Spectroscopic properties of a novel fluorescent complex of aluminium and quinizarin

The addition of aluminium compounds to 1,4-dihydroxyanthraquinone (quinizarin (QH₂)) in either aqueous or non-aqueous solutions results in the formation of a highly fluorescent pink-red complex with excitation maxima at 500, 530 and 573 nm and corresponding emission maxima at 585 and 619 nm. Analysis by absorption spectroscopy using mole ratio and continuous variation techniques indicates the formation of 1:1 and 2:1 Al:QH₂ complexes. Fluorescence quantum yields in excess of 0.8 have been measured in n-butanol. Observations on the stability and the spectroscopic properties of the 2:1 complex are presented, together with a plausible structure.