Spin-spin coupling between the two unpaired electrons in cross-conjugated tetrathiafulvalene dication radicals

Spin-spin interactions were examined for bis(tetrathiafulvalenyl) (TTF) derivatives bridged with a 1,1-vinyl group (2,2-diphenyl, 1: 2,2-fluorenylidene, 2; and 2,2-dimethyl, 3). The chemical oxidation of these cross-conjugated TTFs using AgClO₄ yielded characteristic seven-line ESR spectra, indicating the exchange interactions between the unpaired electrons on each TTF moiety. Compounds 2 and 3, in addition, exhibited fine structures and half-field resonances in the frozen solutions, which evidence the triplet interaction in the solid state, even with a twisted geometry of the molecular configuration. These findings substantiate the possibility of spin-spin interactions or triplet ground states predicted for some TTF oligomers.