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Four cocrystals of (S-ox)(ga) (1), (RS-ox)(ga) (2), (S-ox)(pa) (3), and (RS-ox)(pa) (4) were prepared (S-ox = S-oxiracetam, RS-ox = racemic oxiracetam, ga = gallic acid, pa = 3,4-dihydroxybenzoic acid), and their structures were determined by single X-ray diffraction. In 1/2, two ga molecules link two S-ox/RS-ox molecules through intermolecular hydrogen bonds with a new R 2 2 (9) synthon to form a tetramer, the tetramers are further linked by intertetramer hydrogen bonds to generate a 2D sheet, and the adjacent 2D sheets are connected by intersheet hydrogen bonds to form the 3D structure of 1/2. In 3/4, the ox molecules form a 1D helical chain through intermolecular hydrogen bonds, and the helical chains are further linked by pa molecules through intermolecular hydrogen bonds to form a 2D sheet. The results of hygroscopic stability experiments indicate that the hygroscopic stability of Sox is much enhanced after the formation of cocrystal 1.

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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.