Fluorescence imaging in the spectral region beyond the conventional near-infrared biological window (700-900 nm) can theoretically afford high resolution and deep tissue penetration. Although some efforts have been devoted to developing a short-wave infrared (SWIR; 900-1700 nm) imaging modality in the past decade, long-wavelength biomedical imaging is still suboptimal owing to the unsatisfactory materials properties of SWIR fluorophores. Taking advantage of organic dots based on an aggregation-induced emission luminogen (AIEgen), herein microscopic vasculature imaging of brain and tumor is reported in living mice in the SWIR spectral region. The long-wavelength emission of AIE dots with certain brightness facilitates resolving brain capillaries with high spatial resolution (≈3 µm) and deep penetration (800 µm). Owning to the deep penetration depth and real-time imaging capability, in vivo SWIR microscopic angiography exhibits superior resolution in monitoring blood-brain barrier damage in mouse brain, and visualizing enhanced permeability and retention effect in tumor sites. Furthermore, the AIE dots show good biocompatibility, and no noticeable abnormalities, inflammations or lesions are observed in the main organs of the mice. This work will inspire new insights on development of advanced SWIR techniques for biomedical imaging.

Second near-infrared (NIR-II, 1000−1700 nm) fluorescence bioimaging has attracted tremendous scientific interest and already been used in many biomedical studies. However, reports on organic NIR-II fluorescent probes for in vivo photoinduced imaging and simultaneous therapy, as well as the longterm tracing of specific biological objects, are still very rare. Herein we designed a single-molecular and NIR-II-emissive theranostic system by encapsulating a kind of aggregation-induced emission luminogen (AIEgen, named BPN-BBTD) with amphiphilic polymer. The ultra-stable BPN-BBTD nanoparticles were employed for the NIR-II fluorescence imaging and photothermal therapy of bladder tumors in vivo. The 785 nm excitation triggered photothermal therapy could completely eradicate the subcutaneous tumor and inhibit the growth of orthotopic tumors. Furthermore, BPN-BBTD nanoparticles were capable of monitoring subcutaneous and orthotopic tumors for a long time (32 days). Single-molecular and NIR-II-emitted aggregation-induced emission nanoparticles hold potential for the diagnosis, precise treatment, and metastasis monitoring of tumors in the future.

Currently, a serious problem obstructing the large-scale clinical applications of fluorescence technique is the shallow penetration depth. Two-photon fluorescence microscopic imaging with excitation in the longer-wavelength near-infrared (NIR) region (>1100 nm) and emission in the NIR-I region (650-950 nm) is a good choice to realize deep-tissue and high-resolution imaging. Here, we report ultradeep two-photon fluorescence bioimaging with 1300 nm NIR-II excitation and NIR-I emission (peak ∼810 nm) based on a NIR aggregation-induced emission luminogen (AIEgen). The crab-shaped AIEgen possesses a planar core structure and several twisting phenyl/naphthyl rotators, affording both high fluorescence quantum yield and efficient two-photon activity. The organic AIE dots show high stability, good biocompatibility, and a large two-photon absorption cross section of 1.22 × 10 GM. Under 1300 nm NIR-II excitation, in vivo two-photon fluorescence microscopic imaging helps to reconstruct the 3D vasculature with a high spatial resolution of sub-3.5 μm beyond the white matter (>840 μm) and even to the hippocampus (>960 μm) and visualize small vessels of ∼5 μm as deep as 1065 μm in mouse brain, which is among the largest penetration depths and best spatial resolution of in vivo two-photon imaging. Rational comparison with the AIE dots manifests that two-photon imaging outperforms the one-photon mode for high-resolution deep imaging. This work will inspire more sight and insight into the development of efficient NIR fluorophores for deep-tissue biomedical imaging.

2,3-bis(4-(phenyl(4-(1,2,2-triphenylvinyl)phenyl)amino)phenyl)fumaronitrile (TTF) shows unique aggregation-induced emission (AIE) characteristics. Under the excitation of a 1560 nm femtosecond laser, simultaneous three-photon-excited luminescence (3PL) and third-harmonic-generation signals can be observed from its nanoaggregate and the solid state. TTF is further encapsulated with DSPE-mPEG (a type of amphiphilic polymer) to form AIE-active nanoparticles. 3PL brain imaging of mice is achieved based on the nanoparticles.

The traditional design strategies for highly bright solid‐state luminescent materials rely on weakening the intermolecular π–π interactions, which may limit diversity when developing new materials. Herein, we propose a strategy of tuning the molecular packing mode by regioisomerization to regulate the solid‐state fluorescence. TBP‐e‐TPA with a molecular rotor in the end position of a planar core adopts a long‐range cofacial packing mode, which in the solid state is almost non‐emissive. By shifting molecular rotors to the bay position, the resultant TBP‐b‐TPA possesses a discrete cross packing mode, giving a quantum yield of 15.6±0.2 %. These results demonstrate the relationship between the solid‐state fluorescence efficiency and the molecule's packing mode. Thanks to the good photophysical properties, TBP‐b‐TPA nanoparticles were used for two‐photon deep brain imaging. This molecular design philosophy provides a new way of designing highly bright solid‐state fluorophores.