Daniel J. Wilson

Modern paints and coatings are designed for a variety of applications, ranging from fine art to extraterrestrial thermal control. These systems can be engineered to provide lasting color, but there are a limited number of materials that can undergo transient changes in their visual appearance in response to external stimuli without requirements for advanced fabrication strategies. The authors describe color‐changing paint formulations that leverage the redox‐dependent absorption profile of xanthommatin, a small‐molecule colorant found throughout biology, and the electronic properties of titanium dioxide, a ubiquitous whitening agent in commercial coatings. This combination yields reversible photoreduction upon exposure to sunlight, shifting from the oxidized (yellow) form of xanthommatin, to the reduced (red) state. The extent of photoreduction is dependent on the loading density and size of titanium dioxide particles, generating changes in hue angle as large as 77% upon irradiation. These coatings can be blended with non‐responsive supplemental colorants to expand the accessible color palette, and irradiated through masks to create transient, disappearing artwork. These formulations demonstrate energy‐efficient photochromism using a simple combination of a redox‐active dye and metal oxide semiconductor, highlighting the utility of these materials for the development of optically dynamic light‐harvesting materials.

In this report the design, fabrication, and testing of inkjet‐printed electrochromic pixels (ECPs) incorporating the biochrome, xanthommatin (Xa) as programmable display units is described. As a redox sensitive chromophore, Xa is present in some species as a physiological indicator with red (reduced) or yellow (oxidized) colors associated with different behavioral or developmental stages. These features have been recently leveraged in some materials applications, illustrating a bio‐inspired design solution to color‐changing sensors and displays. This paper describes an extension of these applications to print individually addressable ECPs that can be processed in a mild annealing step to introduce localized conductivity on initially nonconductive substrates. When formulated together with a poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) carrier ink, an addition of 0.19 wt% Xa is enough to generate dynamic ECPs which can be batch printed as lateral electrodes on any substrate to serve as both conductors and display units across electrically isolated boundaries. Application of low potentials triggers reversible color changes that span the red/yellow color space and can cycle for days. These results represent an important step towards the incorporation of alternative active materials like Xa to manufacture and scale low‐power, color‐changing pixels and patterns.