Synthesis And Liquid Crystalline Phase Behaviors Of Fullerene Block Molecules Based On Flexible Tail And Spacer

In this thesis,the cooperative effects of flexible alkyl tail and spacer on the selfassembly structures of a series of sphere-cone-shaped fullerene supramolecular liquid crystals(LCs)were studied.Based on the previous work,LC compounds T-Cn-Cm-C60(n=4-10;m=6,10,12)consist of a rigid spherical fullerene C60,a flexible alkyl spacer and a soft conical terminal tail were designed and synthesized.The thermal and phase behaviors of these fullerene-based LC molecules were investigated through TGA,DSC,POM,SAXS,2D WAXD,TEM,and AFM analyses.Moreover,the influences of the length.of the spacer and the volume of the conical tail on the self-assembly structures,as well as their cooperative effects on the molecular packing rules in the self-assembled layers,were discovered and summarized.Interestingly,a unique lamellar superlattice structure containing both single and double layered fullerene nanosheets(SLQ)was formed by the compounds with a long spacer(m=10,12)and a small conical tail(n=4-7).Our results not only provide significant research supports on the packing rule of fullerene LC molecules in confined situations and the formation mechanism of lamellar superlattices,but also demonstrate an effective strategy to construct fullerene nanomaterials with nano-precision strcutures.The research contents are listed below:1.A series of fullerene LC molecules T-Cn-C10-C60(n=4-10)containing a 1,10decanedioxyl spacer were synthesized.Then their LC phase behaviors and self-assembly structures were studied.Among the compounds,those with a small conical tail(n=4-7)showed two different lamellar LC phases upon heating.The low-temperature phase had a larger thickness,while the high-temperature was thinner.TEM observations were carried out to discover the morphology along the layer normal.It’s interesting to find that in the low-temperature phase,demonstrating SLQ phase.The SLQ phase is due to the unmatched cross-sectional area of the spherical C60 and the conical tail.Meanwhile,the crystalline fullerene nanosheets were tough,so that the mismatch could not be solved by increasing the interface curvature or breaking the layer continuity.Consequently,the next best solution,in which the molecules flipped in each sub-layer to balance the cross-sectional area of the incompatible moieties,was chosen,producing a novel supramolecular layered superlattice LC structure.Increasing the temperature,the conical tail expanded,which breaks the area ratio required by the superlattice.This induced the formation of a sandwich-like layered LC phase(SQ),which had four layers of fullerene nanosheets in the middle,alkyl tails at both sides and the spacers of the inner layer molecules penetrating through the space between C60s.Similarly,when the terminal conical tail was large(n=8-10),the compounds could not form the superlattice structure.Instead,only the SQ phase was shown.2.Further increasing the spacer length,a series of molecules with a 1,12dodecanedioxyl spacer were synthesized(T-Cn-C12-C60,n=4-8).The effects of a longer spacer and the volume of conical tails on the phase behaviors were investigated.According to SAXS and TEM results,when the cone is small(n=4),two different LC phases were formed as the C10 spacer molecules.Increasing the cone size(n=5-7),only the SLQ phase was shown,while the SQ phase formed with an even larger cone(n=8).This indicates that a relatively longer spacer promotes the formation of the layered superlattice.Meanwhile,the samples with n=5-7 maintained the superlattice structure even at high temperatures.This is mainly due to that the C12 spacer is more difficult to penetrate through the space between C60s,as it is longer and more flexible.On the other hand,compared with the n=4 molecule.the samples with n=5-7 have a larger cone.Our findings about the hierarchical selfassembly structure of fullerene based supramolecular LCs provide an effective and facile strategy’ to obtain superlattice nanomaterials.3.A series of molecules with a short 1,6-hexanedioxl spacer were synthesized(T-CnC6-C60,n=4-8).Structural analysis results showed that none of the samples could form a superlattice structure.They had a three-layered sandwich-like lamellar structure(ST phase)in the low temperatures,while four-layered lamellar structure(SQ phase)in the high temperatures.This result,combined with the investigations on the long spacer samples,revealed that in the sphere-cone-shaped fullerene LC molecules,a relatively longer spacer and smaller cone help the formation of the layered superlattice structure.