Synthesis and Properties of a Highly Congested Tri(9‐anthryl)methyl Radical

Abstract

The synthesis of persistent, neutral organic radicals is challenging because of their inherent reactivities. Herein, we report the synthesis and characterization of a highly congested mesityl‐substituted tri(9‐anthryl)methyl (TAntM) radical (1). The scaffold was successfully synthesized by circumventing the steric hindrance imposed by the bulky groups surrounding the central methyl carbon atom. The radical has a threefold propeller structure, and the unpaired electron is mainly localized on the central carbon atom. Owing to its congested structure, 1 is remarkably stable, which facilitated handling under ambient conditions. Evaluation of the dynamic behavior of the TAntM scaffold indicated that the stability is due to the bulky anthryl units and the mesityl substituents. Because of its high persistence, wide‐range absorption, and good reversible redox properties, 1 has promising applications in organic devices.

Anthracene‐Attached Persistent Tricyclic Aromatic Hydrocarbon Radicals

“…The reaction of 2 d with SnCl 2 ⋅2 H 2 O afforded not a radical monomer Ant‐DPM but a tail‐to‐tail σ‐dimer, (Ant‐DPM) 2 , in good yield (62 %, Scheme ). The facile dimerization of Ant‐DPM probably arises from the flexibility of the diphenylmethyl skeleton compared with the other radicals, resulting in the σ‐dimer formation at 10‐position of the anthryl group . Thus, the rigidity of the tricyclic radical scaffold plays an important role in the persistence of Ant‐5 , Ant‐6 , and Ant‐7 .…”

“…Interestingly, a toluene solution of the σ‐dimer of Ant‐5 showed a slight color change from pale yellow to purple at high temperature (100 °C), indicating dissociation from σ‐dimer to a monomeric radical. In addition, a mechanical grinding also caused the dissociation of the Ant‐5 σ‐dimer, which can be recognized by a color change from yellow to purple (Figure S7, Supporting Information). It is noteworthy that these features could not be observed for the σ‐dimers of Ant‐DPM and Ant‐7 even though the C(sp 3 )‐C(sp 3 ) σ‐bond length of the σ‐dimers of Ant‐DPM , Ant‐5 , and Ant‐7 (1.567–1.575 Å) are calculated to be close to the normal C(sp 3 )‐C(sp 3 ) σ‐bond length.…”

Platforms for Stable Carbon‐Centered Radicals

“…[28][29][30][31][32][33] In 2018, Nishiuchi, Kubo,a nd co-workers reported that 10-protected 9-anthryl groups served to furnish an excellently stable radical, 5Mes. [34] Theradical 5H,lacking a10-mesityl group,forms the tail-to-tail s-dimer 6 both in the solid state and in solution with abond dissociation enthalpy of 19.7 kcal mol À1 in toluene,t hus showing the importance of substituents at the 10-position.…”

Platforms for Stable Carbon‐Centered Radicals

“…Recently, the highly luminescent properties of triarylmethyl radicals were reported as promising materials in organic light‐emitting diodes (OLEDs) . In 2018, Nishiuchi, Kubo, and co‐workers reported that 10‐protected 9‐anthryl groups served to furnish an excellently stable radical, 5Mes . The radical 5H , lacking a 10‐mesityl group, forms the tail‐to‐tail σ‐dimer 6 both in the solid state and in solution with a bond dissociation enthalpy of 19.7 kcal mol −1 in toluene, thus showing the importance of substituents at the 10‐position.…”