Bioinspired Water-Vapor-Responsive Organic/Inorganic Hybrid One-Dimensional Photonic Crystals with Tunable Full-Color Stop Band

Bioinspired organic/inorganic hybrid one-dimensional photonic crystals (1DPCs) are prepared by alternating thin films of titania and poly(2-hydroxyethyl methacrylate-co-glycidyl methacrylate) (PHEMA-co-PGMA) by spin-coating, which is a simple, reproducible, and low-cost approach. Their optical properties are tuned by changing the number of layers, incident angles, and the thickness of the layers. The color of the 1DPCs can span the entire visible spectral range when the period or the refractive index is changed. Due to the response of PHEMA-co-PGMA to water vapor, the 1DPCs possess fast water-vapor responsiveness and reversible full-color switching. The color of the 1DPCs varies from blue to green, yellow, orange, and red under differing humidities, covering the whole visible range. At high water-vapor concentrations, the color of the 1DPCs rapidly changes from blue to red and comes back to the original state immediately after exposure to air; this behaviour is like that of some animals in nature. The repeatability of the reversible response of the 1DPCs to water vapor is perfect and can be repeated more than 100 times. The as-prepared 1DPCs successfully combine structural color and water-vapor sensitivity, which is promising for use as materials for colorful detection across the full color range.