Organic Mixed-Valence Compounds and the Overhauser Effect in Insulating Solids

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2021-01, Vol.125 (3), p.867-874
• Main Authors: Pylaeva, Svetlana, Marx, Patrick, Singh, Gurjot, Kühne, Thomas D, Roemelt, Michael, Elgabarty, Hossam
• Format: Article
• Language: English
• Subjects: A: Structure, Spectroscopy, and Reactivity of Molecules and Clusters
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/acs.jpca.0c11296

Recent experiments have shown that the organic free radical 1,3-bisdiphenylene-2-phenylallyl (BDPA) can induce an Overhauser effect dynamic nuclear polarization in insulating solids, a feat previously considered not to be possible. Here, we establish that this peculiar ability of the BDPA radical stems from its mixed-valence nature and the ensuing intramolecular charge transfer. Using state-of-the-art DMRGSCF calculations, we confirm the class II mixed-valence nature of BDPA with the characteristic double-well potential energy surface, and we investigate the mechanism of the consequent electron hopping. A two-component vibronic Hamiltonian is then employed to compute the rate of electron hopping from a quantum dynamical time-propagation of the density matrix. The predicted hyperfine coupling oscillations indeed fall within the frequency range required for an Overhauser effect. The paradigm of mixed-valence compounds as a mining source opens many possibilities for the development and fine tuning of novel polarizing agents.