Metalation of tetraphenylporphyrin with nickel on a TiO2(110)-1 × 2 surface

Abstract

The in situ metalation of tetraphenylporphyrin (2HTPP) with Ni on the reconstructed TiO₂(110)-1 × 2 surface, resulting in the formation of adsorbed nickel(II)-tetraphenylporphyrin (NiTPP), has been investigated by synchrotron radiation photoemission spectroscopy (SRPES), scanning tunnelling microscopy (STM) and ab initio Density Functional Theory (DFT) calculations. The metalation can be realized at room temperature irrespective of the deposition order of Ni and 2HTPP, which however leads to different metalation degrees. Increasing the substrate temperature or Ni : 2HTPP ratio results in higher metalation degree, which ultimately reaches its limit at ∼85% (Ni : 2HTPP = 3 : 1) and ∼49% (Ni : 2HTPP = 1 : 1) for post- and pre-deposition of Ni, respectively. The reaction from 2HTPP to NiTPP is accompanied by changes of the molecular adsorption conformation and the adsorption site from a tilted two-lobed feature on added Ti₂O₃ rows to a four-lobed feature on top of troughs or cross-links of the TiO₂(110)-1 × 2 surface. This interpretation of the STM data is supported by DFT-based STM simulations.