Geometry optimized models of (a) free-base porphine (2H-P) and (b) copper porphine (Cu-P). Both molecules are flat in gas phase.
STM images of porphines on Cu(111) recorded at T ≃ 6 K. (a) Overview of 2H-P on Cu(111). The main axis of the molecules is defined by the two bright protrusions (dashed lines). The molecules are oriented with their secondary axis (marked with a solid line for three molecules) along the dense-packed directions of the single crystal surface indicated by the star in the bottom right (U b = −1.3 V, I t = 0.08 nA, 20×10 nm2). (b) Detailed image of 2H-P showing submolecular resolution (U b = −0.2 V, I t = 0.08 nA, 1.7×1.6 nm2). (c) Overview of porphines after annealing to 423 K. In contrast to (a) and (b) the molecules show a central protrusion pointing to metalated species, while the molecular orientation on the surface is unchanged (U b = −1.35 V, I t = 0.1 nA, 20×10 nm2). (d) Submolecular resolution of a single Cu-P (U b = −0.2 V, I t = 8.3 nA, 1.7×1.6 nm2).
N1s XP spectra of 2H-P on Cu(111). The (a) calculated ionization energies of isolated 2H-P (=N- and -NH-) and Cu-P (NCu) allow the assignment of the experimental N1s XP spectra (b-e). The two peaks of (b) a freshly prepared bilayer of 2H-P are assigned to iminic (A, blue) and pyrrolic (B, green) nitrogen species. By stepwise annealing to (c) 373 K, (d) 393 K, and (e) 433 K additional peaks (E and E′) appear which are assigned to coordinated nitrogen atoms in Cu-P in the first (E′, orange) and second (E, red) layer. STM images and ball-and-stick models of the molecule before (top) and after (bottom) the metalation illustrate the change.
The angle-resolved N K-edge NEXAFS spectra of (a) a submonolayer of 2H-P (recorded at RT) vary considerably from those of (b) a bilayer of 2H-P, indicating a strong interaction with the substrate. Annealing the bilayer to (c) 373 K and (d) 393 K leads to a change of the spectra which is assigned to the formation of Cu-P. Further annealing to (e) 433 K reduces the coverage to a (sub)monolayer of Cu-P. The inset illustrates the incidence angle θ.
The differences of the C K-edge NEXAFS spectra between (a) a submonolayer of 2H-P and (b) a bilayer of 2H-P indicate an electron transfer from the substrate to the molecule. The annealing of the bilayer to (c) 373 K and (d) 393 K leads to a change in spectra which is in agreement with a metalation of 2H-P to Cu-P. Further annealing to (e) 433 K results in a submonolayer of Cu-P whose signatures indicate a strong interaction with the Cu surface. The inset illustrates the incidence angle θ.
Comparison of experimental (a) and (c) and simulated (b) and (d) C K-edge NEXAFS spectra. Calculated resonances (bars) were broadened (solid line) to allow a better comparison with the experiment. The experimental 53°-curve of (a) a 2H-P bilayer is well reproduced by (b) the calculation for an isolated 2H-P molecule. Annealing to (c) 393 K leads to a change of peaks B and C in the measured data. The assignment to the formation of Cu-P is corroborated by (d) the simulated Cu-P spectrum.
Article metrics loading...
Full text loading...