Synthesis of Photosensitive Bottlebrush Block Copolymers for Tunable Photonic Pigments via Light-Driven Engineering of Chain Conformation.

Structurally colored bottlebrush block copolymers (BBCPs) offer a safer and more environmentally friendly alternative to traditional toxic pigments. For practical applications, precise control of their photonic bandgap is essential to generate various colors. A novel amphiphilic BBCPs designed with photosensitive o-nitrobenzyl ester (NE) groups strategically positioned near the main chain of the hydrophilic block is presented. Under UV radiation, these NE groups convert to acid groups, enhancing the hydrophilicity of the hydrophilic block. This leads to increased hydration and chain extension when assembled at the water-in-oil (W/O) interface of a water-in-oil-in-water (W/O/W) emulsion system. The light-driven engineering of BBCP conformation enables significant control over interfacial curvature, resulting in varied internal droplet diameters and domain spacing in the final photonic pigment particles after solvent removal. Despite the inherent rigidity of BBCPs, approach achieves photonic bandgap tuning across the entire visible spectrum using only three different BBCPs. These structural colored pigments show promise for applications in sensing systems, cosmetics, and inks.