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Two novel meso-CF3 BODIPY-based fluorescent rotors have been rationally prepared and sensitively respond to viscosity in living cells with fluorescence “turn-on” effect, attributing to the special restricted rotation of meso-CF3...

Meso-substituted boron dipyrromethenes (BODIPYs) provide a potential and innovative strategy for the synergistic construction of aggregation-induced emission (AIE) probes and fluorescent rotors for monitoring cellular viscosity changes, which play critical roles in understanding the function of viscosity in its closely associated diseases. Therefore, for the first time, a BODIPY-based fluorescent probe (1) with a rotatable meso-benzothiazole group was rationally designed and synthesized, showing both good viscosity-responsive and AIE properties. Probe 1 through direct linkage with the thiazole group, showed nearly no emission in low viscous solvents; however, a strong emission at 534 nm appeared and increased gradually with the increase in viscosity, attributing to the efficient restriction of the rotatable meso-benzothiazole group. The intensity (log I 534) displayed a good linear relationship with viscosity (log η) in the viscous range of 0.59–945 cP in methanol/glycerol mixtures. Interestingly, 1 showed enhanced emission at 534 nm in 70% water compared to pure acetonitrile due to the aggregation-induced inhibited rotations. Cellular imaging suggested that 1 could successfully sense lysosomal viscosity changes induced by lipopolysaccharide, nystatin, low temperature, and dexamethasone in living cells, which could be further applied in autophagy monitoring by tracing viscosity changes. As a comparison, its analogue 2 directly linking with the phenyl group showed no viscosity-responsive or AIE properties. Therefore, for the first time, we reported a meso-benzothiazole-BODIPY-based fluorescent rotor with AIE and lysosomal viscosity-responsive properties in nervous cells, which was further applied in monitoring autophagy, and this work thus could provide an innovative strategy for the design of potential AIE and viscosity-responsive probes.

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The photooxygenation of amyloid-β (Aβ) protein is considered a promising strategy against Alzheimer's disease (AD). The inhibition of Aβ aggregation or depolymerization of Aβ aggregates can effectively alleviate and improve the condition of AD. Herein, we report a series of "off−on" near-infrared quinolinium photosensitizers (QM20−QM22) based on D-π-A structures using a target-sensing catalyst activation (TaSCAc) strategy. They exhibit turn-on fluorescence when bonded to Aβ aggregates and generate singlet oxygen to achieve the specific imaging and photooxygenation of Aβ aggregates, leading to attenuated Aβ aggregates, enhancing their clearance through the microglial lysosomal pathway, decreasing their neurotoxicity. This study will shed light on the development of the photooxygenation of misfolded proteins for the treatment of neurodegenerative diseases.