Stable pillar[5]arene-based pseudo[1]rotaxanes formed in polar solution

Article abstract of DOI:10.1016/j.cclet.2016.05.004

Mono-alkyl-functionalized pillar[5]arenes P1, P2, and P3 were synthesized by click reaction, which exhibited different self-assembly behavior in polar solvent DMSO. Stable pseudo[1]rotaxane was formed by the self-complexation from P1 or P2, whereas, concentration-dependent pseudorotaxane structures were generated by P3 which bearing more flexible side chain. Interestingly, the obtained pseudo[1]rotaxanes exhibited a dynamic fast assembly process upon adding NaBF₄, resulting in the formation of Na⁺-induced pseudorotaxanes.

Full text of DOI:10.1016/j.cclet.2016.05.004

Accepted Manuscript
Title: Stable pillar[5]arene-based pseudo[1]rotaxanes formed
in polar solution
Author: Xuan Wu Lei Gao Jun-Zhao Sun Xiao-Yu Hu
Le-Yong Wang
PII:
S1001-8417(16)30111-5
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.cclet.2016.05.004
CCLET 3689
To appear in:
Chinese Chemical Letters
Received date:
Revised date:
Accepted date:
23-2-2016
18-4-2016
28-4-2016
Please cite this article as: X. Wu, L. Gao, J.-Z. Sun, X.-Y. Hu, L.-Y. Wang, Stable
pillar[5]arene-based pseudo[1]rotaxanes formed in polar solution, Chinese Chemical
Letters (2016), http://dx.doi.org/10.1016/j.cclet.2016.05.004
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Graphical Abstract
Stable pillar[5]arene-based pseudo[1]rotaxanes formed in polar solution
Xuan Wu, Lei Gao, Jun-Zhao Sun, Xiao-Yu Hu*, Le-Yong Wang
Key Laboratory of Mesoscopic Chemistry of MOE and Collaborative Innovation Center of Chemistry for Life Sciences, School
of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China
Mono-alkyl-functionalized pillar[5]arenes P1, P2, and P3 were synthesized by click reaction, which exhibited different self-assembly behavior
in polar solvent DMSO. Stable pseudo[1]totaxane was formed by the self-complexation from P1 or P2, whereas, concentration-dependent
pseudorotaxane structures were generated by P3. Moreover, the obtained pseudo[1]rotaxanes exhibited a dynamic fast assembly process upon
+
adding NaBF , resulting in the formation of Na -induced pseudorotaxanes.
4
Page 1 of 10

Stable pillar[5]arene-based pseudo[1]rotaxanes formed in polar solution
∗
Xuan Wu, Lei Gao, Jun-Zhao Sun, Xiao-Yu Hu , Le-Yong Wang
Key Laboratory of Mesoscopic Chemistry of MOE and Collaborative Innovation Center of Chemistry for Life Sciences, School of Chemistry and Chemical
Engineering, Nanjing University, Nanjing 210023, China
ARTICLE INFO
ABSTRACT
Article history:
Mono-alkyl-functionalized pillar[5]arenes P1, P2, and P3 were synthesized by click reaction,
which exhibited different self-assembly behavior in polar solvent DMSO. Stable
pseudo[1]totaxane was formed by the self-complexation from P1 or P2, whereas, concentration-
dependent pseudorotaxane structures were generated by P3 which bearing more flexible side
Received 23 February 2016
Received in revised form 18 April 2016
Accepted 28 April 2016
Available online
chain. Interestingly, the obtained pseudo[1]rotaxanes exhibited a dynamic fast assembly process
+
upon adding NaBF
4
, resulting in the formation of Na -induced pseudorotaxanes.
Keywords:
Pillar[5]arene
Pseudo[1]rotaxanes
Dynamic self-assembly
+
Na -induced pseudorotaxanes
Polar solution
1
. Introduction
Mechanically interlocked molecules (MIMs) have attracted tremendous attention due to their beautiful architectures, topological
importance, and potential applications in constructing switches [1, 2], logic gates [3], sensors [4-7], drug delivery systems [8], artificial
molecular machines [9-12], and surface materials [13, 14]. Among the various types of MIMs, pseudo[1]rotaxane [15] has been a
research hotspot for its unique structure, where the wheel is threaded by its own axle, playing an important role in the MIM family. As
the fundamental building blocks in fabricating complicated structures, so far many researches have been conducted to explore their
dynamic behaviors or potential applications [16, 17].
Due to the dynamic nature of pseudo[1]rotaxane, the external environment plays an essential role in the stability of this inclusion
structure, for example, the polarity of the solvent [18], temperature [19], and other external stimuli [20-22], which greatly affect the
binding affinity of the cyclic host molecules with the threaded guest molecules. As we know, solvent with strong polarity, such as
DMSO, usually destroys the host−guest interaction, thus prohibiting the formation of pseudo[1]roataxane structure. Up to now, various
types of pseudo[1]rotaxanes have been reported in non-polar or weak polar solvents, especially in the pillar[n]arene family, where the
polarity of the solvents greatly affected the pillararene-based host−guest interaction and played a vital role in the formation of
pseudo[1]totaxanes [23-29]. Although some reported pillar[n]arene-based pseudo[1]rotaxanes could partially exist in the mixed
solution of non-polar solvent with partial DMSO [25, 29], the self-inclusion structures would be totally destroyed in DMSO solution.
Therefore, the construction of stable pseudo[1]rotaxanes in strong polar solvent remains a challenging work, which usually needs
reasonable structural design; and it is not only essential in investigating the formation process of pseudo[1]rotaxane, but also has
potential applications in constructing artificial molecular machines.
Recently, we have synthesized a biotin modified pillar[5]arene-based pseudo[1]rotaxane [29], which could form a self-inclusion
structure in chloroform or acetone, while such self-inclusion structure would be gradually destroyed by increasing the polarity of the
solvent, exhibiting a slow-exchange process within NMR time scale. In order to further understand the self-assembly process of such
pseudo[1]rotaxane, herein, a mono-functionalized pillar[5]arene derivative (P2) bearing alkyl chain as the ending group and short EGn
(ethylene glycol) chain as flexible linker was synthesized. To our delight, it was found that a stable pseudo[1]rotaxane could be formed
in DMSO (Scheme 1), which also showed responsiveness to sodium cation. Subsequently, to further investigate the formation process
of such pseudo[1]rotaxane, two similar pillar[5]arene derivatives (P1 and P3) bearing different length of ethylene glycol chains were
synthesized. And the results showed that P1 bearing a shorter EG chain than P2 could also form stable pseudo[1]rotaxane in DMSO,
n
whereas, concentration-dependent pseudorotaxane structures were formed under the same condition by P3 which bearing a longer and
more flexible EG chain. The present study indicated that the flexibility of the side chain plays a vital role in the formation of
n
pseudo[1]rotaxanes.
—
——
∗
Corresponding author.
E-mail address: huxy@nju.edu.cn
Page 2 of 10

Scheme 1. Schematic illustration of the dynamic behaviour of pseudo[1]roataxanes.
2
. Experimental
2
.1 General information
All reactions were performed in air atmosphere unless otherwise stated. The commercially available reagents and solvents were
either employed as purchased or dried according to procedures described in the literature. Column chromatography was performed
with silica gel (200-300 mesh) produced by Qingdao Marine Chemical Factory, Qingdao (China). All yields were given as isolated
yields. NMR spectra were recorded on a Bruker DPX 300 MHz spectrometer (or Bruker DPX400 MHz spectrometer) with internal
standard tetramethylsilane (TMS) and solvent signals as internal references at 298 K, and the chemical shifts (δ) were expressed in
ppm and J values were given in Hz. Low-resolution electrospray ionization mass spectra (LR-ESI-MS) were obtained on Finnigan Mat
TSQ 7000 instruments. High-resolution electrospray ionization mass spectra (HR-ESI-MS) were recorded on an Agilent 6540Q-TOF
LCMS equipped with an electrospray ionization (ESI) probe operating in positive-ion mode with direct infusion. Melting points (M.p.)
were determined using a Focus X-4 apparatus (made in China) and were not corrected.
2
.2 The synthetic procedures for mono-functionalized pillar[5]arene derivatives P2
HO
O
TsCl, TEA HO
DCM
O
NaN
3
DMF, 50 o
O
OH
O
OTs
C
O
1
48%
99
%
HO
O
COOH
DCC, DMAP, DCM
0%
O
N
3
N3
O
O
O
2
5
3
Br
N
O
O
N
N
O
O
AP5
TBTA, Cu(CNCH ) PF
6
O
O
Br
3
4
CH
2
CH
2
5
4%
4
O
O
O
O
CH2
CH2
4
O
AP5
O
Br
Br
P2
Scheme 2. The synthetic route of P2.
The detailed synthesis procedures for compounds 1-3 were provided in Supporting information.
P2: Tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]amine (TBTA) (0.05 g, 0.1 mmol) and [Cu(CH CN) ]PF (0.04 g, 0.1 mmol) were
3
4
6
added to a solution of 3 (0.29 g, 1.0 mmol) and AP5 [29] (1.52 g, 1.0 mmol) in chloroform (20 mL) under argon atmosphere, and the
o
mixture was stirred at 25 C for 12 h (Scheme 2). The resulting solution was concentrated in vacuum, and the crude product was
purified by column chromatography (dichloromethane) to afford the target molecule P2 as a white solid (1.10 g, 0.54 mmol, 54%). Mp
o
1
1
44−146 C. H NMR (300 MHz, DMSO-d , 298 K): δ 8.16 (s, 1H, CH), 7.03−6.79 (m, 10H, ArH), 5.00 (s, 2H, OCH ), 4.58 (t, 2H, J
6 2
Page 3 of 10

=
4.3 Hz, NCH ), 4.29−4.05 (m, 18H, OCH ), 3.73−3.64 (m, 31H, ArCH , BrCH , OCH , and OCH ), 3.49−3.41 (m, 6H, OCH ), 1.84
2 2 2 2 2 3 2
13
(t, 2H, J = 7.8 Hz, COCH ), 0.65−0.53 (m, 7H, CH and CH ), -0.13−-0.20 (m, 4H, CH ). C NMR (100 MHz, DMSO-d , 298 K): δ
2 2 3 2 6
1
6
73.1, 150.1, 149.0, 148.94, 148.90, 148.8, 148.7, 143.0, 128.40, 128.35, 128.27, 128.1, 128.0, 127.8, 127.4, 124.2, 115.1, 114.8, 113.0,
9.5, 69.4, 68.6, 68.4, 68.3, 68.0, 62.9, 61.6, 55.47, 49.45, 33.3, 32.6, 32.3, 32.2, 32.1, 32.0, 29.9, 28.4, 27.3, 24.0, 21.8, 13.7. HR-ESI-
+
+
MS: m/z Calcd. for C H Br N NaO [M + Na] 1827.9152, found 1827.9158.
68
83
8
3
14
2
.3 The synthesis of P1
The detailed synthesis procedures for compounds 4-6 were provided in Supporting information.
P1: Tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]amine (TBTA) (0.05 g, 0.1 mmol) and [Cu(CH CN) ]PF (0.04 g, 0.1 mmol) were
3
4
6
added to a solution of 6 (0.24 g, 1.0 mmol) and AP5 (1.52 g, 1.0 mmol) in chloroform (20 mL) under argon atmosphere, and the
o
mixture was stirred at 25 C for 12 h (Scheme 3). The resulting solution was concentrated in vacuum, and the crude product was
purified by column chromatography (dichloromethane) to afford the target molecule P1 as a white solid (1.02 g, 0.54 mmol, 54%). Mp
o
1
1
65−167 C. H NMR (300 MHz, DMSO-d , 298 K): δ 8.14 (s, 1H, NCH), 7.12−6.82 (m, 10H, ArH), 5.01 (s, 2H, NCH ), 4.61 (t, 2H,
6 2
J = 4.7 Hz, OCH ), 4.20−4.01 (m, 18H, OCH ), 3.86−3.62 (m, 33H, ArCH , OCH , OCH , and BrCH ), 1.85−1.81 (m, 2H, COCH ),
2
2
2
2
3
2
2
13
0
.62 (brs, 2H, CH ), 0.40 (brt, 3H, J = 7.1 Hz, CH ), 0.27 (brd, 2H, J = 7.3 Hz, CH ), -0.44 (brs, 4H, CH ). C NMR (100 MHz,
2 3 2 2
DMSO-d , 298 K): δ 173.1, 150.4, 149.02, 148.96, 148.9, 148.8, 148.7, 128.34, 128.25, 128.21, 128.12, 128.10, 127.99, 127.97, 127.5,
6
1
5
15.5, 115.0, 114.84, 114.81, 114.68, 114.66, 114.54, 114.53, 114.3, 112.9, 68.62, 68.57, 68.36, 68.29, 68.27, 68.23, 68.1, 68.0, 62.5,
5.3, 49.4, 33.4, 32.6, 32.2, 32.1, 32.0, 31.94, 31.92, 29.4, 28.8, 28.5, 28.4, 28.3, 27.2, 23.9, 21.7, 13.5. HR-ESI-MS: m/z Calcd. for
+
+
C H Br N NaO [M + Na] 1783.8890, found 1783.8904.
66
79
8
3
13
TsCl, TEA
O
NaN3
O
O
HO
N3
HO
OTs
HO
OH
DMF, 50 o
45%
C
DCM
5
4
46%
AP5
COOH
N
3
O
O
DCC, DMAP, DCM
TBTA, Cu(CNCH
3 4 6
) PF
O
O
6
7
5%
54%
O
O
Br
N
N
N
O
O
CH
2
CH
2
4
O
O
Br
P1
Scheme 3. The synthetic route of P1.
2
.4 The synthesis of P3
The detailed synthesis procedures for compounds 7-9 were provided in Supporting information.
P3: Tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]amine (TBTA) (0.05 g, 0.1 mmol) and [Cu(CH CN) ]PF (0.04 g, 0.1 mmol) were
3
4
6
added to a solution of 9 (0.24 g, 0.72 mmol) and AP5 (1.52 g, 1.0 mmol) in chloroform (20 mL) under argon atmosphere, and the
o
mixture was stirred at 25 C for 12 h (Scheme 4). The resulting solution was concentrated in vacuo. The crude product was purified by
column chromatography (dichloromethane) to afford the target molecule P3 as a white solid (1.10 g, 0.054 mmol, 54%). Mp 148−149
o
1
C. H NMR (400 MHz, DMSO-d , 298 K): δ 8.18 (s, 1H, NCH), 7.06−6.82 (m, 10H, ArH), 5.05 (s, 2H, NCH ), 4.57 (t, 2H, J = 5.0
6
2
Hz, OCH ), 4.23 (brs, 13H, ArCH , and OCH ), 4.14−4.06 (m, 4H, OCH ), 3.86−3.65 (m, 32H, BrCH , and OCH ), 3.60−3.34 (m, 10H,
2
2
3
2
2
2
OCH ), 2.05 (t, 2H, J = 7.7 Hz, COCH ), 1.09−1.06 (m, 2H, CH ), 0.93−0.88 (m, 2H, CH ), 0.69 (t, 3H, J = 7.2 Hz, CH ), 0.56 (brs,
2
2
2
2
3
1
3
4
1
6
2
H, CH2). C NMR (100 MHz, DMSO-d , 298 K): δ 173.0, 150.0, 149.02, 149.01, 148.96, 148.92, 148.90, 148.84, 148.78, 148.5,
6
43.0, 128.5, 128.4, 128.2, 128.0, 127.9, 127.5, 124.4, 115.18, 115.16, 114.9, 114.8, 114.6, 114.5, 114.3, 113.7, 113.2, 69.7, 69.6,
9.54, 69.46, 68.7, 68.6, 68.44, 68.39, 68.3, 68.0, 62.9, 61.6, 55.5, 49.5, 33.4, 32.6, 32.3, 32.22, 32.16, 32.13, 30.3, 28.7, 28.45, 28.40,
+
+
7.6, 24.1, 21.9, 13.8. HR-ESI-MS: m/z Calcd. for C H Br N NaO [M + Na] 1871.9415, found 1871.9421.
7
0
87
8
3
15
Page 4 of 10

O
O
O
O
TsCl, TEA
DCM
O
O
COOH
, CH CN
8%
HO
O
O
OH
TsO
O
OTs
K
2
CO
3
3
7
73%
4
O
O
NaN
3
O
O
TsO
O
N3
O
O
DMF, 50 o
C
9
8
76%
O
Br
N
O
O
N
N
O
O
O
O
AP5
TBTA, Cu(CNCH
4%
CH
2
CH
2
3
)
4
PF
6
4
O
O
5
Br
P3
Scheme 4. The synthetic route of P3.
3
. Results and discussion
Initially, mono-functionalized pillar[5]arene derivative P2 was synthesized by means of copper (I) catalyzed azide-alkyne
cycloaddition [30]. The alkynyl-functionalized pillar[5]arene AP5 was synthesized according to reported literature [29]. Meanwhile,
the azide-modified compound 3 was obtained by using commercially available triethylene glycol as the starting material (Scheme 2). It
was obvious that in DMSO-d the protons on the alkyl chain (H –H ) shifted upfield, indicating the inclusion of the alkyl chain into the
6
a
f
1
cavity of the pillar[5]arene (Fig. 1b). Then, the self-complexation behavior of P2 in solution was studied by H NMR spectroscopy in
different solvents. From the spectra of P2 (Fig. 1), obviously upfield chemical shifts of the protons (H ) on the alkyl chain could be
a–f
observed in nonpolar solvent (chloroform), weak polar solvent (acetone), and polar solvent (DMSO), which suggested that the solvent
polarity had little effect on the inclusion behaviour of P2. Moreover, from the 2D NOESY spectroscopy in DMSO-d , strong NOE
6
correlations between protons (H ) on the alkyl chain and the protons (H ) on phenyl rings of pillar[5]arene could be observed (Fig. 2),
a-f
1
further indicating that the alkyl chain was threaded into the cavity of pillar[5]arene. The above results were very different from those
previous reports on pseudo[1]rotaxanes that were formed from mono-functionalized pillar[n]arenes, where solvent with strong polarity
would completely destroy the inclusion structures [23, 29]. However, in our system, stable inclusion structures could be formed in high
polar solvent (DMSO) and exhibited a dynamic fast-exchange process within the NMR time scale.
1
Fig. 1. H NMR spectra (400 MHz, 298 K) of P2 (5 mmol/L) in different solvents: (a) CDCl , (b) DMSO-d , and (c) acetone-d . (“*” indicates
3
6
6
the solvent residue).
Page 5 of 10

Fig. 2. Partial 2D NOESY spectrum of P2 (400 MHz, DMSO-d , 298 K).
6
1
To investigate whether this inclusion behaviour was intermolecular or intramolecular, variable concentration H NMR spectroscopy
of P2 at different concentrations in the range of 7.0–80 mmol/L was carried out in DMSO-d (Fig. 3), which showed that the inclusion-
6
structure formed by P2 was concentration independent, suggesting that P2 exists predominantly in the form of pseudo[1]rotaxane. The
above result was also supported by the theoretical equation of self-inclusion equilibrium in solution (Supporting information).
Subsequently, high resolution electrospray ionization mass spectrometry (HR-ESI-MS) investigation was performed, in which one
+
indicative peak corresponding to [M + Na] at m/z 1827.9158 was clearly observed and no other peaks corresponding to higher
molecular weight interlocked structures could be observed, confirming the presence of P2 as the pseudo[1]rotaxane structure in DMSO
[
31]. Moreover, strong NOE correlations between the proton on triazole group (H ) and the protons (H ) on ethylene glycol units
m g-l
could also be observed (Fig. 2), indicating that intramolecular hydrogen-bonding interaction between the proton on the triazole ring
and the oxygen atoms on the ethylene glycol chain was exist, which might be the main driving force for the formation of the self-
inclusion structure.
1
Fig. 3. H NMR spectra (300 MHz, 298 K) of P2 at variant concentrations in DMSO-d indicate its concentration-independent property: (a) 7
6
mmol/L, (b) 15 mmol/L, (c) 20 mmol/L, (d) 25 mmol/L, (e) 40 mmol/L, (f) 60 mmol/L, and (g) 80 mmol/L.
This interesting and abnormal phenomenon had greatly attracted our attention. To further investigate the formation process of this
type of pseudo[1]rotaxane, another two pillar[5]arene derivatives bearing shorter (P1) or longer (P3) EG chain as flexible linker were
n
1
also synthesized by click reaction. From their H NMR spectra in different solvents (Fig. 4), obvious upfield chemical-shifts of the
protons on the alkyl chain of P1 could be observed in chloroform, acetone as well as DMSO, indicating the formation of inclusion
structure in these solvents. Moreover, this inclusion structure formed from P1 could also be confirmed by 2D NOESY analysis based
on the NOE correlation signals between the protons on the alkyl side chain and pillar[5]arene cavity (Fig. S25 in Supporting
information). However, with respect to P3 which bearing longer and more flexible side chain, only slight upfield chemical shifts could
1
be observed from the H NMR spectra of P3 in nonpolar solvent (chloroform), weak polar solvent (acetone) as well as polar solvent
1
(
DMSO), indicating the tendency of forming unthreaded structures in dilute solution. Moreover, comparing the H NMR spectra of P1,
P2, and P3 in DMSO-d (Fig. 4A), it was observed that the protons on the alkyl chain of P1 exhibited the largest upfield shifts, while
6
those alkyl chain protons of P3 showed the smallest upfield shifts. And similar phenomena could also be observed in both chloroform
Page 6 of 10

and acetone (Fig. 4B and Fig. 4C). The above difference might be caused by the flexibility of the side chain, which would hinder the
inclusion tendency of the alkyl side chain due to its random movement.
1
Fig. 4. H NMR spectra of P1, P2, and P3 (A): 7 mmol/L, 400 MHz, DMSO-d , 298 K; (B): 7 mmol/L, 400 MHz, acetone-d , 298 K; (C): 3
6
6
mmol/L, 400 MHz, CDCl , 298 K.
3
In the following study, variable concentration experiments in DMSO suggested that the inclusion-structure formed from P1 was also
concentration independent (Fig. 5), indicating the formation of pseudo[1]rotaxane similar to that of P2. Whereas, P3 exhibited different
1
result: as shown in Fig. 6, the H NMR spectra of P3 in DMSO-d at different concentrations of 10, 20 and 50 mmol/L were recorded,
6
and it was found that the protons on the alkyl chain gradually shifted upfield upon increasing the concentration, which meant the
inclusion structure formed by P3 was concentration-depended, suggesting the formation of other concentration-dependent
pseudorotaxane structures in high concentration.
Page 7 of 10

1
Fig. 5. H NMR spectra (400 MHz, 298 K) of P1 at variant concentrations in DMSO-d : (a) 10 mmol/L, (b) 50 mmol/L.
6
1
Fig. 6 Partial H NMR spectra (400 MHz, 298 K) of P3 at variant concentrations in DMSO-d indicate its concentration-dependent property:
6
(a) 10 mmol/L, (b) 20 mmol/L, and (c) 50 mmol/L.
Subsequently, study of host−guest chemistry between pillar[5]arene and alkyl chain was carried out in DMSO-d by using 1,4-
6
1
dimethoxypillar[5]arene (DMP5) as the model host molecule and azide-modified compound 6 as guest molecule (Fig. 7). From the H
NMR spectra of DMP5 with 10 equiv. of guest compound 6, it was found that the chemical shifts of protons on DMP5 almost did not
show any changes, indicating that the host−guest interaction was too weak in DMSO. The above results also demonstrated that
pillararene-based host-guest interaction might not be the main driving force for such inclusion behaviour.
1
Fig. 7 H NMR spectra (300 MHz, DMSO-d , 298 K) of (a) DMP5 (5 mmol/L), (b) 6 (50 mmol/L) + DMP5 (5 mmol/L), (c) 6 (50 mmol/L).
6
(“*” indicates the solvent residue).
On the basis of the above observations and our previous work on the biotin functionalized pseudo[1]rotaxane [29], we could draw
the conclusion that the intramolecular hydrogen-bonding interaction might play a vital role in the formation of pseudo[1]rotaxane,
which can make the side chain bend back to thread into its own cavity; whereas, pillararene-based host−guest interaction had almost no
contribution to the pseudo[1]rotaxane formation in polar solvent; moreover, the flexibility of the side chain might affect its inclusion
Page 8 of 10

tendency thus hinder the formation of pseudo[1]rotaxanes, so mono-functionalized pillar[5]arenes with longer and flexible side chain
will lead to the generation of concentration-dependent pseudorotaxane.
After understanding the formation process of such pseudo[1]rotaxanes, we further tended to investigate their dynamic behaviours in
polar solution. As we know, most pillararene-based host−guest interactions will be destroyed in high polar solution, such as DMSO, so
adding competitive guests might have no effect on this self-inclusion structure. Inspired by the host-guest interaction between crown
ethers with alkaline metal cation [32], we wondered whether such pseudo[1]rotaxane structures would show responsiveness to sodium
cation due to the presence of electronegative ethylene glycol chains. Along this line, NaBF was added gradually to the P2 solution in
4
1
DMSO-d . From the H NMR spectra (Fig. 8), it was observed that the protons on the alkyl chain exhibited slight upfield shifts upon
gradually adding Na , indicating the alkyl chain showed a stronger tendency to thread into the cavity of pillar[5]arene. Meanwhile,
6
+
protons H and H that belong to the triazole and its neighboring groups showed the same upfield changing tendency (Fig. S27 in
m
n
Supporting information), which might result from the destroy of the hydrogen bonds between the triazole ring and ethylene glycol
+
chain, thus led to the generation of Na -induced more tightening self-inclusion structure. Moreover, similar results could also be
observed by adding NaBF to the solution of P1 (Fig. 9).
4
1
Fig. 8 Partial H NMR spectra (400 MHz, 298 K, DMSO-d ) of P2 (5 mmol/L) with different equivalents of NaBF : (a) 0 equiv., (b) 1.0
6
4
equiv., (c) 2.0 equiv., (d) 5.0 equiv., (e) 30.0 equiv., (f) 35.0 equiv., and (g) 60.0 equiv..
1
Fig. 9 H NMR spectra (400 MHz, 298 K, DMSO-d ) of P1 (5 mmol/L) with different equivalents of NaBF : (a) 0 equiv., (b) 40 equiv.
6
4
4
. Conclusion
In summary, mono-alkyl-functionalized pillar[5]arenes (P1, P2, and P3) bearing different length of ethylene glycol chains as
flexible linkers were synthesized in a facial way. Among which P1 and P2 exhibited self-inclusion behavior in strong polar solvent
DMSO, leading to the generation of stable pseudo[1]rotaxanes; whereas, P3 with longer and more flexible side chain led to the
formation of concentration-dependent pseudorotaxane structures at high concentration in DMSO. Furthermore, the pseudo[1]rotaxane
+
formed by P1 or P2 exhibited stimuli-responsiveness to Na , resulting in the formation of more tightening inclusion structures, which
+
might be driven by the interaction between the positively charged Na and electronegative ethylene glycol chain. The discovery of
stable pseudo[1]rotaxanes formed in polar solvent represents a special type of inclusion phenomenon, and further studies on the
controllable switch of pseudo[1]rotaxanes and their applications are now ongoing in our lab.
Page 9 of 10

Acknowledgment
We gratefully acknowledge the financial support from the National Natural Science Foundation of China (Nos. 21472089,
2
1572101), and the National Natural Science Foundation of Jiangsu (No. BK20140595).
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