Hierarchical self-assembly of p-terphenyl derivative with dumbbell-like amphiphilic and rod-coil characteristics

Article abstract of DOI:10.1016/j.tetlet.2008.07.048

As water is gradually added, a p-terphenyl derivative with dumbbell-like amphiphilic and rod-coil characteristics can hierarchically self-assemble to metastable rectangle columns architecting sheets first and then to stable quasi-hexagonal columns architecting rolled sheets, and finally to rod-like nanostructures in MeOH/H₂O solution. Interestingly, the formed sheet, rolled sheet, and nanorod possess blue-light emitting property.

Full text of DOI:10.1016/j.tetlet.2008.07.048

Tetrahedron Letters 49 (2008) 5522–5526
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Hierarchical self-assembly of p-terphenyl derivative with dumbbell-like
amphiphilic and rod-coil characteristics
Qilong Zhou a,b, Ting Chen a,b, Jintao Zhang , Lijun Wan , Ping Xie , Charles C. Han ,
Shouke Yan , Rongben Zhang
a
a,b
a
a
a
a,*
a,
*
Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, PR China
Graduate School of the Chinese Academy of Sciences, Beijing 100039, PR China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
As water is gradually added, a p-terphenyl derivative with dumbbell-like amphiphilic and rod-coil char-
acteristics can hierarchically self-assemble to metastable rectangle columns architecting sheets first and
then to stable quasi-hexagonal columns architecting rolled sheets, and finally to rod-like nanostructures
Received 13 April 2008
Revised 3 July 2008
Accepted 8 July 2008
Available online 11 July 2008
in MeOH/H
2
O solution. Interestingly, the formed sheet, rolled sheet, and nanorod possess blue-light emit-
ting property.
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords:
Amphiphile
Nanorod
Rod-coil
Self-assembly
Molecular self-assembly recently has attracted considerable
attention for its use in the design and fabrication of nanostructures,
leading to the development of advanced materials;1 and many
efforts have always been focused on designing new building blocks
driving force, however, we are more interested in their self-assem-
bling behavior in solution, especially the direct preparation of
nanostructure materials from them. Herein, we designed and syn-
thesized a novel symmetrical building block A, which possessed
the characteristics of both dumbbell-like amphiphile and rod-coil
molecule. It consisted of three parts, that is, rigid p-terphenyl core,
hydrophilic trihydroxymethyl and amide groups on each end, and
coil-like alkoxy chain on both sides of the core (Scheme 1 and Fig.
S1). Interestingly, it could hierarchically self-assemble into various
2
for exploration of novel properties and functions. Bolaamphiphile
and rod-coil molecules have been extensively studied as important
building blocks in self-assembly research. The former, containing a
hydrophobic skeleton and two hydrophilic heads on both ends, can
form a variety of nanostructures in solution, such as monolayer
vesicles, fibers, and tubules;3 and the latter imparts microphase
separation of the rod and coil blocks into ordered periodic struc-
tures in nanoscale dimensions due to the mutual repulsion of the
2
nanostructures in MeOH/H O solution depending on the amount of
water, and its self-assembling behavior was completely different
from that of the general bolaamphiphiles and rod-coil molecules.3
In addition, the formed sheet, rolled sheet, and nanorod have blue-
emitting property.
,4
4
dissimilar blocks. Contrary to the conventional bolaamphiphile
with flexible alkyl chains as hydrophobic spacer, the dumbbell-like
amphiphile with rigid hydrophobic spacer, especially that which
possesses rod-coil characteristic, was scarcely investigated, though
combination of multi-supramolecular driving forces in one mole-
cule would lead to more abundant and special nanostructures
The synthetic route of compound A is outlined in Scheme 1. 4-
Dihydroxybroanylbenzoic acid (1) was synthesized by a reported
9
method. 1,4-Dibromo-2,5-didodecyloxybenzene (2) was easily
1
0
synthesized according to the reported procedure. Compound 3
was synthesized by Pd-catalyzed Suzuki cross-coupling reaction
in 68% yield from 1 and 2. And compound A was obtained in 60%
yield by the amidation reaction of tri(hydroxymethyl)aminometh-
ane (Tris) with the acyl chloride of 3 at 0 °C in dimethyl acetamide
(DMA).
5
and mesophases. Recently, Tschierske’s group thoroughly and sys-
tematically studied the thermotropic liquid crystalline behavior of
the bolaamphiphiles with biphenyl spacer and a lateral grafting
6
,7
hydrophobic chain,
following their previous research on the
lyotropic liquid crystalline behavior of p-terphenyl amphiphiles
with a lateral hydrophilic group.8 For such molecules with multi-
Compound A is soluble in MeOH up to 4 mg/mL and insoluble
even in hot water. When water was added gradually (one drop
per 5 s by using a 1 mL syringe) to 1 mL solution of A in MeOH
(
2 mg/mL) with stirring, the mixture became cloudy within min-
*
Corresponding authors. Tel./fax: +86 10 62559373 (R.Z.).
E-mail addresses: skyan@iccas.ac.cn (S. Yan), zhangrb@iccas.ac.cn (R. Zhang).
utes or hours as described in Table 1, depending on the amount
0
040-4039/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2008.07.048

Q. Zhou et al. / Tetrahedron Letters 49 (2008) 5522–5526
5523
Table 1
COOH
COOH
Conditions and morphologies of self-assembled nanostructures formed from com-
pound A in MeOH/H
2
O solution
a
A1
A2
A3
A4
A5
b
a
Water (mL)
Timeb
0.1
0.2
12 h
Rod, sheet
(1b)
0.3
5 h
Rod
(1c)
0.4
5 min
Rolled sheet (1d
and e)
0.5
Br
B(OH)2
1
OC12H25
—
c
1 min
Rolled sheet
(S2)
OC12H25
e
Morphology
Sheet
(1a)
(
Fig.)
OH
C12H25
O
a
b
c
Br
The amount of water added.
Time of precipitate emergence.
No precipitate appears in 2 weeks.
c
d
Br
OH
OH
OH
OC12H25
COOH
2
3
ca. 80 nm to 200 nm and the length up to several micrometers
were formed, and the end of the rod is solid instead of being hollow
OC12H25
HO
(
Figs. 1c and S2). From the coexistence phenomenon of sheets and
O
OH
f
g
H
N
H
N
O
rods, we can infer that a transition state of rolled sheet would exist,
through which the rod can be transformed from sheet. For that, a
series of control experiments were conducted and as expected, sta-
ble rolled sheets were found when a large amount of water was
used as in A4 and A5 (Figs. 1d, e, and S3). In addition, when 0.1
or 0.2 mL more water was added into A3 after 24 h, no rolled sheet
was found by TEM, which further supported our presumption that
rolled sheet is a ‘frozen’ transition state. Furthermore, to investi-
gate the effect of time on the morphologies, TEM observations
were conducted, respectively, three days later and 2 weeks later,
and no difference in morphology was found for the same sample.
We noted such self-assembling phenomena, especially the forma-
tion of the regular solid nanorod, are distinctly different from those
HO
C12H25
O
HO
A
2
Scheme 1. Synthetic route of compound A. Reagents and conditions: (a) (1) Mg/I ,
THF, reflux 12 h; (2) B(OMe)
+
3
, ꢁ78 °C, 4 h/ rt, 12 h; (3) H /H
2
O, 30 min, 70%; (b)
CO , reflux, 8 h,
, dioxane/EtOH, reflux
3
, 12 h, 82%; (g) tri(hydroxymethyl)aminomethane, DMA,
ꢁ
KMnO
4
, H
5%; (d) Br
2 h, 68%; (f) SOCl
°C,4 h/ rt, 12 h, 60%.
2
O/OH , 24 h, 60%; (c) 1-bromododecane, acetone, Na
2
3
7
7
0
2
, CCl
4
, rt, 12 h, 94%; (e) 2 M Na
2 3 3 4
CO , Pd(PPh )
2
, CHCl
of water. After 24 h, the superstratum was monitored by TEM and
SEM, and remarkably different morphologies were observed as
shown in Figures 1, S2, and S3.
3
of usual bolaamphiphiles, even those with rigid naphthalene
1
1
diimide or azobenzen spacer.
It is evidently demonstrated that the amount of water added
determines the morphologies of the self-assembled arrays. For
A1, the morphology was sheet-like (Fig. 1a); and in A2, some
rod-like nanostructures appeared and coexisted with the sheets
A1 was spin-coated on a glass slide (1 cm ꢀ 1 cm), and then
X-ray powder diffraction was conducted. The three peaks in the
small-angle region (Fig. 2a) can be indexed as 10-, 01-, 11-reflec-
tions of a rectangular 2D lattice based on the reciprocal spacings
1
/2
(Fig. 1b). In A3, however, only regular rods with the width from
of 10-:11- is 1:2 . The lattice parameters amount to a = 2.8 nm
Figure 1. Electron microscopy pictures of self-assembled sheets (a, TEM); sheet and rod (b, TEM); nanorods and its end (inset) (c, SEM); and rolled or folded sheet (d, TEM; e,
SEM) formed in A1, A2, A3, and A4, respectively, listed in Table 1, respectively.

5
524
Q. Zhou et al. / Tetrahedron Letters 49 (2008) 5522–5526
absorption at 281.4 nm red-shifted to 285.8 nm and then to
87.4 nm, and the bands became broad. Additionally, we also
recorded the change in absorption spectra with time of curve d
i.e., the amount of water is 1.5 mL, Fig. 3 inset). As time goes by,
2
(
the intensity of absorption decreases and the maxima absorption
band shows a little red-shift in 30 mins. Hence, it is reasonable
to consider that p-stacking of p-terphenyl and hydrophobic effects
of the p-terphenyl groups themselves and the long alkyl chains
attached to them are the main driving force of the different self-
assembling structures.
FT-IR spectra of A1–A4 (Fig. S5) all showed two peaks at 1641
ꢁ1
and 1531 cm for the amide I and II bands, supporting the exis-
1
3a,b
tence of the amide hydrogen-bonds.
Because the amide’s
hydrogen-bonds can exist in high polar solvent (e.g., N-methyl-
pyrrolidone) and even aqueous solution, it is also reasonable to
consider that the amide’s hydrogen-bond should be one of the
Figure 2. Power X-ray diffractograms of the self-assembled aggregates from A1 (a)
and A3 (b) listed in Table 1.
13
driving forces for the different assembling structures.
STM technology was used to further investigate the driving
force of self-assembly and the molecular packing of compound A
(Fig. 4a). As expected, it forms a uniform and well-ordered quasi-
rectangle network adlayer in a scale of 50 nm (Fig. S6), which
can be regarded as alternative hydrophobic and hydrophilic do-
mains. The particular bright bar corresponds to the p-terphenyl
skeleton due to its larger electronic density. The length of the bar
is measured to be 1.4 ± 0.2 nm and is consistent with the size of
p-terphenyl core based on the CPK model of monomolecule (Fig.
S1). The distance between two adjacent parallel p-terphenyl
groups is ca. 1.64 nm, corresponding to length of alkoxy group on
the p-terphenyl. The packing model is proposed in Figure 4b. The
microphase separation of the hydrophobic and hydrophilic parts
in compound A can be evidently seen in the STM picture, though
the interaction between the long alkoxy group and the highly ori-
ented pyrolytic graphite (HOPG) substrate is another important
factor in the formation of such a self-assembled pattern. In con-
trast, bolaamphiphiles formed lamellar arrays on HOPG in gen-
and b = 2.7 nm. Meanwhile, the diffractogram of the dried assem-
blies of A3 and A4 shows five reflection peaks in this region. Their
reciprocal spacings are close to the ratio 1:(31 ):(4 ):(7 ):(9 ),
/2
1/2
1/2
1/2
and so they can be indexed as 10-, 11-, 20, 21-, and 30-reflections
of a quasi-hexagonal columnar structure with lattice parameter
hex = 2.9 nm for A3 and 3.0 nm for A4.12 The representative graph
a
of A3 is shown in Figure 2b, and their lattice spacings are listed in
Table S1. The diffractogram of the crystal of compound A from hot
saturated MeOH/H O (v/v = 4:1) solution showed no reflections in
2
the small-angle region (2h < 4), which excluded the possibility of
crystallization of the samples (Fig. S4). Noticeably, as the amount
of water increases, the packing model of molecule A transforms
from the metastable rectangle into a more stable quasi-hexagonal
columnar structure. Similar phase transition was also observed by
Tschierske et al. in the mesophase of bolaamphiphile liquid crystal
depending on the length of grafting alkyl chain.6 Next, we try to
clarify what kind of driving force leads to the formation of colum-
nar structure rather than classic monomolecular layer-based vesi-
1
6
3
,13
eral, and network structure is often formed from the assembly
cles or tubular structure formed by general bolaamphiphiles
1
7
of two or more kinds of molecules.
and how the molecules are packed in such columns.
Based on the above-mentioned results, we consider that the
dumbbell-like amphiphiles are prone to form a rectangle or hexag-
onal framework due to the size mismatch of hydrophilic heads and
the terphenyl core with long side alkoxy chains when the self-
p-Terphenyl is a well-known luminescent species in the near
1
4
UV region, which can be employed in monitoring the self-assem-
1
5
bling process. Compound A shows three absorption maxima at
50 nm, 281.4 nm, and 333.8 nm, and the molar extinction coeffi-
cient at 281.4 nm, standing for the p- terphenyl,14 is ca.
2
assembly is mainly driven by hydrophobic effect and
p-stacking
ꢁ
1
ꢁ1
of terphenyl; and the long alkoxy chains fill exactly in the space be-
2
2
3774 M cm . Water (0.5–2 mL) was added to five samples of
tween the terphenyl groups to stabilize such a framework. Inspired
mL methanol solution of A (0.05 mM), respectively, and the
7
a
by Tschierske’s molecule packing model in the columnar struc-
ture of liquid crystal, a possible molecular packing model of the
columns is proposed in Figure 5.
change in absorption spectra was recorded and is shown in Figure
. When the amount of water was more than 1.5 mL, the maxima
3
At last, the formation mechanism of self-assembled arrays fea-
turing a variety of morphologies will be discussed. In the initial
stage of self-assembly, the rectangle columns with hydroxy-con-
taining hydrophilic domains and alkoxy and terphenyl-based
hydrophobic domains are dispersed on the sheet surface. Such do-
mains play a role like ‘glue’ on the sheet and therefore it can be
iconically regarded as a two-faced sticky paper. As the amount of
water increases, the rectangle columns are transformed to more
stable hexagonal columns; at the same time, the sheets begin to
roll tightly into solid bars. The process is shown in Figure 6. As
for the general bolaamphiphiles, however, the surface of their
self-assembled entities would be uniform, non-sticky and compat-
ible with solvent system, which makes them unlikely to roll into
solid rod, but liable to form monomolecular layer-based tubular
3
18
or vesicle structure. Yao and co-workers first reported the for-
mation of submicrotubes from rolled sheet-like structure, how-
ever, no report on the formation of the organic solid nanorods
via the mechanism on rolling up self-assembled sheets was given
till now to the best of our knowledge.
2
Figure 3. Absorption spectra of A in MeOH/H O solution with different amounts of
water, and the change of d with time (inset).

Q. Zhou et al. / Tetrahedron Letters 49 (2008) 5522–5526
5525
Figure 4. STM images of the well-ordered assembly of A on HOPG (a) and the corresponding packing model, alkoxy groups on the periphery are omitted for simplification (b).
Tunnelling conditions: Ebias 619.2 mv, set point 753 pA.
Figure 5. Possible molecule packing model in rectangle (a) and quasi-hexagonal (b)
columnar structure, in which four and six terphenyls enclosed a column of alkoxy
chains, respectively.
Figure 7. The photoluminescence (PL) spectrum of the formed nanorod in A3
(
excitation 330 nm).
terphenyl, and the hydrogen-bonding of amide, compound A first
packed into rectangle and then to quasi-hexagonal columnar
structure in MeOH/H O solution with the increasing amount of
2
water; and the corresponding morphology of self-assemblies
transformed from sheets to rolled-up sheets, and finally to rods
via a rolling and propagating process instead of vesicles formed
from the usual bolaamphiphilic compound. Interestingly, all the
formed sheets, rolled sheets, and nanorods possess a blue-emitting
property.
Figure 6. The schematic map of the self-assembling process from A to sheet, then
rolled sheet and finally rod.
Acknowledgments
The superstratum in A1–A5 was spin-coated on a quartz plate.
Their photoluminescence (PL) spectra have the same maximum
emission wavelength of ca. 438 nm (the typical spectrum of A3 is
shown in Fig. 7). Such results indicated that the formed sheets,
rolled sheets, and nanorods can emit blue light, though we cannot
observe blue-emitting nanorods directly. We consider such blue-
emitting sheet, especially nanorods would be a promising photolu-
minescent material.
The financial supports of the Outstanding Youth Fund (No.
0425414) and the National Natural Science Foundations of China
No. 50521302) as well as MOST under grant Nos. 2007CB935902
and 2007CB935904 are gratefully acknowledged.
2
(
Supplementary data
In summary, we have designed and synthesized a p-terphenyl
derivative A combining the structure characteristics of dumbbell-
like amphiphile with rod-coil molecule, and studied its hieratical
Supplementary data (general experimental procedure and the
corresponding characterization are available) associated with this
article can be found, in the online version, at doi:10.1016/j.tetlet.
2008.07.048.
assembly behavior. Driven by hydrophobic effect,
p-stacking of

5
526
Q. Zhou et al. / Tetrahedron Letters 49 (2008) 5522–5526
Tschierske, C.; Wittenberg, M.; Wendorff, J. H. J. Am. Chem. Soc. 1998, 120,
0669–10675.
. Fry, A. J.; Britton, W. E. J. Org. Chem. 1973, 38, 4016–4021.
0. (a) Khatyr, A.; Ziessel, R. J. Org. Chem. 2000, 65, 3126–3134; (b) Li, G.; Wang, X.;
Wang, F. Tetrahedron Lett. 2005, 46, 8971–8973.
References and notes
1
9
1
1
.
(a) Lehn, J. M. Science 1993, 260, 1762–1763; (b) Vauthey, S.; Santoso, S.; Gong,
H. Y.; Watson, N.; Zhang, S. G. Proc. Natl. Acad. Sci. U.S.A. 2002, 99, 5355–5360;
(
1
c) Sone, E. D.; Zubarev, E. R.; Stupp, S. I. Angew. Chem., Int. Ed. 2002, 41, 1705–
709.
1
1. (a) Kobayashi, H.; Koumoto, K.; Jung, J. H.; Shinkai, S. J. Chem. Soc., Perkin Trans.
2
2002, 1930–1936; (b) Tomasulo, M.; Naistat, D. M.; White, A. J. P.; Williams,
2
.
(a) Zubarev, E. R.; Sone, E. D.; Stupp, S. I. Chem.-Eur. J. 2006, 12, 7313–7327; (b)
Zhang, X.; Chen, Z.; Wurthner, F. J. Am. Chem. Soc. 2007, 129, 4886–4887.; (c)
Fenniri, H.; Deng, B. L.; Ribbe, A. E.; Hallenga, K.; Jacob, J.; Thiyagarajan, P. Proc.
Natl. Acad. Sci. U.S.A. 2002, 99, 6487–6492.
D. J.; Raymo, F. M. Tetrahedron Lett. 2005, 46, 5695–5698.
1/2
1
1
2. Hexagonal columnar lattice parameter ahex = (4/3) dh100i, where dh100i =
1/2
(
d100 + 3
d110 + 2d200)/3.
3. (a) Tang, H. D.; Sun, J.; Jiang, J. Q.; Zhou, X. S.; Hu, T. J.; Xie, P.; Zhang, R. J.
Am. Chem. Soc. 2002, 124, 10482–10488; (b) Shimizu, T.; Iwaura, R.; Masuda,
M.; Hanada, T.; Yase, K. J. Am. Chem. Soc. 2001, 123, 5947–5955; (c) Fuhrhop, J.
H.; Blumtritt, P.; Lehmann, C.; Luger, P. J. Am. Chem. Soc. 1991, 113, 7437–
3.
4.
5.
(a) Escamilla, G. H.; Newkome, G. R. Angew. Chem., Int. Ed. Engl. 1994, 33, 1937–
1
940; (b) Fuhrhop, A. H.; Wang, T. Y. Chem. Rev. 2004, 104, 2901–2937.
(a) Kim, J.-K.; Lee, E.; Lee, M. Angew. Chem., Int. Ed. 2006, 45, 7195–7198; (b)
Lee, M.; Cho, B. K.; Zin, W. C. Chem. Rev. 2001, 101, 3869–3892.
(a) Song, B.; Wei, H.; Wang, Z. Q.; Zhang, X.; Smet, M.; Dehaen, W. Adv. Mater.
7439.
1
1
4. Berqamini, G.; Ceroni, P.; Balzani, V.; Villavieja, M. D.; Kandre, R.; Zhun, I.;
Lukin, O. ChemPhysChem 2006, 7, 1980–1984.
5. (a) Tian, Z. Y.; Chen, Y.; Yang, W. S.; Yao, J. N.; Zhu, L. Y.; Shuai, Z. G. Angew.
Chem., Int. Edit. 2004, 43, 4060–4063; (b) Jonkheijm, P.; van der Schoot, P.;
Schenning, A. P. H. J.; Meijer, E. W. Science 2006, 313, 80–83.
6. Tao, F.; Bernasek, S. L. Langmuir 2007, 23, 3513–3522.
7. Lei, S. B.; Wang, C.; Yin, S. X.; Wang, H. N.; Xi, F.; Liu, H. W.; Xu, B.; Wan, L. J.;
Bai, C. L. J. Phys. Chem. B 2001, 105, 10838–10841.
8. Zhao, Y. S.; Yang, W.; Xiao, D.; Sheng, X.; Yang, X.; Shuai, Z.; Luo, Y.; Yao, J.
2
007, 19, 416–420; (b) Li, Z.; Kesselman, E.; Talmon, Y.; Hillmyer, M. A.; Lodge,
T. P. Science 2004, 306, 98–101.
6
.
.
Cheng, X. H.; Das, M. K.; Baumeister, U.; Diele, S.; Tschierske, C. J. Am. Chem. Soc.
2
004, 126, 12930–12940.
7
(a) Cheng, X. H.; Prehm, M.; Das, M. K.; Kain, J.; Baumeister, U.; Diele, S.; Leine,
D.; Blume, A.; Tschierske, C. J. Am. Chem. Soc. 2003, 125, 10977–10996; (b)
Kolbel, M.; Beyersdorff, T.; Cheng, X. H.; Tschierske, C.; Kain, J.; Diele, S. J. Am.
Chem. Soc. 2001, 123, 6809–6818.
1
1
1
8
.
(a) Kolbel, M.; Beyersdorff, T.; Sletvold, I.; Tschierske, C.; Kain, J.;
Diele, S. Angew. Chem., Int. Edit. 1999, 38, 1077–1080; (b) Schroter, J. A.;
Chem. Mater. 2005, 17, 6430–6435.