Water Formation for the Metalation of Porphyrin Molecules on Oxidized Cu(111)

Herein the formation of water molecules in the intermediate step of the redox reaction of porphyrins self-metalation on O/Cu(111) is demonstrated. Photoemission measurements show that the temperature on which porphyrins pick-up a substrate metal atom on O/Cu(111) is reduced by about 185 +/- 15K with respect to the pure Cu(111). DFT calculations clearly indicate that the formation of a water molecule is less expensive than the formation of H-2 on the O/Cu(111) substrate and, in some cases, it can be also exothermic.