From supramolecular bundles toward noncovalent polymers

Secondary dialkylammonium (R2NH2 +) ions have been shown (Chapter 1) to form complexes, possessing a pseudorotaxane superstructure, with a variety of crown ethers such as dibenzo[24]crown-8 (DB24C8), bis(metaphenylene)[25]crown-8 (BMP25C8) and bis(paraphenylene)[34]-crown-10. This molecular recognition motif has been employed in the noncovalent synthesis of a variety of nanoscale architectures in the solution and solid states. A nanoscale architecture which has been studied recently by several research groups is one that leads to the formation of supramolecular polymers in which the components are held together by noncovalent bonds to form long chains.; A supramolecular bundle was self-assembled (Chapter 2) between a tritopic crown ether consisting of three DB24C8 macrocycles and a trifurcated trisammonium salt. X-Ray crystallography revealed the solid state superstructure of this 1:1 complex to be a triply-threaded bundle and 1H NMR spectroscopy revealed that, in solution, this superstructure is indeed the predominant species present. This bundle is extremely stable under favorable conditions but can be disassembled by the addition of DMSO. Stoppering the ends of the trisammonium component of the bundle has led to a triply-interlocked "rotaxane"-like species being formed.; Since this triply-threading recognition motif is extremely stable, it was argued that appropriate modification of it might lead to monomers that could self-assemble into supramolecular, or noncovalent, polymers. Monomers were synthesized (Chapter 3) that consist of either six BMP25C8 appendages or six dibenzylammonium moieties attached to a hexathiobenzene core. These monomers have three appendages pointing away from the plane of the benzenoid core and three appendages pointing in the opposite direction. 1H NMR Spectroscopy of a solution of the two monomers indicated that they do aggregate. The clustering of the crown ether and dialkylammonium moieties in the monomers was found to be detrimental to the individual strength of binding to complementary monovalent ligands. However, the monomers should exhibit increased binding strength to complementary polyvalent ligands as is the case with the supramolecular bundle which was discussed in Chapter 2.