Synthesis and magnetic behaviour of poly(1,3-phenylene)-based polyradical carrying N-tert-butylaminoxyl radicals

Abstract

The synthesis and magnetic behaviour of poly[6-(N-oxyl-N-tert-butylamino)biphenyl-3,3′-ylene] 2 are described. Polyradical 2 was prepared by the Pd-catalyzed polycondensation of N-tert-butyl-2,4-dibromoaniline and 1,3-phenylenebis(trimethylene boronate), followed by oxidation with 3-chloroperoxybenzoic acid. The degree of polymerisation determined by SEC (size exclusion chromatography) was ∼18. Polyradical 2 was stable in both solution and the solid state. The spin concentrations of 2 determined by EPR and SQUID were 0.75 and 0.82 spin per repeating unit, respectively. Magnetic susceptibility (χ) measurements on 2 were carried out on a SQUID magnetometer and these showed that the magnetic interaction between the unpaired electron spins was antiferromagnetic (θ=–0.98 K). The fact that no ferromagnetic interaction was observed was ascribed to a twisting of the nitroxide moieties from the π-conjugated main chain, and this was confirmed by X-ray crystallographic analysis of the corresponding model monoradical, N-tert-butyl-N-(2,4-diphenylphenyl)aminoxyl.