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

Abstract

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-hexaaz atrinaphthylene (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 pi-pi 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 pi- 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.