Multicolor fluorescent switches in gel systems controlled by alkoxyl chain and solvent

Article abstract of DOI:10.1039/c0ob00091d

Two simple molecules, 1 and 2 with D-π-A structure and alkoxyl groups, respectively, were designed and synthesized. Both compounds can gelatinize THF-water and DMSO. And compound 2 forms gel in acetone by ultrasonic stimulus. Interestingly, these gels exhibit aggregation-induced emission (AIE) during the sol-gel phase transformation. Moreover, the molecular self-assembled and photophysical properties can be controlled by the number of the alkoxyl chains and the type of the solvents. For example, 1 has an identical packing model and fluorescent colour in THF-water and DMSO gels. Contrarily, the self-assembly of molecule 2 strongly depends on the solvent. Furthermore, the gel phases of 2 formed in three solvents possess different fluorescent colours. Such as, THF-water gel emits yellow fluorescence, acetone gel has orange emission and red fluorescence appears in DMSO.

Full text of DOI:10.1039/c0ob00091d

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www.rsc.org/obc | Organic & Biomolecular Chemistry
Multicolor fluorescent switches in gel systems controlled by alkoxyl chain and
solvent†
Yue Xu,b Pengchong Xue,*a Defang Xu,a Xiaofei Zhang,a Xingliang Liu,a Huipeng Zhou,a Junhui Jia,a
Xinchun Yang,a Fengyong Wanga and Ran Lu*a
Received 7th May 2010, Accepted 6th July 2010
DOI: 10.1039/c0ob00091d
Two simple molecules, 1 and 2 with D-p-A structure and alkoxyl groups, respectively, were designed
and synthesized. Both compounds can gelatinize THF–water and DMSO. And compound 2 forms gel
in acetone by ultrasonic stimulus. Interestingly, these gels exhibit aggregation-induced emission (AIE)
during the sol–gel phase transformation. Moreover, the molecular self-assembled and photophysical
properties can be controlled by the number of the alkoxyl chains and the type of the solvents. For
example, 1 has an identical packing model and fluorescent colour in THF–water and DMSO gels.
Contrarily, the self-assembly of molecule 2 strongly depends on the solvent. Furthermore, the gel
phases of 2 formed in three solvents possess different fluorescent colours. Such as, THF–water gel emits
yellow fluorescence, acetone gel has orange emission and red fluorescence appears in DMSO.
that all gels formed by 1 and 2 in different solvents exhibited
Introduction
the aggregation-induced emission activity. Moreover, molecular
Recently, low-molecular-mass gelators (LMMG) have become a
assemblies and photophysical properties could be controlled by
hot topic in materials science.1 Various functional gel systems
with potential applications in light harvesting, photoswitches, gas
sensors, drug transfer and release, medical therapy, ion discerning,
templated transcription and solar cell have been constructed.2 In
the number of the alkoxyl chains and the type of the solvents.
For example, 1 has a uniform molecular packing model and the
same fluorescent color in the both gel phases. However, the self-
assembly and fluorescent characteristic of 2 strongly depend on
particular, the functionalities of p-conjugated LMMGs can be
tailored by incorporating stimuli-responsive units, for example, pH
sensitive, temperature-responsive and photoactive moieties. These
stimuli responsive organogels, alternatively called “smart” or
“intelligent” gels, usually show reversible changes in morphologies
and/or physical properties in response to various external stimuli
so as to result in many different kinds of switches based on these
gels.3
If a p-conjugated gelator exhibited the aggregation-induced
emission (AIE) activity,4 the fluorescence of the gel formed
by it should respond to temperature. In other words, this gel
can give strong emission while nonemissive or weak fluorescent
system is observed when the temperature is above Tgel (sol–gel
phase transition temperature). Thus, a smart fluorescent switch in
response to temperature stimulus can be obtained. Although some
p-conjugated gel systems with AIE activity have been reported by
our group and others,5 there is no investigation about the influence
of the solvent and the alkoxyl chain on the characteristics of AIE
and fluorescent switch in gel systems.
the solvent. Molecule 2 can be arranged into two kinds of the
lamellar structures with different layer periods in THF–water and
DMSO gels. Moreover, the gels of 2 formed in the three solvents
possess different fluorescent colors. For instance, THF–water gel
emits yellow fluorescence, acetone gel has orange emission and
red fluorescent color appears in DMSO. Thus, the temperature-
responsive and multicolor fluorescent switches could be easily
obtained by adjusting the type of the solvents and the number
of the alkoxyl chains.
Results and discussion
Photophysical properties of 1 and 2 in solution and crystal state
Because 1 and 2 are typical D-p-A type molecules (alkoxyl is
an electron-pushing group and nitro is the electron-pulling unit),
their UV-vis absorption and fluorescent spectra may be distinct in
solvents with different polarities. As shown in Fig. 1, the maximal
absorption of 1 in benzene is located at 370 nm, which shifts to
390 nm for 2 because of the stronger electron-pushing ability of the
donors of 2 (two alkoxyl groups). In THF, the maximal absorption
peaks shift to 372 and 391 nm for 1 and 2, respectively, and 376 and
392 nm in CHCl3. It is very clear that the absorption peaks of 1 and
2 have slight red-shifts with the increase of the solvent polarity.
This indicates that the differences in the dipole moments of the
Franck–Condon (FC) excited states and the ground states of 1
and 2 are quite small.6 Unlike absorption spectra, the fluorescent
spectra of 1 and 2 exhibit obvious red-shifts in polar solvents
compared with those in nonpolar ones (Fig. 1b). In the case of
1, the emission maximum at 456 nm in toluene shifts to 460 nm
in benzene, 484 in THF, 493 in CHCl3 and 518 nm in CH2Cl2,
In this paper, we designed two p-conjugated gelators, 1 and
2 with one and two alkoxyl chains, respectively. It was found
aState Key Laboratory of Supramolecular Structure and Materials, College
of Chemistry, Jilin University, Changchun, 130012, P. R. China. E-mail:
xuepengchong@jlu.edu.cn, luran@jlu.edu.cn; Tel: 86-431-88499179
bTest Science Experiment Center, Jilin University, 2699 Qianjin Street,
Changchun, 130012, P. R. China
† Electronic supplementary information (ESI) available: Frontier orbital,
XRD patterns of two crystals, time-dependent UV-vis spectra of 1 in
THF–water (v/v = 1/1), polarized light microscopic photos, UV–vis
spectrum of 2 in acetone and temperature-dependent FL spectra. See
DOI: 10.1039/c0ob00091d
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Fig. 1 Absorption (a) and fluorescence (b) spectra of 1 and 2 in various dilute solutions, absorption and fluorescence (c) of 1 and 2 crystals and photos
(d) of solutions and crystals under the irradiation of 365 nm UV light.
giving the large solvatochromic shifts of 4, 28, 37 and 62 nm,
respectively. Similarly, compound 2 also shows a large red-shift
of 93 nm from toluene to CH2Cl2. Therefore, the pronounced
ICT characteristics of the excitation states can be deduced.7 In
addition, DFT calculation (B3LYP/6-31G) also indicates that
the maximal absorption bands of 1 and 2 are assignable to the
intramolecular charge transfer (ICT) transition from the HOMO
mainly localized over the donor party to the LUMO mainly
localized on the acceptor (nitro unit, Fig. S1†). It is worth
mentioning that both 1 and 2 show weak emission in solutions. For
example, the fluorescent quantum yields (Uf) of 1 and 2 in THF
are only 0.0055 and 0.0059, respectively. However, the powders of
1 and 2 can emit strong fluorescence. As seen in Fig. 1c and d, 1
shows strong yellow-green light with a maximum at 529 nm, and
2 gives intense red emission (the maximal peak at 622 nm). These
data reveal that molecular aggregation can induce the emission
enhancement of 1 and 2 compared with those in solution state. It
has been reported that the enhanced emission of organic molecules
in the crystal state has been interpreted in terms of the intra-
and intermolecular effects exerted by the fluorophore aggregation.
Intramolecular effects on the fluorescent enhancement can be
explained by the conformational changes of the chromophores.
It is supposed that the twisted conformations of chromophores in
solution tend to suppress the radiative process, whereas planar
ones of chromophores activate the radiation process in the
crystal state. Effects on fluorescent changes by intermolecular
interactions are correlated with the aggregation type, such as H-
and J-aggregation. H-aggregates, where molecules are arranged in
parallel with strong intermolecular interactions, prefer to induce
the nonradiative deactivation process. Formation of H aggregates
is characterized by the blueshift of the UV-vis absorption peak
relative to isolated species. In contrast, J-aggregates, where the
molecules are arranged in head-to-tail direction and the transition
from the lowest couple excited state of molecule to ground state is
allowed, induce a relatively high fluorescent efficiency along with
an absorption bathochromic shift.8 In this case, the existence of a
cyano group is advantageous in the twisted conformation in the
isolated state owing to the steric interaction between the bulky
cyano unit and the neighboring hydrogen atoms,9 which can be
supported by the geometry optimization with DFT calculation,
as shown in Fig. 2. Such twisted conformation always suppresses
the radiation transition and then leads to weak fluorescence.4 On
the other hand, the dihedral angle between the adjacent groups
can be depressed in the aggregated state, which is supported by
UV-vis absorption spectra. The maximal absorption bands of 1
and 2 in crystal state locate at 401 and 418 nm (red-shifts of 31
and 28 nm compared with those in dilute benzene solutions) with
the new shoulder bands at 443 and 461 nm, respectively (Fig. 1c).
The peaks at 401 and 418 nm are associated with the molecular
transitions with planar conformations, whose conjugation lengths
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Microscopic observation. The light microscopy pictures (Fig.
S4†) of the gels of 1 and 2 in THF–water and DMSO illustrate
that 1 prefers to form long and thick fibers, and 2 prefers to self-
assemble into thinner fibers, especially in DMSO. Scanning elec-
tron microscope (SEM) was further used to study the microscopic
structure of the gels. As shown in Fig. 3a and c, an extended
fibrillar network was formed by numerous long and thick fibers
with high aspect ratio, width of 150–500 nm and length of tens
micrometres, in the THF–water and DMSO gels of 1. On the other
hand, a large amount of thinner fibers could be observed in gels of
2 (Fig. 3b and 3d). This suggests that two gelator molecules tend
to self-assemble into 1-D fiber.
Fig. 2 A schematic representation of planarization of 1 and 2 from twisted
conformation after aggregation. Long alkoxyl chains were replaced by
methoxyl groups for easy calculation and clarity.
are extended, while the bands at 443 and 461 nm are assigned to
the J aggregates of 1 and 2, respectively.9 When the hot solution of
1 in THF–water (v/v = 1/1) was cooled for 1 min, the clear solution
became turbid and the maximal absorption peak at 377 nm red-
shifts to 387 nm, indicating J aggregation. However, at the moment
system still emits weak fluorescence. After 3 min, one new peak
around 450 nm appears, accompanying with rapid increase of the
emission intensity. Therefore, the formation of J aggregate may
be considered to be the reason for the enhanced emission.5 In
addition, further red-shifts of 42 and 43 nm of the peaks ascribing
to J aggregates compared with those in planar conformation
show similar p–p interaction between aromatic units, and further
indicate that two alkoxyl chains do not display a more efficient
p–p interaction.
Furthermore, we obtained the small- and wide-angle powder
X-ray diffraction patterns of the crystals (Fig. S3†). It is very clear
that two diffraction patterns show strong and sharp diffraction
peaks in both low and wide angle regions. The diffraction peaks
which appeared in the low-angle region illustrate the lamellar
lattices with the long-range periods of 2.74 and 5.26 nm for 1
and 2, respectively. The sharp diffraction peaks suggest the short-
range ordering in wide angle region.10 These data indicate the high
ordering of the molecular stacking.
Fig. 3 SEM images of xerogels of 1 in THF–water (v/v = 3/1, a), DMSO
(c); 2 in THF–water (v/v = 3/1, b) and DMSO (d).
Absorption spectral investigation. The absorption spectral
changes were determined to monitor the interactions between
the chromophores during the gel formation. The time-dependent
UV-Vis absorption spectra of compound 1 and 2 in THF–water
and DMSO are shown in Fig. 4. The hot solution of 1 in THF–
water (v/v = 3/1) gave a strong absorption maximum at 378 nm,
which decreased rapidly when the sample was cooled to room
temperature naturally. Its absorbance could decrease by 77%
after 8 min. Moreover, a new peak at ca. 450 nm, appeared
and became stronger and stronger with prolonging time. Similar
spectral change was also observed in DMSO system of 1 and
the three solvent systems of 2 (THF–water, DMSO and acetone).
These spectral changes reveal that both gelators in the gel phases
are also arranged into J aggregates.
Self-assembled properties in gel phases
Gelation ability. The gelation ability of 1 and 2 was checked by
the standard heating-and-cooling method. From Table 1, we can
find that they easily dissolve in many solvents, such as CHCl3,
benzene, cyclohexane, THF and ethyl acetate. Notably, 2 can
form stable gel in DMSO and THF–water, while the gels of 1 in
DMSO and THF–water can be easily destroyed by being shaken.
In addition, 2 can gelatinize acetone by ultrasonic stimulation. So,
compound 2 bearing two alkoxyl chains shows stronger gelation
ability than that of 1 with one alkoxyl chain, suggesting that the
alkoxyl chain has an effect on the molecular gelation ability.
Table 1 The gelation ability of 1 and 2 in organic solventsa
IR spectral observation. To explore the role of cyano units
and alkoxyl chains in molecular assemblies, the IR spectra of 1
and 2 in solution and gel phase were measured. As shown in
Fig. 5, in dichlorobenzene solution cyano stretching appeared
at 2216 and 2214 cm-1 for 1 and 2, respectively. In the case
of xerogels, significant changes in the cyano stretching region
were noticeable. The corresponding absorption peaks shifted to
2213 and 2212 cm-1, respectively, implying the existence of cyano
interactions in gel phases.11 In addition, the antisymmetric and
symmetric stretching vibration bands of CH2 groups are located
at 2928 and 2856 cm-1 for 1 and 2 in dichlorobenzene solution,
Solvent
1
2
Solvent
1
2
CH2Cl2
CHCl3
THF
DMSO
Benzene
Toluene
Ethanol
S
S
S
G
S
S
P
S
S
S
G
S
S
P
Acetone
P
S
S
Gb
S
S
S
P
Cyclohexanone
Ethyl acetate
Butyl acetate
Cyclohexane
n-Hexane
S
P
P
G
P
G
THF–waterc
a [1] and [2] = 1.0 wt/vol% (g mL-1%); G – gel; P – precipitate; S – soluble.
b Gel induced by ultrasonic stimulation. c v/v = 3/1.
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Fig. 4 Time-dependent UV-vis spectra of 1 in THF–water (v/v = 3/1, a) and DMSO (c) at 0.05 wt/vol; 2 in THF–water (v/v = 3/1, b) and DMSO (d)
at 0.1 wt/vol%. The samples in a and c were tested from 60 ◦C to room temperature. The samples in b and d are 100 ◦C to room temperature. The testing
interval is 60 s.
X-Ray diffraction studies. To reveal the molecular packing
of the gelators in the gel phases, the low-angle XRD patterns
of xerogels of 1 and 2 obtained from THF–water and DMSO
were investigated and shown in Fig. 6. It is clear that the X-ray
diffraction peak locations of the xerogels of 1 are the same as
those in crystal sate, which indicates that molecule 1 also adopts
a lamellar packing structure with the domain spacing evaluated
to be 2.74 nm in two solvent gel systems. The slight difference
between the two solvent patterns is that the strengths of diffraction
Fig. 5 FT-IR spectra of 2 and 1 in THF–water xerogels (a and c) and in
dichlorobenzene (b and d) solutions. e is IR spectrum of dichlorobenzene.
indicating the existance of the gauche conformations and free
rotation of alkyl chain. On the other hand, in xerogels they were
shifted to 2917 and 2850 cm-1, respectively, meaning that the alkyl
chains adopt all-trans extended conformation and their mobility is
restricted after gel formation.12 These results indicate that cyano
interactions and van der Waals interactions between the alkyl
chains also play an important role in the self-assembly of gelators.
Fig. 6 Small angle XRD patterns of xerogels of 1 and 2 in THF–water
and DMSO.
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peaks from THF–water are stronger and sharper than those from
DMSO. So, the molecular array in THF–water is more ordered
than that in DMSO. The good diffraction pattern for 2 in DMSO
is characterized by four reflection peaks of 6.31, 3.15, 2.09 and
1.57 nm in the low angle region, which have a periodicity of 1/1,
1/2, 1/3 and 1/4. Apparently, a good lamellar organization within
the aggregates of 2 in DMSO gel was formed with an interlayer
distance of 6.31 nm,13 which is longer than the period in the crystal
state (5.26 nm). On the other hand, the intensity of the diffraction
peaks of THF–water gel is weak and the lattice period shifts to
5.97 nm. Therefore, the solvent plays a crucial role in the molecular
packing of 2 in the long range in the gel phase, which is different
from gel systems of 1.
Molecular packing model. As noted before, both compounds
can self-assemble into 1-D ordered fibres, in which molecules are
packed into J aggregates with the planarization of chromophores.
To further clarify how the gelator molecules were arranged
within the superstructure, the geometric optimization of gelators
was firstly estimated by using AM1 force field, and then the
optimized molecules were used to simulate the energy-minimized
packing model by using the MM+ molecular mechanics force field
(Hyperchem 8.0).14 It is revealed that 1 has V-shaped configuration
and its length is 3.3 nm in fully extended configuration, which
is much longer than the long-range period (2.74 nm) obtained
from the XRD measurement. After energy minimization, a linear
molecular array with a sheet structure for 1 could be obtained, as
shown in Fig. 7a, in which a tilted molecular arrangement could
be observed and the aromatic moieties formed excellent head-
to-tail stacking (J aggregate) with a intermolecular distance of
˚
3.3 A. However, the width of the sheet (ca. 3.0 nm) is still larger
than 2.74 nm. There is a possibility that the sheets also adopt a
tilted packing model in another stacking axis, as represented in
Fig. 7b, because V-shaped configuration suppresses the parallel
packing. In such a model, the long-range period is in accordance
with the period obtained from XRD data.
Molecule 2 with the same extended molecular length as that
of 1 also prefers to self-assemble along 1D direction. Because the
lattice periods in THF–water and DMSO gels obtained from XRD
investigations are much larger than the molecular length with the
fully extended structure, the two kinds of the bimolecular lamellar
is possible for molecule 2, as shown in Fig. 5c and f. In the first
packing model with the bimolecular layer (Fig. 7c), the length of
the repeated unit is ca. 6.0 nm (Fig. 7e), being in agreement with the
value of THF–water gel. If this bimolecular layer has a mismatch
arrangement, as illustrated in Fig. 7d, the layer period is identical
to that of crystal of 2 (Fig. 7d). In another possible bimolecular
layer, two monomolecular sheets are arranged parallel to each
other and it exhibits a long-range period of 6.3 nm (Fig. 7f and
7g). Therefore, molecule 2 may self-assemble into 1-D nanofibers
with this bimolecular packing model in DMSO.
Fig. 7 A schematic representation of molecular packing models of 1 in
THF–water, DMSO and crystal state (a and b), and 2 in crystal state (c,
d), THF–water (c, e) and DMSO (f and g).
Gelation-induced emission enhancement. Based on the above
discussions, it is known that 1 and 2 exhibit the aggregation-
induced emission in crystal state, which may be induced by
the formation of J aggregates and the planarization of the
fluorophores. It inspires us to study the fluorescent properties of 1
and 2 in gel phases. Fig. 8 shows the time-dependent fluorescence
spectra of 1 and 2 in THF–water and DMSO. It clearly shows
that the hot solutions of 1 and 2 are weakly luminescent, while
their emissions are enhanced significantly with the temperature
decreasing. For example, the photoluminescence spectrum of 1
in hot THF–water solution is nearly a flat line parallel to the
abscissa (Fig. 8a). After cooling the hot solution for 1 min the
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Fig. 8 Time-dependent fluorescence spectra of 1 in THF–water (a) and DMSO (c), 2 in THF–water (b), DMSO (d) and acetone (e). Red lines are the
fluorescence curves of 1 and 2 in THF solution. The concentrations of all samples are 0.1 wt/vol%. The samples in a and b firstly were heated to 60 ◦C
and cooled to room temperature naturally. The samples in c and d firstly were heated to 100 ◦C. The testing interval time is 30 s.
emission at 535 nm increases slowly, afterwards, the emission
intensity increases swiftly. After 5 min the gel is formed and the
maximal peak blue-shifts to 525 nm, whose strength is 40-fold
higher than that in the hot THF–water solution and ca. 90-fold
higher than that of THF solution at the same concentration. In hot
DMSO solution 1 gives one weak emission band at 550 nm, which
gradually increases and also blue-shifts to 525 nm with 20-fold
increase in the emission intensity. This suggests that the solvent
polarity dose not affect the emission peak location and molecular
packing of 1 in gel phases. Moreover, blue-shift of emission peaks
may be induced by the disappearance of polar solvent effect
because of the formation of large molecular aggregates, as shown
in Fig. 3a and c.
Contrarily, the weak emission peak at 540 nm of 2 in hot THF–
water solution red-shifted markedly to 574 nm accompanying with
an enhancement of the emission when the sample was cooled
down naturally for 3 min. After 13 min the system transferred into
yellow gel phase with strong yellow fluorescence, whose intensity
is 7-fold higher than that in the hot THF–water solution. On
the other hand, the hot DMSO solution of 2 can be quickly
gelatinized within 1 min. The maximal emission peak of 2 in hot
DMSO solution is located at 608 nm, which slightly red-shifts to
610 nm in gel phase. The red-shift in emission spectra indicates the
delocalization of the exciton across the self-assembled aggregates.
Due to efficient exciton migration within the aggregates, emission
occurs mainly from aggregates of lower energy resulting in a red
shift in the wavelength.15 Similarly, AIE is observed in DMSO gel
of 2, and its DMSO gel emits strong red fluorescence with 25-
fold enhancement (Fig. 8d). Moreover, the gel phase formed by
2 in acetone also possesses excellent AIE characteristic with 70-
fold enhancement and emits strong orange fluorescence (maximal
peak at 584 nm). Therefore, the emitting color of 2 in gel phase and
fluorescence enhanced degree can be controlled by the solvent.
Temperature-dependent fluorescence spectra of 1 and 2 in
different solvent systems can tell us the fluorescent transi-
tion temperature. At a concentration of 0.1 wt/vol%, THF–
water and DMSO gels of 1 have same transition temperature
(40 ◦C), THF–water and acetone gels of 2 possess lower transition
temperature (35 ◦C). However, DMSO gel of 2 show highest
transition temperature and reach 60 ◦C (Fig. S6†). Thus, the
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multicolor and temperature-sensitive fluorescent switches can be
obtained.
Conclusions
Two new D-p-A type organogelators 1 and 2 bearing one and
two alkoxyl units, respectively, were synthesized. It is interesting
that aggregation-induced emission can be realized in the gel phase.
Moreover, the morphologies of assemblies and AIE activity can
be controlled by the alkoxyl chain and solvent. In THF–water
and DMSO gel systems, 1 shows the same packing model and
the photophysical properties. Contrarily, the self-assembly and
fluorescence characteristics of molecule 2 strongly depend on the
solvent. Finally, the temperature-sensitive fluorescence switches
with different emitted colors can be obtained by easily adjusting
the type of the solvents and the number of the alkoxyl chains.
Scheme 2 Synthesis route of 1 and 2.
was added. After 2 h the solution was cooled down to room
temperature and a large amounts of yellow solids were separated
out from the solution. Pure product could be obtained by the
vacuum filtration and washing with cooled ethanol. Yield 90.2%.
mp 107–108 ◦C. nmax/cm-1 3070, 2961, 2917, 2850, 2213, 1580,
1508, 1471 and 1334. Element analysis (%): Calcd for C31H42N2O3,
C, 75.88; H, 8.63; N, 5.71; Found: C, 75.80; H, 8.60; N, 5.68.
1H NMR (500 MHz, TMS, CDCl3) d 8.22 (d, J = 8.5 Hz, 2 H),
7.61 (d, J = 8.5 Hz, 2 H), 7.42 (s, 1 H), 7.07 (d, J = 8.5 Hz, 2 H),
6.75 (d, J = 8.5 Hz, 2 H), 3.94 (t, J = 6.5 Hz, 2 H), 1.76 (m, 2
H), 1.42 (m, 2 H), 1.33–1.25 (m, 24 H), 0.88 (t, J = 6.5 Hz, 3 H).
13C NMR (125 MHz, CDCl3) d 162.12, 147.51, 145.12, 141.20,
131.98, 126.32, 125.45, 124.34, 117.80, 115.14, 105.91, 68.41,
31.93, 29.68, 29.36, 29.09, 25.98, 22.70, 14.12.
Experimental Section
Instruments. Infrared spectra were recorded using a Nicolet-
360 FTIR spectrometer by incorporating the samples into KBr
disks. The UV–vis spectra were recorded on a Mapada UV-
1800pc spectrophotometer. C, H, and N elemental analyses were
performed on a Perkin-Elmer 240 C elemental analyzer. Photolu-
minescence measurements were taken on a Varian FLR006 lumi-
nescence spectrophotometer. X-ray Diffraction (XRD) patterns
were determined on a Rigaku D/max-rA X-ray diffractometer
(Z)-3-(3,4-Bis(hexadecyloxy)phenyl)-2-(4-nitrophenyl)acrylo-
nitrile (2). 2 was synthesized by the same procedure of 1. Yield
80.0%. mp 98–100 ◦C. nmax/cm-1 3046, 2955, 2918, 2849, 2211,
1578, 1514, 1466, 1441 and 1333. Element analysis (%): calcd for
C47H74N2O4, C, 77.21; H, 10.20; N, 3.83; Found: C, 77.10; H, 10.18;
N, 3.79. 1H NMR (500 MHz, TMS, CDCl3): 8.23 (d, J = 8.5 Hz, 2
H), 7.62 (d, J = 8.5 Hz, 2 H), 7.41 (s, 1 H), 6.74 (m, 2 H), 6.57 (s, 1
H), 3.98 (t, J = 6.5 Hz, 2 H), 3.64 (t, J = 6.5 Hz, 2 H), 1.86 (m, 2 H),
1.80 (m, 2 H), 1.49 (m, 2 H), 1.44 (m, 2 H), 1.33–1.25 (m, 48 H),
0.88 (t, J = 6.5 Hz, 6 H). 13C NMR (125 MHz, CDCl3) d 244.61,
244.56, 152.56, 149.16, 147.48, 145.47, 141.27, 126.31, 125.69,
125.45, 124.34, 117.93, 113.18, 112.62, 105.74, 69.33, 69.12, 31.94,
29.72, 29.39, 29.13, 29.05, 26.04, 22.70, 14.12
˚
with graphite-monochromatized Cu-Ka radiation (l = 1.5418 A).
The accelerating voltage was set at 50 kV, with 100 mA fluxes
at a scanning rate of 0.02◦ S-1 in the 2 q range of 1–10◦ and
0.05◦ S-1 in the 2q range of 10–40◦. The XRD patterns of the
xerogels were obtained by casting wet gel samples in a glass flask
followed by the evaporation of the solvent naturally. Scanning
electron microscope (SEM) observations were carried out on a
Japan Hitachi model X-650 Scaning electron microscope. The
samples for these measurements were prepared by casting little
amounts of wet gels on silicon wafers and drying naturally, and
1
then being coated by gold film. H and 13C NMR spectra were
recorded on a Mercury Plus 500 MHz NMR.
Acknowledgements
Synthetic procedures and characterizations
This project was sponsored by the Scientific Research Foundation
for the Returned Overseas Chinese Scholars, State Education Min-
istry, Open Project of the State Key Laboratory of Supramolecular
Structure and Materials (SKLSSM200901), the National Natural
Science Foundation of China (NNSFC 20874034), and the 973
Program (2009CB939701).
Molecules 1 and 2 could be easily obtained by the dehy-
dration reaction of 4-(hexadecyloxy)benzaldehyde (3) and 3,4-
bis(hexadecyloxy)benzaldehyde (4) with 4-nitrophenylacetonitrile,
respectively, as shown in Scheme 1 and 2. 3 and 4 were obtained
by previously described synthetic procedures.16
Notes and references
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Scheme 1 Molecular structures of 1 and 2.
(Z)-3-(4-(Hexadecyloxy)phenyl)-2-(4-nitrophenyl) acrylonitrile
(1).
A
solution of
3
(0.6 g, 1.7 mmol) and 4-
nitrophenylacetonitrile (0.28 g, 1.7 mmol) in ethanol (20
mL) was heated to dissolve and then 0.1 mL of piperidine
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