In a fourth generation poly(propylene amine) dendrimer decorated with 32 dansyl units at the periphery and containing 30 aliphatic amine units in the interior, the strong fluorescence of all the dansyl units is quenched when a Co 2+ ion is incorporated into the dendrimer.

We have investigated the interaction of Co 2+ ions (as nitrate salt) with dendrimers of the poly-(propylene amine) family functionalized in the periphery with fluorescent dansyl units. Each dendrimer nD, where the generation number n goes from 1 to 5, comprises 2 (n+1) dansyl functions in the periphery and 2 (n+1) -2 tertiary amine units in the interior. For comparison purposes, the behavior of a monodansyl reference compound (I) has also been investigated. The results obtained have shown that: (i) the absorption and fluorescence spectra of the reference compound I are not affected by addition of Co 2+ ions; (ii) in the case of the dendrimers, the absorption spectra are unaffected, but a strong quenching of the fluorescence of the peripheral dansyl units is observed; (iii) the fluorescence quenching takes place by a static mechanism involving coordination of metal ions in the interior of the dendrimers; (iv) metal ion coordination by the dendrimers is a fully reversible process; (v) a strong amplification of the fluorescence quenching signal is observed with increasing dendrimer generation. For the larger dendrimers (n ) 3, 4, and 5), at very low metal ion concentration 1:1 metal/dendrimer species are formed, in which the Co 2+ ion guest quenches each one of the dansyl units that becomes excited after light absorption.

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