Reassessing the Adsorption Behavior and on-Surface Reactivity of a Brominated Porphyrin on Cu(111)

On-surface coupling reactions and molecular conformation are essential processes for building tailored functional molecular nanostructures. Here, we study the thermal debromination and reactivity of free-base tetra(4-bromophenyl)porphyrin (H2TBrPP) on Cu(111) as a function of the substrate temperature. It has been previously reported in the literature that C-Br bonds remain intact at room temperature (RT) and that the Br···Cu(111) interaction induces a drastic surface reconstruction around the molecule periphery and a distortion in the adsorbate itself. However, based on a combination of STM and XPS experiments, supported by density functional theory (DFT) calculations, we instead demonstrate that debromination readily occurs at RT, leading to a new interpretation of both the adsorption behavior and the molecular coupling of H2TBrPP on Cu(111). For the molecules deposited on the metallic substrate held above RT, our STM measurements show the growth of ordered 2D metal-organic frameworks (MOFs).