Ultrabirght organic nanocrystals by amphiphile-templated crystallization for high-contrast NIR-II bioimaging.

Fluorescence imaging in the second near-infrared window (NIR-II) has emerged as a powerful, radiation-free diagnostic tool with high temporal and spatial resolution. However, the low brightness of organic fluorophores remains a major challenge for precise clinical diagnosis. To tackle this, here, we present ultrabright NIR-II nanocrystals via an amphiphile-templated crystallization strategy. Amphiphilic dispersants bearing fluorophore-mimetic hydrophobic domains provides a template for the ordered assembly of NIR-II AIEgens through specific molecular recognition, yielding well-defined crystalline architectures. This approach promotes dense molecular packing of AIEgens, effectively constraining intramolecular rotations while forming robust water-resistant interfaces that prevent dark-state formation. As a result, the nanocrystals exhibit a sevenfold improvement over amorphous systems. The ultrabright organic nanocrystals enabled high-resolution imaging for abdominal vasculature (110 μm vs. >200 μm for amorphous counterparts), and supported the first NIR-II luciferase reporter gene assay for in vivo visualization of endogenous gene expression and cellular viability. This work provides an advanced platform for designing ultrabright NIR-II nanomaterials by crystallization, with significant implications for enhanced diagnostic precision and therapeutic efficacy in image-guided biomedical applications.