Dual Role of a Novel Heteroleptic Cu(I) Complex in Visible-Light-Driven CO2 Reduction.

A novel mononuclear Cu(I) complex was synthesized via coordination with a benzoquinoxalin-2'-one-1,2,3-triazole chelating diimine and the bis[(2-diphenylphosphino)phenyl] ether (DPEPhos), to target a new and efficient photosensitizer for photocatalytic CO2 reduction. The Cu(I) complex absorbs in the blue-green region of the visible spectrum, with a broad band having a maximum at 475 nm (ϵ =4500 M-1 cm-1), which is assigned to the metal-to-ligand charge transfer (MLCT) transition from the Cu(I) to the benzoquinoxalin-2'-one moiety of the diimine. Surprisingly, photo-driven experiments for the CO2 reduction showed that this complex can undergo a photoinduced electron transfer with a sacrificial electron donor and accumulate electrons on the diimine backbone. Photo-driven experiments in a CO2 atmosphere revealed that this complex can not only act as a photosensitizer, when combined with an Fe(III)-porphyrin, but can also selectively produce CO from CO2. Thus, owing to its charge-accumulation properties, the non-innocent benzoquinoxalin-2-one based ligand enabled the development of the first copper(I)-based photocatalyst for CO2 reduction.

Reaching strong absorption up to 700 nm with new benzo[g]quinoxaline-based heteroleptic copper(I) complexes for light-harvesting applications.

Heteroleptic copper(I) complexes, with a diimine as a chromophoric unit and a bulky diphosphine as an ancillary ligand, have the advantage of a reduced pseudo Jahn-Teller effect in their excited state over the corresponding homoleptic bis(diimine) complexes. Nevertheless, their lowest absorption lies generally between 350 to 500 nm. Aiming at a strong absorption in the visible by stable heteroleptic Cu(I) complexes, we designed a novel diimine based on 4-(benzo[g]quinoxal-2'-yl)-1,2,3-triazole derivatives. The large π-conjugation of the benzoquinoxaline moiety shifted bathochromically the absorption with regard to other diimine-based Cu(I) complexes. Adding another Cu(I) core broadened the absorption and extended it to considerably longer wavelengths. Moreover, by fine-tuning the structure of the dichelating ligand, we achieved a panchromatic absorption up to 700 nm with a high molar extinction coefficient of 8000 M-1 cm-1 at maximum (λ = 570 nm), making this compound attractive for light-harvesting antennae.

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)]0/+ (CuL, CuLH) and their dinuclear analogues (Cu2 L', Cu2 L'H2 ), 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 Cu2 L' and Cu2 L'H2 . 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.

New Photosensitizers Based on Heteroleptic CuI Complexes and CO2 Photocatalytic Reduction with [NiII (cyclam)]Cl2.

Earth-abundant metal complexes have been attracting increasing attention in the field of photo(redox)catalysis. In this work, the synthesis and full characterisation of four new heteroleptic CuI complexes are reported, which can work as photosensitizers. The complexes bear a bulky diphosphine (DPEPhos=bis[(2-diphenylphosphino)phenyl] ether) and a diimine chelating ligand based on 1-benzyl-4-(quinol-2'yl)-1,2,3-triazole. Their absorption has a relative maximum in the visible-light region, up to 450 nm. Thus, their use in photocatalytic systems for the reduction of CO2 with blue light in combination with the known catalyst [NiII (cyclam)]Cl2 was tested. This system produced CO as the main product through visible light (λ=420 nm) with a TON up to 8 after 4 hours. This value is in line with other photocatalytic systems using the same catalyst. Nevertheless, this system is entirely noble-metal free.

Randomized, multicenter trial of lateral Trendelenburg versus semirecumbent body position for the prevention of ventilator-associated pneumonia.

PURPOSE: The lateral Trendelenburg position (LTP) may hinder the primary pathophysiologic mechanism of ventilator-associated pneumonia (VAP). We investigated whether placing patients in the LTP would reduce the incidence of VAP in comparison with the semirecumbent position (SRP). METHODS: This was a randomized, multicenter, controlled study in invasively ventilated critically ill patients. Two preplanned interim analyses were performed. Patients were randomized to be placed in the LTP or the SRP. The primary outcome, assessed by intention-to-treat analysis, was incidence of microbiologically confirmed VAP. Major secondary outcomes included mortality, duration of mechanical ventilation, and intensive care unit length of stay. RESULTS: At the second interim analysis, the trial was stopped because of low incidence of VAP, lack of benefit in secondary outcomes, and occurrence of adverse events. A total of 194 patients in the LTP group and 201 in the SRP group were included in the final intention-to-treat analysis. The incidence of microbiologically confirmed VAP was 0.5% (1/194) and 4.0% (8/201) in LTP and SRP patients, respectively (relative risk 0.13, 95% CI 0.02-1.03, p = 0.04). The 28-day mortality was 30.9% (60/194) and 26.4% (53/201) in LTP and SRP patients, respectively (relative risk 1.17, 95% CI 0.86-1.60, p = 0.32). Likewise, no differences were found in other secondary outcomes. Six serious adverse events were described in LTP patients (p = 0.01 vs. SRP). CONCLUSIONS: The LTP slightly decreased the incidence of microbiologically confirmed VAP. Nevertheless, given the early termination of the trial, the low incidence of VAP, and the adverse events associated with the LTP, the study failed to prove any significant benefit. Further clinical investigation is strongly warranted; however, at this time, the LTP cannot be recommended as a VAP preventive measure. CLINICALTRIALS. GOV IDENTIFIER: NCT01138540.