Synthesis of phenylnitroxides bridged by an sp(3)-linkage.

Silicon- and carbon-bridged phenylnitroxides were synthesized. They exhibited similar ESR profiles independent of the nature of the sp(3) bridge and the substitution mode of the phenylene units. The spectra revealed a quintet signal at room temperature, which became a broad triplet by lowering the temperature. Accumulated ESR measurements at 77 K led to the successful observation of a signal at Deltam(s) = 2, indicating that the triplet state was involved in this system.