain sensors either lack directional sensitivity or require complex signal processing and device design strategies to ensure anisotropic optical responses. To the best of our knowledge, there have been no reports on utilizing anisotropic mechanical substrates to obtain directional optical responses. Herein, we propose an anisotropic plasmomechanical sensor to distinguish between the applied force direction and the force magnitude. We employ a simple strain-engineered topological elastomer to mechanically transform closely packed metallic nanoparticles (NPs) into anisotropic directional rearrangements depending on the applied force direction. The proposed structure consists of a heterogeneous-modulus elastomer that exhibits a highly direction-dependent Poisson effect owing to the periodically line-patterned local strain redistribution occurring due to the same magnitude of applied external force. Consequently, the reorientation of the self-assembled gold (Au)-NP array manifests dual anisotropy, i.e., force- and polarization-direction-dependent plasmonic coupling. The cost-effectiveness and simple design of our proposed heterogeneous-modulus platform pave the way for numerous optical applications based on dynamic transformation and topological inhomogeneities.

Adaptive coloration enabled by the reversible osmotic annealing of chromatophore-like microcapsules

Generating dynamic color change in an adaptive, bio-inspired microcapsule that can be activated to reversibly switch between pigment-based and structure-based coloration mechanisms.

Chameleon-like Photoluminescent Janus Nanoparticles as Full-Color Multicomponent Organic Nanoinks: Combination of Förster Resonance Energy Transfer and Photochromism for Encryption and Anticounterfeiting with Multilevel Authentication.

Increasing the security by the multilevel authentication mechanism was the most significant challenge in recent years for the development of anticounterfeiting inks based on photoluminescent nanomaterials. For this purpose, the greatest strategy is the use of multicomponent organic materials and a combination of Förster resonance energy transfer (FRET) with the intelligent behavior of photochromic compounds like spiropyran. Here, the hydroxyl-functionalized polymer nanoparticles were synthesized by emulsion copolymerization of methyl methacrylate (MMA) and 2-hydroxyethyl methacrylate (HEMA) in different compositions (0-30 wt % of HEMA). Results illustrated that the size of the nanoparticles changed from 64 to 204 nm, and a morphology evolution from spherical to Janus shape was observed by increasing the concentration of HEMA. Photoluminescent inks with red, green, and blue (RGB) fluorescence emissions were prepared by modification of nanoparticles containing 15 wt % of HEMA with spiropyran, fluorescein, and coumarin, respectively. To develop dual-color and multicolor photoluminescent inks that display static and dynamic emission, RGB latex samples were mixed together in different ratios and printed on cellulosic paper. Results display that the fluorescence emission of developed inks can be photoswitched between different statuses, including white to blue, green to blue, green to red/orange, purple to pink, and white to pink, utilizing the FRET phenomenon, photochromism, and a combination of both phenomena. Samples containing spiropyran displayed dynamic color changes in the emission to red, orange, and pink depending on the composition. Hence, developed dual-color and multicolor photoluminescent inks were used for printing of security tags and also painting of some hand-drawn artworks, which obtained results indicating high printability, maximum fluorescence intensity, high resolution, and fast responsivity upon UV-light irradiations of 254 nm (for static mode) and 365 nm (for dynamic mode). In addition, the multilevel authentication mechanism by a static emission under UV-light irradiation of 254 nm, a dynamic emission under UV-light irradiation of 365 nm, and photochromic color change was observed, resulting in increasing the security of developed inks. Actually, developed multicolor photoluminescent inks are the most efficient candidates for developing a new category of chameleon-like high-security anticounterfeiting inks that have tunable optical properties and complex multilevel authentication mechanisms.

Dynamic multicolor luminescent anti-counterfeiting based on spiropyran-engineered gold nanoclusters

Multicolor luminescent materials with time-dependent optical responses are attractive for developing advanced anti-counterfeiting techniques, but it still remains challenging to rationally design and fabricate these emerging materials. Herein, we report the design of novel dynamic luminescent materials based on spiropyran-engineered gold nanoclusters (AuNCs) for anti-counterfeiting applications. Encapsulating fluorescent AuNCs with spiropyran-labeled bovine serum albumin enables the construction of dynamic multicolor luminescent nanoparticles (DML NPs) based on fluorescence resonance energy transfer. These AuNCs-based DML NPs exhibit photochromism and dynamic fluorescence color change from green to yellow to orange-red with the extension of UV irradiation time. Moreover, the photochromism and dynamic fluorescent behavior is highly reversible when exposed to the irradiation of visible light. By taking advantage of photochromic and time-dependent dynamic fluorescence, potential application in optical information storage, dynamic anti-counterfeiting authentication and multi-mode anti-counterfeiting are successfully demonstrated based on DML NPs-deposited polyvinyl alcohol film. This study provides a new strategy of designing novel dynamic multicolor luminescent materials with promising optical properties, which can further advance the practical application of AuNCs-based luminescent materials in the field of information encryption and anti-counterfeiting.

Dynamic light filtering over dermal opsin as a sensory feedback system in fish color change

Dynamic color change has evolved multiple times, with a physiological basis that has been repeatedly linked to dermal photoreception via the study of excised skin preparations. Despite the widespread prevalence of dermal photoreception, both its physiology and its function in regulating color change remain poorly understood. By examining the morphology, physiology, and optics of dermal photoreception in hogfish (Lachnolaimus maximus), we describe a cellular mechanism in which chromatophore pigment activity (i.e., dispersion and aggregation) alters the transmitted light striking SWS1 receptors in the skin. When dispersed, chromatophore pigment selectively absorbs the short-wavelength light required to activate the skin’s SWS1 opsin, which we localized to a morphologically specialized population of putative dermal photoreceptors. As SWS1 is nested beneath chromatophores and thus subject to light changes from pigment activity, one possible function of dermal photoreception in hogfish is to monitor chromatophores to detect information about color change performance. This framework of sensory feedback provides insight into the significance of dermal photoreception among color-changing animals.