Design and synthesis of photoactive ionic amorphous molecular materials

Article abstract of DOI:10.1039/c1jm11735a

Compounds bearing electrostatic charges have unique properties including outstanding ionic-conductivity when compared with neutral ones. On the other hand, amorphous molecular materials harness the advantages of small molecules with high purity, defined s

Full text of DOI:10.1039/c1jm11735a

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PAPER
Design and synthesis of photoactive ionic amorphous molecular materials†
Alexi K. Nedeltchev, Haesook Han and Pradip K. Bhowmik*
Received 20th April 2011, Accepted 1st July 2011
DOI: 10.1039/c1jm11735a
Compounds bearing electrostatic charges have unique properties including outstanding ionic-
conductivity when compared with neutral ones. On the other hand, amorphous molecular materials
harness the advantages of small molecules with high purity, defined structures and monodispersity,
while still being easily processable into thin films and fibers. Here, we report a series of bis(pyridinium
salt)s that combine these properties to form ionic amorphous molecular materials. Their design allowed
them to vitrify efficiently upon slow cooling. They exhibited glass-transition temperatures in the range
ꢀ
ꢀ
of 81–191 C and had excellent thermal stabilities of up to 461 C. Fibers were easily drawn from their
melts that were visible to the naked eye. Although they were completely conjugated and had large
molecular sizes, they were soluble in many common organic solvents. Additionally, they fluoresced blue
and green light in both solution and solid states. They could be useful for high-performance
applications in opto- and microelectronic fields, among others.
Introduction
their unique solvating properties, low vapor pressure and low
toxicity, they are useful for versatile applications that range from
Amorphous molecular materials are atypical due to their ther-
modynamic non-equilibrium state; as a result, they exhibit glass-
reaction media for organic and polymer synthesis to extractors to
13–17
lubricants.
Most recently, they have been investigated as
1–3
transition (T ) temperatures. They have gained a significant
g
potential drugs since they lack the phenomenon of poly-
18
morphism. Even though there is an abundance of these organic
interest in the scientific community since they can form stable
thin films as similar to amorphous polymeric materials. Molec-
ular glasses possess several advantages over polymers since they
can be prepared in high purity, have defined molecular structures
without end groups and are monodispersed. Similarly, they
outperform small crystalline molecules because they are homo-
geneous without grain boundaries, transparent, and do not
salts, up until now they have not been seriously considered as
amorphous molecular materials because most of them are either
highly crystalline or ionic liquids. They are usually studied as
19
materials in either crystalline or liquid states. Moreover, they
havelowthermaltransitionsandonly moderatethermalstabilities.
Here we demonstrate a series of bis(pyridinium salt)s that
combine amorphous character with electrostatic charges to form
high-performance ionic amorphous molecular materials. They
1–7
scatter light.
This suite of properties makes amorphous
molecular materials attractive for applications in opto- and
microelectronics including organic light emitting diodes
ꢀ
have excellent thermal stabilities that are as high as 461 C, which
(
OLEDs), light emitting electrochemical cells (LECs), organic
are comparable with those of high-performance polymers. They
field effect transistors (OFETs), organic photovoltaic cells and
g
exhibit high T temperatures that are desirable for most appli-
8–12
organic lasers, among others.
To prepare molecular
cations and can be effectively tuned by modifications of either the
dications or the anions. Since they have good solubilities in
a wide range of common organic solvents, they can be processed
efficiently into thin films and fibers from their melts and/or
solutions. Additionally, they emit blue or green light in both the
solution and solid states. We believe that this series of materials is
the cornerstone that would open up a new field in materials
science. Their general chemical structures and designations are
shown in Scheme 1.
compounds that vitrify efficiently is a challenging task since small
compounds tend to crystallize readily. In his several reviews,
Shirota identified a few important structural characteristics that
were found to promote a glassy state in these molecular mate-
rials. Large molecular size, rigidity, asymmetricity and presence
of bulky substituents are the general guidelines that need to be
4,5
met to make amorphous molecular materials.
In parallel efforts, numerous organic ionic compounds have
been developed as ionic liquids, both protic and aprotic. Due to
Results and discussions
Department of Chemistry, University of Nevada Las Vegas, 4505
Maryland Parkway Box 454003, Las Vegas, NV, 89154, USA. E-mail:
pradip.bhowmik@unlv.edu
Thermal transitions
The thermal transitions of the materials described herein,
compiled in Table 1, were found to be strongly dependent on the
†
1
Electronic supplementary information (ESI) available. See DOI:
0.1039/c1jm11735a
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moieties that promoted the amorphous state and increased the Tg
temperatures of the materials (Fig. 1b). Compound 2a (Y paired
2
ꢀ
with X ) produced a material that vitrified at 190 C after
1
ꢀ
melting. This chemical structure results in an increase in 39 C of
g
the T compared to 1a, which had the same anion. After melting
the solvent induced crystals, compound 2b sustained a stable
ꢁ1
ꢀ
glassy state upon slow cooling at a rate of 10 C min , unlike
compound 1b, which crystallized readily. Its T
ꢀ
g
was also
substantially increased by 54 C compared to 1b. The last two
bulky anions afforded amorphous materials that could not be
crystallized by means of a solvent. Compound 2c had a T at
g
ꢀ
ꢀ
1
85 C in the first heating cycle and 191 C in the second heating
ꢀ
cycle. Compound 2d had a T at 119 C in the second heating
g
ꢀ
cycle, which is 38 C higher compared with that of compound 1d.
From these data we can deduce that the thermal transitions and
glass-forming properties are governed by the chemical architec-
tures of the dications and the anions. In the first set of materials,
only compound 1a and 1d vitrified efficiently, whereas
compound 1b could be formed into glass only by rapid cooling
and compound 1c did not melt at all. In the second set of
materials, large quinoline side groups were introduced where all
the materials sustained stable amorphous states and their Tg
temperatures were increased substantially. Here, we should stress
that most of the materials formed a glassy state upon slow
cooling—this method is essential in order to make uniform
glasses with no cracks or deformations, which are beneficial to
the fabrication for material devices.
Scheme 1 Chemical structures of bis(pyridinium salt)s 1a–d and 2a–d.
nature of the anions as well as of the side groups appended to the
dications. This variation of the T values by the exchange of the
g
anions is commonly manifested in many poly(pyridinium salt)s
20–22
and viologen polymers.
Fig. 1a shows the thermal transitions
for the first set of ionic molecular materials (1a–d). Compound
1
1 1
a, which is composed of Y and X , showed a stable glass
ꢀ
ꢀ
ꢁ1
transition T
g
at 151 C upon slow cooling at a rate of 10 C min
after melting the solvent induced crystals. Interestingly,
2
exchanging the anion from tosylate (X ) to triflimide (X )
1
strongly promoted the rate of crystallization in compound 1b,
Thermal stability
which crystallized readily after cooling from its melt. A glassy
state of 1b was obtained by rapidly cooling a melted sample with
ꢀ
It is an important feature used for materials operating at harsh
conditions. The materials in this study exhibited decomposition
liquid nitrogen, which had a T of 115 C. This approach was
g
ꢀ
undesirable since, by doing so, cracks and deformations formed
in the glassy states. From this point onward, we undertook two
approaches to improve the glass-forming property. The first one
was to make materials with two additional anions. In the second
approach, we prepared a dication with bulky asymmetric quin-
temperatures in the range of 257–461 C, some of which are
comparable to the thermal stabilities of high performance poly-
25
mers such as Kevlar. We established that chemical modification
of either the dications or the anions has an effect on the thermal
decomposition temperatures of ionic materials much like poly
19–21
oline groups (Y
trifluoromethyl)phenyl]borate (X
with limited success. Y paired with X
2
). Tetraphenylborate (X
) were used as anions, but
afforded a crystalline
3
) and tetrakis[3,5-bis
(pyridinium salt)s and viologen polymers.
The exchange of
(
4
tosylate (X ) to triflimide (X ) resulted in an increase of the
1
2
ꢀ
1
3
thermal stability in both sets of compounds by 79 C in both
cases (Fig. S1a†). X (compared to X ) had significantly weaker
compound 1c that did not melt before its decomposition
temperature; while Y paired with X (compound 1d) did melt
2
1
1
4
nucleophilic character. Therefore, it decomposed the dication
nucleophilically at higher temperatures. Additionally, the
exchange of tetraphenylborate (X3) to tetrakis[3,5-bis
ꢀ
and did form glass with T at 81 C. The second set of materials
g
used dication Y , which had asymmetric kinked quinoline
2
Table 1 Thermal properties of bis(pyridinium salt)s of 1a–d and 2a–d
Compound
1a
1b
1c
1d
2a
2b
2c
2d
st
ꢀ
ꢀ
a
b
b
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
1
heating
346 C (T
m
)
115 C (T
g
),
),
)
)
—
235 C (T
m
)
323 C (T
m
)
359 C (T
m
)
185 C (T
g
)
)
124 C (T
g
)
)
ꢀ
1
3
54 C (T
c
ꢀ
23 C (T
m
nd
2
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
heating
151 C (T
g
)
323 C (T
m
—
81 C (T
ꢀ
g
),
),
190 C (T
g
)
169 C (T
g
)
191 C (T
g
119 C (T
g
1
2
0.70
48 C (T
c
ꢀ
m
35 C (T )
c
m
T
T
g
/T
0.69
372 C
0.65
461 C
—
330 C
0.78
366 C
0.70
445 C
—
257 C
—
326 C
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
d
in N
2
398 C
a
b
c
No melting was observed before decomposition. Ratio of
Glassy state was obtained by quenching a liquid phase obtained on melting with liquid N
absolute temperatures (K).
2
.
1
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ꢀ
ꢁ1
Fig. 1 DSC thermograms of (a) 1a and 1d obtained from the second heating cycle at heating and cooling rates of 10 C min in nitrogen and 1b
obtained from the first heating cycle of a liquid nitrogen-quenched sample at an identical heating rate; and (b) 2a–d obtained from the second heating
ꢀ
ꢁ1
m
cycle at heating and cooling rates of 10 C min in nitrogen. Note that the usual crystal-to-liquid transition (T ) values for 1b and 1d are not shown here
for clarity, but they are included in Table 1.
(
trifluoromethyl)phenyl]borate (X
ꢀ
4
) resulted in the increase of
withdrawing quinoline side groups, had weaker thermal stability
compared to Y . These trends of the thermal stabilities should be
ꢀ
6
8 C and 59 C, respectively. X
4
had a reduced negative charge
1
due to the electron-withdrawing trifluoromethyl groups
noted when designing ionic amorphous molecular materials
(Fig. S1b†).
compared to X , which explained the higher stability of 1d and 2d
3
compared to 1c and 2c, respectively. The chemical modification
of dications also had an important effect on the decomposition of
these materials. The exchange of Y to Y generated a decrease of
X-Ray powder diffraction, polarizing optical, scanning electron
microscopy and transmission electron microscopy
1
2
ꢀ
ꢀ
ꢀ
ꢀ
6
C, 16 C, 73 C and 72 C for anions X
respectively. These differences were presumably due to the elec-
trophilic nature of the dication. Y , which had electron-
1 2 3 4
, X , X , and X ,
For further examination of the amorphous properties of the
compounds, we used X-ray powder diffraction (XRD) studies.
2
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The solvent induced crystals exhibited distinctive sharp peaks
with high intensities denoting a high degree of crystallinity. In
contrast, after melting these crystals followed by cooling, a glass
was formed with broad peaks and low intensities in both small
and wide angles; this is characteristic of an amorphous state.
Representative XRD patterns of the crystal and the glass state of
compound 2a are given in Fig. S3†. When the compounds in this
study were melted between two cover glasses uniform isotropic
films were formed. Fig. 2a shows a representative polarized
optical microscope (POM) photomicrograph of the glassy state
of compound 2a under a red quarter plate. Many cracks were
seen in this film since it was cooled down quickly after melting.
Alternatively, a steadier and slower cooling rate yielded a glassy
film free from deformations. Interestingly enough, we were able
to successfully draw fibers with a pair of tweezers from the melts
of the compounds that formed the amorphous state. They were
as long as six inches and their thickness was in the range of 50–
120 mm. Fig. 2b shows an image of melt-drawn fiber of
compound 2b with a digital camera irradiated with UV light. To
examine the morphology of these fibers, we examined them with
POM and scanning electron microscopy (SEM) studies. The
POM photomicrograph of the fiber of compound 2b shown in
Fig. 2c seemed to have a very smooth surface and no evidence of
birefringence. This was also supported by the SEM image in
Fig. 2d and 2e. In addition to the surface, we were able to
examine the cross-section of these microfibers, which was also
very uniform. This is the first example of ionic amorphous
molecular material that is capable of forming these fibrous
structures. Even though the mechanism of their formation and
their orientations are not clear at this point, a combination of
Fig. 2 (a) Photomicrograph of compound 2a in deformed glassy state (magnification 400ꢂ), (b) photograph of hand-drawn fiber from the melt of
compound 2b irradiated with a hand-held UV light and (c) photomicrograph of the fiber from the melt of compound 2b (400ꢂ); SEM images of the fibers
from melts of (d) 2b and (e) 2d; and TEM images of (f) compound 2a from 5 wt% CH
3
OH solution (3900ꢂ) and compound 2b (g) from 5 wt% THF
solution (5000ꢂ) and (h) from 5 wt% CH
3
CN solution (1700ꢂ).
1
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Fig. 3 Emission spectra of (a) compounds 1a–d in acetonitrile, (b) compounds 2a and2b in acetonitrile, (c) compounds 1a–d cast from acetonitrile and
(d) compounds 2a and 2b cast from acetonitrile at various excitation wavelengths.
intermolecular interactions including electrostatic, p–p stacking
and van der Waals is a definite possibility. No birefringence was
were able to dissolve them into solvents with low polarity such as
chloroform (3 ¼ 5.5) and THF (3 ¼ 7.58), solvents with medium
polarity such as acetone (3 ¼ 23.1) and solvents with high
polarity such as methanol (3 ¼ 32.6) acetonitrile (3 ¼ 37.5) and
DMSO (3 ¼ 47.2). Their high solubility in various organic
solvents is attributed to their inherent electrostatic charges as
well as amorphous nature, which is in stark contrast with neutral
observed in POM studies; and these fibers exhibited only T
g
values because of their amorphous nature. In the literature, most
fibers generated through self-assemblies are pulled from orga-
nogels or by the phase transfer method. This is done by using
a specific solvent or a combination of solvents that promote the
23,24
26,27
formation of nanotubes, tapes or fibers.
TEM images from
conjugated molecular materials with poor solubility.
the solutions of these compounds in organic solvents revealed
some interesting morphologies (Fig. 2f–h). In Fig. 2f, compound
UV-Vis and photoluminescent properties
2
a formed a film with numerous bubbles that were distributed
Light emission is a unique property for many materials that can
be utilized for many applications in modern science and tech-
nology. As such, it has recently become the focus for the devel-
uniformly throughout the film. Conversely, compound 2b
behaved differently in various organic solvents. In THF, it
formed a thin film defined by extensive furrows and ridges
5–12
opment of optoelectronic devices.
Given the excellent
(
Fig. 2g). In a polar aprotic solvent such as acetonitrile, there was
solubility of these materials in various common organic solvents,
we were able to study their fluorescence in different solvents with
a wide range of polarities (3 ¼ 5.5–37.5). The data of their optical
properties including UV-Vis absorption, photoluminescence,
and quantum yields are compiled in Table 2. The light emission
the development of doughnut-shaped microstructures
throughout the sample (Fig. 2h).
Solubility in organic solvents
High solubility is a desired quality in both molecular and poly-
meric materials in order to efficiently process them into thin films
and fibers. Generally, highly rigid materials such as Kevlar have
spectra of the first set of compounds (1a–d) in CH CN are shown
3
in Fig. 3a. They emitted blue light with lem values in the range of
454–467 nm when excited with 325–330 nm light. This small
range denotes that the variation of the anions has a little effect on
the light emission. Their full-width at half-maximum (fwhm)
values were fairly high (100–110 nm), suggesting that the
25
limited solubility. Even though the materials herein have rela-
tively large molecular weights and are completely conjugated,
their solubility in common organic solvents was exceptional. We
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Table 2 Optical properties of bis(pyridinium salt)s 1a–d and 2a–d
Compound
UV abs CH
Band Gap/eV
PL lem CHCl
1a
1b
1c
1d
2a
2b
2c
2d
3
CN/nm
335
3.31
335
3.31
335
3.31
—
—
457
—
467
110
330
3.31
424
461
452
265, 340
265, 345
335
3.26
489
523
539
538
542
121
345
3.26
3.26
3.26
a
3
/nm
401, 443
463
452
454
395
457
460
454
110
463
120
511
494
537
537
541
121
500
109
532
531
538
538
541
121
500
93
529
535
537
538
540
121
503
90
a
PL lem THF/nm
PL lem Acetone/nm
a
PL lem CH
PL lem CH
3
OH/nm
CN/nm
CN/nm
473
463
100
462
105
1.1
476, 485
455
100
3
fwhm CH
3
b
c
c
PL lem film/nm
fwhm film/nm
—
—
0.9
432
79
1.3
—
—
1.2
c
c
d
(%)
F
F
1.0
2.1
1.8
1.5
a
b
c
d
3
The compound was not soluble. Thin film was cast from CH CN. Light-emission from thin film was too weak to measure. Quantum yield was
28
calculated against diphenyl anthracene in cyclohexane as a standard (F
F
¼ 0.9).
fluorescence behavior stemmed from multiple chromophores.
The light emission properties of these ionic materials varied
significantly with the change of polarity of organic solvents; these
results were a manifestation of solvatochromic property. For
example, compound 1a emitted light with lem as low as 401 nm in
than in the solution state, which in turn, reducing the p–p
stacking and causing a hypsochromic shift. Their fwhm values
were also in the narrow range of 90–109 nm. Although we did not
quantify their light emission efficiency in the solid state, but we
observed that some anions affected the intensity of light emission
significantly. For example, we were able to make films of 1c and
CHCl3 and lem as high as 473 nm in CH OH indicative of
3
a bathochromic shift of 72 nm, suggesting that the excited state
was more polar than the ground state. This result was the
evidence of a positive solvatochromism property. Compounds 1b
and 1d showed similar behavior with the differences of lem values
of 68 nm and 61 nm, respectively. The poor solubility of
compound 1c in most organic solvents precluded to determine its
light emission properties. Fig. 3b shows the photoluminescence
spectra for the second set of compounds (2a–d). The modification
of the dication from Y to Y resulted in a large bathochromic
2c, which had an X anion, but their light emissions were too low
3
to measure. Interestingly, compounds 1d and 2d, which had an
4
X anion, did have detectable light emission, even though their
intensities were low (Fig. 3c and d). The light emission properties
of 1d and 2d can be attributed to the presence of trifluoromethyl
electron-withdrawing groups in the aromatic moieties.
The light-emission properties of amorphous ionic molecular
materials are mainly affected by chemical structural modifica-
tions of the dications, because the primary chromophore is
located in the chemical structures of dications. Generally, anions
in this study seemed to have little effect on the light emission in
solution. In contrast, they played an important role in the light
emission and quantum yields in the solid state as observed in the
cases of 1c, 1d, 2c, and 2d. The extensive optical studies per-
formed on this novel class of amorphous ionic molecular mate-
rials could serve as an essential guideline of how their optical
properties could be fine-tuned for their potential applications.
We also briefly examined their potential as fluorophores in the
biological systems. As examined with fluorescence microscopy
1
2
shift of 72–98 nm. This behavior was expected since the quinoline
side groups further extended the conjugation of the dication, thus
shifting the light emission bathochromically. The exchange of the
anion had a negligible effect on the light emission in the solution
state of materials 2a–d as observed in the first set of compounds.
Their fwhm values were quite large and increased compared with
those of compounds 1a–d. In the second set of materials, we also
observed a positive solvatochromism. However, it was less
pronounced than in the first set. The quantum yields of these
3
ionic materials were studied in CH CN. They showed moderate
ꢁ1
values in the range of 0.9–2.1%; this is not very high for organic
materials but is comparable to the values of polymeric materials.
Their optical band gaps, determined from the onset of their UV-
Vis absorption spectra, were in the range of 3.26 to 3.31 eV.
These values are generally high for neutral light-emitting poly-
studies (Fig. S7 and 8†), an aliquot of 100 mg mL solution of
compound 2a in phosphate-buffered saline (PBS) successfully
stained cancer cells within 20 min and, therefore, they could be
potentially used as fluorophores for staining various cellular
materials. Additionally, DNA electrophoresis gels stained with
compound 1a showed binding with the DNA, but the fluores-
cence output was weaker compared with that of ethidium
bromide, which may be an indication of the extent of their
binding abilities via electrostatic interactions (Fig. S9†). These
preliminary data show that some of these ionic compounds have
some activity towards biological molecules, the potential of
which remains to be explored.
8,9
mers but are comparable to those of previously reported poly
2
0,21
(
pyridinium salt)s.
Next, we explored the photoluminescent properties of these
ionic materials in the thin films cast from CH CN to assess their
3
potential for optoelectronic applications. The light emission
spectra of the first set of materials are plotted in Fig. 3c. They
exhibited lem values in the blue range similar to those in solu-
tions. Their fwhm values were quite broad that ranged from 79–
1
20 nm. In contrast, the lem values of compounds 2a–d were
Conclusions
shifted hypsochromically from solutions to solid states. They
showed lem peaks in the narrow range of 500 nm to 503 nm,
We prepared a series of new photoactive amorphous ionic
materials via both ring-transmutation and metathesis reactions.
They displayed very good thermal stabilities that were dependent
which is 38–42 nm less than those in CH
3
CN solutions. These
results suggested that they were less ordered in the solid state
1
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on the nature of both the anions and the dications. Most of these
compounds vitrified successfully upon slow cooling after melting
the solvent-induced crystals. They had excellent solubilities in
a wide range of common organic solvents. They can be processed
easily into thin films and fibers from their melts or solutions,
thereby avoiding cumbersome and expensive techniques such as
153.9, 149.0, 147.1, 145.8, 137.7, 137.3, 136.8, 136.6, 136.2, 133.1,
130.1, 130.0, 129.9, 129.8, 129.7, 129.5, 128.9, 128.8, 128.7, 128.2,
127.9, 127.5, 126.9, 125.6, 125.4, 123.5, 119.9, 20.7; Anal. calcd
70 4 2 6
for C96H N S O : C 80.09, H 4.90, N 3.89, S 4.45; found: C
79.89, H 4.91, N 3.87, S 4.43%.
3
vapor deposition technique. Additionally, their luminescence
Compound 1b. 1.00 g (0.886 mmol) compound 1a was dis-
solved in 25 mL of methanol. 0.534 g (1.86 mmol) lithium tri-
flimide was dissolved in a minimum amount of methanol. They
were added together and a white precipitate formed quickly. The
properties produced blue and green light in both the solution and
solid states. Their quantum yields were moderate. Here, we
demonstrated a versatile method for the synthesis of a novel class
of materials and how their physical properties could be fine-
tuned. These amorphous ionic materials combine into one the
excellent properties of both conventional amorphous materials
and ionic compounds. They are homogeneous, transparent and
easy to process. These new smart materials could be used as
components for OLEDs, LECs, OFEDs, organic laser, and even
as solid electrolytes for battery applications. They constitute
a class of materials at the frontier of ionic liquids, conventional
molecular glasses and ionic polymers and display unique prop-
erties unattainable with other related class of materials.
ꢀ
reaction was kept at 40 C overnight to ensure completion. The
product was precipitated out and washed with water. It was
recrystallized from methanol to yield 1.06 g (0.847 mmol, yield
1
96%) of white crystals. H-NMR (400 MHz, d -DMSO) d ppm
6
13
8.87 (s, 4H), 8.66 (s, 4H), 7.50–7.43 (m, 15H), 7.39 (m, 15H); C-
NMR (100 MHz, d -DMSO) d ppm 156.4, 153.0, 138.9, 136.6,
132.9, 129.9, 129.7, 129.6, 128.5, 128.0, 125.5, 121.0, 117.8; Anal.
Calcd for C56 12: C 53.76, H 3.06, N 4.48, S 10.25;
6
38 4 4 8
H N S O F
found: C 54.01, H 2.95, N 4.58, S 10.33%.
Compound 2b. The similar reaction procedure was followed as
for the preparation of compound 1b by using a compound 2a
instead of compound 1a. The crude product was recrystallized
Experimental section
from methanol to yield 0.530 g (0.320 mmol, yield 92%) of yellow
1
crystals. H NMR (400 MHz, d -DMSO) d ppm 8.87 (s, 4H), 8.67
Starting materials and synthesis of intermediates
6
0
19
4
,4 (1,4-Phenylene)bis(2,6-diphenylpyrylium)ditosylate
and
(s, 4H), 8.29 (dd, J ¼ 7.49, 2.14 Hz, 4H), 8.05 (d, J ¼ 2.48 Hz,
4H), 7.96 (d, J ¼ 8.98 Hz, 2H), 7.83 (dd, J ¼ 9.03, 2.27 Hz, 2H),
7.70–7.58 (m, 6H), 7.58–7.51 (m, 6H), 7.45 (m, 20H), 7.12 (dd,
29
sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate
were
prepared according to the known procedures. The synthesis of
the 2,4-diphenylquinolin-6-amine will be reported elsewhere. The
other starting compounds and reagents were purchased from
either Sigma-Aldrich or TCI and were used as received.
1
3
J ¼ 7.79, 1.47 Hz, 4H); C NMR (100 MHz, d
6
-DMSO) d ppm
157.6, 156.5, 153.9, 149.0, 147.1, 137.7, 136.8, 136.7, 136.2, 133.1,
130.1, 130.1, 130.0, 129.8, 129.7, 129.5, 129.4, 128.8, 128.2, 127.5,
126.9, 125.6, 123.6, 121.0, 119.9, 117.8; Anal. calcd for
C H N S O F12: C 62.31, H 3.41, N 5.07, S 7.72; found: C
86 56 6 4 8
0
Compound 1a. 5.00 g (5.66 mmol) 4,4 (1,4-phenylene)bis(2,6-
diphenylpyrylium)ditosylate and 1.11 g (11.9 mmol) aniline were
ꢀ
62.28, H 3.18, N 5.12, S 7.76%.
added in 50 mL of DMSO. The reaction was kept at 130–140 C
for 24 h under nitrogen. After completion of the reaction, the
reaction flask was cooled down to room temperature and the
product was precipitated out in water. The precipitate was
washed with acetone and air-dried It was then recrystallized from
Compound 1c. 0.500 g (0.441 mmol) compound 1a was dis-
solved in 25 mL of methanol. 0.318 g (0.928 mmol) sodium tet-
raphenylborate was dissolved in minimum amount of water.
They were added together and a yellow precipitate formed
ꢀ
ethanol/methanol mixture to yield 5.00 g (4.41 mmol, yield 79%)
1
of off-white fluffy crystals. H NMR (400 MHz, d
quickly. The reaction was kept at 40 C overnight to ensure
6
-DMSO)
completion. The precipitate was collected and washed with
water. It was then recrystallized from acetonitrile to yield 0.450 g
d ppm 8.84 (s, 4H), 8.65 (s, 4H), 7.53–7.43 (m, 16H), 7.42–7.31
1
(0.345 mmol, yield 79%) of yellow crystals. H NMR (400 MHz,
(
m, 12H), 7.19 (m, 6H), 7.08 (d, J ¼ 7.88 Hz, 4H), 2.26 (s, 6H);
1
3
C NMR (100 MHz, d -DMSO) d ppm 156.4, 153.8, 145.7,
6
d
6
-DMSO) d ppm 8.84 (s, 4H), 8.64 (s, 4H), 7.50–7.41 (m, 12H),
7.41–7.33 (m, 12H), 7.23–7.13 (m, 22H), 6.91 (t, J ¼ 7.4 Hz,
-DMSO)
1
1
7
6
38.9, 137.4, 136.6, 132.9, 129.9, 129.8, 129.8, 129.6, 128.5, 128.4,
13
28.0, 127.9, 125.5, 125.4, 20.7; Anal. calcd for C66
H
52
2
N S
2
O
6
: C
16H), 6.78 (t, J ¼ 7.2 Hz, 8H); C NMR (100 MHz, d
6
6.72, H 5.07, N 2.71, S 6.21; found: C 76.50, H 5.00, N 2.74, S
.15%.
d ppm 164.5, 164.0, 163.5, 156.9, 154.3, 139.4, 137.1, 135.9, 133.4,
130.4, 130.4, 130.2, 128.9, 128.5, 126.0, 125.7, 121.9; Anal. calcd
for C98
78 2 2
H N B : C 90.17, H 6.02, N 2.15; found: C 90.15, H 5.85,
Compound 2a. The identical reaction procedure was followed
N 2.22%.
as for the preparation of compound 1a but 2,4-diphenylquinolin-
-amine was used instead of aniline as starting material. The
6
Compound 2c. The similar reaction procedure was followed as
for the preparation of compound 1c but compound 2a was used
instead of compound 1a. The crude product was eluted in chlo-
roform through a column chromatography over silica gel. The
volume of chloroform was reduced under reduced pressure and
the pure compound was precipitated out in hexane to yield 0.400
crude product was recrystallized from ethanol/methanol mixture
1
to yield 3.60 g (2.50 mmol, yield 89%) of beige crystals. H NMR
(
(
(
400 MHz, d -DMSO) d ppm 8.85 (s, 4H), 8.66 (s, 4H), 8.33–8.24
6
m, 4H), 8.05 (d, J ¼ 1.76 Hz, 4H), 7.95 (d, J ¼ 8.99 Hz, 2H), 7.85
dd, J ¼ 9.02, 2.29 Hz, 2H), 7.68–7.58 (m, 6H), 7.58–7.51 (m,
1
6
2
H), 7.51–7.45 (m, 12H), 7.45–7.37 (m, 12H), 7.16–7.06 (m, 8H),
g (0.230 mmol, yield 66%) of light brown solid. H NMR (400
ꢀ
1
3
.27 (s, 6H); C NMR (100 MHz, d
6
-DMSO) d ppm 157.6, 156.4,
MHz, d -DMSO, 50 C) d ppm 8.81 (s, 4H), 8.60 (s, 4H),
6
This journal is ª The Royal Society of Chemistry 2011
J. Mater. Chem., 2011, 21, 12717–12724 | 12723

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8
7
6
7
.31–8.22 (m, 4H), 8.05–7.96 (m, 4H), 7.94 (d, J ¼ 8.98 Hz, 2H),
.80 (dd, J ¼ 8.95, 2.23 Hz, 2H), 7.68–7.56 (m, 6H), 7.56–7.49 (m,
H), 7.49–7.42 (m, 8H), 7.42–7.30 (m, 12H), 7.25–7.15 (m, 16H),
.15–7.06 (m, 4H), 6.90 (t, J ¼ 7.40 Hz, 16H), 6.77 (t, J ¼ 7.17
the support of this research. A.K.N. acknowledges the Graduate
College (UNLV) for providing him a Nevada Stars Graduate
Assistantship for the period of 2006–2008. The work is in part
supported by the NSF under Grant No. 0447416 (NSF EPSCoR
RING-TRUE III), NSF-Small Business Innovation Research
(SBIR) Award (Grant OII-0610753), NSF-STTR Phase I Grant
No. IIP-0740289, and NASA GRC Contract No.
NNX10CD25P. We also sincerely acknowledge Dr Longzhou
Ma for his expertise in the analyses of TEM studies and Van Vo
for her expertise in fluorescence microscopy studies.
13
6
Hz, 8H); C NMR (100 MHz, d -DMSO) d ppm 164.1, 163.6,
1
1
1
63.1, 162.6, 157.7, 156.6, 154.1, 149.1, 147.2, 137.8, 136.7, 136.7,
36.3, 135.5, 133.0, 130.1, 130.0, 129.9, 129.7, 129.4, 128.8, 128.7,
28.2, 127.5, 126.9, 125.7, 125.1, 123.7, 121.4, 119.9; Anal. calcd
for C130
96 4 2
H N B : C 89.95, H 5.57, N 3.23; found: C 90.10, H
5
.51, N 3.27%.
Compound 1d. 0.300 g (0.265 mmol) compound 1a was dis-
solved in 25 mL of methanol. 0.490 g (0.556 mmol) sodium tet-
rakis[3,5-bis(trifluoromethyl)phenyl]borate was also dissolved in
a minimum amount of methanol. They were added together. The
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4
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off-white crystals. H NMR (400 MHz, d
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-DMSO) d ppm 8.89 (s,
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4
7
H), 8.70 (s, 4H), 7.71 (s, 8H), 7.68–7.60 (m, 16H), 7.49 (m, 12H),
13
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6
1
1
2
53.9, 139.0, 136.7, 134.1, 134.0, 133.0, 129.7, 128.6, 128.1, 125.6,
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9
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2 2 48
1
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1
1
1
as for the preparation of compound 1d but compound 2a was
used instead of compound 1a. The crude product was eluted in
chloroform through column chromatography over silica gel. The
impurities eluted out first of the column and the main product
was then eluted out with the addition of methanol. The solvent
methanol was removed under reduced pressure to give an oily
viscous liquid. It was then dissolved in chloroform and precipi-
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1
1
1
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1
0.145 mmol, yield 70%) of yellow solid. H NMR (400 MHz, d
(
6
-
DMSO) d ppm 8.89 (s, 4H), 8.70 (s, 4H), 8.31 (dd, J ¼ 7.43, 1.94
Hz, 4H), 8.07 (d, J ¼ 3.01 Hz, 4H), 7.98 (d, J ¼ 9.00 Hz, 2H), 7.86
1
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2
(
dd, J ¼ 8.97, 2.16 Hz, 2H), 7.72 (s, 9H), 7.67–7.62 (m, 22H), 7.57
m, 6H), 7.53–7.48 (m, 8H), 7.47–7.39 (m, 12H), 7.14 (d, J ¼ 6.54
(
2
2
2
1 P. K. Bhowmik, H. Han and A. K. Nedeltchev, Polymer, 2006, 47,
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13
6
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1
1
1
60.7, 160.2, 157.7, 156.6, 154.0, 149.1, 147.2, 137.8, 136.9, 136.8,
36.3, 134.1, 134.0, 133.2, 130.2, 130.0, 129.8, 129.6, 129.5, 128.8,
28.7, 128.3, 127.6, 127.0, 125.7, 125.4, 123.7, 122.6, 120.0, 117.7;
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80 4 2 48
2
4 D. S. Tsekova, B. Escuder and J. F. Miravet, Cryst. Growth Des.,
2
C 61.83, H 2.68, N 1.95%.
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Acknowledgements
P.K.B. acknowledges the University of Nevada Las Vegas for an
Applied Research Initiative, the donors of the Petroleum
Research Fund, administered by the American Chemical Society,
and an award (CCSA# CC5589) from Research Corporation for
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2724 | J. Mater. Chem., 2011, 21, 12717–12724
This journal is ª The Royal Society of Chemistry 2011