High-Performance Turn-On Fluorescent Metal–Organic Framework for Detecting Trace Water in Organic Solvents Based on the Excited-State Intramolecular Proton Transfer Mechanism

Abstract

Simple, fast, and sensitive detection of trace water in organic solvents is an urgent requirement for chemical industries. Herein, combining the unusual excited-state intramolecular proton transfer (ESIPT) mechanism with the effective strategy of pore space partition, for the first time, we construct a powerful fluorescent metal−organic framework (SNNU-301) probe with excellent water stability. The SNNU-301 probe shows a remarkable performance for turn-on ESIPT-based fluorescence response to water in nine common organic solvents, exhibiting wide linear ranges, low limit of detection values, and ultrafast response, especially in dimethyl sulfoxide (0−5.2%; 0.011%, v/v; 110 s). The typical ESIPT-sensitive linker 2,5dihydroxyterephthalate (DHBDC) imparts it with discriminative detection properties via enol−keto tautomerism, and lightresponsive triangular tri(pyridin-4-yl)-amine (TPA) realizes pore space partition. The theoretical calculation gives an in-depth explanation about the proton transfer mechanism. Comparative experiments and GCMC simulation provide evidence that the synergy of the ESIPT process and TPA of the framework further boosts its performance effectively. Definitely, this work not only offers a promising candidate with fast detection speed, high sensitivity, excellent universality, and visual observation for the determination of water in organic solvents but also provides valuable guidance for the design of high-performance fluorescent probes.

Taking Advantage of a Luminescent ESIPT-Based Zr-MOF for Fluorochromic Detection of Multiple External Stimuli: Acid and Base Vapors, Mechanical Compression, and Temperature

“…When the DHT linker is taking part in the MOF structure, the carboxylate groups are anchored to the Zr metal atoms, because the ESIPT reaction is less favored, and therefore, the enol species can emit light. The observation of two emission bands corresponding to enol and keto tautomers of DHT linkers have been previously described for other DHT-based MOFs. ,, Moreover, we have observed that the relative intensity ratio between these two emission bands depends on the excitation wavelength (Figure ). When the UiO-66-(OH) 2 MOF is photoexcited with higher energies (lower wavelengths), the emission of the keto tautomer (525 nm) is enhanced.…”

“…This is followed by a charge reorganization, leading to the formation of the keto tautomer, whose emission maximum falls in the region of ∼525 nm (as previously demonstrated), reflecting the increase in intensity of this band. Similar mechanism has been proposed to explain the response of DHT-based MOFs to the presence of different chemicals in solution such as water or F – . ,, The photoluminescence quantum yield of UiO-66-(OH) 2 is weak, 0.34%, and it increases by ∼5 (1.60%) and ∼2 (0.55%) times in the presence of HCl and Et 3 N, respectively. This further corroborates the turn-on sensing mechanism.…”

“…In this sense, one of the most commonly used organic linkers for the fabrication of ESIPT-based LMOFs is 2,5-dihydroxyterephthalic acid (DHT). − This linker can emit light from the enol (blue color) or keto (green-yellowish color) tautomers when it is part of the MOF network, and the ultimate emission color of the material depends on the efficiency of the ESIPT reaction to form the keto species. , For example, it has been reported that depending on the metal used in the synthesis, the DHT-based MOFs had different crystalline structures, affecting the ESIPT reaction and, therefore, modifying the final emission color of the material . Most of the DHT-based MOFs have been employed to detect traces of water, different ions, and harmful chemical compounds in solutions. − ,− However, their use in the detection of volatile compounds is more scarce. ,, To the best of our knowledge, there are no examples of luminescent UiO-66-(OH) 2 used for specific detection of vapors of base and acid compounds nor external physical stimuli (e.g., changes in temperature or pressure).…”

Excited-State Intramolecular Proton Transfer (ESIPT) Based Metal–Organic Supramolecular Optical Materials: Energy Transfer Mechanism and Luminescence Regulation Strategy

“…To date, according to the types of ESIPT sites, most studied ESIPT ligands to construct metal–organic supramolecular materials can be divided into derivatives of azoles, quinolines, pyrimidines, salicylates, etc. And the general metal ions can include the d 10 -type ions (Zn 2+ , Cd 2+ , In 3+ ), ,,− ,,,,− alkali-earth ions (Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ ), ,,,− Zr 4+ ions, , rare earth ions (Ln 3+ ), ,, etc. Basically, the strategy for the construction of ESIPT metal–organic supramolecular materials must consider the following three principles.…”

“…In general, metal–organic optical functional materials have remarkable advantages, including adjustable frame structures, convenient assembly process, and diverse luminescent mechanisms. With the fast development of modern characterization techniques and supramolecular self-assembly research, studies based on the design and application of ESIPT metal–organic optical materials have been attracting considerable interest. ,,− The construction and PL regulation of ESIPT-attributed metal–organic materials with strong photothermal stability, spectral response specificity and excellent optical performance is considered to an important direction for the development of new ESIPT materials. ,, …”