Synthesis And Chiroptical Properties Of Helical Substituted Polyacetylenes Carrying Urea Groups

Helical substituted polyacetylenes are typicalπ-conjugated polymers, and attracted much attention due to form regulated secondary structures and response to enternal stimuli. In this paper, we synthesized serials of polyacetylene derivatives bearing amino acid and urea moieties. The stiff main background as the scafford for signing integrate-site urea moieties, the special three dimension structures trigger urea pendant forming multi-point hydrogen-bonding, then the influence of anion on chiroptical properties of substituted helical polyacetylene were studied.Novel chiral substituted phenylacetylene monomer containing amino acid and urea moiety, namely, (S)-methyl-3-(4-ethynyl)-2-(3-hexylureido)propanoate was synthetized and polymerized with (nbd)Rh+[η6-C6H5B-(C6H5)3] to give corresponding polymers with number-average molecular weight ranging from 4300-6100 in 76-84% yields. The polymer was soluble in toluene, CHCl3, CH2Cl2 and THF, while insoluble in hexane, diethyl ether, and methanol. Large specific rotations and intensity circular dichroism (CD) signals demonstrated that the polymer take on a helical structure with predominantly one-handed screw sense. The polymer possessed c/s-stereoregular structure determined by 1H NMR spectoscopices. Liquid infrared spectroscopic (IR) showed that the helical structure of the polymer stabilized by intermolecular hydrogen-bonding. The helical structure can be tuned by environmental stimuli including addition methanol and heating. The helical structure of polymer was suspectiveable to anion such as F-, Cl-, Br-, OH-, and NO3-. Especially, OH-displays the highest modulating abilities. Anion titration liquid-IR demonstrated the anion break the intermolecular hydrogen-bonding formed between the urea groups, deformed the polymer helical structures.Novel chiral N-propargylamides monomer containing amino acid and urea moiety, namely, (S)-3-hexylureido-2-ethylphenyl-N-propargylamides, was synthesized and polymerized with (nbd)Rh+[η-C6H5B-(C6H5)3] to give corresponding polymer with number-average molecular weight in the range of 4100-6100 in 74% yield. The polymer was soluble in toluene, CHCl3, CH2Cl2 and THF, while insoluble in hexane, diethyl ether, and acetonitrile. The specific rotation and CD spectra study reveal that the polymer to form a helix with predominatyly one-handed screw sence. The helical structure of the polymer was stable to methanol and heating. Anion titration CD spectoscopices showed the chiroptical properties of polymer can be modulated by anion, such as F-, Cl-, and NO3-, polymer turned the CD signs from plus to minus by the addition of F-.