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Lanthanide metal-organic frameworks (Ln-MOFs) have excellent optical properties and structural diversity, providing a unique platform for the development of fluorescent sensing and optical materials. In the work described herein, a series of isostructural 3D Ln-MOFs [Ln(L)(H 2 O)]·2H 2 O (Ln = Eu ( 1 ), Gd ( 2 ), Tb ( 3 ), H 3 L = 3,3',3″-[1,3,5-benzenetriyltris(carbonylimino)]tris-benzoate) are fabricated under solvothermal conditions. The good thermal, water, and acid-base stabilities of 3 are prerequisites for fluorescent sensing applications. 3 can be used as a ratiometric broad-spectrum fluorescent sensor for toluenediamines (TDAs) in real urine with the advantages of visualization, ultrasensitivity, and selectivity. Interestingly, a smartphone-assisted intelligent sensing platform manifests promising results for the detection of TDAs, providing a chance for further development of portable diagnostic tools. In addition, by tuning the ratios of Eu 3+ /Tb 3+ and Eu 3+ /Gd 3+ /Tb 3+ , nine bimetallic-doped Eu x Tb 1- x ( x = 0.10-0.90, 4 - 12 ) and one trimetallic-doped Gd 0.95 Tb 0.015 Eu 0.035 ( 13 ) were obtained. 4 - 12 exhibit a gradient of luminescent colors from yellow-green to pink with different ratios of Eu 3+ and Tb 3+ ions. Meanwhile, the trimetallic-doped Gd 0.95 Tb 0.015 Eu 0.035 ( 13 ) shows near-white-light emission with a quantum yield of 8.76%. Interestingly, the inks made with 1 - 13 are invisible under ambient light but show visual color-tunable luminescence under a 254 nm UV lamp, which may facilitate their anti-counterfeiting applications.

The construction and investigation of dual-functional coordination polymers (CPs) with proton conduction and luminescence sensing is of great significance in clean energy and agricultural monitoring fields. In this work, an Mn-based coordination polymer (Mn-CP), namely, [Mn 0.5 (HL)] (H 2 L = HOOCC 6 H 4 C 6 H 4 CH 2 PO(OH)OCH 3 ), was hydrothermally synthesized. Mn-CP has a one-dimensional (1D) chain structure, in which uncoordinated -COOH groups can serve as potential sites for fluorescence sensing. Moreover, Mn-CP shows good water and pH stabilities, offering the feasibility for proton conduction and sensing applications. Mn-CP displays comparatively high proton conductivity of 1.07 × 10 -4 S cm -1 at 368 K and 95% relative humidity (RH), which is promising for proton conduction materials. Moreover, it can serve as a repeatable, highly selective, and visualized fluorescence sensor for detecting oxytetracycline (OTC). More importantly, Mn-CP reveals an amazing quantitative sensing of OTC in actual samples such as seawater, aquaculture freshwater, soil infiltration solutions, and tap water. This work proves the excellent application potential of dual-functional CPs in the field of clean energy and environmental protection, especially for the fluorescence detection of antibiotics in aquaculture systems.

Several fluorescent probes have been designed to detect ClO - in biological systems based on the isomerization mechanism of C = N bonds. Particularly, fluorescein has emerged as an important fluorophore for detecting ClO - because of its unique properties. Previously, we introduced the fluorescein analog F-1 with an active aldehyde group. In this study, two ClO - fluorescent sensors (F-2 and F-3) with imine groups were designed and synthesized using diaminomaleonitrile and 2-hydrazylbenzothiazole as amines. The electron cloud distribution of F-2 and F-3 in ground and excited states was explored via Gaussian calculations, reasonably explaining their photophysical properties. The fluorescence detection of ClO - in solution using the two probes (F-2 and F-3) was realized based on the mechanism of imine deprotection with ClO - . NaClO concentration titration demonstrated that the colorimetric detection of ClO - with the naked eye could be achieved using both F-2 and F-3. However, after adding ClO - , the fluorescence intensity of probe F-2 increased, whereas that of probe F-3 first decreased and then increased. Probes F-2 and F-3 exhibited good selectivity, anti-interference capability, and sensitivity, with the detection limits of 169.95 and 37.30 µM, respectively. Owing to their low cell toxicity, probes F-2 and F-3 can be applied to detect ClO - in vivo. The design approach adopted in this study will further advance the future development of ClO - chemical probes through the removal of C = N bond isomerization., (© 2023. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

By selecting a bisphosphonic ligand H 4 L (H 4 L = 4-F-C 6 H 4 CH 2 N(CH 2 PO 3 H 2 ) 2 ) and a coligand oxalate (H 2 C 2 O 4 ), three isostructural lanthanide metal-organic frameworks (Ln-MOFs) with a 2D layer structure, [Ln(H 3 L)(C 2 O 4 )]·2H 2 O (Ln = Eu (1), Gd (2), or Tb (3)), were hydrothermally prepared. By tuning the molar ratio of Eu 3+ , Gd 3+ , and Tb 3+ in the above reactions, six bimetallic or trimetallic doped Ln-MOFs (Eu x Tb 1- x ( x = 0.02 (4), 0.04 (5), and 0.06 (6)), Gd 0.94 Eu 0.06 (7), Gd 0.96 Tb 0.04 (8) and Gd 0.95 Tb 0.03 Eu 0.02 (9)) were obtained. The powder X-ray diffraction (PXRD) patterns of doped Ln-MOFs 4-9 show that they are isomorphous with 1-3. The bimetallic doped Ln-MOFs show a gradual variation of luminous colors between yellow-green, yellow, orange, pink, and light blue. Meanwhile, the trimetallic doped Gd 0.95 Tb 0.03 Eu 0.02 Ln-MOF (9) displays near white-light emission with a quantum yield of 11.39%. Interestingly, the luminous inks of 1-9 are invisible and color tunable, which makes it possible to promote their anti-counterfeiting applications. Additionally, 3 displays good thermal, water, and pH stabilities, which provides the feasibility for its sensing application. The luminescence sensing experiments show that 3 can serve as a highly selective, reusable, and ratiometric luminescent sensor of sulfamethazine (SMZ). Moreover, 3 shows an excellent SMZ detection performance in real samples, such as mariculture water and real urine. Owing to the visible variation of the response signal under a UV lamp, portable SMZ test paper was prepared.

Developing high-accuracy luminescent sensors for detecting emerging environmental pollutants is of great importance and is still a challenge. Utilizing a 4-carboxyphenylphosphonic acid (H 3 pbc) ligand, a novel one-dimensional (1D) Zn-based coordination polymer with the formula [Zn 2 (Hpbc) 2 (2,2'-bipy)(H 2 O)]·H 2 O (Zn-CP, H 3 pbc = 4-HOOCC 6 H 4 PO 3 H 2 , 2,2'-bipy = 2,2'-bipyridine) has been hydrothermally synthesized. Each of the 1D chains was linked via π-π stacking interactions and formed a supramolecular framework. Furthermore, due to the existence of uncoordinated -COOH groups, the terbium-functionalized hybrid (Tb3+@Zn-CP) was prepared by introducing Tb 3+ ions into the structure through coordinated postsynthetic modification (PSM). Tb3+@Zn-CP shows the characteristic emission of Tb 3+ ions due to the "antenna effect" of the H 3 pbc ligand. Based on the excellent luminescence properties and structural stabilities of Zn-CP and Tb3+@Zn-CP, they can be used as highly sensitive and selective luminescent probes of the UV filter BP (benzophenone) depending on multiquenching effects. In addition, their obvious color change can be easily distinguished by the naked eye under ultraviolet light, which was successfully used in the preparation of portable BP test paper. More importantly, Tb3+@Zn-CP is the first example of CPs as a ratiometric luminescent sensor for BP. This work provides a novel strategy for the construction of ratiometric luminescent probes of BP-type UVFs through coordinated postsynthetic modification.

Fluorescein derivatives with thermally activated delayed fluorescence (TADF) show much stronger competition ability and vaster prospects than traditional fluorescein dyes due to their prominent long lifetime. It will be of great significance to synthesize more fluorescein derivatives with TADF. In this work, compounds DCF-MPYA and FL with TADF properties were obtained by fine tuning the substituents' structure on the basis of fluorescein derivative DCF-MPYM. Their long-lived triplet excited states (21.78 μs, 32.0 μs) were proved by nanosecond time-resolved transient difference absorption spectra. The steady-state and time-resolved fluorescence spectra showed that DCF-MPYA and FL exhibited red fluorescence around 645 nm and 651 nm, respectively. The results of sensitivity to oxygen and heavy atoms further demonstrated that the time-resolved fluorescence spectra originate from the delayed fluorescence. The time correlated single-photon counting (TCSPC) data indicated that DCF-MPYA and FL showed long-lived lifetimes of 13.16 μs and 23.72 μs, respectively. The energy gap (Δ E ST ) between the singlet (S 1 ) and triplet (T 1 ) states of DCF-MPYA and FL was calculated to be 3.32 meV and 9.98 meV from the decay rate of DF as a function of temperature. The small energy gap is conducive to the occurrence of efficient TADF at room temperature. Meanwhile, Gaussian calculation was employed to observe the electron density of DCF-MPYA and FL in the ground and excited states. The calculation results indicate that the shapes and energy levels of the highest occupied molecular orbitals (HOMOs), lowest unoccupied molecular orbitals (LUMOs), and LUMOs+1 for the monoanion and dianion forms are similar and thus DCF-MPYA and FL exhibit almost the same luminescence properties. Finally, DCF-MPYA and FL with low toxicity were used in confocal and time-resolved fluorescence imaging. Our construction strategy will be beneficial for developing more fluorescein derivatives with TADF in the future., Competing Interests: The authors declare no competing financial interest., (This journal is © The Royal Society of Chemistry.)

The preparation of single-chain magnets (SCMs) with photo-switchable bistable states is essential for the development of high-density photo-recording devices. However, the reversible switching of the SCM behavior upon light irradiation is a formidable challenge. Here we report a well-isolated double zigzag chain {[Fe(bpy)(CN) 4 ] 2 [Co(phpy) 2 ]}·2H 2 O (bpy = 2,2'-bipyridine, phpy = 4-phenylpyridine), which exhibits reversible redox reactions with interconversion between FeIIILS(μ-CN)CoIIHS(μ-NC)FeIIILS (LS = low-spin, HS = high-spin) and FeIIILS(μ-CN)CoIIILS(μ-NC)FeIILS linkages under alternating irradiation with 808 and 532 nm lasers. The bidirectional photo-induced metal-to-metal charge transfer results in significant changes of anisotropy and intrachain magnetic interactions, reversibly switching the SCM behavior. The on-switching SCM behavior driven by light irradiation at 808 nm could be reversibly switched off by irradiation at 532 nm. The results provide an additional and independent way to control the bistable states of SCMs by switching in the 0 → 1 → 0 sequence, with potential applications in high density storage and molecular switches.