ELECTRONIC-STRUCTURE OF THIAPORPHYRINS - AN X-RAY PHOTOELECTRON SPECTROSCOPIC STUDY

The electronic structure of 5,10,15,20-tetraphenylporphyrin (H(2)tpp) modified with one and two sulfur core atoms has been investigated by X -ray photoelectron spectroscopy (XPS). The nitrogen Is binding energie s (b.e.s) were excellent sensors of the electronic effects of the core -modified porphyrins. They clearly show that there is an increase in e lectron density on the core nitrogen atoms when the two NH groups in H (2)tpp are replaced by sulfur atoms, the nitrogen Is b.e. decreasing b y about 1.5 eV. The carbon Is core level also decreases in b.e. on cor e modification with sulfur atoms. The results obtained are in good agr eement with those from UV/VIS, fluorescence spectroscopy, electrochemi cal studies, X-ray diffraction and extended-Huckel calculations. They indicate that there is an interaction between the nitrogen and sulfur atoms and a mechanism is suggested for it. No evidence was found for i nteraction among sulfur atoms and the participation of their d orbital s in the electronic structure. Copper and nickel complexes of the mono thiaporphyrin were also subjected to XPS analysis.