We report the synthesis, structure, and photoluminescence properties of a new bismuth based luminescent metal-organic framework (LMOF). The framework is comprised of a 9-coordinated Bi3+ building unit and 4′, 4′, 4′′′′′, 4′′′′′-(ethene-1,1,2,2-tetrayl)tetrakis([1,1′-biphenyl]-4-carboxylic acid) (H4tcbpe) organic linker, which has strong yellow aggregation induced emission (AIE). The structure can be viewed as two interpenetrated 4,4-anionic nets that are stabilized by K+ ions forming one-dimensional helical inorganic chains by connecting bismuth nodes through shared oxygen bonds. The as-made LMOF has a bluish emission centered at 459 nm with an internal quantum yield of 57% when excited at 360 nm. The emission properties of the LMOF were found to be highly solvochromic with respect to DMF. Upon partial solvent removal, the framework undergoes significant red-shifting to a greenish emission centered at 500 nm. Complete removal of DMF results in additional red-shifting fluorescence coupled with structural changes. The resulting material has strong blue-excitable (455 nm) yellow emission centered at 553 nm, with a quantum yield of 74%, which is maintained after heating in air for 5 days at 90 °C. This is the second highest quantum yield value for blue-excited yellow emission among all reported LMOFs.

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.

Luminescent metal-organic frameworks (LMOFs) with diverse structural features and promising fluorescence-based applications have attracted wide attention in the past two decades. In this work, a LMOF with the formula [Ca₄(tcbpe-F)₂(H₂O)₃] (1, LMOF-411) has been constructed from calcium (Ca) and 1,1,2,2-tetrakis(4-(4-carboxyphenyl)phenyl)ethene (H₄tcbpe-F). Compound 1 features a three-dimensional framework with a 10-nodal net topology. Due to the relatively high hydration energy of Ca²⁺, compound 1 readily transforms into a new phase formulated as [Ca(H₂tcbpe-F)(H₂O)₂] (1') upon exposure to water. Combining experimental characterization and theoretical calculations, we elucidated the mechanism of H₂O-induced phase transition from 1 to 1'. Notably, the water induced phase transformation can be detected visibly from the change in luminescence, which originates from the fluorescent linker. Compound 1 emits green light (λ _em = 490 nm) under UV excitation, while compound 1' emits bright yellow light (λ _em = 550 nm) under blue excitation (450 nm). Compound 1' represents the first Ca based LMOF yellow phosphor and its luminescence quantum yield reaches 68%. It can be coated directly onto a commercial blue light-emitting-diode (LED) chip to fabricate a white LED (WLED).

Adsorptive separation by porous solids provides an energy-efficient alternative for the purification of important chemical species compared to energy-intensive distillations. Particularly, the separation of linear hexane isomers from its branched counterparts is crucial to produce premium grade gasoline with high research octane number (RON). Herein, we report the synthesis of a new, flexible zinc-based metal-organic framework, [Zn₅(μ₃-OH)₂(adtb)₂(H₂O)₅·5 DMA] (Zn-adtb), constructed from a butterfly shaped carboxylate linker with underlying (4,8)-connected scu topology capable of separating the C6 isomers nHEX, 3MP, and 23DMB. The sorbate-sorbent interactions and separation mechanisms were investigated and analyzed through in situ FTIR, solid state NMR measurements and computational modeling. These studies reveal that Zn-adtb discriminates the nHEX/3MP isomer pair through a kinetic separation mechanism and the nHEX/23DMB isomer pair through a molecular sieving mechanism. Column breakthrough measurements further demonstrate the efficient separation of linear nHEX from the mono- and dibranched isomers.

Fluorosis has been regarded as a worldwide disease that seriously diminishes the quality of life through skeletal embrittlement and hepatic damage. Effective detection and removal of fluorinated chemical species such as fluoride ions (F^-) and perfluorooctanoic acid (PFOA) from drinking water are of great importance for the sake of human health. Aiming to develop water-stable, highly selective and sensitive fluorine sensors, we have designed a new luminescent MOF In(tcpp) using a chromophore ligand 2,3,5,6-tetrakis(4-carboxyphenyl)pyrazine (H₄tcpp). In(tcpp) exhibits high sensitivity and selectivity for turn-on detection of F^- and turn-off detection of PFOA with a detection limit of 1.3 μg L^-1 and 19 μg L^-1, respectively. In(tcpp) also shows high recyclability and can be reused multiple times for F^- detection. The mechanisms of interaction between In(tcpp) and the analytes are investigated by several experiments and DFT calculations. These studies reveal insightful information concerning the nature of F^- and PFOA binding within the MOF structure. In addition, In(tcpp) also acts as an efficient adsorbent for the removal of F^- (36.7 mg g^-1) and PFOA (980.0 mg g^-1). It is the first material that is not only capable of switchable sensing of F^- and PFOA but also competent for removing the pollutants via different functional groups.