Binary Organic Nanoparticles with Bright Aggregation-Induced Emission for Three-Photon Brain Vascular Imaging

Fluorogens with aggregation-induced emission (AIEgens) are promising optical agents for cellular and vascular imaging. AIEgens with bright emission in the far-red and near-infrared (NIR) regions are highly desirable, but the traditional strategies, i.e., introducing donor-acceptor (D-A) structures into AIEgens, generally lead to fluorogens with photoluminescence that is vulnerable to the polarity of the surrounding environment. In addition, because of the intrinsic rotor structure, AIEgens usually show absorption in the short-wavelength region, which is not optimized for imaging applications. In this contribution, we report binary organic nanoparticles (NPs) with tunable emission and high quantum efficiency in the red and far-red regions. By increasing the intermolecular distance, the obtained NPs offered enhanced luminescence quantum yields from 0.01 to 0.23 and increased three-photon excitation (3PE) cross sections, enabling high-quality and deep brain vascular imaging on an 8-week-old BALB/C mouse with up to 1.68 mm upon excitation at 1610 nm.