Resorufin in the Channels of Zeolite L

Dominik Brühwiler, Niklaus Gfeller, and Gion Calzaferri
Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, CH-3000 Bern 9, Switzerland


Zeolite L containing the resorufin anion (Res-) in its anionic framework can be prepared by incorporating the neutral resorufin molecule (ResH) from the gas phase and then exchanging the protons with potassium ions which leads to dark violet colored microcrystals. The reversibility of the deprotonation/protonation reaction of resorufin can be monitored by measuring the UV/vis absorption spectrum of the samples. The absorption spectra of Res- and ResH and their solvent dependence was interpreted using the EHMO-EDiT theory. While Res- is strongly fluorescent in solution, the fluorescence is completely quenched when Res- is located inside the channels of potassium zeolite L. This allows the investigation of the exit kinetics of the resorufin molecules as a function of the size of the solvent molecules which enter the zeolite channels and displace the incorporated resorufin molecules irreversibly. The following series was found for the displacement rate: water >> methanol > ethanol > 1-propanol > 1-butanol. Three cases can be distinguished concerning the mechanism of the displacement process: In case 1 the solvent molecules can pass a dye molecule inside the channel easily. For this case the exit kinetics can be explained by a homogeneous Markoff chain. In case 2 the solvent molecules are considerably hindered when passing a dye molecule inside the channel, and in case 3 the solvent molecules are too large to pass a dye molecule and, hence, the exit rate of dye molecules is zero. While water corresponds to case 1, 1-butanol can be assigned to case 3 and may therefore be used to remove resorufin molecules or molecules with similar properties from the outer surfaces of zeolite L without displacing the intercalated molecules.

published in: J. Phys. Chem. B 1998, 102, 2923.

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