Mechanochromic and Solvomechanochromic Fluorescent Photonic Crystals for Dual-Mode Modulating Fluorescence and Multilevel Anticounterfeiting.

Fluorescent photonic crystals (FPCs) are ideal candidates for regulating dyes' fluorescence through their unique photonic band gaps (PBGs). However, challenges, including the lack of dynamic regulation of fluorescence, dye release in solvents, and instability, dramatically limit their practical applications. Here, we report mechanochromic and solvomechanochromic rhodamine B (RhB)-based FPCs with dynamic regulation of photoluminescence (PL) by stretching and swelling, brilliant fluorescent and structural colors, and no release of the RhB in solvents. The FPCs with force/solvent-responsive nonclose-packing structures were fabricated by (1) preparing RhB-silica particles by combining click chemistry and cohydrolysis processes and (2) self-assembling these particles in poly(ethylene glycol) phenyl ether acrylate followed by a photopolymerization. Maximal PL inhibition (37%, stretching strain of 6.8%) and enhancement (150%, swelling time of 8 min) were gained when PBGs and their blue edges are precisely adjusted to the PL peak position, respectively. Compared with stretching, PL regulation is more efficient by swelling. These characteristics benefit from the rational design and combination of unique compositions, chemical bonds, nonclosely packed micro/nanostructures, and solvents for swelling. Moreover, these FPCs have been used to encrypt photonic patterns, which display background/strain/angle/UV-dependent color contrasts, showing their potential applications in multilevel anticounterfeiting, optical devices, wireless sensors, etc.