Yong Heng Xing

Erythromycin (ERY) residues have emerged as a critical global concern to food safety and environmental security in recent years. Detecting ERY in food and environment is important for safeguarding public health. In this study, a metal-organic framework [Me₂NH₂][Eu(TCBPEF)(HCOO)(DMF)]·2.5DMF Eu-TCBPEF, H₄TCBPEF = 4',4‴,4‴″,4‴″″-(ethene-1,1,2,2-tetrayl)tetrakis(3-fluoro-[1,1'-biphenyl]-4-carboxylic acid) was synthesized and utilized as a fluorescence "turn-on" sensor for real-time visual monitoring of ERY, which demonstrated the first TPE-based MOF for ERY detection. Eu-TCBPEF could selectively detect ERY in water with a limit of detection (LOD) of 0.327 μM and exhibited excellent detection performance for ERY in seawater and chicken samples with good recovery percentage ranging from 96.9% to 105.4%. Furthermore, a portable Eu-TCBPEF@PVA was fabricated, enabling real-time and on-site monitoring of ERY in combination with a smartphone-assisted platform. In addition, Eu-TCBPEF exhibited a remarkable mechanofluorochromism: the fluorescent color can be reversibly switched between cyan and yellow upon grinding and exposure to acetonitrile. This study presents a dual-function MOF that provides new insights into the function of TPE-based MOFs and meanwhile offers an effective solution for on-site monitoring of antibiotic residues in food and environment, with promising applications in advanced anticounterfeiting security materials.

La-MOF complex with six metal cores was synthesized by an in situ reaction of terephthaloyl chloride and La(NO3)3·6H2O under solvothermal conditions. During the reaction process, it was surprisingly found that the terephthaloyl chloride was hydrolyzed into 1,4-H2BDC and then coordinated with La(NO3)3·6H2O to form a six-core metal–organic framework, complex 1, [La6(1,4-BDC)9(μ-H2O)(H2O)(DMF)6]·H2O·3DMF, which was constructed by two 4-centered building blocks [La4(COO)10] and [La4(COO)10(μ-H2O)] and the ligand 1,4-BDC2–. Complex 1 was characterized by infrared spectroscopy (IR), fluorescence spectra, thermogravimetric (TG) analysis, PXRD, and UV–vis spectra, etc. Moreover, a fluorescence sensing experiment was carried out with complex 1 to detect harmful substances (TNP, DNP, ONP, Fe3+, and Cr2O72–). The results indicate that the fluorescence intensity can be reduced to varying degrees by five kinds of detection compounds. Especially, the fluorescence quenching constant KSV of complex 1 for TNP detection is as high as 1.18 × 105 M–1. In the above fluorescence sensing experiment, it was found that the detection wavelength in the ultraviolet region was due to the contribution of the ligand, which is not conducive to future practical applications. Therefore, we successfully prepared another two complexes (2 and 3) containing rare earth elements europium and terbium by regulating the ligand and rare earth ions. The experimental results showed that complexes 2 and 3 also have detection effects on the five harmful substances mentioned above. However, their detection wavelengths have undergone a significant redshift, which is more advantageous for future visual fluorescence detection.

Smart metal-organic framework (MOF) chromic materials that respond to chemical or electrical stimuli are highly desirable for daily life and optoelectronic applications. Three novel MOFs: [Mn(H₂NDISA)(DMF)₂] (1), [Zn(H₂NDISA)(DMF)₂] (2), and [Cd(H₂NDISA)(DMF)₂] (3) are first synthesized and characterized, based on a H₄NDISA ligand (H₄NDISA (N,N'-bis(3-carboxy-4-hydroxyphenyl)-1,4,5,8-naphthalenetetradicarboximide)) with free hydroxyl active sites. Structural analysis reveals that complexes 1-3 display a 3D supramolecular network, a 2D layered structure, and a 1D chain structure, respectively, because of different intermolecular interactions, affording them with dimension-dependent multistimulus-responsive chromism behaviors. Alkali metal ion-induced chromism is related to topological structures of the complexes, as well as the type and concentration of ions. Regarding alkaline earth metal ions, complexes 1-3 change from yellow to red in Be²⁺. As for fourth-period transition-metal ions, complexes 1-3 display deep red and brown colors in Fe³⁺ and Cu²⁺, respectively, rendering these complexes as selective and sensitive visual ion detectors when fabricated as portable polyvinylidene difluoride-polyethylene glycol@1-3 films (PVDF-PEG@1-3 films). Furthermore, complexes 1-3 exhibit electrochromic switching properties, and chromic voltages are related to dimension of MOFs, which may provide proof-of-concept for low-energy electrochromic applications. This study might enrich the potential application of naphthalenediimide-based MOF materials in cation detection and optoelectronic devices.

Viologen-encapsulated metal-organic frameworks (MOFs) have attracted significant interest owing to their responsiveness to multiple external stimuli, which enhances their potential applications in sensing and environmental monitoring. Here, we synthesized the novel viologen-encapsulated Ho-MOF material (pbpy)·[Ho₂(NH₂-BDC)₄(H₂O)]·3H₂O (complex 1) via an in situ method using 2-aminoterephthalic acid (NH₂-H₂BDC) and the viologen derivative dichloro-1,1'-(1,4-benzylidene)-di(4,4'-bipyridine) (pbpy·2Cl), along with the control material [Ho₄(NH₂-BDC)₅(DMA)₂(μ₃-OH)₂]·3H₂O (complex 2) without a viologen for comparison. Complex 1 exhibited dual detection capability for Th(IV) and nitroaromatic compounds (NACs), demonstrating significant advantages in sensing performance compared to complex 2. These results highlight the critical role of viologen incorporation in improving sensor functionality. Moreover, we prepared a MOF-based PVDF composite film material capable of rapidly detecting Th(IV) and NACs, demonstrating potential for practical sensing applications. In addition, thanks to the presence of a viologen inside the channels, complex 1 could achieve rapid and visual detection of N₂H₄·H₂O. EPR results indicate that the color change is due to the generation of viologen radicals. These properties make the material a promising candidate for multianalyte detection, advancing the development of multistimulus responsive materials.