C O M M U N I C A T I O N S
Figure 3. Contributions of the components of the supramolecular system
to fluorescence intensity under the switching conditions. Fluorescence was
measured at 388 nm on excitation with 318 nm light. Each experiment
shown consists of three steps: heating (160 °C for 2 min), irradiation (365
nm for 50 min at 20 °C), and repeat of the heating. (1) trans-3 + trans-1
+
2·2; (2) trans-3 in 2·2; (3) trans-3; (4) trans-3 + trans-1; (5) 4 in 2·2;
(
6) 4 in 2·2 + trans-3 in solution; (7) 4 in 2·2 + trans-3 + 5 in solution.
1
See Supporting Information for H NMR spectra.
encapsulation and cannot be achieved by less than complete combina-
tions of the components. We aim to incorporate these findings and
2
those of encapsulated 4,4′-dimethylbenzil in future optically addres-
Figure 2. Reversible fluorescence intensity switching by light and heat. Five
cycles of guest exchange and concomitant fluorescence change are shown. The
numbers shown correspond to paired experiments for fluorescence measurement
and H NMR spectra. Odd experiment numbers indicate heating steps (160 °C
for 2 min); even numbers indicate irradiation steps (365 nm for 50 min at 20
sable devices such as Boolean logic gates.
Acknowledgment. We are grateful to the Skaggs Institute for
Research for financial support and the Alexander von Humboldt
Stiftung for a Feodor Lynen Fellowship for H.D. H.D. is also Skaggs
Postdoctoral Fellow and was supported by the Swiss National Science
Foundation (SNF).
1
°
C). (A) Fluorescence measured at 388 nm on excitation at 318 nm. (B)
1
Corresponding H NMR spectra for each step. The blue arrow indicates proton
signals of free trans-3 in solution; the black arrow indicates two aromatic proton
signals of encapsulated trans-3.
Supporting Information Available: Experimental procedures, fluo-
1
converted to trans-1. Thus, trans-1 quenches the fluorescence of trans-3
much more efficiently than cis-1 does.
rescence spectra, and H NMR spectra. This material is available free of
charge via the Internet at http://pubs.acs.org.
To establish the influence of capsule 2·2 on stilbene fluorescence,
equiv of 4,4′-dimethylbenzanilide (4) were used to occupy the
2
References
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In summary, we have demonstrated how the external stimuli light
and heat can be used to control encapsulation of a guest and thereby
manipulate its fluorescence. The fluorescence on/off property we
observe in our system is a result of the supramolecular events of
JA103912A
J. AM. CHEM. SOC. 9 VOL. 132, NO. 29, 2010 9985