Viridium:\nA Stable Radical and Its π‑Dimerization

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