Flexible Photonic Crystal Films with Brilliant Structural Colors and Excellent Durability Enabled by High-Refractive-Index Polythiourea

Flexible and self-supporting photonic crystal (PC) materials hold great promise for curved displays, wearable devices, and soft electronics. However, their practical application is often hindered by insufficient color brilliance and durability. To address these challenges, a novel flexible polythiourea (PTU) with a high refractive index (RI) was designed to encapsulate ordered SiO2 microsphere arrays. This strategy achieved a high RI contrast (Δn ≈ 0.2), enabling the fabrication of flexible and self-supporting PC films with brilliant structural colors and excellent durability. The PTU incorporates structural units of high molar refractivity (benzene rings and sulfur atoms) and thiourea hydrogen bonds, forming densely packed polymer networks with an RI of 1.65. Consequently, the resulting SiO2/PTU PC films exhibit significantly stronger reflectivity and brighter colors than SiO2/PBA (n ≈ 1.47) and SiO2/PU (n ≈ 1.53) PC films. Moreover, these films demonstrate remarkable durability, retaining their structural colors after being subjected to 45% tensile strain, hot-pressing at 8 MPa, or 18 h of immersion in common liquids. The structural color fabrics were constructed by hot-pressing the PC films onto fabrics, and the structural integrity and optical performance were maintained after 100 cycles of folding, rubbing, and washing. Furthermore, the adhesive performance of these PC films to multiple substrates and curved surfaces makes them suited for diverse applications, including high-durability decorative coatings, advanced anticounterfeiting labels, and nonfading decorative electronics.