51232-06-5Relevant academic research and scientific papers
Ligand-Assisted Electron Transfer from the Triplet State of Zinc Tetraphenylporphyrin to 1,4-Benzoquinone
Seki, Hiroshi,Hoshino, Mikio,Shizuka, Haruo
, p. 3630 - 3634 (2007/10/02)
Effects of axial ligands on the electron transfer from excited triplet state of zinc tetraphenylporphyrin (ZnTPP) to benzoquinone (BQ) have been studied by usung a laser flash technique.For the reaction of pyridinate complex of ZnTPP (Py-ZnTPP) as well as ZnTPP, quantum yield of the porphyrrin cation radicals resulting from the electron transfer, Φion, were determined in various solvents of different dielectric constant (ε).Remarkable enhancement in Φion due to axial ligation of pyridine has been found in the solvents having relatively moderate dielectric constant (9A comparison of the ε dependence of Φion for the reaction of the triplet ZnTPP to that for the triplet Py-ZnTPP has demonstrated that the axial pyridine causes partial neutralization of the effective charge of Py-ZnTPP cation radical.When the axial pyridine is replaced by several kinds of the substituted pyridines having different pKa, chloride ion, or ethanol, a significant change in Φion is revealed in dichloroethane.The change in Φion was found to depend on the ability of the ligand to transfer negative charge toward the porphyrin ring via the zinc ion.The ligand ability should cause reduction of effective charge on the porphyrin ring moiety of the ligand-bound ZnTPP cation radical which interacts with the BQ anion radical.Cosequently it has been concluded that the enhancement in Φion due to axial ligation is ascribed to the reduction of the effective charge of the cation radical which results in easier separation of the cation radical from its complex paired with BQ anion radical.
A Systematic Investigation of the Effects of Axial Ligands and Peripheral Substituents on the Electronic Structures of Zinc(II) Tetraphenylporphyrin ?-Cation Radicals: Electrochemical EPR and Spectroscopic Observation
Ichimori, Kohji,Ohya-Nishiguchi, Hiroaki,Hirota, Noboru
, p. 2753 - 2762 (2007/10/02)
A detailed study of the effect of axial ligand and peripheral substituent on the ?-system of zinc(II) tetraphenylporphyrin ?-cation radical has been made using an electrochemical EPR technique.It is confirmed from the EPR spectra that most of the anions and bases examined coordinate the radicals axially.The spin density on the nitrogen nuclei in the radicals increases with the polarizability of the axial ligand estimated from the optical spectra of the parent neutral complexes.For the fourteen complexes with different substituents on the phenyl groups examined here, there is a linear correlation between the Hammett substituent constant and the spin density.It is also shown that the para position of the phenyl group carries the spin density comparable to that of the ortho position, which indicates considerable conjugation between the porphyrin ring and the phenyl groups.In most cases, there exist two kinds of radical species which give rise to broad and sharp EPR spectra at low temperature.It is suggested that the difference in the motional states of the phenyl groups in the radicals is responsible for the different EPR spectra.
