Origin of Mechanochromism in Polydiacetylene Compounds Jinsang Kim, Department of Materials Sci. & Eng., University of Michigan, Ann Arbor, MI 48109-2136 We purpose a series of organic syntheses and studies involving Langmuir techniques for assembling and controlling polydiacetylene monolayers through which we will uncover the true nature of the polydiacetylene signal event. We designed diacetylene molecules with amphiphilic properties allowing us to control their molecular conformations in situ. We completed the synthesis of the amphiphilic diacetylene molecules in the second year and the diacetylenes have shown a reversible pressure-area isotherm. Using the Langmuir method and the designed amphiphilic properties of the diacetylene molecules, we created monolayer of them at the air-water interface and compressed and released the monolayer by using the two barriers. The reversible pressure-area isotherms both molecules below show that the monolayers have amphiphilic property. Our next goal to achieve is to photo-polymerize the resulting monolayers and investigate their phase transfer change behavior by using fiber optics. A. Chemical structure of diacetylenes. B. Head-to-tail organization. C. Pressure-induced conformation change. Reversible Pressure-Area Isotherm of investigated diacetylene monomer