Synthesis of a Pendant Polyradical with a New π-Conjugated Polymer Backbone Containing an Anthracene Skeleton and Its Ferromagnetic Spin Coupling

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A poly(9,10-anthryleneethynylene)-based polyradical with pendant stable phenoxyls was newly synthesized via polymerization of the corresponding bromoethynylanthracene monomer using Pd(0) catalysts. The average molecular weight of the polymer reached Mn = 5 × 103 by the polymerization reaction for a few hours, and the polymer 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 polyradical 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, and the results revealed moderately strong ferromagnetic spin coupling (2J = 39 ± 3 cm-1) through the π-conjugated chain, depending on the degree of spin density distribution on the anthracene backbone.