Air stable high-spin blatter diradicals: non-Kekulé versus Kekulé structures

Abstract

Air stable high-spin diradicals under ambient conditions are relatively rare. We report two 1,2,4-benzotriazinyl based diradicals, non-Kekulé o-DBT and Kekulé p-DBT, with a highly twisted bridge. The studies of magnetic susceptibilities reveal that both diradicals possess singlet ground states and small singlet–triplet energy gaps (ΔE_s–t = −0.21 and −0.18 kcal mol⁻¹ for o-DBT and p-DBT, respectively), leading to a thermal accessible triplet excited state. Furthermore, variable-temperature electron spin resonance discloses that the average distance between the two spin centers of o-DBT and p-DBT increases with increasing temperature. Finally, both diradical molecules show very high stabilities under high power irradiation and thermal treatment. In particular, the powder of o-DBT exhibits excellent thermal stability up to 270 °C without noticeable decomposition.