Fluorescent Eu³⁺/Tb³⁺ Metal–Organic Frameworks for Ratiometric Temperature Sensing Regulated by Ligand Energy

Abstract

This work presents three series of Eu/Tb metal–organic frameworks (MOFs) containing benzophenone-4,4′-dicarboxylic acid (H2BPNDC), 4,4′-dicarboxydiphenyl ether (H2OBA), and terephthalic acid (H2BDC) as the ligands. Eu/Tb MOFs have the same structural features in that their 3D frameworks are simplified as 2,3,10-connected {42.6}2{46.618.819.102}­{4}2 topological networks. The solid-state fluorescence spectra of three Eu/Tb MOF series are attributed to the combined emissions of 5D0 → 7F J (J = 1–4) transitions in Eu3+ and 5D4 → 7F J (J = 6–5) transitions in Tb3+. The n Eu:n Tb of Eu/Tb MOFs is optimized as 1:69 based on the relationships between I Tb(545)/I Eu(614) and n Eu:n Tb; that is, Eu0.0143Tb0.9857-L (L = BPNDC2–, OBA2–, and BDC2–) were selected to carry out the following temperature (T)-sensing tests. The fluorescence mechanism of Eu0.0143Tb0.9857-L can be explained by a ligand-to-metal charge transfer combined with an intermetallic Tb3+ → Eu3+ energy transfer. The T-dependent fluorescence indicates linear relationships with sensitivities of 1.85% K–1 for Eu0.0143Tb0.9857-BPNDC, 6.49% K–1 for Eu0.0143Tb0.9857-OBA, and 0.28% K–1 for Eu0.0143Tb0.9857-BDC. The influence of T on the lowest excited triplet energy levels (T1 values) of the ligands reveals that the ligand energy regulation impacts their fluorescence properties, including the sensitivity, fluorescence quenching rate, quantum yield, and fluorescence lifetime. This shows that Eu0.0143Tb0.9857-BPNDC is sufficiently sensitive to T, making it applicable in noncontact T measurements.

Eu(III)-Functionalized MOF-Based Dual-Emission Ratiometric Sensor Integrated with Logic Gate Operation for Efficient Detection of Hippuric Acid in Urine and Serum

“…When excited at 325 nm, the normalized solid-state luminescence emissions of H 4 TPTA, bimb, NiMOF , and Eu 3+ @NiMOF were obtained and are shown in Figure S11. The pristine NiMOF displayed blue cyan emission at 454 nm, responding corresponding to the transfer of π* → π electrons of the organic linkers. − As expected, Eu 3+ @NiMOF presented bright red fluorescence emission, with the characteristic peaks located on 628 and 700 nm that could be assigned to the 5D 0 –7F 2 and 5D 0 –7F 4 transition. , According to the Judd-Ofelt theory, the sensitive 5D 0 –7F 2 transition at 628 nm also proved there are strong coordination interactions between Eu 3+ ions and the framework. Moreover, the color changes of the two samples under sunlight and UV light are shown in Figure S12.…”

Ultralong Near Infrared Room Temperature Phosphorescence in Cu(I) Metal‐Organic Framework Based‐on D–π–A–π–D Linkers

“…[12] Cu(I)-MOFs that contained Cu(I) ions with a d 10 configuration have gained attention in luminescent sensing which seldom been reported. [13][14][15][16] However, a wide variety of Cu(I) complexes have been developed in the past two decades based on their interesting properties and applications from the viewpoint of basic science. [17] At present, the decay times of most reported Cu(I) materials, whether thermal activation delayed fluorescence (TADF) or phosphorescence, are usually on microsecond scale in ambient conditions.…”

Ratiometric Luminescent Thermometer Based on the Lanthanide Metal–Organic Frameworks by Thermal Curing

“…However, the emission lifetimes exhibit different trends at the subsequent stages. The emission decay profiles of Tb-MOFs@TGIC showed multiexponential decays from 250 to 400 K (Figure b and Table S3), and two types of emission species existed in the solid state, and the emission lifetime values of Tb 3+ in Tb-MOFs@TGIC quickly declined, which suggests that there may be simultaneous ligand energy regulation and energy back transfer of Tb 3+ → TGIC, and the short component corresponds to the energy back transfer from Tb 3+ ( 5 D 4 → 7 F 5 , 544 nm) to TGIC (454 nm). , With the increase of temperature, the BenT phenomenon of Tb 3+ to TGIC increases, resulting in a decrease in the Tb 3+ emission intensity. In Tb-MOFs@TGIC, the most likely sensitization pathway involves ISC from the S 1 state to the T 1 state of TGIC, energy transfer from the T 1 state of the antenna TGIC to the 5 D 4 state of Tb 3+ , and the back energy transfer (BenT) effect of Tb 3+ → TGIC enhancing with the increase of temperature via the Förster transfer mechanism. , …”