Understanding and Controlling the 1,4-Phenylene Diisocyanide-Gold Oligomer Formation Pathways

The pathways for the spontaneous self-assembly of one-dimensional oligomeric chains from the adsorption of 1,4-phenylene diisocyanide (PDI) on Au(111) surface are explored using density functional theory. It has been shown previously that the chain comprises repeating -(Au-PDI)- structures. The results show that the chains form from mobile Au-PDI adatom complexes and that chains propagate by the adatom complex coupling to a terminal isocyanide group which lies close to parallel to the surface and the activation barrier for this propagation step is similar to 28 kJ/mol. It is also found that the Au-PDI adatom complex is attracted to the terminal isocyanide, thereby facilitating the oligomerization process. The insights into the oligomerization pathway are used to explore whether an external electric field applied to diisocyanide functionalized molecules that contain a dipole moment can be used to align them. It is found that molecules with dipole moments of similar to 1 D show significant alignment with an electric field of similar to 10(8) V/m and almost complete alignment when the electric field reaches similar to 10(9) V/m. This suggests that the self-assembly chemistry of dipolar diisocyanides can be used to create oriented systems.