Association of the tris(dipicolinato)europium(III) anion with cetyltrimethylammonium micelles

Abstract

The ⁵D_o luminescence lifetime of the Eu(pdc)^3–₃ complex ion on the surface of cetyltrimethylammonium (CTA)micelles is longer than that of the ion in free solution. The effect of the lower symmetry environment in increasing the rate of the radiative relaxation is much less than the effect of the decrease in the rate of the radiationless relaxation due to the exclusion of water molecules from the second coordination sphere. This provides a method of studying the equilibrium between bulk and micellar surface complex ions which is complementary to that using the corresponding Tb(pdc)^3–₃ probe, although the behaviour of the two systems is different. If sufficient complex ion is available, most of the anion sites on the micelle are occupied by the complex ion. Exchange between the micellar surface and the bulk solution is fast compared to the emission lifetime.