Conjugated Polymers Carrying Stable Radicals and Their Spin Control

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Synthesis and magnetic properties of new conjugated polymers carrying stable radicals were studied in connection with their electronic structure.Acetylene monomers, (3, 5-di-tert-butyl-4-hydroxyphenyl) acetylene and p-ethynylphenyl hydrogalvinoxyl, were synthesized using Vilsmeier method, and organolithium reagents, respectively. These monomers were polymerized with metathesis or Wilkinson catalyst to yield their polyacetylene derivatives, poly[(3, 5-di-tert-butyl-4-hydroxyphenyl)acetylene] (1) and poly (p-ethynylphenyl hydrogalvinoxyl) (2), with molecular weight of ca. 10^4. The polymers were soluble in common organic solvents and converted to the corresponding conjugated polyradicals via heterogeneous chemical oxidation using PbO_2 or alkaline K_3Fe (CN)_6. The polyradical 2 with extremely high spin concentration were obtained by regulating the oxidative conditions. The polyradicals were quite stable in solution and even in the solid state because of resonance stabilization and/or a steric effect of the substituens.Electronic state of these polyradicals were analyzed using ultraviolet photoelectron spectroscopy (UPS) and solution ESR spectra. The existence of significant pi-conjugation along the main chain in these polyradicals were examined by UPS. Decrease and increase in ionization threshold could be explained by the steric effect of sidechain substituent. ESR spectra with hyperfine structure for the oxidized 1 indicated that the phenoxy radical conjugates through the polyacetylene main chain over ca. 7 monomer units as a "neutral soliton". Antiferromagnetic interaction between the unpaired electrons was observed in 1 and from the temperature dependency of the ESR signal intensity.This research project revealed that magnetic properties of polyradical with polyacetylene backbone depend both on conjugated electronic state along main chain and on special arrangement of sidechain radical substituent.