Triplet dimers of silylbenzene anion radicals in low-temperature glass matrices

Anion radicals of o- and p-bis(trimethylsilyl)benzenes were found by ESR spectroscopy to form the corresponding triplet dimers in 2-methyltetrahydrofuran (MeTHF) glass matrices at low temperatures. The temperature dependence of the signal intensity of a triplet dimer has shown that the dimer has the triplet ground state. The spin–spin distances estimated with the D values increased with the increasing size of alkali metal countercations, indicating that the triplet dimer has a π−–M+–π− type sandwich structure. The stability of the triplet dimer depended remarkably on the coordination ability of the solvent; no triplet dimer was observed in tetrahydrofuran (THF).