Gecko-inspired smart photonic crystal films with versatile color and brightness variation for smart windows

Many reptiles, such as Phelsuma geckos, skillfully employ both structural and pigmentary elements to generate versatile colors. Meanwhile, they can also modulate skin brightness through the dispersion and aggregation of pigment-containing cells. Inspired by this amazing biological process, the thermochromic pigments and viologen-based electrochromic materials were ingeniously integrated into colloidal photonic crystals to fabricate multi-responsive photonic crystal films for the first time. Through modulating the reflection and absorption of light, i.e., structural and pigmentary components, the as-prepared photonic crystal films could display RGB colors under different environmental temperatures and tune the color brightness in response to external electric field, mimicking the versatile color variation of geckos. The introduction of viologen resulted in a more vivid color thanks to its absorption of incoherent scattering light inside the colloidal particles aggregates. Furthermore, we employed a new strategy called shear-induced technique to assemble monodisperse microspheres into ordered nanostructure, which could produce large-sized photonic crystal films. As a demonstration, the multi-responsive photonic crystal films were used as a prototype of new generation smart windows, fusing both active (electrochromic) and passive (thermochromic) ways for light modulation, which could serve as interior mood regulator for the person in car.