An emerging class of phase transformation materials are the photomechanical molecular materials that respond to a light stimulus. These materials consist of discrete molecules that are held together by intermolecular interactions and have a crystalline order that is intermediate to inorganic crystals and polymers. On exposure to light, these materials undergo an abrupt solid-to-solid change in their crystal structure that is characterized by a wide range of extreme deformations, such as jumping to distances >103 their size, exploding into several pieces, and exhibiting complicated modes of deformations like coiling, twisting, and bending. The origin of these variations in mechanical deformations of the photomechanical materials is still an open question. We are developing a continuum theory for photomechanical materials to understand how structural transformations and microstructural evolution pathways make some materials jump while others bend or twist.
