F. Vogtle et al., Coordination of Co2+ ions in the interior of poly(propylene amine) dendrimers containing fluorescent dansyl units in the periphery, J AM CHEM S, 122(42), 2000, pp. 10398-10404
We have investigated the interaction of Co2+ ions las nitrate salt) with de
ndrimers of the poly(propylene amine) family functionalized in the peripher
y with fluorescent dansyl units. Each dendrimer no, where the generation nu
mber n goes from 1 to 5, comprises 2((n+1)) dansyl functions in the periphe
ry and 2((n+1)) - 2 tertiary amine units in the interior. For comparison pu
rposes, the behavior of a monodansyl reference compound (I) has also been i
nvestigated. The results obtained have shown that: (i) the absorption and f
luorescence spectra of the reference compound I are not affected by additio
n of Co2+ ions; (ii) in the case of the dendrimers, the absorption spectra
are unaffected, but a strong quenching of the fluorescence of the periphera
l 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 r
eversible process; (v) a strong amplification of the fluorescence quenching
signal is observed with increasing dendrimer generation. For the larger de
ndrimers (n = 3, 4, and 5), at very low metal ion concentration 1:1 metal/d
endrimer species are formed, in which the Co2+ ion guest quenches each one
of the dansyl units that becomes excited after light absorption.