Smart composite films of nanometric thickness based on copper-iodine coordination polymers. Toward sensors

Liquid reagents are not enough for liquid assisted grinding in the synthesis of [(AgBr)(n-pica)]n

This study investigates the mechanochemical reactions between AgBr 3-picolylamine and 4-picolylamine. The use of different stoichiometry ratios of the reagents allows [(AgBr)(n-pica)]n and [(AgBr)2(n-pica)]n to be obtained, and we report the new structures of [(AgBr)2(3-pica)]n and [(AgBr)2(4-pica)]n which are characterized by the presence of the following: (a) infinite inorganic chains, (b) silver atom coordinated only by bromide atoms and (c) argentophilic interactions. Furthermore, we studied the interconversion of [(AgBr)(n-pica)]n/[(AgBr)2(n-pica)]n by mechanochemical and thermal properties. The in situ experiments suggest that [(AgBr)(3-pica)]n is kinetically favoured while [(AgBr)2(3-pica)]n is converted into [(AgBr)(3-pica)]n only with a high excess of the ligand. Finally, the liquid nature of the ligands is not sufficient to assist the grinding process, and the complete reaction is observed with the addition of a small quantity of acetonitrile.

Copper(I)-Iodide Clusters as Carriers for Regulating and Visualizing Release of Aroma Molecules

Achieving the controlled release of functional substances is indispensable in many aspects of life. Especially for the aroma molecules, their effective delivery of flavor and fragrance is challenging. Here, selected pyridines, as highly volatile odorants, were individually coordinated with copper(I) iodide (Cu^II) via a straightforward one-pot synthesis method, rapidly forming pure or even crystalline Cu^II cluster-based profragrances at room temperature. The obtained profragrances enabled the stable and high loading of volatile fragrances under ambient conditions and guaranteed their long-lasting release during heating. Furthermore, the intrinsic emission luminescence of these solid-state profragrances decayed along with the aroma release, which can serve as an additional indicator for monitoring the delivery process. This research sets a precedent for using Cu^II clusters as dual-purpose release agents and greatly expands their potential applications.

Luminescent and sustainable d10 coinage metal thiolate coordination polymers for high-temperature optical sensing

The d¹⁰ coinage metal coordination polymers (CPs) are known to display photophysical properties which can be tuned depending on the functionality of the ligand. Three new CPs made of d¹⁰ coinage metals and methyl thiosalicylate, [M(o-SPhCO₂Me)]_n (M = Cu, Ag, Au), are reported. They are all constructed from one-dimensional metal-sulfur networks, in which Cu and Ag are three-coordinated to sulfur atoms, whereas Au is only two-coordinated. It results that both Cu(I) and Ag(I) CPs show orange photoemission at room temperature, and the Au(I) one exhibits near-infrared emission at low temperatures. The intense orange-emissive Ag(I) CP and the blue-emissive coumarin 120 have been mixed in an organic matrix, the polyvinylidene fluoride (PVDF), to form a dual luminescent flexible composite film. This film, evaluated for thermometry, shows great sensitivity for temperatures up to 100°C, a temperature never reached with non-lanthanide-based CPs.

Triphenylamine, Carbazole or Tetraphenylethylene-Functionalized Benzothiadiazole Derivatives: Aggregation-Induced Emission (AIE), Solvatochromic and Different Mechanoresponsive Fluorescence Characteristics

The development of mechanochromic fluorophors with high-brightness, solid-state fluorescence is very significant and challenging. Herein, highly solid-state emissive triphenylamine, carbazole and tetraphenylethylene-functionalized benzothiadiazole derivatives were developed. These compounds showed remarkable aggregation-induced emission and solvatochromic fluorescence characteristics. Furthermore, these fluorogenic compounds also displayed different mechanically triggering fluorescence responses.

Achieving gas pressure-dependent luminescence from an AIEgen-based metal-organic framework

Materials exhibiting aggregation-induced emission (AIE) behaviour enable strong emission in solid state and can respond to various external stimuli, which may facilitate the development of materials for optical sensing, bioimaging or optoelectronic devices. Herein, we use an AIE luminogen 2’,5’-diphenyl-[1,1’:4’,1”-terphenyl]-4,4”-dicarboxylic acid as the ligand to prepare an AIEgen-based MOF (metal-organic framework) named FJI-H31. FJI-H31 exhibits bright luminescence under ambient conditions (under air and at room temperature), but almost no emission is observed under vacuum. Our investigation shows that the emission intensity displays a smooth and reversible enhancement with increased gas pressure, which may be attributed to the restriction of intramolecular motion brought by structural deformation under pressure stimulus. Unlike most pressure-responsive MOFs, the luminescence reverts to its original state once gas pressure recovers. By virtue of its unique optical properties, a luminescent MOF with sensing ability of gas-pressure is realized.

Compounds displaying aggregation-induced emission behavior may have application in the preparation of smart materials. Here, the authors report a luminogen-containing metal-organic framework for which luminescence intensity changes are observed in response to gas pressure.

Transition Metal Coordination Compounds as Novel Materials for Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) are a novel solar cell alternative characterized by lower toxicity by using coordination transition metal compounds while providing high performance benchmarks, such as power conversion efficiency. Particular attention should be paid to compounds containing Cu, which can act both as dyes and as redox mediators, even though compounds relying on other transition metals are also frequently reported. In this paper, examples of compounds containing transition metals in combination with several ligands are presented, and their basic photovoltaic parameters are given.

Near-infrared emitting copper(I) complexes with a pyrazolylpyrimidine ligand: exploring relaxation pathways

Mononuclear copper(I) complexes [CuL2]I (1), [CuL2]2[Cu2I4]·2MeCN (2) and [CuL2]PF6 (3) with a new chelating pyrazolylpyrimidine ligand, 2-(3,5-dimethyl-1H-pyrazol-1-yl)-4,6-diphenylpyrimidine (L), were synthesized. In the structures of complex cations [CuL2]+, Cu+ ions coordinate...

Multi-stimulus semiconductor Cu(i)–I-pyrimidine coordination polymer with thermo- and mechanochromic sensing

The 1D-[Cu(aClpym)I]n coordination polymer behaves as an intelligent material with response to different stimuli since its emission is altered with temperature and with varying modes of pressure, making it a potential multi-response material.

Two 6/10-connected Cu12S6 cluster-based organic frameworks: crystal structure and proton conduction

Nowadays, although the exploration of proton conductive materials has ranged from traditional sulfonated polymers to novel crystalline solid materials such as MOFs, COFs, and HOFs, research on crystalline cluster-based organic framework materials is very limited. Here, a pair of homologues Cu(i)-based organic framework containing a Cu12S6 cluster, [Cu12(MES)6(H2O)3]n (1) and {[Cu12(MPS)6(H2O)4]·6H2O}n (2) (H2MES = 2-mercaptoethanesulfonate acid and H2MPS = 2-mercaptoethanesulfonate acid), were hydrothermally synthesized under the same conditions and fully investigated for their proton conduction. Their structures were characterized by means of single-crystal X-ray diffraction, elemental analysis, thermogravimetric analyses, and PXRD measurements. The two MOFs show significant structural differences in the topological fashions. MOF 1 has a three-dimensional network and can be simplified into two topology types: a 10-connected gpu structure with a Schläfli symbol (312·426·57) and a 3,12-connected new topology with a point symbol {3·42}2{310·418·519·614·74·9}. MOF 2 also has a three-dimensional framework and topology as a 6-connected pcu primitive cubic network with a Schläfli symbol {412·63}. The two MOFs show different proton conduction parameters, but both indicate temperature-dependent proton conductive features. Intriguingly, the two MOFs exhibit high water stability and their proton conductivities are 3.63 × 10-5 and 2.75 × 10-5 S cm-1 under 333 K and 98% RH, respectively. The suggested mechanism for the synthesis for 1 and 2, and their proton conductivity performance comparison has been discussed in detail. In addition, Hirshfeld surface and fingerprint analysis on the two MOFs were computed to compare contacts between the molecules, which is essential for analyzing the relationships between their hydrogen bonds and proton conductivity properties.

Self-Assembly and Aggregation-Induced Emission in Aqueous Media of Responsive Luminescent Copper(I) Coordination Polymer Nanoparticles

Luminescent copper(I)-based compounds have recently attracted much attention since they can reach very high emission quantum yields. Interestingly, Cu(I) clusters can also be emissive, and the extension from small molecules to larger architecture could represent the first step towards novel materials that could be obtained by programming the units to undergo self-assembly. However, for Cu(I) compounds the formation of supramolecular systems is challenging due to the coordinative diversity of copper centers. This works shows that this diversity can be exploited in the construction of responsive systems. In detail, the changes in the emissive profile of different aggregates formed in water by phosphine-thioether copper(I) derivatives were followed. Our results demonstrate that the self-assembly and disassembly of Cu(I)-based coordination polymeric nanoparticles (CPNs) is sensitive to solvent composition. The solvent-induced changes are related to modifications in the coordination sphere of copper at the molecular level, which alters not only the emission profile but also the morphology of the aggregates. Our findings are expected to inspire the construction of smart supramolecular systems based on dynamic coordinative metal centers.

Cu(I)-I-2,4-diaminopyrimidine Coordination Polymers with Optoelectronic Properties as a Proof of Concept for Solar Cells

Two coordination polymers with formulas [CuI(dapym)]_n and [Cu₂I₂(dapym)]_n (dapym = 2,4-diaminopyrimidine) have been synthesized in water at room temperature. According to the stoichiometry used, mono (1D) and the two-dimensional (2D) structures can be obtained. Both are made up of Cu₂I₂ double chains. Their high insolubility in the reaction medium also makes it possible to obtain them on a nanometric scale. Their structural flexibility and short Cu-Cu distances provoke interesting optoelectronic properties and respond to physical stimuli such as pressure and temperature, making them interesting for sensor applications. The experimental and theoretical studies allow us to propose different emission mechanisms with different behaviors despite containing the same organic ligand. These behaviors are attributed to their structural differences. The emission spectra versus pressure and temperature suggest competencies between different transitions, founding critical Cu₂I₂ environments, i.e., symmetric in the 1D compound and asymmetric for the 2D one. The intensity in the 2D compound's emission increases with decreasing temperature, and this behavior can be rationalized with a structural constriction that decreases the Cu-Cu and Cu-I distances. However, compound 1D exhibits a contrary behavior that may be related to a change of the organic ligand's molecular configuration. These changes imply that a more significant Π-Π interaction counteracts the contraction in distances and angles when the temperature decreased. Also, the experimental conductivity measurements and theoretical calculations show a semiconductor behavior. The absorption of the 1D compound in UV, its intense emission at room temperature, and the reduction to nanometric size have allowed us to combine it homogeneously with ethyl vinyl acetate (EVA), creating a new composite material. The external quantum efficiency of this material in a Si photovoltaic mini-module has shown that this compound is an active species with application in solar cells since it can move the photons of the incident radiation (UV region) to longer wavelengths.

Convenient synthesis of copper(I) halide quasi-one-dimensional coordination polymers: their structures and solid-state luminescent properties

The heterogeneous reaction between copper(i) halide and pyridine derivative ligand in a suspension conveniently afforded luminescent copper(i) complexes. The progress of the reaction was confirmed by powder X-ray diffraction (PXRD) and thermogravimetric (TG) measurements. The structure of the obtained complexes was clarified by comparison with the X-ray analysis of a single crystal obtained by the homogeneous reaction in a solution. The reaction was affected by the type of solvent and substituents on the pyridine ligand. The reaction proceeded quantitatively, not depending on copper(i) halide, when ethyl acetate and 3-bromopyridine were used as the solvent and ligand, respectively. X-ray analysis of the single-crystals obtained by the corresponding reaction in solution revealed that the reaction in suspension afforded the same stair-shaped quasi-one-dimensional structure. The obtained copper(i) complex powders displayed luminescence, which was attributed to the halide/metal-to-ligand charge transfer (XMLCT), as elucidated by crystal orbital distribution and principal component of excitation based on density functional theory (DFT) calculations.

The role of coordination compounds in virus research. Different approaches and trends

This article aims to provide an overview of the studies focused on using coordination compounds as antiviral agents against different types of viruses. We present various strategies so far used to this end. This article is divided into two sections. The first collects the series of designed antiviral drugs based on coordination compounds. This approach has been developed for many years, starting from the 70s with the discovery of cis-platin (cis-DDP). It has been mainly focused on studying the synergistic effect of a wide variety of new compounds obtained by combining metal ions with organic antiviral ligands. Then, we collect various strategies analyzing the coordination compounds interacting with viruses using different processes such as wrapping viruses, rapid detection of RNA or DNA virus, or nanocarriers. These recent and novel insights help to study viruses from other points of view, allowing to measure their physical and chemical properties. We also highlight a section in which the issue of viruses from a disinfection viewpoint is addressed, using coordination compounds as a tool able to control the release of antiviral and biocide agents. This is an emerging and promising field but this approach is actually little developed. We finally provide a section with a general conclusion and perspectives.

Copper(i)–iodide cluster structures as functional and processable platform materials

This review provides a complete overview of the progress towards implementation of CuI-nanoclusters in functional materials and devices.

Vapochromic luminescence of a spin-coated copper(I) complex thin film by the direct coordination of vapour molecules

A homogeneous thin film of a simple and highly luminescent Cu(i) complex, [CuI(PPh3)2(py)] (PPh3 = triphenylphosphine, py = pyridine) (Cu-py), was fabricated via spin coating using polyvinylpyrrolidone (PVP) and pyridine without destroying the complex. The thin film (Cu-py@PVP), with a thickness of 1 μm, exhibited efficient response to vapour, exhibiting reversible luminescence changes between blue-green and yellow upon exposure to vapours of N-heteroaromatic compounds such as py and 2-methylpyrazine (Mepyz). Vapochromic luminescence colour change resulting from ligand substitution was also observed in the crystal state, but the response of the thin film was remarkably faster than that of the crystalline samples. The vapour-induced ligand exchange on the thin film was fully characterised by comparing the luminescence properties of the Cu-py crystal with the newly prepared Cu(i) complex, [CuI(Mepyz)(PPh3)2] (Cu-Mepyz).

New Promises and Opportunities in 3D Printable Inks Based on Coordination Compounds for the Creation of Objects with Multiple Applications

This review focuses on the usefulness of coordination bonds to create 3D printable inks and shows how the union of chemistry and 3D technology contributes to new scientific advances, by allowing amorphous or polycrystalline solids to be transformed into objects with the desired shape for successful applications. The review clearly shows how there has been considerable increase in the manufacture of objects based on the combination of organic matrices and coordination compounds. These coordination compounds are usually homogeneously dispersed within the matrix, anchored onto a proper support or coating the printed object, without destroying their unique properties. Advances are so rapid that today it is already possible to 3D print objects made exclusively from coordination compounds without additives. The new printable inks are made mainly with nanoscale nonporous coordination polymers, metal-organic gels, or metal-organic frameworks. The highly dynamic coordination bond allows the creation of objects, which respond to stimuli, that can act as sensors and be used for drug delivery. In addition, the combination of metal-organic frameworks with 3D printing allows the adsorption or selective capacity of the object to be increased, relative to that of the original compound, which is useful in energy storage, gas separation, or water pollutant elimination. Furthermore, the presence of the metal ion can give them new properties, such as luminescence, that are useful for application in sensors or anticounterfeiting. Technological advances, the combination of various printing techniques, and the properties of coordination bonds lead to the creation of surprising, new, printable inks and objects with highly complex shapes that will close the gap between academia and industry for research into coordination compounds.

Multifunctional coordination polymers based on copper(i) and mercaptonicotinic ligands: synthesis, and structural, optical and electrical characterization

Three new coordination polymers (CPs) named [Cu(6mna)]n (CP1), [CuCl(H6mna)(H2O)0.33]n (CP2), and {[(CuI)2H2dtdn].MeCN}n (CP3), (H6mna = 6-mercaptonicotinic acid, and H2dtdn = 6,6'-dithiodinicotinic acid) have been synthesized and their structures determined by single-crystal X-ray diffraction. Complexes 1 and 3 are 2D-CPs while complex 2 is a 1D-CP. The optical properties of these complexes have been evaluated in the solid state, at room temperature and at 77 K, and compared with those of the starting ligands. The electrical conductivity of CPs 1-3 has been evaluated and their thermal stabilities have been studied. CP2 shows an interesting crystal arrangement, where the connection between the ligand and the copper forms a channel-like structure characterized by an intrinsic disorder. Crystal data collected at low temperatures for this complex revealed minor structural changes in the CuCu distances and Cu-S-Cu angles along the chain, excluding phase transition. In CP1, the N and S atoms are involved in metal coordination bonds giving rise to a 2D coordination polymer. In CP3, the Cu-I bonds compose double ladder-like structures, bridged by H2dtdn ligands. The electrical conductivities of CPs 1-3 suggest their semiconductive behavior.

A supersalt-type copper(i)-thiolate cluster with applications for mechano/thermochromism and the oxygen evolution reaction

A new copper(i)-thiolate (Cu-S) cluster with a CsCl unit (1, [Cu₁₂(μ₄-SCH₃)₆(NH₃)₁₂][Cu₁₂(μ₄-SCH₃)₆Cl₁₂]) exhibited interesting mechanochromic and thermochromic luminescence properties. Additionally, heteroatom-rich 1 could also be used as an electrocatalyst for the oxygen evolution reaction in alkaline media. The supersalt-type Cu-S cluster for the first time realized mechano/thermochromic and electrocatalytic applications.

Cu(i)-I coordination polymers as the possible substitutes of lanthanides as downshifters for increasing the conversion efficiency of solar cells

This study tries to provide new solutions to increase the efficiency of conversion of photons in solar cells, using photoluminescent Cu(i) coordination polymers (CPs) as possible alternative materials of lower cost, than those used today, based on lanthanides. The selected CP of chemical formula [Cu(NH2MeIN)I]n (NH2MeIN = methyl, 2-amino isonicotinate) absorbs in the utraviolet and emits in the visible region, being also easily nanoprocessable, by a simple and one-pot bottom-up approach. Nanofibers of this CP can be embedded in organic matrices such as ethyl vinyl acetate (EVA), forming transparent and homogenous films, with a thermal stability of up to approximately 150 °C. These new materials maintain the optical properties of the CP used as a dopant, ([Cu(NH2MeIN)I]n), with emission in yellow (570 nm) at 300 K, which is intensified when the working temperature is lowered. In addition, these materials can be prepared with varying thicknesses, from a few microns to a few hundred nanometers, depending on the deposition method used (drop casting or spin coating respectively). The study of their external quantum efficiency (EQE) found an increase in the UV range, which translates into an increase in the conversion efficiency. The optimal CP concentration is 5% by weight in order to not diminish the transparency of the composite material. The calculated cost on the possible incorporation of this material into solar cells shows a 50% decrease over the cost reported in similar studies based on the use of lanthanides.

A new heteroleptic phosphorescent cuprous complex supported by a BINAP ligand: synthesis, structure, luminescence properties and theoretical analyses

Luminescent cuprous complexes are an important class of coordination compounds due to their relative abundance, low cost and ability to display excellent luminescence. The heteroleptic cuprous complex solvate rac-(acetonitrile-κN)(3-aminopyridine-κN)[2,2'-bis(diphenylphosphanyl)-1,1'-binaphthyl-κ²P,P']copper(I) hexafluoridophosphate dichloromethane monosolvate, [Cu(C₅H₆N₂)(C₂H₃N)(C₄₄H₃₂P₂)]PF₆·CH₂Cl₂, conventionally abbreviated as [Cu(3-PyNH₂)(CH₃CN)(BINAP)]PF₆·CH₂Cl₂, (I), where BINAP and 3-PyNH₂ represent 2,2'-bis(diphenylphosphanyl)-1,1'-binaphthyl and 3-aminopyridine, respectively, is described. In this complex solvate, the asymmetric unit consists of a cocrystallized dichloromethane molecule, a hexafluoridophosphate anion and a complete racemic heteroleptic cuprous complex cation in which the cuprous centre, in a tetrahedral CuP₂N₂ coordination, is coordinated by two P atoms from the BINAP ligand, one N atom from the 3-PyNH₂ ligand and another N atom from a coordinated acetonitrile molecule. The UV-Vis absorption and photoluminescence properties of this heteroleptic cuprous complex have been studied on polycrystalline powder samples, which had been verified by powder X-ray diffraction before recording the spectra. Time-dependent density functional theory (TD-DFT) calculations and a wavefunction analysis reveal that the orange-yellow phosphorescence emission should originate from intra-ligand (BINAP) charge transfer mixed with a little of the metal-to-ligand charge transfer ³(IL+ML)CT excited state.

Thermo-responsive light-emitting metal complexes and related materials

This review discusses the fundamentals and design strategies for the development of thermo-responsive metal–ligand coordination materials and the applications of these materials in temperature sensing, bioimaging, information security, etc.

Modulation of Electronic Mobility of a One-Dimensional Coordination Polymeric Molecular Wire with Light

Metal ions often influence the photoswitching efficiency of a photochromic system. This article reports a one-dimensional polymer having cyclic azobenzenes coordinated to silver ions that are bridged by nitrates. The coordination polymer (CP-2) displays a photoresponsive behavior. The switching ability in the polymer form was faster compared to the parent azobenzene ligand without the metal ions. Azobenzenes are reported to be poorly conducting. Here, although the azobenzene ligand does not show significant electronic mobility, the coordination polymer (CP-2) displays a modest conductivity. The conductance in the cis form of the polymer is significantly higher compared to the trans form. Upon exposure to visible light, the cis form undergoes photoisomerization to the trans form with a drastic drop in the electronic mobility. The trans form can be reverted to the cis form thermally or by using UV light. Thus, this system offers a reversible control of the conductivity using light.

Fluorescence enhancement of fungicide thiabendazole by van der Waals interaction with transition metal dichalcogenide nanosheets for highly specific sensors

Many molecules quench their fluorescence upon adsorption on surfaces. Herein we show that the interaction of thiabendazole, a widespread used fungicide of the benzimidazole family, with nanosheets of transition metal dichalcogenides, particularly of WS2, leads to a significant increase, more than a factor of 5, of the fluorescence yield. This surprising effect is rationalized by DFT calculations and found to be related to the inhibition of the intramolecular rotation between the benzimidazole and thiazole groups due to a bonding rigidization upon interaction with the MoS2 surface. This non-covalent adsorption leads to a redistribution of the molecular LUMO that blocks the non-radiative energy dissipation channel. This unusual behaviour does not operate either for other molecules of the same benzimidazole family or for other 2D materials (graphene or graphene oxide). Moreover, we found that a linear dependence of the emission with the concentration of thiabendazole in solution, which combined with the specificity of the process, allows the development of a highly sensitive and selective method towards thiabendazole determination that can be applied to real river water samples. An excellent detection limit of 2.7 nM, comparable to the best performing reported methods, is obtained with very good accuracy (Er ≤ 6.1%) and reproducibility (RSD ≤ 4.1%) in the concentration range assayed.

Micro and Nano Smart Composite Films Based on Copper-Iodine Coordination Polymer as Thermochromic Biocompatible Sensors

Herein is presented the preparation and characterization of a composite material obtained by the combination of nanosheets of a coordination polymer (CP) based on the copper(I)-I double chain with response to temperature and pressure with polylactic acid (PLA) as biodegradable organic matrix. The new films of composite materials are generated using a simple and low-cost method and can be created with long lateral dimensions and thicknesses ranging from a few microns to a few nanometers. Studies show that the new material maintains the optical response versus the temperature, while the elasticity and flexibility of the PLA totally quenches the response to pressure previously observed for the CP. This new material can act as a reversible sensor at low temperatures, thanks to the flexibility of the copper(I)-iodine chain that conforms the CP. The addition of CP to the PLA matrix reduces the elastic modulus and ultimate elongation of the organic matrix, although it does not reduce its tensile strength.