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

The kinetics of photoinduced intramol. charge sepn. 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 redn. potentials of three donor-acceptor-donor mols. differ strongly as a consequence of the four substituents (R = 4-tert-butylphenoxy, H, or Cl) at the bay position of the central perylene bisimide unit. The expts. indicate that charge sepn. in these mols. occurs from the first excited singlet state of the perylene bisimide moiety to the charge-sepd. state (CSS) and to the lowest electronically excited state level of the charge-sepd. state (CSS*). For R = H and Cl, the rates for charge sepn. and charge recombination decrease with increasing change in the Gibbs free energy, and hence the mols. represent an exceptional example of mols. in which both charge sepn. and recombination occur close to or in the Marcus inverted region. [on SciFinder (R)]