Photoinduced intercomponent excited-state decays in a molecular dyad made of a dinuclear rhenium(I) chromophore and a fullerene electron acceptor unit

novel molecular dyad, 1, made of a dinuclear {[Re2(mu-X)(2)(CO)(6)(mu-pyridazine)]} component covalentlylinked to a fullerene unit by a carbocyclic molecular bridge has been prepared and its redox, spectroscopic, and photophysical properties -including pump-probe transient absorption spectroscopy in the visible and near-infrared region -have been investigated, along with those of its model species. Photoinduced, intercomponent electron transfer occurs in 1 from the thermally-equilibrated, triplet metal/ligand-to-ligand charge-transfer ((MLLCT)-M-3) state of the dinuclear rhenium(I) subunit to the fullerene acceptor, with a time constant of about 100 ps. The so-formed triplet charge-separated state recombines in a few nanoseconds by a spin-selective process yielding, rather than the ground state, the locally-excited, triplet fullerene state, which finally decays to the ground state by intersystem crossing in about 290 ns.