Surfaces provide platforms for self-assembly of well-defined molecular structures. By adjusting the balance of molecular-molecular interactions and molecule-surface interactions, diverse molecular patterns can be created. Beyond molecular self-assembly, “on-surface covalent coupling” or “on-surface reaction” under ultrahigh vacuum (UHV) conditions became a new concept in the very recent years to create robust, ordered molecular surface structures that may also exhibit novel properties. For instance, starting from designed small primer molecules, on-surface synthesis of graphene nanoribbons (GNRs) has been achieved.1 By using high index metal crystal surfaces with anisotropic characteristic, we are able to align the GNRs in one direction, which is necessary for spectroscopic studies of electronic properties. With surface constrain at atomic scale, some products are not possible to be synthesized by standard reactions in solutions, for instance, lineal alkan polymerization without involvement of activating groups.2 Important breakthroughs in the this research area give a clear signal for the opening of a new avenue in realizing robust functionalized molecular surfaces and designing new catalysts for unusual chemical reactions.

Reference
1. Cai, J., Ruffieux, P., Jaafar, R., Bieri, M., Braun, T., Blankenburg, S., Muoth, M., Seitsonen, A. P., Saleh, M., Feng, X., Müllen, K. & Fasel, R. Nature, 2010, 466, 470.
2. Zhong, D.Y.; Franke, J.; Podiyanachari, S.K.; Blömker, T.; Zhang, H.M.; Kehr, G.; Erker, G.;
Fuchs, H.; Chi, L.F. Science, 2011, 334, 213.