Light-Responsive Block Copolymers Jean-Marc Schumers, Charles-Andre ´ Fustin,* Jean-Franc ¸ois Gohy* Introduction Since the mid 1990s, the concept of ‘‘smart’’ polymeric materials has hatched out and briskly grown as attested by the number of articles published in the last years. [1–5] These stimuli-responsive polymers are able to show sharp responses to environmental changes such as pH, tempera- ture, light, redox, or chemical changes. Block copolymers are usually cornerstones for those systems. Indeed, they undergo microphase separation at the nanoscale leading to well-defined morphologies in solution and in the solid state. [6–8] The resulting nanostructures have potential applications in nanotechnology such as drug delivery, catalysis, filtration, templating, etc. In addition, as block copolymers display distinct sequences, the stimuli-respon- siveness can be localized in only one part of the polymer and systems in which different blocks can distinctly respond to different stimuli can be designed. This paves the way toward multi-addressable systems showing very complex behavior. This recent burst in the field of stimuli-responsive block copolymers has to be related to the development of novel synthetic methods toward block copolymers. Actu- ally, for almost 15 years, controlled-radical polymerizations (CRPs) encompassing atom transfer radical polymerization (ATRP), reversible addition–fragmentation chain transfer (RAFT), and nitroxide-mediated polymerization (NMP) have emerged as powerful tools for the preparation of stimuli- responsive block copolymers with well-defined structures and narrow molar mass distribution. [9–14] Among the aforementioned stimuli, light has attracted much attention since it can be localized in time and space and can also be triggered from outside of the system. Indeed, photo-processes usually start/stop when the light is switched on/off and generate only limited amount of by- products since no additional reagents are needed. More- over, a lot of parameters such as the intensity and the wavelength of light can be adjusted during the reaction time which enables good control over the reaction. Concerning light-responsive block copolymers (LRBCs) in particular, only some features have been previously pointed out. [2–5] We propose here a detailed review on the state of the art. This paper summarizes the different photo-sensitive moieties that have been incorporated so far into block copolymers such as azobenzene and o-nitroben- zyl chromophores and some of their related applications. The paper is divided into two main parts. The first one reviews LRBCs in solution and the second one discusses their bulk behavior. Applications such as light-triggered drug delivery, holography, and nanoporous materials will be presented in order to illustrate the potential of those materials. Feature Article J.-F. Gohy, C.-A. Fustin, J.-M. Schumers Institute of Condensed Matter and Nanosciences (IMCN), Universite ´ catholique de Louvain, Place L. Pasteur, 1, Louvain-la- Neuve, Belgium Fax: (þ32) 10479269; E-mail: jean-francois.gohy@uclouvain.be; charles-andre.fustin@uclouvain.be Stimuli-responsive polymers are the subject of intense research because they are able to show responses to various environmental changes. Among those stimuli, light has attracted much attention since it can be localized in time and space and it can also be triggered from outside of the system. In this paper, we review light-responsive block copolymers (LRBCs) that combine characteristic features of block copolymers, e.g., self-assembly behavior, and light-responsive sys- tems. The different photo-responsive moieties that have been incorporated so far in block copo- lymers as well as the proposed applications are discussed. 1588 Macromol. Rapid Commun. 2010, 31, 1588–1607 ß 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com DOI: 10.1002/marc.201000108