A molecular shuttle for driving a multilevel fluorescence switch

Article abstract of DOI:10.1002/chem.200701105

A [2]rotaxane-based molecular shuttle comprised a macrocycle mechanically interlocked to a chemical dumbbell has been prepared in high yields by a thermodynamically controlled, template-induced clipping procedure. This molecular shuttle has two different recognition sites, namely, NH ₂⁺- and amide, separated by a phenyl unit. The macrocycle exhibits high selectivity for the -NH₂⁺- recognition sites in the protonated form through noncovalent interactions, which include 1)N ⁺-H-O hydrogen bonds; 2) C-H...O interactions between the CH ₂NH₂⁺CH₂ protons on the thread and the oligo(ethylene glycol) unit in the macrocycle; 3) π...π stacking interaction between macrocycle and aromatic unit. Upon deprotonation of the [2]rotaxane the macrocy-cle glides to the amide recognition site due to the hydrogen bonds between the -CONH- group and the oligo(ethylene glycol) unit in the macrocycle. The deprotonation process requires about 10 equivalents of base (iPr₂NEt) in polar acetone, while the amount of base is only 1.2 equivalents in apolar tetrachloroethane. Upon addition of Li⁺. the conformation of the [2]rotaxane was altered as a result of the collective interactions of 1) hydrogen bonds between pyridine nitrogen and amide hydrogen atoms; 2) coordination between the oligo(ethylene glycol) unit, amide oxygen atom and Li ⁺ cation. Then, when Zn²⁺ ions are added, the macrocycle returns to the deprotonated -NH- recognition site owing to coordination of the macrocycle and -NH- from the axle with the Zn²⁺ ion. All the above-mentioned movement processes are reversible through the alternate addition of TFA/ iPr₂NEt, Li/[12]-crown-4 and Zn ²⁺/ethylenediaminetetraacetate (EDTA), by virtue of hydrogen bonding and metalion complexation. Significantly, the three independent movement processes are all accompanied by fluorescent responses: 1) complete repression in the protonated form ; 2) low-level expression in the deprotonated form: 3) medium-level expression following addition of Li⁺; 4) high-level expression on complexation with Zn²⁺.

Full text of DOI:10.1002/chem.200701105

DOI: 10.1002/chem.200701105
A Molecular Shuttle for Driving a Multilevel Fluorescence Switch
Weidong Zhou, Junbo Li, Xiaorong He, Cuihong Li, Jing Lv, Yuliang Li,* Shu Wang,
Huibiao Liu, and Daoben Zhu[a]
Abstract: A [2]rotaxane-based molecu-
lar shuttle comprised a macrocycle me-
chanically interlocked to a chemical
“dumbbell” has been prepared in high
yields by a thermodynamically control-
led, template-induced clipping proce-
dure. This molecular shuttle has two
cle glides to the amide recognition site
due to the hydrogen bonds between the
cation. Then, when Zn2+ ions are
added, the macrocycle returns to the
À
À
À
À
CONH group and the oligo(ethy-
lene glycol) unit in the macrocycle. The
deprotonation process requires about
10 equivalents of base (iPr2NEt) in
polar acetone, while the amount of
base is only 1.2 equivalents in apolar
tetrachloroethane. Upon addition of
Li+, the conformation of the [2]ro-
taxane was altered as a result of the
collective interactions of 1) hydrogen
bonds between pyridine nitrogen and
amide hydrogen atoms; 2) coordination
between the oligo(ethylene glycol)
unit, amide oxygen atom and Li+
deprotonated NH recognition site
owing to coordination of the macrocy-
À
À
cle and NH from the axle with the
Zn2+ ion. All the above-mentioned
movement processes are reversible
through the alternate addition of TFA/
iPr2NEt, Li/[12]-crown-4 and Zn2+/eth-
ylenediaminetetraacetate (EDTA), by
virtue of hydrogen bonding and metal-
ion complexation. Significantly, the
three independent movement processes
are all accompanied by fluorescent re-
sponses: 1) complete repression in the
protonated form; 2) low-level expres-
sion in the deprotonated form;
3) medium-level expression following
addition of Li+; 4) high-level expres-
À
different recognition sites, namely,
+
À
NH2
and amide, separated by a
phenyl unit. The macrocycle exhibits
+
À
À
high selectivity for the NH2
nition sites in the protonated form
recog-
through
noncovalent
interactions,
which include 1) N+ H···O hydrogen
À
À
bonds; 2) C H···O interactions be-
tween the CH2NH2+CH2 protons on
the thread and the oligo(ethylene
glycol) unit in the macrocycle; 3) p···p
stacking interaction between macrocy-
cle and aromatic unit. Upon deproto-
nation of the [2]rotaxane the macrocy-
Keywords: fluorescence · molecular
devices · rotaxanes · supramolecular
chemistry · template synthesis
sion on complexation with Zn2+
.
Introduction
employed in the construction of classical mechanically inter-
locked molecules: electron donor–acceptor interaction be-
tween a tetracationic cyclophane and dioxynaphthalene or
Mechanically interlocked molecules such as catenanes and
rotaxanes have received a great deal of attention due to
their multiple controllable and reversible alternations of
conformation through induced relative movement of their
non-covalently interacting components on application of ex-
ternal stimuli.[1] Various noncovalent interactions have been
tetrathiafulvalene,[2] N+ H···O hydrogen bonds and C
H···O interactions in secondary dialkylammonium ions and
recognition by crown ether macrocycles,[3] metal cation–
ligand coordination in pyridine–copper architectures[4] and
amide–amide hydrogen bonds in short peptides and iso-
phthalamide macrocycles.[5] With the development of supra-
molecular chemistry, some weak noncovalent interactions
À
À
[a] W. Zhou, J. Li, X. He, C. Li, J. Lv, Prof. Y. Li, Prof. S. Wang,
Dr. H. Liu, Prof. D. Zhu
have also been found to have the ability to stabilize the opti-
[6]
À
mized conformation, such as C H···p interactions and
CAS Key Laboratory of Organic Solid
Center for Molecular Sciences, Institute of Chemistry
Chinese Academy of Sciences
electron-transfer processes.[7] Thus, construction of multista-
ble molecular shuttles became possible by combination of
the above interactions. The alternation of relative positions
of the above-mentioned interlocked components constitutes
a basic kind of mechanical switch, capable of varying physi-
cal properties such as conductivity,[8] circular dichroism[9]
Beijing, 100080 (China)
Fax : (+86)10-8261-6576
E-mail: ylli@iccas.ac.cn
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author.
754
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 754 – 763

FULL PAPER
and fluorescence.[10] Some of these molecular mechanical
switches have been designed specifically to perform particu-
lar functions, such as molecular muscles,[11] molecular eleva-
tors[12] and even molecular walkers.[13] However, most cur-
rent artificial systems controlled by molecular shuttles are
operated only as on/off switches and not in an adjustable
multilevel mode. The availability of robust artificial switches
which exhibit a single signal at desired levels in response to
fixed doses of different inducers rather than minute concen-
tration changes of a single inducer would be more desirable
in the field of biotechnology.[14] With this in mind, we de-
signed and constructed a multistable system to study the
properties and operational mechanisms of this kind of artifi-
cial shuttles as a prelude to optimizing their performance
(Figure 1).
lents of Li+ ions, the conformation of the [2]rotaxane is al-
tered by a combination of Li–oligo(ethylene glycol) interac-
tion[15] and weak hydrogen bonds between amide and pyri-
dine groups. When 1.1 equivalents of Zn2+ ions are added,
the pyridine/aniline moiety in the macrocycle and the amine
in the thread complex with Zn2+, and the macrocycle re-
turns to the amine site. It is well known that photoinduced
electron transfer takes place from the aniline and amine
groups to the anthracene unit,[16] which can be influenced by
the alternation of distance between them, protonation/de-
protonation and metal ion complexation/decomplexation of
aniline and amine groups.[5e,17] Thus, in this system, protona-
tion/deprotonation and metal-ion complexation/decomplex-
ation of aniline and amine, which can induce movement of
the macrocycle, will all affect the fluorescent emission of the
anthracene unit. By means of the above three movement
processes, this shuttle enables multilevel expression of fluo-
rescence in response to different triggers: 1) complete re-
pression in the absence of any stimulus; 2) slight expression
in response to base; 3) low-level expression following ad-
dition of Li+; 4) high-level expression in the presence of
Zn2+
.
Results and Discussion
Synthesis: Two threads 1-H and P-H were synthesized for
the construction of the [2]rotaxane and the multistable me-
chanical switch. According to the literature,[18] [2]rotaxanes
can be prepared in high yields by a thermodynamically con-
trolled, template-induced clipping procedure (Scheme 1), by
mixing together of three components: a pyridine dialdehyde,
À
a diamine and a dumbbell thread compound containing a
Figure 1. Graphical representation of the movement processes in the mul-
tistable molecular shuttle.
+
À
CH2NH2 CH2 center. The target [2]rotaxane 2-H was ob-
tained in 75% yield after purification by chromatography
on silica when 1-H was used as template. A similar experi-
ment using P-H as template gave independent P-H and
macrocycle after purification by chromatography on silica,
that is, the pyrene unit is not large enough to function as a
bulky stopper for this macrocycle. The single-crystal struc-
ture of the macrocycle (Figure 2a) shows that the largest in-
tramacrocycle distance is 9.222 Š, between O1 and O5, in
the solid state.[18c] Though the conformation in the solid
state is different from that in solution, this conformation
possibly exists among the various states of free rotation in
solution. In the pyrene unit, the largest distance, between
H1 and H5, is 6.861 Š, slightly smaller than the cavity of the
macrocycle (Figure 2b). Thus, the pyrene unit is small
enough for the thread to leave the macrocycle. In Stoddartꢁs
model, a 3,5-dimethoxybenzyl group acts as a bulky stopper
for the macrocycle.[18] As shown in Figure 2c, the largest dis-
tance, between H1 and H2, is 7.905 Š in the solid state,
which is smaller than the cavity of the macrocycle, too. In
addition, the methoxyl group can rotate freely around the
Here we describe a multilevel fluorescence switch in
which acid/base- and metal-ion complexation/decomplexa-
tion-induced shuttling of the macrocycle along the thread
drives changes in the interaction between the macrocycle
and the fluorescent chromophore in the thread. The molecu-
lar shuttle consists of a thread bearing an anthracene group
as a fluorescent probe and an aniline-containing oligo(ethy-
lene glycol) macrocycle mechanically interlocked on the
thread. The thread has two potential H-bonding stations: a
+
À
À
secondary dialkylammonium ( NH2
) center and an
amide center, separated by a phenylene group. Under low-
pH conditions, the macrocycle is assembled around an am-
monium cation center through a combination of strong N+
À
À
H···O hydrogen bonds and weak C H···O interactions be-
tween macrocycle and thread. Addition of 1.2 equivalents of
iPr2NEt as base to the [2]rotaxane in apolar solution causes
deprotonation of the ammonium recognition site. As a
result, the hydrogen bonds between dialkylammonium and
oligo(ethylene glycol) groups are switched off, and the mac-
rocycle moves to the amide recognition site due to the hy-
drogen bond between them. Upon addition of 1.2 equiva-
À
C O single bond, and this might reduce the distance be-
tween H1 and H2 to that between H1 and H5 in the pyrene
unit. In their model,[18] the steric hindrance from the C H
À
Chem. Eur. J. 2008, 14, 754 – 763
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
755

Y. Li et al.
downfield shift due to a combi-
+
À
À
nation of C H···O and N
H···O hydrogen bonds. The sig-
nals of Hp, Hs and Hv on the
macrocycle exhibited clear up-
field shifts in 2-H, which can be
attributed to the shielding
effect of phenylene ring A. This
confirms
effect between phenylene ring
and the pyridine aniline
a mutual shielding
A
moiety in the macrocycle. Thus,
the 1H NMR spectra support
formation of rotaxane 2-H and
selective binding of the macro-
+
À
À
cycle with the NH2
center.
Clear evidence for the forma-
tion of the [2]rotaxane was also
obtained from electrochemical
experiments in acetonitrile so-
lution (Figure 5). The macrocy-
cle exhibited two successive ir-
reversible one-electron reduc-
tion waves around 0.97 and
1.28 V relative to a silver-wire
electrode. When the macrocycle
locked around the axle, the two
oxidation potentials become
less positive by about 170 and
50 mV, respectively, which can
Scheme 1. i) 2-Chloroacetyl chloride, Et3N/CHCl3, 08C, 85%; ii) 4-hydroxy-
benzaldehyde, K2CO3, acetone, KI, reflux, 8 h, 80%; iii) EtOH, molecular
sieves (4 Š), reflux, 8 h; iv) NaBH4, EtOH, 258C, 8 h, 75%; v) CF3CO2H,
acetone, then NH4PF6, water; vi) 2,6-pyridinedicarboxaldehyde, tetraethy-
lene glycol bis(2-aminophenyl)ether, MeNO2, 10 min, then BH3·THF, room
temperature, 4 h, 70%.
bonds in methyl groups may restrain the macrocycle on the
thread.
The HRMS (N-SIMS NBA) of 2-H (Figure 3) revealed a
high intensity signal at m/z 1168.5566 corresponding to [2-
H]+, that is, loss of PF6 ions from the salt. The 1H NMR
spectra of 1-H and 2-H in CDCl2CDCl2/CD3COCD3 (10/1)
are shown in Figure 4. As expected for complexation, the
1H NMR signals for the four protons Hf and Hg adjacent to
+
NH2 experienced a significant downfield shift of 0.5 ppm
with respect to those in free 1-H.[16a,18] The signals corre-
sponding to phenylene protons Hi and Hj exhibited substan-
tial downfield shift due to the shielding effect of the macro-
cycle (see Scheme 2). In this way, the macrocycle was proba-
bly, to some extent, sandwiching the phenylene A spacer so
as to benefit from supplementary stabilization by means of
weak p–p stacking interactions. The signals of the oligo-
(ethylene glycol) moiety of the macrocycle experienced
Figure 2. a) Solid-state structure of the macrocycle (CCDC-263073–
CCDC-263075 from The Cambridge Crystallographic Data Centre).[18c]
b) and c) Models of pyrene and 3,5-dimethoxybenzyl groups (The MM2
force field was used to calculate the minimum-energy conformation).
756
www.chemeurj.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 754 – 763

A Multilevel Fluorescence Switch
FULL PAPER
Figure 5. Cyclic voltammetric (CV) curves for 1-H, macrocycle, and 2-H.
CV experiments were performed at room temperature in dried acetoni-
trile solutions containing 0.04m TBAPF6 as supporting electrolyte. A
three-electrode configuration consisting of a glassy carbon working elec-
trode, a Pt counterelectrode and an Ag wire quasi-reference electrode
was used.
Figure 3. HRMS (N-SIMS NBA) of 2-H.
characteristic of aromatic shielding from the encapsulating
macrocycle. At the same time, the signals assigned to He ex-
perienced an upfield shift from d=8.54 to 8.49 ppm, due to
reduced withdrawal of electrons on deprotonation of the di-
alkylammonium center. The signal for Ha shifted downfield
by 0.13 ppm in the rotaxane as a result of the loss of aromat-
ic shielding from the encapsulating macrocycle. All these
features indicate that the macrocycle migrates from the di-
alkylammonium center to the amide center upon addition of
iPr2NEt in acetone.
The fraction of 2 is about 61% when 2 equivalents of
iPr2NEt are added, and increases to 86 and about 91% on
addition of 6 and 10 equivalents of iPr2NEt, respectively.
This indicates that the complexation constant between the
dialkylammonium group and iPr2NEt is not very large under
these conditions, which might be due to the high polarity of
acetone. When CDCl2CDCl2/CD3COCD3 (10/1) was used as
Figure 4. Partial 1H NMR spectra (600 MHz, 298 K, 10À3 m, CDCl2CDCl2/
CD3COCD3 10/1) of 1-H (a), 2-H (b) and macrocycle (c).
solvent in
a neutralization experiment, approximately
1.2 equivalents of iPr2NEt were needed to neutralize the di-
alkylammonium center completely. These results showthat
the complexation constant is smaller in more polar sol-
vents.[3]
be ascribed to the electronic interaction between the macro-
cycle and the dialkylammonium center.[3] The reduction po-
tential of the anthracene axle did not exhibit any clear dif-
ference during formation of the [2]rotaxane.
The 1H NMR spectra of 2-H, 2 and 1 in CDCl2CDCl2/
CD3COCD3 (10/1) are shown in Figure 7. Upon addition of
1.2 equivalents of iPr2NEt to 2-H, the dialkylammonium
group was neutralized and the hydrogen bonds between
macrocycle and ammonium group were switched off. The
signals for Hf and Hh shifted upfield by 0.92 and 0.24 ppm,
respectively, which indicates deprotonation of the dialkylam-
Movement processes: Switching of the ring between differ-
ent recognition sites can be monitored by 1H NMR,
NOESY, UV/Vis and fluorescence spectroscopy.
NMR spectroscopy: The 1H NMR titration of 2-H with
iPr2NEt in CD3COCD3 is outlined in Figure 6. Upon addi-
tion of iPr2NEt, two single peaks for the four protons Hf
monium center and breaking of the C H···O hydrogen
À
bonds. Two characteristics reflect the site of the macrocycle
on the thread: 1) the characteristic resonances for the meth-
ylene protons Hk adjacent to the amide group experienced a
significant upfield shift of 0.71 ppm compared with free
thread 1, which should be due to the shielding effect of the
macrocycle; 2) substantial downfield shift by 0.51 ppm was
observed for the signal of Hl from the amide compared with
+
and Hg adjacent to NH2 shift upfield from d=5.53 and
5.23 to 4.87 and 4.62 ppm, respectively, which indicates de-
protonation of the dialkylammonium group and breaking of
À
C H···O hydrogen bonds. The upfield shift of the methylene
resonance (d(Hk)=0.62 ppm) near the amide station in 2 is
Chem. Eur. J. 2008, 14, 754 – 763
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
757

Y. Li et al.
Figure 6. Partial 1H NMR spectra (400 MHz, 298 K, 10À3 m, CD3COCD3)
of 2-H (a), 2-H+2 equiv iPr2NEt (b), 2-H+6 equiv iPr2NEt (c), 2-H+
10 equiv iPr2NEt (d), and 2 (e).
Figure 7. Partial 1H NMR spectra (600 MHz, 298 K, 10À3 m, CDCl2CDCl2/
CD3COCD3 10/1) of 2-H (a), 2 (b), and 1 (c). Partial NOESY spectrum
of 2 (bottom).
that in free thread 1, which can be ascribed to the hydrogen
bond between macrocycle and amide.[19] Both features sup-
port that the macrocycle moves to the amide recognition
site due to the hydrogen bonds between them.[19]
Hv of aniline (Figure 7), which indicate that they are adja-
cent to each other in space. The above two features support
formation of a stable conformation in which the macrocycle
encircles the amide site, while the pyridine aniline moiety
shields phenylene unit A, and the oligo(ethylene glycol) sec-
tion encircles the hydrogen atom of the amide group (shown
for 2 in Scheme 2).
The signals for Hq/q’ and Hw/w’ separated into two different
sets of signals as a consequence of losing their planes of
symmetry orthogonal to the principal axis in the molecular
shuttle.[3] The signals for phenylene ring A protons Hi and
Hj in 2 shifted downfield by 0.16 and 0.73 ppm compared to
those in 2-H, but still less than d=7.0 ppm. This suggests
that the shielding effect of the macrocycle was reduced due
to the movement of the macrocycle, but still existed to some
extent. Meanwhile, the NOESY spectrum exhibited cross-
peaks between the signals for Hj of phenylene ring A and
When 1.2 equivalents of Li+ were added to a solution of 2
at room temperature, dramatic changes in the 1H NMR
spectrum were observed (Figure 8). The single peak corre-
sponding to the methylene protons Hk shifted downfield by
1.5 ppm compared with that in 2, and by 0.75 ppm compared
with that in the free thread. The signals for the oligo(ethy-
lene glycol) unit shifted downfield, too. These phenomena
758
www.chemeurj.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 754 – 763

A Multilevel Fluorescence Switch
FULL PAPER
over, a NOESY experiment showed cross-peaks between
the signals for Hj of phenylene ring A and those for Hy of
the oligo(ethylene glycol) unit (Figure 8), which indicate
that phenylene ring A and oligo(ethylene glycol) unit are
close to each other in space. This steric interaction could
À
lead to weak C H···p interaction between them, which
would induce significant splitting of the signals for Hi and Hj
in p-phenylene unit A.[6] As shown in Figure 8b, the two
“doublets” for Hi and Hj shifted by À0.5 and 0.08 ppm, re-
spectively, compared with those in 2, and the splitting in-
creased from 0.28 to 0.86 ppm. This enlarged splitting of the
signals for Hi and Hj in p-phenylene unit A verifies the exis-
À
tence of the C H···p interaction. All these changes in chem-
ical shift suggested that the macrocycle still encircled the
amide site. However, the oligo(ethylene glycol) section is
closer to phenylene unit A, and the pyridine/aniline moiety
encircles the amide hydrogen atom in this state. These fea-
tures required alternation of conformation of the [2]ro-
taxane to some extent (see 2-Li in Scheme 2).
When 1.1 equivalents of Zn2+ ions were added to 2-Li,
À
À
the four protons Hf and Hh adjacent to NH experienced
significant downfield shifts of 0.82 and 0.23 ppm compared
with those of 2-Li. As shown in Figure 9b, the signals corre-
sponding to pyridine and aniline all exhibited clear down-
field shifts compared with the free macrocycle,[18] which can
be attributed to coordination between the pyridine/aniline
moiety and Zn2+. The remarkable downfield shift of four
À
À
protons Hf and Hh adjacent to NH also indicated coordi-
nation between dialkylamine ( NH ) and Zn2+. Thus, the
1H NMR spectra support selective binding of the pyridine/
À
À
À
À
aniline moiety in the macrocycle and NH of the thread
with the Zn2+ ion and formation of rotaxane 2-Zn (see
Scheme 2).
Optical properties: Figure 10 depicts UV/Vis spectra of 1
and 2 under different stimuli. Only the anthracene moiety
absorbs in the spectral region above 300 nm, and hence all
changes in the UV/Vis spectra in this region are due to al-
teration of electronic state of the anthracene unit. The ab-
sorption features of neutral thread 1 are similar to those of
neutral rotaxane 2, that is, there is no obvious interaction
between macrocycle and anthracene unit in the ground state
in this conformation. When Zn2+ or TFA was added to solu-
tions of 1 and 2, three absorption peaks arising from the an-
thracene unit experienced a red shift of 4 nm, which can be
ascribed to restriction of the interaction between lone-pair
electrons of amine and anthracene units in the ground state
due to complexation or protonation.
Figure 8. Partial 1H NMR spectra (600 MHz, 298 K, 10À3 m, CDCl2CDCl2/
CD3COCD3, v/v, 10/1) of 2 (a), 2-Li (b), and 1 (c). Partial NOESY spec-
trum of 2-Li (bottom).
can be attributed to coordinative interaction between the
oligo(ethylene glycol) moiety on the macrocycle, the amide
oxygen atom and the Li+ ion.[15] Upon addition of Li+, the
oligo(ethylene glycol) moiety of the macrocycle and the
amide oxygen atom encircle the Li+ ion and coordinate to
it, which leads to clear downfield shifts of Hk and the pro-
tons of the oligo(ethylene glycol) moiety. In addition, the
signals for pyridine protons Ho and Hp shifted downfield by
0.85 and 0.42 ppm, respectively. This could be attributed to
the strengthened hydrogen bonds between pyridine nitrogen
and amide hydrogen atoms as a result of the conformational
change of the macrocycle on coordination to Li+.[15a] More-
Clear evidence for multilevel switching with different
inputs was obtained from fluorescence experiments in
CH2Cl2/THF (10/1). As shown in Figure 11a, 1-H exhibited
strong emission at 423 nm, while the neutral form 1 exhibit-
ed weak emission around 413 nm. This quenching effect can
be attributed to photoinduced electron transfer (PET) from
[16,17]
À
À
amine ( NH ) to anthracene.
The anthracene fluores-
cence of 2-H was quenched completely, due to strong PET
from the aniline unit of the macrocycle to anthracene. Upon
Chem. Eur. J. 2008, 14, 754 – 763
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
759

Y. Li et al.
Scheme 2. Movement processes of the multistable molecular shuttle under different stimuli. i) iPr2NEt; ii) CF3CO2H; iii) LiClO4; iv) [12]crown-4; v) Zn-
(ClO4)2; vi) EDTA.
Figure 9. Partial 1H NMR spectra (600 MHz, 298 K, 10À3 m, CDCl2CDCl2/
CD3COCD3, 10/1) of macrocycle (a), 2-Zn (b), and 1 (c).
addition of 1.2 equivalents of iPr2NEt to 2-H, the emission
of the anthracene moiety increased slightly but was still less
than that of 1, which indicated the PET from aniline to an-
thracene moiety was restricted to some extent due to the
elongated distance. The similar fluorescence intensity of 2-
Li to that of neutral 1 implies that PET from aniline to an-
thracene was completely quenched in this state. This might
be due to further elongation of the spatial distance between
them or blockage of PET by the presence of Li+. Upon ad-
dition of Zn2+ ions to 2, the fluorescence intensity was re-
Figure 10. Absorption spectra of 1-H, 1, 1-Zn, 2-H, 2, 2-Li, and 2-Zn in
CH2Cl2/THF (10/1, 1”10À5 m) at room temperature.
760
www.chemeurj.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 754 – 763

A Multilevel Fluorescence Switch
FULL PAPER
2-H, the macrocycle moved from the dialkylammonium
+
À
À
( NH2 ) center to the amide station, and thus the distance
between aniline and anthracene moieties was enlarged. In 2,
PET from secondary dialkylamine to anthracene was recov-
ered and the PET from aniline to anthracene was decreased.
Therefore, the fluorescent emission of 2 was less than that
of free thread 1, in which only PET from secondary dialkyl-
amine to anthracene occurs. In this conformation, the pyri-
dine/aniline moiety was more adjacent to the phenylene unit
A of the thread, and the oligo(ethylene glycol) moiety was
centered around the amide hydrogen atom in space. Upon
addition of Li+ ions, the conformation of this [2]rotaxane
was altered, and the pyridine/aniline moiety turned towards
the amide hydrogen atom, which further increased the dis-
tance between aniline and anthracene moieties and de-
creased the PET process between them (Scheme 2). The
PET from secondary dialkylamine to anthracene was not af-
fected in this process. In the fluorescence spectra, the fluo-
rescence intensity of 2-Li is similar to that of neutral thread
1, that is, PET from aniline on the macrocycle to anthracene
was quenched completely. Similar to previous reports, the
electron lone pair of the amino group next to the anthra-
cene unit can not quench the emission completely.[16d] Thus,
emission quenching of anthracene by the macrocycle may
be of greater importance than that by the dialkylamine, be-
cause PET from aniline to anthracene unit may be stronger.
When Zn2+ ions are added, the pyridine/aniline moiety of
the macrocycle and the dialkylamine group in the thread co-
ordinate to the Zn center, which would completely eliminate
PET from aniline and dialkylamine to anthracene and re-
cover the emission entirely.[16,17] In the fluorescence spectra,
2-Zn exhibited intensive fluorescent emission similar to that
of 1-H, which indicated that no PET process was present.
Thus, the fluorescence behavior supports the model pro-
posed from the analysis of the 1H NMR spectra. These
movement processes can be repeated many times without
degradation by alternate addition of TFA/iPr2NEt, Li/
[12]crown-4 and Zn2+/EDTA, which are all perceived
through changes in fluorescence (Figure 11b and c).
Figure 11. a) Fluorescence spectra of 1-H, 1, 2-H, 2, 2-Li, and 2-Zn in
CH2Cl2/THF (10/1, 1”10À5 m) at room temperature (lex =370 nm). The
inset shows the magnified fluorescence spectra of 1, 2, 2-Li, and 2-H.
Fluorescence-intensity changes at 414 nm (b) and 422 nm (c) after alter-
nating additions of Li (half integers)/[12]crown-4 (integers) and Zn (half
integers)/EDTA (integers) to 2 and 2-Li over six complete cycles, respec-
tively (lex =370 nm).
covered and became as large as that of 1-H+, and this sug-
gests complete abolishment of PET from amine and aniline
to anthracene. In particular, when 1.2 equivalents of Zn2+
were introduced into a solution of 2-Li, the fluorescence in-
tensity also recovered and became equal to that of 1-H+.
This might due to the much stronger complexation ability
between the pyridine/aniline moiety and Zn2+ relative to
that between oligo(ethylene glycol) unit and Li+. By means
of the above three movement processes, this shuttle enables
multilevel expression of fluorescence in response to differ-
ent triggers: 1) complete repression in the absence of any
stimulus; 2) slight expression in response to base; 3) low-
level expression following addition of Li+; 4) high-level ex-
Conclusion
We have presented a multistable molecular shuttle with
three successive independent movement processes driven by
acid/base and metal-ion complexation/decomplexation,
which are all accompanied by fluorescent responses. By
means of the three movement processes, this shuttle enables
multilevel expression of fluorescence in one system in re-
sponse to different triggers. In addition, this artificial multi-
level molecular shuttle provides a model for interconnection
of different noncovalent interactions, namely, hydrogen
bonding and metal-ion complexation, to achieve multistable
controllable systems with regular responses.
pression in the presence of Zn2+
.
The observations in fluorescence experiments were in ac-
1
cordance with the H NMR spectra. Upon deprotonation of
Chem. Eur. J. 2008, 14, 754 – 763
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
761

Y. Li et al.
TOF): m/z 688 [1-H·PF6ÀPF6]; elemental analysis (%) calcd: C 70.50, H
Experimental Section
4.95, N 3.36; found: C 70.47, H 4.99, N 3.34.
P-H·PF6 was synthesized from 2-(4-formylphenoxy)-N-(4-tritylphenyl)-
acetamide and pyrenyl-1-methanamine by using a similar procedure as
described for the preparation of 1-H·PF6. 1H NMR (CD3COCD3,
400 MHz, 298 K): d 8.17 (d, 1H, J=8.0 Hz), 8.14–7.95 (m, 9H), 7.44 (d,
2H, J=8.51 Hz), 7.23–7.11 (m, 19H), 6.82 (d, 2H, J=8.51 Hz), 5.3 (s,
2H), 4.5 (s, 2H), 4.47 ppm (s, 2H); 13C NMR ([D6]DMSO, 100 MHz,
298 K): d=166.5, 156.1, 146.4, 141.6, 136.08, 132.9, 130.75, 130.42, 130.33,
129.9, 129.47, 128.57, 127.46, 127.27, 126.97, 125.9, 125.7, 124.8, 124.47,
124.13, 124.05, 118.9, 114.47, 67.33, 64.06, 50.89 ppm; MS (MALDI-
TOF): m/z 711 [1-H·PF6ÀPF6].
Rotaxane 2-H·PF6: A solution of 2,6-pyridinedicarboxaldehyde (29 mg,
0.2 mmol), tetraethylene glycol bis(2-aminophenyl)ether (80 mg,
0.2 mmol) and 1-H·PF6 (166 mg, 0.2 mmol) in CH3NO2 (10 mL) was
stirred at room temperature for 10 min. BH3·THF (1.0 m in THF, 1 mL,
1 mmol) was added to the mixture, which was left stirring at room tem-
perature for 4 h. The solvent was then evaporated off and the residue
was partitioned between 2m aqueous NaOH and CHCl3. The organic ex-
tracts were dried and the solvent evaporated again. The residue was dis-
solved in Me2CO, and a fewdrops of TFA were added to the solution.
The solvent was evaporated off, the residual oil was dissolved in a mix-
ture of H2O and Me2CO and a saturated aqueous solution of NH4PF6
was added. The Me2CO was then removed and the aqueous solution was
extracted with CH2Cl2 several times. The organic extracts were dried
(MgSO4) and concentrated to dryness to yield [2]rotaxane 2-H·PF6
(181 mg, 70%) as a white powder. 1H NMR (CD3COCD3, 400 MHz,
298 K): d=9.26 (s, 1H), 9.0 (br, 2H), 8.55 (s, 1H), 8.21 (d, 2H, J=
8.72 Hz), 8.04 (d, 2H, J=8.72 Hz), 7.59 (d, 2H, J=8.16 Hz), 7.52 (t, 1H),
7.47 (t, 2H), 7.37 (t, 2H), 7.29–7.13 (m, 19H), 7.07 (t, 4H, J=8.76 Hz),
6.62–6.60 (br, 6H), 6.48 (d, 2H), 6.27 (d, 2H), 5.53 (s, 2H), 5.23 (s, 2H),
4.56 (s, 2H), 4.51 (s, 2H), 4.02 (m, 2H), 3.95 (m, 8H), 3.78 (m, 6H), 3.68
(d, 2H, J=14.8 Hz), 3.32 ppm (d, 2H, J=12.6 Hz); HRMS (N-SIMS
NBA): m/z 1168.5566, [2-H·PF6ÀPF6]; MS (MALDI-TOF): m/z 1168 [2-
H·PF6ÀPF6]; elemental analysis (%) calcd: C 69.45, H 5.67, N 5.33;
found C 69.43, H 5.71, N 5.31.
Unless stated otherwise, all reagents and anhydrous solvents were pur-
chased and used without further purification. Column chromatography:
SiO2 (200–300 mesh). TLC glass plates coated with SiO2 F254 were vi-
sualized by UV light. 1H and 13C NMR spectra were recorded on a
Bruker AV 400 or 600 MHz instrument at a constant temperature of
258C. Chemical shifts are reported in parts per million from lowto high
field and referenced to TMS. MALDI-TOF mass spectra were recorded
on a Bruker Biflex III MALDI-TOF spectrometer. UV/Vis spectra were
measured on a Hitachi U-3010 spectrometer. Fluorescence excitation and
emission spectra were recorded using a Hitachi F-4500 FL fluorimeter at
a constant temperature of 258C; the slit was set at 5 nm when measuring
in different solvents.
2-Chloro-N-(4-tritylphenyl)acetamide: 2-Chloroacetyl chloride (0.67 g,
6 mmol) was added to a solution of 4-tritylbenzenamine (2 g, 5.9 mmol)
and Et3N (1 mL) in CHCl3 at 08C. Then the mixture was stirred at room
temperature for 8 h and washed with distilled water (3”50 mL). The col-
lected organic layers were dried over NaSO4, and the chloroform was re-
moved in vacuo to give the product 2-chloro-N-(4-tritylphenyl)acetamide
(2.05 g, 85%) after purification by flash chromatography (CH2Cl2).
1H NMR (CDCl3, 400 MHz): d=8.17 (s, 1H), 7.42 (d, 2H, J=9 Hz),
7.27–7.15 (m, 17H), 4.17 ppm (s, 2H); 13C NMR (CDCl3, 100 MHz): d=
163.8, 146.6, 143.9, 134.5, 131.9, 131.1 127.6, 126.0, 119.2, 64.7, 42.9 ppm;
EI-MS: m/z 411; elemental analysis (%) calcd for C27H22ClNO: C 78.73,
H 5.38, N 3.40; found: C 78.68, H 5.41, N 3.41.
2-(4-Formylphenoxy)-N-(4-tritylphenyl)acetamide: 2-Chloro-N-(4-trityl-
phenyl)acetamide (2 g, 4.8 mmol) and 4-hydroxybenzaldehyde (610 mg,
5 mmol) were dissolved in acetone, and then anhydrous potassium car-
bonate (1.38 g, 10 mmol) and [18]crown-6 (132 mg, 0.5 mmol) were
added. The reaction mixture was refluxed gently for about 8 h and then
cooled to room temperature. After acetone was removed under reduced
pressure, the residue was dissolved in CHCl3 and the solution washed
with water, dried over Na2SO4, filtered and concentrated in vacuo. The
crude product was purified by chromatography on SiO2 with CH2Cl2/n-
hexane (1/1) to give pure 2-(4-formylphenoxy)-N-(4-tritylphenyl)acet-
amide (1.92 g, 80% yield) as slightly yellowpowder. 1H NMR (CDCl3,
400 MHz): d=9.93 (s, 1H), 8.11 (s, 1H), 7.90 (d, 2H, J=7.97 Hz), 7.45
(d, 2H, J=8.00 Hz), 7.26–7.10 (m, 17H), 7.11 (d, 2H, J=8.06 Hz),
4.69 ppm (s, 2H); 13C NMR (CDCl3, 100 MHz) d=198.2, 163.5, 147.2,
146.1, 143.5, 134.5, 131.9, 131.1 127.6, 126.5, 126.0, 119.2, 64.4, 42.1 ppm;
EI-MS: m/z 497; elemental analysis (%) calcd for C34H27NO3: C 82.07, H
5.47, N 2.81; found: C 82.04, H 5.51, N 2.87.
Acknowledgements
This work was supported by the National Natural Science Foundation of
China (20531060, 20571078) and the Major State Basic Research Devel-
opment Program (2007CB936, 2006CB932100).
1-H·PF6:
2-(4-Formylphenoxy)-N-(4-tritylphenyl)acetamide
(1.0 g,
2.0 mmol) was added to a degassed solution of 9-aminomethylanthracene
(414 mg, 2.0 mmol) in anhydrous EtOH/CHCl3(80 mL, 3/1). Then molec-
ular sieves were added, and the resulting mixture was heated at 808C for
8 h. After cooling to room temperature, the molecular sieves were fil-
tered off and washed with CHCl3. Then NaBH4 (1 g, 27 mmol) was
added to the filtrate at 08C, which was stirred for 8 h after warming to
room temperature. Water (10 mL) was added carefully to quench the
excess NaBH4. The solvent was then evaporated off, and the residue was
partitioned between water and CHCl3. The organic extracts were dried
and the solvent was removed in vacuo. Then the residue was dissolved in
Me2CO and a fewdrops of TFA were added to the solution. The solvent
was evaporated off, the oily residue was dissolved in a mixture of H2O
and Me2CO and a saturated aqueous solution of NH4PF6 was added. The
Me2CO was then removed and the aqueous solution was extracted with
CH2Cl2 several times. The organic extracts were dried (MgSO4) and the
solvent concentrated to dryness to yield axle 1-H·PF6 (1.1 g, 70%) as a
light yellowpowder. 1H NMR (CD3COCD3, 400 MHz, 298 K): d=9.35 (s,
1H), 8.8 (s, 2H), 8.30 (d, 2H, J=8.78 Hz), 8.19 (d, 2H, J=8.78 Hz), 7.74
(d, 2H, J=8.25 Hz), 7.70–7.56 (m, 6H), 7.280 (m, 6H), 7.21–7.15 (m,
15H), 5.69 (s, 2H), 4.98 (s, 2H), 4.75 ppm (s, 2H); 13C NMR
(CD3COCD3, 100 MHz, 298 K): d=166.3, 159.1, 146.9, 142.6, 136.2,
132.4, 131.4, 131.3, 131.0, 130.9, 130.7, 129.5, 127.6, 126.1, 125.6, 123.9,
123.3, 121.7, 119.0, 115.4, 67.4, 64.5, 54.1, 52.0, 43.2 ppm; MS (MALDI-
[1] a) V. Balzani, A. Credi, F. M. Raymo, J. F. Stoddart, Angew. Chem.
2000, 112, 3484–3530; Angew. Chem. Int. Ed. 2000, 39, 3348–3391;
b) Acc. Chem. Res. 2001 34(6), 409–522, special issue (Ed.: J. F.
Stoddart); c) V. Balzani, A. Credi, M. Venturi, Molecular Devices
andMachines: A Journey into the Nano World , Wiley-VCH, Wein-
heim, 2003; d) E. R. Kay, D. A. Leigh, F. Zerbetto, Angew. Chem.
2007, 119, 72–196; Angew. Chem. Int. Ed. 2007, 46, 72–191; e) Adv.
Funct. Mater. 2007, 17(5) 671–840 special issue (Eds.: A. Credi, H.
Tian).
[2] a) P. L. Anelli, N. Spencer, J. F. Stoddart, J. Am. Chem. Soc. 1991,
113, 5131–5133; b) R. A. Bissell, E. Cordova, A. E. Kaifer, J. F.
Stoddart, Nature 1994, 369, 131–137; c) H.-R. Tseng, S. A. Vignon,
J. F. Stoddart, Angew. Chem. 2003, 115, 1529–1533; Angew. Chem.
Int. Ed. 2003, 42, 1491–1495; d) M. Asakawa, P. R. Ashton, V. Bal-
zani, A. Credi, C. Hamers, G. Mattersteig, M. Montalti, A. N. Ship-
way, N. Spencer, J. F. Stoddart, M. S. Tolley, M. Venturi, A. J. P.
White, D. J. Williams, Angew. Chem. 1998, 110, 357–361; Angew.
Chem. Int. Ed. 1998, 37, 333–337; e) H.-R. Tseng, D. M. Wu,
N. X. L. Fang, X. Zhang, J. F. Stoddart, ChemPhysChem 2004, 5,
111–116; f) C. P. Collier, J. O. Jeppesen, Y. Luo, J. Perkins, E. W.
Wong, J. R. Heath, J. F. Stoddart, J. Am. Chem. Soc. 2001, 123,
12632–12641; g) Y. Luo, C. P. Collier, J. O. Jeppesen, K. A. Nielsen,
E. Delonno, G. Ho, J. Perkins, H.-R. Tseng, T. Yamamoto, J. F. Stod-
762
www.chemeurj.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 754 – 763

A Multilevel Fluorescence Switch
FULL PAPER
dart, J. R. Heath, ChemPhysChem 2002, 3, 519–525; h) A. H. Flood,
A. J. Peters, S. A. Vignon, D. W. Steuerman, H.-R. Tseng, S. Kang,
J. R. Heath, J. F. Stoddart, Chem. Eur. J. 2004, 10, 6558–6564; i) Y.
Liu, A. H. Flood, P. A. Bonvallet, S. A. Vignon, B. H. Northrop, H.-
R. Tseng, J. O. Jeppesen, T. J. Huang, B. Brough, M. Baller, S. Ma-
gonov, S. D. Solares, W. A. Goddard, C.-M. Ho, J. F. Stoddart, J.
Am. Chem. Soc. 2005, 127, 9745–9759; j) T. D. Nguyen, H.-R.
Tseng, P. C. Celestre, A. H. Flood, Y. Liu, J. F. Stoddart, J. I. Zink,
Proc. Natl. Acad. Sci. USA 2005, 102, 10029–10034; k) P. R. Ashton,
V. Baldoni, V. Balzani, A. Credi, H. D. A. Hoffmann, M.-V. Martí-
nez-Díaz, F. M. Raymo, J. F. Stoddart, M. Venturi, Chem. Eur. J.
2001, 7, 3482–3493.
2004, 6, 4507–4509; c) N. Kihara, Y. Tachibana, H. Kawasaki, T.
Takata, Chem. Lett. 2000, 506–509.
[7] a) A. Mateo-Alonso, C. Ehli, G. M. Aminur Rahman, D. M. Guldi,
G. Fioravanti, M. Marcaccio, F. Paolucci, M. Prato, Angew. Chem.
2007, 119, 3591–3595; Angew. Chem. Int. Ed. 2007, 46, 3521–3525;
b) A. Mateo-Alonso, G. Fioravanti, M. Marcaccio, F. Paolucci, D. C.
Jagesar, A. M. Brouwer, M. Prato, Org. Lett. 2006, 8, 5173–5176;
c) A. Mateo-Alonso, G. Fioravanti, M. Marcaccio, F. Paolucci, G. M.
Aminur Rahman, C. Ehli, D. M. Guldi, M, Prato, Chem. Commun.
2007, 1945–1947.
[8] A. H. Flood, J. F. Stoddart, D. W. Steuerman, J. R. Heath, Science
2004, 306, 2055–2056.
[3] a) M.-V. Martínez-Díaz, N. Spencer, J. F. Stoddart, Angew. Chem.
1997, 109, 1991–1994; Angew. Chem. Int. Ed. Engl. 1997, 36, 1904–
1907; b) P. R. Ashton, R. Ballardini, V. Balzani, I. Baxter , A. Credi,
M. C. T. Fyfe, M. T. Gandolfi, M. Gómez-López, M.-V. Martínez-
Díaz, A. Piersanti, N. Spencer, J. F. Stoddart, M. Venturi, A. J. P.
White, D. J. Williams, J. Am. Chem. Soc. 1998, 120, 11932–11942;
c) J. D. Badjic, V. Balzani, A. Credi, S. Silvi, J. F. Stoddart, Science
2004, 303, 1845–1849; d) J. D. Badjic, C. M. Ronconi, J. F. Stoddart,
V. Balzani, S. Silvi, A. Credi, J. Am. Chem. Soc. 2006, 128, 1489–
1499; e) J. D. Badjic, V. Balzani, A. Credi, J. N. Lowe, S. Silvi, J. F.
Stoddart, Chem. Eur. J. 2004, 10, 1926–1935.
[4] a) N. Armaroli, V. Balzani, J.-P. Collin, P. GaviÇa, J.-P. Sauvage, B.
Ventura, J. Am. Chem. Soc. 1999, 121, 4397- 4408; b) T. Iijima, S. A.
Vignon, H.-R. Tseng, T. Jarrosson, J. K. M. Sanders, F. Marchioni,
M. Venturi, E. Apostoli, V. Balzani, J. F. Stoddart, Chem. Eur. J.
2004, 10, 6375–6392; c) U. Letinois-Halbes, D. Hanss, J. M. Beierle,
J.-P. Collin, J.-P. Sauvage, Org. Lett. 2005, 7, 5753–5756; d) C. O.
Dietrich-Buchecker, J.-P. Sauvage, J.-M. Kern, J. Am. Chem. Soc.
1984, 106, 3043–3045; e) M. Cesario, C. O. Dietrich-Buchecker, J.
Guilhem, C. Pascard, J.-P. Sauvage, J. Chem. Soc. Chem. Commun.
1985, 244–247; f) M. Cesario, C. O. Dietrich, A. Edel, J. Guilhem,
J. P. Kintzinger, C. Pascard, J.-P. Sauvage, J. Am. Chem. Soc. 1986,
108, 6250–6254; g) A.-M. Albrecht-Gary, C. Dietrich-Buchecker, Z.
Saad, J.-P. Sauvage, J. Am. Chem. Soc. 1988, 110, 1467–1472; h) C.
Dietrich-Buchecker, J.-P. Sauvage, J.-M. Kern, J. Am. Chem. Soc.
1989, 111, 7791–7800; i) B. Mohr, J.-P. Sauvage, R. H. Grubbs, M.
Weck, Angew. Chem. 1997, 109, 1365–1367; Angew. Chem. Int. Ed.
Engl. 1997, 36, 1308–1310; j) A. Livoreil, C. O. Dietrich-Buchecker,
J.-P. Sauvage, J. Am. Chem. Soc. 1994, 116, 9399–9400; k) F. Bau-
mann, A. Livoreil, W. Kaim, J.-P. Sauvage, Chem. Commun. 1997,
35–36; l) A. Livoreil, J.-P. Sauvage, N. Armaroli, V. Balzani, L. Fla-
migni, B. Ventura, J. Am. Chem. Soc. 1997, 119, 12114–12124;
m) D. J. Cardenas, A. Livoreil, J.-P. Sauvage, J. Am. Chem. Soc.
1996, 118, 11980–11981.
[5] a) A. S. Lane, D. A. Leigh, A. Murphy, J. Am. Chem. Soc. 1997, 119,
11092–11093; b) W. Clegg, C. Gimenez-Saiz, D. A. Leigh, A.
Murphy, A. M. Z. Slawin, S. J. Teat, J. Am. Chem. Soc. 1999, 121,
4124–4129; c) M. Asakawa, G. Brancato, M. Fanti, D. A. Leigh, T.
Shimizu, A. M. Z. Slawin, J. K. Y. Wong, F. Zerbetto, S. Zhang, J.
Am. Chem. Soc. 2002, 124, 2939–2950; d) A. Altieri, G . Bottari, F.
Dehez, D. A. Leigh, J. K. Y. Wong, F. Zerbetto, Angew. Chem. 2003,
115, 2398–2402; Angew. Chem. Int. Ed. 2003, 42, 2296–2300;
Angew. Chem. Int. Ed. 2003, 42, 2296–2300; e) G. W. H. Wurpel,
A. M. Brouwer, I. H. M. van Stokkum, A. Farran, D. A. Leigh, J.
Am. Chem. Soc. 2001, 123, 11327–11328; f) G. Bottari, F. Dehez,
D. A. Leigh, P. J. Nash, E. M. Perez, J. K. Y. Wong, F. Zerbetto,
Angew. Chem. 2003, 115, 6066–6069; Angew. Chem. Int. Ed. 2003,
42, 5886–5889; g) M. N. Chatterjee, E. R. Kay, D. A. Leigh, J. Am.
Chem. Soc. 2006, 128, 4058–4073; h) D. A. Leigh, J. K. Y. Wong, F.
Dehez, F. Zerbetto, Nature 2003, 424, 174–179; i) J. V. Hernandez,
E. R. Kay, D. A. Leigh, Science 2004, 306, 1532–1537; j) E. M.
Perez, D. T. F. Dryden, D. A. Leigh. G . Teobaldi, F. Zerbetto, J.
Am. Chem. Soc. 2004, 126, 12210–12211.
[9] G. Bottari, D. A. Leigh, E. M. Perez, J. Am. Chem. Soc. 2003, 125,
13360–13361.
[10] a) E. M. Perez, D. T. F. Dryden, D. A. Leigh, G. Teobaldi, F. Zerbet-
to, J. Am. Chem. Soc. 2004, 126, 12210–12211; b) Q.-C. Wang, D.-H.
Qu, J. Ren, K. Chen, H. Tian, Angew. Chem. 2004, 116, 2715–2719;
Angew. Chem. Int. Ed. 2004, 43, 2661–2665; c) D.-H. Qu, Q.-C.
Wang, J. Ren, H. Tian, Org. Lett. 2004, 6, 2085–2088.
[11] a) M. C. Jimꢂnez, C. Dietrich-Buchecker, J.-P. Sauvage Angew.
Chem. 2000, 112, 3422–3425; Angew. Chem. Int. Ed. 2000, 39, 3284–
3287; b) M. C. Jimꢂnez-Molero, C. Dietrich-Buchecker, J.-P. Sauvage
Chem. Commun. 2003, 1613–1616; c) M. C. Jimꢂnez-Molero, C.
Dietrich-Buchecker, J.-P. Sauvage, Chem. Eur. J. 2002, 8, 1456–1466.
[12] J. D. Badjic, C. M. Ronconi, J. F. Stoddart, V. Balzani, S. Silvi, A.
Credi, J. Am. Chem. Soc. 2006, 128, 1489–1499.
[13] a) W. B. Sherman, N. C. Seeman, Nano Lett. 2004, 4, 1203–1207;
b) J.-S. Shin, N. A. Pierce, J. Am. Chem. Soc. 2004, 126, 10834–
10835.
[14] B. P. Kramer, W. Weber, M. Fussenegger, Biotechnol. Bioeng. 2003
83(7), 810–820.
[15] a) G. Kaiser, T. Jarrosson, S. Otto, Y.-F. Ng, A. D. Bond, Angew.
Chem. 2004, 116, 1993–1996; Angew. Chem. Int. Ed. 2004, 43, 1959–
1962; b) P. H. Kwan, T. M. Swager, J. Am. Chem. Soc. 2005, 127,
5902–5909; c) S. A. Vignon, T. Jarrosson, T. Iijima, H.-R. Tseng,
J. K. M. Sanders, J. F. Stoddart, J. Am. Chem. Soc. 2004, 126, 9884–
9885.
[16] a) P. R. Ashton, R. Ballardini, V. Balzani, I. Baxter, A. Credi,
M. C. T. Fyfe, M. T. Gandolfi, M. Gomez-Lopez, M.-V. Martínez-
Díaz, A. Piersanti, N. Spencer, J. F. Stoddart, M. Venturi, A. J. P.
White, D. J. Williams, J. Am. Chem. Soc. 1998, 120, 11932–11942;
b) A. P. de Silva, H. Q. N. Gunaratne, C. P. McCoy, J. Am. Chem.
Soc. 1997, 119, 7891–7892; c) A. P. de Silva, I. M. Dixon, H. Q. N.
Gunaratne, T. Gunnlaugsson, P. R. S. Maxwell, T. E. Rice, J. Am.
Chem. Soc. 1999, 121, 1393–1394; d) D. C. Magri, G. J. Brown, G. D.
McClean, A. P. de Silva, J. Am. Chem. Soc. 2006, 128, 4950–4951.
[17] a) Y. Li, H. Li, Y. Li, H. Liu, S. Wang, X. He, N. Wang, D. Zhu,
Org. Lett. 2005, 7, 4835–4838; b) A. P. de Silva, H. Q. N. Gunaratne,
T. Gunnlaugsson, A. J. M. Huxley, C. P. McCoy, J. T. Rademacher,
T. E. Rice, Chem. Rev. 1997, 97, 1515–1566; c) D. A. Leigh, M. A. F.
Morales, E. M. Perez, J. K. Y. Wong, C. G. Saiz, A. M. Z. Slawin,
A. J. Carmichael, D. M. Haddleton, A. M. Brouwer, W. J. Buma,
G. W. H. Wurpel, S. Leon, F. Zerbetto, Angew. Chem. 2005, 117,
3122–3127; Angew. Chem. Int. Ed. 2005, 44, 3062–3067.
[18] a) P. T. Glink, A. I. Oliva, J. F. Stoddart, A. J. P. White, D. J. Wil-
liams, Angew. Chem. 2001, 113, 1922–1927; Angew. Chem. Int. Ed.
2001, 40, 1870–1875; b) M. Horn, J. Ihringer, P. T. Glink, J. F. Stod-
dart, Chem. Eur. J. 2003, 9, 4046–4054; c) F. Aricó, T. Chang, S. J.
Cantrill, S. I. Khan, J. F. Stoddart, Chem. Eur. J. 2005, 11, 4655–
44666.
[19] D. A. Leigh, A. R. Thomson, Org. Lett. 2006, 8, 5377–5379.
Received: July 18, 2007
Revised: September 18, 2007
Published online: October 24, 2007
[6] a) N. Kihara, M. Hashimoto, T. Takata, Org. Lett. 2004, 6, 1693–
1696; b) Y. Tachibana, N. Kihara, Y. Furusho, T. Takata, Org. Lett.
Chem. Eur. J. 2008, 14, 754 – 763
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
763