Rational Design of an Air‐Stable, High‐Spin Diradical with Diazapyrene

Abstract Stable carbon‐based polyradicals exhibiting strong spin‐spin coupling and slow depolarization processes are particularly attractive functional materials. A new molecular motif synthesized by a convenient method that allows the integration of stable, high‐spin radicals to (hetero)aromatic polycycles has been developed, as illustrated by a non‐Kekulé diradical showing a triplet ground state with long persistency ( τ 1/2 ≈31 h) in air. Compared to the widely used 1,3‐phenylene, the newly designed (diaza)pyrene‐4,10‐diyl moiety is for the first time demonstrated to confer ferromagnetic (FM) spin coupling, allowing delocalized non‐disjoint SOMOs. With the X‐ray crystallography unambiguously proving the diradical structure, the triplet ground state was thoroughly characterized. A large Δ E S‐T of 1.1 kcal/mol, proving the strong FM coupling effect, was revealed consistently by superconducting quantum interference device (SQUID) measurements and variable‐temperature electron paramagnetic resonance (EPR) spectroscopy, while the zero‐field splitting and triplet nutation characters were examined by continuous‐wave and pulsed EPR spectroscopy. A millisecond spin‐lattice relaxation time was also detected. The current study not only offers a new molecular motif enabling FM coupling between carbon‐based spins, but more importantly presents a general method for installing stable polyradicals into functional π‐systems.