Jm. Degraziano et al., FREE-ENERGY DEPENDENCE OF PHOTOINDUCED CHARGE SEPARATION RATES IN PORPHYRIN DYADS, Journal of physical chemistry, 98(7), 1994, pp. 1758-1761
A series of covalently linked porphyrin dyads in which the thermodynam
ic driving force for interporphyrin photoinduced charge separation spa
ns a range of 1.13 eV has been prepared. Time-resolved fluorescence st
udies have yielded 22 rate constants for photoinduced electron transfe
r in dichloromethane solution ranging from 4.1 x 10(7) to 5.0 X 10(11)
s(-1). The data are consistent with the theoretical treatments of Mar
cus and Levich, although there is no evidence for inverted behavior. I
n the normal region, electron transfer between free base porphyrin moi
eties is about 4 times faster than transfer involving a zinc porphyrin
and having the same thermodynamic driving force, based on electrochem
ical measurements. Photoinduced electron transfer to an excited single
t state and electron transfer from an excited singlet state have the s
ame dependence upon free energy change.