Intrazeolite Photochemistry. 22. Acid−Base Properties of Coumarin 6. Characterization in Solution, the Solid State, and Incorporated into Supramolecular Systems

Abstract

The spectroscopic properties of the dye coumarin 6 in solution are reported. Relatively large shifts are seen in both the absorption and fluorescence spectra upon protonation. The very large Stokes shift that is seen for the dye in its solid state and as the hydrochloride salt reveals that the dye molecules are forming aggregates, which is a phenomenon that is also seen in very high concentrations of coumarin 6 in solution. The acidbase properties of coumarin 6 in heterogeneous systems such as zeolites and clays are also presented. We have found that this dye molecule is extremely sensitive to the presence of Lewis and Brønsted sites and were able to detect acidity in the faujasite zeolite NaY which is usually considered to be nonacidic. Two series of faujasite zeolites, one in which the Brønsted 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 Brønsted 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 fluorescence spectra resulted in detection of two species of the dye in those zeolites with intermediate acidity.The ability of coumarin 6 to sense small amounts of Lewis and Brønsted sites makes it an attractive molecule to study other systems as well.

Manufacturing and testing flexible microfluidic devices with optical and electrical detection mechanisms

“…[19,20] In neutral form, Coumarin 6 absorbs with a maximum centered at ~450 nm. Upon addition of low quantities of acid, monoprotonation at the N atom in the heterocyclic ring occurs first, accompanied by a shift in absorption maximum to 520 nm.…”

Photoimaging and Lithographic Processes in Polymers

“…The detection and quantification of the acid formed have been done in two ways: in situ within the photoresist film, and in solution, the exposed film being developed with an appropriate solvent, and the acid titrated with a base in the presence of an acid-base indicator whose spectroscopic properties were easily monitored [18,[34][35][36][37][38][39].…”

“…In Scheme 12.8, we present a selection of acid sensors employed both in solution and in films [18,34,37,39,40].…”

Supramolecular photochemistry in zeolites: From catalysts to sunscreens

“…Although the formula for X-and Y-type zeolites, M x/n [(AlO 2 )x (SiO 3 )y], does not indicate reactive acid sites, their existence is well documented [1,3,24,33,34]. Zeolite acid and base sites can have a profound effect on guest behavior.…”

“…This method adapted the approach developed by Hammett for determining the strengths of strong solution-phase acids and relies on the use of indicator bases that change color upon protonation. This technique has been widely applied over the last 50 years but recently, new methodologies employing fluorescence spectroscopy, for example, have emerged [33]. IR and Raman spectroscopy with pyridine and ammonium probes [38][39][40], as well as NMR using alkylamines, trialkylphosphines, and other probes [41][42][43][44] place.…”