Metal–organic frameworks (MOFs) display a wide range of luminescent behaviors resulting from the multifaceted nature of their structure. In this critical review we discuss the origins of MOF luminosity, which include the linker, the coordinated metal ions, antenna effects, excimer and exciplex formation, and guest molecules. The literature describing these effects is comprehensively surveyed, including a categorization of each report according to the type of luminescence observed. Finally, we discuss potential applications of luminescent MOFs. This review will be of interest to researchers and synthetic chemists attempting to design luminescent MOFs, and those engaged in the extension of MOFs to applications such as chemical, biological, and radiation detection, medical imaging, and electro-optical devices (141 references).

Luminescent Metal–Organic Frameworks

Lanthanide-based luminescent hybrid materials.

Interpretation of europium(III) spectra

Cerium dioxide (CeO2, ceria) is becoming an ubiquitous constituent in catalytic systems for a variety of applications. 2016 sees the 40th anniversary since ceria was first employed by Ford Motor Company as an oxygen storage component in car converters, to become in the years since its inception an irreplaceable component in three-way catalysts (TWCs). Apart from this well-established use, ceria is looming as a catalyst component for a wide range of catalytic applications. For some of these, such as fuel cells, CeO2-based materials have almost reached the market stage, while for some other catalytic reactions, such as reforming processes, photocatalysis, water-gas shift reaction, thermochemical water splitting, and organic reactions, ceria is emerging as a unique material, holding great promise for future market breakthroughs. While much knowledge about the fundamental characteristics of CeO2-based materials has already been acquired, new characterization techniques and powerful theoretical methods are dee...

Fundamentals and Catalytic Applications of CeO2-Based Materials

Advanced oxidation processes (AOPs), defined as those technologies that utilize the hydroxyl radical (·OH) for oxidation, have received increasing attention in the research and development of wastewater treatment technologies in the last decades. These processes have been applied successfully for the removal or degradation of toxic pollutants or used as pretreatment to convert recalcitrant pollutants into biodegradable compounds that can then be treated by conventional biological methods. The efficacy of AOPs depends on the generation of reactive free radicals, the most important of which is the hydroxyl radical (·OH). The authors summarize the formation reactions of ·OH and the mechanisms of pollutants degradation. They cover six types of advanced oxidation processes, including radiation, photolysis and photocatalysis, sonolysis, electrochemical oxidation technologies, Fenton-based reactions, and ozone-based processes. Controversial issues in pollutants degradation mechanism were discussed. They review t...

Advanced Oxidation Processes for Wastewater Treatment: Formation of Hydroxyl Radical and Application

A kind of monomer (abbreviated as HQ-TESPI) was prepared by modifying 8-hydroxyquinoline (abbreviated as HQ) with 3-(triethoxysilyl)-propyl isocyanate (abbreviated as TESPI) through the hydrogen transfer nucleophilic addition in this study. Then the monomer was used to coordinate with the metal ions (Al3+, Zn2+, Eu3+, Tb3+) according to the complexation theory. On the other hand, the monomer was simultaneously used to occur hydrolysis and condensation together with tetraethoxysilane (abbreviated as TEOS) to form silica-based organic–inorganic hybrid thin films (abbreviated as Al-HQ-TESPI, Zn-HQ-TESPI, Eu-HQ-TESPI and Tb-HQ-TESPI, respectively) by the means of spin-coating technology. The resultant thin films showed characteristic photoluminescence originated from the modified 8-hydroxyquinolinates. The target materials exhibit strong green-colored fluorescence (Al-HQ-TESPI), cyan-colored fluorescence (Zn-HQ-TESPI) and olivine-colored fluorescence (Eu-HQ-TESPI, Tb-HQ-TESPI). These hybrid thin films can be prospected to be used in the field of photoluminescence.

Fabrication and photoluminescence of molecular hybrid films based on the complexes of 8-hydroxyquinoline with different metal ions via sol–gel process

We report a novel technology for fabricating sol–gel derived nano-scale molecular hybrid materials that contain NHC( O)NH groups anchored to a silica network. The modified 2-amino pyridine is grafted by 3-(triethoxysilyl)-propyl isocyanate and applied to coordinate to RE 3+ (Eu 3+ , Tb 3+ ) through nitrogen atoms of the heterocycle of pyridine group and further formed Si O backbones after hydrolysis and polycondensation processes. For analogy and luminescence efficiency purpose, we added 1,10-phenanthroline to the above hybrids in order to increase the conjugating effects and sensitize rare earth ions emissions. IR, ultraviolet absorption and luminescence spectra were utilized to characterize the structure and photophysical properties of the obtained hybrid material and the above spectroscopic data reveal that the triplet energy of 1,10-phenanthroline in this favorable hybrid system matches with the emissive energy level of RE 3+ .

Molecular assembly of red and green nanophosphors from amine-functionalized covalent linking hybrids with emitting centers of Eu3+ and Tb3+ ions

Synthesis and crystal structure of a novel two-dimensional 3d–4f heterometallic coordination polymer constructed from three-ply-like layers

A new kind of sol–gel derived organic–inorganic hybrid material was prepared for the first time.In this case the organic portion of an acylamine derivation grafted by 3-aminopropyl trimethoxysilane and covalently linked together via sulfonamide linkages. Fourier transform infrared (FTIR), in ultraviolet absorption (UV) spectra and 1H nuclear magnetic resonance (NMR) spectra were used to confirm these modifications and the X-ray diffraction (XRD) spectra were used to determine the framework. The material’s phosphorescent spectra and luminescence spectra were recorded. An efficient intramolecular energy transfer process between acylamine and lanthanide ions took place within these molecular-based hybrids. Strong green and red emissions were achieved for Tb3+ and Sm3+ ions, respectively.

Attractive sulfonamide bridging bonds constructing lanthanide centered photoactive covalent hybrids

A novel luminescent lanthanide metal organic framework (Ln-MOF) is synthesized by in situ encapsulating Eu(3+) ions to partial replace the transition-metal clusters in the channels of CPM-17-Zn nanocrystals. The Eu(3+) functionalized zeolite-type MOF hybrid system shows excellent luminescence property and photo-stability in aqueous environment for the sensitization and protection from the host framework. Subsequently, as a highly selective and sensitive sensor, its nanocrystals can be used to detect Cd(2+) in aqueous solution. In addition, the possible sensing mechanism based on ion exchange is discussed in detail. This work is one of the few cases for detecting Cd(2+) in aqueous solution based on a zeolite-type MOF. The good fluorescence stability, low detection limit and broad linear range in aqueous environment make this probe to be expected to have potential application in intracellular sensing and imaging of Cd(2+) potentially.

Bing Yan

Papers

Fabrication and photoluminescence of molecular hybrid films based on the complexes of 8-hydroxyquinoline with different metal ions via sol–gel process

Molecular assembly of red and green nanophosphors from amine-functionalized covalent linking hybrids with emitting centers of Eu3+ and Tb3+ ions

Synthesis and crystal structure of a novel two-dimensional 3d–4f heterometallic coordination polymer constructed from three-ply-like layers

Attractive sulfonamide bridging bonds constructing lanthanide centered photoactive covalent hybrids

Zeolite-type metal organic frameworks immobilized Eu3+ for cation sensing in aqueous environment