Synthesis,Structure and Photophysical Properties of a New Class of Inherently Chiral Boron(III) Chelates—The tert-Leucine Complexes

A new family of boron(III) chelates is introduced whereby molecular chirality, confirmed by circular dichroism, is imported during synthesis such that isolation of the diastereoisomers does not require separation procedures. The photophysical properties of two members of the family have been examined: the N,O,O-salicylaldehyde-based derivative shows pronounced intramolecular charge-transfer character in fluid solution and is weakly fluorescent, with a large Stokes shift. The corresponding 2-methylamino-benzaldehyde-derived N,N,O-chelate absorbs and fluoresces in the visible region with a much smaller Stokes shift. Orange fluorescence is also observed for this compound as a cast film. Temperature-dependence studies show that decay of the fluorescent state is weakly activated but emission is less than quantitative at 77 K. Quite rare for boron(III)-based chelates, this derivative undergoes intersystem crossing to form a meta-stable triplet-excited state. X-ray crystal structures are reported for both compounds, along with simulated ECD spectra.     

Precursor Design Strategies for the Low-Temperature Synthesis of Functional Oxides: It's All in the Chemistry

Solution-based (multi)metal oxide synthesis has been carried out employing a large diversity of precursor routes. The selection of an appropriate synthesis strategy is frequently dictated by the resulting material properties, although this choice should also be based on green chemistry principles, atom economy considerations and energy efficiency. In order to limit the required energy budget to convert the chemical precursor to the target oxide material, various approaches were recently reported. This Review summarizes some frequently encountered low-temperature routes, critically assessing their application window and advantages. More specifically, auto-combustion synthesis, UV-assisted decomposition routes, sol–gel network adjustments and precursor complex design concepts are discussed. It is expected that this toolbox of low-temperature strategies may assist further progress in the field, stimulating novel applications, such as flexible electronics or organic–oxide hybrid materials, which are very sensitive to the temperature requirements.     

Near-Infrared BODIPY-Acridine Dyads Acting as Heavy-Atom-Free Dual-Functioning Photosensitizers

Boron dipyrromethene (BODIPY) dyes represent a particular class within the broad array of potential photosensitizers. Their highly fluorescent nature opens the door for theragnostic applications, combining imaging and therapy using a single, easily synthesized chromophore. However, near-infrared absorption is strongly desired for photodynamic therapy to enhance tissue penetration. Furthermore, singlet oxygen should preferentially be generated without the incorporation of heavy atoms, as these often require additional synthetic efforts and/or afford dark cytotoxicity. Solutions for both problems are known, but have never been successfully combined in one simple BODIPY material. Here, we present a series of compact BODIPY-acridine dyads, active in the phototherapeutic window and showing balanced brightness and phototoxic power. Although the donor–acceptor design was envisioned to introduce a charge transfer state to assist in intersystem crossing, quantum-chemical calculations refute this. Further photophysical investigations suggest the presence of exciplex states and their involvement in singlet oxygen formation.     

Newton polygons and curve gonalities

We give a combinatorial upper bound for the gonality of a curve that is defined by a bivariate Laurent polynomial with given Newton polygon. We conjecture that this bound is generically attained, and provide proofs in a considerable number of special cases. One proof technique uses recent work of M. Baker on linear systems on graphs, by means of which we reduce our conjecture to a purely combinatorial statement.     

Oligoether-strapped meso-pyrimidinylporphyrins

Bis(oligoether-strapped) zinc(II)-meso-pyrimidinylporphyrins were readily synthesized via nucleophilic aromatic substitution reactions of biscathechol-substituted tri- or tetraethylene glycol straps on the upper and lower faces of a Zn(II)-A₂B₂-meso-dichloropyrimidinylporphyrin precursor. The crown ether-like bridges surrounding the porphyrin core create peculiar cavities above and below the macrocyclic plane with appealing features for supramolecular host–guest chemistry.     

Solute-solvent interactions in cryosolutions: a study of halothane-ammonia complexes

The formation of C-H···N bonded complexes of halothane with ammonia has been studied using infrared and Raman spectroscopy of solutions in the liquid rare gases argon, krypton and xenon, of supersonic jet expansions and of room temperature vapor phase mixtures. For the solutions and for the vapor phase experiments, the formation of complexes with 1:1 and 1:2 stoichiometry was observed. The complexation enthalpy for the 1:1 complex was determined to be -20 (1) kJ mol(-1) in the vapor phase, -17.0 (5) kJ mol(-1) in liquid xenon and -17.3 (6) kJ mol(-1) in liquid krypton. For the 1:2 complex in liquid xenon, the complexation enthalpy was determined to be -31.5 (12) kJ mol(-1). Using the complexation enthalpies for the vapor phase and for the solutions in liquid xenon and krypton, a critical assessment is made of the Monte Carlo Free Energy Perturbation approach to model solvent influences on the thermodynamical properties of the cryosolutions. The influences of temperature and solvent on the complexation shifts of the halothane C-H stretching mode are discussed.     

Fluorous linker facilitated synthesis of teichoic acid fragments

The use of perfluorooctylpropylsulfonylethanol as a new phosphate protecting group and fluorous linker is evaluated in the stepwise solution phase synthesis of a number of biologically relevant (carbohydrate substituted) glycerol teichoic acid fragments. Teichoic acid fragments, up to the dodecamer level, were assembled by means of phosphoramidite chemistry, using a relatively small excess of the building blocks and a repetitive efficient purification procedure of the protected intermediates by fluorous solid phase extraction (F-SPE).     

Dynamic covalent assembly of stimuli responsive vesicle gels

We describe the reversible formation of stimuli-responsive vesicle gels from polymerised dynamic covalent surfactants, by simple mixing of soluble surfactant precursors in water under ambient conditions.