Antiaromatic Nanographenes via a BODIPY-Fusion Strategy

The synthesis of antiaromatic molecules with intense near-infrared (NIR) absorption is challenging due to their inherently forbidden HOMO-LUMO transitions. Herein, we report the synthesis of anthracene- and anthanthrene-fused boron dipyrromethene (BODIPY) with different substituents through oxidative cyclodehydrogenation. These BODIPY-fused nanographenes have distinct antiaromatic characteristics, as supported by a 1H NMR analysis and theoretical calculations. They exhibit narrow electrochemical HOMO-LUMO energy gaps as low as 0.84 eV and NIR absorption of up to 1600 nm. Transient-absorption spectroscopy revealed a rapid decay of their excited states. Water-soluble nanoparticles were obtained from encapsulating two of these BODIPY-fused nanographenes in an amphiphilic polymer and these exhibit outstanding photostability and a high photothermal conversion efficiency of 68 and 57%, respectively. These findings demonstrate that the BODIPY-fusion strategy effectively endows nanographenes with antiaromaticity and NIR absorption.