Synthesis and properties of novel stilbazolium analogues as second-order nonlinear optical chromophores

Article abstract of DOI:10.1246/bcsj.78.180

This study synthesized a series of methoxystilbazolium analogues with π-conjugation extended by attaching a fused aromatic ring, i.e., 6-styrylisoquinolinium and 4-[2-(2-naphthyl)ethenyl]pyridinium derivatives with methoxy substituents. We evaluated their transition energies (E_egS) and second-order hyperpolarizabilities (βs) experimentally using their absorption spectra and a hyper-Rayleigh scattering measurement, respectively. Subsequently, we calculated βs using the MOPAC PM3 method. These values were compared with those of 4-[4-(4-methoxyphenyl)-1,3-butadienyl]pyridinium derivative, which is a stilbazolium analogue with π-conjugation that is simply extended by an increase of the double-bond number between two aromatic rings. This study clarified that the fused-ring systems possess large βs, irrespective of their relatively short absorption wavelengths, compared to the double-bond elongation system.

Full text of DOI:10.1246/bcsj.78.180

1
80 Bull. Chem. Soc. Jpn., 78, 180–186 (2005)
ꢀ 2005 The Chemical Society of Japan
Synthesis and Properties of Novel Stilbazolium Analogues
as Second-Order Nonlinear Optical Chromophores
y
yy
yyy
Kyoko Tsuji, Naoyuki Nishimura, Xuan-Ming Duan, Shuji Okada,
yyyyy
yyyy
Hiro Matsuda,1;
ꢀ
Hidetoshi Oikawa,
and Hachiro Nakanishi
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Sendai 980-8577
1
Photonics Research Institute, National Institute of Advanced Industrial Science and Technology,
1-1-1 Higashi, Tsukuba 305-8565
Received June 21, 2004; E-mail: hnakanis@tagen.tohoku.ac.jp
This study synthesized a series of methoxystilbazolium analogues with ꢀ-conjugation extended by attaching a
fused aromatic ring, i.e., 6-styrylisoquinolinium and 4-[2-(2-naphthyl)ethenyl]pyridinium derivatives with methoxy sub-
stituents. We evaluated their transition energies (Eegs) and second-order hyperpolarizabilities (ꢁs) experimentally using
their absorption spectra and a hyper-Rayleigh scattering measurement, respectively. Subsequently, we calculated ꢁs us-
ing the MOPAC PM3 method. These values were compared with those of 4-[4-(4-methoxyphenyl)-1,3-butadienyl]pyri-
dinium derivative, which is a stilbazolium analogue with ꢀ-conjugation that is simply extended by an increase of the
double-bond number between two aromatic rings. This study clarified that the fused-ring systems possess large ꢁs, ir-
respective of their relatively short absorption wavelengths, compared to the double-bond elongation system.
Organic materials have been extensively investigated con-
between the calculated and experimental ꢁ values, the relative
order of the values shows good agreement. The microscopic ꢁ
value of organic molecules can be approximately described by
the two-level model, in which the ground and first excited
states determine the electronic properties of the molecule. In
cerning their large nonlinear optical (NLO) properties and ul-
trafast response times compared with inorganic materials and
semiconductors. Those special characteristics are attributable
4
1
to their ꢀ-electron systems. Their magnitude of second-order
optical nonlinearities is indicated by a second-order hyperpo-
this model, the ꢁ value is described as
larizability (ꢁ) at the molecular level and a second-order
Eeg fꢀꢃeg
ð2Þ
NLO susceptibility (ꢂ ) at the molecular aggregate level.
ꢁ /
;
2
ð1Þ
2
2
2
2
2
ð2Þ
ðEeg ꢁ h ! ÞðEeg ꢁ 4h ! Þ
To obtain materials with a large ꢂ , their component mole-
cules should have a large ꢁ value and be aligned in a noncen-
trosymmetric orientation. The ꢁ value of molecules can be es-
timated using various quantum chemical calculations. The ꢁ
value can also be evaluated experimentally using the elec-
tric-field-induced second-harmonic generation (EFISH) meth-
od or the hyper-Rayleigh scattering (HRS) method.3 The
HRS method is especially effective for ꢁ-value evaluation of
ionic and non-dipolar species. Although some differences exist
in which Eeg is the transition energy from the ground state to
the first excited state, ꢀꢃeg is the difference in the dipole mo-
ments between the ground and first excited states, f is the os-
cillator strength of the transition, and ! is the input laser fre-
quency. Equation 1 implies that molecules with donor and ac-
ceptor groups connected by ꢀ-conjugated systems tend to have
2
a large ꢁ because of an enhanced ꢀꢃ . For that reason, many
eg
ꢀ-conjugated organic compounds have been studied using
both theoretical and experimental methods.
Among organic materials, ionic ꢀ-conjugated com-
pounds,5,6 such as 4-{[2-(4-dimethylamino)phenyl]ethenyl}-
1
y Present address: Photonics Research Institute, National Institute
of Advanced Industrial Science and Technology, 1-1-1 Higashi,
Tsukuba 305-8565
-methylpyridinium p-toluenesulfonate (DAST),7,8 have at-
tracted great interest in the field of second-order NLO materi-
als because of their several advantages of use in their crystal-
line form. Those attributes include crystal-structure controlla-
bility by changing the counter ion, as well as a high hardness
and melting point that are attributable to the Coulombic inter-
yy Present address: Technical Institute of Physics and Chemistry,
Chinese Academy of Sciences, Jia No. 3, Datun-lu, Chaoyang,
Beijing 100101, P. R. China
5
yyy Present address: Department of Polymer Science and Engi-
neering, Faculty of Engineering, Yamagata University,
4-3-16 Jonan, Yonezawa 992-8510
action together with the van der Waals interaction, and a large
9
ꢁ
DAST, which was first discovered by our group, and then re-
because of charged ꢀ-conjugation systems. In particular,
7
yyyy Present address: NanoMaterials Laboratory, National Insti-
8
tute for Materials Science, 3-13 Sakura, Tsukuba 305-0003
ported by S. R. Marder et al. as a second-order NLO material,
shows a very large second-order NLO coefficient (d) and an
electro-optic (EO) coefficient (r): d11 of 330 pm/V at 1907
yyyyy Present address: Planning Headquarters, National Institute
of Advanced Industrial Science and Technology, 1-3-1
Kasumigaseki, Chiyoda-ku, Tokyo 100-8921
10
11
nm and r11 of 160 pm/V at 820 nm. Crystal-growth proce-
Published on the web January 13, 2005; DOI 10.1246/bcsj.78.180

K. Tsuji et al.
Bull. Chem. Soc. Jpn., 78, No. 1 (2005)
181
dures of DAST with higher optical quality and larger size are
being investigated, because DAST is a superior crystalline
compound for EO device applications.12 Recently, DAST has
also been acknowledged as being an efficient THz-wave gen-
erator using difference-frequency generation.13 Nevertheless,
it is still necessary to enhance the second-order NLO proper-
ties so that they will be superior to those of DAST. Such an
enhancement is an interesting subject for future study.1
Our investigation by a semiempirical calculation has re-
vealed two strategies to attain large second-order NLO proper-
ties for the DAST analogues.14 One is extended ꢀ-conjugation
of stilbazolium derivatives through increasing the number of
double bonds between two aromatic rings. In this approach,
large ꢁ values were obtained, but the absorption maximum
tended to extend to longer wavelengths. The other strategy is
elongated ꢀ-conjugation by fused aromatic rings, such as
naphthyl and isoquinolium groups, instead of phenyl and pyri-
dinium groups, respectively. In this case, we expected that
these compounds would show a blue shift of the absorption
maximum wavelength (ꢄeg), even though the compounds have
similar ꢁ values in the double-bond extension system. The de-
sign of molecules having both a large ꢁ value and a short ꢄeg
presents a difficult trade-off. Therefore, the second approach
seemed to be worth investigating, starting from the synthesis
of compounds.
quinoline (5), as precursors. The HRS measurements of these
compounds seemed to be possible using a conventional
Nd:YAG laser because of their blue-shifted absorption cutoff
wavelengths (ꢄcutoffs) in comparison with those of dimethyl-
amino derivatives, such as DAST.
Results and Discussion
4,15
Chromophore Preparation. The preparation of stilbazo-
lium analogues with iodide anion 1–3 is shown in Fig. 2. Chro-
mophores 1 and 2 were synthesized through a condensation re-
action of 1,4-dimethylpyridinium iodide (7), and the corre-
sponding aldehyde with piperidine as a base catalyst in the
same manner as DAST preparation. In the case of 1, the reac-
tion gave complicated products when methanol was used as
the reaction solvents, and the isolation of 1 was troublesome.
On the other hand, the reaction in ethanol–acetone afforded
1 as brownish-yellow needles without a difficult purification
process because of the decreased solubility of 1 in the solvent.
Regarding chromophore 2, crystals including one water mole-
cule per ion pair were obtained as hygroscopic yellowish-
orange needles through recrystallization of the precipitates,
which were obtained from the methanolic reaction mixture.
Water-containing crystals were changed into absolute crystals
through recrystallization from acetone–ethanol under dried
condition. To prepare 3, 5 was first synthesized according to
published references.1
8–20
This study prepared methoxy-substituted stilbazolium ana-
logues 1 with the conjugated double-bond extension, 2 and
That is, Schiff base 8 was treated
with acid to give 5. 2,6-Dimethylisoquinolinium iodide (6)
was prepared by the reaction of 5 and methyl iodide in quan-
titative yield. Under the same conditions as for the preparation
of 1 and 2 using piperidine in methanol or ethanol, the desired
3 was not obtained from 6 and p-anisaldehyde; the starting ma-
terials were almost entirely recovered. The reaction of 6 and
the aldehyde in the presence of pyrrolidine,21 instead of piper-
idine in ethanol under reflux, gave 3 as a brownish-yellow
powder that was inferred to contain one water molecule per
ion pair. Their structure and composition were identified by
3
, with the extended ꢀ-conjugation by a fused aromatic ring
and the original salt 4, as shown in Fig. 1. Although 1 and 2
were prepared in a previous study,16 their detailed procedures
of synthesis have not been reported. Isoquinolinium derivative
3
were compared with those of the simple stilbazolium deriva-
was synthesized for the first time. Their absorption spectra
1
1,17
tive 4,
and their second-order NLO properties are dis-
cussed herein based on experimental and theoretical studies us-
ing HRS measurements and a semiempirical MO calculation,
respectively. The HRS measurements of salts of 1 through 3
using an external reference method have not been reported.
These salts have iodide with ꢁ ¼ 0 as a counter anion. For that
reason, only the cation parts contribute to showing HRS sig-
nals. The MO calculation was extended to several geometries
in this work to show a comparison of the experimental quanti-
ties in solution. We chose methoxy derivatives that were all
obtainable from commercial reagents, except 6-methyliso-
1
H NMR, IR, and elemental analysis. Furthermore, IR, ele-
mental analysis, and DSC measurements were used to confirm
whether water was contained in their crystals or not. In a fol-
lowing investigation, 1 and 2 without water and 3 including
water were used.
Absorption Spectra. UV–visible absorption spectra of
chromophores 1–3 in methanol were measured (Fig. 3). The
ꢄ
egs for 1–3 were 411, 397, and 396 nm, respectively. These
−
−
I
I
+
N
+
Me
Me
N
c
c
e
a
Me
f
a
Me
d
d
1
O
b
2
O
b
−
−
I
I
Me
+
N
Me
+
N
c
c
e
a
Me
a
Me
f
d
d
O
b
O
b
3
4
Fig. 1. Structure of stilbazolium analogues investigated in this study. Roman letters indicate atom positions as a reference for
Table 2.

1
82 Bull. Chem. Soc. Jpn., 78, No. 1 (2005)
Stilbazolium Analogues as NLO Chromophores
−
I
OHC
NH
+
Me
N
Me
+
+
OMe
1
EtOH−Acetone, rt
44%
7
OHC
NH
7
2
MeOH, rt
OMe
62%
EtO
EtO
OEt
Me
CHO +
OEt
N
Toluene, reflux
H N
2
Me
quant.
8
Me
Me
H SO / P O
MeI
2
4
2
5
−
+
I
N
DME, rt
N
1
70 °C
Me
2
1%
98%
6
5
NH
6
+
OHC
OMe
3
EtOH, reflux
6
7%
Fig. 2. Synthetic procedure for stilbazolium analogues.
Table 1. Experimental ꢁ (ꢁ0,expt) and Eeg (Eeg,expt) Values
of Stilbazolium Analogues 1–4
0
ꢁ30
Compound
ꢁ0,expt/10
esu
Eeg,expt/eV
1
2
3
4
370
330
350
3.02
3.12
3.13
aÞ
aÞ
140
3.25
a) From Ref. 23.
were split in a complex fashion. The ꢄcutoffs of 1–3 were
22, 499, and 497 nm, respectively; the ꢄcutoffs of 2 and 3
are also more blue-shifted than those of 1.
5
Hyperpolarizability. Using the HRS method, the experi-
mental ꢁ values (ꢁobs) of 1–3 at 1064 nm in methanol were
ꢁ
30
ꢁ30
evaluated as 1090 ꢂ 10
esu, 870 ꢂ 10
esu, and 900 ꢂ
ꢁ
0
30
1
esu, respectively. No absorption occurred at 532 nm
Fig. 3. UV–visible absorption spectra of stilbazolium
analogues 1, 2, and 3 in methanol.
for these three compounds in methanol. For that reason, the ef-
22
fect from two-photon fluorescence, which enhances the appa-
rent signal intensity at the HRS wavelength, was negligibly
small. Therefore, we simply estimated the ꢁ0,expt values—
experimental ꢁ at zero frequency—from the ꢁobs values using
the two-level model (see Eq. 3 in the Experimental section).
Table 1 summarizes these values. For a comparison, data for
the simple stilbazolium iodide 423 were also added in addition
to data for 1–3. Figure 4 shows the relation between their val-
ues of ꢄeg and ꢁ0,expt. The points of 2 and 3 are in the upper
area of the straight line through the points of 1 and 2. Our pre-
vious study concerning the double-bond extension system be-
tween two aromatic rings of DAST showed that the relation of
values can be converted directly into experimental transition
energies from the ground to the excited states (Eeg) of the stil-
bazolium cation, Eeg,expt (Table 1). As anticipated by the calcu-
1
4
lation results, ꢀ-conjugation elongation using fused rings
was confirmed to shift ꢄeg to shorter wavelengths than in the
case of ꢀ-conjugation elongation by increasing the double-
3
ꢁ1
bond number. The " values of 1–3 were 34100 dm mol
ꢁ
1
3
ꢁ1
ꢁ1
3
ꢁ1
ꢁ1
cm , 20300 dm mol cm , and 22800 dm mol cm
and those of 2 and 3 were smaller than that of 1 by about
0–67%. Figure 3 shows that it was characteristic that the ab-
,
6
24
sorption bands of 2 and 3, constituted by fused aromatic rings,
were slightly broad, indicating that their molecular orbitals
the calculated ꢁ at zero frequency (ꢁ0,calc) and the measured
eg in methanol25 was almost linear up to the compound with a
ꢄ

K. Tsuji et al.
Bull. Chem. Soc. Jpn., 78, No. 1 (2005)
183
The HRS method was performed in methanol. Therefore, the
obtained ꢁ values were considered to be the average ones
for several conformers, which are rotation isomers surrounding
C–C single bonds. In the case of non-fused-ring systems, such
as 1 and 4, only the methoxy group rotation can generate con-
formers. On the other hand, for 2 and 3, belonging to the fused-
ring system, rotations about the single bond between the C–C
double bond and a fused ring (naphthyl or isoquinolinium
group) are also possible to give conformers with minimum en-
ergy. Table 2 lists their respective ꢁ0,calc values, calculated Eeg
(
Eeg,calc), and calculated dipole moment in the ground state
(
ꢃ ) of these conformers, together with their calculated heats
g
of formation (ꢀH). In that table, angles ꢅ and ꢆ are defined to
be dihedral angles of Ca–Ob–Cc–Cd and Ca–Ob–Ce–Cf, re-
spectively, where the subscripts of the atoms indicate atom po-
sitions in the cations, as shown in Fig. 1. The differences be-
tween the ꢀH values of the conformers of each ionic species
are very small. Consequently, all of the conformers can exist in
methanol. In addition, the physical quantities of these species
should be the numerical average of the conformers. However,
it is noteworthy that the methoxy group rotation shows almost
Fig. 4. Experimental ꢁ at zero frequency (ꢁ0,expt) vs ab-
sorption maximum wavelength (ꢄeg). Squares are for
fused-ring system; circles are for a non-fused-ring system.
Numbers in the figure correspond to compounds in Fig. 1.
The dashed line shows a hypothetical linear relation for
the non-fused-ring system (see text).
no effect on ꢁ0,calc, Eeg,calc, and ꢃ . Even for rotation of the
g
fused-ring group, the decrease in the ꢁ values was calculated
to be less than 6%. The differences of Eeg,calc and ꢃ among
g
double-bond number of four. Applying the linear relationship
between ꢄeg and ꢁ0,expt, the hypothetical compound, which be-
these conformations are either nonexistent or less than those
of ꢁ0,calc. These results indicate that the ꢁ0,calc values for those
conformers with the lowest energy in Table 2 are useful as rep-
resentative values for a comparison with the ꢁ0,expt values in
Table 1. The ratios of ꢁ0,expt=ꢁ0,calc for 1–4 are 1.4, 1.7, 2.0,
and 1.1, respectively. Because the ratios of 2 and 3 were found
to be larger than those of 1 and 4, peculiar effects may exist for
ꢁ in the fused-ring system regarding methanol solvation.
Moreover, such effects may not have been accounted for
in the calculations. On the other hand, the ratios of
Eeg,expt=Eeg,calc were almost constant, around 1.1–1.2.
longs to a double-bond extension system and has ꢁ of around
0
ꢁ30
3
40 ꢂ 10
esu, should have a ꢄeg of about 405 nm. Accord-
ingly, for extended ꢀ-conjugation systems with fused aromatic
rings, such as 2 and 3, we clarified that their ꢄeg values were
about 10 nm shorter than those of a double-bond extension sys-
tem having the same ꢁ value.
The relationship between the molecular structures obtained
from the calculation and the calculated physical quantities was
investigated to compare these experimental values with the
calculated ones. We obtained several optimized structures with
þ
þ
Conclusion
the minimum energy for cations 1 –4 : all of these structures
are planar, including two aromatic rings connected to the dou-
ble bond and oxygen and carbon atoms of the methoxy group.
This study synthesized novel methoxy-substituted stilbazo-
lium analogues 1–3. Their second-order NLO properties were
þ
þ
Table 2. Calculated ꢀH, ꢁ (ꢁ
Whose Structures Are Expressed by the Dihedral Angles ꢅ and ꢆ
), Eeg (Eeg,calc), and ꢃ Values of Stilbazolium Cation Conformers 1 –4 ,
0
0,calc
g
aÞ
ꢃ
ꢃ
ꢁ1
ꢁ30
esu
Cation
þ
ꢅ/
179.9
.0
179.9
ꢆ/
ꢀH/kJ mol
ꢁ0,calc/10
Eeg,calc/eV
ꢃ /Debye
g
1
—
—
788.27
788.60
266
264
2.51
2.51
17.60
17.86
0
þ
2
180.0
0.9
180.0
0.0
806.59
805.80
806.88
804.08
218
211
205
199
2.58
2.60
2.58
2.60
18.79
18.99
18.77
18.62
0
0
.8
.1
1
79.9
þ
3
180.0
179.9
0.0
180.0
0.0
799.52
799.86
799.69
800.02
176
174
167
166
2.76
2.76
2.75
2.74
17.29
17.60
17.11
17.16
0
0
.0
.0
1
80.0
180.0
.1
þ
4
—
—
731.95
732.24
135
133
2.69
2.69
13.59
13.75
0
a) Angles ꢅ and ꢆ are dihedral angles of Ca–Ob–Cc–Cd and that of Ca–Ob–Ce–Cf, respectively. See Fig. 1
for reference on atom positions.

1
84 Bull. Chem. Soc. Jpn., 78, No. 1 (2005)
Stilbazolium Analogues as NLO Chromophores
investigated and their absorption spectra in methanol were
measured. Thereby, we clarified that the ꢄegs of extended ꢀ-
conjugation compounds 2 and 3 with fused aromatic rings,
such as isoquinolinium and naphthyl groups, became shorter
than that of double-bond extension compound 1. For methoxy-
stilbazolium analogues 1–3, the ꢁ values in methanol were
evaluated experimentally using the HRS method. Subsequent-
ly, they were compared with the calculated ones using a semi-
empirical MO method. The relationship between their ꢄeg and
7.75 (1H, dm, J ¼ 15:3 Hz), 8.00 (2H, d, J ¼ 6:8 Hz), and 8.61
(2H, d, J ¼ 6:8 Hz).
4-[2-(6-Methoxy-2-naphthyl)ethenyl]-1-methylpyridinium
Iodide (2): Piperidine (5 drops) was added to a solution of 7
(
8
2.01 g, 8.5 mmol) and 6-methoxy-2-naphthaldehyde (1.58 g,
3
.5 mmol) in methanol (40 cm ) at room temperature. After stir-
ring for 4.5 h, piperidine (5 drops) was added again. The mixture
was stirred for 3 days. The resulting precipitate was then collected
by filtration and purified by recrystallization from methanol to
obtain 2 xH2O (2.12 g, ca. 58%), where x was determined to be
ꢄ
ꢁ0,expt
showed that extended ꢀ-conjugation systems with fused
about 1.5 by microanalysis. Anhydrous 2 was obtained by recrys-
tallization from the acetone–ethanol mixture. Yellow needles, mp
aromatic rings had a shorter ꢄeg than a double-bond extension
system when compared at the same ꢁ value. Namely, the fu-
sion of aromatic rings to stilbazolium analogues is effective
to realize chromophores with a large ꢁ value within an up-
per-limited absorption wavelength. The counter-anion ex-
change of 1 and 2 from iodide to p-toluenesulfonate was found
to give second-order NLO active crystals, with the d values ex-
pected to be comparable to those of DAST.16 Current studies
are pursuing the crystal growth of these salts and the explora-
tion of more efficient noncentrosymmetric crystal structures
for methoxystilbazolium analogues 1–3.
ꢃ
2
44.5–245.5 C (Found: C, 56.48; H, 4.51; N, 3.29; I, 31.50%.
Calcd for C19H18INO: C, 56.59; H, 4.50; N, 3.47; I, 31.47%);
ꢁ1
IR (KBr) ꢈmax/cm 3029, 2938, 1646, 1613, 1561, 1520, 1482,
1
395, 1266, 1221, 1192, 1171, 982, 849, 808, and 509; UV
(
MeOH) ꢄmax/nm 227 (log " 4.70), 274 (4.19), and 397 (4.31);
H NMR (400 MHz, CD3OD) ꢇ 3.94 (3H, s), 4.29 (3H, s), 7.19
1H, dd, J ¼ 9:0, 2.4 Hz), 7.29 (1H, d, J ¼ 2:4 Hz), 7.46 (1H,
1
(
d, J ¼ 16:3 Hz), 7.83 (1H, d, J ¼ 8:8 Hz), 7.83 (1H, d, J ¼ 9:0
Hz), 7.88 (1H, dd, J ¼ 8:8, 1.7 Hz), 8.05 (1H, d, J ¼ 16:3 Hz),
8.08 (1H, s), 8.15 (2H, d, J ¼ 6:8 Hz), and 8.67 (2H, d, J ¼ 6:8
Hz).
6
prepared quantitatively from p-tolualdehyde and 2-aminoacetalde-
-Methylisoquinoline (5): Schiff base 8 (10.0 g, 43 mmol),
Experimental
General. The melting points were measured using a Yanaco
1
hyde diethyl acetal in toluene under reflux,18 was added dropwise
3
MP-500 micro melting-point apparatus without any correction. H
to a mixture of conc. H2SO4 (20 cm ) and diphosphorus pentaox-
and 13C NMR spectra were measured with a spectrometer (JNM-
LA400; JEOL). H and 13C NMR chemical shifts were expressed
as ꢇ down-field from internal tetramethylsilane. IR spectra were
recorded on a spectrometer (FTIR-8100M; Shimadzu Corp.). Mi-
croanalyses were performed at the Microanalytical Room of Insti-
tute for Chemical Reaction Science, Tohoku University. UV–
visible spectra were measured with a spectrophotometer (V-570;
ide (12.0 g, 85 mmol) at 170 C under nitrogen and heated for 30
ꢃ
1
min.19 The mixture was cooled to room temperature and then
poured into an aqueous KOH solution to become basic. The prod-
ucts were extracted several times with ether, washed with saturat-
ed NaCl solutions, and dried over Na2SO4. After removal of the
solvent, the residue was subjected to column chromatography
(ether) to give 1.31 g (21%) of 5. Pale cream scales (ether), mp
ꢁ
5
ꢃ
20
ꢃ
Jasco Inc.). Methanol solutions of about 1 ꢂ 10 M (1 M ¼
87.0–88.5 C (lit. 88.5–89.5 C) (Found: C, 83.60; H, 6.37; N,
9.28%. Calcd for C10H9N: C, 83.88; H, 6.34; N, 9.78%); IR
ꢁ
1
1
mol dm ) were used to measure ꢄeg. Methanol solutions of
about 1 ꢂ 10ꢁ M were used to determine ꢄcutoff corresponding
4
(KBr) ꢈmax/cm
1495, 1399, 1385, 1360, 1275, 1217, 1044, 1028, 970, 957, 891,
839, 801, 777, 646, and 475; H NMR (400 MHz, CDCl3) ꢇ
ꢁ1
3056, 3031, 3006, 2975, 2942, 1630, 1582,
to the wavelength at which the absorbance was less than 10 3.
DSC measurements were made on an instrument (DSC 8240B;
Rigaku Corp.) at a heating rate of 10 K/min.
ꢁ
1
2.56 (3H, s), 7.44 (1H, dd, J ¼ 8:3, 1.5 Hz), 7.57 (1H, d, J ¼
5:8 Hz), 7.60 (1H, br s), 7.87 (1H, d, J ¼ 8:3 Hz), 8.48 (1H, d, J ¼
5:8 Hz), and 9.19 (1H, s); 13C NMR (100 MHz, CDCl3) ꢇ 21.65,
119.58, 124.96, 126.76, 126.95, 129.10, 135.65, 140.25, 142.69,
and 151.70.
The reagents and solvents were purchased from commercial
suppliers, and were used without further purification. Column
chromatography was carried out using silica gel (Wakogel C-
3
00; Wako Pure Chemical Industries, Ltd.). 1,4-Dimethylpyridi-
nium iodide (7) was synthesized according to a procedure that
was reported earlier.26
2,6-Dimethylisoquinolinium Iodide (6): Methyl iodide (5.3
3
cm , 85 mmol) was added to a solution of 5 (8.07 g, 56 mmol)
3
Synthesis. 4-[4-(4-Methoxyphenyl)-1,3-butadienyl]-1-meth-
ylpyridinium Iodide (1): Piperidine (20 drops) was added to a
solution of 1,4-dimethylpyridinium iodide (7) (4.01 g, 17.0 mmol)
and 4-methoxycinnamaldehyde (3.17 g, 17.0 mmol) in acetone
in 1,2-dimethoxyethane (55 cm ) at room temperature. The mix-
ture was stirred for 2 days. The resulting precipitate was then col-
lected by filtration to obtain 6 (15.7 g, 98%). Pale yellow needles
ꢃ
(dimethoxyethane–methanol), mp 199.0–200.0 C (Found: C,
46.20; H, 4.09; N, 4.63; I, 44.60%. Calcd for C11H12IN: C,
3
3
(
25 cm ) and ethanol (5 cm ) at room temperature. The mixture
ꢁ1
was stirred overnight. The resulting precipitate was then collected
by filtration and purified by recrystallization from an ethanol–ace-
tone mixture to obtain 1 (2.87 g, 44%). Brownish yellow needles,
46.34; H, 4.24; N, 4.91; I, 44.51%); IR (KBr) ꢈmax/cm 2977,
1644, 1611, 1512, 1435, 1397, 1370, 1358, 1285, 1188, 1167,
1
831, 820, and 635; H NMR (400 MHz, CD3OD) ꢇ 2.71 (3H, s),
ꢃ
mp 224.5—225.5 C (Found: C, 53.72; H, 4.72; N, 3.52; I,
4.50 (3H, s), 7.92 (1H, dd, J ¼ 8:5, 1.5 Hz), 8.09 (1H, br s),
8.34 (1H, d, J ¼ 8:5 Hz), 8.34 (1H, d, J ¼ 6:8 Hz), 8.51 (1H,
dd, J ¼ 6:8, 1.2 Hz) and 9.74 (1H, br s).
3
3
1
8
4
3.28%. Calcd for C17H18INO: C, 53.84; H, 4.78; N, 3.69; I,
ꢁ
1
3.46%); IR (KBr) ꢈmax/cm 3033, 3007, 1642, 1588, 1557,
509, 1470, 1291, 1252, 1190, 1175, 1146, 1046, 1007, 862,
12, and 515; UV (MeOH) ꢄmax/nm 218 (log " 4.44), 268 (sh,
6-[2-(4-Methoxyphenyl)ethenyl]-2-methylisoquinolinium Io-
dide (3): Pyrrolidine as a catalyst21 (3 drops) was added to a
1
3
.21), 281 (4.24), and 411 (4.53); H NMR (400 MHz, CD3OD)
solution of 6 (0.45 g, 1.6 mmol) and p-anisaldehyde (0.23 cm ,
3
ꢇ 3.83 (3H, s), 4.26 (3H, s), 6.81 (1H, d, J ¼ 15:3 Hz), 6.95
2H, d, J ¼ 8:8 Hz), 7.0–7.1 (2H, m), 7.53 (2H, d, J ¼ 8:8 Hz),
1.9 mmol) in ethanol (3.6 cm ) under reflux. Then reflux was con-
tinued for 3 h. Again, pyrrolidine (3 drops) was added to the mix-
(

K. Tsuji et al.
Bull. Chem. Soc. Jpn., 78, No. 1 (2005)
ꢁiꢃ ¼ ꢁ ꢃ þ ꢁ ꢃ þ ꢁ ꢃ ;
185
X
ture. After being refluxed for 3 h, the reaction mixture was cooled
to room temperature. The resulting precipitate was collected by
filtration to obtain 3 H2O (0.44 g, 67%). Brownish-yellow micro-
needles (acetone–ethanol), mp 222.0–222.5 C (Found: C, 54.02;
H, 4.41; N, 3.19; I, 30.43%. Calcd for C19H20INO2: C, 54.17; H,
ð5Þ
i
x
x
y
y
z
z
i
ꢄ
ꢃ
and
X
ꢁi
¼
ꢁ :
ð6Þ
ijj
ꢁ
1
4
1
1
.79; N, 3.32; I, 30.12%); IR (KBr) ꢈmax/cm 3004, 2930, 1647,
619, 1599, 1574, 1509, 1456, 1420, 1402, 1266, 1258, 1244,
169, 1024, 959, 830, 650, and 556; UV (MeOH) ꢄmax/nm 222
j
This ꢁ value is the vector component in the gas phase at zero fre-
quency, and is abbreviated as ꢁ0,calc.
1
(
(
8
log " 4.66), 247 (4.49), 302 (sh, 4.04), and 396 (4.36); H NMR
400 MHz, CD3OD) ꢇ 3.85 (3H, s), 4.47 (3H, s), 7.00 (2H, d, J ¼
The transition energy (Eeg) in gas phase was also calculated
using a multielectron configuration interaction (MECI) treatment,
performed by the MECI keyword, as implemented in the MOPAC
program. Keywords of 1SCF and C.I. ¼ 5 were added to consider
one hundred microstate configurations between the highest three
occupied and the lowest three unoccupied molecular orbitals.
SINGLET and GEO-OK were also used as keywords only for
calculating the singlet states of interest, and for overriding the
geometric safety checks, respectively.
:9 Hz), 7.36 (1H, d, J ¼ 16:3 Hz), 7.66 (2H, d, J ¼ 8:9 Hz), 7.68
(
(
1H, d, J ¼ 16:3 Hz), 8.25 (1H, s), 8.32 (1H, d, J ¼ 6:8 Hz), 8.33
2H, m), 8.46 (1H, dd, J ¼ 6:8, 1.5 Hz), and 9.62 (1H, s).
HRS Measurement. The ꢁ values of compounds 1, 2, and 3
in methanol solution were evaluated experimentally using the
HRS technique. The fundamental beam at 1064 nm was obtained
from a Q-switched Nd:YAG laser (LS-412; Spectron Laser Sys-
tems, Ltd.) with a 10-ns pulse width and about a 10-mJ pulse en-
ergy. The beam was irradiated on a small quartz cell containing a
methanol solution. The HRS experimental set-up and details to
The authors wish to thank Mr. Noboru Fukasaku and Mr.
Hiroaki Yokota (Daiichi Pure Chemicals Co., Ltd.) for collab-
oration in the synthesis of 6-methylisoquinoline. This research
was partially supported by New Energy and Industrial Tech-
nology Development Organization (NEDO) as a Regional
Consortium Project.
3
,17
obtain the ꢁ value have been described in previous papers.
p-Nitroaniline was used as the external reference with ꢁ ¼ 34:5 ꢂ
ꢁ
30
4
1
0
esu at 1064 nm in methanol. In the external reference
method,27 the ꢁ values for the samples were evaluated using
ꢀ
ꢁ
as
ar
2
2
ꢁs ¼ ꢁr
;
ð2Þ
References
in which subscripts s and r indicate the values for the sample and
the reference, respectively. ꢁ denotes the second-order hyperpo-
larizabilities at the fundamental wavelength; a is the slope of
the line drawn for the quadratic coefficient GB2 vs Nsolute (the
number density of the sample or reference in a methanol solution).
Then, the ꢁ value for the sample by the HRS method (ꢁobs) was
corrected for any resonance effects using the two-level model to
obtain those at zero frequency, namely the static ꢁ (ꢁ0,expt). The
1
‘‘Nonlinear Optical Properties of Organic and Polymeric
Materials (ACS Symp. Ser., 233),’’ ed by D. J. Williams, Ameri-
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ꢁ0,expt
is given by
"
#"
#
ꢀ
ꢁ
ꢀ
ꢁ
2
2
ꢄ
eg
ꢄ
eg
ꢁ0,expt
¼ ꢁobs 1 ꢁ
1 ꢁ 4
;
ð3Þ
ꢄ
ꢄ
2
1975).
3
B. F. Levine and C. G. Bethea, J. Chem. Phys., 63, 2666
in which ꢄ is the fundamental wavelength of the laser light. The
concentrations of sample and reference solutions were changed
(
K. Clays and A. Persoons, Phys. Rev. Lett., 66, 2980
1
6
17
successively in the order of about 1 ꢂ 10 –1 ꢂ 10 molecules
(
(
1991); K. Clays and A. Persoons, Rev. Sci. Instrum., 63, 3285
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4
1977).
5
ꢁ3
19
19
ꢁ3
cm , and about 1 ꢂ 10 –5 ꢂ 10 molecules cm , respectively.
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to remove dust particles.
J. L. Oudar and D. S. Chemla, J. Chem. Phys., 66, 2664
(
Semiempirical MO Calculation. The optimized molecular
conformations, transition energy (Eeg,calc), dipole moment in
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and Polymeric Materials (ACS Symp. Ser., 233),’’ ed by D. J.
Williams, American Chemical Society, Washington, D. C.
ground state (ꢃ ) and ꢁ (ꢁ
) values of compounds 1, 2, 3,
0,calc
g
2
8
and 4 were calculated using the PM3 method in the program sys-
tem MOPAC 94, provided on a CAChe WorkSystem (ver. 4.1.1;
Sony/Tektronix Corp.).
(
1983), p. 27.
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3
57, 393 (1992).
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7
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2
9
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3
ꢁ
¼ 5
ꢁ ꢃ ;
ð4Þ
i
i
kꢃk
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(
1
7