Construction And Properties Study Of Functionalized Rotaxane Dendrimers

Rotaxane dendrimers are a newly emerging large family of high-order mechanically interlocked molecules(MIMs),in which one or more rotaxane units is introduced into the dendrimer skeleton.Attributed to the integrated combination of the controllable switchable rotaxanes and the star-shaped and highly branched dendrimers,increasing attention has been paid to the design and synthesis of diverse rotaxane dendrimers,which have enabled them to be versatile platforms for the construction of novel supramolecular dynamic materials and integrated artificial molecular machines etc.During the past three decades,diverse rotaxane dendrimers as a vital subset of MIMs have been constructed,which have shown a wide range of promising applications in nanoreactor,gene delivery,smart material and artificial light-harvesting systems.However,possibly due to the lack of efficient functionalization strategies,the synthesis of functionalized rotaxane dendrimers,which could serve as privileged candidates for the construction of artificial molecular machines and smart materials,still remains a major challenge.In order to tackle with such a big challenge in the field of high-order MIMs,the research described in this dissertation focuses on the construction of novel functionalized rotaxane dendrimers and the further exploration of their properties and applications.On one hand,by developing the efficient strategies,the precise synthesis of functionalized rotaxane dendrimers has been explored.On the other hand,on the basis of the investigations on the properties of the resultant functionalized rotaxane dendrimers,the diverse applications in the fields of photosensitizers,artificial light-harvesting systems,aggregation-induced emission materials and dynamic smart materials,have been further developed.The main research content of this dissertation can be divided into five parts,and the details are shown below.In Chapter One,the development of rotaxanes is reviewed firstly,especially focusing on the synthetic strategies and the applications in artificial molecular machines.Secondly,the research progress of dendrimers is summarized.In addition,a detailed introduction of rotaxane dendrimers is carried out,including the classification,the synthetic methodologies and the applications.In Chapter Two,starting from an anthracene-functionalized[2]rotaxane precursor,a new family of functionalized rotaxane dendrimers containing up to twenty-one platinum atoms and forty-two anthracene units as photosensitizer moieties have been successfully constructed through an efficient and controllable divergent approach.Notably,the photosensitization efficiencies of the resultant rotaxane dendrimers gradually increased with the increase of dendrimer generation.The enhanced ¹O₂generation efficiency was attributed to the enhancement of intersystem crossing(ISC)through the simple and efficient incorporation of multiple heavy atoms and photosensitizer moieties on the axles and wheels of the rotaxane units,respectively,which has been validated by UV–visible and fluorescence techniques,time-dependent density functional theory calculations,photolysis model reactions,and apparent activation energy calculations.In Chapter Three,starting from the same anthracene-functionalized[2]rotaxane precursor with stimuli-responsiveness,we constructed a group of functionalized rotaxane dendrimers containing up to fifty-six anthracene moieties(energy donor)on the wheels of the rotaxane units and one zinc(II)porphyrin moiety(energy acceptor)at the central core.Notably,the artificial light-harvesting systems based on rotaxane dendrimers incorporate a large number of rotaxane subunits on the dendritic skeleton in a monodisperse manner,which thus allowed for the high energy transfer efficiencies and antenna effects.More importantly,with the addition and removal of acetate anions,the directional and reversible motion of rotaxane unit on each branches was realized,thus leading to dynamic regulation of antenna effect in resultant rotaxane dendrimers.In Chapter Four,starting from an AIEgen-functionalized[2]rotaxane,the precise synthesis of a new family of AIEgen-branched rotaxane dendrimers was realized through a controllable divergent approach.In the resultant AIE macromolecules,up to twenty-one AIEgens locate at the tails of each branches,making them first successful example of AIEgen-branched dendrimers.Attributed to the solvent-induced switching feature of the rotaxane branches,the integrated rotaxane dendrimers displayed interesting dynamic feature upon the aggregation-induced emission process.Moreover,novel artificial light-harvesting systems were further constructed based on these AIEgen-branched rotaxane dendrimers,which revealed impressive generation-dependent photocatalytic performances for both photooxidation reaction and aerobic cross-dehydrogenative coupling(CDC)reaction.In Chapter Five,by introducing artificial molecular muscle as the key building blocks,we present the first successful preparation of a new family of daisy chain dendrimers,in which the individual[c2]daisy chain rotaxane units serve as the branches of dendrimer skeleton.In particular,the third-generation daisy chain dendrimer with twenty-one[c2]daisy chain rotaxane moieties was realized,which might be among the most complicated discrete high-order MIMs comprised of multiple[c2]daisy chain rotaxane units.Interestingly,such unique topological arrangements of multiple stimuli-responsive[c2]daisy chain rotaxanes endowed the resultant daisy chain dendrimers controllable and reversible nanoscale dimension modulation through the collective and amplified extension/contraction of each[c2]daisy chain rotaxane branch upon the addition of acetate anions or DMSO molecules as external stimulus.Furthermore,on the basis of such an intriguing size switching feature of daisy chain dendrimers,dynamic composite polymer films were constructed through the incorporation of daisy chain dendrimers into polymer films,which could undergo fast,reversible,and controllable shape transformations when DMSO molecules were employed as stimulus.