Photoresponsive Azo Polymer Films

Abstract

Polymers containing aromatic azo chromophores have been the subject of intense investigation due to their unique functions and potential applications. Many of the photoresponsive functions are related to solid films made of the azo polymers. Light absorption and electronic excitation of the aromatic azo cores are the essential steps triggering photochemical effects. Owing to the trans–cis isomerization of azo chromophores, azo polymers can exhibit a variety of photoresponsive functions, such as molecular orientation, macroscopic anisotropy, surface relief structure formation, photomechanical deformations of azo liquid crystal elastomers (LCEs), and nonlinear optical properties. Many of these functions are unprecedented for polymers and other materials, attracting research interest both for fundamental understanding and possible applications. This article starts with the introduction of basic concepts and terminology, which are typically used to describe the photoresponsive properties. The following sections are devoted to azo polymer syntheses, methods to prepare solid films, and main functions of the solid films. Some of the most interesting functions such as the photoinduced orientation and anisotropy, photoinduced surface patterning, and photomechanical actions of azo LCEs are discussed in detail. The basic background and concepts are discussed at the level appropriate as a brief introduction. The material design and preparation, structure–property relationship, mechanism, and models are also presented.

Colorant, Photochromic

“…These transformations have been explored for use in optical switching and data storage. The geometry change associated with photoisomerization attracts much interest as a means of creating polymeric materials that undergo reversible photomechanical deformation [14,19]. Films which contract upon exposure to UV light and then expand when irradiated with visible light have been used to demonstrate the concept of lightdriven motors (follow this link for a video).…”