Construction of the single molecule electroluminescence devices using insulated conducting polymers

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The goal of this project is to construct one-dimensional supramolecular structure consisting of optically functional conducting polymers and insulating molecules, evaluating the potential application as a single-molecular electroluminescence device.Several methods were explored to construct insulated molecular wires (IMW): Synthesis of IMW consisting of cyclic molecules (e. g. cyclodextrins) and electroluminescent conducting polymers (e. g. polythiophenes), self-assembly of conducting polymers into 1-D nanowires, and template wetting with anodic alumina porous template and solutions of insulating molecules and conducting polymers. We obtained polythiophene nanofibers with the rectangular cross section of height 3-4 nm and width 24-27 nm. The nanofiber length longer than several um indicates their high aspect ratio on the order of 10^3.This research also revealed that the interface between metal and 1-D supramolecular structure is so important for the construction of organic electronic devices that the electric contact of polymers with metals affects the device performance significantly in electrical and luminescent properties. In this project, we found the chemisorption behavior of polythiophene onto gold substrate: When poly (alkylthiophene) molecules are immersed with gold substrate in toluene solution, the rings of polythiophene open and form specific bond with gold substrate self-assemblingly. The chemisorption reduced the contact resistance and improved the FET performance of poly (alkylthiophene) considerably. We also succeeded in the end modification of polythiophenes with selenols, forming specific bonds with metals. As a result of applying this molecule to single molecule force spectroscopy (SMFS) using an atomic force microscope (AFM), a close relation between conformation and optical properties of conducting polymers was revealed in a single molecular scale.