Obtaining Reversible, High Contrast Electrochromism, Electrofluorochromism, and Photochromism in an Aqueous Hydrogel Device Using Chromogenic Thiazolothiazoles

Abstract There have been an increasing number of materials developed that show multifunctional chromogenic properties (such as electrochromism, electrofluorochromism, or photochromism), but to date, few materials have shown all three properties. Materials that are electrochemically and optically active are attractive for a diverse set of applications that include smart‐windows, lighting, sensing, energy production, and conservation. This is especially attractive for building developers interested in adaptive or environmentally responsive façades. Achieving systems made from cost‐effective, readily synthesized materials will make them easy to utilize in a variety of fields. Low‐cost devices are developed using water‐soluble, chromogenic thiazolo(5,4‐d)thiazole (TTz) dyes that show high device performance in three areas: electrochromism, electrofluorochromism, and photochromism and are all contained within a highly fluorescent aqueous polyvinyl alcohol/borax hydrogel device. The dyes incorporate a rigid, heterocyclic TTz structure that enables the development of devices with excellent reversibility and stable cycling for 250 cycles. The TTz hydrogel‐containing devices also exhibit photochromism under illumination, which can be electrochemically cycled back to the colorless state. In addition, coupling photochromism with electrochromism lowers the power necessary for a comparable electrochromic color change. Last, the hydrogel‐containing devices also show electrofluorochromism, where fluorescence can be turned off by > 90%.