Antiaromatic Nanographenes via a BODIPY-Fusion Strategy
Kaisheng Wang, Koshiro Isono, Hideaki Takano, Juwon Oh, Shohei Kawakami, Ryota Sugimori, Ryohei Kishi, Daiki Shimizu, Sandipa Bhandari, Masatoshi Ishida, Dongho Kim, Hiroshi Shinokubo
Abstract
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 1 H 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.