All‐Optical Control of Shape. Issue 2 (12th November 2018) - Donovan, Brian R.
Abstract: Photoresponsive liquid crystal elastomers (LCEs) are a unique class of anisotropic materials capable of undergoing large‐scale, macroscopic deformations when exposed to light. Here, surface‐aligned, azobenzene‐functionalized LCEs are prepared via a radical‐mediated, thiol‐acrylate chain transfer reaction. A long‐lived, macroscopic shape deformation is realized in an LCE composed with an o‐fluorinated azobenzene (oF‐azo) monomer. Under UV irradiation, the oF‐azo LCE exhibits a persistent shape deformation for >72 h. By contrasting the photomechanical response of the oF‐azo LCE to analogs prepared from classical and m‐fluorinated azobenzene derivatives, the origin of the persistent deformation is clearly attributed to the underlying influence of positional functionalization on the kinetics of cis → trans isomerization. Informed by these studies and enabled by the salient features of light‐induced deformations, oF‐azo LCEs are demonstrated to undergo all‐optical control of shape deformation and shape restoration. Abstract : Photoresponsive azobenzene liquid crystal elastomers harness the advantages of light‐induced, stimuli‐responsive behavior and are capable of large reversible shape transformations. Via modification of the ortho ‐ position of an azobenzene molecule, stable and long‐lived deformed states are achieved. Concurrently, light‐activation of both the trans → cis and cis → trans isomerizations of the modified‐azobenzene molecule facilitates all‐optical control over shape reconfiguration for complex origami patterns.