Crystalline assemblies of molecular machines for light-powered actuation

Photon powered molecular machines can be assembled into crystals that undergo deformations like expansion, bending, twisting, and coiling. We will review various types of photomechanical crystals, emphasizing the importance of morphology, and show that their theoretical work densities are several orders of magnitude greater than standard actuator materials like piezoelectrics. This class of crystals can also support feedback mechanisms that lead to complex oscillations and translational motion that mimics biological flagella. The combination of organic chemistry, crystal engineering and photochemistry provides a promising approach to make light-responsive materials that can do useful amounts of work.