Polymorphic Copper Iodide Anions: Luminescence Thermochromism and Mechanochromism of (PPh4)2[Cu2I4]

Interplay of the Cu⋯Cu distance and coordination geometry as a factor affecting the quantum efficiency in dimeric copper(I) halide complexes with derivatives of 4-pyrazolylpyrimidine-2-thiol

Two bicyclic pyrazolylpyrimidine compounds, 2-benzylthio-4-(3,5-dimethyl-1H-pyrazol-1-yl)pyrimidine (LH) and 2-benzylthio-4-(3,5-dimethyl-1H-pyrazol-1-yl)-6-methylpyrimidine (LMe), were synthesized and studied as ligands for the preparation of copper(I) halido complexes. In the solid state, LH and LMe demonstrate dual excitation-wavelength dependent emission, i.e. fluorescence at higher excitation energies and phosphorescence at lower excitation energies due to the presence of a heavy sulphur atom. The reactions of LH and LMe with CuBr and CuI afforded a series of centrosymmetric binuclear complexes of the [Cu2L2Hal2] type (L = LH, Hal = Br, I; L = LMe, Hal = I). The possibility of rotation of the benzylthio group relative to the pyrazolylpyrimidine core leads to the isolation of two polymorphic modifications of the copper(I) iodido complex with LH, which differ by the Cu⋯Cu distance by more than 0.2 Å (2.86 Å for [Cu2(LH)2I2] (form I)vs. 2.65 Å for [Cu2(LH)2I2] (form II)). The isolation of the [Cu2(LH)2I2] complex in two different crystalline forms made it possible to reveal the influence of a rarely explored factor, namely the change in the Cu⋯Cu distance in a single molecule, on the photoluminescence quantum efficiency. Two structural indices, τdim, which showcases the degree of merging of CuLHal monomers into the centrosymmetric [Cu2L2Hal2] dimers, and τplan, which characterises the degree of planarization of the N2CuHal2CuN2 unit, were introduced and used for combined experimental and theoretical analyses of the relation between the structure of the complexes and their luminescence. All complexes exhibit phosphorescence of the ligand-to-halide charge transfer (LXCT) character in the orange region. According to TD-DFT calculations, an increase in the Cu⋯Cu distance facilitates structural rearrangement in the T1 state followed by a rapid decrease in the T1-S0 energy gap and subsequent non-radiative decay via electron-phonon coupling, which substantiates the higher photoluminescence quantum yield (PLQY) of [Cu2(LH)2I2] (form II) (Cu⋯Cu 2.65 Å) compared to that of [Cu2(LH)2I2] (form I) (Cu⋯Cu 2.86 Å).

Luminescent Properties and Thermal Stability of [PPh4][Cu3I4] with a Unique Helical Structure

Hybrid halocuprates (I) with organic cations show great potential for optoelectronic applications due to their tunable luminescence and high thermal stability. In this study, the iodocuprate (I) [PPh4][Cu3I4], featuring unique helical chains of face-sharing tetrahedra, was synthesized and characterized. This compound exhibits a bandgap of 3.1 eV and orange luminescence at low temperature, attributed to self-trapped exciton emission. [PPh4][Cu3I4] demonstrates exceptional thermal stability among hybrid halocuprates with decomposition above 380 °C, forming a stable melt at ~255 °C without Cu+ oxidation in ambient atmosphere.

Structural and Photophysical Differences in Crystalline Trigonal Planar Copper Iodide Complexes with 1,2-Bis(methylpyridin-2-yl)disilane Ligands

We synthesized trigonal planar Cu(I) iodide complexes with 1,2-bis(methylpyridin-2-yl)disilane ligands L1-L4 and investigated how the substitution position of the methyl group on the pyridine ring in σ-π conjugation affects their structure and physical properties. The structures were characterized by NMR, elemental analysis, and single-crystal X-ray diffraction. In the crystalline state, the methylpyridyl groups of CuIL1-CuIL3 were coordinated with Cu(I) in an anticlinal conformation relative to the Si-Si σ bond, whereas those of CuIL4 were coordinated with Cu(I) in a synperiplanar conformation relative to the Si-Si σ bond. The conformational difference in the crystalline state was influenced by the N-Cu-N bite angle and the emission wavelength. CuIL1-CuIL3 exhibited blue-green emission (λem: 476-494 nm), and CuIL4 exhibited green-yellow emission (λem: 512 nm) with high emission quantum yields (Φ: 0.59-0.86) in the crystalline state at 293 K. These Cu(I) complexes exhibited thermally activated delayed fluorescence from the S1 state at 293 K and phosphorescence from the T1 state at 77 K in the crystalline state. The optical properties in the crystalline state were discussed by DFT and TD-DFT calculations. These complexes also displayed aggregation-induced emission in THF-water solution (fw > 80%), although they did not show emission in dehydrated THF.

Luminescence Thermochromism of a Noncluster Copper Iodide Complex

Hybrid copper(I) halide materials are currently attracting significant attention due to their exceptional luminescence properties, offering great potential for the development of multifunctional emissive materials with, in addition, eco-friendly features. A binuclear copper iodide complex, based on the [Cu2I2L4] motif with phosphite derivatives as ligands, has been synthesized and structurally characterized. Photophysical investigations indicate that this complex displays luminescence thermochromic properties, which are characterized by a temperature-dependent change in the relative intensity of two emission bands. The high-contrast luminescence thermochromism, with an important color variation from purple to cyan, is ascribed to the thermal equilibrium of two different excited states. While thermochromism is relatively known for multimetallic complexes, the perfectly controlled thermochromism of the studied compound is unprecedented for a binuclear complex. From theoretical investigations, this original feature is due to the coordination of phosphite ligands, which induces a specific energy layout of the complex, presenting vacant orbitals of varying nature. This single-component, dual-emissive binuclear complex, displaying relevant sensitivity temperature response, presents great potential for luminescence ratiometric thermometry applications. This study underlines the relevance of the ligand engineering strategy in developing original, emissive, and sustainable copper-based materials.

Near Ultraviolet-Excitable Cyan-Emissive Hybrid Copper(I) Halides Nonlinear Optical Crystals with Near-Unity Photoluminescence Quantum Yield and High-Efficiency X-ray Scintillation

Designing and synthesizing multifunctional hybrid copper halides with near ultraviolet (NUV) light-excited high-energy emission (<500 nm) remains challenging. Here, a pair of broadband-excited high-energy emitting isomers, namely, α-/β-(MePh3P)2CuI3 (MePh3P=methyltriphenylphosphonium), were synthesized. α-(MePh3P)2CuI3 with blue emission peaking at 475 nm is firstly discovered wherein its structure contains regular [CuI3]2- triangles and crystallizes in centrosymmetric space group P21/c. While β-(MePh3P)2CuI3 featuring distorted [CuI3]2- planar triangles shows inversion symmetry breaking and crystallizes in the noncentrosymmetric space group P21, which exhibits cyan emission peaking at 495 nm with prominent near-unity photoluminescence quantum yield and the excitation band ranging from 200 to 450 nm. Intriguingly, β-(MePh3P)2CuI3 exhibits phase-matchable second-harmonic generation response of 0.54×KDP and a suitable birefringence of 0.06@1064 nm. Furthermore, β-(MePh3P)2CuI3 also can be excited by X-ray radioluminescence with a high scintillation light yield of 16193 photon/MeV and an ultra-low detection limit of 47.97 nGy/s, which is only 0.87 % of the standard medical diagnosis (5.5 μGy/s). This work not only promotes the development of solid-state lighting, laser frequency conversion and X-ray imaging, but also provides a reference for constructing multifunctional hybrid metal halides.

Luminescence Behavior of Cationic and Neutral CuI Complexes of Phosphine and Pyridine Embedded 1,2,3-Triazole

Synthesis of a potentially polydentate, phosphine and pyridine embedded 1,2,3-triazole, o-Ph2P(C6H4)C(CH)-1,2,3-N3(CH2)(Py) (1) (here onward referred to as "P∩N3∩N") and its copper complexes are described. Reactions of 1 with CuX yielded mononuclear [Cu{(P∩N3∩N)2-κ2-P,N}]X (2 - 4; X = I, CuBr2 and CuCl2) and dinuclear [Cu2{(P∩N3∩N)2-κ4-P,N,N,N}]X (5 X = OTf, 6 X = BF4) complexes. Interestingly, the cationic complex [Cu{(P∩N3∩N)2-κ2-P,N}]I (2) in acetonitrile changes into neutral complex [Cu3(μ2-I)2(μ3-I)(NCCH3){(P∩N3∩N)-κ4(μ2-P,N)(μ2-N,N)}](7), which on addition of dichloromethane reverts back to the cationic form. The photoluminescent characteristics of cationic complexes are significantly impacted by the nature of counteranions and hence the corresponding photoluminescence quantum yields. Cationic complex 2 showed an increase in quantum yield and lifetime on changing over to neutral complex 7. TD-DFT calculations also assisted in assessing the photophysical properties.

Mechanoresponsive luminescence triggered by phase transition of a supercooled copper(I) complex

Under mechanical stimulation, a copper(I) complex in its supercooled liquid state transforms into a crystalline phase, showing a dramatic emission color change from red to green that is accompanied by a 20-fold increase in the photoluminescence quantum yield up to 87%. This reversible phase transition relies on the intriguing ability of this copper complex to form a supercooled metastable state.

Dual-Emissive γ-[Cu4I8]4- Enables Luminescent Thermochromism in an Organic-Inorganic Hybrid Copper(I) Halide

A highly luminescent (C13H28N2)2Cu4I8 single crystal containing isolated γ-[Cu4I8]4- anionic cluster was synthesized without the use of unsaturated cations. To the best of our knowledge, compounds bearing such like anions are not dual-emitting under UV excitation. However, dual emission does occur in (C13H28N2)2Cu4I8. Moreover, the emission bands were found to be temperature-sensitive, allowing tuning of the emission colors from blue (0.19, 0.20) to green (0.33, 0.47) in the Commission International de L' Eclairage (CIE) chromaticity coordinates. Remarkably, the color could be restored on returning to the initial temperature, confirming an efficient and reversible luminescent thermochromic effect in (C13H28N2)2Cu4I8. The origin of this excellent optical performance is discussed, and the difference in the mechanism with the dual-emissive Cu(I) halide complexes is also elucidated. Overall, our work provides a promising way to achieve efficient luminescent thermochromism. The developed (C13H28N2)2Cu4I8 represents one of the viable alternatives for eco-friendly luminescent thermochromic materials.

Cluster-Centered Excited-State-Induced Bright Low-Energy Emissive Hybrid Copper Iodide Constructing Stable White LEDs

Herein, we successfully synthesized a stable copper iodide hybrid with a 0D structure, (C20H20P)2Cu2I4, in which [Cu2I4]2- dimers with a short Cu-Cu distance (2.64 Å) are isolated and surrounded by [C20H20P]+ organic cations. Bright broadband yellow emission (576 nm) featuring a wide excitation range from 240 to 450 nm was achieved, along with a large Stokes shift (211 nm), long-lived lifetime (1.99 μs), and zero self-absorption. The results combined with crystal structure, spectroscopy analysis, and theoretical studies reveal that a cluster-centered excited state is responsible for this yellow emission. Importantly, the structure of (C20H20P)2Cu2I4 remains unchanged even after soaking in water for 30 days or heating at 80 °C for 240 h due to the intermolecular interaction. Furthermore, a stable white LED showing a naturally correlated color temperature (CCT) of 6573 K and CIE color coordinate of (0.31, 0.37) was also demonstrated. This work demonstrates efficient light emitters based on lead-free and stable metal halides for lighting, providing an important reference for the development of stable, high-performance metal halide phosphors.

Photophysical studies for Cu(i)-based halides: broad excitation bands and highly efficient single-component warm white-light-emitting diodes

Designing and synthesizing cuprous halide phosphors unifying efficient low-energy emission and a broad excitation band is still a great challenge. Herein, by rational component design, three novel Cu(i)-based metal halides, DPCu₄X₆ [DP = (C₆H₁₀N₂)₄(H₂PO₂)₆; X = Cl, Br, I], were synthesized by reacting p-phenylenediamine with cuprous halide (CuX), and they show similar structures, consisting of isolated [Cu₄X₆]^2- units separated by organic layers. Photophysical studies uncover that the highly localized excitons and rigid environment give rise to highly efficient yellow-orange photoluminescence in all compounds with the excitation band spanning from 240 to 450 nm. The bright PL in DPCu₄X₆ (X = Cl, Br) originates from self-trapped excitons due to the strong electron-phonon coupling. Intriguingly, DPCu₄I₆ features a dual-band emissive characteristic, attributed to the synergistic effect of halide/metal-to-ligand charge-transfer (X/MLCT) and triplet cluster-centered (³CC) excited states. Benefiting from the broadband excitation, a high-performance white-light emitting diode (WLED) with a high color rendering index of 85.1 was achieved using single-component DPCu₄I₆ phosphor. This work not only unveils the role of halogens in the photophysical processes of cuprous halides, but also provides new design principles for high-performance single-component WLEDs.

A review on functional nanoarchitectonics nanocomposites based on octahedral metal atom clusters (Nb6, Mo6, Ta6, W6, Re6): inorganic 0D and 2D powders and films

This review is dedicated to various functional nanoarchitectonic nanocomposites based on molecular octahedral metal atom clusters (Nb₆, Mo₆, Ta₆, W₆, Re₆). Powder and film nanocomposites with two-dimensional, one-dimensional and zero-dimensional morphologies are presented, as well as film matrices from organic polymers to inorganic layered oxides. The high potential and synergetic effects of these nanocomposites for biotechnology applications, photovoltaic, solar control, catalytic, photonic and sensor applications are demonstrated. This review also provides a basic level of understanding how nanocomposites are characterized and processed using different techniques and methods. The main objective of this review would be to provide guiding significance for the design of new high-performance nanocomposites based on transition metal atom clusters.

Thermo-, Mechano-, and Vapochromic Dinuclear Cuprous-Emissive Complexes with a Switchable CH3CN-Cu Bond

A thermo-, mechano-, and vapochromic bimetallic cuprous-emissive complex has been reported, and the origin and application of its tri-stimuli-responsive luminescence have been explored. As revealed by single-crystal structure analysis, thermo- and vapochromic luminescence adjusted by heating at 60 °C and CH₃CN vapor fuming, accompanied by a crystalline-to-crystalline transition, is due to the breaking and rebuilding of the CH₃CN-Cu bond, as supported by ¹H nuclear magnetic resonance (NMR), Fourier-transform infrared (FT-IR) spectroscopy, powder X-ray diffraction (PXRD), thermogravimetry (TG), and time-dependent density functional theory (TD-DFT) analyses of the CH₃CN-coordinated species [Cu₂(μ-dppa)₂(μ-η¹(N)η²(N,N)-fptz)(CH₃CN)](ClO₄)·H₂O (1) and its CH₃CN-removed derivative [Cu₂(μ-dppa)₂(μ-η¹(N)η²(N,N)-fptz)](ClO₄)·H₂O (2). Luminescence mechanochromism, mixed with a crystalline-to-amorphous transition where the initial crystalline is different for 1 and 2, is mainly assigned as the destruction of the CH₃CN-Cu bonding and/or the O···HN_dppa and OH···N_triazolyl hydrogen bonds. It is also suggested that a rational use of switchable coordination such as weak metal-solvent bonding is a feasible approach to develop multi-stimuli-responsive luminescent materials and devices.

Self-Assembly of Mechanoluminochromic Ladder-Shaped Gold(I) Clusters Promoted Using Cooperative Aurophilicity

The self-assembly of mechanoluminochromic polynuclear gold(I) complexes has attracted more and more attention in the field of supramolecular gold(I) chemistry. In this work, we adopted a stepwise self-assembly strategy to precisely synthesize two polynuclear gold(I) supramolecular clusters. Through cooperative Au^I···Au^I and Au-N interactions, the gold(I) clusters 1⁺•BF₄^- and 2⁴⁺•4BF₄^- with Au₄ and Au₁₆ cores, respectively, were successfully constructed. In these supramolecular clusters, (dppm)Au₂Cl₂ coordination motifs and trithiocyanuric linkers were stepwise assembled via sequential thiolate-chloride/phosphine coordination substitution and Au-S/Au-N coordination bond rearrangement. Two well-defined gold(I) supramolecular clusters displayed intense emission both in the solid state and in solution. Furthermore, the ladder-shaped cluster 2⁴⁺•4BF₄^- exhibited reversible mechanochromic luminescence behavior in the solid state as well as aggregation-caused redshifted emission in solution. Upon mechanical grinding, the emission of the cluster 2⁴⁺•4BF₄^- changed from yellow at 582 nm to red at 612 nm. The initial emission could be fully recovered by treatment with acetonitrile.

Solely 3-Coordinated Organic-Inorganic Hybrid Copper(I) Halide: Hexagonal Channel Structure, Turn-On Response to Mechanical Force, Moisture, and Amine

Herein, we report a novel organic-inorganic hybrid Cu^I halide PyCs₃Cu₂Br₆ (Py: pyridinium), where pyridinium and cesium ions coexist. We successfully develop a novel strategy for fabricating turn-on responsive materials. PyCs₃Cu₂Br₆ has a higher single-crystal symmetry (no. 191) than its all-inorganic counterpart Cs₃Cu₂Br₅ (no. 62), and the incorporation of organic pyridinium varied the coordination environment of Cu^I. PyCs₃Cu₂Br₆ formed a triangle planar structure with solely 3-coordinated Cu^I ions, which quenched its luminescence. However, PyCs₃Cu₂Br₆ presented a hexagonal channel structure, which enabled it with turn-on response upon mechanical force, heat, moisture, and amine vapor. Such structure offered channels for active molecules to diffuse and interact with pyridiniums, leading to the stimuli-triggered phase change to highly emissive Cs₃Cu₂Br₅. To our best knowledge, for the first time, we discover a novel 3-coordinated organic-inorganic hybrid Cu^I halide with turn-on response to external stimuli. We believe that our study will contribute to expanding the landscape of smart stimulus-responsive materials and lay the foundation for their wide applications.

Copper Iodide Clusters Coordinated by Emissive Cyanobiphenyl-Based Ligands

Copper(I) halides are currently the subject of intensive research because of their rich photophysical properties combined with economic and eco-friendly advantages for practical applications. The molecular copper iodide cluster of the general formula [Cu₄I₄L₄] (L = ligand) is a well-known photoluminescent compound, and the possibility to enlarge the panel of its photophysical properties is studied here, by exploring ligands bearing a distinct emitter. The comparative study of five copper iodide clusters coordinated by different phosphine ligands functionalized by the emissive cyanobiphenyl (CBP) group is thus described in this work. The emissive properties of the ligands have a great impact onto the photophysical properties of the cluster. Compared with classical [Cu₄I₄L₄] copper iodide clusters, the origin of the emission bands is largely modified. The CBP moiety of electron acceptor character significantly lowers in energy the vacant orbitals and consequently affects the global energetic layout. These clusters present dual emission based on two different emissive centers which interplay through energy transfer. This study demonstrates that the design of original ligands is an effective approach to enrich the photophysical properties of the appealing family of copper halide complexes.

A tricolor-switchable stimuli-responsive luminescent binuclear Cu(i) complex with switchable NH⋯O interactions

Blue-green-yellow tricolor luminescence conversion is attributed to the loss and recovery of CH2Cl2 solvent molecules and the destruction and restoration of the orderly packing array caused by the breaking and rebuilding of NH⋯O hydrogen bonds.

Sensitive luminescence mechanochromism and unique luminescence thermochromism tuned by bending the P–O–P skeleton in the diphosphonium/iodocuprate(i) hybrid

The unique luminescence mechano/thermochromism of a diphosphonium/iodocuprate(i) hybrid is led by the mechanically induced adjustments in cuprophilic interactions and bent P–O–P backbone upon heating.

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...

A Mechanochromic and Vapochromic Luminescent Cuprous Complex Based on a Switchable Intramolecular π···π Interaction

An in-depth study on a stimuli-responsive tetranuclear cuprous luminescent complex is reported and gives new insights into the origin and possible use of the observed stimuli-responsive luminescence. Its crystalline polymorphs with two different shapes are obtained by using different crystallization solvents and show distinct emissions, with one being blue emissive and the other being yellow emissive. Upon grinding, only the blue-emitting polymorph has a marked change in the emission color from blue to yellow, and its ground sample exhibits a yellow emission similar to that of the yellow-emitting polymorph. Interestingly, the yellow-emitting polymorph after exposure to acetone vapor can emit a blue emission and display luminescence mechanochromism similar to that of the blue-emitting polymorph. Single-crystal structural analyses of the two different polymorphs reveal the relationship between the mechanochromic luminescence and the geometrical configuration of the {Cu(μ-dppm)₂Cu} unit and intramolecular "pyridyl/phenyl" π···π interactions, supported as well by their PXRD, FT-IR, TGA, and PL studies in various states and by TD-DFT analyses. The results demonstrate the different roles of switchable intramolecular π···π interactions and the geometrical configuration of the {Cu(μ-dppm)₂Cu} unit in this stimuli-responsive luminescence and potential applications of such stimuli-responsive luminescence in optical sensing and anticounterfeiting encryption technologies and deepen the understanding of such stimuli-responsive luminescence originating from switchable intramolecular π···π interactions. In addition, it is clearly suggested that the rational utilization of switchable intramolecular π···π interactions is a feasible route for developing stimuli-responsive intelligent luminescent materials and devices.

Aggregation-Enhanced Room-Temperature Phosphorescence from Au(I) Complexes Bearing Mesogenic Biphenylethynyl Ligands

Gold(I) complexes, enabling to form linear coordination geometry, are promising materials for manifesting both aggregation-induced emission (AIE) behavior due to strong intermolecular Au-Au (aurophilic) interactions and liquid crystalline (LC) nature depending on molecular geometry. In this study, we synthesized several gold(I) complexes with rod-like molecular skeletons where we employed a mesogenic biphenylethynyl ligand and an isocyanide ligand with flexible alkoxyl or alkyl chains. The AIE behavior and LC nature were investigated experimentally and computationally. All synthesized gold(I) complexes exhibited AIE properties and, in crystal, room-temperature phosphorescence (RTP) with a relatively high quantum yields of greater than 23% even in air. We have demonstrated that such strong RTP are drastically changed depending on the crystal-size and/or crystal growth process that changes quality of crystals as well as the aggregate structure, of e.g., Au-Au distance. Moreover, the complex with longer flexible chains showed LC nature where RTP can be observed. We expect these rod-like gold(I) complexes to have great potential in AIE-active LC phosphorescent applications such as linearly/circularly polarizing phosphorescence materials.

Solid-State Structures and Photoluminescence of Lamellar Architectures of Cu(I) and Ag(I) Paddlewheel Clusters with Hydrogen-Bonded Polar Guests

Two hexanuclear paddlewheel-like clusters appending six carboxylic-acid pendants have been isolated with the inclusion of polar solvent guests: [Cu₆(Hmna)₆]·7DMF (1·7DMF) and [Ag₆(Hmna)₆]·8DMSO (2·8DMSO), where H₂mna = 2-mercaptonicotininc acid, DMF = N,N’-dimethylformamide, and DMSO = dimethyl sulfoxide. The solvated clusters, together with their fully desolvated forms 1 and 2, have been characterized by FTIR, UV–Vis diffuse reflectance spectroscopy, TG-DTA analysis, and DFT calculations. Crystal structures of two solvated clusters 1·7DMF and 2·8DMSO have been unambiguously determined by single-crystal X-ray diffraction analysis. Six carboxylic groups appended on the clusters trap solvent guests, DMF or DMSO, through H-bonds. As a result, alternately stacked lamellar architectures comprising of a paddlewheel cluster layer and H-bonded solvent layer are formed. Upon UV illumination (λ_ex = 365 nm), the solvated hexasilver(I) cluster 2·8DMSO gives intense greenish-yellow photoluminescence in the solid state (λ_PL = 545 nm, Φ_PL = 0.17 at 298 K), whereas the solvated hexacopper(I) cluster 1·7DMF displays PL in the near-IR region (λ_PL = 765 nm, Φ_PL = 0.38 at 298 K). Upon complete desolvation, a substantial bleach in the PL intensity (Φ_PL < 0.01) is observed. The desorption–sorption response was studied by the solid-state PL spectroscopy. Non-covalent interactions in the crystal including intermolecular H-bonds, CH⋯π interactions, and π⋯π stack were found to play decisive roles in the creation of the lamellar architectures, small-molecule trap-and-release behavior, and guest-induced luminescence enhancement.

Molecular copper iodide clusters: a distinguishing family of mechanochromic luminescent compounds

Mechanochromic luminescent materials displaying switchable luminescence properties in response to external mechanical force are currently attracting wide interest because of their multiple potential applications. In the growing number of mechanochromic luminescent compounds, mechanochromic complexes based on copper present appealing features with a large variety of mechanochromic properties and economical advantages over other metals. Among Cu-based compounds, molecular copper iodide clusters of cubane geometry with formula [Cu₄I₄L₄] (L = organic ligand) stand out. Indeed, they can exhibit multiple luminescent stimuli-responsive properties, being particularly suitable for the development of multifunctional photoactive systems. This perspective describes the survey of these mechanochromic luminescent cubane copper iodide clusters. Based on our investigations, their mechanochromic luminescence properties are presented along with the study of the underlying mechanism. Establishment of structure-property relationships supported by various characterization techniques and associated with theoretical investigations permits gaining insights into the mechanism at play. Studies of other researcher groups are also described and illustrate the interest shown by these mechanochromic compounds. Mechanically responsive films are reported, demonstrating their potential use in a range of applications of such copper-based stimuli-responsive materials. Current challenges faced by the development of technological applications are finally outlined.

Multistimuli Responsive Solid-State Emission of a Zinc(II) Complex with Multicolour Switching

The development of smart luminescent materials, especially those stimulus-responsive fluorescent materials that can switch between different colors repeatedly under external stimulation based on a single molecule, is of great significance but a challenge. In this work, a novel zinc(II)-Schiff base complex (ZnL₂) was obtained and characterized. Upon exposure to the HCl and NH₃ vapors, it displayed remarkable tricolor acidochromic behavior with high contrast and rapid response under the ambient light as well as UV light (365 nm). The XPS analyses of ZnL₂ crystals before and after HCl/NH₃ fuming show that the acidochromism originates principally from the adsorption of vapor and the gas-solid reaction equilibrium on the crystal surface. The reddish-brown color of the HCl-fumigated ZnL₂ crystals could be attributed to the generation of HL at the surface of ZnL₂, and red-shifted emission could be ascribed to the self-absorption effect. The single crystal X-ray diffraction data indicate that these processes cause slight changes in the molecular conformation and crystal packing. ZnL₂ shows reversible mechanochromic luminescence behavior between yellow and orange emission during the grinding-fuming/heating cycles due to the modulation between amorphous and crystalline states. Moreover, ZnL₂ was successfully made into test paper for the rapid detection of HCl/NH₃ vapors and mechanical stimuli.

Dinuclear Copper Complex Immobilized on a Janus-Type Material as an Interfacial Heterogeneous Catalyst for Green Synthesis

We herein describe a rational design of a heterogeneous catalyst composed of a dinuclear cuprate anion being immobilized electrostatically on one surface of Janus-type nanosheets while the other surface is decorated with highly hydrophobic octyl groups. The catalyst was found to be well dispersible in the organic phase of a biphasic aqueous/organic mixture. It was characterized by means of elemental analysis, atomic absorption spectroscopy, mass spectrometry, N₂ absorption-desorption analysis, thermogravimetric analysis, scanning electron microscopy (SEM), and solid-state ¹³C and ²⁹Si cross-polarization magic-angle spinning nuclear magnetic resonance spectroscopy. The Janus nature of the catalyst was investigated by employing a selective surface labeling method and by means of SEM. The catalyst shows higher activity compared to a non-Janus analogue in a biphasic synthesis. It was successfully used for the azide-alkyne cycloaddition and the Chan-Lam C-N coupling reaction. In addition, new and simple ways have been established for the production of a coumarin-triazole derivative and for the synthesis of the biologically active compound Monastrol via a solvent-free Biginelli reaction. The role of the dinuclear copper centers is discussed mechanistically.

A family of Mn(ii) complexes exhibiting strong photo- and triboluminescence as well as polymorphic luminescence

New Mn(ii) complexes supported by diphosphine dioxides exhibit strong room-temperature phosphorescence as well as bright triboluminescence and polymorphic luminescence.

Reversible Mechanochromic Luminescence of Tetranuclear Cuprous Complexes

Mechanochromic luminescence materials have attracted rapidly growing interest. Nevertheless, the designed synthesis of such materials remains a challenge, and there have been few examples based on weak intramolecular interactions. Herein, we report a new approach for preparing mechanochromic luminescence materials of Cu(I) complexes, i.e., constructing a photoluminescence system that bears a large coplanar multinuclear Cu(I) unit showing weak intramolecular π···π interactions with the planar rings of the coordinated ligands in the molecule. Using it, a series of novel mechanochromic luminescent tetranuclear Cu(I) complexes have been successfully designed and synthesized. As revealed by single-crystal X-ray crystallography, these Cu(I) complexes share an identical {Cu₄[μ₃-η²(N,N),η¹(N),η¹(N)-pyridyltetrazole]₂}²⁺ planar fragment whose coplanar pyridyl rings exhibit weak intramolecular π···π interactions with the phenyl rings of the coordinated phosphine ligands in the molecule. All of these Cu(I) complexes exhibit reversible mechanochromic luminescence, which can be attributed to the change in the rigidity of the molecular structure resulting from the disruption and restoration of intramolecular π···π interactions between the pyridyl and phenyl rings triggered by grinding and CH₂Cl₂ vapor, as supported by powder X-ray diffraction and Fourier transform infrared spectrometry. In addition, the results might provide a new route for developing mechanochromic luminescence materials of Cu(I) complexes for intelligent responsive luminescent devices.

Versatility of the bis(iminopyrrolylmethyl)amine ligand: tautomerism, protonation, helical chirality, and the secondary coordination sphere with halogen bonds in the formation of copper(II) and nickel(II) complexes

The reaction of N,N-di(2,6-bis(isopropyl)phenylimino-pyrrolyl-α-methyl)-N-methylamine H2L1 with copper(i) sources such as CuX (X = Cl (1), Br (2), and I (3)) afforded bis(chelated) ionic copper(ii) complexes of the type [CuL1H]X. A similar type of mononuclear structure was obtained with Cu(NO3)2·(H2O)3. Conversely, binuclear copper(ii) complexes [Cu2(μ-L1)(μ-OOCCH3)(μ-OH)](4) and [Cu2(μ-L1H)(μ-OOCPh)(μ-O)] (5) were obtained from the reaction of Cu(O2CR)2·H2O with H2L1. Notably, these reactions in the presence of a base yielded the neutral copper(ii) complex [CuL1] (6). This product was also obtained from the reaction of complex 2 or 4 with NaOH in methanol. All structures feature a dianionic imino-pyrrole motif and a protonated central amine function except 4. The reaction of H2L1 with NiCl2·DME gave the mononuclear complex [NiCl2(L1H2)], 7. In contrast to this, the reaction of the newly synthesized sterically less encumbered ligand N,N-di(phenylimino-pyrrolyl-α-methyl)-N-methylamine H2L2 with NiCl2·DME gave the binuclear complex [NiCl(L2H2)(HOMe)]2[Cl]2 (8). Both 7 and 8 show the amine-azafulvene ligand form and coordination of the central amine. The reaction of complex 7 with NaHBEt3 yielded a neutral complex [NiL1] (8) containing the imino-pyrrole form. In the molecular structures, interesting secondary coordination spheres incorporating guest molecules such as CHCl3 and MeOH in the crystal lattices and the presence of helical enantiomers were observed and analysed. In one case, CHCl3 was found inside an unusual cage-like structure supported by halogen bonds. Preliminary DFT calculations on the geometry of the nickel complex with H2L1 showed that the pentacoordinated tbp geometry is more stable than the square planar geometry.