PHOTOPHYSICS OF LINKED DONOR-ACCEPTOR SYSTEMS - THROUGH-SPACE AND THROUGH-BOND INTERACTIONS

Possible competition between through-sigma-bond and through-space interaction on the one hand and between through-sigma- and through-pi-bond interaction on the other has been studied in flexibly and rigidly linked donor-acceptor systems. In a first part, pyrenyl-substituted donor-acceptor compounds were studied, where a permethylated oligosilane chain acts as a flexible spacer. The possible involvement of a sigma delocalized oligosilane chain in the electron transfer process is studied. Intramolecular electron transfer was observed from a permethylated hexasilane chain towards pyrene in the excited state. Through-space ground-state interactions were observed for the donor-acceptor substituted hexamethyl trisilane chain. In order to study the electron transfer process via through-sigma- and through-pi-bond interactions, rigid trichromophoric compounds in an A1-D-A2 configuration were studied. One of the acceptors is directly bound to the donor moiety, while the other acceptor is separated from the donor by a rigid spacer of three sigma bonds. The study of these compounds by means of absorption, stationary and time-resolved emission spectroscopy reveals a competition between the two possible electron transfer directions in one of the trichromophoric compounds.