Radical-containing Porous Organosilica Host Phases Studied by Advanced Electron Paramagnetic Resonance Techniques

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This project is aimed at investigation of a new family of functional nanostructured materials – porous organosilica phases, including periodic mesoporous organosilica (PMO), decorated with stable radicals – using advanced Electron Paramagnetic Resonance (EPR) techniques. Such organosilica phases attract a lot of attention as prospective robust sorbents for small molecules, including gases, and the use of stable radicals attached to the surface of mesoporous materials enhances their functional properties. At the same time, these paramagnetic dopants are excellent signalling molecules for EPR. In particular, adsorption of other paramagnetic and diamagnetic molecules in porous organosilica host phases and the role of stable radicals and interaction with them are of practical interest. Within this project, we propose the synthesis of new radical-labeled porous organosilica host phases, their physicochemical characterization and extensive structural and functional study by EPR. First of all, radical attachment modes and their local surrounding in bare materials will be characterized by continuous wave and pulse multifrequency EPR. Next, adsorption and desorption of various guest molecules including nitric oxide (NO), nitrogen dioxide (NO2), volatile radicals such as TEMPO and others, will be studied in detail. We aim at in-depth understanding of interactions between guest molecules and various radical sites in the pores of organosilica phases, and on elucidation of mechanistic aspects of adsorption. This information becomes available via application of advanced pulse EPR methods such as ENDOR (Electron-Nuclear Double Resonance), HYSCORE (Hyperfine Sublevel Correlation Spectroscopy), DEER/PELDOR (Double Electron-Electron Resonance), etc. The detailed understanding of local structure and function of radical centers in porous organosilica host phases is anticipated as a result of proposed project. This will strongly aid in developing further strategies for directed design of such radical-decorated porous materials for gas separation, storage, sensing, catalytic and other potential applications.