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.

Yuming Yang,†,§ Qiang Zhao,‡,§ Wei Feng,† and Fuyou Li*,† †Department of Chemistry and State Key Laboratory of Molecular Engineering of Polymers and Institutes of Biomedical Sciences, Fudan University, Shanghai 200433, P. R. China ‡Key Laboratory for Organic Electronics and Information Displays (KLOEID) and Institute of Advanced Materials (IAM), Nanjing University of Posts and Telecommunications, Nanjing 210046, P. R. China.

Luminescent chemodosimeters for bioimaging.

Exposure to even very low levels of lead, cadmium, and mercury ions is known to cause neurological, reproductive, cardiovascular, and developmental disorders, which are more serious problems for children particularly. Accordingly, great efforts have been devoted to the development of fluorescent and colorimetric sensors, which can selectively detect lead, cadmium, and mercury ions. In this critical review, the fluorescent and colorimetric sensors are classified according to their receptors into several categories, including small molecule based sensors, calixarene based chemosensors, BODIPY based chemosensors, polymer based chemosensors, DNA functionalized sensing systems, protein based sensing systems and nanoparticle based sensing systems (197 references).

Fluorescent and colorimetric sensors for detection of lead, cadmium, and mercury ions

This critical review covers the advances made using the 4-bora-3a,4a-diaza-s-indacene (BODIPY) scaffold as a fluorophore in the design, synthesis and application of fluorescent indicators for pH, metal ions, anions, biomolecules, reactive oxygen species, reactive nitrogen species, redox potential, chemical reactions and various physical phenomena. The sections of the review describing the criteria for rational design of fluorescent indicators and the mathematical expressions for analyzing spectrophotometric and fluorometric titrations are applicable to all fluorescent probes (206 references).

Fluorescent indicators based on BODIPY

A Ratiometric Fluorescent Probe Based on FRET for Imaging Hg2+ Ions in Living Cells

The manufacture of new full-color displays is one of the main tasks in flat-panel display systems and lighting technology. Different applications place different demands on emitted light: in some cases a white-light source is needed, and in others pure colors are necessary. Thus, white emission should ideally be composed of three (blue, green, and red) or two (blue and yellow) primary colors and cover the whole visible range from 400 to 700 nm, and the emitter should have the ability to emit the primary colors simultaneously with equal intensities to produce white light and the pure colors separately in a tunable way. Considerable interest exists for such color-tunable materials, which can be used to define or modify environments, moods, and brands. Traditional methods of such white light generation typically rely on mixing various primary colors from different emitting materials. An alternative approach for the generation of efficient (white) light sources is to use a single-component emitter, which can have advantages such as greater stability, better reproducibility, no phase separation, and simpler fabrication processes. 8] Although a few materials show white-light emission as a single-emitting component, none has been reported to produce well-separated blue, green, and red emissions beside white light. Since energy transfer typically quenches one or more of the emission pathways and thereby restricts the transitions that define the output spectrum, the design of color tunable single-component emitters requires readily tailorable different fluorophores and fine-tuning of the energy-transfer processes between the different fluorophores. On the other hand, lanthanide-containing materials, which exhibit excellent sharp-emission luminescence properties with suitable sensitization, have attracted considerable interest and been effectively used in designing white-emitting nanoparticles. With judiciously chosen red(Eu, Pr, Sm), green(Tb, Er), and blue-emissive (Tm , Ce, Dy) ions doped in an suitable host, it is possible to obtain phosphors which emit across the entire visible spectrum with high color purity. Specifically, an Eu-containing singlecomponent complex has been reported to offer white-light emission in a carefully designed system which only allows partial energy transfer between the sensitizing fluorophore and the Eu center. Herein we report the design and synthesis of a new fluorophore that exhibits tunable emission of three primary colors (blue, green, and red) and white light, by combining an Eu moiety as the origin of red light with an organic ligand that comprises a blue-emitting coumarin fluorophore and a green-emitting Rhodamine 6G fluorophore. Coumarin-Rhodamine CR1 was synthesized by reaction of 7-diethylamino-2-oxo-2H-chromen-3-carboxylic chloride and N-(Rhodamine-6G)lactamethylenediamine and recrystallized from ethanol as yellow crystals. Single-crystal X-ray structural analysis confirms the coexistence of two fluorophores in CR1 (Supporting Information Figure S1), whereby the Rhodamine 6G moiety is in a luminescence-inactive ringclosed tautomeric form. Europium compound CR1-Eu (1) was prepared by refluxing ligand CR1 and [Eu(tta)3] in THF (tta = 1,1,1-trifluoro-3-(2-thenoyl)acetone) and purified by recrystallization as an amorphous yellow powder. Elemental analysis and H NMR spectroscopic characterization suggest the chemical formula [Eu(tta)2(CR1)2](tta) for 1 (Figure 1).

A Color‐Tunable Europium Complex Emitting Three Primary Colors and White Light

Cu2+-based metal-organic framework (Cu−TCA) (H3TCA = tricarboxytriphenyl amine) having triphenylamine emitters was assembled and structurally characterized. Cu−TCA features a three-dimensional porous structure consolidated by the well-established Cu2(O2CR)4 paddlewheel units with volume of the cavities approximately 4000 nm3. Having paramagnetic Cu2+ ions to quench the luminescence of triphenylamine, Cu−TCA only exhibited very weak emission at 430 nm; upon the addition of NO up to 0.1 mM, the luminescence was recovered directly and provided about 700-fold fluorescent enhancement. The luminescence detection exhibited high selectivity – other reactive species present in biological systems, including H2O2, NO3−, NO2−, ONOO−, ClO− and 1O2, did not interfere with the NO detection. The brightness of the emission of Cu−TCA also led to its successful application in the biological imaging of NO in living cells. As a comparison, lanthanide metal-organic framework Eu−TCA having triphenylamine emitters and characteristic europium emitters was also assembled. Eu−TCA exhibited ratiometric fluorescent responses towards NO with the europium luminescence maintained as the internal standard and the triphenylamine emission exhibited more than 1000-fold enhancement.

Luminescent Metal‐Organic Frameworks for Selectively Sensing Nitric Oxide in an Aqueous Solution and in Living Cells

Highly efficient energy transfer in the light harvesting system composed of three kinds of boron-dipyrromethene derivatives.

An inorganic-organic silica material (SBA-P2), prepared by immobilization of the 1,8-naphthalimide-based receptor P2 within the channels of the mesoporous silica material SBA-15, is characterized by transmission electron microscopy and several spectroscopic methods. SBA-P2 features a high affinity Cu 2+ -specific fluorescence response in aqueous solution with a detection limit for Cu 2+ of ca. 0.65 ppb (10 × 10 ―9 M) under optimized conditions. It can extract Cu 2+ from the solution with only trace amounts remaining. Through isolating of the toxic ions within the mesopores of the silica, SBA-P2 has the potential to work as a toxicide for Cu 2+ in living systems. The fluorogenical responses are reversible and do not vary over a broad (4.0 to 9.0) pH range suitable for application under physiological conditions. The fluorescence responses of Cu 2+ in vitro (human breast cancer cells) and in vivo (five-day-old zebrafish) demonstrate the possibility offurther application in biology.

Multifunctional Mesoporous Silica Material Used for Detection and Adsorption of Cu2+ in Aqueous Solution and Biological Applications in vitro and in vivo

Xiaolin Zhang

Papers

A Ratiometric Fluorescent Probe Based on FRET for Imaging Hg2+ Ions in Living Cells

A Color‐Tunable Europium Complex Emitting Three Primary Colors and White Light

Luminescent Metal‐Organic Frameworks for Selectively Sensing Nitric Oxide in an Aqueous Solution and in Living Cells

Highly efficient energy transfer in the light harvesting system composed of three kinds of boron-dipyrromethene derivatives.

Multifunctional Mesoporous Silica Material Used for Detection and Adsorption of Cu2+ in Aqueous Solution and Biological Applications in vitro and in vivo