Three Robust Blue-Emitting Anionic Metal-Organic Frameworks with High Stability and Good Proton Conductivities.

Three anionic luminescent metal-organic frameworks (LMOFs; [M(tcbpe)(CH3)2NH2]·H2O; M = In3+, Eu3+, Gd3+; tcbpe = 4',4‴,4‴″,4‴‴'-(ethene-1,1,2,2-tetrayl)tetrakis[(1,1'-biphenyl)-4-carboxylic acid]) are synthesized by employing the tetraphenylethene core ligand H4tcbpe with M3+ ions. They stack in the similarly 4-fold-interpenetrated three-dimensional porous structure. All give blue emission when excited at 365 nm, with fluorescence quantum yields of 34.8% (MOF-In), 7.1% (MOF-Eu), and 28.1% (MOF-Gd). Somewhat surprisingly, these three complexes are extremely stable both in various solvents and across a broad pH range: MOF-In is stable between pH = 0 and 14, and MOF-Eu and MOF-Gd are stable between pH = 0 and 13. Additionally, they also show good proton conductivities of 2.29 × 10-5 S·cm-1 (MOF-In), 2.02 × 10-4 S·cm-1 (MOF-Eu), and 1.24 × 10-4 S·cm-1 (MOF-Gd) at high temperature under 98% relative humidity. To the best of our knowledge, this is the first reported LMOF series combining aggregation-induced emission behavior with good proton conductivities.

Rational design of a high-efficiency, multivariate metal-organic framework phosphor for white LED bulbs.

Developing rare-earth element (REE) free yellow phosphors that can be excited by 455 nm blue light will help to decrease the environmental impact of manufacturing energy efficient white light-emitting diodes (WLEDs), decrease their cost of production, and accelerate their adoption across the globe. Luminescent metal-organic frameworks (LMOFs) demonstrate strong potential for use as phosphor materials and have been investigated intensively in recent years. However, the majority are not suitable for the current WLED technology due to their lack of blue excitability. Therefore, designing highly efficient blue-excitable, yellow-emitting, REE free LMOFs is much needed. With an internal quantum yield of 76% at 455 nm excitation, LMOF-231 is the most efficient blue-excitable yellow-emitting LMOF phosphor reported to date. Spectroscopic studies suggest that this quantum yield could be further improved by narrowing the material's bandgap. Based on this information and guided by DFT calculations, we apply a ligand substitution strategy to produce a semi-fluorinated analogue of LMOF-231, LMOF-305. With an internal quantum yield of 88% (λ em = 550 nm) under 455 nm excitation, this LMOF sets a new record for luminescent efficiency in yellow-emitting, blue-excitable, REE free LMOF phosphors. Temperature-dependent and polarized photoluminescence (PL) studies have provided insight on the mechanism of emission and origin of the significant PL enhancement.

NanoPOP: Solution-Processable Fluorescent Porous Organic Polymer for Highly Sensitive, Selective, and Fast Naked Eye Detection of Mercury.

Fluorescence-based detection is one of the most efficient and cost-effective methods for detecting hazardous, aqueous Hg2+. We designed a fluorescent porous organic polymer (TPA-POP-TSC), with a "fluorophore" backbone and a thiosemicarbazide "receptor" for Hg2+-targeted sensing. Nanometer-sized TPA-POP-TSC spheres (nanoPOP) were synthesized under mini-emulsion conditions and showed excellent solution processability and dispersity in aqueous solution. The nanoPOP sensor exhibits exceptional sensitivity (Ksv = 1.01 × 106 M-1) and outstanding selectivity for Hg2+ over other ions with rapid response and full recyclability. Furthermore, the nanoPOP material can be easily coated onto a paper substrate to afford naked eye-based Hg2+-detecting test strips that are convenient, inexpensive, fast, highly sensitive, and reusable. Our design takes advantage of the efficient and selective capture of Hg2+ by thiosemicarbazides (binding energy = -29.84 kJ mol-1), which facilitates electron transfer from fluorophore to bound receptor, quenching the sensor's fluorescence.

A robust two-dimensional zirconium-based luminescent coordination polymer built on a V-shaped dicarboxylate ligand for vapor phase sensing of volatile organic compounds.

We report herein a new two-dimensional zirconium-based luminescent coordination polymer Zr6(sdba)4(µ3-O)4(µ3-OH)4(HCOO)2(OH)2(H2O)2 (1) [sdba = 4,4'-sulfonyldibenzoate] exhibiting selective fluorescence responses towards a variety of volatile organic compounds upon exposure in the vapor phase. Having a unique two-dimensional signal response towards aromatic molecules, including but not limited to nitroaromatic explosives, it is capable of identifying a diverse set of analytes. In addition, compound 1 shows its remarkably high sensitivity toward acetone vapors.

Sensing and capture of toxic and hazardous gases and vapors by metal-organic frameworks.

Toxic and hazardous chemical species are ubiquitous, predominantly emitted by anthropogenic activities, and pose serious risks to human health and the environment. Thus, the sensing and subsequent capture of these chemicals, especially in the gas or vapor phase, are of extreme importance. To this end, metal-organic frameworks have attracted significant interest, as their high porosity and wide tunability make them ideal for both applications. These tailorable framework materials are particularly promising for the specific sensing and capture of targeted chemicals, as they can be designed to fit a diverse range of required conditions. This review will discuss the advantages of metal-organic frameworks in the sensing and capture of harmful gases and vapors, as well as principles and strategies guiding the design of these materials. Recent progress in the luminescent detection of aromatic and aliphatic volatile organic compounds, toxic gases, and chemical warfare agents will be summarized, and the adsorptive removal of fluorocarbons/chlorofluorocarbons, volatile radioactive species, toxic industrial gases and chemical warfare agents will be discussed.

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

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.

Chromophore-Based Luminescent Metal-Organic Frameworks as Lighting Phosphors.

Energy-efficient solid-state-lighting (SSL) technologies are rapidly developing, but the lack of stable, high-performance rare-earth free phosphors may impede the growth of the SSL market. One possible alternative is organic phosphor materials, but these can suffer from lower quantum yields and thermal instability compared to rare-earth phosphors. However, if luminescent organic chromophores can be built into a rigid metal-organic framework, their quantum yields and thermal stability can be greatly improved. This Forum Article discusses the design of a group of such chromophore-based luminescent metal-organic frameworks with exceptionally high performance and rational control of the important parameters that influence their emission properties, including electronic structures of chromophore, coligands, metal ions, and guest molecules.

Effective Detection of Mycotoxins by a Highly Luminescent Metal-Organic Framework.

We designed and synthesized a new luminescent metal-organic framework (LMOF). LMOF-241 is highly porous and emits strong blue light with high efficiency. We demonstrate for the first time that very fast and extremely sensitive optical detection can be achieved, making use of the fluorescence quenching of an LMOF material. The compound is responsive to Aflatoxin B1 at parts per billion level, which makes it the best performing luminescence-based chemical sensor to date. We studied the electronic properties of LMOF-241 and selected mycotoxins, as well as the extent of mycotoxin-LMOF interactions, employing theoretical methods. Possible electron and energy transfer mechanisms are discussed.

A Family of Highly Efficient CuI-Based Lighting Phosphors Prepared by a Systematic, Bottom-up Synthetic Approach.

Copper(I) iodide (CuI)-based inorganic-organic hybrid materials in the general chemical formula of CuI(L) are well-known for their structural diversity and strong photoluminescence and are therefore considered promising candidates for a number of optical applications. In this work, we demonstrate a systematic, bottom-up precursor approach to developing a series of CuI(L) network structures built on CuI rhomboid dimers. These compounds combine strong luminescence due to the CuI inorganic modules and significantly enhanced thermal stability as a result of connecting individual building units into robust, extended networks. Examination of their optical properties reveals that these materials not only exhibit exceptionally high photoluminescence performance (with internal quantum yield up to 95%) but also that their emission energy and color are systematically tunable through modification of the organic component. Results from density functional theory calculations provide convincing correlations between these materials' crystal structures and chemical compositions and their optophysical properties. The advantages of cost-effective, solution-processable, easily scalable and fully controllable synthesis as well as high quantum efficiency with improved thermal stability, make this phosphor family a promising candidate for alternative, RE-free phosphors in general lighting and illumination. This solution-based precursor approach creates a new blueprint for the rational design and controlled synthesis of inorganic-organic hybrid materials.

Achieving exceptionally high luminescence quantum efficiency by immobilizing an AIE molecular chromophore into a metal-organic framework.

We design a new yellow phosphor with high quantum yield by immobilizing a preselected chromophore into a rigid framework. Coating a blue light-emitting diode (LED) with this compound readily generates white light with high luminous efficacy. The new yellow phosphor demonstrates great potential for use in phosphor-converted white LEDs.