Spectroelectrochemical Study of Organic-Inorganic Hybrid Nano-Molecular Clusters Exhibiting Voltage-Gated Fluorescence Switching and Electrochromism

Abstract

Polyhedral boranes especially the twelve vertex closo-dodecaborate and the ten vertex closo-decaborate anions exhibit remarkably high thermal stability and resistance to oxidative degradation. Such high stability is attributed to the extensive delocalization of their framework bonding electrons, giving rise to three dimensional aromaticity. The substitution chemistry of polyhedral boron chemistry using aromatic ligands was previously limited in scope. However, we recently reported new and extensive polysubstitution chemistry for these ions. The structural characterization of the products revealed that up to ten of B-H vertices may be replaced with phenyl, substituted phenyl, or polycyclic aromatic hydrocarbons as ligands through the formation of stable boron-carbon bonds. The resulting organic-inorganic hybrid nano-molecular ions are pseudospherical whose diameters range between 1.3 – 3.5 nanometers depending on the ligands involved. These polyarylborane clusters are found to exhibit interesting electronic and spectroscopic properties, including high solution-phase fluorescence quantum yields, high molar absorptivities, and extraordinarily large stoke shifts. Furthermore, the fluorescence emission, excitation and absorption spectra for most of these products change reversibly upon applying product-specific electrochemical potentials, thus resulting in redox-controlled fluorescence switching and electrochromism. The properties of each polyarylborane depend upon the composition and the structure of the bound ligands, and these may be tailored through chemical modification of the surface. Our study suggest that these new nanomaterials may have potential for applications in biomedical imaging and sensor development. This presentation will focus on the details of syntheses, structural characterization, electrochemical and spectroelectrochemical properties of polyarylboranes.