Distance-Dependent Activation Energies for Hole Injection from Protonated 9-Amino-6-chloro-2-methoxyacridine into Duplex DNA

The recent investigation of the apparently anomalous attenuation factor (β > 1.5 Å-1) for photoinduced hole injection into DNA duplexes modified by protonated 9-amino-6-chloro-2-methoxyacridine (X+) led to the conclusion that in addition to the electronic couplings, the activation energy must also be distance-dependent. In this communication we report the verification of this postulate by direct measurements of the activation energies for a series of (X+)-modified DNA duplexes which sample an appreciable range of donor−acceptor distances (∼4−11 Å). The resulting changes in thermal activation energy can be explained within the framework of a distance-dependent reorganization energy.