Isomeric squaraine-based [2]pseudorotaxanes and [2]rotaxanes: Synthesis, optical properties, and their tubular structures in the solid state

Article abstract of DOI:10.1002/chem.201000773

On the basis of formation of [2]pseudorotaxane complexes between triptycene-derived tetralactam macrocycles la and lb and squaraine dyes, construction of squaraine-based [2]rotaxanes through clipping reactions were studied in detail. As a result, when two symmetrical squaraines 2d and 2e were utilized as templates, two pairs of isomeric [2]rotaxanes 3a-b and 4a-b as diastereomers were obtained, owing to the two possible linking modes of triptycene derivatives. It was also found, interestingly, that when a nonsymmetrical dye 2 g was involved, there existed simultaneously three isomers of [2]rotaxanes in one reaction due to the different directions of the guest threading. The ¹H NMR and 2D NOESY NMR spectra were used to distinguish the isomers, and the yield of [2]rotaxane 5 a with the benzyl group in the wider rim of the host la was found to be higher than that of another isomer 5 b with an opposite direction of the guest, which indicated the partial selection of the threading direction. The X-ray structures of 3 b and 4 a showed that, except for the standard hydrogen bonds between the amide protons of the hosts and the carbonyl oxygen atoms of the guests, multiple Ji-Ji stacking and C-H-ji interactions between triptycene subunits and aromatic rings of the guests also participated in the complexation. Crystallographic studies also revealed that the [2]rotaxane molecules 3 b and 4 a further self-assembled into tubular structures in the solid state with the squaraine dyes inside the channels. In the case of 4 a, all the nonsymmetrical macrocyclic molecules pointed in one direction, which suggests the formation of oriented tubular structures. Moreover, it was also found that the squaraines encapsulated in the triptycenederived macrocycles were protected from chemical attack, and subsequently have potential applications in imaging probes and other biomedical areas.

Full text of DOI:10.1002/chem.201000773

FULL PAPER
DOI: 10.1002/chem.201000773
Isomeric Squaraine-Based [2]Pseudorotaxanes and [2]Rotaxanes: Synthesis,
Optical Properties, and Their Tubular Structures in the Solid State
Min Xue,[a, b] Yong-Sheng Su,[a, b] and Chuan-Feng Chen*[a]
Abstract: On the basis of formation of
[2]pseudorotaxane complexes between
triptycene-derived tetralactam macro-
cycles 1a and 1b and squaraine dyes,
construction of squaraine-based [2]ro-
taxanes through clipping reactions
were studied in detail. As a result,
when two symmetrical squaraines 2d
and 2e were utilized as templates, two
pairs of isomeric [2]rotaxanes 3a–b and
4a–b as diastereomers were obtained,
owing to the two possible linking
modes of triptycene derivatives. It was
also found, interestingly, that when a
nonsymmetrical dye 2g was involved,
there existed simultaneously three iso-
mers of [2]rotaxanes in one reaction
due to the different directions of the
NOESY NMR spectra were used to
distinguish the isomers, and the yield
of [2]rotaxane 5a with the benzyl
group in the wider rim of the host 1a
was found to be higher than that of an-
other isomer 5b with an opposite direc-
tion of the guest, which indicated the
partial selection of the threading direc-
tion. The X-ray structures of 3b and 4a
showed that, except for the standard
hydrogen bonds between the amide
protons of the hosts and the carbonyl
oxygen atoms of the guests, multiple
between triptycene subunits and aro-
matic rings of the guests also partici-
pated in the complexation. Crystallo-
graphic studies also revealed that the
[2]rotaxane molecules 3b and 4a fur-
ther self-assembled into tubular struc-
tures in the solid state with the squar-
aine dyes inside the channels. In the
case of 4a, all the nonsymmetrical mac-
rocyclic molecules pointed in one di-
rection, which suggests the formation
of oriented tubular structures. More-
over, it was also found that the squar-
aines encapsulated in the triptycene-
derived macrocycles were protected
from chemical attack, and subsequently
have potential applications in imaging
probes and other biomedical areas.
À
p···p stacking and C H···p interactions
Keywords: rotaxanes · self-assem-
bly · squaraines · triptycenes · tubu-
lar structures
1
guest threading. The H NMR and 2D
Introduction
The insertion of two bulky stoppers at the ends of the axle
yields a [2]rotaxane. When the three-dimensional and non-
symmetrical macrocycle is used as the wheel, an axle with
different terminal groups can insert into the macrocycle
from both rims, thus leading to two isomeric [2]pseudoro-
taxanes or [2]rotaxanes. Early examples of isomeric [2]ro-
taxanes were reported by Kaifer et al. with an a-cyclodex-
trin as a wheel.[3] Later, Tian et al. reported the a-cyclodex-
trin-based unidirectional [2]rotaxanes controlled by the
dethreading rate of the former [2]pseudorotaxnes.[4] Mean-
while, the calix[6]arene platform, as a new type of nonsym-
metrical wheel, was reported by Arduini et al. and a series
of unidirectional calix[6]arene-based [2]pseudorotaxanes or
[2]rotaxanes were constructed with hydrogen-bonding inter-
actions as the control elements.[5] The above examples have
succeeded in the formation of oriented [2]rotaxanes, which
have potential utility in the construction of unidirectional
molecular devices with new properties. However, nonsym-
metrical macrocycles that can be used in this context only
focused on the a-cyclodextrins and calix[6]arene derivatives.
Pseudorotaxanes and rotaxanes, important classes of inter-
locked chemical species, have attracted increasing attention
due to their specific structural features and wide applica-
tions in molecular machines and devices.[1,2] A [2]pseudoro-
taxane can be described as a molecular system in which a
macrocycle (wheel) is threaded by a linear subunit (axle).
[a] M. Xue, Y.-S. Su, Prof. C.-F. Chen
Beijing National Laboratory for Molecular Sciences
CAS Key Laboratory of Molecular Recognition and Function
Institute of Chemistry, Chinese Academy of Sciences
Beijing 100190 (China)
Fax : (+86)10-62554449
E-mail: cchen@iccas.ac.cn
[b] M. Xue, Y.-S. Su
Graduate School, Chinese Academy of Sciences
Beijing 100049 (China)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201000773.
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Until now, less effort has been directed to develop the syn-
thesis of alternative nonsymmetrical macrocycles. Such mol-
ecules present the opportunity for new unidirectional func-
tional [2]rotaxanes. Isomeric phenomena on [2]rotaxanes in-
vestigated previously were caused by the direction of guest
insertion. When the guest is symmetrical, can isomeric [2]ro-
taxanes still be formed by the effect of the host? This is also
an interesting question to explore.
[2]rotaxanes have been obtained from both the linking
modes of triptycene derivatives and the directions of the
guest insertion. Moreover, we also investigated the struc-
tures and photochemical properties of the interlocked mole-
cules and interestingly found that the [2]rotaxanes further
self-assembled into tubular structures in the solid state.
Squaraines are a family of fluorescent near-IR dyes with
specific photophysical properties for wide potential applica-
tions in imaging, nonlinear optics, photovoltaics, and ion
sensing.[6] However, they are susceptible to chemical attack
and aggregation in polar solvents, which limit their applica-
tions.[7] Recent development of squaraine-based rotaxanes
by Smith et al. provides efficient routes to solve both of
these problems.[8] And some of the squaraine rotaxanes can
act as fluorescent imaging probes and chemosensors.[9]
Other examples of squaraine-based complexes came from
the Na+-complexed molecular cages.[10] The rotaxane-encap-
sulation is a new aspect for squaraine dyes and still has
many undiscovered aspects, such as their novel structural
features, interaction modes, and a “secondary” self-assem-
bly.
Results and Discussion
Design of isomeric squaraine-based [2]pseudorotaxanes and
[2]rotaxanes: Our preliminary studies showed that the mac-
rocycles 1a and 1b could encircle the squaraine dye 2b to
form two [2]pseudorotaxane complexes with association
constants of (6.8Æ0.3)ꢁ105 and (1.3Æ0.3)ꢁ106 mÀ1 in
chloroform, respectively.[12] With rigid 3D structures, tripty-
cene derivatives can often form macrocycles with a pair of
diastereomers due to different linking modes during the re-
action process.[13] It is of interest to construct squaraine-
based isomeric [2]pseudorotaxanes and [2]rotaxanes by
using this new route (Scheme 1) and compare their struc-
tures and photochemical properties. To achieve this goal,
Recently, we have been inter-
ested in developing new supra-
molecular systems based on
triptycene with a unique 3D
rigid structure.[11] As a result,
we have synthesized one pair of
novel triptycene-based tetralac-
tam macrocycles 1a and 1b and
found that they formed remark-
ably stable [2]pseudorotaxanes
with the squaraine 2b, which
Scheme 1. Schematic representation of the two possible [2]pseudorotaxane or [2]rotaxane isomers due to dif-
ferent linking modes of the triptycene derivatives.
could subsequently protect the
dye from polar solvents.[12] In
this paper, we describe in detail
the complexation of the macro-
cycles 1a and 1b with different functionalized squaraine de-
rivatives. Consequently, we have designed and synthesized a
series of squaraine-based [2]pseudorotaxanes and [2]ro-
taxanes. In particular, isomeric [2]pseudorotaxanes and
symmetrical squaraines 2a–e with different terminal groups
were designed. We supposed to choose one squaraine with
bulky stopper groups, which could prevent the unthreading
of the squaraine through the triptycene-derived macrocycles
and thus be used as a template to synthesize isomeric [2]ro-
taxanes by a clipping reaction.
It was also known that macrocycle 1a with a boat confor-
mation displayed a nonsymmetrical environment for the
squaraine molecule. We supposed if nonsymmetrical squar-
aine dyes were chosen as templates, isomeric [2]rotaxanes
could be obtained from different directions of insertion of
the squaraine guest (Scheme 2). For this purpose, the new
nonsymmetrical squaraines 2 f and 2g were designed.
Synthesis and structures of the [2]pseudorotaxanes and
[2]rotaxanes: All the symmetrical squaraine derivatives 2a–
e were prepared by reacting two equivalents of the aniline
precursors with squaraine acid by using a straightforward
method.[14] Whereas nonsymmetrical squaraine derivatives
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Isomeric Squaraine-Based [2]Pseudorotaxanes and [2]Rotaxanes
FULL PAPER
and 2e were mixed with host
1a or 1b (1:1) in CDCl3, the
1H NMR spectra did not exhibit
any signals for complexes, even
after being heated at 333 K for
several days. This indicated that
the N,N-bis
ACHTUNGTREN(NUGN n-butyl) and N,N-
bis(benzyl) stopper groups are
AHCTUNGTRENNUNG
large enough to prevent the
squaraines from forming [2]ro-
taxanes with triptycene-derived
macrocycles 1a and 1b through
the slippage method. For the
nonsymmetrical squaraine 2 f,
Scheme 2. Schematic representation of the two possible [2]pseudorotaxane or [2]rotaxane isomers due to dif-
ferent directions of squaraine insertion.
1H NMR spectroscopic studies
1
2 f and 2g were synthesized in two steps by the stable semi-
squaraine intermediates by using standard literature proce-
dures.[15]
showed the formation of complex 1b·2 f. The H NMR spec-
trum of host 1a and guest 2 f (1:1) mixed in CDCl3 displayed
two new sets of resonances, and the intensity of one set was
higher than the other, which suggested that two isomeric
[2]pseudorotaxane complexes based on 1a and 2 f were ob-
tained, and the complexation showed a slight selectivity.
Similar to the cases of squaraines 2d and 2e, it was found
that squaraine 2g with two different bulky stoppers could
not form [2]pseudorotaxane complexes with hosts 1a and
1b at room temperature or at 333 K (Scheme 3).
From the formation of two [2]pseudorotaxane complexes
1a·2b and 1b·2b, it is easy to conclude that squaraine 2a
with smaller terminal groups than those of 2b can also
thread the wheels 1a and 1b to yield [2]pseudorotaxane
complexes 1a·2a and 1b·2a. In the case of 2c, as shown in
Figure S17 in the Supporting Information, the 1H NMR
spectrum of host 1b and guest 2c (1:1) mixed in CDCl3 dis-
played only one set of well-defined resonances differing
greatly from those for the free host and guest, which indicat-
ed that squaraine 2c could also penetrate through the mac-
According to the above results, squaraines 2d, 2e, and 2g
with bulky stopper groups were chosen as the templates to
synthesize [2]rotaxanes through clipping reactions. Thus,
squaraine-based [2]rotaxanes 3–5 were subsequently ob-
tained by condensing pyridine-2,6-dicarbonyl dichloride and
2,7-diaminotriptycene in the presence of an appropriate
squaraine derivative in total yields of 31–37% after purifica-
tion by silica-gel column chromatography (Scheme 4).[17]
When 2d was used as the template, two different products
3a and 3b formed and showed the same peak at m/z: 1318.9
for M+ and similar polarity, which suggested that they were
a pair of diastereomers. Meanwhile, compounds 4a and 4b
could also be obtained as isomers similar to the case of 3a
and 3b. However, when the nonsymmetrical squaraine 2g
was used as a template, there existed three products with
the same peak at m/z: 1386.8 for M+ and with similar polar-
ity, which meant three isomers were yielded during the for-
mation of [2]rotaxanes 5.
rocycle 1b to form
a [2]pseudorotaxane-type complex
1
1b·2c. However, the H NMR spectrum of a mixture of the
host 1a and guest 2c (1:1) in CDCl3 only exhibited signals
for free 1a and 2c,[16] which suggested no insertion process
at room temperature. When we tried to heat the mixture of
1a and 2c in CDCl3 at 333 K for more than one day, the
1H NMR spectra showed that with the signals for free 1a
and 2c being weak, new signals appeared and gradually in-
creased with time, which became predominant after six days
(Figure 1). These observations suggested that [2]rotaxane
1a·2c was obtained through slippage. When squaraines 2d
Structures of these isomeric [2]rotaxanes were first con-
1
firmed by H NMR spectroscopy. As shown in Table 1 and
associated atom labelling in the structures of 2a–f, the
Table 1. Changes in chemical shift (Dd [ppm]) for [2]rotaxanes 3–5.
a
b
c
A
B
C
A’
B’
C’
3a À0.50 À0.70 1.77
0.88
0.69
0.28 À1.04 À0.63 À0.24
3b À0.41 À0.46 1.95 À0.83 À0.37 À0.02
4a À0.35 À1.11 1.54
0.80
0.55
0.28 À1.04 À0.68 À0.26
4b À0.29 À0.37 1.76 À0.92 À0.43
0.14
5a À0.36 À1.11 1.58 À1.08 À0.66 À0.26
5b À1.14 À0.29 1.63 0.84 0.61 0.29 À0.9 À0.65 À0.25
5c À0.68, À0.21 1.92, À0.97 À0.50 À0.02 À0.81 À0.52 À0.05
À0.64 1.93
0.90
0.63
0.27
Figure 1. Time-dependent 1H NMR spectra of 1a·2c in CDCl3 at
298 K (a), at 333 K after 1 d (b), at 333 K after 2 d (c), at 333 K after
4 d (d), at 333 K after 6 d (e). [1a]=[2c]=3.0 mm. Associated protons
are labelled in structures 2a–f.
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C.-F. Chen et al.
Scheme 3. Interaction modes between macrocycles 1a–b and squaraines 2a–e.
1H NMR spectra of 3–5 all showed striking downfield shifts
(Dd=1.54–1.95 ppm) for Hc and upfield shifts (Dd=À0.21–
À1.14 ppm) for Ha and Hb, which were well consistent with
those of the [2]pseudorotaxanes, and thus indicated the for-
mation of the [2]rotaxane-type complexes. For [2]rotaxanes
3 and 4, protons HA(A’), HB(B’), and HC(C’) in 3a and 4a dis-
played two sets of signals with one set upfield-shifted and
the other downfield-shifted, which possibly resulted from
the nonsymmetrical environment provided by the macrocy-
cle. Protons HA(A’), HB(B’), and HC(C’) in compounds 3b and
4b displayed only one set of signals that shifted upfield,
which suggested a symmetrical environment. Compared to
the cis macrocycle 1a with the trans isomer 1b, it was found
that 1a was a three-dimensional nonsymmetrical macrocycle
with a boat conformation, which might induce the nonsym-
metrical environment for the squaraines.[18] Thus, [2]ro-
Scheme 4. Synthetic routes for [2]rotaxanes 3–5.
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Isomeric Squaraine-Based [2]Pseudorotaxanes and [2]Rotaxanes
FULL PAPER
taxanes 3a and 4a were confirmed as the cis isomers, where-
as [2]rotaxanes 3b and 4b were the trans isomers. In the
case of [2]rotaxanes 5, the H NMR spectra of the three iso-
the standard hydrogen bonds, the triptycene subunits also
form multiple edge-to-face p···p stacking interactions in 3b
1
À
and C H···p interactions in 4a with the aromatic rings of
mers all became complicated because of the nonsymmetrical
squaraine 2g. It was found that both signals of HA–C and
HA’–C’ in [2]rotaxane 5c shifted upfield, whereas in [2]ro-
taxanes 5a and 5b, the signals of HA–C displayed opposite
shifts relative to those of HA’–C’, which suggested that 5c was
the trans isomer and both 5a and 5b were cis isomers. The
different shielding or deshielding effect on HA–C and HA’–C’
between 5a and 5b indicated the different directions of
squaraine 2g. 2D NOESY NMR spectroscopic studies pro-
vided the most diagnostic evidence for estimating the direc-
tion. An NOE signal of 5b corresponding to the contacts
between HC of 2g and Hd of 1a was detected, which suggest-
ed the position of the narrower rim for the benzyl stopper
group in 5b.[19] In contrast, 5a is the isomer with the benzyl
group in the wider rim of host 1a and the nbutyl group in
the narrower rim. From the synthetic conclusion it was
known that the yield of 5a (16%) was higher than that of
5b (9%). This meant that the benzyl stopper group, which
is larger and more rigid than the nbutyl stopper group, pref-
erentially located in the wider rim of macrocycle 1a. Thus,
partially oriented squaraine-based [2]rotaxanes were
formed. Besides the two cis isomers 5a and 5b, the trans
isomer 5c also had a distinct characteristic different from
other trans isomers 3b and 4b, which was the partition of
two sets of signals for bridging CH proton Ha and NH
proton Hc due to the nonsymmetrical environment induced
by squaraine 2g with different stopper groups.
squaraines. The key crystallographic distances show that
both of the cavities of 1a and 1b became slightly larger
after encapsulation of squaraine molecules than those of
free macrocycles. Meanwhile, the shape of squaraine dyes
also changed after being inserted into the cages, especially
for 2e in the cis [2]rotaxane 4a, which became obviously
curved and bent (Figure 2c and d). This phenomenon might
À
result from the C H···p interactions between the terminal
benzyl stopper groups and the triptycene subunits. Relative
to 2e in [2]rotaxane 4a, squaraine 2d in [2]rotaxane 3b kept
its planar structure after threading the trans macrocycle 1b
(Figure 2a and b).
Optical properties of [2]rotaxanes: The absorption and
emission properties of the [2]rotaxanes 3–5 and the relevant
free squaraines were measured in CHCl3. A direct compari-
son of [2]rotaxanes and the appropriate free squaraines re-
vealed a redshift in both absorption (11–15 nm) and fluores-
cence emission (8–11 nm) (Table 2). The fluorescence quan-
Table 2. Photophysical properties for [2]rotaxanes 3–5 and the relevant
free squaraines in CHCl3.[a]
[b]
Compound
labs [nm]
Log e
lem [nm]
Ff
2d
2e
2g
3a
3b
4a
4b
5a
5b
5c
640
630
634
653
653
643
642
649
645
647
5.58
5.53
5.55
5.46
5.49
5.45
5.54
5.49
5.44
5.49
664
654
659
673
675
665
665
670
667
669
0.73
0.70
0.71
0.49
0.51
0.27
0.34
0.47
0.37
0.55
The X-ray crystal structures of [2]rotaxanes 3b and 4a are
illustrated in Figure 2.[20] In both cases, the hydrogen-bond-
ing interactions (dH···O =2.22 ꢂ, qNÀH···O =144.078 for 3b, and
dH···O =2.19 ꢂ, qNÀH···O =150.348 for 4a) between the amide
protons of hosts and the carbonyl oxygen atoms of guests
exist and they are a little stronger than the corresponding
hydrogen bonds in [2]pseudorotaxane 1b·2b.[12] Along with
[a] Solutions were excited at 580 nm and emission monitored in the
region 590–750 nm for estimating Ff. [b] Fluorescence quantum yields
were determined by using 4,4-[bis-(N,N-dimethylamino)phenyl] squaraine
dye as the standard (Ff =0.7 in CHCl3); error limit Æ5%.
tum yields for the [2]rotaxanes were all decreased relative
to those of free guests, but the trans isomeric [2]rotaxanes
3b, 4b, and 5c showed higher quantum yields than those of
cis isomers 3a, 4a, 5a, and 5b. We further investigated the
chemical stabilities of these compounds by treating both the
[2]rotaxanes and their corresponding squaraines with a large
excess of l-cysteine in THF/H2O 3:1 solutions. The subse-
quent time-dependent changes in absorption and emission
for [2]rotaxanes 5 and squaraine 2g are shown in Figure 3
and indicate that macrocycles 1a and 1b both provide steric
shells for 2g to prevent the attack by the nucleophilic spe-
cies. It was also found that the trans isomers had better effi-
ciency than the cis isomers, partially because of the location
of the macrocycle 1b on both sides of the cyclobutene core
of squaraine derivatives. [2]Rotaxanes 4a and 4b showed
relatively weak ability for protection of 2e, possibly due to
Figure 2. Crystal structures: a) Top view and b) side view of 3b. c) Top
view and d) side view of 4a. Hydrogen atoms are omitted for clarity.
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C.-F. Chen et al.
Figure 4. Packing of 3b: Representation of the tubular structure and the
noncovalent interactions (a) between a) squaraines of different [2]ro-
taxane molecules (toluene molecules are omitted) and b) macrocycle
host and toluene solvent (squaraine molecules are omitted). Hydrogen
atoms not involved in the interactions are omitted for clarity.
Figure 3. Changes in emission (top) and absorption (bottom) upon addi-
tion of l-cysteine (10 mm) to 1ꢁ10À5 m solutions of 2g and 5a–c in THF/
H2O 3:1 at 298 K.
the bulky stopper groups of squaraine that changed the
shape of 2e in the macrocycles (see the Supporting Informa-
tion).
Tubular-assembled structures of [2]rotaxanes in the solid
state: Interestingly, the structural studies on squaraine-based
[2]rotaxanes 3b and 4a in the solid state revealed tubular
assemblies consisting of molecules stacked above one anoth-
er. In each case, the pore size of the porous column was de-
fined by the cavity size of the wheel-like macrocycles, and
squaraine molecules were encapsulated in the channels. Two
intermolecular interactions dominated the assembly of 3b,
which were the offset p···p stacking interactions between
squaraine 2d of one [2]rotaxane molecule and the adjacent
2d of another 3b molecule with an interfacial distance of
À
Figure 5. Packing of 4a: Representation of a) the noncovalent interac-
tions (a) between macrocycle hosts and squaraines of different [2]ro-
taxane molecules and b) the oriented nonsymmetrical channel-like struc-
ture of 4a. Hydrogen atoms not involved in the interactions are omitted
for clarity.
3.44 ꢂ (Figure 4a), and two C H···p interactions (dCÀH···p
=
2.75, 2.76 ꢂ) between the macrocycle 1b of [2]rotaxane and
toluene solvent molecules (Figure 4b). In the case of 4a, the
interactions that kept the [2]rotaxane molecules together in-
À
that with the squaraine guests inside the macrocycles, in ad-
dition to the solvent interactions, macrocycles 1a and 1b in
these [2]rotaxanes formed honeycombed suprastructures,
which could not be seen in the free macrocycles (see the
Supporting Information).
cluded C H···O hydrogen bonds (dH···O =2.43 ꢂ, qCÀH···O
=
À
172.688) and C H···p interactions (dCÀH···p =2.80, 2.84 ꢂ) be-
tween squaraine 2e of one [2]rotaxane molecule and macro-
cycle 1a of another [2]rotaxane molecule (Figure 5a). More-
over, [2]rotaxane 4a with nonsymmetrical macrocycles self-
assembled together in an oriented arrangement (Figure 5b).
Thus, an oriented nonsymmetrical channel-like structure
was constructed in the solid state.[21] It was further found
Conclusion
In summary, a series of [2]pseudorotaxanes and [2]rotaxanes
based on the triptycene-derived macrocycles 1a–b and
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Isomeric Squaraine-Based [2]Pseudorotaxanes and [2]Rotaxanes
FULL PAPER
154.1, 154.3, 183.3, 187.2, 190.4 ppm; MALDI-TOF MS: m/z: 556.5 [M]+;
elemental analysis calcd (%) for C38H40N2O2: C 81.98, H 7.24, N 5.03;
found: C 81.77, H 7.35, N 5.24.
squaraines 2a–g were constructed. As expected, we found
that a new type of three-dimensional and nonsymmetrical
macrocycle 1a could form isomeric [2]rotaxanes due to the
direction of the guest insertion with partial selection. Mean-
while, the different linking modes of triptycene derivatives
also provided a new route to form isomeric [2]rotaxanes
through the templated synthetic process. Consequently, in
the case of [2]rotaxanes 5, three isomers were simultaneous-
ly obtained from one reaction. Structural features and pho-
tophysical properties of these inclusion complexes were in-
vestigated, and it was found that the chemical stabilities of
[2]rotaxanes 3–5 were increased relative to free squaraines.
Moreover, we also found that the [2]rotaxanes 3b and 4a
could self-assemble into a secondary arrangement of extend-
ed channels through multiple noncovalent interactions in
the solid state, in which the squaraine molecules were inside
as an axle. Especially for nonsymmetrical [2]rotaxane 4a, an
oriented channel-like suprastructure was formed. We believe
that the method for construction of multiple isomeric [2]ro-
taxanes presented here can open unprecedented perspec-
tives in the field of rotaxanes. Studies on the construction of
unidirectional squaraine-based [2]rotaxanes based on this
approach are underway in our laboratory.
General procedure to synthesize [2]rotaxanes 3–5: A solution of pyri-
dine-2,6-dicarbonyl dichloride (0.2 mmol) in dry CH2Cl2 (10 mL) and a
solution of 2,7-diaminotriptycene (0.2 mmol) in dry CH2Cl2 (10 mL) were
added dropwise, respectively, into a solution of the relevant squaraine
(0.1 mmol) and Et3N (0.6 mmol) in dry CH2Cl2 (100 mL) at 08C over a
period of 2.5 h under an argon atmosphere. The mixture was stirred until
it gradually warmed up to room temperature and was then stirred for
24 h. The solution was concentrated in vacuo and then the mixture was
purified by column chromatography over silica gel (200–300 mesh) to
afford the squaraine [2]rotaxanes 3–5.
1
Product 3a: Yield: 17%; m.p. >3008C; H NMR (300 MHz, CDCl3): d=
0.91 (t, J=7.2 Hz, 6H), 1.05 (t, J=7.2 Hz, 6H), 1.22–1.30 (m, 4H), 1.39–
1.46 (m, 4H), 1.48–1.56 (m, 4H), 1.85–1.95 (m, 4H), 3.19 (t, J=7.2 Hz,
4H), 3.71 (t, J=7.5 Hz, 4H), 4.46 (s, 2H), 5.26 (s, 2H), 6.13 (d, J=9 Hz,
2H), 6.86–6.91 (m, 4H), 6.96–7.01 (m, 2H), 7.20 (d, J=8 Hz, 4H), 7.33–
7.35 (m, 4H), 7.39 (d, J=1 Hz, 4H), 7.45 (d, J=9.0 Hz, 2H), 7.69 (dd,
J=8, 1 Hz, 4H), 8.12 (t, J=7.8 Hz, 2H), 8.54 (d, J=7.8 Hz, 4H), 9.26 (d,
J=9 Hz, 2H), 11.19 ppm (s, 4H); 13C NMR (75 MHz, CDCl3): d=13.8,
13.9, 20.1, 20.4, 29.5, 29.7, 51.4, 51.7, 52.8, 53.1, 112.7, 113.8, 117.9, 118.9,
123.28, 123.32, 123.5, 124.8, 125.3, 125.4, 132.7, 133.3, 134.5, 138.8, 141.6,
144.0, 144.7, 145.7, 149.8, 153.1, 162.1, 185.6 ppm; MALDI TOF-MS:
m/z: 1318.9 [M]+; elemental analysis calcd (%) for C86H78N8O6·0.5H2O:
C 77.75, H 5.99, N 8.43; found: C 77.57, H 6.13, N 8.20.
1
Product 3b: Yield: 15%; m.p. >3008C; H NMR (300 MHz, CDCl3): d=
1.10 (t, J=6.3 Hz, 12H), 1.43–1.48 (m, 8H), 1.63–1.74 (m, 8H), 3.41 (br,
8H), 4.85 (s, 2H), 5.10 (s, 2H), 6.39 (d, J=6.2 Hz, 4H), 6.80–6.93 (m,
8H), 7.06–7.11 (m, 6H), 7.23–7.25 (m, 2H), 7.55 (d, J=7.3 Hz, 4H), 7.64
(d, J=6.2 Hz, 4H), 8.12 (t, J=7.7 Hz, 2H), 8.50 (d, J=7.7 Hz, 4H),
11.26 ppm (s, 4H); 13C NMR (75 MHz, CDCl3): d=14.1, 20.3, 29.6, 52.10,
52.13, 52.71, 53.71, 113.4, 118.2, 119.2, 119.9, 122.8, 123.3, 123.5, 125.0,
125.3, 132.3, 134.2, 139.1, 141.7, 144.1, 144.5, 145.3, 149.4, 162.0,
185.3 ppm; MALDI TOF-MS: m/z: 1318.9 [M]+, 1341.9 [M+Na]+,
1358.0 [M+K]+; elemental analysis calcd (%) for C86H78N8O6: C 78.28, H
5.96, N 8.49; found: C 78.07, H 6.13, N 8.32.
Product 4a: Yield: 18%; m.p. 282–2838C; 1H NMR (600 MHz, CDCl3):
d=4.45 (s, 2H), 4.54 (s, 4H), 5.08 (s, 4H), 5.26 (s, 2H), 6.23 (d, J=9 Hz,
2H), 6.96–7.00 (m, 8H), 7.03 (t, J=7.1 Hz, 2H), 7.16 (d, J=8 Hz, 4H),
7.29 (d, J=1 Hz, 4H), 7.30–7.35 (m, 8H), 7.37 (d, J=7.3 Hz, 2H), 7.40–
7.43 (m, 10H), 7.46 (d, J=9 Hz, 2H), 7.58 (dd, J=8, 1 Hz, 4H), 8.06 (t,
J=7.7 Hz, 2H), 8.47 (d, J=7.7 Hz, 4H), 9.24 (d, J=8.8 Hz, 2H),
11.07 ppm (s, 4H); 13C NMR (75 MHz, CDCl3): d=52.8, 53.3, 53.9, 54.7,
112.9, 114.6, 117.9, 119.1, 119.2, 120.3, 123.3, 123.6, 124.9, 125.3, 125.5,
126.2, 126.4, 128.0, 128.20, 128.24, 129.05, 129.13, 129.4, 132.9, 133.8,
134.3, 135.1, 135.7, 138.8, 141.6, 143.9, 144.7, 145.6, 149.6, 154.9, 155.7,
162.0, 181.1, 185.2, 187.2 ppm; MALDI TOF-MS: m/z: 1454.8 [M]+,
1477.9 [M+Na]+, 1493.9 [M+K]+; elemental analysis calcd (%) for
C98H70N8O6·H2O: C 79.87, H 4.92, N 7.60; found: C 79.82, H 4.93, N 7.70.
Experimental Section
General: Melting points, taken on an electrothermal melting point appa-
ratus, are uncorrected. The 1H NMR and 13C NMR spectra were mea-
sured on a Bruker DMX300 NMR spectrometer. 2D COSY and NOESY
experiments were measured on a Bruker DMX600 NMR spectrometer.
MALDI-TOF MS were obtained on a Bruker BIFLEXIII mass spec-
trometer. Elemental analyses were performed by the Analytical Labora-
tory of the Institute of Chemistry, CAS.
General procedure to synthesize squaraines 2a–e: The appropriate bis-
ACHTUNGTRENNUNGaniline derivatives (0.7 mmol) and triethyl orthoformate (2 mL) were
added to a solution of squaric acid (0.35 mmol) in 2-propanol (50 mL)
and the mixture was refluxed overnight. The reaction mixture was cooled
and filtered and the pure product was obtained by washing the solid with
methanol.
Procedure to synthesize squaraines 2 f and 2g: Reaction of the appropri-
ate dialkyl aniline derivatives and the squaryl chloride provided the semi-
squaraine intermediates according to the literature conditions.[15] The
N,N-bisbenzylaniline (0.35 mmol), the appropriate semisquaraine inter-
mediate (0.35 mmol), and triethyl orthoformate (2 mL) were added to a
100 mL flask containing 2-propanol (50 mL). The reaction mixture was
then refluxed for 20 h. The hot reaction mixture was filtered and the
solid was washed with 2-propanol. Column chromatography (chloroform/
EtOAc 15:1) of the crude product over silica gel (100–200 mesh) gave
the pure products 2 f and 2g.
Product 2 f: Yield: 34%; m.p. 2238C; 1H NMR (300 MHz, CDCl3): d=
3.24 (s, 6H), 4.80 (s, 4H), 6.83 (d, J=9 Hz, 2H), 6.91 (d, J=9 Hz, 2H),
7.19–7.22 (m, 4H), 7.31–7.40 (m, 6H), 8.43 (d, J=9 Hz, 2H), 8.48 ppm
(d, J=9 Hz, 2H); MALDI-TOF MS: m/z: 472.3 [M]+; elemental analysis
calcd (%) for C32H28N2O2: C 81.33, H 5.97, N 5.93; found: C 81.15, H
6.06, N 5.99.
Product 4b: Yield: 14%; m.p. >3008C; 1H NMR (300 MHz,
[D6]DMSO): d=4.94 (s, 10H), 5.22 (s, 2H), 6.23 (d, J=9.2 Hz, 2H),
6.96–7.00 (m, 8H), 7.03 (t, J=7.1 Hz, 2H), 7.16 (d, J=8 Hz, 4H), 7.29 (d,
J=1 Hz, 4H), 7.30–7.35 (m, 8H), 7.37 (d, J=7.3 Hz, 2H), 7.40–7.43 (m,
10H), 7.46 (d, J=8.8 Hz, 2H), 7.58 (dd, J=8, 1 Hz, 4H), 8.06 (t, J=
7.7 Hz, 2H), 8.47 (d, J=7.7 Hz, 4H), 9.24 (d, J=8.8 Hz, 2H), 11.07 ppm
(s, 4H); MALDI TOF-MS: m/z: 1454.8 [M]+, 1477.9 [M+Na]+; elemen-
tal analysis calcd (%) for C98H70N8O6·0.8H2O: C 80.07, H 4.91, N 7.62;
found: C 80.02, H 5.13, N 7.54.
1
Product 5a: Yield: 16%; m.p. >2928C; H NMR (600 MHz, CDCl3): d=
1.05 (t, J=7.3 Hz, 6H), 1.49–1.55 (m, 4H), 1.87–1.92 (m, 4H), 3.72 (t, J=
7.8 Hz, 4H), 4.45 (s, 2H), 4.53 (s, 4H), 5.25 (s, 2H), 6.21 (d, J=9.3 Hz,
2H), 6.87–6.92 (m, 4H), 6.97–7.00 (m, 6H), 7.15 (d, J=8 Hz, 4H), 7.31
(d, J=9 Hz, 2H), 7.31–7.36 (m, 12H), 7.37 (d, J=9.3 Hz, 2H), 7.57 (dd,
J=8, 2 Hz, 4H), 8.07 (t, J=7.7 Hz, 2H), 8.49 (d, J=7.7 Hz, 4H), 9.25 (d,
J=9 Hz, 2H), 11.11 ppm (s, 4H); 13C NMR (75 MHz, CDCl3): d=13.9,
20.4, 29.71, 29.74, 51.7, 52.8, 53.1, 53.8, 112.6, 113.9, 118.0, 119.1, 119.3,
123.3, 123.6, 124.7, 125.3, 125.4, 126.2, 127.9, 129.1, 133.1, 133.5, 134.3,
Product 2g: Yield: 27%; m.p. 2048C; 1H NMR (300 MHz, CDCl3): d=
0.98 (t, J=7.3 Hz, 6H), 1.33–1.46 (m, 4H), 1.59–1.69 (m, 4H), 3.44 (t, J=
7.6 Hz, 4H), 4.78 (s, 4H), 6.71 (d, J=9 Hz, 2H), 6.86 (d, J=9 Hz, 2H),
7.20–7.22 (m, 4H), 7.26–7.38 (m, 6H), 8.34 (d, J=9 Hz, 2H), 8.38 ppm
(d, J=9 Hz, 2H); 13C NMR: (75 MHz, CDCl3): d=13.9, 20.2, 29.6, 51.3,
54.0, 112.5, 112.9, 119.5, 120.9, 126.5, 127.7, 129.0, 132.8, 133.9, 136.2,
Chem. Eur. J. 2010, 16, 8537 – 8544
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8543

C.-F. Chen et al.
135.4, 138.8, 141.6, 143.9, 144.7, 145.6, 149.6, 153.9, 154.9, 162.0, 182.0,
185.3, 185.4 ppm; MALDI TOF-MS: m/z: 1386.9 [M]+, 1409.9 [M+Na]+,
1426.0 [M+K]+; elemental analysis calcd (%) for C92H74N8O6·H2O: C
78.61, H 5.45, N 7.97; found: C 78.56, H 5.33, N 7.77.
281; d) A. Arduini, R. Bussolati, A. Credi, A. Pochini, A. Secchi, S.
Silvi, M. Venturi, Tetrahedron 2008, 64, 8279–8286; e) A. Arduini,
R. Bussolati, A. Credi, G. Faimani, S. Garaudꢃe, A. Pochini, A.
Secchi, M. Semeraro, S. Silvi, M. Venturi, Chem. Eur. J. 2009, 15,
3230–3242.
Product 5b: Yield: 9%; m.p. >3008C; 1H NMR (600 MHz, CDCl3): d=
0.96 (t, J=7.4 Hz, 6H), 1.41–1.47 (m, 4H), 1.70–1.74 (m, 4H), 3.20 (t, J=
7.8 Hz, 4H), 4.47 (s, 2H), 5.08 (s, 4H), 5.27 (s, 2H), 6.09 (d, J=9 Hz,
2H), 6.97–7.00 (m, 4H), 7.20 (d, J=8.0 Hz, 4H), 7.36–7.37 (m, 4H),
7.40–7.42 (m, 6H), 7.45 (d, J=9 Hz, 2H), 7.48 (d, J=9 Hz, 2H), 7.52–
7.53 (m, 4H), 7.69 (dd, J=8.0, 1.8 Hz, 4H), 7.71–7.72 (m, 4H), 8.10 (t,
J=7.7 Hz, 2H), 8.51 (d, J=7.7 Hz, 4H), 9.23 (d, J=9 Hz, 2H),
11.16 ppm (s, 4H); 13C NMR (75 MHz, CDCl3): d=13.0, 21.6, 28.2, 50.3,
51.7, 53.5, 55.7, 113.2, 116.6, 117.7, 122.2, 123.74, 123.77, 124.1, 124.4,
125.3, 126.9, 127.7, 128.2, 129.8, 131.2, 132.76, 132.80, 133.0, 133.3, 134.1,
134.9, 137.7, 140.4, 142.8, 143.6, 144.6, 148.6, 160.9, 166.6, 183.1,
184.4 ppm; MALDI TOF-MS: m/z: 1386.8 [M]+, 1409.8 [M+Na]+,
1425.8 [M+K]+; elemental analysis calcd (%) for C92H74N8O6·1.5H2O: C
78.11, H 5.49, N 7.92; found: C 77.97, H 5.28, N 7.88.
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1
Product 5c: Yield: 12%; m.p. >3008C; H NMR (600 MHz, CDCl3): d=
1.09 (t, J=7.4 Hz, 6H), 1.44–1.50 (m, 4H), 1.65–1.70 (m, 4H), 3.40 (t, J=
7.6 Hz, 4H), 4.77 (s, 4H), 4.83 (s, 1H), 4.87 (s, 1H), 5.10 (s, 2H), 6.22 (d,
J=9 Hz, 2H), 6.37 (d, J=9 Hz, 2H), 6.82–6.86 (m, 4H), 6.87 (d, J=2 Hz,
2H), 6.89 (d, J=8 Hz, 2H), 6.91 (d, J=8.0 Hz, 2H), 7.06 (d, J=7.3 Hz,
2H), 7.08 (d, J=8 Hz, 2H), 7.24–7.26 (m, 4H), 7.30 (d, J=7.4 Hz, 2H),
7.40–7.44 (m, 4H), 7.46 (dd, J=8, 2 Hz, 2H), 7.51–7.54 (m, 6H), 7.62
(dd, J=8, 2 Hz, 2H), 8.10 (t, J=7.7 Hz, 2H), 8.46 (d, J=7.7 Hz, 2H),
8.47 (d, J=7.7 Hz, 2H), 11.23 (s, 2H), 11.24 ppm (s, 2H); 13C NMR
(75 MHz, CDCl3): d=14.1, 20.3, 30.0, 51.5, 52.1, 52.8, 53.7, 54.5, 112.4,
112.5, 119.18, 119.23, 119.78, 119.81, 120.1, 122.7, 123.0, 123.2, 123.3,
123.4, 124.9, 125.3, 126.4, 126.5, 127.98, 128.01, 129.2, 132.0, 132.9, 134.0,
134.2, 136.5, 139.1, 141.6, 141.7, 144.1, 145.2, 145.3, 149.5, 153.3, 161.9,
162.0, 185.2 ppm; MALDI TOF-MS: m/z: 1386.8 [M]+, 1409.9 [M+Na]+,
1425.9 [M+K]+; elemental analysis calcd (%) for C92H74N8O6·H2O: C
78.61, H 5.45, N 7.97; found: C 78.42, H 5.19, N 8.11.
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Acknowledgements
We thank the National Natural Science Foundation of China (20625206,
20972162), the Chinese Academy of Sciences, and the National Basic Re-
search Program (2007CB808004, 2009ZX09501-018) for financial support.
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[16] In this case, signals of macrocycle 1a displayed little shift, possibly
due to the weak interactions between the macrocyclic host and the
adjacent squaraine molecule 2c outside the macrocycle.
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[17] The yield of each isomer for [2]rotaxanes 3–5 is shown in Scheme 4.
[18] The nonsymmetrical environment induced by macrocycle 1a also
1
appeared in complex 1a·2b as judged by the H NMR spectrum (see
reference [12]).
[19] See the Figure S24 in the Supporting Information.
[20] CCDC-770092 (3b) and 770093 (4a) contain the supplementary
crystallographic data for this paper. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
[21] An example for an oriented channel-like structure: A. Arduini, A.
Credi, G. Faimani, C. Massera, A. Pochini, A. Secchi, M. Semeraro,
S. Silvi, F. Ugozzoli, Chem. Eur. J. 2008, 14, 98–106.
Received: March 27, 2010
Published online: June 10, 2010
8544
www.chemeurj.org
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 8537 – 8544