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Persistent Room‐Temperature Radicals from Anionic Naphthalimides: Spin Pairing and Supramolecular Chemistry
Author(s) -
Huang Wenhuan,
Chen Biao,
Zhang Guoqing
Publication year - 2019
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201902882
Subject(s) - chemistry , electron paramagnetic resonance , photochemistry , intramolecular force , supramolecular chemistry , radical , phosphorescence , excited state , carbanion , triplet state , electron acceptor , pairing , crystallography , molecule , fluorescence , stereochemistry , crystal structure , organic chemistry , nuclear magnetic resonance , physics , superconductivity , quantum mechanics , nuclear physics
N ‐Substituted naphthalimides (NNIs) have been shown to exhibit highly efficient and persistent room‐temperature phosphorescence from an NNI‐localized triplet excited state, when the N ‐substitution is a sufficiently strong donor and mediates an intramolecular charge‐transfer (ICT) state upon photo‐excitation. This work shows that, when the electron‐donating ability of the N ‐substitution is further increased in the presence of a carbanion or phenoxide, spontaneous electron transfer (ET) occurs and results in radical anions, verified with electron‐paramagnetic resonance (EPR) spectroscopy. However, the EPR‐active anion is surprisingly persistent and impervious to nucleophilic and radical reactions under anionic conditions. The stability is thought to originate from an intramolecular spin pairing between the N ‐donor and the NI acceptor post ET, which is demonstrated in supramolecular chemistry.