Double-Layer Hydrogels with Tunable Mechanofluorochromic Response for Smart Display

Mechanofluorochromic materials that render sensitive fluorescence color/pattern change upon mechanical stimuli have drawn extensive attention. However, traditional mechanofluorochromism relies on the chemical transformations of mechanophores, but their types are quite few. It remains challenging to develop mechanofluorochromic materials with customized fluorescence color changing response. Herein, a generally applicable strategy is proposed to present a class of double-layer mechanofluorochromic hydrogels based on the facile integration of two different-colored fluorescent hydrogels. Due to the UV transmittance change of top layer under Poisson's effect, the emission intensity ratio of the upper and lower hydrogels exhibits a strain-dependent change, resulting in a force-triggered overlapping color variation. Both the UV transmittance of top layer and the fluorescence emission of bottom layer can be readily modulated to enrich the variety of mechanofluorochromism. Besides, the bottom layer is available to be printed by ion inks to fabricate patterned double-layer fluorescent hydrogel, holding great potential to design flexible mechanofluorochromic platforms for smart display and information encryption.