Synthesis and nonlinear optical properties of 1,3,5-methoxy-2,4,6-tris(styryl)benzene derivatives

Article abstract of DOI:10.1021/ol025739n

Matrix presented Novel two-dimensional octupoles containing donors at the core and acceptors at the edge of peripheral groups were synthesized by Horner-Wittig reactions. These chromophores show very large first hyperpolarizability and good thermal stabil

Full text of DOI:10.1021/ol025739n

ORGANIC
LETTERS
2002
Vol. 4, No. 10
1703-1706
Synthesis and Nonlinear Optical
Properties of
1,3,5-Methoxy-2,4,6-tris(styryl)benzene
Derivatives†
Bong Rae Cho,* Khalil Chajara, Hyun Jung Oh, Kyung Hwa Son, and
Seung-Joon Jeon
Molecular Opto-Electronics Laboratory, Department of Chemistry and Center for
Electro- and Photo-ResponsiVe Molecules, Department of Chemistry, Korea UniVersity,
1-Anamdong, Seoul 136-701, Korea
chobr@korea.ac.kr
Received February 18, 2002
ABSTRACT
Novel two-dimensional octupoles containing donors at the core and acceptors at the edge of peripheral groups were synthesized by Horner−
Wittig reactions. These chromophores show very large first hyperpolarizability and good thermal stability and are attractive candidates for
nonlinear optical materials.
There is much research effort to develop octupolar nonlinear
optical (NLO) molecules for possible applications in optical
and optoelectronic devices.1,2 An advantage of such mol-
ecules in comparison to the more conventional dipolar NLO
molecules is that the second harmonic response of octupoles
does not depend on the polarization of the incident light
because they are more isotropic than the dipolar NLO
molecules.1d We are particularly interested in the two-
dimensional octupoles because there exists a design strategy
for such molecules with large â values.3 Theoretical studies
predicted and experimental results confirmed that the first
hyperpolarizability of the two-dimensional octupoles such
as crystal violet, subphthalocyanine, 1,3,5-tricyano-2,4,6-
tris(ethynyl)benzene, triphenylamine, 1,3,5-tricyano-2,4,6-
tris(styryl)benzene, and 1,3,5-tris[(p-styryl)phenyl]benzene
derivatives increases with the extent of charge transfer.2,3
(2) (a) del Rey, B.; Keller, U.; Torres, T.; Rojo, G.; Agullo´-Lo´pez, F.;
Nonell, S.; Mart´ı, C.; Brasselet, S.; Ledoux, I.; Zyss, J. J. Am. Chem. Soc.
1998, 120, 12808. (b) 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. (c) Brunel, J.; Ledoux, I.; Zyss,
J.; Blanchard-Desce, M. Chem. Commun. 2001, 923. (d) Wolff, J. J.;
Wortman, R. AdV. Phys. Org. Chem. 1999, 32, 121. (e) Wolff, J. J.; Siegler,
F.; Matschiner, R.; Wortman, R. Angew. Chem., Int. Ed. 2000, 39, 1436.
(f) Lambert, C.; No¨ll, G.; Scha¨mlzlin, E.; Meerholz, K.; Bra¨uchle, C. Chem.
Eur. J. 1998, 4, 512. (g) Lambert, C.; Gaschler, W.; Scha¨mlzlin, E.;
Meerholz, K.; Bra¨uchle, C. J. Chem. Soc., Perkin Trans. 2 1999, 577. (h)
Lambert, C.; Gaschler, W.; No¨ll, G.; Weber, M.; Scha¨mlzlin, E.; Bra¨uchle,
C.; Meerholz, K. J. Chem. Soc., Perkin Trans. 2 2001, 964. (i) Cho, B. R.;
Lee, S. J.; Lee, S. H.; Son, K. H.; Kim, Y. H.; Doo, J.-Y.; Lee, G. J.;
Kang, T. I.; Lee, Y. K.; Cho, M.; S.-J. Jeon. Chem. Mater. 2001, 13, 1438.
(j) Cho, B. R.; Park, S. B.; Lee, S. J.; Son, K. H.; Lee, S. H.; Lee, M.-J.;
Yoo, J.; Lee, Y. K.; Lee, G. J.; Kang, T. I.; Cho, M.; S.-J. Jeon. J. Am.
Chem. Soc. 2001, 123, 6421.
† This paper is dedicated to Prof. Jung-Il Jin of Korea University, Seoul,
Korea, on the occasion of his 60th birthday.
(1) (a) Joffre, M.; Yaron, D.; Silbey, R. J.; Zyss, J. J. Chem. Phys. 1992,
97, 56. (b) Zyss, J.; Ledoux, I. Chem. ReV. 1994, 94, 77. (c) Dhnault, C. J.;
Ledoux, I.; Samuel, I. D. W.; Zyss, J.; Bourgault, M.; Le Bozec, H. Nature
1995, 374, 339. (d) Brasselet, S.; Zyss, J. Opt. Soc. Am. B 1998, 15, 257.
10.1021/ol025739n CCC: $22.00 © 2002 American Chemical Society
Published on Web 04/12/2002

Scheme 1a
a Reagents and condition: (a) (i) HCHO/HBr/AcOH, 60-70 °C, 3 h; (ii) P(OEt)3, 120 °C, 3 h, 80%. (b) (i) LDA/THF, 0 °C, 1 h; (ii)
p-CNC6H4CHO, 12 h, rt; (iii) DIBAL-H/THF, -40 °C, 3 h, 65%. (c) (i) LDA/THF, 0 °C, 1 h, (ii) 4-O2N-thiophene-2-CHO, 12 h, rt, 34
%. (d) (i) LDA/THF, 0 °C, 1 h; (ii) p-O2NC6H4CHO, 12 h, rt, 30%; (e) H2A/DMF, 80 °C, 2-3 h, 68-80%.
Hence, to obtain octupoles with a maximum â value, one
should simultaneously increase the π orbital energy, conju-
gation length, and donor-acceptor strength. For practical
application of the NLO molecules, they must be arranged
noncentrosymmetrically in the solid state to exhibit signifi-
cant second harmonic generation (SHG). In case of dipolar
molecules, noncentrosymmetric alignment of the chro-
mophores is usually achieved by electrical poling.4 Although
there has been a major breakthrough in the development of
electro-optic modulators by using this approach, the very high
voltage required for the electric poling has been a serious
problem in device fabrication.4b In addition, because the
dipoles favor antiparallel pairing, there is a relaxation
problem.4a An ideal solution to these problems would be
spontaneous formation of noncentrosymmetric NLO materi-
als that do not undergo relaxation. Two-dimensional octu-
poles are of particular interest in this respect. It was predicted
that the octupolar molecules may favor the formation of
noncentrosymmetric crystals as a result of the lack of ground-
state dipole moment.2b,g The prediction was experimentally
confirmed in a few cases, where the octupoles have been
shown to assemble noncentrosymmetric crystals and exhibit
significant second harmonic generation (SHG).2b,i,j Moreover,
the octupolar crystals and thin films could find useful
applications as SHG and optical waveguide materials if the
molecules are arranged noncentrosymmetrically in the bulk
state. Therefore, it is worthwhile to develop octupolar
molecules for NLO applications.
The first step in obtaining efficient organic NLO materials
is to synthesize molecules with high nonresonant molecular
hyperpolarizabilities. We have previously reported the
synthesis and NLO properties of 1,3,5-trinitro- and 1,3,5-
tricyano-2,4,6-tris(styryl)benzene derivatives.2i,j The maxi-
mum â value was obtained from 1,3,5-tricyano-2,4,6-tris(p-
diphenylaminostyryl)benzene having the donor-acceptor pair
at the edges of 1,4-bis(styryl)benzene moieties. To further
enhance â values, it is essential to use stronger donor-
acceptor pairs, while maintaining the conjugation bridge to
the optimum length. However, change of the acceptors to
other than a nitro or cyano group at the core is difficult for
synthetic reasons. Also, a bulky acceptor is expected to cause
a steric hindrance, which would in turn distort the planarity
to decrease â.2i In this work, we have synthesized a series
of 1,3,5-trimethoxy-2,4,6-tris(styryl)benzene derivatives, in
which the donors are attached to the central phenyl group
and the acceptors are varied (Scheme 1). A variety of strong
acceptors have now been introduced at the peripheral phenyl
groups. We have determined the first hyperpolarizability and
thermal stability of these octupoles. The structure-property
relationship is established.
Synthesis of the octupoles (1-5) is shown in Scheme 1.
1,3,5-Trimethoxy-2,4,6-tris[(diethoxyphosphoryl)methyl]-
benzene (A) was synthesized by the bromomethylation of
1,3,5-trimethoxybenzene followed by the phosphorylation
with P(OEt)3. Horner-Wittig reactions between A and
substituted benzaldehyde or 5-nitro-2-thiophenecarbaldehyde
afforded compounds 1-3 in modest to high yields. Com-
pounds 4 and 5 were prepared by DIBAL reduction of 1 to
afford 1,3,5-trimethoxy-2,4,6-tris(p-formylstyryl)benzene (B),
followed by the condensation with appropriate carbon acids.5
(3) (a) Lee, Y.-K.; Jeon, S.-J.; Cho, M. J. Am. Chem. Soc. 1998, 120,
10921. (b) Lee, W.-H.; Lee, H.; Kim, J.-A.; Choi, J.-H.; Cho, M.; Jeon,
S.-J.; Cho, B. R. J. Am. Chem. Soc. 2001, 123, 10658.
(4) (a) 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.
(b) Shi, Y.; Zhang, C.; Zhang, H.; Bechtel, J. H.; Dalton, L. R.; Robinson,
B. H.; Steier, W. H. Science 2000, 288, 119.
(5) (a) Lemke R. Synthesis 1974, 359. (b) Zhang, C.; Ren, A. S.; Wang,
F.; Zhu, J.; Dalton, L. R. Chem. Mater. 1999, 11, 1966.
1704
Org. Lett., Vol. 4, No. 10, 2002

1
The structure of 1-5 was unambiguously confirmed by H
due to the self-absorption and multiphoton excitation, the
fundamental wavelength was shifted to 1360 nm with the
OPO laser (Continuum Surelite OPO, 5 ns pulses), which
was pumped by the 355-nm third harmonic of the Nd:YAG
laser (Continuum SL-II-10, Q-switched, 10 Hz).7 HRS
measurements of 1-5 were carried out in dilute CHCl3
solution (1 × 10-4 to 1 × 10-2 M) by a normalized internal
reference method.3,6 As shown in Figure 1, 1-5 showed
neither absorption nor emission band at 680 nm, where we
collect the HRS signal. This result indicates the reliability
of the HRS measurement, as it is neither underestimated by
absorption nor overestimated by the multiphoton fluores-
cence.8
and 13C NMR, IR, and elemental analysis.
Figure 1 shows the absorption and emission spectra of
1-5. As expected, a red shift of the absorption band is
The linear and nonlinear optical data and the thermal
stability of 1-5 are summarized in Table 1. For comparison,
Table 1. Linear and Nonlinear Optical Data and Thermal
Stabilities of 1,3,5-Trimethoxy-2,4,6-tris(styryl)benzene
Derivatives
Tidg
a
b
compd
λmax
λcut-off
∆ν˜c
âd,e
â(0)e,f
1
2
3
4
5
337
370
420
415
445
488
686
388
444
498
480
534
568
6088
7.1
16
34
5.2
11
20
363
305
309
354
377
422
3062
3853
5522
56
35
319
223
2169
163
124
911
TCTBh
J DAi
a In nm. b Wavelength at which the transmittance is 95%. c Stokes shift
in cm-1 d Determined at 1360 nm. e 10-30 esu. f Corrected at λ f ∞ using
.
a three-level model.1a g Initial decomposition temperature (°C) determined
by thermal gravimetric analysis (TGA). h 1,3,5-Tricyano-2,4,6-tris[4-(p-
diphenylaminostyryl)benzene.3j i Julodinyl-(CHdCH)3-A, where A is N,N′-
diethylbarbituric acid.10
Figure 1. Absorption and emission spectra of 1-5 in CHCl3.
the data for closely related 1,3,5-tricyano-2,4,6-tris(p-di-
phenylaminostyryl)benzene and the â value of the most
efficient dipolar NLO chromophore, julodinyl-(CHdCH)3-
A, where A is N,N′-diethylthiobarbituric acid, are included.3j,10
Interestingly, both λmax and â(0) increase as the acceptor
strength and the conjugation length increase. The parallel
increase in these values is consistent with the theoretical
prediction that the â value of the two-dimensional octupoles
should increase with the extent of charge transfer.3 For a
given acceptor, the absorption maximum and the â(0)
increase as the conjugation bridge is changed from phenyl
to a thienyl group (2 and 3). This is again due to the increased
charge transfer. Because the thienyl group has smaller
aromatic resonance energy than the phenyl group, it should
facilitate the charge transfer from the donor to the acceptor
to stabilize the excited state. This would in turn increase λmax
and â, as observed. Similar results were previously reported
for the dipolar NLO chromophores.11 The most important
observed with increasing electron-withdrawing ability and
conjugation length. Except for 2, which did not emit
fluorescence, all of the compounds show relatively large
Stokes shifts ranging from 3000 to 6100 cm-1. This indicates
that the nuclear reorganization is taking place after excitation
prior to emission as a result of significant electronic
redistribution. For a given donor-acceptor pair, the Stokes
shift increases with the conjugation length (4 and 5).
However, it is much smaller for a compound with a thienyl
group in the conjugation bridge (3), probably because of the
shorter conjugation length. It also decreases significantly
when there are additional cyano groups as the acceptor (1
and 4). This result could be attributed to the additional site
for the electron redistribution, which may reduce the excited-
state nuclear reorganization.9
The â values of the octupoles were measured by the hyper-
Rayleigh scattering (HRS) method.3,6 To avoid complications
(8) (a) Stadler, S.; Bourhill, G,; Bra¨uchle, C. J. Phys. Chem. 1996, 100,
6927. (b) Song, O. K.; Woodford, J. N.; Wang, C. H. J. Phys. Chem. A
1997, 101, 3222.
(6) Hendricks, E.; Clay, K.; Persoons, A. Acc. Chem. Res. 1998, 31,
675.
(9) Havibga, E. E.; van Pelt, P. Ber. Bunsen-Ges. 1979, 83, 816.
(10) Marder, S. R.; Cheng, L.-T.; Tieman, B. G.; Friedlie, A. C.;
Blanchard-Desce, M.; Perry, J. W.; Skindhoj, J. Science 1994, 253, 511.
(7) Stadler, S.; Dietrich, R.; Bourhill, G.; Brauchle, Ch. Opt. Lett. 1996,
21, 251.
Org. Lett., Vol. 4, No. 10, 2002
1705

result of the present study is that 5 exhibits a â(0) value of
163 × 10-30 esu, which is larger than that of closely related
1,3,5-tricyano-2,4,6-tris(p-diphenylaminostyryl)benzene, de-
spite the modest electron-donating ability of the methoxy
group (Table 1).3j,12 This underlines the importance of
grafting strong acceptors at the edge of peripheral groups to
obtain a large â value. Also, this result suggests an interesting
possibility that the â value of such molecules could be further
increased if a stronger donor is introduced in the core.
Furthermore, 5 shows improved transparency/nonlinearity
trade-off in comparison to the latter. Finally, these octupoles
show very high thermal stability as indicated by their initial
decomposition temperatures (Tid) ranging from 305 to
377 °C.
In conclusion, we have synthesized a series of two-
dimensional octupoles with large first hyperpolarizability and
good thermal stability by grafting modest donors at the core
and strong acceptors at the edge of the peripheral groups.
Optimization has led to compounds with among the largest
nonresonant hyperpolarizability (â(0) ) 163 × 10-30 esu).
The large first hyperpolarizability and good thermal sta-
bility make them attractive candidates for nonlinear optical
materials.
Acknowledgment. This work is supported by NRL-
MOST and CRM-KOSEF. K.C. and H.J.O. were supported
by BK21 program.
(11) (a) Varanasi, P. R.; Jen, K.-Y.; Chandrasekhar, J.; Namboothiri, I.
N. N.; Rathna, A. J. Am. Chem. Soc. 1996, 118, 12443. (b) Cho, B. R.;
Son, K. N.; Lee, S. J.; Kang, T. I.; Han, M. S.; Jeon, S. J.; Song, N. W.;
Kim, D. Tetrahedron Lett. 1998, 39, 3167.
Supporting Information Available: Synthesis of 1-5
and determination of â values by hyper-Rayleigh scattering.
This material is available free of charge via the Internet at
http://pubs.acs.org.
(12) The most efficient octupoles are 4,4′-bis(dibutylaminostryl)-[2,2′]-
bipyridine Ru(III) complex (λmax ) 509 nm, â(0) ) 240 × 10-30 esu);1c
1,3,5-tricyano-2,4,6-tris[4-(p-diethylaminophenylethynyl)benzene (λmax
)
476 nm, â(0) ) 428 × 10-50 Cm3 V-2);3e 1,3,5-tris(methylsufonylbistryl)-
benzene (λmax ) 377 nm, â(0) ) 510 × 10-30 esu).2c
OL025739N
1706
Org. Lett., Vol. 4, No. 10, 2002