1,3,5-Tricyano-2,4,6-tris(vinyl)benzene derivatives with large second-order nonlinear optical properties

Full text of DOI:10.1021/ja0025595

J. Am. Chem. Soc. 2001, 123, 6421-6422
6421
Scheme 1
1,3,5-Tricyano-2,4,6-tris(vinyl)benzene Derivatives
with Large Second-Order Nonlinear Optical
Properties
Bong Rae Cho,* Soon Bong Park, Seung Jae Lee,
Kyung Hwa Son, Sang Hae Lee, Myung-Ja Lee, Jun Yoo,
Yun Kyong Lee, Geon Joon Lee, Tae Im Kang,
Minhaeng Cho, and Seung-Joon Jeon*
Molecular Opto-Electronics Laboratory
Department of Chemistry and Center for
Electro- and Photo-ResponsiVe Molecules
Korea UniVersity, 1-Anamdong, Seoul 136-701, Korea
ReceiVed July 13, 2000
ReVised Manuscript ReceiVed January 2, 2001
Application of the nonlinear optical materials to the optical
and optoelectronic devices requires large second-order nonlinear
optical property and thermal stability.1,2 Much effort has been
focused to optimize the physical properties of the donor-acceptor
dipoles in order to meet these criteria. While there has been a
great progress in improving these properties, it has become
apparent that the dipolar molecules have certain limitations. One
such problem is the difficulty associated with aligning the dipoles
noncentrosymmetrically in the solid sate to achieve maximum
bulk effect [ø(2)]. Because the dipoles favor antiparallel pairing
in the solid state to nullify bulk nonlinearity, various approaches
including crystallization, poled polymer, Langmuir-Blodgett film,
and self-assembly technique have been employed to overcome
the attractive forces between the dipoles.3 Recently, Dalton and
Steier reported that dipole-based polymers can be fabricated to
an electrooptic modulator with huge bandwidth acceptance and
low modulation voltage, which is the major breakthrough in this
area.1
An alternative approach to overcoming this difficulty would
be to use the octupolar compounds with three-fold symmetry.4
These compounds are of particular interest not only because they
exhibit moderate to very large â, but because they are less prone
to relaxation due to the lack of the ground-state dipole moment,
once they are assembled to exhibit large bulk nonlinearity. The
challenge is the macroscopic organization of the two-dimensional
octupoles in noncentrosymmetric assemblies. Because the electric
poling method is not applicable to these octupolar molecules with
zero permanent dipole moment, optical poling has been explored
to tackle this problem.5 A straightforward solution to this problem
would be the spontaneous arrangement of the NLO chromophores
in the solid state. Planar octupoles with three-fold symmetry
appear particularly attractive for this purpose. We recently
suggested that, by using a simple three-state model, the first
hyperpolarizability of the octupolar molecules increases as the
extent of charge transfer from the peripheral donor to central
acceptor is increased.6,7 This prediction was confirmed by carrying
out both semiempirical and ab initio quantum chemistry calcula-
tions of crystal violet derivatives and other types of octupolar
molecules. These observations provide a firm basis for the design
and synthesis of the planar octupoles with large â values. Here
we show that octupolar compounds containing three donor-
acceptor dipoles within a molecule not only show large first
hyperpolarizability and high thermal stability, but also exhibit
significant second harmonic generation (SHG) in the powder state.
The synthesis of the octupolar compounds is shown in Scheme
1. Compounds 1b, 1c, 1, 2a, 2c, and 2e were prepared by refluxing
tricyanomesitylene with N-formylamine dimethylacetal or sub-
stituted benzaldehyde. Compounds 2f and 3d-f were synthesized
in 61-86% yields by the Wittig reaction of 1,3,5-tricyano-2,4,6-
tris[(diethoxyphosphoryl)methyl]benzene with p-diphenylamino-
benzaldehyde or 4-(p-dialkylaminostyryl)benzaldehyde.
The â values of the octupoles were measured at 1560 nm by
Hyper-Rayleigh Scattering (HRS) method.8 To avoid complica-
tions due to the multiphoton excitation, the excitation wavelength
was shifted to 1560 nm with the OPO laser (Continuum Surelite
OPO, 5 ns pulses), which was pumped by 355 nm third harmonic
of the Nd:YAG laser (Continuum SL-II-10, Q-switched,10 Hz).9
The possibility of the multiphoton fluorescence was examined
by irradiating the solutions of 2a, 2f, 3d, and 3e whose λcut-off
values are larger than others, at 1560 nm under the same condition.
For all compounds, the spectra showed one sharp HRS signal at
780 nm without fluorescence background (Figures S1-4 in the
Supporting Information). This result strongly negates such pos-
sibility. Furthermore, the observed signal showed strictly quadratic
dependence on laser intensity, demonstrating that it is the HRS
signal that we are observing (Figure S5 in the Supporting
Information). It is well established that the dominant â tensor
component of the dipolar compounds is âzzz.3 For the octupolar
compounds, the nonzero tensor elements are âyyy, âyxx, âxyx, and
4,6
âxxy
.
Here, the molecular y-axis is assumed to be one of the
three C2-axis. We have measured the sum of orientationally
averaged hyperpolarizabilities, â2
and â2 , by using the
ZZZ
XZZ
HRS method, where the incident beam travels in the X-direction
and the scattered light is measured in the Y-direction. More
(1) (a) Shi, Y.; Zhang, C.; Zhang, H.; Bechtel, J. H.; Dalton, L. R.;
Robinson, B. H.; Steier, W. H. Science, 2000, 288, 119. (b) Dalton, L. R.;
Steier, W. H.; Robinson, B. H.; Zhang, C.; Ren, A.; Garner, S.; Chen, A.;
Londergan, T.; Irwin, L.; Carlson, B.; Fifield, L.; Phelan, G.; Kincaid, C.;
Amend, J.; Jen, A. J. Mater. Chem. 1999, 9, 1905.
8
specifically, â2
) (24/105)â2yyy and â2
) (16/105)â2
.
ZZZ
XZZ
yyy
The HRS signal of the CHCl3 solution of the compounds was
collected and the â was calculated by using the internal reference
method.8 In this method the solvent is the reference and the â
value of CHCl3 is -0.49 ×10-30 esu.10
(2) Zyss, J.; Ledoux, I. Chem. ReV. 94, 77-105 1994.
(3) (a) Marder, S. R.; Perry, J. W. Science, 1994, 263, 1706. (b) Saadeh,
H.; Wang, L.; Yu, L. J. Am. Chem. Soc. 2000, 122, 546.
The results of UV-vis absorption and second-order nonlinear
optical measurements are summarized in Table 1. For all
(4) (a) Zyss, J. Nonlinear Opt. 1991, 1, 3. (b) Joffre, M.; Yaron, D.; Silbey,
R. J.; Zyss, J. J. Chem. Phys. 1992, 97, 5607. (c) Zyss, J. J. Chem. Phys.
1993, 98, 6583. (d) Blanchard-Desce, M.; Baudin, J.-B.; Jullien, L.; Lorne,
R.; Ruel, O.; Brasselet, S.; Zyss, J. Opt. Mater. 1999, 12, 333. (f) Thalladi,
V. R.; Brasselet, S.; Weiss, H.-C.; Bla¨ser, D.; Katz, A. K.; Carrell, H. L.;
Boese, R.; Zyss, J.; Nangia, A.; Desiraju, G. R. J. Am. Chem. Soc. 1998, 120,
2563.
(6) Lee, Y.-K.; Jeon, S.-J.; Cho, M. J. Am. Chem. Soc. 1998, 121, 10921.
(7) Lee, H.; An, S.-Y.; Cho, M. J. Phys. Chem. B 1999, 103, 4992.
(8) Hendrickx, E.; Clay, K.; Persoons, A. Acc. Chem. Res. 1998, 31, 675.
(9) Stadler, S.; Dietrich, R.; Bourhill, G.; Brauchle, Ch. Opt. Lett. 1996,
21, 251.
(5) Brasselet, S.; Zyss, J. Opt. Lett. 1997, 22, 1464.
10.1021/ja0025595 CCC: $20.00 © 2001 American Chemical Society
Published on Web 06/09/2001

6422 J. Am. Chem. Soc., Vol. 123, No. 26, 2001
Communications to the Editor
Table 1. Selected Optical Data and Thermal Stability for the
Octupolar Compounds
efficiencies of 1b, 2c, 2f, and 3f were determined because they
showed good crystallinity required for the measurement. The
powder samples were packed into a sample holder and pushed in
contact with the hemi cylindrical prism of SF59 glass (n780)1.8955,
n1560)1.9253). The sample holder was rotated to scan the
incidence angle and the detection part was rotated independently
with coincidence of a rotational center. The incident-angle-
dependent second harmonic was detected at the same excitation
wavelength used in the HRS measurement. The reliability of this
method was confirmed by measuring the d coefficients of the
powder sample of m-nitroaniline (mNA). Because of the uncer-
tainty in the refractive index measurement, the figure of merit
(M)17 which is proportional to the second harmonic generation
efficiency was estimated.
â(0)a
Td /
i
λmax
(nm, ꢀ)
λcut-off
â
entry
D
compd
(nm) (10-30 esu) (10-30 esu) °Cb
1
2
3
4
5
6
7
8
9
NMe2
piperidyl
OMe
NEt2
piperidyl
NPh2
NBu2
piperidyl
NPh2
1b
1e
2a
2c
2e
2f
3d
3e
3f
389 (105,100) 455
396 (113,000) 474
35
25
20
121
118
223
219
178
184
25
17
14
65
69
124
116
108
107
340
319
385
390
418
422
340
402
404
388 (41,800)
493 (82,200)
468 (74,900)
478
560
565
488 (101,700) 568
499 (82,200)
461 (47,400)
468 (80,300)
633
576
558
a Corrected at λ f ∞ using a three-level model.4b b Determined by
thermal gravimetric analysis (TGA).
The powder sample of 1b showed no SHG. On the other hand,
the M/MmNA values for the powder samples of 2c, 2f, and 3f are
found to be 3.4, 0.36, 2.1, respectively. The value of M/MmNA
for 2c indicates that the SHG value of this compound is
approximately 45-fold larger than that of urea.18 Although the
origin of the significant bulk nonlinearity observed for these
compounds is currently under investigation, it is believed that
they form noncentrosymmetric crystals spontaneously during
precipitation.
In conclusion, we have synthesized a series of octupolar NLO
molecules 1-3. They show large first hyperpolarizability, high
thermal stability, and significant SHG in the powder state. The
spontaneous arrangement of the octupolar NLO molecules in the
solid sate to produce bulk nonlinearity may ultimately lead to
electrooptic devices without electric poling.
compounds the λcut-off, the wavelength at which the transmittance
is 95%, is shorter than 650 nm. The λmax increases when the
conjugation length is increased from 1 to 2, but remains nearly
constant by a further increase in the conjugation (entries 2, 5,
and 8). On the other hand, â(0) increases gradually as the donor
strength (entries 3-5) and the conjugation length are increased
(entries 2, 5, and 8). The change of â with the octupolar structural
variation is consistent with our theoretical prediction.6,7 Moreover,
the steeper increase in â than λmax indicates an improved
transparency-nonlinearity tradeoff for the octupoles compared with
the dipoles, in which both â and λmax increase monotonically with
the conjugation length.11,12 We have also measured the â values
for dipolar 4-cyanostilbene derivatives, in which MeO, Et2N, and
piperidine are substituted at the 4′-position under the same
-30
condition. The values of â(0) are 4, 10, and 11 × 10
esu,
respectively. The â(0) values of the octupoles are 3-6-fold larger
than those of the corresponding dipoles, indicating that the former
has larger â(0) per molecular weight. Recently, a very large â(0)
was reported for the acetylene analogue of 2c.13 The result is
somewhat surprising because the donor-acceptor dipoles with
acetylenic bridging units usually yield smaller NLO responses
than the corresponding ethylenic structures.14 Finally, these
octupoles show very high thermal stability as indicated by their
Acknowledgment. This work is supported by a National Research
Laboratory Grant by Korea Ministry of Science and Technology and
CRM-KOSEF. S.H.L., M.-J.L., and Y.K.L. were supported by BK21
scholarship.
Supporting Information Available: General experimental procedures
and 1H and 13C NMR and elemental analyses of all new compounds,
contribution of multiphoton fluorescence to the HRS signal, and the
quadratic dependence of the HRS signal on laser intensity (PDF). This
information is available free of charge via the Internet at http://pubs.acs.org.
i
initial decomposition temperatures (Td ) ranging from 319 to 422
°C.15
JA0025595
The ø(2) values of the powdered samples of the octupoles were
measured by the second harmonic with evanescent wave (SHEW)
method.16 Among the compounds we synthesized, the SHG
(15) One of the reviewers pointed out that the photochemical stability of
the NLO molecules is also important. Although we did not measure the
photochemical stabilities of compounds 1-3 quantitatively, they were stable
in the solid- and solution states for at least one year under room light. In
addition, both the HRS and SHG data were reproducible when the same
experiments were repeated with the same sample for several times.
(16) Kiguchi, M.; Kato, M.; Kumegawa, N.; Taniguchi, Y. J. Appl. Phys.
1994, 75, 4332.
(10) Kazjar, F.; Ledoux, I.; Zyss, J. Phys. ReV. A. 1987, 36, 2210.
(11) Blanchard-Desce, M.; Alain, V.; Bedworth, P. V.; Marder, S. R.; Fort,
A.; Runser, C.; Barzoukas, M.; Lebus, S.; Wortmann, R. Chem. Eur. J. 1997,
3, 1091.
(12) Andraud, C.; Zabulon, T.; Collet, A.; Zyss, J. Chem. Phys. 1999, 245,
243.
(17) The figure of merit is defined by M ) d2/n2ω(nω)2, where nω and n2ω
are the refractive index at frequency ω and 2ω, respectively.
(13) Wolff, J. J.; Siegler, F.; Matschiner, R.; Wortman, R. Angew. Chem.,
Int. Ed. 2000, 39, 1436.
(18) Dmitriev, V. G. Gurzadyan, G. G. Nikogosyan, D. N. Handbook of
Nonlinear Optical Crystals; Springer-Verlag: Berlin, 1991; pp 120-121.
(14) Kanis, D. R.; Ratner, M. A.; Marks, T. J. Chem. ReV. 1994, 94, 195.