Coverage- and Temperature-Dependent Rates of Metalation, Ring Fusion, and Polymerization of Benzoporphyrins on Cu(111)

Using scanning-tunneling microscopy (STM), temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and density-functional theory (DFT), we have investigated metalation, ring fusion, and polymerization of three different benzoporphyrins, tetraphenyltransdisbenzoporphyrin (2-Benzo), copper-tetraphenyltransdibenzoporphyrin (Cu 2-Benzo), and tetraphenyltetrabenzoporphyrin (4-Benzo), from 280 to 1000 K on Cu(111), and compare with previous data of tetraphenylporphyrin (0-Benzo) on Cu(111). Using STM, we observe 2-Benzo to adsorb as individual, rather-immobile molecules at room temperature, which coalesce into elongated islands of metalated molecules at 373 K. N 1 s XPS spectra confirm the metalation, and DFT-calculated structures and simulated STM images confirm the appearance in STM. Upon further heating to 398 K, the islands become rough and irregularly shaped, before completely breaking up at 423 K, most likely related to intramolecular ring fusion. Heating to 950 K leads to complete polymerization and a rough structure on the surface. Using H₂ TPD, we follow the coverage-dependent rates of metalation, ring fusion, and polymerization for all four molecules. The metalation rate is found to correlate with, sometimes abrupt, changes in the adsorption structures, whereas the rates of ring fusion and polymerization decrease gradually with increasing coverage, for all molecules.