A TIME-RESOLVED ELECTRON-PARAMAGNETIC RESONANCE STUDY ON THE PHOTOINDUCED ELECTRON-TRANSFER REACTIONS FROM METALLOPORPHYRINS TO QUINONES

The photoinduced electron transfer reactions in the systems of zinc tetraphenylporphyrin (ZnTPP) and magnesium tetraphenylporphines (MgTPPs) and 1,4-benzoquinone were investigated by means of a time-resolved electron paramagnetic resonance (EPR) technique and deuteration of the compounds. Three kinds of reaction intermediate - the porphyrin cation, the quinone anion and their ion pair - were definitely assigned by reference to their EPR parameters. From simultaneous observations of the separated ions (SIs) and the ion pair, it is established that the rates from a contact ion pair to a solvent separated ion pair (SSIP) and from an SSIP to an SI are accelerated by axial ligation and addition of the salt respectively. The magnitudes of these effects were different for the ZnTPP and MgTTP systems, and their origins are briefly discussed.