Abstract
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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