Self-assembly of indolocarbazole-containing macrocyclic molecules

Article abstract of DOI:10.1039/c0ob00033g

A successful approach for the synthesis of indolocarbazole-containing macrocycles based upon π-π stacking preorganization of indolocarbazole planes and click-chemistry reactions has been developed. The macrocycles are able to form folded structures with t

Full text of DOI:10.1039/c0ob00033g

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www.rsc.org/obc | Organic & Biomolecular Chemistry
Self-assembly of indolocarbazole-containing macrocyclic molecules†
Yingjie Zhao,a,b Yuliang Li,*a Yongjun Li,*a Changshui Huang,a Huibiao Liu,a Siu-Wai Lai,c Chi-Ming Chec
and Daoben Zhua
Received 22nd April 2010, Accepted 11th June 2010
First published as an Advance Article on the web 12th July 2010
DOI: 10.1039/c0ob00033g
A successful approach for the synthesis of indolocarbazole-containing macrocycles based upon p–p
stacking preorganization of indolocarbazole planes and click-chemistry reactions has been developed.
The macrocycles are able to form folded structures with the help of hydrogen-bonding and p–p stacking
interactions. Two of the receptors were successfully characterized by single-crystal X-ray diffraction
analysis. Our results confirmed that they showed different interesting self-assembly with the anions due
to the N–H ◊ ◊ ◊ X- and the triazole C–H ◊ ◊ ◊ X- hydrogen-bonding.
Introduction
Molecular receptors designed to bind anionic guests is a attracting
area of research.1 Many recognized anion receptors have been
widely employed such as amides,2 pyrrole,3 indole,4, 5, 6 urea,7, 8
guanidiniums9 and so on. Among them, the indolocarbazole-
based anion receptors attracted much more attention due to
the strong anion binding ability and emerged as an important
anion-binding agents reported by Beer and co-workers.4 Inclu-
sion of indolocarbazole-containing macrocyclic derivatives was
described by the Jeong and co-workers.5, 10 Moreover, Flood
and co-workers found that 1,2,3-triazoles had strong C–H ◊ ◊ ◊ X-
contacts very recently.11 Strategies in the synthesis of anion
receptors including high dilution techniques,12 supramolecular
templated techniques,13 were demonstrated and the shape diversity
of the receptors were generated, such as linear-like,8 tripod-
like,14 shape-persistent macrocycles,5, 10 capsule15 and cryptand.16
Understanding the structure–function relationships that relate
specifically to receptors could lead to new “design rules” for
producing benign, high-performance receptors substances. We
envisioned the construction of larger structures to increase the size
and complexity of the substrates within the molecular recognition
event. As the model shown in Fig. 1, we proposed the structure
of the new receptors in which two planes could form folded
structure. The cavity formed can self-assemble some anions
by the H-donating groups. Here, we developed the synthesis
of indolocarbazole-containing macrocycles benefiting from p–
p stacking preorganization of indolocarbazole plane. The plane
was coupled with resorcin through flexible chain by “click
chemistry”, four novel molecular receptors with different numbers
of indolocarbazoles were synthesized.
Fig. 1 Schematic of the p–p stacking interactions in macrocycle 2 and
the interaction with the anion.
Results and discussion
Macrocycles 1, 2, 3 and 4 were obtained with the yield for the
final click step of 90% for 1, 40% for 4, 15% for 2 and < 5%
for 3 respectively (Scheme 1). Compound 5 was synthesized in
accordance with Jeong’s literature procedures.5 It was observed
that macrocycle 1 was obtained in a yield of 90% and < 5%
of macrocycle 2 was formed in a highly dilute concentration.
However, high-concentration benefits to obtain macrocycle 2, the
yield of macrocycle 2 increased to about 15% and a new macrocycle
3 appeared in a yield of < 5% in high-concentration, meanwhile
the yield of macrocycle 1 reduced to about 20%. This is due to easy
formation of p–p aggregation between indolocarbazole planes. On
the contrary, < 5% of macrocycle 2 was formed in a highly dilute
concentration, because the interaction of p–p aggregation is weak.
The structural features of the macrocycles 1 and 2 were
confirmed by single-crystal X-ray diffraction analysis (Fig. 2).
Macrocycles 1 and 2 can form a folded structure attributing to the
p–p interaction between the indolocarbazole and the resorcin ring
in macrocycle 1 or between the indolocarbazoles in macrocycle
2. The macrocycle 1 contains an internal cavity surrounded by
hydrogen atoms in N–H group and other two hydrogen atoms in
triazole C–H group. The distance between the indolocarbazole
aBeijing National Laboratory for Molecular Sciences (BNLMS), CAS
Key Laboratory of Organic Solids, Institute of Chemistry, Chinese
Academy of Sciences, Beijing 100190, P.R. China. E-mail: ylli@iccas.
ac.cn, liyj@iccas.ac.cn; Fax: (+) 86-10-82616576; Tel: (+) 86-10-62588934
bGraduate University of Chinese Academy of Sciences, Beijing 100190,
P.R. China
˚
plane and the resorcin ring is about 3.1 A. The two nitrogen
cDepartment of Chemistry, The University of Hong Kong, Pokfulam Road,
Hong Kong
atoms which closed to the indolocarbazoles in two triazoles were
turned to the same direction, one of the nitrogen atoms can
interact by hydrogen-bonding with one N–H (Ha) and the other
can interact with the outside Hc. The distance between the two
† Electronic Supplementary Information (ESI) available: Synthesis, 2D
1H NMR studies, UV/visible, 1H NMR binding studies and X-ray
crystallographic data. See DOI: 10.1039/c0ob00033g
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Scheme 1 Reaction conditions: a) CuI, DBU, toluene, pseudo high-dilu-
tion condition, dropwise, 70 ◦C, 5 h, 90% for 1 and 70 ◦C, 24 h, 40% for 4;
b) CuI, DBU, toluene, concentrated solution, 70 ◦C, 24 h, 15% yields for
2 and <5% for 3.
˚
triazoles is 6.7 A, the length is enough to support a linear C–
H ◊ ◊ ◊ Cl interaction.17 In the macrocycle 2, the intramolecular p–
p interaction is between the two indolocarbazoles (the distance
˚
between the two indolocarbazole plane is 3.5 A.). The nitrogen
atoms in triazoles turn to the internal cavity resulting in hydrogen
bonding interaction between the two N–H (Ha) and the nitrogen
atoms in triazoles. The semicircular defined a space-filling cavity
˚
with a diameter of about 6.0 A.
The properties of macrocycles 1, 2 and 4 in solution were studied
by 1H NMR spectroscopy (Fig. 3). In macrocycle 4, two benzene
rings were introduced to prohibit the p–p stacking of the two
planes, the H atoms in resorcin ring of macrocycle 4 (Hh, Hf and
Hg) and compounds 6, 7 show the same chemical shift. However,
in macrocycle 1, the resorcin ring can fold leading to p–p stack
with the indolocarbazole plane, the Hh and Hg significantly shifted
upfield about 0.5 and 0.34 ppm respectively. The results indicate
macrocycle 1 in solution can maintain the conformation similar
to that in the solid phase (the X-ray crystal structures analysis).
Compared to 1, the N–H (Ha) signals of 2 were significantly shifted
downfield (1.1 ppm) indicating a stronger hydrogen bonding
interaction between the Ha and the nitrogen atoms in triazoles.
The Hc shifted upfield about 0.8 ppm, which could be attributed
to the weakened hydrogen bonding interaction between the Hc and
the nitrogen atoms in triazoles because the triazole-N turned to the
internal cavity and formed hydrogen bond with the N–H (Ha). The
2D 1H NMR NOESY of macrocycle 2 in D2-tetrachloroethane at
0 ◦C showed the correlation between the indolocarbazole and the
chain which indicated the folded conformation of the macrocycle
2 (see ESI, Fig. S1†). For the resorcin ring protons, compared to
macrocycle 1, the Hh, Hf and Hg shifted upfield much more (0.75,
0.55 and 0.75 ppm respectively), that could attribute to the shield
effect of the indolocarbazole planes, which is sliding relative to
each other in the solution (ESI, Fig. S2†). The upfield shift of
Fig. 2 Crystal structures of the macrocycles 1 and 2 (dotted line showed
the hydrogen-bond interaction).
1
Fig. 3 Aromatic region of the H NMR spectra (400 MHz, CDCl3) of
macrocycles 1, 2, 4, compounds 6, 7.
protons Hd and He further supported the p–p aggregation of the
two indolocarbazole planes.
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The absorption and fluorescence spectra also showed the p–p
interaction (Fig. S5†). The absorption of 2 showed a 3.5 nm red
shift in comparison to 1. The fluorescence spectra also showed the
red shift and a remarkable increase at about 419 nm compared to
the macrocycle 1. Cl-responsive changes in the UV correlated with
p–p stacking was confirmed (Fig. 4). With the increase of the Cl-,
absorption of 2 showed a 4 nm blue shift which indicated that the
p–p stacking between the two indolocarbazoles was weaken by the
Cl-. The data of 1H NMR combined with the UV and FL spectra
supported the folded structure of the macrocycle 2 in solution.
Fig. 4 UV spectral changes during titration of macrocycle 2 (1.0 ¥ 10-5
M) with n-Bu4NCl at 298 K in a CH2Cl2 solution.
The spherical anions F-, Cl-, Br- and I- were confirmed for
binding to macrocycles 1 and 2 using 1H NMR and UV titrations.
Ab initio modeling (HF/3-21G) of the complexes formed between
macrocycles 1, 2 and the halides (Fig. 5) revealed two different
binding modes. The volume of the anion affected the interaction
with the N–H (Ha). In macrocycle 1, both the Cl- and Br- ions
can lie in the cavity which was formed from indole N–H (Ha) and
the twisted triazole C–H (Hb). The small F- ion is close to the side
of indole N–H (Ha), and the I- anion size is bigger, can only be
outside of the cavity and interact with the triazole C–H (Hb). For
macrocycle 2, the four anions are all in the center of the cavity
formed by the two indole ring plane. According to these data, two
different binding mode with the receptors is expected.
Fig. 5 Models (HF/3-21G) of the structures for halide complexation
with macrocycles 1 and 2.
Table 1 Association constants (Ka, M-1) and triazole-H chemical shifts
of complexes (CDCl3) formed between 1, 2 and anions
Chemical shift
(d, pm)
Association
constant (Ka, M-1)
The association constants (Ka) were determined by nonlinear
fitting analyses of the H NMR titration curves (Table 1). Job’s
Anion
1
2
1
2
1
F-
9.01
9.55
9.44
8.88
9.10
9.81
9.25
7.85
11600
1500
325
3010
120
16
plots (UV, Fig. S4†) showed that 1 and 2 formed 1 : 1 complexes
with all the chosen anions. For the macrocycle 1, the association
constants for the four anions are in the order of F->Cl->Br->I-.
This is probably attributed to the charge density of the anion
surfaces and to the size complementarities of the anions and the
internal cavity, which is in line with the molecular modeling results.
For the macrocycle 2, the association constants are much smaller
than the macrocycle 1 with an order of F->Cl->Br->I-. The
smaller binding affinity of macrocycle 2 with halides may arise
from the greater rigidity of 1.
Cl-
Br-
I-
106
4
(The errors in the Ka values were within 10%.)
the macrocycle 1 and the anions. With the increase of the halides’
size, the triazole C–H (Hb) shifted to a greater extent than the
N–H (Ha) protons. The downfield shift of the Hc indicates the
increasing hydrogen bonding interaction between the Hc and the
nitrogen atoms in the triazole when the triazole C–H (Hb) turned
to the internal cavity to bind with the halides. The decreasing p–
p interaction between the indolocarbazole and the resorcin ring
The binding properties of 1 and 2 in solution were studied
by 1H NMR (Fig. S3†). With the addition of anions, the
Ha and Hb signals of macrocycle 1 were significantly shifted
downfield suggesting the formation of hydrogen bonds between
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plane by addition of anions resulted in the hydrogen signals of the
resorcin ring plane significantly shifted downfield.
Macrocycle 2. 1,8-Diaza [5.4.0] bicycloundec-7-ene (DBU)
(4.0 mmol, 0.7 mL), 5 (416 mg, 1.0 mmol) and 6 (336 mg, 1.0
mmol) was added to THF (3 mL) and toluene (50 mL), degassed
(argon◦) for 30 min and heated to 70 ◦C while flushing with argon.
At 70 C, CuI (0.02 mmol, 3.8 mg) was added to the mixture. A
In macrocycle 2, the F- ion is small and can penetrate into
the cavity to interact with the Ha leading to Ha shifted downfield
largely (2.2 ppm). Hb shifted downfield 1.2 ppm. In the case of Cl-
anion, Ha shifted downfield slightly (0.36 ppm), while Hb shifted
downfield 1.5 ppm. For Br- anion, Ha shifted upfield 0.15 ppm
due to the combination effects of the broken of the hydrogen
bonding between the Ha and the triazoles-N and the failure of
the construction of N–H (Ha) ◊ ◊ ◊ Br- bonding. But the Hb shifted
upfield significantly (1.2 ppm). The titration with the I- anion
◦
mixture solution was heated at 70 C for over 20 h under argon.
The mixture was concentrated in vacuo. The product was purified
via chromatography (SiO2, CH2Cl2 : Ethyl acetate : methanol
1
20 : 20 : 1) to afford 2 (110 mg, 15% yield) as a yellow solid. H
NMR (400 MHz, CDCl3) d 11.32 (s, 4H), 7.99 (s, 8H), 7.83 (s,
4H), 7.01 (s, 4H), 6.41 (t, J = 7.7 Hz, 2H), 5.98 (s, 2H), 5.76 (d,
J = 8.0 Hz, 4H), 4.85 (s, 8H), 4.46 (s, 8H), 4.06 (s, 16H), 1.33 (s,
36H). 13C NMR (100 MHz, CDCl3) d 159.4, 147.0, 141.7, 134.4,
129.2, 126.6, 125.2, 121.9, 121.4, 119.3, 116.97, 112.7, 111.9, 107.8,
100.7, 70.6, 70.1, 67.2, 51.0, 34.7, 32.2. MALDI-TOF, Calcd for
C88H96N16O8 Na (M+Na)+ 1527.75; Found 1527.3 (M+Na)+.‡
1
showed little changes in the H NMR. The results indicates that
the anions of F-, Cl-and Br- were able to enter into the cavity. F-
and Cl- can interact with N–H (Ha) and the triazole protons (Hb).
Br-can only interact with Hb. The I- is too large to enter into the
1
cavity showing a little change in the H-NMR. This indicates a
different mode of self-assembly compared to that of macrocycle 1.
Macrocycle 3. 1H NMR (600 MHz, CDCl3) d 11.08 (s, 6H),
8.03 (s, 6H), 7.98 (s, 6H), 7.85 (s, 6H), 7.21 (s, 6H), 6.53 (s, 3H),
5.93 (s, 9H), 4.61 (s, 12H), 4.12 (s, 12H), 3.78 (d, 24H), 1.37(s,
54H), 13C NMR (150 MHz, CDCl3) d 159.2, 147.0, 141.7, 134.3,
129.2, 126.2, 125.0, 121.2, 121.2, 119.1, 115.7, 112.9, 111.7, 107.1,
100.8, 70.0, 69.6, 66.8, 50.5, 34.5, 32.0. MALDI-TOF, Calcd for
C132H144N24O12Na (M+Na)+ 2280.13; Found 2279.3. HRMS (ESI)
Calcd for C132H145N24O12 (M+H)+ 2258.14683; Found 2258.16672
(M+H)+.
Conclusion
In summary, we have demonstrated a successful approach for
the synthesis of indolocarbazole-containing macrocycles based
upon p–p stacking preorganization of indolocarbazole planes
and “click-chemistry” reactions. Our results confirm that two
different self-assembly mode between the macrocycles 1, 2 and the
anions. Especially the interesting folded structures was achieved
by macrocycle 2 and the anions leading to a new creation. Further
investigations on highly response binding with other anions such
as tetrahedral or trigonal anions by weak interaction tuning are
under way.
Macrocycle 4. 1,8-Diaza [5.4.0] bicycloundec-7-ene (DBU)
(4.0 mmol, 0.7 mL) was added to toluene (200 mL), degassed
(argon◦) for 30 min and heated to 70 ◦C while flushing with argon.
At 70 C, CuI (0.02 mmol, 3.8 mg) was added to the mixture. A
solution of the 5 (208 mg, 0.5 mmol) and 7 (274 mg, 0.5 mmol)
in THF (5 mL) and toluene (30 mL) was added to the solution
slowly over 20 h and stirred for another 4 h under argon. The
mixture was concentrated in vacuo. The product was purified via
chromatography (SiO2, CH2Cl2 : Ethyl acetate : petroleum ether :
Experimental
Synthesis of Macrocycles 1, 2, 3 and 4
Macrocycle 1. 1,8-Diaza [5.4.0] bicycloundec-7-ene (DBU)
(4.0 mmol, 0.7 mL) was added to toluene (200 mL), degassed
(argon◦) for 30 min and heated to 70 ◦C while flushing with argon.
At 70 C, CuI (0.02 mmol, 3.8 mg) was added to the mixture. A
solution of the 5 (208 mg, 0.5 mmol) and 6 (168 mg, 0.5 mmol)
in THF (5 mL) and toluene (30 mL) was added to the solution
slowly over 4 h and stirred for another 1 h under argon. The
mixture was concentrated in vacuo. The product was purified
via chromatography (SiO2, CH2Cl2 : Ethyl acetate : methanol
1
methanol 5 : 5 : 10 : 1) to afford 4 (190 mg, 40% yield). H NMR
(400 MHz, CDCl3) d 10.71 (s, 2H), 8.16 (s, 2H), 8.08 (s, 2H), 7.99
(s, 2H), 7.65 (s, 2H), 7.29 (d, J = 8.6 Hz, 4H), 7.11 (t, J = 8.2 Hz,
1H), 6.91 (d, J = 8.7 Hz, 4H), 6.51 (s, 1H), 6.47 (d, J = 8.2 Hz, 2H),
5.60 (s, 4H), 4.17 – 4.03 (m, 8H), 3.86 (m, 8H), 1.50 (s, 18H). 13
C
NMR (100 MHz, CDCl3) d 159.9, 159.0, 148.2, 142.3, 134.9, 129.8,
129.1, 127.6, 126.4, 125.3, 121.3, 119.5, 119.1, 116.3, 115.2, 112.7,
112.0, 107.0, 102.2, 69.8, 69.7, 67.6, 67.5, 53.9, 34.8, 32.1. MALDI-
TOF (M), Calcd for C58H60N8O6 (M) 964.46; Found 964.8. HRMS
(ESI) Calcd for C58H61N8O6 (M+H)+ 965.47141; Found 965.46902
(M+H)+.
1
20 : 20 : 1) to afford 1 (330 mg, 90% yield) as a yellow solid. H
NMR (400 MHz, CDCl3) d 10.19 (s, 2H), 8.21 (s, 2H), 8.18 (s,
2H), 8.01 (s, 2H), 7.81 (s, 2H), 6.62 (t, J = 8.0 Hz, 1H), 6.52 (s,
1H), 6.18 (d, J = 8.1 Hz, 2H), 4.70 (s, 4H), 4.13 (s, 8H), 3.83 (s,
4H), 1.52 (s, 18H). 13C NMR (101 MHz, CDCl3) d 159.3, 146.6,
142.5, 134.5, 129.9, 126.4, 125.4, 121.4, 121.1, 119.9, 116.1, 113.1,
112.0, 107.7, 101.9, 69.5, 69.3, 68.0, 50.6, 34.8, 32.2. MALDI-TOF
(M), Calcd for C44H48N8O4 (M) 752.38; Found 752.5.‡
Acknowledgements
We are grateful for financial support from the National Nature Sci-
ence Foundation of China (20831160507, 20971127 and 90922017)
and the National Basic Research 973 Program of China.
‡ Crystallographic data for Macrocycle 1: C45H52N8O5,Mr = 784.95,
monoclinic, space group = P21/c, a = 15.612(3), b = 13.356(3), c =
Notes and references
-1
˚
20.763(4) A, b = 102.05(3), T = 173 K, Z = 4, m = 0.082 mm ,
RF (RwF
)
=
0.0649(0.1380) for 28188 observed independent reflec-
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monoclinic, space group = P21/c, a = 21.048(4), b = 11.504(2), c =
-1
˚
17.527(4) A, b = 102.01(3), T = 173 K, Z = 4, m = 0.084 mm , RF (RwF ) =
0.0646(0.1309) for 28221 observed independent reflections
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