Fig. 7. A visual demonstration of the information encryption material on a time scale.

a Schematic representations of the process of fabricating such a material and its dynamic fluorescence. Yellow dots represent the dry silica gel powder loaded with compound PY16, which turned blue and orange after adding dichloromethane and water, respectively. b Photographs of the encrypted letter “E” before and after treatment with dichloromethane, displaying time-dependent multiple pieces of information in which the correct piece can be identified only at a specified time. c Schematic representations and fluorescence images (d) of the dynamic 3D code on a time scale. The blue- and orange-coloured information self-erased into yellow as time passed, leading to the generation of a 4D code with time-dependent security.