Large second-order NLO activity in poly(4-vinylpyridine) grafted with PdII and CuII chromophoric complexes with tridentate bent ligands containing heterocycles

Article abstract of DOI:10.1002/ejic.200701171

Two N-salicylidene-N′-acylhydrazines tridentate ligands containing heterocycles were prepared and utilized for the synthesis of mononuclear acentric complexes of Cu^II and Pd^II and pyridine serves as an additional ligand (ML^x

Full text of DOI:10.1002/ejic.200701171

FULL PAPER
DOI: 10.1002/ejic.200701171
Large Second-Order NLO Activity in Poly(4-vinylpyridine) Grafted with PdII
and CuII Chromophoric Complexes with Tridentate Bent Ligands Containing
Heterocycles
Fabio Borbone,[a] Antonio Carella,[a] Ugo Caruso,[a] Giuseppina Roviello,[a] Angela Tuzi,*[a]
Principia Dardano,[b] Stefano Lettieri,[b] Pasqualino Maddalena,[b] and Alberto Barsella[c]
Keywords: Nonlinear optics / Polymers / Tridentate ligands / Copper / Palladium
Two N-salicylidene-NЈ-acylhydrazines tridentate ligands
containing heterocycles were prepared and utilized for the
synthesis of mononuclear acentric complexes of CuII and PdII
and pyridine serves as an additional ligand (MLxPy, M =
metal, Lx = ligand). Characterization also includes single-
crystal X-ray diffraction analysis. These complexes
show high second-order nonlinear optical activity (µβ =
The polymers exhibit good thermal stability, high glass-
transition temperatures and the absence of crystallinity. The
second-order nonlinear optical (NLO) properties of thin,
transparent poled films, prepared by spin coating and ther-
mal corona poling, were investigated for some of the poly-
mers. The value of the d33 parameter was measured at 1064
and 1500 nm (i.e., with and without resonance contribute). In
the latter case, the d33 values are 21 and 12 pm/V for PCuLII
and PPdLII, respectively. A high time stability of the NLO
properties of these materials was found.
620ϫ10–48esu for both CuLIIPy and PdLIIPy and µβ
=
1600ϫ10–48 and 1400ϫ10–48 esu for CuLIPy and PdLIPy,
respectively, at incident wavelength of 1907 nm). The prop-
erties of polymers (PMLx) obtained by grafting poly(4-vinyl-
pyridine) with fragments of the complexes are also reported.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
during the poling procedure. In particular, CuII, PdII and
NiII complexes of some N-salicylidene-NЈ-aroylhydrazines
are easily coordinated by the nitrogen atom of the pyridine
group of poly(4-vinylpyridine), and they were found to give
amorphous, simple-to-formulate, soluble and stable NLO
polymers (Scheme 1).[5]
Introduction
Nonlinear optically active polymers are widely studied
for their great applicative potential in electrooptical devices
with broad bandwidth and low drive voltage.[1,2] The main
problem with these materials is related to the low time sta-
bility of the dipole orientation, and several approaches are
being investigated to obtain highly active materials with
long-term stability of the NLO properties. As far as side-
chain systems are concerned, we have recently proposed a
simple way of grafting chromophoric metal complexes onto
polymeric matrices by means of a coordination bond be-
tween a side-chain donor group and a transition-metal
ion.[3,4] It was observed that these polymers show some
interesting properties, such as a rather high glass-transition
temperature related to the free polymeric backbone, high
thermal stability and good solubility. Furthermore, the pos-
sibility of reversible thermal cleavage of the polymer–metal
bond may promote enhanced chromophore orientation
Scheme 1.
In this paper, we report on the synthesis and the charac-
terization, including single-crystal X-ray diffraction analysis
and EFISH measurements of µβ, of some CuII and PdII
chromophoric complexes (MLxPy; M = Cu, Pd; x = I, II)
containing a thiophene or a furan ring in their conjugated
path (Scheme 2).
Owing to the presence of heterocycles and to their bent
molecular shape, it is expected that they would possess
good NLO activity. In fact, as demonstrated by theoreti-
cal[6] and experimental[7] reports, the presence of heterocy-
cles contributes to a general increase in NLO activity rela-
tive to a fully aromatic system and, according to Dalton
[a] Dipartimento di Chimica “Paolo Corradini”, Università di
Napoli “Federico II”, Complesso Universitario di Monte S.
Angelo,
via Cintia, 80126, Napoli, Italy
Fax: +39-081-674090
E-mail: angela.tuzi@unina.it
[b] Dipartimento di Scienze Fisiche, Università di Napoli “Feder-
ico II”, Complesso Universitario di Monte S. Angelo,
via Cintia, 80126, Napoli, Italy
[c] IPCMS-CNRS, GONLO,
23 Rue du Loess, 67037 Strasbourg Cedex, France
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Large Second-Order NLO Activity in Poly(4-vinylpyridine)s
perimental Section. Both thermogravimetric and calori-
metric analysis showed the loss of pyridine molecules upon
heating. For CuLIPy (Figure 1) the thermogravimetric
curve is characterized by the presence of two steps. The first
one, starting at 150 °C, is related to the loss of pyridine; the
second one, starting at 300 °C, is due to thermal decompo-
sition. The PdLIPy complex (Figure 2) shows different ther-
mogravimetric behaviour: the curve is characterized by only
one step at 230 °C. In this case, the loss of pyridine and
thermal decomposition are superimposed.
Scheme 2.
et al.,[1] a bent molecular shape seems to favour efficient
chromophore orientation and therefore high NLO activity.
A notable problem in the synthesis of these ligands lies
in the low yield of the hydrazide synthesis (Scheme 3, Com-
pound I) reported in the literature.[4] This problem is due
to the low chemical stability of the thiophene ring in basic
solutions. For this reason, the adopted ligand synthesis ex-
cludes the presence of a large excess of hydrazine, which
is needed in the literature procedure, and it is performed
following a procedure suggested by Gordon.[8] In this way,
the synthesis of organic ligands requires only a few simple
steps (Scheme 3) and great improvements in purity and
yield of the ligands are obtained, as described in the Experi-
mental Section. The successive grafting of the complexes
with commercial poly(4-vinylpyridine) is a fast and simple
operation. Grafting is easily performed in one step by add-
ing the appropriate suspension of the complex to the poly-
mer solution and recovering the grafted polymer form the
reaction mixture by precipitation. Alternatively, the former
grafted polymer solution may be utilized directly for the
preparation of films by means of spin-coating techniques.
Figure 1. (a) Calorimetric and (b) thermogravimetric curves for the
CuLIPy complex.
Figure 2. (a) Calorimetric and (b) thermogravimetric curves for the
PdLIPy complex.
A similar behaviour is observed for analogous MLIIPy,
and the thermogravimetric curve shows two steps for the
Cu complex and only one for the Pd complex. In this case,
the thermal stability is lower than that observed for MLIPy.
From the thermogravimetric data, it is possible to deter-
mine that the loss of pyridine produces the formation of
dimeric species (MLI)2 (Scheme 4), as already described[4]
for analogous complexes.
Scheme 3.
Grafted polymers (PMLx, M = Cu, Pd; x = I, II) con-
taining 35 wt.-% of the chromophoric complexes on poly(4-
vinylpyridine) were synthesized and characterized, includ-
ing d33 calculations from SHG measurements and tempera-
ture/time stability analysis.
Results and Discussion
Complexes (MLxPy: M = Cu, Pd; x = I, II)
The mononuclear complexes were prepared from the ap-
propriate ligand following the procedure reported in the Ex- Scheme 4.
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A. Tuzi et al.
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These observations are coherent with X-ray analysis data Table 1. Selected bond lengths [Å], bond angles [°] and torsion
angles [°] for CuLIPy, PdLIPy and PdLIIPy with ESDs in parenthe-
ses.
showing that one pyridine molecule is coordinated to the
metal in both MLIPy complexes, and for CuLIPy, one more
CuLIPy
pyridine molecule is present as a crystallization solvent per
two molecules of complex.
Cu1–O1
1.894(2)
1.940(2)
1.914(3)
2.001(3)
1.378(4)
93.9(1)
N2–C11
N2–N3
N3–C12
O2–C12
1.294(4)
1.394(3)
1.319(4)
1.301(4)
The molecular structures of CuLIPy, PdLIPy and Cu1–O2
PdLIIPy are sketched in Figures 3, 4 and 5, respectively, and
Cu1–N2
Cu1–N5
selected bond lengths and angles are reported in Table 1.
N1–C5
O1–Cu1–N2
O1–Cu1–N5
O2–Cu1–N2
O1–Cu1–N5–C23 –168.1(3)
C2–N1–C5–C10 –161.8(4)
O2–Cu1–N5
N2–Cu1–N5
C15–S1–C18
C7–C8–C11–N2
92.5(1)
173.7(1)
90.0(2)
179.4(3)
92.2(1)
81.2(1)
C13–C14–C15–S1 –0.3(5)
C11–N2–N3–C12 –176.0(3)
S1–C18–N4–O3
178.9(4)
PdLIPy
Pd1–O1
Pd1–O2
Pd1–N2
Pd1–N5
1.980(1)
2.006(2)
1.933(2)
2.056(2)
1.381(4)
94.69(9)
89.89(8)
80.75(9)
N2–C11
N2–N3
N3–C12
O2–C12
1.289(4)
1.395(3)
1.309(4)
1.309(3)
N1–C5
O1–Pd1–N2
O1–Pd1–N5
O2–Pd1–N2
O1–Pd1–N5–C23 –160.0(2)
C2–N1–C5–C10 –177.9(3)
O2–Pd1–N5
N2–Pd1–N5
C15–S1–C18
C7–C8–C11–N2
94.68(9)
175.39(9)
90.21(1)
–178.3(3)
Figure 3. X-ray molecular structure of CuLIPy. Thermal ellipsoids
are shown at the 30% probability level. Pyridine solvent molecule
is not shown.
C13–C14–C15–S1 2.3(4)
C11–N2–N3–C12 0.1(3)
S1–C18–N4–O3
–1.8(4)
PdLIIPy
Pd1–O1
Pd1–O2
Pd1–N2
Pd1–N5
N1–C5
N2–C11
O1–Pd1–N2
O1–Pd1–N5
O2–Pd1–N2
1.978(4)
N2–N3
N3–C12
O2–C12
O3–C13
O3–C16
1.405(6)
1.320(7)
1.294(6)
1.376(6)
1.375(6)
2.005(4)
1.947(4)
2.058(5)
1.357(7)
1.303(7)
95.4(2)
O2–Pd1–N5
N2–Pd1–N5
C13–O3–C16
94.1(2)
174.5(2)
106.0(4)
90.1(2)
80.5(2)
O1–Pd1–N5–C23 –168.2(4)
C2–N1–C5–C10 –178.8(6)
C11–N2–N3–C12 177.3(5)
C7–C8–C11–N2 176.3(5)
N3–C12–C13–O3 –0.4(8)
O3–C16–C17–C22 –2.0(9)
C19–C20–N4–O5 0.5(8)
Figure 4. X-ray molecular structure of PdLIPy. Thermal ellipsoids
are shown at the 30% probability level. Only one statistical position
for the disordered ethyl group is shown.
Some similar features may be observed in the three com-
plexes. The tridentate ligand is always in the enolic form, as
it is usually found in similar complexes.[4] The coordination
geometry of the metal is always square planar, and the
mean plane of the coordinated pyridine molecule is slightly
tilted with respect to the mean coordination plane [angles
between mean planes are in the range from 12.7(3)° to
18.63(7)°]. The heteroatom of the heterocyclic group is al-
ways on the opposite side of the coordinated pyridine mole-
cule. The amino group is always planar, which thus indi-
cates a degree of conjugation between the N atom and the
bonded phenyl ring; moreover, the overall planarity of the
molecule in the three complexes suggests the possibility of
extension of conjugation to the whole molecule through the
metal.
The square-planar coordination geometry found around
the metal in PdLIPy and PdLIIPy is typical of PdII com-
plexes. CuII complexes with similar N-salicylidene-NЈ-
aroylhydrazine ligands may exhibit different geometrical en-
vironments driven by packing forces.[4] In CuLIPy, the ob-
Figure 5. X-ray molecular structure of PdLIIPy. Thermal ellipsoids
are shown at the 30% probability level. Only one statistical position
for the disordered ethyl group is shown. Solvent molecules are
shown, symmetry operations: i = –x + 1, –y, –z + 2; ii = –x +
1/2, –y + 1/2, z.
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Large Second-Order NLO Activity in Poly(4-vinylpyridine)s
served square-planar geometry could also be favoured by linear properties can be inferred by comparison of these
packing forces, as the almost complete planarity of the values with those of similar chromophores previously re-
molecule allows parallel facing of the entire molecule at a ported,[4] where the thiophene ring is replaced by a full aro-
strict van der Waals distance (shorter distance is Cu···N3i = matic system. This contribution is relevant for the copper
3.04 Å; i = –x, –y, –z).
complex (1100ϫ10–48 esu), whereas no enhancement is
The overall molecular geometries of CuLIPy and PdLIPy observed for the palladium complex whose coefficient re-
are very similar, and the only difference is the mutual ar- mains nearly constant within the experimental error
rangement of the ethylic groups bonded to the amminic N (1500ϫ10–48 esu). CuLIIPy and PdLIIPy show lower µβ co-
atom. A different and more bent molecular shape is instead efficients (both 620ϫ10–48 esu), probably due to the shorter
observed in PdLIIPy as a consequence of the presence of a central sequence of consecutive double bonds (two instead
longer nitrophenyl group attached to the furan ring (Fig- of three) with respect to the LI complexes.
ure 6).
Polymers
Polymers (PMLx, x = I,II) are obtained by grafting
(MLx)2 onto commercial poly(4-vinylpyridine) (Aldrich,
Mw = 60000). The dimeric species is split in solution and a
single complex fragment is anchored onto the pyridine
groups of the polymer backbone, as previously observed.[4]
According to this observation, the composition of 35 wt.-%
of the chromophore appears to be a good balance between
chromophore content and solubility of the final polymer.
The main thermodynamic and spectroscopic data are re-
ported in Table 2 together with the metal content.
Figure 6. Superimposition of the molecular structures of PdLIPy
Table 2. Some relevant data for polymers.
(open line) and PdLIIPy (bold line) in a view perpendicular to the
coordination plane. Atoms are drawn as spheres of arbitrary radius.
H atoms and ethylic groups are not shown.
[e]
[f]
%
exp.
Tg[a][°C] Td[b][°C] ηinh[c][dL/g] λmax[d][nm] %calcd.
PCuLI
PCuLII
PPdLII
188
192
199
220
290
340
0.18
0.22
0.23
516
462
454
6.19
5.75
7.07
6.15
5.73
7.11
Complexes containing LII are not easily crystallizable,
and this is probably because of their strongly bent shape.
Voids may be formed during the crystallization process, so
the presence of a suitable crystallization solvent seems to be
a necessary condition to form a stable crystalline phase. In
particular, single crystals of PdLIIPy suitable for X-ray
analysis were only obtained from THF containing hydro-
quinone as a stabilizing agent, and resolution of the struc-
ture revealed the presence of both substances as crystalli-
zation solvents (Figure 5). The THF molecule is statistically
disordered on the binary axis along the c axis, the hydroqui-
none molecule sits on an inversion centre and is hydrogen
bonded to the imminic N atom of an adjacent molecule
[O6–H···N3 2.011(7) Å, 173.57°].
UV/Vis spectra of mononuclear complexes show two op-
tical transitions (see Experimental Section) localized at
330–380 and 450–510 nm. Similar compounds reported in
the literature[9] show analogous optical behaviour, and the
higher-energy transition was assigned to an intraligand π–
π* charge transfer and the second one to a charge transfer
involving the metal as a bridge between the strong donor
and acceptor groups.
[a] Glass-transition temperature. [b] Decomposition temperature
(measured at 5% weight loss). [c] Inherent viscosity. [d] UV absorp-
tion maximum. [e] Calculated metal content as Pd or CuO. [f] Ex-
perimental metal content as Pd or CuO.
The DSC and TGA curves of both PCuLII and PPdLII
polymers show the expected thermal stability with decom-
position temperatures near 290 and 340 °C, respectively.
For PCuLI, polymer decomposition starts at 220 °C, which
is 30 °C higher than Tg. This behaviour is not in agreement
with that observed for analogous polymers previously re-
ported,[4] whose decomposition temperatures lie beyond
300 °C. The thermogravimetric analysis of complex CuLIPy
(Figure 1) shows a plateau between 400 and 600 °C, which
corresponds to CuS residue. Sulfide formation is confirmed
by subsequent treatment at higher temperatures in air,
which produces a residue corresponding to CuO. The lower
stability observed for the CuLIPy complex when grafted
onto a polymeric backbone may be related to the formation
of the stable compound CuS, which induces breaking of the
thiophene ring and the beginning of decomposition.
Second-order NLO activity of mononuclear complexes
was measured by the electric field-induced second-har-
monic (EFISH) technique in chloroform solution. The µβ
coefficient of CuLIPy is higher (1600ϫ10–48 esu) than that
Preparation of Poled Films and SHG Measurements
NLO characterization was carried out by measuring the
of PdLIPy (1400ϫ10–48 esu) and both fall into line with the d33 component of nonlinear second-order optical suscep-
expected values for this class of chromophores. The role tibility χ(2) on poled thick films deposited by spin-coating
played by the heterocycle in determining the molecular non- on soda–lime glass slides. In order to prepare the poled
Eur. J. Inorg. Chem. 2008, 1846–1853
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A. Tuzi et al.
FULL PAPER
films, appropriate amounts of polymers (about 50 mg/mL)
were dissolved in 1,1,2,2-tetrachloroethane, and the solu-
tions were filtered through 0.2-µm Teflon filters. A spin
coater SCS P6700 was utilized for the formation of the
polymer film, and the instrument was operated at a rate of
1000 rpm for 60 seconds at room temperature, whereas the
solution was deposited at about 120 °C. Residual solvent
was removed by keeping the films at 120 °C under vacuum.
The film thickness was measured with an Alphastep 200
profilometer. The poling treatment was performed under an
argon atmosphere by use of a vertical golden wire as a co-
rona electrode. The wire tip was at a distance of 1 cm from
the film surface. The samples were both heated to the pol-
ing temperature (205 °C for PPdLII and 190 °C for PCuLII)
under applied voltage of 10 and 9 KV for PPdLII and PCu-
LII, respectively, and held for 30 min and then cooled down
to room temperature at about 3 °C/min. Finally, the electric
field was removed (Figure 7).
Figure 8. Maker fringes pattern of transmitted SH signal for the
reference X-cut quartz plate and (inset) PCuLII poled film. The
closed circles and the full-line curves represent the experimental
data and the best-fit curve, respectively.
93 pm/V for PPdLII were measured for the d33 coefficient at
1064 nm, whereas values of 21 pm/V for PCuLII and 12 pm/
V for PPdLII were measured at 1500 nm. The highest NLO
activity observed for PCuLII is unexpected if compared
with the intrinsic activity of the chromophores
(620ϫ10–48 esu for both). This behaviour could be related
to the high mobility of the chromophoric fragments grafted
onto the polymer that favoured a higher polar order ob-
tained in the poling process. Both the high degree of empty
spaces due to the bent shape of the molecule and the visco-
elastic phase of the polymer system above Tg favour this
high mobility. This difference in polar order is quite evident
also by UV/Vis analysis, where the order parameter for
PCuLII (0.23) results sensibly higher with respect to PPdLII
(0.17). One more facet to point out is the one order of mag-
nitude difference between the d33 values at 1064 and
1500 nm. This behaviour could be reasonably ascribed to
the resonance contribution that affects the measurement at
1064 nm due to absorption at the second harmonic
(532 nm) in the visible spectrum (Figure 9).[11,12]
Figure 7. Best poling conditions for polymers PCuLII and PPdLII.
The Maker fringes technique allows the NLO coefficients
to be determined by measuring the second harmonic signal
generated by the sample as a function of the angle of inci-
dence. Absolute values of the d33 coefficient of an isotropic
nonlinear film can be determined once the experimental
setup is calibrated by performing measurements on a sam-
ple whose second-order nonlinear optical susceptibility is
known. Here we employed a 1-mm thick X-cut quartz plate
for calibration. The Maker fringes pattern of X-cut quartz
is shown in Figure 8, where the full line corresponds to the
best-fit curve obtained by using the expression for the trans-
mitted SH power.[10]
The nonlinear second-order optical susceptibility (d33
component) of the polymer film is determined at wave-
length λ = 1064 nm and λ = 1500 nm by comparing the
results of the numerical fit obtained for investigated sam-
ples and the reference quartz plate, once their thickness and
refractive index at the fundamental and at the SH wave-
length are given and once the Kleinmann symmetry condi-
tion (d15 = d31) is assumed for the polymeric poled film.
Figure 9. UV/Vis spectra for the PCuLII polymer.
Finally, in Figure 10 the trend of nonlinear response in
Figure 8 shows also the Maker fringes pattern of trans- time at a temperature of 80 °C is shown.
mitted SH signal for PCuLII poled film measured at
It can be seen that, after an initial loss of 30% in the
1500 nm. The closed circles and the full-line curve represent beginning 300 h, the NLO activity remains constant for a
the experimental data and the best-fit curve, respectively. period as long as 750 h. This very large time stability is a
The high NLO activity of these materials is shown from very important feature in view of a possible use of the re-
the d33 determinations; values of 167 pm/V for PCuLII and ported polymers for applications.
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Large Second-Order NLO Activity in Poly(4-vinylpyridine)s
ues are reported. Thermogravimetric measurements were per-
formed by utilizing a Mettler TG50 apparatus. Optical observations
were performed with a Zeiss Axioscop polarizing microscope
equipped with an FP90 Mettler hot stage. Intrinsic viscosities of
polymer solutions with a concentration of 0.500 g/L in N,N-di-
methylformamide (DMF) were measured at 25.0 °C by utilizing an
Ubbelohde viscosimeter. 1H NMR spectra were recorded with a
Varian XL 200 or 300 MHz instrument. UV/Vis absorption spectra
were recorded with a Jasco V560 spectrophotometer; sample solu-
tions were examined in the190–900 nm range at a scanning rate of
120 nm/min
(E)-3-(5-Nitrothiophen-2-yl)acryloyl Hydrazide: (E)-3-(5-Nitro-
thiophen-2-yl)acrylic acid was prepared as described by Taniguchi
and Kato.[13] The hydrazide was synthesized by following the pro-
cedure described by Gordon et al.[14] (E)-3-(5-nitrothiophen-2-yl)-
acrylic acid (2.00 g, 10.0 mmol) was heated at reflux in SOCl2 to
obtain the corresponding chloride. This was dissolved in dry THF
(20 mL) and slowly dropped into a solution of tert-butyl carbazate
(2.65 g, 20.0 mmol) in dry THF (20 mL) whilst stirring. After 1 h,
the solvent was distilled to isolate a yellow solid corresponding to
a mixture of tBOC-protected (E)-3-(5-nitrothiophen-2-yl)acryloyl
hydrazide and exceeding tert-butyl carbazate. To this mixture was
added trifluoroacetic acid (20 mL) at room temperature, and the
solution was stirred for 2 h. The acid was removed in vacuo, and
the residue was triturated with 10% aqueous sodium hydrogen car-
bonate to obtain a yellow solid that was isolated by vacuum fil-
tration and washed with water. Crystallization (acetone/heptane)
yielded the pure product (1.16 g, 54.3%). M.p. 202 °C (dec.). 1H
NMR (200 MHz, [D6]DMSO, 25 °C): δ = 4.56 (s, 2 H, NH2), 6.56
(d, J = 15.6 Hz, 1 H, CH=), 7.46 (d, J = 4.3 Hz, 1 H, CH th.), 7.59
(d, J = 15.6 Hz, 1 H, CH=), 8.08 (d, J = 4.3 Hz, 1 H, CH th.), 9.52
(s, 1 H, NH) ppm.
Figure 10. Time stability of NLO activity at 80 °C for the PCuLII
and PPdLII polymers.
Conclusions
An easy and inexpensive synthetic path was successfully
applied in the preparation of new CuII and PdII chromo-
phoric complexes containing heterocycles, and the NLO
properties of the grafted polymers were investigated. The
molecular structures of the complexes with pyridine exhibit
similar geometric features. All the ligands are in the enolic
form and then act as tridentate ligands; the metal coordina-
tion geometry is square-planar; the heteroatom of the het-
erocyclic group is always in the opposite side of the coordi-
nated pyridine; the whole molecular geometry is planar
with a more bent shape when the LII substituent is present
in the complexes. All synthesized polymers show good solu-
bility, thermal stability and a suitable glass-transition tem-
perature. The better thermal stability was found for grafted
polymers containing an LII substituent. The high NLO ac-
tivity of these materials is shown by the d33 determinations;
values of 21 pm/V for PCuLII and 12 pm/V for PPdLII were
calculated for d33 coefficients in nonresonant conditions
(1500 nm). The d33 values were also calculated in resonant
conditions (1064 nm) and were recorded as 167 and 93 pm/
V for PCuLII and PPdLII, respectively. To the best of our
knowledge this is one of the few examples in which the d33
values in both resonant and nonresonant conditions are
compared. Finally, measurements of SHG decay at 80 °C
evidence a good stability of the polar order with time. Ow-
ing to their excellent properties, the ease and versatility of
their synthetic path, the possibility to modulate Tg and their
solubility as a function of complex content, these materials
are good candidates to be employed in the production of
electrooptic devices as wave guides or Mach-Zehnder mod-
ulators.
Ligand LI: (E)-3-(5-Nitrothiophen-2-yl)acryloyl hydrazide (3.00 g,
14.1 mmol) and 4-(N,N-diethylamino)-2-hydroxybenzaldehyde
(2.85 g, 14.8 mmol) were dissolved in boiling DMF (50 mL). After
10 min, the solution was poured into water (300 mL) containing
concentrated sulfuric acid (8 mL). The dark-red solid obtained was
isolated by vacuum filtration and recrystallized from boiling DMF
1
(80 mL). Yield: 3.52 g (64.4%). M.p. 216 °C. H NMR (200 MHz,
[D6]DMSO, 25 °C): δ = 1.02 (t, J = 6.9 Hz, 6 H, CH3), 3.29 (q, J
= 6.9 Hz, 4 H, CH2), 6.02 (s, 1 H, CH ar.), 6.19 (d, J = 9.0 Hz, 1
H, CH ar.), 6.60 (d, J = 15.6 Hz, 1 H, CH=), 7.15 (d, J = 9.0 Hz,
1 H, CH ar.), 7.47 (d, J = 4.3 Hz, 1 H, CH th.), 7.67 (d, J =
15.6 Hz, 1 H, CH=), 8.04 (d, J = 4.3 Hz, 1 H, CH th.), 8.14 (s, 1 H,
CH=N), 11.10 (s, 1 H, NH), 11.66 (s, 1 H, OH) ppm. C18H20N4O4S
(388.12): calcd. C 55.66, H 5.19, N 14.42; found C 55.48, H 5.20,
N 14.38.
(CuLI)2: Water (40 mL) containing copper(II) acetate monohydrate
(0.467 g, 2.57 mmol) was poured into a stirred boiling solution of
LI (1.00 g, 2.57 mmol) in DMF (100 mL). A dark solid precipitated
that was filtered after cooling and washed repeatedly with water.
Yield: 97%. C36H36Cu2N8O8S2 (898.07): calcd. C 48.05, H 4.03, N
12.45; found C 48.11, H 4.07, N 12.41.
Experimental Section
The differential scanning calorimetry (DSC) technique was em-
ployed for the characterization of the phase behaviour, transition
temperature and enthalpies. For the DSC analysis, an indium-cal-
ibrated Perkin–Elmer Pyris apparatus was utilized. Samples were
examined under a dry nitrogen atmosphere with a temperature-
scanning rate of 10 °C/min. The phase-transition temperatures were
measured at the maximum of the transition endotherm for poly-
mers, whereas for low molecular weight compounds the onset val-
CuLIPy: LI (1.00 g, 2.57 mmol) was dissolved in pyridine (20 mL)
whilst stirring. Copper(II) acetate monohydrate (0.467 g,
2.57 mmol) was added to the boiling LI solution. Then, water
(20 mL) was slowly poured into the solution, and after few minutes
the mixture was left to cool to room temperature. The dark crystal-
line solid obtained was isolated by vacuum filtration and washed
with water. Yield: 86%. UV/Vis: λ (ε, dm3/molcm): 380 (2.5ϫ104),
510 (2.5ϫ104) nm. C23H23CuN5O4S·1/2C5H5N (567.60): calcd. C
Eur. J. Inorg. Chem. 2008, 1846–1853
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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A. Tuzi et al.
FULL PAPER
53.86, H 4.52, N 13.55, S 5.64; found C 53.80, H 4.52, N 13.50, S
5.66.
Yield: 98%. C44H40Cu2N8O10 (966.15): calcd. C 54.60, H 4.17, N
11.58; found C 54.65, H 4.17, N 11.54.
CuLIIPy: The (CuLII)2 complex (1.00 g) was dissolved in boiling
pyridine (15 mL). After 5 min, water (10 mL) was slowly added to
(PdLI)2: A solution of LI (1.00 g, 2.57 mmol) and PdII bisbenzo-
nitrile dichloride (0.987 g, 2.57 mmol) in DMF (20 mL) was heated
to 80–100 °C. After 5 min, water (60 mL) containing sodium ace-
tate (2.00 g) was poured in order to precipitate a dark solid that
was filtered and washed with water. Yield: 96%. C36H36N8O8Pd2S2
(984.02): calcd. C 43.87, H 3.68, N 11.37; found C 43.86, H 3.68,
N 11.35.
precipitate
λ
a brown, crystalline solid. Yield: 97%. UV/Vis:
(ε, dm3/molcm): 400 (2.4ϫ104), 456 (2.6ϫ104) nm.
C27H25CuN5O5·2H2O (598.14): calcd. C 54.13, H 4.88, N 11.69;
found C 54.02, H 4.90, N 11.71.
(PdLII)2: LII (1.00 g, 2.37 mmol) was dissolved in boiling THF
(30 mL). PdII bisbenzonitrile dichloride (0.920 g, 2.40 mmol) in
THF (10 mL) and sodium acetate (1.00 g) in water (20 mL) were
added. The pH was raised to 9 and a dark-red solid precipitated,
which was then filtered and washed with water and ethyl acetate.
Yield: 97%. C44H40N8O10Pd2 (1052.09): calcd. C 50.15, H 3.83, N
10.63; found C 50.15, H 3.83, N 11.64.
PdLIIPy: The (PdLII)2 complex (1.00 g) was dissolved in boiling
pyridine (15 mL). After 5 min, water (10 mL) was slowly added to
precipitate an orange, crystalline solid. Yield: 95%. 1H NMR
(200 MHz, [D]CHCl3, 25 °C): δ = 1.21 (t, J = 10.2 Hz, 6 H, CH3),
3.40 (q, J = 10.2 Hz, 4 H, CH2), 6.24 (dd, J1 = 14.1 Hz, J2 = 3.6 Hz,
1 H, CH ar.), 6.37 (d, J = 3.6 Hz, 1 H, CH ar.), 6.93 (d, J = 5.1 Hz,
1 H, CH fur.), 7.12 (d, J = 5.1 Hz, 1 H, CH fur.), 7.22 (d, J =
14.1 Hz, 1 H, CH ar.), 7.54 (t, J = 10.2 Hz, 2 H, Py), 7.79 (s, 1 H,
CH=N), 7.90 (d, J = 13.2 Hz, 2 H, CH ar.), 7.92 (t, J = 11.0 Hz,
1 H, Py), 8.24 (d, J = 13.2 Hz, 2 H, CH ar.), 8.95 (d, J = 8.1 Hz,
2 H, Py) ppm. UV/Vis: λ (ε, dm3/molcm): 352 (2.4ϫ104), 450
(3.3ϫ104) nm. C27H25N5O5Pd·2H2O (641.11): calcd. C 50.51, H
4.55, N 10.91; found C 50.60, H 4.54, N 10.91.
Polymers (PMLx): All polymers were synthesized by dissolving
poly(4-vinylpyridine) (0.650 g) and the (MLx)2 complex (0.350 g)
in boiling DMF and precipitating in water (100 mL). The product
was washed repeatedly with water. Yield: 98%.
The synthesis of PPdLI gave an insoluble and crosslinked-like prod-
uct probably due to further polymerization of the ethylene bridges
contained in the chromophore structure so that no characterization
was possible for this polymer.
PdLIPy: LI (1.00 g, 2.57 mmol) and PdII bisbenzonitrile dichloride
(0.987 g, 2.57 mmol) were dissolved in pyridine (35 mL). The solu-
tion was kept boiling and water (30 mL) was added. After cooling
to room temperature dark crystals of the PdLIPy complex were
obtained, filtered and washed with water. Yield: 84%. 1H NMR
(200 MHz, [D]CHCl3, 25 °C): δ = 1.21 (t, J = 6.8 Hz, 6 H, CH3),
3.39 (q, J = 6.8 Hz, 4 H, CH2), 6.24 (dd, J1 = 8.8 Hz, J2 = 2.4 Hz,
1 H, CH ar.), 6.35 (d, J = 2.4 Hz, 1 H, CH ar.), 6.88 (d, J =
15.6 Hz, 1 H, CH=), 7.05 (d, J = 4.4 Hz, 1 H, CH th.), 7.19 (d, J
= 8.8 Hz, 1 H, CH ar.), 7.45 (d, J = 15.6 Hz, 1 H, CH=), 7.53 (t,
J = 6.8 Hz, 2 H, Py), 7.65 (s, 1 H, CH=N), 7.80 (d, J = 4.4 Hz, 1
H, CH th.), 7.93 (t, J = 7.6 Hz, 1 H, Py), 8.93 (d, J = 5.4 Hz, 2 H,
Py) ppm. UV/Vis: λ (ε, dm3/molcm): 330 (2.6ϫ104), 494 (2.4ϫ104)
nm. C23H23N5O4PdS (571.05): calcd. C 48.30, H 4.05, N 12.24, S
5.61; found C 48.38, H 4.05, N 12.20, S 5.63.
5-(4-Nitrophenyl)furan-2-carboxylic Acid: The acid was synthesized
according to Holla et al.[15] 4-Nitroaniline (1.38 g, 10.0 mmol) were
suspended in water (125 mL) containing HCl (37 wt.-%, 25 mL) at
0–5 °C. NaNO2 (0.720 g, 10.4 mmol) in water (25 mL) was slowly
added whilst stirring. After 15 min, water (50 mL) containing 2-
furoic acid (1.12 g, 10.0 mmol) was poured into the solution. Am-
monium cerium(IV) nitrate (4.00 g) dissolved in water (10 mL) was
added dropwise, and the solution was stirred for 2 h at room tem-
perature. By cooling the solution an orange solid precipitated. This
was purified by dissolving in excess KOH solution, filtering and
precipitating at low pH. Finally the yellow solid was recrystallized
from acetone/heptane. Yield: 70%. M.p. 256 °C. 1H NMR
(200 MHz, [D6]DMSO, 25 °C): δ = 7.35 (d, J = 4.0 Hz, 1 H, CH
fur.), 7.43 (d, J = 4.0 Hz, 1 H, CH fur.), 8.03 (d, J = 8.8 Hz, 2 H,
CH ar.), 8.30 (d, J = 8.8 Hz, 2 H, CH ar.) ppm.
SHG Measurements: Measurements of nonlinear coefficient d33
were performed by means of the Maker fringes technique.[16] The
laser beam at fundamental frequency was provided by an optical
parametric oscillator (OPO), whose wavelength can be tuned in the
near-infrared range (800–1600 nm). The OPO was pumped by a
Q-switched Nd:YAG laser having 10 ns pulse duration and 10 Hz
repetition rate. The laser beam impinged on a variable attenuator
made by a half-wave retardation plate and a polarizing beam
splitter cube, which allowed continuous variation of optical power
impinging on the sample. The fundamental beam reflected by the
polarizing beam splitter cube impinged on a potassium dideuter-
iophosphate (KDP) crystal, whose second harmonic signal, de-
tected by a photodiode, was employed as a reference signal in order
to take into account the power fluctuations of the fundamental
laser beam. A double Fresnel rhomb selected the proper polariza-
tion direction for the fundamental beam impinging on the sample,
which was placed on a goniometric stage to allow variation of the
angle of incidence. A coloured filter absorbed the unwanted signal
at fundamental wavelength transmitted through the sample,
whereas the second harmonic signal was detected by a high sensi-
tivity amplified photodiode. Both the electric signals coming from
photodiodes are acquired by a computer interfaced Tektronix
TDS540 500 MHz bandwidth digitizing oscilloscope.
5-(4-Nitrophenyl)furan-2-carbohydrazide: The hydrazide was syn-
thesized as described above for trans-3-(5-nitro-2-thienyl)acryloyl
hydrazide. This gave a yellow solid that was recrystallized from ace-
tone/heptane. Yield: 85%. 1H NMR (200 MHz, [D6]DMSO,
25 °C): δ = 7.32 (d, J = 2.4 Hz, 1 H, CH fur.), 7.39 (d, J = 2.4 Hz,
1 H, CH fur.), 8.13 (d, J = 8.8 Hz, 2 H, CH ar.), 8.31 (d, J =
8.8 Hz, 2 H, CH ar.), 9.90 (s, 1 H, NH) ppm.
Ligand LII: Ligand LII was synthesized as described above for li-
gand LI. An orange solid was obtained by recrystallization from
1
DMF. Yield: 75%. M.p. 222 °C. H NMR (200 MHz, [D6]DMSO,
25 °C): δ = 0.97 (t, J = 6.9 Hz, 6 H, CH3), 3.21 (q, J = 6.9 Hz, 4
H, CH2), 5.99 (d, J = 2.1 Hz, 1 H, CH ar.), 6.17 (dd, J1 = 9.0 Hz,
J2 = 2.1 Hz, 1 H, CH ar.), 7.11 (d, J = 9.0 Hz, 1 H, CH ar.), 7.26
(d, J = 3.6 Hz, 1 H, CH fur.), 7.36 (d, J = 3.6 Hz, 1 H, CH fur.),
8.06 (d, J = 8.7 Hz, 2 H, CH ar.), 8.21 (d, J = 8.7 Hz, 2 H, CH
ar.), 8.37 (s, 1 H, CH=N), 11.06 (s, 1 H, NH), 11.75 (s, 1 H, OH)
ppm. C22H22N4O5·H2O (440.17): calcd. C 59.99, H 5.49, N 12.72;
found C 60.09, H 5.48, N 12.75.
(CuLII)2: LII (1.00 g, 2.37 mmol) was dissolved in boiling DMF
(40 mL). Copper(II) acetate monohydrate (0.520 g, 2.60 mmol) was
added and after 10 min the complex was precipitated by adding
water (5 mL). The brown solid was filtered and washed with water.
X-ray Analysis: Single crystals of CuLIPy, PdLIPy and PdLIIPy
suitable for X-ray analysis were obtained at room temperature by
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 1846–1853

Large Second-Order NLO Activity in Poly(4-vinylpyridine)s
Table 3. Crystal data and structure refinement details.[a]
CuLIPy
PdLIPy
PdLIIPy
Chemical formula
Formula weight
Temperature [K]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
2(C23H23N5O4SCu)·C5H5N
1137.27
293
monoclinic
P21/c
9.051(2)
18.837(4)
16.5670(4)
90.
C23H23N5O4SPd
571.92
293
monoclinic
P21/c
11.665(2)
12.098(2)
19.179(4)
90.
8(C27H25N5O5Pd)·4(C6H6O2)·C4H8O
5360.06
173
orthorhombic
Pccn
19.577(2)
35.358(4)
8.43(1)
90.
β [°]
109.89(2)
90.
2656.1(9)
2, 1.422
118.50(1)
90.
2378.6(8)
4, 1.597
90.
90.
5835(7)
1, 1.525
γ [°]
V [Å3]
Z, Dcalcd. [g/cm3]
µ [1/mm]
0.943
0.908
0.689
θ range [°]
3.08, 27.50
25944/5985 (Rint = 0.0507)
336, 0
0.0436, 0.1013
0.0989, 0.1299
0.640, –0.383
3.25, 27.51
15073/5397 (Rint = 0.0428)
327, 6
0.0332, 0.0733
0.0598, 0.0833
0.393, –0.623
3.06, 25.00
19158/5067 (Rint = 0.0924)
384, 1
0.0601, 0.1486
0.1005, 0.1647
1.363, –1.242
Reflections collected/unique
Parameters, restraints
R1, wR2 [I Ͼ 2σ (I)][b]
R1, wR2 (all data)
∆ρmax, ∆ρmin [e/Å3]
2
2 2
2 2 1/2
[a] Common wavelength (Mo-Kα) = 0.71073 Å. [b] R1 = ∑||Fo| – |Fc|| ͞ ∑|Fo|; wR2 = [∑w(Fo – Fc ) ⁄ ∑w(Fo ) ]
.
slow evaporation of a pyridine solution for CuLIPy and PdLIPy
and of a THF solution for PdLIIPy. Data were collected with a
Bruker-Nonius KappaCCD diffractometer (Mo-Kα radiation, thick
slices, φ scans plus ω scans to fill the asymmetric unit) at room
temperature for CuLIPy and PdLIPy and at 173 K in flowing N2
for PdLIIPy. Semiempirical absorption corrections (multiscan SA-
DABS) were applied. All structures were solved by using the direct
methods (SIR97) program[17] and anisotropically refined by the
full-matrix least-squares method on F2 against all independent
measured reflections (SHELXL-97 program of SHELX-97 pack-
age[18]). H atoms in all structures were placed in calculated posi-
tions with Ueq equal to those of carrier atom and refined by the
riding method. In the asymmetric unit of CuLIPy the pyridine
molecule present as crystallization solvent is located on an inver-
sion centre so that it is statistically disordered on two sites with
occupancy factor 0.5. In PdLIPy, one of the ethylic groups is disor-
dered on two different positions with refined occupancy factors
0.55 and 0.45. In the crystals of PdLIIPy, both THF and hydroqui-
none solvent molecules are found. The molecule of THF is located
on a binary axis along c with statistical positional disorder, the
molecule of hydroquinone is located on an inversion centre. Some
crystal, collection and refinement data are reported in Table 3.
[1] L. R. Dalton, A. W. Harper, R. Ghosn, W. H. Steiner, M. Ziari,
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[8] M. S. Gordon, J. G. Krause, M. A. Linneman-Mohr, R. R.
Parchue, Synthesis 1980, 3, 244–245.
[9] S. Di Bella, I. Fragalà, I. Ledoux, M. A. Diaz-Garcia, P. G.
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CCDC-644411, -644412 and -644413 contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif.
[14] M. S. Gordon, J. G. Krause, M. A. Linneman-Mohr, R. R.
Parchue, Synthesis 1980, 3, 244–245.
[15] K. S. Bhat, B. S. Holla, Heterocycl. Commun. 2003, 9, 625–628.
[16] P. D. Maker, R. W. Terhune, M. Nisenoff, C. M. Savage, Phys.
Rev. Lett. 1962, 8, 21–22.
Acknowledgments
[17] A. Altomare, M. C. Burla, M. Camalli, G. L. Cascarano, C.
Giacovazzo, A. Guagliardi, A. G. G. Moliterni, G. Polidori, R.
Spagna, J. Appl. Cryst. 1999, 32, 115–119.
[18] G. M. Sheldrick, SHELXL-97, University of Göttingen, Ger-
many, 1997.
Research supported by Fondo per gli Investimenti della Ricerca di
Base (FIRB) 2001 grant from Ministero dell’Università e della
Ricerca (MIUR, n. RBNEOI P4JF). Thanks are also due to Centro
Interdipartimentale di Metodologie Chimico Fisiche (CIMCF) of
University “Federico II” of Naples for NMR spectroscopic and X-
ray facilities.
Received: October 30, 2007
Published Online: February 28, 2008
Eur. J. Inorg. Chem. 2008, 1846–1853
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1853