Nanotubes Assembly Based On Calixarenes By Intermolecular Forces

As calixarenes contain a π-based cavity and several reactable positions, they are broadly used as building blocks to construct well preorganized host molecules which have widely been applied in areas as gas adsorption, enzyme mimics, drug carries, nanotubes and fullerene chemistry, etc. However, reports based on self-assembly and assembly form calixarenes nanotubes are still not so many. Our research focuses on the nanotubes formed by the self-assembly of calixarene and thiacalixarene which contains different conformations and supramolecular action groups.In chapter one, the survey of supramolecular chemistry and host-guest chemistry are briefly introduced. The structural characteristics and modifications of calixarenes are also introduced. In the end, the nanotubes assembly based on calixarenes by n hydrogen bonding and π-π stacking interactions are reviewed.In chapter two, different conformations of calix[4]arene derivatives bearing aldehyde, cyano and carboxyl acid groups at the upper rim are synthesized. Cone thiacalix[4]arene derivatives contaning aldehyde, cyano and hydroxy groups at the upper rim are synthesized. Inferred by the reaction product, isopropyl groups are dealkylated after aldehyde groups have been introduced to the upper rim. The carbocation mechanism of pillararene formation is presented, which support Holler’s theory.In chapter three, during the absence of strong hydrogen bond, we use chloroform/ cyclohexane as a solvent for crystallization, and the self-assembly of nine thiacalix[4]arene derivatives are studied. Compared with the "classical" calixarenes, thiacalixarene has larger cavities and more favours of interdigitation aromatic yielding the classical head-to-head dimeric motif. S…π interaction between sulfur and neighbouring thiacalixarene can work in a positive way, making the assembling even more stable. Cone conformation thiacalix[4]arene derivatives bearing formyl groups form "head-to-head" dimers and "honeycomb" shaped nanotube structure by hierarchical self-assembly. Cone conformation thiacalix[4]arene derivatives bearing cyano groups are linked together through the connection of solvent molecules. CHCl3 molecules are oriented so as to form Cl…Cl, Cl…π and cyano…Cl interaction with neighbouring nanotubes. Because the invert aromatic ring reduces the repulsion, partial cone thiacalix [4] arene derivatives bearing cyano group also form "head-to-head" dimers and "honeycomb" shaped nanotube structure by hierarchical self-assembly. The neighboring of 1,3-alternate thiacalix[4]arene derivatives can connect each other in a "side-by-side" manner by S…π and S…S interaction. Through the study of the self-assembly behavior of thiacalix[4]arene derivatives, we find that the variation in the conformation of the host molecules does not dominate the formation in this case, as long as host molecules can be circumvented in an appropriate manner to form nanotubes.In chapter four, the influence of the crystallization medium (solvent/guest type) of different conformations calix[4]arene derivatives bearing carboxylic acid groups at the upper rim and on the formation of hydrogen-bonded nanotubes are studied. When the carboxyl acid groups are located in the same side (cone conformations), they can form different types of hydrogen bonded with other molecules.In the extended structure, neighboring calixarenes connect each other to form hydrogen-bonded dimeric capsules through complementary COOH…COOH if the carboxyl acid orientates towards the cavity (dihedral angle of less than 30°).Adjacent calixarenes will form hydrogen-bonded one-dimensional wave structure if carboxyl acid orientates outwards. Solvent plays a crucial role in supramolecular arrays. We can find that calixarenes assemble in the presence of pyridine (Py acting as a template) to form hydrogen-bonded dimeric capsules through complementary Py…COOH. Tetrahydrofuran is more just a facilitating role in the crystal and it can fill the gap. During the absence of strong hydrogen bonding of the case, methanol can be used as a complementary hydrogen bonding to connect calixarenes in a "head-to-head" or "side-by-side" manner.In chapter five, during the absence of strong hydrogen bond, the self-assembly of calix[4]arene derivatives are studied. Due to lack of supramolecular point, calixarene derivatives could form network structure by C-H-O, C-H-…π and O…π interactions. The steric effects of substituents groups at the lower rim will lead to different self-assembly behavior of calix[4]arene derivative. No substituent groups at the lower rim, cone conformation calix[4]arene derivatives bearing formyl groups form "honeycomb" shaped nanotube structure by hierarchical self-assembly.In order to reduce the repulsion of adjacent molecules that are synthesized by introduing n-propyl to the lower rims,1,3-alternate calix[4]arene tetraformyl connects each other by mutually perpendicular and formation of three-dimensional through C-H…O hydrogen bonds. For the tetraisopropoxy,1,3-alternate calix[4]arene tetraformyl forms three-dimensional structures by close-packed because the formyl groups orientate towards the cavity. Introduction of cyano or benzoyl groups to calixarenes can provide different supramolecular points, which can assist molecular self-assembly.