O 1s spectrum of RuCO-OEP sublimed at 253 ± 5 °C (center), compared to that of Ru-OEP sublimed at 415 ± 5 °C (bottom), where the CO ligand is thermally desorbed. Correspondingly, the characteristic π* transition of the axial CO ligand disappears. It reappears after exposure to air (top).
Preparation of a well-ordered thin film of FeCl-OEP dye molecules by in situ sublimation (bottom and center). Care needs to be taken to keep the sublimation temperature below the decomposition temperature. At higher temperatures (411 ± 5 °C, top), nitrile fragments can be detected at the N 1s edge by their characteristic π* peak at 399.9 eV (see Figs. 6(b) and 6(c) in Ref. 50 ).
N 1s spectra of bipyridine-based molecules. The lowest N 1s-to-π* transition shifts down by 0.15 eV when replacing Ru by Fe, due to a decrease in the N 1s core level binding energy that is caused by an extra transfer of negative charge from Fe to the N ligands.
N 1s spectra of phenanthroline-based molecules. The lowest N 1s-to-π* transition shifts down by 0.3 eV when replacing Ru by Fe. Similar to the bipyridine-based molecules, the shift is due to a decrease in the N 1s core level binding energy.
N 1s spectra of OEP-based molecules. The lowest N 1s-to-π* transition shifts down by 0.2 eV going from RuCO-OEP to FeCl-OEP (second and third curves). Removal of the CO ligand from RuCO-OEP increases the transition energy by 0.2 eV (top curve). In H2-OEP, the lowest π* transition splits because of two inequivalent N atoms (bottom curve).
C 1s spectra of bipyridine-based molecules. The C 1s-to-π* transition energy increases by 0.15 eV when replacing Ru by Fe. The second π* transition at higher energy shifts by the same amount, suggesting a transition into the same π* orbital from a second set of C atoms with higher binding energy (those binding to N).
C 1s spectra of phenanthroline-based molecules. The C 1s-to-π* transition energy increases by 0.05 eV when replacing Ru by Fe. The smaller shift compared to the bipyridine-based molecules is likely due to delocalization of the charge transfer over the larger π system of phenanthroline.
C 1s spectra of OEP-based molecules with a planar N cage. The C 1s-to-π* transition energy decreases by about 0.1 eV when going from Ru- to Fe-based OEPs, opposite to the behavior of the dye molecules with three-dimensional cages in Figs. 6 and 7 .
Observed N 1s-to-π* transition energies.
Observed C 1s-to-π* transition energies.
Calculated N 1s-to-π* transition energies for Ru- and Fe-OEPs. The results for the N 1s core level and the LUMO are obtained relative to the vacuum level from a transition state calculation (with 1.5 electrons in the N 1s core level), while the N 1s-to-π* transition is obtained from a ΔSCF calculation. The N charge has been obtained using the Bader analysis. 57
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