Energy transfer switching in a bistable molecular machine

Article abstract of DOI:10.1021/ol051567t

(Figure Presented) A novel [2]rotaxane, containing pyrene and perylene bisimide as both stoppers and photoactive units, has been prepared. The shuttling of the protonated macrocycle switched the energy transfer (EN) from a pyrene moiety to a perylene moie

Full text of DOI:10.1021/ol051567t

ORGANIC
LETTERS
2005
Vol. 7, No. 22
4835-4838
Energy Transfer Switching in a Bistable
Molecular Machine
Yongjun Li, Hao Li, Yuliang Li,* Huibiao Liu, Shu Wang, Xiaorong He,
Ning Wang, and Daoben Zhu*
CAS Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of
Sciences, and Graduate School of the Chinese Academy of Sciences, Chinese Academy
of Sciences, Beijing 100080, P. R. China
ylli@iccas.ac.cn
Received July 5, 2005
ABSTRACT
A novel [2]rotaxane, containing pyrene and perylene bisimide as both stoppers and photoactive units, has been prepared. The shuttling of the
protonated macrocycle switched the energy transfer (EN) from a pyrene moiety to a perylene moiety, which resulted in changes of fluorescence
of the perylene moiety.
Molecular machines that are controllable, reversible, and
readable at a molecular level are of great interest because of
their potential applications in the creation of nanometer-scale
molecular devices.1 Mechanically interlocked molecules, such
as catenanes and rotaxanes, have received a great deal of
attention in the design of molecular machines because of
their ability to switch between two or more states as a result
of induced relative movement of their noncovalently interact-
ing components on application of external stimuli.2 This
shuttling motion can be driven chemically,3 electrochemi-
cally,4 or photochemically.5 The use of photons as input
(light-driven shuttling) is now under prominent consideration
because excitation with lasers can lead to a fast response
2001, 291, 2124. (h) Kihara, N.; Hashimoto, M.; Takata, T. Org. Lett. 2004,
6, 1693. (i) Herna´ndez, J. V.; Kay, E. R.; Leigh, D. A. Science 2004, 306,
1532. For pseudorotaxanes, see: (a) Ballardini, R.; Balzani, V.; Gandolfi,
M. T.; Prodi, L.; Venturi, M.; Philp, D.; Ricketts, H. G.; Stoddart, J. F.
Angew. Chem., Int. Ed. Engl. 1993, 32, 1301. (b) Ishow, E.; Credi, A.;
Balzani, V.; Spadola, F.; Mandolini, L. Chem. Eur. J. 1999, 5, 984. (c)
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C.; Kim, K. Angew. Chem., Int. Ed. 2003, 42, 4097. For catenanes see: (a)
Ashton, P. R.; Goodnow, T. T.; Kaifer, A. E.; Reddington, M. V.; Slawin,
A. M. Z.; Spencer, N.; Stoddart, J. F.; Vincent, C.; Williams, D. J. Angew.
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Sauvage, J.-P. J. Am. Chem. Soc. 1996, 118, 11980. (c) Andrievsky, A.;
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J. F. Angew. Chem., Int. Ed. 2001, 40, 1216. (e) Leigh, D. A.; Wong, J. K.
Y.; Dehez, F.; Zerbetto, F. Nature 2003, 424, 174.
(3) Ashton, P. R.; Ballardini, R.; Balzani, V.; Baxter, I.; Credi, A.; Fyfe,
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W.; Heath, J. R.; Stoddart, J. F. J. Am. Chem. Soc. 2001, 123, 12632. (b)
Altieri, A.; Gatti, F. G.; Kay, E. R.; Leigh, D. A.; Martel, D.; Paolucci, F.;
Slawin, A. M. Z.; Wong, J. K. Y. J. Am. Chem. Soc. 2003, 125, 8644.
(1) (a) Balzani, V.; Credi, A.; Raymo, F. M.; Stoddart, J. F. Angew.
Chem., Int. Ed. 2000, 39, 3348. (b) Molecular machines special issue: Acc.
Chem. Res. 2001, 34, 409. Electronic devices based on molecular machines
have been reported, see: (c) Collier, C. P.; Wong, E. W.; Belohradsky,
M.; Raymo, F. M.; Stoddart, J. F.; Kuekes, P. J.; Williams, R. S.; Heath, J.
R. Science 1999, 285, 391. (d) Collier, C. P.; Mattersteig, G.; Wong, E.
W.; Luo, Y.; Beverly, K.; Sampaio, J.; Raymo, F. M.; Stoddart, J. F.; Heath,
J. R. Science 2000, 289, 1172.
(2) For rotaxanes, see: (a) Bissell, R. A.; Cordova, E.; Kaifer, A. E.;
Stoddart, J. F. Nature 1994, 369, 133. (b) Collin, J.-P.; Gavin˜a, P.; Sauvage,
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K.; Kunitake, M.; Nakashima, N. J. Am. Chem. Soc. 1997, 119, 7605. (d)
Armaroli, N.; Balzani, V.; Collin, J.-P.; Gavin˜a, P.; Sauvage, J.-P.; Ventura,
B. J. Am. Chem. Soc. 1999, 121, 4397. (e) Leigh, D. A.; Troisi, A.; Zerbetto,
F. Angew. Chem., Int. Ed. 2000, 39, 350. (f) Kawaguchi, Y.; Harada, A.
Org. Lett. 2000, 2, 1353. (g) Brouwer, A. M.; Frochot, C.; Gatti, F. G.;
Leigh, D. A.; Mottier, L.; Paolucci, F.; Roffia, S.; Wurpel, G. W. H. Science
10.1021/ol051567t CCC: $30.25
© 2005 American Chemical Society
Published on Web 09/24/2005

and can function in a small space without producing any
byproducts.5,6 Light-driven translational motion has been
achieved in rotaxanes with use of photoinduced electron
transfer (ET),4,5 excited-state changes in hydrogen bonding,5c
and E/Z photoisomerization of azobenzene dumbbells.2c,5c,5d
Recording the changes of 1H NMR, absorption, and circular
dichroism spectroscopies5e are the usual methods used to
monitor the co-conformational changes of rotaxanes. The use
of changes in fluorescence as an output signal is preferable
because it is easy to transform these changes into the easily
detectable output signals and is inexpensive. But reports
based on rotaxanes that can be induced to switch between
different fluorescent states (output) in response to clean inputs
are rare.7
Scheme 1
Here we describe a fluorescence switch in which light-
induced shuttling of the macrocycle along the thread
produces the changes of the interaction between two chro-
mophores in the thread. The molecular shuttle Z1/E1 consists
of a benzylic amide macrocycle mechanically locked onto a
thread, Z2/E2, featuring two potential H bonding stationss
a fumaramide group and a succinic amide ester units
separated by a C12 alkyl spacer, and highly fluorescent
perylene bisimide and pyrene (which were sufficiently bulky
to also act as “stoppers”) attached to the fumaramide group
and a succinic amide ester (Scheme 1). The macrocycle
contains two pyridine units, which are good fluorescence
quenchers of perylene bisimide and pyrene upon protonation.
It is well-known that there exist both photoinduced electron
and energy transfer processes in the pyrene-perylene dyads.8
The relative orientation of the donor and acceptor transition
dipoles, and the distance between the donor and acceptor
molecules have great influence on the energy transfer and
electron-transfer process. 9 So with proper spacers to control
the distance between fluorescence units and H bonding
stations, we can design a molecular machine with a macro-
cycle to control the energy and/or electron transfer between
the perylene and pyrene moieties. This molecular machine
can be a switch, and features the convenient use of optical
input and easy reading of the optical output.
Rotaxane E1 was prepared in 35% yield from thread E2
and converted into Z1 by photoisomerization (Scheme 1).
(5) (a) Ashton, P. R.; Ballardini, R.; Balzani, V.; Credi, A.; Dress, K.
R.; Ishow, E.; Kleverlaan, C. J.; Kocian, O.; Preece, J. A.; Spencer, N.;
Stoddart, J. F.; Venturi, M.; Wenger, S. Chem. Eur. J. 2000, 6, 3558. (b)
Wurpel, G. W. H.; Brouwer, A. M.; van Stokkum, I. H. M.; Farran, A.;
Leigh, D. A. J. Am. Chem. Soc. 2001, 123, 11327. (c) Asakawa, M.; Ashton,
P. R.; Balzani, V.; Brown, C. L.; Credi, A.; Matthews, O. A.; Newton, S.
P.; Raymo, F. M.; Shipway, A. N.; Spencer, N.; Quick, A.; Stoddart, J. F.;
White, A. J. P.; Williams, D. J. Chem. Eur. J. 1999, 5, 860. (d) Stanier, C.
A.; Alderman, S. J.; Claridge, T. D. W.; Anderson, H. L. Angew. Chem.,
Int. Ed. 2002, 41, 1769. (e) Bottari, G.; Leigh, D. A.; Pe´rez, E. M. J. Am.
Chem. Soc. 2003, 125, 13360.
Since the xylylene rings of the macrocycle shielded encap-
sulated regions of the thread, the position of the macrocycle
in CDCl3 could be determined for each pair of rotaxane
diastereomers by comparing the chemical shift of the protons
in the rotaxane with those of the corresponding thread.6 The
1H NMR spectra of E1/Z1 and E2/Z2 in CDCl3 (400 MHz,
298 K) are shown in Figure 1. The Hi and Hj protons of the
fumaramide group were shielded in the rotaxane E1,
compared with the thread E2, by δ 1.08 ppm, whereas the
chemical shifts of the Hb and Hc protons of the succinic
amide ester group were similar in both compounds. In the
(6) Altieri, A.; Bottari, G.; Dehez, F.; Leigh, D. A.; Wong, J. K. Y.;
Zerbetto, F. Angew. Chem., Int. Ed. 2003, 42, 2296.
(7) (a) Leigh, D. A.; Morales, M. AÄ . F.; Pe´rez, E. M.; Wong, J. K. Y.;
Saiz, C. G.; Slawin, A. M. Z.; Carmichael, A. J.; Haddleton, D. M.; Brouwer,
A. M.; Buma, W. J.; Wurpel, G. W. H.; Leo´n, S.; Zerbetto, F. Angew.
Chem., Int. Ed. 2005, 44, 3062. (b) Wang, Q.-C.; Qu, D.-H.; Ren, J.; Chen,
K.-C.; Tian, H. Angew. Chem., Int. Ed. 2004, 43, 2661. (c) Pe´rez, E. M.;
Dryden, D. T. F.; Leigh, D. A.; Teobaldi, G.; Zerbetto F. J. Am. Chem.
Soc. 2004, 126, 12210.
(8) Kaletas¸, B. K.; Dobrawa, R.; Sautter, A.; Wu¨rthner, F.; Zimine, M.;
De Cola, L.; Williams, R. M. J. Phys. Chem. A 2004, 108, 1900.
(9) Fo¨rster, T. Ann. Phys. 1948, 55.
4836
Org. Lett., Vol. 7, No. 22, 2005

Figure 1. 1H NMR spectra of (a) thread E2, (b) [2]rotaxane E1,
(c) thread Z2, and (d) [2]rotaxane Z1. The assignments correspond
to the lettering shown in Scheme 1.
maleamide isomer, the situation was completely reversed.
The Z olefin protons (Hi′ and Hj′) resonated at almost
identical chemical shifts in the rotaxane and thread, whereas
the succinic amide ester methylene groups (Hb and Hc) were
each shielded by >1.5 ppm in the rotaxane.
The absorption spectra of E2, Z2, E1, and Z1 showed
superposition features of the pyrene and perylene moieties,
only Z1 showed red-shifted pyrene absorption. The absorp-
tion patterns allow the virtually selective excitation of pyrene
and perylene moieties in these compounds (Figure S1).
As shown in Figure 2a, upon excitation of pyrene moiety
in E2 and Z2, both compounds had strongly quenched pyrene
emission (λmax ) 377 nm) and enhanced perylene emission
(λmax ) 556 nm) compared with pyrene and perylene
reference, which indicate the present of a photoinduced
energy transfer process.8 In the case of excitation of E2 and
Z2 at 500 nm, where only the perylene moiety absorbs,
energy transfer could not be observed; however, the emission
intensity of the perylene unit of E2 and Z2 was quenched
(∼30%) as compared with the reference compound Pery-
ref. It is well-known that pyrene and perylene are good donor
and acceptor groups, respectively; therefore it is not surpris-
ing that an electron transfer occurs from the excited
perylene.9 All these indicated the presence of both photo-
induced electron and energy transfer processes in these
pyrene-perylene dyads as reported by the Wu¨rthner group.8
The fluorescence intensity of perylene in Z2 was quenched
stronger than that in E2, which may be due to the shorter
distance between pyrene and perylene bisimide in Z2 because
Figure 2. (a) Fluorescence emission spectra (λexc ) 345 nm, 2 ×
10-6 M, 298 K) of E1/E2, Z1/Z2, py-ref, and pery-ref in CHCl3.
Inset: λexc at 500 nm. All spectra are corrected according to
absorptions at 345 or 500 nm, and below 475 nm a multiplying
factor of 5 is used. (b) Fluorescence emission spectra changes
(λexc ) 345 nm) of E1 upon the addition of CF3COOH (TFA).
Inset: λexc at 500 nm. (c) Fluorescence emission spectra changes
(λexc ) 345 nm) of Z1 upon the addition of CF3COOH (TFA).
Inset: λexc at 500 nm.
Org. Lett., Vol. 7, No. 22, 2005
4837

of the easier intramolecular folding. For rotaxane E1 and
Z1, the macrocycle prevented the intramolecular folding of
the thread, so the photoinduced electron transfer was slowed
and the emission of the perylene moiety was enhanced
compared with that of the thread E2 and Z2 (Figure 2a and
Figure 4a).
Figure 3. Changes in fluorescence intensity at 556 nm (excited at
345 nm) for CH2Cl2 solution of pronated E1 on alternating
irradiation at 254 and 365 nm for four complete cycles.
Figure 4. Schematic presentation describing the intertranslation
of different states: (a) the macrocycle influence of the intramo-
lecular folding and (b) the protonated macrocycle acting as a
switcher for the energy transfer from pyrene to perylene moiety.
In the rotaxane Z1, the protonation of the pyridines in the
macrocycle by CF3COOH (TFA) resulted in the quenching
of the emission of pyrene through electron transfer (Figure
2c).10 The energy transfer from pyrene to perylene moiety
was then switched off, and the fluorescence of the perylene
moiety became weaker. In the case of E1, the photoinduced
electron transfer from the perylene moiety to pyridinium was
less efficient, which may due to the larger distance between
the perylene moiety and the fumaramide group, and the
fluorescence of perylene and pyrene moieties could not be
quenched by pyridinium, that is, TFA had no effect on the
emission spectra of E1 as shown in Figure 2b.
There existed different photostationary states of E1/Z1 at
different wavelengths (relative percentage of E1/Z1 was not
tested),5e,7c and evident fluorescent change could be achived
by irradiating with light of different wavelengths. Because
of the reversibility of the photoisomerization process, the
photoinduced shuttling motion of the macrocycle could be
repeated with reversible fluorescent output signals (Figure
3). Thus, the photinduced shuttling motion could be easily
detected by means of a fluorescent output signal at 556 nm.
This molecular shuttle worked remarkably well.
weakened the electron transfer from the pyrene to the
perylene moiety, and the protonated macrocycle could act
as a switcher for the energy transfer from the pyrene to the
perylene moiety, which resulted in changes of fluorescence
of the perylene moiety.
In conclusion, we have synthesized a novel pyrene,
perylene bisimide containing [2]rotaxane in which the
macrocycle can be shuttled between co-conformations that
position it close to either pyrene or perylene bisimide. The
protonated macrocycle can act as a switcher for the energy
transfer from the pyrene to the perylene moiety, which elicits
a fluorescence response.
Acknowledgment. This work was supported by the Major
State Basic Research development Program and the National
Natural Science Foundation of China (20131040, 50372070,
20418001, 20473102, and 20421101).
Supporting Information Available: Full experimental
details pertaining to the preparation of E1/Z1. This material
is available free of charge via the Internet at http://pubs.acs.org.
Thus this molecular shuttle could be made a fluorescence
switch as depicted in Figure 4. The macrocycle in the thread
(10) Palit, D. K.; Sapre, A. V.; Mittal, J. P. Chem. Phys. Lett. 1997,
269, 286.
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