Tetrahedral bipyridyl copper(I) complexes: A new class of non-dipolar chromophore for nonlinear optics

Article abstract of DOI:10.1039/a901972c

The synthesis of 4,4'-bis(dialkylaminostyryl)-6,6'-dimethyl-2,2'-bipyridine ligands is described; the corresponding tetrahedral bis(bipyridyl) copper(I) complexes have been prepared, and their second-order nonlinear optical properties determined by harmon

Full text of DOI:10.1039/a901972c

Tetrahedral bipyridyl copper(i) complexes: a new class of non-dipolar
chromophore for nonlinear optics
a
a
b
b
b
Thierry Renouard, Hubert Le Bozec,* Sophie Brasselet, Isabelle Ledoux and Joseph Zyss
a
Laboratoire de Chimie de Coordination et Catalyse, UMR 6509 CNRS-Universit e´ de Rennes 1, Campus de
Beaulieu, 35042 Rennes Cedex, France. E-mail: lebozec@univ-rennes.fr
ENS Cachan, Laboratoire de Photonique Quantique et Mol e´ culaire, 61 avenue du Pr e´ sident Wilson, 94235 Cachan,
France
b
Received (in Oxford, UK) 12th March 1999, Accepted 9th April 1999
The synthesis of 4,4A-bis(dialkylaminostyryl)-6,6A-dimethyl-
,2A-bipyridine ligands is described; the corresponding tetra-
the synthesis of such ligands and we show that the correspond-
2
ing copper(i) complexes represent a new class of nondipolar
NLO organometallic chromophore combining good transpar-
ency and large nonlinearity.
hedral bis(bipyridyl) copper(i) complexes have been pre-
pared, and their second-order nonlinear optical properties
determined by harmonic light scattering (HLS) at 1.34 mm;
these new octupolar complexes exhibit large molecular
hyperpolarisabilities b.
The new ligands 2a and 2b were prepared by a controlled
functionalisation of the 4,4A-positions of 4,4A,6,6A-tetramethyl-
2,2A-bipyridine 1: dilithiation of 1 with LDA at 220 °C
followed by reaction with 2 equiv. of p-dibutylaminobenzalde-
hyde afforded the corresponding dialcohol, and subsequent
dehydration with pyridinium toluene-p-sulfonate (PTPS) in
boiling toluene yielded exclusively 2a in 75% overall yield.
Ligand 2b was prepared analogously as described for 2a
(Scheme 1). The observation of a strong NOE (10%) between
A new concept of octupolar non-linearities of two- and three-
dimensional (2D and 3D) molecules has recently been proposed
and has opened new perspectives in elaboration of efficient
1
nonlinear optical materials. Research on octupolar structures
has mainly focused on organic chromophores with threefold
symmetry such as 1,3,5-triamino-2,4,6-trinitrobenzene and
the methyl groups at C6 and the H
,6A
5,5A
protons clearly
2
3
2,4
related derivatives, crystal violet, trisubstituted amines and
established the regioselectivity of the reaction. In their UV–VIS
2,5
cyanine salts. The first examples of nondipolar tetrahedral
spectra, 2a,b show typical bands at ca. 390 nm (e ≈ 50 000
6
7
8
3
21
21
organotin, phosphonium and biphenyl chromophores have
recently been investigated. Organotransition metal complexes
also offer many possibilities for the design of 3D non-
centrosymmetric octupolar molecules owing to the large
diversity of metals, ligands and geometries. Thus, nonlinearities
of tris(bipyridine) ruthenium(ii) complexes has been demon-
strated9 and we have recently reported the enhanced molec-
ular hyperpolarisability b of octahedral ruthenium(ii) com-
plexes possessing three bipyridine ligands substituted in
dm mol cm ) which are assigned to intramolecular charge-
transfer transitions.16
Copper(i) complexes were obtained upon treatment of the
ligands 2a,b (2 equiv.) with [Cu(MeCN) ]PF (1 equiv.) in
4 6
dichloromethane solution (Fig. 1). The red complexes 3a,b
were isolated in nearly quantitative yield and their structures
,10
1
were demonstrated by FAB-MS and H NMR spectroscopy. In
1
the H NMR spectra, the methyl groups in the 6,6A positions are
characteristically shifted upfield by 0.45 ppm with respect to the
free ligands, and according to the strong vicinal coupling
constants of the olefinic protons (JHH ≈ 16 Hz) no detectable
E/Z isomerization of the alkenyl fragments is observed. The
UV–VIS spectra recorded in dichloromethane are dominated by
intense intraligand charge-transfer bands (lILCT ≈ 420 nm, e ≈
1
1
4
,4A-positions by p-dialkylaminostyryl groups. In the course
of our study of nondipolar complexes for NLO, we have been
interested in the generation of metal complexes displaying
tetrahedral coordination geometries. Copper(i)–bipyridine or
–
phenanthroline complexes with substituents a to the nitrogen
3
21
21
atoms are known to give stable tetrahedral molecules of D2d
80 000 dm mol cm ) which are 30–40 nm red-shifted upon
complexation. It is noteworthy that the bis(bipyridyl)copper(i)
derivatives 3a,b have a considerably blue-shifted ILCT band
when compared to the corresponding tris(bipyridyl)ruthe-
nium(ii) complexes (lILCT ≈ 515 nm),11 which is of crucial
importance for second-harmonic generation. The MLCT transi-
symmetry12 and such complexes have been widely used to
13
prepare molecular architectures such as catenates and knots,
helicates14 and polymers. Using this approach, we sought to
design 4,4A-dialkenyl-6,6A-dimethyl-2,2A-bipyridines in which
the alkenyl fragments bear p-donor groups. Here we describe
15
Scheme 1
Chem. Commun., 1999, 871–872
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this observed decrease of b as compared to the octupolar
ruthenium species.
To summarize, we have synthesized and investigated a new
class of nondipolar NLO complexes showing good transpar-
ency/efficiency trade-off. Work towards the incorporation of
such chromophores into macromolecular architectures are
under progress.
Notes and references
1
J. Zyss, Nonlinear Opt., 1991, 1, 3; J. Chem. Phys., 1993, 98, 6583; J.
Zyss and I. Ledoux, Chem. Rev., 1994, 94, 77.
2
I. Ledoux, J. Zyss, J. S. Siegel, J. Brienne and J. M. Lehn, Chem. Phys.
Lett., 1990, 172, 440; T. Verbiest, K. Clays, C. Semyr, J. Wolff, D.
Reihoudt and A. Persoons, J. Am. Chem. Soc., 1994, 116, 9320; J. L.
Bredas, F. Meyers, B. M. Pierce and J. Zyss, J. Am. Chem. Soc., 1992,
114, 4928; R. Wortmann, C. Glana, P. Kr a¨ mer, R. Matschiner, J. J.
Wolff, S. Kraft, B. Treptow, E. Barbu, D. L a¨ ngle and G. G o¨ ltz, Chem.
Eur. J., 1997, 3, 1765.
Fig. 1
I
tion [Cu ? p*(bpy)] is typically observed at ca. 480 nm with
relatively smaller absorption coefficients and can be discerned
in the spectra as a shoulder of the more intense ILCT band.
As EFISH experiment is precluded for nondipolar and/or
ionic molecules like 3, the molecular hyperpolarisability b was
measured by means of the harmonic light scattering technique
3
4
5
J. Zyss, T. Chauvan, C. Dhenaut and I. Ledoux, Chem. Phys., 1993, 177,
2
81.
S. Stadler, Ch. Br a¨ uchle, S. Brandl and R. Gompper, Chem. Mater.,
996, 8, 414.
(
HLS).17 The experiments were performed in chloroform at a
1
fundamental wavelength of 1.34 mm, generated by a Q-
S. Stadler, Ch. Br a¨ uchle, S. Brandl and R. Gompper, Chem. Mater.,
1996, 8, 676.
switched, mode-locked Nd:YAG laser providing subnano-
second pulse train at 10 Hz repetition rate. The T
d
(or D
2
)
6 M. Lequan, C. Branger, J. Simon, T. Thami, E. Chauchard and A.
Persoons, Adv. Mater., 1994, 6, 851.
symmetry reduces the nonlinear microscopic coefficient to only
one non-vanishing term, bxyz, which can be easily deduced from
the following relation: < b HLS > = 4/7 b2xyz. The experimen-
7
C. Lambert, E. Schm a¨ lzlin, K. Meerholz and C. Br a¨ uchle, Chem. Eur.
J., 1998, 4, 512.
2
2
1/2
> 1/2, deduced from
8 M. Blanchard-Desce, J.-B. Baudin, O. Ruel, L. Julien, S. Brasselet and
J. Zyss, Opt. Mater., 1997, 6, 276.
tally determined < b > , the static < b
0
2
<
b > using a degenerate three-level dispersion model valid in
the case of purely octupolar molecules, and the corresponding
xyz coefficients for 3a,b are given in Table 1.
9
J. Zyss, C. Dhenaut, T. Chauvan and I. Ledoux, Chem. Phys. Lett., 1993,
06, 409.
18
2
b
1
0 I. D. Morrison, R. G. Denning, W. M. Laidlaw and M. A. Stammers,
Rev. Sci. Instrum., 1996, 67, 1445.
a
b
Table 1 Linear and nonlinear optical data
1
1 C. Dhenaut, I. Ledoux, I. F. W. Samuel, J. Zyss, M. Bourgault and H. Le
Bozec, Nature, 1996, 374, 339; Owing to possible two-photon excited
luminescence,10 the reported hyperpolarisabilities were overestimated
3
1030
1030
HLS0/esu bxyz/esu
1030
1030
xyz0/esu
l/nm (e/dm
Complex mol cm21)
21
bHLS/esu
b
b
2
1/2
230
and new measurements gave < b > as ≈ 800–1000 3 10
esu: S.
Brasselet, C. Dhenaut, I. Ledoux and J. Zyss, unpublished results.
3
3
a
a
424(83300)
84(sh)
420(73800)
75(sh)
. b HLS measurements in CHCl
144
78
190
169
103
93
1
2 P. J. Burke, K. Henrick and D. R. McMillin, Inorg. Chem., 1982, 21,
4
1
881; D. A. Bardwell, J. C. Jeffery, C. A. Otter and M. D. Ward,
b
128
70
Polyhedron, 1996, 15, 191.
4
1
3 J.-P. Sauvage, Acc. Chem. Res., 1990, 23, 319; C. O. Dietrich-Bucheker
and J.-P. Sauvage, Chem. Rev., 1987, 87, 795; C. O. Dietrich-Bucheker,
J. F. Nierengarten, J.-P. Sauvage, N. Armaroli and L. De Cola, J. Am.
Chem. Soc., 1993, 115, 11 237; C. O. Dietrich-Bucheker, J.-P. Sauvage,
A. De Cian and J. Fischer, J. Chem. Soc., Chem. Commun., 1994,
In CH
2
Cl
2
3
at 1.34 mm. The error in the
measurements is estimated to be ±10%.
Results show that chromophores 3a and 3b exhibit micro-
scopic optical nonlinearities which are larger than those of
recently reported tetrahedral molecules such as the tetra-
kis(dibutylaminoazobenzenephosphonium)chromophore [lmax
2
231.
1
4 J.-M. Lehn, A. Rigault, J. Siegel, J. Harrowfield, B. Chevrier and D.
Mores, Proc. Natl. Acad. Sci. USA, 1987, 84, 2565; J. M. Lehn and A.
Rigault, Angew. Chem., Int. Ed., 1998, 27, 1095; M. T. Youinou, R.
Ziessel and J.-M. Lehn, Inorg. Chem., 1991, 30, 2144; G. Baum, E. C.
Constable, D. Fenske, C. E. Housecroft and T. Kulke, Chem. Commun.,
1999, 195.
0
230
7
=
511 nm; bHLS = 56.7 3 10
esu]. Dibutylaminophenyl
is slightly more efficient than the methyl(octyl)aminophenyl
donor group, a trend that have already been observed for
1
5 W. Velten and M. Rehahn, Chem. Commun., 1996, 2639.
16 M. Bourgault, T. Renouard, B. Lognon e´ , C. Mountassir and H. Le
octahedral trisbipyridyl ruthenium(ii) complexes bearing the
same dialkylaminophenyl groups.11 Compared to these latter
Bozec, Can. J. Chem., 1997, 75, 318.
complexes, the copper(i) derivatives 3 have lower bHLS values.
At first glance, this may be due to the presence of four vs. six
1
7 R. W. Terhune, P. D. Maker and C. M. Savage, Phys. Rev. Lett., 1965,
1, 681.
8 M. Joffre, D. Yaron, R. J. Silbey and J. Zyss, J. Chem. Phys., 1992, 97,
607.
6
+
donor groups and to the less efficient acceptor strength of Cu
1
vs. Ru2+ metallic ion. A more pronounced blue-shift of the
absorption maximum is observed in the copper complexes, and
the higher energy of the ILCT excited state also contributes to
5
Communication 9/01972C
872
Chem. Commun., 1999, 871–872