Time-of-flight SIMS was used to study monolayers of the siloxane terminated porphyrin Zn-TESP (C67H75N5O5SiZn) attached to magnesium oxide (MgO) substrates in a silanisation reaction. Time-of-flight SIMS spectra show dependence of the coverage on the preparation temperature. The fragmentation pattern of the porphyrin suggests a strong bond formation to MgO, as was previously reported for SiO2. No signal of physisorbed porphyrin—as previously described for TiO2—could be detected, indicating chemisorbed species under all investigated preparation conditions. Copyright © 2012 John Wiley & Sons, Ltd.