Dimensionality Control of Self-Assembled Azobenzene Derivatives on a Gold Surface

Well-defined nanostructures constructed with functional molecules provide a feasible route to realize molecular nanotechnology. Synthesis of selectively interacting molecules is essential to develop nanostructures with desired functionalities and dimensions. Substantial efforts have been devoted to achieve finely controlled supramolecular structures on surfaces using various interactions such as van der Waals (vdW), dipolar, hydrogen boning, and metal–ligand interactions. Yet, controlling the dimensions of a supramolecular assembly by changing the strength of the intermolecular vdW interactions, in particular through attaching alkyl chains of different lengths, has not been reported so far. Here, we present the dimensionality control of self-assembled azobenzene derivatives, from one-dimensional chain to two-dimensional island, on an Au(111) surface by exploiting vdW interactions assisted by hydrogen bonding. The designed azobenzene derivatives have alkoxy groups with different chain lengths (6, 8, and 10 carbons). Depending on the alkyl chain length, the molecules self-assemble into two different stacking structures, which determine the dimensionality of the superstructures. Furthermore, we demonstrate that the reconstructed herringbone structures of the substrate determine the stacking structure and growth direction at the elbow of the Au(111) surface. Our results provide a new perspective for engineering well-defined nanostructures with functional molecules as well as deeper insights into the mechanism of molecular self-assembly on surfaces