Photo-Catalyzed α-Arylation of Enol Acetate Using Recyclable Silica-Supported Heteroleptic and Homoleptic Copper(I) Photosensitizers

Earth-abundant photosensitizers are highly sought after for light-mediated applications, such as photoredox catalysis, depollution and energy conversion schemes. Homoleptic and heteroleptic copper(I) complexes are promising candidates in this field, as copper is abundant and the corresponding complexes are easily obtained in smooth conditions. However, some heteroleptic copper(I) complexes suffer from low (photo)stability that leads to the gradual formation of the corresponding homoleptic complex. Such degradation pathways are detrimental, especially when recyclability is desired. This study reports a novel approach for the heterogenization of homoleptic and heteroleptic Cu complexes on silica nanoparticles. In both cases, the photophysical properties upon surface immobilization were only slightly affected. Excited-state quenching with aryl diazonium derivatives occurred efficiently (108 -1010  M-1  s-1 ) with heterogeneous and homogeneous photosensitizers. Moderate but almost identical yields were obtained for the α-arylation of enol acetate using the homoleptic complex in homogeneous or heterogeneous conditions. Importantly, the silica-supported photocatalysts were recycled with moderate loss in photoactivity over multiple experiments. Transient absorption spectroscopy confirmed that excited-state electron transfer occurred from the homogeneous and heterogeneous homoleptic copper(I) complexes to aryl diazonium derivatives, generating the corresponding copper(II) center that persisted for several hundreds of microseconds, compatible with photoredox catalysis applications.

The Tail Wags the Dog: The Far Periphery of the Coordination Environment Manipulates the Photophysical Properties of Heteroleptic Cu(I) Complexes

In this work we show, using the example of a series of [Cu(Xantphos)(N^N)]+ complexes (N^N being substituted 5-phenyl-bipyridine) with different peripheral N^N ligands, that substituents distant from the main action zone can have a significant effect on the physicochemical properties of the system. By using the C≡C bond on the periphery of the coordination environment, three hybrid molecular systems with -Si(CH3)3, -Au(PR3), and -C2HN3(CH2)C10H7 fragments were produced. The Cu(I) complexes thus obtained demonstrate complicated emission behaviour, which was investigated by spectroscopic, electrochemical, and computational methods in order to understand the mechanism of energy transfer. It was found that the -Si(CH3)3 fragment connected to the peripheral C≡C bond changes luminescence to long-lived intra-ligand phosphorescence, in contrast to MLCT phosphorescence or TADF. The obtained results can be used for the design of new materials based on Cu(I) complexes with controlled optoelectronic properties on the molecular level, as well as for the production of hybrid systems.

Visible-emitting Cu(i) complexes with N-functionalized benzotriazole-based ligands

Bidentate benzotriazole-based N-ligands are suited for the preparation of luminescent heteroleptic copper(i) complexes with noticeable emissions related to 3MLCT transitions.

Heteroleptic [Cu(P^P)(N^N)][PF6] Compounds with Isomeric Dibromo-1,10-Phenanthroline Ligands

A series of [Cu(P^P)(N^N)][PF6] compounds are reported in which N^N is 2,9-dibromo-1,10-phenanthroline (2,9-Br2phen), 3,8-dibromo-1,10-phenanthroline (3,8-Br2phen) or 4,7-dibromo-1,10-phenanthroline (4,7-Br2phen) and P^P is bis(2-(diphenylphosphano)phenyl)ether (POP) or 4,5-bis(diphenylphosphano)-9,9-dimethylxanthene (xantphos). The compounds were characterized by solution multinuclear NMR spectroscopy, mass spectrometry and a single-crystal X-ray analysis. Each compound underwent a partially reversible or irreversible copper-centred oxidation, the highest potential being for 2,9-Br2phen-containing compounds. In solution, the compounds are weak yellow or orange emitters, whereas powdered samples exhibit yellow emissions with photoluminescence quantum yields of up to 45% for [Cu(xantphos)(2,9-Br2phen)][PF6] with an excited state lifetime τ1/2 = 9.9 μs. Values of λemmax for [Cu(POP)(2,9-Br2phen)][PF6] and [Cu(xantphos)(2,9-Br2phen)][PF6] are blue-shifted with respect to compounds with the 3,8-and 4,7-isomers, both in solution and in the solid state.

Ligand electronic fine-tuning and its repercussion on the photocatalytic activity and mechanistic pathways of the copper-photocatalysed aza-Henry reaction

Subtle electronic ligand effects have a strong impact on the mechanistic pathway of a photocatalytic coupling reaction.

Synthesis and Characterization of Three New Emissive Mononuclear CuI Heteroleptic Complexes with Functionalized 6-Cyano-2,2′-bipyridine Chelating Ligands

A new series of luminescent mononuclear CuI complexes with functionalized 6-cyano-2,2′-bipyridine chelating ligands, [Cu(xantphos)(cbpy)]ClO4 (1), [Cu(xantphos)(4,4’-Me2cbpy)]ClO4·CH2Cl2·H2O (2), and [Cu(POP)(cbpy)]ClO4·CH2Cl2 (3) (xantphos=4,5-bis(diphenylphosphino)-9,9-dimethylxanthene; POP=bis(2-diphenylphosphinophenyl)ether; 4,4’-Me2cbpy=4,4’-dimethyl-6-cyano-2,2′-bipyridine; cbpy=6-cyano-2,2′-bipyridine) have been successfully prepared, and their structures and photophysical properties are investigated. Single crystal structures of the three complexes reveal a distorted tetrahedral coordination geometry around the CuI centres with the P atoms of diphosphane ligands and N donors of 2,2′-bipyridine ring. Luminescence measurements indicate that these CuI complexes display good emission properties both in the solution and solid states at room temperature, which can be well modulated through modifying the structure of 6-cyano-2,2′-bipyridine. It is shown that the introduction of two electron-donating methyl groups at the 4,4’-positions of the 6-cyano-2,2′-bipyridine is favourable to enhance the luminescence properties of the CuI complexes.

[Cu(POP)(N^S)][PF6] and [Cu(xantphos)(N^S)][PF6] compounds with 2-(thiophen-2-yl)pyridines

A series of [Cu(POP)(N^S)][PF₆] and [Cu(xantphos)(N^S)][PF₆] compounds (POP = bis(2-(diphenylphosphino)phenyl)ether, xantphos = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene) in which the N^S ligand is a 2-(thiophen-2-yl)pyridine (1), 2-(thiophen-2-yl)-6-methylpyridine (2), 2-(5-methylthiophen-2-yl)pyridine (3) or 2-(5-methylthiophen-2-yl)-6-methylpyridine (4) have been prepared and characterized in solution and the solid state. Single crystal structures of [Cu(POP)(1)][PF₆], [Cu(xantphos)(1)][PF₆], [Cu(xantphos)(2)][PF₆], [Cu(POP)(3)][PF₆]·CH₂Cl₂, and [Cu(xantphos)(4)][PF₆] confirm chelating N^S and P^P ligands, and distorted tetrahedral copper(i) centres. There is close cation⋯anion association, particularly in [Cu(xantphos)(1)][PF₆]. Although the compounds are stable over days in CH₂Cl₂ solution, they are susceptible to the effects of competing ligands such as chloride ion and MeCN. Analysis of the NMR spectroscopic data of a solution of [Cu(POP)(3)][PF₆] with added Cl⁻, gives a K_d value of 0.14 ± 0.03 mM, indicative of ion-pairing. [Cu(POP)(N^S)][PF₆] and [Cu(xantphos)(N^S)][PF₆] exhibit quasi-reversible or irreversible Cu⁺/Cu²⁺ oxidations. They are blue emitters in solution, and the presence of the 5-methyl group in the thiophene ring in 3 and 4 leads to a red-shift in the emission. The highest photoluminescence quantum yields are for [Cu(POP)(2)][PF₆] (30.8%) and [Cu(POP)(4)][PF₆] (33.2%), both of which have a 6-methyl-substituted pyridine ring in the N^S ligand. Excited-state lifetimes are <5 ns. On going from solution to powder samples, red-shifts of 133 to 163 nm are observed leading to yellow emitters. The brightest emitter, [Cu(xantphos)(1)][PF₆], was tested in a LEC device but showed poor electroluminescence and poor charge transporting characteristics.

[Cu(P^P)(N^S)][PF₆] with N^S = 2-(thiophen-2-yl)pyridines show close cation⋯anion association in the solid-state; complex cation association with Cl⁻ occurs in solution. The compounds are blue-emitters in solution with a red-shift of the emission on going to the solid.

Phosphane tuning in heteroleptic [Cu(N^N)(P^P)]+ complexes for light-emitting electrochemical cells

The effects on photo-and electroluminescent properties of structurally modifying the bisphosphane in [Cu(N^N)(P^P)]⁺ complexes (N^N = bpy, 6-Mebpy, 6,6′-Me₂bpy) are described.

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.

CF3 Substitution of [Cu(P^P)(bpy)][PF6 ] Complexes: Effects on Photophysical Properties and Light-Emitting Electrochemical Cell Performance

Herein, [Cu(P^P)(N^N)][PF₆ ] complexes (P^P=bis[2-(diphenylphosphino)phenyl]ether (POP) or 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (xantphos); N^N=CF₃ -substituted 2,2'-bipyridines (6,6'-(CF₃ )₂ bpy, 6-CF₃ bpy, 5,5'-(CF₃ )₂ bpy, 4,4'-(CF₃ )₂ bpy, 6,6'-Me₂ -4,4'-(CF₃ )₂ bpy)) are reported. The effects of CF₃ substitution on their structure as well as their electrochemical and photophysical properties are also presented. The HOMO-LUMO gap was tuned by the N^N ligand; the largest redshift in the metal-to-ligand charge transfer (MLCT) band was for [Cu(P^P){5,5'-(CF₃ )₂ bpy}][PF₆ ]. In solution, the compounds are weak yellow to red emitters. The emission properties depend on the substitution pattern, but this cannot be explained by simple electronic arguments. Among powders, [Cu(xantphos){4,4'-(CF₃ )₂ bpy}][PF₆ ] has the highest photoluminescence quantum yield (PLQY; 50.3 %) with an emission lifetime of 12 μs. Compared to 298 K solution behavior, excited-state lifetimes became longer in frozen Me-THF (77 K; THF=tetrahydrofuran), thus indicating thermally activated delayed fluorescence (TADF). Time-dependent (TD)-DFT calculations show that the energy gap between the lowest-energy singlet and triplet excited states (0.12-0.20 eV) permits TADF. Light-emitting electrochemical cells (LECs) with [Cu(POP)+(6-CF₃ bpy)][PF₆ ], [Cu(xantphos)(6-CF₃ bpy)][PF₆ ], or [Cu(xantphos){6,6'-Me₂ -4,4'-(CF₃ )₂ bpy}][PF₆ ] emit yellow electroluminescence. The LEC with [Cu(xantphos){6,6'-Me₂ -4,4'-(CF₃ )₂ bpy}][PF₆ ] had the fastest turn-on time (8 min), and the LEC with the longest lifetime (t_1/2 =31 h) contained [Cu(xantphos)(6-CF₃ bpy)][PF₆ ]; these LECs reached maximum luminances of 131 and 109 cd m^-2 , respectively.

The effects of introducing sterically demanding aryl substituents in [Cu(N^N)(P^P)]+ complexes

[Cu(6-Arbpy)(POP)][PF₆] and [Cu(6-Arbpy)(xantphos)][PF₆] compounds in which Ar is a sterically hindered aryl substituent are described; structural and solution dynamical consequences of the bulky groups are investigated.

Neutral Mononuclear Copper(I) Complexes: Synthesis, Crystal Structures, and Photophysical Properties

Neutral green-emitting four-coordinate Cu(I) complexes with general formula POPCu(NN), where POP = bis[2-(diphenylphosphino)phenyl]ether and NN = substituted 2-pyridine-1,2,4-triazole ligands, were synthesized. The crystal structures of (POPCuMeCN)(+)(PF6)(-) (1), POPCuPhPtp (2a, PhPtp = 2-(5-phenyl-2H-[1,2,4]triazol-3-yl)-pyridine), and POPCu(3,5-2FPhPtp) (2d, 3,5-2FPhPtp = 2-(5-(3,5-difluorophenyl)-2H-1,2,4-triazol-3-yl)pyridine) were determined by single-crystal X-ray diffraction analysis. The electronic and photophysical properties of the complexes were examined by UV-vis, steady-state, and time-resolved spectroscopy. At room temperature, weak emission was observed in solution, while in the solid state, all complexes exhibit intense green emission with quantum yield up to 0.54. The electronic and photophysical properties were further supported by calculation performed at the (time-dependent) density functional theory level. One of the complexes was also tested as dopant in electroluminescent devices.

Peripheral halo-functionalization in [Cu(N^N)(P^P)]+ emitters: influence on the performances of light-emitting electrochemical cells

Trends in the performance data of [Cu(N^N)(P^P)]⁺-based LECs in which N^N ligands bear peripheral F, Cl, Br or I substituents reveal that fluoro-groups are beneficial, but heavier halo-substituents lead to poor devices.

Copper(I) complexes as alternatives to iridium(III) complexes for highly efficient oxygen sensing

The complex [Cu(xantphos)(dmp)][PF6] (dmp = 2,9-dimethyl-1,10-phenanthroline) in a nanostructured metal oxyde matrix shows better sensitivity to oxygen (KSV = 9.74 ± 0.87 kPa(-1) between 0 and 1 kPa pO2 and 5.59 ± 0.15 kPa(-1) between 0 and 10 kPa pO2) than cyclometallated iridium complexes in the same conditions.

[Cu(bpy)(P^P)]⁺ containing light-emitting electrochemical cells: improving performance through simple substitution

Light-emitting electrochemical cells (LECs) containing [Cu(POP)(N^N)][PF6] (POP = bis(2-diphenylphosphinophenyl)ether, N^N = 6-methyl- or 6,6'-dimethyl-2,2'-bipyridine) exhibit luminance and efficiency surpassing previous copper(I)-containing LECs.

Polymeric one- and two-dimensional copper(i) iodide complexes showing photoluminescence tunable by azaaromatic ligands

Photoluminescent properties of four low-dimensional [(CuI)_xL]_n complexes were investigated in the solid state at ambient temperature. A photoluminescence quantum yield of 73% was recorded for [(CuI)₂(46dmpm)]_n.