Rainbow Photonic Crystals: Self-Assembly of Carbohydrate Bottlebrushes Block Copolymers

Tunable and responsive photonic crystal systems are the subject of great research interest owing to their ability to actively respond to chemical, physical, biological, and other external stimuli. In this study, a new series of well-defined and novel carbohydrate-based bottlebrush copolymers are introduced, exhibiting narrow molecular weight (M_n) distributions in the range of 823.5 to 1455.0 kDa. These bottlebrushes self-assemble into 1D photonic crystals (1D-PCs), and their self-assembly in lamellae structures is investigated using a wide range of techniques. The 1D-PCs formed from different bottlebrushes display a full spectrum of colors, ranging from colorless to rainbow colors, including blue, green, orange, and red, effectively spanning the entire UV-vis range. Remarkably, a very fast (a few seconds) change in the color is obtained simply by different solvent, a consequence of the lamellae domain swelling. This demonstrates the impressive tunability, fast responsiveness, and reversibility of these systems. Furthermore, by mixing the bottlebrushes with small carbohydrates, their optical properties can be further modified, achieving a red shift in reflective colors from orange to red. This approach provides a flexible strategy for tailoring the optical characteristics of photonic crystals without the need for synthesizing new carbohydrate-based bottlebrushes, thus offering a versatile platform for controlling their properties.