Multi‐Emission from Single Metal–Organic Frameworks under Single Excitation

Abstract

species under single wavelength excitation. Single-excitation is simple for practical applications, but high requirement is needed as the multi-emission centers are integrated and excited together. Multiemission organic molecules are developed for sensing and lighting applications, [3] but each emissive molecule is well designed with elaborate and complex construction. The simple and general synthesis strategies of multi-emission matrix are urgently demanded in theory and practice.Metal-organic frameworks (MOFs), prepared with metal ions (or metal clusters) and organic ligands, have been widely adopted for gas storage and separation, [4] catalysis, [5] sensing, [4a,6] and bio-imaging. [7] The rational selection and combination of emissive building blocks (organic ligands and metal nodes) provide thousands of possibilities for the design of multi-emission MOFs. [2c,8] Further, the channels or pores of MOFs could act as holder to load guest species, ranging from ions, nanoparticles to dyes to create multi-emission MOFs. Classification of Multi-Emission MOFsEmission occurs when the absorbed energy creates excited state of a species and then comes back to the ground state. [12] Tracing the source, we classify the multi-emission MOFs, according to the excitation centers as illustrated in Scheme 1. Organic aromatic ligands show wide light absorption for potential excitation centers. The single ligand absorbs photon as single absorption site, while its different chemical states gave different emissions, such as the keto and enol states for excited-state intramolecular proton transfer (ESIPT) as excited tautomer. [9,13] In lanthanide MOFs (Ln-MOF), antenna effect realizes the energy transfer from the excited ligand to Ln ions for the multiemission based om Ln ions and ligand. [14] Ascribe to antenna effect, though multi-emission comes from different Ln ions and/or ligands, the energy absorption and excited site is the ligand, which is regarded as single excitation site. However, it is critically required to delicately regulate the exact energy relationship between the ligand and Ln ions to ensure the efficient energy transfer.Multi-emission from multiple excitation sites should own the overlapped excitation wavelength to realize the single wavelength excited emission. However, the different excitation and emission Multi-emission materials have come to prominent attention ascribed to their extended applications other than single-emission ones. General and robust design strategies of a single matrix with multi-emission under single excitation are urgently required. Metal-organic frameworks (MOFs) are porous materials prepared with organic ligands and metal nodes. The variety of metal nodes and ligands makes MOFs with great superiority as multi-emission matrices. Guest species encapsulated into the channels or pores of MOFs are the additional emission sites for multi-emission. In this review, multi-emission MOFs according to the different excitation sites are summarized and classified. The emission mechanisms are dis...

Water-Stable Eu6-Cluster-Based fcu-MOF with Exposed Vinyl Groups for Ratiometric and Fluorescent Visual Sensing of Hydrogen Sulfide

“…Lanthanide metal–organic frameworks (LnMOFs), assembled from lanthanide-containing nodes or clusters and organic ligands through coordination bonds, − combine the lanthanide luminescence properties (e.g., long fluorescence lifetime, large Stokes shift, and narrow emission band) and the unique advantages of MOFs such as outstanding designability, permanent porosity, and tunable optical properties. − They have thus received much attention in the development of dual-emitting sensory materials for various sensing applications, such as temperature, ions, gases, small molecules, and pH. − However, studies on pure LnMOFs for H 2 S detection based on dual-emissive centers in combination with H 2 S-reactive sites, up to a point, are still far behind those hot topics. Specifically, dual-emitting probes constructed from the two independent emissions of single-lanthanide MOFs (S’LnMOFs) are very rare . It is understandable because the majority of S’LnMOFs is single-emitting systems that rarely provide the two distinguishable emissions and lack the reactive sites for H 2 S. In 2017, Yin et al used a boric group to tune the lowest triplet excited energy state (T 1 ) of the ligand in which the emission intensity ratio between the ligand and Ln 3+ ions was used as the self-calibrating ratiometric parameter to detect the F – ion .…”

“…Specifically, dual-emitting probes constructed from the two independent emissions of single-lanthanide MOFs (S'LnMOFs) are very rare. 29 It is understandable because the majority of S'LnMOFs is single-emitting systems that rarely provide the two distinguishable emissions and lack the reactive sites for H 2 S. In 2017, Yin et al used a boric group to tune the lowest triplet excited energy state (T 1 ) of the ligand in which the emission intensity ratio between the ligand and Ln 3+ ions was used as the self-calibrating ratiometric parameter to detect the F − ion. 30 Very recently, Zhao et al successfully engineered the T 1 energy of an organic ligand by using the methoxy group to construct a dual-emitting S'LnMOF for ratiometric temperature sensing.…”

An electrochemically deposited ordered hierarchical metal–organic framework-based dual-module sensor for decoding organic vapors

“…[28][29][30][31][32] The isostructural BHP-MOFs were further studied in detail to demonstrate the aforementioned bimetallic strategy. 28,30,33 As shown in Fig. 1b-d, small windows were observed on the shell walls owing to the close-packed PS templates.…”

Detection of Heavy Metal Ions by Ratiometric Photoelectric Sensor

“…With excellent chemical properties and high surface area, metal–organic frameworks (MOFs) have great potential in catalysis, adsorption, and sensing. , Jia et al embedded ruthenium bipyridine (Ru­(bpy) 3 2+ ) into an amino-modified zirconium-MOF to obtain a ratiometric probe (Ru@UiO-66-NH 2 ) to further improve the sensitivity of the sensor (Figure A). When Hg 2+ coordinated with the Ru@UiO-66-NH 2 , the blue FL of UiO-66-NH 2 at 437 nm was significantly quenched by SQE and PET, and the red FL of Ru­(bpy) 3 2+ at 604 nm was no change and served as a reference signal.…”