Main-chain linear polyrotaxanes: Synthesis, characterization, and conformational modulation

Article abstract of DOI:10.1002/chem.201203165

Two functional main-chain linear polyrotaxanes, one a covalent polymeric chain that threads through many macrocycles (P1) and the other a poly[n]rotaxane chain that is composed of many repeating rotaxane units (P2), were synthesized by employing strong crown-ether/ammonium-based (DB24C8/DBA) host-guest interactions and click chemistry. Energy transfer between the wheel and axle units in both polyrotaxanes was used to provide insight into the conformational information of their resulting polyrotaxanes. Steady-state and time-resolved spectroscopy were performed to understand the conformation differences between polymers P1 and P2 in solution. Additional investigations by using dynamic/static light scattering and atomic force microscopy illustrated that polymer P1 was unbending and had a rigid rod-like structure, whilst polymer P2 was curved and flexible. This flexible topology facilitated the self-assembly of polymer P2 into relatively large ball-shaped particles. In addition, the energy transfer between the wheel and axle units was controlled by the addition of specific anions or base. The anion-induced energy enhancement was attributed to a change in electrostatic interactions between the polymer chains. The base-driven molecular shuttle broke the DB24C8/DBA host-guest interactions. These results confirm that both intra- and intermolecular electrostatic interactions are crucial for modulating conformational topology, which determines the assembly of polyrotaxanes in solution. Copyright

Full text of DOI:10.1002/chem.201203165

DOI: 10.1002/chem.201203165
Main-Chain Linear Polyrotaxanes: Synthesis, Characterization, and
Conformational Modulation
Ji-Min Han,[a] Yong-Hong Zhang,[b] Xiao-Ye Wang,[a] Chen-Jiang Liu,*[b]
Jie-Yu Wang,*[a] and Jian Pei*[a]
Abstract: Two functional main-chain
linear polyrotaxanes, one a covalent
polymeric chain that threads through
many macrocycles (P1) and the other a
poly[n]rotaxane chain that is composed
of many repeating rotaxane units (P2),
were synthesized by employing strong
crown-ether/ammonium-based
(DB24C8/DBA) host–guest interac-
tions and click chemistry. Energy trans-
fer between the wheel and axle units in
both polyrotaxanes was used to provide
insight into the conformational infor-
mation of their resulting polyrotaxanes.
Steady-state and time-resolved spectro-
scopy were performed to understand
the conformation differences between
polymers P1 and P2 in solution. Addi-
tional investigations by using dynamic/
static light scattering and atomic force
microscopy illustrated that polymer P1
was unbending and had a rigid rod-like
structure, whilst polymer P2 was
curved and flexible. This flexible topol-
ogy facilitated the self-assembly of pol-
ymer P2 into relatively large ball-
shaped particles. In addition, the
energy transfer between the wheel and
axle units was controlled by the addi-
tion of specific anions or base. The
anion-induced energy enhancement
was attributed to a change in electro-
static interactions between the polymer
chains. The base-driven molecular shut-
tle broke the DB24C8/DBA host–guest
interactions. These results confirm that
both intra- and intermolecular electro-
static interactions are crucial for modu-
lating conformational topology, which
determines the assembly of polyrotax-
anes in solution.
Keywords: click chemistry · energy
transfer · polymers · rotaxanes ·
self-assembly
Introduction
lecular structures of the building units and the conforma-
tions of the as-synthesized polyrotaxanes.[15–18]
The construction of supramolecular polymers has become
one of the most critical challenges facing nanoscience and
nanotechnology.[1–6] Recently, polyrotaxanes, which are con-
structed from the interlocking assembly of wheel and axle
components, have received much attention, not only because
of their unique structures but also because of their potential
applications.[7–14] Key factors that need to be addressed for
the successful application of polyrotaxanes include the crea-
tion of highly ordered and/or higher-dimensional structures,
as well as understanding the relationship between the mo-
The connections between the building units in main-chain
linear polyrotaxanes can be categorized into two types:
1) Covalent polymeric chains that thread through the mac-
rocycles (P1) and 2) poly[n]rotaxanes that do not contain a
covalent polymeric backbone (P2), which means that the
polymer would decompose if the mechanical bonds were re-
moved. A schematic representation of both types of polyro-
taxanes is shown in Scheme 1. Unlike the former case, of
which there are already many fascinating examples, reports
of the latter type of polyrotaxanes, especially reports that
describe their conformation and aggregation in solution or
on surfaces, are scarce.[19–25]
Herein, we report the design and synthesis of two func-
tional main-chain linear polyrotaxanes. For the first time, to
the best of our knowledge, we have performed a direct com-
parison of their structural arrangement, which elucidated
the relationship between their unique properties and their
flexible conformations. As shown in Scheme 2, two energy
donors (A1 and A2) that contained dibenzo[24]crown-8
(DB24C8) groups and one energy acceptor (B2) that con-
tained a dibenzyl-ammonium (DBA) group were used to
form a particular class of functional main-chain linear poly-
rotaxanes (P1 and P2) through strong host–guest interac-
tions between the crown-ether and ammonium moieties.[26]
The CuI-catalyzed azide–alkyne cycloaddition (CuAAC) re-
action[27–31] was utilized to introduce stoppers onto the axle
[a] Dr. J.-M. Han, X.-Y. Wang, Dr. J.-Y. Wang, Prof. J. Pei
Beijing National Laboratory for Molecular Sciences
the Key Laboratory of Bioorganic Chemistry and
Molecular Engineering of the Ministry of Education
College of Chemistry and Molecular Engineering
Peking University, Beijing 100871 (China)
Fax : (+86)10-62758145
E-mail: wangjy1210@gmail.com
jianpei@pku.edu.cn
[b] Y.-H. Zhang, Prof. C.-J. Liu
Key Laboratory of Petroleum and Gas Fine Chemicals
The Ministry of Education
College of Chemistry and Chemical Engineering
Xinjiang University, Urumqi 830046 (China)
E-mail: pxylcj@126.com
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201203165.
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FULL PAPER
mer. We envision that these
new polyrotaxanes can serve as
a platform for investigating the
relationship between the mo-
lecular structures and proper-
ties of these polymers, thus en-
abling the development of
highly elaborate functions of
polyrotaxanes for application
in many areas.
Results and Discussion
Scheme 1. Synthetic routes to polyrotaxanes P1 and P2.
Although the association of
DB24C8 and DBA to form
mechanically interlocked as-
semblies is well-known, poly-
merization of such assemblies
could be extremely hampered
by the steric bulk. As discussed
in our previous work,[32]
a
longer linker between the trux-
ene core and DB24C8 was nec-
essary for the assembly of units
A2 for P2, whilst it was not re-
quired with unit A1 because of
the lower degree of steric hin-
drance in polyrotaxane P1.
Scheme 3 outlines the synthetic
route to our desired mono-
mers, A2 and C2. Unit A2 was
designed to introduce two
DB24C8 units onto a truxene
fragment to become the
“wheel” part of the polyrotax-
Scheme 2. Molecular structures of the building units for the polyrotaxanes. Wheel units A1 and A2 contain
one and two dibenzo[24]crown-8 moieties, respectively; compound B2 is used as the axle unit.
ane. Compound
1 was pre-
pared according to a modified
literature procedure[33] and
molecule, thus enhancing the stability of these mechanically
interlocked structures. The absorption spectrum of B2
showed a large overlap with the emission features of com-
pounds A1 and A2, which was ideal for fluorescence reso-
nance energy transfer (FRET) through interactions between
the transition dipoles (see the Supporting Information, Fig-
ure S1). Fçrster-type energy transfer (ET) between the
wheel and axle units was highly convenient for studying the
conformations of the resulting polyrotaxanes.[32] For in-
stance, we found that polymer P1 behaved like a “rigid
rod”, whereas polymer P2 tended to exist as a random coil
in dilute solution. However, in a condensed state, the indi-
vidual rigid P1 polymers self-assembled into larger rods
with a wide distribution and the flexible P2 polymers assem-
bled into hard balls. In addition, the polymer-chain confor-
mation, as well as polymer aggregation, can be modulated
by adding base, which is expected to impact on the host–
gust interactions in the DB24C8/DBA pair within the poly-
subjected to two Suzuki cross-coupling reactions to afford
compound 3. After reduction with NaBH4 to give compound
4, compound 5 was obtained in high yield by the addition of
PBr3 in CH2Cl2. The nucleophilic-substitution reaction be-
tween compound 5 and NaN3 afforded compound 6 as the
precursor for the click reaction. The CuAAC reaction be-
tween compound 6 and ethynyl-substituted DB24C8[34] gave
unit A2 in moderate yield. The macrocyclic compound was
readily soluble in common organic solvents, such as toluene,
THF, and CH2Cl2. Compound C2 was synthesized from com-
pound 8 through a Suzuki cross-coupling reaction followed
by bromination and nucleophilic substitution by NaN3
(Scheme 3). Compounds A1 and B2 were prepared accord-
ing to our previously reported procedures;[32] their structures
1
and purity were fully characterized and verified by H and
13C NMR spectra, as well as by HRMS (ESI).
A one-pot polymerization strategy was employed for the
synthesis of polymers P1 and P2. In a two-step, three-com-
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C.-J. Liu, J.-Y. Wang, J. Pei et al.
molar ratio of 1:1:4. Typically,
these three reactants were
combined in anhydrous CH2Cl2
to obtain a clear yellow solu-
tion; then, an anhydrous solu-
tion of the CuACTHUNTRGNE(UNG CH3CN)4PF6
catalyst in CH2Cl2 was injected
into the system. The click reac-
tion was allowed to proceed
for five days before the polyro-
taxanes were finally obtained.
After Soxhlet extraction with
CHCl3, polyrotaxanes P1 and
P2 were both obtained as
À
yellow solids with PF6 as the
counterion. Their poor solubili-
ty in CHCl3 and THF, their
1
broadened H NMR spectra in
[D6]DMSO, and gel permea-
tion chromatography (GPC)
analysis all confirmed the suc-
cess of these polymerization
reactions.
The steady-state photophysi-
cal properties of polyrotaxanes
P1 and P2 in dilute solution
were carefully studied. As
shown in Figure 1, polyrotax-
ane P1 showed three distinct
absorption bands at lmax =309,
330, and 395 nm, which were
attributed to the absorption
maxima of truxene, phenyl-
substituted truxene, and oligo(phenylene vinylene) (OPV),
Scheme 3. Synthetic routes to monomers A2 and C2.
ponent reaction, the B2 chain was threaded through wheels
A1 or A2 and stoppered at each end by using azide C2 or
11. For polyrotaxane P1, compounds A1, B2, and C2 were
mixed together in a molar ratio of 4:1:1, whilst, for polymer
P2, compounds A2, B2, and 11 were mixed together in a
respectively, whereas only two absorption bands (at lmax
=
330 and 395 nm) were found in polyrotaxane P2. The ab-
sorption features exhibited an apparent weighted addition
of the energy donors and acceptors, thus indicating that
Figure 1. UV/Vis absorption spectra of solutions of P1 (a) and P2 (b) at different concentrations in DMF at room temperature; no red-shift of lmax was
observed.
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Main-Chain Linear Polyrotaxanes
FULL PAPER
there were no interactions between the donor and the ac-
ceptor in the ground state. Because of the topology of the
rotaxane framework, no chromophore aggregation was
found for either polyrotaxanes upon increasing their concen-
tration. Taking polymer P1 as an example, its absorption
features were identical on increasing the concentration be-
The intramolecular ET was also inefficient because the
donors could only interact with their adjacent acceptors. In
contrast, very efficient ET was observed in polyrotaxane P2.
As shown in Figure 2b, when excited at 330 nm, the fluores-
cence of the A2 unit at about 370 nm was very weak and
the emission band of unit B2 (lmax =456 nm) became domi-
nant. The significant difference in ET efficiency between
polymers P1 and P2 is attributed to their different confor-
mations in solution. Its topographical architecture endows
polyrotaxane P2 with distinct flexibility, thereby resulting in
a random-coil conformation in dilute solution. Although its
concentration was very low and intermolecular ET was
poor, the efficiency of intramolecular ET was still very high,
owing to the “flexible” chains, which allowed the polymers
to fold themselves such that the donors could interact with
more acceptors through spatial interactions.
To gain more insight into the relationship between the
topographical structure and photophysical properties of
these compounds, we compared the emission performance
of polymers P1 and P2 by using time-resolved fluorescence
spectroscopy in DMF. As shown in Figure 2c, when excited
at 390 nm (the excitation wavelength of the B2 unit), both
polyrotaxanes P1 and P2 showed single-exponential-decay
À
cause such a topography effectively suppressed the p p
stacking of the central OPV units, thus displaying no shift in
the absorption spectra.
Because both polyrotaxanes P1 and P2 had analogous
ground states, it was especially interesting to investigate the
significant difference between their emission spectra at vari-
ous concentrations in DMF. As shown in Figure 2, in the
case of polyrotaxane P1 (1ꢁ10À3 mgmLÀ1), two distinct
emission maxima at 370 and 456 nm were observed when
excited at 330 nm, which corresponded to the fluorescence
of units A1 and B2, respectively. This inefficient ET process
in dilute solution was not surprising; it was also observed
for our previously reported [3]rotaxane compound.[32] At
low concentrations, the polyrotaxane existed as separated
polymer chains and the polymer might extend as relatively
rigid rods, owing to the steric bulk of the attached truxene
units. Thus, the intermolecular ET process was impaired.
Figure 2. Emission spectra of P1 (a) and P2 (b) at different concentrations in DMF at room temperature; no red-shift of lmax was observed. The excita-
tion wavelength was set at 330 nm. c) Fluorescence-decay curves for each polyrotaxane in DMF (1ꢁ10À3 mgmLÀ1), in which highly efficient energy trans-
fer was observed in polymer P2. Polyrotaxanes P1 and P2 were excited at 330 nm and 390 nm, respectively. d) Plots of the DLS intensity of polymers P1
and P2 in DMF (1ꢁ10À1 mgmLÀ1) at room temperature.
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C.-J. Liu, J.-Y. Wang, J. Pei et al.
profiles with a lifetime (1.58 ns) that corresponded to the
lifetime of the B2 unit. For polyrotaxane P2, when excited
at 330 nm (the excitation wavelength of the A2 unit), the
decay curve was almost same as that when exited at 390 nm.
However, exciting polymer P1 at 330 nm led to a double-ex-
ponential-decay curve, with lifetimes of 6.40 and 1.71 ns,
which were assigned to the lifetime of truxene and OPV
parts, respectively. This result conclusively demonstrates
that ET happens within polymer P2, thus implying that the
conformation is of vital importance to the ET process.
Inevitably, intermolecular ET gradually became dominant
at higher concentrations. The steric bulk of the A1 units is
assumed to not only retain the rigid conformation of poly-
mer P1, but also to weaken the interactions between differ-
ent polymer chains. However, the electrostatic interactions
between the counterions contribute as the main intermolec-
ular force to pull those polyrotaxane chains together. As a
result, when the concentration increased, such a weak elec-
trostatic interaction enhanced the intermolecular ET proc-
ess, although the efficiency was not so high. On the other
hand, the P2 chains could contract and coil together, thus
inducing a complete fluorescence quenching of unit A2 and
a spontaneous intermolecular/intramolecular ET from com-
pound A2 to B2 at higher concentrations.
Scheme 4. Proposed conformations of the individual polymer chains and
their aggregated assemblies.
polyrotaxanes with various sizes were formed through inter-
molecular electrostatic interactions. These interactions were
relatively weak and the rigid-rod-like conformation of the
polyrotaxane chains in these assemblies were not interrupt-
ed too much. However, the higher degree of freedom in the
connecting units of polymer P2 led to it adopting a curved
shape. The as-formed coiled conformation promoted both
intramolecular ET process in dilute solution and intermolec-
ular ET process within the ball-shaped aggregates in concen-
trated solution.
This hypothesis was supported by DLS analysis (Fig-
ure 2d). The hydrodynamic radius (Rh) of polymer P1
showed a wide distribution, thus indicating that small poly-
rotaxane aggregates with a range of different sizes and indi-
vidual polymers co-existed in solution. In contrast, polyro-
taxane P2 exhibited a sharp peak, with a much larger Rh,
thus clearly revealing that these polymers prefer to aggre-
gate into large assemblies. Moreover, SLS measurements
also gave the mean-square radius of gyration (Rg; Table 1).
We further investigated the solid-state structures of both
polyrotaxanes on a substrate by using tapping-mode AFM.
The AFM samples were prepared by drop-casting highly di-
luted solutions of the polyrotaxane onto a mica surface and
allowing the solvent to evaporate naturally. Because polyro-
taxane P1 did not tend to form large assemblies, relatively
smooth domains with identical heights were observed. How-
ever, polyrotaxane P2 aggregated into large particles with
an average height of 200 nm, which agreed with the size that
was determined by DLS (Figure 3). We hypothesized that
the tendency of these rotaxanes for aggregation on the mica
surface was similar to that in solution.
Table 1. Hydrodynamic radius (Rh) and mean-square radius of gyration
(Rg) of polyrotaxanes P1 and P2 in DMF (1ꢁ10À1 mgmLÀ1).
P1
P2
Rg,app[a] [nm]
Rh,app[a] [nm]
1 (Rg/Rh)
22.3
11.6
1.92
118
138
0.86
[a] app=apparent.
The equation Rg/Rh is traditionally utilized to predict the
shape of such assemblies. Thus, the value of Rg/Rh for poly-
mer P1 is 1.96, which is typical of rigid-rod structures, whilst
polymer P2 gives a value of 0.86, which indicates that the
polymer chains adopt hard ball structures.
Figure 3. AFM topography of polyrotaxanes P1 (a) and P2 (b) on a mica
surface.
On the basis of the above experimental discussion, we
built several general models for polyrotaxanes P1 and P2 in
solution, as shown in Scheme 4. With respect to the outside
sterically hindering groups, polymer P1 performed as a rela-
tively stretched and rigid conformation; thus, its intramolec-
ular ET was inefficient because the donor and acceptor moi-
eties were not close enough to interact with each other. In
the condensed state at higher concentrations, assemblies of
Considering that electrostatic forces might be the key in
promoting the aggregation of these polyrotaxanes at high
concentrations, we suspected that the conformation of the
polyrotaxanes could be modulated by changing the counter-
ions in solution. Thus, exchange of the anions by the addi-
tion of various tetrabutylammonium (TBA) species, such as
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Main-Chain Linear Polyrotaxanes
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Figure 4. Emission spectra of polyrotaxanes P1 (a) and P2 (b) with different counterions in DMF (2ꢁ10À3 mgmLÀ1).
TBAI, TBABr, and TBACl, afforded a series of polyrotax-
anes with different anion sizes and their photophysical prop-
erties were carefully studied. It should be noted that the ab-
sorption features of these polyrotaxanes with various coun-
terions showed identical spectra, thus suggesting that there
was no chromophore aggregation in the ground state. Inter-
estingly, the emission of polyrotaxanes P1 and P2 with IÀ
polyrotaxane P2, which contributed much more than the
changes in the shuttling process to the ET process. However,
because of the week intermolecular interactions in polyro-
taxane P1, we obtained the result as the sum of individual
rotaxane molecules.
À
and PF6 counterions showed almost the same behavior,
Conclusions
thus indicating that the charge density on IÀ was too low to
change the conformation (Figure 4). However, either anions
BrÀ or ClÀ exhibited an enhanced ET process compared to
In summary, we have synthesized two functional main-chain
linear polyrotaxanes, P1 and P2, by employing strong
DB24C8/DBA interactions and click chemistry. The energy
donors and acceptors were attached to DB24C8 and DBA
units, respectively, and their photophysical properties were
studied in detail. All of the results show that the significant
differences of the emission spectra and time-resolved fluo-
rescence between polymers P1 and P2 are due to their dif-
ferent conformations in solution. Moreover, DLS, SLS, and
AFM experiments further reveal that polymer P1 is unbend-
ing and rigid-rod-like in structure and that electrostatic in-
teractions are crucial for its assembly, although large assem-
blies are difficult to form. However, polyrotaxane P2 is
curved and flexible and is much easier mold into ball-
shaped particles. Taking advantage of their unique confor-
mational behaviors, we can modulate their ET efficiency by
replacing the counterions with various anions, as well as by
actuating DB24C8/DBA-based molecular shuttles in the
presence of base. This work not only provides us with a
better insight into the relationship between the structures
and properties of these polyrotaxanes, but also provides a
fundamental platform for innovating in the development of
new functional materials and in finding new applications
based on these superamolecular polymers.
À
PF6 , which could be observed more remarkably in polymer
P1. The maximum at 370 nm became weak, whereas the
emission of the acceptor part was enhanced through an ET
process. We assumed that the higher the charge density on
the anion was, the stronger the electrostatic interactions
were between the polymer chains/segments. Although ET
enhancement was also observed in polyrotaxane P2, the
extent of the enhancement was relatively low, which may be
because the main driving force for ET in polymer P2 was
coiling and its ET was already very efficient.
It is well-known that DB24C8/DBA-based rotaxanes are
good molecular shuttles that are driven by acid/base. Their
host–guest interaction can be suppressed by treatment with
base and reversibly recovered with acid. In this regard, the
polyrotaxanes were treated with tBuOK to break the inter-
actions between DB24C8 and DBA. As shown in Figure 5,
polymer P1 exhibited dual changes in its emission bands:
Enhancement of the energy-donor band and the decrease in
the energy-acceptor band, which originated from lower ET
efficiency through longer distances and fluorescence
quenching by photoinduced electron transfer (PET) from
the amino lone pairs to OPV, respectively. However, the
strong tendency of polyrotaxane P2 for folding and coiling
caused it to retain its efficient ET process and the fluores-
cence of the energy donor (lmax =370 nm) remained weak.
Furthermore, the PET process quenched the fluorescence of
the OPV segment (lmax =456 nm). These results also sup-
ported our hypothesis that a coiling conformation existed in
Experimental Section
Measurements: 1H and 13C NMR spectra were recorded on Varian Mer-
cury plus 300 MHz or ARX400 400 MHz spectrometers at RT in appro-
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C.-J. Liu, J.-Y. Wang, J. Pei et al.
Figure 5. a) Graphical representation of the molecular shuttle (the vertical arrows indicate the location of the threaded ring) and the emission spectra of
polymers P1 (b) and P2 (c) in DMF at room temperature before (solid line) and after the addition of base (dotted line).
priate deuterated solvents. All of the chemical shifts are reported in parts
per million [ppm]. Absorption spectra were recorded on a Perkin–Elmer
Lambda 35 UV/Vis Spectrometer. Fluorescence spectra were recorded
on a Perkin–Elmer LS55 Luminescence Spectrometer. HRMS (ESI)
spectra were recorded on a Bruker Apex IV FTMS in freshly distilled
CHCl3. Time-resolved fluorescence measurement was performed by
using the time-correlated single-photon-counting technique following ex-
citation by a nanosecond flash lamp (Edinburgh Instruments FL900).
GPC was obtained on a Waters GPC 2410 with a refractive-index detec-
tor in DMF by using a calibration curve of the polystyrene standards. Re-
cycling preparative GPC was performed on a JAI LC-9201 recycling
preparative HPLC with 2H GPC column. Tapping-mode atomic force mi-
croscopy (AFM) measurements were performed on a SPA-400 multi-
mode AFM with an SPI3800N probe station. For the preparation of the
samples for AFM analysis, the rigid gel was dropped onto a freshly
cleaved mica surface and dried in air at RT before imaging. A commer-
cial LLS spectrometer (Brookhaven, Holtsville, NY) that was equipped
with a BI-200SM goniometer and a BI-TurboCorr digital correlator was
used to perform both static light scattering (SLS) and dynamic light scat-
tering measurements (DLS) over scattering angles in the range 20–1208.
Na2SO4. After removal of the solvents under reduced pressure, the resi-
due was purified by column chromatography on silica gel (petroleum
ether and petroleum ether/CH2Cl2, 20:1) to give compound 2 as a yellow
solid. Yield: 21%; 1H NMR (400 MHz, CDCl3): d=8.18–8.36 (m, 3H),
7.68–7.70 (d, J=8.0 Hz, 2H), 7.51–7.62 (m, 6H), 7.04–7.06 (d, J=8.0 Hz,
2H), 2.85–3.02 (m, 6H), 2.01–2.16 (m, 6H), 0.85–0.93 (m, 36H), 0.50–
0.93 ppm (m, 30H); 13C NMR (100 MHz, CDCl3): d=159.2, 156.0, 155.9,
154.1, 145.5, 144.8, 144.3, 139.2, 139.1, 139.0, 138.5, 138.4, 137.6, 137.4,
133.7, 129.3, 129.2, 128.1, 126.0, 125.8, 125.5, 125.4, 124.8, 120.8, 120.2,
114.3, 56.0, 55.9, 55.8, 55.4, 37.0, 36.9, 36.8, 31.5, 29.4, 29.3, 23.9, 22.2,
13.9 ppm; HRMS (ESI): m/z calcd for C70H94Br2O: 1108.5666; found:
1108.5667.
Compound 3: Compound 2 (1.80 g, 1.6 mmol), 4-formylphenylboronic
acid (1.06 g, 6.50 mmol), and [PdACHTNUGTRENUNG(PPh3)4] (0.0920 g, 0.0800 mmol) in THF
(50 mL) were added into a flask under a nitrogen atmosphere. An aque-
ous solution of K2CO3 (1.77 g, 12.8 mmol) was added and the mixture
was stirred for 12 h at 808C, before being washed with deionized water,
and extracted with EtOAc. The organic layer was dried over anhydrous
Na2SO4. After removal of solvents under reduced pressure, the residue
was purified by column chromatography on silica gel (CH2Cl2) to give
compound 3 as a yellow solid, Yield: 82%; 1H NMR (400 MHz, CDCl3):
d=10.11 (s, 2H), 8.41–8.51 (m, 3H), 8.03–8.05 (d, J=8.0 Hz, 4H), 7.93–
7.95 (d, J=8.0 Hz, 4H), 7.64–7.76 (m, 8H), 7.06–7.08 (d, J=8.0 Hz, 2H),
3.90 (s, 3H, 3.00–3.08 (m, 6H), 2.15–2.22 (m, 6H), 0.82–1.01 (m, 36H),
0.59–0.62 ppm (m, 30H); 13C NMR (100 MHz, CDCl3): d=191.9, 159.2,
154.6, 154.5, 154.2, 147.3, 145.8, 145.5, 145.3, 140.9, 140.8, 138.9, 138.7,
138.4, 137.8, 137.7, 137.5, 135.1, 133.8, 130.3, 128.1, 127.5, 125.5, 125.1,
125.0, 124.9, 124.8, 120.8, 120.7, 120.2, 114.3, 56.0, 55.9, 55.87, 55.83, 55.4,
37.1, 37.0, 31.4, 29.4, 23.9, 23.9, 22.2, 13.8 ppm; HRMS (ESI): m/z calcd
for C84H104O3: 1160.7980; found: 1160.7971.
A
100 mW, vertically polarized solid-state laser (GNI, Changchun,
China) that was operating at 532 nm was used as the light source.
Materials: Commercial chemicals were purchased and used as received.
All air- and moisture-sensitive reactions were performed under a nitro-
gen atmosphere.
Compound 2: Compound 1 (10.0 g, 9.20 mmol), 4-methoxyphenylboronic
acid (1.12 g, 7.40 mmol), and [PdACHTNUGTRNEUNG(PPh3)4] (0.531 g, 0.460 mmol) in THF
(200 mL) were added into a flask under a nitrogen atmosphere. An aque-
ous solution of K2CO3 (4.06 g, 29.4 mmol) was added and the mixture
was stirred for 12 h at 808C, before being washed with deionized water
and extracted with EtOAc. The organic layer was dried over anhydrous
1508
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Chem. Eur. J. 2013, 19, 1502 – 1510

Main-Chain Linear Polyrotaxanes
FULL PAPER
Compound 4: Compound 3 (1.26 g, 1.10 mmol) was dissolved in THF
(50 mL), lithium aluminum hydride (0.160 g, 4.30 mmol) was added at
08C, and the mixture was stirred for 5 h before being quenched with
aqueous Na2SO4 and extracted with EtOAc. The organic layer was dried
over anhydrous Na2SO4, the solvents were removed under reduced pres-
sure, and the residue was purified by column chromatography on silica
gel (petroleum ether/EtOAc, 1:1) to give compound 4 as a yellow solid.
Yield: 90%; 1H NMR (400 MHz, CDCl3): d=8.40–8.45 (m, 3H), 7.77–
7.79 (d, J=8.0 Hz, 4H), 7.61–7.72 (m, 8H), 7.51–7.53 (d, J=8.0 Hz, 4H),
7.05–7.07 (d, J=8.0 Hz, 2H), 4.79 (s, 4H), 3.05 (s, 3H), 3.01–3.04 (m,
6H), 2.15–2.20 (m, 6H), 0.82–0.99 (m, 36H, 0.58–0.62 ppm (m, 30H);
13C NMR (100 MHz, CDCl3): d=159.1, 154.3, 154.2, 145.2, 145.1, 145.0,
140.8, 139.8, 139.7, 138.7, 138.6, 138.2, 138.0, 133.9, 128.1, 127.5, 127.3,
125.0, 124.9, 124.7, 120.5, 120.1, 114.3, 65.2, 55.6, 55.4, 37.1, 31.5, 29.5,
23.9, 22.3, 13.9 ppm; HRMS (ESI): m/z calcd for C84H108O3: 1164.8293;
found: 1164.8286.
Compound C2: Compound 9 (2.78 g, 8.73 mmol), N-bromosuccinimide
(NBS, 3.26 g, 18.3 mmol), and 2,2’-azobisisobutyronitrile (AIBN, 0.140 g,
0.870 mmol) were dissolved in CCl4 (50 mL) and the mixture was heated
at reflux for 12 h. After removal of the solvent under reduced pressure,
the residue was dissolved in acetone (50 mL) and sodium azide (2.27 g,
34.9 mmol) was added. The mixture was heated at reflux for 12 h. After
filtration and removal of the solvent under reduced pressure, the residue
was purified by column chromatography on silica gel (petroleum ether/
CH2Cl2, 1:1) to give compound C2 as a white solid. Yield: 50% over
2 steps; 1H NMR (300 MHz, CDCl3): d=7.38 (s, 2H), 7.32–7.34 (d, J=
6.0 Hz, 4H), 7.00–7.22 (d, J=6.0 Hz, 4H), 4.33 (s, 4H), 3.88 ppm (s, 6H);
13C NMR (75 MHz, CDCl3): d=159.1, 140.7, 132.8, 131.6, 130.2, 113.8,
113.7, 55.42, 52.2, 52.1 ppm; MS (EI): m/z calcd for C22H20N6O2: 400;
found: 400; elemental analysis calcd (%) for C22H20N6O2: C 65.99,
H 5.03, N 20.99; found: C 65.52, H 5.01, N 21.07.
Compound 6: Compound
4 (0.956 g, 0.820 mmol) was dissolved in
CH2Cl2 (50 mL), phosphorus tribromide (0.890 g, 3.28 mmol) was added
dropwise at 08C, and the reaction was stirred at RT for 5 h before being
quenched with MeOH. The mixture was washed with deionized water
and extracted with EtOAc and the organic layer was dried over Na2SO4.
After removal of the solvent under reduced pressure, the residue was dis-
solved in acetone (50 mL) and sodium azide (0.170 g, 2.60 mmol) was
added. The mixture was heated at reflux for 12 h. After filtration, the sol-
vent was removed under reduced pressure and the residue was purified
by column chromatography on silica gel (petroleum ether/CH2Cl2, 5:1) to
give compound 6 as a white solid. Yield: 73% over 2 steps; 1H NMR
(400 MHz, CDCl3): d=8.40–8.46 (m, 3H), 7.78–7.80 (d, J=8.0 Hz, 4H),
7.62–7.72 (m, 8H), 7.46–7.48 (d, J=8.0 Hz, 4H), 7.05–7.07 (d, J=8.0 Hz,
2H, 4.43 (s, 4H), 3.90 (s, 3H), 3.00–3.03 (m, 6H), 2.13–2.20 (m, 6H),
0.82–0.99 (m, 36H), 0.57–0.62 ppm (m, 30H,); 13C NMR (100 MHz,
CDCl3): d=159.1, 154.4, 154.3, 154.2, 145.2, 145.1, 141.4, 139.9, 139.0,
138.7, 138.3, 138.2, 138.0, 137.9, 134.2, 133.9, 128.8, 128.1, 127.5, 125.1,
124.9, 124.8, 124.7, 120.5, 120.1, 114.3, 55.8, 55.4, 54.6, 37.1, 31.5, 29.5,
23.9, 22.3, 13.9 ppm; HRMS (ESI): m/z calcd for C84H106N6O: 1214.8423;
found: 1214.8411.
Acknowledgements
We appreciate the financial support of this research by the Major State
Basic Research Development Program (No. 2009CB623601), the Ministry
of Science and Technology, and the National Natural Science Foundation
of China.
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Compound A2: A mixture of compound 6 (0.364 g, 0.300 mmol), com-
pound 7 (0.703 g, 1.50 mmol), and CuACTHUNTRGNE(UNG CH3CN)4PF6 (0.240 g, 0.600 mmol)
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145.2, 145.1, 145.0, 141.6, 139.9, 138.9, 138.7, 138.1, 138.0, 137.9, 133.8,
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Compound 9: 1,4-Dibromo-2,5-dimethylbenzene (5.00 g, 19.1 mmol), 4-
methoxyphenylboronic acid (7.20 g, 47.4 mmol), Na2CO3 (8.01 g,
75.6 mmol), [PdACHTUNGTRENNUNG(PPh3)4] (1.03 g, 0.900 mmol), and THF (200 mL) were
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9.0 Hz, 4H), 7.13 (s, 2H), 6.94–6.97 (d, J=9.0 Hz, 4H), 3.84 (s, 6H),
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Received: September 6, 2012
Published online: November 30, 2012
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Chem. Eur. J. 2013, 19, 1502 – 1510