Abstract: The nanostructure studies have been performed to the fluorescent and liquid-crystal molecule (2,5-bis-[2-(3,4-bis-dodecyloxy-phenyl)-vinyl]-3,6-dimethyl-pyrazine(BPDP12)) on highly oriented pyrolytic graphite (HOPG) using scanning tunneling microscopy (STM). The well-organized 2-D monolayer images reveal two kinds of configurations. The structure (I) is a stable and closely packed arrangement, in which all the conjugated cores are parallel to each other and the alkyl chains of the molecules interdigitate over the full length；while the structure (II) is an unstable and unclosely packed arrangement, in which all the conjugated cores are separated by the alkyl chains. The formation of above two structures owes to the competition between the stronger intermolecular π-π interactions and the van der Waals forces of alkyl chains during the self-assembly.

Key words: Scanning tunneling microscopy (STM), Self-assembly, Pyrazine derivative