Scanning Tunneling Microscopy Imaging of Long Oligothiophene Wires Deposited on Au(111) Using Electrospray Ionization

Structural and conformational determination of large and functional organic molecules is of great importance to understand their physical and chemical properties. Here we report on the length dependence of molecular shapes of long oligothiophene wires adsorbed on Au(111), which has been directly visualized by low-temperature scanning tunneling microscopy (STM). The controlled vacuum deposition of the oligothiophene wires from 10 to 120 nm in length has been accomplished by using an electrospray ionization technique. From the high-resolution STM images, we have observed that the oligothiophene molecules longer than around 60 nm tend to form folded (or looped) structures in order to keep compact shapes, which should reflect the molecular shapes in solution or in gas phase.