A study of the strongly fluorescent species formed by the interaction of the dye 1,4-dihydroxyanthraquinone (quinizarin) with Al(III)

Strongly fluorescent species form when Al(111) ions interact with 1,4-dihydroxyanthraquinone (quinizarin, QNZ), in aqueous and non-aqueous media. Speciation studies suggest the supramolecular and/or polymeric nature of these complexes as both their absorbance and fluorescence intensity increase proportionally to the Al(111) equivalents up to 60/1 Al(111)/QNZ and in certain cases even further. iso-Propanol is the solvent that yields the highest quantum yield of fluorescence (Phi = 0.51 for QNZ/Al(111) 1/75). Counterion effects were also studied and Al(acac)(3) was found to be the compound with which the highest quantum yield values were obtained, suggesting an active role for acac(-) in the stabilisation of the QNZ/Al(111) fluorescent species. Potentiometric studies, performed between pH 3 and 6 in dioxane/water 80/20, suggest the formation of 2/1 QNZ/Al(111) species, having global stability constant of 10(40). Studies at higher ratios of Al(111) were precluded by precipitations. (C) 2002 Elsevier Science B.V. All rights reserved.