Tunable Oxygen Connectivity in Carbaporphyrinoid Polymers on Metal Surfaces

Controlling oxygen-mediated connectivity at metal surfaces offers a powerful route to engineer covalent and metal-organic architectures with atomic precision. Here, we demonstrate tunable oxygen-based connectivity in carbaporphyrinoid polymers on Au(111) under ultrahigh vacuum (UHV) conditions. Initial thermal activation of hydroxyl-functionalized dicarbahemiporphyrazine precursors induces carbon-carbon coupling via a [3+3] cycloaromatization, affording one-dimensional polymers equipped with hydroxyl-terminated units. From this intermediate two distinct oxygen-based linkages can be achieved: further annealing induces dehydrogenative coupling of adjacent polymers through the hydroxyls groups to yield dibenzo-p-dioxane (O-heterocyclic) bridges that covalently connect the carbaporphyrinoid macrocycles, whereas dosing cobalt produces extended metal-organic networks stabilized by two-fold O···Co···O coordination motifs accompanied by cobalt-metalated macrocycles. Scanning tunneling microscopy (STM) and non-contact atomic force microscopy (nc-AFM) directly resolve both the coordinated networks and the O-heterocyclic bridging motifs. Complementary DFT and Free energy calculations elucidate the reaction pathways, while x-ray photoelectron spectroscopy (XPS) reveals characteristic chemical shifts that account for C-O-C formation and suggest Co···O coordination. This controllable oxygen-based connectivity provides a versatile platform to tune structure and electronic properties in porphyrinoid-based polymers.