Editorial [Hot Topic: Stimuli-Induced Functions (Guest Editor: Takayuki Suzuki)]

This is the first issue of Current Organic Chemistry dedicated to "stimuli-induced functions". Functional materials currently cover a diverse range of applications. It is ideal to activate these functions at any time and in any environment. To realize this reality, I am convinced that it is necessary to create systems with induced-function that respond to a certain stimuli, e.g. light, heat, or physical force. When people wish to apply the function of the material, they simply input the appropriate stimuli. It is relatively easy to modify the characteristics or add functionality to organic compounds because there are many synthetic techniques already in place. In this issue, I have tried to include a variety of approaches to attaining "stimuli-induced functions. Since the discovery of Tanaka's gel, research into "Polymer gels" has progressed rapidly as an example of a stimuli-induced functional polymer. Because various stimuli such as pH, temperature, and an electric field can induce changes in the gels, many researchers have been studying these gels intensively. The first contribution of this issue, by Yoshida (The University of Tokyo, Tokyo, Japan), reviews the design and recent applications of stimuli-induced gels, and also describes his interesting selfoscillating gels, which are promising as bio-mimetic artificial muscles. The second paper by Minagawa (The University of Tokushima, Tokushima, Japan) and Koyama (Yamagata University, Yonezawa, Japan) describes electrorheological (ER), magnetorheological (MR) and electromagnetorheological (EMR) materials. Such materials include a number of compounds in the organic and inorganic areas. In this paper, they emphasize organic polymers, of which rheological functions are induced by electric and/or magnetic fields. The preparation of the polymers, their field-induced functions and their applications are described. The molecular solenoid is one proposal to provide a new organic material with electric and magnetic properties, both of which are intimately connected with each other; one property should induce the other. A helical and π-conjugated polymer would be a potential candidate for such a functional material, based on the well-defined chiral structure. In the third paper, Nishide and Iwasaki (Waseda University, Tokyo, Japan) focus on helicene derivatives and their interesting optical properties that arise from the stiff structures and molecular ordering. They also describe novel stiff helical ladder polymers, the poly(thiaheterohelicene)s. A material can be useful as a sensor if chemical bonding of a specific species to the material induces an electron transfer reaction. The fourth review by Yuasa and Oyaizu (Tokyo University of Science, Noda, Japan) is a summary of detecting and sensing of reactive oxygen species, which are found in excess in the body as a result of cancer, brain and myocardial infarction, and other diseases. They describe some biosensors including all-synthetic sensors of reactive oxygen species, of which the needle-type sensor is expected to be applicable to certain sites in the living body. I would like to thank all authors for their efforts in making this first issue of "stimuli-induced functions" interesting and informative. It was a great pleasure to be involved in this issue of Current Organic Chemistry as a Guest Editor and I hope you will enjoy reading the papers as much as I have.