Electroactive Nanotubes from π-Conjugated Discotic Molecules

Self-assembly of pi-conjugated molecules is attractive for construction of well-defined, nanometer-scale electroactive materials. This account describes our developments on self-assembled nanotubes from Gemini-shaped hexa-peri-hexabenzocoronenes (HBCs). At first, detailed molecular arrangement in the nanotube is presented, which is perfectly revealed by a synchrotron radiation X-ray diffraction analysis of a macroscopic fiber consisting of highly aligned HBC nanotubes. Next, electroconductive properties of the HBC nanotubes are investigated. By means of direct current and noncontact methods, anisotropic charge-transport properties in the nanotubes are confirmed. The effect of the surface oligoether chains on intertubular conduction is also examined by field-effect transistor measurements. Finally, optoelectronic applications are developed by constructing newly designed nanotubes. These nanotubes possess a coaxial configuration, where an electron-donating graphitic bilayer of pi-stacked HBC arrays is laminated by an electron-accepting molecular layer. Due to the molecular-layer donor/acceptor heterojunction, the nanotubes exhibit remarkable photoconduction and photovoltaic outputs. Furthermore, the optoelectronic properties are modulated by changing the density of electron acceptors on the nanotube surfaces by coassembly of multiple components or utilizing photochromism. These results will advance to electronic and optoelectronic applications of supramolecular nanomaterials.