Lanthanide(III) Ions and 5-Methylisophthalate Ligand Based Coordination Polymers: An Insight into Their Photoluminescence Emission and Chemosensing for Nitroaromatic Molecules

Abstract

The work presented herein reports on the synthesis, structural and physico-chemical characterization, luminescence properties and luminescent sensing activity of a family of isostructural coordination polymers (CPs) with the general formula [Ln2(μ4-5Meip)3(DMF)]n (where Ln(III) = Sm (1Sm), Eu (2Eu), Gd (3Gd), Tb (4Tb) and Yb (5Yb) and 5Meip = 5-methylisophthalate, DMF = N,N-dimethylmethanamide). Crystal structures consist of 3D frameworks tailored by the linkage between infinite lanthanide(III)-carboxylate rods by means of the tetradentate 5Meip ligands. Photoluminescence measurements in solid state at variable temperatures reveal the best-in-class properties based on the capacity of the 5Meip ligand to provide efficient energy transfers to the lanthanide(III) ions, which brings intense emissions in both the visible and near-infrared (NIR) regions. On the one hand, compound 5Yb displays characteristic lanthanide-centered bands in the NIR with sizeable intensity even at room temperature. Among the compounds emitting in the visible region, 4Tb presents a high QY of 63%, which may be explained according to computational calculations. At last, taking advantage of the good performance as well as high chemical and optical stability of 4Tb in water and methanol, its sensing capacity to detect 2,4,6-trinitrophenol (TNP) among other nitroaromatic-like explosives has been explored, obtaining high detection capacity (with Ksv around 105 M−1), low limit of detection (in the 10−6–10−7 M) and selectivity among other molecules (especially in methanol).

Cerium(iii) and 5-methylisophthalate-based MOFs with slow relaxation of magnetization and photoluminescence emission

“…31 Taking these considerations into account, in this work we have chosen the linker 5-methylisopthalate (5Meip) as a ligand with the aim of studying the effect that the methyl group can contribute to the construction of three-dimensional structures. 32,33 Furthermore, the compounds formed should present good luminescence properties given the ability of the 5Meip carboxylate ligand to efficiently transfer energy to the lanthanide centres, generating intense emissions in both the visible and NIR regions, as we have already demonstrated in other previous studies. 33…”

“…32,33 Furthermore, the compounds formed should present good luminescence properties given the ability of the 5Meip carboxylate ligand to efficiently transfer energy to the lanthanide centres, generating intense emissions in both the visible and NIR regions, as we have already demonstrated in other previous studies. 33…”

“…The photoluminescence properties of GR-MOF-17 and GR-MOF-18 were studied for polycrystalline samples in the solid state given the good emissive properties shown by the 5Meip ligand with other lanthanide( iii )-based CPs. 33 As aforementioned in the introduction, the Ce( iii )-centred emission has not been largely studied as compared to other lanthanide( iii ) ions because 5d orbitals are close in energy to the 4f shell due to ligand and crystal fields, in such a way that Ce( iii ) can show 5d–4f-transitions which lie in the visible range. 42 Given that both ground and first excited states derived from the f 1 configuration are spin doublets ( 2 F 5/2 and 2 F 7/2 ), the Ce( iii )-centred emission usually consists of two bands split by spin–orbit coupling, which are sensitive to the coordination environment due to their partial d orbital character.…”

“…S38b†), thus falling in the typical range of phosphorescence. 44 A Gd( iii )-based CP, with formula [Ln 2 (μ 4 -5Meip) 3 (DMF)] n and thus considered as a representative compound in which the 5Meip ligand presents a comparable structure, showed a phosphorescence emission with a τ av of 494 μs at 13 K, 33 from which it was concluded that such phosphorescence comes from the emission of an excited triplet state (centred on the ligand) lying at about 22 000 cm −1 over the ground state. Taking into account that the phosphorescence signal is usually quenched at room temperature by the vibrational modes of the molecules, the measurements were repeated at 15 K in order to slow down the molecular vibrations in the GR-MOF-17 framework.…”

Special Issue “Theoretical Calculation and Molecular Modeling of Nanomaterials”

“…The CPs exhibit tailored crystal structures, efficient energy transfer to lanthanide ions, and intense emissions in the visible and near-infrared regions. Specifically, one of the compounds, 4Tb, demonstrates high quantum yield and excellent sensing capabilities for detecting nitroaromatic-like explosives, with a high detection capacity, a low limit of detection, and selectivity among other molecules [14].…”