Step-by-Step Real-Time Electron Paramagnetic Resonance Monitored Protocol for Synthesizing a Nitroxide-Functionalized Periodic Mesoporous Organosilica.

This protocol describes a step-by-step approach for the synthesis of a periodic mesoporous organosilica (PMO) with wall-embedded nitroxide monoradicals. It starts with the synthesis of an isoindoline-based nitroxide monoradical and its silylationa critical requirement for the condensation with the PMO's bisilylated building block. We also provide detailed instructions on how to synthesize the phenylene (Ph)-PMO's bisilylated precursor, 1,4-bis-(triethoxysilyl)-benzene (BTEB), and subsequent preparation of the Ph-PMO with in situ incorporation of the silylated nitroxide monoradical. The incorporation of the nitroxide into the Ph-PMO was monitored by electron paramagnetic resonance (EPR) spectroscopy, which clearly revealed the decrease in free radical concentration in solution as the condensation progressed. A comparison of the radical-containing Ph-PMO to a reference Ph-PMO, prepared from the same organic precursor in the absence of the radical, by powder X-ray diffraction (PXRD), N2 adsorption-desorption isotherms, thermal gravimetric analysis (TGA), and Fourier transform infrared with attenuated total reflectance (FTIR-ATR), showed that the radical did not induce structural changes to the PMO. All reactions and methodologies described in this protocol were performed at least in triplicate, demonstrating their reproducibility. Completion of the entire protocol takes 22 days (∼3 weeks).