Coordination Properties of Porphyrin Analogues Ionized Forms by Experiment and Quantum Chemistry: 5,10,15,20-Tetraphenyl-21-thia- and 5,10,15,20-Tetraphenyl-21,23-Dithiaporphyrins

Abstract

Modification of porphyrins by a replacement of N atom(s) with a heteroatom(s) resulted in the so called heteroporphyrins which exhibit interesting physicochemical properties. In this work, the spectral properties of ions and neutral forms of 5,10,15,20-tetraphenyl-21,23-dithia porphyrin (S2PP) and 5,10,15,20-tetraphenyl-21-thia-porphyrin (HSPP) have been investigated. According to the spectrophotometric analysis in acetonitrile – perchloric acid solution, the dication H2S2PP2+ reveals an ability to coordinate two ClO4− anions, which was not found for H3SPP2+. This fact, as observed in the UV-Vis absorption spectra, indicates the possibility of exhibiting chemosensory properties of S2PP molecules. The geometries of the neutral and ionized forms were derived from B3LYP/cc-pVTZ calculations. The perimeters of the cavities increase in the series: H2PP→HSPP→S2PP. This trend is kept in case of the ionized forms; the protonation expands the cavity perimeter. Electron density distributions were analyzed in terms of quantum theory of atoms in molecules (QTAIM). The UV-vis spectra simulated on the base of the TD-DFT calculations match the experimental results.