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

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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.