Host-Guest Binding Properties And Self-Assembly Behavior Of Copillar[5]arenes

Pillar[n]arenes, a new class of macrocyclic hosts with para-bridges, have shown interestinghost-guest binding properties for a variety of guests including neutral and electron acceptingmolecules such as viologen, pyridinium salts, acetonitrile, amines and alkanes insupramolecular chemistry due to their highly symmetrical and rigid structure and the highelectron density of their cavity. Since the pillararenes were firstly synthesized by Ogoshi et alin2008, their derivatives have been used extensively in the formation of host-guest chemistry,self-assemble chemistry and fluorescence chemistry. In this paper, a series ofcopillar[5]arenes were successfully synthesized and their guests binding properties,self-assembly behavior were studied. The main content consists of the following chapters:(1) We found an effective method to synthsize a series of copillar[5]arenes in high yields(5085%) by co-oligomerization of various1,4-dialkoxybenzenes with FeCl3as catalyst. Thehost guest properties between the copillar[5]arenes and alkyl bromide were investigated forthe first time by1H NMR measurements. The results show that the host-guet bindingproperties were influenced by changing the alkyl groups of copillar[5]arenes.Copillar[5]arenes3b bearing a6-bromohexyl group could form11complex with1,4-dibromobutane (DBB), but the corresponding11and21complexes can occur forcopillar[5]arenes3f bearing a n-butyl groups under the same conditions. In addition, acomplete complexation selectivity was found between pillar[5]-and pillar[6]arenes, the guestDBB can not be locked into the1,4-bis(ethoxy) pillar[6]arene (BEOP6) due to its large cavity:9.5±0.5in comparison to8.1for pillar[5]arenes.(2) The self-assembly properties of copillar[5]arenes3b and3g bearing two6-bromohexylgroups were studied by1H NMR spectroscopy, specific viscosity, and X-ray measurements.The self-assembly of3b was concentration dependent, namely, it formed the self-inclusionmonomer at low concentration, and the intermolecular complexes–hugging dimers occurredat high concentration. In contrast, the self-assembly of3g was concentration independent andonly occurred in intramolecular self-assembly.(3) We synthesized two novel copillar[5]arenes bearing-hydroxyalkoxy groups ofdifferent carbon chain length and studied their self-assembly properties. By the self-assemblyof copillar[5]arene5bearing6-hydroxyalkoxy group, the formation of a hugging dimer55based on a supramolecular cryptand driven by H-bond interaction was found in the solid state, but was not suitable for copillar[5]arene4bearing4-hydroxyalkoxy group. More importantly,supramolecular complexes of5such as self-inclusion monomer, dimer, and1:1host-guestcomplex could be formed and their transformation process can be reversibly controlled bytuning solvent, temperature, guest, carbon chain length of-hydroxyalkoxy group andappropriate H-bond interaction. In addition, hugging dimers crystals data indicated thedimerization of5was easier and stronger than3b.(4) Systematic research of the structural characterization and the host-guest bindingabilities between three types of pillar[5]arenes (fully symmetric pillar[5]arenes,unsymmetrical pillar[5]arenes and copillar[5]arenes) have been studied. The configurations orsymmetry of their cavities not only have large difference in these three structure types, butalso have more or less variations even in the same structure type or the same host lockeddifferent guest. For example, contrast to crystal3a-1a (two guest molecules of CH3CN werelocked into the1,4-bis(methoxy) pillar[5]arene3a), the crystal3a-1b showed highersymmetry due to its guest1,6-dibromohexane (DBH) symmetrically locked into the cavity of3a. Meanwhile, The1,4-bis(butoxy) pillar[5]arene3a-3also contained two CH3CN guestmolecules as that of3a-1a, but it has the higher symmetrical structure. On the other hand, wefound the complexation behavior of pillar[5]arenes with DBB have been affected by theirdifferent symmetrical structrue and substituents on the aryl rings.(5) The host-guest binding properties of3a,1,4-bis(ethoxy) pillar[5]arene3a-2and3a-3with1,2-dibromoethane (DBE),DBB,DBH and1,4-diiodobutane (DIB) have been studied by1H NMR measurements and found that their complexation properties can be greatlyinfluenced by changing the alkyl groups of pillar[5]arenes, the guest would be significantlyshielded in the host-guest system. For example,the host3a can fully engulf the guest DBE,and the protons of DBB could be barely observed in the1H NMR spectrum even the contentof DBB was increased to6eq in the (3a-3)-DBB system. When3a-3bound with DBB or DIBguest, the benzyl ring rotation in pillar[5]arenes could be inhibited, which lead to planarchirality (PR and PS). In cojunction with the (3g)3-DBB crystal data, we assumed that the(3a-3)-DBB or (3a-3)-DIB system would arrange regularly in CHCl3, this arrangement modelwas dependent on the host and guest concentration. The higher concentration of host or guest,the arrangement model would be more regular and much stronger. Moreover, as theconcentration of guest was increased, its exchange rate became faster at first and then slower.The results that the guest could be fully engulfed and the rotation of units could be inhibitedin host-guest system, can be explained well by this arrangement model.