刚性棒状手性聚硅烷诱导非手性超支化聚芴的超分子手性组装

Supramolecular Chiral Assembly of Achiral Hyperbranched Polyfluorenes Induced by Rigid Rod-Like Chiral Polysilanes

刚性棒状的手性聚硅烷具有独特的圆二色性能且易被光解,属于一种高效的手性诱导支架。为进一步验证手性聚硅烷的支架手性诱导能力,同时丰富其可手性诱导的非手性聚合物的结构种类,通过Suzuki缩聚反应合成得到了具有不同支化单元含量的超支化聚芴(HPF8s),利用刚性棒状的左手(S-)或右手(R-)手性的聚硅烷(PSi-S(R))成功诱导HPF8s的手性组装,同时考察了组装条件对PSi-S(R)作为手性支架诱导HPF8s手性组装行为的影响。结果表明,共溶剂的选择、良溶剂和不良溶剂的体积比、HPF8s与PSi-S(R)的质量浓度比以及HPF8s的支化单元含量对于HPF8/PSi-S(R)异构聚集体的手性表达均具有显著影响。此外,313 nm处的近紫外光辐照能够选择性地完全分解PSi-S(R),从而获得具有圆二色活性的HPF8s均聚集体。

The synthetic chiral polysilane adopts a rigid rod-like spiral structure,which has unique circular dichroism(CD)characteristics in near ultraviolet(UV)region and can be easily decomposed by UV irradiation.Therefore,chiral polysilanes have become excellent chiral scaffolds for inducing supramolecular chiral assembly of achiral polymers in recent years.In order to further verify the chiral scaffolding capability of chiral polysilane and enrich the types of achiral or optically inactive polymers that were induced to perform supramolecular chiral assembly,hyperbranched polyfluorenes(HPF8s)with different branching units were synthesized on the basis of Suzuki polycondensation reaction,which laid a foundation for further realization of chiral supramolecular assembly of hyperbranched main-chain conjugated polymers induced by using chiral polysilanes as the chiral scaffolds.The supramolecular chiral assembly of HPF8s was successfully induced by an enantiomeric pair of rigid rod-like helical polysilanes bearing(S)-and(R)-2-methylbutyl groups(PSi-S(R))in a binary solvent mixtures of chloroform and methanol.Optimizing experimental conditions were crucial for boosting the CD amplitudes of HPF8/PSi-S and HPF8/PSi-R hetero-aggregates.The effects of various conditions on the supramolecular chiral assembly behavior of hyperbranched polyfluorenes induced by chiral polysilanes were systematically investigated.Results showed that the choice of cosolvent,the volume ratio of good and poor solvent,the mass concentration ratio of HPF8s to PSi-S(R),and the branching unit content of HPF8s presented great impacts on the chiral expression of the hetero-aggregates.In addition,the optically active HPF8s homo-aggregates were produced by complete photoscissoring reactions at 313 nm,which could be assigned to the Siσ-Siσ*transitions of PSi-S and PSi-R.