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of the results obtained, however, is unclear. For example, comparison with the spectra
of the component units is neglected and the reported relative intensities apparently
refer to excitation at different wavelengths.
R
O
N
N
O
Pt
R
R
N
N
O
O
O
O
O
R =
O
O
O
C
O
O
O
O
O
N
N
N
O
O
Er
3+
R
R
O
O
C
C
O
O
N
N
N
N
Pt
Pt
N
N
N
N
R
R
10
R
R
Another example of this class of compounds is constituted by a dendron with
carboxylate focal point and a Pt porphyrin substituted with three Fr
´
chet type
dendrons of generations 1-3 (dendron 10 represents the third generation) [
13
a].
These dendrons are able to coordinate Er
3+
ions and form a stable complex contain-
ing a lanthanide ion surrounded by three dendrons and one 2,2
0
:6
0
,2
00
-terpyridine
(tpy) ligand. These complexes have been studied both in tetrahydrofuran (THF)
solution and in thin film. The NIR emission of Er
3+
at 1,530 nm is sensitized by the
Pt porphyrin and not from the Fr
´
chet dendrons. This result is in contrast to the fact
that in the case of dendrons without the coordinated metal ion, an efficient energy
transfer from the dimethoxybenzene units to the Pt porphyrin is reported by the
authors. Coming back to the Er
3+
complexes, the sensitized Er
3+
emission intensity
increases as a function of generation: this effect is much larger (ca. ten times from
generation 1 to 3) in thin film than in THF solution (ca. four times from generation 1
to 3). This has been attributed to an increase in the site-isolation efficiency upon
increasing dendron generation and is consistent with the observed increase in the
lifetime of the luminescent excited state of the lanthanide ion in going from
generation 1 to 3 (
t
¼
0.98, 1.64, and 6.85
s in going from generation 1 to 3).
m
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