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.