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. Highly stable π‐extended nickel corrole radicals and their cations exhibiting superior absorbing capacities across the visible‐to‐near‐infrared (NIR) spectral region are synthesized via the radial fusion of aromatic rings. The nanoparticles encapsulating corrole radicals are high‐performance photothermal agents and enable efficient NIR‐triggered photoacoustic imaging and photothermal therapy in vivo.