Ladderlike ferromagnetic spin coupling network on a π-conjugated pendant polyradical

A poly(9,10-anthryleneethynylene)-based polyradical with two pendant stable phenoxyls in one anthracene skeleton was newly synthesized via polymerization of the corresponding bromoethynylanthracene monomer using a Pd(0) catalyst. The average molecular weight of the polymer reached M̄_n = 5 × 103 and was soluble in common organic solvents. The polyradical was prepared from the corresponding hydroxyl precursor polymer and was appropriately stable at room temperature. The ESR spectrum of the corresponding monomeric radical suggested an effectively delocalized spin density distribution on the backbone anthracene. The magnetization and the static magnetic susceptibility of the polyradical were measured using a SQUID magnetometer. The large average spin quantum number (S̄ = 5/2) of the polyradical indicated that the ferromagnetic spin coupling network of the polyradical had spread throughout the π-conjugated chain and that it was considerably insensitive to spin defects.