Abstract. Absolute net nuclear polarizations and their time and concentration dependences are reported for the products of laser pulse initiated electron transfer from naphthalene and naphthalene derivatives to 1,2-dicyanoethenes. They represent different prototype cases for radical ion pair formation and decay pathways and are used to test predictions from the highfield radical pair theory of CIDNP. By quantitative analyses reaction efficiencies, rate constants for degenerate electron exchange and nuclear relaxation times of the radical ions are obtained.

Absolute net nuclear polarization and their time dependencies are reported for the products of geminate and nongeminate radical ion pairs involved in the electron-transfer reaction between 3C60 and the donor N,Ndimethyl-1-naphthylamine. Their analysis yields rate constants and reaction probabilities and shows that the electron back transfer between C60' -and D ' + is very efficient in benzonitrile/benzene. This is attributed to fast spin relaxation of C60' -. IntroductionBy many important publications, Closs and co-workers1 contributed to the understanding of the phenomenon of chemically induced dynamic nuclear polarization (CIDNP) and to its development for quantitative studies of radical reaction mechanisms and rates. Following earlier investigations along similar lines,2we here present a quantitative time-resolved CIDNP study of the electron-transfer reactions occurring after laser pulse generation of 3Cm in the presence of the electron donor N,Ndimethyl-1-naphthylamine (D). It is well-known from optical3 and ESR observations4 that excitation of Cm produces the triplet within nanoseconds in high yield. It has a rather long first-order lifetime and also decays by a diffusion-controlled triplet-triplet annihilation and a slower ground-state quenching. For a variety

Radical ion pairs generated by photoinduced electron transfer from Nfl-dimethyl-1 -naphthylamine to benzonitrile in acetonitrile solutions undergo reverse electron transfer to the singlet ground state and to the donor excited triplet state of the parent compounds. Both pathways lead to chemically induced nuclear polarization, but on a short time scale the triplet contribution is hidden in the triplet donor molecules. This leads to unusual CIDNP phases and time dependencies which are unravelled by FT NMR measurements and auxillary optical studies.

Radical ion pairs are generated in acetonitrile solution by photoinduced electron transfer from naphthalene derivatives to cyanobenzenes and undergo reverse electron transfer to the singlet ground and to excited triplet states of the parent compounds. Both pathways lead to chemically induced nuclear polarization of the ground state products. They can be separated because the triplet contribution appears delayed by the triplet lifetime. Variation of the radical pair energy leads to a dominance of either the singlet or triplet channel. The analysis of the absolute net CIDNP effects and their time dependencies yields reaction probabilities for the reverse electron transfers which depend on the appropriate energy gaps as described by the Marcus theory, as well as rate constants for degenerate electron and spin exchange processes. For the donor/acceptor system naphthalene/(E)-1,2-dicyanoethene, the triplet pathway is also found dominant.