Monofunctionalized pillar[5]arene-based stable [1]pseudorotaxane

Article abstract of DOI:10.1016/j.cclet.2015.05.030

We reported a new monofunctionalized pillar[5]arene bearing imidazolium moiety that formed stable [1]pseudorotaxane even at high concentration (100 mmol/L) in chloroform. The self-assembly was detailed investigated by multiple methods, including varying concentration ¹H NMR, 2D COSY NMR, 2D NOESY NMR, viscosity measurements, 2D DOSY NMR, and HR-ESI-MS analysis. [1]Rotaxane was obtained efficiently through photo thiol-ene reaction which further confirmed the formation of [1]pseudorotaxane.

Full text of DOI:10.1016/j.cclet.2015.05.030

Chinese Chemical Letters 26 (2015) 843–846
Contents lists available at ScienceDirect
Chinese Chemical Letters
journal homepage: www.elsevier.com/locate/cclet
Original article
Monofunctionalized pillar[5]arene-based stable [1]pseudorotaxane
a,b,c
a
a,
a
a
a
Cai-Li Sun
, Jiang-Fei Xu , Yu-Zhe Chen *, Li-Ya Niu , Li-Zhu Wu , Chen-Ho Tung ,
a,b,
Qing-Zheng Yang **
a
Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences,
Beijing 100190, China
b
College of Chemistry, Beijing Normal University, Beijing 100875, China
c
University of the Chinese Academy of Sciences, Beijing 100049, China
A R T I C L E I N F O
A B S T R A C T
Article history:
We reported a new monofunctionalized pillar[5]arene bearing imidazolium moiety that formed stable
Received 27 March 2015
Received in revised form 22 April 2015
Accepted 4 May 2015
[
1]pseudorotaxane even at high concentration (100 mmol/L) in chloroform. The self-assembly was
1
detailed investigated by multiple methods, including varying concentration H NMR, 2D COSY NMR, 2D
NOESY NMR, viscosity measurements, 2D DOSY NMR, and HR-ESI-MS analysis. [1]Rotaxane was
obtained efficiently through photo thiol-ene reaction which further confirmed the formation of
Available online 28 May 2015
[
1]pseudorotaxane.
Keywords:
ß 2015 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences.
Pillar[5]arene
Self-assembly
Published by Elsevier B.V. All rights reserved.
[
1]pseudorotaxanes
Thiol-ene reaction
1
. Introduction
Pillararenes are a novel kind of macrocyclic host for supramo-
investigated with great interest. They are the building blocks for
the preparation of artificial molecular machines, supramolecular
polymers, supramolecular gels, and other functional supramo-
lecular materials [20–23]. Some of them are promising in
preparation of molecular sensors and in drug delivery [24–
28]. [1]pseudorotaxanes are one of the basic threaded structures
for pseudorotaxane. However, stable pillar[5]arene-based
[1]pseudorotaxanes are still rarely reported because they mostly
exist in dilute solutions mixt with linear oligomers, cyclic dimers
and so on [29]. In 2011, Ogoshi et al. presented firstly the
[1]pseudorotaxanes based on pillar[5]arene with octyltrimethy-
lammonium group, which exhibited self-inclusion complexation
in chloroform. But it was uncertain whether this [1]pseudor-
otaxane could form at high concentration due to the restriction
of solubility [30]. Stoddart et al. investigated detailedly the
lecular chemistry composed of hydroquinone units linked by
methylene bridges at para positions [1,2]. They have held the
spotlight in this field owing to their unique highly rigid structure
and easy functionalization with various substituents at the
hydroquinone unit [3–6]. Because of the electron-rich property,
their cavities can encapsulate many types of cationic guests and
neutral molecules [7–16]. These features make them good
candidate to construct various assemblies with intriguing proper-
ties. Hitherto, many pillararene-based supramolecular architec-
tures have been built, such as the first pillararene-based [c2]daisy
chain containing two mirror image monomers reported by Huang’s
group [17], [2]rotaxane whose motions could be triggered by
solvent and temperature [18], and the double-switchable pillar-
arene-based supramolecular polymer reported by our group [19].
Pseudorotaxanes, a self-assembly threaded structure in which
macrocyclic components encircle linear components, have been
assembling behavior of
a monofunctionalized pillar[5]arene
derivative containing a viologen moiety. It behaved as self-
complexation at low concentration, assembled into supramolec-
ular daisy chain polymers and eventually organogels upon the
increasing of its concentration [31]. Herein, we report a stable
pillar[5]arene-based [1]pseudorotaxane even in concentrated
chloroform solution (100 mmol/L) by reasonable monofunctio-
nalization. The self-complexation was demonstrated by the
*
Corresponding author.
*
* Corresponding author at: Key Laboratory of Photochemical Conversion and
Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese
Academy of Sciences, Beijing 100190, China; College of Chemistry, Beijing Normal
University, Beijing 100875, China.
1
research of H NMR, 2D COSY NMR, 2D NOESY NMR, viscosity
measurements and HR-ESI-MS. Furthermore, [1]rotaxane was
obtained efficiently through thiol-ene reaction confirming the
formation of [1]pseudorotaxane.
E-mail addresses: chenyuzhe@mail.ipc.ac.cn (Y.-Z. Chen), qzyang@mail.ipc.ac.cn
(Q.-Z. Yang).
http://dx.doi.org/10.1016/j.cclet.2015.05.030
001-8417/ß 2015 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. Published by Elsevier B.V. All rights reserved.
1

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44
C.-L. Sun et al. / Chinese Chemical Letters 26 (2015) 843–846
Scheme 1. Illustration of the self-complexation of monofunctionalized pillar[5]arene 1 and the formation of [1]rotaxane.
2
. Experimental
moderate overall yield (Scheme S1 in Supporting information). By
similar method, compound 2, which had the same linear guest part
but without pillar[5]arene unit, was synthesized as a reference
guest (Scheme S1).
All the experimental procedures including materials and
methods, synthesis and characterization details, and copies of
NMR spectra were present in Supporting information.
The self-assembled behavior of 1 in solution was first examined
1
1
3
by H NMR spectroscopy at 40 mmol/L in CDCl . The H NMR
3
. Results and discussion
spectrum of compound 1 showed quite different from compound 2
at the same concentration. The signals of protons on the
As shown in Scheme 1, monofunctionalized pillar[5]arene with
7 8 9
imidazolium unit (H , H , H ) and alkyl chain (H10, H11, H12,
imidazolium was exploited in our system due to the strong
H13) became broader and shifted upfield, including two obvious
4
complexation (K
a
= 1.0 Â 10 L/mol) between pillar[5]arene and
broadened peaks (H11, H12) located at minus ppm. These upfield
shifts resulted from the threading of imidazolium guest into the
pillar[5]arene macrocycle (Fig. 1). In order to confirm the proton
imidazolium cation [32]. To ensure the formation of self-
complexation assemblies, there were two long alkyl chain linked
to imidazolium. One of them was designed to provide the
flexibility and the other one appeared as the guest part. Moreover,
an allyl group was added at the end of the alkyl guest as a reactive
site, which offered the possibility to prepare [1]rotaxane through
thiol-ene reaction. Compound 1 was synthesized in five steps with
1
assignments clearly, two-dimensional correlation spectroscopy H
1
NMR (COSY) was performed in combination with H NMR (Fig. S5
in Supporting information). It was demonstrated that the signals of
protons H
7
–H12 on or next to the imidazolium ring revealed more
than 2 ppm upfield chemical shift, and those of H13, H14 showed a
1
Fig. 1. H NMR (40 mmol/L in CDCl
3
, 400 MHz) spectrum and structure of 1 (a), and 2 (b).

C.-L. Sun et al. / Chinese Chemical Letters 26 (2015) 843–846
845
solutions. As the concentration of 1 increased from 5 mmol/L to
1
00 mmol/L, the value of weight average diffusion coefficients (D)
À10
À10
2
decreased from 6.28 Â 10
to 5.02 Â 10
m /s (D /D100 = 1.25).
5
This slight decrease was insufficient to suggest the change of the
average dimension of aggregates. That was to say as the
concentration increased, the self-assembly kept the same. The
high resolution ESI mass spectrometry of a mixture of 1 revealed
the molecular peak at m/z 1041.5331 corresponding to the
monomer, backing up the result of intramolecular complexation
(
Fig. S1c in Supporting information).
The above result indicated the existed complexation but no
intermolecular aggregates in the chloroform solution of compound
at the concentration of 5–100 mmol/L. It was reasonably deduced
1
that stable [1]pseudorotaxane was formed by the new mono-
functionalized pillar[5]arene, which was different from the usual
assembly as reported by literature when bearing such a long side
chain [17,34–36]. It was probably because this molecule held two
long flexible chains linked to imidazolium, which ensured the
intramolecular interaction between the alkyl chain distant from
the pillar[5]arene and the pillar[5]arene cavity.
1
3
Fig. 2. Partial H NMR (CDCl , 400 MHz) spectra of 1 at different concentrations (the
peaks of complexed part are denoted by asterisks).
fraction of change, while the protons on the other alkyl chain
showed little change. This result indicated that imidazolium
moiety and adjacent alkyl chain, the one distant from pillar[5]-
arene unit, were threaded into the electron-rich cavity and the
other protons were located outside the cavity. In addition, the
NOESY analyst was consistent with this result in which strong NOE
Finally, the formation of [1]pseudorotaxane was proved
considerably by the preparation of [1]rotaxane. Considering the
terminal group of compound 1, we came up with the photo thiol-
ene radical reaction. As an important member of thiol-click family,
thiol-ene reaction possessed the merits of facile condition, rapid
reaction rate, excellent yield, along with strong tolerance for many
kinds of functional groups [37]. Here, compound 3 was selected as
the stopper and dichloromethane was employed as the solvent
(Scheme 1). [1]Rotaxane was obtained successfully both at the
concentration of 20 mmol/L and 100 mmol/L in relatively high
isolated yield (57% and 54%) (Scheme S2 in Supporting informa-
correlation signals were presented between the protons H10, H11
12, H13 and the aromatic or methylene hydrogen atoms of
pillar[5]arene (Fig. S6 in Supporting information).
,
H
The above spectra validated the complexation of compound 1
undoubtedly, but could not supply us the exact information about
whether the assembly was intra- or inter-molecule. To verify the
1
tion). Fig. S7 in Supporting information showed the H NMR spectra
of [1]pseudorotaxane and [1]rotaxane. Except the new peaks from
1
structure of [1]pseudorotaxane, the H NMR spectroscopy of
compound
1
at variable concentration (from 5 mmol/L to
the added stopper as well as the disappearance of double bond
signals, H NMR spectrum kept almost same after reaction,
1
1
00 mmol/L) were measured, which did not show any apparent
changes (Fig. 2). Along with the increase of concentration, only
some signals gave slight broadened trend, indicating that
demonstrating no change of complexation. Besides, we prepared
the control compound 2a through thiol-ene reaction between 2 and
1
compound 1 did not form intermolecular complexes in CDCl
3
.
3 (Scheme S2). In comparison with the H NMR spectrum of 2a, the
The self-complexation behavior of 1 in chloroform was further
studied by viscosity measurements. As presented in Fig. 3a, the
curve in the double logarithmic plots of specific viscosity vs.
concentration at 5–200 mmol/L had a slope of 1.103, suggesting a
linear relationship between specific viscosity and concentration,
which is characteristic for non-interacting assemblies of constant
size, in agreement with the intramolecular-threading even at high
concentrations [33]. Meanwhile, two-dimensional diffusion-or-
assembly of 1a was clear (Fig. S8 in Supporting information). In this
regard, the convenience and efficiency of thiol-ene reaction might
supply a new synthesis strategy for rotaxane.
4. Conclusion
In summary, we described
a stable monofunctionalized
pillar[5]arene-based [1]pseudorotaxane whose self-inclusion
1
1
dered H NMR (DOSY) experiments were also employed to
structure was exhaustively proved via varying concentration H
investigate the self-assembly of compound 1 at different con-
centrations (Fig. 3b). The DOSY spectrum at every concentration
revealed one set of signals, manifesting only one aggregate size in
NMR, 2D COSY NMR, 2D NOESY NMR, viscosity measurements, 2D
DOSY NMR, and HR-ESI-MS analysis. [1]Rotaxane, which was
prepared efficiently through thiol-ene reaction confirmed the
3 3
Fig. 3. (a) Specific viscosity of 1 in CHCl solutions vs. the concentration (293 K). (b) Concentration dependence of diffusion coefficient D (CDCl , 298 K, 600 MHz) of 1.

8
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C.-L. Sun et al. / Chinese Chemical Letters 26 (2015) 843–846
[
[
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We are grateful for the financial support from the 973 Program
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Appendix A. Supplementary data
[
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.cclet.2015.
[
[
[
0
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