Electronic structure of platinum complex/Zn-porphyrinato assembled macrosystems, related precursors and model molecules, as probed by X-ray absorption spectroscopy NEXAFS: theory and experiment

Macromolecular arrays containing Zn-diethynylporphyrin coordinated to platinum tethers were studied using near-edge X-ray-absorption fine-structure (NEXAFS) spectroscopy at the N K-edge. Porphin (Pf), 2,8,12,18-tetraethyl-5, 15-diethynyl-3,7,13,17-tetramethylporphyrin (PfNH) and 2,8,12,18-tetraethyl-5, 15-diethynyl-3,7,13,17-tetramethylporphyrinatozinc(II) (Zn-Pf2), have been taken as experimental models. The resonances assignment is supported by STEX (Static Exchange) calculations for the porphin and Zn-porphin (ZnPf1) molecules. By calculation, four pi* resonances occur for porphin and two for Zn-porphin. Experimentally we detect four resonances for porphin and PfNH, and two for the Zn-complexed ones. They can be assigned to core excitations to a couple of energy splitted pi* orbitals for each not equivalent N atom. Our calculations justify the observed low pi* intensity as due to an extended delocalization of the pi* orbitals. The NEXAFS investigations on platinum complex / Zn-porphyrinato assembled macrosystems [i.e. Pt-ZnPf1, Pt-ZnPf2 and Pt-ZnPf3] show the influence of the Pt theters bound to the porphyrin through the ethynyl moiety on the electronic structure of the tetrapyrrolic cycle.