A high-spin and helical organic polymer: Poly{[4-(dianisylaminium)phenyl] acetylene}

A high-spin polyradical, poly{[4-(dianisylaminium)phenyl]acetylene}1 ⁺, was synthesized as a π-conjugated polymer with an excess of the one-handed helical structure bearing stable aminium cation radicals. [4-(Dianisylamino)phenyl]acetylene (3) was synthesized and polymerized using [Rh(norbornadiene)Cl]₂ in (R)-l-phenylethylamine, (S)-1-phenylethylamine, or triethylamine to produce the corresponding poly{[4-(dianisy-lamino)phenyl]acetylene} 1 (1_(R)-PEA, 1 _(R)-PEA, and I_TEA. The positive and negative Cotton effects were observed at 270-450 nm for the polymers 1_(R)-PEA and 1_(S)-PEA, indicating that an excess of the one-handed helical polyacetylene backbone was induced by the polymerization using chiral solvents despite the achiral monomer. The oxidation of 1 with NOPF₆ gave the corresponding aminium polyradicals 1⁺, and the circular dichroism (CD) spectrum was observed even after the oxidation of the helical polyradical 1_(R)-PEA ⁺. The SQUID and NMR shift measurements indicated a high-spin state of the polyradical at room temperature and a contribution of the well-regulated helical structure to the through-space interaction between the aminium cation radicals.