Absorption and resonant photoemission spectroscopy of transition metal phthalocyanines
Final Report Abstract
In summary, the electronic structure of transition-metal phthalocyanines has been investigated for a series of transition-metal ions from Zn to Mn by soft L-edge X-ray absorption and 2p photoemission spectroscopy. First of all, no temperature dependences in the experimental results have been observed for any of the six complexes, excluding an excited state very close to the ground state, as it has been predicted from crystal field multiplet calculations for CoPc. A simple theoretical model is presented that allows for an interpretation of the polarization dependent absorption data and compare the theoretically derived numbers to those found experimentally. Such a comparison allows excluding certain configurations on one hand and points toward other configurations on the other. For CuPc and NiPc, the data confirm a partially and empty b1g orbital, with a small amount of eg backbonding for NiPc. For CoPc, the results point toward a dominant ground state configuration of b1g0a1g1eg4b2g2, while all other options are out of the error bar region. In case of FePc, a broad range of possible configurations is possible for a spin state of S = 1. These four options could have been narrowed down to one main configuration, namely the one with Eg orbital symmetry. Only for MnPc a single configuration cannot be pointed out. It can only be stated that for S = 3/2 the two configurations b1g0a1g1eg3b2g1 and b1g0a1g1eg2b2g2 are equally well possible from the data. As a second method, a series of transition metal 2p photoemission data is presented. The analysis mainly focuses on the position and intensity of the satellite peak following well-known theoretical thoughts. A small ligand mixing is found for all complexes, leading to a weak covalence. Note this finding further supports a posteriori the conclusions derived from the intensity ratios, since a strong deviation from the atomic configurations also influence the intensity ratio. From the satellite peak position it is inferred on decreasing charge transfer energy Δ with decreasing atomic number. The full theoretical descriptions using charge-transfer multiplet calculations are promising.
Publications
- Transition metal phthalocyanines: Insight into the electronic structure from soft x-ray spectroscopy, The Journal of Chemical Physics 137, 054306 (2012)
T. Kroll, R. Kraus, R. Schönfelder, V. Yu. Aristov, O. V. Molodtsova, P. Hoffmann, and M. Knupfer
(See online at https://doi.org/10.1063/1.4738754)
