Photoinduced charge shift and charge recombination through an alkynyl spacer for an expanded acridinium-based dyad

The photophysical and electrochemical properties of a dyad comprising an expanded acridinium light-harvester, coupled via a triple bond to a trialkyloxybenzene donor, are described. Laser excitation of the dyad in 1,2-dichloroethane (DCE) results in rapid charge shift (5 ps) followed by slower charge recombination (81 ps) to completely restore the ground state. Discrimination between forward and return electron transfer (k(ret)/k(for) ~ 16) is rather poor. There is no indication of triplet formation on the expanded acridinium-based group following charge recombination.