The limited signal of long-wavelength near-infrared-II (NIR-II, 900–1880 nm) fluorophores and the strong background caused by the diffused photons make high-contrast fluorescence imaging in vivo with deep tissue disturbed still challenging. Here, we develop NIR-II fluorescent small molecules with aggregation-induced emission properties, high brightness, and maximal emission beyond 1200 nm by enhancing electron-donating ability and reducing the donor-acceptor (D-A) distance, to complement the scarce bright long-wavelength emissive organic dyes. The convincing single-crystal evidence of D-A-D molecular structure reveals the strong inhibition of the π-π stacking with ultralong molecular packing distance exceeding 8 Å. The delicately-designed nanofluorophores with bright fluorescent signals extending to 1900 nm match the background-suppressed imaging window, enabling the signal-to-background ratio of the tissue image to reach over 100 with the tissue thickness of ~4–6 mm. In addition, the intraluminal lesions with strong negatively stained can be identified with almost zero background. This method can provide new avenues for future long-wavelength NIR-II molecular design and biomedical imaging of deep and highly scattering tissues.

长波长近红外-II（NIR-II，900-1880 nm）荧光团的有限信号和扩散光子引起的强背景使得深部组织受到干扰的体内高对比度荧光成像仍然具有挑战性。在这里，我们通过增强给电子能力和减少供体-受体（DA）距离，开发出具有聚集诱导发射特性、高亮度、最大发射超过1200 nm的NIR-II荧光小分子，以补充稀缺的亮长荧光小分子。波长发射有机染料。DAD分子结构令人信服的单晶证据揭示了超长分子堆积距离超过8 Å对π-π堆积的强烈抑制作用。精心设计的纳米荧光团具有延伸至1900 nm的明亮荧光信号，与背景抑制成像窗口相匹配，使组织图像的信号与背景比达到100以上，组织厚度约为4-6 mm。此外，可以在几乎零背景的情况下识别具有强负染色的管腔内病变。该方法可以为未来长波长NIR-II分子设计和深层和高散射组织的生物医学成像提供新途径。