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Doctoral Dissertation Announcement
Candidate: Isurika Rosini Fernando
Doctor of Philosophy
Title: Metal-organic and Supramolecular Architectures Based on Mechanically Interlocked Molecules
Dr. Gellert Mezei, Chair
Dr. Ekkehard Sinn
Dr. Ramakrishna Guda
Dr. Daniel Kujawski
Date: Tuesday, March 12, 2013 3:00 p.m. to 5:00 p.m.
2902 Wood Hall
The focus of this work is on mechanically interlocked molecules (MIMs), which have unusual physicochemical and mechanical properties with potential applications in nano-scale/molecular devices and high strength materials. Rotaxanes, for example, consist of an axle-like molecule threaded through a wheel-like molecule, with bulky groups at the two ends of the axle preventing the wheel from dissociating. The position of the wheel along the axle can be switched in a controllable and reversible manner by applying external stimuli, a feature that might lead to the next generation of computers. Molecularly woven materials (MWMs), another example of molecules with mechanically interlocked features, are predicted to be unprecedentedly strong while being lightweight and flexible.
With the ultimate goal of achieving control over the functioning of molecular devices in the solid state, a variety of pseudorotaxane building blocks are prepared and characterized, including a novel, rare blue-colored motif. The temperature-dependent assembly/disassembly of pseudorotaxanes is exploited for the construction of single-wavelength colorimetric temperature sensors over a 100 °C window. Pseudorotaxanes based on aromatic crown ether wheels and disubstituted 4,4¢-bipyridinium axles are converted into rotaxanes upon binding to metal complexes (zinc, cadmium, mercury, copper, cobalt), and the formation of ordered crystalline arrays is studied in the solid state. The columnar organization of pseudorotaxanes by Hg2X62– complexes (X = Cl, Br, I), leading to unprecedented dichroic (blue/red) rotaxane crystals, is demonstrated for the first time. From the crystal structures studied it becomes apparent that negatively charged metal complexes are needed for successful assembly with the positively charged pseudorotaxane units. To be able to use the more common, positively charged metal ions for rotaxane framework construction, neutral and negatively charged pseudorotaxanes are synthesized by attaching anionic substituents (carboxylates, sulfonates) to either the wheel or the axle component. It is found that pseudorotaxane formation also enables resolution of two sulfonated crown ether isomers, which are inseparable by conventional methods.
Organic ligands for MWM precursors are designed and synthesized according to multi-step schemes. Helical metal-complexes based on these ligands are prepared and characterized.
Chromatography, Nuclear Magnetic Resonance and UV-Visible spectroscopy, Mass spectrometry, Electrochemistry, Thermogravimetric Analysis and X-ray crystallography are used in identification, purification and characterization of the compounds involved.