PORPHYRIN-QUINONE ELECTRON-TRANSFER REVISITED - THE ROLE OF EXCITED-STATE DEGENERACY IN ULTRAFAST CHARGE-TRANSFER REACTIONS

Ultrafast time-resolved anisotropy experiments in which electronically excited [5-(1',4'-benzoquinonyl)-10,1 5,20-triphenylporphinato]magnes ium (MgPQ) was probed with polarization both parallel and perpendicula r to the pump pulse have been carried out in a variety of solvents. Th ese results show that the photoinduced electron transfer process invol ving the locally-excited MgPQ state is solvent independent, while the thermal charge recombination reaction is solvent dependent. Moreover, these studies indicate that the photoinduced charge separation reacti on may be rate-limited by electronic population equilibration between near degenerate porphyrin Q(x) and Q(y) levels.