Chemistry Reference
In-Depth Information
In acetonitrile-dichloromethane 1:1 v/v solution, their absorption spectra are
dominated by naphthalene absorption bands and they exhibit three types of
emission bands, assigned to naphthyl localized excited states (
l
max
¼
337 nm),
naphthyl excimers (
l
max
ca. 390 nm), and naphthyl-amine exciplexes (
l
max
¼
480 nm) (
solid lines
in Fig.
3
). The tetraamine cyclam core undergoes only
two protonation reactions, which not only prevent exciplex formation for elec-
tronic reasons but also cause strong nuclear rearrangements in the cyclam struc-
ture which affect excimer formation between the peripheral naphthyl units of the
dendrimers.
Extensive investigation has been performed on the interaction of dendrimers
1 and 2 with metal ions [
17
a, e-h]. Complexation with Zn
2+
engages the nitrogen
lone pairs and thereby prevents exciplex formation, with a resulting intense
naphthyl fluorescence (
dashed lines
in Fig.
3
). This strong fluorescent signal is
a
100
80
60
40
20
0
b
100
80
60
40
20
0
300
350
400
450
500
λ
/nm
Fig. 3 Emission spectra of (a) 1 (1.3
10
5
M), and (b) 2 (6.7
10
6
M), before (
solid line
)
and after (
dashed line
) addition of 1.1 equivalents of Zn(CF
3
SO
3
)
2
in CH
3
CN:CH
2
Cl
2
1:1 v/v at
298 K with
l
¼
275 nm
ex
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