1. The association constant, a basic parameter, is a measure of the binding strength between the host and the guest . For the first time we studied concentration dependence of apparent experimental association constants of fast-exchange host-guest systems based on dicationic paraquat derivatives with two monovalent counterions ( G ++ 2X - ) as guest species and neutral crown ethers as hosts. Over the course of these studies we show that such host-guest systems which exhibit variations in the apparent association constant, K a ,exp = [Complex]/[Host][Guest], with concentration involve dissociated complexes (Model 1), while those whose K a,exp are invariant with concentration involve ion paired complexes (Model 2). X-ray crystal structures supported these solution-based assessments.
2. Self-assembled structures, such as pseudorotaxanes , are attractive to materials science for their reversibility at the molecular level, and therefore for their ability to correct structural defects, an option unavailable for traditional, covalently bonded systems. However, in order for a self-assembling, non-covalent macromolecular system to possess properties sufficient to compete with covalently bonded polymers, it must exhibit a strong association between its components. Paraquat derivatives have been widely used as guests in supramolecular chemistry to construct numerous complexes with large crown ethers. In order to prepare large supramolecular systems efficiently from small building blocks, we are interested in improving complexation of paraquats by design of optimized hosts, such as cryptands . We not only prepared powerful hosts for paraquat derivatives but also found a cooperative complexation system based on a cryptand and bisparaquat derivative. 3. The construction of analogs of traditional macromolecules by supramolecular methods is a topic of great current interest due to not only their topological importance but also their potential functions. We designed and prepared the first supramolecular star polymer, a new type of supramolecular poly[ 3] pseudorotaxane , the first supramolecular hyperbranched polymer, the first supramolecular graft copoymer , a supramolecular network, and the first mechanically interlocked hyperbranched polymer. 4. X-ray crystallography not only is a valuable tool to prove directly what we have but also can provide useful information for designs of supramolecular systems. We designed and prepared a series of new supramolecular systems based on X-ray analysis of known systems. 5. The study of pesudorotaxanes is very important because pseudorotaxanes are intermediates to prepare interlocked structures such as rotaxanes and catenanes . These interlocked structures have been used to fabricate nanoelectronic devices. Up to now, the most widely used recognition motifs are the dibenzo-24-crown-8/secondary ammonium and bis- p -phenylene-34-crown-10/paraquat recognition motifs. Recently, I found that monopyridinium salts could be used to prepare pseudorotaxanes with crown ethers and cryptands too as shown by X-ray analyses! Therefore monopyridinium salts will be the third type of general guests for preparing pseudorotaxanes , rotaxanes , catenanes , and related threaded structures with crown ethers after secondary ammonium salts and paraquat derivatives, which were discovered by Stoddart's group in 1980s. 6. Supramolecular nano -structures with high symmetry and precise architecture are a new class of promising materials for future applications in nanotechnology because of their interesting magnetic, photophysical , and electrostatic properties. Crown ethers are one of the most widely used hosts in host-guest chemistry. We designed and prepared a series of functionalized nano-supramolecules containing crown ethers.