NMR investigations of N, N, N′, N′ -tetramethyl-p-phenylenediamine and its oxidized tetrafluoroborate salts

Abstract

Proton and fluorine magnetic resonance absorption and spin–lattice relaxation time measurements have been carried out on N, N, N′,N′-tetramethyl-p-phenylenediamine and its two oxidized compounds containing the BF4 anion moiety. The second moments and the spin–lattice relaxation times are analyzed in terms of the methyl and BF4 group motions. The methyl group motion is greatly influenced by the oxidation states, and the BF4 isotropic motion is found to be remarkably mobile in the environments of these organic cation molecules. The 1H and 19F relaxation times in the paramagnetic state showed two characteristic temperature dependences above and below the phase transition temperature. It is found that, in the high temperature region, the hyperfine interaction is responsible for the 1H relaxation, while the dipolar electron–nuclear interaction is responsible for the 19F relaxation. In the low temperature region, both the 1H and 19F relaxations are controlled by the triplet exciton motions, in addition to the isotropic BF4 rotational motion in the case of the 19F relaxation.