Controlled assembly of large π-conjugated n-type molecules on Au(111)

Controlled assemblies of the n-type 5,6,11,12,17,18-hexaazatrinaphthylene (HATNA) molecule and its derivatives, 5,6,11,12,17,18-hexaazatrinaphthylene-2,8,14-tricarboxylic acid (HATNA–COOH) and 2,8,14-tri(3,4,5-tridodecyloxyphenylaminocarbonyl)-5,6,11,12,17,18-hexaazatrinaphthylene (HATNA-den), on Au(111) electrodes have been investigated using electrochemical scanning tunneling microscopy (ECSTM). Orientations of HATNA and HATNA–COOH molecules on Au(111) electrodes can be manipulated with potential modulation and imaged in situ by ECSTM. By increasing the applied electrode potentials, the HATNA and HATNA–COOH molecules were tuned at the solid/liquid interface to orient from parallel to perpendicular to the electrode surface because of dominating adsorbate–adsorbate interactions such as π–π stacking, hydrogen bonding, and weak dipole–dipole interactions and deprotonation of –COOH groups of the HATNA–COOH molecule at higher positive potentials. However, a stable adsorption orientation independent of applied electrode potentials was observed for the tridendron-containing molecule HATNA-den due to strong interactions between the alkyl chains and the Au(111) substrate, and between π-electrons of the aromatic rings and the Au(111) substrate. The ability to orient adsorbates and to change surface structures by controlling the substrate potential is a great boon to those attempting to create designer two-dimensional structures.