Chemistry Reference
In-Depth Information
FIGURE 11.2
Steady-state fluorescence anisotropy r
ss
of compound
D
, and dendrimers
G2
D
-G5
D
in dichloromethane (dark gray bars) and dichloromethane/propylene glycol 1:30
(v/v) (light gray bars) solution at 298 K [22].
11.3.1.2 Time-Dependent Properties
In dichloromethane solution, the anisotropy
decay of
is too fast to be measured with our equipment since it undergoes full
depolarization during the excited state lifetime. For the dendrimers, the rotational
relaxation time
D
(Table 11.3) can be obtained by fitting the anisotropy data with a
monoexponential decay and upon setting the time-zero anisotropy r
0
equal to that of
the dansyl unit, 0.31. The obtained
y
y
values are not strongly different going fromG2
D
to G5
(from 0.6 to 2.4 ns, Table 11.3), despite the large variation in molecular mass
and volume. Furthermore, these values are not in agreement with those predicted for a
spherical rotor from Eq. 11.3. The hydrodynamic volume V
h
calculated fromEq. 11.4
D
TABLE 11.3 Steady-State and Time-Resolved Anisotropy of Fluorescence in
Dichloromethane (DCM) and Dichloromethane/Propylene Glycol (DCM/PGly) 1:30 (v/v)
Solvent
V
h
(nm
3
)
r
ss
y
(ns)
D
<
0.01
<
0.5
DCM
a
DCM/PGly 1:30
0.04
-
G2
D
DCM
<
0.01
0.6
5.8
a
DCM/PGly 1:30
0.15
-
-
G3
D
DCM
0.01
1.3
12.6
-
a
DCM/PGly 1:30
0.18
-
G4
D
DCM
0.02
1.8
17.4
-
a
DCM/PGly 1:30
0.18
-
G5
D
DCM
0.05
2.4
23.3
-
a
DCM/PGly 1:30
0.18
-
a
Double-exponential decay of fluorescence precluded an accurate determination of the corresponding
y
values.
