Time-resolved CIDNP from photochemically generated radical ion pairs in rigid bichromophoric systems Original Research Article

Laser pulse photoexcitation of rigid donor–spacer–acceptor molecules in various solvents leads to chemically induced dynamic nuclear polarization (CIDNP) of the ground state species. This polarization is created during the simultaneous charge recombination of the intermediate ion pairs via singlet and triplet pathways. The different channels yield polarizations with opposite signs and equal magnitudes and are separated in time because the triplet contribution appears delayed. Their time dependence yields the triplet decay parameters. The CIDNP intensities depend strongly on the spacer length and on the dielectric constant of the medium. They are explained in terms of the radical pair theory combined with the known dependence of rate constants on energy gaps, and provide the exchange interaction in the ion pairs.