Construction And Properties Study Of Rotaxane-Branched Dendrimers

Rotaxane dendrimers,in which one or more rotaxane units are introduced into the skeleton of dendrimers,are a novel type of mechanically interlocked molecules(MIMs).Attributed to the integrated combination of the interesting motion behaviors of rotaxanes and the high symmetry feature of dendrimers,rotaxane dendrimers have attracted more and more attentions due to not only their unique topological structures but also their great potential applications in the construction of artificial molecular machines and supramolecular dynamic materials etc.Depending on the location of the rotaxane unit in dendrimer skeleton,rotaxane dendrimers could be classified into Type I rotaxane dendrimers with rotaxane cores,Type II rotaxane dendrimers with(pseudo)rotaxane termini,and Type III rotaxane dendrimers with rotaxane branches.For rotaxane dendrimers with rotaxane units either as the cores or the terminals,plenty of successful synthetic attempts have been reported due to their relatively simpler structures,and the resultant rotaxane dendrimers have shown wide applications in the fields of biological imaging,gene delivery,and light-harvesting system,etc..However,in the case of rotaxane-branched dendrimers with rotaxane units either as the branches or the branching points or both,especially the high-generation ones,the monodispersed distribution of rotaxane units in the dendrimers lead to stronger steric hindrance upon the increase of the dendrimer generation,thus the synthesis of higher-generation rotaxane-branched dendrimers remains a big challenge.Moreover,due to the lack of efficient synthetic strategies,the in-depth properties investigations such as the stimuli-responsive property of rotaxane-branched dendrimers have rarely been explored.In order to tackle with such challenge,the research described in this dissertation focuses on the construction of novel high-generation rotaxane-branched dendrimers.On one hand,by the rational design of new rotaxane building blocks,the development of new approaches towards the efficient synthesis of novel high-generation rotaxane-branched dendrimers has been explored;on the other hand,by using the newly developed approaches,novel rotaxane-branched dendrimers with interesting stimuli-responsive or aggregation-induced emission features have been successfully constructed.The dissertation can be divided into five parts,the details are shown below.In Chapter one,overviews of the research progress of rotaxanes and dendrimers are firstly presented,focusing on the development of the synthetic strategies and their applications.In addition,a detailed introduction on rotaxane dendrimers,including the synthetic approaches and applications,is demonstrated.In Chapter Two,starting from a dual stimuli-responsive [2]rotaxane precursor,the employment of a controllable divergent approach allowed for the successful synthesis of a family of Type III-A rotaxane-branched dendrimers up to the third generation.The introduction of dual stimuli-responsive rotaxane units into the dendritic scaffold imparted the switchable feature to the resultant rotaxane-branched dendrimers,thus resulting in a novel three-dimensional molecular switching system.The addition and removal of the external stimulus reversibly changed the location of pillar[5]arene rings on the axle,thus influencing the rigidity of all branches.More importantly,the amplified responsiveness of the switchable rotaxane units led to the dimension modulation of the resultant rotaxane-branched dendrimers.In Chapter Three,starting from a pillar[5]arene-based organometallic [2]rotaxane as the key building blocks,taking advantaging of the formation of platinum-acetylide bonds as the dendrimer growth steps,high-generation Type III-B rotaxane-branched dendrimers up to the third generation with 21 switchable rotaxane moieties located on each branching point have been successfully constructed through a convergent approach,thus providing a novel approach towards the synthesis of high-generation Type III-B rotaxane-branched dendrimers.In Chapter Four,by the employment of the controllable divergent approach,high-generation Type III-C rotaxane-branched dendrimers up to the fourth generation as a novel [46]rotaxane have been successfully constructed for the first time.Moreover,the anion-responsive feature of the individual rotaxane building blocks imparted the anion-switching feature to the integrated rotaxane-branched dendrimers.The addition and removal of the external stimulus reversibly changed the location of pillar[5]arene rings on the axle,due to the macrocyclic components located at both branches and branching points,the controllable directional motion of the individual macrocyclic component endows the integrated rotaxane dendrimers a collective expansion-contraction motion,thus allowing for the remarkable and reversible dendrimer size modulation.In Chapter Five,by introducing the organometallic [2]rotaxane as the key building blocks and the aggregation-Induced emission(AIE)luminogen 9,10-distyrylanthrance(DSA)unit as the core,high-generation rotaxane-branched dendrimers with AIE behavior up to the third generation as a novel [15]rotaxane have been successfully synthesized.The existence of DSA unit as the core imparted the interesting generation-dependent AIE feature to the resultant rotaxane-branched dendrimers,i.e.along with the increase of generation,the higher AIE effect was observed.