Charge separation and recombination in photoexcited oligo(p-phenylene vinylene):: Perylene bisimide arrays close to the marcus inverted region

The kinetics of photoinduced intramolecular charge separation and subsequent charge recombination of three oligo(p-phenylene vinylene)-perylene bisimide-oligo(p-phenylene vinylene) arrays has been studied using femtosecond pump-probe spectroscopy in solvents of different polarity. The reduction potentials of three donor-acceptor-donor molecules differ strongly as a consequence of the four substituents (R = 4-tertbutylphenoxy, H, or Cl) at the bay position of the central perylene bisimide unit. The experiments indicate that charge separation in these molecules occurs from the first excited singlet state of the perylene bisimide moiety to the charge- separated state (CSS) and to the lowest electronically excited state level of the charge-separated state (CSS*). For R = H and Cl, the rates for charge separation and charge recombination decrease with increasing change in the Gibbs free energy, and hence the molecules represent an exceptional example of molecules in which both charge separation and recombination occur close to or in the Marcus inverted region.