Asynchronous fluorescence and structural color enabling multilevel sensing and encryption

Abstract

Multimode interactive displays utilizing more than two stimulus-responsive light manipulation schemes have attracted considerable attention. However, sensing displays with asynchronous light control—where two responsive optical phenomena are complementary, thereby minimizing interference between two optical modes—have seldom been demonstrated. Here we report a novel self-assembled material exhibiting asynchronous fluorescence (FL) and structural color (SC), which enables multilevel optical sensing and encryption. Asynchronous FL and SC was achieved by chemically doping aggregation-induced emission luminogens (AIEgens) into one-dimensional block copolymer (BCP) photonic crystals (PCs) comprising alternating lamellae of two dielectric components. The AIEgen-derived FL of a nonswollen BCP PC with no visible SC was deactivated when it was swollen in a solvent, consequently exhibiting fully visible SC. The complementary FL and SC manipulation through reversible molecular (aggregation vs. separation) and structural (nonswollen vs. swollen) alteration aided in developing a multimode sensing display, which could detect temperature and/or nitroaromatic gas in FL mode as well as the pH of a solution in SC mode. The AIEgen-doped BCP PC exhibiting asynchronous FL and SC assisted in constructing a novel write-once-read-many optical encryption system with multilevel security where three levels of quaternary code-type passwords were encrypted with SC, FL, and pH-matched SC.