Reevaluation of the gas-phase valence photoelectron spectra of octaethylporphyrin and tetraphenylporphyrin

Gas-phase valence photoelectron spectra are reported for 2,3,7,8,12,13,17,1 8-octaethylporphyrin (OEPH2) and 5,10,15,20-tetraphenylporphyrin (TPPH2). C omparison of spectra collected with He I and He II sources gives an empiric al assignment of the relative order of the low-energy (2)A(u) and B-2(1u) i on states in the gas phase. For OEPH2, the first ionization at 6.24 eV is a ssigned to the (2)A(u) ion state, with the B-2(1u) ionization located 0.25 eV to higher energy. The photoelectron spectrum reported here is quite diff erent from the previously reported spectrum of OEPH2. The first ionization of TPPH2 is assigned to the B-2(1u) ion state, with the (2)A(u) ionization 0.27 eV to higher energy. The reversal of the ordering of the first two ion izations of OEPH2 and TPPH2 is due to the different site of the substituent s and the different nodal properties of the porphyrin orbitals.