Photochemical and electrochemical properties of zinc Chlorin-C-60 dyad as compared to corresponding free-base chlorin-C-60, free-base Porphyrin-C-60,and zinc porphyrin-C-60 dyads

The photochemical and electrochemical properties of four chlorin-C-60 or po rphyrin-C-60 dyads having die same short spacer between the macrocycle and the fullerene are examined. In contrast with all the previous results on po rphyrin-fullerene dyads, the photoexcitation of a zinc chlorin-C-60 dyad re sults in an unusually long-lived radical ion pair which decays via first-or der kinetics with a decay rate constant of 9.1 x 10(3) s(-1). This value is 2-6 orders of magnitude smaller than values reported for all other porphyr in or chlorin donor-acceptor of the molecule dyad systems. The formation of radical cations of the donor part and the. radical anion of the acceptor p art was also confirmed by ESR measurements under photoirradiation at low te mperature. The photoexcitation of other dyads (free-base chlorin-C-60, zinc porphyrin-C-60, and free-base porphyrin-C-60 dyads) results in formation o f the ion pairs which decay quickly to the triplet excited states of the ch lorin or porphyrin moiety via the higher lying radical ion pair states as i s expected from the redox potentials.