Viridium: A Stable Radical and Its π-Dimerization.

The discovery of a stable organic radical formed under mild, clean, and efficient light-mediated conditions is reported. The structure of the stable acridinium-based radical photoproduct was unambiguously established by single-crystal X-ray diffraction, mass spectrometry, and in solution by EPR, UV/vis, and NMR spectroscopies. The photochemical mechanism of its formation has been elucidated by photophysical experiments coupled with EPR experiments and theoretical investigations. This unique aromatic radical is featured by amphoteric redox behavior and π-dimerization properties. Its ability to π-dimerize has been demonstrated in water and in the less studied perfluorohexane, two solvents of opposite polarity. By a simple counterion exchange, direct comparison of π-dimer thermodynamics between both antagonist solvents allowed an elucidation of the solvophobic behavior in perfluorocarbon.