Inverse Photoemission Spectroscopy of Coinage Metal Corroles: Comparison with Solution-Phase Electrochemistry

Area of Science:

• Materials Science
• Physical Chemistry
• Spectroscopy

Background:

• Coinage metal corroles are macrocyclic compounds with potential applications in electronics and catalysis.
• Understanding their electronic structure, particularly unoccupied orbitals, is crucial for predicting their behavior.
• Electrochemical methods provide insights into successive electron additions, but direct electronic structure information can be limited.

Purpose of the Study:

• To investigate the electronic structures of copper, silver, and gold triphenylcorrole (TPC) complexes.
• To compare the information obtained from inverse photoemission spectroscopy (IPES) with electrochemical measurements.
• To correlate observed electronic differences with the nature of the lowest unoccupied molecular orbital (LUMO).

Main Methods:

• Combined direct and inverse photoemission spectroscopy (IPES) was employed.
• Electrochemical reduction potentials were measured for comparison.
• Analysis focused on ionization potentials, electron affinities, and LUMO characteristics.

Main Results:

• All three coinage metal TPC complexes showed similar ionization potentials.
• IPES spectra revealed significant differences in the lowest unoccupied orbital energies: Cu[TPC] (0.74 eV), Ag[TPC] (1.65 eV), and Au[TPC] (2.40 eV), relative to the Fermi level.
• These spectral differences correlated with electrochemical reduction potentials and the metal- or corrole-centered nature of the LUMO.

Conclusions:

• Inverse photoemission spectroscopy provides valuable complementary information to electrochemistry for studying unoccupied electronic states in coinage metal corroles.
• The electronic properties and LUMO characteristics vary significantly across Cu, Ag, and Au TPC complexes.
• The findings offer a deeper understanding of structure-property relationships in these metalloporphyrin analogues.