A persistent concealed non-Kekulé nanographene: synthesis and in situ characterization

Abstract

Concealed non-Kekulé (CNK) nanographenes have recently gained attention as promising non-Kekulé model systems due to their distinctive antiferromagnetic electronic spins, which offer potential applications in spintronics and quantum information science. However, synthesizing CNK nanographenes in solution remains a significant challenge because of their strong biradical character and high reactivity. In this study, we report the successful synthesis of a novel CNK nanographene with two phenalene units fused in a cis configuration to perylene (c-CNK), which exhibits persistent stability under ambient conditions, with a half-life (t_1/2) of 59 minutes. The formation of c-CNK is confirmed using in situ UV-Vis-NIR spectroscopy, Raman spectroscopy, and high-resolution mass spectrometry. The open-shell character of c-CNK is supported by electron paramagnetic resonance (EPR) spectroscopy by observing an isotropic signal with a g-value of 2.0026. Quantum chemical simulations reveal a high biradical character (y₀ = 0.97) and a singlet open-shell ground state with a small singlet–triplet energy gap (ΔE_S–T) of 0.4 kcal mol⁻¹. This work presents a solution synthesis of a next-generation concealed non-Kekulé nanographene with intrinsic antiferromagnetic electronic spins, highlighting its potential as a promising material for future quantum technologies.