Table 1 Optical properties of 2,6-diphenylbenzo[1,2-d:4,5-d’]bisthia-
zole (DPBBT) derivatives
p-conjugation system. The b(0) values of NLO chromophores
5a and 6a are also about fourteen to twenty times larger than
the p-NA value.
The inherent thermal stability of chromophores 5a and 6a
was investigated by thermogravimetric analysis (TGA). The
chromophores showed good thermal stability to about 330 uC
in nitrogen atmosphere.
In conclusion, we have explored a series of rigid p-PBBT
derivatives as chromophores for second-order nonlinear
applications. These novel chromophores possess highly effi-
cient optical nonlinearities, in that they overcome the trade-off
by using a rigid and planar chromophore, and exhibit high
thermal stability. Our experimental results indicated that the
DPBBT unit with donor and acceptor groups would be suitable
for application in a new series of second-order NLO materials.
The b(0) value increases as the donor strength increases. We are
currently modifying the chromophores so that they will have
better solubility in conventional solvents and will report our
findings in this regard in the future.
Chromophores
lmax(shoulder)/nm
b(0)a
4b
5b
6b
4
5a
6a
238 (347)
275 (348)
277 (354)
355 (468)
369 (470)
347 (477)
—
32.9
40.6
—
185.0
257.8
ab(0) (in units of 10230 esu) values were calculated by using an
approximate two-level model.6
of chromophores 5a and 6a appears around 370 nm and
indicated optical transparency down to scattered light of
wavelength 532 nm; that is, the cut-off is down to y532 nm.
The most bathochromic absorption peak of compounds 5a, 6a
and 4 was shifted to a longer wavelength than that of
precursors 4b–6b because of the expansion of the p-conjugation
system. Compared with 5a, the lmax values of 6a exhibit a
22 nm blue-shifted absorption, while the shoulder of 6a is red
shifted by 7–9 nm relative to 5a and 4. From this result, we
supposed that the shoulder of the DPBBT derivatives with
donor and acceptor groups contributed to the charge-transfer
energy.
Notes and references
{Present address: Department of Materials Science and Engineering,
Kwangju Institute of Science and Technology, Gwangju, 500-712,
Republic of Korea; e-mail: sjhlee@kjist.ac.kr.
The b of each precursor and NLO chromophore was
measured by the hyper-Rayleigh scattering (HRS) technique in
1,1,1,3,3,3-hexafluoropropan-2-ol using the fundamental exci-
tation wavelength of 1064 nm. We used the external reference
method to determine the b values of NLO chromophores 5a, 6a
and their precursor, and used p-nitroaniline (p-NA) as the
reference, as its b value is known.5 The b values of NLO
chromophores 5a and 6a are 405.2 6 10230 esu and 500.2 6
10230 esu, respectively. The nonresonant hyperpolarizability,
b(0), of NLO chromophores 5a and 6a and their precursors
were also calculated by using the two-level model.6 The b(0)
values of NLO chromophores 5a and 6a and their precursors in
1,1,1,3,3,3-hexafluoro-2-propanol are summarized in Table 1.
The b(0) values of 5a and 6a are 185.0 6 10230 esu and 257.8 6
10230 esu, respectively. The b(0) value increased with increasing
donor strength, that is, the b(0) value of 6a was larger than that
of 5a, due to more efficient charge-transfer ability. The b(0)
values of NLO chromophores 5a and 6a are approximately six
times larger than their precursor due to the contribution of the
1
P. N. Prasad and D. L. Williams, Introduction to Nonlinear Optical
Effects in Molecules and Polymers, Wiley, New York, 1991, pp.
132–174.
(a) Ch. Bosshard, K. Sutter, Ph. Pretre, J. Hulliger, M. Florsheimer
and P. Gunter, Organic Nonlinear Optical Materials, Gordon and
Breach Publishers, Switzerland, 1995, pp. 139–179; (b) L. Karki,
F. W. Vance, J. T. Hupp, S. M. LeCours and M. J. Therien, J. Am.
Chem. Soc., 1998, 120, 2606; (c) J.-M. Raimundo, P. Blanchard,
I. Ledoux-Rak, R. Hierle, L. Michaux and J. Roncali, Chem.
Commun., 2000, 1597.
J. Luo, J. Hua, J. Qin, J. Cheng, Y. Shen, Z. Lu, P. Wang and
C. Ye, Chem. Commun., 2001, 171 and references cited therein.
(a) X. Hu, S. Kumar and M. B. Polk, Macromolecules, 1996, 29,
3787; (b) Y.-H. So, Prog. Polym. Sci., 2000, 25, 137 and references
cited therein; (c) H. Vanherzeele, J. S. Meth, S. A. Jenekhe and
M. F. Roberts, J. Opt. Soc. Am. B., 1992, 9, 524–533 and
references cited therein.
K. Clays and A. Persoons, Rev. Sci. Instrum., 1992, 63, 3285 and
references cited therein.
J. L. Oudar and D. S. Chemla, J. Chem. Phys., 1977, 66, 2664.
2
3
4
5
6
2188
J. Mater. Chem., 2002, 12, 2187–2188