pp.53-60 - Arabian Journal for Science and Engineering

SYNTHESIS, CHARACTERIZATION AND NONLINEAR
OPTICAL PROPERTIES OF FOUR NOVEL SCHIFF BASE
COMPOUNDS
Iran Sheikhshoaie * and Samira Saeednia
Department of Chemistry
Shahid Bahonar University of Kerman
Kerman, 76175, Iran
Iran Sheikhshoaie, Samira Saeednia
: ﺔـﺻﻼﺨﻟا
ﻞﻴﻠﺤﺗ ماﺪﺨﺘﺳﺎﺑ ﺎﻬﻔﻴﺻﻮﺗ ﻢﺛ ﻦﻣو ،ﻒﻴﺷ عﻮﻧ ﻦﻣ ﺎﻬﻄﺑاور ﻒﺋﺎﻇﻮﻟا ةدﺪﻌﺘﻣ تﺎﺒآﺮﻣ ﺔﺳاردو ﺮﻴﻀﺤﺘﺑ - ﺚﺤﺒﻟا اﺬه ﻲﻓ - ﺎﻨﻤﻗ ﺪﻘﻟ
يوﻮﻨﻟا ﻲﺴﻴﻃﺎﻨﻐﻤﻟا ﻦﻴﻧﺮﻟا فﺎﻴﻄﻣو ﺔﻴﺠﺴﻔﻨﺒﻟا قﻮﻓ ﺔﻌﺷﻷاو ءاﺮﻤﺤﻟا ﺖﺤﺗ ﺔﻌﺷﻷا ﻒﻴﻃو ، ﻦﻴﺟوﺮﺘﻴﻨﻟاو ﻦﻴﺟورﺪﻴﻬﻟاو نﻮﺑﺮﻜﻟا ﺮﺻﺎﻨﻋ
ﺔﻘﻳﺮﻃ ماﺪﺨﺘﺳﺎﺑ ﺎﻬﺘﺟﺬﻤﻧ ﺖﻤﺗ ﻲﺘﻟا L1 - L4 تﺎﺒآﺮﻤﻟا ﻦﻣ بﺎﻄﻘﺘﺳﻻاو ،(
تﺎﻨﺤﺸﻟا)
ﺔﻴﻧوﺮﺘﻜﻟﻹا ﺺﺋﺎﺼﺨﻟاو ،ﺔﻴﺌﻳﺰﺠﻟا
ﻞآﺎﻴﻬﻟا
1H
ﺔﻴﺋﻮﻀﻟا ﺺﺋﺎﺼﺨﻟا ﻦﻋ ﺊﺒﻨﺗ ﻲﺘﻟا ﺔﻳﺮﻔﺼﻟا ﺮﻴﻏ ﻢﻴﻘﻟا ﻦﻣ ﺮﻴﺜآ ﻰﻠﻋ L4 ءيﺰﺟ يﻮﺘﺤﻳو .( 1-
ﻦﺘﺳوأ جذﻮﻤﻧأ)
ﺔﻴﺒﻳﺮﺠﺘﻟا ﻪﺒﺷ AM1
.( NLO)
ﺔﻴﻄﺨﻟا ﺮﻴﻏ
*
Corresponding Author:
E-mail: i_shoaie@yahoo.com
Paper Received October 4, 2008; Paper Rewritten April 4, 2009; Paper Accepted October 1, 2009
January 2010 The Arabian Journal for Science and Engineering, Volume 35, Number 1A
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Iran Sheikhshoaie, Samira Saeednia
ABSTRACT
Multifunctional Schiff base ligands 2-{(E)-[(2-hydroxypropyl)imino]methyl}phenol L1, 3-{(E)-[(2hydroxypropyl)imino]methyl}-2-naphthol
L2, 2-[(E)-{[(2R)-2-hydroxypropyl]imino}methyl]-4-[(E)phenyldiazenyl]phenol
L3, and 2-[(E)-{[(2R)-2-hydroxypropyl]imino}methyl]-4-[(E)-(4nitrophenyldiazenyl)]phenol
L4 (Figure 1) were synthesized. These Schiff base compounds have been characterized
by C, H, N elemental analysis, FT-IR, UV-Vis, and 1 H NMR spectroscopy. Molecular structures, electronic
properties (charges), and hyperpolarizabilities of compounds L1–L4 were modeled with the semi-empirical AM1
(Austin Model 1) method. The L4 molecule contains a lot of non-zero ß values revealing microscopic non-linear
optic (NLO) properties.
Key words: Schiff base, semi-empirical calculations, NLO property, ONO-tridentate ligand, amino-2-propanol, AM1
method
The Arabian Journal for Science and Engineering, Volume 35, Number 1A January 2010

Iran Sheikhshoaie, Samira Saeednia
SYNTHESIS, CHARACTERIZATION AND NONLINEAR OPTICAL PROPERTIES OF
FOUR NOVEL SCHIFF BASE COMPOUNDS
1. INTRODUCTION
Schiff bases derived from the reaction of aromatic aldehydes and aliphatic or aromatic amines represent an
important series of widely-studied organic ligands. The chemistry of Schiff bases is a field that is being noticed.
These compounds and their metal complexes had a variety of applications, including biological [1–4], clinical [5–8],
analytical [9–12] and industrial [13]. They also play important roles in catalysis [14–20].
The organic molecules which contain both conjugated bonds and acceptor group on one side and a donor group
on the other side are known as nonlinear optical (NLO) materials [21]. A large amount of organic compounds have
been studied as NLO materials [22]. It is obvious that the first and second hyperpolarizabilities (NLO property) in
The donor and acceptor groups have an important role in the first and second hyperpolarizabilties of the π-electron
systems increase, if the donor and acceptor groups become more powerful [23]. Organic molecules with π-electron
delocalization are currently of wide interest as NLO materials in optical switches and NLO devices [24]. Materials
possessing nonlinear optical properties change the propagation characteristics (phase, frequency, amplitude,
polarization, etc.) of the incident light. Nonlinear optics has found many applications in the communications and
photonic industries. Optical switching and memory by NLO effects, which depend on light intensity, are expected to
result in the realization of advanced optical devices in optical fibre communication (OFC) and optical computing,
which makes the maximum use of light characteristics such as parallel and spatial processing capabilities and high
speed.
Quantum chemistry calculations have been shown to be useful in the description of the relationship among the
electronic structure of the molecular systems and their nonlinear optical response [25,26]. The length of bonding
conjugation, the nature of heteroatom participating in this bonding conjugation, the strength of donor and acceptor
groups linked to the bridge, the lowest energy electronic absorption maximum, the molecular asymmetry, and the
effect of geometry conformation, have been considered among the parameters for the optimization of the first and
second hyperpolarizabilities [27,28]. On the other hand, theoretical calculations can be useful to describe the
relationship between the electronic structure of molecular systems and their nonlinear optical (NLO) response. For
the theoretical second optical hyperpolarazibility calculation of the selected systems, the structures were optimized
by Austin model 1 (AM1) [29] by using the MOPAC software [30].
Here we present the synthesis, spectroscopic characterization, and molecular modeling by the semi-empirical
AM1 method of tridentate Schiff base compounds L1-L4 (Figure 1).
H
3
6
4
N
5
2
OH
1
N
N
H
H
CH3 7
OH
9
L1 L2
3
8
6
4
N
5
2
OH
1
H
8
CH3 7
OH
9
O 2 N
January 2010 The Arabian Journal for Science and Engineering, Volume 35, Number 1A
H
N
N
6
4
N
5
2
OH
1
L3
L4
Figure 1. The molecular structures of L1, L2, L3, and L4 Schiff base compounds
3
H
3
H
8
CH3 7
OH
9
6
4
N
5
2
OH
1
H
8
CH3 7
OH
9
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Iran Sheikhshoaie, Samira Saeednia
2. EXPERIMENTAL SECTION
2.1. Reagents and Techniques
All chemicals and solvents were purchased from Aldrich or Merck Chemical Companies and were used as
received without further purification. Elemental (C, H, N) analyses were carried out by standard methods. The FT-IR
spectra (KBr disk) were recorded on a Shimadzu DR-8001 spectrophotometer in the range of 400–4000 cm -1 . In this
study, to calculate dipole moments and all the components of the hyperpolarizability, the origin of the Cartesian
coordinate system (x, y, z) = ( 0, 0, 0) has been chosen at the center of mass of each Schiff base in Figure 1.
2.2. Preparation of L1-L4 Schiff Base Compounds
2-{(E)-[(2-hydroxypropyl)imino]methyl}phenol L1 was prepared by condensation of 2-hydroxy-1salicylaldehyde
(0.01 mol 1.22g) and 1-amino-2-propanol (0.01 mol 0.75 g) in 40 ml ethanol. The reaction m p
46°C, 85% yields. Found: C, 66.91; H, 7.11; N, 7.69. C10H13NO2; C, 67.039; H, 7.262; N, 7.821%. L2, L3, and
L4 Schiff base compounds were also synthesized with the same method and their important properties are shown in
Table 1. Relevant results of the FT-IR measurements (band assignments) are tabulated in Table 2.
Table 1. Some Important Properties With C. H. N. Analysis of the L1-L4 Schiff Base Compounds
Compound
Yield Found (calcd) (%)
Formula
(formula) Color (%) C H N weight(gmol -1 Melting point
) (°C)
L1
C10H13NO2
L2
C14H15NO2
L3
C16H17N3O2
L4
C16H16N4O4
Yellow 85 66.91
( 67.039)
Yellow 78
73.11
(73.363)
Orange 82 67.78
(67.844)
Red 85 58.51
(58.536)
7.11
(7.262)
6.43
(6.550)
5.94
(6.007)
4.83
(4.878)
7.69
(7.821)
5.98
(6.113)
14.86
(14.840)
17.11
(17.073)
179 46-48
229 118-120
283 123
328 180
Table 2. Some Important Absorption Bands in the FT-IR Spectra (400-4000 cm -1 )
for L1-L4 Schiff Base Compounds
Schiff base νC=N (cm -1 ) νOH (cm -1 ) νC-O(phenolic) (cm -1 )
3. UV-VIS SPECTROSCOPY
L1 1641 3354 1236
L2 1613 3348 1227
L3 1666 3280 1232
L4 1620 3289 1230
Apart from the NLO responses it is very helpful to check spectroscopic absorbance in the appropriate
wavelength. The wavelengths obtained by UV-Vis spectra analysis can be helpful in planning the synthesis of the
promising NLO materials [31].
The UV-Vis spectra of the compounds L1-L4 have been studied in dimethylformamid (DMF). The maximum
absorption wavelengths for L1-L4 compounds are shown in Table 3.
The Arabian Journal for Science and Engineering, Volume 35, Number 1A January 2010

Iran Sheikhshoaie, Samira Saeednia
Table 3. The Maximum Absorption Wavelengths (λ, nm) Respectively,
Obtained from UV-Vis Spectral Analysis of L1-L4 Compounds in Dimethylformamid (DMF)
Compound λ, nm (coefficient)
L1
L2
L3
L4
271.7(0.366)
260.5(0.445)
248.790.420)
296.6(0.503)
294.9(0.423)
285.3(0.463)
334.9(0.803)
325.5(0.652)
283.9(0.620)
259.2(0.493)
252.0(0.699)
385.7(0.940)
358.3(0.853)
311.1(0.582)
258.5(0.629)
243.5(0.579)
4. 1 H NMR SPECTROSCOPY
The 1 HNMR data for L1-L4 compounds are shown in Table 4.
Table 4. 1 HNMR Data (ppm) for L1-L4 Compounds in CDCl3
Compound δOH δCH=N δAr-H δCH δCH2 δCH3
L1 8.62 8.40 (7.09-7.25) 3.74 4.12 1.35
L2 8.69 8.80 (7.07-8.02) 3.71 4.3 1.31
L3 8.25 8.45 (7.11-8.03) 3.77 4.6 1.33
L4 7.20 8.46 (7.11-7.91) 3.74 3.91 1.36
It is found that the maximum wavelengths of the π→π* transition for all these compounds (L1- L4) are almost
within 271–334 nm (see Table 3). The maximum absorption wavelengths of the L4 compound found shorter than
400 nm show that such a compound might have non-zero rather high first hyperpolarazibility.
5. COMPUTATIONAL METHOD
Quantum chemical calculations for Schiff bases L1-L4 were done by using the AM1 semi-empirical method with
the MOPAC program package. All geometries were pre-optimized by molecular mechanics and then fully optimized
by the AM1 semi-empirical method. The first hyperpolarizability (βµ value) and total dipole moment (µ) for all
compounds were calculated by AM1 semi-empirical method (see Table 5).
The vector part of the molecular hyperpolarizability, ß-V, is calculated according to the following equations:
β –V = (βx 2 +βx 2 +βx 2 ) 1/2 (1)
where βi (i = x, y, z) is given by,
ßi = (1/3) ∑j=x,y,z (βijj + βjij + βjji ) (2)
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Iran Sheikhshoaie, Samira Saeednia
Table 5. The First Hyperpolarazibilitie (Esu.) and Dipole Moment (Debye) of L1-L4 Schiff Base Compounds
by AM1 Semi-Empirical Method
Schiff base Hyperpolarizability
(Esu.)
Dipole moment
(Debye)
L1 0.0032×10 -30 0.980
L2 0.124×10 -30 1.325
L3 0.012×10 -30 0.920
L4 15.418×10 -30 6.244
Table 6 shows the net charge density on O1, N5, and O9 atoms (coordination sites) for L1-L4 Schiff base
compounds computed by the AM1 semi-empirical method.
Table 6. Calculated Charge Density on Coordination Sites of L1-L4 Schiff Base Compounds
by AM1 Semi-Empirical Method
Schiff base O1 N5 O9
L1 -0.259 -0.223 -0.326
L2 -0.261 -0.229 -0.337
L3 -0.253 -0.238 -0.336
L4 -0.249 -0.236 -0.335
6. RESULTS AND DISCUSSION
We have designed and synthesized four derivatives of salicylaldehyde and naphtaldehyde Schiff base compounds
(L1-L4). All four Schiff base compounds show the characteristic azomethine (-CH=N), OH, and C-O phenolic
vibration at 1620–1641, 3354–3389, and 1236–1230 cm -1 , respectively (see Table 2). The molecular first
hyperpolarizabilities of these compounds have been calculated by using the AM1 semi-empirical method. The
computational approach allows the determination of molecular NLO properties as an inexpensive way to design
molecules by analyzing their potential before synthesis. Table 5 shows the L4 compound has a large first
hyperpolarizabilities (β) or NLO property and dipole moment (µ), because the NO2 group plays an important role in
the NLO property for this compound.
In organic NLO molecules, the Schiff base, especially that derived from the reaction of salicyaldehyde with
amines, have attracted interest [32], because of their relative delocalization of the π–electronic clouds. The donor-
(π–electron bridge)-acceptor (D-π-A) structures, as a simple molecular model, have been successfully used in the
development of second-order NLO compounds.
The negative charge density on O(1), N(5), and O(9) atoms (see Figure 1 and Table 6) indicates that all L1-L4 Schiff
base compounds have three coordination sites (O(2), N(5), and O(9)) for binding to the metal ions in the metal complex
formation.
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