Table 3 EFISH data of chromophores
In conclusion, the combined features of NLO activity and
thermal stability make chromophores 1, 2 and 3 interesting
candidates for the synthesis of potentially second order NLO
active polymer materials.
Chromophore
Solvent
λmax/nm
µgβ/10Ϫ48 esu
1
2
3
CHCl3
CHCl3
DMF
453
428
465
900
1250
1350
Acknowledgements
Financial support of MIUR of Italy (PRIN 2000) is gratefully
acknowledged. Thanks are due to CIMCF of the Università di
Napoli “Federico II” for NMR and MS facilities and to the
director of the CNR Istituto di Biostrutture e Bioimmagini of
Naples for kind permission to use the Nonius diffractometer.
References and Notes
1 L. R. Dalton, A. Harper, A. Ren, F. Wang, G. Todorova, J. Chen,
C. Zhang and M. Lee, Ind. Eng. Chem. Res., 1999, 38, 8–33.
2 Y. Shi, C. Zhang, H. Zhang, J. H. Bechtel, L. R. Dalton,
B. H. Robinson and W. H. Steier, Science, 2000, 288, 119–122.
3 T. Plisˇka, W.-R. Cho, J. Meier, A.-C. Le Duff, V. Ricci, A. Otomo,
M. Canva, G. I. Stegeman, P. Raimond and F. Kajzar, J. Opt. Soc.
Am. B, 2000, 17(9), 1554–1564.
4 V. P. Rao, A. K.-Y. Jen, J. Chandrasekhar, I. N. N. Namboothiri and
A. Rathna, J. Am. Chem. Soc., 1996, 118, 12443–12448.
5 V. P. Rao, A. K.-Y. Jen, K. Y. Wong and K. J. Drost, Tetrahedron
Lett., 1993, 34(11), 1747–1750.
6 A. Abbotto, S. Bradamante, A. Facchetti and G. A. Pagani, J. Org.
Chem., 1997, 62(17), 5755–5765.
7 S. Yuquan, Z. Yuxia, L. Zao, W. Jianghong, Q. Ling, L. Shixiong,
Z. Jianfeng and Z. Jiayun, J. Chem. Soc., Perkin Trans. 1, 1999,
3691–3695.
8 C. W. Dirk, H. E. Katz, M. L. Schilling and L. A. King, Chem.
Mater., 1990, 2, 700–705.
9 W. N. Leng, Y. M. Zhou, Q. H. Xu and J. Z. Liu, Polymer, 2001, 42,
9253–9259.
Fig. 4 DSC thermograms on heating (upper curve) and cooling (down
curve) for 2. Scanning rate 10 K minϪ1
.
The NLO activity of chromophores has been determined by
the EFISH technique in solution and µgβ coefficients are
reported in Table 3. Owing to the absorption features of
chromophores and to the fundamental laser wavelength used,
the reported values may be considered as free from resonance
enhancement, thus allowing safe comparisons. The three
chromophores have in common the first part of the molecular
skeleton, i.e. the 4-(4-dialkylaminophenylazo)phenyl group. To
this, 4-nitrophenyl in 1 and 4Ј-nitrostilben-4-yl in 2 are attached
through a 1,3,4-oxadiazole bridge, while in 3 2-nitro-4-ethenyl-
thiophene is attached. The length of the conjugation path in
1 (taken as the distance between N-aniline and N-nitro atoms)
is 18.3 Å; this increases to about 24–25 Å in the case of 2. For
3 a slightly smaller value than 1 may be derived.
10 R. Centore, A. Tuzi and B. Panunzi, Z. Kristallogr., 1997, 212,
890–894.
11 P. Ambrosanio, R. Centore, S. Concilio, B. Panunzi, A. Sirigu and
N. Tirelli, Polymer, 1999, 40, 4923–4928.
12 P. E. Cassidy, Thermally Stable Polymers, Marcel Dekker,
New York, 1980, p. 179.
13 M. J. Nanjan, in Encyclopedia of Polymer Science and Engineering,
ed. J. I. Kroschwitz, John Wiley, New York, 1985, vol. 12,
pp. 322–339.
14 G. J. Lee, S. W. Cha, S. J. Jeon, J.-I. Jin and J. S. Yoon, J. Korean
Phys. Soc., 2001, 39(5), 912–915.
15 J. O. Morley, J. Chem. Soc., Perkin Trans. 2, 1995, 17–180.
16 U. S. Choi, Bull. Korean Chem. Soc., 1998, 19(3), 299–307.
17 V. Lukesˇ, M. Breza and V. Laurinc, J. Mol. Struct.: THEOCHEM,
2002, 582, 213–224.
18 V. Bruno, A. Castaldo, R. Centore, A. Sirigu, F. Sarcinelli,
M. Casalboni and R. Pizzoferrato, J. Polym. Sci.: Part A: Polym.
Chem., 2002, 40(10), 1468–1475.
19 Sigma-Aldrich Catalogue, 1999–2000, Sigma-Aldrich Co.
20 P. J. Newcombe and R. K. Norris, Aust. J. Chem., 1979, 32,
2647–2658.
21 H. Y. Woo, H.-K. Shim and K.-S. Lee, Macromol. Chem. Phys.,
1998, 199(7), 1427–1433.
The higher value measured for 2 as compared to 1 is con-
sistent with the longer conjugation path.
On the other hand the value measured for 3 which is higher
than 1 and also than 2 is indicative of the high efficiency of the
thiophene heterocycle in giving highly NLO active chromo-
phores.1,4,6 In particular, in 3, an important role should be
played by the acceptor group (NO2) being directly attached to
the heterocycle ring. Finally, the value reported for 3 is compar-
able with that of chromophores having the stronger dicyano-
vinyl electron withdrawing group attached to thiophene ring.25
A fair thermal stability is observed for the chromophores. If
defined as the temperature corresponding to 5% weight loss in a
TGA experiment at a heating run of 10 ЊC minϪ1 under nitrogen
atmosphere, decomposition temperatures are 337 ЊC for 1 and
332 ЊC for 2. A lower value, 240 ЊC, is observed for 3. This,
however, could be also a consequence of the absence of the
acetyl protective groups on the aliphatic tails.
22 G. M. Sheldrick, SHELX-97. University of Göttingen, Germany,
1997.
23 T. Thami, P. Bassoul, M. A. Petit, J. Simon, A. Fort, M. Barzoukas
and A. Villaeys, J. Am. Chem. Soc., 1992, 114, 915–921.
24 A. Castaldo, R. Centore, A. Peluso, A. Sirigu and A. Tuzi, Struct.
Chem., 2002, 13(1), 27–35.
25 V. P. Rao, A. K. Ken, K. Y. Wong, K. Drost and R. M. Mininni,
Proc. SPI - Int. Soc. Opt. Eng.E, 1992, 1775, 32–42.
J. Chem. Soc., Perkin Trans. 2, 2002, 1791–1795
1795