Extremely Long Lived Localized Singlet Diradicals in a Macrocyclic Structure: A Case Study on the Stretch Effect

• Published in: Chemistry : a European journal Vol. 24; no. 55; pp. 14808 - 14815
• Main Authors: Harada, Yuta, Wang, Zhe, Kumashiro, Shunsuke, Hatano, Sayaka, Abe, Manabu
• Format: Journal Article
• Language: English
• Published: WEINHEIM Wiley 01.10.2018; Wiley Subscription Services, Inc
• Subjects: Atmospheric conditions; Case studies; Chemical bonds; Chemistry; Chemistry, Multidisciplinary; kinetic stabilization; macrocycles; Optical materials; Organic chemistry; Oxidation; Physical Sciences; radicals; Science & Technology; stretch effect; NON-KEKULE; radicals; oxidation; REACTIVITY; STATE; COPE REARRANGEMENT; TRANSITION; stretch effect; macrocycles; BIRADICALS; TRIPLET; kinetic stabilization; POLYMER; 1,3-DIPHOSPHACYCLOBUTANE-2,4-DIYL; 4-MEMBERED RING; localized singlet diradical, kinetic stabilization, stretch effect, macrocyclic effect, oxidation
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201803076

Localized singlet diradicals have attracted much attention, not only in the field of bond‐homolysis chemistry, but also in nonlinear optical materials. In this study, an extremely long lived localized singlet diradical was obtained by using a new molecular design strategy in which it is kinetically stabilized by means of a macrocycle that increases the molecular strain of the corresponding σ‐bonded compound. Notably, the lifetime of this diradical (14 μs) is two orders of magnitude longer than that of a standard singlet diradical without a macrocyclic structure (≈0.2 μs) at 293 K. The species is persistent below a temperature of 100 K. In addition to the kinetic stabilization of the singlet diradical, the spontaneous oxidation of its corresponding ring‐closed compound at 298 K produced oxygenated products under atmospheric conditions. Apparently, the “stretch effect” induced by the macrocyclic structure plays a crucial role in extending the lifetime of localized singlet diradicals and increasing the reactivity of their corresponding σ‐bonded compounds. Lifetime stretched: A new kinetic stabilization (stretch) effect affecting the reactivity of localized singlet diradicals, which is induced by the presence of a macrocyclic ring that increases the molecular strain of the corresponding σ‐bonded compound (see figure), was examined. Extremely long‐lived singlet diradicals emerged in this study.