10.1002/anie.201803132
Angewandte Chemie International Edition
COMMUNICATION
triptycene walls. Accordingly, we hypothesized that guest
binding might lead to significant fluorescence changes. Figure 7
shows the fluorescence spectra recorded for 1 (12 µM) in the
between what constitutes host and guest in that each
component contains binding epitopes that fulfil both roles in
each complex.
Finally,
1
displays guest responsive
presence of different guests and Table
2
presents key
fluorescence and is particularly sensitive to pyridinium derived
parameters. Interestingly, in all cases guest binding results in a
hypsochromic shift in emission maximum probably due to
disruption in the π−π interactions between the tryptycene walls.
Most interesting is the divergent behavior of adamantane
derivatives 17, 18, and 19. Whereas the 1•17 and 1•18
complexes display enhanced fluorescence, complex 1•19 is
completely quenched presumably due to photoinduced electron
transfer from the excited state of 1 to the pyridinium guest 19. In
accord with this interpretation is the observation that methyl
viologen complex 1•12 is also heavily quenched. Related
sensing materials have been pioneered by Swager for detection
of nitroaromatics.[16] Host 1 and related compounds – with their
high affinity and selectivity toward hydrophobic cations – may
offer unique opportunities as aqueous sensors for pyridinium
and related quaternary ammoniums that are present in drugs
and other natural products (e.g. NADP).
guests 12 and 19 which quench host fluorescence by
photoinduced electron transfer.
Overall, the work further
establishes acyclic CB[n]-type receptors as versatile and readily
functionalized systems that display both intriguing recognition
behaviour and function.
Acknowledgements
We thank the US National Science Foundation (CHE-1404911
and CHE-1807486) for financial support.
Keywords: cucurbituril • host-guest systems • triptycene •
supramolecular chemistry • fluorescence
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Figure 7. Fluorescence spectra (λex = 214 nm, 298 K, H2O) recorded for 1 (12
µM) in the presence of 2.0 equivalent of guests (8, 9, 13, 16, 17, 18, 19).
Table 2. Guest induced fluorescence change of 1 (λex = 214 nm, 298 K).
1•guest
Host
1
8
9
13
16
17
18
19
λem
(nm)
Δλem
(nm)
(I/I0)%
377
357
- 20
360
-17
368
- 9
361
-16
363
-14
366
-11
354
- 23
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0
100
6.9
58
2.6
57
4.3
113
7.6
79
3.5
112
5.5
123
8.8
6
0.33
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Φ(%)
In summary, we have reported the synthesis of a chimeric
receptor combining the recognition preferences of the
cucurbituril and triptycene. The x-ray crystal structure of 1
reveals self-folded geometry based on π−π interactions
1
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a
between the triptycene walls of 1; 1 further organizes itself into a
honeycomb arrangement that features infinite solvent filled
channels along the c-axis. Host 1 binds to hydrophobic
(di)cations as is typical of CB[n] derived receptors but also
recognized larger guests like blue box 20 and Fujita square 22.
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