A [3]rotaxane with three stable states that responds to multiple-inputs and displays dual fluorescence addresses

Article abstract of DOI:10.1002/chem.200401313

A [3]rotaxane molecular shuttle containing two α-cyclodextrin (α-CD) macrocycles, an azobenzene unit, a stilbene unit, and two different fluorescent naphthalimide units has been investigated. The azobenzene unit and the stilbene unit can be E/Z-photoisome

Full text of DOI:10.1002/chem.200401313

FULL PAPER
DOI: 10.1002/chem.200401313
A [3]Rotaxane with Three Stable StatesThat Respondsto Multiple-Inputs
and Displays Dual Fluorescence Addresses
Da-Hui Qu, Qiao-Chun Wang, Xiang Ma, and He Tian*[a]
Abstract:
A
[3]rotaxane molecular
and Z2 isomers back to the E isomer
by irradiation at 450 nm and 280 nm,
respectively, is accompanied by recov-
ery of the absorption and fluorescence
taxane change in a regular way. When
the a-CD macrocycle stays close to the
fluorescent moiety, the fluorescence of
the moiety become stronger due to the
rigidity of the a-CD ring. As the pho-
toisomerization processes are fully re-
versible, the photo-induced shuttling
motions of the a-CD rings can be re-
peated, accompanied by dual reversible
fluorescence signal outputs. The poten-
tial application of such light-induced
mechanical motions at the molecular
level could provide some insight into
the workings of a molecular machine
with entirely optical signals, and could
provide a cheap, convenient interface
for communication between micro- and
macroworlds.
shuttle containing two a-cyclodextrin
(a-CD) macrocycles, an azobenzene
unit, a stilbene unit, and two different
fluorescent naphthalimide units has
been investigated. The azobenzene unit
and the stilbene unit can be E/Z-photo-
isomerized separately by light excited
at different wavelengths. Irradiation at
380 nm resulted in the photoisomeriza-
tion of the azobenzene unit, leading to
the formation of one stable state of the
[3]rotaxane (Z1-NNAS-2CD); irradia-
tion at 313 nm resulted in the photoiso-
merization of the stilbene unit, leading
to the formation of another stable state
of the [3]rotaxane (Z2-NNAS-2CD).
The reversible conversion of the Z1
spectra of the [3]rotaxane. The
E
isomer and the two Z isomers have
been characterized by 1H NMR spec-
troscopy and by two-dimensional NMR
spectroscopy. The light stimuli can
induce shuttling motions of the two a-
CD macrocycles on the molecular
thread; concomitantly, the absorption
and fluorescence spectra of the [3]ro-
Keywords: cyclodextrins · fluores-
cence · molecular shuttle · photoiso-
merization · rotaxanes
Introduction
doubtedly, photons provide an excellent energy input, be-
cause excitation with light can lead to a fast response and
can work in a small space without producing any by-prod-
ucts.[8–10] To realize their full potential, rotaxanes should
have two basic properties. First, the binary states, “0” and
“1”, must be reversibly interconvertible. Second, the output
signals of the rotaxanes should be easily recognizable. Previ-
ously, the binary states of most molecular machines have
been distinguished by NMR spectra,[14,15] cyclic voltamme-
try,[16] differences in the complexation ability of certain ions
of the two states,[17] and circular dichromism. It is rather in-
convenient to transform these spectral signals into easily de-
tected output codes. Use of a change in fluorescence[18,19] as
an output is an attractive approach because the fluorescent
signal readily allows remote reading and is typically low-
cost. However, reports on rotaxanes that switch between dif-
ferent fluorescent states (output) in response to light inputs
are still rare.[18,19]
Interlocked supramolecules[1,2] such as pseudorotaxanes, ro-
taxanes, and catenanes have attracted a great deal of atten-
tion in recent years because of their challenging construc-
tion and potential applications in areas such as molecular
logic gates,[3] molecular switches,[4] molecular wires,[5] and in-
formation storage.[6] There is a rapidly growing need to
design and construct rotaxanes that can be switched reversi-
bly between two different states using different stimuli.
There are many external stimuli that can be used to make
the molecular machines work: for example, a change in
pH,[7] light,[8–10] electrochemistry,[11,12] or entropy.[13] Un-
[a] D.-H. Qu, Dr. Q.-C. Wang, X. Ma, Prof. Dr. H. Tian
Laboratory for Advanced Materials and Institute of Fine Chemicals
East China University of Science and Technology
Shanghai 200237 (P.R. China)
Fax : (+86)21-642-52288
It is well known that cyclodextrins (CDs) form host–guest
complexes. Many cyclodextrin-based catenanes, rotaxanes,
and polyrotaxanes have been synthesized.[2,5,8,12,15,18,20–22] Pre-
E-mail: tianhe@ecust.edu.cn
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the authors.
Chem. Eur. J. 2005, 11, 5929 – 5937
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
5929

viously we have prepared two light-driven molecular shut-
tles comprising a stilbene unit and an azobenzene unit, re-
spectively, and analyzed their photoisomerization phenom-
ena in solution.[18] In this study, we designed and synthesized
a [3]rotaxane NNAS-2CD (Scheme 1) containing two a-CD
macrocycles, an azobenzene unit, a stilbene unit, and two
different fluorescent naphthalimide moieties: 4-amino-1,8-
naphthalimide-3,6-disulfonic disodium salt (the “N” stopper)
and 1,8-naphthalimide-5-sulfonic sodium salt (the “S” stop-
per). The molecular shuttle NNAS-2CD has several key fea-
tures: two different fluorescence moieties are introduced to
act as “stoppers”; an azobenzene unit and a stilbene unit
provide a means of changing the position of the macrocyclic
CDs on the molecular thread by altering the stereostructure
of the recognition site using various photochemical isomeri-
zation reactions. The great change in position of the a-CD
rings can be used to create obvious changes in properties
(for example, in the fluorescence spectra) of the two stop-
pers in a regular way. The [3]rotaxane NNAS-2CD is, in
fact, a novel molecular shuttle with three stable states. Irra-
diation at 380 nm can induce isomerization of the azoben-
zene unit to convert E-NNAS-2CD into Z1-NNAS-2CD,
and irradiation at 313 nm can induce isomerization of the
stilbene unit to convert E-NNAS-2CD into Z2-NNAS-2CD
(Scheme 2). The two Z isomers could also be shifted back to
the E isomer reversibly by photochemical stimuli. Because
of the good regulation and full reversibility of the fluores-
cence changes of the two stopper units in the photoisomeri-
zation, the shuttling of the CD macrocycles in [3]rotaxane
NNAS-2CD could be characterized by the fluorescence
changes. We suggest that such changes in a property (for ex-
ample, fluorescence) of a rotaxane could easily address for
many different types of molecular devices and biological
systems that rely upon the controlled movement of multiple
components to perform specific tasks at a molecular level.
Herein, we describe the synthesis of a novel [3]rotaxane
molecular shuttle NNAS-2CD and its photoisomerization
reactions. The three stable conformations of the rotaxane
were fully characterized by 1H NMR and two-dimensional
1H ROESY NMR spectroscopy. The light-driven shuttling
motions of the a-CD rings on the molecular thread in the
[3]rotaxane and the fluorescence changes of the two stop-
pers have been investigated.
Results and Discussion
Synthesis and characterization:
NNAS-2CD consists of two a-
CD macrocycles locked on to a
thread that has two binding
sites—an azobenzene site, and
a
stilbene site—trapped me-
chanically by two naphthali-
mide moieties with different
fluorescence
properties:
4-
amino-1,8-naphthalimide-3,6-di-
sulfonic disodium salt (the “N”
stopper) and 1,8-naphthalimide-
5-sulfonic sodium salt (the “S”
stopper). It has been reported
that cyclodextrin-based rotax-
anes can be prepared by Pd-
(OAc)2-catalyzed Suzuki cou-
pling in the presence of CD.[5,18]
First, we mixed 1 and a-CD in
a 1:1 molar ratio in water to
produce 1-a-CD, and 2-a-CD
was obtained by the same
method from 2 and a-CD. The
structures of 1-a-CD and 2-a-
CD
were
confirmed
by
1H NMR and two-dimensional
1H ROESY NMR spectrosco-
py.[23] Surprisingly, the CDs in
1-a-CD and 2-a-CD are basi-
cally coincident in direction: in
the dominant configuration the
wide 2,3-rim is close to the
Scheme 1. The synthetic routes to [3]rotaxane NNAS-2CD. The a-cyclodextrin is drawn with a wide 2,3-rim
and a narrow 6-rim; NNAS is the free dumbbell.
5930
www.chemeurj.org
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2005, 11, 5929 – 5937

Rotaxanes
FULL PAPER
protons on the interior of the
a-CD annulus were found
(from Hb, Hc, Hj, Hk, Hh, Hi to
H3, and from Hd, He, Hf, Hg,
Hh, Hi to H5), which indicates
that the two a-CD rings are lo-
cated around the azobenzene
unit and the stilbene unit re-
spectively. At the same time,
the NOEs from He, Hf, Hg to
H6, from Hc, Hj, Hk to OH-2,3,
and from He, Hf to OH-6 also
prove that the chemical struc-
ture of NNAS-2CD was con-
firmed as shown in Figure 1.
Photoisomerization: Let us
consider the E/Z photoisomeri-
zation of the [3]rotaxane
NNAS-2CD. Good photoisome-
rization abilities have been
found in azobenzene- and stil-
bene-based rotaxanes.[8,18] For
comparison with the [3]ro-
taxane NNAS-2CD and the
Scheme 2. The shuttling motions of the a-CD macrocycles under different photochemical stimuli in the [3]ro-
taxane NNAS-2CD.
stopper.[23] Then, as shown in Scheme 1, we treated 1-a-CD
with 2-a-CD in alkaline aqueous a-CD solution, using a Pd-
(OAc)2 catalyst, in a 1-a-CD/2-a-CD/Pd(OAc)2 molar ratio
of 1:1:0.2, at 858C for 24h, and the [3]rotaxane NNAS-2CD
was isolated in 18% yield by chromatography (silica gel;
upper layer = acetic acid/n-butanol/water, 1.5:3:5). In this
Suzuki coupling reaction, a [2]rotaxane was also obtained in
a very low yield (~2%), and the dumbbell was separated in
a low yield (~1%). A large amount of dumbbell NNAS
(yield 29.5%) can be also synthesized by treating 1 and 2
under the same conditions (but without CD) . The chemical
structure of the [3]rotaxane was fully confirmed by
dumbbell NNAS, we irradiated 1 at 313 nm and 2 at 380 nm
for 2 h (in dimethylformamide solution), respectively. There
1
was little change in the H NMR and the absorption spectra
of 1 and 2,[23] indicating that in the [3]rotaxane E-NNAS-
1
MALDI-TOF mass spectrometry, and H NMR and two-di-
mensional ROESY NMR spectroscopy.
The rotaxane obtained is indeed a [3]rotaxane, which can
be confirmed and characterized by 1H NMR spectra: the
ratio of the integral of Ha or Hl in the dumbbell to the inte-
gral of H1 in the cyclodextrins is 1:6, indicating there are
two cyclodextrin rings in the rotaxane. MALDI-TOF mass
spectrometry[23] also supplied strong evidence in support of
a [3]rotaxane. The spectrum is dominated by signals at m/z
3067.7 (100%) and 3045.7 (60%), which correspond to the
[3]rotaxanes [NNAS-2CD+Na]+ and [NNAS-2CD+1]+, re-
spectively.
Two-dimensional NMR spectroscopy has recently become
an essential method for studying the structures of CDs and
their complexes, since one can conclude that two protons
are closely located in space if an NOE cross-peak is detect-
ed between the relevant proton signals in the ROESY or
NOESY spectrum. The two-dimensional ROESY spectrum
of NNAS-2CD in [D6]DMSO is shown in Figure 1. The
NOEs between the aromatic protons and the H3 and H5
Figure 1. The two-dimensional 1H ROESY NMR spectrum of NNAS-
2CD (500 MHz in [D6]DMSO at 298 K; mixing time 300 ms).
Chem. Eur. J. 2005, 11, 5929 – 5937
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5931

H. Tian et al.
2CD photoisomerization of the azobenzene unit could not
be induced by irradiation at 313 nm and photoisomerization
of the stilbene unit could not be induced by irradiation at
380 nm. However, irradiation of E-NNAS-2CD at 380 nm
caused photoisomerization of the azobenzene unit, which
generates Z1-NNAS-2CD (Scheme 2). The photostationary
equilibrium can be shifted back toward the E isomer by irra-
diation with visible light (>450 nm) or heat; irradiation of
E-NNAS-2CD at 313 nm resulted in photoisomerization of
the stilbene unit, which generates Z2-NNAS-2CD
(Scheme 2). Then irradiation of Z2-NNAS-2CD at 280 nm
shifts the system back toward its original E isomer. The E/Z
photoisomerization reactions of [3]rotaxane NNAS-2CD in
1
solution were investigated by monitoring the H NMR spec-
tral changes. Irradiation at 380 nm leads to two new signals
of equal intensity for Hc’ and Hd’ appearing at d = 6.64and
6.80 ppm, respectively; correspondingly, the initial peaks
appear at d = 7.82 and 7.94ppm. This is reasonable, be-
cause the signals from the aromatic protons of the azoben-
zene unit generally shift upfield upon their isomerization
from trans to cis configuration, as a result of the magnetic
shielding effect of the aromatic rings. The change in the res-
onance of the methylene protons (d = 5.25 ppm, Ha,l) was
also profound. Before irradiation at 380 nm, the chemical
shifts of the protons Ha and Hl are equal. Irradiation at
380 nm causes splitting of the proton peak into one doublet
and one singlet, compared with one singlet peak before the
irradiation. A new signal was found at d = 5.37 ppm (Hl’ of
Z1-NNAS-2CD). This is attributed to the deshielding effect
of a-CD due to the shifting of the ring away from the azo-
benzene unit to the biphenyl unit. New sets of NOEs
(Figure 2) were found: from Hd’, He’, Hj’, Hk’ to H3 and H5,
and from the Hi’ to H3, on the interior of the a-CD annulus;
from Hf’, Hg’, Hh’, Hi’ to OH-6, on the narrow rim of a-CD;
as well as from Hc’, Hd’ to OH-2,3, on the wide rim of a-CD.
All these changes in NMR spectra indicate that NNAS-2CD
underwent azobenzene photoisomerization and generated
Z1-NNAS-2CD, in which the CD-1 ring shifts from the azo-
benzene unit to the biphenyl unit and the CD-2 ring moves
close to the “S” stopper (Scheme 2). Integrals of the two Hd’
and Hd signals appear in a 5:3 ratio, which suggests that at
the photostationary state of azobenzene isomerization (PSS-
A), about 63% of the E-NNAS-2CD was transformed to
the Z1-NNAS-2CD isomer.
Irradiation of E-NNAS-2CD at 313 nm generally results
in the signals of aromatic protons of the stilbene unit shift-
ing upfield: Hh’’, Hi’’ appears at d=6.6–6.7 ppm (initially d=
7.2–7.3 ppm), Hj’’ appears at d=6.95 ppm (initially d=
7.38 ppm), Hg’’ appears at d=7.20 ppm (initially d=
7.52 ppm), indicating that the stilbene unit has already un-
dergone its characteristic photoisomerization. The resonance
of the methylene protons is also split; the Ha’’ signal repre-
sents a doublet at d=5.35 ppm. Also, the coupling constant
of the cis-stilbene protons Hh’’ and Hi’’ in Figure 3c (14Hz) is
smaller than that in the trans-stilbene protons Hh and Hi in
Figure 3a (16 Hz). Reasonably, a decrease in this coupling
constant serves as key evidence for the photoisomerization
Figure 2. The two-dimensional 1H ROESY NMR spectrum (500 MHz in
[D6]DMSO at 298 K; mixing time 300 ms) of NNAS-2CD after irradia-
tion at 380 nm for 2 h.
of the stilbene unit. New sets of NOEs (Figure 4) from Hb’’,
Hc’’, Hf’’, Hg’’ to H3, from Hd’’, He’’ to H5 and H6, and from
Hh’ to H3, as well as from Hk’’, Hh’’, Hi’’ to OH-2,3, on the
wide rim of the a-CD, have been found. All these changes
indicate that NNAS-2CD has undergone stilbene photoiso-
merization and has generated Z2-NNAS-2CD under irradia-
tion at 313 nm, as shown in Scheme 2. Integrals of the two
signals of Hh’’ and Hh (or Hi’’ and Hi) appear in a 5:4ratio,
which suggests that at the photostationary state of the stil-
bene isomerization (PSS-S) about 56% of the E-NNAS-
2CD was transformed to the Z2-NNAS-2CD isomer in that
case.
Luminescence properties: The absorption spectra of the
[3]rotaxane and its two Z isomers in solution have also been
investigated. Irradiation at either 380 nm or 313 nm can lead
to a decrease in absorption at around 350 nm and an in-
crease in absorption at around 280 nm, indicating that pho-
toisomerization of the azobenzene or the stilbene unit
occurs.[23,24] UV irradiation (380 nm) of E-NNAS-2CD (1.0”
10À5 m in DMF) for 30 min causes photoisomerization from
the trans to the cis configuration of the azobenzene unit,
generating Z1-NNAS-2CD, which recovers to the trans con-
figuration upon irradiation at 450 nm for 60 min. The
change is characterized by a rise in absorption at around
270 nm (DA = 0.03) and a decrease in absorption at 350 nm
(DA = 0.06) that is characteristic of the photoisomerization
5932
www.chemeurj.org
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2005, 11, 5929 – 5937

Rotaxanes
FULL PAPER
Figure 4. The two-dimensional 1H ROESY NMR spectrum (500 MHz in
[D6]DMSO at 298 K; mixing time 300 ms) of NNAS-2CD after irradia-
tion at 313 nm for 3 h.
Figure 3. 1H NMR spectra (500 MHz in [D6]DMSO at 298 K) of NNAS-
2CD: a) before irradiation; b) after irradiation at 380 nm for 2 h; c) after
irradiation at 313 nm for 3 h. Both reactions have reached photostation-
ary states.
for 30 min results in the isomerization of the azobenzene
unit, a lower intensity ratio (1.6:1) between the E isomer
and the PSS-A (Figure 5) at the fluorescent emission maxi-
mum lmax = 520 nm (due to the “N” stopper), and mean-
while an enhanced intensity ratio (0.6:1) in the fluorescence
at lmax = 395 nm (due to the “S” stopper). These changes
can be reversed by irradiation at 450 nm for 60 min. By
heating the PSS-A solution to 608C for 2 h, then cooling to
of the azobenzene unit (see the Supporting Information). Ir-
radiation of E-NNAS-2CD at 313 nm for 65 min causes pho-
toisomerization from the trans to the cis configuration of the
stilbene unit, generating another isomer, Z2-NNAS-2CD,
which recovers to the trans configuration of stilbene upon ir-
radiation at 280 nm for 2 h. The change is also characterized
by a rise in absorption at around 270 nm (DA = 0.03) and a
decrease in absorption at 350 nm (DA = 0.05). Similarly, ir-
radiation of the dumbbell NNAS at 380 nm for 5 min causes
an increase at around 270 nm (DA = 0.05) and a decrease
in absorption at 350 nm (DA = 0.09), rapidly generating
Z1-NNAS;[23] irradiation of the dumbbell NNAS at 313 nm
for 15 min causes an increase at around 270 nm (DA =
0.045) and a decrease in the absorption at 350 nm (DA =
0.08), generating another isomer of the dumbbell Z2-
NNAS.[23] The spectral changes for the dumbbell NNAS are
more obvious than for the rotaxane NNAS-2CD; this indi-
cates that the dumbbell NNAS undergoes photoisomeriza-
tion more easily by UV irradiation. It is not surprising that
the photoisomerization becomes more difficult in the pres-
ence of the a-CD ring. The maximum absorption of NNAS-
2CD (the “N” stopper) at around 430 nm changes little, be-
cause it is separated from the residues by the methylene
group.
Figure 5. The fluorescence spectra of a NNAS-2CD solution (1.0”10À5
m
in DMF) after irradiation at 380 nm (0–30 min). A 1.6:1 intensity ratio
between the E isomer and the PSS-A is observed at the emission maxi-
mum at lmax = 520 nm (due to the “N” stopper, lex = 438 nm), and a
Obvious changes in the fluorescence spectra have been
found for the [3]rotaxane NNAS-2CD. Irradiation at 380 nm
0.6:1 ratio is observed at lmax = 395 nm (due to the “S” stopper, lex
=
336 nm).
Chem. Eur. J. 2005, 11, 5929 – 5937
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5933

H. Tian et al.
room temperature, E-NNAS-2CD can also be recovered in
the system. Contrarily, irradiation at 313 nm for 65 min
causes isomerization of the stilbene unit; an enhanced ratio
of 0.6:1 for the fluorescent intensity between the E isomer
and the PSS-S at lmax = 520 nm, and meanwhile a de-
creased ratio of 1.5:1 in the fluorescent intensity at the emis-
sion maximum at lmax = 395 nm, are observed (Figure 6).
of the greater rigidity of the two a-CD rings here than the
single one in the [2]rotaxane. Because of the full reversibili-
ty of the photoisomerization processes, the photoinduced
shuttling motions of the two a-CD rings can be repeated,
and can be addressed with the reversible fluorescent output
signals. By alternating irradiations at 380 nm and 450 nm,
and 313 nm and 280 nm, respectively, we verified that the
photochemical processes (isomerization of both the azoben-
zene and the stilbene) are highly reproducible over more
than six cycles. As Figure 7 demonstrates, the [3]rotaxane
NNAS-2CD has excellent recovery properties.
Figure 6. The fluorescence spectra of a NNAS-2CD solution (1.0”10À5
m
in DMF) after irradiation at 313 nm (0–65 min). A 0.6:1 intensity ratio
between the E isomer and the PSS-S is observed at the emission maxi-
mum at lmax = 520 nm (due to the “N” stopper, lex = 438 nm), and a
1.5:1 intensity ratio at at lmax =395 nm (due to the “S” stopper, lex
=
336 nm).
These changes can be reversed by irradiation at 280 nm for
2 h. The probable cause of the fluorescence changes is the
rigidity of the a-CD ring. When the a-CD macrocycle stays
near the fluorescent stopper, the vibration and the rotation
of the bonds in the methylene group between the stopper
and the recognition site are hindered, which clearly increas-
es the fluorescence intensity of the stopper. This is con-
firmed by the finding of the weaker fluorescent intensity of
the dumbbell NNAS,[23] in which the vibration and rotation
are more facile without the macrocycles. Also, irradiation of
the dumbbell at 380 nm and 313 nm does not induce obvious
changes in the fluorescence intensity of the two stoppers in
the dumbbell NNAS.[23] Since irradiation of the dumbbell
NNAS at 380 nm and 313 nm can photoisomerize the azo-
benzene and stilbene units, the fluorescence of the two Z
isomers obtained changes, albeit only to a very small extent,
due to the changes in the configurations and the possibility
of energy-transfer quenching of one stopper by the other.[23]
This phenomenon is also in agreement with our previous re-
ports.[18] In contrast, a fluorescent intensity ratio of 1:2.65
between the PSS-A and the PSS-S at the emission maxi-
mum at lmax = 520 nm (due to the “N” stopper), and mean-
while another fluorescent signal with an intensity ratio of
2.5:1 at the emission maximum at lmax = 395 nm (due to
the “S” stopper), are observed. The fluorescence changes
observed in this [3]rotaxane NNAS-2CD are more obvious
than that in our previously reported [2]rotaxane,[18b] because
Figure 7. Changes in the fluorescence spectra of the “S” stopper (top, lex
= 336 nm, emission at lmax = 395 nm), and the “N” stopper (below, lex
= 438 nm, emission at lmax = 520 nm) of a NNAS-2CD solution (1.0”
10À5 m in DMF) along with changes in irradiation cycle and light sources.
In one cycle, 380 nm and 450 nm irradiation was first used to isomerize
and recover the azobenzene unit, then 313 nm and 280 nm irradiation
was used to isomerize and recover the stilbene unit. The photochemical
processes are highly reproducible over more than six cycles.
The three stable states of [3]rotaxane NNAS-2CD can be
described as the pure E isomer (“0” state), the PSS-A
(“+1” state), and the PSS-S (“À1” state). The starting
system (the “0” state) can be written with light at 380 nm
and 313 nm to give the PSS-A (“+1” state) and the PSS-S
(“À1” state), respectively. The transform between the “0”
state and the “+1” (or “À1”) state is accompanied by dual
fluorescence addresses at lmax = 520 nm and 395 nm. Also,
the “+1” (or “À1”) state can be shifted back reversibly to
the “0” state with light at 450 nm (or 280 nm). Good reversi-
bility could make it act as a molecular device such as a mul-
5934
www.chemeurj.org
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2005, 11, 5929 – 5937

Rotaxanes
FULL PAPER
(300 mL), The precipitate was collected by filtration, washed with water,
dried, and recrystallized from methanol to give 2a (18.1 g, 67%) as a
white solid. M.p. 209–2108C. The product was pure enough to use in sub-
sequent preparations.
tistate molecular switch with entirely optical signals, or as a
molecular storage medium.
4-(2-p-Tolylvinyl)phenylboronic acid (2b): Compound 2a (17.5 g,
54.7 mmol) was lithiated with n-butyllithium (1.6m, 37.0 mL, 59.2 mmol)
in dry THF (180 mL) at À788C for 3 h. Trimethyl boronate (9.5 mL,
83 mmol) was added to the stirred suspension and the resulting mixture
was allowed to warm to room temperature and stirred for another 8 h,
then acidified with 10% hydrochloric acid. After concentration, a great
deal of yellow solid was precipitated, which was collected by filtration,
washed with water, and dried. The resulting solid was stirred in dichloro-
methane (60 mL) for 1 h, filtered, and dried to give 2b (7.1 g, 53%) as a
Conclusion
A novel light-driven [3]rotaxane molecular shuttle, NNAS-
2CD, has been synthesized and characterized, in which the
two a-CD rings can be made to shuttle back and forth on
the molecular thread that contains an azobenzene unit, a bi-
phenyl unit, and a stilbene unit. The three stable states of
this NNAS-2CD (that is, the E isomer and two Z isomers),
are characterized by NMR experiments including two-di-
mensional NMR spectroscopy and dual fluorescence spec-
tra. The shuttling movement of the a-CD rings can be ad-
dressed by the corresponding reversible fluorescence inten-
sity changes of the two fluorescent stoppers. The output in-
dicating the molecular shuttle movement is a fluorescence
signal, which can be read easily because it allows remote
sensing; thus it offers a further advantage over other spec-
tral signals. The input is photochemical energy, which is su-
perior to chemical or electrochemical input in terms of its
cleanness and convenience. The complete reversibility ex-
hibited by this [3]rotaxane should be emphasized; its most
important feature, however, is that it demonstrates a princi-
ple that could be applied to produce molecular devices that
can change any property that can be made to depend on the
spatial separation of submolecular fragments. The use of
stimulus-induced motion to bring individual components to-
gether to perform specific tasks that could produce an effect
(for example, fluorescence changes) arguably makes such
structures true mechanical molecular machines.
1
white solid. M.p. >2508C; H NMR (500 MHz, [D6]DMSO, 258C, TMS):
d = 8.02 (s, 2H), 7.78 (d, J = 7.7 Hz, 2H), 7.54(d, J = 8.0 Hz 2H), 7.50
(d, J = 8.0 Hz, 2H), 7.27 (d, J = 16.6 Hz, 1H), 7.19 (d, J = 7.7 Hz, 2H),
7.18 (d, J = 16.6 Hz, 1H), 2.31 ppm (s, 3H).
4-[2-(4-Bromomethylphenyl)vinyl]phenylboronic acid (2c): A mixture of
2b (5.0 g, 21.0 mmol), N-bromosuccinimide (4.2 g, 23.6 mmol) and benzo-
yl peroxide (0.30 g) in dry benzene (800 mL) was stirred under reflux for
12 h, then filtered hot. The volume of the filtrate was reduced to about
150 mL under vacuum and the precipitate was collected, washed with
ethanol and dried to give 2c (4.6 g, 69%) as an off-white powder. M.p.
210–2128C (decomp). The product was used in subsequent preparations
without purification.
4-{2-[4-(1,3-Dioxo-1H,3H-benzo[de]isoquinoline-5-sulfon-2-ylmethyl)-
phenyl]vinyl}phenylboronic acid sodium salt (2): Sodium methoxide
(3.7 g) in methane (20 mL, 8.2 mmol) was added to the solution of ben-
zo[de]isoquinoline-1,3-dione-5-sulfonic acid sodium salt[18b] (2.5 g,
8.4mmol) in DMF (20 mL). The mixture was stirred at room tempera-
ture for 4h, then 2c (1.3 g, 4.1 mmol) was added and stirring was contin-
ued for 8 h. The resulting solution was poured into water (100 mL), then
acidified with dilute hydrochloric acid. The precipitate was filtered,
washed with acetone, and dried to give 2 (1.6 g, 36%) as a light yellow
solid. M.p. >2508C; 1H NMR (500 MHz, [D6]DMSO, 258C, TMS): d =
8.71 (s, 1H), 8.69 (s, 1H), 8.59 (d, J = 8.2 Hz, 1H), 8.52 (d, J = 7.3 Hz,
1H), 8.0 (s, 2H), 7.90 (dd, J1 = 8.2 Hz, J2 = 7.3 Hz, 1H), 7.77 (d, J =
8.1 Hz, 2H), 7.54(m, 4H), 7.38 (d,
J = 8.3 Hz, 2H), 7.27 (d, J =
16.4Hz, 1H), 7.19 (d, J = 16.4Hz, 1H), 5.28 ppm (s, 2H).
1-a-CD: Compound 1 (0.15 g, 0.2 mmol), a-CD (0.20 g, 0.21 mmol) and
water (20 mL) were mixed and stirred at 608C for 20 h, then the transpar-
ent solution was evaporated in vacuum and the solid was recrystallized
from water/ethanol (1:4) to give red powder (0.3 g, 86%). M.p. >2508C;
1H NMR (500 MHz, D2O, 25 8C, TMS): d = 9.0 (s, 1H), 8.84(s, 1H),
8.80 (s, 1H), 7.85 (d, J = 8.5 Hz, 2H), 7.70 (d, J = 8.4Hz, 2H), 7.65 (d,
J = 8.5 Hz, 2H), 7.52 (d, J = 8.4Hz, 2H), 5.27 (s, 2H), 5.0 (s, 6H),
3.87–3.56 ppm (m, 36H).
Experimental Section
General: H NMR spectra were measured on a Brücker AM500 spec-
trometer. Elemental analysis was performed on a Perkin-Elmer 2400C in-
strument. Mass spectra (MS) were recorded on an MA1212 instrument
using standard conditions (ESI, 70 eV), the MALDI-TOF spectrum on a
4700-Propeotics analyzer, and UV/Vis spectra on a Varian Cary500 spec-
trophotometer (1 cm quartz cell) at 258C. Fluorescent spectra were re-
corded on a Varian Cary Eclipse fluorescence spectrophotometer (1 cm
quartz cell) at 258C. Photoirradiation was carried on a CHF-XM 500 W
high-pressure mercury lamp with suitable filters (313 nm, 280 nm,
380 nm, half-width 30 nm, type FAL; Lambda Physics, Germany) in a
sealed Ar-saturated 1 cm quartz cell. The distance between the lamp and
the sample cell was 20 cm. Compound 1 and benzo[de]isoquinoline-1,3-
dione-5-sulfonic acid sodium salt were prepared as described previous-
ly.[18b]
2-a-CD: A solution of 2 (0.11 g, 0.21 mmol) in DMF (5 mL) was added
dropwise to the a-CD aqueous solution (0.2 g in 50 mL water). The mix-
ture was heated to 708C for 40 h to give a transparent solution. Most of
the solvent was evaporated in vacuum and acetone (50 mL) was added to
precipitate
a
white solid (0.2 g, 65%). M.p. >2508C; 1H NMR
(500 MHz, D2O, 25 8C, TMS): d = 8.61 (s, 2H), 8.41 (d, J = 6.8 Hz, 1H),
8.31 (d, J = 7.8 Hz, 1H), 7.75 (dd, J1 = 7.8 Hz, J2 = 6.8 Hz, 1H), 7.52
(dd, J1 = 7.2 Hz, J2 = 8.7 Hz, 4H), 7.38 (dd, J1 = 8.7 Hz, J2 = 7.2 Hz,
4H), 7.26 (d, J = 16.4Hz, 1H), 7.16 (d, J = 16.4Hz, 1H), 5.25 (s, 2H),
5.0 (s, 6H), 3.89–3.58 ppm (m, 36H).
NNAS: Compounds 1 (0.15 g, 0.2 mmol) and 2 (0.11 g, 0.21 mmol) and
Pd(OAc)2 (10 mg, 0.044 mmol) were dissolved in aqueous Ar-saturated
sodium carbonate solution (30 mL, 0.2m). The mixture was stirred at
858C for 24h, then cooled and acidified with acetic acid. After concen-
tration in vacuo, the resulting dark solid was purified by column chroma-
tography (silica gel; upper layer = acetic acid/n-butanol/water, 1:2:5) to
give pure NNAS (65 mg, 29.5%) as a yellow powder. M.p. >2508C;
1H NMR (500 MHz, [D6]DMSO, 258C, TMS): d = 8.95 (s, 1H), 8.69–
8.66 (m, 3H), 8.63 (s, 1H), 8.57 (d, J = 8.2 Hz, 1H), 8.50 (d, J = 7.0 Hz,
1H), 8.02 (s, 2H), 7.92 (d, J = 8.2 Hz, 2H), 7.88 (dd, J = 7.0 Hz, J =
8.2 Hz, 1H), 7.84(d, J = 7.7 Hz, 2H), 7.68 (d, J = 8.3 Hz, 2H), 7.51 (m,
4-Methyl-4’-iodostilbene (2a):
A solution of p-iodobenzyl bromide
(25.0 g, 84.2 mmol) in trimethyl phosphite (50 mL, 424 mmol) was heated
under reflux for 4h. The excess phosphite was removed in vacuo, the
yellow residue was dissolved in dried DMF (37 mL) and THF (37 mL),
the resulting solution was cooled to 08C, a solution of sodium methoxide
(4.6 g, 85.2 mmol) in methanol (32 mL) was added dropwise, and the mix-
ture was stirred for 1.5 h at room temperature. Another solution of p-
methylbenzaldehyde (10.5 g, 87.5 mmol) in DMF (70 mL) was then
added dropwise and stirring was continued for another 3 h. More sodium
methoxide solution (1.4g, 26 mmol) in methanol (11 mL) was added and
the resulting mixture was stirred for another 18 h, then poured into water
Chem. Eur. J. 2005, 11, 5929 – 5937
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5935

H. Tian et al.
6H), 7.38 (dd, J = 8.6 Hz, 4H), 7.25 (d, J = 16.5 Hz, 1H), 7.14(d, J =
16.5 Hz, 1H), 5.18 ppm (s, 4H); MS (70 eV, ESI): m/z (%): 1099 (65)
[M+], 1122 (100) [M++Na]; elemental analysis: calcd (%) for
C52H32N5Na3O13S3: C 56.78, H 2.93, N 6.37; found: C 56.76, H 2.92, N
6.39.
M. J. OꢁConnell, P. N. Taylor, J. S. Wilson, F. Cacialli, H. L. Ander-
son, Chem. Eur. J. 2003, 9, 6167–6176.
[6] a) I. Willner, V. Pardo-Yissar, E. Katz, K. T. Ranjit, J. Electroanal.
Chem. 2001, 497, 172–177; b) M. Cavallini, F. Biscarni, S. León, F.
Zerbetto, G. Bottari, D. A. Leigh, Science 2003, 299, 531.
[7] a) M. C. Jimenez-Molero, C. Dietrich-Buchecker, J.-P. Sauvage,
Chem. Eur. J. 2002, 8, 1456–1466; b) R. A. Bissel, E. Córdova, A. E.
Kaifer, J. F. Stoddart, Nature 1994, 369, 133–137.
[8] a) H. Murakami, A. Kawabuchi, K. Kotoo, M. Kunitake, N. Naka-
shima, J. Am. Chem. Soc. 1997, 119, 7605–7606; b) C. A. Stanier,
S. J. Alderman, T. D. W. Claridge, H. L. Anderson, Angew. Chem.
2002, 114, 1847–1850; Angew. Chem. Int. Ed. 2002, 41, 1769–1772.
[9] a) A. M. Brouwer, C. Frochot, F. G. Gatti, D. A. Leigh, L. Mottier,
F. Paolucci, S. Roffa, G. W. H. Wurpel, Science 2001, 291, 2124–
2128; b) 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;
c) 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.
[10] a) N. Armaroli, V. Balzani, J. P. Collin, P. GaviÇa, J.-P. Sauvage, B.
Ventura, J. Am. Chem. Soc. 1999, 121, 4397–4408; b) P. R. Ashton,
R. Ballardini, V. Balzani, A. Credi, K. R. Dress, E. Ishow, C. J. Kle-
verlaan, O. Kocian, J. A. Preece, N. Spencer, J. F. Stoddart, M. Ven-
turi, S. Wenger, Chem. Eur. J. 2000, 6, 3558–3574; c) W. Abraham,
L. Grubert, U. W. Grummt, K. Buck, Chem. Eur. J. 2004, 10, 3562–
3568.
NNAS-2CD: Compounds 1-a-CD (0.14g, 0.080 mmol) and 2-a-CD
(0.12 g, 0.078 mmol) and Pd(OAc)2 (3.8 mg, 0.017 mmol) were dissolved
in aqueous Ar-saturated sodium carbonate solution (20 mL, 0.2m). The
mixture was stirred at 858C for 24h, then cooled and acidified with
acetic acid. After concentration in vacuo, the resulting dark solid was pu-
rified by column chromatography (silica gel; upper layer = acetic acid/n-
butanol/water, 1.5:2:5) to give pure NNAS-2CD (43 mg, 18%) as a
yellow powder. M.p. >2508C; 1H NMR (500 MHz, [D6]DMSO, 258C,
TMS): d = 8.95 (s, 1H), 8.69–8.65 (m, 3H), 8.62 (s, 1H), 8.58 (d, J =
8.1 Hz, 1H), 8.50 (d, J = 7.0 Hz, 1H), 8.02 (s, 2H), 7.92 (d, J = 8.1 Hz,
2H), 7.87 (dd, J = 7.0 Hz, J = 8.2 Hz, 1H), 7.83 (d, J = 7.6 Hz, 2H),
7.69 (d, J = 8.4Hz, 2H), 7.51 (m, 6H), 7.38 (dd, J = 8.6 Hz, 4H), 7.25
(d, J = 16.0 Hz, 1H), 7.14(d, J = 16.0 Hz, 1H), 5.52 (d, J = 6.6 Hz,
12H), 5.44 (s, 12H), 5.25 (s, 4H), 4.79 (s, 12H), 4.49 (s, 12H), 3.76–3.54
(m, 48H), 3.4 (m, 12H), 3.25 ppm (m, 12H); MALDI-TOF: m/z (%):
3067.7 (100) [M++Na], 3045.7 (60) [M++1]; elemental analysis: calcd
(%) for C124H152N5Na3O73S3·12H2O: C 45.66, H 5.44, N 2.15; found: C
45.68, H 5.46, N 2.17.
[11] a) J. D. Cꢂrdenas, A. Livoreil, W. Kaim, J.-P. Sauvage, J. Am. Chem.
Soc. 1996, 118, 11980–11981; b) Y. Liu, A. H. Flood, J. F. Stoddart,
J. Am. Chem. Soc. 2004, 126, 9150–9151; c) O. Lukin, A. Godt, F.
Vçgtle, Chem. Eur. J. 2004, 10, 1878–1883; d) O. Lukin, T. Kubota,
Y. Okamoto, A. Kaufmann, F. Vçgtle, Chem. Eur. J. 2004, 10, 2804–
2810; e) E. Katz, L. Sheeney-Haj-Ichia, I. Willner, Angew. Chem.
2004, 116, 3354–3362; Angew. Chem. Int. Ed. 2004, 43, 3292–3300.
[12] a) A. Mirzoian, A. E. Kaifer, Chem. Eur. J. 1997, 3, 1052–1057;
b) A. Mirzoian, A. E. Kaifer, Chem. Commun. 1999, 1603–1604.
[13] G. Bottari, F. Dehez, D. A. Leigh, P. J. Nash, E. M. PØrez, J. K. Y.
Wong, F. Zerbetto, Angew. Chem. 2003, 115, 6066–6069; Angew.
Chem. Int. Ed. 2003, 42, 5886–5889.
[14] R. Breslow, S. D. Dong, Chem. Rev. 1998, 98, 1997–2012.
[15] a) B. Carrozzini, G. L. Cascarano, C. J. Easton, A. J. Edwards, A. D.
Rae, Chem. Eur. J. 2003, 9, 5971–5977; b) H. Onagi, C. J. Blake,
C. J. Easton, S. F. Lincoln, Chem. Eur. J. 2003, 9, 5978–5988.
[16] W. S. Jeon, A. Y. Ziganshina, J. W. Lee, Y. H. Ko, J.-K. Kang, C.
Lee, K. Kim, Angew. Chem. 2003, 115, 4231–4234; Angew. Chem.
Int. Ed. 2003, 42, 4097–4100.
[17] A. Livoreil, C. O. Dietrich-Buchecker, J.-P. Sauvage, J. Am. Chem.
Soc. 1994, 116, 9399–9400.
[18] a) Q.-C. Wang, D.-H. Qu, J. Ren, K.-C. Chen, H. Tian, Angew.
Chem. 2004, 116, 2715–2719; Angew. Chem. Int. Ed. 2004, 43, 2661–
2665; b) D.-H. Qu, Q.-C. Wang, J. Ren, H. Tian, Org. Lett. 2004, 6,
2085–2088.
[19] a) E. M. PØrez, D. T. F. Dryden, D. A. Leigh, G. Teobaldi, F. Zerbet-
to, J. Am. Chem. Soc. 2004, 126, 12210–12211; b) S. I. Jun, J. W.
Lee, S. Sakamoto, K. Yamaguchi, K. Kim, Tetrahedron Lett. 2000,
41, 471–475; c) V. Balzani, A. Credi, F. Marchioni, J. F. Stoddart,
Chem. Commun. 2001, 1860–1861.
Acknowledgements
This work was supported by the NSFC of China (20273020 and
90401026), and the Education Committee and the Scientific Committee
of Shanghai. We thank Prof. Yu Liu (NanKai University, China) for his
relevant advice on the synthesis.
[1] a) J.-M. Lehn, Supramolecular Chemistry: Concepts and Perspectives,
Wiley-VCH, Weinheim, 1995; b) V. Balzani, M. Venturi, A. Credi,
Molecular Devices and Machines, Wiley-VCH, Weinheim, 2003;
c) V. Balzani, A. Credi, F. M. Raymo, J. F. Stoddart, Angew. Chem.
2000, 112, 3484–3530; Angew. Chem. Int. Ed. 2000, 39, 3348–3391;
d) J.-P. Collin, C. Dietrich-Buchecker, P. Gavina, M. C. Jimenez-
Molero, J.-P. Sauvage, Acc. Chem. Res. 2001, 34, 477–487; e) C. A.
Schalley, K. Beizai, F. Vçgtle, Acc. Chem. Res. 2001, 34, 465–476.
[2] a) A. Harada, Acc. Chem. Res. 2001, 34, 456–464; b) S. A. Nepogo-
diev, J. F. Stoddart, Chem. Rev. 1998, 98, 1959–1976.
[3] a) V. Balzani, A. Credi, M. Venturi, ChemPhysChem 2003, 3, 4 9–
59; b) V. Balzani, Photochem. Photobiol. Sci. 2003, 2, 459–476;
c) F. M. Raymo, Adv. Mater. 2002, 14, 401–414; d) C. P. Collier,
E. W. Wong, M. Belohradsky, F. M. Raymo, J. F. Stoddart, P. J.
Kuekes, R. S. Williams, J. R. Heath, Science 1999, 285, 391–394;
e) C. P. Collier, M. Belohradsky, F. M. Raymo, J. F. Stoddart, J. R.
Heath, J. Am. Chem. Soc. 2000, 122, 5831–5840; f) M. Asakawa,
P. R. Ashton, V. Balzani, A. Credi, G. Mattersteig, O. A. Matthews,
M. Montalti, N. Spencer, J. F. Stoddart, M. Venturi, Chem. Eur. J.
1997, 3, 1992–1996.
[20] a) Y. Liu, Y.-L. Zhao, H.-Y. Zhang, H.-B. Song, Angew. Chem. 2003,
115, 3382–3385; Angew. Chem. Int. Ed. 2003, 42, 3260–3263; b) Y.
Liu, L. Li, Z. Fan, H.-Y. Zhang, X. Wu, S.-X. Liu, X.-D. Guan,
Nano Lett. 2002, 2, 257–261; c) Y. Liu, L. Li, H.-Y. Zhang, Y.-L.
Zhao, X. Wu, Macromolecules 2002, 35, 9934–9938.
[21] a) M. R. Craig, T. D. W. Claridge, M. G. Hutchings, H. L Anderson,
Chem. Commun. 1999, 1537–1538; b) J. Terao, A. Tang, J. J. Mi-
chels, A. Krivokapic, H. L. Anderson, Chem. Commun. 2004, 56–
57.
[22] a) Y. Kawaguchi, A. Harada, Org. Lett. 2000, 2, 1353–1356; b) M.
Okada, A. Harada, Org. Lett. 2004, 6, 361–364; c) H. Shigekawa, K.
Miyake, J. Sumaoka, A. Harada, M. Komiyama, J. Am. Chem. Soc.
2000, 122, 5411–5412.
[4] a) B. L. Feringa, Acc. Chem. Res. 2001, 34, 504–513; b) B. L. Ferin-
ga, Molecular Switches, Wiley-VCH, Weinheim, 2001; c) M. Asaka-
wa, M. Higuchi, G. Mattersteig, T. Nakamura, A. R. Pease, F. M.
Raymo, T. Shimizu, J. F. Stoddart, Adv. Mater. 2000, 12, 1099–1102;
d) G. Bottari, D. A. Leigh, E. PØrez, J. Am. Chem. Soc. 2003, 125,
13360–13361.
[5] a) P. N. Taylor, M. J. OꢁConnell, L. A. McNeill, M. J. Hall, R. T.
Aplin, H. L. Anderson, Angew. Chem. 2000, 112, 3598–3602;
Angew. Chem. Int. Ed. 2000, 39, 3456–3460; b) F. Cacialli, J. S.
Wilson, J. J. Michels, C. Daniel, C. Silva, R. H. Friend, N. Severin, P.
Samorì, J. P. Rabe, M. J. OꢁConnell, P. N. Taylor, H. L. Anderson,
Nat. Mater. 2002, 1, 160–164; c) P. N. Taylor, A. J. Hagan, H. L. An-
derson, Org. Biomol. Chem. 2003, 1, 3851–3856; d) J. J. Michels,
5936
www.chemeurj.org
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2005, 11, 5929 – 5937

Rotaxanes
FULL PAPER
[23] The Supporting Information includes the two-dimensional
1H ROESY NMR spectra of 1-a-CD and 2-a-CD, 1H NMR of
dumbbell NNAS, absorption spectra of compounds 1, 2, NNAS, and
NNAS-2CD, MALDI-TOF mass spectra of NNAS-2CD, and fluo-
rescence spectra of dumbbell NNAS.
[24] H. Meier, Angew. Chem. 2001, 113, 1903–1905; Angew. Chem. Int.
Ed. 2001, 40, 1851–1853.
Received: December 21, 2004
Revised: April 18, 2005
Published online: July 26, 2005
Chem. Eur. J. 2005, 11, 5929 – 5937
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5937