Luminescent copper(I) complexes with halogenido-bridged dimeric core

Investigation of Luminescent Triplet States in Tetranuclear CuI Complexes: Thermochromism and Structural Characterization

To develop new and flexible CuI containing luminescent substances, we extend our previous investigations on two metal-centered species to four metal-centered complexes. These complexes could be a basis for designing new organic light-emitting diode (OLED) relevant species. Both the synthesis and in-depth spectroscopic analysis, combined with high-level theoretical calculations are presented on a series of tetranuclear CuI complexes with a halide containing Cu4 X4 core (X=iodide, bromide or chloride) and two 2-(diphenylphosphino)pyridine bridging ligands with a methyl group in para (4-Me) or ortho (6-Me) position of the pyridine ring. The structure of the electronic ground state is characterized by X-ray diffraction, NMR, and IR spectroscopy with the support of theoretical calculations. In contrast to the para system, the complexes with ortho-substituted bridging ligands show a remarkable and reversible temperature-dependent dual phosphorescence. Here, we combine for the first time the luminescence thermochromism with time-resolved FTIR spectroscopy. Thus, we receive experimental data on the structures of the two triplet states involved in the luminescence thermochromism. The transient IR spectra of the underlying triplet metal/halide-to-ligand charge transfer (3 M/XLCT) and cluster-centered (3 CC) states were obtained and interpreted by comparison with calculated vibrational spectra. The systematic and significant dependence of the bridging halides was analyzed.

All-in-one: a new approach toward robust and solution-processable copper halide hybrid semiconductors by integrating covalent, coordinate and ionic bonds in their structures

Conventional inorganic semiconductors are best known for their superior physical properties and chemical robustness, and their widespread use in optoelectronic devices. However, implementation of these materials in many other applications has been hindered by their poor solubility and/or solution-processability, a longstanding drawback that is largely responsible for issues such as high cost. While recent progress on hybrid perovskites, an important class of inorganic-organic hybrid materials, has shed light on the development of high-performance solution processable semiconductors, they rely heavily on toxic metals and generally suffer from framework instability. To address these issues, a new group of hybrid semiconductors based on anionic copper(i) halide and cationic organic ligands has been developed. These compounds are noted as All-In-One (AIO) structures as they consist of covalently bonded anionic CuX inorganic modules that form both coordinate and ionic bonds with cationic organic ligands. Studies demonstrate that framework stability and solution processibility of these materials are greatly enhanced as a result of such bonds. In the perspective, we highlight the development of this newly emerged type of materials including their crystal structures, chemical and physical properties and possible applications. The untapped potential that the AIO approach can offer for other hybrid families is also discussed.

Facilely controllable synthesis of copper-benzothiadiazole complexes via solvothermal reactions: exploring the customized synthetic approach by experiments

It is very challenging to transform small organic molecules into customized coordination polymer (CP) because the functionalities with desired properties are greatly influenced by several elements, including the assembly modes of the organic linkers and metal nodes, organic linker functionalization, and defects. Therefore, deep cognition for the molecular-level engineering of CP chemistry is very important. Herein, we obtained five new copper-benzothiadiazole complexes via a controllable synthesis approach: [CuII(L1)(CH3CN)]2 (C1), [CuIBr(L1)]n (C2), [CuI3Br3(L2)2]n (C3), [CuICl(L3)]2 (C4), and [CuIICl2(L3)2] (C5). In the exploration, we successfully modulated the structure of the organic linker and the valence state of the metal nodes as well as the assembly modes of the organic linkers and metal nodes through the facilely controllable solvothermal reaction. The results from our experiments also indicated that the fusing process was driven by a CuII/CuI catalytic cycle. In this pathway, oxygen is the final electron acceptor and the solvent DMSO acts as a co-oxidant. In C2 and C3, the ever-expanding macrocycles were constructed from CuX clusters and organic chromophore linkers, forming interesting 1D chain structures, while the supramolecular macrocycles were assembled through hydrogen bonding expanding to a 3D network of C5. Interestingly, C1-C4 exhibit chromophore-based fluorescence, but are not phosphorescence.

Synthesis and Photophysical Properties of Emissive Silver(I) Halogenido Coordination Polymers Composed of {Ag2X2} Units Bridged by Pyrazine, Methylpyrazine, and Aminopyrazine

Luminescent silver(I) coordination polymers having a {Ag₂(μ-X)₂} rhombic core (X = I, Br) were prepared using pyrazine (pyz), methylpyrazine (Mepyz), and aminopyrazine (ampyz) as bridging ligands. Photophysical measurements show that the complexes were strongly luminescent in the solid state at room temperature; further, the emissive excited state of the pyz and Mepyz complexes was a triplet charge-transfer (³CT) excited state, similar to that of their copper(I) congeners, whereas that of the ampyz complex was a intraligand (³IL) excited state. The energy of the ³CT excited state of a silver halogenido complex was revealed to be ca. 5000 cm^-1 higher than that of the corresponding copper complex.

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.

Strategies for optimizing the luminescence and stability of copper iodide organic–inorganic hybrid structures

In this article, the structural characteristics and synthetic methods of copper iodide hybrid materials are introduced, and the strategies for optimizing the stability and luminescence properties of these compounds are reviewed.

Ag(i) and Cu(i) cyclic-triimidazole coordination polymers: revealing different deactivation channels for multiple room temperature phosphorescences

The photophysics of isostructural Ag(i) and Cu(i) 1D and 3D coordination polymers based on cyclic triimidazole reveals excitation wavelength-dependent multiple emissions with different radiative paths according to the coordinated metal.

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).

Crystal Structures and Phosphorescent Properties of Group 14 Dipyridinometalloles and Their Copper Complexes

We recently reported dipyridinosilole (DPyS) and dipyridinogermole (DPyG) as π-conjugated units that show low-temperature phosphorescence. A copper complex of DPG shows solid-state phosphorescence at room temperature. In this work, we prepared diphenyldipyridinostannole (DPySn1). Its optical and electrochemical properties were investigated and compared with those of DPyS1 and DPyG1 with the same phenyl substituents. DPySn1 showed the most red-shifted phosphorescence at 520 nm at 77 K in the solid-state, which is likely due to the intermolecular Sn-pyridine interaction that was confirmed by single-crystal X-ray diffraction. Copper complexes of DPyS1 and DPySn1 were also prepared and it was found that the phosphorescence of these dipyridinometallole-copper complex solids was red-shifted in the order of DPySn1-Cu (617 nm)<DPyG1-Cu (624 nm)<DPyS1-Cu (645 nm). Single-crystal X-ray diffraction studies were performed for DPyS1-Cu and DPySn1-Cu complexes. DPyS1-Cu showed a double-chained polymeric ladder-like structure with Cu₄ I₄ cluster units and DPySn1-Cu possessed a single chain polymeric structure with Cu₂ I₂ units, analogous to DPyG1-Cu.

Modifying the luminescent properties of a Cu(i) diphosphine complex using ligand-centered reactions in single crystals

Here we report how reactions at a chemically reactive diphosphine shift the long-lived luminescent colour of a crystalline three-coordinate Cu(i) complex from green to blue. The results demonstrate how vapochromism and single-crystal-to-single-crystal transformations can be achieved using ligand-centered reactions.

Dicopper(I) Paddle-Wheel Complexes with Thermally Activated Delayed Fluorescence Adjusted by Ancillary Ligands

A suite of paddle-wheel shaped [Cu₂(PymPPh₂)₃(L_an)_n](PF₆)₂ complexes showing efficient thermally activated delayed fluorescence (TADF) has been synthesized. In these complexes, Cu(I) ions are P,N-bridged by three diphenyl(2-pyrimidyl)phosphine (PymPPh₂, L) ligands in a "head-to-tail" fashion, and one or both metals are also capped by the ancillary ligand (L_an = MeOH, Me₂CO, MeCN, PhCN). At ambient temperature, the solid complexes emit TADF with the quantum yield of up to 85% and the lifetimes of from 9.6 to 27 μs. The ancillary ligands, whose orbitals negligibly contribute to the radiative ¹(M + L + L_an)LCT state, remarkably adjust emission energies and ΔE(S₁-T₁) energy splitting magnitudes of the emitters obtained. Thus, depending on structure and/or number of the L_an molecules, the emission maxima vary from 500 to 563 nm, and the ΔE(S₁-T₁) gaps range 550-1100 cm^-1. Such tunable TADF characteristics coupled with the excellent solubility and air-stability make the complexes presented to be promising TADF materials.

Quantitative Thermal Synthesis of Cu(I) Coordination Polymers That Exhibit Thermally Activated Delayed Fluorescence

As a new environmentally friendly route for synthesizing thermally activated delayed-fluorescence (TADF) Cu(I) complexes, we successfully and quantitatively synthesized strongly emissive Cu(I) coordination polymers [Cu₂I₂(PR₃)₂(n,n'-bpy)]_∞ (CuIR-n, R = Ph, Tol; n = 3, 4; bpy = bipyridine) via the quick thermal reaction of three starting materials (CuI, PR₃, and bpy organic ligands) for 1 h in the absence of a solvent. Powder X-ray diffraction and thermogravimetric analyses revealed that melting of the organic ligands significantly promoted the coordination polymerization reaction, and the stoichiometry of three starting materials was crucial to quantitatively affording CuIR-n. Notably, the photophysical properties of CuIR-n obtained by the thermal reaction were almost the same (emission wavelength, quantum yield, and lifetime) as that obtained by generally used solution reactions, probably because CuIR-n was thermally stable enough to prevent the thermal damage and to improve the crystallinity in the heating process. The emission origin of CuIR-n was assignable to TADF at 298 K and phosphorescence at 77 K originating from the metal-to-ligand charge-transfer excited state effectively mixed with the halide-to-ligand charge transfer ((M+X)LCT) state. Thus, the thermal reaction in the melted ligand could be a promising environmentally friendly method for producing TADF Cu(I) luminophores.

Semiconducting crystalline inorganic-organic hybrid metal halide nanochains

One-dimensional (1D) inorganic-organic metal halide hybrids at the molecular level, which can be considered as arrays of nanochains isolated by organic components, have shown remarkable optical and electric properties. This review summarizes their reported structural types and shows how to modify their band gaps and optical and electric properties.

Structural Diversity of Copper(I) Cluster-Based Coordination Polymers with Pyrazine-2-thiol Ligand

Six novel copper(I) cluster-based coordination polymers (CPs) [Cu₉(pzt)₇Cl₂]_n (1), [Cu₂(pzt)Cl]_n (2), [Cu₄(pzt)₃Br]_n (3), [Cu(pzt)]_n (4), [Cu₄(pzt)₃I]_n (5), and [Cu₇(pzt)₆I]_n (6) were solvothermally synthesized using Hpzt (Hpzt = pyrazine-2-thiol) ligand and well-characterized by elemental analysis, infrared (IR) spectroscopy, powder X-ray diffraction (PXRD), and single-crystal X-ray diffraction (SCXRD). Six CPs exhibit either 2D (4 and 6) or 3D (1-3, and 5) network based on diverse multinuclear {Cu_xS_y} clusters. The structural evolutions of 1-6 are greatly influenced by types of metal halides and the ligand-to-metal molar ratio used in the reaction. Among them, compound 1 displays interesting temperature-dependent photoluminescence arising from triplet cluster-centered (³CC) excited state from the cluster metal core. Compounds 1-6 also exhibit photocurrent responses upon visible-light illumination (λ = 420 nm) in the order 6 > 5 > 3 > 1 > 4 > 2. This work not only shows the structural diversity of {Cu_xS_y} clusters-based CPs but also provides an interesting insight into structural modulation using crystal engineering concept.

Cu(i) Iodide coordination polymers with aromatic thioamides

The reaction of 4-pyridinethiobenzamide (PyTBA) with CuI and KI aqueous solution in acetone or THF under slow diffusion gives rise to the formation of single crystals of two coordination polymers [CuIPyTBA]_n·nS (S = acetone; 1/3THF).

A Cu(i)–I coordination polymer fluorescent chemosensor with amino-rich sites for nitro aromatic compound (NAC) detection in water

The detection sensitivity increased as the sizes of [Cu₂I₂(MA)₂] decreased and the selectivity improved by introducing amino-rich ligands.

Strongly emissive white-light-emitting silver iodide based inorganic–organic hybrid structures with comparable quantum efficiency to commercial phosphors

A series of one-dimensional silver iodide based inorganic–organic hybrid structures with tunable white light emissions and high quantum efficiency have been synthesized by Cu substitution.

Copper(i) halide polymers derived from tris[2-(pyridin-2-yl)ethyl]phosphine: halogen-tunable colorful luminescence spanning from deep blue to green

A series of isostructural 1D coordination polymers bearing stair-step [Cu₄X₄] modules is reported. At ambient temperature, they feature bright halogen-modulated colorful luminescence spanning from deep blue to green.

Luminescent vapochromic single crystal to single crystal transition in one-dimensional coordination polymer featuring the first Cu(i) dimer bridged by an aqua ligand

Vapochromic luminescence caused by included solvent mobility is observed in reversible single-crystal to single-crystal (SC–SC) transitions in a one-dimensional coordination polymer bearing the first reported water molecule bridging two Cu(i) ions.

Synthesis, structure and photoluminescence properties of three copper(i) iodide based inorganic–organic hybrid structures with pyrazine derivatives

By using pyrazine derivatives, three different types of copper(i) iodide based inorganic–organic hybrid structures have been prepared.

Family of Highly Luminescent Pure Ionic Copper(I) Bromide Based Hybrid Materials

While a number of highly luminescent copper(I) halide based hybrid materials built on coordinate bonds (Cu-L; L = N, P, S-based ligands) have been obtained, the poor structural stability largely limited their commercialization. In contrast, according to the previous studies, the ionic structures (L-free) are more stable than those built on Cu-L coordinate bonds. However, the extremely weak emission hinders their optical applications. Herein, we report a tetra-alkylammonium-cation-induced strategy for the synthesis of stable and highly luminescent ionic CuBr-based hybrid materials. It is interesting to find that the tetra-alkylammonium cations with different chains could induce diverse CuBr-based anions. Moreover, most of these CuBr-based hybrids are highly luminescent, which makes them promising candidates as an alternative to phosphors and with potential applications in sensing.