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

2.1.2. Low Topology/Framework Density 1003 2.1.3. Side Group Directed Superstructures 1003 2.2. Synthesis Considerations 1003 2.3. Special Properties 1004 3. Metal Imidazolate Frameworks 1004 3.1. Chains and Rings 1004 3.2. Zeolitic and Zeolite-like Frameworks 1006 3.2.1. SOD-Type Zinc(II) 2-Methylimidazolate 1007 3.3. Nonporous 4-Connected Networks 1010 3.4. Polyimidazolates 1011 4. Metal Pyrazolate Frameworks 1011 4.1. Clusters and Chains 1011 4.2. 3D Networks Based on Polypyrazolates 1012 5. Metal 1,2,4-Triazolate Frameworks 1014 5.1. Simple 3-Connected Networks 1015 5.2. Quasi-Imidazolates 1018 5.3. With Coordinative Substituents 1019 5.4. With Secondary Counterions and/or Ligands 1021 6. Metal 1,2,3-Triazolate Frameworks 1023 7. Metal Tetrazolate Frameworks 1025 7.1. Univalent Coinage-Metal Tetrazolate Frameworks 1025

Metal Azolate Frameworks: From Crystal Engineering to Functional Materials

2.4.2. Interpenetrated Ladders 711 2.4.3. Unusual Motifs of Ladders 713 2.4.4. Properties of Ladderlike Chains 713 2.5. Rotaxane Polymers 714 2.5.1. 1D Polyrotaxanes 714 2.5.2. 2D Polyrotaxanes 715 2.5.3. 3D Polyrotaxanes 716 2.5.4. Hydrogen-Bonded Polyrotaxanes 716 2.6. Ribbon/Tape Polymers 717 2.7. Metal Cluster As Building Blocks for 1D CP 718 2.7.1. Metal Carboxylate Clusters 718 2.7.2. Metal Halide Clusters 719 2.7.3. Metal Chalcogenide Clusters 720 2.7.4. Polyoxometalate Clusters 721 2.7.5. Single Molecular Magnets as Building Blocks 722

One-Dimensional Coordination Polymers: Complexity and Diversity in Structures, Properties, and Applications

Triazoles and tetrazoles: Prime ligands to generate remarkable coordination materials

Cu(I) complexes and clusters are the largest class of compounds of relevant photochemical and photophysical interest based on a relatively abundant metal element. Interestingly, Nature has given an essential role to copper compounds in some biological systems, relying on their kinetic lability and versatile coordination environment. Some basic properties of Cu(I) and Cu(II) such as their coordination geometries and electronic levels are compared, pointing out the limited significance of Cu(II) compounds (d 9 configuration) in terms of photophysical properties. Well-established synthetic protocols are available to build up a variety of molecular and supramolecular architectures (e.g. catenanes, rotaxanes, knots, helices, dendrimers, cages, grids, racks, etc.) containing Cu(I)-based centers and exhibiting photo- and electroluminescence as well as light-induced intercomponent processes. By far the largest class of copper complexes investigated to date is that of Cu(I)-bisphenanthrolines ([Cu(NN)2]+) and recent progress in the rationalization of their metal-to-ligand charge-transfer (MLCT) absorption and luminescence properties are critically reviewed, pointing out the criteria by which it is now possible to successfully design highly emissive [Cu(NN)2]+ compounds, a rather elusive goal for a long time. To this end the development of spectroscopic techniques such as light-initiated time-resolved X-ray absorption spectroscopy (LITR-XAS) and femtosecond transient absorption have been rather fruitful since they have allowed us to firmly ground the indirect proofs of the molecular rearrangements following light absorption that had accumulated in the past 20 years. A substantial breakthrough towards highly emissive Cu(I) coordination compounds is constituted by heteroleptic Cu(I) complexes containing both N- and P-coordinating ligands ([Cu(NN)(PP)]+) which may exhibit luminescence quantum yields close to 30% in deaerated CH2Cl2 solution and have been successfully employed as active materials in OLED and LEC optoelectronic devices. Also copper clusters may exhibit luminescence bands of halide-to-metal charge transfer (XMCT) and/or cluster centered (CC) character and they are briefly reviewed along with miscellaneous Cu(I) compounds that recently appeared in the literature, which show luminescence bands ranging from the blue to the red spectral region.

Photochemistry and Photophysics of Coordination Compounds: Copper

Synthesis of CuO nanorods and their catalytic activity in the thermal decomposition of ammonium perchlorate

One-dimensional α-MnO2: Trapping chemistry of tunnel structures, structural stability, and magnetic transitions

The nature of room-temperature ferromagnetism in diluted magnetic semiconductors, ZnO:M (M is Ni, Co, Fe, etc.), remains in debate, most likely because previous theoretical and experimental studies have excluded the magnetic contribution from secondary phases of transition metal oxide nanocrystals including NiO and CoO. In this work, the authors initiated a study on NiO nanocrystals that demonstrated room-temperature ferromagnetic behavior with relatively large coercive forces, in apparent contradiction to the previous conjectures in the literature. With size reduction, NiO nanocrystals showed an abnormal magnetic crossover, which is closely related to weakened superexchange interactions in their multisublattices.

Magnetic crossover of NiO nanocrystals at room temperature

A family of copper coordination polymers containing different N-heterocyclic ligands, namely [Cu(CN)(dmpyz)]n (1),[Cu2(CN)2(imz)]n (2), [Cu3(CN)(trz)2]n (3), [Cu6(CN)6(dmtrz)3]n(4), [Cu2(CN)(5-metta)]n (5), [Cu2(CN)(5-phtta)]n (6), and {[Cu6(CN)6(dmtrz)]2[Cu2(CN)2(dmtrz)2]}n (7) has been prepared and structurally characterized by X-ray crystallography. The crystal structures of 1 and 2 are 1D chain frameworks. Compound 3 is a twofold interpenetrating 2D supramolecular framework in which the cyanide groups act as bridging ligands to link the copper centers into an unusual bilayer motif with large channels. Compounds 4–6 all possess 3D networks. Compound 4 is constructed by two parts: 2D rectangular-grid layers and {Cu2(CN)2(dmtrz)2} building blocks. Compound 5 is built up by X-shaped chains that connect each other in an ABAB arrangement to generate the3D network. The structure of 6 is a 3D network includingone-dimensional square-grid channels, with a shortest Cu2···Cu2A (A: –x + 1, –y + 1, –z) distance of about 2.347(1) A. Compound 7 features a peculiar 3D + 1D network in which 1D guest metal-organic polymer chains are filled in an unusual 3D architecture constructed by double helical host tubes. Compounds 1–7 show a systematic variation in dimensionality from 1D to 3D to 3D + 1D. The luminescence properties of these compounds have been also studied. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

A Series of One‐ to Three‐Dimensional Copper Coordination Polymers Based on N‐Heterocyclic Ligands

Six inorganic−organic compounds based on [MoxOy]n- chains, [Ag2(quinoxaline)2Mo4O13] (1), [Cu2(DMPz)2Mo4O13] (2) (DMPz = 2,5-dimethylpyrazine), [Cu2(4-PBIM)2Mo4O13] (3) [4-PBIM = 2-(4-pyridyl)benzimidazole], [Cu(OPBIM)(H2O) Mo3O10]·H2O (4) [OPBIM = 2-(2-ol-3-pyridinio)benzimidazole], [Co(3-HPBIM)2 (H2O)2Mo6O20] (5) [3-HPBIM = 2-(3-pyridyl)benzimidazolium], [Ni(3-HPBIM)2(H2O)2Mo6O20] (6), have been hydrothermally synthesized and characterized by single-crystal X-ray diffraction. Compounds 1 and 2 represent the first two examples of three-dimensional frameworks constructed from [Mo8O26]n4n- anion chains integrated by M−L polymeric cation chains. Compounds 3 and 4 reveal the peripheral decorated [Mo8O26]n4n- and [Mo3O10]n2n- one-dimensional chains, respectively. The isostructural compounds 5 and 6 feature two-dimensional networks formed from [Mo3O10]2n4n- infinite chains linked by [Co(3-HPBIM)2]4+ fragments. The molybdate chains in compounds 1−3 and 4−6 represent three isomeric forms of [Mo8O26]n4n- and two ...

Li-Juan Chen

Papers

Synthesis of CuO nanorods and their catalytic activity in the thermal decomposition of ammonium perchlorate

One-dimensional α-MnO2: Trapping chemistry of tunnel structures, structural stability, and magnetic transitions

Magnetic crossover of NiO nanocrystals at room temperature

A Series of One‐ to Three‐Dimensional Copper Coordination Polymers Based on N‐Heterocyclic Ligands

A Series of Inorganic−Organic Hybrid Composite Solids Based on Molybdenum Oxide Chains