A ground-state-dominated magnetic field effect on the luminescence of stable organic radicals

• Published in: Chemical science (Cambridge) Vol. 12; no. 6; pp. 225 - 229
• Main Authors: Kimura, Shun, Kimura, Shojiro, Kato, Ken, Teki, Yoshio, Nishihara, Hiroshi, Kusamoto, Tetsuro
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 05-01-2021; The Royal Society of Chemistry
• Subjects: Chemistry; Dimers; Emission; Excimers; Luminescence; Magnetic fields; Magnetic properties; Methyl radicals; Quantum mechanics
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/d0sc05965j

Organic radicals are an emerging class of luminophores possessing multiplet spin states and potentially showing spin-luminescence correlated properties. We investigated the mechanism of recently reported magnetic field sensitivity in the emission of a photostable luminescent radical, (3,5-dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl radical (PyBTM) doped into host
αH
-PyBTM molecular crystals. The magnetic field (0-14 T), temperature (4.2-20 K), and the doping concentration (0.1, 4, 10, and 22 wt%) dependence on the time-resolved emission were examined by measuring emission decays of the monomer and excimer. Quantum mechanical simulations on the decay curves disclosed the role of the magnetic field; it dominantly affects the spin sublevel population of radical dimers in the ground states. This situation is distinctly different from that in conventional closed-shell luminophores, where the magnetic field modulates their excited-state spin multiplicity. Namely, the spin degree of freedom of ground-state open-shell molecules is a new key for achieving magnetic-field-controlled molecular photofunctions.
We investigated the mechanism of the magnetic field effect (MFE) on the emission of a luminescent radical doped into host crystals. It was revealed that the spin sublevel population of radical dimers in the ground states is the key that governs the MFE.