Engineering of acentric stilbazolium salts with large second-order optical nonlinearity and enhanced environmental stability

Article abstract of DOI:10.1021/cg301359n

A series of organic nonlinear optical (NLO) materials based on the stilbazolium derivatives of 4-N,N-dimethylamino-4′-N′-methyl- stilbazolium tosylate (DAST) were synthesized, and the single crystals were grown from the solutions. Single-crystal structure

Full text of DOI:10.1021/cg301359n

Article
pubs.acs.org/crystal
Engineering of Acentric Stilbazolium Salts with Large Second-Order
Optical Nonlinearity and Enhanced Environmental Stability
Zhihua Sun,† Xitao Liu,‡ Xinqiang Wang,‡ Lina Li,† Xiaojun Shi,† Shigeng Li,† Chengmin Ji,†
Junhua Luo,*,† and Maochun Hong†
†Key Laboratory of Optoelectronic Materials Chemistry and Physics, Fujian Institute of Research on the Structure of Matter,
Chinese Academy of Sciences, Fuzhou, Fujian 350002, China
‡State Key Laboratory of Crystal Materials, Institute of Crystal Materials, Shandong University, Jinan, Shandong 250100, China
S
* Supporting Information
ABSTRACT: A series of organic nonlinear optical (NLO) materials
based on the stilbazolium derivatives of 4-N,N-dimethylamino-4′-
N′-methyl-stilbazolium tosylate (DAST) were synthesized, and the
single crystals were grown from the solutions. Single-crystal struc-
ture determinations and Kurtz powder tests reveal that replace-
ment of the p-toluenesulfonate anion in the DAST crystal, forming
4-N,N-dimethylamino-4′-N′-methyl-stilbazolium 4-aminotoluene-
3-sulfonate (1) and 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium
p-chlorobenzenesulfonate (2), constructs new acentric crystals with
quite a large powder second-harmonic generation (SHG) of more
than 3 orders of magnitude larger than that of urea around 2.0 μm,
whereas the other two complexes show their centrosymmetric
structures without any SHG effects. A possible estimation of the
molecular first hyperpolarizabilities βijk performed on 2 further confirms its origin of its enhanced NLO merits. Furthermore,
both 1 and 2 exhibit even higher environmental stabilities, including the antiwater performance and the formation of anhydrous
phases in water-containing solutions. We believe that the findings of the further counterion modification will bring new
stilbazolium derivatives with improved optical nonlinearities and the physicochemical performances.
2-naphthalenesulfonate anion. However, the major impediment
when attempting to engineer NLO stilbazolium materials is
still how to orient the chromophores with large molecular first
hyperpolarizabilities (β) into a noncentrosymmetric arrange-
ment.2d
1. INTRODUCTION
Organic nonlinear optical (NLO) materials have greatly attracted
much attention owing to their promising and wide applications,
such as optical signal processing, integrated photonics, optical
switching, and the frequency conversion, including THz-wave
generation in the past decades.1 Among the organic materials,
stilbazolium crystals with a high chromophore number density
and excellent long-term thermodynamic orientations possess
quite prominent second-order (quadratic) NLO properties. Partic-
ularly, the crystal of 4-N,N-dimethylamino-4′-N′-methyl-
stilbazolium tosylate (DAST) exhibits remarkable bulk quadratic
NLO activities with the powder second-harmonic generation
(SHG) efficiency 3 orders of magnitude larger than that of urea
at 1907 nm.2 Owing to its quite outstanding NLO susceptibilities
Recently, many efforts were extensively made by different
research groups to assemble new stilbazolium materials with the
enhanced merit figures, including the nonlinear optical prop-
erties and the physical performances, such as environmental
stability.6 Taking DAST crystals as the example, a centrosym-
metric monohydrate phase of DAST·H2O is easily formed at
the presence of solvent water.7 In that case, the air humidity
will damage the crystal device, which requires more strict pro-
tecting conditions for crystal growth and practical application.
Additional measurements should be adopted to protect the
crystal devices. To satisfy the requirement of physical properties
by crystal engineering, the molecular assembly of a desired
structure or crystal symmetry is still most challenging owing to
the tendency of imperfect molecular orderings in the crystalline
state.8 One possible strategy is to design the new acentric mo-
lecular complexes with much higher physical stabilities; that is,
(d11 > 1000 pm/V)), large electro-optic coefficients (r111
=
77 pm/V), and low dielectric constants (ε1 = 5.1), the DAST
crystal has been considered as an excellent candidate for high-
speed electro-optic applications, such as THz generators and
detectors, electro-optic modulators, optical parametric gen-
erators, frequency multipliers, etc.3 Hence, the high-performance
properties of DAST have not only accelerated the preparation of
bulk high-quality single crystals and thin films4 but also promoted
the engineering of many stilbazolium derivatives with similar
architectures and the improved merit figures,5 such as DSTMS
with 2,4,6-trimethylbenzenesulfonate anion and DSNS with
Received: September 17, 2012
Revised: November 7, 2012
Published: November 8, 2012
© 2012 American Chemical Society
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introducing substituted anionic or cationic moieties favors the
design of DAST derivatives.6b This strategy has been evidenced
to be a simple, but highly successful, approach. Encouraged by
the pioneering work, herein, a series of stilbazolium derivatives
were synthesized by modifying the structure of DAST coun-
terions through the ion-exchange reaction. Single-crystal structures,
environmental stabilities, and optical properties of the obtained
derivatives were systematically investigated, which reveal that
the anionic modifications of DAST derivatives could assemble
new potential NLO materials.
2. EXPERIMENTAL SECTION
2.1. Synthesis and Crystal Growth. All the chemical reagents
were purchased as high purity (AR grade) and used without any fur-
ther purification. Metathesization of the iodide precursor with the
corresponding sodium/ammonium or silver anionic salts was used to
synthesize the products, as described previously.6c In detail, 4-N,
N-dimethylamino-4′-N′-methyl-stilbazolium 4-aminotoluene-3-sulfonate
(1), 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium p-chlorobenze-
nesulfonate (2), and 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium
p-hydroxylbenzenesulfonate hydrate (3) were synthesized by ion-exchange
reaction of the respective benzenesulfonate ammonium salts with 4-N,
N-dimethylamino-4′-N′-methylstilbazolium iodide, prepared from 4-picoline,
methyl iodide, and 4-N,N-dimethylamino-benzaldehyde in the presence of
piperidine. Complex 4 was obtained with trifloromethanesulfonate silver
salt (see Scheme 1). Subsequently, the raw materials were purified by
Figure 1. Crystals of 1 (a) and 2 (b) grown from the mixed solvents of
water/methanol and their growth morphology.
2.2. Structure Determination and Basic Characterization.
X-ray single-crystal diffraction data were collected on a Rigaku Saturn
70 diffractometer with a CCD detector (graphite-monochromated
Mo Kα radiation, λ = 0.71073) at 293 K. The CrystalClear software
package (Rigaku) was used for data collection, cell refinement, and
data reduction. All the crystal structures were solved by direct methods
and refined by the full-matrix method based on F2 using the SHELXLTL
software package.10 All non-hydrogen atoms were refined anisotropically,
and the positions of hydrogen atoms bound to carbon were generated
geometrically. The N-bound and O-bound H atoms were located from
a difference Fourier map and refined anisotropically. Table 1 presents
the details of data collection and the data summary for 1−4. CCDC
901355−901357 contain the supplementary crystallographic data for
this paper.
Scheme 1. Molecular Structures of the Synthesized
Stilbazolium Derivatives of 1−4
Purities of the grown crystals of 1 and 2 were confirmed by the
X-ray powder diffraction (XRPD) performed on a MiniFlex II X-ray
diffraction instrument. Thermogravimetric analysis (TGA) was recorded
using a NETZSCH STA 449C unit with the heating rate of 10 °C/min
under a nitrogen atmosphere. Nonlinear optical properties were con-
firmed by the Kurtz and Perry technique,11 that is, the second-harmonic
generation (SHG) powder test. The ground microcrystalline powdered
samples were filtrated with different sizes and placed between two glass
plates with a thickness of 2 mm. The measured SHG signals were
converted into the measurable signal voltage with the fundamental beam
being removed by appropriate filters. The collected digital signals were
then investigated by a photomultiplier and displayed with a DS1052E
digital oscilloscope with respect to the corresponding powdered DAST
samples with the same particle sizes of 63−90 μm as reference. A
Q-switching laser with a wavelength of 2.0 μm was used as fundamental
radiation to determine the SHG efficiency. The density functional
theory (DFT) was used to optimize the corresponding crystal structure
of 2, in order to calculate the first hyperpolarizability tensors by using
the hybrid functional B3LYP with the 6-311+ G(d) mode with the finite
field method.
recrystallization three times from methanol solutions. The obtained
fine precipitates were dried in a vacuum for 24 h to remove solvents
before their characterization.
Crystals were grown using the temperature-lowering method and
slow evaporation solution.9 All the growth experiments were carried
out at constant temperatures with the controlled stability of 0.1 °C.
Different solvents were chosen according to the solubility of products in
those solvents, such as methanol, acetonitrile, and water. Herein, the
saturated methanol solutions were prepared at 45−50 °C and then
filtered by 0.2 μm Millipore filters, whereafter, the solutions were slowly
preheated and kept about 5−6 °C above their preliminary status, which
guarantees the dissolution and homogenization of all ingredients. The
temperature-lowering rate was 0.2 °C/day, and crystals with sizes of a
few micrometers were obtained after several days (see Figure 1).
3. RESULTS AND DISCUSSION
X-ray morphology studies indicate that the (001) face is domi-
̅
nant to determine the growth of 1 and 2. However, distinctive growth
habits are observed owing to their different crystallographic symmetry,
that is, the columnar shape of 1 and the plate shape of 2 shown in
Figure 1. It is noteworthy that complex 2 presents a quite similar mor-
phology with that of DAST, favoring the subsequent fabrication of
THz devices. Moreover, single-crystalline thin films of 2 with a relatively
large c-plane surface were easily achieved in acetonitrile solution (see
Figure S1, Supporting Information), which is quite attractive in the
integrated optics applications. The detailed growth and characterization
of the thin films are now in progress.
3.1. Analysis of Crystal Structures. All the molecular
crystal structures of 1−4 are presented in Figure 2. The crystal
structure of 1 belongs to the triclinic crystal system and the
space group symmetry P1 with one ion-pairing counterpart per
unit cell. The three-dimensional packing structure presents a
parallel alignment of the chromophore cations with the alter-
nating perpendicular acentric sheets of counterions. The arrange-
ment of stilbazolium chromophores meets the criterion of the
possible order parameter ⟨cos3ψ⟩ = 1, treated as a prerequisite
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Table 1. Summary of Crystallographic Data for Complexes 1−4
1
2
3
4
empirical formula
formula wt
C23H27N3O3S
425.54
C22H23ClN2O3S
430.93
C22H26N2O5S
430.51
C17H19F3N2O3S
388.40
cryst syst, space group
cell parameters
triclinic, P1
monoclinic, Cc
a = 10.363(5)
b = 11.163(5)
c = 17.892(6)
α = 90°
β = 92.15(3)°
γ = 90°
V = 2068.2(15)
4, 1.384 g/cm3
monoclinic, P21/c
a = 14.208(6)
b = 10.027(4)
c = 16.146(7)
α = 90°
β = 113.042(6)°
γ = 90°
V = 2116.7(15)
4, 1.351 g/cm3
monoclinic, P21/c
a = 17.508(5)
b = 7.607(2)
c = 13.533(4)
α = 90°
β = 93.712(6) °
γ = 90°
V = 1798.4(10)
4, 1.434 g/cm3
a = 7.2651(6)
b = 8.983(2)
c = 10.1090(15)
α = 97.82(8)°
β = 110.42(5)°
γ = 112.30(6)°
V = 543.92(54)
1, 1.299 g/cm3
Z, ρcal
Supporting Information), accounting for the thin film growth
with the large c-plane surface . The planes of the p-chloro-
benzenesulfonate rings are roughly perpendicular to the
molecular planes of the cations. Such a crystal packing of flat
aromatic molecules, coupled with the electrostatic attraction
between the donor of one molecule and the acceptor of an
adjacent molecule, is favorable to the formation of the polar
cationic sheets.2d The acute angle ψ between the cationic long
sheets and the polar a axis of the crystal is about 20.5°, giving
an order parameter ⟨cos3ψ⟩ = 0.82 for the projection of molec-
ular nonlinearities to the polar axis. In the case of the DAST
crystal, the corresponding ψ value is about 20° and the merit
values of ⟨cos3ψ⟩ = 0.83.2a Therefore, similar nonlinear optical
characteristics could be expected for 2 as that of DAST, which
is further confirmed by the powder SHG test (about 1.3 times
larger than that found in DAST; see Table 2).
Figure 2. Molecular structures with various symmetries of complexes
1−4.
The space group symmetries of 3 and 4 are both monoclinic
P21/c with four ion pairs located per unit cell. The crystal
structure and interesting properties of 4 had been described in
other work.14 Herein, we mainly focused on the structure of 3
owing to the planarity of its counterions. Though the cationic
chromophores in 3 are arranged almost parallel, their packing
directions are totally opposite, which cancels out its SHG
activities. Another secondary indicator of its centrosymmetric
structure is the assembling participation of the crystal water.
Similar with the centrosymmetric crystal structure of DAST·H2O,7
the equilibrium O−H···O hydrogen bonds between water and
sulfonate construct a long-chain-like structure and result in the
centrosymmetry. Therefore, the results reveal that only DAST
and its derivates in the anhydrous phases could possess the
possible SHG activities.
3.2. Molecular Hyperpolarizability. To probe the optical
nonlinearity of the obtained stilbazolium derivatives at the mo-
lecular level, we calculated the first hyperpolarizability tensors
by density functional theory (DFT) using the hybrid functional
B3LYP with the 6-311+G(d) mode. Here, complex 2 was chosen
as the representative because of its bulk larger nonlinearities than
that of DAST. The calculated x axis of the coordinate frame was
determined along the crystallographic a direction, and the y axis
was fixed along the b-axis direction in the ab plane. The z axis
was then finally determined to be perpendicular to both x and y
axes according to the right-hand rule. The calculated results of
hyperpolarizability tensors for 2 are listed in Table 3 and com-
pared with other stilbazolium salts.15 When the electron donor
and acceptor are exactly located at each end of a chromophore
molecule, the long axis of the molecule is assumed to be the
main direction of the maximal hyperpolarizability. Though the
βijk components present evident diversities owing to the different
expected for the possible efficient electro-optic or second-order
NLO effects.12 Crystallographic data indicate that H bonds also
play a role in crystal packing and chromophore orientation, in
addition to the strong Coulombic interactions between cationic
and anionic parts. It is clearly shown that N−H···O type H bonds
between the sulfonic oxygen atoms and the neighboring amino
groups construct an infinite two-dimensional anionic plane.
Furthermore, the perfectly parallel chromophores arrange per-
pendicular to the anionic planes. The cation layers and the
anion layers are linked together through H bonds with the H···O
distance of about 2.481 Å. Similar to other stilbazolium deriv-
atives, the weak hydrogen bonds reduce the energy of the whole
system and keep it more stable. However, its influence on micro-
scopic and macroscopic nonlinearities may not be negligible.
The hydrogen bonds in 1 appear in the π-conjugated bridge part
rather at the end of the chromophore, which might diminish the
chromophore hyperpolarizability more seriously. The observed
smaller bulk second-order optical nonlinearities of 1 would
strongly support such a deduction.
Figure 3 presents the packing structure of 2, which is quite
comparative with that of DAST and its derivative, belonging
to the monoclinic space group Cc with the point group m. It
is noteworthy that there is an isostructural crystal with
4-bromobenzenesulfonate as anion,13 which was determined
at 100 K without any atomic disorderings. The well-consistent
XRPD patterns further confirm their isostructures (Figure S2,
Supporting Information). From the packing diagrams, it is
clearly shown that the cationic sheets of organic chromophores
in 2 are interleaved with that of p-chlorobenzenesulfonate anions.
The disordered sulfonate moieties are involved with cations into
chains by weak C−H···O interactions along the c axis (Figure S3,
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Figure 3. (1) Supramolecular interactions of 1 with the triclinic P1 symmetry: the H-bonding interactions of N−H···O (1.991 Å) and weak
C−H···O bonds (2.481 Å) are illustrated by the dashed black lines. (2) Crystal packing of 2 with a monoclinic Cc symmetry viewed along the
crystallographic c axis showing the chromophores perpendicular to the counterions in the ab plane; ψ is the acute angle indicating the orientation of
the chromophore relative to the polar a axis. (3) Supramolecular interactions of 3 with a monoclinic P21/c symmetry: the selected H-bonds of
O−H···O and weak C−H···O are illustrated by the dashed black lines.
βeff is the quadric effective hyperpolarizability averaged over all
possible orientations,15 it is expected that the relative powder
SHG efficiencies of 2 are comparable with those of DAST and
BP3 crystals, and the experimental results in Table 2 further
confirm this prediction.
Table 2. Powder SHG Efficiencies and Thermal and
Environmental Stabilities of 1−4
d
thermal stability
solubility
(g/100 g)
SHG
efficiency
c
(°C)
antiwater
3.3. Thermal and Environmental Stabilities. Thermal
studies in Figure 4 present that complex 3 starts dehydrating its
crystal water at 162 °C, whereas the other three complexes
keep their thermal stabilities around or even above 190 °C
without any weight loss or solid−solid phase transition.
Meaningfully, it is noted that 2 is an organic salt with a
much higher thermal stability than DAST crystal (∼256 °C).
Furthermore, crystal samples of 1 and 2 display no apparent
changes in the optical properties after being heated to 100 °C
for more than 24 h. The environmental stability of several
water-soluble stilbazolium derivatives exhibits some limits for
the practical applications and strict requirement for the crystal
growth conditions. For example, DAST easily forms a hydrated
a
DAST
256
192
297
162
211
1
2
2
2
2
4.2
no
1.0
0.83
∼1.3
0
b
1
2
3
4
5.7
yes
yes
no
b
3.5
b
8.1
b
3.6
yes
0
a
b
c
Methanol solution at 45 °C. Aqueous solution at 45 °C. Whether it
stabilizes in water. Relative to DAST around 2.0 μm.
d
determination of coordinates in Table 3, the total hyper-
polarizability of 2 is still comparable with the maximal values of
DAST and BP3. The results also agree fairly well with their
experimental bulk optical nonlinearities. A class of stilbazolium
salts were evaluated on the molecular hyperpolarizability β, sug-
gesting that their bulk NLO activities are strongly dependent
on the relative arrangement and orientation of the π-conjugated
chromophores in the crystalline lattice.6b,16 Actually, the maximal
component βxxx for 2 is located along the crystallographic a axis,
which makes an acute angle of 20.5° with respect to the charge-
transfer chromophore direction. On the basis of the merit figure
⟨Nβeff⟩2, where N is the number density of chromophores and
phase as DAST·H O with the centrosymmetric structure P1.7a
̅
2
Though being preheated above 145 °C could remove the
crystal water, crystals grown using the reprocessed anhydrous
materials should be completely insulated from water. A similar
structural constitution also exists in 3, which crystallizes in the
centrosymmetric space group P21/c and contains crystal water.
Hence, it was proposed that compound 3 would adopt
the same pretreatments to that of DAST. However, it failed
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Table 3. Calculated Results of the First Hyperpolarizability
Tensors βijk (×10−30 esu) with the Optimized (OPT) and the
b
Experimental (EXP) Crystal Structures for 2
DAST
BP3
complex 2
OPT
EXP
OPT
3.73
EXP
0.61
OPT
EXP
βxxx
βxxy
βxyy
βyyy
βzxx
βxyz
βzyy
βxzz
βyzz
βzzz
−0.11
−0.04
0.05
−0.21
0.03
134.30
48.25
14.48
5.12
151.79
50.40
16.05
6.97
8.12
16.29
30.26
10.37
23.69
49.22
30.58
69.87
85.59
194.06
2.85
−2.27
−96.43
−2.57
2.40
−0.05
−0.06
0.25
−0.42
0.18
32.72
7.90
−7.57
−5.70
0.38
0.00
0.38
−4.85
0.38
−3.89
−1.28
−3.86
193.60
193.85
86.30
2.26
−2.16
−76.69
65.81
2.30
−5.29
1.91
−2.59
158.76
1.65
2.33
6.26
a
a
a
a
βtotal 159.05
231.78
165.05
173.03
a
The maximal hyperpolarizability components along the main charge-
b
transfer direction. The corresponding data of DAST and BP3 cations
are also listed at the B3LYP/6-311+G(d) level cited from ref 15.
Figure 5. Respective XRPD patterns of crystals 1 and 2, grown from
the methanol solutions without or with H2O. The results reveal that
both crystals did not form any hydrated phase or other polymorphs,
showing the identical X-ray diffraction patterns with X-ray structural
determination.
Figure 4. Thermal stabilities for complexes 1−4.
to recrystallize in the anhydrous phase using the heated raw
materials of 3 above 165 °C. In this case, crystals of DAST and
3 cannot be easily obtained by the slow evaporation method
because of their easy formation of the hydrated phases.
Herein, the solubilities of 1 and 2 in water were examined by
the gravimetric method in order to investigate their humidity
resistance. As shown in Table 2, 1 and 2 exhibit comparative
solubilities (5.7 and 3.5 g in 100 g of H2O) with DAST. How-
ever, the crystal growth of 1 and 2 in the water-containing sol-
vents does not form any hydrated phase or other polymorphs
(Figure 5), whereas the centrosymmetric hydrated phase of
DAST was more easily obtained. These interesting findings
suggest that the high environmental stabilities of 1 and 2 without
any hydrated polymorphs may favor their practical application
and crystal growth process. Moreover, as an estimating figure to
indicate the material mechanical resistance, Mohs’ hardness
experiment of 1 was performed and compared by scratching on
the (001) face of DAST. The results indicate that 1 possesses
slightly less hardness than DAST, but similar with that of organic
salt crystals, such as LAMAD and LYTF,17 suggesting that 1 may
have moderate hardness with a Vickers hardness value of around
36, which is favorable for mechanical processing.
Figure 6. Visible/near-IR absorption spectra of crystal samples 1 and 2.
about 700 nm, strong absorption bands are observed, cor-
relating with the charge-transfer process. Both crystal samples
are transparent at longer wavelengths down to about 2100 nm
with weak absorption around 1700 nm, which is most probably
due to the overtones of the C−H stretching vibrations. The
magnitude of transparency can be improved by enhancing the
crystal qualities and polishing process treatment. Therefore, in
the technologically important range with practical applications
3.4. Linear and Nonlinear Optical Properties. Figure 6
shows the unpolarized visible/near-IR absorption spectra of 1
and 2 crystal samples with the thickness of 0.6−0.8 mm. Below
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Figure 7. Phase-matchable curves for the experimental SHG intensities as a function of particle sizes. The respective insets are comparative SHG
signals for the powder samples with particle sizes of 100−150 μm (up) DAST and 1, and (down) DAST and 2.
of 750−1650 nm, the weak absorption reveals that crystals 1
and 2 can be treated as the potential candidates in nonlinear
optics.
signals reveal that 1 and 2 possess respective SHG efficiencies of
0.83 and 1.3 times that of DAST, approximately equal to 830
and 1300 times that of urea. The experimental absence of SHG
signals for 3 and 4 also well agrees with their centrosymmetric
crystallographic structures. All the results of SHG tests reveal that
the assembling modification of the counteranion can produce novel
stilbazolium derivatives with a favorable acentric packing arrange-
ment and the excellent optical second-order nonlinearities.
SHG activities of complexes 1 and 2 were evaluated at 2.0 μm
using the Kurtz and Perry powder technique. The nonresonant
light with the second-harmonic wavelength (1.0 μm) was ob-
served with a precise photodiode, which was quite resistive to the
fundamental wavelength. An appropriate filter was settled for
eliminating the contributions of the potential third-harmonic
generation (λ = 683 nm). The detailed results of SHG effi-
ciencies for all the complexes are shown in Table 2, and the
experimental SHG intensities as a function of particle sizes for
crystalline 1 and 2 are presented in Figure 7. The results indi-
cate that SHG intensities of both 1 and 2 increase with particle
sizes and approach almost saturated, suggesting their phase-
matchable properties of Type I.9,18 Furthermore, the oscilloscope
4. CONCLUSIONS
In summary, a series of organic stilbazolium derivatives were
synthesized as nonlinear optical materials. Single-crystal struc-
ture determination and the Kurtz powder test were carried out
on the obtained derivatives, which indicate that replacing the
p-toluene sulfonate anion of DAST with p-chlorobenzenesul-
fonate and 4-aminotoluene-3-sulfonate anions built similar crystal
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̈
structures with the comparative optical nonlinearities about 3
orders of magnitude larger than that of urea. However, the other
two complexes show their centrosymmetric crystal structures
without any SHG effect. These results suggest that the crystal
packing of stilbazolium salts is very sensitive to the nature of
the counterions, being confirmed by the theoretical results on the
molecular hyperpolarizability. Furthermore, both the asymmetric
complexes possess higher environmental stabilities, including
antiwater performance and the formation of an anhydrous phase,
which favor the forthcoming sample processing and practical
application. We believe that the further modification of counter-
ions will bring the optimized stilbazolium salts with enhanced
NLO properties and physicochemical performances that are
essential for crystal growth and further material processing for
applications.
(10) (a) Sheldrick, G. M. SHELXL-97; University of Gottingen:
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Gottingen, Germany, 1997. (b) Sheldrick, G. M. SHELXS-97;
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ASSOCIATED CONTENT
* Supporting Information
■
University of Gottingen: Gottingen, Germany, 1997.
̈
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Kaatz, P.; Gunter, P. Organic Nonlinear Optical Materials; Gordon and
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The X-ray crystallographic information files of 1−4 as well as
Figures S1−S3. This material is available free of charge via the
Internet at http://pubs.acs.org.
̈
Breach Publisher: London, 1995.
(13) Chantrapromma, S.; Jansrisewangwong, P.; Musora, R.; Fun, H.-
K. Acta Crystallogr., Sect. E 2009, 65, o617 . Data of 4,4-
(dimethylamino)styryl-1-methylpyridinium 4-bromobenzenesulfonate
at 100 K: monoclinic Cc; a = 10.3712(4), b = 10.9937(5), c =
17.9027(8) Å, β = 92.442(3)°; V = 2039.37(15) Å3; Z = 4.
(14) Sun, Z.; Luo, J.; Chen, T.; Li, L.; Xiong, R.-G.; Tong, M.-L.;
Hong, M. Adv. Funct. Mater. 2012. DOI: adfm201201770.
(15) Kim, P.-J.; Jeong, J.-H.; Jazbinsek, M.; Kwon, S.-J.; Yun, H.; Kim,
AUTHOR INFORMATION
Corresponding Author
*E-mail: jhluo@fjirsm.ac.cn.
Notes
■
The authors declare no competing financial interest.
J.-T.; Lee, Y. S.; Baek, I.-H.; Rotermund, F.; Gunter, P.; Kwon, O.-P.
CrystEngComm. 2011, 13, 444.
̈
ACKNOWLEDGMENTS
■
This work was financially supported by the National Natural Science
Foundation of China (51102231, 21222102, and 21171166),
the One Hundred Talent Program of the Chinese Academy of
Sciences, and the 973 Key Programs of the MOST (2010CB933501,
2011CB935904) and Key Project of Fujian Province (2012H0045).
(16) Nicoud, J. F.; Twieg, R. J. Nonlinear Optical Properties of Organic
Molecules and Crystals; Chemla, D. S., Zyss, J., Eds.; Academic Press:
Orlando, FL, 1987.
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Cryst. Growth 1999, 198−199, 568. (b) Sun, Z. H.; Xu, D.; Wang, X.
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