Coordination polymers for energy transfer: Preparations, properties, sensing applications, and perspectives

The influence of structural isomerism on fluorescence and organic dye selective adsorption in two complexes based on flexible ligands

Based on Cd(NO₃)₂·4H₂O and 4,4'-((5-carboxy-1,3-phenylene)bis(oxy))dibenzoic acid (H₃cpbda), two isomeric coordination polymers, {[Cd_1.5(cpbda)(bpa)(H₂O)₂]·1.5H₂O}_n (1), [Cd(H₂cpbda)₂(bpa)_0.5(H₂O)]_n (2), were synthesized by using different solvent-systems. The complexes were characterized by single-crystal X-ray diffraction, IR spectroscopy, powder X-ray diffraction, and thermogravimetric analysis. Owing to the obvious structural difference between the two isomeric complexes, the further fluorescence sensing and dye selection and adsorption were investigated. The 3D tight stacking structure of 1 strengthened the fluorescence emission and the loose 2D layer structure of 2 generated the active selection and adsorption of the Malachite Green Oxalate (MGO) dye.

A One-Dimensional Coordination Polymer Containing Cyclic [Ag4] Clusters Supported by a Hybrid Pyridine and Thioether Functionalized 1,2,3-Triazole

A pyridine and thioether co-supported triazole ligand L (L = 2-((4-(3-(cyclopentylthio)propyl)-1H-1,2,3-triazol-1-yl)methyl)pyridine) has been synthesized using the CuAAC click reaction. This ligand supports the formation of a thermally stable, one-dimensional coordination polymer [L2Ag4]n·4n(BF4) (1) possessing a cationic polymeric structure with [Ag4] metallomacrocycles, in which the ligand L displays chelate/bridging coordination modes using all four potential donors of nitrogen (N) and thioether (S). The dominant direction of the prism crystals of 1 aligns with the propagation of the chain in the lattice.

Photochemistry and photophysics of MOFs: steps towards MOF-based sensing enhancements

In combination with porosity and tunability, light harvesting, energy transfer, and photocatalysis, are facets crucial for engineering of MOF-based sensors.

Sonochemical synthesis of polyoxometalate based of ionic crystal nanostructure: A photocatalyst for degradation of 2,4-dichlorophenol

Single crystals of new polyoxometalate based ionic crystal [Fe(phen)₃]₂[SiW₁₂O₄₀]·3DMF (IC-Fe), (phen=1,10-phenanthroline, DMF=N,N-dimethylformamide) and their nanoparticles (IC-Fe-NPs) have been synthesized via self-assembly of constituent ions and sonochemical reaction, respectively. All materials have been characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), thermal gravimetric (TG), powder X-ray diffraction (PXRD), FT-IR spectroscopy and elemental analyses. Effect of sonication conditions on size and morphology of IC-Fe was investigated including time, concentrations of initial reagents and power of irradiation. Further studies have shown that IC-Fe is not only active in photocatalytic degradation of 2,4-dichlorophenol under visible light irradiation, but also is very stable in the various solvents and it can be easily separated and reused for cycles of reaction.

Erbium(iii)-based metal–organic frameworks with tunable upconversion emissions

A series of Ln-MOFs with varied upconversion luminescence emissions were obtained, which follows an excited state absorption mechanism.

Joining of trinuclear (CuL)2M (M = MnII and CdII) nodes by 1,3- and 1,4-benzenedicarboxylate linkers: positional isomeric effect on co-crystallization

Among the four one-dimensional coordination polymers obtained by joining (CuL)₂M (M = Mn^II and Cd^II) nodes with 1,3- and 1,4-benzenedicarboxylate linkers, the chains derived from 1,3-benzenedicarboxylate are co-crystallized with dimeric Cu^II units.

Neutral two-dimensional organometallic–organic hybrid polymers based on pentaphosphaferrocene, bipyridyl linkers and CuCl

The reaction of the P_n ligand complex [Cp*Fe(η⁵-P₅)] (1: Cp* = η⁵-C₅Me₅) with CuCl in the presence of 4,4′-bipyridine or 1,2-di(4-pyridyl)ethylene leads to the formation of three unprecedented neutral 2D organometallic–organic hybrid networks.

Tuning the dimensionality of organometallic–organic hybrid polymers assembled from [Cp2Mo2(CO)4(η2-P2)], bipyridyl linkers and AgI ions

The first of its kind study of the effect of the organic linker length and reaction temperature on aggregation reactions leading to organometallic–organic hybrid polymers is presented.

2D and 3D lanthanide metal–organic frameworks constructed from three benzenedicarboxylate ligands: synthesis, structure and luminescent properties

Nineteen Ln-MOFs with four different crystal structures were prepared and the luminescence was studied.

Rare earth phosphors based on spherical infinite coordination polymers

New spherical lanthanide infinite coordination polymer (ICP)-based phosphors were obtained and show great potential for light-emitting applications.

Tuning structures and emissive properties in a series of Zn(ii) and Cd(ii) coordination polymers containing dicarboxylic acids and nicotinamide pillars

The influence of the metal, ligand, and solvent on structures and emission properties was monitored.

Tunable photo-luminescence behaviors of macrocycle-containing polymer networks in the solid-state

Two porous polymers were synthesized from tetraphenylethylene (TPE) crosslinked β-cyclodextrins (β-CD) and sulfonatocalix[4]arene (SC4A).

Photonic functional metal–organic frameworks

The recent progress in photonic MOFs for luminescence sensing, white-light emission, photocatalysis, nonlinear optics, lasing devices, and biomedicine is summarized.

Anomalous thermally-activated NIR emission of ESIPT modulated Nd-complexes for optical fiber sensing devices

Highly sensitized NIR emission was modulated using an ESIPT ligand in a Nd-complex, to achieve abnormal NIR enhancement with temperature increasing from 77 to 300 K for the first time.

Construction of two Zn(ii)/Cd(ii) multifunctional coordination polymers with mixed ligands for catalytic and sensing properties

Two Zn(ii)/Cd(ii) coordination polymers with different networks were constructed with mixed ligands. The former compound shows high catalytic activity for Knoevenagel condensation, and the latter compound can selectively recognize l-cysteine through the luminescence quenching effect.

Four Mixed-Ligand Zn(II) Three-Dimensional Metal-Organic Frameworks: Synthesis, Structural Diversity, and Photoluminescent Property

Assemblies of four three-dimensional (3D) mixed-ligand coordination polymers (CPs) having formulas, {[Zn₂(bdc)₂(4-bpdh)]·C₂H₅OH·2H₂O}_n (1), [Zn(bdc)(4-bpdh)]_n (2), {[Zn₂(bdc)₂(4-bpdh)₂]·(4-bpdh)}_n (3), and {[Zn(bdc)(4-bpdh)]·C₂H₅OH}_n (4) (bdc²⁻ = dianion of 1,4-benzenedicarboxylic acid, 4-bpdh = 2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene) have been synthesized and structurally characterized by single-crystal X-ray diffraction method. Structural determination reveals that the coordination numbers (geometry) of Zn(II) ions in 1, 2, 3, and 4 are five (distorted square-pyramidal (SP)), six (distorted octahedral (O_h)), five (trigonal-bipyramidal (TBP)), and four (tetrahedral (T_d)), respectively, and are bridged by 4-bpdh with bis-monodentate coordination mode and bdc²⁻ ligands with bis-bidentate in 1, chelating/bidentate in 2, bis-monodentate and bis-bidentate in 3, and bis-monodentate in 4, to generate two-fold interpenetrating 3D cube-like metal-organic framework (MOF) with pcu topology, non-interpenetrating 3D MOF, two-fold interpenetrating 3D rectangular-box-like MOF with pcu topology and five-fold interpenetrating diamondoid-like MOF with dia topology, respectively. These different intriguing architectures indicate that the coordination numbers and geometries of Zn(II) ions, coordination modes of bdc²⁻ ligand, and guest molecules play important roles in the construction of MOFs and the formation of the structural topologies and interpenetrations. Thermal stabilities, and photoluminescence study of 1–4 were also studied in detail. The complexes exhibit ligands based photoluminescence properties at room temperature.

Preorganized AgI Bimetallic Precursor with Labile Diphosphorus Ligands for a Programmed Synthesis of Organometallic-Organic Hybrid Polymers

An AgI dimer capped with labile organometallic diphosphorus ligands [Cp2 Mo2 (CO)4 (η2 -P2 )] (Cp=C5 H5 ) acts as a highly pre-organized molecular precursor to direct the construction of 1D or 2D, and 3D organometallic-organic hybrid coordination polymers upon reaction with ditopic pyridine-based linkers. The formation of the supramolecular aggregates can be controlled by the stoichiometry of the organic molecules, and the mechanism is supported by DFT calculations.

Anion-directed assembly of lanthanide coordination polymers with SMMs properties based on a dihydrazone ligand

Four new Ln(III)-based coordination polymers (CPs), [Eu(HL)Cl2(DMF)2]·(H2L) (1), [Dy(HL)Cl2(DMF)2]·(H2L) (2), [Er(HL)Cl2(DMF)(CH3OH)]·(DMF) (3) and [Yb(HL)Cl2(DMF)(H2O)]·(DMF) (4) (H2L=2,6-bis[(3-methoxysalicylidene)hydrazinocarbonyl]pyridine) have been synthesized through the reaction of Ln(III) chloride and H2L by using the vapour diffusion method. Interestingly, Cl− as a template agent plays a vital role in the formation of the target complexes. Single-crystal X-ray diffraction studies indicate that 1 and 2 are isostructural and crystallize in triclinic space group P1̅, while complexes 3 and 4 are isostructural and crystallize in monoclinic space group C2/c. Variable temperature magnetization measurement (χ M T–T) demonstrates possible antiferromagnetic interactions in complex 2. Alternating-current (ac) susceptibility measurement furthermore indicated frequency dependence for both the in-phase (χ′) and out-of-phase (χ″) components in 2, suggesting that there is a slow relaxation behavior of the magnetization, which is typical of single-molecule magnets (SMMs). This is the first time that Ln(III) CPs based on such a dihydrazone ligand has been reported so far.

Semiconducting Coordination Polymers Based on the Predesigned Ternary Te-Fe-Cu Carbonyl Cluster and Conjugation-Interrupted Dipyridyl Linkers

A series of semiconducting cluster-incorporated Cu-based coordination polymers, namely, 1D zigzag polymers [{TeFe₃ (CO)₉ Cu₂ }(L)]_n (L=1,2-bis(4-pyridyl)ethane (bpea), 1; L=1,2-bis(4-pyridyl)ethylene (bpee), 5), 2D honeycomb-like polymers [{TeFe₃ (CO)₉ Cu}Cu(L)_2.5 ]_n (L=bpea, 2; L=bpee, 6), and 2D wave-like cation-anion polymer [{Cu₂ (L)₄ }({TeFe₃ (CO)₉ Cu}₂ (L))]_n (L=1,3-bis(4-pyridyl)propane (bpp), 4), as well as the macrocycle [{TeFe₃ (CO)₉ Cu₂ }₂ (bpp)₂ ] (3) have been quantitatively synthesized via the liquid-assisted grinding from the pre-designed cluster [TeFe₃ (CO)₉ Cu₂ (MeCN)₂ ] with conjugated or conjugation-interrupted dipyridyl linkers. Notably, the most conjugation-interrupted bpp-bridged polymer 4 exhibited extraordinary semiconducting characteristics with an ultra-narrow bandgap of 1.43 eV and a DC conductivity of 1.5×10^-2 Ω^-1  cm^-1 , which violates our knowledge, mainly attributed to the through-space electron transport via non-classical C-H⋅⋅⋅O(carbonyl) hydrogen bonds and aromatic C-H⋅⋅⋅π interactions. The incorporated Te-Fe-CO anions can not only provide numerous possibilities for secondary interactions within these Cu-based polymers but also serve as a redox-active coordination ligand to promote their conductivities. The intriguing structure-property relationships were studied by X-ray and DFT analyses and further demonstrated by significant change in the oxidation state of Cu atoms by XPS and Cu K-edge XANES.

Ratiometric fluorescence detection of superoxide anion based on AuNPs-BSA@Tb/GMP nanoscale coordination polymers

A novel ratiometric fluorescence nanosensor for superoxide anion (O₂^•- ) detection was designed with gold nanoparticles-bovine serum albumin (AuNPs-BSA)@terbium/guanosine monophosphate disodium (Tb/GMP) nanoscale coordination polymers (NCPs) (AuNPs-BSA@Tb/GMP NCPs). The abundant hydroxyl and amino groups of AuNPs-BSA acted as binding points for the self-assembly of Tb³⁺ and GMP to form core-shell AuNPs-BSA@Tb/GMP NCP nanosensors. The obtained probe exhibited the characteristic fluorescence emission of both AuNPs-BSA and Tb/GMP NCPs. The AuNPs-BSA not only acted as a template to accelerate the growth of Tb/GMP NCPs, but also could be used as the reference fluorescence for the detection of O₂^•- . The resulting AuNPs-BSA@Tb/GMP NCP ratiometric fluorescence nanosensor for the detection of O₂^•- demonstrated high sensitivity and selectivity with a wide linear response range (14 nM-10 μM) and a low detection limit (4.7 nM).

Raman Under Water - Nonlinear and Nearfield Approaches for Electrochemical Surface Science

Electrochemistry is re-gaining attention among scientists because the complex interplay between electronic and chemical interfacial processes lies at the bottom of a broad range of important research disciplines like alternative energy conversion or green catalysis and synthesis. While rapid progress has been made in recent years regarding novel technological applications, the community increasingly recognizes that the understanding of the molecular processes that govern macroscopic device properties is still rather limited - which hinders a systematic and more complete exploration of novel material and functionality space. Here, we discuss advanced Raman spectroscopies as valuable analysis tools for electrochemists. The chemical nature of a material and its interaction with the environment is contained in the label-free vibrational fingerprint over a broad energy range so that organic species, solid-state materials, and hybrids thereof can be investigated alike. For surface studies, the inherently small Raman scattering cross sections can be overcome with advanced nonlinear or nearfield-based approaches that provide signal enhancements between three and seven orders of magnitude, sufficient to detect few scatterers in nano-confined spaces or adsorbate (sub)monolayers. Our article highlights how advanced Raman techniques with extreme chemical, spatial and temporal resolution constitute valuable alternative surface analysis tools and provide otherwise inaccessible information about complex interfacial (electro)chemical processes.

A series of multifunctional coordination polymers based on terpyridine and zinc halide: second-harmonic generation and two-photon absorption properties and intracellular imaging

How can imaging be improved? Coordination polymers (CPs) show fascinating potential in optoelectronic optics but limited potential in bioimaging. Without doubt, it was very meaningful when CPs were first used in second-harmonic generation (SHG) imaging. Herein, through reasonable design and synthesis, a series of nonlinear optical CPs bearing very good one-photon excited fluorescence (OPEF), two-photon excited fluorescence (TPEF) and very strong SHG properties has been presented. Further study demonstrated that the nanoscale CPs show very strong SHG signals which have been applied in the three-dimensional imaging of thick block tissue with higher spatial resolution through simultaneous multichannel nonlinear optical (NLO) imaging technology. After simple encapsulation by polymeric micelles, the nanoscale CPs were successfully applied in SHG bio-imaging within the living cells. This finding throws light on the design of nanoscale NLO CPs and offers a simple avenue to develop novel effective exogenous SHG imaging agents.

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.

Nanoscale metal-organic frameworks coated with poly(vinyl alcohol) for ratiometric peroxynitrite sensing through FRET

This work describes a facile yet powerful approach to energy-transfer NMOF (nanoscale metal–organic framework) fabrication for ratiometric peroxynitrite (ONOO^–) sensing.

This work describes a facile yet powerful approach to energy-transfer NMOF (nanoscale metal–organic framework) fabrication for ratiometric peroxynitrite (ONOO^–) sensing. Poly(vinyl alcohol) (PVA) is chosen to organize the energy donor (NMOF) and acceptor (molecular probes). PVA can conveniently graft onto the NMOF surface and bind to the molecular probes bearing the arylboronic acid group through multiple weak coordination interactions. Due to efficient Förster resonance energy transfer (FRET), the bright blue fluorescence of the NMOF is quenched while the green or red emission from the acceptor is enhanced. Upon reacting with ONOO^–, the ONOO^– sensors depart from the NMOF and the FRET is interrupted and the fluorescence of the NMOF recovered. Based on this strategy, we developed two ratiometric ONOO^– nanosensors for the detection of ONOO^– in solutions and living cells. This work is the first report of NMOF ONOO^– sensors through FRET and could inspire the design of other NMOF based chemical sensors and biosensors.

Synthesis and characterization of a photochromic magnesium(II) coordination polymer based on a naphthalene diimide ligand

Naphthalene diimides, which are planar, chemically robust and redox-active, are an attractive class of electron-deficient dyes, which can undergo a single reversible one-electron reduction to form stable radical anions in the presence of electron donors upon irradiation. This makes them excellent candidates for organic linkers in the construction of photochromic coordination polymers. Such a photochromic one-dimensional linear coordination polymer has been prepared using N,N′-bis(3-carboxyphenyl)naphthalene-1,8:4,5-tetracarboximide (H2BBNDI). Crystallization of H2BBNDI with magnesium nitrate in an N,N′-dimethylformamide (DMF)/ethanol/H2O mixed-solvent system under solvothermal conditions afforded the one-dimensional coordination polymer catena-poly[[bis(dimethylformamide-κO)magnesium(II)]-bis[μ-N-(3-carboxylatophenyl)-N′-(3-carboxylphenyl)naphthalene-1,8:4,5-tetracarboximide-κ2 O:O′]], [Mg(C28H13N2O8)2(C3H7NO)2] n . The asymmetric unit contains half of a magnesium cation, one HBBNDI− ligand and one DMF molecule. Two partially deprotonated HBBNDI− ligands bridge two magnesium cations to form a one-dimensional chain. Strong inter-chain π–π interactions between the naphthalene rings of the HBBNDI− ligand and the imide rings of adjacent chains provide a two-dimensional structure. The supramolecular three-dimensional framework is stabilized by π–π interactions between naphthalene rings of neighbouring two-dimensional supramolecular networks. The complex exhibits a reversible photochromic behaviour, which may originate from the photoinduced electron-transfer generation of radicals in the HBBNDI− ligand.

Cadmium–1,4-cyclohexanedicarboxylato coordination polymers bearing different di-alkyl-2,2′-bipyridines: syntheses, crystal structures and photoluminescence studies

Cd(ii) polymers, in acetone, can be used as luminescent materials for detection of CH₃CN.