Synthesis, Characterization, and Photophysical Properties of Heteroleptic Copper(I) Complexes with Functionalized 3-(2′-Pyridyl)-1,2,4-triazole Chelating Ligands

Copper-catalyzed C(sp3)-H alkylation of fluorene with primary and secondary alcohols using a borrowing hydrogen method

Despite the limited success of copper-catalyzed alkylations, (NNS)CuCl proved to be an effective catalyst for the sp3 C-H alkylation of fluorene with alcohols. Various primary alcohols and challenging secondary alcohols were successfully used. The practical applicability of the method was effectively tested with several post-functionalization reactions. This copper-catalyzed alkylation of fluorene involved a borrowing hydrogen mechanism.

A luminescent Cu2I2P2S2-type binuclear complex and its fluorescence sensing for pyridine

Luminescent CuI complexes are an important class of coordination compounds due to their relative abundance, low cost and ability to display excellent luminescence. The title Cu2I2P2S2-type binuclear complex, di-μ-iodido-bis[(thiourea-κS)(triphenylphosphine-κP)copper(I)], [Cu2I2(CH4N2S)2(C18H15P)2], conventionally abbreviated as Cu2I2TPP2TU2, where TPP and TU represent triphenylphosphine and thiourea, respectively, is described. In this complex, each CuI atom adopts a CuI2PS four-coordination mode and pairs of atoms are connected to each other by two μ2-I ligands to form a centrosymmetric binuclear cluster. It was also found that the paper-based film of this complex exhibited obvious luminescence light-up sensing for pyridine and 4-methylpyridine.

Synthesis and Photophysical Properties of Silver(I) Coordination Polymers Bridged by Dimethylpyrazine: Comparison of Emissive Excited States between Silver(I) and Copper(I) Congeners

Highly luminescent silver(I) coordination polymers [Ag2X2(PPh3)2(Me2pyz)]n (X = I, Br, Cl; Me2pyz: 2,5-dimethylpyrazine) were prepared together with copper congeners [Cu2X2(PPh3)2(Me2pyz)]n (X = I, Br). All the complexes showed thermally activated delayed fluorescence from the charge-transfer states in the visible region, from blue to red. The isomorphous relationship among the complexes allowed a detailed discussion of the effect of halogenido ligands and crystal packing on their luminescence energy. The relaxation in the emissive excited states (ESs) was determined to be more remarkable in silver complexes than in copper complexes despite their isomorphous structures, and the electronic effect of halogenido ligands was comparable to the effect of relaxation in emissive ESs.

Multistimuli-responsive multicolor solid-state luminescence tuned by NH-dependent switchable hydrogen bonds

Revealing the stimuli-responsive mechanism is the key to the accurate design of stimuli-responsive luminescent materials. We report herein the multistimuli-responsive multicolor solid-state luminescence of a new dicopper(I) complex [{Cu(bpmtzH)}2(μ-dppa)2](ClO4)2 (1), and the multistimuli-responsive mechanism is clarified by investigating its four different solvated compounds 1·2CH3COCH3·2H2O, 1·2DMSO·2H2O, 1·4CH3OH, and 1·4CH2Cl2. It is shown that luminescence mechanochromism is associated with the breakage of the hydrogen bonds of bmptzH-NH with counter-ions such as ClO4- induced by grinding, while luminescence vapochromism is attributable to the breaking and forming of hydrogen bonds of dppa-NH with solvents, such as acetone, dimethylsulfoxide, and methanol, caused by heating and vapor fuming. In addition, those results might provide new insights into the design and synthesis of multistimuli-responsive multicolor luminescent materials by using various structure-sensitive functional groups, such as distinct N-H ones, to construct switchable hydrogen bonds.

Mechanochromic and Selective Vapochromic Solid-State Luminescence of a Dinuclear Cuprous Complex

The unraveling of the stimuli-responsive mechanism is crucial to the design and precise synthesis of stimuli-responsive luminescent materials. We report herein the mechanochromic and selective vapochromic solid-state luminescence properties of a new bimetallic cuprous complex [{Cu(bpmtzH)}2(μ-dppm)2](ClO4)2 (1), and the corresponding response mechanisms are elucidated by investigating its two different solvated polymorphs 1·2CH2Cl2 (1-g) and 1·2CHCl3 (1-c). Green-emissive 1-g and cyan-emissive 1-c can be interconverted upon alternate exposure to CHCl3 and CH2Cl2 vapors, which is principally attributable to a combined alteration of both intermolecular NHbpmtzH···OClO3- hydrogen bonds and intramolecular "triazolyl/phenyl" π···π interactions induced by different solvents. Solid-state luminescence mechanochromism present in 1-g and 1-c is mainly ascribed to the grinding-induced breakage of the NHbpmtzH···OClO3- hydrogen bonds. It is suggested that intramolecular π···π-triazolyl/phenyl interactions are affected by different solvents but not by grinding. The results provide new insights into the design and precise synthesis of multi-stimuli-responsive luminescent materials by the comprehensive use of intermolecular hydrogen bonds and intramolecular π···π interactions.

Structure and emission properties of dinuclear copper(i) complexes with pyridyltriazole

A new series of five highly emissive binuclear heteroleptic pyridyltriazole-Cu(i)-phosphine complexes 1-5 was synthesized and examined by different experimental (IR, elemental and thermogravimetric analysis, single crystal X-ray diffraction technique, UV-vis and fluorescence spectroscopy) and quantum chemical aproaches. Complexes 1-5 exhibited excellent stimuli-responsive photoluminescent performance in the solid state at room temperature (quantum yield (QY) = 27.5-52.0%; lifetime (τ) = 8.3-10.7 μs) and when the temperature was lowered to 77 K (QY = 38.3-88.2; τ = 17.8-134.7 μs). The highest QY was examined for complex 3 (52%) that can be explained by the small structural changes between the ground S₀ and exited S₁ and T₁ states leading to the small S₁-T₁ triplet gap and efficient thermally-activated delayed fluorescence. Moreover, complex 4 demonstrates reversible mechanochromic and excitation dependent luminescence.

Photoactive Copper Complexes: Properties and Applications

Photocatalyzed and photosensitized chemical processes have seen growing interest recently and have become among the most active areas of chemical research, notably due to their applications in fields such as medicine, chemical synthesis, material science or environmental chemistry. Among all homogeneous catalytic systems reported to date, photoactive copper(I) complexes have been shown to be especially attractive, not only as alternative to noble metal complexes, and have been extensively studied and utilized recently. They are at the core of this review article which is divided into two main sections. The first one focuses on an exhaustive and comprehensive overview of the structural, photophysical and electrochemical properties of mononuclear copper(I) complexes, typical examples highlighting the most critical structural parameters and their impact on the properties being presented to enlighten future design of photoactive copper(I) complexes. The second section is devoted to their main areas of application (photoredox catalysis of organic reactions and polymerization, hydrogen production, photoreduction of carbon dioxide and dye-sensitized solar cells), illustrating their progression from early systems to the current state-of-the-art and showcasing how some limitations of photoactive copper(I) complexes can be overcome with their high versatility.

Polyoxometalate-Supported Copper(I)-Pyrazole Complex: Unusual Stability, Geometrical Isomers, Organic Transformation, and Computation

We have described the synthesis and characterization of a polyoxometalate (POM)-supported copper(I)-pyrazole complex, [Cu^I(C₁₅H₁₂N₂)₂] [PW₁₂O₄₀{Cu^I(C₁₅H₁₂N₂)₂}₂]·CH₃OH (1). There are three Cu(I)-pyrazole coordination complexes in compound 1, out of which two are supported by the {PW₁₂O₄₀}^3- Keggin POM by coordinate covalent bonds from the POM surface through oxygen donors to the Cu(I) centers of two Cu(I) complexes and one remains uncoordinated to the POM surface, acting as a cationic complex species in the crystals of 1. The POM-coordinated Cu(I) complexes have a T-shaped geometry, and the uncoordinated Cu(I) complex is a linear one. During the solvothermal synthesis of compound 1, remarkably, the associated 1,5-diphenylpyrazole ligand is formed from cinnamaldehyde phenylhydrazone through oxidative cyclization at the cost of Cu(II) reduction to Cu(I), and then, these two (copper(I) and pyrazole ligand) form the coordination complex. Compound 1 undergoes desolvation on heating the single crystals of compound 1 at 55 °C in the aerial atmosphere with the formation of the desolvated compound [Cu^I(C₁₅H₁₂N₂)₂][PW₁₂O₄₀{Cu^I(C₁₅H₁₂N₂)₂}₂] (2). Interestingly, when an aqueous suspension of compound 1 is bubbled with O₂ gas at room temperature, it undergoes solid-to-solid transformation, resulting in the formation of the compound [Cu^I(C₁₅H₁₂N₂)₂]₃[PW₁₂O₄₀] (3). Compounds 1, 2, and 3 have been characterized by routine spectral analyses (including cyclic voltammetry and X-ray photoelectron spectroscopy (XPS) studies) and unambiguously by single-crystal X-ray crystallography. We have performed density functional theory (DFT) calculations on compound 1 to understand the rationale of its unusual stability toward oxidation.

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.

Ethynyl π-coordinated and non-coordinated mononuclear Cu(i) halide diphosphine complexes: synthesis and photophysical studies

Complexes 4 and 5 emit yellow green delayed fluorescence and complexes 1–3 and 6 and 7 show yellow green to greenish yellow prompt fluorescence.

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.

Mononuclear Copper(I) 3-(2-pyridyl)pyrazole Complexes: The Crucial Role of Phosphine on Photoluminescence

A series of emissive Cu(I) cationic complexes with 3-(2-pyridyl)-5-phenyl-pyrazole and various phosphines: dppbz (1), Xantphos (2), DPEPhos (3), PPh₃ (4), and BINAP (5) were designed and characterized. Complexes obtained exhibit bright yellow-green emission (ca. 520–650 nm) in the solid state with a wide range of QYs (1–78%) and lifetimes (19–119 µs) at 298 K. The photoluminescence efficiency dramatically depends on the phosphine ligand type. The theoretical calculations of buried volumes and excited states explained the emission behavior for 1–5 as well as their lifetimes. The bulky and rigid phosphines promote emission efficiency through the stabilization of singlet and triplet excited states.

Time-Resolved Spectroscopy and Electronic Structure of Mono-and Dinuclear Pyridyl-Triazole/DPEPhos-Based Cu(I) Complexes

Chemical and spectroscopic characterization of the mononuclear photosensitizers [(DPEPhos)Cu(I)(MPyrT)]0/+ (CuL, CuLH) and their dinuclear analogues (Cu2 L', Cu2 L'H2 ), backed by (TD)DFT and high-level GW-Bethe-Salpeter equation calculations, exemplifies the complex influence of charge, nuclearity and structural flexibility on UV-induced photophysical pathways. Ultrafast transient absorption and step-scan FTIR spectroscopy reveal flattening distortion in the triplet state of CuLH as controlled by charge, which also appears to have a large impact on the symmetry of the long-lived triplet states in Cu2 L' and Cu2 L'H2 . Time-resolved luminescence spectroscopy (solid state), supported by transient photodissociation spectroscopy (gas phase), confirm a lifetime of some tens of μs for the respective triplet states, as well as the energetics of thermally activated delayed luminescence, both being essential parameters for application of these materials based on earth-abundant copper in photocatalysis and luminescent devices.

Bis(2-nitrophenyl) selenide, bis(2-aminophenyl) selenide and bis(2-aminophenyl) telluride: structural and theoretical analysis

Three organoselenium and organotellurium compounds containing ortho substitutents, namely, bis(2-nitrophenyl) selenide, C₁₂H₈N₂O₄Se, 2, bis(2-aminophenyl) selenide, C₁₂H₁₂N₂Se, 3, and bis(2-aminophenyl) telluride, C₁₂H₁₂N₂Te, 7, have been investigated by both structural and theoretical methods. In the structures of all three compounds, there are intramolecular contacts between both Se and Te with the ortho substituents. In the case of 2, this is achieved by rotation of the nitro group from the arene plane. For 3, both amino groups exhibit pyramidal geometry and are involved in intramolecular N-H...Se interactions, with one also participating in intermolecular N-H...N hydrogen bonding. While 3 and 7 are structurally similar, there are some significant differences. In addition to both intramolecular N-H...Te interactions and intermolecular N-H...N hydrogen bonding, 7 also exhibits intramolecular N-H...N hydrogen bonding. In the packing of these molecules, for 2, there are weak intermolecular C-H...O contacts and these, along with the O...N interactions mentioned above, link the molecules into a three-dimensional array. For 3, in addition to the N-H...N and N-H...Se interactions, there are also weak intermolecular C-H...Se interactions, which also link the molecules into a three-dimensional array. On the other hand, 7 shows intermolecular N-H...N interactions linking the molecules into R₂²(16) centrosymmetric dimers. In the theoretical studies, for compound 2, AIM (atoms in molecules) analysis revealed critical points in the Se...O interactions with values of 0.017 and 0.026 a.u. These values are suggestive of weak interactions present between Se and O atoms. For 3 and 7, the molecular structures displayed intramolecular, as well as intermolecular, hydrogen-bond interactions of the N-H...N type. The strength of this hydrogen-bond interaction was calculated by AIM analysis. Here, the intermolecular (N-H...N) hydrogen bond is stronger than the intramolecular hydrogen bond. This was confirmed by the electron densities for 3 and 7 [ρ_(r) = 0.015 and 0.011, respectively].

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.

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.

Luminescent phosphine copper(i) complexes with various functionalized bipyridine ligands: synthesis, structures, photophysics and computational study

A new series of luminescent phosphine copper(i) complexes with cyano- and hydroxyl-substituted 2,2′-bipyridine ligands have been synthesized and structurally characterized. Their luminescent properties have also been investigated in detail.

Heterobimetallic copper(i) complexes bearing both 1,1′-bis(diphenylphosphino)ferrocene and functionalized 3-(2′-pyridyl)-1,2,4-triazole

Copper(i) 1,1′-bis(diphenylphosphino)ferrocene complexes are well regulated by functional 3-(2′-pyridyl)-1,2,4-triazole exhibiting mono-anionic η²(N1,N2) and neutral η²(N1,N2) and η²(N1,N4) chelating modes.

Photoluminescent Phosphinine Cu(I) Halide Complexes: Temperature Dependence of the Photophysical Properties and Applications as a Molecular Thermometer

Luminescent thermometers have attracted much attention, because of their fast response, high sensitivity, and noninvasive operation, relative to other traditional thermometers. The extensive studies on the temperature-dependent luminescent properties of Cu(I) complexes make this low-cost metal source a promising candidate as a component of thermometers. Herein, we prepared three luminescent phosphinine Cu(I) complexes whose emission lifetimes are precisely dependent on the temperature variations. For practical utilization, sensor films have been fabricated by doping these Cu(I) complexes into the matrices of polyacrylamide. These films not only exhibit excellent linear correlations between the temperature and emission lifetime over the wide range of 77-337 K, but also show high sensitivity (with the best one to -6.99 μs K^-1). These are essential factors for the application in luminescent molecular thermometers. Moreover, the emission mechanism for these Cu(I) complexes are rationalized by the combination of experimental and theoretical results.

Cu(I) complexes regulated by N-heterocyclic ligands: Syntheses, structures, fluorescence and electrochemical properties

Three mononuclear Cu(I) complexes, namely, [Cu(2-PBO)(PPh₃)₂]·ClO₄·2CH₂Cl₂ (1), [Cu(3-PBO)(PPh₃)₂(ClO₄)]·CH₂Cl₂ (2) and [Cu(PBM)(PPh₃)₂]·ClO₄ (3) (2-PBO = 2-(2'-Pyridyl)benzoxazole, 3-PBO = 2-(3'-Pyridyl)benzoxazole, PBM = 2-(2'-Pyridyl)benzimidazole, PPh₃ = triphenylphosphine) have been synthesized and characterized by elemental analyses, IR, ¹H NMR, ¹³C NMR, X-ray single crystal diffraction and thermal analysis. Photoluminescent investigation shows that complexes 1-3 exhibit distinct tunable light green (512 nm)-to-yellow (557 nm) photoluminescence by varying the N-heterocyclic ligands. Three complexes show intense 2-PBO-based yellow, 3-PBO-based light green and intense PBM-based bright green luminescence upon irradiation with a standard UV lamp (λ_ex = 254 nm) at room temperature. Moreover, the electrochemical properties of 1-3 have been investigated by cyclic voltammetry. The results suggest the frontier molecular orbits and the HOMO-LUMO energy gaps of these cuprous complexes are effectively adjusted through the introduction of different N-heterocyclic ligands, thus achieving the selective luminescence of the cuprous complexes.

Three zinc iodide complexes based on phosphane ligands: syntheses, structures, optical properties and TD-DFT calculations

Three zinc iodide complexes based on phosphane ligands, namely diiodidobis(triphenylphosphane-κP)zinc(II), [ZnI₂(C₁₈H₁₅P₂)₂], (1), diiodidobis[tris(4-methylphenyl)phosphane-κP]zinc(II), [ZnI₂(C₂₁H₂₁P₂)₂], (2), and [bis(diphenylphosphoryl)methane-κ²O,O']zinc(II) tetraiodidozinc(II), [Zn(C₂₅H₂₂O₂P₂)₃][ZnI₄], (3), have been synthesized and characterized. Single-crystal X-ray diffraction revealed that the structures of (1) and (2) are both mononuclear four-coordinated ZnI₂ complexes containing two monodentate phosphane ligands, respectively. Surprisingly, (2) spontaneously forms an acentric structure, suggesting it might be a potential second-order NLO material. The crystal structure of complex (3) is composed of two parts, namely a [Zn(dppmO₂)₃]²⁺ cation [dppmO₂ is bis(diphenylphosphoryl)methane] and a [ZnI₄]^2- anion. The UV-Vis absorption spectra, thermal stabilities and photoluminescence spectra of the title complexes have also been studied. Time-dependent density functional theory (TD-DFT) calculations reveal that the low-energy UV absorption and the corresponding light emission both result from halide-ligand charge-transfer (XLCT) excited states.

The coordination- and photochemistry of copper(i) complexes: variation of N^N ligands from imidazole to tetrazole

Prediction rules for the coordination chemistry of copper(i) with neutral or deprotonated N^N ligands and different phosphines were derived and related to their photoluminescence.

A novel luminescent ionic trinuclear Cu3I2 cluster cuprous complex supported by a P^N ligand: synthesis, structure characterization, properties and TD-DFT calculations

Luminescent cuprous complexes are an important class of coordination compounds due to their relative abundance, low cost and ability to display excellent luminescence. The title ionic trinuclear Cu₃I₂ complex, tris[μ₂-diphenyl(pyridin-2-yl)phosphane-κ²P:N]di-μ₃-iodido-tricopper(I)(3 Cu-Cu) hexafluoridophosphate, [Cu₃I₂(C₃₉H₃₂NP)₃]PF₆, conventionally abbreviated as [Cu₃I₂(Ph₂PPy)₃]PF₆, is described. Each Cu^I atom is coordinated by two μ₃-iodide ligands and by a P and an N atom from two Ph₂PPy ligands, giving rise to a CuI₂PN tetrahedral coordination geometry about each Cu^I centre. The electronic absorption and photoluminescence properties of this trinuclear cluster have been studied on as-synthesized samples, which had been examined previously by powder X-ray diffraction. A detailed time-dependent density functional theory (TD-DFT) study was carried out and showed a green emission derived from a halide-to-ligand charge transfer and metal-to-ligand charge transfer ³(X+M)LCT excited state.