Chemistry Reference
In-Depth Information
TABLE 14.1 Photophysical Properties of Selected Phosphorescent Probes Based on Pt
and Pd Porphyrin-AG Dendrimers
Absorption,
l
(nm)
Gen Compound
k
q
(mmHg
1
s
1
)
b
Phosphorescence
a
f
a
l
max
(nm)
t
0
(
m
s)
PtP-OPEG
b
0
389
520
682
0.05
37
1208
15
PtP-(AG
1
OPEG)
8
1
390
520
681
0.09
48
521
3
PtP-(AG
2
OPEG)
8
2
398
516
671
0.14
53
120
3
PdP-(AG
2
OPEG)
8
2
403
532
708
0.07
720
97
4
PtP-(AG
3
OPEG)
8
3
409
515
664
0.18
66
66.6
0.2
PtTBP-(AG
2
OPEG)
8
2
432
621
791
0.24
54
171
5
PdTBP-(AG
2
OPEG)
8
2
446
635
816
0.03
270
122
5
a
Quantum yields and lifetimes are measured in deoxygenated aqueous solutions.
b
Measured using
2
m
M solution of the probe in 50mM phosphate buffer, pH
¼
7.4, 23
C.
better encapsulated and consequently are much less likely to experience intermo-
lecular porphyrin-to-porphyrin contacts. In addition, better encapsulation can lead to
a less quenching by the solvent and/or less efficient nonradiative T
1
!
S
0
relaxation.
The rate of the latter is determined by the magnitude of the spin-orbit coupling, which
in
-extended porphyrins is strongly affected by the macrocycle vibrations [61].
Increase in the size of the dendrimer and tighter confinement of the porphyrin inside
the folded dendrimer may contribute to the decreased flexibility of themacrocycle and
lower the rate of its nonradiative decay.
The effect of dendritic encapsulation on phosphorescence quenching by oxygen in
the series of Pt porphyrin-AG dendrimers is exemplified in Figure 14.14a.
p
(b)
(a)
Gen 0
50 mM phosphate buffer (pH 7.2)
Rat blood plasma
3
×
10
4
1.5
×
10
5
2
×
10
4
Gen 1
1.0
×
10
5
60
1
×
10
4
45
5.0
×
10
4
Gen 2
Gen 3
30
0
24
48
72
Time (h)
0
0
50
100
150
0
50
100
150
p
O
2
(mmHg)
p
O
2
(mmHg)
FIGURE 14.14
(a) Stern-Volmer oxygen quenching plots of Pt porphyrin dendrimers in
aqueous solutions. The solid lines show the fits of the data to the Stern-Volmer equation. (b)
Stern-Volmer plots of gen 2 dendrimer in phosphate buffer solution and in rat blood at 36.9
C.
Inset: measurements at air saturation taken at 1min intervals during 80 h [89].
