Topological control of spin states in disjoint diradicals.

The meta- and para-bis-allylbenzene radical anions have been generated and investigated using mass spectrometry. The ions are formed by reaction of the corresponding bis-2-propenylbenzenes with atomic oxygen anion. Reactivity of the ions indicates that the ions most likely have a bis-allylbenzene structure. Reaction of the ions with carbon disulfide creates CS(2) adducts, which, upon collision-induced dissociation, decompose to regenerate the bis-allylbenzene anion or carbon disulfide radical anion. The branching ratios for the two products indicate differences in the electronic structures of the neutral bis-allylbenzene diradicals. The difference in branching ratios and corresponding estimated electron affinities is interpreted in terms of different electronic states being formed, with the para diradical a singlet and the meta diradical either a ground-state triplet or a singlet with a very small singlet-triplet splitting. The difference in electron affinities is used to estimate a singlet-triplet splitting of 0.06 eV for the para diradical. The studies show that topology can be used to control the electronic properties of disjoint, tetramethyleneethane (TME)-like diradicals.