Light-controllable cucurbit[7]uril-based molecular shuttle

Article abstract of DOI:10.1021/jo301807y

The design and construction of novel artificial molecular machines can be categorized as a currently important field of modern chemistry. In the present work, a novel photoresponsive [3]rotaxane containing two cucurbit[7]uril (CB[7]) rings and a dumbbell

Full text of DOI:10.1021/jo301807y

Article
pubs.acs.org/joc
Light-Controllable Cucurbit[7]uril-Based Molecular Shuttle
Liangliang Zhu,† Hong Yan,† Xiao-Jun Wang,† and Yanli Zhao*,†,‡
†Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University,
21 Nanyang Link, Singapore 637371
‡School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798
S
* Supporting Information
ABSTRACT: The design and construction of novel artificial
molecular machines can be categorized as a currently
important field of modern chemistry. In the present work, a
novel photoresponsive [3]rotaxane containing two
cucurbit[7]uril (CB[7]) rings and a dumbbell component
consisting of one trans-azobenzene unit along with two
viologen units was developed. Each viologen group was
encircled by a CB[7] ring with a rapid shuttling equilibration
distribution extended to the trans-azobenzene unit located in
the middle of the dumbbell component. Upon the trans-to-cis
photoisomerization of the azobenzene unit under UV light irradiation, a shuttling restriction of the CB[7] rings along the
dumbbell component was observed. The equilibration distribution of the macrocycles on the dumbbell component can be
recovered by the cis-to-trans photoisomerization of the azobenzene unit under visible light irradiation. Such a controllable
1
shuttling process was fully characterized by H NMR spectroscopy and was easily indicated by fluorescent changes of the
[3]rotaxane.
complexed by the CB[7] ring with a high binding affinity (105
INTRODUCTION
■
to 106 M−1), and this host−guest inclusion process can be
Mechanically interlocked molecules (MIMs) that bear a
controlled relative motion pattern between components have
been studied extensively because these fascinating prototypes
present great potentials for applications in artificial molecular
extended to the nearby groups via an equilibrating distribution
of the ring at room temperature.7 Herein, a [3]rotaxane (R1 in
Figure 1) containing two CB[7] rings and a dumbbell
switches and machines.1 Among these MIMs, light-driven
component comprising an azobenzene group directly linked
by two viologen units was synthesized. Since the shuttling
molecular shuttles or motors are of considerable interest
equilibrium distribution of the CB[7] rings in the [3]rotaxane
because their response to a photochemical process is usually
was extended from the viologen units to the azobenzene one,
rapid and precise and can be operated remotely without
generating any chemical waste.2 In particular, dynamically
driven shuttling via photoisomerization is more popular, as such
a process can be easily conducted in situ.3 Cucurbit[n]urils
(CBs) are an important class of macrocyclic molecules which
stand out among molecular hosts on account of their water
solubility, structural symmetry, and selective recognition toward
positively charged species with extremely high binding
constants (up to 1015 M−1 in water).4 Due to these features,
the CB rings have been employed to fabricate robust host−
guest architectures or networks for a variety of applications.5
Research on CB-based molecular shuttles directly driven by the
photoisomerization is, however, still scarce, and only a few of
research groups have demonstrated CB-based host−guest
complexes with a light-driven association/dissociation process
to the best of our knowledge.6 Constructing light-controllable
CB-based rotaxanes remains a challenge, simply because the
binding abilities of the CB rings with light-active groups (e.g.,
azobenzene and stilbene) are relatively low.
the shuttling process was affected by the trans−cis photo-
isomerization of the azobenzene unit. The isophthalate group
was introduced as one stopper of the CB[7]-based [3]rotaxane
R1 that was prepared by a slippage approach,9 while the
naphthalimide moiety was chosen as the other stopper as well
as a fluorescence indicator. Because the dumbbell compound (1
in Figure 1) is unsymmetrical and relatively complicated, we
also prepared two simplified dumbbell-like compounds (2 and
3) for the constructions of CB[7]-based [2]rotaxanes (R2 and
R3) as references.
The synthetic route and details for the preparation of the
dumbbell compounds 1−3 and the rotaxanes R1−R3 are
presented in the Experimental Section. An improved slippage
approach8 was employed to prepare these CB[7]-based
rotaxanes. Taking advantage of the annular diameter (5.4−7.3
Å)4c,d of the CB[7] ring that closes to the size of the stopper
isophthalic acid (7.0 Å), in our study, the CB[7] rings were
threaded onto the dumbbell components in boiling water at
In order to overcome this obstacle, a model MIM with a
shuttling equilibrium distribution of the CB ring along the axle
was taken into consideration. Viologen unit can be effectively
Received: August 24, 2012
Published: October 31, 2012
© 2012 American Chemical Society
10168
dx.doi.org/10.1021/jo301807y | J. Org. Chem. 2012, 77, 10168−10175

The Journal of Organic Chemistry
Article
Figure 1. Schematic representations of dumbbell molecules 1−3 and the corresponding rotaxanes R1−R3. The protons are defined alongside the
structural formula.
1
Figure 2. H NMR spectra (400 MHz, DMSO-d6, 295 K) of (A) dumbbell molecule 3 and (B) [2]rotaxane R3 along with a conformational
representation of the CB[7] shuttling distribution.
100 °C, a temperature when the CB[7] ring was expanded.
Once the solution was cooled to room temperature, the rings
were shrinked back and were prevented by the isophthalate
stopper from dethreading, resulting in the formations of the
corresponding rotaxanes in a relatively high yield without the
purification by column chromatography. This synthetic
methodology was clearly evidenced by the NMR and MS
spectra of the rotaxanes R1−R3. As 1-adamantanamine
hydrochloride presents a high binding affinity of over 1012
M−1 with CB[7] at room temperature, it would competitively
bind with the CB[7] ring if R1 is a complex. In a control
CB[7] ring cannot be threaded by the dumbbell molecule at
room temperature because there was no proton shift observed
from the dumbbell molecule in the presence of the CB[7] ring
at room temperature in either water or dimethyl sulfoxide
(DMSO) (Figures S2 and S3 in the Supporting Information).
Since the rotaxanes show relatively low water solubility, we
performed the experiments in DMSO.
RESULTS AND DISCUSSION
■
Shuttling of CB[7] in Rotaxanes. Although the NOE
1
patterns in H NOESY spectra were employed to assist the
1
experiment, there was no H NMR spectral change observed
characterizations (Figures S4−S7 in the Supporting Informa-
tion), it was still not easy to assign all the proton resonances in
[3]rotaxane R1. Therefore, two reference rotaxanes R2 and R3
with relatively simple structures were investigated first. It is
when mixing an excess amount of 1-adamantanamine hydro-
chloride with R1, confirming the formation of the rotaxane
architecture (Figure S1 in the Supporting Information). The
10169
dx.doi.org/10.1021/jo301807y | J. Org. Chem. 2012, 77, 10168−10175

The Journal of Organic Chemistry
Article
well-known that the proton resonances of a guest molecule
exhibit upfield shifts when it is located in the CB cavity on
account of the shielding effect, while the resonances will
undergo downfield shifts when the guest molecule is outside
the cavity and near the portal of the CB ring owing to a
deshielding effect.9 The resonances of the protons Hg‑m in the
1H NMR spectrum (Figure 2) of [2]rotaxane R3 shift upfield,
whereas those of the protons Hf and Hn shift downfield, as
compared with the corresponding protons in the dumbbell
molecule 3. These results clearly indicate that the protons Hg‑m
are inside the CB[7] cavity, and the CB[7] ring shuttles around
the viologen unit within the range between the protons Hf and
Hn on the NMR time scale at room temperature. Other protons
in the dumbbell component are far away from the CB[7] ring
of two viologen binding sites on the dumbbell component for
the encirclement of two CB[7] rings. With the assistance from
the control studies of [2]rotaxanes R2 and R3, all of the proton
signals in [3]rotaxane R1 can be assigned. As seen from Figures
4 and 5, the resonances of the protons Hg‑o and Hr‑w in
[3]rotaxane R1 reveal upfield shifts, while only the protons He,
Hf, Hp, Hq, and Hx show downfield shifts. These observations
indicate that the two CB[7] rings shuttle separately around
each viologen unit. Their shuttling ranges are along the axle
from Hf to Hp and from Hq to Hx, respectively, demonstrating
that the shuttling equilibrium distributions of the two CB[7]
rings are extended from the viologen units to the phenyl groups
of the azobenzene unit. The thermal stability of the [3]rotaxane
was also investigated. Heating the temperature to 90 °C
followed by cooling to room temperature can enable the
[3]rotaxane to change back to the initial state (Figure S8 in the
Supporting Information).
1
and are scarcely affected by the ring. As compared to the H
NMR spectrum of the dumbbell compound 2, the resonance
shifts of some protons can be observed in the spectrum of
[2]rotaxane R2 (Figure 3). There was no new proton peak
Restriction of Shuttling Equilibration Distribution
upon Photoisomerization. Upon UV light irradiation, the
1H NMR spectra of both dumbbell molecule 1 and [3]rotaxane
R1 show a group of upfield shifts for the protons Ho‑r in the
aromatic region, corresponding to the azobenzenyl unit turning
from the trans form to its cis form. The maximum photo-
isomerization efficiency is 40−50% according to the NMR
integral studies of these protons. In contrast, the resonances of
the protons Hj, Hm, Ht, and Hw on the viologen units as well as
other protons on the dumbbell component did not show
obvious shifts (Figure 5A,D for comparison). Similar to the
case in the initial trans form of [3]rotaxane R1, two CB[7] rings
can still shuttle around the viologen units in the cis form of
[3]rotaxane R1, evidenced by the upfield shifts of the protons
Hj′, Hm′, Ho′, Hr′, Ht′, and Hw′ as well as the downfield shifts of
the protons Hp′ and Hq′ (Figure 5C,D for comparison).
However, the extent of these resonance shifts in the cis form is
different as compared with the corresponding resonance shifts
in the trans form. Each of those protons Hj′, Hm′, Ht′, and Hw′
on the viologen units exhibits bigger upfield shift (ΔδHj′ =
−0.78 ppm, ΔδHm′ = −0.67 ppm, ΔδHt′ = −0.84 ppm, and
ΔδHw′ = −0.53 ppm, the resonance peaks labeled in blue in
Figure 5C,D) than corresponding protons in the trans form
(ΔδHj = −0.73 ppm, ΔδHm = −0.61 ppm, ΔδHt = −0.72 ppm,
and ΔδHw = −0.50 ppm, the resonance peaks labeled in blue in
Figure 5A,B). On the contrary, the protons Ho′/r′ and Hp′/q′ on
the azobenzene unit show less upfield and downfield shifts,
respectively (ΔδHo′ = −0.10 ppm, ΔδHr′ = −0.30 ppm, ΔδHp′
= +0.08 ppm, and ΔδHq′ = +0.14 ppm, the resonance peaks
labeled in red in Figure 5C,D) than corresponding protons
(ΔδHo = −0.30 ppm, ΔδHr = −0.51 ppm, ΔδHp = +0.09 ppm,
and ΔδHq = +0.16 ppm, the resonance peaks labeled in red in
Figure 5A,B). These observations indicate a compensation
mechanism; that is, the shuttling equilibrium distribution of the
CB[7] rings was partly diverted from the azobenzene unit to
the viologen units on account of structural restriction after the
trans-to-cis photoisomerization (Figure 6). The distribution of
the CB[7] rings on the alkyl chain was not significantly affected
by the photoisomerization because there were no proton shifts
1
Figure 3. H NMR spectra (400 MHz, DMSO-d6, 295 K) of (A)
dumbbell molecule 2 and (B) [2]rotaxane R2 along with a
conformational representation of the CB[7] shuttling distribution.
observed, indicating that [2]rotaxane R2 remains a symmetric
conformation on the NMR time scale. The resonances of the
protons Hd and He on the dumbbell shift upfield, whereas that
1
of Hf shift downfield in the H NMR spectrum of [2]rotaxane
R2, demonstrating that the protons Hd and He are inside the
CB[7] cavity while the protons Hf are around the rim of the
ring. According to the fact that these proton signals are still
coalesced, it can be concluded that the CB[7] ring in
[2]rotaxane R2 shuttles rapidly along the axle with a main
distribution on two pyridinium units of the viologen moiety in
order to include the protons Hd and He.
1
1
observed in H NMR spectra. Thus, a light-controlled ring
The formation of [3]rotaxane R1 was confirmed by the H
shuttling mechanism that relied on the equilibrium distribution
change was demonstrated for the [3]rotaxane.
Shuttling Equilibrium Distribution Change Indicated
by Spectra. The fluorescent band at ∼385 nm basically
originates from the emission of the 1,8-naphthalimide group.
The trans-to-cis photoisomerization of the dumbbell molecule 1
NMR and ESI-MS studies, indicating a 2:1 host−guest
architecture. It was not easy to prepare a CB[7]-based
[2]rotaxane from dumbbell molecule 1. Even an equal amount
of the CB[7] ring and dumbbell molecule 1 was added, the
product was still the [3]rotaxane where one dumbbell was
encircled by two CB[7] rings, simply because of the coexistence
10170
dx.doi.org/10.1021/jo301807y | J. Org. Chem. 2012, 77, 10168−10175

The Journal of Organic Chemistry
Article
1
Figure 4. H NMR spectra (400 MHz, DMSO-d6, 295 K) of (A) dumbbell molecule 1 and (B) [3]rotaxane R1 along with a conformational
representation of the CB[7] shuttling distribution.
1
Figure 5. Partial H NMR spectra (400 MHz, DMSO-d6, 295 K) of (A) dumbbell molecule 1, (B) [3]rotaxane R1, (C) [3]rotaxane R1 after
sufficient photoirradiation at 365 nm, and (D) dumbbell molecule 1 after sufficient photoirradiation at 365 nm.
did not cause any obvious emission intensity change before and
after UV light irradiation (curves a and b in Figure 7). In
contrast, the emission intensity of [3]rotaxane R1 increases by
about 33% after the trans-to-cis photoisomerization (curves c
and d in Figure 7). Clearly, the fluorescent change is the result
of the shuttling equilibrium distribution change of the CB[7]
rings along the dumbbell component. The fluorescent
enhancement may be attributed to the conformational
modulation effect of the rigid CB[7] ring.10 The flexible
dumbbell molecule 1 may adopt a bent conformation where the
10171
dx.doi.org/10.1021/jo301807y | J. Org. Chem. 2012, 77, 10168−10175

The Journal of Organic Chemistry
Article
CONCLUSION
■
A new cucurbit[7]uril-based [3]rotaxane with light-controllable
shuttling distribution change of the macrocycles along the
dumbbell component has been developed. The key step in the
synthetic process is to incorporate the azobenzene unit with
two viologen groups in the dumbbell component, resulting in a
rapidly equilibrating distribution for the cucurbit[7]uril rings;
that is, the cucurbit[7]uril rings encircle the viologen units with
a shuttling extension to the azobenzene unit. The trans-to-cis
photoisomerization of the azobenzene unit leads to the
restriction of the shuttling distribution to a certain extent and
makes the rings more concentrated on the viologen units. This
[3]rotaxane with alterable shuttling equilibrium distribution has
1
been effectively characterized by H NMR spectroscopy and
easily indicated by spectral variations. The fabrication and
investigation of such kind of molecular shuttle could be
valuable for enhancing the performance of cucurbituril-based
molecular machines.
Figure 6. Schematic representation for light-controlled CB[7] ring
shuttling equilibrium distribution in [3]rotaxane R1.
EXPERIMENTAL SECTION
■
Instruments. H NMR, 13C NMR, and H NOESY NMR spectra
were recorded on an NMR spectrometer. The electronic spray
ionization mass spectra (ESI-MS) were recorded on a quadrupole ion
trap mass spectrometer. The high-resolution mass spectra (HR-MS)
were obtained on a Q-TOF mass spectrometer. Absorption spectra
were recorded on a UV−vis−NIR spectrophotometer, while the
emission spectra were recorded on a fluorescence spectrophotometer.
Melting points were determined using an automated melting point
system. The photoirradiation was carried out on a UV lamp (15 W)
with an irradiation wavelength of 365 nm in a sealed Ar-saturated 1 cm
quartz cell.
1
1
Materials. Benzoyl peroxide, 4,4′-bipyridine, N-bromosuccinimide,
cucurbit[7]uril (CB[7]), 1,6-dibromohexane, 5-methylisophthalic acid,
1,8-naphthalimide, sodium methoxide, and p-toluidine were purchased
commercially and used as received. All of the solvents and inorganic
reagents were commercially available. Synthetic routes for the
preparations of the dumbbell compounds 1, 2, and 3 are shown in
Figure 8.
Compound 1a. This compound was prepared according to the
literature report.11
Figure 7. Emission spectra (λex = 340 nm) of dumbbell molecule 1
(0.021 mM in DMSO, 295 K) (a) before and (b) after irradiation at
365 nm for 300 s, when compared with significant emission change for
[3]rotaxane R1 (0.021 mM in DMSO, 295 K) (c) before and (d) after
irradiation at 365 nm for 300 s.
Compound 1b. 1,8-Naphthalimide (0.86 g, 4.36 mmol) was
suspended in a mixture of N,N-dimethylformamide (DMF) (20 mL)
and DMSO (20 mL), and then sodium methoxide (0.224 g, 4.14
mmol) was added to the solution with stirring at room temperature.
The suspension turned to a clear solution after several minutes. Then,
1,6-dibromohexane (3.02 g, 12.4 mmol) was added into the solution,
and the solution mixture was kept stirring for 6 h. The mixture
solution was poured into water (250 mL), and solid crude product was
slowly precipitated. The crude product was filtered and recrystallized
by ethanol to afford 1b (1.25 g, 85.6%): mp 95−96 °C. 1H NMR (400
MHz, DMSO-d6, 295 K, TMS): δ = 8.49 (m, 4H), 7.88 (t, J = 8.0 Hz,
2H), 4.05 (t, J = 8.0 Hz, 2H), 3.54 (t, J = 8.0 Hz, 2H), 1.82 (dd, J1 = J2
= 8.0 Hz, 2H), 1.65 (dd, J1 = J2 = 8.0 Hz, 2H), 1.43 (m, 4H). 13C
NMR (100 MHz, DMSO-d6, 295 K, TMS): δ = 163.9, 134.8, 131.8,
131.2, 127.8, 127.7, 122.6, 35.6, 32.6, 27.8, 27.8, 26.1. HR-MS (ESI):
calcd for C18H19NO279Br [M + H]+ m/z = 360.0599, found m/z
360.0594.
Compound 1c. A solution of 1b (1.2 g, 3.3 mmol) and 4,4′-
bipyridine (3.6 g, 23.1 mmol) in acetonitrile (35 mL) was stirred at 80
°C for 1 day. After cooling to room temperature, the mixture was
filtered. The solid was washed with acetonitrile to provide a white
compound 1c (1.36 g, 79.9%): mp 226−227 °C (decomp.). 1H NMR
(400 MHz, DMSO-d6, 295 K, TMS): δ = 9.25 (d, J = 4.0 Hz, 2H),
8.88 (d, J = 4.0 Hz, 2H), 8.65 (d, J = 8.0 Hz, 2H), 8.50 (m, 4H), 8.06
(d, J = 8.0 Hz, 2H), 7.89 (t, J = 8.0 Hz, 2H), 4.66 (t, J = 8.0 Hz, 2H),
4.06 (t, J = 8.0 Hz, 2H), 1.99 (br, 2H), 1.67 (br, 2H), 1.41 (m, 4H).
13C NMR (100 MHz, DMSO-d6, 295 K, TMS): δ = 163.9, 152.6,
viologen and 1,8-naphthalimide units are close to each other,
resulting in fluorescence quenching on account of intra-
molecular charge transfer between the viologen unit and 1,8-
naphthalimide unit. In the [3]rotaxane, UV-light-induced
equilibrium distribution change makes the CB[7] rings more
concentrated on the viologen units. The encirclements of the
CB[7] rings on the viologen units protect the viologen units
from the potential charge transfer, restoring the fluorescence.10
In addition, time-dependent absorption changes of the
[3]rotaxane were recorded upon the photoirradiation (Figures
S9−S11 in the Supporting Information). Similar light-control-
lable shuttling behavior of the [3]rotaxane in aqueous solution
and on the [3]rotaxane-doped poly(methyl methacrylate)
(PMMA) film was also explored (Figures S12 and S13 in the
Supporting Information). The observations indicate that the
light-triggered shuttling equilibrium distribution change of the
ring can be easily distinguished by spectral variations.
10172
dx.doi.org/10.1021/jo301807y | J. Org. Chem. 2012, 77, 10168−10175

The Journal of Organic Chemistry
Article
Figure 8. Synthetic routes for the preparations of the dumbbell compounds 1, 2, and 3. Reagents and conditions: (i) 4,4′-bipyridine, (ii) 1,6-
dibromohexane and sodium methoxide, (iii) bis(4-bromomethylphenyl)diazene.
151.5, 145.8, 134.9, 132.6, 131.2, 127.8, 127.6, 125.9, 122.5, 122.4,
60.3, 31.0, 27.8, 26.4, 25.6. HR-MS (ESI): calcd for C28H26N3O2 [M −
Br]+ m/z = 436.2025, found m/z 436.2025.
25.6. HR-MS (ESI): calcd for C42H38N5O279Br81Br [M − Br]+ m/z =
804.1372, found m/z 804.1377.
Dumbbell Compound 1. A suspension of compound 1e (650 mg,
0.74 mmol) in DMF (20 mL) was heated to 90 °C, and then
compound 1d (326 mg, 0.74 mmol) was added into the solution. The
mixture solution was kept stirring at 90 °C for 6 h. Some precipitates
were observed. The mixture solution was filtered while it was hot. The
solid was washed with a small amount of cool DMF to give orange
product 1 (383 mg, 39%): mp >250 °C. 1H NMR (400 MHz, DMSO-
d6, 295 K, TMS): δ = 9.59 (m, 6H), 9.41 (d, J = 8.0 Hz, 2H), 8.84 (d, J
= 8.0 Hz, 2H), 8.80 (m, 6H), 8.58 (s, 2H), 8.47 (m, 5H), 7.94 (m,
4H), 7.87 (m, 6H), 6.09 (m, 6H), 4.71 (t, J = 8.0 Hz, 2H), 4.05 (t, J =
8.0 Hz, 2H), 3.92 (s, 6H), 2.00 (br, 2H), 1.65 (br, 2H), 1.40 (m, 4H).
13C NMR (100 MHz, DMSO-d6, 295 K, TMS): δ = 165.4, 163.9,
152.6, 149.7, 149.7, 149.7, 149.0, 146.4, 146.4, 146.3, 146.2, 138.0,
137.9, 135.9, 135.2, 134.9, 131.8, 131.6, 131.2, 131.0, 130.8, 127.8,
127.8, 127.8, 127.7, 127.2, 123.8, 122.5, 63.2, 62.7, 61.3, 53.2, 31.1,
27.8, 26.4, 25.6. MS (ESI): calcd for [M − 3Br]3+ m/z = 363.12, found
m/z 363.27; [M − 4Br]4+ m/z = 251.85, found m/z 251.95. HR-MS
(ESI): calcd for C63H57N7O679Br81Br2 [M − Br]+ m/z = 1248.1879,
found m/z 1248.1898.
[3]Rotaxane R1. Compound 1 (13.2 mg, 0.01 mmol) and CB[7]
(23.3 mg, 0.02 mmol) were dissolved in deionized water (5 mL), and
the solution was heated to 100 °C. The solution was kept stirring at
the temperature for 10 h and was quickly cooled using an ice bath.
Then, the aqueous solution was poured into ethanol (30 mL), and the
product was precipitated. The product R1 (15.6 mg, 42.7%) was
collected by centrifugation (6000 rps, 20 min): mp >250 °C. 1H NMR
(400 MHz, DMSO-d6, 295 K, TMS): δ = 9.10 (d, J = 4.0 Hz, 2H),
9.00 (d, J = 4.0 Hz, 2H), 8.85 (d, J = 4.0 Hz, 2H), 8.83 (s, 2H), 8.66
(d, J = 8.0 Hz, 2H), 8.58 (s, 1H), 8.46 (m, 4H), 8.12 (d, J = 8.0 Hz,
2H), 8.03 (d, J = 8.0 Hz, 2H), 7.87 (m, 2H), 7.56 (d, J = 8.0 Hz, 2H),
Compound 1d. A solution of 1a (0.94 g, 3.3 mmol) and 4,4′-
bipyridine (3.6 g, 23.1 mmol) in acetonitrile (55 mL) was stirred at 80
°C for 1 day. After cooling to room temperature, the mixture was
filtered. The solid was washed with acetonitrile to give a pale yellow
1
compound 1d (1.1 g, 75.7%): mp 222−223 °C (decomp.). H NMR
(300 MHz, DMSO-d6, 295 K, TMS): δ = 9.43 (d, J = 9.0 Hz, 2H),
8.87 (d, J = 6.0 Hz, 2H), 8.65 (d, J = 6.0 Hz, 2H), 8.56 (s, 2H), 8.51
(s, 1H), 8.01 (d, J = 6.0 Hz, 2H), 6.04 (s, 2H), 3.92 (s, 6H). 13C NMR
(100 MHz, DMSO-d6, 295 K, TMS): δ = 165.7, 153.7, 151.1, 145.6,
141.6, 135.3, 134.8, 131.7, 131.0, 126.4, 122.6, 62.6, 53.3. HR-MS
(ESI): calcd for C21H19N2O4 [M − Br]+ m/z = 363.1345, found m/z
363.1346.
Compound 1e. Bis(4-bromomethylphenyl)diazene12 (4.0 g, 10.9
mmol) was dissolved in DMF (75 mL) at 100 °C. The solution was
then added with compound 1c (0.8 g, 1.56 mmol) and stirred at 100
°C for 7 h. The mixture solution was filtered while it was hot. The
filtrate was then poured into toluene (300 mL) to precipitate some
orange solid. The mixture was kept overnight and then filtered. The
solid was washed with hot chloroform (50 mL) and acetonitrile (40
mL) and dried in vacuo, affording pure orange compound 1e (997 mg,
72.3%): mp >250 °C. 1H NMR (400 MHz, DMSO-d6, 295 K, TMS):
δ = 9.56 (d, J = 8.0 Hz, 2H), 9.39 (d, J = 8.0 Hz, 2H), 8.81 (d, J = 8.0
Hz, 2H), 8.77 (d, J = 8.0 Hz, 2H), 8.49 (m, 4H), 7.98 (d, J = 8.0 Hz,
2H), 7.88 (m, 4H), 7.83 (d, J = 8.0 Hz, 2H), 7.68 (d, J = 8.0 Hz, 2H),
6.06 (s, 2H), 4.82 (s, 2H), 4.70 (t, J = 8.0 Hz, 2H), 4.05 (t, J = 8.0 Hz,
2H), 2.00 (br, 2H), 1.65 (br, 2H), 1.40 (m, 4H). 13C NMR (100 MHz,
DMSO-d6, 295 K, TMS): δ = 163.9, 151.9, 149.8, 149.0, 146.4, 146.2,
134.9, 131.8, 131.2, 131.0, 130.7, 127.8, 127.8, 127.7, 127.6, 127.2,
123.7, 123.6, 123.5, 123.1, 122.5, 63.2, 62.8, 61.3, 34.0, 31.1, 27.8, 26.4,
10173
dx.doi.org/10.1021/jo301807y | J. Org. Chem. 2012, 77, 10168−10175

The Journal of Organic Chemistry
Article
7.36 (d, J = 8.0 Hz, 2H), 7.01 (d, J = 4.0 Hz, 2H), 6.98 (d, J = 8.0 Hz,
2H), 6.82 (d, J = 4.0 Hz, 2H), 6.26 (s, 2H), 6.17 (s, 2H), 6.06 (s, 2H),
5.58−5.34 (m, 56H), 4.62 (br, 2H), 4.24−4.04 (m, 30H), 3.91 (s,
6H), 2.02 (br, 2H), 1.90 (br, 2H), 1.52 (br, 2H), 1.37 (br, 2H). 13C
NMR (100 MHz, DMSO-d6, 295 K, TMS): δ = 165.9, 164.1, 155.5,
155.3, 155.3, 155.1, 152.1, 148.5, 148.4, 148.0, 147.2, 137.3, 134.5,
134.0, 133.3, 131.6, 131.5, 130.8, 129.1, 128.3, 127.8, 127.5, 124.5,
123.9, 123.8, 123.8, 123.5, 123.1, 122.8, 122.6, 70.4, 70.3, 63.4, 63.0,
62.4, 52.9, 52.2, 52.0, 48.6, 30.8, 28.2, 27.2, 25.5, 21.1, 13.7. MS (ESI):
calcd for [M − 4Br]4+ m/z = 833.52, found m/z 833.60. HR-MS
(ESI): calcd for C37H37N16O8 [M − 4Br]4+ m/z = 833.2980, found m/
z 833.2969.
calcd for C40H39N16O10 [M − 2Br]2+ m/z = 903.3035, found m/z
903.3031.
Preparations of 1- and R1-Doped Poly(methyl methacrylate)
Solid Films. Compound 1 or [3]rotaxane R1 was dispersed into an
anisole solution containing 10 wt % of PMMA in order to form a
solution with the concentration of 1 μM. Then, the solid film was
obtained by spin-coating this solution on one side of 1 mm quartz
cuvette. The cuvette was inserted into the cuvette holder at an angle
about 45° to the incident light for the fluorescence test.
ASSOCIATED CONTENT
■
S
* Supporting Information
Dumbbell Compound 2. A solution of 1a (3.76 g, 13.2 mmol) and
4,4′-bipyridine (147 mg, 0.94 mmol) in acetonitrile (70 mL) was
stirred at 80 °C for 1 day. After cooling to room temperature, the
mixture solution was filtered. The solid was washed with acetonitrile to
Characterization spectra. This material is available free of
charge via the Internet at http://pubs.acs.org.
1
give a pale yellow compound 2 (452 mg, 65.9%): mp >250 °C. H
AUTHOR INFORMATION
■
NMR (400 MHz, DMSO-d6, 295 K, TMS): δ = 9.56 (d, J = 8.0 Hz,
4H), 8.74 (d, J = 8.0 Hz, 4H), 8.57 (s, 4H), 8.52 (s, 2H), 6.08 (s, 4H),
3.92 (s, 12H). 13C NMR (100 MHz, DMSO-d6, 295 K, TMS): δ =
165.4, 149.8, 146.3, 135.9, 135.2, 131.6, 131.0, 127.8, 62.7, 53.2. HR-
MS (ESI): calcd for C32H30N2O881Br [M − Br]+ m/z = 651.1165,
found m/z 651.1171.
Corresponding Author
*E-mail: zhaoyanli@ntu.edu.sg.
Notes
The authors declare no competing financial interest.
[2]Rotaxane R2. Compound 2 (14.5 mg, 0.02 mmol) and CB[7]
(23.3 mg, 0.02 mmol) were dissolved in deionized water (5 mL), and
the solution was heated to 100 °C. The solution was kept stirring at
the temperature for 10 h and was quickly cooled using an ice bath.
Then, the aqueous solution was poured into ethanol (30 mL), and the
product was precipitated. The product R2 (14.4 mg, 38.1%) was
collected by centrifugation (6000 rps, 20 min): mp >250 °C. 1H NMR
(400 MHz, DMSO-d6, 295 K, TMS): δ = 9.25 (br, 4H), 8.85 (d, J =
8.0 Hz, 4H), 8.57 (s, 4H), 8.47 (s, 2H), 6.02 (s, 4H), 5.65−5.62 (m,
14H), 5.38 (br, 14H), 4.15 (m, 14H), 3.91 (s, 12H). 13C NMR (100
MHz, DMSO-d6, 295 K, TMS): δ = 165.7, 155.1, 150.4, 145.2, 138.3,
134.9, 131.1, 128.5, 125.3, 70.5, 59.8, 54.1, 52.8. MS (ESI): calcd for
[M − 2Br]2+ m/z = 866.78, found m/z 866.92. HR-MS (ESI): calcd
for C37H36N15O11 [M − 2Br]2+ m/z = 866.2719, found m/z 866.2641.
Dumbbell Compound 3. A solution of 1c (516 mg, 1.0 mmol) and
1a (574 mg, 2.0 mmol) in a mixture solution of DMF (5 mL) and
acetonitrile (30 mL) was stirred at 90 °C for 1 day. After cooling to
room temperature, the mixture solution was filtered. The solid was
washed with acetonitrile to provide a pale yellow compound 2 (497
ACKNOWLEDGMENTS
■
We thank the Singapore National Research Foundation
Fellowship (NRF2009NRF-RF001-015), Singapore National
Research Foundation CREATE programSingapore Peking
University Research Centre for a Sustainable Low-Carbon
Future, and Nanyang Technological University for financial
support. L.L.Z. thanks Dr. H.C. Zhang and Mr. M.H. Li for
helpful discussions.
REFERENCES
■
(1) (a) Fang, L.; Olson, M. A.; Stoddart, J. F. Chem. Soc. Rev. 2010,
39, 17−29. (b) Balzani, V.; Credi, A.; Silvi, S.; Venturi, M. Chem. Soc.
Rev. 2006, 35, 1135−1149. (c) Durot, S.; Reviriego, F.; Sauvage, J.-P.
Dalton Trans. 2010, 39, 10557−10570. (d) Beves, J. E.; Blight, B. A.;
Campbell, C. J.; Leigh, D. A.; McBurney, R. T. Angew. Chem., Int. Ed.
2011, 50, 9260−9327. (e) Qu, D.-H.; Tian, H. Chem. Sci. 2011, 2,
1011−1015.
(2) (a) Silvi, S.; Venturi, M.; Credi, A. Chem. Commun. 2011, 47,
2483−2489. (b) Saha, S.; Stoddart, J. F. Chem. Soc. Rev. 2007, 36, 77−
92. (c) Ma, X.; Tian, H. Chem. Soc. Rev. 2010, 39, 70−80. (d) Qu, D.-
H.; Feringa, B. L. Angew. Chem., Int. Ed. 2010, 49, 1107−1110.
(e) Hua, Y.; Flood, A. H. J. Am. Chem. Soc. 2010, 132, 12838−12840.
(f) Zhao, Y.-L.; Stoddart, J. F. Langmuir 2009, 25, 8442−8446.
(g) Ferris, D. P.; Zhao, Y.-L.; Khashab, N. M.; Khatib, H. A.; Stoddart,
J. F.; Zink, J. I. J. Am. Chem. Soc. 2009, 131, 1686−1688.
(3) (a) Murakami, H.; Kawabuchi, A.; Kotoo, K.; Kunitake, M.;
Nakashima, N. J. Am. Chem. Soc. 1997, 119, 7605−7606.
(b) Cheetham, A. G.; Hutchings, M. G.; Claridge, T. D. W.;
Anderson, H. L. Angew. Chem. 2006, 118, 1626−1629. (c) Inoue, Y.;
Kuad, P.; Okumura, Y.; Takashima, Y.; Yamaguchi, H.; Harada, A. J.
Am. Chem. Soc. 2007, 129, 6396−6397. (d) Willner, I.; Pardo-Yissar,
V.; Katz, E.; Ranjit, K. T. J. Electroanal. Chem. 2001, 497, 172−177.
(e) Zhu, L.; Ma, X.; Ji, F.; Wang, Q.; Tian, H. Chem.Eur. J. 2007, 13,
9216−9222. (f) Dawson, R. E.; Lincoln, S. F.; Easton, C. J. Chem.
Commun. 2008, 3980−3982. (g) Zhu, L.; Yan, H.; Nguyen, K. T.;
Tian, H.; Zhao, Y. Chem. Commun. 2012, 48, 4290−4292. (h) Zhu, L.;
Yan, H.; Ang, C. Y.; Nguyen, K. T.; Li, M.; Zhao, Y. Chem.Eur. J.
2012, 18, 13979−13983.
(4) (a) Mock, W. L.; Shih, N.-Y. J. Org. Chem. 1986, 51, 4440−4446.
(b) Liu, S.; Ruspic, C.; Mukhopadhyay, P.; Chakrabarti, S.; Zavalij, P.
Y.; Isaacs, L. J. Am. Chem. Soc. 2005, 127, 15959−15967. (c) Lee, J.
W.; Samal, S.; Selvapalam, N.; Kim, H.-J.; Kim, K. Acc. Chem. Res.
2003, 36, 621−630. (d) Lagona, J.; Mukhopadhyay, P.; Chakrabarti,
S.; Isaacs, L. Angew. Chem., Int. Ed. 2005, 44, 4844−4870. (e) Masson,
1
mg, 61.9%): mp >250 °C. H NMR (400 MHz, DMSO-d6, 295 K,
TMS): δ = 9.57 (d, J = 8.0 Hz, 2H), 9.38 (d, J = 8.0 Hz, 2H), 8.78 (d, J
= 8.0 Hz, 2H), 8.74 (d, J = 8.0 Hz, 2H), 8.58 (s, 2H), 8.49 (m, 5H),
7.89 (m, 2H), 6.08 (s, 2H), 4.69 (t, J = 8.0 Hz, 2H), 4.05 (t, J = 8.0
Hz, 2H), 3.92(s, 6H), 2.00 (br, 2H), 1.66 (br, 2H), 1.39 (m, 4H). 13C
NMR (100 MHz, DMSO-d6, 295 K, TMS): δ = 165.4, 163.9, 149.8,
149.1, 146.3, 146.2, 135.9, 135.2, 134.9, 131.8, 131.6, 131.2, 131.0,
127.8, 127.8, 127.7, 127.2, 122.5, 62.7, 61.3, 53.2, 31.1, 27.8, 26.4, 25.6.
HR-MS (ESI): calcd for C39H37N3O681Br [M − Br]+ m/z = 724.1854,
found m/z 724.1845.
[2]Rotaxane R3. Compound 3 (16.1 mg, 0.02 mmol) and CB[7]
(23.3 mg, 0.02 mmol) were dissolved in deionized water (5 mL), and
the solution was heated to 100 °C. The solution was kept stirring at
the temperature for 10 h and was quickly cooled using an ice bath.
Then, the aqueous solution was poured into ethanol (30 mL), and the
product was precipitated. The product R3 (12.1 mg, 30.7%) was
collected by centrifugation (6000 rps, 20 min): mp >250 °C. 1H NMR
(400 MHz, DMSO-d6, 295 K, TMS): δ = 9.05 (d, J = 4.0 Hz, 2H),
8.80 (s, 2H), 8.53 (s, 1H), 8.49 (d, J = 8.0 Hz, 2H), 8.42 (m, 4H), 7.84
(m, 2H), 6.94 (d, J = 8.0 Hz, 2H), 6.77 (d, J = 8.0 Hz, 2H), 6.23 (s,
2H), 5.44−5.29 (m, 28H), 4.53 (br, 2H), 4.16−3.98 (m, 16H), 4.69 (t,
J = 8.0 Hz, 2H), 4.05 (t, J = 8.0 Hz, 2H), 3.92(s, 6H), 1.91 (br, 4H),
1.50 (br, 2H), 1.26 (m, 2H). 13C NMR (100 MHz, DMSO-d6, 295 K,
TMS): δ = 165.7, 164.0, 155.1, 150.1, 148.3, 147.7, 146.6, 137.1, 134.5,
133.6, 131.5, 131.4, 131.0, 130.7, 127.8, 127.4, 124.0, 122.9, 122.6,
70.2, 63.4, 63.0, 56.6, 52.9, 30.5, 28.1, 27.2, 25.6, 19.1. MS (ESI): calcd
for [M − 2Br ]2+ m/z = 903.35, found m/z 903.37. HR-MS (ESI):
10174
dx.doi.org/10.1021/jo301807y | J. Org. Chem. 2012, 77, 10168−10175

The Journal of Organic Chemistry
Article
E.; Ling, X.; Joseph, R.; Kyeremeh-Mensah, L.; Lu, X. RSC Adv. 2012,
2, 1213−1247.
(5) (a) Kim, K. Chem. Soc. Rev. 2002, 31, 96−107. (b) Nau, W. M.;
Ghale, G.; Hennig, A.; Bakirci, H.; Bailey, D. M. J. Am. Chem. Soc.
2009, 131, 11558−11570. (c) Appel, E. A.; Biedermann, F.; Rauwald,
U.; Jones, S. T.; Zayed, J. M.; Scherman, O. A. J. Am. Chem. Soc. 2010,
132, 14251−14260. (d) Liu, Y.; Yu, Y.; Gao, J.; Wang, Z.; Zhang, X.
̈
Angew. Chem., Int. Ed. 2010, 49, 6576−6579. (e) Tuncel, D.; Ozsar,
O.; Tiftika, H. B.; Salih, B. Chem. Commun. 2007, 1369−1371. (f) An,
Q.; Chen, Q.; Zhu, W.; Li, Y.; Tao, C.-a.; Yang, H.; Li, Z.; Wan, L.;
Tian, H.; Li, G. Chem. Commun. 2010, 46, 725−727. (g) Zou, D.;
Andersson, S.; Zhang, R.; Sun, S.; Åkermark, B.; Sun, L. J. Org. Chem.
2008, 73, 3775−3783. (h) Jiang, W.; Wang, Q.; Linder, I.; Klautzsch,
F.; Schalley, C. A. Chem.Eur. J. 2011, 17, 2344−2348. (i) Kolman,
V.; Khan, M. S. A.; Babinsky, M.; Marek, R.; Sindelar, V. Org. Lett.
́
2011, 13, 6148−6151. (j) Choudhury, S. D.; Mohanty, J.; Pal, H.;
Bhasikuttan, A. C. J. Am. Chem. Soc. 2010, 132, 1395−1401.
(k) Nguyen, H. D.; Dang, D. T.; van Dongen, J. L. J.; Brunsveld, L.
Angew. Chem., Int. Ed. 2010, 49, 895−898. (l) Yin, J.; Chi, C.; Wu, J.
Org. Biomol. Chem. 2010, 8, 2594−2599. (m) Sinha, M. K.; Reany, O.;
Yefet, M.; Botoshansky, M.; Keinan, E. Chem.Eur. J. 2012, 18,
5589−5605.
(6) (a) Kim, Y.; Ko, Y. H.; Jung, M.; Selvapalam, N.; Kim, K.
Photochem. Photobiol. Sci. 2011, 10, 1415−1419. (b) Sun, Y.-L.; Yang,
B.-J.; Zhang, S. X.-A.; Yang, Y.-W. Chem.Eur. J. 2012, 18, 9212−
9216.
(7) (a) Moon, K.; Kaifer, A. E. Org. Lett. 2004, 6, 185−188. (b) Liu,
Y.; Li, X.-Y.; Zhang, H.-Y.; Li, C.-J.; Ding, F. J. Org. Chem. 2007, 72,
3640−3645.
(8) (a) Raymo, F. M.; Houk, K. N.; Stoddart, J. F. J. Am. Chem. Soc.
1998, 120, 9318−9322. (b) Iijima, T.; Vignon, S. A.; Tseng, H.-R.;
Jarrosson, T.; Sanders, J. K. M.; Marchioni, F.; Venturi, M.; Apostoli,
E.; Balzani, V.; Stoddart, J. F. Chem.Eur. J. 2004, 10, 6375−6392.
(9) (a) Wyman, I. W.; Macartney, D. H. Org. Biomol. Chem. 2010, 8,
247−252. (b) Zhang, H.; Wang, Q.; Liu, M.; Ma, X.; Tian, H. Org.
Lett. 2009, 11, 3234−3237. (c) Sindelar, V.; Cejas, M. A.; Raymo, F.
M.; Kaifer, A. E. New J. Chem. 2005, 29, 280−282. (d) Ko, Y. H.; Kim,
H.; Kim, Y.; Kim, K. Angew. Chem., Int. Ed. 2008, 47, 4106−4109.
(10) (a) Kandoth, N.; Choudhury, S. D.; Mohanty, J.; Bhasikuttan, A.
C.; Pal, H. J. Phys. Chem. B 2010, 114, 2617−2626. (b) Zhu, L.; Lu,
M.; Tian, H. Tetrahedron 2012, 68, 79−84.
(11) Qu, D.-H.; Ji, F.-Y.; Wang, Q.-C.; Tian, H. Adv. Mater. 2006, 18,
2035−2038.
(12) Zhu, L.; Lu, M.; Qu, D.; Wang, Q.; Tian, H. Org. Biomol. Chem.
2011, 9, 4226−4233.
10175
dx.doi.org/10.1021/jo301807y | J. Org. Chem. 2012, 77, 10168−10175