ABSENCE OF DIELECTRIC-RELAXATION EFFECTS ON INTRAMOLECULAR ELECTRON-TRANSFER IN PORPHYRIN QUINONE CYCLOPHANES

We have measured photoinduced intramolecular electron transfer rates k(et) in two porphyrin-dichloroquinone cyclophanes varying the polarity, the temperature, and the dielectric relaxation time of the solvent. The reaction is most likely activationless or in the inverted region in all solvents. The adiabaticity parameter kappa=4piV(eff)2/HBARlambda(s)tau(l) for dynamic dielectric solvent control is estimated to cover the range 0.2 less-than-or-equal-to kappa less-than-or-equal-to 400. Nevertheless the rate k(et) was found to be almost independent of the solvent properties (k(et) > 5 X 10(11) s-1) casting doubt on current ideas of dielectric relaxation effects on electron transfer.