Highly efficient organic THz generator pumped at near-infrared: Quinolinium single crystals

Article abstract of DOI:10.1002/adfm.201101458

A novel highly efficient ionic electro-optic quinolinium single crystals for THz wave applications is reported. Acentric quinolinium derivatives, HMQ-T (2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium 4-methylbenzenesulfonate) and HMQ-MBS (2-(4-hydroxy-

Full text of DOI:10.1002/adfm.201101458

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Highly Efficient Organic THz Generator Pumped at
Near-Infrared: Quinolinium Single Crystals
Pil-Joo Kim, Jae-Hyeok Jeong, Mojca Jazbinsek, Soo-Bong Choi, In-Hyung Baek,
Jong-Taek Kim, Fabian Rotermund, Hoseop Yun, Yoon Sup Lee, Peter Günter,
and O-Pil Kwon*
can intersect with optical phonons due to
molecular rotations and vibrations. Other
features include high absorbance of semi-
conducting and conducting materials, low
absorbance of dielectric materials and
harmlessness for biological systems.[3,4] Up
to now, a limited number of efficient THz
generators have been reported,[3] therefore
one of most important aims in THz wave
technology is the development of broad-
band and highly efficient nonlinear optical
materials for THz generation.
A novel highly efficient ionic electro-optic quinolinium single crystals for
THz wave applications is reported. Acentric quinolinium derivatives, HMQ-T
(2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium 4-methylbenzenesul-
fonate) and HMQ-MBS (2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium
4-methoxybenzenesulfonate) exhibit high order parameters cos3θp = 0.92 and
cos3θp = 1.0, respectively, as well as a large macroscopic optical nonlinearity,
which is in the range of the benchmark stilbazolium DAST (N,N-dimeth-
ylamino-N’-methylstilbazolium 4-methylbenzenesulfonate) and phenolic
polyene OH1 (2-(3-(4-hydroxystyryl)-5,5-dimethylcyclohex-2-enylidene)
malononitrile) crystals. As-grown unpolished bulk HMQ-T crystals with a side
length of about 6 mm and thickness of 0.56 mm exhibit 3.1 times higher THz
generation efficiency than 0.37 mm thick OH1 crystals and about 8.4 times
higher than 1 mm thick inorganic standard ZnTe crystals at the near-infrared
fundamental wavelength of 836 nm. Therefore, HMQ crystals with high order
parameter obviously have a very high potential for high power THz-wave
generation and its applications.
Electro-optic crystals[5] are promising
materials for broadband THz generation
by employing either optical rectification
(OR)[6] or difference frequency generation
(DFG).[7] Presently, inorganic crystals such
as ZnTe and GaAs are the most popular
THz sources for these techniques.[3,8]
Recently, using organic electro-optic
crystals, a great improvement in THz
generation and detection has been dem-
onstrated.[9–15] The state-of-the-art ionic organic crystals based
on dimethylamino-stilbazolium[16,17] and non-ionic configura-
tionally locked polyene (CLP) groups[4,12,13,18,19] exhibit a large
macroscopic nonlinearity with largest diagonal electro-optic
coefficients of up to r = 53 pm V-1 at 1.3 μm,[20,21] while inor-
ganic ZnTe crystals have r41 = 4.1 pm V-1.[12] The larger macro-
scopic nonlinearities of organic stilbazolium and CLP crystals,
compared to inorganic crystals, result in significantly larger
THz generation efficiency, with over one order of magnitude
larger figure of merit for THz generation: 4200 (pm V-1)2 for
DAST (N,N-dimethylamino-N’-methylstilbazolium 4-methyl-
benzenesulfonate), 4300 (pm V-1)2 for DSTMS (N,N-dimethyl-
amino-N’-methylstilbazolium 2,4,6-trimethylbenzenesulfonate),
5300 (pm V-1)2 for OH1 (2-[3-(4-hydroxystyryl)-5,5-dimethylcy-
clohex-2-enylidene]malononitrile), 370 (pm V-1)2 for ZnTe and
86 (pm V-1)2 for GaAs.[12,19]
The characteristics of organic crystals, including the non-
linear optical properties, can still be improved or optimized for
THz applications. In particular, the benchmark OH1, DSTMS,
and DAST crystals exhibit their best THz generation efficiency
at the fundamental wavelength in the infrared (IR) region in
the range of 1.0–1.6 μm.[10a,11b,12] Below this pump wavelength
region, i.e., in the near-infrared (NIR) region 0.7–1.0 μm, which
is an important wavelength region for commercial high-power
1. Introduction
Recently, terahertz (THz) wave applications such as THz time-
domain spectroscopy and THz imaging[1,2] became impor-
tant due to the unique interactions of these electromagnetic
waves with frequencies in the range of 0.3–30 THz, which
P.-J. Kim, J.-H. Jeong, Prof. O-P. Kwon
Department of Molecular Science and Technology
Ajou University
Suwon 443-749, Korea
E-mail: opilkwon@ajou.ac.kr
Dr. M. Jazbinsek, Prof. P. Günter
Rainbow Photonics AG and Nonlinear Optics Laboratory
ETH Zurich, CH-8093 Zurich, Switzerland
Dr. S.-B. Choi, I.-H. Baek, Prof. F. Rotermund, Prof. H. Yun
Division of Energy Systems Research
Ajou University
Suwon 443-749, Korea
J.-T. Kim, Prof. Y. S. Lee
Department of Chemistry
Korea Advanced Institute of Science and Technology (KAIST)
Daejeon 305-701, Korea
DOI: 10.1002/adfm.201101458
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iodide with (dialkylamino)-bithiophene electron donor group
was measured[22b] to be μβz = 1250 × 10-48 esu, similar to
1-methylpyridinium salt (βz is the vector component of the
hyperpolarizability tensor βijk along the direction of the dipole
moment μ).[22b]
N+
N
e
M
OH
H3C
+
-O3S
R
H3CO3S
R
In order to investigate the electron accepting characteristics
of 1-methyl quinolinium with the 4-hydroxy-3-methoxybenzene
electron donor, we calculated the molecular hyperpolariz-
ability tensor βijk of 2-(4-hydroxy-3-methoxystyryl)-1-methyl-
quinolinium (HMQ) cation by quantum chemical calculations
with finite field (FF) density functional theory (DFT)[23] using
B3LYP/6-311+G*.[24] The direction of the –O–H group can
strongly influence the characteristics of molecular optical non-
linearities, including the main direction and the maximal ampli-
tude of the first hyperpolarizability tensor βijk.[25] In many cases,
the C–O–H plane practically coincides with the plane of phenyl
and methoxy groups.[12,19,25] In addition, the expected direction
of the O–H group in the gas phase is such that the hydrogen is
close to the methoxy group, as shown in Figure 1. This is due
to the high tendency to form strong intramolecular hydrogen
bonds of O–H···O–CH3.[25] Therefore, for the quantum chem-
ical calculation of the optimized molecular conformation (OPT)
of the HMQ cation, the molecular arrangement illustrated in
Figure 1 was used. For the optimized HMQ cation, denoted
HMQ (OPT), we then calculated the zero-frequency hyperpo-
CH3
O
CH3
O
H
O
H
O
CHO
N+
H3C
R
r.
Abb
er ne
idi
e
OH
i
M
,
p p
CH3
HMQ-T
-O3S
R
OCH3 HMQ-MBS
Figure 1. Synthetic route of the investigated methylquinolinium HMQ-T
and HMQ-MBS.
femto-second Ti:sapphire laser sources, most of these crystals
show a lower THz generation efficiency resulting from non-
optimal phase matching.[10a,11b,12] In addition, high photochem-
ical stability and large wavelength range are also important,
which are related to the linear absorption of the crystals. There-
fore, the development of new organic crystals with highly effi-
cient THz generation and good phase-matchability in the NIR
region is a challenging topic.
Here, we report on a series of novel highly efficient ionic
electro-optic quinolinium single crystals well-suited for
THz wave applications. Acentric quinolinium derivatives,
HMQ-T (2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium
4-methylbenzenesulfonate) and HMQ-MBS (2-(4-hydroxy-3-
larizability tensor βijk by FF method and evaluated the maximal
[23]
first-order hyperpolarizability βmax
.
The results are listed in
Table 1 and further details in Table S1 in the Supporting Infor-
mation (SI).
Although the HMQ cation possesses relatively weaker phe-
nolic and methoxy electron donors compared to conventional
dimethylamino electron donor,[5,26] the HMQ (OPT) cation with
1-methylquinolinium electron acceptor exhibit a large maximal
first-order hyperpolarizability βmax of 145 ×10-30 esu, which is
similar as for DAST (159 ×10-30 esu)[27] with 1-methylpyrid-
inium electron acceptor and dimethylamino electron donor, and
is higher than in OH1 molecules (104 ×10-30 esu).[12a] 1-Meth-
ylquinolinium derivatives having the dimethylamino group as
electron donor as in DAST exhibit a larger maximal first-order
hyperpolarizability βmax (184 × 10-30 esu). This means that the
electron accepting strength of 1-methylquinolinium is larger
than the one of the widely used 1-methylpyridinium acceptor.
Therefore, HMQ and its derivatives with 1-methylquinolinium
as acceptor can be interesting materials for nonlinear optical
applications, including THz wave generation.
methoxystyryl)-1-methylquinolinium
4-methoxybenzenesul-
fonate) exhibit high order parameters and large macroscopic
optical nonlinearities, which are in the range of the benchmark
DAST, DSTMS, and OH1 crystals. We show that as-grown bulk
HMQ-T crystals with a side length of about 6 mm exhibit 3.1
times higher THz generation efficiency than benchmark best
OH1 crystals and about 8.4 times higher than inorganic ZnTe
crystal at the fundamental wavelength of 836 nm.
2. Results and Discussion
2.1. Design and Molecular Optical Nonlinearity
The chemical structure of the investigated quinolinium deriva-
tives, HMQ-T and HMQ-MBS are shown in Figure 1. While
benchmark ionic electro-optic crystals showing large optical
nonlinearities, such as DAST,[16,20] DSTMS[11] and DAPSH[17a,b]
use 1-methylpyridinium or 1-phenylpyridinium salts, HMQ-T
and HMQ-MBS use 1-methylquinolinium salt for the electron
acceptor group. However, up to now the electron-accepting
characteristics of 1-methylquinolinium derivatives have been
only scarcely investigated.[22] By electric-field induced second
harmonic generation (EFISH) experiments with the non-polar
solvent chloroform, in which ionic cations and anions were not
dissociated thus allowing such measurements for ionic mol-
ecules, the electron-accepting ability of 1-methylquinolinium
2.2. Synthesis and Characterization
The methathesized synthesis and the resulting crystal structures
of HMQ-T and HMQ-MBS have been published previously.[28,29]
Here, we report on the optimization of the synthesis procedure,
as well as on the relevant physical properties including the
linear and the nonlinear optical properties, bulk crystal growth
and THz wave generation with these materials.
In this work, the HMQ derivatives were synthesized by two
methods: i) metathesization of 2-(4-hydroxy-3-methoxystyryl)-
1-methylquinolinium iodine (HMQ-I) with silver(I) methyl-
benzenesulfonate for HMQ-T as reported previously;[28] and,
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Table 1. Physical and structural data of HMQ crystals in comparison with benchmark DAST[27] and OH1[12a] crystals: the wavelength of the maximum
absorption λmax in methanol solution, the melting temperature Tm, the thermal weight-loss temperature Ti, the maximal first-order hyperpolarizability
β
max determined by quantum chemical calculations considering OPT cation and EXP cation molecules, order parameter cos3(θp), where the angle θp
between the main charge-transfer axis of the crystal and hyperpolarizabilities β of the molecules, the diagonal component of the effective hyperpo-


(2)
ef f
2
2
larizability tensor
.
is the calculated figure of merit for non-resonant powder SHG generation relative to DAST. Powder SHG
βi j k ∝ χi jk
N
(βef f
)
efficiency was measured at a fundamental wavelength of 1.9 μm relative to DAST powder.


eff
2
N 2 (βef f
)
Tm/Ti
[°C]
Order parameter
Powder SHG
Crystal structure
(point group) symmetry
λmax
[nm]
β
max (OPT)
β
max (EXP)
|βiii |
cos3(θp)
[10-30 esu]
[10-30 esu]
[10-30 esu]
HMQ-T
439
441
475
426
273/297
265/291
250/250
212/325
145
145
159
104
169
178
194
93
0.92
1.0
155
178
161
63
0.77
0.94
1
0.63
0.23
1.0
monoclinic Pn (m)
monoclinic Pc (m)[29]
monoclinic Cc (m)
HMQ-MBS
DAST[27]
OH1[12a]
0.83
0.69
0.3
0.5
orthorhombic
Pna21 (mm2)
ii) condensation reactions of vanillin with dimethylquinolinium
4-methylbenzenesulfonate for HMQ-T and with dimethylquino-
linium 4-methoxybenzenesulfonate for HMQ-MBS (see Figure 1
and the Experimental Section). We encountered few limitations
for bulk crystal growth and optical experiments using the
previously reported methathesization method. We observed a
relatively low solubility of HMQ-I in the reaction solvent meth-
anol (0.14 g per 100 g methanol at 40 °C). Due to the low solu-
bility of HMQ-I in the reaction solvent, the methathesization
of larger amounts, which are needed for bulk crystal growth, is
relatively hard. Additionally, in many cases the physical proper-
ties of phenolic π-conjugated materials are highly sensitive to
impurities and environmental conditions.[12a,25] The residual
silver(I) iodide accompanying from the methathesization can
lead to variations of the physical and optical properties in solu-
tion and in the solid state. In inductively coupled plasma (ICP)
analysis of our HMQ-T materials synthesized by methathesiza-
tions, we observed up to 24 ppm silver, while silver has not been
detected for materials synthesized by condensation. In addition,
the color of crystalline materials from methathesization is dark
brown, while the one from the condensation method is brighter
orange. Moreover, we found polymorphism in HMQ-T: the dark
brown HMQ-T material recrystallized from methanol after the
synthesis of methathesizations exhibit different powder X-ray
diffraction (XRD) patterns compared to the reported crystal
structure in the literature.[28] Therefore, for further characteri-
zation and crystal growth we used the HMQ-T and HMQ-MBS
materials synthesized by condensation as shown in Figure 1.
The physical and structural data of HMQ derivatives are
listed in Table 1. For comparison, two of the best organic crys-
talline materials, ionic DAST and non-ionic OH1 crystals, are
also listed.[12a,27] According to the well known nonlinearity-
transparency trade-off,[5] a similar and a higher maximal first-
order hyperpolarizability βmax of the HMQ cation than the one
of DAST and OH1 crystals, respectively, can be expected to
correlate with a similar and a higher wavelength of maximum
absorption λmax of the HMQ derivatives as compared to the ones
found in DAST and OH1 crystals. We measured the absorption
properties of HMQ derivatives in methanol solution. As listed
in Table 1, HMQ-T and HMQ-MBS have a larger wavelength
of maximum absorption λmax than OH1 as expected, but much
lower than DAST: 439 nm for HMQ-T, 440 nm for HMQ-MBS,
426 nm for OH1, and 475 nm for DAST. In a different solvent,
acetonitrile, the wavelength of the maximum absorption λmax
(427 nm for HMQ-T and HMQ-MBS, see Figure S1 in the SI)
is still considerably lower than for DAST (471 nm). The low
absorption of HMQ derivatives combined with a relatively large
molecular nonlinearity may be an advantage considering the
photochemical stability and larger transparency range. While
DAST crystals having dimethylamino electron donor shows
only one absorption peak at the wavelength of the maximum
absorption λmax of about 475 nm, both HMQ-T and HMQ-MBS
crystals having phenolic electron donor show additional absorp-
tion peaks at higher wavelength in the range of 500–700 nm in
both methanol and acetonitrile solutions (see in Figure S1 in
the SI). This may be due to the phenolic electron donor, which
is highly sensitive to the environmental condition, allowing the
co-existence of various resonance states, benzenoid and quinoid
forms.
We also investigated the thermal properties of HMQ mate-
rials by differential scanning calorimetry (DSC) and thermal
gravimetric analysis (TGA) at a scanning rate of 10 °C min-1.
As shown in Figure 2, HMQ-T crystals exhibit a high thermal
stability with thermal weight-loss temperature Ti up to more
than 290 °C, which is higher than that for DAST crystals of
120
100
80
60
40
20
0
12
10
8
TGA
6
4
DSC
2
0
-2
-4
-6
-8
-10
50
100 150 200 250 300 350 400
Temperature (oC)
Figure 2. TGA and DSC thermodiagram of HMQ-T (solid line) and HMQ-
MBS (dotted line) crystals.
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(a)
o
1.944 A
b
a
o
2.220 A
c
(b)
b
c
a
(c)
b
c
a
Figure 3. Molecular conformation (a) and crystal packing diagram (top view of an acentric chain (b) and the stack of two acentric chains (c)) projected
along the a-axis of HMQ-T crystals.
260 °C.[16c] The melting temperature Tm is 273 °C for HMQ-T
hydrogen bonds between phenolic OH group and sulfonate
group[28,29]: –O–H···O–S– groups with O···O distances of
and 265 °C for HMQ-MBS, which are also higher than that for
DAST (Tm = 256 °C).[16c]
about 2.66 Å for HMQ-T and about 2.65 Å for HMQ-MBS (see
Figure 3a and Figure 4a). The molecular conformation of HMQ
cation in HMQ-T and HMQ-MBS crystals is different.[28,29] In
2.3. Macroscopic Optical Nonlinearity in Crystals
both HMQ-T and HMQ-MBS crystals, the phenolic group (i.e.,
4-hydroxy-3-methoxyphenyl group) and the –CH=CH– group
are practically in the same plane. However, in both crystals
the quinolinium group is not in same plane as the HO–Ph–
CH=CH– group due to steric hindrance between the hydrogen
atoms on the N-substituted methyl group of the quinolinium
group and the hydrogen atom on the –CH=CH– group: the
twisted angle between the plane of the phenyl ring on the phe-
nolic group and the plane of the pyridinium ring including the
nitrogen atom (N+) on the quinolinium group is about 17° for
HMQ-T[28] and about 27° for HMQ-MBS,[29] while 29° for HMQ
(OPT) cations. In addition, the O–H electron-donor group has
a different direction in these crystals: in the HMQ-T crystals
the O–H direction is toward the neighboring O–CH3 group
with strong intramolecular hydrogen bond with the oxygen
To examine the macroscopic optical nonlinearities, we first ana-
lyzed the single X-ray structures of HMQ-T and HMQ-MBS
crystals. The crystal structure for HMQ-T crystals has been ana-
lyzed newly here, but was found to be identical to that reported
in the literature,[28] and for HMQ-MBS crystals the crystal struc-
ture reported elsewhere[29] wasused. The molecular conforma-
tion and crystal packing diagram of HMQ-T and HMQ-MBS
crystals are shown in Figure 3 and Figure 4. The HMQ-T and
HMQ-MBS crystals exhibit monoclinic Pn and Pc space groups,
respectively, with point group symmetry m.
The main supramolecular interactions in the HMQ-T and
HMQ-MBS crystals are strong Coulomb forces between 1-meth-
ylquinolinium cations and sulfonate anions, as well as strong
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Figure 4. Molecular conformation (a) and crystal packing diagram (top view of an acentric chain (b) and the stack of two acentric chains (c)) projected
along the b-axis of HMQ-MBS crystals.
atom on the neighboring O–CH3 group with H···O distance of
2.22Å,[28] similarlyasintheOPTmoleculewithH···Odistanceof
2.12 Å, while the opposite direction appears in HMQ-MBS[29]
(see Figure 3a and Figure 4a). We attribute this difference to
different positions of the counter anions, which determines
the direction of the OH group, forming strong hydrogen bonds
with the sulfonated group as discussed above, which outweighs
the intramolecular hydrogen bond with the oxygen atom. As
shown in Figure 3b and Figure 4b, the pairs of the HMQ cation
and anion form an acentric polar layer, which are stacked one
by one (see Figure 3c and Figure 4c).
method,[23] in order to investigate the influence of different
molecular geometry with a different tilt angle in the π-conjugated
bridge[30] and the different direction of the O–H group in the solid
state.[25] The resulting maximal first-order hyperpolarizability
βmax is listed in Table 1 and more details are given in Table S1 in
the SI. For both EXP conformations in the crystal, the maximal
first-order hyperpolarizability βmax slightly increases compared to
optimized molecules of HMQ (OPT), 169 ×10-30 esu for HMQ-T
(EXP) and 178 ×10-30 esu for HMQ-MBS (EXP) compared to
145 ×10-30 esu for OPT molecules, and the difference between the
two crystalline conformations is relatively small. Although the
HMQ cation possesses a different direction of the electron-donor
OH group in the solid state, still in the same plane as the phenyl
ring, the microscopic optical nonlinearities are maintained.
We calculated the microscopic nonlinearity of HMQ cations
(EXP), determined by single X-ray structural analysis in each
crystal, by density functional theory using the finite filed (FF)
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(a)
Y||b
X
βmax
βmax
θp
βmax,1
βmax,2
θp
polar axis
Z
C
(b)
βmax
Y||b
X
βmax
A
βmax,1
βmax,2
polar axis
Z
Figure 5. Orientation of the molecules within one unit cell in the crystallographic abc system and the Cartesian XYZ system (the angle between the
crystallographic c axis and Z is ψ = 1.3° for HMQ-T and 7.0° for HMQ-MBS). The dotted and the solid vectors present the polar axis and the direction
of the hyperpolarizabilities β of the chromophores, respectively. The angle between the main charge-transfer axis of the crystal Z and hyperpolariz-
abilities β of the molecules is θp = 13.8°, leading to an order parameter of cos3θp = 0.92 for HMQ-T and θp = 0.5°, leading to an order parameter of
cos3θp = 1.0 for HMQ-MBS.
When nonlinear optical chromophores possess an asym-
metric shape or the position of electron donor and acceptor is
not exactly at each end of the long axis of a molecule, we cannot
close to 1.0: cos3(θp) = 0.92 for HMQ-T and 1.0 for HMQ-MBS,
which is higher than for both DAST and OH1 crystals as listed
in Table 1. Such an alignment optimizes the diagonal suscepti-
bility element and is very favorable for THz-wave generation.
We evaluated the diagonal and off-diagonal component of the
simply assume that the long axis of molecule is the main direc-
[31]
tion of the first-order hyperpolarizability βmax
,
which is an
(2)
eff
important information for the evaluation of macroscopic optical
nonlinearities. Because the position of the nitrogen atom (N+)
in the quinolinium acceptor of the HMQ cation is not at the
end, but at a side of the long axis of the molecule, we evaluated
the direction of the maximal first-order hyperpolarizability βmax
of HMQ cation based on the FF calculation details reported
in Table S1 of the SI. The resulting directions are indicated in
Figure 5, which shows the projections to the YZ plane of the
Cartesian XYZ system. The Cartesian XYZ system was chosen
so that the Y axis is parallel to the crystallographic (symmetry)
b axis and the Z axis in the ac crystallographic plane is along
the polar axis of the crystal, or more precisely along the main
charge transfer axis of the crystal. For both crystals the polar
axis Z is almost parallel to the c crystallographic axis, as shown
in Figure 5.
effective hyperpolarizability tensor β ∝ χi jk in the Cartesian
i jk
XYZ system, considering all hyperpolarizability tensor compo-
nents βmnp calculated by the FF method and the orientation of
the chromophores in the crystallographic system.[23] The diag-
eff
iii
onal component of the effective hyperpolarizability tensor β
is listed in Table 1 and other non-zero off-diagonal component
in Table S2 in the SI. Due to the high order parameter cos3θp,
close to 1.0, the off-diagonal component of HMQ-T and HMB-
MBS can be ignored. HMQ-T and HMQ-MBS crystals exhibit
a large diagonal component of the effective hyperpolarizability
eff
β
tensor,
= 155 ×10-30 esu and 178 ×10-30 esu, respectively,
333
which is larger than for DAST (161 × 10-30 esu) and OH1 (63 ×
10-30 esu) crystals. DAST and OH1 have been evaluated previ-
ously using analogous calculation methods.[12,27]
In order to screen the macroscopic optical nonlinearity, we
performed powder second harmonic generation (SHG) tests[32]
at a non-resonant fundamental wavelength of 1.9 μm. The SHG
efficiency was measured relative to that of the well-character-
ized ionic DAST crystals. HMQ-T and HMQ-MBS crystalline
powders exhibit a large macroscopic nonlinearity with SHG
The angle θp between the main charge-transfer axis of the
crystal and the maximal first-order hyperpolarizability βmax of
the molecules is close to zero: θp = 13.8° for HMQ-T and 0.5°
for HMQ-MBS. This means that in both crystals the chromo-
phores align almost perfectly parallel with the order parameter
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2.4. Bulk Single Crystals
0.8
The solubility of HMQ-T and HMQ-MBS in methanol is shown
in Figure 7a. The solubility of HMQ-T is higher than for HMQ-
MBS: 0.89 g per 100g methanol for HMQ-T and 0.56 g per 100g
methanol for HMQ-MBS at 50 °C. The solid line in Figure 7a is
according to the well-known van’t Hoff thermodynamic equilib-
rium equation assuming an ideal solution.[11a,33]
We grew bulk HMQ-T and HMQ-MBS single crystals by the
slow cooling method in methanol starting at 40 °C and a cooling
rate of 1 °C per day. In both crystals first nucleates appeared at
about 25–26 °C. Typical as-grown HMQ-T and HMQ-MBS crys-
tals are of yellow color as shown in Figure 7b and Figure 7c,
respectively, which are brighter than orange-red OH1 crystals,
as well as dark-red DAST crystals. The as-grown HMQ-T crys-
tals have flat and parallel surfaces with a good optical quality,
while HMQ-MBS crystals have a more complex morphology.
0.6
0.4
0.2
0.0
1550 nm
500
1000
1500
2000
Wavelength (nm)
Figure 6. Transmission spectra of an unpolished HMQ-T crystal (b-plate)
with a thickness of 0.32 mm using un-polarized light.
(a)
7
efficiencies of about 0.63 and 0.23 times that of DAST powder,
respectively. The SHG efficiency of HMQ-MBS reported previ-
ously[29] was considerably lower, only about 0.45 times that of
urea (note that DAST exhibits a 3 orders of magnitude higher
SHG efficiency with respect to urea at 1.9 μm[16]); Unfortunately
the authors did not disclose the wavelength, at which their effi-
ciency was measured.[29] Presumably, when using a commonly
employed 1.064 μm fundamental wavelength, the generated
SHG signal at 0.532 μm is mostly absorbed by HMQ-T powder
(see Figure 6), which can explain this discrepancy.
6
5
HMQ-T
HMQ-MBS
4
3
We can estimate the theoretically expected powder test effi-
ciency from the effective hyperpolarizability tensor elements
e ff
2
β
by considering the number density of chromophores
i jk
3.1
3.2
3.3
3.4
N and the averaged contribution over different orientation of
crystallites by considering the corresponding point group sym-
1/T(10-3K-1)


metry.[32] The resulting figure of merit, N2 (βeff
)
, neglects the
2
contributions of the intermolecular interactions in the crystals
as well as possible phase matching enhancements, but usually
gives a good first-order estimation for the expected macroscopic
(b)
(c)
(001)


nonlinear optical properties.[12,18,19,25] The values of N2 (βeff
)
2
relative to OH1 are for HMQ-T 2.6 times OH1 and for HMQ-
MBS 3.2 times OH1, which is for both considerably more than
experimentally measured. However, the chromophores with the
OH group may be extremely sensitive to environmental condi-
tions, e.g., the microscopic hyperpolarizability of OH1 chromo-
phores may differ by a factor of 2 in different solvents.[12a] Note
(010)
1 mm


2
that the N2 (βeff
)
figure of merit for OH1 is about 30% of
DAST, while the experimentally measured powder test almost


2
twice larger. Relative to DAST, N2 (βeff
)
of HMQ-T is 76%,
which is in a very good agreement with the experimental
powder test efficiency for DAST. For HMQ-MBS on the other
hand, the experimental and theoretical values differ by a factor
of 3.7 relative to DAST. These discrepancies may point to a
large environmental influence of the microscopic nonlinearity
of HMQ chromophores to the environment. Still we can con-
clude that the new HMQ crystals exhibit excellent second-order
nonlinear optical properties in the range of the presently best
materials DAST and OH1. This is furthermore confirmed by
the THz generation measurements described in Section 2.5.
1 mm
1 mm
Figure 7. a) Solubility of HMQ-T and HMQ-MBS crystals in methanol:
mole fraction x in logarithmic scale vs. inverse temperature (T-1). Pho-
tographs of as-grown (b) HMQ-T and (c) HMQ-MBS crystals by slow
cooling method in methanol.
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We investigated the morphology of the as-grown HMQ-T crys-
tals by X-ray diffraction. The parallel surfaces are along the b
crystallographic planes, which means that the polar c-axis is in
the plane as shown in Figure 7b. Therefore, compared to the
morphology of HMQ-MBS crystals with non-parallel surfaces,
as-grown HMQ-T crystals are more suitable for THz wave
generation.[13]
of the generated THz fields are shown in Figure 8b, which were
obtained by fast Fourier transform (FFT) of the THz time traces
of Figure 8a. The amplitude THz-wave generation efficiency of
HMQ-T crystals is 8.4 and 3.1 times larger than for ZnTe and
OH1 crystals, respectively: the peak-to-peak amplitude of the
THz field is 20.2 kV cm-1 for HMQ-T, 2.4 kV cm-1 for ZnTe,
and 6.5 kV cm-1 for OH1 crystals. Even though the conditions
of phase matching and thickness have not yet been optimized,
HMQ-T crystals obviously have a very high potential for high
power THz generation and its applications.
According to the crystal characteristics, including the mor-
phology, the HMQ-T crystals were chosen here for the charac-
terization of the physical properties and for THz wave genera-
tion. Figure 6 shows the transmission spectrum of an unpol-
ished HMQ-T crystal (b-plate) with a thickness of 0.32 mm
using unpolarized light incident normal to the sample. The
cut-off wavelength λcut-off of HMQ-T is about 595 nm, which is
considerably shorter than for OH1 (around 640 nm) and DAST
(around 680 nm) crystals. The lower cut-off wavelength λcut-off
can be advantageous: i) photochemical stability; and, ii) a larger
transparency range and therefore a wider range of possible
operation wavelengths. The HMQ-T crystals possess an absorp-
tion peak at about 1675 nm, but low absorption at 1550 nm,
while a relatively strong absorption at about 1550 nm of OH1
crystals[12a] limits its application possibilities at this technologi-
cally very important wavelength. Therefore, HMQ-T crystals
possess larger transparence range from 595 nm 1550 nm than
OH1 from 640 nm to 1400 nm. In addition, the allowance of
the fundamental wavelength of 1550 nm may be useful for
using widely available laser pump sources at this wavelength,
e.g., femtosecond lasers for THz-wave generation and CW tel-
ecommunication lasers for electro-optic applications.
3. Conclusions
We have reported on novel highly efficient ionic electro-optic
quinolinium single crystals for nonlinear optics, in particular
for THz wave applications. Acentric quinolinium derivatives,
HMQ-T and HMQ-MBS exhibit a high order parameter cos3θp
(a)
14
12
HMQ-T
OH1
10
ZnTe
8
6
4
2
0
-2
-4
-6
-8
-10
2.5. THz-Wave Generation
We generated THz waves by using optical rectification (OR)
using femtosecond-laser pump pulses in various nonlinear
optical crystals, and detected these waves by the electro-optic
sampling (EOS) method.[13] We used fundamental optical
pulses with a duration of 170 fs at 836 nm with repetition rate
of 1 kHz from a regenerative amplified Ti:sapphire laser. For all
nonlinear optical materials the same THz electro-optic detector
crystal (ZnTe) was used. The measurements were performed at
room temperature in air with a humidity of 28%. The details of
our experimental setup for the generation and detection of THz
waves are given in the SI.
A HMQ-T crystal with (010) surfaces and a thickness of
0.56 mm was used for THz generation. For comparison we also
used a ZnTe crystal with polished (110) surfaces and a thickness
of 1.0 mm, which is the most widely used inorganic THz gen-
erator material,[8] and organic OH1 crystal with (100) surfaces
and a thickness of 0.37 mm, which is one of the state-of-the-art
electro-optic crystals with very attractive properties for THz-wave
generation.[12] Note that for OH1 crystals a larger thickness is not
expected to result in a higher THz generation efficiency at this
pump wavelength, since the coherence length for 836 nm pump
fs lasers at 1 THz is only about 0.2 mm.[12b] Due to the relatively
good optical quality of the crystals with flat surfaces, as-grown
HMQ-T and OH1 crystals were used without polishing.
48
50
52
54
56
58
60
Time delay (ps)
(b)
0.6
0.5
0.4
0.3
0.2
0.1
0.0
HMQ-T
OH1
ZnTe
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Frequency (THz)
Figure 8. Terahertz pulses generated in single crystals of 0.56 mm-thick
HMQ-T (solid line), benchmark 0.37 mm-thick OH1 crystal (dotted line)
and inorganic 1 mm thick ZnTe (dashed line) at a fundamental wave-
length of 836 nm with the pulse duration of 170 fs. a) Time-trace of the
terahertz electric field ETHz(t). b) The spectra of ETHz (ν).
Figure 8a shows time traces of the generated THz waves
from nonlinear optical crystals in our experiment. The spectra
©
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Adv. Funct. Mater. 2012, 22, 200–209
2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
207

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X-ray Crystal Structure Analysis of HMQ-MBS:[29] C26H25NO6S, Mr =
479.54, monoclinic, space group Pc, a = 10.9895(1) Å, b = 7.1363(1) Å,
c = 15.6341(2) Å, β = 110.300(1)°, V = 1149.94(3) Å3, Z = 2, T = 297(2)
K, CCDC 629589.
close to 1.0 and a large macroscopic optical nonlinearity, which
are in the range of the benchmark ionic stilbazolium DAST and
non-ionic phenolic polyene OH1 crystals. Bulk HMQ-T crys-
tals with good optical quality, a side length of about 6 mm and
thickness of 0.56 mm, without polishing procedure, exhibit 3.1
times higher THz generation efficiency than the 0.37 mm thick
OH1 crystal and about 8.4 times higher than 1 mm thick inor-
ganic ZnTe crystal at the fundamental wavelength of 836 nm.
Therefore, HMQ crystals with high order parameter are very
attractive materials for THz wave technology.
Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
Acknowledgements
4. Experimental Section
This work was supported by the Basic Science Research Program (2011-
0004065) and the Priority Research Centers Program (2011-0022978)
through the National Research Foundation of Korea (NRF) funded by
the Ministry of Education, Science and Technology. I-HB and FR were
supported by NRF (2011-0017494) funded by MEST.
Synthesis: All chemicals were purchased from commercial suppliers.
2-Methylquinoline and vaniline for the synthetic route with condensation, as
shown in Figure 1, were purchased from Sigma–Aldrich and used without
further purification. 1H-NMR spectroscopy data were recorded on a Varian
400 MHz. All chemical shifts are reported in ppm (δ) relative to (CH3)4Si.
2 - ( 4 - H y d r o x y - 3 - M e t h o x y s t y r y l ) - 1 - M e t h y l q u i n o l i n i u m
4-Methylbenzenesulfonate (HMQ-T): Methyl p-toluenesulfonate (32.34 mL,
0.21 mol (98%)) and 2-methylquinoline (29.8 mL, 0.21 mol (95%)) were
dissolved in methanol (50 mL) and the solution was stirred at 50 °C for
1 d. The solution color changed from colorlessness to light pink. After cooling
the solution to room temperature, a precipitate was obtained by evaporating
Received: June 29, 2011
Revised: August 27, 2011
Published online: October 24, 2011
[1] a) Special issue on “T-ray Imaging, Sensing & Detection”, Pro-
ceed. IEEE. 2007, 95, 1514–1704; b) R. M. Woodward, V. P. Wallace,
R. J. Pye, B. E. Cole, D. D. Arnone, E. H. Linfield, M. Peppern,
J. Invest. Dermatol. 2003, 120, 72; c) T. Loffler, K. Siebert, S. Czasch,
T. Bauer, H. G. Roskos, Phys. Med. Biol. 2002, 47, 3847; d) Z. D. Taylor,
R. S. Singh, M. O. Culjat, J. Y. Suen, W. S. Grundfest, H. Lee,
E. R. Brown, Opt. Lett. 2008, 33, 1258.
[2] a) K. L. Nguyen, T. Friscic, G. M. Day, L. F. Gladden, W. Jones,
Nat. Mater. 2007, 6, 206; b) P. Knobloch, C. Schildknecht,
T. Kleine-Ostmann, M. Koch, S. Hoffmann, M. Hofmann, E. Rehberg,
M. Sperling, K. Donhuijsen, G. Hein, K. Pierz, Phys. Med. Biol. 2002,
47, 3875; c) J. F. Federici, B. Schulkin, F. Huang, D. Gary, R. Barat,
F. Oliveira, D. Zimdars, Semicond. Sci. Technol. 2005, 20, S266;
d) M. C. Beard, G. M. Turner, C. A. Schmuttenmaer, J. Phys. Chem.
B 2002, 106, 7146.
methanol and adding 1,2-dimethoxyethane.
A white-pink powder of
1,2-dimethylquinolinium4-methylbenzenesulfonatewasobtainedbyfiltration
and dried in vacuum oven at 60 °C (yield = 76%). 1,2-Dimethylquinolinium
4-methylbenzenesulfonate (40 g, 0.121 mol) and vanillin (18.5 g, 0.121
mol) were dissolved in methanol (100 mL). The catalyst piperidine (2.4 mL,
0.0242 mol) was added by stirring under reflux for 3 d. After cooling to room
temperature, an orange crystalline powder was obtained. The final product
was obtained by recrystallization in methanol and dried in vacuum oven at
1
60 °C for 1 h (yield = 22%). H-NMR (400 MHz, CD3OD, δ): 8.83 (d, 1H,
J = 8.8, C5H2N), 8.44 (d, 1H, J = 9.2, C6H4), 8.40 (d, 1H, J = 8.8, C5H2N), 8.24
(d, 1H, J = 8.0, C6H4), 8.15 (m, 1H, C6H4), 8.06 (d, 1H, J = 15.6, CH), 7.90
-
(m 1H, C6H4), 7.69 (d, 1H, J = 15.2, CH), 7.68 (d, 2H, J = 6.4, C6H4SO3-),
7.52 (s, 1H, C6H3), 7.39 (dd, 1H, C6H3), 7.20 (d, 2H, J = 8.4, C6H4SO3 ),
6.91 (d, 1H, J = 8.0, C6H3), 4.57 (s, 3H, OMe), 4.00 (s, 3H, Me), 2.36 (s, 3H,
NMe). Elemental analysis for C26H25NO5S, Calcd. C 67.37, H 5.43, N 3.02, S
6.92; Found: C 67.40, H 5.53, N 3.02, S 7.02.
[3] a) M. Tonouchi, Nat. Photonics 2007, 1, 97; b) B. Ferguson,
X. C. Zhang, Nat. Mater. 2002, 1, 26; c) C. Sirtori, Nature 2002,
417, 132; c) A. M. Sinyukov, L. M. Hayden, J. Phys. Chem. B
2004, 108, 8515; d) X. Zheng, C. V. Malaughlin, P. Cunningham,
L. M. Hyden, J. Nanoelectron. Optoelectron. 2007, 2, 1; e) M. Walther,
B. M. Fischer, A. Ortner, A. Bitzer, A. Thoman, H. Helm, Anal. Bio-
anal. Chem. 2010, 397, 1009.
2-(4-Hydroxy-3-Methoxystyryl)-1-Methylquinolinium 4-Methoxybenzenesul-
fonate (HMQ-MBS): HMQ-MBS was synthesized in a similar manner as
HMQ-T, by the condensation reactions of vanillin with dimethylquinolinium
1
4-methoxybenzenesulfonate (yield = 40%). H-NMR (400 MHz, CD3OD,
δ): 8.81 (d, 1H, J = 8.8, C5H2N), 8.42 (d, 1H, J = 8.8, C6H4), 8.38 (d, 1H,
J = 9.2, C6H4), 8.22 (d, 1H, J = 8.0, C5H2N), 8.13 (m, 1H, C6H4), 8.05 (d,
1H, J = 15.6, CH), 7.88 (m 1H, C6H4), 7.72 (m, 2H, C6H4SO3-), 7.66 (d,
1H, J = 16.0, CH), 7.50 (s, 1H, C6H3), 7.38 (dd, 1H, C6H3), 6.91 (m, 2H,
C6H4SO3-), 6.89 (m, 1H, C6H3), 4.55 (s, 3H, NMe), 4.00 (s, 3H, OMe),
3.80 (s, 3H, OMe). Elemental analysis for C26H25NO6S, Calcd. C 65.12, H
5.25, N 2.92, S 6.69; Found: C 65.19, H 5.21, N 2.94, S 6.78.
[4] O. P. Kwon, S. J. Kwon, M. Stillhart, M. Jazbinsek, A. Schneider,
V. Gramlich, P. Günter, Cryst. Growth Des. 2007, 7, 2517.
[5] a) M. Jazbinsek, O. P. Kwon, Ch. in Handbook of Organic Electronics
and Photonics (Ed: S. H. Nalwa), American Scientific Publishers,
Los Angeles 2008, Ch. 1; b) Ch. Bosshard, M. Bösch, I. Liakatas,
M. Jäger, P. Günter, in Nonlinear Optical Effects and Materials (Ed:
P. Günter), Springer-Verlag, Berlin 2000, Ch. 3; c) Introduction to
Organic Electronic and Optoelectronic Materials and Devices (Ed:
S. S. Sun, L. R. Dalton), CRC Press, Boca Raton, USA 2008.
[6] X. C. Zhang, X. F. Ma, Y. Jin, T. M. Lu, E. P. Boden, P. D. Phelps,
K. R. Stewart, C. P. Yakymyshyn, App. Phys. Lett. 1992, 61, 3080.
[7] a) K. Suizu, K. Miyamoto, T. Yamashita, H. Ito, Opt. Lett. 2007, 32,
2885; b) K. Miyamoto, H. Minamide, M. Fujiwara, H. Hashimoto,
H. Ito, Opt. Lett. 2008, 33, 252.
X-ray Crystal Structure Analysis of HMQ-T: C26H25NO5S, Mr = 463.55,
monoclinic, space group Pn, a = 6.9304 (3) Å, b = 11.1154 (5) Å, c =
14.7594 (5) Å, β = 100.3072 (9)°, V = 1118.62 (7) Å3, Z = 2, T = 290(1)
K, μ(MoK ) = 0.18 mm-1. Of 10 740 reflections collected in the θ range
3.4°–27.4° using ω scans on a Rigaku R-axis Rapid S diffractometer,
4492 were unique reflections (Rint = 0.025, completeness = 99.1%).
The structure was solved and refined against F2 using SHELX97,[34] 299
2
variables, wR2 = 0.098, R1 = 0.033 (3370 reflections having Fo2 > 2σ(Fo )),
GOF = 1.09, Flack parameter x = -0.08(8), and max/min residual
electron density 0.25/–0.21 eÅ-3. Further details of the crystal structure
investigation(s) may be obtained from the Cambridge Crystallographic
Data Centre (CCDC, 12 Union Road, Cambridge CB2 1EZ, UK; tel.: +44
(1223) 336408, fax: +44 (1223) 336033, e-mail: deposit@ccdc.cam.ac.uk)
on quoting the depository number CCDC-824804 for HMQ-T.
[8] a) T. Löffler, T. Hahn, M. Thomson, F. Jacob, H. G. Roskos, Opt.
Express 2005, 13, 5353; b) X. Wang, W. Sun, Y. Zhang, Optik 2010,
121, 1148.
©
208 wileyonlinelibrary.com
2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Funct. Mater. 2012, 22, 200–209

www.afm-journal.de
www.MaterialsViews.com
[9] a) P. Y. Han, M. Tani, F. Pan, X. C. Zhang, Opt. Lett. 2000, 25,
675; b) T. Taniuchi, S. Okada, H. Nakanishi, J. Appl. Phys. 2004,
95, 5984; c) K. Kuroyanagi, K. Yanagi, A. Sugita, H. Hashimoto,
H. Takahashi, S. Aoshima, Y. Tsuchiya, J. Appl. Phys. 2006, 100,
043117; d) T. Matsukawa, Y. Mineno, T. Odani, S. Okada, T. Taniuchi,
H. Nakanishi, J. Cryst. Growth. 2007, 299, 344.
S. J. Kwon, M. Jazbinsek, V. Gramlich, P. Günter, Adv. Funct. Mater.
2007, 17, 1750.
[19] a) O. P. Kwon, S. J. Kwon, M. Jazbinsek, J. Y. Seo, J. T. Kim, J. I. Seo,
Y. S. Lee, H. Yun, P. Günter, Chem. Mater. 2011, 23, 239; b) O. P. Kwon,
M. Jazbinsek, H. Yun, J. I. Seo, J. Y. Seo, S. J. Kwon, Y. S. Lee,
P. Günter, CrystEngComm 2009, 11, 1541.
[10] a) A. Schneider, M. Neis, M. Stillhart, B. Ruiz, R. U. A. Khan,
P. Günter, J. Opt. Soc. Am. B 2006, 9, 1822; b) A. Schneider,
M. Stillhart, P. Günter, Opt. Express. 2006, 14, 5376; c) A. Schneider,
P. Günter, App. Opt. 2006, 45, 6598; d) A. Schneider, I. Biaggio,
P. Günter, Appl. Phys. Lett. 2004, 84, 2229.
[11] a) Z. Yang, L. Mutter, M. Stillhart, B. Ruiz, S. Aravazhi, M. Jazbinsek,
A. Schneider, V. Gramlich, P. Günter, Adv. Funct. Mater. 2007, 17,
2018; b) M. Stillhart, A. Schneider, P. Günter, J. Opt. Soc. Am. B.
2008, 25, 1914.
[12] a) O. P. Kwon, S. J. Kwon, M. Jazbinsek, F. D. J. Brunner, J. I. Seo,
Ch. Hunziker, A. Schneider, H. Yun, Y. S. Lee, P. Günter, Adv. Funct.
Mater. 2008, 18, 3242; b) F. D. J. Brunner, O. P. Kwon, S. J. Kwon,
M. Jazbinsek, A. Schneider, P. Günter, Opt. Express 2008, 16, 16496.
[13] J. Y. Seo, S. B. Choi, M. Jazbinsek, F. Rotermund, P. Günter,
O. P. Kwon, Cryst. Growth Des. 2009, 9, 5003.
[14] a) J. J. Carey, R. T. Bailey, D. Pugh, J. N. Sherwood, F. R. Cruickshank,
K. Wynne, Appl. Phys. Lett. 2002, 81, 4335; b) H. Hashimoto,
H. Takahashi, T. Yamada, K. Kuroyanagi, T. Kobayashi, J. Phys.: Con-
dens. Matter 2001, 13, L529; c) V. Krishnakumar, R. Nagalakshmi,
Cryst. Growth Des. 2008, 8, 3882.
[20] F. Pan, G. Knopfle, Ch. Bosshard, S. Follonier, R. Spreiter,
M. S. Wong, P. Günter, Appl. Phys. Lett. 1996, 69, 13.
[21] Ch. Hunziker, S. J. Kwon, H. Figi, F. Juvalta, O. P. Kwon,
M. Jazbinsek, P. Günter, J. Opt. Soc. Am. B 2008, 25, 1678.
[22] a) B. J. Coe, J. J. Hall, J. A. Harris, B. S. Brunschwig, S. J. Coles,
M. B. Hursthouse, Acta Crystallogr. E 2005, 61, o464; b) C. G. Fortuna,
C. Bonaccorso, F. Qamar, A. Anu, I. Ledouxb, G. Musumarra, Org.
Biomol. Chem. 2011, 9, 1608.
[23] S. J. Kwon, O. P. Kwon, J. I. Seo, M. Jazbinsek, L. Mutter, V. Gramlich,
Y. S. Lee, H. Yun, P. Günter, J. Phys. Chem. C 2008, 112, 7846.
[24] a) A. D. Becke, J. Chem. Phys. 1993, 98, 5648; b) J. P. Perdew, Phys.
Rev. B 1986, 33, 8822.
[25] O. P. Kwon, M. Jazbinsek, J. I. Seo, E. Y. Choi, H. Yun,
F. D. J. Brunner, P. Günter, Y. S. Lee, J. Chem. Phys. 2009, 130, 134708.
[26] O. Kwon, S. Barlow, S. A. Odom, L. Beverina, N. J. Thompson,
E. Zojer, J. L. Bredas, S. R. Marder, J. Phys. Chem. A 2005, 109,
9346.
[27] P. J. Kim, J. H. Jeong, M. Jazbinsek, S. J. Kwon, H. Yun, J. T. Kim,
Y. S. Lee, I. H. Baek, F. Rotermund, P. Günter, O. P. Kwon, CrystEng-
Comm 2011, 13, 444.
[15] F. D. J. Brunner, A. Schneider, P. Günter, Appl. Phys. Lett. 2009, 94,
061119.
[28] S. Chantrapromma, B. Jindawong, H. K. Fun, Acta Cryst. E 2007,
E63, o4928.
[16] a) S. R. Marder, J. W. Perry, W. P. Schaefer, Science 1989, 245, 626;
b) S. R. Marder, J. W. Perry, C. P. Yakymyshyn, Chem. Mater. 1994, 6,
1137; c) F. Pan, M. S. Wong, Ch. Bosshard, P. Günter, Adv. Mater.
1996, 8, 592.
[17] a) B. J. Coe, J. A. Harris, I. Asselberghs, K. Wostyn, K. Clays,
A. Persoons, B. S. Brunschwig, S. J. Coles, T. Gelbrich, M. E. Light,
M. B. Hursthouse, K. Nakatani, Adv. Funct. Mater. 2003, 13, 347;
b) H. Figi, L. Mutter, Ch. Hunziker, M. Jazbinsek, P. Günter,
B. J. Coe, J. Opt. Soc. Am. B 2008, 25, 1786; c) J. Ogawa, S. Okada,
Z. Glavcheva, H. Nakanishi, J. Cryst. Growth. 2008, 310, 836.
[18] a) O. P. Kwon, B. Ruiz, A. Choubey, L. Mutter, A. Schneider,
M. Jazbinsek, P. Günter, Chem. Mater. 2006, 18, 4049; b) O. P. Kwon,
[29] S. Chantrapromma, B. Jindawong, H. K. Fun, P. S. Patil, Anal. Sci.
2007, 23, x81.
[30] a) O. P. Kwon, M. Jazbinsek, H. Yun, J. I. Seo, E. M. Kim, Y. S. Lee,
P. Günter, Cryst. Growth Des. 2008, 8, 4021; b) O. P. Kwon,
M. Jazbinsek, J. I. Seo, P. J. Kim, H. Yun, Y. S. Lee, P. Günter, J. Phys.
Chem. C 2009, 113, 15405.
[31] O. P. Kwon, M. Jazbinsek, J. I. Seo, P. J. Kim, E. Y. Choi, Y. S. Lee,
P. Günter, Dyes Pigm. 2010, 85, 162.
[32] K. Kurtz, T. T. Perry, J. Appl. Phys. 1968, 39, 3798.
[33] J. R. Brice, in Crystal Growth Processes, John Wiley and Sons, New
York 1986, Ch. 2.
[34] G. M. Sheldrick, Acta Crystallogr. 2008, A64, 112.
©
wileyonlinelibrary.com
Adv. Funct. Mater. 2012, 22, 200–209
2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
209