Porous Organic Cage with Water Vapor-Triggered Structural Transition for Actuation Applications

Fabricating smart humidity-responsive actuators that can convert the potential of humidity into other forms of energy, such as mechanical energy and electricity, is of great importance in the context of the intelligence age and energy crisis. Here, a flexible porous organic cage that can undergo a reversible structural transformation between α and β phases upon humidity stimulation is successfully fabricated into a humidity-responsive actuator by using a polymer with intrinsic microporosity (PIM-1) as a matrix. The humidity-responsive mechanism is unveiled in depth by various characterizations. We find that the inherent porosity of PIM-1 significantly enhances the performance of the resulting actuator. These actuators can be used to perform bionic motions, such as serving as smart grippers and crawling robots. After further coupling with a piezoelectric film, the formed bilayer device can output stable voltage-level power upon periodic humidity switching. This work demonstrates the first example of using a porous molecular cage as a humidity-responsive actuator and energy transducer, providing new insights into the design and fabrication of smart materials for advanced applications.