On-Surface Synthesis of Covalently-Linked Carbaporphyrinoid-Based Low-Dimensional Polymers

The synthesis of porphyrinoid-based low-dimensional polymers has recently attracted considerable interest in view of their intriguing electronic, optical, and catalytic properties. Here, this is introduced by the surface-assisted synthesis of two carbaporphyrinoid-based polymers of increasing dimensionality under ultrahigh-vacuum conditions. The structural and electronic characterization of the resulting polymers has been performed by scanning tunneling and non-contact atomic force microscopies, complemented by theoretical modeling. First, a carbon-carbon coupling between dicarbahemiporphyrazine precursors is achieved by thermal activation of their isopropyl substituents via a [3+3] cycloaromatization, giving rise to one-dimensional (1D) polymers. Second, the same precursor is functionalized with chlorine atoms to complement the [3+3] cycloaromatization with orthogonal dehalogenation and homocoupling, affording two-dimensional (2D) molecular nanostructures. In addition, both low-dimensional free-base porphyrinoid-based polymers are exposed to an atomic flux of cobalt atoms, giving rise to cobalt-metalated macrocycles, with the metal atoms coordinated only to the two pyrrolic nitrogens, in contrast to the typical four-fold coordination that occurs inside tetrapyrroles. This on-surface protocol renders atomically precise covalently-linked porphyrinoid polymers and provides promising model systems toward the exploration of low-coordinated metals with utility in diverse technological areas.