Photoswitchable polymerization catalysis: state of the art, challenges, and perspectives.

Adjusting the length, composition, and microstructure of a polymer during the process of its formation in principle allows achieving the desired properties, thereby enabling custom-design of the thus generated polymer for its targeted function. Over the past years, different stimuli have been applied to manipulate responsive catalyst systems in situ; among them light takes center stage as perhaps the most promising stimulus. Here, we highlight recent progress in the area of photoswitchable polymerization catalysis. In particular, we focus on the challenge of combining photoswitchable and catalytically active units in a manner that both entities are somehow coupled and interact, yet also retaining their switching and catalysis functions under suitable conditions. We introduce the requirements for an ideal case of a photoswitchable polymerization catalyst system and use them to analyze the current state of the art. Based on our analysis of the status quo, we point to scientific challenges in the field and sketch perspectives including potential applications.