resumo
Zn - Al hydrotalcite-like compounds intercalated by 1,3,6,8-pyrenetetrasulfonate (PTS), 1-pyrenesulfonate ( PS) and 1-pyrenecarboxylate ( PC) anions were synthesised by an ion-exchange procedure. The materials were characterised by powder X-ray diffraction at different temperatures, thermogravimetric analysis, FTIR, C-13{H-1} CP/MAS NMR and photoluminescence techniques. In the fully hydrated states, the interlayer distances are 13.7 angstrom for Zn - Al - PTS, 18.9 angstrom for Zn - Al - PS, and 24.8 angstrom for Zn - Al - PC. These can be ascribed to a monolayer arrangement for intercalated PTS anions and bilayer arrangements for the 1-pyrenyl derivatives. The samples exhibit different thermal decomposition pathways, and in the case of Zn - Al - PTS the removal of physisorbed and interlayer water leads to a change in the orientation of the organic anion with respect to the hydroxide layers. The structural transformation is fully reversible upon hydration. The photophysical characterisation of the bulk materials was based on the determination of their emission and fluorescence excitation spectra, and the fluorescence lifetimes. From the steady-state (monomer and "excimer-like'' bands) and time-resolved (triple exponential decays) data, evidence for the presence of a structure with similar characteristics to pyrene dimer together with monomer (by comparison with the emission of dilute solutions of PS and PC), pre-associated and (possibly) dynamic excimer species could be presented.
palavras-chave
LAYERED DOUBLE HYDROXIDE; HYDROTALCITE-LIKE COMPOUNDS; EXCIMER FORMATION; AL-HYDROTALCITE; ENERGY-TRANSFER; FLUORESCENCE; CRYSTAL; CHROMOPHORES; HYBRID; NANOCOMPOSITES
categoria
Chemistry; Materials Science
autores
Gago, S; Costa, T; de Melo, JS; Goncalves, IS; Pillinger, M
nossos autores
Isabel Maria de Sousa Gonçalves
Professor associado