Hai-Ping Wang

Ultrafast water sensing and thermal imaging by a metal-organic framework with switchable luminescence

A convenient, fast and selective water analysis method is highly desirable in industrial and detection processes. Here a robust microporous Zn-MOF (metal–organic framework, Zn(hpi2cf)(DMF)(H2O)) is assembled from a dual-emissive H2hpi2cf (5-(2-(5-fluoro-2-hydroxyphenyl)-4,5-bis(4-fluorophenyl)-1H-imidazol-1-yl)isophthalic acid) ligand that exhibits characteristic excited state intramolecular proton transfer (ESIPT). This Zn-MOF contains amphipathic micropores (<3 Å) and undergoes extremely facile single-crystal-to-single-crystal transformation driven by reversible removal/uptake of coordinating water molecules simply stimulated by dry gas blowing or gentle heating at 70 °C, manifesting an excellent example of dynamic reversible coordination behaviour. The interconversion between the hydrated and dehydrated phases can turn the ligand ESIPT process on or off, resulting in sensitive two-colour photoluminescence switching over cycles. Therefore, this Zn-MOF represents an excellent PL water-sensing material, showing a fast (on the order of seconds) and highly selective response to water on a molecular level. Furthermore, paper or in situ grown ZnO-based sensing films have been fabricated and applied in humidity sensing (RH<1%), detection of traces of water (<0.05% v/v) in various organic solvents, thermal imaging and as a thermometer.

Lanthanide homometallic and d–f heterometallic MOFs from the same tripodal ligand: structural comparison, one photon (OP) vs. two photon (TP) luminescence and selective guest adsorption behavior

In this paper, we report the design of a new functionalized tripodal ligand triCB-NTB (4,4′,4′′-(2,2′,2′′-nitrilotris(methylene)tris(1H-benzo[d]imidazole-2,1-diyl)tris(methylene))tribenzoic acid) and its assembly of Eu(III) homometallic or Zn(II)-Eu(III) heterometallic lanthanide-based metal–organic frameworks (MOFs). C3 symmetric Eu(III) center is achieved in the homometallic MOF, [Eu(triCB-NTB)]·DMAc·4H2O (1). The C3 axis of the three coordinated imino N atoms on the propeller-extended central triCB-NTB ligand coincides with the C3 axis that directs the three para-methyl carboxylic benzene arms on three surrounding ligands coordinating with the central Eu(III) simultaneously. Therefore, a (6, 3) pattern is formed in the framework with relatively large porosity. In the Zn-Eu heterometallic framework, [EuZn(triCB-NTB)(H2O)(Cl)2]·2DMAc·H2O (2), the N atoms on the triCB-NTB are coordinated with Zn(II) and the carboxylic O atoms are coordinated with Eu(III). A paddle-wheel linked Eu(III)2 cluster is formed and 1D loop-and-chain structure is obtained. Two ligands, two Zn(II) ions and two Eu(III)2 clusters constitute one box-like unit on the loop chain. Due to the non-inversion symmetry imposed on the central Eu(III) and the large polarizability of the ligand, both one photon (OP) luminescence based on the energy transfer from the ligand to Eu3+ and two photon (TP) luminescence based on the hypersensitive transition of the Eu3+ ions are observed in the two lanthanide-based MOFs. This satisfies the urgent needs of multi-mode luminescent lanthanide complex. Simultaneously, N2 gas and selective vapor adsorptions were also detected in the porous structure of complexes 1 and 2 due to their benzene-filled channels. The six-pointed-star like cavities in 1 can let the gas and vapor molecules go in and out smoothly subject to changes in the pressure, while the narrower and more irregular channels in 2 show irreversible adsorption behavior for benzene and cyclohexane vapor molecules in vacuum under room temperature.

Dynamic Spacer Installation for Multirole Metal–Organic Frameworks: A New Direction toward Multifunctional MOFs Achieving Ultrahigh Methane Storage Working Capacity

A robust Zr-MOF (LIFM-28) containing replaceable coordination sites for additional spacer installation has been employed to demonstrate a swing- or multirole strategy for multifunctional MOFs. Through reversible installation/uninstallation of two types of spacers with different lengths and variable functional groups, different tasks can be accomplished using the same parent MOF. An orthogonal optimizing method is applied with seven shorter (L1-7) and six longer (L8-13) spacers to tune the functionalities, achieving multipurpose switches among gas separation, catalysis, click reaction, luminescence, and particularly, ultrahigh methane storage working capacity at 5-80 bar and 298 K.

An Efficient Visible and Near-Infrared (NIR) Emitting Sm(III) Metal-Organic Framework (Sm-MOF) Sensitized by Excited-State Intramolecular Proton Transfer (ESIPT) Ligand.

We report herein an unprecedented example of a luminescent Sm(III) metal-organic framework (Sm-MOF), in which both the visible and near-infrared (NIR) emissions of Sm(3+) ions are able to be sensitized by an excited-state intramolecular proton transfer (ESIPT) ligand. Due to the solvent-mediated interchange between enol and keto excited states of the ligand and subsequent energy transfer rate to Sm(3+) ions, the luminescent decay lifetime of the Sm-MOF can be tuned in different solvent-grinding systems.

A naked eye colorimetric sensor for alcohol vapor discrimination and amplified spontaneous emission (ASE) from a highly fluorescent excited-state intramolecular proton transfer (ESIPT) molecule

A highly fluorescent HPI-based excited-state intramolecular proton transfer (ESIPT) molecule is designed and adopted as a naked-eye colorimetric sensor to distinguish methanol, ethanol and isopropanol vapors. Amplified spontaneous emission was also observed for the C1-form single crystal of the molecule attributed to its intrinsic four-level energy states.

Rigidifying Effect of Metal–Organic Frameworks: Protect the Conformation, Packing Mode, and Blue Fluorescence of a Soft Piezofluorochromic Compound under Pressures up to 8 MPa

We demonstrate that the conformation, packing mode, and blue fluorescence of a soft piezofluorochromic compound can be preserved by structurally fixing it into a solid calcium metal-organic framework (Ca-MOF, LIFM-40), which can survive pressures up to 8 MPa. DFT calculations have been combined with experimental results to indicate that the ligands adopting a specific conformation and packing without π···π interactions are the reasons for its rigidified blue emission.

PMMA-copolymerized color tunable and pure white-light emitting Eu3+–Tb3+ containing Ln-metallopolymers

By anchoring lanthanide coordination monomers onto a PMMA polymer backbone via a pre-designed vinylbenzyl-substituted NTB-type ligand, we succeeded in the fabrication of homo or hetero Ln-metallopolymers that can emit tunable and designable multicoloured photoluminescence as well as white light emission. Copolymerization results in the fine-tuning of the energy state of the ligand in the metallopolymer compared with that in the coordination monomer, thereby changing the energy transfer efficiency to Eu3+ and Tb3+ centers in opposite ways. And further designing of hetero-lanthanide metallopolymers leads to additional energy transfer between Eu3+ and Tb3+, facilitating the generation of pure white light emission. In general, the facile and controllable synthesis procedure, versatile and reproducible combination of lanthanides, ligands and polymer backbones, and relatively high white light emitting luminous efficiency (>5%) prove this method to be promising in future lighting WPLED applications.

A Robust Metal–Organic Framework Combining Open Metal Sites and Polar Groups for Methane Purification and CO2/Fluorocarbon Capture

A 3D porous perchlorinated metal-organic framework (MOF), LIFM-26, featuring dual functionality, that is, functional polar groups and open metal sites, has been synthesized using perchlorinated linear dicarboxylate to link trigonal prismatic Fe3 (μ3 -O) units. LIFM-26 exhibits good thermal and chemical stability, and possesses high porosity with a BET surface area of 1513 m2  g-1 , compared with isoreticular MOF-235 and Fe3 O(F4 BDC)3 (H2 O)3 (F4 BDC=2,3,5,6-tetrafluorobenzene-1,4-dicarboxylate). Most strikingly, LIFM-26 features good gas sorption/separation performance at 298 K and 1 atm with IAST selectivity values reaching up to 36, 93, 23, 11, 46, and 202 for CO2 /CH4 , CO2 /N2 , C2 H4 /CH4 , C2 H6 /CH4 , C3 H8 /CH4 , and R22/N2 (R22=CHClF2 ), respectively, showing potential for use in biogas/natural gas purification and CO2 /R22 capture.

Observation of cascade f → d → f energy transfer in sensitizing near-infrared (NIR) lanthanide complexes containing the Ru(II) polypyridine metalloligand

Distinguishable d → f or f → d energy transfer processes depending on lanthanide ions are observed in isomorphous d–f heterometallic complexes containing the Ru(II) metalloligand (LRu), which lead to sensitized NIR emission (for Nd3+ and Yb3+) or enhanced red emission of LRu (for Eu3+ and Tb3+), and represent the first eye-detectable evidence of f → d energy transfer processes in Ln–Ru bimetallic complexes. Based on the systematic luminescence and decay lifetime study, cascade f → d → f energy transfer has been proposed in Ln1–Ru–Ln2 trimetallic systems for improved NIR sensitization.

Face-Capped M(4) L4 Tetrahedral Metal-Organic Cage: Iodine Capture and Release, Ion Exchange, and Electrical Conductivity.

An M(4) L4 type metal-organic cage (MOC-19) has been synthesized from the one-pot reaction of tri(pyridinylmethylene)phenylbenzeneamine (TPBA) with hydrated Zn(ClO4 )2 under mild conditions and characterized by single-crystal X-Ray diffraction. Iodine capture studies show that the porous crystals of MOC-19 exhibit a versatile behavior to accumulate iodine species not only in vapor (for I2 ) but also in solution (for I2 and I3 (-) ), and anion-exchange experiments indicate the capacity to extract IO3 (-) anions from aqueous solution. Enrichment of iodine species from KI/I2 aqueous solution proceeds facilely, revealing a pseudo-second-order kinetics of I3 (-) adsorption. Furthermore, the electrical conductivity of MOC-19 single crystals could be significantly altered by I2 inclusion.