In a control experiment we also measured the CIDNP of deoxygenated solutions of DMUM (100 mM) and 2MInd (25 mM) in acetonitrile. The spectra are shown in Figure 2. DMUM shows emission at 3.26 and 3.34 ppm due to the two methyl groups at N 3 and N1, respectively, and enhanced absorptions at 7.37 ppm for the proton a t C6. 2MInd shows again enhanced absorption at 2.46 ppm and, in addition, emission at 6.19 ppm for the proton at C3, as well as weak emission and absorption for the aromatic protons. The phases can be explained again with the aid of Kaptein's rules by assuming conditions similar to those in the DMUD case for geminate recombination, but now with a large and negative coupling to the C6 and little coupling to the C5 proton (7.37 vs 5.66 ppm). This agrees with spin density calculations for DMUM radical anion which predict high spin density at C6 and small spin density at C5.I3There is a distinct difference between the CIDNP spectra of DMUM formed from DMUD cleavage (Figure 1) or from the purely cyclic E T process (Figure 2). This is the consequence of the difference of precursors, i.e., the parent radical anions and their spin density distributions. We did not observe any CIDNP signal due to the C6 ring proton for DMUM after DMUD cleavage which could arise from geminateI6 and from nongeminate 2Mlnd+ DMUM-pairs. This implies that the splitting of DMUDdoes not compete effectively with the geminate reverse ET and that the concentration of free DMUM-is low. Further work is in progress to elucidate more kinetic information and donor and solvent dependences.

No abstract

No abstract

No abstract

No abstract