Poly[bis(4-methoxyphenyl)arniniumacetylene]s 1+ were designed and synthesized as π-conjugated polymer bearing multiple aminium radicals. Bis(4-methoxyphenyl)aminoacetylene and 1-methyl-2-bis(4-methoxyphenyl) aminoacetylene were synthesized and polymerized with a metathesis catalyst to yield poly[bis(4-methoxyphenyl)aminoacetylene] la and poly[1-methyl-2-bis(4- methoxyphenyl)aminoacetylene] 1b, respectively. The oxidation of 1 with SbCl5 gave the corresponding aminium polyradicals 1+. The introduction of a methyl group onto the polyacetylene backbone in 1b+ significantly enhanced the chemical stability or life-time of the poly(aminium radical). The high-spin ground state with an average 5 (spin quantum number) = 4/2 for lb+ was proven by magnetic susceptibility, magnetization, and ESR measurements.
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