A C66 Nanographene with Six Azulene Units and NIR-II Absorption: Toward Azulene-Based Carbon Allotropes

The interest in non-alternant conjugated polycyclic aromatic hydrocarbons (PAHs) as models for novel carbon allotropes has been rapidly increasing, particularly with a focus on azulene-embedded molecular scaffolds. However, the lack of efficient synthetic strategies continues to hinder systematic studies of their structure–property relationships and restricts their potential in optoelectronic applications - especially for systems incorporating more than two azulene units. Here, we report the synthesis of a C66 nanographene, 2-diMes, the first known non-alternant PAH featuring six azulene subunits within a fully conjugated framework. This purely hydrocarbon, closed-shell compound exhibits one of the smallest HOMO–LUMO gaps reported for neutral PAHs. The non-alternant topology of 2-diMes gives rise to absorption in the near-infrared (NIR) region, with an onset extending up to 1300 nm, and an exceptionally narrow electrochemical gap of 1.13 V. In addition, 2-diMes was employed for sensing of alkali metal cations and as a NIR-II photoacoustic dye. Remarkably, it combines a strong photoacoustic response in the NIR-II region, with an absorption onset extending to 1450 nm and high photostability. These properties, together with its excellent solubility in common organic solvents, position 2-diMes as a highly promising candidate for organic electronic materials and theranostic applications.