Tailoring and Unraveling Surface Functionalization of Nanomaterials via Self‐Reporting NIR‐Induced Upconversion Energy Transfer Process

ABSTRACT The surface functionalization chemistry of nanomaterials remains a black box, where the dynamic modification process is conventionally imperceptible, which severely limits the rational design of advanced nanohybrids. Herein, a holistic strategy that transforms upconversion nanorods (UCNR) surface functionalization from an empirically treated outcome into an optically self‐reporting process via near‐infrared (NIR)‐mediated photoinduced electron/energy transfer‐reversible addition‐fragmentation chain transfer (PET‐RAFT) polymerization is present. This three‐in‐one design, where the UCNR concurrently acts as a NIR‐harvesting antenna, polymerization substrate, and optical signaling unit, enables the precise, temporally controlled growth and monitoring of polymer shells with tunable thickness and grafting density. Critically, a linear correlation between the evolving polymer shell architecture and the upconversion luminescence intensity was unraveled, thereby turning the optical signal into a real‐time, nondestructive probe that reveals the invisible surface modification process. Building upon this self‐monitoring capability, the polymer brushes were further engineered to template the in situ growth of gold nanoparticles, establishing a cascaded energy transfer pathway for efficient photothermal conversion. Using the nanohybrids as a built‐in ratiometric fluorescent nanothermometer, the nanohybrid enables real‐time temperature feedback during NIR irradiation as precise nanothermometry. This work establishes a new paradigm for creating intelligent, self‐sensing nanoplatforms with profound implications for precision theranostics and adaptive photonic materials.