The SUMO (Singly Unoccupied\nMolecular Orbital)-LUMO\n(Lowest Unoccupied Molecular Orbital) Inversion Radicals

Herein,\nSUMO-LUMO inversion (SLI) radicals <b>2a</b>–<b>2c</b> were designed by the combination of the tris(2,4,6-trichlorophenyl)methyl\n(TTM) radical and pyridinium derivatives (electron-withdrawing groups)\nfor the first time. The energy of the LUMO lies below that of the\nSUMO, which deviated from the Aufbau principle as an alternative electronic\nconfiguration beyond the well-established SOMO-HOMO inversed system.\nThus, for SLI radicals, the injection of one extra electron preferred\nto occupy the LUMO rather than the SUMO, giving diradicals, one of\nwhich <b>3</b> had been fully confirmed by single crystal analysis,\nVT-NMR and VT-EPR experiments, as well as DFT calculations. Furthermore,\nSLI radicals <b>2a</b>–<b>2c</b> exhibit photoluminescent\nproperties and good photostability under UV irradiation (<i>t</i><sub>1/2</sub> > 24 days for <b>2c</b>). This finding would\nopen up new exploration on SLI radicals and their potential applications\nas photoelectromagnetic material.