A new series of five three-dimensional Ln(III) metal-organic frameworks (MOFs) formulated as [Ln4(μ6-L)2(μ-HCOO)(μ3-OH)3(μ3-O)(DMF)2(H2O)4] n {Ln3+ = Tb3+ (1), Eu3+ (2), Gd3+ (3), Dy3+ (4), and Er3+ (5)} was successfully obtained via a solvothermal reaction between the corresponding lanthanide(III) nitrates and 2-(6-carboxypyridin-3-yl)terephthalic acid (H3L). All of the obtained compounds were fully characterized, and their structures were established by single-crystal X-ray diffraction. All products are isostructural and possess porous 3D networks of the fluorite topological type, which are driven by the cubane-like [Ln4(μ3-OH)3(μ3-O)(μ-HCOO)]6+ blocks and μ6-L3- spacers. Luminescent and sensing properties of 1-5 were investigated in detail, revealing a unique capability of Tb-MOF (1) for sensing acetone and metal(III) cations (Fe3+ or Ce3+) with high efficiency and selectivity. Apart from a facile recyclability after sensing experiments, the obtained Tb-MOF material features a remarkable stability in a diversity of environments such as common solvents, aqueous solutions of metal ions, and solutions with a broad pH range from 4 to 11. In addition, compound 1 represents a very rare example of the versatile Ln-MOF probe capable of sensing Ce3+ or Fe3+ cations or acetone molecules.

Multifunctional Ln-MOF Luminescent Probe for Efficient Sensing of Fe3+, Ce3+, and Acetone.

Counterfeiting and inverse engineering of security and confidential documents, such as banknotes, passports, national cards, certificates, and valuable products, has significantly been increased, w...

Photoluminescent and Chromic Nanomaterials for Anticounterfeiting Technologies: Recent Advances and Future Challenges.

Very bright mechanoluminescence and remarkable mechanochromism using a tetraphenylethene derivative with aggregation-induced emission

“Unity is force” – Aesop. It is a common phenomenon that traditional chromophores exhibit high fluorescence in dilute solutions, yet luminescence is quenched at high concentrations or in the aggregate state, i.e. “aggregation-caused quenching” (ACQ). Tang reported the unusual photophysical observation that luminogens can exhibit weak or no fluorescence in solution, yet they are highly emissive in the aggregate or solid state; this is defined as aggregation-induced emission (AIE). The discovery of AIE helped solve the ACQ effect in traditional luminophores. Pyrene is an important polycyclic aromatic hydrocarbon (PAH), which exhibits very different photophysical behavior in solution versus the aggregate state, and the ACQ effect has played a dominant role in pyrene chemistry. The ACQ effect is harmful for some practical applications and is a challenge in organic light-emitting diodes (OLEDs) and light-emitting electrochemical cells, for which the effect is more severe in the solid state. Thus, how to overcome the ACQ effect observed in pyrene chemistry still remains a challenge. In this review, we discuss how following basic AIE mechanisms such as the restriction of intramolecular motion (RIM), excited-state intramolecular proton transfer (ESIPT), and twisted intramolecular charge transfer (TICT), can transform pyrene-based ACQ luminogens to AIE luminogens with excellent optical properties. Furthermore, prospective applications of pyrene-based AIEgens are discussed, as is the potential for designing new organic functional materials.

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Pyrene-based aggregation-induced emission luminogens and their applications

Two-dimensional (2D) metal–organic frameworks (MOFs) play an essential role in response to external stimuli by changing their physical or chemical properties. This Review mainly aims at the recent ...

Recent Progress in Stimulus-Responsive Two-Dimensional Metal-Organic Frameworks

A novel blue-emitting Zn(II) MOF featuring parallel 2D+2D interpenetrated layers and tubelike channels was generated and shown to efficiently accommodate lanthanide(III) cations (Ln3+ = Eu3+, Tb3+, or a mixture of Eu3+/Tb3+), resulting in the Ln3+-encapsulated functional materials with a tunable emission color, including red, green, and nearly pure white light Furthermore, the thermal-responsive luminescence was investigated for the lanthanide-codoped MOF to exhibit the chromic transition from white at room temperature to blue around liquid nitrogen temperature

An Efficient Blue-Emissive Metal–Organic Framework (MOF) for Lanthanide-Encapsulated Multicolor and Stimuli-Responsive Luminescence

Luminogenic materials with aggregation-induced emission (AIE) have recently aroused great attention due to their potential application in many fields. However, aggregation induced ratiometric luminescence in addition to emission turn-on has been scarcely studied. Here, a structure tunable pyrene benzohydrazonate-based molecular platform exhibits a drastic aggregation-induced color change (Δλem,max ∼ 130 nm) and a high solid-state quantum yield (QYmax ∼ 54.5%). The exciting switch behaviour is triggered by intermolecular hydrogen-bonding through the carbohydrozone bridge, which leads to fixation of the molecular conformations. In addition, by virtue of the multiple excimer state of the pyrenyl unit, a broad range of carbohydrozone-based materials with high contrast mechanochromic luminescence have been developed. These systems represent stimuli-responsive optoelectronic switching devices leading toward multistate dynamic molecular systems in both solution and the solid state.

Aggregation-induced ratiometric emission and mechanochromic luminescence in a pyrene-benzohydrazonate conjugate

Hydrazone-based derivatives modified by substitution at different positions were utilized to prepare a series of bis-homoleptic cobalt complexes. One species, [CoIII(L1)2]+ (1), which incorporated deprotonated ligands, adopted a Co(III) diamagnetic ground state. However, the substituent of a hydrogen atom with a methyl group precluded the possibility of deprotonation upon metal coordination, which led to two species, [CoII(L2Me)2]2+ (2) and [CoII(L3NO2)2]2+, (3) which underwent a gradual spin crossover with an adjustable substituent effect and a mixed character of low-spin (doublet) and high-spin (quartet) populations in wide temperature ranges. Depending on the electronic effects of the substituents on the ligand, the multielectron redox behavior of the cobalt center was systematically modulated as well. This result demonstrates redox-switchable spin crossover in a new hydrazone-based Co(II) system, in which the deprotonation of the coordination pocket and substituent groups in aromatic ligands can have a profound effect on the redox potential and spin state of the metal center.

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Yang Liu

Papers

An Efficient Blue-Emissive Metal–Organic Framework (MOF) for Lanthanide-Encapsulated Multicolor and Stimuli-Responsive Luminescence

Aggregation-induced ratiometric emission and mechanochromic luminescence in a pyrene-benzohydrazonate conjugate

Hydrazone-based cobalt complexes toward multielectron redox and spin crossover

Self-assembly of tetranuclear metallogrid with an asymmetric ligand derived from 2-oxo-quinoline derivative