A Photoresponsive Orthogonal Supramolecular Complex Based on Host–Guest Interactions

Article abstract of DOI:10.1002/chem.201604634

We synthesized a novel green-light-responsive tetra-ortho-isopropoxy-substituted azobenzene (ipAzo). Cis-ipAzo forms a strong host–guest complex with γ-cyclo dextrin (γ-CD) whereas trans-ipAzo binds weakly. This new photoresponsive host–guest interaction

Full text of DOI:10.1002/chem.201604634

A Journal of
Accepted Article
Title: A photoresponsive orthogonal supramolecular complex based on
host-guest interactions
Authors: Dongsheng Wang, Manfred Wagner, Andrew Saydjari, Julius
Mueller, Svenja Winzen, Hans-Jürgen Butt, and Si Wu
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To be cited as: Chem. Eur. J. 10.1002/chem.201604634
Link to VoR: http://dx.doi.org/10.1002/chem.201604634
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Chemistry - A European Journal
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A photoresponsive orthogonal supramolecular complex based on
host-guest interactions
[
a]
[a]
[a, b]
[a]
[a]
Dongsheng Wang, Manfred Wagner, Andrew K. Saydjari,
Julius Mueller, Svenja Winzen,
[
a]
[a]
Hans-Jürgen Butt, and Si Wu*
[
6]
Abstract: We synthesized a novel green-light-responsive tetra-
ortho-isopropoxy-substituted azobenzene (ipAzo). Cis ipAzo forms a
strong host-guest complex with γ-cyclodextrin (γ-CD) while trans
ipAzo binds weakly. This new photoresponsive host-guest
interaction is reverse to the well-known azobenzene (Azo)/α-
cyclodextrin (α-CD) complex, which is strong only between trans Azo
and α-CD. By combining the UV-light-responsive Azo/α-CD and
photoresponsive surfaces, and macroscopic self-assemblies.
To realize the photoresponsive orthogonal supramolecular
system, another host-guest complex responsive to irradiation
with the wavelength far from UV light is needed. Incorporation of
electron-donating groups ortho or para to the Azo moiety red-
shifts the photoswitching wavelength for the trans-to-cis
isomerization. In our previous work, by modifying the Azo
moiety with methoxy groups, the synthesized tetra-ortho-
methoxy-substituted Azo (mAzo) shows red light induced trans-
to-cis isomerization and different supramolecular properties
[
7]
green-light-responsive ipAzo/γ-CD host-guest complexes,
a
photoresponsive orthogonal supramolecular system is developed.
[
8]
compared with normal Azo. Neither trans nor cis mAzo can
form host-guest complex with α-CD. However, strong host-guest
complex is formed between trans mAzo and β-cyclodextrin (β-
CD), while the host-guest interaction between cis mAzo and β-
CD is weak. The observed supramolecular properties of mAzo
likely derive from the bulky substituent groups and the larger
hydrophobic cavity of β-CD as compared to α-CD. However,
while trans Azo has been reported to form strong host-guest
complex with β-CD, the mAzo/β-CD complex is not suitable to
be applied for the photoresponsive orthogonal supramolecular
Introduction
Light as a clean, efficient and precise external stimulus has been
extensively used to control processes and functions in chemistry,
[
1]
biology
and
materials
science.
Photoresponsive
supramolecular materials obtain plenty of attention due to the
multi-functionality and efficient reactivity.
[2]
Photoresponsive
materials develop more complex recently. More than one
chromophore is included, and multiple sources of light with
various wavelengths can be applied to control the systems
orthogonally in several independent states, which make the
photoresponsive orthogonal materials able to react to complex
external irradiations and show various properties. However,
most of the photoresponsive chromophores have significantly
overlapping absorption bands in the UV-visible region, which
[9]
system. Another photoresponsive host-guest complex is still
needed.
[
3]
[
1f, 3a]
limit the targeted excitation.
Azobenzene (Azo), well-known for UV light induced trans-to-cis
isomerization and blue light or heating induced cis-to-trans
isomerization, has been widely investigated for its
photoresponsive host-guest supramolecular interaction with α-
[
4]
cyclodextrin (α-CD). Generally, trans Azo is able to enter the
hydrophobic cavity of α-CD in water environment to form a 1:1
[
5]
host-guest complex. In contrast, cis Azo does not fit α-CD
cavity and is more hydrophilic than trans Azo, which slides out of
the hydrophobic cavity and further induces disassembly of the
host-guest
complex
(Scheme
1).
Photoresponsive
supramolecular materials based on the Azo/α-CD host-guest
interaction have been constructed for various applications,
including supramolecular hydrogels, drug delivery systems,
Scheme 1. Schematic illustration of the photoresponsive host-guest
interaction between Azo and α-CD, and between ipAzo and γ-CD. Blue light or
heating induces the assembly of the Azo/α-CD complex, while UV light
irradiation induces the disassembly of the complex. Green light irradiation
induces the assembly of the ipAzo/γ-CD complex, while blue light or heating
induces the disassembly of the complex.
[
[
a]
b]
D. Wang, Dr. M. Wagner, A. K. Saydjari , J. Mueller, Dr. S. Winzen,
Prof. Dr. H.-J. Butt, Dr. S. Wu
Max-Planck Institute of Polymer Research
Ackermannweg 10, D-55128, Mainz, Germany
E-mail: wusi@mpip-mainz.mpg.de
A. K. Saydjari
Department of Chemistry
Yale University
Here, we synthesized green-light-responsive tetra-ortho-
isopropoxy-substituted Azo (ipAzo) with four larger substituent
groups than mAzo. Interestingly, a strong host-guest complex
was observed between cis ipAzo and γ-cyclodextrin (γ-CD),
while the host-guest interaction between trans ipAzo and γ-CD
was weak (Scheme 1). The result was the reverse of the Azo/α-
225 Prospect St. New Haven, CT 06520, USA
Supporting information for this article is given via a link at the end of
the document.
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CD complex. The potential application to fabricate
photoresponsive orthogonal supramolecular systems was
investigated by combining the green-light-responsive ipAzo/γ-
CD complex with the known UV-light-responsive Azo/α-CD host-
guest complex.
ipAzo-Py was separated from that of cis ipAzo-Py in the green-
light region. Thus, green light could excite the trans ipAzo-Py n-
π* transition and induce the trans-to-cis isomerization.
[
10]
Approximately 80% of trans ipAzo-Py switched to cis ipAzo-Py
2
after 530 nm green light irradiation for 30 min (40 mW/cm )
(
Figure 1b). The cis ipAzo-Py could be switched back to the
trans form by heating or blue light irradiation (470 nm) (Figure
S4-S7).
Results and Discussion
1
Figure 2. H NMR spectra (700 MHz in D
2
O at 298K) of trans/cis ipAzo-Py
mixture before (blue) and after (red) adding of γ-CD. ([trans ipAzo-Py]:[cis
ipAzo-Py]≈1:1, [ipAzo-Py]=1 mM, [ipAzo-Py]:[γ-CD]=1:1)
Host-guest Interaction between ipAzo-Py and γ-CD
To investigate the supramolecular interaction between ipAzo-Py
and γ-CD, trans ipAzo-Py in D
2
O was irradiated with green light
2
(
20 mW/cm ) for 30 min to obtain ~50% cis ipAzo-Py ([trans
1
ipAzo-Py]:[cis ipAzo-Py]≈1:1). H NMR spectra were recorded
for the trans ipAzo-Py/cis ipAzo-Py mixture before and after
adding γ-CD, respectively (Figure 2). No obvious shift of the
proton signals in the aromatic region of trans ipAzo-Py could be
observed after adding γ-CD, suggesting no supramolecular
complex was formed between trans ipAzo-Py and γ-CD.
However, after adding γ-CD, significant shifts of cis ipAzo-Py
proton signals in the aromatic region could be observed, due to
the host-guest complex formation between cis ipAzo-Py and γ-
1
Figure 1. UV/vis (a) ([ipAzo-Py]=0.4 mM in H
NMR (b) (250 MHz in D
2
O/methanol, v:v=9:1) and
H
2
O at 298 K, [ipAzo-Py]=1 mM) spectra of ipAzo-Py
before (black lines) and after (red lines) green light irradiation (530 nm, 40
mW/cm , 30 min). The inset in (a) shows the enlarged absorption spectra of
ipAzo-Py in the green light region. The signal at δ=2.25 may come from
1
CD. H NMR and UV/vis titration results further supported that
2
the cis ipAzo-Py could form a 1:1 host-guest complex with γ-CD,
while no supramolecular complex was formed between trans
ipAzo-Py and γ-CD (Figure S8-S13).
impurity, and will not affect the host-guest interaction.
The green-light-responsive host-guest interaction between
ipAzo-Py and γ-CD was further confirmed by two-dimensional
nuclear Overhauser effect spectroscopy (2D NOESY) and
electrospray ionization mass spectrometry (ESI-MS) (Figure 3,
S15, S16). No correlation could be observed between the
protons of trans ipAzo-Py and γ-CD, indicating that trans ipAzo-
Py does not form a complex with γ-CD (Figure 3, left). After
irradiation with green light, strong correlation between the
protons of cis ipAzo-Py (proton a`, b`, c` and d`) and the inner
protons of γ-CD could be observed. These results indicated that
cis ipAzo-Py entered the hydrophobic cavity of γ-CD deeply to
form the host-guest complex (Figure 3, S14). The 2D NOESY
results were in good accordance with the ESI-MS
Photoisomerization of ipAzo-Py
However, the solubility of ipAzo in water was poor, which
hindered supramolecular investigations. To increase the
hydrophilicity, ipAzo-Py was synthesized by grafting pyridine to
ipAzo (Experimental Section). Due to the amphiphilicity, ipAzo-
Py may form aggregates in water (Figure S1-S3).
The photoisomerization of ipAzo-Py was investigated by UV/vis
1
absorption spectroscopy and H NMR (Figure 1). After green
light irradiation, trans ipAzo-Py switched to the cis form, inducing
a decrease in the π-π* transition band and an increase in the n-
π* transition band (Figure 1a). The n-π* transition band of trans
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Figure 3. 2D NOESY spectra (700 MHz in D
2
O at 298 K) of trans ipAzo-Py/γ-CD (left) and cis ipAzo-Py/γ-CD (right). The red/green rectangles in the spectra
show whether there are correlations between the protons of ipAzo-Py and the protons of γ-CD. ([ipAzo-Py]=2 mM, [ipAzo-Py]:[γ-CD]=1:1)
spectra. A strong peak at m/z=1902.71 corresponding to the
singly charged host-guest complex cis ipAzo-Py/γ-CD could be
observed, which was weak for the mixture of trans ipAzo-Py and
γ-CD. (Figure S15, S16).
These results were also well supported by DFT calculated
molecular models of trans ipAzo and cis ipAzo (Figure 4). Both
trans ipAzo and cis ipAzo showed highly nonplanar structures
due to sterics of the grafted isopropoxy groups. In contrast to the
reported Azo/α-CD system, the calculated width of trans ipAzo
was larger than the hydrophobic cavity of γ-CD while the
calculated width of cis ipAzo was smaller than the hydrophobic
cavity of γ-CD. Thus, the surprising behavior of ipAzo/γ-CD
system derives from a different mechanism of disassembly;
[
12]
Figure 4. DFT calculated molecular models of Azo molecules. CD cavity sizes were from literature.
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Figure 5. (a) Schematic illustration of the photoresponsive orthogonal supramolecular system formed by Azo/α-CD and ipAzo/γ-CD host-guest complexes. (b) 2D
NOESY spectra (700 MHz in D O at 298 K) of the photoresponsive orthogonal supramolecular system in “both closed” state (II, left), “single open” state (I, middle),
2
and “both open” state (III, right). The green rectangle shows the correlation between the protons of trans Azo-Py and the protons of γ-CD, the purple rectangle
shows the correlation between the protons of trans Azo-Py and the protons of α-CD, the yellow rectangle shows the correlation between the protons of cis ipAzo-
Py and the protons of γ-CD. ([Azo-Py]=2 mM, [Azo-Py]:[ipAzo-Py]:[α- CD]:[γ-CD]=1:1:1:1)
The light used to induce trans-to-cis photoisomerization of Azo
and ipAzo were orthogonal to each other with respect to
a
Table 1. Association constants (K
a
) between α-CD or γ-CD and ipAzo or Azo.
wavelength (Figure S17, S18). Then, to design an orthogonal
supramolecular system using the Azo/α-CD and ipAzo/γ-CD
host-guest complexes, trans Azo should only combine with α-CD
rather than γ-CD, while cis ipAzo should only combine with γ-CD
Guest
-
1
a
K (M )
trans ipAzo
26.4±8.0
25.9±5.1
cis ipAzo
trans Azo
1340.0±510.0
149.0±1.2
cis Azo
25.4±9.4
16.0±20.0
[
11]
rather than α-CD.
The host-guest interactions between
α-CD
γ-CD
28.3±6.9
Azo/ipAzo and α-CD/γ-CD were therefore quantified by
Host
measuring the association constants (K ) of the host-guest
a
1659.0±57.0
complexes (Supporting Information, Figure S19-S30). The
association constants are listed in Table 1, where Azo-Py and
ipAzo-Py were used as the guest molecules, and a modified
Benesi-Hildebrand equation was used for the calculation of the
association constants between Azos and CDs. Trans Azo-Py
showed a high association constant with α-CD, while the
association constant between cis Azo-Py and α-CD was low, in
[
a] The details for measuring K
a
are provided in Supporting Information
(Equation S1 and Figure S19-S30). Error bars represent one standard
deviation as calculated from orthogonal distance regression.
[6a, d]
accordance with reported results.
Both trans and cis Azo-Py
instead of the guest width being too small for the host cavity, the
guest width is too large.
showed low association constants with γ-CD, indicating weak
host-guest interactions between Azo-Py and γ-CD. The results
were further consistent with calculated molecular models
Photoresponsive orthogonal supramolecular system
Combining the widely-reported UV-light-responsive Azo/α-CD
host-guest complex with this novel green-light-responsive
ipAzo/γ-CD host-guest complex, we foresaw the potential for
photoresponsive orthogonal supramolecular systems.
(
Figure 4). Because the hydrophobic cavity of γ-CD is too large
for both trans and cis Azo, trans Azo-Py may enter the
hydrophobic cavity of γ-CD to form a weak supramolecular
complex. However, the trans Azo-Py/γ-CD complex is unstable
and can be disassembled in the presence of α-CD (Figure S32).
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In the mixture of trans Azo-Py, α-CD, and γ-CD ([Azo-Py]:[α-
CD]:[γ-CD]=1:1:1), ~80% of trans Azo-Py formed host-guest
complex with α-CD, while only ~10% of trans Azo-Py/γ-CD
complex could be formed (SI). For ipAzo-Py, γ-CD showed a
much higher association constant with cis ipAzo-Py compared to
the trans isomer, while very low association constants were
shown for both trans and cis ipAzo-Py with α-CD. These results
were attributed to the hydrophobic cavity size of α-CD being
smaller than the width of ipAzo (Figure 4).
responsive supramolecular colloids, polymers, surfaces, and
gels. We also expect that more interesting photoresponsive
orthogonal supramolecular structures could be realized by
combining the UV-light-responsive Azo/α-CD and green-light-
responsive ipAzo/γ-CD host-guest complexes, including
photoresponsive hierarchical self-assemblies, dual-drug release
systems, and photoresponsive interpenetrating polymer network
[
13]
hydrogels.
From the above results, the photoresponsive orthogonal
supramolecular system could be described as in Figure 5a. Experimental Section
Strong host-guest complexes could only be formed between
trans Azo and α-CD, and between cis ipAzo and γ-CD, which
were UV/blue-light-responsive and green/blue-light-responsive,
respectively. After heating or blue light irradiation, the system of
Azo, ipAzo, α-CD, and γ-CD was in the thermodynamic “single
open” state (I). Green light irradiation transformed the system to
the “both closed” state (II) while UV irradiation transformed the
system to the “both open” state (III). Each of these state were
easily obtained from any other by the application of heat or blue
light (I, “single open”), green light (II, “both closed”), or UV light
Materials and Reagents
2-nitroresorcinol (C H NO , CAS No. 601-89-8), 2-iodopropane (C H I,
6
5
4
3
7
CAS No. 75-30-9), 6-bromohexanoic acid (C
), phloroglucinol (C , CAS No. 108-73-6), 2-bromopropane (C
CAS No. 75-26-3), pyridine (C N, 110-86-1), and tin (II) chloride
dihydrate (SnCl 2H O, CAS No. 10025-69-1) were purchased from Alfa
Aesar. 4-Aminoazobenzene (C12 CAS No. 60-09-3), N, N`-
dicyclohexylcarbodiimide (DCC) (C13 CAS No. 538-75-0), 4-
, CAS No. 1122-58-3), and
, CAS No. 7632-00-0) were purchased from Sigma
6
H
11BrO
2
, CAS No. 4224-70-
8
6 6
H O
3
3 7
H
Br,
5
H
5
2
2
11 3
H N ,
H
22
N
2
,
(dimethylamino)pyridine (DMAP) (C
7
H
10
N
2
(
III, “both open”).
NOESY was used to confirm the formation of the
sodium nitrite (NaNO
2
2D
Aldrich. α-Cyclodextrin (α-CD) (C36H60O30, CAS No. 10016-20-3), γ-
cyclodextrin (γ-CD) (C48 CAS No. 17465-86-0), and N-(3-
dimethylaminopropyl)-N`-ethylcarbodiimide hydrochloride (EDC) (C
Cl, CAS No. 25952-53-8) were purchased from Acros Organics. All the
orthogonal supramolecular system in the mixture of trans Azo-
Py, cis ipAzo-Py, α-CD, and γ-CD (II, “both closed” state)
80 40
H O ,
8
H
18
N
3
(
Figure 5b, left). In the 2D NOESY spectrum, the proton signals
solvents (HPLC grade) were purchased from Sigma Aldrich and were
directly used without any further purification. Milli-Q water (resistivity:
of α-CD and γ-CD overlapped heavily. However, the signal at
δ=3.8 (belonging to the inner protons of γ-CD) displayed strong
correlation with the protons of cis ipAzo-Py (yellow rectangle),
while the correlation between the protons of trans Azo-Py and
the inner protons of γ-CD was relatively weak (green rectangle).
Thus, correlation of trans Azo-Py and the overlapped region of
α-CD and γ-CD (purple rectangle) consisted mostly of signal
from a strong trans Azo-Py/α-CD complex. The 2D NOESY
results indicated that a majority of trans Azo-Py/α-CD and cis
ipAzo-Py/γ-CD complexes, in other words, the orthogonal
supramolecular system, could be formed from the mixture of
trans Azo-Py, cis ipAzo-Py, α-CD, and γ-CD (II, “both closed”
state). After blue light or UV light irradiation, the “single open” (I)
or “both open” (III) states of the orthogonal supramolecular
system could be obtained (Figure 5b, middle, right).
18.2 MΩ×cm) provided by a Sartorius Arium 611 VF Purification System
was used throughout the project.
Methods
1
13
H and C nuclear magnetic resonance (NMR) spectra were recorded on
1
1
a Bruker Avance 250 MHz spectrometer. The 2D H, H-NOESY spectra
were recorded on a Bruker Avance 700 MHz spectrometer. Mass spectra
(
MS) were obtained using a VG instrument ZAB 2-SE-FPD. Electrospray
ionization mass spectra (ESI-MS) were obtained using Waters
instrument Q-Tof Ultima 3 micromass. UV/vis absorption spectra were
measured on Lambda 900 spectrometer (Perkin Elmer). ITC
a
a
experiments were performed with a NanoITC Low Volume from TA
Instruments (Eschborn, Germany). The reported DFT calculations were
performed without any symmetry constraints, using 6-311G(d,p) basis set,
and B3LYP functional in Gaussian09. Optimized geometries for trans and
cis isomers were easily obtained by initializing the dihedral angle about
o
the nitrogen-nitrogen double bond at
0
or 180 respectively.
Conclusions
Photoisomerization was induced by the LEDs with the wavelengths of
65, 470 and 530 nm (device types LCS-0365-03-22, LCS-0470-03-22
3
In the present research, a novel photoresponsive host-guest
interaction between ipAzo and γ-CD was demonstrated.
Opposite of the known interaction between Azo and α-CD, trans
ipAzo was unable to form supramolecular complex with γ-CD.
However, after green light irradiation, a strong 1:1 host-guest
complex could be formed between cis ipAzo and γ-CD. With the
UV-light-responsive Azo/α-CD and green-light-responsive
ipAzo/γ-CD host-guest complexes, the potential to design
photoresponsive orthogonal supramolecular systems was
confirmed. As a new photoresponsive host-guest interaction, the
ipAzo/γ-CD complex has potential to construct green-light-
and LCS-0530-03-22, Mightex Systems). The output intensities of the
LEDs were controlled by an LED controller (device type SLC-MA04-MU,
Mightex Systems) and were calibrated by an optical power meter (Model
407A, Spectra-Physics Corporation).
Synthesis
The route for the synthesis of the chemicals is shown in Scheme S1.
Synthesis of 2. 2-nitroresorcinol (1 in Scheme S1, 1550 mg, 10 mmol),
2
-iodopropane (3910 mg, 23 mmol) and K
2 3
CO (4140 mg, 30 mmol) were
o
dissolved into 100 mL of DMF. After stirring under 90 C for 16 h, the
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Chemistry - A European Journal
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DMF was removed by rotating evaporation. The residue was washed by
ethyl acetate (EA) 3 times to obtain the rough product. The black solid
Synthesis of ipAzo-Py. ipAzo-Br (97 mg, 0.16 mmol) was dissolved in
THF (20 mL). Then, pyridine (20 mL) was added. The mixture was stirred
o
was further purified by chromatography using dichloromethane as eluent
overnight at 60 C under Ar. The solvents were removed by roto-
1
to obtain product 2. Yield: 75%. H NMR (DMSO-d
6
, 250 MHz): δ=7.40 (t,
evaporation. The obtained dark red solid was dissolved in methanol. The
solution was added slowly to plenty of petroleum ether under stirring, and
J=8.5 Hz, 1H), δ=6.87 (d, J=8.6 Hz, 2H), δ=4.73 (hept, J=6.1 Hz, 2H),
δ=1.24 (d, J=6.1 Hz, 12 H). 13C-NMR (DMSO-d , 63 MHz): δ=153.5,
6
the red precipitate was filtered and dried under vacuum to obtain ipAzo-
1
δ=138.2, δ=121.3, δ=108.9, δ=70.0, δ=22.0. MS cal: m/z=239.1 found:
Py. Yield: 90%. H NMR (D
2
O, 250 MHz): δ=8.53 (d, J=5.6 Hz, 2H),
m/z=239.3.
δ=8.21 (t, J=8.1 Hz, 1H), δ=7.73 (t, J=7.0 Hz, 2H), δ=6.99 (t, J=8.4 Hz,
H), δ=6.54 (d, J=8.5 Hz, 2H), δ=6.29 (s, 2H), δ=4.31 (m, 2H), δ=2.34 (t,
1
J=7.2 Hz, 2H), δ=1.75-1.23 (m, 6H), δ=0.90 (d, J=5.7 Hz, 24H). ESI-MS
cal: m/z=604.3 found: m/z=605.3
2 2
Synthesis of 3.2 (2300 mg, 10 mmol) and excess of SnCl 2H O (4500
mg, 20 mmol) were dissolved into 30 mL of EA. The mixture was kept
o
stirring under 60 C for 20 h. Then the mixture was poured into excess
saturated Na
2
CO
3
aqueous solution and a copious white precipitate was
Synthesis of Azo-Br. 6-bromohexanoic acid (246 mg, 1.3 mmol), EDC
(248 mg, 1.3 mmol), DMAP (20 mg, 0.2 mmol) and 4-aminoazobenzene
(256 mg, 1.3 mmol) were dissolved in 60 mL of dichloromethane, the
mixture was kept stirring under room temperature for 72 h. After the
reaction, the solvent was removed by roto-evaporation. The rough
formed immediately. The precipitate was filtrated and the clear solution
was washed with EA 3 times to obtain the rough product. The oil-like
product was further purified by chromatography using dichloromethane
1
as eluent to obtain the product 3. Yield: 85%. H NMR (DMSO-d
6
, 250
MHz): δ=6.87 (s, 3H), δ=4.48 (hept, J=6.0 Hz, 2H), δ=4.05 (s, 2H),
product was further purified by chromatography using dichloromethane
13
1
6
δ=1.28 (d, J=6.1 Hz, 12H). C NMR (DMSO-d , 63 MHz): δ=144.8,
as eluent to get the product of Azo-Br. H NMR (DMSO-d
6
, 250 MHz):
δ=128.7, δ=115.4, δ=107.4, δ=70.1, δ=22.0. MS cal: m/z=209.1 found:
δ=10.34 (s, 1H), δ=7.94-7.79 (m, 6H), δ=7.65-7.47 (m, 3H), δ=3.52 (t,
m/z=209.2
J=7.4 Hz, 2H), δ=2.35 (t, J=7.2 Hz, 2H), δ=1.82 (t, J=7.3 Hz, 2H), δ=1.62
13
6
(t, J=7.2 Hz, 2H), δ=1.42 (t, J=7.3 Hz, 2H). C NMR (DMSO-d , 63
[
14]
MHz): δ=171.53, δ=151.96, δ=147.32, δ=142.36, δ=131.0, δ=129.39,
δ=123.62, δ=122.25, δ=119.12, δ=39.31, δ=33.72, δ=30.49, δ=24.93,
δ=24.22. MS cal: m/z=375.1 found: m/z=375.2
Synthesis of 5. The synthesis of 5 was followed previous literature.
4
(
1260 mg, 10 mmol), 2-bromopropane (7320 mg, 60 mmol), K CO (8280
mg, 60 mmol) and KI (400 mg, 2.4 mmol) were dissolved into 100 mL of
DMF. The reaction was kept stirring under 90 C for 48 h. Then the DMF
2
3
o
was removed by rotating evaporation and the residue was washed by EA
Synthesis of Azo-Py. Azo-Br (60 mg, 0.16 mmol) was dissolved in THF
3
times to obtain the rough product. The black oil-like rough product was
(20 mL) and pyridine (20 mL) was added. The mixture was stirred
overnight at 60 C under Ar and solvents were removed by roto-
evaporation. The obtained yellow solid was dissolved in methanol and
the solution was added slowly to excess petroleum ether under stirring.
o
further purified by chromatography using dichloromethane/methanol (1:5)
as eluent to obtain product 5. Yield: 28%. H NMR (DMSO-d
δ=6.03 (s, 1H), δ=5.86 (s, 2H), δ=5.61 (s, 1H), δ=4.46 (m, 2H), δ=1.31 (d,
J=6.1 Hz, 12H). C NMR (DMSO-d
1
6
, 250 MHz):
13
6
, 63 MHz): δ=159.7, δ=157.8,
The yellow precipitate was filtered and dried under vacuum to obtain the
1
δ=96.9, δ=96.2, δ=71.3, δ=20.9. MS cal: m/z=210.1 found: m/z=210.3
Azo-Py. H NMR (D
2
O, 250 MHz): δ=8.73 (d, J=5.9 Hz, 2H), δ=8.34 (t,
J=8.1 Hz, 1H), δ=7.94 (t, J=7.1 Hz, 2H), δ=7.76 (m, 4H), δ=7.50 (m, 5H),
δ=4.53 (t, J=7.3, 2H), δ=2.29 (t, J=7.2 Hz, 2H), δ=1.96 (q, J=7.1 Hz, 2H),
δ=1.60 (t, J=7.4 Hz, 2H), δ=1.29 (m, 2H). C NMR (DMSO-d , 63 MHz):
6
δ= 171.53, δ=151.96, δ=147.32, δ=145.44, δ=144.72, δ=142.36,
δ=131.00, δ=129.39, δ=128.04, δ=123.62, δ=122.25, δ=119.12, δ=60.50,
δ=36.03, δ=30.37, δ=24.93, δ=23.71. ESI-MS cal: m/z=373.2 found:
m/z=374.2
Synthesis of ipAzo-OH. The synthesized 3 (823 mg, 3.9 mmol) was
13
2
dissolved in the mixture of 0.75 mL of H O and 0.97 mL of HCl (37 wt.%).
o
After the solution was cooled to 0~5 C, NaNO
2
(276 mg, 4 mmol) in 4
mL H O was added quickly. The solution was stirred for 20 min and the
2
o
temperature of the solution was kept at 0~5 C. The synthesized 5 (823
mg, 3.9 mmol) and NaOH (300 mg, 7.5 mmol) were dissolved in 3 mL of
2
H O and then the mixture was added slowly in the diazonium salt solution
o
at 0~5 C. After stirring overnight the dark red solid was collected and
purified by chromatography using EA/THF (1:1) as eluent to get the
Acknowledgements
1
4
product ipAzo-OH. Yield: 50%. H NMR (MeOD-d , 250 MHz, with ~5 mg
of NaOH, 298K): δ=7.06 (t, J=8.3 Hz, 1H), δ=6.67 (d, J=8.4 Hz, 2H),
13
D.W. is supported by the CSC program. A.S. acknowledges the
DAAD RISE program. This work was supported by the Deutsche
Forschungsgemeinschaft (DFG, WU 787/2-1) and the Fonds der
Chemischen Industrie (FCI, Nr. 661548). We acknowledge D.
Vollmer, W. Sun and P. Weis for kind help.
δ=5.96 (s, 2H), δ=4.55 (m, 4H), δ=1.27 (dd, J=21.8, 6.0 Hz, 24H).
C
NMR (MeOD-d , 176 MHz, with ~5 mg of NaOH, 243K): δ=173.1,
4
δ=155.0, δ=150.1, δ=137.6, δ=126.1, δ=125.0, δ=107.7, δ=98.2, δ=70.5,
δ=21.1. MS cal: m/z=430.3 found: m/z=430.2
Synthesis of ipAzo-Br. 6-bromohexanoic acid (246 mg, 1.3 mmol), DCC
(
1
268 mg, 1.3 mmol), DMAP (20 mg, 0.2 mmol) and ipAzo-OH (568 mg,
.3 mmol) were dissolved in 60 mL of dichloromethane, the mixture was
Keywords: Supramolecular chemistry • Photochemistry • Host-
guest systems • Azo compounds • Orthogonal systems
kept stirring under room temperature for 72 h. After removing the
precipitate and solvent by filtration and roto-evaporation, the rough
product was further purified by chromatography using dichloromethane
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Chemistry - A European Journal
10.1002/chem.201604634
FULL PAPER
FULL PAPER
A photoresponsive orthogonal
Dongsheng Wang, Manfred Wagner,
Andrew K. Saydjari, Julius Mueller,
Svenja Winzen, Hans-Jürgen Butt, and
Si Wu*
supramolecular system is developed
by combining the UV-light-responsive
Azo/α-CD and green-light-responsive
ipAzo/γ-CD host-guest complexes.
Page No. – Page No.
A photoresponsive orthogonal
supramolecular complex based on
host-guest interactions
This article is protected by copyright. All rights reserved.