Adsorption, self-assembly and self-metalation of tetra-cyanophenyl porphyrins on semiconducting CoO(100) films

The adsorption properties of free base 5,10,15,20-tetrakis(p-cyanophenyl)porphyrin (2H-TCNPP) on thin films rock salt (rs) CoO(100) Au(111) was studied in ultra-high vacuum by a combination low-temperature scanning tunneling microscopy and spectroscopy (STM/STS) density functional theory (DFT). Films rs-CoO(100) are prepared with excellent quality suitable thickness range. Particularly, we found that only 1 nm show semiconducting energy gap $E_\mathrm{g}=(2.5\pm 0.2)\,\textrm{eV}$. Upon deposition at 300 K, 2H-TCNPP adsorbs flat-lying self-assembles long-range ordered superstructure is stable 80 K. geometry the molecules surface within self-assembly analyzed DFT. We find self-assemblies stabilized hydrogen bridge bonding via cyano groups. Our STS data shows molecular states fundamental CoO. By comparison calculated DOS determine energetic positions frontier orbitals first three LUMO located band gap, whereas HOMO shifted eV below CoO conduction edge. annealing to 420 K change their appearance STM images new prominent electronic state center molecule formed. interpret this changed configuration as Co-TCNPP created self-metalation oxide surface.