Synthesis of Novel Porphyrin Tripods and Their Electron-Transfer Properties

Abstract

Electron-transfer properties of a novel porphyrin tripod (TPZn3) were investigated. When TPZn3 is oxidized by tris(2,2'-bipyridyl)ruthenium(III) complex ([Ru(bpy)3]3+), the oxidized species (TPZn3)ⁿ⁺ (n = 0-3) exhibit the characteristic NIR absorption due to the pi-bond formation among the porphyrin rings. The similar electronic interactions are observed by Vis-NIR and ESR measurements at various temperatures. The porphyrin tripod can form complex with electron acceptors bearing with pyridyl group by axial coordination. The binding constant of TPZn3 and pyridyl fullerene (PyC⁶⁰) is determined to be 1.1 x 10⁵ M^-1 in o-dichlorobenzene, while the reference monomer does not exhibit complex formation. The dynamics of photoinduced electron transfer from the excited state of TPZn3 to PyC⁶⁰ are investigated in comparison of the corresponding monomer porphyrin by using laser flash photolysis measurements. The electron-transfer from ¹TPZn3* to electron acceptors are prominently accelerated as compared to the reference monomer because of the pi-pi interactions between TPZn3 and PyC⁶⁰ as well as the axial coordination.