Electron hopping in pi-stacked covalent and self-assembled perylene diimides observed by ENDOR spectroscopy.

We have carried out room-temperature, solution-phase electron paramagnetic resonance and electron-nuclear double resonance studies on a series of radical anions based upon perylene-3,4:9,10-bis(dicarboximide) (PDI). The following systems were studied: two PDI monomers, a covalent, cofacial dimer, and two covalent trefoil-PDI3 molecules, one of which self-assembles into pi-stacked dimers. Full sharing of the unpaired electron in the covalent and self-assembled dimers is revealed by a halving of the hyperfine coupling constants in these species, relative to those of the monomers. These results and the electronic absorption spectra show that electron hopping on a >107 Hz time scale occurs between a reduced and neutral chromophoric pair.