A Different Perspective on Tuning the Photophysical and Photochemical Properties: The Influence of Constitutional Isomers in Group 6 Carbonyl Complexes with Pyridyl-Mesoionic Carbenes.

Exploring novel and existing design principles to tune the photochemical and photophysical properties of transition-metal complexes is an important goal in contemporary research. Here, we highlight the influence of constitutional isomers of pyridyl-1,2,3-triazolylidene mesoionic carbene (MIC) ligands on the photophysical and photochemical properties of the corresponding tetracarbonyl group 6 metal complexes (M = Cr, Mo, W). All new complexes [M()] presented herein incorporate a linked pyridyl-MIC ligand and were fully characterized by X-ray diffraction analysis, elemental analysis, and H NMR and IR spectroscopy.

Stable Molybdenum(0) Carbonyl Complex for Upconversion and Photoredox Catalysis.

Photoactive complexes with earth-abundant metals have attracted increasing interest in the recent years fueled by the promise of sustainable photochemistry. However, sophisticated ligands with complicated syntheses are oftentimes required to enable photoactivity with nonprecious metals. Here, we combine a cheap metal with simple ligands to easily access a photoactive complex.

Cooperativity-Driven Reactivity of a Dinuclear Copper Dimethylglyoxime Complex.

In this report, we present the dinuclear copper(II) dimethylglyoxime (H dmg) complex [Cu (H dmg)(Hdmg)(dmg)] (1), which, in contrast to its mononuclear analogue [Cu(Hdmg) ] (2), is subject to a cooperativity-driven hydrolysis. The combined Lewis acidity of both copper centers increases the electrophilicity of the carbon atom in the bridging μ -O-N=C-group of H dmg and thus, facilitates the nucleophilic attack of H O. This hydrolysis yields butane-2,3-dione monoxime (3) and NH OH that, depending on the solvent, is then either oxidized or reduced.

Mechanistic and Kinetic Investigations of ON/OFF (Photo)Switchable Binding of Carbon Monoxide by Chromium(0), Molybdenum(0) and Tungsten(0) Carbonyl Complexes with a Pyridyl-Mesoionic Carbene Ligand.

Invited for the cover of this issue are Gereon Niedner-Schatteburg, Biprajit Sarkar and co-worker at TU Kaiserslautern and the University of Stuttgart. The image depicts the selective dissociation of an axial CO from a metal complex. Read the full text of the article at 10.

Unexpected Boost in Activity of a Cu(I) Photosensitizer by Stabilizing a Transient Excited State.

In this study, we present a slight but surprisingly successful structural modification of the previously reported heteroleptic Cu(I) photosensitizer ([(xantphos)Cu(biipo)]PF; = 16-benzo-[4',5']-isoquinolino-[2',1':1,2]-imidazo-[4,5-]-[1,10]-phenanthrolin-16-one). As a key feature, bears a naphthalimide unit at the back, which is directly fused to a phenanthroline moiety to extend the conjugated π-system. This ligand was now altered to include two additional methyl groups at the 2,9-positions at the phenanthroline scaffold.

Mechanistic and Kinetic Investigations of ON/OFF (Photo)Switchable Binding of Carbon Monoxide by Chromium(0), Molybdenum(0) and Tungsten(0) Carbonyl Complexes with a Pyridyl-Mesoionic Carbene Ligand.

This work tackles the photochemistry of a series of mononuclear Cr , Mo and W carbonyl complexes containing a bidentate mesoionic carbene ligand of the 1,2,3-triazol-5-ylidene type. FTIR spectroscopy, combined with density functional theory calculations, revealed a clean photo-induced reaction in organic solvents (acetonitrile, pyridine, valeronitrile) to give mainly one photoproduct with monosubstitution of a carbonyl ligand for a solvent molecule. The highest photodissociation quantum yields were reached for the Cr complex under UV irradiation (266 nm).

Chromone-methanol clusters in the electronic ground and lowest triplet state: a delicate interplay of non-covalent interactions.

Chromone offers two energetically almost equivalent docking sites for alcohol molecules, in which the hydroxyl group is hydrogen bonded to one of the free electron pairs of the carbonyl O atom. Here, the delicate balance between these two competing arrangements is studied by combining IR/R2PI and UV/IR/UV spectroscopy in a molecular beam supported by quantum-chemical calculations. Most interestingly, chromone undergoes an efficient intersystem crossing into the triplet manifold upon electronic excitation, so that the studies on aromatic molecule-solvent complexes are for the first time extended to such a cluster in a triplet state.

The overlooked NIR luminescence of Cr(ppy).

Cr(ppy), a structural analog of the green phosphorescent Ir(ppy), emits even in solution at room temperature from a weakly distorted spin-flip state at 910 nm (Hppy = 2-phenylpyridine). The low energy arises from an enhanced covalence of the Cr-C bonds as compared to Cr-N bonds. Lower temperature reduces thermally activated decay increasing the emission intensity.

Comprehensive Picture of the Excited State Dynamics of Cu(I)- and Ru(II)-Based Photosensitizers with Long-Lived Triplet States.

Ru(II)- and Cu(I)-based photosensitizers featuring the recently developed ligand (16H-benzo-[4',5']-isoquinolino-[2',1',:1,2]-imidazo-[4,5-]-[1,10]-phenanthrolin-16-one) were comprehensively investigated by X-ray crystallography, electrochemistry, and especially several time-resolved spectroscopic methods covering all time scales from femto- to milliseconds. The analysis of the experimental results is supported by density functional theory (DFT) calculations. The ligand consists of a coordinating 1,10-phenanthroline moiety fused with a 1,8-naphthalimide unit, which results in an extended π-system with an incorporated electron acceptor moiety.

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)] (CuL, CuLH) and their dinuclear analogues (Cu L', Cu L'H ), 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 Cu L' and Cu L'H . 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.

Ultrafast and long-time excited state kinetics of an NIR-emissive vanadium(iii) complex I: synthesis, spectroscopy and static quantum chemistry.

In spite of intense, recent research efforts, luminescent transition metal complexes with Earth-abundant metals are still very rare owing to the small ligand field splitting of 3d transition metal complexes and the resulting non-emissive low-energy metal-centered states. Low-energy excited states decay efficiently non-radiatively, so that near-infrared emissive transition metal complexes with 3d transition metals are even more challenging. We report that the heteroleptic pseudo-octahedral d-vanadium(iii) complex VCl(ddpd) (ddpd = ,'-dimethyl-,'-dipyridine-2-yl-pyridine-2,6-diamine) shows near-infrared singlet → triplet spin-flip phosphorescence maxima at 1102, 1219 and 1256 nm with a lifetime of 0.

Strongly Red-Emissive Molecular Ruby [Cr(bpmp)] Surpasses [Ru(bpy)].

Gaining chemical control over the thermodynamics and kinetics of photoexcited states is paramount to an efficient and sustainable utilization of photoactive transition metal complexes in a plethora of technologies. In contrast to energies of charge transfer states described by spatially separated orbitals, the energies of spin-flip states cannot straightforwardly be predicted as Pauli repulsion and the nephelauxetic effect play key roles. Guided by multireference quantum chemical calculations, we report a novel highly luminescent spin-flip emitter with a quantum chemically predicted blue-shifted luminescence.

NIR-Emissive Chromium(0), Molybdenum(0), and Tungsten(0) Complexes in the Solid State at Room Temperature.

The development of NIR emitters based on earth-abundant elements is an important goal in contemporary science. We present here Cr(0), Mo(0), and W(0) carbonyl complexes with a pyridyl-mesoionic carbene (MIC) based ligand. A detailed photophysical investigation shows that all the complexes exhibit dual emissions in the VIS and in the NIR region.

Transient FTIR spectroscopy after one- and two-colour excitation on a highly luminescent chromium(III) complex.

The development of photoactive transition metal complexes with Earth-abundant metals is a rapidly growing research field, where a deeper understanding of the underlying photophysical processes is of great importance. A multitude of potential applications in the fields of photosensitizing, optical sensing, photoluminescence and photoredox catalysis motivates demanding spectroscopic studies. We applied a series of high-level spectroscopic methods on the previously reported highly luminescent chromium(iii) complex [Cr(ddpd)2](BF4)3 (ddpd = N,N'-dimethyl-N,N'-dipyridine-2-ylpyridine-2,6-diamine) possessing two near-IR emissive doublet states with microsecond lifetimes.

Thermally Activated Delayed Fluorescence and Phosphorescence Quenching in Iminophosphonamide Copper and Zinc Complexes.

The synthesis of copper and zinc complexes of four variably substituted iminophosphonamide ligands is presented. While the copper complexes form ligand-bridged dimers, the zinc compounds are monomeric. Due to different steric demand of the ligand the arrangement of the ligands within the dimeric complexes varies.

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

To develop new and flexible Cu 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 Cu complexes with a halide containing Cu X 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.

Chromium(0) and Molydenum(0) Complexes with a Pyridyl-Mesoionic Carbene Ligand: Structural, (Spectro)electrochemical, Photochemical, and Theoretical Investigations.

This work reports on the synthesis and in-depth electrochemical and photochemical characterization of two chromium(0) and molydenum(0) metal complexes with bidentate pyridyl-mesoionic carbene (MIC) ligands of the 1,2,3-triazol-5-ylidene type and carbonyl coligands. Metal complexes with MIC ligands have turned out to have very promising electrocatalytic and photochemical properties, but examples of MIC-containing complexes with early-transition-metal centers remain extremely rare. The electrochemistry of these new MIC complexes was studied by cyclic voltammetry and especially spectroelectrochemistry in the IR region consistent with a mainly metal-centered oxidation, which is fully reversible in the case of the chromium(0) complex.

A Vanadium(III) Complex with Blue and NIR-II Spin-Flip Luminescence in Solution.

Luminescence from Earth-abundant metal ions in solution at room temperature is a very challenging objective due to the intrinsically weak ligand field splitting of first-row transition metal ions, which leads to efficient nonradiative deactivation via metal-centered states. Only a handful of 3d metal complexes ( ≠ 10) show sizable luminescence at room temperature. Luminescence in the near-infrared spectral region is even more difficult to achieve as further nonradiative pathways come into play.

Spin Crossover and Long-Lived Excited States in a Reduced Molecular Ruby.

The chromium(III) complex [Cr (ddpd) ] (molecular ruby; ddpd=N,N'-dimethyl-N,N'-dipyridine-2-yl-pyridine-2,6-diamine) is reduced to the genuine chromium(II) complex [Cr (ddpd) ] with d electron configuration. This reduced molecular ruby represents one of the very few chromium(II) complexes showing spin crossover (SCO). The reversible SCO is gradual with T around room temperature.

Luminescence and Light-Driven Energy and Electron Transfer from an Exceptionally Long-Lived Excited State of a Non-Innocent Chromium(III) Complex.

Photoactive metal complexes employing Earth-abundant metal ions are a key to sustainable photophysical and photochemical applications. We exploit the effects of an inversion center and ligand non-innocence to tune the luminescence and photochemistry of the excited state of the [CrN ] chromophore [Cr(tpe) ] with close to octahedral symmetry (tpe=1,1,1-tris(pyrid-2-yl)ethane). [Cr(tpe) ] exhibits the longest luminescence lifetime (τ=4500 μs) reported up to date for a molecular polypyridyl chromium(III) complex together with a very high luminescence quantum yield of Φ=8.

Highly soluble fluorine containing Cu(i) AlkylPyrPhos TADF complexes.

Luminescent Cu(i) AlkylPyrPhos complexes with a butterfly-shaped CuI core and halogen containing ancillary ligands, with a special focus on fluorine, have been investigated in this study. These complexes show extremely high solubilities and a remarkable (photo)chemical stability in a series of solvents. A tunable emission resulting from thermally activated delayed fluorescence with high quantum yields was determined by luminescence and lifetime investigations in solvents and solids.

The effects of dexamethasone and oxygen in ventilated adult sheep with early phase acute respiratory distress syndrome.

Background: Acute respiratory distress syndrome (ARDS) is a life-threating condition with high morbidity and mortality. Inflammation is the main factor in the pathogenesis of ARDS. Therefore systemic corticosteroids are a rational therapeutic approach, but the effect of corticosteroids is still unclear.

Insulin resistance, obesity and the metabolic syndrome. Is there a therapeutic role for endothelin-1 antagonists?

There is increasing evidence to suggest that chronic activation of the endothelin-1 system can lead to heterologous desensitization of the glucose-regulatory and mitogenic actions of insulin with subsequent development of glucose intolerance, hyperinsulinemia, impaired endothelial function and exacerbation of cardiovascular disease. Effects are mediated through a variety of mechanisms that include attenuation of key insulin signalling pathways and decreased tyrosine phosphorylation of insulin receptor substrates IRS-1, SHC and G alpha q/11. Other actions involve hemodynamic changes leading to reduced delivery of insulin and glucose to peripheral tissues as well as enhanced hepatic glycogenolysis, decreased glucose-transporter translocation and modulation of various adipokines that regulate insulin action.