Synthesis and spectroelectrochemical study of novel polyhedral borane derivatives
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The substitution chemistry of dodecahydro-closo-dodecaborate (2-) and decahydro-closodecaborate (2-) as well as the spectroelectrochemical properties of the resulted compounds which we refer to herein as "polyaryl boranes" was investigated in this research. Polyaryl boranes are a new class of organic-inorganic hybrid nanomolecular ions derived from the substitution chemistry between polyhedral boranes and aromatic hydrocarbons. The properties of each polyaryl borane were dependent upon the composition and the structure of bound ligands, and these maybe tailored through chemical modification of the surface. Analytical tools such as high-resolution mass spectrometry, nuclear magnetic resonance and infra-red spectroscopies were employed for the structural characterization of polyaryl boranes. Methods have been optimized for making, controlling and analyzing the polyaryl boranes. These polyarylation reactions are found to be acid catalyzed. On the contrary, the presence of minute amounts of base inhibited the reaction progress any further. Three-dimensional aromaticity resulted from the delocalization of [pi] electrons from aromatic hydrocarbon ligands into the boron-cage framework via the newly formed exo-hedral B-C bonds. Polyaryl borane clusters are found to exhibit interesting electronic and spectroscopic properties including high-solution phase fluorescence quantum yields, high molar absorptivities and extra-ordinarily large stoke shifts. The electrochemical studies revealed multiple reversible and/or quasi-reversible redox processes at different oxidation states of polyaryl boranes. Furthermore, the fluorescence emission, excitation and absorption spectra for most polyaryl boranes change reversibly upon applying product-specific electrochemical potentials, thus resulting in redox controlled fluorescence switching and electrochromism. Also, the molar absorptivities of polyaryl boranes found to be much higher compared to their respective ligands alone. This research suggests that the new nanomaterials synthesized may have the potential for applications in biomedical imaging and sensor development.
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Ph. D.