Temperature Independent Ultrafast Photoinduced Charge Transfer in Donor−Acceptor Pairs Forming Exciplexes

Abstract

The temperature dependence of photoinduced electron transfer reactions of phthalalocyanine- and porphyrin-fullerene dyads, in which donor and acceptor moieties are covalently linked to each other, was studied. The dyads form an intramolecular exciplex as a transient state before the formation of the charge separation state. It was observed that the formation rates of the exciplex and the charge separated states, as well as the charge recombination rate, were all independent of temperature and thus activationless processes. It seems to be a general rule that the aromatic π−π interaction between the donor and acceptor moieties is an important factor for exciplex formation as transient states in photoinduced electron transfer reactions and this causes barrierless charge separation and recombination reactions.