Light-Triggered Self-Growth of 3D Photonic Structures with Vertical Helical-Pitch Gradients Engineering

Natural structural colors often emerge from interactions between chiral lattices and three-dimensional (3D) microstructures, yet integrating surface topography with structural order in artificial photonic materials remains challenging. Here, we develop a light-driven self-growth strategy for programmable 3D photonic structures by engineering through-thickness gradients in a preassembled chiral nematic cellulose scaffold. Confined UV photopolymerization drives localized reactions and directional mass transport, creating coupled gradients in cross-linking density, polymer concentration, and helical pitch. These gradients enable continuous structural-color tuning from blue to red, while differential swelling-induced buckling produces patterned protrusions with programmable heights. The resulting interpenetrating network provides structural integrity and mechanical robustness. Combined with photomask lithography, this approach yields spatially resolved multicolor architectures featuring programmable 3D topographies, angle-dependent optical responses, and self-cleaning properties. It further enables four-channel optical encryption integrating polarization, multipeak reflection, 3D topography, and photoluminescence, demonstrating gradient engineering as a versatile route to advanced multifunctional bioinspired photonic material design.