Chemistry Reference
In-Depth Information
S
fluorophores, and (iii) energy migration among the
S
units. Contrary to what
happens for the Gn
energy migration is expected to
be fast because of the strong overlap between the absorption (
D
dendrimers, in the case of G2
S
l
max
¼
310 nm) and
emission (
353 nm) bands of the stilbenyl moiety, as demonstrated by the
much higher values of J (3.4
l
max
¼
10
15
cm
3
/M) and R
0
(1.7 nm) reported for stilbenyl
rather than dansyl fluorophores.
Both the stilbenyl model compound
S
and the second-generation dendrimer G2
S
are fluorescent with a very short excited state lifetime (
200 ps), so that fluorescence
anisotropy decay could not be measured with our equipment.
<
11.3.2.1 Steady-State Properties
As shown in Figure 11.3a, the fluorescence
anisotropy of the reference compound
increases upon increasing the fraction of
propylene glycol in the solvent mixtures (from pure acetonitrile to 1:30 (v/v)
acetonitrile/propylene glycol). This is an expected result since in such a molecular
S
FIGURE 11.3
Steady-state anisotropy r
ss
in acetonitrile (squares), acetonitrile/propylene
glycol 1:2 (v/v) (triangles), and 1:30 (v/v) (circles) solutions at 298 K of compounds
S
(a) and
G2
S
(b). Emission spectra in acetonitrile solution are also reported [22].
