Scanning Tunneling Microscope Observation of a Polar Liquid Crystal and Its Computer Simulation*1

Abstract

The scanning tunneling microscope (STM) constructed in the laboratory was utilized to observe the molecular arrangement of a new type of liquid crystalline molecule, 5-(p-dodecyloxyphenyl)pyrazine-2-carbonitrile (DOPPC), which has large dipole moments along the molecular axis. The DOPPC molecules adsorbed on a graphite substrate showed several different STM images with regular two-dimensional molecular arrays. They revealed a novel interdigitated double-row structure, differing from the single-row and the double-row structures proposed for the STM images of cyanobiphenyl liquid crystals. Moreover, a computer calculation was conducted based on electrostatic multipole-multipole interaction and simulated the most energetically preferable molecular arrangement, which agreed well with the observed STM image.