Incorporating crystalline smart materials to fabricate 4D printed photomechanical actuators with photovoltaic...

Fabricating macroscale smart actuators that can convert light energy into other forms of energy, especially mechanical and electrical energy, is of great significance. Herein, a simple and efficient 4D printed method for fabricating photomechanical actuators based on micro/nano-scale crystals is developed. The high versatility and generality of this method are successfully demonstrated using nine different types of photoresponsive crystalline actuators, including acylhydrazone-, anthracene-, olefin-, and azobenzene-based molecular crystals and covalent organic frameworks (COFs). The low-cost neutral silicone sealant elastomer is first chosen as the photomechanical 4D printing matrix. Notably, these actuators can be used to perform bionic motions (the first windmills spin using crystalline material, dragonflies fly, and sunflowers bloom) under the stimulation of visible light and can realize energy conversion from mechanical energy into electricity when coupled with a piezoelectric membrane. This work provides new insights into the design and manufacturing of smart photomechanical actuators and electricity generators and expands the application scope of COFs.