Fluorescence-color-changing biomimetic tough films with simultaneous shape-deformation triggered by pH

Stimuli-responsive materials with complex practical functions that could imitate certain behaviors of living organisms have wide potential applications in frontier fields. However, the fabrication of stimuli-responsive films with simultaneous change in fluorescence color and shape in response to a single stimulus, especially by a simple fabrication strategy, remains a challenge. Herein, a simple hydrogel-film-post crosslinking strategy is proposed to prepare films that exhibit fluorescence change accompanying with shape deformation under pH stimulus. The synchronous changes are realized by the combination of dynamic boron chemistry and pH-sensitive lanthanide complexes. Under different pH conditions, the protonation/deprotonation of the ligands coordinated to Eu3+ ions could generate switchable on/off fluorescence behavior, while the association/dissociation of borate ester bonds between 3-aminobenzeneboronic acid (SA-PBA) and polyvinyl alcohol (PVA) could lead to macroscopic deformation. The existence of borate ester bonds is beneficial to the mechanical properties of composite films. Under pH stimulus, the film-based artificial flower could simulate the flowering of natural flowers accompanying with color changes and the film-based gripper could grasp object with a visual signal, which demonstrates that the SA-PBA/PVA/EuL films have great potential for wide application.