Synthesis and magnetic property of poly[bis(4-methoxyphenyl) aminiumacetylene]s

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.