INTRAZEOLITE PHOTOCHEMISTRY - 22 - ACID-BASE PROPERTIES OF COUMARIN 6- CHARACTERIZATION IN SOLUTION, THE SOLID-STATE, AND INCORPORATED INTO SUPRAMOLECULAR SYSTEMS

The spectroscopic properties of the dye coumarin 6 in solution are rep orted. Relatively large shifts are seen in both the absorption and flu orescence spectra upon protonation. The very large Stokes shift that i s seen for the dye in its solid state and as the hydrochloride salt re veals that the dye molecules are forming aggregates, which is a phenom enon that is also seen in very high concentrations of coumarin 6 in so lution. The acid-base properties of coumarin 6 in heterogeneous system s such as zeolites and clays are also presented. We have found that th is dye molecule is extremely sensitive to the presence of Lewis and Br onsted sites and were able to detect acidity in the faujasite zeolite NaY which is usually considered to be nonacidic. Two series of faujasi te zeolites, one in which the Bronsted acidity increases and the other in which the Lewis acidity increases, were also studied. The dication of the dye was detected in both HY100 and CBV 740, the zeolites with the highest Bronsted and highest Lewis acidity, respectively, used in the present study. Due to the large shifts seen for coumarin 6 in its neutral, monocation, and dication forms, both the absorption and fluor escence spectra resulted in detection of two species of the dye in tho se zeolites with intermediate acidity. The ability of coumarin 6 to se nse small amounts of Lewis and Bronsted sites makes it an attractive m olecule to study other systems as well.