Photochemical and Electrochemical Properties of Zinc Chlorin-C_(60) Dyad as Compared to Corresponding Porphyrin-C_(60) Dyads

摘要

The photochemical and electrochemical properties of zinc chlorin-C_(60) dyad are examined in comparison with those of corresponding porphyrin-C_(60) dyads using the same short spacer. In contrast with the all previous results on porphyrin-fullerene dyads, the photoexcitation of a zinc chlorin-C_(60) dyad results in a unusually long-lived radical ion pair which decays via first-order kinetics with a decay rate constant of 9.1 x 10~3 s~(-1). This value is two to six orders of magnitude smaller than values reported for all other porphyrin or chlorin donor-acceptor dyad systems. The formation of radical cations of the donor part and the radical anion of the acceptor part was also confirmed by ESR measurements under photoirradiation at low temperature. The photoexcitation of other dyads (free-base chlorin-C_(60), zinc porphyrin-C_(60) and free-base porphyrin-C_(60) dyads) results in formation of the triplet excited states of the chlorin or porphyrin moiety via the higher lying radical ion pair states as is expected from the redox potentials.