Design of interelectronic exchange in phenoxyl- and nitroxyl- based systems

A series of model compounds, having phenoxyl, nitroxyl and nitronyl nitroxide radical pendant groups, were studied in order to better understand exchange coupling of several linker units. Stability of these radical containing model compounds was found to be as important as the delocalization of the radicals for further study in polymeric systems. Also, structure-property relations of different morphologies of poly(2,6-di-tert-butyl-4-$(2\sp\prime,4\sp\prime,6\sp\prime$-tri-tert-butyl-phenyloxalato) phenyl acetylene were examined using spectroscopic techniques. Stability of the polyradical and the side reactions seen within this polymer were clearly explaining to us why paramagnetic behavior is being observed instead of expected ferromagnetic coupling. Ferrocenyl radical precursors were found to be highly susceptible for auto-oxidation and further reduction under basic solution media. Similar behavior was seen for the studied (2,6-di-tert-butyl-4-nitronylnitroxyl) phenoxyl diradical. The unusual ESR spectra of these compounds implied their easy auto-oxidation due to strong electron donating ability of both ferrocene and para-hydroxyl groups. Studying nitronyl nitroxide radical precursors of the above compounds enabled us to observe step by step oxidation of these compounds for the first time using ESR spectroscopy. This study gave us important clues for studying the mechanism of the nitronyl nitroxide radical formation in our systems. High delocalization capability of phenoxyl radicals having para acetylenic units formed an important barrier preventing us from observing exchange coupling behavior of acetylenic model compounds. Further study is needed for this group of molecules in order to eliminate reactive sides within the structures. ESR study of these compounds can be possible only after synthesis of stable acetylenic radical precursors