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Aggregation‐induced emission luminogens (AIEgens) as a new class of optical probes for two‐photon imaging (2PI) have attracted extensive attention in the research community. However, their non‐radiative energy dissipation plays a non‐negligible role in energy consumption, thereby weakening their performance in 2PI. Exploration of a facile and general approach to control the energy relaxation pathways is thus a fascinating yet significantly challenging task. To address this concern, an organic doping method is proposed herein by using TPE‐Br as the doping AIEgen and MeOTTMN as the functional AIEgen. With increased amount of doping molecules, a steadily strengthened brightness (up to 29‐fold of quantum yield) is observed at the expense of reactive oxygen species production. Remarkably, an ultradeep imaging depth of 1000 µm in a mouse brain is realized via 2PI using the heavily organic‐doped AIEgen(ODA) nanoparticles (NPs). Such result is far superior to the imaging depth of 156 µm enabled by MeOTTMN NPs. The safe use of ODA NPs is further evaluated by in vitro and in vivo toxicity assessment. This study thus provides an attractive paradigm to control the energy relaxation of AIEgen NPs and maximize their performance in 2PI while circumventing the difficulties in molecular engineering. [ABSTRACT FROM AUTHOR]

In recent years, with increasing demands for in vivo fluorescence imaging and photodynamic therapy, light in the second near‐infrared window (NIR‐II; 1000–1700 nm) has attracted tremendous interest because it offers numerous merits, including deep penetration, minimal phototoxicity, diminished tissue autofluorescence, and reduced tissue absorption and scattering. Among the diverse types of nanoparticles, organic nanoprobes with aggregation‐induced emission (AIE) characteristics have emerged as a better option owing to their ultra‐brightness, excellent photostability, low cytotoxicity, and tailorable optical properties. Recent efforts in the AIE realm have revealed advancements in molecular design for long wavelength absorption and multiphoton excitation, which efficiently modulate the working optical region to the NIR‐II region. In this review, the current status of AIE nanoprobes in the NIR‐II window is summarized. Starting with molecular design strategies, recent efforts in fluorescence imaging and photodynamic therapy are then discussed. Finally, perspectives and challenges in this newly emerging field are given. This review hopes to encourage more innovative ideas in material design and biomedical applications for promoting AIE nanoprobes for future clinical translation. [ABSTRACT FROM AUTHOR]

[Display omitted] • A two-photon photodynamic photosensitizer with mitochondrion-targeting and AIE characteristics was prepared. • The integration of Ir make 50 times enhancement of ROS production compared to its counterpart molecule. • TPABP-Ir@BSA NPs exhibits satisfactory biosafety. • A 90% tumor suppression was achieved by type-I&II synergetic photochemical reactions under hypoxic environment. In recent years, two-photon photodynamic therapy (TP-PDT) has received extensive attention in cancer treatment owing to its unique advantages of deep tissue penetration and high spatial–temporal controls. However, the high oxygen dependency of photosensitizers still remained as the major obstacle which undermined its overall therapeutic efficacy, especially in hypoxic-tolerant tumors. Exploration of new TP-PDT strategy with less-oxygen-dependency and subcellular organelle-targeting ability is an appealing yet seriously challenging task. In this work, a mitochondrion-targeting TP-PDT protocol based on type-I PSs with aggregation-induced emission (AIE) characteristics is proposed for the first time. Of the two synthesized AIE-active PSs, TPABP-Ir is demonstrated superior reactive oxygen species (ROS) production (both type I&II) owing to the doping of Ir(III). After encapsulation into bovine serum albumin (BSA) matrix, TPABP-Ir@BSA nanoparticles (Ir-NPs) are capable of realizing mitochondrion-targeting, high ROS production, and suppression of tumor growth under 880 nm femtosecond laser excitation. This study provides a novel treatment strategy which maximizes the PDT efficacy and offers a conceptual but practical paradigm for cancer treatment in translational nanomedicine. [ABSTRACT FROM AUTHOR]