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(III) 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(III) equivalents up to 60/1 Al(III)/QNZ and in certain cases even further. opanol is the solvent that yields the highest quantum yield of fluorescence (Φ=0.51 for QNZ/Al(III) 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(III) fluorescent species. iometric studies, performed between pH 3 and 6 in dioxane/water 80/20, suggest the formation of 2/1 QNZ/Al(III) species, having global stability constant of 1040. Studies at higher ratios of Al(III) were precluded by precipitations.