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.

or completely in the state of aggregation, impeding the progress of some specific applications. [2] In 2001, the uncommon luminogen system noted as aggregationinduced emission (AIE) [3] broke down the captivity of Förster's discovery named aggregation-caused quenching (ACQ), which brought a new wonderland for organic fluorophores. The intrinsic tendency to form aggregates in concentrated solutions or the solid state actively promotes the emission intensity of the fluorophores with AIE characteristics. Years of unremitting exploration has accumulated design experience of diverse AIEgens [4] and shaped plentiful innovated applications for stimuli sensing, [5] optoelectronic systems, [6] molecular detection, [7] bio-imaging, [8,9] and so on. Taking advantages of AIE dots with high resistance to photobleaching and excellent reliability, multifarious specific bio-sensing modes, including bio-imaging, launched on a grand. [8,10] The development of the AIE universe provides potential diagnostic and therapeutic means in clinic. Nowadays, efforts of AIEgens for fluorescence imaging in mice have already been

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.

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With the advantages of high resolution and deep penetration depth, two-photon excited NIR-II (900–1880 nm) fluorescence (2PF) microscopic bioimaging is promising. However, due to the lack of imaging systems and suitable probes, few such works, to our best knowledge, were demonstrated utilizing NIR-II excitation and NIR-II fluorescence simultaneously. Herein, we used aqueously dispersible PbS/CdS quantum dots with bright NIR-II fluorescence as the contrast agents. Under the excitation of a 1550 nm femtosecond (fs) laser, they emitted bright 2PF in the NIR-II region. Moreover, a 2PF lifetime imaging microscopic (2PFLIM) system was implemented, and in vivo 2PFLIM images of mouse brain blood vessels were obtained for the first time to our best knowledge. To improve imaging speed, an in vivo two-photon fluorescence microscopy (2PFM) system based on an InGaAs camera was implemented, and in vivo 2PFM images of QDs-stained mouse brain blood vessels were obtained.

Compared with visible light, near-infrared (NIR) light has deeper penetration in biological tissues. Three-photon fluorescence microscopy (3PFM) can effectively utilize the NIR excitation to obtain high-contrast images in the deep tissue. However, the weak three-photon fluorescence signals may be not well presented in the traditional fluorescence intensity imaging mode. Fluorescence lifetime of certain probes is insensitive to the intensity of the excitation laser. Moreover, fluorescence lifetime imaging microscopy (FLIM) can detect weak signals by utilizing time-correlated single photon counting (TCSPC) technique. Thus, it would be an improved strategy to combine the 3PFM imaging with the FLIM together. Herein, DCDPP-2TPA, a novel aggregation-induced emission luminogen (AIEgen), was adopted as the fluorescent probes. The three-photon absorption cross-section of the AIEgen, which has a deep-red fluorescence emission, was proved to be large. DCDPP-2TPA nanoparticles were synthesized, and the three-photon fluorescence lifetime of which was measured in water. Moreover, in vivo three-photon fluorescence lifetime microscopic imaging of a craniotomy mouse was conducted via a home-made optical system. High contrast cerebrovascular images of different vertical depths were obtained and the maximum depth was about 600 [Formula: see text]m. Even reaching the depth of 600 [Formula: see text]m, tiny capillary vessels as small as 1.9 [Formula: see text]m could still be distinguished. The three-photon fluorescence lifetimes of the capillaries in some representative images were in accord with that of DCDPP-2TPA nanoparticles in water. A vivid 3D reconstruction was further organized to present a wealth of lifetime information. In the future, the combination strategy of 3PFM and FLIM could be further applied in the brain functional imaging.

Booming AIE universe has set off an upsurge in recent years, driving much innovation in academic, industrial and medical world. Superb reliability and biocompatibility equip AIE dots with tremendous potential for fluorescence bioimaging and even clinical translation. The utilization on non-human primates imaging are vital for AIE dots assisted clinical theranostics, which still remains unexplored yet. Additionally, fluorescence bioimaging in second near-infrared window (NIR-II, 900-1700 nm) is widely recognized as an effective technology for deep-penetration mammals optical imaging. Here, we designed a novel AIEgen with a large molar extinction coefficient of ~5×104 mM−1 cm−1 at ~770 nm and the PEGylated AIE dots possessed an extremely high NIR-II photoluminescence quantum yield (PLQY) as 13.6%, exhibiting bright fluorescence beyond 1100 nm and even 1500 nm (near-infrared IIb, NIR-IIb). Assisted by the AIE dots, large-depth cerebral vasculature (beyond 600 μm) as well as real-time blood flowing were monitored through the skull and high-spatial-frequency non-invasive NIR-IIb (beyond 1500 nm) imaging gave a precise presentation of gastrointestinal tract in marmosets. Importantly, after intravenous or oral administration, the definite excretion of AIE dots from the body was demonstrated. It was the first attempt for AIE dots assisted NIR-II fluorescence imaging in non-human primates and we wished this work could promote the development of AIE dots for clinical application.