Synthesis,Optical Activity,and Chiral Recognition Ability Of Helical Poly(Phenylacetylene) Derivatives

Helical poly(phenylacetylene)derivatives exhibit unique electronic,magnetic and optical properties because of their distinctive spiral structure,and have significant potential applications in many fields,such as molecular recognition,asymmetric synthesis,enantioseparation,and optical materials.In this work,a series of helical poly(phenylacetylene)s bearing L-valine derivatives as pendants were synthesized,their optical activity and chiral recognition ability were investigated.First of all,the functionalized phenylacelene monomers with L-valine ethyl ester and L-valinol(PAA-Val and PAA-Val-OH)were synthesized via Sonogashira coupling reaction,elimination reaction,eaterification reaction,and amidation reaction.Then other seven phenylacetylene monomers with carbamate groups of L-valinol were synthesized via the reaction between isocyanates and the active hydroxyl group of PAA-Val-OH.The polymerization of phenylacetylene monomers carried out using Rh(nbd)BPh4 as the catalyst to yield a series of poly(phenylacetylene)derivatives.The structure of monomers and polymers were characterized by ~1H NMR,IR,and SEC.The results showed that the poly(phenylacetylene)derivatives possessed cis-transoid configuration.The main-chain helical conformations of the poly(phenylacetylene)derivatives were confirmed through the analyses of circular dichroism and optical rotation spectra.Solvents and temperature have obvious influences on the helical conformation of the poly(phenylacetylene)derivatives.The poly(phenylacetylene)derivatives possessed various helical conformations in variable solvents,and those bearing carbamate groups may have a tightly twisted helical conformation and lower stereoregularity in THF.The stability of the helical conformations enhanced at lower temperatures,their stereoregularity increased with the decrease of the temperature and this phenomenon is reversible within a certain temperature range.Coated type helical poly(phenylacetylene)-based chiral stationary phases were prepared using suitable coating solvent.Influences of ethoxycarbonyl,hydroxyl,carbamate groups,substituents at phenyl carbamate groups on chiral recognition ability were investigated by high-performance liquid chromatography.The results showed that poly(phenylacetylene)derivative bearing L-valine ethyl ester as pendants(PPAA-Val)showed higher chiral recognition ability than others,especially baseline separation of rac-11 and rac-14 was achieved.Chiral recognition ability of poly(phenylacetylene)derivative bearing L-valinol as pendants(PPAA-Val-OH)decreased compared to that of PPAA-Val.The introduction of carbamate groups,the type and position of the substituents at phenyl carbamate groups have influences on chiral recognition of the poly(phenylacetylene)derivatives.When substituents at phenyl carbamate groups of the poly(phenylacetylene)derivatives were electron donating groups,higher chiral recognition was obtained.