Trigonal Copper(I) Complexes with Cyclic (Alkyl)(amino)carbene Ligands for Single-Photon Near-IR Triplet Emission

Molecular near-IR (NIR) triplet-state emitters are of importance for the development of new, organic-electronics-based telecommunication technologies as optical fibers operating in the corresponding spectral bands allow for data transfer over much longer distances due to the significantly lower attenuation. However, achieving such low-energy triplet excited states with good radiative rate constants is very challenging, and studies regarding the single-photon emission of organometallics in this energy range are scarce. We have prepared a series of trigonal Cu^I CAAC complexes bearing chelating ligands with O, N, S, and Se donor atoms and studied their photophysical properties in this context. The compounds show weak low-energy absorption in solution between 400 and 500 nm due to mixed Cu → CAAC ¹MLCT/LLCT states, resulting in yellow-green to orange appearance, which we have also correlated to the ¹⁵N NMR resonances of the π-accepting carbene ligand. In the solid state, phosphorescence from dominant ³(Cu → CAAC) CT states is observed at room temperature. The emission of the complexes is bathochromically shifted in comparison to structurally related linearly coordinated copper(I) CAAC complexes due to structural reorganization in the excited state to a T-shape. For [Cu(dbm)(CAAC^Me)], the broad phosphorescence with outstanding λ_max = 760 nm tailors out to ca. 1100 nm and leads to its proof-of-concept application as a nonclassical single-photon light source, constituting key functional units for the implementation of tap-proof data transfer.

Aggregation‐Induced Dual Phosphorescence from ( o ‐Bromophenyl)‐Bis(2,6‐Dimethylphenyl)Borane at Room Temperature

Designing highly efficient purely organic phosphors at room temperature remains a challenge because of fast non‐radiative processes and slow intersystem crossing (ISC) rates. The majority of them emit only single component phosphorescence. Herein, we have prepared 3 isomers (o, m, p‐bromophenyl)‐bis(2,6‐dimethylphenyl)boranes. Among the 3 isomers (o‐, m‐ and p‐BrTAB) synthesized, the ortho‐one is the only one which shows dual phosphorescence, with a short lifetime of 0.8 ms and a long lifetime of 234 ms in the crystalline state at room temperature. Based on theoretical calculations and crystal structure analysis of o‐BrTAB, the short lifetime component is ascribed to the T₁^M state of the monomer which emits the higher energy phosphorescence. The long‐lived, lower energy phosphorescence emission is attributed to the T₁^A state of an aggregate, with multiple intermolecular interactions existing in crystalline o‐BrTAB inhibiting nonradiative decay and stabilizing the triplet states efficiently.

Cyclic (Amino)(aryl)carbenes Enter the Field of Chromophore Ligands: Expanded π System Leads to Unusually Deep Red Emitting CuI Compounds

A series of copper(I) complexes bearing a cyclic (amino)(aryl)carbene (CAArC) ligand with various complex geometries have been investigated in great detail with regard to their structural, electronic, and photophysical properties. Comparison of [CuX(CAArC)] (X = Br (1), Cbz (2), acac (3), Ph₂acac (4), Cp (5), and Cp* (6)) with known Cu^I complexes bearing cyclic (amino)(alkyl), monoamido, or diamido carbenes (CAAC, MAC, or DAC, respectively) as chromophore ligands reveals that the expanded π-system of the CAArC leads to relatively low energy absorption maxima between 350 and 550 nm in THF with high absorption coefficients of 5-15 × 10³ M^-1 cm^-1 for 1-6. Furthermore, 1-5 show intense deep red to near-IR emission involving their triplet excited states in the solid state and in PMMA films with λ^em_max = 621-784 nm. Linear [Cu(Cbz)(^DippCAArC)] (2) has been found to be an exceptional deep red (λ_max = 621 nm, ϕ = 0.32, τ_av = 366 ns) thermally activated delayed fluorescence (TADF) emitter with a radiative rate constant k_r of ca. 9 × 10⁵ s^-1, exceeding those of commercially employed Ir^III- or Pt^II-based emitters. Time-resolved transient absorption and fluorescence upconversion experiments complemented by quantum chemical calculations employing Kohn-Sham density functional theory and multireference configuration interaction methods as well as temperature-dependent steady-state and time-resolved luminescence studies provide a detailed picture of the excited-state dynamics of 2. To demonstrate the potential applicability of this new class of low-energy emitters in future photonic applications, such as nonclassical light sources for quantum communication or quantum cryptography, we have successfully conducted single-molecule photon-correlation experiments of 2, showing distinct antibunching as required for single-photon emitters.

Palladium-Catalyzed Homocoupling of Highly Fluorinated Arylboronates: Studies of the Influence of Strongly vs Weakly Coordinating Solvents on the Reductive Elimination Process

C-C reductive elimination from [PdL₂(C₆F₅)₂] to form polyfluorinated biaryls has been a challenge for over 50 years. Thus, palladium-catalyzed homocoupling of arylboronates (Ar_F-Bpin) containing two ortho-fluorine substituents is very difficult, as the reaction typically stops at the [PdL₂(Ar_F)₂] stage after two transmetalation steps. The transmetalated complexes cis-[Pd(MeCN)₂(C₆F₅)₂] (3a), cis-[Pd(MeCN)₂(2,4,6-C₆F₃H₂)₂] (3b), and cis-[Pd(MeCN)₂(2,6-C₆F₂H₃)₂] (3e) have been isolated from the reaction of Ar_F-Bpin with Pd(OAc)₂ in acetonitrile solvent, with no homocoupling observed. However, catalytic homocoupling proceeds smoothly in a "weakly coordinating" arene solvent as long as no ancillary ligands or coordinating solvents are present. DFT computations reveal that the active catalyst formed by arene solvent coordination leads to an overall reduced barrier for the reductive elimination step compared to the formation of stable [PdL₂(Ar_F)₂] complexes in the presence of a donor ligand or solvent L.

Copper-Catalyzed Triboration of Terminal Alkynes Using B2 pin2 : Efficient Synthesis of 1,1,2-Triborylalkenes

We report herein the catalytic triboration of terminal alkynes with B2 pin2 (bis(pinacolato)diboron) using readily available Cu(OAc)2 and Pn Bu3 . Various 1,1,2-triborylalkenes, a class of compounds that have been demonstrated to be potential matrix metalloproteinase (MMP-2) inhibitors, were obtained directly in moderate to good yields. The process features mild reaction conditions, a broad substrate scope, and good functional group tolerance. This copper-catalyzed reaction can be conducted on a gram scale to produce the corresponding 1,1,2-triborylalkenes in modest yields. The utility of these products was demonstrated by further transformations of the C-B bonds to prepare gem-dihaloborylalkenes (F, Cl, Br), monohaloborylalkenes (Cl, Br), and trans-diaryldiborylalkenes, which serve as important synthons and have previously been challenging to prepare.

Triarylborane-Based Helical Donor-Acceptor Compounds: Synthesis, Photophysical, and Electronic Properties

The synthesis and characterization of 10-(dimesitylboryl)-N,N-di-p-tolylbenzo[c]phenanthren-4-amine (3-B(Mes)₂ -[4]helix-9-N(p-Tol)₂ 1) and 13-(dimesitylboryl)-N,N-di-p-tolyldibenzo[c,g]phenanthren-8-amine (3-B(Mes)₂ -[5]helix-12-N(p-Tol)₂ 2) are reported herein. Their electrochemical and photophysical properties have been studied experimentally and theoretically. The donor and acceptor-substituted helicene derivatives exhibit moderate fluorescence quantum yields in THF (Φ_f =0.48 and 0.61 for 1 and 2, respectively), which are higher than unsubstituted ones (Φ_f =0.18 for [4]helicene; Φ_f <0.05 for [n]helicenes (n≥5)). In the solid state, the Φ_f values are higher (Φ_f =1.00 and 0.55 for 1 and 2, respectively) than those in solution, most likely due to the restrictions of molecular motions. The S₁ ←S₀ transitions of 1 and 2 are predominately HOMO→LUMO transitions. Upon excitation with UV light, the interplanar angle between the two terminal aryl rings of the [5]helix core of 2 decreases (S₁ state compared with S₀ state), which is similar to placing a spring under an external force.

[Modification of the concentration of creatinine and sodium in blood serum and urine and the fractional elimination of sodium by electrolyte therapy in calves]

In 32 calves, creatinine and sodium concentrations were determined in blood and urine samples taken simultaneously four times during two periods of two days each (control period: milk or milk replacer; trial period: oral electrolyte solution). Creatinine urine/serum ratios and fractional elimination of sodium (FENa) were calculated. The influence of the type of liquid feed on these parameters was evaluated statistically. Calves fed milk replacer had higher urine sodium concentrations and FENa than calves fed whole milk. All parameters determined were influenced by intake of oral electrolyte solution: creatinine concentrations in serum and urine decreased, whereas sodium concentrations in serum and urine, as well as FENa, increased. It is concluded that sodium content of liquid feed significantly influences FENa.