Helicity induction on poly(phenylacetylene)s bearing phosphonic acid pendants with chiral amines and memory of the macromolecular helicity assisted by interaction with achiral amines in dimethyl sulfoxide

Two novel stereoregular poly(phenylacetylene)s bearing a phosphonic acid residue (poly-1) and its monoethyl ester (poly-2) as pendants were prepared by the polymerization of diethyl (4-ethynylphenyl)phosphon ate followed by hydrolysis of the diethyl ester groups and polymerization of ethyl (4-ethynylphenyl)phosphonate, respectively. The polymers were found to form a predominantly one-handed helical conformation upon complexation with various chiral amines through noncovalent acid-base interactions in dimethyl sulfoxide (DMSO). The complexes exhibited an induced circular dichroism (ICD) in the UV-visible region of the polymer backbones. In particular, poly-2 is an induced helical polymer more sensitive to the chirality of amines than poly-1 and poly((4-carboxyphenyl)acetylene) and yields the same Cotton effect sign when complexed with chiral amines of the same absolute configuration. Moreover, the macromolecular helicity of poly-1 and poly-2 induced by chiral amines was "memorized" after the chiral amines were completely removed and replaced with various achiral diamines and oligoamines in DMSO. In sharp contrast to the same memory effect on the induced helical poly((4-carboxyphenyl)acetylene), the helical structures of poly-1 and poly-2 could not be efficiently maintained by achiral monoamines. The effect of the structure of the achiral diamines and oligoamines on the efficiency of the helicity retention and the stability of the memorized polymers were also investigated.