Synthesis of Ru(II) and Os(II) Photosensitizers Bearing one 9,10-diamino-1,4,5,8-tetraazaphenanthrene Scaffold

The synthesis of eight novel Ru(II) and Os(II) photosensitizers bearing a common 9,10-disubstituted-1,4,5,8-tetraazaphenanthrene backbone is reported. With Os(II) photosensitizers, the 9,10-diNH2-1,4,5,8-tetraazaphenanthrene could be directly chelated onto the metal center via the heteroaromatic moiety, whereas similar conditions using Ru(II) resulted in the formation of an o-quinonediimine derivative. Hence, an alternative route, proceeding via the chelation of 9-NH2-10-NO2-1,4,5,8-tetraazaphenanthrene and subsequent ligand reduction of the corresponding photosensitizers was developed. Photosensitizers chelated via the polypyridyl-type moiety exhibited classical photophysical properties whereas the o-quinonediimine chelated Ru(II) analogues exhibited red-shifted absorption (520 nm) and no photoluminescence at room temperature in acetonitrile. The most promising photosensitizers were investigated for excited-state quenching with guanosine-5’-monophosphate in aqueous buffered conditions where reductive excited-state electron transfer was observed by nanosecond transient absorption spectroscopy

Excited-state behavior and photoinduced electron transfer of pH-sensitive Ir(III) complexes with cyclometallation (C/N–) ratios between 0/6 and 3/3

The first coordination sphere of Ir(III) 2,2′ -bipyridine / 2-phenylpyridine complexes can be tuned to achieve either C– or N–chelation in ratios that range between 0/6 and 3/3. Of particular interest is the synthesis of Ir(III) complexes bearing a 2,2′ -bipyridine ligand coordinated in a N,C3 pattern, leaving an exposed pyridine moiety, accessible for acid-base chemistry or coordination to a second transition metal center. The protonated forms of these “rolled-over” Ir(III) complexes were isolated in a straight-forward procedure using trifluoroacetic acid. The photophysical, photochemical and electrochemical properties of both the protonated and unprotonated Ir(III) complexes were investigated by steady-state and time-resolved spectroscopies, as well as by density functional theory calculations. The nature of the excited states was shown to depend on both the ligand coordination pattern and protonation state of the complex. In addition, the unprotonated and protonated analogues were efficiently quenched by hydroquinone and benzoquinone in acetonitrile with quenching rate constants close to the solvent diffusion limit. The results presented herein have direct implications for proton sensitive photoredox chemistry and the development of photo-acids and photo-bases

Tuning the excited-state deactivation pathways of dinuclear ruthenium(ii) 2,2′-bipyridine complexes through bridging ligand design

A detailed photophysical investigation of two dinuclear ruthenium(II) complexes is reported. The two metallic centers were coordinated to a bis-2,2′-bipyridine bridging ligand, connected either through the para (Lp, Dp) or the meta position (Lm, Dm). The results obtained herein were compared to the prototypical [Ru(bpy)3]2+ parent compound. The formation of dinuclear complexes was accompanied by the expected increase in molar absorption coefficients, i.e. 12 000 M−1 cm−1, 17 000 M−1 cm−1, and 22 000 M−1 cm−1 at the lowest energy MLCTmax transition for [Ru(bpy)3]2+, Dm and Dp respectively. The Lp bridging ligand resulted in a ruthenium(II) dinuclear complex that absorbed more visible light, and had a longer-lived and more delocalized excited-state compared to a complex with the Lm bridging ligand. Variable temperature measurements provided valuable information about activation energies to the uppermost 3MLCT state and the metal-centered (3MC) state, often accompanied by irreversible ligand-loss chemistry. At 298 K, 48% of [Ru(bpy)3]2+* excited-state underwent deactivation through the 3MC state, whereas this deactivation pathway remained practically unpopulated (<0.5%) in both dinuclear complexes

Red Absorbing Cyclometalated Ir(III) Diimine Photosensitizers Competent for Hydrogen Photocatalysis

Two new cyclometalated Ir(III) diimine complexes were used as photosensitizers for homogeneous hydrogen evolution reaction (HER). These complexes were characterized by electrochemistry, ultraviolet–visible absorption, time-resolved and steady-state photoluminescence spectroscopy as well as by theoretical methods. The metal–ligand-to-ligand charge transfer character of their lowest excited state was shown to be competent for efficient H2 photoproduction in the presence of [Co(dmgH)2(py)Cl] as the hydrogen evolution catalyst, triethanolamine as the sacrificial electron donor, and HBF4 as the proton source. Under optimized experimental conditions, both complexes displayed HER over a period of more than 90 h, with turnover numbers reaching up to 11,650, 10,600, and 174 molH2 molPS–1 under blue-, green-, and red-light irradiation, respectively. Both complexes showed higher stability and efficiency vs HER than most of the previously described systems of the same kind

Sources of variances in clinical trials of potential novel therapies for influenza A. Applicable to all acute viral infections.

<p>Sources of variances in clinical trials of potential novel therapies for influenza A. Applicable to all acute viral infections.</p

Schematic illustration of key infection-related quantities that define the course of acute viral infections.

<p>Black line: viral load curve over time. Filled area indicates viral load area under the curve (AUC). X-axis: time in days post infection. Y-axis: log₁₀ viral load (TCID₅₀/ml).</p

Viral load curves, temperature curves and total symptom score curves of nine patients.

<p>Viral load curves, temperature curves and total symptom score curves of nine patients.</p

Schematic illustration of changes expected in key infection-related quantities in treated versus untreated individuals (treated before time of peak viral load on day 1).

<p>Treatments acting on the infection rate or viral production rate have a strong impact on infection, if given before the time of peak viral load (a, b). They reduce peak viral load, duration of infection and viral load area under the curve (AUC). Treatments acting on virus clearance have a weaker effect on the course of infection, if given before the time of peak viral load (c). Black line: viral load curve in untreated infection. Red line: viral load curve in treated infection. Fill indicates viral load area under the curve in treated infection.</p

Pairwise correlations between infection-related quantities, between infection-related quantities and temperature area under the curve, and between infection-related quantities and symptom score area under the curve.

<p>Correlations that are significant using the Bonferroni correction for multiple comparisons are indicated by an asterisk. Correlations that are significant using the less stringent Benjamini-Hochberg correction are indicated by a diamond. Values below the diagonal show Pearson’s correlation coefficient, values above the diagonal show uncorrected p-values for each correlation. AUC_S: total symptom score area under the curve. AUC_T: temperature area under the curve. R₀: basic reproductive number. AUC_V: viral load area under the curve. FDC: fraction of dead cells at end of infection. t_peak: time to peak viral load. V_peak: peak viral load. t_g: generation time. IGR: initial viral growth rate. LDR: late viral decay rate. D: duration of infection.</p