Rational Design of a Bifunctional, Two‐Fold Interpenetrated Zn II ‐Metal–Organic Framework for Selective Adsorption of CO 2 and Efficient Aqueous Phase Sensing of 2,4,6‐Trinitrophenol

Ratiometric Luminescent Sensor of Picric Acid Based on the Dual-Emission Mixed-Lanthanide Coordination Polymer

Powerful explosive sensors play a key role in public security and environmental protection. Herein, we report a series of isostructural lanthanide coordination polymers [Ln₂L_1.5(NMP)₂] _n (LnL: Ln = Eu, Gd, Tb, Dy, Ho, and Er; H₄L = [1,1':4',1″-terphenyl]-2',4,4″,5'-tetracarboxylic acid; NMP = N-methyl-2-pyrrolidone) and mixed-Ln LnL (Eu _xTb_{1- x}L, Eu _xGd_{1- x}L, Tb _xGd_{1- x}L, and Eu _xTb_{0.02- x}Gd_0.98L). Luminescence studies show that both H₄L and GdL emit strong fluorescence and phosphorescence at 77 K while only fluorescence at room temperature, and TbL exhibits strong Tb³⁺ characteristic emission, although the energy difference between the triplet excited state of H₄L (20661 cm^-1) and the ⁵D₄ energy level of Tb³⁺ (20500 cm^-1) is very small. By doping Eu³⁺ and Tb³⁺ into GdL, we obtained Eu _xTb_{0.02- x}Gd_0.98L emitting warm white light. For TbL and Tb_0.01Gd_0.99L showing dual emission, upon addition of picric acid (PA) into their suspensions in Tris-HCl buffer, Tb³⁺ emission decreases slowly; however, the ligand-based emission is sharply quenched, rendering TbL and Tb_0.01Gd_0.99L excellent single-lanthanide and mixed-lanthanide ratiometric luminescence PA sensor materials, respectively.

Exploitation of the Flexidentate Nature of a Ligand To Synthesize Zn(II) Complexes of Diverse Nuclearity and Their Use in Solid-State Naked Eye Detection and Aqueous Phase Sensing of 2,4,6-Trinitrophenol

Three Zn(II) complexes, [Zn₂(HL)₂(NO₃)₂]·H₂O (1), [(Zn₄L₂)(μ₃-OH)₂](NO₃)₂·0.5H₂O (2), and [(Zn₆L₂)( o-van)₂(μ₃-OCH₃)₂(μ₃-OH)₂](NO₃)₂ (3), have been synthesized by exploiting the flexidentate nature of a multidentate Schiff base ligand, H₂L ( N, N'-bis(3-methoxysalicylidene)diethylenetriamine), by changing the reaction conditions and stoichiometry of the reactants. All three complexes are highly fluorescent in solution as well as in solid and have been used as luminescence sensors toward nitrophenol explosives in both the media. In aqueous/methanol medium, these complexes show very high selectivity and sensitivity with detection limit in ppb (2.03) or nM level (8.89 nM) for picric acid. The yellow color of all three Zn(II) complexes changes to red on mixing with small amount (∼5%) of picric acid in solid state, revealing the potential of these complexes for practical use in naked eye detection of 2,4,6-trinitrophenol (TNP) or picric acid in ambient light. In order to identify the host-guest interactions between Zn(II) complex and TNP, single crystals of the adduct of TNP with Zn(II) complex, [Zn₂(HL)₂(H₂O)₂][C₆H₂N₃O₇]₂ (4), were grown. Its X-ray crystal structure reveals that two picrate ions are attached to a dinuclear host with the help of H-bonding and π···π interactions, throwing light into the quenching mechanism and selectivity of detection.

Two azo-functionalized luminescent 3D Cd(ii) MOFs for highly selective detection of Fe3+ and Al3+

Two 3D luminescent Cd(ii) MOFs (Cd-MOF-1 and Cd-MOF-2) exposing azo functional sites displayed selective detection of Fe³⁺ and Al³⁺ metal ions with high sensitivities.

Two luminescent lanthanide–organic frameworks containing bithiophene groups for the selective detection of nitrobenzene and Fe3+

Two isostructural lanthanide–organic frameworks containing bithiophene groups can be used as fast-response fluorescent probes for the sensitive detection of nitrobenzene and Fe³⁺ ions through fluorescence quenching.