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

A novel molecular dyad, 1 , made of a dinuclear {[Re 2 (μ-X) 2 (CO) 6 (μ-pyridazine)]} component covalently-linked 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 ( 3 MLLCT) 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.