Organic molecules with high spin ground states have proven to be a promising class of molecules with uses as molecules with magnetism, MRI contrasting agents, stimuli responsive materials, and spintronics. While heteroatom-centered radicals have been well-developed, the development of carbon-centered radicals have been hindered by the poor stability and difficulty of synthesis. Recently, dicyanomethyl aryl radicals have been proved to be air-stable carbon-centered radicals of which the stability doesn’t rely on the steric hindrance. First, a series of dicyanomethyl aryls with different substituents at the para-position ranging from the electron-rich to electron-deficient groups were synthesized. Based on variable-temperature electron paramagnetic resonance (VT-EPR) and variable-temperature UV-Vis studies, binding constants for dimizeration of all the dicyanomethyl aryl radicals were calculated. These studies indicate that electron-rich substituents favor the radical species, while withdrawing groups favor the dimer. To evaluate the effect of chemical structure on the strength and nature of such spin interactions, 14 tethered aryl dicyanomethyl diradicals were synthesized, and the structure and thermodynamic properties of the diradicals were investigated. An X-ray crystal structure indicates that this type of diradicals form intramolecular sigma dimer with an elongated C-C bond. A 5-carbon linked julolidine diradical showed reverse color change upon heating and interacts as a -dimer rather than a sigma dimer.<br/>Extending this work work to high-spin, macrocycle, and helical dicyanomethyl aryl radicals are in progress. So far, the crystal structures of these molecules demonstrate that these molecules are promising building blocks to form stimuli-responsive materials with extraordinary stability. At the same time, carbon radicals have been recognized reactive intermediates, which with well-designed radical precursors, might unravel new type of radical-involved mechanisms.

Synthesis and characterization of dicyanomethyl aryl radicals

2019 Fall National Meeting

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