Dual control of passive light output direction by light and mechanical forces in elastic crystals

Abstract

Crystals with elastic and photomechanical properties are rather scarce, but very important. Herein, we report an elastic crystal based on the photo-reactive acylhydrazone derivative (E)-N′-([1,1′-biphenyl]-4-ylmethylene)picolinohydrazide (BPMP). Under ultraviolet (UV) irradiation, the crystal bent away from the UV light. Upon heating, the bent crystal returned to a nearly straight state, demonstrating a reversible bending behavior. The ¹H nuclear magnetic resonance (¹H NMR) data revealed that the molecules in the crystal underwent reversible E ↔ Z isomerization under light and heating conditions. Applying or withdrawing mechanical forces allowed the crystal to be reversibly bent multiple times, displaying excellent elastic properties. Interestingly, the output direction of 635 nm red light could be controlled by controlling the bending of the crystal through light and mechanical force. Therefore, this work provides new ideas for the design of multifunctional elastic crystals.