Use of cyclodextrins and fluorescence spectroscopy to probe the dual fluorescence of 9-anthroic acid

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We report here a study of 9-anthroic acid (9-anthracenecarboxylic acid) in aqueous and solid solutions of β-cyclodextrin in which we demonstrate the use of cyclodextrins, in combination with fluorescence spectroscopy, to probe molecular processes. The dual fluorescence of 9-anthroic acid is dependent on the pH, the solvent, and the concentration of the acid. The origin of this dual fluorescence has been a point of controversy for many years. The small cavity of β-cyclodextrin cannot include more than one 9-anthroic acid molecule and is used in this study to distinguish between a unimolecular and bimolecular model for the dual fluorescence of 9-anthroic acid. The formation of a host/guest inclusion complex of 9-anthroic acid with β-cyclodextrin should reduce the presence of dimers, and as a result, a decrease in the corresponding fluorescence intensity would be expected if aggregation is the source of the observed dual fluorescence. However, we have observed that the broad fluorescence, which some have previously attributed to dimers, increases in the presence of β-cyclodextrin. Therefore, we conclude that acid-base equilibrium is a more plausible explanation for the observed dual emission rather than the formation of dimers. In this paper, the results of this study are discussed in detail. © 1996 American Chemical Society.

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Journal of Physical Chemistry

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