Low‐Power NIR‐II Excitable Organic Phototheranostic Agents With NIR‐IIb Emission for Precise Cancer Theranostics

ABSTRACT

Organic small‐molecule phototheranostic agents (OPTAs) with second near‐infrared (NIR‐II, 1000–1700 nm) absorption show great potential for precise cancer theranostics. However, achieving simultaneous NIR‐IIb (1500–1700 nm) emission and high photothermal conversion efficiency (PCE) under low‐power 1064 nm excitation remains challenging due to competing radiative and nonradiative decay pathways. Herein, we report a facile molecular design strategy using noncovalent conformational locks (NoCLs) to develop efficient NIR‐II excitable OPTAs with both bright NIR‐IIb emission and superior PCE. Two A–D–A'–D–A type molecules (NCF and QCF) are synthesized. By introducing S···N NoCLs, QCF adopts a more planar and rigid conformation, facilitating compact J ‐aggregation and enhanced intramolecular charge transfer. Therefore, QCF nanoparticles (NPs) exhibit a strong NIR‐II absorption at 1143 nm, dual emission at 1338/1550 nm, and a high PCE of 75% under low‐power 1064 nm laser irradiation (0.3 W cm ⁻² ). Single‐crystal and theoretical analyses confirm that S···N NoCLs promote planarization, suppress nonradiative decay, and strengthen intermolecular interactions. In vivo, QCF NPs enable high‐resolution NIR‐IIb vascular/tumor imaging and effective tumor ablation with excellent biosafety. This work establishes NoCLs as a generalizable design principle for next‐generation NIR‐II OPTAs with synergistic optical and therapeutic properties, advancing imaging‐guided cancer theranostics.