Investigation On Chiral Assembly Of Achiral Main Chain Conjugated Polymers Induced By Chiral Polysilane

The construction of supramolecular chirality is one of the main tasks of biology and materials science.Natural chiral substances or synthetic chiral polymers can act as chiral templates/scaffolds to induce the chirality/helicity of achiral polymers.It is a simple and effective method to construct supramolecular chirality of achiral substances.Rigid rod-like helical polysilanes can be used as efficient chiral scaffolds to induce the chirality of optically inactive polymers by non-covalent bond interactions,which is an emerging method of chiral induction.Chiral polysilanes have unique UV absorption and circular dichroism in the range of 300-400 nm.Meanwhile,polysilanes can be rapidly decomposed.under UV light irradiation.Furthermore,the CD/CPL activity of induced polymer can be memoried after the removal of helical polysilane by UV-irradiation.This chiral scaffold induction method enriches not only the chiral induction methodology,but also the types of chiral polymers,which provides the new options and new ideas for the preparation of chiral polymers.The main work herein is to induce chiral assembly of various achiral linear conjugated polymers and hyperbranched polymers that containing fluorene and/or azobenzene units by chiral polysilanes.By this way,we can further enrich the structural types of achiral polymers used for chiral assembly induced by chiral polysilane which act as a chiral scaffold.The specific research contents are as follows:(1)The rigid rod-like chiral polysilanes(PSi-S and PSi-R)induce chiral assembly of achiral linear conjugated polymers.PSi-S/-R can act as effective chiral scaffolds to induce the chiral assembly of achiral main-chain azobenzene containing polymer(PF8Azo)in a mixture of chloroform-methanol cosolvents.A series of experimental conditions were investigated to optimize the appropriate cosolvents,the volume ratio of good and poor solvent,the molar ratio of PF8Azo to PSi-S/-R.This is crutial for enhancing the chiral expression of PF8Azo/PSi-S and PF8Azo/PSi-R hetero-aggregates.Photoisomerization of PF8Azo/PSi-S and PF8Azo/PSi-R hetero-aggregates prepared under optimized conditions occurred under alternating irradiation of dual-wavelength visible light.In addition,the near-ultraviolet light at 313 nm can selectively and completely decomposed chiral poly silanes,then the optically active PF8Azo homo-aggregates were produced.Whereas,the side chain azobenzen-containing polymer(PMMAzo)cannot efficiently wrap around the semiflexible PSi helical main chains due to inefficient intermolecular interactions between two kinds of polymer chains.The polycarbazole(PCz8)has a relatively high polarity.Therefore,the chiral polysilane fails to induce the chiral assembly of PMMAzo and PCz8.(2)The rigid rod-like chiral polysilanes(PSi-S and PSi-R)induce chiral assembly of hyperbranched main-chain conjugated polymers.In order to further realize chiral assembly of hyperbranched main-chain conjugated polymers induced by chiral polysilanes as chiral scaffolds,hyperbranched polyfluorenes(HPF8s)with different branching units were synthesized by Suzuki polycondensation reaction.The effects of various assembly conditions on the chiral assembly behavior of hyperbranched polyfluorenes induced by chiral polysilanes were investigated in detail.The experimental 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 had great impact on the chiral expression of HPF8/PSi-S and HPF8/PSi-R hetero-aggregates.In addition,the chirality of HPF8s can still be maintained after the decomposition of the chiral polysilane by ultraviolet light irradiation.