Interfacial Reactions of Tetraphenylporphyrin with Cobalt‐Oxide Thin Films

Abstract

We have studied the adsorption and interfacial reactions of 2H-tetraphenylporphyrin (2HTPP) with cobalt-terminated Co 3 O 4 (111)a nd oxygen-terminated CoO(111)t hin films using synchrotron-radiation X-ray photoelectrons pectroscopy.A lready at 275 K, we find evidence for the formation of am etalateds pecies, most likely CoTPP,o nb oth surfaces. The degree of self-metalation increases with temperature on both surfaces until 475 K, where the metalation is almostc omplete. At 575 Kt he porphyrin coverage decreases drastically on the reducible cobalt-terminated Co 3 O 4 (111)surface, while highert emperatures are needed on the non-reducible oxygen-terminated CoO(111). The low temperature self-metalation is similar to that observed on MgO(100)s urfaces, but drastically different from that observed on TiO 2 (110), where no self-metalation is observeda tr oomt emperature. Figure 4. LEED diffraction patterns and Co 2p spectra of clean CoO(111)a nd Co 3 O 4 (111)a tr oom temperaturea nd of Co 3 O 4 (111)w ith adsorbed 2HTPP aftera nnealing to 675 K.Figure 5. N1 sX PS spectraa fter adsorption of 2HTPP on Co 3 O 4 (111)a nd on CoO(111)a t2 75 Ka nd on MgO (100) [13] and TiO 2 (110) [12] at room temperature.

Self‐Metalation of Anchored Porphyrins on Atomically Defined Cobalt Oxide Surfaces: In situ Studies by Surface Vibrational Spectroscopy

“…Noteworthy are previous XPS studies with non‐functionalized 2HTPP, which showed that metalation is possible at low‐temperatures on CoO(111) . Here it was found that in the submonolayer region 61 % of 2HTPP were already metalated at 175 K. Based on these findings, we propose that a small fraction of the MCTPP multilayer film undergoes metalation already upon deposition at 150 K. However, metalation remains restricted to a minor fraction of molecules in the first monolayer.…”

“…We studied the adsorption of 2HTPP and MCTPP on Co 3 O 4 (111), which showed clear impact of the functionality on the tilting angles of the molecules at the surface within the monolayer (note that self‐metalation was not investigated in this study) . However, self‐metalation was observed for non‐functionalized 2HTPP on Co 3 O 4 (111) and CoO(111) at room temperature, very similar to MgO(100) . This work suggests that self‐metalation on oxide surfaces is possible, but the reaction is by no means a simple process.…”

Adsorption and self-assembly of porphyrins on ultrathin CoO films on Ir(100)

“…Higher temperatures could not be applied to 2 without changing the appearance of the molecules. This is attributed to metalation of the free-base porphyrin with Co ions [12,13]. Both molecules adsorb flat-lying on the cobalt oxide film.…”

“…The research revealed numerous ways to steer self-assembly and on-surface reactions by a careful choice of functionalization and substrates [2]. Despite its importance for applications, the investigation of the structure and binding of porphyrins on semiconducting and, notably, metal oxide surfaces remains scarce [3][4][5][6][7][8][9][10][11][12][13]. We chose here to investigate two different porphyrins on thin films of cobalt(II) oxide (CoO).…”

“…Functionalization of porphyrins may introduce new properties of the molecular adlayer, for example, by introducing elements that allow for strong anchoring [8,[10][11][12][13]. This may, however, counteract the possibility to form ordered layers when, due to the enhanced molecule-substrate interaction, the molecules become immobile or the functional groups used as anchors cannot give rise to intermolecular forces anymore.…”