Chameleon-inspired supramolecular materials based on cucurbit[7]uril and viologens exhibiting full-color tunable photochromic behavior

Inspired by Chameleons' skin color tuning in response to environmental changes, we design and prepare three inclusion complexes based on the cucurbit[7]uril (Q[7]) host and three viologen guests. Upon light irradiation, the colors of these inclusion complexes in the solid state turn from light colors to vivid three primary colors, i.e., red, green, and blue, respectively. Ultraviolet-visible (UV-vis) diffuse reflectance and electron spin resonance (ESR) spectra reveal that the photochromism can be attributed to the generation of viologen radicals, originating from the photoinduced electron transfer. The results of quantum chemical calculation indicate that Q[7] in the inclusion complexes acts as the electron donor in the photoinduced electron transfer process. Using a color mixing approach and finely manipulating the proportions of the three inclusion complexes, a series of composite photochromic materials (CPMs) can be manufactured, covering a full-color gamut in visible light. On the other hand, due to the ignorable size and shape change of CPMs during the photochromatic processes, the CPMs-based reversible photochromic "printing" and photofading "erase" properties were also used for quick response (QR) code. Therefore, these prominent intelligent features of CPMs open new avenues to explore optical regulated nano-platforms for multiple anti-counterfeiting, biomimetics, and military camouflage applications.