Oligopyrroles and their metal complexes are versatile materials for surface and interface functionalization [1]. While monolayers of these molecules can sometimes be prepared by physical vapor deposition under vacuum conditions, this approach is limited to chemically and thermally stable species. An interesting alternative is the on-surface synthesis, which provides access to monolayers of species that are too fragile for vapor deposition or that cannot be made by solution-based synthesis at all. In this contribution, I introduce several strategies for the on-surface synthesis of oligopyrroles: (1) On-surface metalation of pre-deposited free-base porphyrin, phthalocyanine, or corrole ligands. With this approach, surface-stabilized complexes with metal centers in unusual oxidation states can be prepared. The attachment of additional ligands on the metal center can lead to bonding competition such as the surface trans effect. (2) Phthalocyanines, naphthalocyanines and their expanded homologs can be prepared by template-directed on-surface synthesis from suitable dinitrile-based precursors. (3) On-surface synthesis also gives access to linear open-chain counterparts of phthalocyanines, which represent a novel class of non-cyclic oligopyrroles. Structure, electronic properties and reactivities of the oligopyrrole monolayers will be discussed on the basis of extensive experimental and theoretical results.

[1] J.M. Gottfried, Surface Chemistry of Porphyrins and Phthalocyanines, Surf. Sci. Rep. 70 (2015) 259-379.