Polydiacetylene Based Chiral Supramolecular Self-Assemblies:Fabrication And Properties

Chirality is a fundamental character of nature,the asymmetric structure of biomacromolecules in lives play a decisive role in vital movements.The study of chiral induction,transfer,amplification and modulation is of great significance to the origin and evolution of living matter.Taking the natural system as a blueprint,construction of chiral supramolecular assemblies through non-covalent interactions like hydrogen bonding,electrostatic interactions,?-? stacking and hydrophobic interactions has drawn extensive attention in supramolecular chemistry and material science,for its potential application in mimicking the structure and function of biomacromolecules,enantioselective recognition and sensing,asymmetric catalysis and bio-pharmaceutical field.In 1971,professor Kagan firstly reported the asymmetric synthesis of diarylethene derivatives by circularly polarized light.However,the exact mechanism of chiral induction,transfer and amplification in the circularly polarized light induced asymmetric supramolecular assembly process is not fully understood,the influence of molecular structure and the type of chemical bond is not discussed.To solve the above mentioned questions,we designed and prepared several disk-like molecules containing diacetylene units,and the chiral introduction,transfer and amplification in liquid crystal and gel systems were investigated during circularly polarized light triggered self-assembly process.The optical properties of these supramolecular assemblies were also studied.The specific content of this thesis are as follows:1)Chirality transfer efficiency of hydrogen bond and covalent bond in liquid crystal phase.We designed and synthesized three discotic diacetylene(DA)LC monomers,in which the peripheral diacetylene flexible chains linked to the triazole derivative(TTB)cores through H-bonding or covalent bonds.When the DA moieties were connected by hydrogen bond,it was interesting to note that CD signals could only be observed at the corresponding absorption band for polydiacetylene(PDA)backbone but not TTB derivative cores after CPL irradiation.However,both these two regions displayed obvious CD signals when DA moieties were covalently connected.Moreover,the monomer which contain six DA moieties showed maximum g-value among three different LC monomers.On the basis of the above results,we concluded that the strong junction bonding interaction between the central cores and the peripheral arms favoured chirality transfer within the supramolecular columnar assemblies.2)Chiral memory and amplification effects in crystalline and liquid crystal phases.Chiral dopants play an important role in the field of chiral supramolecular.In the previous work,circularly polarized light(CPL)was not capable to induce the enantio-selective polymerization of diacetylene units in the crystalline phase,so we introduced chiral limonene in the sample preparation process and obtained chiral polydiacetylene in the crystalline state successfully,although limonene was removed before polymerization.All the samples exhibited obvious CD signals corresponding absorption band of PDA chains both polymerized in crystalline and liquid crystalline phase.And the handedness of PDA backbones could be rigorously controlled with the same handedness of limonene.Thus,we successfully fabricated chiral PDA chains though chiral memory effect.Afterwards,we compared the g-factor of the sample irradiated with Ultra-violet(UV)light in crystalline and LC phase.As expected,the chiral induction process for the HB complex in the LC phase was considerably faster than that in the crystal phase,and the g-value of PDA chain was three times bigger than that obtained in crystal phase,this result indicates liquid crystalline phase is more favorable of chirality transfer.3)CPL triggered hierarchical self-assembly of achiral porphyrin derivatives(TPPDA).Herein,a novel CPL-triggered asymmetric self-assembly strategy is developed to construct chiral supramolecular assemblies from achiral porphyrin derivatives.CPL irradiation is applied only at the initial stage of the self-assembly process.It is noteworthy that the supramolecular gel exhibits remarkable CD activity,moreover,the handedness of the preformed porphyrin gel can be induced and modulated by the rotational direction of CPL.Furthermore,the desired handedness of porphyrin assemblies can be permanently locked by non-polarized ultraviolet(UV)light irradiation,which"crosslinks" diacetylene units in the peripheral region and 'locks" of the configuration of the porphyrin cores.This work provides a better understanding of the mechanism of interaction between circularly polarized light and molecules,as well as the mechanism and rule of chiral induction,transfer,amplification and modulation,and presents a new method for the fabrication of reliable chiral supramolecular assemblies.4)Photoelectric properties of the porphyrin based supramolecular assemblies.Single TPPDA microfiber drawn from above chiral TPPDA gel exhibited a propagation loss of ?=195 cm-1,corresponding to the transmission loss of 0.022 dB ?m-1,which is much lower than that of conjugated polymer fibers(ranging from 100 to 2000 cm-1).The lower propagation losses should be ascribed to the preferential H-aggregation of TPPDA molecules induced by inter-molecular hydrogen bonding and ?-? stacking within the supramolecular assenblies,which can reduce the self-absorption of the guided fluorescence signal.This work is of great fundamental value for the designing of novel functional nanostructures for application in one-dimensional optical wave guide materials.