IrIII and RuII Complexes Containing Triazole‐Pyridine Ligands: Luminescence Enhancement upon Substitution with β‐Cyclodextrin

Novel 2‐(1‐substituted‐1H‐1,2,3‐triazol‐4‐yl)pyridine (pytl) ligands have been prepared by “click chemistry” and used in the preparation of heteroleptic complexes of Ru and Ir with bipyridine (bpy) and phenylpyridine (ppy) ligands, respectively, resulting in [Ru(bpy)₂(pytl‐R)]Cl₂ and [Ir(ppy)₂(pytl‐R)]Cl (R=methyl, adamantane (ada), β‐cyclodextrin (βCD)). The two diastereoisomers of the Ir complex with the appended β‐cyclodextrin, [Ir(ppy)₂(pytl‐βCD)]Cl, were separated. The [Ru(bpy)₂(pytl‐R)]Cl₂ (R=Me, ada or βCD) complexes have lower lifetimes and quantum yields than other polypyridine complexes. In contrast, the cyclometalated Ir complexes display rather long lifetimes and very high emission quantum yields. The emission quantum yield and lifetime (Φ=0.23, τ=1000 ns) of [Ir(ppy)₂(pytl‐ada)]Cl are surprisingly enhanced in [Ir(ppy)₂(pytl‐βCD)]Cl (Φ=0.54, τ=2800 ns). This behavior is unprecedented for a metal complex and is most likely due to its increased rigidity and protection from water molecules as well as from dioxygen quenching, because of the hydrophobic cavity of the βCD covalently attached to pytl. The emissive excited state is localized on these cyclometalating ligands, as underlined by the shift to the blue (450 nm) upon substitution with two electron‐withdrawing fluorine substituents on the phenyl unit. The significant differences between the quantum yields of the two separate diastereoisomers of [Ir(ppy)₂(pytl‐βCD)]Cl (0.49 vs. 0.70) are attributed to different interactions of the chiral cyclodextrin substituent with the Δ and Λ isomers of the metal complex.     

Iridium(III) Complexes with Sulfonyl and Fluorine Substituents: Synthesis,Stereochemistry and Effect of Functionalisation on their Photophysical Properties

The synthesis and photophysical and electrochemical characterisation of new heteroleptic iridium complexes with electron‐withdrawing sulfonyl groups and fluorine atoms bound to phenylpyridine ligands are reported. The emission energy of these materials strongly depends on the position of the sulfonyl groups and on the number of fluorine substituents. A 90 nm wide tuning range of photoluminescence from the blue‐green (λ_em=468 nm) of iridium(III)bis[2‐(4′‐benzylsulfonyl)phenylpyridinato‐N,C2′][3‐(pentafluorophenyl)‐pyridin‐2‐yl‐1,2,4‐triazolate] to the orange (λ_em=558 nm) of iridium(III)bis[2‐(3′‐benzylsulfonyl)phenylpyridinato‐N,C2′](2,4‐decanedionate) has been achieved. Emission quantum yields ranging from 47 to 71 % have also been found for degassed solutions of the complexes, and a surprisingly high value of 16 % was recorded for iridium(III)bis[2‐(5′‐benzylsulfonyl‐3′,6′‐difluoro)phenylpyridinato‐N,C2′](2,4‐decanedionate) in air‐equilibrated dichloromethane. A unusual stereochemistry of the benzylsulfonyl‐substituted dimer and heteroleptic complexes has been detected by ¹H NMR spectroscopy, and is characterised by the mutual cis disposition of the pyridyl nitrogen atoms of the phenylpyridine ligands, which differs from the most common trans arrangement reported in the literature.     

Enantiopure, supramolecular helices containing three-dimensional tetranuclear lanthanide(III) arrays: synthesis, structure, properties, and solvent-driven trinuclear/tetranuclear interconversion

The enantiomerically pure pinene-bipyridine-based receptor, (-) or (+) L(-), diastereoselectively self-assembles in dry acetonitrile in the presence of Ln(III) ions (Ln = La, Pr, Nd, Sm, Eu, Gd, and Tb) to give a C3-symmetrical, pyramidal architecture with the general formula [Ln4(L)9(mu3-OH)](ClO4)2) (abbreviated as tetra-Ln4L9). Three metal centers shape the base: an equilateral triangle surrounded by two sets of helically wrapping ligands with opposite configurations. This part of the structure is very similar to the species [Ln3(L)6(mu3-OH)(H2O)3](ClO4)2) (recently reported by us and abbreviated as tris-LnL2) formed by the ligand and the Ln(III) ions when the reactions are performed in methanol. The tetranuclear structure is completed by a capping, helical unit LnL3 whose chirality is also predetermined by the chirality of the ligand. A complete characterization of these isostructural, chiral compounds was performed in solid state (X-ray, IR) and in solution (ES-MS, NMR, CD, UV-vis and emission spectroscopies). The sign and the intensity of the CD bands in the region of the pi pi* transitions of the bipyridine (absolute Delta epsilon values at 327 nm are about 280 M(-1) x cm(-1)) are highly influenced by the helicity of the capping fragment LnL3. The photophysical properties (lifetime, quantum yield) of the visible (Eu and Tb complexes) and NIR (Nd complex) emitters indicate a good energy transfer between the ligands and the metal centers. The two related superstructures tetra-Ln4L9 and tris-LnL2 can be interconverted in acetonitrile, the switching process depending on the amount of water present in the solvent, the size of the Ln(III) ion, and the concentration. The weak chiral recognition capabilities of the self-assembly leading to the formation of tetra-Ln4L9 either by direct synthesis from a racemic mixture of the ligand and Ln(III) ions or by the conversion of a tris-Ln[(+/-)-L]2 racemate were likewise demonstrated.     

Nonuniqueness of equilibrium states for axisymmetric elastic shells in tension

The problem of nonuniqueness of static axisymmetric solutions for a non-linearly elastic cylindrical shell in which the ends are pulled apart with a constant traction while retaining the radii of its ends fixed is studied. In the elastic case, we prove the existence of buckled states and the possibility of necking. In the hyperelastic case a global existence and nonuniqueness theorem is proved, via the energy criterion.     

Quantitative studies of long-term stable, top-down fabricated silicon nanowire pH sensors

We report a simple and effective method to develop long-term stable, top-down fabricated silicon nanowire (SiNW) pH sensors along with systematic studies on the performance of the sensors. In this work, we fabricated the SiNW pH sensors based on top-down fabrication processes. In order to improve the stability of the sensor performance, the sensors were coated with a passivation layer (PECVD-based silicon nitride) for effective electrical insulation and ion-blocking. The stability, pH sensitivity, and repeatability of the sensor response are critically analyzed with regard to the physics of sensing interface between sample liquid and the sensor surface. Also, trade-off between the stability and pH sensitivity of the sensor response is discussed.     

Gaussian Limiting Behavior of the Rescaled Solution to the Linear Korteweg–de Vries Equation with Random Initial Conditions

We analyze the asymptotic behavior of the rescaled solution to the linear Korteweg–de Vries equation when the initial conditions are supposed to be random and weakly dependent. By means of the method of moments we prove the Gaussianity of the limiting process and we present its correlation function. The same technique is applied to the analysis of another third-order heat-type equation.     

Improved extraction of vegetable oils under high-intensity ultrasound and/or microwaves

Ultrasound-assisted extraction (UAE) and microwave-assisted extraction (MAE) techniques have been employed as complementary techniques to extract oils from vegetable sources, viz, soybean germ and a cultivated marine microalga rich in docosahexaenoic acid (DHA). Ultrasound (US) devices developed by ourselves, working at several frequencies (19, 25, 40 and 300 kHz), were used for US-based protocols, while a multimode microwave (MW) oven (operating with both open and closed vessels) was used for MAE. Combined treatments were also studied, such as simultaneous double sonication (at 19 and 25 kHz) and simultaneous US/MW irradiation, achieved by inserting a non-metallic horn in a MW oven. Extraction times and yields were compared with those resulting from conventional procedures. With soybean germ the best yield was obtained with a ‘cavitating tube’ prototype (19 kHz, 80 W), featuring a thin titanium cylinder instead of a conventional horn. Double sonication, carried out by inserting an immersion horn (25 kHz) in the same tube, improved the yield only slightly but halved the extraction time. Almost comparable yields were achieved by closed-vessel MAE and simultaneous US/MW irradiation. Compared with conventional methods, extraction times were reduced by up to 10-fold and yields increased by 50–500%. In the case of marine microalgae, UAE worked best, as the disruption by US of the tough algal cell wall considerably improved the extraction yield from 4.8% in soxhlet to 25.9%. Our results indicate that US and MW, either alone or combined, can greatly improve the extraction of bioactive substances, achieving higher efficiency and shorter reaction times at low or moderate costs, with minimal added toxicity.