Self-assembly behaviors of the cholesteryl trimeric-phenylene vinylene derivative in the H2O/THF system

Article abstract of DOI:10.1016/j.cclet.2013.09.011

Cholesteryl trimeric phenylene vinylene (Chol-TPV) has been synthesized and characterized. The self-assembly behaviors of Chol-TPV in THF/H₂O system at different water content (water content: 40% and 80%) and different solute concentration (solute concentration: 1.0 × 10^-5 mol/L and saturated concentration) were studied using UV-vis spectrophotometry, photoluminescence spectrophotometry, and circular dichroism spectroscopy. Based on an analysis of the UV-vis and photoluminescence spectra, Chol-TPV shows the typical H-type aggregation at saturated concentration in 80% aqueous THF. However, Chol-TPV shows the non-typical H-type aggregation under other conditions. The circular dichroism signal suggests that the Chol-TPV exists in the right handed helical architectures with high water content at a concentration of 1.0 × 10^-5 mol/L, and a helix inversion was found at saturated concentration.

Full text of DOI:10.1016/j.cclet.2013.09.011

Chinese Chemical Letters 25 (2014) 99–103
Contents lists available at ScienceDirect
Chinese Chemical Letters
journal homepage: www.elsevier.com/locate/cclet
Original article
Self-assembly behaviors of the cholesteryl trimeric-phenylene
vinylene derivative in the H2O/THF system
Yu-Zhen Zhao a, Zhen-Lin Zhang a, Ying Li a, Xue-Qiang Liu b, Shi-Min Liu a,
a,
Jin-Ku Yu a, , Hai-Quan Zhang
*
*
a State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China
b College of Information Science and Engineering and Key Laboratory for Special Fiber and Fiber Sensor of Hebei Province, Yanshan University,
Qinhuangdao 066004, China
A R T I C L E I N F O
A B S T R A C T
Article history:
Cholesteryl trimeric phenylene vinylene (Chol-TPV) has been synthesized and characterized. The self-
assembly behaviors of Chol-TPV in THF/H2O system at different water content (water content: 40% and
80%) and different solute concentration (solute concentration: 1.0 ꢁ 10ꢀ5 mol/L and saturated
concentration) were studied using UV–vis spectrophotometry, photoluminescence spectrophotometry,
and circular dichroism spectroscopy. Based on an analysis of the UV–vis and photoluminescence spectra,
Chol-TPV shows the typical H-type aggregation at saturated concentration in 80% aqueous THF. However,
Chol-TPV shows the non-typical H-type aggregation under other conditions. The circular dichroism signal
suggests that the Chol-TPV exists in the right handed helical architectures with high water content at a
concentration of 1.0 ꢁ 10ꢀ5 mol/L, and a helix inversion was found at saturated concentration.
ß 2013 Jin-Ku Yu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Received 28 May 2013
Received in revised form 11 July 2013
Accepted 16 July 2013
Available online 28 October 2013
Keywords:
Cholesteryl phenylene vinylene
Self-assembly
Helical architectures
1. Introduction
poor solvent in a good solvent system, and this molecular
aggregation could lead to dramatic change of absorption, photo-
Mesoscopic order in
because it dictates the performance of the organic electronic
devices [1]. Due to its favorable optical and electronic properties,
self-assembly of linear
stage among different classes of
been used in the design of organic electronic devices. Oligo (p-
phenylene vinylene)s (OPVs) are a preferred class of linear
p
-conjugated systems is a significant topic,
luminescence and circular dichroism spectra [7]. In order to
understand the influence of van der Waals force and
interaction on the self-assembly behaviors of cholesteryl OPVs
chromophores in good/poor solvent system, we designed a Chol-
TPV compound and studied its self-assembly behaviors in THF/H2O
using spectroscopic methods.
p–p
p
-conjugated molecules is at the center
p
-conjugated systems and has
p
-
conjugated molecules as their optical and electronic properties
strongly depend upon their aggregated structures [2,3]. The
2. Experimental
hydrogen bonding and
p–p stacking interactions are the main
2.1. General
driving forces for the OPVs molecular self-assembly, which can
adjust the structure of the molecular aggregations [4]. Cholesterol
derivatives have been found to be efficient gelators due to their
tendency to form one dimensional stack of the steroid units. There
have been several reports on cholesteryl OPVS chromophoric
systems that self-assemble to form the helical architectures [5,6].
However, the introduction of the cholesteryl groups into OPVs
The 1H NMR spectrum was recorded on an AVANCZ 500
spectrometer at 298 K in CDCl3 as a solvent and tetramethylsilane
(TMS) as an internal standard. FT-IR spectra were recorded on a
Perkin–Elmer spectrophotometer in the 400–4000 cmꢀ1 region
using a powered sample on a KBr plate. UV–vis absorption spectra
were recorded on an UV-3100 spectrophotometer. Photolumines-
cence measurements were carried out with a RF-5301PC. CD
spectra were recorded on a Bio-kine32 V451-[Acquire spectra
(MOS-450)] spectrophotometer.
inhibits
p–p interactions of the OPVs chromophores owing to
strong van der Waals force of the steroid units. It is known that the
aggregation of chiral molecules is initiated upon the addition of
2.2. Reagents
*
Corresponding authors.
Potassium tert-butanolate (BuOK) and cholesteryl chloride
were purchased from Aldrich Chemical Co. The p-xylene, CCl4, N-
E-mail addresses: yujinku@ysu.edu.cn (J.-K. Yu), hqzhang@ysu.edu.cn
(H.-Q. Zhang).
1001-8417/$ – see front matter ß 2013 Jin-Ku Yu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
http://dx.doi.org/10.1016/j.cclet.2013.09.011

100
Y.-Z. Zhao et al. / Chinese Chemical Letters 25 (2014) 99–103
bromosuccinimide (NBS), K2CO3, triphenylphosphine, 4-hydro-
xybenzaldehyde, N,N0-dimethyl formamide (DMF) were purchased
from Beijing Chemical Co.
ethyl acetate (10/1) as eluent. Chol-TPV was obtained as yellow–
green solid in 58.6% yield. FT-IR (KBr, cmꢀ1): 2925, 2853, 965, 549,
510; 1H NMR (500 MHz, CDCl3):
d 7.47–7.46 (d, 4H, Ph-H); 7.45–
7.447(d, 4H, Ph-H); 7.08–7.07 (d, 4H, Ph-H); 5.22–5.21 (m, 2H, –
CH255CH2); 3.72–3.71 (m, 2H, –CH); 2.38–1.72 (m, 56H, –CH);
1.51–0.96 (m, 34H, –CH). Elemental analysis calcd. (%) for
C76H106O2 (1050.82): C 86.80, H 10.16, O 3.04; found: C 86.81,
H 10.15, O 3.02.
Preparation of H2O/THF mixed solvents: Chol-TPV was dissolved
in THF, and then added H2O to prepare THF/H2O mixed solution,
the water volume percentages were found to be 0, 40% and 80%,
respectively. The concentration of Chol-TPV in mixed solvents was
at 1.0 ꢁ 10ꢀ5 mol/L and saturated solution.
2.3. Synthesis and structural characterizations
1,4-Bis-bromomethylbenzene: p-Xylene (6.2 mL, 50 mmol) and
N-bromosuccinimide (NBS) (21.3 g, 110 mmol) were added to a
solution of CCl4 (100 mL) in a 250 mL three-necked flask. After the
temperature reached to 80 8C, BPO (0.1 mg) was added into the
flask. The mixture was vigorously stirred for 8 h at 80 8C under N2.
The residue was cooled and the filtrate was concentrated,
subsequently recrystal by absolute ethyl alcohol. 1,4-bis-bromo-
methylbenzene was obtained as white powder in 84% yield. FT-IR
(KBr, cmꢀ1): 1516, 1456 (
g
C55C); 750 (
g
C–Br). 1H NMR (500 MHz,
3. Results and discussion
CDCl3): 7.55–7.36 (m, 4H, Ph-H); 3.81–3.74 (m, 4H, –CH2Br).
d
4,40-Bis (triphenylphosphonium-bromide emethyl) benzene: A
mixture of 1,4-bis-bromomethylbenzene (7.93 g, 10 mmol) and
triphenylphosphine (17.29 g, 66 mmol) were dissolved in DMF
(100 mL). The mixture was vigorously stirred for 24 h at 176 8C in a
round-bottom flask. The residue was cooled and filtrated gave to
4,40-bis(triphenylphosphonium-bromide emethyl) benzene as
white power with yield 72%. FT-IR (KBr, cmꢀ1): 3354 (PPh3). 1H
The synthetic route for the Chol-TPV is outlined in Scheme 1. On
the basis of a detailed analysis of IR, 1H NMR, elemental analyses,
and mass spectra, the structure was found to be consistent with the
Chol-TPV structure.
UV–vis absorption spectra of Chol-TPV in THF/H2O are shown in
Fig. 1. The absorption spectra in THF and 40% THF/H2O with a
solute concentration of 1.0 ꢁ 10ꢀ5 mol/L shows same features and
maximum peak (369 nm), indicating the TPV chromophore did not
demonstrate excitonic coupling. That implies that the distance (d)
of the adjacent TPV chromophores is greater than the distance
required to produce an excitonic coupling effect of TPV chromo-
phores (ꢂ0.5 nm) [8]. The Chol-TPV molecular self-assemble is
initiated with the addition of water, leading to a dramatic spectral
blue-shift. The value of maximal peak is decreased with higher
water content and solute concentration. As shown in Fig. 1, the
maximal peak appeared at 341 nm in water content of 80% with a
Chol-TPV concentration of 1.0 ꢁ 10ꢀ5 mol/L (Fig. 1a), and maximal
peak appeared at 305 nm in water content of 80% with a saturated
Chol-TPV concentration (Fig. 1b). Furthermore, maximal peak
appeared at 344 nm in water content of 40% with a saturated Chol-
TPV concentration. These spectral characteristics indicate that the
excitonic coupling occurred between the TPV chromophores. In
other words, the nearest distance (d) in adjacent TPV chromo-
phores is smaller than that 0.5 nm under these condition. At the
saturated Chol-TPV concentration, when water content increase to
80% the strong light absorption appeared at the long wavelength
NMR (500 MHz, CDCl3):
d 7.76–7.60 (30 H, Ph-H); 6.92–6.91 (4H,
Ph-H); 5.38 (4 H, –CH2Br).
Synthesis of compound 1: A mixture of p-hydroxybenzaldehyde
(10 mmol), kalium iodide (1 mmol), potassium carbonate
(30 mmol) and cholesteryl chloride (10 mmol) were dissolved
in DMF (200 mL). Then, this mixture was heated to reflux for
180 min. After the reaction mixture was cooled to room
temperature, the solvent was removed in vacuum, the residue
was dissolved in ether (200 mL), and the ether solution was
washed with water (100 mL), organic layer is dried using MgSO4,
and concentrated. The product was chromatographied on silica
gel column using petroleum ether/ethyl acetate (10/2) as eluent.
Compound 1 was obtained as white solid in 58.6% yield. FT-IR
(KBr, cmꢀ1): 3081, 2933, 2867, 2729, 1703, 1597, 1516, 1457,
1318, 1250, 1153, 1003, 837, 607, 503; 1H NMR (500 MHz, CDCl3):
d
9.87 (s, 1H, CHO); 7.81–7.80 (d, 2H, Ph-H); 7.00–6.99 (d, 2H,
Ph-H); 5.22 -5.21 (m, 1H, -C=CH-); 3.72 -3.71 (m, 1H, -OCH-); 2.34
-1.64 (m, 28H, -CH-, -CH2-); 0.99-0.97 (m, 15H, -CH3). Elemental
analysis calcd. (%) for C34H50O2 (490.38): C 83.21, H 10.27, O 6.52;
found: C 83.23, H 10.26, O 6.51.
region (l > 410 nm) [9] (Fig. 1b).
Synthesis of Chol-TPV: 4,40-Bis(triphenylphosphonium-bromide
emethyl) benzene (0.16 g, 0.2 mmol) and cholesterol ester
benzaldehyde (0.2 g, 0.4 mmol) were dissolved in THF (15 mL).
The anhydrous THF containing the potassium tert-butoxide (BuOK)
(0.0672 g, 0.6 mmol) was added dropwise into the foregoing
mixture at the speed of one drop every three seconds. The resulting
solution was stirred at 0 8C for 24 h and the reaction environment
was protected by N2. The solvent was evaporated and the residue
was chromatographied on silica gel column using petroleum ether/
The Photoluminescence spectra of Chol-TPV in THF/H2O system
are shown in Fig. 2. The maximum emission peak of Chol-TPV had a
light red-shift in 40% THF/H2O compared with that in THF with the
solute concentration of 1.0 ꢁ 10ꢀ5 mol/L (Fig. 2a). When the water
content increases to 80%, a marked blue-shift was found. However,
an entirely different phenomenon was found in 40% (the maximum
emission peak appeared at 372 nm, and the fine structure of
emission spectrum became indistinct.) or 80% THF/H2O (the
maximum emission peak appeared at 456 nm and 484 nm,
P(Ph)
NBS
3
H C
3
CH
3
BrH C
2
CH Br
2
(Ph) PBrH C
CH BrP(Ph)
2 3
3
2
BPO, ClC
4
DMF
BuOK
THF
CH
CH
CH
K CO
3
3
2
3
OHC
O
CH
3
OHC
OH
Cl
+
DMF
3
1
H C
3
O
H C
3
CH
3
O
CH
3
Chol-TPV
Scheme 1. Synthetic routes of Chol-TPV.

Y.-Z. Zhao et al. / Chinese Chemical Letters 25 (2014) 99–103
101
0% H2O: Concentration: 1.0 ×1.0 -5 mol/L
40% H2O: Saturated solution
a
0% H2O: Concentration: 1.0 ×1.0-5 mol/L
40% H2O: Concentration: 1.0 ×1.0-5 mol/L
80% H2O: Concentration: 1.0 ×1.0 -5mol/L
b
80% H2O: Saturated solution
light scattering of
nano-aggregates
320
340
360
380
400
420
440
300
350
400
450
500
550
Wavelength (nm)
Wavelength (nm)
Fig. 1. Absorption spectra of Chol-TPV in THF/H2O. (a) Concentration of 1.0 ꢁ 10ꢀ5 mol/L and (b) saturated solution.
Fig. 2. Photoluminescence spectra of Chol-TPV in THF/H2O. (a) Concentration of 1.0 ꢁ 10ꢀ5 mol/L and (b) saturated solution; excition wavelength: 360 nm; the excition
wavelength is 340 nm in 40% H2O saturated solution.
respectively.) saturated solution compared with that in THF with a
Chol-TPV concentration of 1.0 ꢁ 10ꢀ5 mol/L (Fig. 2b). Combined
with absorption spectra and the photoluminescence spectra, the
Chol-TPV shows the spectral characteristic of the typical H-
aggregation in 80% THF/H2O saturated concentration (blue shift in
the intense absorption, red shift in photoluminescence) [10].
Under other condition, the Chol-TPV shows the spectral charac-
teristic of the no-typical H-aggregation (blue shift in the intense
absorption and Photoluminescence).
The CD spectra of Chol-TPV in the THF/H2O system with
different water content and different solute concentration
are shown in Fig. 3. The solution of Chol-TPV in THF is circular
dichroism-inactive. However, the CD spectrum of Chol-TPV in
40% THF/H2O and 80% THF/H2O with the solute concentration
of 1.0 ꢁ 10ꢀ5 mol/L showed an excition-coupled bisignate
signal with negative
positive max = 366 nm and 317 nm) Cotton effects. This
behavior is characteristic of a right-handed helical bias of the
(lmax = 338 nm and 292 nm) and
(
l
Fig. 3. CD spectra of Chol-TPV in THF/H2O system. (a) Concentration of 1.0 ꢁ 10ꢀ5 mol/L and (b) saturated solution.

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Y.-Z. Zhao et al. / Chinese Chemical Letters 25 (2014) 99–103
Fig. 4. Probable mode of self-assembly of Chol-TPV in THF/H2O under different water content and different concentration.
supramolecular chirality. Surprisingly, the CD spectrum of
saturated Chol-TPV in 80% THF/H2O showed a strange behavior
4. Conclusion
with first a positive (
l
max = 304 nm) followed by two negative
In this paper, we designed and synthesized cholesteryl trimeric
phenylene vinylene in order to understand the influence of van der
(
l
max = 360 nm and 412 nm) Cotton effects. The non-bisignate
exciton couplet with opposite signals indicates the possibility of
different chiral dispositions. A helix inversion is reasonable
because the initially formed 1D aggregate with a right-handed
twist may wind in the opposite direction during the higher-
order assembly to result in an ultimate left-handed twist
[5].
Waals force and p–p interactions on its self-assembly behaviors in
the THF/H2O system. With different water content and the solute
concentration, the cholesteryl trimeric p-phenylene vinylene
forms different aggregated structures, leading to the dramatically
different spectral characteristic. Cholesteryl trimeric phenylene
vinylene in THF/H2O forms right-handed helical architectures
and changes into left-handed helical architectures at higher
concentrations.
Based on the observations on the differences of the photo-
physical and chiroptical properties of the Chol-TPV in different
water content and different solute concentration, the self-
assembly behaviors of the Chol-TPV molecule in THF/H2O system
can be described as follows (A mode of the molecular self-
assembly in THF/H2O system with different water content and
solute concentration is shown in Fig. 4.): The cholesteryl groups in
adjacent molecules approach each other as the water content
increases. When the water content is close to 40% with the Chol-
TPV concentration of 1.0 ꢁ 10ꢀ5 mol/L, the molecules form chiral
aggregates due to strong van der Waals interactions among the
steroid units. But data of the UV–vis spectra suggest that the
chromophore did not show excitonic coupling under this
condition, indicating the interactions among TPV chromophores
are very weak (Fig. 4b). When water content is close to 80% with
the Chol-TPV concentration of 1.0 ꢁ 10ꢀ5 mol/L, the maximum
absorption and emission spectra shows a marked blue shift,
suggesting TPV chromophores form strong excitonic coupling
(Fig. 4c). When the concentration of Chol-TPV increased from
1.0 ꢁ 10ꢀ5 mol/L to the saturated concentration, a helix inversion
occurred (Fig. 4d).
Acknowledgments
This work was supported by the National Science Foundation of
China (No. 51173155) and the Hebei Province Science Foundation
of China (No. F2011203160).
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