Stimuli-Responsive Biomimetic Metallic Luster Films Using Dye Absorption and Specular Reflection from Layered Microcrystals

Inspired by the coloring mechanism of insects, we demonstrated the preparation of metallic luster materials by a combination of dye absorption and specular reflection from layered microcrystals. Metallic luster films were prepared by the recrystallization of diacetylene derivatives with different linker chains bearing azobenzene moieties. The lamellar structure of the molecules formed plate-like microcrystals, which were piled up to form layered films. A gold-like texture was observed due to the combination of the absorption of the azobenzene moiety and specular reflection from the surface of layered microcrystals. The film of the diacetylene derivative with a dodeca-5,7-diynedioate moiety used as a linker maintained its golden color regardless of light or thermal stimuli. In contrast, the color of the film composed of the diacetylene derivative containing the docosa-10,12-diynedioate linker turned purple due to solid-state polymerization by UV-light irradiation and maintained its metallic gloss. Additionally, the glossy color changed reversibly with changing temperature. The responsiveness of metallic luster films to stimuli was controlled by changing the linker chain length. The photo- and thermal-responsive metallic luster materials presented here can have a significant impact on decoration and ink applications.