The synthesis of tetrahedral bipyridyl metallo-octupoles with large second- and third-order nonlinear optical properties

Article abstract of DOI:10.1016/j.dyepig.2011.06.013

Two new 4,4′-bis(donor)-6,6′-diphenyl- 2,2′-bipyridine ligands and their corresponding D_2d (Cu^I, Ag^I, Zn^II) octupolar metal complexes were synthesized, and their linear and nonlinear optical properties were inve

Full text of DOI:10.1016/j.dyepig.2011.06.013

Dyes and Pigments 92 (2011) 681e688
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
The synthesis of tetrahedral bipyridyl metallo-octupoles with large
second- and third-order nonlinear optical properties
,
b
c
d
Huriye Akdas-Kilig a , Jean-Pierre Malval , Fabrice Morlet-Savary , Anu Singh ,
*
Loic Toupet a, Isabelle Ledoux-Rak d, Joseph Zyss d, Hubert Le Bozec a
a SciencesChimiques de Rennes, UMR 6226, CNRS-Université de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, France
b Institut de Sciences des Matériaux de Mulhouse, LRC CNRS 7228, Université de Haute Alsace, 15 rue Jean Starcky, 68057 Mulhouse, France
c Département de Photochimie Générale, Université de Haute-Alsace, ENSCMu, 3 rue Alfred Werner, 68093 Mulhouse Cedex, France
d Laboratoire de Photonique Quantique et Moléculaire, UMR CNRS 8537, Institut d’Alembert, ENS Cachan, 61 avenue du Président Wilson, 94235 Cachan, France
a r t i c l e i n f o
a b s t r a c t
Two new 4,40-bis(donor)-6,60-diphenyl- 2,20-bipyridine ligands and their corresponding D2d (CuI, AgI,
ZnII) octupolar metal complexes were synthesized, and their linear and nonlinear optical properties were
investigated. A single crystal X-ray structure was also determined for the bis[4,40-bis(diethylaminos-
Article history:
Received 8 March 2011
Received in revised form
8 June 2011
Accepted 10 June 2011
Available online 22 June 2011
tyryl)-6,60-diphenyl-bipyridine]copper(I) complex, which revealed
a
distorded pseudo-tetrahedral
geometry. Molecular second-order nonlinear optical properties were determined for the complexes
using the Harmonic Light Scatterring technique at 1.91 m. These metallo-chromophores display large
m
first hyperpolarizabilities b1.91 in the range of 211e340 ꢀ 10ꢁ30 esu, which increase with the Lewis acidity
of the metal ion. The two-photon absorption properties of the bipyridyl ligands and related complexes
were determined using either the two-photon emission method for fluorescent compounds or the open
aperture Z-scan technique for non emissive ones. The complexes display red-shifted two-photon
absorption bands compared to their metal-ion free chromophores, as well as a large increase of the
maximum two-photon absorption cross-sections.
Keywords:
Nonlinear optics
Octupolar tetrahedral complexes
Harmonic light scattering
Two-photon emission fluorescence
Z-scan
Bipyridine
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
fifteen years [13e19]. In this context, our research group has been
involved in the NLO properties of bipyridyl metal complexes. We
Molecular nonlinear optical (NLO) materials have been the focus
of intensive investigations for several decades from both the
fundamental and practical points of view for their possible appli-
cations in the domain of optoelectronics and photonics [1e4].
Among them, transition metal complexes are especially interesting
because they offer, compared to organic molecules, additional
advantages due to their structural, electronic and optical properties
[5e12]. Greater design flexibility can be achieved by varying the
metal, its oxidation state, the ligand environment and the geom-
etry. In addition, many complexes are known to possess low-lying
charge transfer transitions such as intraligand (ILCT), metal-to-
ligand (MLCT) and ligand-to-metal (LMCT), which can be associ-
have previously shown that ligands such as donor-substituted
bipyridyl are excellent building blocks for the construction of
either dipolar compounds [20e22] or non-dipolar metal complexes
of D3 symmetry [23e25]. These studies have underlined the
important role of both the metallic core and the bipyridyl substit-
uents to enhance the quadratic nonlinear optical responses of such
chromophores. These molecules are also attractive for third-order
nonlinear applications, including two-photon absorption (TPA),
and recent experimental and theoretical studies on tris(bipyridyl)
metal complexes have revealed moderate to large TPA cross-
sections s2 [26e30].
The design of tetrahedral (Td) or pseudo-tetrahedral (D2d) metal
complexes with quadratic NLO and TPA properties has been scarcely
studied, in comparison with octahedral D3 metal complexes [13,31].
Bipyridyl ligands also allow the design of D2d octupoles by coordi-
nation of two bipyridines to metal ions, such as CuI, AgI or ZnII. This
type of geometry has been extensively used to design new archi-
tectures that feature an original topology, such as catenates or knots
[32]. The key feature to stabilize the tetrahedral geometry is
the incorporation of either alkyl or aryl substituents at the
ated with large second-order nonlinearities b.
Metal complexes of nitrogen-heterocyclic ligands, such as
pyridines and oligopyridines, represent an important class of NLO
chromophores which have received much attention during the last
* Corresponding author. Tel.: þ33 (0)2 23 23 43 67; fax: þ33 (0)2 23 23 69 39.
E-mail address: huriye.akdas@univ-rennes1.fr (H. Akdas-Kilig).
0143-7208/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2011.06.013

682
H. Akdas-Kilig et al. / Dyes and Pigments 92 (2011) 681e688
6,60-positions in the bipyridyl ligand. We have previously reported
the first examples of pseudo-tetrahedral Cu(I), Ag(I) and Zn(II)
complexes containing the 4,40-dialkylaminostyryl-6,60-dimethyl-
2,20-bipyridine ligand a (Scheme 1), which have been shown to
display moderate to good second-order NLO responses b [24]. These
preliminary results prompted us to prepare and study a series of
complexes featuring bipyridine ligands with phenyl groups as
HLS signal from two-photon fluorescence becomes negligible, as its
harmonic at 955 nm lies far from the fluorescence domain. The values
of b1.91 and the corresponding dipersion free hyperpolarizabilities b0
for all the complexes are reported in Table 1. These “static” b0 values
are inferred from experimental ones using a two-level dispersion
model according to Ref. [37]. Although this model is not valid for 2- or
3-dimensional charge transfer processes [38], it has been shown that
in the case of purely octupolar systems, the 3-level dispersion
equation is equivalent to the 2-level one owing to the degeneracy of
the two excited states [39]. In the case of MLCT additional transition
for copper complexes, the weak molar absorption coefficient asso-
substituents a to the nitrogen atoms. Here we describe the synthesis
of ligands b and c and we show that the corresponding metal
complexes represent a new class of D2d tetrahedral organometallic
chromophores. The replacement of methyl by phenyl substituents is
expected to give rise to stable pseudo-tetrahedral complexes with
larger second- and third-order nonlinearities, as the consequence of
ciated to it makes its contribution to the
b values almost negligible.
HLS measurements were carried out in concentrated dicholoro-
methane solution (1e5 ꢀ10ꢁ2 mol Lꢁ1) with a concentrated solution
of ethyl-violet as reference (b1.91 ¼170 ꢀ 10ꢁ30 esu).
extended conjugated p-systems.
In order to include the effect of varying the donor moiety, we
have also incorporated on the 4,40-positions a diphenylaminostyryl
The TPA cross sections (d) of fluorescent chromophores were
group, because its contains an enhanced
p
-conjugation which is
determined using the relative two-photon excited fluorescence
(TPEF) method [40,41]. These measurements were performed with
a femtosecond mode-locked Ti: Sapphire laser (Spectra-Physics,
Mai Tai: pulse duration: w100 fs; repetition rate: 80 MHz; wave-
length range: 690e1020 nm). A 10ꢁ4 M solution of fluorescein [41]
in water at pH ¼ 11 (dr ¼ 38 ꢂ 9.7 GM at 782 nm) was used as the
also expected to increase the NLO responses. The effect of alkyl vs
aryl substitution on the molecular hyperpolarizability has already
been observed on push-pull derivatives, and explained by an
enhanced
p-conjugation in the case of diarylamino donor groups
[33e36].
reference (r). The value of
d for a sample (s) is given by:
2. Experimental
SSFrhrcr
dS
¼
dr
S
rFShScS
2.1. Materials
where S is the detected two-photon excited fluorescence integral
All reactions were performed under argon with Schlenk tech-
niques. All reagents and solvents were of commercial quality and
were purified or dried and stored under nitrogen using standard
procedures.
area, c the concentration of the chromophores, and is the fluo-
F
rescence quantum yield of the chromophores. is the collection
h
efficiency of the experimental set-up and accounts for the wave-
length dependence of the detectors and optics as well as the
difference in refractive indices between the solvents in which the
reference and sample compounds are dissolved. The measurements
were conducted in a regime where the fluorescence signal showed
a quadratic dependence on the intensity of the excitation beam, as
expected for two-photon-induced emission. The collection of the
two-photon-induced fluorescence signal was performed at the same
excitation wavelength (i.e. 782 nm) for fluorescein and compounds.
The concentration of the compounds in CH2Cl2 was in the range of
0.5e3 ꢀ 10ꢁ4 M. The laser intensity was in the range of 0.2e2 ꢀ GW/
cm2. The experimental error on the reported cross section is 15e20%.
The two-photon absorption cross sections for the non-
fluorescent compounds were measured at 800 nm and 900 nm by
using open-aperture Z-scan method [42,43] with the same femto-
second laser used for TPEF. After passing through a beam expander
(ꢀ4), the laser beam is focused using an f ¼ 10 cm lens and passed
through a quartz cell (1 mm optical path length). The position of the
2.2. Measurements
NMR spectra (1H, 13C) were recorded at room temperature on
BRUKER DPX200 and DMX500 spectrometers operating at 200.12
and 500.13 MHz. UVeVisible spectra were recorded on a Cary 5000
spectrophotometer. Fluorescence experiments were performed in
dilute dichloromethane solution (z10ꢁ5 mol Lꢁ1) with a PTI spec-
trometer. High-resolution mass spectra were obtained on a Bruker
Micro-TOF-Q II instrument or a ZabSpec TOF Micromass instrument
at CRMPO, University of Rennes 1. Elemental analyses were per-
formed by the CRMPO, University of Rennes 1.
The Harmonic Light Scattering (HLS) technique was used for the
molecular hyperpolarisability (b) measurements which were per-
formed in dicholoromethane at a fundamental wavelength of
1.91
mm. Using this wavelength ensures that any contribution to the
R2N
R2N
n+,
NR2
Y
Y
N
Y
N
N
M
N
Y
N
N
Y
NR2
Y
R2N
NR2
x =a, b, c
xCu Mn+ = Cu+, X = PF6
-
a
R = Bu, Y = Me
R = Et, Y = Ph
R = Ph, Y = Ph
xAg Mn+ = Ag+, X = OTf-
xZn Mn+ = Zn2+, X = OTf-
b
c
Scheme 1. Chemical structures of representative bipyridyl pro-ligands a, b and c and corresponding pseudo-tetrahedral Copper(I), Silver(I) and Zinc(II) complexes.

H. Akdas-Kilig et al. / Dyes and Pigments 92 (2011) 681e688
683
Table 1
temperature. The solution, which immediately turned brown, was
then heated at 90 ꢃC overnight. Addition of water led to the
formation of a pale brown mixture. Dimethylformamide was
removed by trap-to-trap method, the mixture was extracted by
dichloromethane, dried over MgSO4, and the solvent was removed
under vacuum. Recrystallization from a dichloromethane-pentane
Crystal and structure refinement data of complex bCu
.
Empirical
formula
Formula weight 1645.64
Crystal system
Space group
a (Å)
C93.50 H95
q
range (ꢃ)
2.60 to 27.00
Cl3 Cu F6 N8 P
Index range
ꢁ12 ꢄ h ꢄ 17
ꢁ21 ꢄ k ꢄ 20
ꢁ27 ꢄ l ꢄ 26
30,637
18,285
Full-matrix
Least-squares
Triclinic
P-1
mixture gave b as a orange microcrystalline powder (230 mg,
13.8741(9)
16.4820(10)
21.2900(10)
70.931(7)
86.407(6)
84.681(6)
4578.8(5)/2
1.194 g/cmꢁ3
0.403
Reflns collected
Unique reflns
Refinement method
on F2
0
79%). 1H NMR (CD2Cl2, 500 MHz):
d
ppm 8.68 (s, 2H, H6,6 ), 8.31
b (Å)
c (Å)
0
(d, J ¼ 8.3 Hz, 4H, C6H4e), 7.92 (s, 2H, H3,3 ), 7.58 (m, 12H,
C6H5e þ eCH]CHe), 7.10 (d, J ¼ 16.3 Hz, 4H, eCH]CHe), 6.75
(d, J ¼ 9.0 Hz, 4H, C6H5e), 3.46 (q, J ¼ 7.1 Hz, 8H, CH3CH2e), 1.24
a
b
g
(ꢃ)
(ꢃ)
(ꢃ)
Goodness-of-fit on F2 0.919
R1 [I > 2
wR2 [I > 2
s
(I)]
(I)]
0.0970
0.2470
0.2175
0.2874
(t, J ¼ 7.1 Hz, 12H, CH3CH2e). 13C NMR (CDCl3, 400 MHz):
d ppm
V (Å3), Z
s
Dcalc
R1 (all data)
156.8, 156.5, 148.1, 147.3, 140.0, 133.1, 128.7, 128.68, 128.64, 127.1,
123.7, 121.6, 117.0, 116.8, 111.6, 44.4, 12.6. Anal. found: C, 83.09; H,
7.05; N, 8.72. C46H46N4$0.5H2O Calc.: C, 83.22; H, 7.14; N, 8.44, m/z
(Micro-TOF-Q II) 655.3793; ([M þ H]þ, C46H47N4 requires
655.3795).
m
(mmꢁ1
)
wR2 (all data)
F (000)
1722
Residual (e Åꢁ3
)
1.349 and ꢁ0.720
sample cell is varied along the laser-beam direction (z-axis) using
a Z-step motorized stage controlled by a computer. At constant
incident excitation, the local power density within the sample is
changed and the corresponding transmitted laser beam, T(z),
recorded with a silicon photodetector (Ophir PD300) is monitored
in connection with the z-position of the cell. The on-axis peak
intensity of the incident pulses at the focal point, I0, ranged from 40
to 45 GW cmꢁ2. If we assume that the linear absorption of the
sample is negligible at working wavelength and that the laser
exhibits a Gaussian beam profile, the nonlinear absorption coeffi-
2.3.2. Synthesis of ligand c
Compound c was prepared according to the above procedure,
from
6,60-diphenyl-4,40-dimethyl-[2,20]-bipyridine
(160 mg,
0.47 mmol), 4-diphenylaminobenzaldehyde (285 mg, 1.04 mmol,
2.2 equiv.) and tBuOK (214 mg, 1.9 mmol) in DMF (15 mL), (250 mg,
0
62%). 1H NMR (CDCl3, 500 MHz):
d
ppm 8.68 (s, 2H, H6,6 ), 8.24 (d,
0
J ¼ 7.2 Hz, 4H, C6H4e), 7.87 (s, 2H, H3,3 ), 7.58 (t, J ¼ 7.4 Hz, 4H,
C6H5e), 7.49 (m, 6H, C6H5e),), 7.32 (t, J ¼ 7.3 Hz, 6H, C6H5e), 7.12
(m, 22H, C6H5e). 13C NMR (CDCl3, 500 MHz):
d ppm 157.0, 148.3,
cient
b (Note that there is some confusion over the term b in
147.3, 146.6, 139.7, 132.5; 130.2; 129.3; 128.9; 128.7; 128.0; 127.1;
124.8; 123.4; 123.0; 117.4; 117.0. Anal. found: C, 82.60; H, 5.32; N,
6.61. C62H46N4$0.75CH2Cl2 Calc.: C, 82.75; H, 5.26; N, 6.15; m/z
(Micro-TOF-Q II) 847.3802, ([M þ H]þ, C62H47N4 requires 847.3795).
nonlinear optics, since it is sometimes used to describe the second-
order polarizability, and occasionally for the two-photon absorp-
tion coefficient) can be calculated from the curve fitting to the
experimental transmittance with the following equation (1):
2.3.3. General procedure for the preparation of bis(bipyridyl)metal
complexes
b
lI0
TðzÞ ¼ 1 ꢁ
(1)
ꢀ
ꢀ
ꢁ ꢁ
2
z
z0
2 1 þ
Diphenylbipyridyl ligand (50 mg, 0.076 mmol) and the corre-
sponding Metal salts (0.5 equiv) were mixed in dichloromethane
(10 mL). After stirring overnight at room temperature, the
dichloromethane was evaporated. The solid was purified further by
recrystallization from a CH2Cl2/pentane mixture (v/v ¼ 1:10).
where z0 corresponds to the diffraction length of the incident beam,
l the optical path length. The 2PA cross-section, d, (in units of 1 GM:
10ꢁ50 cm4 s photonꢁ1 moleculeꢁ1) is then determined by using the
relationship:
2.3.3.1. Complex [Cu(b)2][PF6] (bCu). Dark-brown powder, 73%
yield; 1H NMR (CD2Cl2, 500 MHz):
d ppm 7.93 (s, 4H), 7.55 (m, 24H),
d
NAd
10ꢁ3
b
¼
7.12 (m, 4H), 6.99 (m, 12H), 6.79 (d, J ¼ 8.0 Hz, 8H), 3.49
h
n
(q, J ¼ 7.1 Hz, 16H), 1.27 (t, J ¼ 7.1 Hz, 24H). 13C NMR (CD2Cl2,
where h is the Planck constant, n the frequency of the incident laser
500 MHz): d ppm 156.6,153.3,150.2,148.8,147.5,138.8,135.3,129.0,
beam, NA the Avogadro constant and d is the concentration of the
chromophore (mol Lꢁ1). The concentration of the compounds in
CH2Cl2 was in the range of 1e3 ꢀ10ꢁ3 M. The rhodamine 6G in
methanol [44] (16.2 ꢂ 2.4 GM at 806 nm) was used for the cali-
bration of our measurement technique.
127.5, 127.3, 122.6,120.7, 118.9, 117.3, 111.5, 44.4, 12.4. Anal. found: C,
73.72; H, 7.13; N, 6.13. C92H92CuF6N8P$2C5H12 Calc.: C, 73.79; H,
7.03; N, 6.74; m/z (Zabspec-TOF) 1371.6741, ([M þ H]þ, C92H92N8Cu
requires 1371.67409).
It should be noted that the Z-scan measurement as nonlinear
transmission method is strongly dependent on the local intensity at
the focal point. Due to the variation of the focal beam size before
and after the focal point and to self-focusing of the laser beam
across the sample, the two-photon absorption cross sections
measured with Z-scan method could differ significantly from those
obtained with the fluorescence-based method
2.3.3.2. Complex [Ag(b)2][OTf] (bAg). Gold powder, 75% yield; 1H
NMR (CD2Cl2, 500 MHz):
d ppm 7.96 (s, 4H), 7.73 (s, 4H), 7.57
(m, 20H), 7.03 (m, 16H), 6.78 (s, 8H), 3.49 (q, J ¼ 7.1 Hz, 16H), 1.27
(t, J ¼ 7.1 Hz, 24H). 13C NMR (CD2Cl2, 500 MHz):
d ppm 158.7, 153.8,
149.0, 140.5; 135.7, 129.1, 128.1, 127.0, 122.0, 119.5, 118.8, 118.0, 111.5,
44.5, 12.3. Anal. found: C, 72.59; H, 7.32; N, 5.78. C93H92AgF3
-
N8O3S$3C5H12 Calc.: C, 72.75; H, 7.24; N, 6.28. m/z (Zabspec-TOF)
1415.6526, ([M þ H]þ, C92H92N8Ag requires 1415.64959).
2.3. Synthesis
2.3.3.3. Complex [Zn(b)2][OTf]2 (bZn). Violet powder, 70% yield; 1H
2.3.1. Synthesis of ligand b
NMR (CD2Cl2, 500 MHz):
d
ppm 8.62 (s, 4H), 7.83 (d, J ¼ 15.9 Hz,
In a Schlenk flask, 6,60-diphenyl-4,40-dimethyl-[2,20]-bipyridine
1 (150 mg, 0.44 mmol) and 4-diethylaminobenzaldehyde (372 mg,
1.78 mmol, 4 equiv.) were dissolved in dimethylformamide (15 mL)
and tBuOK (200 mg, 1.78 mmol) was slowly added at room
4H), 7.73 (d, J ¼ 8.0 Hz, 8H), 7.64 (s, 4H), 7.31 (d, J ¼ 8.0 Hz, 12H),
7.24 (d, J ¼ 7.1 Hz, 4H), 7.15 (t, J ¼ 7.2 Hz, 8H), 6.81 (d, J ¼ 6.4 Hz, 8H),
3.49 (q, J ¼ 7.1 Hz, 16H), 1.27 (t, J ¼ 7.1 Hz, 24H). 13C NMR (CD2Cl2,
500 MHz): d ppm 158.8, 154.7, 150.9, 141.7, 138.1, 132.2, 131.6, 130.2,

684
H. Akdas-Kilig et al. / Dyes and Pigments 92 (2011) 681e688
128.1, 126.1,123.3,120.8,117.9, 116.8,112.7, 45.8,13.6. Anal. found: C,
70.93; H, 8.02; N, 4.46. C94H92F6N8O6S2Zn$6C5H12 Calc.: C, 70.71; H,
7.85; N, 5.32.
3. Results and discussion
3.1. Synthesis and characterization
2.3.3.4. Complex [Cu(c)2][PF6] (cCu). Dark-brown powder, 73% yield;
The 6,60-diphenyl-4,40-dimethyl-[2,20]-bipyridine 1 was synthe-
sized according to previously reported procedures [46]. The target
bipyridine derivatives b and c were readily prepared by means of
a double Knoevenagel condensation between 1 and the corre-
sponding aldehyde derivatives, respectively, in the presence of tert-
BuOK (Scheme 2). This coupling reaction afforded derivative b and c
as orange microcrystals (average yield 80%), which were fully char-
acterized by 1H and 13C NMR and UV/Vis spectroscopy.
Copper(I), silver(I) and zinc(II) complexes were obtained upon
treatment of the ligands b and c (2 equiv.) with respectively
[Cu(MeCN)4]PF6, AgOTf and Zn(OTf)2 (1 equiv.) in dichloromethane
solution at room temperature. The complexes were isolated in
nearly quantitative yield and their structures were demonstrated
by high resolution mass spectroscopy, 1H, 13C NMR spectroscopy,
UVevisible and fluorescence spectroscopy. The 1H NMR spectra
confirm the strong vicinal coupling constants of the olefinic protons
(JHH z 16 Hz) and no E/Z isomerization of the alkenyl fragments
was detected.
1H NMR (CD2Cl2, 500 MHz):
d
ppm 7.55 (d, 16H), 7.38 (m, 24H), 7.16
(m, 52H). 13C NMR (CD2Cl2, 500 MHz):
d
ppm 149.3, 147.0, 146.9,
129.49, 129.47, 129.44, 128.5, 127.54, 127.46, 125.4, 124.0, 122.5,
122.0, 111.6. Anal. found: C, 74.27; H, 4.41; N, 5.94. C128H98AgF3
-
N8O3S$1.5CH2Cl2 Calc.: C, 74.25; H, 4.72; N, 5.52; m/z (Micro-TOF-Q
II) 1755.6724, ([Cþ], C124H92N8Cu requires 1755.6735).
2.3.3.5. Complex [Ag(c)2][OTf] (cAg). Gold powder, 75% yield; 1H
NMR (CD2Cl2, 500 MHz):
20H), 7.37 (m, 16H), 7.16 (m, 48H). 13C NMR (CD2Cl2, 500 MHz):
ppm 149.3, 147.1, 135.1, 129.8, 129.6, 128.5, 127.54, 127.15, 125.4,
d ppm 8.01 (s, 4H), 7.55 (s, 4H), 7.59 (m,
d
124.0, 122.3, 122.2, 120.3, 119.2, 118.6. Anal. found: C, 69.77; H, 4.94;
N, 4.90. C128H98AgF3N8O3S$3CH2Cl2 Calc.: C, 69.70; H, 4.48; N, 5.08.
2.3.3.6. Complex [Zn(c)2][OTf]2 (cZn). Violet powder, 70% yield; 1H
NMR (CD2Cl2, 500 MHz):
4H), 7.73 (d, J ¼ 8.5 Hz, 8H), 7.69 (s, 4H), 7.35 (m, 30H), 7.17 (m, 42H).
13C NMR (CD2Cl2, 400 MHz):
ppm 157.1, 152.8, 149.3, 149.1, 146.1,
d
ppm 8.87 (s, 4H), 7.93 (d, J ¼ 16.3 Hz,
d
3.2. Crystal structure of complex bCu
139.0, 135.9, 130.5, 128.7, 128.3, 127.5, 126.1, 124.9, 123.4, 123.0,
120.6, 119.9, 119.6. Anal. found: C, 67.48; H, 4.01; N, 5.32.
C
128H98AgF3N8O3S$3CH2Cl2 Calc.: C, 67.00; H, 4.27; N, 4.85; m/z
The complex [Cu(b)2][PF6] was also characterized in the solid
state by X-ray diffraction method on single-crystals (See ESI for
selected bond lengths and angles, crystal data and refinement
parameters). Suitable crystals were obtained in a few days upon
slow diffusion at room temperature of pentane into a CH2Cl2
solution of the complex. The [Cu(b)2][PF6] dark-brown complex
crystallizes in the triclinic system with P-1 as the space group
(Fig. 1). The crystal also contains dichloromethane molecules in
addition to [Cu(b)2][PF6] complexes.
As expected and often observed, the cationic part of the
structure is composed of a Cu(I) metal ion also coordinated to two
ligands b with CueN distances varying between 2.015 and 2.057 Å.
The coordination geometry around the metal center is pseudo
tetrahedral with the NCuN angle varying between 82.8ꢃ and
131.9ꢃ. Both bipyridine units are in cis configuration with dihedral
angles of 11.31 and 20.41ꢃ between the two pyridines. A relevant
feature is the torsion angle between the two coordinated bipyr-
idines which is ca 61.03ꢃ, so that the planes are far from being
(Micro-TOF-Q II) 878.3352, ([Cþþ], C124H92N8Zn requires 878.3362).
2.4. X-ray diffraction crystallography
Single crystals suitable for X-ray crystal analysis were obtained
by slow diffusion of pentane into a dichloromethane solution of bCu
at room temperature. Crystals were removed from their mother
solution, coated with oil and rapidly transferred to the diffrac-
tometer in order to prevent solvent evaporation. The samples were
studied on a Xcalibur Oxford Diffraction automatic diffractometer
with graphite monochromated Mo-Ka radiation. The structure was
solved with SIR-97, which revealed the non-hydrogen atoms of the
structure. After anisotropic refinement all the hydrogen atoms
were found with a Fourier difference synthesis. The whole structure
was refined with SHELXL97 by the full-matrix least-squares tech-
niques [use of F magnitude; x, y, z, (ij for C, N and O atoms, x, y, z in
riding mode for H atoms)]. ORTEP views were realized with PLA-
TON98 [45]. The crystal structure has been deposited at the Cam-
bridge Crystallographic Data Centre and allocated the deposition
number CCDC 794182. These data can be obtained free of charge at
www.ccdc.cam.ac.uk/conts/retrieving.html [of from Cambridge
Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ;
Fax: (internat.) þ44-1223/336-033; E-mail: deposit@ccdc.cam.ac.
uk]. The crystal and structure refinement data of bCu are listed
in Table 1.
perpendicular. Four interligand
pep stacking (z3.8 Å) between
pyridines and the four phenyl rings flatten the coordination
geometry around the copper center from tetrahedral coordination,
which is a common feature in copper(I) complexes [47]. This
strong distortion has been described earlier for several particularly
interesting [Cu(NN)2]þ complexes [48,49]. For example, the X-ray
structure of [Cu(dnpp)2]PF6 [50] described by McMillin and
coworkers (dnnp ¼ 2,9-dineopentyl-1,10-phenanthroline) reveals
R2N
Ph
Ph
R2N
DMF / tBuOK
CHO
N
N
N
1) PhLi, Tol.
2) MnO2
N
N
N
Ph
Ph
b R = NEt2
R = NPh2
1
c
NR2
Scheme 2. Synthesis of bipyridine derivatives b and c.

H. Akdas-Kilig et al. / Dyes and Pigments 92 (2011) 681e688
685
Fig. 1. ORTEP drawing of compound bCu (50% probability thermal ellipsoids); for clarity H atoms, solvents and counter-anions were omitted.
that the dihedral angle between the least-squares planes of the
dnpp ligands is only 63.4(1)ꢃ.
addition a typical MLCT transition [CuI / p*(bpy)] is found at ca.
440 nmwith smaller absorption coefficients and can be discerned in
the spectra as a shoulder of the more intense ILCT band [51]. A more
important red shift of z120 nm is observed for the zinc(II) series.
The red shift of the ILCT transition induced by complexation can be
correlated to the Lewis acidity of the metallic ion: the Zn2þ complex
within each series does show the largest lILCT value, but those for the
analogous Cuþ and Agþ species are essentially indistinguishable,
a feature already demonstrated for the tetrahedral series with the
4,40-dialkenyl-6,60-dimethyl-2,20-bipyridine ligand [13].
Compounds b, c are fluorescent in dichloromethane at 298 K,
with fluorescence quantum yield ranging from 0.15 to 0.64. The
fluorescence quantum yield for compound b is consistent with the
values previously described for donor-substituted bipyridyl ligands
[52], but it increases dramatically to 0.64 for the ligand c. This
enhancement effect of diphenylamino vs diethylamino has previ-
ously been observed by Cho and co-workers [53] for organic
octupolar 1,3,5-tricyano-2,4,6-tris(styryl)benzene derivatives. The
corresponding metal complexes display different luminescent
3.3. Optical properties
3.3.1. Linear optical properties
The electronic absorption spectral data for all the ligands and the
complexes recorded in dichloromethane are summarized in Table 2.
Ligands b and c display intense intramolecular charge transfer
bands (ICT) at lmax z 400 nm. All complexes exhibit strong
absorption bands in the visible region. These bands are sensitive to
the nature of the donor group and the metallic core (Table 2). Two
types of transitions can be observed: intraligand charge transfer
(ILCT) and metal-to-ligand charge transfer (MLCT). In the case of
silver(I) and zinc(II) complexes, UV-visible spectra exhibit one broad
intense absorption band assigned to the ILCT transition. The elec-
tronic spectra of the copper(I) complexes also exhibit red-shifted
intense absorptions (Dlabs(complex vs. ligand) ¼ 26e28 nm) in the
visible region assigned to intraligand charge transfer bands. In
Table 2
Optical and nonlinear optical data.
labs/nma
lem/nm
Stokes
Fem
b1.91d/10ꢁ30
esu
b0e/10ꢁ30
esu
lTPA nm
dTPA/GM
lMAX
(
dMAX
)
Method
c
Compound
b
(
3max
)
shift/cmꢁ1
b
400 (71)
426 (102)
438 (sh)
428 (122)
527 (112)
398 (45)
428 (79)
445 (sh)
431 (84)
513 (101)
394 (67)
495
e
4798
e
0.15
e
e
e
780
800/900
160
2080/712
810 (171)
TPEF
Z-scan
bCu
268
203
bAg
bZn
c
550
707
502
e
5182
4831
5205
e
0.10
0.005
0.64
e
241
401
e
182
258
e
780
900
780
800/900
355
850 (677)
800 (200f)
TPEF
Z-scan
TPEF
500
180f
cCu
300
227
1931/988
Z-scan
cAg
cZn
a
562
712
e
5408
5448
0.33
0.006
e
283
358
e
214
236
e
780
800/900
780
210
670/2093
125
800 (427)
800 (141)
TPEF
Z-scan
TPEF
a
In CH2Cl2.
b
Units ¼ 103 Molꢁ1 cmꢁ1
.
c
d
e
f
Fluorescence quantum yield with ꢂ10% error.
Measured by HLS at 1.91
m
m in CH2Cl2 (precision ꢂ10%) solution (10ꢁ3 mol Lꢁ1).
Deduced from a two-level model.
Addition of tetramethylguanidine (base).

686
H. Akdas-Kilig et al. / Dyes and Pigments 92 (2011) 681e688
behavior depending on the nature of the metal ion. Photo-
luminescence is observed for the silver(I) complexes bAg and cAg in
diluted dichloromethane solution at room temperature (Table 2).
They exhibit a broad, intense structureless emission band assigned
to ligand-centered emission with large Stokes shifts (5182 and
5408 cmꢁ1, respectively). The complexation induces a red-shift of
the emission wavelength when compared to that of free ligands
b and c (Dlem(complex vs. ligand) ¼ 55e60 nm). By contrast, cop-
per(I) complexes bCu and cCu does not show any luminescence in
dichloromethane, upon excitation either at the MLCT or the ILCT
wavelength, whereas a very weak red-shifted photoluminescence
is observed for the zinc(II) complexes bZn and cZn at ca. 710 nm.
1.00
0.95
0.90
0.85
0.80
C
C
C
Cu
Zn
3.3.2. Non linear optical properties
The Harmonic Light Scattering (HLS) technique was used for the
-0.2
0.0
0.2
molecular first hyperpolarizability
ments were performed in dichloromethane at a fundamental
wavelength of 1.91 m. Using this wavelength ensures that any
b measurements. The measure-
z / cm
m
Fig. 3. Open aperture Z-scan traces for compounds in dichloromethane at 900 nm.
([c]: 2.8 ꢀ 10ꢁ3 M, [cCu]: 1.1 ꢀ10ꢁ3 M, [cZn]: 1.8 ꢀ 10ꢁ3 M). Theoretical fitting (full lines)
using equation (1) (see text).
contribution to the HLS signal from two-photon fluorescence
becomes negligible, as its harmonic at 955 nm lies far from the
fluorescence domain. The values of b1.91 and static hyper-
polarizabilities b0 are given in Table 2. These data clearly show the
large quadratic NLO activity of these new multipolar chromophores.
As previously observed for donor-substituted bipyridine metal
complexes [54], the quadratic NLO response increases with the
Lewis acidity of the metal center and the b0 values roughly follow
those found for the relative energies of the ILCT transitions which
linear absorption ones. This effect clearly indicates that the low-
energy ILCT transition is two-photon active which is consistent
with the noncentrosymmetric feature of the chromophores. Inter-
estingly the maximum TPA cross sections are of the same order of
magnitude (w170 GM at 780 nm). This suggests that both dieth-
ylamino and diphenylamino substituents have similar effects
dominate the second-order nonlinear response, i.e. Zn2þ > Cuþ
z
Agþ. All the complexes bM and cM (M ¼ Cu, Ag, Zn) exhibit b1.91 and
b0 values which are much larger than those of previously reported
for pseudo-tetrahedral (D2d) metal complexes featuring 4,40-dibu-
tylaminostyryl-6,60-dimethyl-2,20-bipyridine a (Scheme 1) (aCu
toward the TPA ability of the D-p-A chromophores. Such an
equivalency has also been observed for a series of bis dialkylamino-
or diarylamino-substituted bis(styryl)benzenes [40]. The pre-
organization of the ligands around a metal-ion core leads to
substantial changes of the TPA spectra. For instance, the coordi-
nation to Agþ induces a red shift of the TPA band as previously
observed for linear absorption spectra (Fig. 2).
b1.91 ¼113 ꢀ10ꢁ30 esu; aAg b1.91 ¼90 ꢀ 10ꢁ30 esu; aZn b1.91
¼
245 ꢀ10ꢁ30 esu). This enhancement of the second-order NLO
response can be reasonably attributed to an increase in the
p-
Moreover, the maximum TPA cross-section is multiplied by
factor 3.9 and 2.1 for bAg and cAg respectively and as compared to
their corresponding ligands. This effect is amplified with the
increase of the Lewis acidity of the cation which promotes
delocalization on the bipyridine ligands induced by the phenyl
substituents, a feature that has also been observed in the case of
iridium and ruthenium complexes featuring substituted phenan-
throline ligands [55,56].
a
stronger electron-withdrawing ability of bipyridyl and
The two-photon absorption cross-sections were measured using
either the TPEF (two-photon excited fluorescence) method for
fluorescent compounds or using the open aperture Z-scan tech-
nique for non emissive ones. The ligands b,c exhibit similar TPA
bands with maxima absorption wavelengths twice that of their
strengthens the charge transfer character of the ILCT transition. It is
to be noted that free ligands show a weak nonlinear absorption
behavior at 900 nm (
d
< 20 GM) whereas their corresponding Zn2þ
and Cuþ complexes exhibit very large
d
superior to 1000 GM
(Fig. 3). Theoretical calculations relative to analogues of these
octupolar tetrahedral complexes [57] predicted such very large TPA
enhancements. We therefore demonstrate that metal ions can be
used as a 3D template to generate highly two-photon active
compounds with increased dimensionality [58].
4. Conclusion
In this study we have described the synthesis, linear properties
and second and third-order nonlinearities of a series of D2d [Cu(I),
Ag(I), Zn(II)] octupolar metal complexes featuring two new func-
tionalized 4,40-dialkenyl-6,60-diphenyl-2,20-bipyridine ligands.
These compounds are found to display relatively large first hyper-
polarizabilities b0 values, in the range 182e258 ꢀ 10ꢁ30 esu, which
follow the expected relationship with respect to the ILCT energies
and the strength of the Lewis acidity of the metallic center.
Remarkably, the presence of the phenyl substituents on the ortho
positions of the bipyridine ligands produces stable pseudo-
tetrahedral complexes with a strong enhancement of the second-
order NLO responses, as compared to those of the related chro-
mophores featuring methyl substituents. Finally, these complexes
Fig. 2. One and two-photon absorption spectra of
dichloromethane.
c
(black) and cAg (gray) in

H. Akdas-Kilig et al. / Dyes and Pigments 92 (2011) 681e688
687
[23] Sénéchal K, Maury O, Le Bozec H, Ledoux I, Zyss J. Zinc(II) as a versatile
template for the design of dipolar and octupolar NLO-phores. Journal of the
American Chemical Society 2002;124:4560e1.
[24] Le Bouder T, Maury O, Bondon A, Costuas K, Amouyal E, Ledoux I, et al.
Synthesis, photophysical and nonlinear optical properties of macromolecular
architectures featuring octupolar tris(bipyridine) ruthenium(II) moieties:
evidence for a supramolecular self-ordering in a dentritic structure. Journal of
the American Chemical Society 2003;125:12284e99.
represent an interesting new family of two-photon absorption dyes
which display red-shifted TPA bands compared to their metal ion-
free chromophores and a large increase of the TPA cross sections.
Acknowledgment
[25] Maury O, Viau L, Sénéchal K, Corre B, Guégan J-P, Renouard T, et al. Synthesis,
linear, and quadratic-nonlinear optical properties of octupolar D3 and D2d
bipyridyl metal complexes. Chemistry e A European Journal 2004;10:4454e66.
[26] Coe BJ, Samoc M, Samoc A, Zhu L, Yi Y, Shuai Z. Two-photon absorption
properties of iron(II) and ruthenium(II) trischelate complexes of
2,20:4,400:404000-quaterpyridinium ligands. The Journal of Physical Chemistry A
2007;111:472e8.
This work is supported by COST D 035-0010-05. We also thank
the CNRS (Centre National de la Recherche Scientifique) and the
University of Rennes1 for financial support.
References
[27] Feuvrie C, Maury O, Le Bozec H, Ledoux I, Morrall JP, Dalton GT, et al. Nonlinear
optical and two-photon absorption properties of octupolar tris(bipyridyl)metal
complexes. The Journal of Physical Chemistry A 2007;111:8980e5.
[28] Coe BJ, Fielden J, Foxon SP, Brunschwig BS, Asselberghs I, Clays K, et al.
Combining very large quadratic and cubic nonlinear optical responses in
[1] Chemla DS, Zyss J. Nonlinear optical properties of organic molecules and
crystals. Orlando: Academic Press; 1987.
[2] Nalwa HS, Miyata S. Nonlinear optics of organic molecules and polymers. Boca
Raton: CRC Press; 1997.
[3] Prasad NP, Williams DJ. Introduction to nonlinear optical effects in molecules
and polymers. New York: Wiley; 1991.
[4] Zyss J. Molecular nonlinear optics: materials, physics and devices. Boston:
Academic Press; 1994.
extended, tris-chelate metallochromophores with six p-conjugated pyridinium
substituents. Journal of the American Chemical Society 2010;132:3496e513.
[29] Dragonetti C, Balordi M, Colombo A, Roberto D, Ugo R, Fortunati I, et al. Two-
photon absorption properties of Zn(II) complexes: Unexpected large TPA cross
section of dipolar [ZnY2(4,40-bis(para-di-n-butylaminostyryl)-2,20-bipyr-
idine)] (Y ¼ Cl, CF3CO2). Chemical Physics Letters 2009;475:245e9.
[30] Mazzucato S, Fortunati I, Scolaro S, Zerbetto M, Ferrante C, Signorini R, et al.
Two-photon absorption of Zn(ii) octupolar molecules. Physical Chemistry
Chemical Physics 2007;9:2999e3005.
[31] Das S, Nag A, Goswami D, Bharadwaj PK. Zinc(II)- and copper(I)-mediated
large two-photon absorption cross sections in a bis-cinnamaldiminato Schiff
Base. Journal of the American Chemical Society 2006;128:402e3.
[32] Dietrich-Buchecker CO, Sauvage JP. Interlocking of molecular threads: from
the statistical approach to the templated synthesis of catenands. Chemical
Reviews 1987;87:795e810.
[33] Moylan CR, Twieg RJ, Lee VY, Swanson SA, Betterton KM, Miller RD. Nonlinear
optical chromophores with large hyperpolarizabilities and enhanced thermal
stabilities. Journal of the American Chemical Society 1993;115:12599e600.
[34] Whitaker CM, Patterson EV, Kott KL, McMahon RJ. Nitrogen and oxygen
donors in nonlinear optical materials: effects of alkyl vs phenyl substitution
on the molecular hyperpolarizability. Journal of the American Chemical
Society 1996;118:9966e73.
[35] Jen AKY, Cai Y, Bedworth PV, Marder SR. Synthesis and characterization of
highly efficient and thermally stable diphenylamino-substituted thiophene
stilbene chromophores for nonlinear optical applications. Advanced Materials
(Weinheim, Germany) 1997;9:132e5.
[36] Staub K, Levina GA, Barlow S, Kowalczyk TC, Lackritz HS, Barzoukas M, et al.
Synthesis and stability studies of conformationally locked 4-(diarylamino)
aryl- and 4-(dialkylamino)phenyl-substituted second-order nonlinear optical
polyene chromophores. Journal of Materials Chemistry 2003;13:825e33.
[37] Oudar JL. Optical nonlinearities of conjugated molecules. Stilbene derivatives
and highly polar aromatic compounds. The Journal of Chemical Physics 1977;
67:446e57.
[38] Zyss J, Brasselet S. Multipolar symmetry patterns in molecular nonlinear
optics. Journal of Nonlinear Optical Physics and Materials 1998;7:397e439.
[39] Weibel JD, Yaron D, Zyss J. Quantum and tensorial modeling of multipolar
nonlinear optical chromophores by a generalized equivalent internal poten-
tial. The Journal of Chemical Physics 2003;119:11847e63.
[40] Rumi M, Ehrlich JE, Heikal AA, Perry JW, Barlow S, Hu Z, et al. Structur-
eeproperty relationships for two-photon absorbing chromophores: bis-donor
diphenylpolyene and bis(styryl)benzene derivatives. Journal of the American
Chemical Society 2000;122:9500e10.
[41] Webb WW, Xu C. Measurement of two-photon excitation cross sections of
molecular fluorophores with data from 690 to 1050 nm. Journal of the Optical
Society of America B 1996;13:10.
[5] Nalwa HS. Organometallic materials for nonlinear optics. Applied Organo-
metallic Chemistry 1991;5:349e77.
[6] Marder SR, Bruce DW, O’Hare D. Metal-containing materials for nonlinear
optics. In: Inorganic materials. Chichester, UK: John Wiley and Sons; 1992.
[7] Long NJ. Organometallic compounds for nonlinear opticsdthe search for en-
light-enment! Angewandte Chemie International Edition in English 1995;34:
21e38.
[8] Heck J, Dabek S, Meyer-Friedrichsen T, Wong H. Mono- and dinuclear ses-
quifulvalene complexes, organometallic materials with large nonlinear optical
properties. Coordination Chemistry Reviews 1999;190e192:1217e54.
[9] Whittall IR, McDonagh AM, Humphrey MG, Samoc M. In: Stone FGA,
Robert W, editors. Advances in organometallic chemistry, vol. 42. Academic
Press; 1998. p. 291e362.
[10] Andraud C, Maury O. Lanthanide complexes for nonlinear optics: from
fundamental aspects to applications. European Journal of Inorganic Chem-
istry; 2009:4357e71.
[11] Coe BJ, McCleverty JA, Meyer TJ. Nonlinear optical properties of metal
complexes. In: Comprehensive coordination chemistry II. Oxford, UK: Elsevier
Pergamon; 2004.
[12] Di Bella S. Second-order nonlinear optical properties of transition metal
complexes. Chemical Society Reviews 2001;30:355e66.
[13] Renouard T, Le Bozec H, Brasselet S, Ledoux I, Zyss J. Tetrahedral bipyridyl
copper(I) complexes: a new class of non-dipolar chromophore for nonlinear
optics. Chemical Communications; 1999:871e2.
[14] Cariati E, Pizzotti M, Roberto D, Tessore F, Ugo R. Coordination and organo-
metallic compounds and inorganic-organic hybrid crystalline materials for
second-order non-linear optics. Coordination Chemistry Reviews 2006;250:
1210e33.
[15] Kanis DR, Lacroix PG, Ratner MA, Marks TJ. Electronic structure and quadratic
hyperpolarizabilities in organotransition-metal chromophores having weakly
Coupled.pi.Networks. Unusual mechanisms for second-order response. Jour-
nal of the American Chemical Society 1994;116:10089e102.
[16] Roberto D, Ugo R, Bruni S, Cariati E, Cariati F, Fantucci P, et al. Quadratic
hyperpolarizability enhancement of para-substituted pyridines upon coordi-
nation to organometallic moieties: the ambivalent donor or acceptor role of
the metal. Organometallics 2000;19:1775e88.
[17] Roberto D, Ugo R, Tessore F, Lucenti E, Quici S, Vezza S, et al. Effect of the
coordination to M(II) metal centers (M
¼
Zn, Cd, Pt) on the quadratic
hyperpolarizability of various substituted 5-X-1,10-phenanthrolines (X
¼
Donor Group) and of trans-4-(Dimethylamino)-40-stilbazole. Organometallics
2002;21:161e70.
[42] Sheik-Bahae M, Said AA, Wei TH, Hagan DJ, Stryland EWV. IEEE Journal of
Quantum Electronics 1990;26:760.
[43] Sheik-Bahae M, Said AA, Stryland EWV. High Sensitivity, single beam n2
measurements. Optical Letters 1989;14:955e7.
[18] Tessore F, Roberto D, Ugo R, Mussini P, Quici S, Ledoux-Rak I, et al. Large,
concentration-dependent enhancement of the quadratic hyperpolarizability
of [Zn(CH3CO2)2(L)2] in CHCl3 on substitution of acetate by triflate. Ange-
wandte Chemie International Edition 2003;42:456e9.
[44] Sengupta P, Balaji J, Banerjee S, Philip R, Kumar GR, Maiti S. Sensitive
measurement of absolute two-photon absorption cross sections. The Journal
of Chemical Physics 2000;112:9201e5.
[19] Bruce DW, Thornton A. Electronic hyperpolarisabilities of some mesogenic
stilbazole complexes of Rh(I) and Ir(I), molecular crystals and liquid crystals
science and technology. Section A. Molecular Crystals and Liquid Crystals
1993;231:253e6.
[45] Spek AL. PLATON, a multipurpose crystallographic tool. The Netherlands:
Utrecht University; 1998.
[20] Bourgault M, Baum K, Le Bozec H, Pucetti G, Ledoux I, Zyss J. Synthesis and
molecular hyperpolarisabilities of donor-acceptor bipyridyl metal complexes
(M ¼ Re, Zn, Hg). New Journal of Chemistry 1998;22:517e22.
[46] Linnell R. Notes - 4,40,6,60-tetramethyl-2,20-bipyridine. The Journal of Organic
Chemistry 1957;22:1691e2.
[47] Munakata M, Kitagawa S, Asahara A, Masuda H. Bulletin of Chemical Society of
Japan 1987;60:1927e9.
[48] Klemens FK, Fanwick PE, Bibler JK, McMillin DR. Crystal and molecular
structure of [Cu(bcp)2]BF4.cntdot.CH3OH (bcp ¼ 2,9-dimethyl-4,7-diphenyl-
1,10-phenanthroline). Inorganic Chemistry 1989;28:3076e9.
[21] Hilton A, Renouard T, Maury O, Le Bozec H, Ledoux I, Zyss J. New bipyridyl
ligands bearing azo- and imino-linked chromophores. Synthesis and
nonlinear optical studies of related dipolar zinc complexes[dagger]. Chemical
Communications; 1999:2521e2.
[22] Boucekkine A, Feuvrie C, Maury O, Ledoux I, Le Bozec H. Effects of the metal
center and substituting groups on the linear and nonlinear optical properties
of substituted styryl-bipyridine metal(II) dichloride complexes: DFT and
TDDFT computational investigations and harmonic light scattering measure-
ments. The Journal of Physical Chemistry A 2010;114:5429e38.
[49] Eggleston MK, Fanwick PE, Pallenberg AJ, McMillin DR. A twist on the copper
center in the crystal structure of [Cu(dnpp)2]PF6 and the charge-transfer
excited state? (dnpp
Chemistry 1997;36:4007e10.
¼
2,9-Dineopentyl-1,10-phenanthroline). Inorganic

688
H. Akdas-Kilig et al. / Dyes and Pigments 92 (2011) 681e688
[50] McMillin DR, McNett KM. Photoprocesses of copper complexes that bind to
DNA. Chemical Reviews 1998;98:1201e20.
[51] Parker WL, Crosby GA. Assignment of the charge-transfer excited states of
bis(N-heterocyclic) complexes of copper(I). The Journal of Physical Chemistry
1989;93:5692e6.
[55] Valore A, Balordi M, Colombo A, Dragonetti C, Righetto S, Roberto D, et al.
Novel ruthenium(ii) complexes with substituted 1,10-phenanthroline or 4,5-
diazafluorene linked to a fullerene as highly active second order NLO chro-
mophores. Dalton Transactions 2010;39:10314e8.
[56] Valore A, Cariati E, Dragonetti C, Righetto S, Roberto D, Ugo R, et al. Cyclo-
metalated IrIII complexes with substituted 1,10-phenanthrolines: a new class
of efficient cationic organometallic second-order NLO chromophores. Chem-
istry e A European Journal 2010;16:4814e25.
[57] Zhang X-B, Feng J-K, Ren A-M. Theoretical study of one- and two-photon
absorption properties of octupolar D2d and D3 bipyridyl metal complexes.
The Journal of Physical Chemistry A 2007;111:1328e38.
[58] Beljonne D, Wenseleers W, Zojer E, Shuai Z, Vogel H, Pond SJK, et al. Role of
dimensionality on the two-photon absorption response of conjugated mole-
cules: the case of octupolar compounds. Advanced Functional Materials 2002;
12:631e41.
[52] Maury O, Guegan JP, Renouard T, Hilton A, Dupau P, Sandon N, et al. Design
and synthesis of 4,40-pi-conjugated 2,20 -bipyridines:
a versatile class of
tunable chromophores and fluorophores. New Journal of Chemistry 2001;25:
1553e66.
[53] Cho BR, Son KH, Lee SH, Song Y-S, Lee Y-K, Jeon S-J, et al. Two photon
absorption properties of 1,3,5-tricyano-2,4,6-tris(styryl)benzene derivatives.
Journal of the American Chemical Society 2001;123:10039e45.
[54] Maury O, Le Bozec H. Molecular engineering of octupolar NLO molecules and
materials based on bipyridyl metal complexes. Accounts of Chemical Research
2005;38:691e704.