Molecular Engineering of Corrole Radicals by Polycyclic Aromatic Fusion: Towards Open‐Shell Near‐Infrared Materials for Efficient Photothermal Therapy

Open-shell radicals are promising near-infrared (NIR) photothermal agents (PTAs) owing to their easily accessible narrow band gaps, but their stabilization and functionalization remain challenging. Herein, highly stable π-extended nickel corrole radicals with [4n+1] π systems are synthesized and used to prepare NIR-absorbing PTAs for efficient phototheranostics. The light-harvesting ability of corrole radicals gradually improves as the number of fused benzene rings on β-pyrrolic locations increases radially, with naphthalene- and anthracene-fused radicals and their one-electron oxidized [4n] π cations exhibiting panchromatic visible-to-NIR absorption. The extremely low doublet excited states of corrole radicals promote heat generation via nonradiative decay. By encapsulating naphthocorrole radicals with amphiphilic polymer, water-soluble nanoparticles Na-NPs are produced, which exhibit outstanding photostability and high photothermal conversion efficiency of 71.8 %. In vivo anti-tumor therapy results indicate that Na-NPs enable photoacoustic imaging of tumors and act as biocompatible PTAs for tumor ablation when triggered by 808 nm laser light. The "aromatic-ring fusion" strategy for energy-gap tuning of corrole radicals opens a new platform for developing robust NIR-absorbing photothermal materials.