Lanthanide Complexes that Respond to Changes in Cyanide Concentration in Water.

Cyanide ions are shown to interact with lanthanide complexes of phenacylDO3A derivatives in aqueous solution, giving rise to changes in the luminescence and NMR spectra. These changes are the consequence of cyanohydrin formation, which is favored by the coordination of the phenacyl carbonyl group to the lanthanide center. These complexes display minimal affinity for fluoride and can detect cyanide at concentrations less than 1 µm. By contrast, lanthanide complexes with DOTAM derivatives display no affinity for cyanide in water, but respond to changes in fluoride concentration.

Substituent effects on fluoride binding by lanthanide complexes of DOTA-tetraamides.

Fluoride binding by a series of europium and ytterbium complexes of DOTA-tetraamide ligands derived from primary, secondary and tertiary amides has been studied by NMR and luminescence spectroscopies. In all the systems studied, fluoride binding results in a change in the nature of the magnetic anisotropy at the metal centre from an easy axis, to an easy plane anisotropy. This results in reversal of the peaks in the NMR spectra, and in changes to the fine structure of the luminescence spectra. Furthermore, changes to the periphery of the binding cavity are implicated in determining the affinity constant for fluoride. There are clear differences in the entropic contribution to the free energy of activation between systems with benzylic amides and those with methylamides.

Kinetically Stable Lanthanide Complexes Displaying Exceptionally High Quantum Yields upon Long-Wavelength Excitation: Synthesis, Photophysical Properties, and Solution Speciation.

We demonstrate how highly emissive, kinetically stable complexes can be prepared using the macrocyclic scaffold of DO3A bearing coordinating aryl ketones as highly effective sensitizing chromophores. In the europium complexes, high quantum yields (up to 18% in water) can be combined with long-wavelength excitation (370 nm). The behavior in solution upon variation of pH, studied by means of UV-vis absorption, emission, and NMR spectroscopies, reveals that the nature of the chromophore can give rise to pH-dependent behavior as a consequence of deprotonation adjacent to the carbonyl group. Knowledge of the molecular speciation in solution is therefore critical when assessing the luminescence properties of such complexes.

Using substituted cyclometalated quinoxaline ligands to finely tune the luminescence properties of iridium(III) complexes.

The syntheses of five new heteroleptic iridium complexes [Ir(L(1-4))(2)(Diobpy)]PF(6) (where Diobpy = 4,4'-dioctylamido-2,2'-bipyridine) and [Ir(L(3))(2)(bpy)]PF(6) (where L = para-substituted 2,3-diphenylquinoxaline cyclometalating ligands; bpy = 2,2'-bipyridine) are described. The structures of [Ir(L(3))(2)(Diobpy)]PF(6) and [Ir(L(3))(2)(bpy)]PF(6) show that the complexes each adopt a distorted octahedral geometry with the expected trans-N, cis-C arrangement of the cyclometalated ligands. Electrochemical studies confirmed subtle perturbation of the Ir(III/IV) redox couple as a function of ligand variation. Luminescence studies showed the significant contribution of (3)MLCT to the phosphorescent character with predictable and modestly tunable emission wavelengths between 618 and 636 nm. DFT studies provided approximate qualitative descriptions of the HOMO {located over the Ir(5d) center (11-42%) and the phenylquinoxaline ligand (54-87%)} and LUMO {located over the ancillary bipyridine ligands (ca. 93%)} energy levels of the five complexes, confirming significant MLCT character. TD-DFT calculations indicate that UV-vis absorption and subsequent emission has substantial MLCT character, mixed with LLCT. Predicted absorption and emission wavelengths are in good general agreement with the UV-vis and luminescence experiments.