Manipulation of photophysical properties of pure organic materials via simple alteration is attractive but extremely challenging because of the lack of valid design strategies for achieving ultralong afterglow or efficient room-temperature phosphorescence. Herein, we report a first photophysical manipulation of organic ionic crystals from ultralong afterglow to highly efficient phosphorescence by variation of halides in the crystals. Crystal structural analysis reveals ultralong organic afterglow of tetraphenylphosphonium chloride is promoted by strong intermolecular electronic coupling in the crystal, and theoretical analysis demonstrates that the tremendous boost of the phosphorescence of tetraphenylphosphonium iodide is caused by the coupling effects of significant heavy atom effect from iodine atoms and a small energy difference between the first singlet and triplet states. This work contributes to regulating long-lived emissive behaviors of pure organic ionic crystals in a controlled way and will promote the development of optical switches controlled by external stimuli.

Hydrophobicity-guided self-assembled particles of silver nanoclusters with aggregation-induced emission were fabricated and used in sensing and bioimaging.

Butyrylcholinesterase (BChE) mainly contributing to plasma cholinesterase activity is an important indicator for routinely diagnosing liver function and organophosphorus poisoning in clinical diagnosis, but its current assays are scarce and frequently suffer from some significant interference and instability. Herein, we report a redox-controlled fluorescence nanoswtich based on reversible disulfide bonds, and further develop a fluorometric assay of BChE via thiol-triggered disaggregation-induced emission. Thiol-functionalized carbon quantum dots (thiol-CQDs) with intense fluorescence is found to be responsive to hydrogen peroxide, and their redox reaction transforms thiol-CQDs to nonfluorescent thiol-CQD assembly. The thiols inverse this process by a thiol-exchange reaction to turn on the fluorescence. The fluorescence can be reversibly switched by the formation and breaking of disulfide bonds caused by external redox stimuli. The specific thiol-triggered disaggregation-induced emission enables us to assay BChE activity in a fluorescence turn-on and real-time way using butyrylthiocholine iodide as the substrate. As-established BChE assay achieves sufficient sensitivity for practical determination in human serum, and is capable of avoiding the interference from micromolar glutathione and discriminatively quantifying BChE from its sister enzyme acetylcholinesterase. The first design of reversible redox-controlled nanosiwtch based on disulfide expands the application of disulfide chemistry in sensing and clinical diagnostics, and this novel BChE assay enriches the detection methods for cholinesterase activity.

Manipulation of the emission properties of pure organic molecules through external stimuli is attractive but challenging. Herein, a dual-emissive hexathiobenzene-based molecule is reported with significant aggregation-induced phosphorescence characteristics, and demonstrates reversible switching among blue, green, and yellow phosphorescence by controlling molecular aggregation state or protonation state. Variation of solvent or pH value manipulates the interconversion between fluorescence and phosphorescence, while the change in protonation state in organic solvent switches two short-lived emissions in a controllable manner. Such a controlled manipulation is achieved by the rational design of combining a twisted structure and the proper arrangement of energy gaps among different excited states. This work provides a new design principle for organic molecules with efficient room-temperature phosphorescence and tunable singlet-triplet emissive properties, and contributes to the design and development of smart materials and intelligent optoelectronic devices.

Ultralong room-temperature phosphorescence (RTP) of organic materials is extremely attractive for its tremendous potential use. However, the design of organic materials with ultralong and efficient RTP is very challenging due to the lack of general design principles. A new design principle for organic materials with ultralong room-temperature phosphorescence based on π-π-dominated supramolecular aggregates in crystal is proposed, and strong intermolecular electronic coupling with specific molecular alignment is identified to be responsible for supramolecular behavior in persistent emission. Small substituents in molecular structure favor the formation of supramolecular aggregates in the crystal, thus facilitating the generation of ultralong RTP under ambient conditions. Our results also reveal that the introduction of heavy atoms into supramolecular aggregates as a general rule can be used to achieve efficient persistent phosphorescence.

The ordered membrane electrode assembly (MEA) is currently the frontier research field of proton exchange membrane fuel cells (PEMFCs). The ordered MEA is effective in increasing the utilization of the Pt catalyst and reducing the Pt catalyst loading and cost. Due to a larger specific surface area and faster rate of proton transfer, a Nafion array was used to prepare a high-performance MEA. In order to realize the ideal performance, the critical mission is to make a well-dispersed Nafion array. However, the pillars in the Nafion array are prone to form bundles induced by surface tension of water, resulting in a severe reduction in the specific surface area. In this work, we successfully prepared a well-dispersed Nafion array by the freeze-drying method, which greatly improved the performance of the ordered MEA of a PEMFC. The percentage of isolated pillars in the Nafion array is improved from about 0.8% after natural drying to about 90% after freeze-drying. The specific surface area of the Nafion array membrane after freeze-drying increases to 4.74, which is 2.1 times that after natural drying, and is close to the theoretical value of 4.99, indicating that the well-isolated array possesses a larger specific surface area to load a catalyst. Consequently, the electrochemical surface area of the catalyst layer reaches as high as 131.5 m2 gPt –1, which is 1.6 or 2.5 times that with the Nafion array after natural drying or without the Nafion array. For the ordered MEA, a long-term stability is vital for PEMFC operation. In this work, the lifetime of the ordered MEA with the Nafion array after freeze-drying is excellent compared to the Nafion array after natural drying and without the array. Besides, the scanning electron microscopy characterization clearly shows that the Nafion array remains a well-dispersed structure even after hot-pressing and plays a pivotal role in PEMFC operation. Therefore, this research proves that the freeze-drying method can effectively solve the aggregation of the Nafion array during drying and further proves that the well-dispersed Nafion array could show much higher performance. More importantly, this work provides an ideal basic material for the preparation of the ordered MEA.

The proton exchange membrane fuel cell (PEMFC) is one of the most promising energy conversion devices. However, a PEMFC is hindered by the serious problem of water management. Herein, a Janus gas diffusion layer (Janus GDL) that can spontaneously transport water from the hydrophobic side to the hydrophilic side was prepared by layer-by-layer filtration and laser drilling. The Janus GDL exhibits a remarkable antiflooding capability at the equivalent current density of 3.25 A cm–2 (2.3–2.5 times compared to the commercial GDL) in the half-cell. Because of the low water breakthrough pressure (29 Pa), the Janus GDL drains excessive water immediately, thus preventing heavy electrode floodings. As a result, the Janus GDL shows a higher peak power density (1.89 W cm–2 vs 1.17 W cm–2 of commercial GDL). Therefore, the Janus GDL is promising for use in PEMFCs and other electrochemical devices to get a good water management.

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