The interaction between gold nanoparticles and cationic and anionic dyes: enhanced UV-visible absorption

The interactions of charge stabilised gold nanoparticles with cationic and anionic dyes are reported. The nanoparticles were synthesised by the Turkevich citrate reduction method. It was found that when a solution of thiazine dye is titrated against gold citrate hydrosol, at a critical concentration of dye there is an enhanced maximum absorption in the dye. The extinction coefficient is increased up to ten-fold. This enhancement was observed for a number of cationic thiazine dyes, of which methylene blue and toluidine blue are established light-activated antimicrobial agents. The same enhancement was not observed for anionic, acidic dyes such as rose bengal which showed no communication with the gold nanoparticles and showed UV-visible titration experiments with well formed isosbestic points. By studying the interaction of the dye and gold nanoparticles under conditions of different ionic strength and by using a zetasizer and TEM to measure the gold nanoparticle size it was demonstrated that the cause of enhancement was not due to nanoparticle aggregation. It is proposed that thiazine cationic dyes coordinate around a gold nanoparticle and give significantly enhanced UV-visible absorption

Variable photon energy photoelectron spectroscopy of tris-cyclopentadienyl lanthanides

The gas phase photoelectron (PE) spectra of LnCp3 (Cp = η-C5H5; Ln = Pr, Nd, Sm), measured with a wide range of photon energy, are reported. Resonances observed in the photon energy regions of 4d to 4f excitation enable identification of ion states resulting from 4f ionization. For all three compounds molecular ion states characteristic of both 4f(n) and 4f(n-1) configurations are observed (Pr, n = 2; Nd, n = 3; Sm, n = 6). The molecular ion ground states have a hole in the uppermost ligand orbital of a' symmetry and are reached by either ligand or f electron ionization. The results are discussed in the context of the previously reported spectra of the Ce, Yb and Lu analogues. For YbCp3 f orbital/ligand interaction is proposed in the molecular ground state and for CeCp3(+) in the molecular ion ground state. For PrCp3 and NdCp3 final state effects are proposed as the origin of the dual configuration structure in their PE spectra. When the contributing orbitals are close in energy the 4f/a' interaction can give rise to significant covalent bonding even in the absence of effective overlap