Super-stable two-dimensional radical conjugated metal-organic frameworks for efficient NIR-II photothermal conversion

Abstract

Radical-functionalized chromophores hold promise as noninvasive NIR-II agents due to their narrow HOMO-SOMO gaps, but inherent instability from radical quenching has limited their practical applications. Here, we report a molecularly engineered class of two-dimensional conjugated metal-organic frameworks (2D c-MOFs) that simultaneously integrate stable radicals (>24 months), extended π-delocalization, and metal-ligand coordination. This synergistic architecture achieves an ultrabroad NIR-II absorption peak extending beyond 1400 nm with extinction coefficients approaching ~10⁶ M⁻¹ cm⁻¹, which outperform traditional photothermal agents by orders of magnitude. Through strategic graft of side chains, we promote vibrational relaxation pathways, markedly enhancing nonradiative decay and enabling a photothermal conversion efficiency of 92.9%. In cell experiments, 2D c-MOFs achieve complete tumor cell ablation under ultralow NIR-II irradiation intensity (0.1 W cm⁻²) that highlights their potential for deep-tissue photothermal therapy. Our work establishes a robust and generalizable molecular design strategy for developing stable radical-based NIR-II agents with exceptional photothermal performance, paving the way for their application in deep-tissue therapy.