Chemistry - A European Journal
10.1002/chem.201806337
COMMUNICATION
+
-
+
-
and (2H2+Cl-
–(7H2+Cl-
Table 3. Photophysical properties of (2 Cl )
2
@CB[8]
2
–(7 Cl )
2
@CB[8]
2
2 2
) @CB[8]
2
2 2
) @CB[8]
2
.
R =
λ
abs
λ
em
φ
[%]
R =
λ
abs
λ
em
φ
[%]
[nm][
587
547
561
560
601
551
a]
[a]
[nm]
328
336
336
360
353
341
[nm]
498
478
482
536
521
489
[a]
[a]
[
nm]
(
(
(
(
(
(
2H2+Cl-
3H2+Cl-
4H2+Cl-
5H2+Cl-
6H2+Cl-
7H2+Cl-
2 2
) @CB[8]
2 2
) @CB[8]
2 2
) @CB[8]
2 2
) @CB[8]
2 2
) @CB[8]
2 2
) @CB[8]
2
2
2
2
2
2
H
367
353
354
391
380
366
4
(2 Cl )
+
-
2
@CB[8]
2
@CB[8]
2
@CB[8]
2
@CB[8]
2
@CB[8]
2
@CB[8]
2
2
2
2
2
2
H
82
80
78
42
5
+
-
CHO
COCH
26
18
10
2
(3 Cl )
CHO
+
-
3
(4 Cl )
COCH
3
+
-
CH
Br
3
(5 Cl )
CH
Br
3
+
-
(6 Cl )
+
-
CH
2
OH
12
(7 Cl )
CH
2
OH
43
[
a]
λex = λabs
In conclusion, the effect of supramolecular complexation on
the photophysical properties of simple charge-transfer dyes 2 –
Keywords: Cucurbituril • fluorescence enhancement •
+
host-guest complex • restriction of intramolecular motion •
7+
and their protonated forms in aqueous solution is reported.
luminescence
The free fluorophores are weakly emissive due to formation of a
TICT state as indicated by experiment as well as theory.
However, the compounds exhibit strong luminescence in the
solid state and in viscous matrices like polymer blends, where
molecular rotations are hindered. Complexation with CB[7]
results in the formation of 1:1 complexes and the TICT state is
destabilized in the unpolar environment inside the host cavity. In
contrast, the fluorophores form 2:2 complexes with CB[8] with a
cofacial antiparallel arrangement of the dyes as shown by
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27-fold increase for 2+ yielding φ = 82%). The two tuning
parameters (change of pH and host–guest complexation) of the
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The authors thank Felix Witte for his help with the DFT
calculations. We are grateful for funding from the Deutsche
Forschungsgemeinschaft (CRC 765) and the Deutsche
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