Copper Halides Research Articles

Characterization and Reactivity Studies of Mononuclear Tetrahedral Copper(II)-Halide Complexes.

Structures, physicochemical properties, and reactivity of the whole series of copper(II)-halide complexes (1X; X = F, Cl, Br, and I) were examined using a TMG3tach tridentate supporting ligand consisting of cis,cis-1,3,5-triaminocyclohexane (tach) and N,N,N',N'-tetramethylguanidine (TMG). The tach ligand framework with the bulky and strongly electron-donating TMG substituents enforces the copper(II) complexes to take a tetrahedral geometry, as inferred from the electron paramagnetic resonance (EPR) spectra, exhibiting relatively large gz and small Az values. The electronic absorption spectra of 1X agreed with the simulation spectra obtained by time-dependent density functional theory (TD-DFT) calculations on a slightly distorted tetrahedral geometry. 1I and 1Br gradually decomposed to generate the corresponding copper(I) complex and halide radical X•, and in the case of 1Br, intramolecular hydroxylation of a methyl group of the TMG substituent took place under aerobic conditions, which may be caused by the reaction of the generated copper(I) complex and dioxygen (O2), generating a reactive oxygen species. 1X except 1I showed hydrogen atom abstraction (HAA) reactivity toward 1,4-cyclohexadiene (CHD), where 1F exhibited the highest reactivity with a second-order rate constant as 1.4 × 10-3 M-1 s-1 at 25 °C. Such an HAA reactivity can be attributed to the higher basicity of F- and/or large bond dissociation free energy of conjugate acid H-F as well as the unstable copper(II) electronic state in the tetrahedral geometry.

(ODA)2CuBr4: A stable lead-free perovskite as efficient photocatalyst for dehydrogenative coupling of quinoxalin-2(1H)-ones with amines

A novel stable lead-free copper halide perovskite (ODA)2CuBr4 was prepared by intercalating the long hydrophobic alkyl group octadecyl ammonium (ODA) between the inorganic layers. The as-synthesized (ODA)2CuBr4 shows excellent photocatalytic performance in the visible-light-driven dehydrogenation coupling of quinoxalin-2(1H)-ones with amines at room temperature. In addition, the photocatalyst could be recovered and recycled for up to five consecutive runs without significant losing of its catalytic activity.

Zero-Dimensional Broadband Yellow Light Emitter (TMS)3Cu2I5 for Latent Fingerprint Detection and Solid-State Lighting.

We report a new hybrid organic-inorganic Cu(I) halide, (TMS)3Cu2I5 (TMS = trimethylsulfonium), which demonstrates high efficiency and stable yellow light emission with a photoluminescence quantum yield (PLQY) over 25%. The zero-dimensional crystal structure of the compound is comprised of isolated face-sharing photoactive [Cu2I5]3- tetrahedral dimers surrounded by TMS+ cations. This promotes strong quantum confinement and electron-phonon coupling, leading to a highly efficient emission from self-trapped excitons. The hybrid structure ensures prolonged stability and nonblue emission compared to unstable blue emission from all-inorganic copper(I) halides. Substitution of Cu with Ag leads to (TMS)AgI2, which has a one-dimensional chain structure made of edge-sharing tetrahedra, with weak light emission properties. Improved stability and highly efficient yellow emission of (TMS)3Cu2I5 make it a candidate for practical applications. This has been demonstrated through utilization of (TMS)3Cu2I5 in white light-emitting diode with a high Color Rendering Index value of 82 and its use as a new luminescent agent for visualization of in-depth latent fingerprint features. This work illuminates a new direction in designing multifunctional nontoxic hybrid metal halides.

Cubane Copper(I) Iodide Clusters with Remotely Functionalized Phosphine Ligands: Synthesis, Structural Characterization and Optical Properties

We present here the synthesis, chemical, and photophysical study of a series of three new copper halide derivatives, namely 2a–c. They are all tetranuclear copper-iodide clusters of general formula [Cu(μ3-I)P]4 consisting of a cubane-like {Cu4I4} motif and P = phosphine. They differ in the type of the phosphines used as ligands: a monophosphine with a single pendant ester unit (complex 2a), two pendant ester units (2b), and a diphosphine containing two esters in the linker (2c). The molecular structure of the complexes was determined by single-crystal X-ray diffraction analysis. All the investigated derivatives were found to be photo- and thermally-stable luminescent species. In the solid state, the complexes display intense and long-lived photoluminescence in the orange region with PLQY values of 0.43–0.84 at room temperature associated mainly with a 3CC excited state with mixed 3XMCT character.

Wafer-scale heterogeneous integration of self-powered lead-free metal halide UV photodetectors with ultrahigh stability and homogeneity

Large-scale growth and heterogeneous integration with existing semiconductors are the main obstacles to the application of metal halide perovskites in optoelectronics. Herein, a universal vacuum evaporation strategy is presented to prepare copper halide films with wafer-scale spatial homogeneity. Benefiting from the electric field manipulation method, the built-in electric fields are optimized and further boost the self-powered UV photodetecting performances of common wide-bandgap semiconductors by more than three orders of magnitude. Furthermore, with effective modulation of the interfacial charge dynamics, the as-fabricated GaN-substrate heterojunction photodetector demonstrates an ultrahigh on/off ratio exceeding 107, an impressive responsivity of up to 256 mA W–1, and a remarkable detectivity of 2.16 × 1013 Jones at 350 nm, 0 V bias. Additionally, the device exhibits an ultrafast response speed (tr/td = 716 ns/1.30 ms), an ultra-narrow photoresponse spectrum with an FWHM of 18 nm and outstanding continuous operational stability as well as long-term stability. Subsequently, a 372-pixel light-powered imaging sensor array with the coefficient of variation of photocurrents reducing to 5.20% is constructed, which demonstrates exceptional electrical homogeneity, operational reliability, and UV imaging capability. This strategy provides an efficient way for large-scale integration of metal halide perovskites with commercial semiconductors for miniature optoelectronic devices.

Copper-based halide films with high photoluminescence quantum yield in the visible region deposited in situ by double source aerosol-assisted chemical vapor deposition

A huge family of luminescent low-dimensional metal halides for optoelectronic applications has emerged recently as a green alternative to the highly toxic lead halide phosphors. To date, studies on the controlled deposition of these materials as films to be integrated into optoelectronic architectures remain scarce. Here, the synthesis and characterization of highly luminescent films of copper halide phosphors with emissions in violet: K2CuCl3, blue: Cs5Cu3Cl6I2, and green: Cs3Cu2Cl5 are reported. The films were obtained by multisource aerosol-assisted chemical vapor deposition (AACVD) from methanolic solutions at low temperature and under ambient conditions. Photoluminescent quantum yield values obtained for the films deposited on quartz substrates have values of 52% for K2CuCl3, 85% for Cs5Cu3Cl6I2, and 99% for Cs3Cu2Cl5. These values were highly influenced by the substrate since for samples deposited on glass substrates the values are 26.17% for K2CuCl3, 60.47% for Cs5Cu3Cl6I2, and 59.7% for Cs3Cu2Cl5. Different textured morphologies, with valuable applications in light-harvesting, were found for each stoichiometry. Finally, x-ray photo-emitted spectroscopy was employed to demonstrate the existence of only Cu(I) highly emissive species, suggesting that AACVD could be an excellent alternative for metal halide film deposition.

Colloidal Synthesis and Optical Properties of Cs2CuCl4 Nanocrystals

Lead-free copper halide perovskite nanocrystals (NCs) are emerging materials with excellent photoelectric properties. Herein, we present a colloidal synthesis route for orthorhombic Cs2CuCl4 NCs with a well-defined cubic shape and an average diameter of 24 ± 2.1 nm. The Cs2CuCl4 NCs exhibited bright, deep blue photoluminescence, which was attributed to the Cu(II) defects. In addition, passivating the Cs2CuCl4 NCs by Ag+ could effectively improve the photoluminescence quantum yield (PLQY) and environmental stability.

Columnar Liquid Crystals of Copper(I) Complexes with Ionic Conductivity and Solid State Emission.

Two neutral copper(I) halide complexes ([Cu(BTU)2X], X = Cl, Br) were prepared by the reduction of the corresponding copper(II) halides (chloride or bromide) with a benzoylthiourea (BTU, N-(3,4-diheptyloxybenzoyl)-N'-(4-heptadecafluorooctylphenyl)thiourea) ligand in ethanol. The two copper(I) complexes show a very interesting combination of 2D supramolecular structures, liquid crystalline, emission, and 1D ionic conduction properties. Their chemical structure was ascribed based on ESI-MS, elemental analysis, IR, and NMR spectroscopies (1H and 13C), while the mesomorphic behavior was analyzed through a combination of differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and powder X-ray diffraction (XRD). These new copper(I) complexes have mesomorphic properties and exhibit a hexagonal columnar mesophase over a large temperature range, more than 100 K, as evidenced by DSC studies and POM observations. The thermogravimetric analysis (TG) indicated a very good thermal stability of these samples up to the isotropization temperatures and over the whole temperature range of the liquid crystalline phase existence. Both complexes displayed a solid-state emission with quantum yields up to 8% at ambient temperature. The electrical properties of the new metallomesogens were investigated by variable temperature dielectric spectroscopy over the entire temperature range of the liquid crystalline phase. It was found that the liquid crystal phases favoured anhydrous proton conduction provided by the hydrogen-bonding networks formed by the NH…X moieties (X = halide or oxygen) of the benzoylthiourea ligand in the copper(I) complexes. A proton conductivity of 2.97 × 10-7 S·cm-1 was achieved at 430 K for the chloro-complex and 1.37 × 10-6 S·cm-1 at 440K for the related bromo-complex.

Low-temperature liquid-phase formation of environmentally stable copper halide nanocrystal superlattices and their application to anticounterfeiting patterns

Nanocrystal superlattices have the potential to create a new class of semiconductor materials by combining the photophysical properties of individual nanocrystals with bulk-like structure performance. However, the principles underlying the direct formation of superlattices in liquid phase have not been thoroughly investigated, particularly, those consisting of exciton self-trapping metal halides. Here, we explore the formation of Cs3Cu2Br5 nanocrystal superlattices via liquid-phase crystallization of growing nanocrystals over a reaction period of only a few seconds. Importantly, the reaction temperature and the precursor concentration were found to be key parameters governing the concomitant nanocrystal growth and superlattice formation. The resulting Cs3Cu2Br5 superlattices had a well-defined face-centered cubic structure and emitted a single-band bright blue emission when exposed to 280 nm light. Owing to their advantages, such as low toxicity, reabsorption-free, narrow absorption, strong emission, and high environmental stability, the Cs3Cu2Br5 superlattices were applicable to anti-counterfeiting applications. Our findings shed light on the liquid-phase assembly of nanocrystals into superlattices and highlight the potential applications of the superlattices.

Synthesis, structures and thermal dependence of photoluminescence of copper(I) halide metallacycle and 1-D chain complexes

In this work, we report the synthesis, X-ray crystal structures, and temperature dependence of solid-state photoluminescence properties of two cuprous iodide complexes, namely, [(mpbi)CuI]n (1) and [(bimb)CuI]n (2) (mpbi = 1,1′-(5-methyl-1,3-phenylene)bis (1H-imidazole), bimb = 1,2-bis((imidazole-1-yl)methyl)benzene). The complexes exhibit efficient solid-state emission at room temperature, with peak emission wavelengths at 580 and 650 nm, respectively. Two complexes display outstanding thermal stability. The X-ray diffraction analysis revealed that the structure of 1 is a discrete metallacycle with the copper atom in the structure adopting a less common triangular configuration, while the structure of 2 is a one-dimensional chain structure of Cu2I2 binuclear rhomboid. The temperature dependence of photoluminescence in the wide temperature range is investigated, which demonstrates that the thermal quenching of luminescence of copper complexes can be regulated by cuprophilic interaction.

First-Principles Investigation on the Stability, Electronic Structure, and Exciton Self-Trapping Mechanism of 0D and 1D Cs3Cu2Cl5

Copper(I) halides with broadband emission from self-trapped excitons (STEs) are promising luminescent materials due to their structural diversities and intriguing photophysical properties. Despite great efforts invested in these materials, an in-depth understanding of their structural variations and the corresponding STE emission mechanisms is still lacking. Here, first-principles calculations reveal two distinct STEs in 0D and 1D polymorphs of Cs3Cu2Cl5, which feature the same chemical composition but different crystal structures. The electronic band structure analysis reveals that the strong Cu–Cl 4s–3p coupling along the 1D [Cu2Cl5]3– chain brings a large band dispersion, resulting in an increase of optical anisotropy in the 1D structure. The STE in 0D Cs3Cu2Cl5 involves the formation of one Cu–Cu bond and the breakage of two Cu–Cl bonds within an isolated [Cu2Cl5]3– unit. In contrast, the exciton self-trapping in the 1D structure is found to be associated with the formation of one Cu–Cu bond accompanied by two Cu–Cl bonds in the [Cu2Cl5]3– chain. Despite significant structural differences in 0D and 1D Cs3Cu2Cl5, quantitative characterizations of the configuration coordinate diagrams in the two polymorphs lead to similar STE emission energies (2.38 and 2.48 eV for 0D and 1D, respectively), which theoretically explains similar green-light emission experimentally observed in both compounds. This study provides important insights for understanding complex relations between the structural dimensionality, building units, and emission properties in low-dimensional metal halides.

Syntheses, Structures, and Photoluminescence of Copper-Based Halides

Copper-based halides have been found to be a new family of lead-free materials with high stability and superior optoelectrical properties. In this work, we report the photoluminescence of the known (C8H14N2)CuBr3 and the discovery of three new compounds, (C8H14N2)CuCl3, (C8H14N2)CuCl3·H2O, and (C8H14N2)CuI3, which all exhibit efficient light emissions. All these compounds have monoclinic structures with the same space group (P21/c) and zero-dimensional (0D) structures, which can be viewed as the assembly of promising aromatic molecules and different copper halide tetrahedrons. Upon the irradiation of deep ultraviolet light, (C8H14N2)CuCl3, (C8H14N2)CuBr3,, and (C8H14N2)CuI3 show green emission peaking at ∼520 nm with a photoluminescent quantum yield (PLQY) of 3.38, 35.19, and 17.81%, while (C8H14N2)CuCl3·H2O displays yellow emission centered at ∼532 nm with a PLQY of 2.88%. A white light-emitting diode (WLED) was successfully fabricated by employing (C8H14N2)CuBr3 as a green emitter, demonstrating the potential of copper halides for applications in the green lighting field.

Solvent-Free Grinding Synthesis of Hybrid Copper Halides for White Light Emission.

Lead-free metal halides (LMHs) have recently attracted numerous attention in solid-state lighting due to their unique structures and outstanding optoelectronic properties. However, conventional preparation processes with the utilization of toxic organic solvents and high temperatures seem to impede commercial applications of LMHs. In this work, we successfully synthesize Cu+-based metal halides (TMA)3Cu2Br5-xClx (TMA: tetramethylammonium) with high photoluminescence quantum yields (PLQYs) via a solvent-free mechanical grinding method. By changing the ratio of halide ions (Cl- and Br-) in precursors, the emission wavelength of the prepared (TMA)3Cu2Br5-xClx can be tuned from 535 to 587 nm, which are employed as emitters in the fabrication of white-light-emitting diodes (WLEDs). The achieved WLEDs exhibit a high color rendering index value of 84 and standard Commission Internationale de l'Éclairage (CIE) coordinates of (0.324, 0.333). This feasible and solvent-free preparation strategy not only promotes the mass production of LMHs but also highlights the promising potential for efficient solid-state illumination.

Ultrabright Light Emission Properties of All-Inorganic and Hybrid Organic–Inorganic Copper(I) Halides

All-inorganic and hybrid copper(I) halides have recently emerged as candidate optical materials due to their extremely high light emission efficiencies, nontoxic and earth-abundant elemental compositions, and low-cost solution processability. Originally inspired and motivated by the research on the halide perovskites family, the development of copper(I) halide light emitters has been following its unique path. In this perspective, we discuss the distinct low-dimensional crystal structures of all-inorganic halides, which enable strong charge localization and formation of room-temperature self-trapped excitonic (STE) states, giving rise to largely Stokes-shifted light emission with near-unity quantum yields. Due to their unique electronic structures, all-inorganic copper halides are predominantly blue emitters with unusually weak tunability of their optical properties (e.g., halide substitution has a minimal impact on their photoluminescence properties). These shortcomings paved the way for the exploration of more robust and diverse families of hybrid organic–inorganic copper(I) halides, which are discussed next. Our discussions of crystal and electronic structures and optical properties of all-inorganic and hybrid Cu(I) halides are complemented by the reported uses of these materials in optoelectronic applications. Finally, we identify remaining fundamental questions, knowledge gaps, and practical challenges and outline several paths forward for addressing these issues, including through new materials discovery and in-depth studies of photophysics of Cu(I) halides and derivative materials.

Synthesis of copper(II) halide dimers with 2-amino-5-methylpyridine and serendipitous copper catalyzed synthesis of 3-bromo-2-ethyl-5-methyl-1H-pyrrolo[2,3-b]pyridine

Reaction of CuX2·nH2O (X = Cl, n = 2; X = Br, n = 0) with 2-amino-5-methylpyridine (5MAP) in acetonitrile yielded [(5MAP)2CuX2]2 (1, Cl; 2, Br). The compounds are isomorphous and crystallize in the monoclinic space group P21 /n as bihalide bridged dimers. Variable temperature magnetic measurements show very weak exchange in the two compounds (-2.1(1) K) which may correlate with previously proposed magnetostructural correlations for bihalide bridged Cu(II) dimers. In attempts to prepare 2 in 2-butanone as solvent, [(3-Br-2-Et-5-Mepyrpy)(CH3CO2)4Cu2] (3) was serendipitously isolated (3-Br-2-Et-5-Mepyrpy = 3-bromo-2-ethyl-5-methyl-7H-pyrrolido[2,3-b]pyridinium). The bicyclic ligand was synthesized in situ by condensation of 5MAP with the solvent; the acetate ions were generated by copper(II) catalyzed Baeyer-Villiger oxidation of the solvent. A mechanism for the synthesis is proposed. The resulting Cu-paddlewheel compound exhibits strong (-400 K) antiferromagnetic interactions.

Two‐Step Sequential Process for Fabricating Graphene Nanosheets Decorated with Copper Halide Nanocrystals and Their Optoelectronic Applications

AbstractNanocrystals of Cs3Cu2I5, a metal halide with promising potential as a perovskite substitute, are successfully grown on graphene nanosheets. An intermediate stage of physically exfoliated graphene nanosheets, concurrent with the formation of copper‐based seeds on graphene surface, is developed, for the first time, allowing for the subsequent growth of Cs3Cu2I5 nanocrystals (CsNCs) to obtain CsNCs‐decorated graphene nanohybrids (CsGNHs). The morphology and properties of the CsGNHs depend on the input amount of graphene nanosheets during the reaction. The photoluminescence intensity of the CsGNHs decreases with increasing graphene content, indicating that graphene facilitates nonradiative energy transfer from the CsNCs in the CsGNHs. The inherent self‐trapping exciton emission of the CsNCs is also affected by the graphene substrate. As the graphene content increases, the emission peaks of the CsGNHs broaden and diminish. The CsGNHs emit a stable solid‐state luminescence with a large Stokes shift (zero self‐absorption) under a high‐energy ultraviolet (UV) light. Consequently, the CsGNHs can act as optoelectronic transducers and selectively generate a turn‐on photocurrent response under specific‐wavelength UV light. Additionally, a new anticounterfeiting strategy is developed using the CsGNHs as a luminescent black ink to fabricate luminescent quick‐response codes with fake pixels.

First-principles calculations to investigate structural, electronic and optical properties of ternary copper halides AlCumXn (A = K, Rb, Cs; X = Cl, Br, I)

Low-dimensional ternary metal halides have recently attracted much attention due to their excellent photoelectric performance is of significant interests. Considering the remarkable photoelectric properties of some copper - based halides, herein, we investigate the structural, electronic and optical properties of 3D, 1D and 0D structured ternary copper halides, including ACuX3, ACu2X3, A2CuX3, A4CuX6, and A3Cu2X5 using the first-principles. Their binding energies (Eb) and formation energies (Ef) were calculated, which confirmed the thermodynamic stability of these compounds. Most of these halides are direct band gap semiconductors. The valence band tops of these five type materials are mainly provided by Cu-d orbitals and halide X-p orbitals, while the conduction band bottoms are mainly provided by Cu-s and X-p orbitals. In addition,these ternary copper halides show significant light absorption characteristics, especially in the visible light range. Our results show AlCumXn (A = K, Rb, Cs; X = Cl, Br, I) would have wide photoelectric application potential.

Large-Scale, Uniform-Patterned CsCu2 I3 Films for Flexible Solar-Blind Photodetectors Array with Ultraweak Light Sensing.

Cesium copper halide perovskite is one of the promising materials for solar-blind light detection. However, most of the cesium copper halide perovskite-based photodetectors (PDs) are focused on ultraviolet A detection and realized on the rigid substrate in the single device configuration. Here, a flexible solar-blind PDs array (10×10 pixels) based on the CsCu2 I3 film patterns for ultraweak light sensing and light distribution imaging is reported. Large-scale CsCu2 I3 film arrays are synthesized with various shapes and uniform dimensions through a simple vacuum-heating-assisted solution method. Benefiting from excellent air stability and superior resistance to the photodegrading of the CsCu2 I3 film, the array device exhibits long-term stable photoswitching behavior for 8h and ultralow light detection capability to resolve the light intensity of 6.1 nW cm-2 with a high responsivity of 62 A W-1 , and the array device can acquire clear images of "G", "X", and "U" showing the input light distribution. Moreover, the flame detection and warning system based on a curved solar-blind PDs array is demonstrated, which can be used for multi-flame monitoring and locating. These results can encourage potential applications of the CsCu2 I3 film-based PDs array in the field of optical communication and environment monitoring.

Luminescent Water-Dispersible Nanoparticles Engineered from Copper(I) Halide Cluster Core and P,N-Ligand with an Optimal Balance between Stability and ROS Generation

The present work introduces the solvent exchange procedure as a route for conversion of the Cu4I4L2 complex, where the Cu4I4 cluster core is coordinated with two P,N-ligands (L), into an aqueous colloid. The analysis of both colloidal and supernatant phases revealed some losses in CuI going from the initial Cu4I4L2 complex to Cu2I2L3-based nanoparticles. The comparative analysis of IR, 31P NMR spectroscopy, ESI mass-spectrometry and luminescence data argued for a contribution of the “butterfly”-like structures of the Cu2I2 cluster core to Cu2I2L3-based nanoparticles, although the amorphous nature of the latter restricted structure evaluation from the PXRD data. The green luminescence of the colloids revealed their chemical stability under pH variations in the solutions of some amino acids and peptides, and to specify the temperature and concentration conditions triggering the oxidative degradation of the nanoparticles. The spin trap-facilitated ESR study indicated that the oxidative transformations were followed by the generation of reactive oxygen species (ROS). The physiological temperature level (310 K) enhanced the ROS generation by nanoparticles, but the ROS level was suppressed in the solution of GSH at pH = 7.0. The cytotoxicity of nanoparticles was evaluated in the M-HeLa cell line and is discussed in correlation with their cell internalization and intracellular oxidative transformations.

Ligand induced phase-controlled synthesis of copper halide perovskite nanocrystals towards tunable white light emission

Recently, copper halides have attracted considerable interest for their excellent photoluminescence properties, low-cost and non-toxicity. Herein, we report the phase control in the synthesis of Cs3Cu2I5 and CsCu2I3 nanocrystals. The crystalline phase of the products can be tuned by changing the volume ratio of the ligand pair of oleic acid (OA) and oleylamine (OLA). Blue-emissive Cs3Cu2I5 and yellow-emissive CsCu2I3 nanocrystals can be obtained with the ratio of OA/OLA of 0.5:0.5 and 1:0.6, respectively. Interestingly, the composite of Cs3Cu2I5 and CsCu2I3 with ratio of OA/OLA of 1:0.8 exhibits tunable white light emission from cold white to pure white to neutral white.