Azaacene Diradicals Based on Non‐Kekulé Meta‐Quinodimethane with Large Two‐Photon Cross‐Sections in the Infrared Spectral Region

Abstract

Non‐Kekulé quinoidal azaacences m‐A (1a,b) were synthesized and compared to their para‐ and ortho‐quinodimethane analogues. m‐Adisplay high diradical characters (1b: y0 = 0.88) due to their meta‐quinodimethane (m‐QDM) topology. Electron paramagnetic, nuclear magnetic resonance spectroscopies and supraquantum interference device measurements in combination with quantum‐chemical calculations revealed singlet ground states for m‐A with singlet‐triplet gaps ΔEST (0.13‐0.25 kcal mol‐1) and thermally populated triplet states. These non‐Kekulé structures are over all void of zwitterionic character and possess record high two‐photon absorption cross sections over a broad spectral range in the near‐infrared.