Angewandte
Chemie
spectroscopy.[9] The direct measurement of the very small
absorption difference eE(f,n˜)ꢁe(n˜) is carried out with linearly
polarized light that is polarized parallel (f = 08) and perpen-
dicular (f = 908) to the applied electric field E (Figure 4);
ative alignment of the two dyes in the complex becomes
possible in an external electric field with an unprecedented
degree of dye alignment for this type of chromophore. We
intend to apply this concept to optimized NLO and PR
chromophores and to design self-complementary merocya-
nine dye building blocks that afford supramolecular poly-
mers[17] with improved nonlinear optical and photorefractive
properties.
Received: December 23, 2005
Revised: February 20, 2006
Published online: May 3, 2006
Keywords: chromophores · dyes/pigments · hydrogen bonds ·
.
nonlinear optics · supramolecular chemistry
[1] a) J. J. Wolff, R. Wortmann, Adv.Phys.Org.Chem.
1999, 32,
121 – 217; b) T. Verbiest, S. Houbrechts, M. Kauranen, K. Clays,
A. Persoons, J.Mater.Chem. 1997, 7, 2175 – 2189.
[2] F. Würthner, R. Wortmann, K. Meerholz, ChemPhysChem 2002,
3, 17 – 31.
[3] a) S. Dähne, Chimia 1991, 45, 288 – 296; b) S. R. Marder, C. B.
Gorman, F. Meyers, J. W. Perry, G. Bourhill, J.-L. BrØdas, B. M.
Pierce, Science 1994, 263, 511 – 514; c) M. Barzoukas, M.
Blanchard-Desce, R. Wortmann, Proc.SPIE-Int.Soc.Opt.
Eng. 1999, 3623, 194 – 204; d) S. Beckmann, K.-H. Etzbach, P.
Krämer, K. Lukaszuk, R. Matschiner, A. J. Schmidt, P. Schuh-
macher, R. Sens, G. Seybold, R. Wortmann, F. Würthner, Adv.
Mater. 1999, 11, 536 – 541.
Figure 4. Measured data points of the EOA spectra L(f)en˜ꢁ1 for
~
~
^
*
^
*
f=08 ( ,
, ) and f=908 ( , , ) as well as multilinear
~
~
regression curves (g, a, c) of merocyanines 9 ( , , g)
^
^
* *
and 10 ( , , a) and their complex 9·10 ( , , a) in toluene
(T=298 K, Eꢂ4106 Vmꢁ1, ca. 10ꢁ6 m).
eE(f,n˜) is the molar decadic absorption coefficient of the
solution in an externally applied field.
For dyes 9 and 10 as well as complex 9·10, Figure 4 shows
increased absorbance when the light beam is polarized
parallel to the direction of the electric field (open symbols)
and decreased absorbance when it is polarized perpendicular
to the direction of the electric field (filled symbols). Signifi-
cantly, for complex 9·10 the observed effect is far more
pronounced than for the individual dyes. To explain this
observation, it should be taken into account that for highly
dipolar chromophores like 9 and 10 and the associate 9·10,
Len˜ꢁ1 is mainly determined by the square of the ground-state
dipole moment mg. Consequently, the fact that Len˜ꢁ1 for
complex 9·10 is more than four times larger than the sum of
the Len˜ꢁ1 of 9 and 10 (Figure 4) unequivocally confirms
cooperative orientation of these dyes in the electric field.
The quantitative evaluation of the optical and electro-
optical data provides ground-state dipole moments mg,
excited-state dipole moments ma, and the integral absorption
IA for 9, 10 and 9·10 (Table 1). These results corroborate the
qualitative conclusion for the collective orientation and our
predictions for a geometry of 9·10 in which all moments seem
to be approximately parallel to each other and to the longest
axis of the head-to-tail assembly of two chromophores as well.
Also, the excited-state dipole moments ma, determined
through Len˜ꢁ1 due to the shift of the absorption band, gives
a further hint for cooperative orientation of the two
chromophores in complex 9·10. This will be discussed in
detail in a forthcoming paper.
[4] a) D. M. Burland, R. D. Miller, C. A. Walsh, Chem.Rev. 1994,
94, 31 – 75; b) L. R. Dalton, A. W. Harper, B. Wu, R. Ghosn, J.
Laquindanum, Z. Liang, A. Hubbel, C. Xu, Adv.Mater. 1995, 7,
519 – 540.
[5] a) L. R. Dalton, A. W. Harper, B. H. Robinson, Proc.Natl.
Acad.Sci.USA 1997, 94, 4842 – 4847; b) Y. V. Pereverzev, O. V.
Prezhdo, L. R. Dalton, ChemPhysChem 2004, 5, 1821 – 1830.
[6] a) R. Wortmann, U. Rꢀsch, M. Redi-Abshiro, F. Würthner,
Angew.Chem. 2003, 115, 2126 – 2129; Angew.Chem.Int.Ed.
2003, 42, 2080 – 2083; b) F. Würthner, S. Yao, T. Debaerde-
maeker, R. Wortmann, J.Am.Chem.Soc. 2002, 124, 9431 – 9447;
c) F. Würthner, S. Yao, Angew.Chem. 2000, 112, 2054 – 2057;
Angew.Chem.Int.Ed. 2000, 39, 1978 – 1981.
[7] Hydrogen bond directed NLO-active solid-state material pre-
pared by vapor-phase deposition have been reported: a) C. Cai,
M. M. Bꢀsch, Y. Tao, B. Müller, Z. Gan, A. Kündig, C. Bosshard,
I. Liakatas, M. Jäger, H. P. Günter, J.Am.Chem.Soc. 1998, 120,
8563 – 8564; b) P. Zhu, H. Kang, A. Facchetti, G. Evmenenko, P.
Dutta, T. J. Marks, J.Am.Chem.Soc. 2003, 125, 11496 – 11497.
For an amorphous solid state material formed by hydrogen bond
directed self-assembly, see: H. Saadeh, L. Wang, L. Yu, J.Am.
Chem.Soc. 2000, 122, 546 – 547.
[8] According to electrostatic considerations, for spherical mole-
cules the parallel orientation (Figure 1b) is favored. However,
for typical flat and elongated dye molecules the antiparallel side-
on association (Figure 1a) is preferred due to the smaller
intermolecular distance: C. P. J. M. van der Vorst, S. J. Picken in
Polymers as Electrooptical and Photooptical Active Media (Ed.:
V. P. Shibaev), Springer, Berlin, 1996, pp. 173 – 211.
[9] a) W. Liptay in Excited States, Vol.1 (Ed.: E. C. Lim), Academic
Press, New York, 1974, pp. 129 – 229; b) R. Wortmann, K. Elich,
S. Lebus, W. Liptay, P. Borowicz, A. Grabowska, J.Phys.Chem.
1992, 96, 9724 – 9730.
In summary, this work introduces the first supramolecular
architecture in which two dipolar dyes are assembled in a
head-to-tail fashion by multiple hydrogen bonds with sum-
mation of their dipole moments. In this geometry a cooper-
[10] a) S. K. Chang, A. D. Hamilton, J.Am.Chem.Soc.
1988, 110,
1318 – 1319. For recent applications of the Hamilton receptor for
Angew. Chem. Int. Ed. 2006, 45, 3842 –3846
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3845