Energy- and charge-transfer processes in flexible organic donor-acceptor dyads

Organic donor-bridge-acceptor dyads consisting of a triphenyldiamine donor that was linked to a perylenebisimide acceptor by a flexible nonconjugated bridge have been investigated by complementary spectroscopic techniques as a function of the length and the polarity of the linker. Time-resolved fluorescence spectroscopy revealed a quenching of the donor emission accompanied by a corresponding rise in the acceptor fluorescence, which indicates an efficient energy transfer between the donor and acceptor moieties. A second fluorescence quenching process that affects the acceptor emission is ascribed to a ground-state electron transfer from the donor to the acceptor. The lifetimes of the radicals that were determined by transient-absorption spectroscopy covered the range from 10 to 100 ms.