Reversible Solution π‐Dimerization and Long Multicenter Bonding in a Stable Phenoxyl Radical

• Published in: Chemistry : a European journal Vol. 24; no. 56; pp. 14906 - 14910
• Main Authors: Bonanno, Nico M., Poddutoori, Prashanth K., Sato, Kazunobu, Sugisaki, Kenji, Takui, Takeji, Lough, Alan J., Lemaire, Martin T.
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 09.10.2018
• Subjects: Bonding strength; Chemistry; density functional calculations; Density functional theory; Dimerization; Dimers; Low temperature; molecular devices; Molecular orbitals; multicenter bonding; Radicals; stable radicals; π-dimerization; molecular switching; Multicenter bonding; Stable radicals; π-dimerization
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201802204

Reversible solution π‐dimerization is observed in the stable neutral phenoxyl radical 2,6‐bis‐(8‐quinolylamino)‐4‐(tert‐butyl)phenoxyl baqp and is spectroscopically characterized. This behavior, not previously observed for π‐extended phenoxyl radicals, is relevant to the formation of long multicenter bonding in the π‐dimer at low temperature akin to previously reported phenalenyl radicals. Our experimental data are supported in a quantitative manner by results from density functional theory (DFT) and ab initio molecular orbital theory calculations. Our theoretical results indicate that the solution dimer features strong bonding interactions between the two phenoxyl rings but that the stability of the dimer is also related to dispersion interactions between the flanking nearly parallel quinolyl rings. The reversible solution π‐dimerization of a π‐extended phenoxyl radical is reported for the first time. The dimerization was characterized using variable temperature UV/Vis‐NIR, EPR, and 1H NMR spectroscopy. Theoretical results comprehensively indicate the presence of long, multicenter bonding interactions in the dimer between the phenoxyl rings and stabilization of the dimer through dispersion interactions between the flanking quinolyl rings.