Binding of Dinuclear Ruthenium Complexes, SWNTs and Nanoparticles for Hybrid Nanocomposite Materials
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Binding of Dinuclear Ruthenium Complexes, SWNTs and Nanoparticles for Hybrid Nanocomposite Materials Jeffrey R. Alston1 and Jordan C. Poler1 1 University of North Carolina at Charlotte, 9201 University City Blvd., Charlotte, NC 28223, U.S.A. ABSTRACT Integration of nanomaterials into composite systems is the next evolutionary step in nanoscale science. Until recently nanocomposites are formed by embedding nanomaterial components into matrices, through chemical bonding or with various wrapping agents. We seek to show that through directed self assembly nanomaterials can be coupled with photosensitizing ruthenium complexes while avoiding chemical augmentation and insulating effects from polymer, surfactant or DNA wrapping. We have synthesized dinuclear ruthenium complexes (dimers) possessing rigid conjugated ʌ-electron systems that form a nanoscale pocket. The pocket is dimensionally suited to interact strongly with nanomaterials forming an architecture that could facilitate photon collection and charge transfer across the interaction. This study explores the binding interaction of our ruthenium dimers with SWNTs. The binding strength varies relative to the magnitude of formal charge which trends with DFT simulations that predict SWNT dimer interactions. SWNT surface saturation by ruthenium dimers can be observed using UV-visible spectroscopy and characterized with adsorption isotherms. We also explore a new technique to measure nanomaterial interactions, isothermal titration calorimetry (ITC). We show that ITC can be used to directly measure the binding enthalpy of nano material surface interactions in solution. INTRODUCTION Nanoparticles will be integral components of the complex materials that will be used to build technology in the near future. The assembly of the nanomaterials into complex composites will rely on our ability to predict and understand the binding and surface interactions of nanoparticles with partnering matter, i.e., ligands, proteins, polymers and other nanomaterials. Single-walled carbon nanotubes (SWNTs) are one-dimensional nanomaterials that vary in diameter and chirality. There has long been an interest in SWNTs as nanocomposite materials due to their mechanical and electrical properties, and like all nanomaterials due to their high surface to volume ratio. Potential applications of SWNTs in nanocomposite materials range from nanoelectronics as sensors, transistors and electrodes to structural scaffold on which more complex systems can be built. SWNTs make ideal components in material composites to which they will impart their unique properties. In this report we investigate adsorption interactions of unique ruthenium dimer complexes onto SWNTs. The ruthenium dimers possess a rigid structure formed by a tetradentate tetrapyridophenazine ligand bridging two ruthenium centers. The rigid structure of these complexes construct a nanoscale pocket lined with the conjugated ʌ electron systems of the coordinated ligands. SWNTs have a diameter of approximately 1 nm and a maximum available surface area
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