Preparation and photophysical studies of [Ln(hfac)3DPEPO], Ln = Eu, Tb, Yb, Nd, Gd; interpretation of total photoluminescence quantum yields.

Synthesis and photophysical characterisation of [Ln(hfac)3DPEPO] complexes (with Ln = Eu, Tb, Yb, Nd, Gd) has been carried out to investigate the factors responsible for the variation in total photoluminescence quantum yield within this family of emissive lanthanide complexes. Electronic absorption and emission spectroscopy, in conjunction with DFT calculations of the excited state of the Eu complex, elucidate the role of each ligand in the sensitisation of the lanthanide through the antenna effect. The X-ray crystal structure of [Gd(hfac)3DPEPO] has been determined and shows an 8-coordinate environment around the Gd and a ten-membered chelate ring involving the DPEPO ligand. Total photoluminescence quantum yields were measured to be 6%, 1% and 2% for Ln = Tb, Nd and Yb, respectively, in comparison with around 80% for Ln = Eu. The lower quantum yield for Nd and Yb, compared with Eu, can be attributed to more efficient quenching of the excited Ln state by high-energy oscillations within the ligands, whereas the lower quantum yield for Tb is assigned to a combination of poor energy transfer from the ligand excited state to the Tb and longer radiative lifetime.

Design and function of pre-organised outer-sphere amidopyridyl extractants for zinc(II) and cobalt(II) chlorometallates: the role of C-H hydrogen bonds.

Four new sterically hindered pyridines, L(1)-L(4)-containing amido substituents at the 2-position act as efficient solvent extractants for [CoCl(4)](2-) or [ZnCl(4)](2-) from acidic chloride solutions through protonation of the pyridino N-centre to form the neutral outer-sphere complexes [(LH)(2)MCl(4)]. These ionophores show very high selectivity for chlorometallate anions over chloride ion and are readily stripped to liberate the free-metal chlorides without the formation of inner-sphere complexes [ML(2)Cl(2)]. Single-crystal X-ray structure determinations of [(L(2)H)(2)CoCl(4)] and [(L(2)H)(2)ZnCl(4)] (L(2) = 2-(4,6-di-tert-butylpyridin-2-yl)-N,N'-dihexylmalonamide) coupled with (1)H NMR spectroscopy and DFT calculations on L(2)H(+) and other complexes of [ZnCl(4)](2-) confirm that the pyridinium NH group does not address the outer co-ordination sphere of the metallanion, but rather forms a hydrogen bond to the pendant amide groups and thus pre-organizes the ligand to present both C-H and amido N-H hydrogen-bond donors to the [MCl(4)](2-) ions. The selectivity for chlorometallates over chloride ions shown by this class of extractants arises from their ability to present several polarized C-H units towards the charge-diffuse ions [MCl(4)](2-), whereas the smaller, "harder" chloride anion prefers to be associated with the amido N-H hydrogen-bond donors.

Optically trapped microsensors for microfluidic temperature measurement by fluorescence lifetime imaging microscopy.

The novel combination of optical tweezers and fluorescence lifetime imaging microscopy (FLIM) has been used, in conjunction with specially developed temperature-sensitive fluorescent microprobes, for the non-invasive measurement of temperature in a microfluidic device. This approach retains the capability of FLIM to deliver quantitative mapping of microfluidic temperature without the disadvantageous need to introduce a fluorescent dye that pervades the entire micofluidic system. This is achieved by encapsulating the temperature-sensitive Rhodamine B fluorophore within a microdroplet which can be held and manipulated in the microfluidic flow using optical tweezers. The microdroplet is a double bubble in which an aqueous droplet of the fluorescent dye is surrounded by an oil shell which serves both to contain the fluorophore and to provide the refractive index differential required for optical trapping of the droplet in an external aqueous medium.

Cis-trans isomerisation of azobenzenes studied by laser-coupled NMR spectroscopy and DFT calculations.

In a combined experimental and computational study of a group of para-substituted azobenzenes, the effects of substituents and solvent on the kinetics of thermal cis-to-trans isomerisation have been examined and the success of DFT calculations in predicting kinetic parameters assessed. Mono-substituted species are predicted to isomerise by inversion in both non-polar and polar solvent, whereas for push-pull azobenzenes the mechanism is predicted to change from inversion to rotation on going from non-polar to polar solvent. Computed free energies of activation qualitatively reproduce experimental trends but do not quantitatively predict the kinetics of cis-trans isomerisation. The polarisable continuum model of solvation fails to predict the experimentally observed influence of solvent on the entropy of activation.

Structural characterisation of the photoisomers of reactive sulfonated azo dyes by NMR spectroscopy and DFT calculations.

1H NMR spectroscopy coupled with in situ laser irradiation has been used together with density functional theory (DFT) computation to examine the structures of the photoisomers of a series of sulfonated reactive azo dyes. Assignment of 1H NMR spectra acquired at the photostationary state has allowed, for the first time, NMR characterisation of unstable cis isomers of commercially relevant water-soluble azo dyes. Structural features of the two isomeric forms predicted by DFT calculations are clearly reflected in the experimental NMR data. The trans-cis photoisomerisation process could be unambiguously identified in each case, based on the large chemical shift change observed for resonances associated with aromatic protons adjacent to the azo linkage.