X-ray photoelectron spectroscopy of metal free porphyrazine, phthalocyanine and naphthalocyanine: density functional calculations

A theoretical investigation of the core-level electronic structure of metal free porphyrazine, phthalocyanine and naphthalocyanine based on density functional theory has been conducted. The sign-reversed energies of the N 1s orbital with small discrepancy of about 8 eV are reported, which is improved compared with that of previous SCF/DZ and SCF/DZP calculations, 25 eV. The sign-reversed energies of the C 1s orbital for these three compounds are reported for the first time also with discrepancy of about 8 eV. Our result has demonstrated that density functional calculations at B3LYP/6-31G(d) level are more suitable for studying the absolute core-level energies of phthalocyanine and its analogues and/or derivatives than SCF calculations, in addition to giving reasonable result on the relative changes in the core-level energies. A comparison between the core-level molecular orbital and X-ray photoelectron spectroscopy (XPS) properties for these molecules is made. The effect of extended π-electron conjugation on the N XPS properties of these compounds is discussed. The data of the C 1s orbital reported in the present work will be helpful for future experimental and theoretical XPS research works on these compounds.