Near edge structures of Mg-, Co-, Cu- and Zn-tetraphenylporphyrins measured by PESA and calculated with DV-X alpha

The near-edge electronic structures of several tetraphenylprophyrins (TPPs), modified by substituting the central metal atoms (M), were measured using photoelectron spectroscopy in air (PESA), and were estimated using the DV-Xα molecular orbital calculation method. The metal atoms used were Mg, Co, Cu and Zn. The ionization thresholds and the photoelectron emission yields of these TPPs changed significantly from compound to compound. The thresholds for ionization or photoemission can be divided into two groups, i.e. 1) less than 5.26 eV for Mg II TPP and Zn II TPP, and 2) more than 5.38 eV for Co II TPP and Cu II TPP. DV-Xα calculations demonstrated that the upper valence band primarily consists of C2p in Mg II TPP and Zn II TPP, M3d in Co II TPP, and M3d and N2p in Cu II TPP. Such valence band components can be used to explain the difference in observed photoemission threshold energies and to elucidate the change in photoemission yields for electrons with low kinetic energy.