where Dn is Dn of a O–DNDA–O moiety; Dn , Dn of the alkyl tails;
1
4 (a) C. C. Otilia, L.-C. Chien and S.-T. Wu, Mol. Cryst. Liq. Cryst.,
2
H. J. Coles, Mol. Cryst. Liq. Cryst., 2005, 433, 259; (c)
S. H. Simpson, R. M. Richardson and S. Hanna, J. Chem. Phys.,
2005, 123, 134904.
5 (a) M. Hird, A. J. Seed, K. J. Toyne, J. W. Goodby, G. W. Gray and
D. G. McDonnell, J. Mater. Chem., 1993, 3, 851; (b) A. J. Seed,
K. J. Toyne and J. W. Goodby, J. Mater. Chem., 1995, 5, 2201.
2
004, 411, 1135; (b) O. Hadeler, M. N. Pivnenko, M. J. Coles and
m, carbon number of alkoxy tails; n, a volume fraction of a methylene
unit of alkoxy tails, respectively. As a result, Dn of O–DNDA–O
0
moiety is approximated as 0.91, it is hardly different from that of O–
1
0b
DPDA–O moiety, 0.90. On the other hand, in a relation of alkoxy
tail lengths and Dn values, it is revealed that DNDA–OCm main-
tains higher Dn values than that of DPDA–OCm on increasing
0
0
6
(a) G. J. Cross, A. J. Seed, K. J. Toyne, J. W. Goodby, M. Hird and
M. C. Artal, J. Mater. Chem., 2000, 10, 1555; (b) M. Hird,
K. J. Toyne, J. W. Goodby, G. W. Gray, V. Minter, R. P. Tuffin
and D. G. McDonnell, J. Mater. Chem., 2004, 14, 1731.
alkoxy tail lengths. It is thought to be due to decreased influence of
the dilution effect by the alkoxy tails, with respect to DNDA–OCm
having a larger mesogen.
7
(a) S. Gauza, C.-H. Wen, S.-T. Wu, N. Janarthan and C.-S. Hsu, Jpn.
J. Appl. Phys., 2004, 43, 7634; (b) C. Sekine, K. Iwakura, N. Konya,
M. Minai and K. Fujisawa, Liq. Cryst., 2001, 28, 1375; (c) S.-T. Wu,
C.-S. Hsu and K.-F. Shyu, Appl. Phys. Lett., 1999, 74, 344; (d)
K. Okano, A. Shishido and T. Ikeda, Adv. Mater., 2006, 18, 523; (e)
K. Okano, O. Tsutsumi, A. Shishido and T. Ikeda, J. Am. Chem.
Soc., 2006, 128, 15368.
In conclusion, we have synthesized compounds of the DNDA–
OCm series and measured their birefringence in the nematic phase as
well as the wavelength and temperature dependence of the birefrin-
gence. Our results showed that this series exhibited extremely high
birefringence, with DNDA–OC2 showing the highest value of 0.62 at
8
9
(a) C. Sekine, N. Konya, M. Minai and K. Fujisawa, Liq. Cryst.,
2001, 28, 1361; (b) C. Sekine, M. Ishitobi, K. Iwakura, M. Minai
and K. Fujisawa, Liq. Cryst., 2002, 29, 355.
5
50 nm. The nematic birefringence decreased with an increase in the
alkoxy tail length of m because of the dilution effect. The birefrin-
gence of DNDA–OC6 was found to be higher than that of DPDA–
OC6 at 550 nm at standardized temperature. In addition, with respect
(a) B. Grant, Mol. Cryst. Liq. Cryst., 1978, 48, 175; (b) S.-T. Wu and
L. R. Dalton, J. Appl. Phys., 1989, 65, 4372; (c) S.-T. Wu, H. B. Meng
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S. S. Keast, J. M. Kim, K. J. Miller, R. M. Murray, A. G. Norton,
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31, 175; (e) C. M. Hudson, R. A. Shenoy, M. E. Neubert and
R. G. Petschek, Liq. Cryst., 1999, 2, 241; (f) Y. Goto, T. Inukai,
A. Fujita and D. Demus, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect.
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to Dn
1), those of DNDA–OCm are greater compared to DPDA–OCm
0
values, that is, the case of perfectly oriented birefringence (S ¼
because of the longer p-conjugation of the naphthalene skeleton.
Thus, our investigations show that the DNDA–OCm series of
compounds has great potential for use as high-Dn materials.
1
0 (a) Y. Arakawa, S. Nakajima, R. Ishige, M. Uchimura, S. Kang,
G. Konishi and J. Watanabe, J. Mater. Chem., 2012, 22, 8394; (b)
M. Uchimura, S. Kang, R. Ishige, J. Watanabe and G. Konishi,
Chem. Lett., 2010, 39, 513; (c) Y. Arakawa, S. Nakajima, S. Kang,
M. Shigeta, G. Konishi and J. Watanabe, Liq. Cryst., 2012, DOI:
10.1080/02678292.2012.696730; (d) Y. Arakawa, S. Nakajima,
S. Kang, G. Konishi and J. Watanabe, J. Mater. Chem., 2012,
DOI: 10.1039/C2JM32489J.
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2
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1
3910 | J. Mater. Chem., 2012, 22, 13908–13910
This journal is ª The Royal Society of Chemistry 2012