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.