Scanning Probe Microscope Application for Single Molecules in a π-Conjugated Polymer Toward Molecular Devices Based on Polymer Chemistry

Abstract

π-conjugated polymers are useful substances with excellent performances. To date, we have mainly conducted the following studies. First, we imaged the higher-order structure of a single molecule of a chiral helical π-conjugated polymer. To be more precise, we elucidated the higher-order structure by directly measuring the main-chain chiral helical structure using a scanning tunneling microscope. Second, we discovered a new phenomenon, which is that the color of the fluorescence of a single polymer molecule changes on the order of seconds, by directly observing the dynamic function of photon emission based on the thermal fluctuation of a single molecule of a fluorescent π-conjugated polymer using a total internal reflection fluorescence microscope (TIRFM), which we developed. In addition, we simultaneously imaged the structure and function of a fluorescent π-conjugated polymer. This was achieved using a combination of an atomic force microscope (AFM) and an objective-type TIRFM(AFM-TIRFM). Afterwards, we achieved a high-speed (fast-scan) atomic force microscopy image of the random movement of a single π-conjugated polymer chain in a solution at room temperature. On the basis of an analysis, we have demonstrated that movement, which complies with Einstein’s law of Brownian motion, is based on thermal energy. We anticipate that our studies will be the basis for creating innovative molecular devices such as molecular motors or molecular electronics/photonics materials that utilize thermal energy as a driving source.