Synchronizing Multicolor Changes and Shape Deformation Into Structurally Homogeneous Hydrogels via a Single Photochromophore

Abstract

The design of synthetic hydrogels that can mimic their biological counterparts in the simultaneous production of multicolor change and shape transformation in response to environmental stimuli is of great importance toward intelligent camouflage, encryption, and actuation. Previous efforts have focused primarily on developing heterogeneous hydrogels that highly rely on respective mechanisms to achieve color and shape changes separately, and synergistically synchronizing such two variations into structurally homogenous hydrogels via a single chromophore has been challenging. Here, the molecular design of a structurally homogenous hydrogel simultaneously exhibiting synchronized multicolor change and shape deformation triggered by a single stimulus of light is reported. The synchronization mechanism originates from a coupled alteration upon irradiation in the fluorescence emission and charge states of a spiropyran photochromophore covalently incorporated into the hydrogel network, thus leading to macroscale color change and shape variation in the hydrogel, respectively. Following this principle, both positive and negative phototropic deformation are obtained concomitantly with synchronized but flexibly tunable multicolor changes upon light illumination and demonstrated the ingenious application of biomimetic actuation, encryption, and camouflage by the rational combination of these two systems. This work represents an innovative molecular design strategy for developing bioinspired materials with synchronized functions via a single compound.

Keywords: color change; hydrogel; photochromphore; shape deformation; spiropyran.