Pina, J, de Melo JS, Pina F, Lodeiro C, Lima JC, Parola AJ, Soriano C, Clares MP, Albelda MT, Aucejo R, Garcia-Espana E.
2005.
Spectroscopy and coordination chemistry bisnaphthalene-bisphenanthroline ligand of a new displaying a sensing ability for metal cations, 2005. Inorganic Chemistry. 44:7449-7458.
AbstractA new fluorescent macrocyclic structure (0) bearing two naphthalene units at both ends of a cyclic polyaminic chain containing two phenanthroline units was investigated with potentiometric and fluorescence (steady-state and time-resolved) techniques. The fluorescence emission spectra show the simultaneous presence of three bands: a short wavelength emission band (naphthalene monomer), a middle emission band (phenanthroline emission), and a long-wavelength band. All three bands were found to be dependent on the protonation state of the macrocyclic unit (including the polyaminic and phenanthroline structures). The existence of the long-wavelength emission band is discussed and is shown to imply that a bending movement involving the two phenanthroline units leads to excimer formation. This is determined by comparison with the excimer emission formed by intermolecular association of 1,10-phenanthroline. With ligand L1, excimer formation occurs only at pH values above 4. At very acidic pH values, the protonation of the polyamine bridges is extensive leading to a rigidity of the system that precludes the bending movement. The interaction with metal cations Zn(II) and Cu(II) was also investigated. Excimer formation is, in these situations, increased with Zn(II) and decreased with Cu(II). The long-emission band is shown to present a different wavelength maximum, depending on the metal, which can be considered as a characteristic to validate the use of ligand L1 as a sensor for a given metal.
Galindo, F, Lima JC, Luis SV, Melo MJ, Parola AJ, Pina F.
2005.
Water/humidity and ammonia sensor, based on a polymer hydrogel matrix containing a fluorescent flavylium compound, 2005. Journal of Materials Chemistry. 15:2840-2847.
AbstractFlavylium compounds can conveniently be encapsulated in water permeable cross-linked poly(2-hydroxyethyl methacrylate) ( PHEMA) polymer hydrogel matrices. The polymer is also permeable to gases, for example ammonia and hydrogen chloride. The ability of the polymer to concentrate water from the surrounding atmosphere was demonstrated. The absorption and emission spectra of the encapsulated flavylium compounds are very dependent on the pH, and by consequence ammonia ( or hydrogen chloride) can be easily detected. The intensity of the fluorescence emission of the flavylium cation (AH+ species obtained in acidic media) is very dependent on the water content due to the efficient excited state proton transfer involving the AH(+)* excited state and water. The combination of flavylium emission sensitivity to water and ability of the polymer to concentrate water from the surrounding atmosphere, confers this material potential utility as a humidity sensor with high sensitivity.
Kuhn, FE, Zhao J, Abrantes M, Sun W, Afonso CAM, Branco LC, Goncalves IS, Pillinger M, Romao CC.
2005.
Catalytic olefin epoxidation with cyclopentadienyl-molybdenum complexes in room temperature ionic liquids. Tetrahedron Letters. 46:47-52., Number 1
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