Preparation And Properties Of Pillararene-based Polypseudorotaxanes

Polypseudorotaxanes constructed by incorporating multiple pseudorotaxane units intothe polymeric framework assisted by noncovalent interactions are a class of morecomplicated supramolecular assemblies. Depending on the location of the pseudorotaxaneunit, polypseudorotaxanes can be mainly divided into three types: main-chainpolypseudorotaxanes, side-chain polypseudorotaxanes, and others (such as branched andcrosslinked polypseudorotaxanes). Recently, polypseudorotaxanes have attracted greatinterest, due to their potential applications in the fabrication of stimuli-responsive materials,self-healing materials, molecular machines and fluorescent sensors. Pillararenes withunique symmetrical pillar architectures and-electron rich cavities are a new type ofmacrocyclic hosts, which were first reported by Ogoshi and co-workers in2008. Theunique rigid structure renders them outstanding candidates to bind various guestsselectively. Therefore, pillararenes have been used for the fabrication ofpolypseudorotaxanes, vesicles, molecular springs, microtubes and other functionalizedsupramolecular systems. In this dissertation, we focus on the preparation of three types ofsupramolecular polypseudorotaxanes via the pillararene-based host-guest recognitionmotifs, and investigation of their properties and applications. Moreover, a series of guestmolecules containing ferrocene and fluorene units were prepared and the influence ofoxidant KMnO4to their optical properties was further revealed.The main content consists of the following chapters:In Chapter2, we have successfully synthesized a pillar[5]arene-modified conjugatedpolymer (P1) by Cu-catalyzed homocoupling reaction, and novel side-chainpolypseudorotaxanes can be formed via the host-guest interactions between pillar[5]areneand n-octylpyrazinium hexafluorophosphate salt. The fluorescence intensity of theside-chain polypseudorotaxanes is much weaker than that of P1due to the efficient electrontransfer from the conjugated backbone to n-octylpyrazinium cation. Upon addition of Cl tothe solution of the side-chain polypseudorotaxanes, a disassembly process occurred, leadingto the partial recovery of the fluorescence of P1. Moreover, after adding Br and I to thesolution of the polypseudorotaxanes system, respectively, the fluorescence enhancementcould also be observed, and the fluorescence enhancement increases in the order of I Br Cl. The differences in fluorescence intensity could be easily distinguished by the naked eye under UV light (365nm) illumination. Such fluorescence enhancement differencescould be attributed to the different binding affinity of Cl, Br, and I to then-octylpyrazinium cation during the formation of ion pairs.In Chapter3, we designed and synthesized a ureidopyrimidinone bifunctionalizedpillar[5]arene (UPyP5), and linear supramolecular polymers could be obtained based on theself-complementary dimerization of the quadruple hydrogen bonded unitureidopyrimidinone (UPy) at relatively high concentration. By using the method ofviscosity measurement, the critical polymerization concentration of UPyP5inCHCl3/CH3CN (v/v=1.5:1) solution was estimated to be about19mM. When bisparaquatderivative (D1) was added into the solution of UPyP5, a supramolecularpolypseudorotaxane network constructed by cross-linking the quadruple hydrogen bondedlinear supramolecular polymers via the threading of bisparaquat molecules into the cavityof the pillar[5]arene units was formed, and this was confirmed by the combination ofvarious techniques, such as variable-concentration1H NMR, two-dimensional diffusionordered1H NMR spectroscopy (DOSY), reduced viscosity and dynamic laser lightscattering (DLS) measurement. Furthermore, transmission electron microscopy (TEM)images of the supramolecular polypseudorotaxane network revealed the formation ofspherical nanoparticles in the solid state.In Chapter4, we have synthesized a pillar[5]arene-functionalized tetraphenylethylene(TPEP5) derivative and a neutral guest molecule containing triazole groups (G2) throughCu-catalyzed “click” reaction, and supramolecular polypseudorotaxane networks could beobtained driven by the host-guest interactions between pillar[5]arene and G2. Thefluorescence emission of TPEP5in solution is weak due to the active intramolecularrotations of the multiple phenyl rings in tetraphenylethylene that consume its excitonenergy through nonradiative channels. However, after adding G2to the solution of TPEP5,the formation of the polypseudorotaxane networks via the threading of G2into the cavity ofthe pillar[5]arene units restricted the rotation of phenyl rings in tetraphenylethylene, whichblocks the nonradiative energy dissipation pathways, and as a result the emission of TPEP5is gradually enhanced. These results indicate that TPEP5is a typical aggregation-inducedemission molecule. Moreover, a collapse of the polypseudorotaxane networks occurredupon addition of the completive guest adiponitrile, which facilitates the internal rotationwithin tetraphenylethylene moieties, and thus the fluorescence becomes weak.In Chapter5, guest molecules with ferrocene as the side group (FFB1), in the backbone (FFB2) and as the end groups (FFB3) were synthesized by Suzuki couplingreaction. The fluorescence of FFB1, FFB2and FFB3in THF were strongly quenched byferrocene via an intramolecular photoinduced electron transfer (PET) process. However,after adding oxidant KMnO4to the solution of FFB1, FFB2and FFB3, respectively, thefluorescent intensity of these compounds were increased and could be up to75times. Thefluorescence amplification and response time to oxidant were affected by the position andnumbers of ferrocene in these conjugated compounds. The results show that fluorescenceenhancement is linear with concentration of oxidant and rapidly responds to oxidant whenone ferrocene exists in conjugated structures. Response time became slow and fluorescenceenhancement is quadratic with concentration of oxidant when there are two ferrocenes inone conjugated molecule. Moreover, the construction of redox-responsive inclusioncomplexes based on the host-guest interactions between per-butylated pillar[6]arene and aferrocenium cation is now underway in our lab.