Synthesis and third-order optical nonlinearities of ferrocenyl Schiff base

Article abstract of DOI:10.1016/j.cplett.2011.08.035

Four ferrocenyl Schiff bases were synthesized from ferrocenecarboxaldehyde and aromatic amine. The yields were 46-73%. These compounds have a D-A structure and third-order nonlinear optical (NLO) properties. The third-order nonlinear optical properties of the compounds were measured using femtosecond degenerate four-wave mixing. The third-order NLO susceptibilities of the compounds were 2.21-3.32 × 10^-13 esu. The second-order hyperpolarizabilities of the molecules were 2.10-3.15 × 10^-31 esu. The response times were 42-63 fs.

Full text of DOI:10.1016/j.cplett.2011.08.035

Chemical Physics Letters 514 (2011) 114–118
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Chemical Physics Letters
journal homepage: www.elsevier.com/locate/cplett
Synthesis and third-order optical nonlinearities of ferrocenyl Schiff base
⇑
Jian-Hong Jia, Xiao-Min Tao, Yu-Jin Li, Wei-Jian Sheng, Liang Han, Jian-Rong Gao , Yu-Fen Zheng
State Key Laboratory Breeding Base of Green Chemistry-Synthesis Technology, Zhejiang University of Technology, Hangzhou 310014, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Four ferrocenyl Schiff bases were synthesized from ferrocenecarboxaldehyde and aromatic amine. The
yields were 46–73%. These compounds have a D-A structure and third-order nonlinear optical (NLO)
properties. The third-order nonlinear optical properties of the compounds were measured using
femtosecond degenerate four-wave mixing. The third-order NLO susceptibilities of the compounds were
Received 26 February 2011
In final form 14 August 2011
Available online 19 August 2011
2.21–3.32 ꢀ 10ꢁ13 esu.
The
second-order
hyperpolarizabilities
of
the
molecules
were
2.10–3.15 ꢀ 10ꢁ31 esu. The response times were 42–63 fs.
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
response [28–30]. Electrons in frontier orbitals are fed back by
the d-electrons of the iron atom. A d orbital participates in and ex-
Third-order nonlinear optical (NLO) materials have attracted
considerable interest in the last two or so decades because of their
potential applications in the development of photonic device such
as optical data storage, optical communication, and optical limiting
pands the p electron system of the metallocene ring. An iron atom
also has a variety of oxidation states, and the whole ferrocene
group becomes a good electron donating group after the iron atom
is combined with the metallocene ring. The common
p-electron
[1–3]. Metal organic nonlinear optical materials with the
p
-conju-
bridge groups include carbon–carbon double bonds (AC@CA)
and carbon–nitrogen double bonds (AC@NA), of which the former
are more reported. The electron donating part in the push–pull sys-
tem usually selects aromatic rings, heteroaromatics and other
chromophores, and some organic pigment chromophores with
gated system have been investigated as alternatives to inorganic
species due to their low cost, fast and large nonlinear response
over a broad frequency range, inherent synthetic flexibility, high
optical-damage threshold, and intrinsic tailorability [4,5]. Recently,
a variety of metal organic nonlinear optical materials have been re-
ported, such as phthalocyanines [6–8], 1,3-dithiole-2-thione-4,5-
dithiolate complexes [9–12], and porphyrins [13–15].
For ferrocene metal organic compounds, due to their unique
electrochemical and optical properties, and their potential applica-
tions in optical information processing, communications, inte-
grated optics [16–20] and other high-tech fields, they have
attracted extensive attention of researchers, which have also be-
come a research priority in functional materials.
Nonlinear optical properties (NLO) are important indexes to
study organic nonlinear optical materials. The early studies on
nonlinear properties of ferrocene metal organic compounds were
mainly focused on second-order properties [21–24]. With the
deepening of the study, the third-order nonlinear properties of fer-
rocene metal organic compounds are gradually becoming a re-
search priority [25–27].
the large
p conjugated structure are fine components to construct
organic third-order NLO materials. In this Letter, we designed and
synthesized four ferrocenyl schiff bases 1–4 (Figure 1) which with
the bridge of carbon–nitrogen double bonds (AC@NA), so as to en-
hance their third-order optical nonlinearities. Their structures
were characterized by UV, IR, 1H NMR and HRMS. The third-order
NLO properties were measured using femtosecond degenerate
four-wave mixing (DFMW) technique. The relationship between
molecular structure and optical property was analyzed. The results
show that these anthraquinone derivatives possess large and ultra-
fast third-order NLO responses and have potential applications in
photonics.
2. Experimental
2.1. Preparation of NLO materials
Organic NLO materials are generally formed by the connection
of the electron donating group and the electron withdrawing group
2.1.1. Synthesis of ferrocenecarboxaldehyde
through the
p electronic bridge, which have the large D-p-A conju-
To a three-neck flask, were added 5.0 g of dry ferrocene
(26.88 mmol) and 75 mL of dichloromethane. Then 19.6 g of tri-
ethyl orthoformate (132.17 mmol) was added dropwise to the
mixture with stirring. After the ferrocene was completely dis-
solved, 30.0 g of anhydrous AlCl3 was slowly added, and the reac-
tion mixture was stirring at room temperature for 3 h. Then the
gated system. The push–pull system helps to improve the molecu-
lar polarizability, so as to obtain a higher nonlinear optical
⇑
Corresponding author.
E-mail address: zgdjjh@163.com (J.-R. Gao).
0009-2614/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.cplett.2011.08.035

J.-H. Jia et al. / Chemical Physics Letters 514 (2011) 114–118
115
2
3
Figure 1. The synthetic route of ferrocenyl Schiff base derivatives.
Figure 2. Experimental setup of DFWM.
reaction was quenched with sodium hydrosulphite saturated solu-
tion (100 mL) and the mixture was extracted with ethyl ether
(100 mL). After concentrated under reduced pressure, the residue
was purified by chromatography on silica gel (petroleum ether:-
ethyl acetate = 5:1) to afford 3.5 g red solid with the yield of 70%
[31].
1H,Ar-H), 7.543–7.525 (m, 2H,Ar-H), 7.474 (s, 1H,Ar-H), 7.012–
6.998 (d, J = 7.0 Hz, 1H,Ar-H), 4.925 (s, 2H), 4.550 (s, 2H), 4.309
(s, 5H). HRMS(ESI), m/z: 340.0812 (M+).
Compound 3 was synthesized according to the general proce-
dure. After the reaction was completed, the mixture was cooled
to room temperature. The resluting percipitate was collected by fil-
tration, washed with ethanol, and dried. The product was obtained
as a brown solid in 59% yield. 1H NMR (500 MHz, CDCl3) d 9.105 (s,
1H, CH@N), 8.738 (s, 1H, Ar-H), 8.337–8.303 (d, J = 17.0 Hz, 1H,Ar-
H), 7.990–7.972 (d, J = 9.0 Hz, 1H, Ar-H), 4.968 (s, 2H, C5H4), 4.780
(s, 2H, C5H4), 4.337 (s, 5H, C5H5). HRMS(ESI), m/z: 392.0156 (M+).
Compound 4 was obtained as a purple solid in 47% yield. 1H
NMR (500 MHz, CDCl3) d:8.990–8.941 (d, J = 24.5 Hz, 1H, CH@N),
8.445 (s, 1H,C2HSN2), 4.896–4.800 (d, J = 48.0 Hz, 2H, C5H4),
4.689–4.612 (d, J = 38.5 Hz, 2H, C5H4), 4.307–4.281 (d, J = 13.0 Hz,
5H, C5H5). HRMS(ESI), m/z: 297.0047 (M+).
1H NMR (500 MHz, CDCl3) d 9.96 (s, 1H), 4.80 (s, 2H), 4.61 (s,
2H), 4.28 (s, 5H).
2.1.2. General procedure for synthesis of ferrocenyl Schiff base
derivatives 1–4
Ferrocenecarboxaldehyde (0.1 g, 0.47 mmol), aromatic amine
(0.49 mmol), and 50 mL xylene were added to a 100 mL three-neck
flask. After the ferrocenecarboxaldehyde was completely dissolved
with stirring, 0.1 g of basic Al2O3 (0.98 mmol) was added. The reac-
tion mixture was refluxed for 10 h and then concentrated under re-
duced pressure. The residue was purified by chromatography on
silica gel to afford corresponding products.
2.1.3. Nonlinear optical measurements
Compound 1 was obtained as a red solid in 56% yield. 1H NMR
The third-order NLO properties were measured using femtosec-
ond DFWM technique, with a Ti : Sapphire laser. Figure 1 shows the
experimental setup. The pulse width was determined to be 80 fs on
a SSA25 autocorrelator. The operating wavelength was centered at
800 nm. The repetition rate of the pulses was 1 kHz. During the
measurement, the laser was very stable (rms < 0.1%). The input
beam was split into two beams k1 and k2 with nearly equal energy
by use of a beam splitter, then focused on a plot of the sample. The
(500 MHz, CDCl3)
d 8.309 (s, 1H, CH@N), 7.338–7.315 (d,
J = 11.5 Hz, 2H,Ar-H), 7.083–7.066 (d, J = 8.5 Hz, 2H,Ar-H), 4.787
(s, 2H,C5H4), 4.503 (s, 2H, C5H4), 4.238 (s, 5H, C5H5). HRMS (ESI),
m/z: 323.0175 (M+).
Compound 2 was obtained as a red solid in 73% yield. 1H NMR
(500 MHz, CDCl3) d 8.439 (s, 1H, CH@N), 8.302 (s, 1H,Ar-H),
7.879–7.872 (d, J = 3.5 Hz, 1H,Ar-H), 7.720–7.704 (d, J = 8.0 Hz,

116
J.-H. Jia et al. / Chemical Physics Letters 514 (2011) 114–118
12p
vð3Þ
beam k2 passed through a delay line driven by a stepping motor in
order that the optical path length difference between k2 and k1
beams could be adjusted during the measurement. The angle be-
tween beams k1 and k2 were about 5°. When k1 and k2 were over-
lapped spatially in the sample, the generated signal beam k3 or k4
passed through an aperture, recorded by a photodiode and then
analyzed by a Lock-in amplifier and computer (see Figure 2).
The experiments were performed at 22 °C in dichloromethane
solutions using a 1 mm-thick quartz cell. As a reference, the optical
nonlinearity of the standard sample (CS2) was also observed. All
samples were measured at a concentration of 5.0 ꢀ 10ꢁ5 mol/L.
n2 ¼
n2
where n is the linear refractive index of the solution, measured by
2WAJ Abbe refractometer.
The second hyperpolarizability c of a molecule in isotropic med-
ia is related to the solution v(3) by:
vð3Þ
c
¼
Nf4
where N is the number density of the solute per milliliter, and f4 is
the local field correction factor which is [(n2 + 2)/3]4 (n is the linear
refractive index of the solution).
The temporal response of the phase conjugate signal as a func-
tion of the delay time of the input beam is shown in Figure 4. The
3. Results and discussion
Compounds 1–4 can be prepared by the condensation reaction
between ferrocenecarboxaldehyde and aromatic amines in the
presence of the base catalyst. The UV–Vis absorption spectra of
four compounds have been tested in dichloromethane solutions,
and the results are shown in Figure 3. The laser wavelength
(800 nm) used in the experiment of DFWM was out of the absorp-
tion region. Thus the off-resonant third-order optical nonlinearities
of the compounds could be measured. The solvent dichlorometh-
ane has no nonlinear signal under the light intensity adopted. So
the third-order optical nonlinearities measured come from four
anthraquinone derivatives.
response times (
sity of the optical conjugate wave (I) is peak height.The values of
(3), n2,
and response times for the samples deduced and calcu-
lated from the experimental results are listed in Table 1.
s) of the samples is half-peak width, and the inten-
v
c
The results have showed that the
c values of the obtained
compounds 1–4 were 2.10–3.15 ꢀ 10ꢁ31 esu. Saswati Ghosal
et al. [25] used the femtosecond laser (the light source is Nd:
YAG laser, wavelength of 602 nm, pulse width of 400 fs) and the
optical path of the DFWM experiment, and the measured
c
was
1.61 0.18 ꢀ 10ꢁ35 esu. The
c value of 1-ferrocenyl-2-phenyl vinyl
(FcCH@CHC6H5) which took carbon–carbon double bond as
the bridge group was 8.55 1.98 ꢀ 10ꢁ35 esu. It can be seen from
the comparison that, the second-order hyperpolarizabilities of
the molecules of the synthesized ferrocenyl Schiff bases are several
orders higher than other ferrocene metal organic materials, which
thus are a class of third-order nonlinear optical materials with
exceptional performance.
The third-order nonlinear optical susceptibility v(3) is measured
via a comparison with that of a reference sample CS2, calculated
from the DFWM signal (I), the linear refractive index (n), the sam-
ple thickness (L) and absorption correction factor using the follow-
ing equation [32].
ꢀ ꢁ
ꢀ
ꢁ
IS 1=2 Lr ns 2 aL expð
a
L=2Þ
vðr3Þ
vðs3Þ
¼
For 4-chlorobenzene, 6-nitrobenzothiazole and 1,3,4-thiadia-
zole all have the electron-withdrawing function, in molecules of
the D-A type, they can interact with the electron-rich ferrocenyl
at the other side of a molecule, which increases the probability of
Ir
Ls nr 1 ꢁ expðꢁ
a
LÞ
where the subscripts ‘s’ and ‘r’ represent the parameters for the
sample and CS2. And
a indicates the linear absorption coefficient.
Lexpð
a
The fraction a1ꢁexpðꢁL=2Þ comes from the sample absorption and equals
charge transfer. Therefore, the c values of Compounds 1,3,4 are all
a
to 1 approximatelyLÞwhile the sample has little absorption around
the employed laser wavelength . The values of vr(3) and nr for CS2
are 6.7 ꢀ 10ꢁ14 esu and 1.632, respectively [33].
higher than that of Compound 2. What’s more, 1,3,4-thiadiazole
has smaller delocalization energy than the benzene ring and the
benzothiazole ring. As a result, intramolecular charge transfer is
more prone to occur under the action of external electric field.
The nonlinear refractive index n2 in isotropic media is estimated
through the equation [34,35]
Therefore, Compound 4 shows the highest
c value.
Figure 3. The UV–Vis absorption spectra of Compound 1–4.

J.-H. Jia et al. / Chemical Physics Letters 514 (2011) 114–118
117
Figure 4. DFWM signal versus delay time for Compound 1–4 in dichloromethane solution.
Table 1
time is 42–63 fs. Compared with the ferrocene metal organic mate-
rials, the synthesized ferrocenyl Schiff bases have good third-order
nonlinear optical properties.
The values of v(3)
, c, and the respond times for Compound 1–4.
Compounds
n
I
v(3)/1 ꢀ 10ꢁ13
c
/1 ꢀ 10ꢁ31
s/fs
esu
esu
Acknowledgements
1
2
3
4
1.4290 3.09064 3.25
1.4286 1.42435 2.21
1.4292 3.01609 3.21
1.4292 3.21539 3.32
3.09
2.10
3.05
3.15
42.77
45.90
63.01
51.09
We are very grateful to Dr. Shian Zhang from the Key Laboratory
of Optical and Magnetic Resonance Spectroscopy in East China
Normal University, for the DFWM experiment and the helpful dis-
cussion. This research was financially supported by the National
Natural Science Fund of China (Grant no. 20876148).
4. Conclusions
Starting from the ferrocene, by formylation and the condensa-
tion reaction with aromatic amines, four new metal organic
third-order nonlinear optical materials of the ferrocenyl Schiff base
class are synthesized, with the yields of 46–73%. The material
structures are characterized by 1H NMR and MS. The UV–Vis
absorption spectra have showed that the absorption wavelengths
of the compounds generate red shift compared with that of ferro-
cene, which indicates that the conjugation system of compounds is
enhanced by the imine bridge group. The femtosecond laser and
the optical path of the DFWM experiment are used to determine
the third-order nonlinear optical properties of each compound in
the non-resonant state. Their third-order nonlinear susceptibilities
v(3) are 2.21–3.32 ꢀ 10ꢁ13 esu, and the second-order hyperpolariz-
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