Stimuli responsive materials: new avenues toward smart organic devices Roie Yerushalmi, a Avigdor Scherz, a Milko E. van der Boom* a and Heinz-Bernhard Kraatz* b DOI: 10.1039/b505212b ‘‘Smart’’ patternable polymer-based materials that can be designed from various molecular building blocks show great potential, as they may be used in many fields, including nanotechnology, biochemistry, organic and physical chemistry, and materials science. The focus of this highlight will be on the basic design characteristics of practical Stimuli Responsive Materials (SRMs), the wide range of potential applications and the challenges to be accomplished in this rapidly expanding area. In particular, recent developments are described which are related to two of the many fundamental aspects of stimuli triggered responses: those that are photo-triggered and those that are solvent triggered. These selected state-of-the-art examples demonstrate the large scope and diversity in terms of activation mechanism, response time and property control. Introduction The rapidly developing field of nano- technology has provided a strong impetus for the development of ‘‘smart’’ polymer-based materials that can be designed from a wide range of functional molecular building blocks. 1,2 The func- tionality of individual molecular units and the macroscopic properties of Stimuli Responsive Materials (SRMs) places many fields, including nano- technology, biochemistry, organic and physical chemistry, and materials science, in an ever close proximity. Recent developments in this area have demonstrated that patternable SRMs on a micro- or even submicro-meter scale show great promise, 3 as they may be used, for example, in drug-release sys- tems and memory elements. The develop- ment of photo- and electrochemically active mesoscopic polymeric materials is expected to play a major role in nano- scale applications. Molecular structures which can be externally triggered to contract or expand, in a controlled fashion, are expected to become key components in prototype ‘‘all-organic’’ devices and may find eventually applica- tions ranging from artificial muscles, targeted drug delivery or sensing mate- rials to robotics and molecular electro- nics. 4 These materials are often designed so that the conformational changes of the individual subunits are additive, and thus produce a measurable coherent mechanical response to an external stimulus (e.g. light, heat, pH, metal ions, solvent polarity, electric field). Several strategies were developed by Tanaka et al., 4 Hoffman et al., 6 Chilkoti et al., 7 Lopez et al. 8 and many others 9–14 in order to achieve such characteristics. While many studies are focused on the relationship between the shape and the kinematic properties of the materials, a Departments of Organic Chemistry and Plant Sciences, Weizmann Institute of Science, 76100 Rehovot, Israel. E-mail: milko.vanderboom@weizmann.ac.il b Department of Chemistry, University of Saskatchewan, 110 Science Place, Saskatoon, SK S7N 5C9, Canada Roie Yerushalmi received his Ph.D. from the Weizmann Institute of Science, Israel in 2005. His studies with Professor Avigdor Scherz focused on the design of mole- cular systems for monitoring fragmental charge transfer between interacting chemical entities in solution and inter- faces. His research interests relate to model systems of enzymatic reactions, coordina- tion chemistry, molecular design of thin films, and appli- cation quantum mechanical methods. He will soon join the group of Professor Charles M. Lieber at Harvard University as a post-doctoral fellow. Avigdor Scherz is Professor at the Department of Plant Sciences at the Weizmann Institute and Head of the Minerva-Avron Center for Photosynthesis. His interests include photodynamic therapy, rational design, synthesis and application of new PDT reagents, physicochemical aspects of photosynthesis and biological redox reactions, photobiology, and chlorophyll chemistry and spectroscopy. He was a visiting scholar at the University of Chicago and a visiting professor at the University of Tokyo. Professor Scherz holds the Robert and Yadelle professorial chair in Biochemistry. Roie Yerushalmi Avigdor Scherz HIGHLIGHT www.rsc.org/materials | Journal of Materials Chemistry 4480 | J. Mater. Chem., 2005, 15, 4480–4487 This journal is ß The Royal Society of Chemistry 2005