A flexible organic dyad consisting of a perylene bisimide antenna covalently linked to a [60]fullerene has been synthesized and studied by electrochemistry, steady-state spectroscopy, and time-resolved spectroscopy. We found that the energy absorbed by the perylene bisimide is transferred to the fullerene with an efficiency close to 100%. The fullerene in turn undergoes intersystem crossing followed by triplet energy transfer back to the perylene bisimide with an efficiency of at least 20%. Hence the perylene bisimide unit acts as an antenna for the fullerene, i.e., effectively extending the fullerene absorption far into the visible spectral range, while at the same time the fullerene acts as a triplet sensitizer for the perylene bisimide. This has severe consequences for the exploitation of the dye antenna-fullerene concept for light harvesting in solar cells.

It takes three: The key functionalities of an optical transistor, gating and amplification, are demonstrated exploiting the photophysical properties of a molecular triad (see picture). Two building blocks of the triad are highly efficient fluorophores, whereas the third building block is a photochromic molecule that can be reversibly interconverted between two bistable forms by light.

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.

Organic semiconductor devices such as light-emitting diodes and solar cells frequently comprise a blend of molecular or polymeric materials. Consequently, resonant energy transfer between the components plays a major role in determining device performance. Energy transfer may take place through either single-step donor-acceptor transfer, realized for example as Förster transfer, or as a sequence of donor-donor transfers toward the acceptor site. Here we use a well-defined model system comprising an oligofluorene trimer, pentamer, or heptamer as the donor in combination with an anthracene derivative as the acceptor in order to study the rate and mechanism of energy transfer in thin films by time-resolved photoluminescence spectroscopy. We find the transfer process to be entirely dominated by sequential donor-donor transfer. In addition, we observe a strong dependence on oligomer length with an optimum energy transfer rate for the pentamer.