Magnetoluminescence in a Photostable, Brightly Luminescent Organic Radical in a Rigid Environment

We investigated the emission properties of a photostable luminescent organic radical, (3,5-dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl radical (PyBTM), doped into host molecular crystals. The 0.05 wt %-doped crystals displayed luminescence attributed to a PyBTM monomer with a room-temperature emission quantum yield of 89 %, which is exceptionally high among organic radicals. The 10 wt %-doped crystals exhibited both PyBTM monomer and excimer-centered emission bands, and the intensity ratio of these two bands was modulated drastically by applying a magnetic field of up to 18 T at 4.2 K. This is the first observation of a magnetic field affecting the luminescence of organic radicals, and we also proposed a mechanism for this effect.