Portland State University. Department of Chemistry
Carl C. Wamser
Date of Award
Doctor of Philosophy (Ph.D.) in Chemistry
1 online resource (xii, 120 pages)
Porphyrins -- Analysis, Porphyrins -- Synthesis
Spectrophotometric titrations for a full series of 4-aminophenyl/4-pyridyl meso-substituted porphyrins were carried out using methanesulfonic acid in DMSO to study the hyperporphyrin effect across different substitution patterns. The series included zero, one, two (cis and trans), three, and four meso(4-aminophenyl) groups, with the remaining meso substituents being 4-pyridyl groups. The peripheral pyridyl groups consistently protonate before the interior porphyrin pyrrole nitrogens, which protonate before the aminophenyl groups. Aminophenyl substituents increase the basicity of the pyrrole nitrogens and lead to distinctive hyperporphyrin spectra with a broad Soret band and a strong red absorption. The structure proposed to give rise to these spectra is the previously proposed charge-transfer interaction between the aminophenyl and the protonated pyrrole. A novel hyperporphyrin structure involving charge-transfer interactions between two peripheral substituents is also proposed in one case - the triply protonated (+3) porphyrin with three aminophenyl and one pyridyl substituents; two of the aminophenyl groups delocalize the charges on the interior nitrogens while the third aminophenyl group delocalizes with the protonated pyridyl.
The NMR titrations for a full series of 4-aminophenyl/4-pyridyl meso-substituted porphyrins were also performed by methanesulfonic acid in DMSO. Zero, one, two (cis), three, and four meso(4-aminophenyl) groups, with the remaining meso substituents being 4-pyridyl groups are the primary compounds studied here. The inductive effect of the meso-substituents and the π system of the macrocycle both determine the hyperporphyrin spectra, in which inductive effect has stronger influence on cis-A2Py2P and APy3P. TAPP and A3PyP both show slow exchanges from free base to hyperporphyrin, indicating these hyperporphyrin structures are stable. Both 1H-NMR and 2D NOESY spectra further validate the existence of the novel D-type hyperporphyrin from A3PyPH3+3.
Electrochemical studies of these hyperporphyrins were also performed. The porphyrins involved here are zero, two (cis & trans), three, and four meso (4-aminophenyl) groups, with the remaining meso substituents being 4-pyridyl groups. The acid titrations were done in DMSO using methanesulfonic acid. Both TAPP and A3PyP can be extensively reduced with up to five distinct reduction waves. The hyperporphyrin from A3PyP, unlike that from TAPP, shows stable structures during the reduction, and A3PyPH3+3 was proposed to have the ability to reduce protons into hydrogen in a catalytic cycle.
Wang, Chenyi, "Spectroscopy, NMR, and Electrochemistry Studies of Protonated Aminophenyl/Pyridyl Porphyrins and Their Application in Hydrogen Evolution" (2015). Dissertations and Theses. Paper 2223.