FLUORESCENCE OF METHYLVIOLOGEN INTERCALATED INTO MONTMORILLONITE AND HECTORITE AQUEOUS SUSPENSIONS

Methylviologen (MV2+) when intercalated into montmorillonite and hectorite aqueous suspensions has been investigated by using steady-state and time resolved fluorescence spectroscopy. As the [MV2+]/[clay] ratio increased, different fluorescence behavior was observed for the two clays. In hectorite the fluorescence intensity decreased with an increase in ratio, the curve being biphasic. In montmorillonite there was an initial increase in fluorescence intensity and then the fluorescence decreased in an approximately linear fashion. In hectorite the fluorescence decay of MV2+ was fit to two exponential decay terms, with lifetimes depending on the ratio. The longer decay time ranged from 3.8 to 4.4 ns and the shorter decay time ranged from 1.0 to 1.4 ns. The fractional fluorescences were constant over the entire ratio range studied. In the case of montmorillonite the fluorescence decay of MV2+ fit three exponential components, which had the same values at all ratios. These decay times were 0.93, 0.37, and 0.083 ns. The fractional fluorescence values were independent of the ratio of [MV2+]/[clay]. The most consistent rationalization of these results was to propose a model wherein the intercalated MV2+ molecules were involved in self-quenching processes. The data may suggest a distribution of fluorescence decay times reflecting the heterogeneity of the clay structures.