The rate and equilibrium constants of the network of chemical species involving the dye 2'-methoxyflavylium tetrafluoroborate were characterized using stopped flow and flash photolysis in both acidic and alkaline aqueous solution. The trans-chalcone is the thermodynamic stable species in acidic solutions 2 < pH < 7; irradiation of trans-chalcone at low pH leads to the corresponding coloured flavylium cation. The system reverts to its initial state in a few hours, in the dark. The kinetics of the various steps in the system were determined; flash photolysis revealed that the rate determining process of flavylium formation is the ring closure to give the corresponding hemiketal. In alkaline medium the ionized transchalcone is the stable form and clear evidence for the existence of a hemiketal species was obtained. A write-read-erase cycle can be performed with this compound. (c) 2008 Elsevier Ltd. All rights reserved.

A simple and rapid liquid chromatographic method with diode-array UV-vis spectrophotometric detection has been developed for the authentication of dragon's blood resins from Dracaena and Daemonorops trees. Using this method it was discovered that the flavylium chromophores, which contribute to the red colour of these resins, differ among the species and could be used as markers to differentiate among species. A study of parameters, such as time of extraction, proportion of MeOH and pH, was undertaken to optimise the extraction of the flavyliums. This method was then used to make extracts from samples of dragon's blood resin obtained from material of known provenance. From the samples analysed 7,6-dihydroxy-5-methoxyflavylium (dracorhodin), 7,4'-dihydroxy-5-methoxyflavylium (dracoflavylium) and 7,4'-dihydroxyflavylium were selected as species markers for Daemonorops spp., Dracaena draco and Dracaena cinnabari, respectively. The chromatograms from these samples were used to build an HPLC-DAD database. The ability to discriminate among species of dragon's blood using the single marker compounds was compared with a principal components analysis of the chromatograms in the HPLC-DAD database. The results from the HPLC-DAD method based on the presence of these flavylium markers was unequivocal. The HPLC-DAD method was subsequently applied to 37 samples of dragon blood resins from the historical samples in the Economic Botany Collection, Royal Botanic Gardens, Kew. The method identified anomalies in how samples in this collection had been labelled. It is clear that the method can be used to evaluate the provenance of samples used in different areas of cultural heritage. It also could be used to monitor the trade of endangered species of dragon's blood and the species being used in complex formulations of traditional Chinese medicine. (C) 2008 Elsevier B.V. All rights reserved.

The macrocyclic phenanthrolinophane 2,9-[2,5,8-triaza-5-(N-anthracene-9-methylamino) ethyl]-[9]-1,10-henanthrolinophane(L) bearing a pendant arm containing a coordinating amine and an anthracene group forms stable complexes with Zn(II), Cd(II) and Hg(II) in solution. Stability constants of these complexes were determined in 0.10 mol dm(-3) NMe4Cl H2O-MeCN (1:1, v/v) solution at 298.1+/-0.1 K by means of potentiometric (pH metric) titration. The fluorescence emission properties of these complexes were studied in this solvent. For the Zn(II) complex, steady-state and time-resolved fluorescence studies were performed in ethanol solution and in the solid state. In solution, intramolecular pi-stacking interaction between phenanthroline and anthracene in the ground state and exciplex emission in the excited state were observed. From the temperature dependence of the photostationary ratio (I-Exc/I-M), the activation energy for the exciplex formation (E-a) and the binding energy of the exciplex (-DeltaH) were determined. The crystal structure of the [ZnLBr](ClO4).H2O compound was resolved, showing that in the solid state both intra- and inter-molecular pi-stacking interactions are present. Such interactions were also evidenced by UV-vis absorption and emission spectra in the solid state. The absorption spectrum of a thin film of the solid complex is red-shifted compared with the solution spectra, whereas its emission spectrum reveals the unique featureless exciplex band, blue shifted compared with the solution. In conjunction with X-ray data the solid-state data was interpreted as being due to a new exciplex where no pi-stacking (full overlap of the pi-electron cloud of the two chromophores-anthracene and phenanthroline) is observed. L is a fluorescent chemosensor able to signal Zn(II) in presence of Cd(II) and Hg(II), since the last two metal ions do not give rise either to the formation of pi-stacking complexes or to exciplex emission in solution.

Speciation studies in aqueous solution on the interaction Of Cu2+ and Zn2+ with a series of polyaminic ligands N-naphthalen-1-ylmethyl-N'-[2-[(naphthalen-1-ylmethyl)- amino]-ethyl)-ethane-l,2-diamine (LI), N-naphthalen-lylmethyl-iV-(2-{2-[(naphthalen-1-ylmethyl)-amino]-ethyl- amino]-ethyl)-ethane-l,2-diamine (L2) and N-naphthalen-1-ylmethyl-N'-[2-(2-{2-[(naphthalen-1-ylmethyl)-amino]- ethylamino)-ethylamino)-ethyl]-ethane-1,2-diamine (L3) containing two naphthylmethyl groups at their termini and N-1-(2-{2-[(naphthalen-1-ylmethyl)-amino]-ethyl-amino)-ethyl)-ethane-1,2-diamine (L4) containing just one naphthylmethyl group have been carried out at 298.1 K in 0.15 mol dm (-3) NaCl. In the case of the tetraamines L2 and L4, their coordination capabilities towards Cd2+, Ni2+, Co2+ and Pb2+ have also been considered. The stability constants follow the general Irving-Williams sequence. The steady-state fluorescence emission studies on the interaction with metal ions show that while Cu2+ produces a chelation enhancement of the quenching (CHEQ), the interaction with Zn2+ leads to a chelation enhancement of the fluorescence (CHEF). Finally, ligands L1, L2 and L3 have been successfully covalently attached to silica surfaces and some preliminary results of their emissive properties are given.

A phase-change thermochromic system was designed through the reversible transformation of the 4-substituted flavylium dye 4-(2-carboxyphenyl)-7-diethylamino-4'-dimethyl-amino-1-benzopyrylium into its leuco form, in the presence of a developer (ethyldiisopropylamine) and a suitable solvent (e.g., acetonitrile, n-pentadecanonitrile). The leuco form of the flavylium-based dye is a spirolactone species whose ring opens at low temperature (below the solvent melting point) to form the blue flavylium cation. Decarboxylation of the lactone to give 4-phenyl-7-diethylamino-4'-dimethylamino-1-benzopyrylium was observed upon irradiation of the system with UV light, erasing the thermochromic effect.

The formation of Eu(III) nanoparticles in borosilicate sol-gels and the glass formation heat treatment effect on those particles were studied using luminescence techniques. The presence of the particles was observed using transmission electron microscopy (TEM) images followed by analysis with energy dispersive X-ray spectroscopy (EDS). These experiments showed the presence of particles with a large quantity of europium and chlorine and only small amounts of oxygen with sizes ranging from 30 to 100 nm. Heat treatment at 400, 600, and 800 degrees C lead to glass samples in which those particles were no longer observed. Steady-state and time-resolved luminescence techniques allowed a detailed study of Eu(III) photophysics in sot-gel and glass samples. In sol-gel matrices, the (5)D(0) -> (7)F(0) transition is very weak, hinting at Eu(III) species experiencing a rather symmetric crystal field. The (5)D(0) -> (7)F(2) transition intensity is not very strong, which according to a Judd-Ofelt analysis indicates low interaction with the anions present in the sol-gel matrices. This picture reverses after heat treatment, indicating a replacement of chloride anions with oxygen as preferential ligands of Eu(III). Time-resolved luminescence shows in a more detailed way these aspects. Sol-gel samples display nonexponential kinetics, which are attributed to Eu(III) species present in the nanoparticles surface (bound to oxygen) and Eu(III) in the core of the nanoparticles (bound to chloride). Glass samples display single-exponential luminescence decays, in which the decay constant approaches the values calculated for the radiative rate constant with Judd-Ofelt analysis. It is concluded that, in sol-gel, mechanisms like electron-phonon coupling suppress the Eu(III) luminescence, which disappear as soon as the nanoparticles are disrupted after heat treatment.