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Abstract

Proflavine, ion-exchanged on synthetic mica-type montmorillonite Barasym SSM-100, hec-torite, Laponite and sepiolite in aqueous suspensions, gives in addition to a monoprotonated molecule, a dimer and a diprotonated molecule. The first two molecules are found only on hectorite, Laponite, and sepiolite, whereas all three species are found on Barasym. The first 1–2 μmole of proflavine protonate in contact with 1 g of Barasym. The reaction occurs on the external surface and is similar to the highly selective Cs+ uptake by illite. Dimerization is the result of a simple concentration effect on the surface and gives rise to metachromatic behavior. No π-electron interaction with surface oxygens need be invoked. On the surface the monomelic, monoprotonated molecules have an extinction coefficient of 58,000 at 453 nm, and their dimerization constant is 1700. The quantum yield of dimer emission is 0.017. The emission of the monomer is quenched by the dimer both on the external surface and on the interlamellar surface by Perrin’s mechanism of quenching, in absence of diffusion, with an effective quenching radius of 2.7 nm. At loadings < 1% of the cation-exchange capacity, adsorption takes place mainly on the external surface.

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