Atomic-Thin 2D Copper Sulfide Nanocrystals with over 94% Photothermal Conversion Efficiency as Superior NIR-II Photoacoustic Agents

Exploring photothermal nanomaterials is essential for new energy and biomedical applications; however, preparing materials with intense absorption, highly efficient light-to-heat conversion, and enhanced photostability still faces the enduring challenge. Herein, the study synthesizes atomic-thin (≈1.6 nm) 2D copper sulfide (AT-CuS) plasmonic nanocrystals and find its extraordinary photothermal conversion efficiency (PCE) reaching up to 94.3% at the second near-infrared (NIR-II) window. Photophysical mechanism studies reveal that the strong localized surface plasmon resonance (LSPR) and out-of-plane size effect of AT-CuS induce strong optical absorption and non-equilibrium carrier scattering, resulting in a significant carrier-phonon coupling (7.18 × 10¹⁷ J K⁻¹ s⁻¹ m⁻³), ultimately enhancing the heat generation. Such a photothermal nanomaterial demonstrates at leastmes stronger NIR-II photoacoustic (PA) signal intensity than that of most commonly used miniature gold nanorods, together with greater biocompatibility and photo-/thermal-stability, enabling noninvasive PA imaging of brain microvascular in living animals. This work provides an insight into the rational exploration of superb NIR-II photothermal and photoacoustic agents for future practical utilizations.