摘要
A series of novel cis poly(phenylacetylene)s(PPAs)substituted at meta-position(s)by two alkoxycarbonyl pendants,Le.,sP-Me-C8/rP-Me-C8,P-Me-C12,sP-Et-C4,sP-2C4 and sP-Oct-C4,were synthesized under the catalysis of[Rh(nbd)Cl]2(nbd=norbornadiene).The dependence of elongation,screw sense,and stimuli response of helical polyene backbone on the structure of pendant,solvent,and temperature was systematically investigated in both solution and solid states.Because of n→π*interaction between vicinal carbonyl groups,sP-Me-C8/rP-Me-C8 could adopt contracted cis-cisoid helix in THF,toluene,CH2Cl2,and CHCl3.Such an intramolecular interaction was sensitive to the hydrogen bond donating ability of solvent and temperature,but insensitive to the dielectric constant and polarity of solvent.In poly(3-methoxycarbonyl-5-alkoxycarbonylphenylacetylene),the longer the chiral alkyl chain was,the easier the stable cis-cisoid helix could be achieved.However,when the methoxycarbonyl was changed to ethoxycarbonyl,sec-butyloxycarbonyl,and octyloxycarbonyl pendant groups,only cistransoid helix was obtained at room temperature due to the increased steric hindrance.Moreover,lowering temperature was found to facilitate the stabilization of n→π*interactions,and reversible temperature-dependent stereomutations were achieved in sP-Me-C8 and sP-Et-C4depending on the solvent where they were dissolved.These results suggested that the long alkyl chain,small pendant size,and lower temperature favored the stabilization of intramolecular n→π*interactions and the formation of contracted,cis-cisoid helices for poly(3,5-diestersubstituted phenylacetylene)s.
基金
This work was financially supported by the National Natural Science Foundation of China(Nos.51833001 and 21674002).
