Design and estimation of fluorescent chiral sensor : from uni-molecular system to organized approach

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Synthesis of optical sensors being capable of recognizing and reading out the shape of analyte precisely is one of scientific challenge in the area of molecular recognition chemistry. Most notably, chiral sensing would be desirable not only in analytical chemistry but also in pharmacology. In this project, our strategy to develop elaborated sensing systems is based on the anion recognition. A family of isothiuronium salts, which are known as synthetic intermediates for the conversion of alkyl halides to the corresponding thiols, has potential as one of key functional groups toward this end. Indeed, a sophisticated combination of the functional entity and suitable fluorophore could allow production of a new type of chemosensors via regulation of the efficiency of the photoinduced electron transfer process. In 2002, we tried to develop an isothiouronium derived uni-molecular system for chiral recognition as well as an organized molecular layer. In the latter case, by use of newly synthesized amphiphilic isothiouronium compounds, we successfully prepared the corresponding organized molecular films. Now the detailed molecular recognition phenomena at air-water interface are under investigation.Alternative approach is to develop a novel achiral-to-chiral transformation at the molecular level using "dynamic" host-guest interaction. In this context, chirality-transfer control has been successfully achieved using a 2,2'-biphenyl- 20-crown-6-bridged bis(zinc(II) porphysic). Further, chirality-induction in a large-sized crown ether with a highly conformational flexibility was obtained through K^+ and I coordinated self-assembly in the solid state. Taken together, I believe that these findings would open new way to "dynamic" chiral recognition.