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%.
Solvatofluorochromic molecules provide strikingly high fluorescent outputs to monitor a wide range of biological, environmental, or materials‐related sensing processes. Here, thiazolo[5,4‐d]thiazole (TTz) fluorophores equipped with simple alkylamino and nitrophenyl substituents for solid‐state, high‐performance chemo‐responsive sensing applications are reported. Nitroaromatic substituents are known to strongly quench dye fluorescence, however, the TTz core subtly modulates intramolecular charge transfer (ICT) enabling strong, locally excited‐state fluorescence in non‐polar conditions. In polar media, a planar ICT excited‐state shows near complete quenching, enabling a twisted excited‐state emission to be observed. These unique fluorescent properties (spectral shifts of 0.13 – 0.87 eV and large transition dipole moments Δµ = 20.4 – 21.3 D) are leveraged to develop highly sought‐after chemo‐responsive, organic vapor optical sensors. The sensors are developed by embedding the TTz fluorophores within a poly(styrene‐isoprene‐styrene) block copolymer to form fluorescent dye/polymer composites (ΦF = 70 – 97%). The composites respond reversibly to a comprehensive list of organic solvents and show low vapor concentration sensing (e.g., 0.04% solvent saturation vapor pressure of THF – 66 ppm). The composite films can distinguish between solvent vapors with near complete fluorescent quenching observed when exposed to their saturated solvent vapor pressures, making this an extremely promising material for optical chemo‐responsive sensing.
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