Poly(1,2-phenylenevinylene) ferromagnetically 3,5-bearing phenoxyl radicals

A π-conjugated but non-Kekulé- and nondisjoint-type molecule, poly(1,2-phenylenevinylene) 3,5-disubstituted with pendant phenoxyl radicals (1a), was designed as a new high-spin organic polymer and synthesized by the head-to-tail coupling polymerization of 2-bromo-3,5-bis(3,5-di-tert-butyl-4-aceotoxyphenyl)styrene (3) using a palladium catalyst. The corresponding high-spin dimer model compound bearing four phenoxyl radicals (2a) was also synthesized. The stepwise radical formation in 1 and 2 was electrochemically studied. The ESR signal at ΔM_s = ±2 indicated a triplet ground state for 1 and 2. However, the SQUID data revealed that the spin concentration and the average spin quantum number of 1a and 2a remained at ca. 0.5 spin/phenol unit and 2/2, respectively. A degradation at the vinylene bridge was suggested after the radical generation.