Structural and Photoelectrical Characterization of Thin Films of a Novel Amphiphilic Oxa[9]helicene Derivative

Polycyclic, highly-conjugated, and ortho-fused aromatic compound, 9-tetraethyleneglycoxy-11-oxa[9]helicene (TO9H), was synthesized and used to explore the feasibility of fabricating thin films and the photoelectrochemical properties of resultant films. Since TO9H has both the hydrophobic helicene part and the hydrophilic tetraethyleneglycoxy (TEG) chain, it behaved as a water-insoluble amphiphile and hence formed a stable Langmuir monolayer at the air water interface. Homogeneous films with thickness up to a few hundred angstroms were deposited by using a spin-coating method. Both of the monolayers and the spin-coated films were characterized by several methods. Brewster angle microscopic (BAM) images and atomic force microscopic (AFM) topographic images revealed the homogeneous surface of the TO9H monolayer at the air water interface and of the deposited monolayer and films on solid substrates, respectively. By using an X-ray reflectivity (XR) technique, the thickness, roughness, and electron density of layers or films were determined. The photo current evolution was measured using conventional three electrode systems with light irradiation from a xenon lamp and obtained results showed that the compound TO9H generated a substantial amount of photocurrent under illumination of light.