Novel azo octupoles with large first hyperpolarizabilities

Article abstract of DOI:10.1039/b300777d

Novel two-dimensional octupoles containing azo groups and their oligomers have been synthesized and their first hyperpolarizabilities were determined. The λ_max and β(0) values of azo octupoles are nearly the same regardless of the nature of the

Full text of DOI:10.1039/b300777d

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Novel azo octupoles with large first hyperpolarizabilities{
Myung Ja Lee,a Mingjun Piao,a Mi-Yun Jeong,a Sang Hae Lee,a Kyung Min Kang,a
Seung-Joon Jeon,a Tong Gun Limb and Bong Rae Cho*a
aMolecular Opto-Electronics Laboratory, Department of Chemistry and Center for
Electro- and Photo-Responsive Molecules, Korea University, 1-Anamdong, Seoul 136-701,
Korea. E-mail: chobr@korea.ac.kr
bDepartment of Physics, Korea University, 1-Anamdong, Seoul 136-701, Korea
Received 20th January 2003, Accepted 7th March 2003
First published as an Advance Article on the web 26th March 2003
Novel two-dimensional octupoles containing azo groups and their oligomers have been synthesized and their
first hyperpolarizabilities were determined. The lmax and b(0) values of azo octupoles are nearly the same
regardless of the nature of the bridge or the conjugation length. On the other hand, 1,3,5-tricyano-2,4,6-tris-
[4-(p-diethylaminostyryl)styryl]benzene has a larger b(0) value than the corresponding azo analogue probably
due to the more efficient conjugation ability of CLC compared with the NLN bond. The b(0)/MW of the
octupoles are larger than the corresponding dipoles, whereas those of the azo octupoles are comparable to
the latter. Also, retention of monomeric b(0) is observed in the octupolar oligomers.
moment. Accordingly, various derivatives of subphthalocyanine,
Introduction
truxenone, 1,3,5-tris[(p-styryl)phenyl]benzene, 1,3,5-tricyano-
2,4,6-tris(ethynyl)benzene, triphenylamine, 1,3,5-methoxy-
2,4,6-tris(styryl)benzene, 1,3,5-trinitro-2,4,6-tris(styryl)benzene,
1,3,5-tricyano-2,4,6-tris(styryl)benzene have been synthesized
and their structure–property relationships investigated.6,7
In view of the wide interest in dipolar azo compounds, it
seems worthwhile to synthesize the corresponding octupolar
molecules. It is expected that these molecules would exhibit
similar first hyperpolarizabilities to those of corresponding
octupoles containing CLC bonds. In addition, because the azo
compounds could be arranged along the long axis by using
optical and electrical alignment, it might be possible to utilize
the azo group to align them non-centrosymmetrically in the
bulk material to obtain significant second harmonic genera-
tion (SHG).8 Furthermore, these molecules may find useful
applications in optical devices, such as in optical memory,
optical display, and optical switching, that utilize the photo-
responsive azo group.9
In this work, we have synthesized a series of dipoles (1d,e),
and two-dimensional octupoles and oligomers containing azo
groups (2b–d, P1, and P2) and investigated their nonlinear
optical properties (Chart 1). We were interested in learning the
effects of (i) incorporating three units of dipolar molecules
(1a,d,e) into the octupolar structure (2a,d,e), (ii) successively
grafting azo groups at the periphery of 2a (2b–d), (iii) changing
the conjugation bridge from CLC to NLN (2d,e), and (iv) the
molecular weight of the oligomers (P1 and P2) on the linear
and nonlinear optical properties. The results of these studies
are reported here.
There is contemporary research interest in the synthesis of
efficient nonlinear optical (NLO) materials with large first
hyperpolarizabilities.1 Among the most extensively investi-
gated NLO chromophores are azobenzene derivatives.2 They
are relatively easy to synthesize and exhibit similar first hyper-
polarizabilities to those of corresponding stilbene derivatives.
Also, poled NLO polymers containing azobenzene moieties
have been shown to exhibit significant electro-optic coeffi-
cients. On the other hand, the dipolar character of these
molecules causes considerable drawbacks. Dipole–dipole inter-
actions favor anti-parallel arrangements of the chromo-
phores resulting in relaxation of the poled polymers and a
subsequent cancellation of the nonlinear response of bulk
materials. Moreover, the highly anisotropic structure of
electro-optic materials containing polar rod-like molecules
is not compatible with the polarization independent NLO
response required for devices to be inserted in optical tele-
communication systems.3
Recently, octupolar molecules with three-fold symmetry
have been developed as an alternative NLO chromophore.4
An advantage of such molecules in comparison to the dipo-
lar molecules is that the second harmonic response of the
octupoles does not depend on the polarization of the incident
light because they are more isotropic than the dipolar NLO
molecules.4d Secondly, there is a design strategy for the
synthesis of octupoles with large first hyperpolarizabilities.5
According to the VB-3CT model, the b values of two-
dimensional octupoles increase gradually with the extent of
charge transfer. Hence, the b values of such molecules could be
significantly enhanced by simultaneously increasing the donor–
acceptor strength, the p orbital energy, and the conjugation
length. Thirdly, two-dimensional octupoles have been shown
to be advantageous over dipolar systems with regard to the
formation of noncentrosymmetric crystals.6 Finally, electro-
optic materials containing octupolar molecules are less likely
to undergo relaxation due to the lack of a ground state dipole
Chart 1 X ~ Y ~ Z ~ Et2N (a); X ~ Y ~ Et2N, Z ~ NLN–C6H4-p-
NEt2 (b); X ~ Y ~ NLN–C6H4-p-NEt2, Z ~ NEt2 (c); X ~ Y ~ Z ~
NLN–C6H4-p-NEt2 (d); X ~ Y ~ Z ~ CHLCH–C6H4-p-NHex2 (e);
X ~ NLN–C6H4-p-NHex2, Y ~ NHex2, Z ~ –CH2CH2NMe2 (f);
X ~ NLN–C6H4-p-NHex2, Y ~ Z ~ –CH2CH2N(Me)- (g)
{Electronic supplementary information (ESI) is available: molar
absorptivity spectra of 1a,d,e, P1 and P2 in THF and plots of I2v vs.
number density for 1a,d,e and 2a,c,e in THF at 1064 nm. See http://
www.rsc.org/suppdata/jm/b3/b300777d/
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J. Mater. Chem., 2003, 13, 1030–1037
This journal is # The Royal Society of Chemistry 2003
DOI: 10.1039/b300777d

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Scheme 1 Reagents and conditions: (a) i) LDA/THF/278 uC; ii)
ArCHO (1.2 equiv.), RT, 1 day, 65–92%. (b) i) LDA/THF/278 uC;
ii) ArCHO (3.2 equiv.), RT, 1 day, 65%. (c) i) LDA/THF/278 uC; ii)
ArCHO (1.8 equiv.), RT, 1 day, 68–92%.
Scheme 2 Reagents and conditions: (a) i) LDA/THF/278 uC, 30 min;
ii) Hex2NPhCHO, RT, 1 day, 92%. (b) i) LDA/THF/278 uC, 30 min;
ii) Hex2NPhNLNPhCHO, RT, 1 day, 92%; iii) KF/DMF, 82%. (c) i)
CH2LC(Me)COCl/Et3N, 0 uC, 1 h, 50%; ii) AIBN/THF, 70 uC, 1 day,
55%; (d) i) LDA/THF/278 uC, 30 min; ii) Hex2NPhNLNPhCHO,
RT, 1 day, 87%; iii) KF/DMF, 72%. (e) 2,4-(NCO)2PhMe/DMSO/
MeCOiBu, 75%
Results and discussion
Synthesis
Dipolar molecules 1d,e were synthesized by the Horner–Wittig
reactions between 4-(diethoxyphosphorylmethyl)benzonitrile
and 4-(p-diethylaminophenylazo)benzaldehyde or 4-(p-diethyl-
aminostyryl)benzaldehyde as described in the Experimental
section. Synthesis of octupolar molecules containing the azo
groups (2b–d) was accomplished by the same methods by using
1,3,5-tricyano-2,4,6-tris[(diethoxyphosphoryl)methyl]benzene
(A) and substituted benzaldehyde derivatives (Scheme 1). A
was prepared by the bromination of 1,3,5-tricyanomesitylene
followed by phosphorylation with P(OEt)3.6c 4-(p-Diethylamino-
phenylazo)benzaldehyde was prepared by the DIBAL-H
reduction of 4-(p-diethylaminophenylazo)benzonitrile, which
was obtained by the coupling of the p-cyanobenzene diazonium
ion with N,N-dialkylaniline. Condensation between A and
p-diethylaminobenzaldehyde or 4-(p-diethylaminophenylazo)-
benzaldehyde afforded the intermediates B and C in 65–92%
yields. Compound 2d was prepared in 65% yield by reacting
A with an excess amount of 4-(p-diethylaminophenylazo)-
benzaldehyde under the same conditions, whereas 2b,c were
synthesized from B or C and the appropriate benzaldehyde
derivatives. The structures of 1d,e and 2b–d were unambi-
guously confirmed by1H, and13C NMR, IR, and elemental
analysis.
then polymerized under typical free radical polymerization
conditions to afford P1. Oligomer P2 was obtained in 75%
yield from the reaction of tolylene-2,4-diisocyanate with E,
which was synthesized by the reaction between C’ and 4-(p-
dihexylaminophenylazo)benzaldehyde. The molecular weight
and polydispersity of these oligomers were determined relative
to a polystyrene standard by GPC using THF as the eluent.
The Mn of P1 and P2 are 3426 (PDI ~ 1.87) and 10253
(PDI ~ 1.47), respectively. These oligomers have rather small
molecular weights and contain approximately 3 to 9 octupolar
units within a molecule.
One-photon absorption spectra
Table 1 shows that lmax of 1a,d,e increases in the order 1a v
1e v 1d (see Fig. S1 in the supplementary information{). The
oscillator strengths, f, of 1a,d are similar, whereas that of 1e is
significantly larger.
Fig. 1 shows the molar absorptivity spectra for 2a–e. All of
the molecules exhibit maximum absorption peaks near 485 nm,
regardless of the nature of the bridge or the conjugation length.
This indicates that the successive grafting of phenylazo or
styryl groups at the periphery of 2a does not significantly
increase the charge transfer, probably because the structures
of 2b–e are distorted and so interrupt the effective conjuga-
tion. On the other hand, the higher energy band near 370 nm
To synthesize oligomer P1, D was prepared by successively
reacting B’ with p-dihexylaminobenzaldehyde and 4-(p-dihexyl-
aminophenylazo)benzaldehyde (Scheme 2). Reaction of D
with methacryloyl chloride produced a monomer, which was
Table 1 Linear and nonlinear optical properties of dipolar and octupolar molecules and their oligomers in THF
eb
n1/2
fd
be,f,g
b(0)f,g,h
byyy
a
c
f,i
Entry
Compound
lmax
1
2
3
4
5
6
7
8
9
10
1a
1d
1e
2a
2b
2c
2d
2e
P1
P2
398
464
416
481
484
485
485
480
485
474
38 400
3730
4720
4580
3700
4080
4560
5070
5400
4730k
4900k
0.62
0.63
1.1
1.7
1.5
130
824
457
1730
1580
1720
1840
2350
1320k
1320k
49
160
150
252
215
230
246
348
176k
218k
118j
386j
362j
408
30 700
55 800
103 000
82 800
69 200
90 900
102 000
97 100k
89 800k
1.4
2.0
399
564
2.3
2.0k
1.9k
aAbsorbance maximum in nm. bMolar extinction coefficient in mol L21 cm21. Band width at half-height in THF. dOscillator strength was esti-
c
f
mated from the relationship: f ~ 4.319 6 1029en1/2
.
eDetermined at 1064 nm. 10230 esu. gEstimated uncertainty, ¡15%. hCorrected at lA‘
using a three-level model (see ref. 4a). Calculated from the relationships vb2w ~ (6/35)bzzz and vb2w ~ (8/21)byyy for 1D and D3 chro-
i
2
2
j
mophores, respectively (see ref.12) . bzzz
.
kThe values are per octupolar unit in the oligomers.
J. Mater. Chem., 2003, 13, 1030–1037
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Fig. 1 Molar absorptivity spectra of 2a–e in THF.
Fig. 2 HRS and two-photon fluorescence spectra of 2d in THF excited
by 1064 nm laser photons. The spectrum was averaged over 200 laser
pulses at each wavelength while changing the wavelength in 0.1 nm
increments.
monotonically increases as the chromophore structure is
gradually changed from 2a to 2e, probably due to the
absorption by the additional phenylazo or styryl groups.
Note that the absorption spectra of 2d,e are very similar except
for the larger molar absorptivity of the latter. However, the
width of the absorption peak, i.e., n1/2, becomes increasingly
broader from 2a to 2e, probably because the number of
conformers increases with molecular size (Table 1). Also, the
oscillator strength calculated by the relationship f ~ 4.319 6
1029en1/2 increases in the order 2b,c v 2a v 2d v 2e. The
absorption spectra of P1 and P2 are nearly the same as that of
2b except for the slight bathochromic shift of the lmax of the
latter (Table 1 and Fig. S1). Similar blue shifts were observed
respectively, and G is a proportionality constant depending
upon the scattering geometry and the solvent environment of
the chromophore.
As shown in Figs. 2 and S2, all of the chromophores emitted
a sharp HRS signal at 532 nm along with the broad two-photon
fluorescence (TPF) when excited by 1064 nm laser photons.
They also have absorption bands at 532 nm (Figs. 1 and S1).
Therefore, corrections have been made for both TPF and
absorption to obtain the intensity of the second-harmonic light
actually generated.11a,b
To accurately determine the b values, the total HRS and
TPF intensity was measured by averaging 200 laser pulses
in the range of 528–536 nm. The fluorescence intensity was
subtracted from the total signal intensity to obtain the pure
HRS signal (Fig. 3b).11a The HRS intensity was further
corrected for the absorption by using eqn. (2),
in other polymers.11b,16a,16b Appreciable changes in the e, n1/2
and f values are noticable, indicating some interchromophore
interactions within the oligomers.
,
Comparison of the spectral data reveals that the lmax of
2a,d,e are red shifted by 83, 21, and 64 nm, respectively,
compared with 1a,d,e, indicating that the charge transfer (CT)
energy of the octupoles are significantly smaller than the
corresponding dipoles (Table 1). This might be due to the
fact that the former are not just three molecules of the latter
arranged in a symmetrical way but are an extension of the latter
by sharing a central phenyl group. Also, the oscillator strengths
increase by 2.7-, 3.3-, and 2.2-fold by the same variation of
the chromophore structure. It was previously reported that the
ratio between the oscillator strengths of dipolar and octupolar
molecules should be close to or smaller than 1 : 3, if there is
no or significant interactions between the dipolar units. The
observed ratios are in the range of 2–3, despite the significant
interactions between the subchromophores. Hence the pre-
sent results cannot be explained by the simple additivity rule.
Noteworthy is the significantly smaller charge transfer energies
and much larger oscillator strengths of the octupoles than
the corresponding dipoles.
I
2v(obs) ~ I2v(true)e2slN
(2)
where I2v(obs) and I2v(true) are the intensities of the second
harmonic light detected after absorption and that actually
generated, respectively, s ~ 1000eln(10)/NA, where NA is
Avogadro’s number and e is the molar absorptivity expressed
in units of M21 cm21, l is the path length of the scattering cell,
and N is the number density of the chromophore.11b
In Fig. 3, the corrected HRS intensities vs. Nc of compounds
First hyperpolarizabilities (b) of 1, 2, P1, and P2
The b values were measured at 1064 nm by the hyper-Rayleigh
scattering (HRS) method.10,11 The HRS signal intensities from
dilute solutions (6 6 1026–3 6 1023 M) of 1, 2, P1, and P2 in
THF were collected at 532 nm and the b values were calculated
by the external reference method using p-nitroaniline as the
reference.11c The data reported were averaged over 200 pulses
at each wavelength and the estimated uncertainty is ¡15%.
The HRS intensity of a very dilute NLO solution is given by
eqn. (1),
Fig. 3 Plot of I2v vs. number density for 2d in THF at 1064 nm. The
solid lines represent the linear squares fit through the experimental
data. Insets: (a) the same plot for p-nitroaniline; (b) HRS and TPF
spectrum of 2d (c ~ 4.25 6 1015 molecules mL21) obtained by
averaging 200 laser pulses in the range of 528–536 nm. The HRS
intensity was obtained by subtracting the TPF intensity from the total
signal intensity.
2
I2v ~ GIv2(Nsbs2 1 Ncbc )
(1)
where Ns and Nc are the number density of the solvent and
chromophore, respectively, bs and bc are the effective molecular
first hyperpolarizabilities of the solvent and chromophores,
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J. Mater. Chem., 2003, 13, 1030–1037

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2d and p-nitroaniline are plotted. The corresponding plots for
1a,d,e and 2a,c,e are depicted in Fig. S2 in the supplementary
information. {In the low concentration region, they are linear,
as expected from eqn. (1). The b values of the chromophores
were calculated using p-nitroaniline (bst ~ 21.4 6 10230 esu) as
the external reference.11c According to the external reference
method, b can be calculated by using eqn. (3),
respectively.12 The values are 3.5, 1.0, and 1.6 for 2a,d,e,
respectively. The values for 2a,e are much larger than those for
the triarylamine derivatives. Other groups and ourselves have
previously reported similar enhancements of hyperpolarizabil-
ity in octupolar molecules compared to their dipolar counter-
parts.7c–h However, in no case has such a large enhancement
been observed. On the other hand, the ratio for 2a is similar
to those of the triphenylamine derivatives.
As can be seen in Table 1, lmax increases by 83 nm and the
oscillator strength increases by 2.7-fold as the chromophore
structure is changed from 1a to 2a. Although it is not possible
to compare m12 of 2a and (m2–m1) of 1a with existing data, the
large ratio of byyy/bzzz ~ 3.5 calculated for 2a can be attributed
to the smaller CT energy and larger transition moment of 2a
than 1a (eqn. (4)). Similar but smaller changes in the lmax
(Dlmax ~ 64 nm) and oscillator strength (2.1-fold) are observed
on changing from 1e to 2e, hence a smaller ratio of 1.6 for 2e.
Since the oscillator strength increases by 3.2-fold from 1d to 2d;
the smallest ratio of 1.0 for 2d is probably due to the modest
decrease in the CT energy (Dlmax ~ 21 nm).
bc ~ bst (mc/mst)1/2
(3)
where bc and bst are the effective molecular hyperpolariza-
bilities for the chromophore and standard, respectively, and
mc and mst are the slopes of the plots in Fig. 3 for the
chromophores and the standard, respectively. The calculated
b values are summarized in Table 1.
The first hyperpolarizability of a D3 symmetric molecule can
be expressed by the three-level model (eqn. (4)),
1
ꢀ201ꢀ12
v201
v401
byyy
~
|
|
(4)
(v021{4v2)(v201{v2)
B
It is interesting to compare the b values of 2d,e. The value of
b for 2d is significantly smaller than for 2e, indicating that NLN
is not as efficient a conjugation bridge as CLC in the octupolar
molecules. Similarly, the first hyperpolarizabilities of ethylene
and azo bridged donor–acceptor dipoles were found to be
smaller than that of the CLC analogue.14 Since the CT energy
and ground state transition moment m01 of 2d,e are similar, this
result indicates that the transition moment m12 between the
excited states of 2d should be smaller than 2e. A plausible
explanation for this result might be that the azo group may
reduce the amount of charge transfer from the donor to the
acceptor, which would in turn decrease the state dipole moment
difference along the individual arms to attenuate m12 and b.
For practical applications, it is useful to graft the NLO
molecules into a polymer. An ideal approach would be to
design a polymer such that the monomeric NLO property is
maximally utilized. However, considering that the HRS of a
NLO chromophore is related to the fluctuations of molecular
orientation and local density, a polymeric environment is
expected to decrease the HRS intensity because the fluctuation
would be inhibited.11b On the other hand, the monomeric b
is significantly enhanced by vector addition in semi-rigid NLO
polymers such as helical poly(isocyanides) with azo dyes.15
Similar results were observed in polynorbonenes having
pendant chromophores, dendrimers containing a dipolar
azobenzene chromophore, and an octupolar ruthenium com-
plex, in which the chromophores are ordered in a semi-rigid,
optimized acentric organization, resulting in a coherent second
harmonic emission at the supramolecular level.16
where m01 is the transition moment between the ground and
degenerate first excited CT state, m12 is the transition moment
connecting these degenerate excited states, v01 is the CT energy
and v is the energy of the incident laser light.4a The equation is
identical to that of a two-level model of molecular nonlinearity
for the dipoles if m12 is substituted by (m2 2 m1), where m1 and
m2 are the dipole moments in the ground and in the first excited
CT state, respectively.13
Table 1 shows that the b(0) value increases as the conjuga-
tion length increases from 1a to 1d,e and remains the same for
1d,e (entries 1–3). When the chromophore structure is changed
from 1a to 1d, lmax increases by 66 nm without an appreciable
change in the oscillator strength, which is proportional to
the square of the transition moment (m012). Hence the 3-fold
increase in b(0) from 1a to 1d is primarily due to the smaller
CT energy. A similar increase in b(0) from 1a to 1e can be
attributed to both a smaller CT energy and a larger oscillator
strength. On the other hand, lmax decreases but the oscillator
strength increases by the change from 1d to 1e. Therefore, the
nearly identical b(0) values of 1d,e indicate that these two
opposing factors contribute to the b(0) values to similar
extents.
When the structure of the octupolar molecule is gradually
changed from 2a to 2d by successively grafting phenylazo
groups at the periphery of 2a, b(0) remains nearly the same
(entries 4–7). However, a further change to 2e results in a
remarkable increase in b(0) to 348 6 10230 esu, which is
comparable to the most efficient octupoles reported to date.{
Hence, if other applications that utilize azo groups are
excluded, azo octupoles 2b–d are inferior to 2a and 2e in
terms of b(0)/MW. Moreover, b(0) of 2a is 5-fold larger than
1a, whereas those of 2d,e are 1.5- and 2.3-fold larger than 1d,e,
indicating that the b(0)/MW value of 2a is larger than 1a but
those of 2d,e are inferior or comparable to 1d,e (entries 1 &
4, 2 & 7, 3 & 8).
Fig. 4 shows that the slope of the plot of I2v vs. number
density of the octupolar units for 2b is somewhat larger than
According to tensor addition calculations, the bxxy ~ 2byyy
value of a D3 symmetric molecule is 3/4 of the bzzz value of
a dipolar analogue if subchromophore interactions are negli-
gible.4b In the case of triarylamine derivatives, bzzz(dipole) :
b
comparison, the corresponding ratios for 2a,d,e have been
yyy(octupole) ratios of 0.94–1.0 have been reported.7f,g For
calculated by using the relationships vb2w ~ (6/35)bzzz
2
and vb2w ~ (8/21)byyy for 1D and D3 chromophores,
2
{The most efficient octupoles are 1,3,5-trimethoxy-2,4,6-tris{p-[2-(3-
dicyanomethylidene-5,5-dimethylcyclohex-1-enyl)vinyl]styryl}benzene
(lmax ~ 319 nm, b(0) ~ 163 6 10230 esu),7h 4,4’-bis(dibutylamino-
styryl)-2,2’-bipyridine Zn(II) complex (lmax ~ 466 nm, b(0) ~ 241 6
Fig. 4 Plots of I2v vs. number density for 2b, P1, and P2 in THF at
1064 nm. The solid lines represent the linear squares fit through the
experimental data.
10230 esu),4e and 1,3,5-tris(methylsufonylbistyryl)benzene (lmax
377 nm, b(0) ~ 510 6 10230 esu).7b
~
J. Mater. Chem., 2003, 13, 1030–1037
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those for P1 and P2. However, the calculated b(0) values of
these molecules are nearly the same within experimental error
(Table 1, entries 5, 9 and 10). The retention of monomeric b
noted in these oligomers can be attributed to the small change
in the fluctuation. Because only 3–9 units of 2b are con-
nected by the flexible linkers in these oligomers, the fluctuation
behavior of P1 and P2 is not expected to be very much different
from 2b, and hence there is little difference in HRS intensity.
Recently, Wang and co-workers reported nearly identical b
values for DR19 and its flexible polymer.11b We also reported
similar results in octupolar oligomers.7j Hence, the retention of
monomeric b seems to be a general phenomenon in flexible
polymers.
synthesis of 1d except that 4-(diethoxyphosphorylmethyl)-
benzonitrile and 4-(p-diethylaminostyryl)benzaldehyde were
used. Yield 53%; mp 271uC; IR (KBr, cm21) 2220 (CN);1H-
NMR (300 MHz, CDCl3) d 7.64 (d, 2H, J ~ 9.0 Hz), 7.58 (d,
2H, J ~ 9.0 Hz), 7.49 (s, 4H), 7.40 (d, 2H, J ~ 9.0 Hz), 7.21 (d,
1H, J ~ 16.5 Hz), 7.09 (d, 1H, J ~ 16.5 Hz), 7.07 (d, 1H, J ~
16.5Hz), 6.88 (d, 1H, J ~ 16.5 Hz), 6.86 (d, 2H, J ~ 9.0 Hz),
3.39 (q, 4H, J ~ 6.5 Hz), 1.19 (t, 6H, J ~ 6.5 Hz). Anal. Calcd
for C27H26N2: C, 85.68; H, 6.92; N, 7.40. Found: C, 85.65; H,
6.86; N, 7.28%.
Synthesis of azo octupoles (2b–d)
In conclusion, we have synthesized novel octupolar NLO
molecules and oligomers containing azo groups with large first
hyperpolarizabilities. The octupoles exhibit much larger b
values than the corresponding dipoles, probably due to smaller
CT energies and larger oscillator strengths. On the other hand,
azo octupole 2d has a signifcantly smaller b than the CLC
analogue 2e, indicating that the NLN bond is not such an
efficient conjugation bridge as the CLC bond in octupolar
molecules. Finally, retention of monomeric b is observed in
flexible polymers. These molecules may ultimately find useful
applications as electro-optic materials.
4-(p-Dialkylaminophenylazo)benzonitrile. A solution of
NaNO2 (0.97 g, 14 mmol) in HCl(aq) (1 M, 30 mL) was
added dropwise to a solution containing 4-cyanoaniline (1.5 g,
14 mmol) in HCl(aq) (5 M, 30 mL) and stirred for 2 h
at 0–5 uC. To this solution was added N,N-dialkylaniline
(14 mmol) in HCl(aq) (1 M, 30 mL). A small amount of
THF was added to dissolve all of the starting materials, if
necessary. After stirring for 1 h, the pH was adjusted to 4–5
with AcONa. The solid product that precipitated was filtered
and dried in air for 1 day.
4-(p-Diethylaminophenylazo)benzonitrile. Yield 76%; mp
114 uC; IR (KBr, cm21) 2219 (CN); 1H NMR (300 MHz,
CDCl3) d 7.88 (d, 2H, J ~ 9.0 Hz), 7.85 (d, 2H, J ~ 9.0 Hz),
7.74 (d, 2H, J ~ 8.9 Hz), 6.73 (d, 2H, J ~ 8.9 Hz), 3.47 (q, 4H,
J ~ 7.2 Hz), 1.24 (t, 6H, J ~ 7.2 Hz).
Experimental section
Synthesis of octupolar molecules and oligomers (1, 2 P1, and P2)
Compounds 1a, 2a, and 2e were available from a previous
study.6c The syntheses of 1d,e, 2b–d, P1, and P2 are described
below.
4-(p-Dihexylaminophenylazo)benzonitrile. Yield 78% (oil);
IR (KBr, cm21) 2223 (CN); 1H NMR (300 MHz, CDCl3) d 7.88
(d, 2H, J ~ 8.7 Hz), 7.85 (d, 2H, J ~ 8.7 Hz), 7.72 (d, 2H, J ~
9.0 Hz), 6.68 (d, 2H, J ~ 9.0 Hz), 3.37 (t, 4H, J ~ 7.8 Hz), 1.64
(m, 4H), 1.34 (m, 12H), 0.91 (t, 6H, J ~ 6.4 Hz).
Synthesis of 4-[4-(p-diethylaminophenylazo)styryl]benzonitrile
(1d) and 4-[4-(p-diethylaminostyryl)styryl]benzonitrile (1e)
4-(Diethoxyphosphorylmethyl)benzonitrile. a-Bromo-p-toluo-
nitrile (2.0 g, 3.5 mmol) was dissolved in 10 ml of triethyl
phosphite. The mixture was heated at 160 uC for 2 hours.
After cooling, the excess triethyl phosphite was evaporated
under reduced pressure. The residue was dissolved in methyl-
ene chloride and washed with water. The product was purified
by flash column chromatography using ethyl acetate as the
eluent. Yield 2.1 g (85%);1H-NMR (300 MHz, CDCl3) d 7.62
(d, 2H, J ~ 9.0 Hz), 7.44 (d, 2H, J ~ 9.0 Hz), 4.05 (q, 4H, J ~
7.5 Hz), 3.20 (d, 2H, J ~ 21.0 Hz), 1.26 (t, 6H, J ~ 6.0 Hz).
4-(p-Dialkylaminophenylazo)benzaldehyde. A solution of
DIBAL-H in hexane (1.0 M, 3.3 mL) was added dropwise
to
a solution of 4-(p-dialkylaminophenylazo)benzonitrile
(1.7 mmol) in THF (10 mL) at 278 uC under nitrogen. The
solution was warmed to ambient temperature and stirred for
3 h. The reaction was quenched by adding an aqueous solution
of AcOH (10%, 10 mL) and the product was extracted with
CH2Cl2 and purified by column chromatography using
hexane–CH2Cl2 ~ 5 : 1 as the eluent.
4-[4-(p-Diethylaminophenylazo)styryl]benzonitrile (1d). LDA
(1.5 M in THF, 0.71 mL, 1.1 mmol) was added dropwise to a
solution containing 4-(diethoxyphosphorylmethyl)benzonitrile
(0.21 g, 0.87 mmol) in 10 mL of THF and stirred for 30 min at
278 uC. To this solution was added 4-(p-diethylaminophenyl-
azo)benzaldehyde (0.20 g, 0.71 mmol) in 10 mL of THF and
the reaction was allowed to proceed for 1 day at room
temperature. The reaction was quenched with H2O and the
product was extracted with CH2Cl2 and purified by column
chromatography using CH2Cl2 as the eluent. Yield 0.25 g
(92%); mp 257 uC; IR (KBr, cm21) 2221 (CN);1H-NMR
(300 MHz, CDCl3) d 7.87 (d, 2H, J ~ 9.0 Hz), 7.85 (d, 2H, J ~
9.0 Hz), 7.65 (d, 2H, J ~ 9.0 Hz), 7.62 (d, 2H, J ~ 9.0 Hz), 7.59
(d, 2H, J ~ 9.0 Hz), 7.26 (d, 1H, J ~ 15.0 Hz), 7.13 (d, 1H, J ~
15.0 Hz), 6.72 (d, 2H, J ~ 9.0 Hz), 3.46 (q, 4H, J ~ 6.5 Hz),
1.24 (t, 6H, J ~ 6.5 Hz). 13C-NMR (75 MHz, CDCl3) d 153.5,
150.5, 143.5, 142.0, 137.2, 132.7, 132.1, 127.8, 127.3, 127.1,
125.7, 122.9, 119.3, 111.2, 110.8, 45.0, 12.9. Anal. Calcd for
C25H24N4: C, 78.92; H, 6.36; N, 14.73. Found: C, 78.96; H,
6.52; N, 14.56%.
4-(p-Diethylaminophenylazo)benzaldehyde. Yield 84%; mp
108 uC; IR (KBr, cm21) 1801 (CLO); 1H-NMR (300 MHz,
CDCl3) d 10.0 (s, 1H), 7.97 (d, 2H, J ~ 8.4 Hz), 7.93 (d, 2H,
J ~ 8.4 Hz), 7.89 (d, 2H, J ~ 9.0 Hz), 6.73 (d, 2H, J ~ 9.0 Hz),
3.47 (q, 4H, J ~ 7.2 Hz), 1.24 (t, 6H, J ~ 7.2 Hz).
4-(p-Dihexylaminophenylazo)benzaldehyde. Yield 76% (oil);
1
IR (KBr, cm21) 1756 (CLO); H-NMR (300 MHz, CDCl3) d
10.0 (s, 1H), 7.97 (d, 2H, J ~ 8.4 Hz), 7.93 (d, 2H, J ~
8.4 Hz), 7.88 (d, 2H, J ~ 9.0 Hz), 6.74 (d, 2H, J ~ 9.0 Hz), 3.37
(t, 4H, J ~ 7.8 Hz), 1.63 (m, 4H), 1.34 (m, 12H), 0.91 (t, 6H,
J ~ 6.4 Hz).
1,3,5-Tricyano-2-(4-diethylaminostyryl)-4,6-bis(diethoxyphos-
phorylmethyl)benzene (B) and 1,3,5-tricyano-2,4-bis(4-di-
ethylaminostyryl)-6-(diethoxyphosphorylmethyl)benzene (C).
Intermediate B was synthesized by the same procedure as
described above for the synthesis of 1d except that A and
4-(p-diethylaminophenylazo)benzaldehyde were used in a ratio
of 1 : 1.2 and the benzaldehyde derivative was added dropwise
to the ylide solution over 30 minutes at 278 uC, and the
4-[4-(p-Diethylaminostyryl)styryl]benzonitrile (1e). Synthe-
sized by the same procedure as described above for the
1034
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reaction was conducted at room temperature for 6 h. To
synthesize C, the reactant ratio was increased to 1 : 1.8 and
the benzaldehyde derivative was added rapidly to the ylide
solution.
130.2, 129.4, 128.6, 125.7, 122.8, 121.4, 116.1, 114.9, 111.4, 111.0,
107.7, 106.8, 44.7, 44.6, 12.7, 12.6. Anal. Calcd for C57H56N10: C,
77.70; H, 6.41; N, 15.90. Found: C, 77.64; H, 6.87; N, 15.49%.
Synthesis of oligomer P1
1,3,5-Tricyano-2-[4-(p-diethylamino)styryl]-4,6-bis(diethoxy-
phosphorylmethyl)benzene (B). Yield 65%; 1H-NMR (300
MHz, CDCl3) d 7.81 (d, 1H, J ~ 16.2 Hz), 7.52 (d, 2H, J ~
8.7 Hz), 7.18 (d, 1H, J ~ 16.2 Hz), 6.67 (d, 2H, J ~ 8.7 Hz),
4.23 (q, 8H, J ~ 7.2 Hz), 3.74 (d, 4H, J ~ 23.1 Hz), 3.41 (q, 4H,
J ~ 7.1 Hz), 1.36 (t, 12H, J ~ 7.2 Hz), 1.19 (t, 6H, J ~ 7.1 Hz).
1,3,5-Tricyano-2-{p-[N-(2-tert-butyldimethylsilanyloxyethyl)-
N-methylamino]styryl}-4,6-bis(diethoxyphosphorylmethyl)ben-
zene (B’). Synthesized by the same procedure as described for
2d except that A (3.6 g, 5.9 mmol), LDA (1.5 M in THF, 10 mL,
16 mmol), and 4-[N-(2-tert-butyldimethylsilanyloxyethyl)-N-
methylamino]benzaldehyde (1.4 g, 4.7 mmol) in THF (90 mL)
were used. The product was purified by column chromato-
graphy using hexane–ethyl acetate ~ 1 : 3 as the eluent. Yield
68%; 1H-NMR (300 MHz, CDCl3) d 7.89 (d, 1H, J ~ 16.2 Hz),
7.52 (d, 2H, J ~ 8.7 Hz), 7.20 (d, 1H, J ~ 16.2 Hz), 6.71 (d, 2H,
J ~ 8.7 Hz), 4.26 (q, 8H, J ~ 6.9 Hz), 3.78 (t, 2H, J ~ 5.7 Hz),
3.74 (d, 4H, J ~ 23.1 Hz), 3.57 (t, 2H, J ~ 5.7 Hz), 3.07 (s, 3H),
1.36 (t, 12H, J ~ 6.9 Hz), 0.88 (s, 9H), 0.24 (s, 6H).
1,3,5-Tricyano-2,4-bis[4-(p-diethylamino)styryl]-6-(diethoxy-
phosphorylmethyl)benzene (C). Yield 78 %; 1H-NMR (300
MHz, CDCl3) d 7.81 (d, 2H, J ~ 16.2 Hz), 7.52 (d, 4H, J ~
8.7 Hz), 7.18 (d, 2H, J ~ 16.2 Hz), 6.67 (d, 4H, J ~ 8.7 Hz),
4.23 (q, 4H, J ~ 7.2 Hz), 3.74 (d, 2H, J ~ 23.1 Hz), 3.41 (q, 8H,
J ~ 7.1 Hz), 1.36 (t, 6H, J ~ 7.2 Hz), 1.19 (t, 12H, J ~ 7.1 Hz).
1,3,5-Tricyano-2,4,6-tris[4-(p-diethylaminophenylazo)styryl]-
benzene (2d). LDA (1.5 M in THF, 3.4 mL, 5.1 mmol) was
added dropwise to a solution containing A (0.76 g, 1.3 mmol)
in 15 mL of THF and stirred for 30 min at 278 uC. To this
solution was added 4-(p-diethylaminophenylazo)benzaldehyde
(1.2 g, 4.1 mmol) in 20 mL of THF and the reaction was
allowed to proceed for 1 day at room temperature. The reaction
was quenched with H2O and the product was extracted with
ethyl acetate and purified by column chromatography using
CH2Cl2 as the eluent. Yield 0.83 g (65%); mp 114–115 uC; IR
1,3,5-Tricyano-2-{p-[N-(2-tert-butyldimethylsilanyloxyethyl)-
N-methylamino]styryl}-4-(p-dihexylaminostyryl)-6-(diethoxy-
phosphorylmethyl)benzene (B@). Synthesized by the same
procedure as described for 2d except that B’ (3.2 g, 4.3 mmol),
LDA (1.5 M in THF, 6.3 mL, 9.5 mmol), and dihexylamino-
benzaldehyde (0.99 g, 3.4 mmol) in THF (120 mL) were used.
The product was purified by column chromatography using
1
hexane–ethyl acetate ~ 1 : 1 as the eluent. Yield 92%; H-NMR
(300 MHz, CDCl3) d 7.84 (d, 1H, J ~ 16.2 Hz), 7.82 (d, 1H,
J ~ 16.2 Hz), 7.53 (d, 2H, J ~ 9.0 Hz), 7.52 (d, 2H, J ~
9.0 Hz), 7.22 (d, 1H, J ~ 16.2 Hz), 7.20 (d, 1H, J ~ 16.2 Hz),
6.71 (d, 2H, J ~ 8.7 Hz), 6.65 (d, 2H, J ~ 8.7 Hz), 4.26 (q, 4H,
J ~ 6.9 Hz), 3.78 (t, 2H, J ~ 5.7 Hz), 3.74 (d, 2H, J ~
23.1 Hz), 3.57 (t, 2H, J ~ 5.7 Hz), 3.37 (t, 4H, J ~ 7.8 Hz),
3.07 (s, 3H), 1.64 (m, 4H), 1.36 (t, 6H, J ~ 6.9 Hz), 1.34 (m,
12H), 0.91 (t, 6H, J ~ 6.4 Hz), 0.88 (s, 9H), 0.24 (s, 6H).
1
(KBr, cm21) 2219 (CN); H-NMR (300 MHz, CDCl3) d 7.90
(d, 6H, J ~ 8.7 Hz), 7.88 (d, 6H, J ~ 8.7 Hz), 7.84 (d, 3H, J ~
16.2 Hz), 7.76 (d, 6H, J ~ 8.4 Hz), 7.49 (d, 3H, J ~ 16.2 Hz),
6.74 (d, 6H, J ~ 8.4 Hz), 3.47 (q, 12H, J ~ 7.2 Hz), 1.24 (t,
18H, J ~ 7.2 Hz). 13C-NMR (75 MHz, CDCl3) d154.2, 150.3,
148.5, 143.2, 141.7, 135.3, 128.6, 125.6, 122.7, 120.9, 115.7,
110.9, 108.5, 44.8, 12.8. Anal. Calcd for C63H60N12: C, 76.80;
H, 6.14; N, 17.06. Found: C, 76.94; H, 6.22; N, 16.84%.
1,3,5-Tricyano-2-[4-(p-dihexylaminophenylazo)styryl]-4-{p-[N-
(2-tert-butyldimethylsilanyloxyethyl)-N-methylamino]styryl}-6-
(p-dihexylaminostyryl)benzene (D’). Synthesized by the same
procedure as described for 2d except that B@ (2.1 g, 2.3 mmol),
LDA (1.5 M in THF, 1.9 mL, 2.8 mmol), and 4-(p-dihexyl-
aminophenylazo)benzaldehyde (1.0 g, 2.6 mmol) in THF
(90 mL) were used. The product was purified by column
chromatography using hexane–ethyl acetate ~ 1 : 1 as the
eluent. Yield 92%; 1H-NMR (300 MHz, CDCl3) d 7.86 (d,
2H, J ~ 8.7 Hz), 7.84 (d, 2H, J ~ 8.7 Hz), 7.81 (d, 1H, J ~
16.5 Hz), 7.78 (d, 1H, J ~ 16.5 Hz), 7.74 (d, 1H, J ~ 16.5 Hz),
7.70 (d, 2H, J ~ 8.7 Hz), 7.51 (d, 2H, J ~ 9.0 Hz), 7.50 (d, 2H,
J ~ 8.7 Hz), 7.41 (d, 1H, J ~ 16.5 Hz), 7.21 (d, 1H, J ~
16.2 Hz), 7.19 (d, 1H, J ~ 16.2 Hz), 6.74 (d, 2H, J ~ 9.0 Hz),
6.68 (d, 2H, J ~ 9.0 Hz), 6.62 (d, 2H, J ~ 9.0 Hz), 3.83 (t, 2H,
J ~ 5.5 Hz), 3.55 (t, 2H, J ~ 5.5 Hz), 3.36 (t, 4H, J ~ 7.8 Hz),
3.31 (t, 4H, J ~ 7.8 Hz), 3.05 (s, 3H), 1.62 (m, 4H), 1.61 (m,
4H), 1.34 (m, 12H), 1.33 (m, 12H), 0.92 (t, 6H, J ~ 6.4 Hz),
0.91 (t, 6H, J ~ 6.4 Hz), 0.88 (s, 9H), 0.02 (s, 6H).
1,3,5-Tricyano-2,4-bis(p-diethylaminostyryl)-6-[4-(p-diethyl-
aminophenylazo)styryl]benzene (2b) and 1,3,5-tricyano-2-(p-diethyl-
aminostyryl)-4,6-bis[4-(p-diethylaminophenylazo)styryl]benzene
(2c). Synthesized by the same procedure as described for 2d
except that B or C was used in place of A.
1,3,5-Tricyano-2,4-bis(p-diethylaminostyryl)-6-[4-(p-diethyl-
aminophenylazo)styryl]benzene (2b). Yield 89%; mp 168 uC;
IR (KBr, cm21) 2208 (CN); 1H-NMR (300 MHz, CDCl3) d
7.88 (d, 4H, J ~ 8.7 Hz), 7.81 (d, 2H, J ~ 16.2 Hz), 7.76 (d, 1H,
J ~ 16.2 Hz), 7.72 (d, 2H, J ~ 9.0 Hz), 7.54 (d, 4H, J ~
8.7 Hz), 7.45 (d, 1H, J ~ 16.2 Hz), 7.22 (d, 2H, J ~ 16.2 Hz),
6.74 (d, 2H, J ~ 9.0 Hz), 6.69 (d, 2H, J ~ 8.7 Hz), 6.66 (d, 2H,
J ~ 8.7 Hz), 3.44 (q, 8H, J ~ 7.2 Hz), 3.43 (q, 4H, J ~ 7.2 Hz),
1.22 (t, 12H, J ~ 7.2 Hz), 1.21 (t, 6H, J ~ 7.2 Hz). 13C-NMR
(75 MHz, CDCl3) d153.8, 150.2, 149.2, 148.7, 143.1, 142.2,
140.7, 135.7, 129.9, 128.4, 125.5, 122.6, 122.1, 122.1, 121.7,
116.5, 116.4, 115.1, 111.2, 110.9, 106.7, 105.9, 44.8, 44.6, 12.8,
12.6. Anal. Calcd for C51H52N8: C, 78.83; H, 6.75; N, 14.42.
Found: C, 78.95; H, 6.82; N, 14.23%.
1,3,5-Tricyano-2-[4-(p-dihexylaminophenylazo)styryl]-4-{p-[N-
(2-hydroxyethyl)-N-methylamino]styryl}-6-(p-dihexylaminostyryl)-
benzene (D). A solution of D’ (3.5 g, 3.1 mmol) and KF (0.71 g,
12 mmol) in DMF (80 mL) was stirred for 1 h. To this solution,
HBr(aq) (38%, 4.0 mL) was slowly added and stirred overnight.
The solution was neutralized with NaOH(aq), filtered, washed
several times with water, and dried in air. Yield 87%; mp
116 uC; IR (KBr, cm21) 3447 (OH), 2219 (CN); 1H-NMR
(300 MHz, CDCl3) d 7.86 (d, 2H, J ~ 8.7 Hz), 7.84 (d, 2H, J ~
8.7 Hz), 7.80 (d, 1H, J ~ 16.5 Hz), 7.76 (d, 1H, J ~ 16.5 Hz),
7.72 (d, 1H, J ~ 16.5 Hz), 7.70 (d, 2H, J ~ 8.7 Hz), 7.53 (d, 2H,
J ~ 9.0 Hz), 7.50 (d, 2H, J ~ 8.7 Hz), 7.43 (d, 1H, J ~
16.5 Hz), 7.20 (d, 1H, J ~ 16.2 Hz), 7.19 (d, 1H, J ~ 16.2 Hz),
1,3,5-Tricyano-2-(diethylaminostyryl)-4,6-bis[4-(p-diethyl-
aminophenylazo)styryl]benzene (2c). Yield 82%; mp w300 uC;
IR (KBr, cm21) 2219 (CN); 1H-NMR (300 MHz, CDCl3) d 7.88
(d, 2H, J ~ 8.7 Hz), 7.82 (d, 1H, J ~ 16.2 Hz), 7.77 (d, 2H, J ~
16.2 Hz), 7.72 (d, 4H, J ~ 8.7 Hz), 7.54 (d, 2H, J ~ 9.0 Hz), 7.43
(d, 2H, J ~ 16.2 Hz), 7.22 (d, 1H, J ~ 16.2 Hz), 6.72 (d, 4H, J ~
9.0 Hz), 6.69 (d, 4H, J ~ 9.0 Hz), 6.68 (d, 4H, J ~ 9.0 Hz), 3.47
(q, 4H, J ~ 7.2 Hz), 3.45 (q, 8H, J ~ 7.2 Hz), 1.23 (t, 6H, J ~
7.2 Hz), 1.21 (t, 12H, J ~ 7.2 Hz). 13C-NMR (75 MHz, CDCl3) d
154.5, 154.2, 150.4, 149.6, 149.2, 148.7, 143.3, 143.0, 141.3, 135.7,
J. Mater. Chem., 2003, 13, 1030–1037
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6.76 (d, 2H, J ~ 9.0 Hz), 6.69 (d, 2H, J ~ 9.0 Hz), 6.63 (d, 2H,
J ~ 9.0 Hz), 3.84 (t, 2H, J ~ 5.5 Hz), 3.57 (t, 2H, J ~ 5.5 Hz),
3.34 (t, 4H, J ~ 7.8 Hz), 3.30 (t, 4H, J ~ 7.8 Hz), 3.07 (s, 3H),
1.62 (m, 4H), 1.61 (m, 4H), 1.34 (m, 12H), 1.33 (m, 12H), 0.92
(t, 6H, J ~ 6.4 Hz), 0.91 (t, 6H, J ~ 6.4 Hz). 13C-NMR
(75 MHz, CDCl3) d 154.1, 151.1, 150.8, 149.8, 149.3, 149.2,
148.8, 143.2, 142.6, 142.2, 141.0, 135.8, 129.9, 129.7, 128.5,
125.6, 123.6, 122.7, 121.7, 116.5, 116.4, 115.2, 115.1, 112.1,
111.5, 111.1, 106.9, 106.4, 106.1, 60.2, 54.6, 51.2, 51.1, 39.0,
31.6, 27.4, 27.2, 26.7, 22.6, 14.0. Anal. Calcd for C66H82N8O:
C, 79.00; H, 8.24; N, 11.17; O, 1.59. Found: C, 79.03; H, 8.41;
N, 11.12; O, 1.46%.
1,3,5-Tricyano-2-[4-(p-dihexylaminophenylazo)styryl]-4,6-bis-
{p-[N-(2-tert-butyldimethylsilanyloxyethyl)-N-methyl]aminostyryl}-
benzene (E’). Synthesized by same procedure as described for
2d except that C’ (2.5 g, 2.8 mmol), LDA (1.5 M in THF,
2.2 mL, 3.4 mmol), and 4-(p-dihexylaminophenylazo)benz-
aldehyde (1.1 g, 3.1 mmol) in THF (20 mL) were used. The
product was purified by column chromatography using
hexane–ethyl acetate ~ 1 : 1 as the eluent. Yield 87%; 1H-
NMR (300 MHz, CDCl3) d 7.89 (d, 2H, J ~ 16.2 Hz), 7.88 (d,
2H, J ~ 8.7 Hz), 7.85 (d, 2H, J ~ 8.7 Hz), 7.80 (d, 1H, J ~
16.2 Hz), 7.72 (d, 4H, J ~ 8.7 Hz), 7.53 (d, 4H, J ~ 8.7 Hz),
7.44 (d, 2H, J ~ 16.2 Hz), 7.22 (d, 1H, J ~ 16.2 Hz), 6.70 (d,
2H, J ~ 9.0 Hz), 6.68 (d, 2H, J ~ 9.0 Hz), 3.79 (t, 4H, J ~
7.8 Hz), 3.54 (t, 4H, J ~ 7.8 Hz), 3.37 (t, 4H, J ~ 7.8 Hz), 3.07
(s, 6H), 1.62 (m, 4H), 1.34 (m, 12H), 0.91 (t, 6H, J ~ 6.4 Hz),
0.88 (s, 18H), 0.03 (s, 12H).
Monomer. To a stirred solution of D (0.75 g, 0.75 mmol)
and Et3N (0.31 g, 2.3 mmol) in anhydrous THF (10 mL),
methacryloyl chloride (0.11 g, 1.05 mmol) was added dropwise
and stirring was continued for 1 hour at 0 uC under nitrogen.
The solvent was evaporated and the crude product was taken
up in CH2Cl2. The product was isolated by the usual work up
procedure and purified by column chromatography with ethyl
acetate–hexane ~ 1 : 1 as eluent. The product was a red oil.
Yield 0.53 g (66%); 1H-NMR (300 MHz, CDCl3) d 7.88 (d, 2H,
J ~ 8.7 Hz), 7.86 (d, 2H, J ~ 8.7 Hz), 7.80 (d, 1H, J ~
16.5 Hz), 7.76 (d, 1H, J ~ 16.5 Hz), 7.72 (d, 1H, J ~ 16.5 Hz),
7.70 (d, 2H, J ~ 8.7 Hz), 7.53 (d, 2H, J ~ 9.0 Hz), 7.50 (d, 2H,
J ~ 8.7 Hz), 7.43 (d, 1H, J ~ 16.5 Hz), 7.20 (d, 1H, J ~
16.2 Hz), 7.19 (d, 1H, J ~ 16.2 Hz), 6.76 (d, 2H, J ~ 9.0 Hz),
6.69 (d, 2H, J ~ 9.0 Hz), 6.63 (d, 2H, J ~ 9.0 Hz), 6.07 (s, 1H),
5.57 (s, 1H), 4.35 (t, 2H, J ~ 5.5 Hz), 3.72 (t, 2H, J ~ 5.5 Hz),
3.36 (t, 4H, J ~ 7.8 Hz), 3.32 (t, 4H, J ~ 7.8 Hz), 3.07 (s, 3H),
1.92 (s, 3H), 1.61 (m, 4H), 1.60 (m, 4H), 1.34 (m, 12H), 1.33 (m,
12H), 0.92 (t, 6H, J ~ 6.4 Hz), 0.91 (t, 6H, J ~ 6.4 Hz); 13C-
NMR (75 MHz, CDCl3) d 167.25, 154.09, 150.75, 150.44,
149.88, 149.27, 148.78, 143.16, 142.65, 142.22, 141.01, 135.86,
135.70, 129.98, 129.73, 128.90, 128.54, 126.10, 125.54, 123.53,
122.71, 122.07, 121.67, 116.42, 116.25, 115.05, 111.92, 111.42,
111.03, 106.85, 106.11, 61.67, 51.28, 51.05, 50.72, 38.82, 38.72,
31.64, 29.67, 27.29, 27.20, 26.74, 25.31, 22.64, 18.31, 18.21,
14.03.
1,3,5-Tricyano-2-[4-(p-dihexylaminophenylazo)styryl]-4,6-bis-
{p-[N-(2-hydroxyethyl)-N-methylamino]styryl}benzene (E). Syn-
thesized by the same procedure as described for D. Yield 72%;
1
mp 158 uC; IR (KBr, cm21) 3434 (OH), 2219 (CN); H-NMR
(300 MHz, CDCl3) d 7.88 (d, 2H, J ~ 16.2 Hz), 7.87 (d, 2H, J ~
8.7 Hz), 7.85 (d, 2H, J ~ 8.7 Hz), 7.78 (d, 1H, J ~ 16.2 Hz),
7.68 (d, 4H, J ~ 8.7 Hz), 7.51 (d, 4H, J ~ 8.7 Hz), 7.38 (d, 2H,
J ~ 16.2 Hz), 7.19 (d, 1H, J ~ 16.2 Hz), 6.72 (d, 2H, J ~
9.0 Hz), 6.69 (d, 2H, J ~ 9.0 Hz), 3.84 (t, 4H, J ~ 7.8 Hz), 3.55
(t, 4H, J ~ 7.8 Hz), 3.37 (t, 4H, J ~ 7.8 Hz), 3.05 (s, 6H), 1.64
(m, 4H), 1.34 (m, 12H), 0.91 (t, 6H, J ~ 6.4 Hz). 13C-NMR
(75 MHz, CDCl3) d 153.7, 151.0, 150.8, 148.8, 148.6, 143.0,
142.3, 141.0, 135.7, 129.8, 128.8, 128.5, 125.6, 123.3, 122.5,
121.5, 116.3, 115.7, 112.0, 111.1, 106.6, 106.1, 60.1, 54.6, 51.2,
38.9, 31.6, 27.3, 26.7, 22.6, 14.0. Anal. Calcd for C57H64N8O2:
C, 76.65; H, 7.22; N, 12.55; O, 3.58. Found: C, 76.65; H, 7.26;
N, 12.44; O, 3.65%.
Oligomer P2. To a three-necked flask equipped with a
mechanical stirrer and a condenser, C (0.92 g, 1.0 mmol),
tolylene-2,4-diisocyanate (0.18 g, 1.0 mmol), and DMSO–
methyl isobutyl ketone (3 mL, 1 : 1) were added under nitrogen.
The mixture was stirred at 70 uC until all of the reactants were
dissolved, and then heated for 3 h at 120 uC. To this solution
was added 10 ml of DMSO, and the mixture was then cooled
to room temperature and poured into a large amount of water.
The precipitate was collected and dried in vacuo, then purified
by Soxhlet extraction for 18 h using ethyl acetate as solvent.
Oligomer P1. The monomer described above (0.62 g,
0.58 mmol), AIBN (6.0 mg, 0.04 mmol), and anhydrous
THF (3 mL) were introduced into a pressure tube under
nitrogen. The pressure tube was sealed and heated for 24 h
at 70 uC. The mixture was cooled to room temperature and
poured into methanol. The produce that precipitated was
filtered, washed with acetone–methanol ~ 1 : 3 as eluent, and
dried under vacuum. Yield, 0.40 g (65%); Mn ~ 3426, PDI ~
1.87; mp 150–160 uC; IR (KBr, cm21) 2216 (CN), 1726 (CLO),
1181 (C–O); 1H-NMR (300 MHz, CDCl3) d 7.77 (m, 9H), 7.37
(m, 5H), 7.10 (m, 2H), 6.64 (m, 6H), 4.06 (m, 2H), 3.54 (m, 2H),
3.32 (m, 8H), 2.99 (m, 3H), 1.58 (m, 8H), 1.30 (m, 26H), 0.89
(m, 15H).
The product was dried in vacuo. Yield 0.6 g (55%); Mn
~
10 253, PDI ~ 1.49; mp 178–196 uC; IR (KBr, cm21) 3427 (N–
H), 2219 (CN), 1716 (CLO), 1171 (C–O); 1H-NMR (300 MHz,
CDCl3) d 7.83 (m, 7H), 7.68 (m, 4H), 7.45 (m, 6H), 7.10 (m,
2H), 6.67 (m, 6H), 3.79 (m, 4H), 3.55 (m, 4H), 3.35 (m, 4H),
2.99 (m, 6H), 2.30 (m, 3H), 1.62 (m, 4H), 1.34 (m, 12H), 0.91
(m, 6H).
Determination of the first hyperpolarizabilties (b)
Synthesis of oligomer P2
The b values were measured at 1064 nm by the hyper-Rayleigh
Scattering (HRS) method using a Nd:YAG laser (Electro-
Optics Inc. Continuum PII 8000, 10 Hz, 9.3 ns pulse
width).10,11 Solutions of increasing concentrations (6 6
1026–3 6 1023 M) of 1–2, P1, and P2 in THF were cleaned
to remove microscopic particles by passing them through
0.2 mm Millipore filters. The emitted photons from the sample
cuvettes were collimated and focused on the monochromator
by two lenses at the right angle. The HRS and two-photon
fluorescence (TPF) spectrum of 2d was obtained by averaging
200 laser pulses at each wavelength while changing the
wavelength in 0.1 nm increments from 475 to 700 nm. To
determine the b values, 200 laser pulses were averaged in the
wavelength range of 528–535 nm. The TPF intensity was
subtracted from the total signal intensity to obtain a pure
1,3,5-Tricyano-2,4-bis{p-[N-(2-tert-butyldimethylsilanyloxyethyl)-
N-methylamino]styryl}-6-(diethoxyphosphorylmethyl)benzene
(C’). Synthesized by the same procedure as described for 2d
except that A (3.4 g, 5.6 mmol), LDA (1.5 M in THF, 12 mL,
18 mmol), and 4-[N-(2-tert-butyldimethylsilanyloxyethyl)-N-
methylamino]benzaldehyde (1.3 g, 4.5 mmol) in THF (90 mL)
were used. The product was purified by column chromato-
graphy using hexane–ethyl acetate ~ 1 : 3 as the eluent. Yield
83%; 1H-NMR (300 MHz, CDCl3) d 7.81 (d, 2H, J ~ 16.2 Hz),
7.50 (d, 4H, J ~ 8.7 Hz), 7.18 ( d, 2H, J ~ 16.2 Hz), 6.70 (d.
4H, J ~ 8.7 Hz), 4.24 (q, 4H, J ~ 6.9 Hz), 3.79 (t, 4H, J ~
5.7 Hz), 3.74 (d, 2H, J ~ 23.1 Hz), 3.55 (t, 4H, J ~ 5.7 Hz),
3.07 (s, 6H), 1.36 (t, 6H, J ~ 6.9 Hz), 0.88 (s, 18H), 0.24 (s,
12H).
1036
J. Mater. Chem., 2003, 13, 1030–1037

View Article Online
HRS signal.11a The HRS intensity was further corrected for
self-absorption by using eqn. (2).11b The corrected HRS
intensities were plotted against the number density (Nc) of
the chromophores. The b values of the chromophores were
calculated by the external reference method using p-nitroani-
line (bst ~ 21.4 6 10230 esu) as the reference (eqn. (3)).11b,c The
estimated uncertainty of this measurement is ¡15%.
7
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M. Blanchard-Desce, Chem. Commun., 2001, 923; (c) J. J. Wolff
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Acknowledgements
This work was supported by NRL-MOST and CRM-
KOSEF. MJL, MP, and SHL received support from the
BK21 program.
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