Metal–organic frameworks (MOFs) are a unique class of crystalline solids comprised of metal cations (or metal clusters) and organic ligands that have shown promise for a wide variety of applications Over the past 15 years, research and development of these materials have become one of the most intensely and extensively pursued areas A very interesting and well-investigated topic is their optical emission properties and related applications Several reviews have provided a comprehensive overview covering many aspects of the subject up to 2011 This review intends to provide an update of work published since then and focuses on the photoluminescence (PL) properties of MOFs and their possible utility in chemical and biological sensing and detection The spectrum of this review includes the origin of luminescence in MOFs, the advantages of luminescent MOF (LMOF) based sensors, general strategies in designing sensory materials, and examples of various applications in sensing and detection

Luminescent metal–organic frameworks for chemical sensing and explosive detection

Metal–organic frameworks (MOFs) or porous coordination polymers (PCPs) are open, crystalline supramolecular coordination architectures with porous facets. These chemically tailorable framework materials are the subject of intense and expansive research, and are particularly relevant in the fields of sensory materials and device engineering. As the subfield of MOF-based sensing has developed, many diverse chemical functionalities have been carefully and rationally implanted into the coordination nanospace of MOF materials. MOFs with widely varied fluorometric sensing properties have been developed using the design principles of crystal engineering and structure–property correlations, resulting in a large and rapidly growing body of literature. This work has led to advancements in a number of crucial sensing domains, including biomolecules, environmental toxins, explosives, ionic species, and many others. Furthermore, new classes of MOF sensory materials utilizing advanced signal transduction by devices based on MOF photonic crystals and thin films have been developed. This comprehensive review summarizes the topical developments in the field of luminescent MOF and MOF-based photonic crystals/thin film sensory materials.

Metal-organic frameworks: functional luminescent and photonic materials for sensing applications.

Luminescent sensors based on metal-organic frameworks

Among the recent developments in metal-organic frameworks (MOFs), porous layered coordination polymers (CPs) have garnered attention due to their modular nature and tunable structures. These factors enable a number of properties and applications, including gas and guest sorption, storage and separation of gases and small molecules, catalysis, luminescence, sensing, magnetism, and energy storage and conversion. Among MOFs, two-dimensional (2D) compounds are also known as 2D CPs or 2D MOFs. Since the discovery of graphene in 2004, 2D materials have also been widely studied. Several 2D MOFs are suitable for exfoliation as ultrathin nanosheets similar to graphene and other 2D materials, making these layered structures useful and unique for various technological applications. Furthermore, these layered structures have fascinating topological networks and entanglements. This review provides an overview of different aspects of 2D MOF layered architectures such as topology, interpenetration, structural transformations, properties, and applications.

Two-Dimensional Metal-Organic Framework Materials: Synthesis, Structures, Properties and Applications.

MOF based luminescence tuning and chemical/physical sensing

Reactions of CuX (X = Br−, I− or CN−) with various types of 2,2′-dipyridylamine (dpa) derivatives have been performed via a hydrothermal–solvothermal method and the products have been structurally characterized by X-ray crystallography. Four ligands with different coordination motifs were employed in the reactions, including angular N,N,N′,N′-tetra(2-pyridyl)-2,6-pyridinediamine (tppda); linear N,N,N′,N′-tetra(2-pyridyl)-1,4-phenylenediamine (tppa) and N,N,N′,N′-tetra(2-pyridyl)biphenyl-4,4′-diamine (tpbpa); and star-shaped tris-[4-(2,2′-dipyridylamino)-phenyl]amine (tdpa), which yielded eight copper(I) complexes exhibiting different stoichiometries of Cu–dpa and variable coordination modes of dpa. The compound [Cu2(tppda)(μ-I)2]n (1) forms a one dimensional (1D) coordination polymer exclusively through double μ2-I bridges, which arranges to two dimensional (2D) metal–organic frameworks (MOFs) via the face-to-face π⋯π stacking interactions from pyridyl rings. The compound [Cu6(tppa)(μ3-Br)6]n (2) forms a 2D network linked through multiple μ3-Br bridges. The compound [Cu2(tppa)(μ-CN)2]n (3) is also a 2D MOF containing 1D (CuCN)n chains. The compounds [Cu(tpbpa)Br]n (4) and [Cu4(tpbpa)2(μ-I)4]n (5) display two different 1D assemblies: a zig-zag chain for 4 and a linear structure for 5. The compound [Cu4(tpbpa)(μ-CN)4]n (6) shows a pseudo-4,82 topological net, while the compound [Cu8(tpbpa)(μ-CN)8]n·2nH2O (7) exhibits a three-dimensional (3D) framework containing a ⋯PM⋯ double helical structure, although both of them contain (CuCN)n chains. The compound [Cu2(tdpa)(μ-I)2]n (8) is a zig-zag chain based on the star-shaped molecule tpda, in which one of three dpa-arms is free of coordination to metal ions. All complexes exhibit luminescence in the solid state.

Yaowen Chen

Papers

Copper(I) coordination polymers of 2,2′-dipyridylamine derivatives: syntheses, structures, and luminescence

Self-assembled hetero-bimetallic sandwich with Ag–Ag bridging using a flexible two-arm ferrocene amide linker