Photoinduced electron transfer in the solid state: rate vs. free energy dependence in fixed-distance porphyrin-acceptor molecules

The authors recently reported that the ion-pair states in two porphyrin-triptycene-acceptor molecules are destabilized by as much as 0.9 eV in going from a polar liquid to a rigid glass. To obtain a quantitative picture of the dependence of charge-separation rate on free energy of reaction in the rigid glass they present electron transfer rate data on 14 porphyrin-triptycene-acceptor molecules, which possess sufficiently large, negative free energies for charge separation to allow electron transfer to compete with excited singlet state decay in glassy 2-methyltetrahydrofuran (MTHF) at 77 K.