Organic photomechanical materials transform molecular-scale photochemical reactions into a wide variety of mechanical behaviors, such as bending, twisting, coiling and peeling. Polymer-based materials such liquid crystal elastomers provide a way to build and pattern photomechanical structures but suffer from low elastic moduli, low-energy-density and slow response rate. Directly assembling photochromes into neat molecular crystals can lead to a higher energy, hardness and response speed. But large molecular crystals suffer from fracture and challenges in growth. Recently, we showed that photomechanical nanocrystals can be organized and aligned on macroscopic length scales using a porous inorganic template. We first used a diarylethene molecule that undergoes a reversible photochromic isomerization under light irradiation as the active organic component, then used porous aluminum oxide template as the component to provide structural support and directionality. This hybrid organic–inorganic photomechanical material acts as a bending actuator. Using ultraviolet and visible photons as power inputs, as little as 0.1 mg of reacted material generates enough force to tilt a 1.28 g mirror and steer a laser beam. The motion can be cycled multiple times both in air and water. We then used a derivative of cinnamic acid that undergoes a negative photochromic reaction under light, with the aiming of generating larger force. Although the motion of mirror tilting cannot be cycled multiple times, we obtained an order of magnitude larger displacement by using this compound. Our experiments illustrate how photomechanical molecular crystals can be incorporated into macroscopic actuator structures. Using this hybrid approach, it is possible to building such hybrid component to function as photo-switches and actuators in the near future.

Macroscopic photon-powered actuators based on organized photomechanical nanocrystals

2019 Fall National Meeting

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