Many aggregation-induced emission (AIE) materials are featured by the diphenylethene (DPE) moiety which exhibits rich photophysical and photochemical activities. The understanding of these activities behind AIE is essential to guide the design of fluorescent materials with improved performance. Herein by fusing a flexible DPE with a rigid spiro scaffold, we report a class of novel deep-blue material with solid-state fluorescent quantum yield (ΦF) up to 99.8%. Along with the AIE phenomenon, we identified a reversible photocyclization (PC) on DPE with visible chromism, which is, on the contrary, popularized in solutions but blocked by aggregation. We studied the steric and electronic effects of structural perturbation and concluded that the PC is a key process behind the RIMs (restriction of intramolecular motions) mechanism for these materials. Mitigation of the PC leads to enhanced fluorescence in solutions and loss of the AIE characteristics.

To test the impact of the COVID-19 pandemic on air quality, this article matches the city-level real-time air quality monitoring data with the big data on population migration provided by Baidu. The article uses urban samples from the same data sample of the Chinese lunar calendar in 2019 to construct the counterfactual status of the COVID-19 pandemic. Then, the difference-indifferences (DID) model is employed to estimate the impact of the COVID-19 pandemic on air quality. It is found that the COVID-19 pandemic caused PM2.5 and AQI to decrease by about 7 μg/m 3 and 5-points, respectively.

The analysis of albumin has clinical significance in diagnostic tests and obvious value to research studies on the albumin-mediated drug delivery and therapeutics. The present immunoassay, instrumental techniques, and colorimetric methods for albumin detection are either expensive, troublesome, or insensitive. Herein, a class of water-soluble tetrazolate-functionalized derivatives with aggregation-induced emission (AIE) characteristics is introduced as novel fluorescent probes for albumin detection. They can be selectively lighted up by site-specific binding with albumin. The resulting albumin fluorescent assay exhibits a low detection limit (0.21 nM), high robustness in aqueous buffer (pH = 6–9), and a broad tunable linear dynamic range (0.02–3000 mg/L) for quantification. The tetrazolate functionality endows the probes with a superior water solubility (>0.01 M) and a high binding affinity to albumin (K D = 0.25 μM). To explore the detection mechanism, three unique polar binding sites on albumin are computationally identified, where the multivalent tetrazolate–lysine interactions contribute to the tight binding and restriction of the molecular motion of the AIE probes. The key role of lysine residues is verified by the detection of poly-l-lysine. Moreover, we applied the fluorogenic method to quantify urinary albumin in clinical samples and found it a feasible and practical strategy for albumin analysis in complex biological fluids.

Reaction‐based photo‐responsive molecular systems have been used as a reliable platform for building intelligent materials, but often suffer from high inactivity in terms of conversion efficiency and reversibility when it comes to solid‐state applications. Herein, a class of Spiro‐conjugated diphenylindene (DPI) aggregation‐induced emission materials that exhibit solid‐state photocyclization‐based photochromism and photoluminescence, achieved by manipulating through‐space CBr···π halogen interactions is reported. In the crystalline state, the Spiro bridge enables a pair of perpendicularly configured CBr···π interactions that suppress photoluminescence while activating a highly reversible (>10 000 cycles) and efficient photochromism based on photocyclization. After breaking this intermolecular CBr···π interaction, for example, by grinding, the solid‐state photochromic properties are sensitively de‐activated. In addition, this spontaneously reversible photochromism behavior gives a controllable decolorization time (from a few seconds to a few minutes), depending on the light exposure conditions, while displaying a luminescence change. In a proof‐of‐principle study, these photo‐function features demonstrate an attractive potential for novel anti‐counterfeiting applications. This work reveals the efficient regulation of CBr···π halogen interactions for spatial molecular packing, molecular electronic transitions, and chemical transformations, paving the way for the development of solid‐state intelligent materials with good reversibility.

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A "turn-on" fluorescent sensing strategy was developed for ultrasensitive detection of heavy metal mercury ion (Hg 2+ ) directly in water. It utilized an aqueous soluble aggregation-induced emission (AIE)-active probe, named 1,1,2,2-tetrakis(4-(1Htetrazol-5-yl)phenyl)ethene (TPE-4TA), composing of a luminescent tetraphenylene core and multiple anionic tetrazolate spawns. The probe retained dark when molecularly dissolved in water. However, mercury ions can ligate with multiple tetrazolate groups to form infinite coordination polymer particles spontaneously, thus inducing a fluorogenic AIE response for in situ analysis. Moreover, by embedding this AIE sensing molecules in a hydrophilic polyvinyl alcohol substrate, the resulting hydrogel film allowed in situ detection of Hg 2+ on a laser-induced fluorescence analysis setup in aqueous environment. This strategy worked effectively in common aqueous environments with pH from 4 to 7.5 and showed high sensitivity (limit of detection down to 0.38 ppb/1.9 nM), good selectivity and a wide linearity range for quantification. This work may lead to a reliable and promising platform for on-site environmental water analysis.

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