ABSTRACT
Photoactuating materials convert photon energy into directional translation at meso-to macroscales by reversibly changing their shape or volume when irradiated with light. Because they can be powered wirelessly and controlled remotely and are insensitive to magnetic noise and potentially compatible with rapid (>100 Hz) work cycles, particularly when compared to materials that require diffusive mass transport, photoactuating materials are of growing interest in chemistry, materials science, engineering, and soft matter physics. Here, we de„ne photophysical actuation as that due to heating, pyroelectric and piezoelectric effects (Mizutani et al. 2008) resulting from photon absorption, radiation forces (Juodkazis et al. 2000), or their combination. This chapter is devoted to photochemical actuation, in which aspect ratio(s) of an irradiated material changes due to photoisomerization of its constituent molecular components (e.g., photoactive monomers or dopants), and we will use the terms photoactuation and photochemical actuation interchangeably. Photochemical actuating materials are ensembles of molecular chromophores that exist in at least two isomers of signi„cantly different molecular shape (Figure 3.1). Dimensional change at the macroscale is a cumulative effect of a large number of often independent molecular-scale structural rearrangements, each induced by the absorption of a photon. Photochemical actuation provides perhaps the most direct link between chemical reactivity at the molecular level and useful properties of the bulk material. Consequently, the classical chemical concepts, including molecular design and reaction dynamics, may be particularly impactful in the development of new photoactuating materials and understanding the behavior of the existing ones at the molecular level.
