Highly Efficient Stable Luminescent Radical-Based X-ray Scintillator.

Stable luminescent radicals are open-shell emitters with unique doublet emission characteristics. This feature makes stable luminescent radicals exhibit widespread application prospects in constructing optical, electrical, and magnetic materials. In this work, a stable luminescent radical-based X-ray scintillator of AuPP-1.0 was prepared, which exhibited a high X-ray excited luminescence (XEL) efficiency as well as excellent stability. A mechanism study showed that the heavy atom of Au in AuPP-1.0 endowed it with effective absorption of X-rays, and the doublet emission characteristics of AuPP-1.0 significantly increased its exciton utilization rate in the radioluminescence process. Moreover, AuPP-1.0 has good processability to fabricate a flexible screen for high-quality X-ray imaging, whose resolution can reach 20 LP mm-1. This work demonstrates that the doublet emission is beneficial for improving the exciton utilization rate of radioluminescence, providing a brand-new strategy for the construction of high-performance X-ray scintillators.

Photo-Activated Circularly Polarized Luminescence Film Based on Aggregation-Induced Emission Copper(I) Cluster-Assembled Materials.

In this study, a pair of chiral copper(I) cluster-assembled materials (R/S-2) was prepared, exhibiting unique photo-response characteristics with a concentration-wavelength correlation property in DMSO solution. By the combination of R/S-2 with a polymethyl methacrylate (PMMA) matrix, the first photo-activated circularly polarized luminescence (CPL) film was developed, the CPL signal (glum =9×10-3 ) of which could be induced by UV light irradiation. Moreover, the film exhibited a reversible photo-response and extremely good fatigue resistance. Mechanism study revealed that the photo-response properties of the R/S-2 solution and film are attributed to the aggregation-induced emission (AIE) characteristics of R/S-2 and a photo-induced deoxygenation process. This study enriches the types of luminescent cluster-assembled molecules and provides a new strategy for the construction of metal cluster-based stimuli-responsive composite materials.

High Performance Dynamic X-ray Flexible Imaging Realized Using a Copper Iodide Cluster-Based MOF Microcrystal Scintillator.

X-ray imaging technology has achieved important applications in many fields and has attracted extensive attentions. Dynamic X-ray flexible imaging for the real-time observation of the internal structure of complex materials is the most challenging type of X-ray imaging technology, which requires high-performance X-ray scintillators with high X-ray excited luminescence (XEL) efficiency as well as excellent processibility and stability. Here, a macrocyclic bridging ligand with aggregation-induced emission (AIE) feature was introduced for constructing a copper iodide cluster-based metal-organic framework (MOF) scintillator. This strategy endows the scintillator with high XEL efficiency and excellent chemical stability. Moreover, a regular rod-like microcrystal was prepared through the addition of polyvinyl pyrrolidone during the in situ synthesis process, which further enhanced the XEL and processibility of the scintillator. The microcrystal was used for the preparation of a scintillator screen with excellent flexibility and stability, which can be used for high-performance X-ray imaging in extremely humid environments. Furthermore, dynamic X-ray flexible imaging was realized for the first time. The internal structure of flexible objects was observed in real time with an ultrahigh resolution of 20 LP mm-1 .

Restriction of Intramolecular Vibration in Aggregation-Induced Emission Luminogens: Applications in Multifunctional Luminescent Metal-Organic Frameworks.

Butterfly-like molecules of oxacalix[2]arene[2]pyrazine (OAP) are reported, which exhibit the typical characteristics of aggregation-induced emission (AIE) via the restriction of intramolecular vibration (RIV) mechanism. Unlike any of the reported RIV-type AIE molecules, the synthetic procedures of which are complicated and have associated high costs, OAP AIEgens can be synthesized in a facile manner by a one-step catalyst-free reaction using commercially available materials. Notably, OAP AIEgens are ideal ligands for constructing metal-organic frameworks (MOFs) due to their built-in pyrazine coordination sites. OAP-based MOFs exhibit multiple potential applications in reversible gas response, encrypted information storage, and construction of white light-emitting devices. This work builds on RIV-type AIEgens, offers additional selections of bridging ligands for constructing luminescent MOFs and provides a visualized prototype to understand the effect of the RIV process on the luminescence properties of MOFs.

Luminescent MOFs constructed by using butterfly-like AIE ligands.

In this work, a series of butterfly-like isomers named oxacalix[2]naphthalene[2]pyrazine (ONP) were conveniently synthesized by a one-step catalyst-free reaction in a facile manner, and they exhibit typical characteristics of aggregation-induced emission (AIE). The mechanism study shows that restriction of intramolecular vibration (RIV) is the reason for their AIE properties. The pyrazine groups endow ONP molecules with good coordination ability, which makes them ideal ligands for constructing metal-organic frameworks (MOFs). Thus, three ONP-based luminescent MOFs were constructed, and they exhibit intense emission with lifetimes in the order of microseconds. More importantly, different ONP isomers have different binding capacities, and thus only one kind of MOF can be obtained even when using an isomer mixture of ONP ligands. This result suggested that the conformation of ONPs is an important determining factor for their application as bridging ligands. This work not only reports a series of new RIV-type AIEgens, but also offers a new platform for the construction of luminescent MOFs.

Thermally Activated Delayed Fluorescence Coinage Metal Cluster Scintillator.

X-ray scintillators are widely used in medical imaging, industrial flaw detection, security inspection, and space exploration. However, traditional commercial scintillators are usually associated with a high use cost because of their substantial toxicity and easy deliquescence. In this work, an atomically precise Au-Cu cluster scintillator (1) with a thermally activated delayed fluorescence (TADF) property was facilely synthesized, which is environmentally friendly and highly stable to water and oxygen. The TADF property of 1 endows it with an ultrahigh exciton utilization rate. Combined with the effective absorption of X-ray caused by the heavy-atom effect and a limited nonradiative transition caused by close packing in the crystal state, 1 exhibits an excellent radioluminescence property. Moreover, 1 has good processability for fabricating a large, flexible thin-film device (10 cm × 10 cm) for high-resolution X-ray imaging, which can reach 40 µm (12.5 LP mm-1). The properties mentioned earlier make the coinage metal cluster promising for use as a substitute for traditional commercial scintillators.

Aggregation-induced barrier to oxygen-a new AIE mechanism for metal clusters with phosphorescence.

Metal clusters are useful phosphors, but highly luminescent examples are quite rare. Usually, the phosphorescence of metal clusters is hindered by ambient O2 molecules. Transforming this disadvantage into an advantage for meaningful applications of metal clusters presents a formidable challenge. In this work, we used ligand engineering to judiciously prepare colour-tuneable and brightly emitting Cu(I) clusters that are ultrasensitive to O2 upon dispersion in a fluid solution or in a solid matrix. When the O2 scavenger dimethyl sulfoxide (DMSO) was used as the solvent, joint photo- and oxygen-controlled multicolour switches were achieved for the first time for metal cluster-based photopatterning and photo-anticounterfeiting. More importantly, an aggregation-induced barrier to oxygen, a new aggregation-induced emission mechanism for metal clusters, was proposed, providing a new pathway to realizing the intense emission of metal clusters in the aggregated state. These results are expected to promote the application of metal clusters and enrich the luminescence theory of metal cluster aggregates.

A Type of Atypical AIEgen Used for One-Photon/Two-Photon Targeted Imaging in Live Cells.

Aggregation-induced emission luminogens (AIEgens) with a large electron donor and acceptor (D-A) conjugated system have been widely used in the development of organic light emitting diodes (OLEDs), chemosensors, and bioimaging materials due to their excellent properties such as high quantum yields, long emission wavelengths, controllable luminescence lifetimes, and nonlinear optics (NLO) properties. However, most of the AIE materials have been derived from limited classic AIE cores such as tetraphenylethene (TPE) and tetraphenylpyrazine (TPP), and thus, tedious syntheses or later modifications toward those AIEgens have always been unavoidable. In this report, a type of atypical AIEgens (designated as ASIQs) composed of large conjugated structures with a natural electron D-A system is disclosed, which shows large Stokes shifts, high photostabilities, excellent cell permeabilities, low biotoxicities, and good two-photon excited capacities, making them suitable for applications of one-photon/two-photon targeted imaging in live cells. In short, this work offers a type of atypical AIEgens which will possibly become an ideal platform leading to more structurally diverse and functionally excellent AIE-based luminescent materials.