In polarizing optical microscopy, 2a–d in mesophases exhibit
pseudo-focal conic textures, which are characteristic of colum-
nar mesophases. Except for 2d, these textures are maintained at
room temperature, demonstrating the stability of the liquid
crystalline phases at room temperature. To obtain information
on the structures of 2a–d in the mesophases, X-ray diffraction
studies were carried out using synchrotron radiation. The X-ray
pattern (Fig. 1) of the mesophase of 2c at room temperature
shows an intense peak and two weak peaks in the small-angle
region with reciprocal Bragg spacings in a ratio 1+A3+2. These
peaks were assigned to the (100), (110) and (200) reflections of
a hexagonal arrangement with a lattice constant a = 33.02 Å. In
the wide-angle region a broad halo at 4.43 Å is observed, which
is related to the liquid-like correlations between the molten
aliphatic chains. Similar X-ray diffraction patterns are observed
for other compounds in their mesophases. It is not clear how the
cone-shaped molecules are arranged in the mesophase. How-
ever, as previously suggested in bowl-shaped mesogens, the
cones may be stacked in a head-to-tail fashion to form a polar
column which in turn forms a hexagonal array with random
polarity.
We measured the molecular first hyperpolarizabilities (b) of
2a–c using HRS techniques.10 Regardless of the alkyl chain
length these compounds have a strong absorption band at ~ 602
nm and an intense emission at ~ 612 nm. Since they are highly
fluorescent, high-frequency demodulation of multiphoton fluo-
rescence was used to retrieve their fluorescence-free first
hyperpolarizability values. A detailed description of the experi-
mental set-up is given elsewhere.9a The measurements were
performed in CHCl3 solution. Disperse Red 1 was used as the
external reference with b = 54 3 10230 esu at 1300 nm.9c The
inherent fluorescence-free first hyperpolarizability values for
2a–c are the same within the experimental uncertainties: (189 ±
30) 3 10230 esu at 1300 nm. Using a three-level model,11 the
dispersion-free b value (b0) was calculated to be (21 ± 3) 3
10230 esu. These results are in good agreement with the recently
reported b value of 40 3 10230 esu at 1460 nm and b0 value of
10 3 10230 esu for a similar SubPc compound.6b
This work was supported by the Creative Research Initiative
Program of the Korean Ministry of Science and Technology and
by research grants from the Fund for Scientific Research -
Flanders (FWO-V) (G.0338.98 and G.0407.98), the Belgian
government (IUAP P4/11, ‘Supramolecular Chemistry and
Supramolecular Catalysis’), the University of Leuven (GOA/
95/01). G. O. is a Research Assistant and K. C. is a Senior
Research Associate of the FWO-V. The X-ray measurements
were performed at the Pohang Accelerator Laboratory (Beam-
line 3C2).
Notes and references
‡ All the compounds have been fully characterized by 1H NMR, UV-VIS,
IR and mass spectrometry and gave satisfactory elemental analyses.
Selected data for 2a: Compound 1a (2.13 g, 4.50 mmol) was dissolved in
1-chloronaphthalene (4 ml) under Ar. After cooling of the solution in an ice
bath a solution of BCl3 (1.5 ml, 1.5 mmol, 1 M solution in n-heptane) was
added. The mixture was stirred at 0 °C for 10 min and then heated to 100 °C
for 4 h. After cooling to room temperature, the mixture was diluted with
acetone. The crude product was isolated by filtration and purified by column
chromatography on silica gel using CH2Cl2 as eluent (0.30 g, 14%);
dH(CDCl3, 300 MHz) 0.88 (t, 18H), 1.59 (m, 84H), 1.89 (m, 12H), 3.31 (m,
12H), 8.51 (s, 6H); dC(CDCl3, 75 MHz) 14.52, 23.09, 28.86, 29.56, 29.72,
29.74, 29.96, 30.01, 32.31, 34.08, 119.91, 128.69, 141.23, 149.53;
nmax(KBr)/cm21 2955, 2924, 2853, 2360, 2342, 1597, 1462, 1419, 1368,
1080, 979; lmax(CHCl3)/nm (log e) 602 (5.00), 558 (4.50), 415 (4.53), 389
(4.52), 306 (4.85); Fluorescence (excitation was at 360 nm, CHCl3): lmax
/
nm 613, 504; m/z (FAB-MS) 1463 [M+H]+ (Calc. for C84H132BClN6S6: C,
68.88; H, 9.08; N, 5.74. Found: C, 68.48; H, 9.18; N, 5.48%). Compounds
2b–d were synthesized by the same method as 2a.
1 S. Chandrasekar, in Advances in Liquid Crystals, ed. G. H. Brown,
Academic Press, New York, vol. 5, 1982; S. Chandrasekar, Liq. Cryst.,
1993, 14, 3.
2 J. Simmerer, B. Glusen, W. Paulus, A. Kettner, P. Schuhmacher, D.
Adam, K. H. Etzbach, K. Siemensmeyer, J. H. Wendorff, H. Ringsdorf
and D. Haarer, Adv. Mater., 1996, 8, 815; E. J. Osburn, A. Schmidt,
L. K. Chau, S. Y. Chen, P. Smolenyak, N. R. Armstrong and D. F.
O’Brian, Adv. Mater., 1996, 8, 815; C.-Y. Liu, H.-L. Pan, M. A. Fox and
A. J. Bard, Science, 1993, 261, 897.
3 J. Malthete and A. Collet, J. Am. Chem. Soc., 1987, 109, 7544; G.
Cometti, E. Dalcanale, A. Du vosel and A.-M. Levelut, J. Chem. Soc.,
Chem. Commun., 1990, 163; J. Malthete, Adv. Mater., 1994, 6, 315; B.
Xu and T. M. Swager, J. Am. Chem. Soc., 1993, 115, 1159; B. Xu and
T. M. Swager, J. Am. Chem. Soc., 1995, 117, 5011.
4 M. Geyer, F. Plenzig, J. Rauschnabel, M. Hanack, B. del Rey, A. Sastre
and T. Torres, Synthesis, 1996, 1139; N. Kobayashi, J. Porphyriyns
Phthalocyanines, in the press.
5 N. Kobayashi, R. Kondo, S. Nakajima and T. Osa, J. Am. Chem. Soc.,
1990, 112, 9640; A. Weitemeyer, H. Kliesch and D. Wohrle, J. Org.
Chem., 1995, 60, 4900; A. Sastre, B. del Rey and T. J. Torres, J. Org.
Chem., 1996, 61, 8591.
6 (a) A. Sastre, T. Torres, M. A. Diaz-Garcia, F. Agullo-Lopez, C.
Dhenaut, S. Brasselet, I. Ledoux and J. Zyss, J. Am. Chem. Soc., 1996,
118, 2746; (b) B. del Rey, U. Keller, T. Torres, G. Rojo, F. Agullo-
Lopez, S. Nonell, S. Marti, S. Brasselet, I. Ledoux and J. Zyss, J. Am.
Chem. Soc., 1998, 120, 12 808.
7 S. J. Kim, S. H. Kang, K.-M. Park, H. Kim, W.-C. Zin, M.-G. Choi and
K. Kim, Chem. Mater., 1998, 10, 1889; S. H. Kang, M. Kim, H.-K. Lee,
Y.-S. Kang, W.-C. Zin and K. Kim, Chem. Commun., 1999, 93.
8 J. Simon and P. Bassoul, in Phthalocyanines: Properties and Applica-
tions, ed. C. C. Leznoff and A. B. P. Lever, VCH, Weinheim, 1992, vol.
2, ch. 6.
In summary, we have synthesized liquid crystalline SubPcs
exhibiting hexagonal columnar mesophases at room tem-
perature. Since they are highly fluorescent, their inherent first
hyperpolarizability values were measured by HRS using
fluorescence suppression techniques. In the mesophases, the
cone-shaped molecules appear to be stacked in a head-to-tail
fashion to form a polar column which in turn forms a hexagonal
array with random polarity. Despite the nonlinearity/transpar-
ency trade-off that appears better for dipolar that for octupolar
chromophores,12 the incorporation of dipolar chromophores
into stable macroscopic ensembles has been hampered by strong
antiparallel dipolar interactions, leading to centrosymmetric
arrangements with zero bulk susceptibility. The polar organiza-
tion of these SubPcs in the liquid crystalline phase will results
in a thermodynamically stable non-zero second order suscepti-
bility. The next challenging goal is to align all the columns with
the same polarity to achieve large ferroelectricity and second
order bulk susceptibility. We are currently working along this
line.
9 (a) G. Olbrechts, R. Strobbe, K. Clays and A. Persoons, Rev. Sci.
Instrum., 1998, 69, 2233; (b) K. Clays, G. Olbrechts, T. Munters, A.
Persoons, O.-K. Kim and L.-S. Choi, Chem. Phys. Lett., 1998, 293, 337;
(c) G. Olbrechts, K. Wostyn, K. Clays and A. Persoons, Opt. Lett., 1999,
24, 403.
10 E. Hendrickx, K. Clays and A. Persoons, Acc. Chem. Res., 1998, 31,
675.
11 J. Zyss, T. Chauvan, C. Dhenaut and I. Ledoux, Chem. Phys., 1993, 177,
281.
12 S. Stadler, R. Dietrich, G. Bourhill and Ch. Bräuchle, Opt. Lett., 1996,
21, 251.
Fig. 1 X-Ray diffraction pattern of 2c taken at room temperature.
Communication 9/04254G
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Chem. Commun., 1999, 1661–1662