Thiazole azo dyes with lateral donor branch: Synthesis, structure and second order NLO properties

Article abstract of DOI:10.1016/j.dyepig.2012.08.002

Three azo dyes with a thiazole based donor-π-acceptor structure containing a methoxyphenyl group as the lateral donor branch were synthesized and fully characterized. The formyl azo dye precursor was synthesized using 5-formylaminothiazole derivative as t

Full text of DOI:10.1016/j.dyepig.2012.08.002

Dyes and Pigments 96 (2013) 45e51
Contents lists available at SciVerse ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Thiazole azo dyes with lateral donor branch: Synthesis, structure and second
order NLO properties
,
b
,
c
a
c
d
Reda M. El-Shishtawy a , Fabio Borbone , Zahra M. Al-amshany , Angela Tuzi , Alberto Barsella ,
*
Abdullah M. Asiri a e, Antonio Roviello c
,
a Chemistry Department, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia
b Dyeing, Printing and Textile Auxiliaries Department, Textile Research Division, National Research Centre, Dokki, Cairo 12622, Egypt
c Dipartimento di Scienze Chimiche, Università degli Studi di Napoli Federico II, Complesso Universitario di Monte Sant’Angelo, Via Cintia 21, 80126 Napoli, Italy
d IPCMS-DON, 23 rue du Loess, BP 43 67034 Strasbourg Cedex 2, France
e The Center of Excellence for Advanced Materials Research, King Abdulaziz University, Jeddah 21589, Saudi Arabia
a r t i c l e i n f o
a b s t r a c t
Article history:
Three azo dyes with a thiazole based donor-p-acceptor structure containing a methoxyphenyl group as
Received 21 March 2012
Received in revised form
14 July 2012
Accepted 1 August 2012
Available online 7 August 2012
the lateral donor branch were synthesized and fully characterized. The formyl azo dye precursor was
synthesized using 5-formylaminothiazole derivative as the diazo component and N,N-diethylaninline as
the coupling component. Knoevenagel condensation of this precursor with different acceptors, namely,
indandione, malononitrile and dicyanovinylindanone afforded the desired nonlinear optical chromo-
phores aec, respectively.
The optical property, thermal stability and second order nonlinear optical activity were evaluated
and a single crystal structural characterization was performed for two of the dyes. All nonlinear optical
dyes aec have good nonlinearity and good thermal stability. Compared with dyes a and b, dye c shows
more than triple second order nonlinear optical response, the result that makes this molecule an unusual
example of asymmetrical 2D charge transfer chromophore.
Keywords:
Heterocyclic azo dyes
NLO chromophore
Optical property
Crystal structures
Hyperpolarizability
Thermal stability
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
stabilization upon polarization [4e7]. Therefore, ground state less
aromatic D-p-A type chromophores have been designed by
The rapid progress of hi-tech applications based on optoelec-
tronics has inspired many scientists to develop novel designs for
functional dyes [1]. Organic second-order nonlinear optical (NLO)
replacing the benzene ring of a chromophore with easily polariz-
able five-membered heteroaromatic rings, such as thiophene,
pyrrole and thiazole, resulting in an enhanced molecular hyper-
polarizability [8]. Also, recent theoretical calculations suggest that
heterocyclic rings play a subtle role in the second-order NLO
properties of donor-acceptor compounds and the increase or
decrease of NLO properties of these heteroaromatic systems
depends not only on the electronic nature of the aromatic rings, but
also on the location of these heterocycles in the system [9].
materials typically take the form of dipolar D-
chromophores, where D (A) is an electron donor (acceptor) group
and is a conjugated bridge [2]. This structural feature results in
p-A type organic
p
the requisite ground-state charge asymmetry and the redistribu-
tion conjugation of electric charges under the influence of electric
fields by virtue of its p-conjugated system [3]. NLO chromophores
with high first order molecular hyperpolarizability and good
thermal and photochemical stabilities have been actively pursued.
Azo dyes are the most widely used class of colorants because of
their versatile applications in various fields that range from textile
to non-textile applications [10]. In this context, thiazole azo dyes
similar to other heterocyclic analogs have the advantage of bright
and strong shades that range from red to green and blue [11e14]. In
addition, thiazole azo dyes are of great importance since they have
pronounced bathochromic absorptions compared to corresponding
benzenoid dyes as the heterocyclic ring can act as auxiliary electron
acceptor due to the electronegativity of the nitrogen and sulfur
atoms [9b,c,15,16]. In this interest, recent reports on heterocyclic
azo dyes as NLO chromophores have been reported [13,17e20].
Several reports indicated that ground state benzenoid D-p-A
type chromophores are less polarizable than a simple polyene of
comparable length indicating insufficient intramolecular charge
transfer (CT), which is a direct consequence of the loss of aromatic
* Corresponding author. Chemistry Department, Faculty of Science, King Abdu-
laziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia. Tel.: þ966 563398296;
fax: þ9662 695 2292.
E-mail address: elshishtawy@hotmail.com (R.M. El-Shishtawy).
0143-7208/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2012.08.002

46
R.M. El-Shishtawy et al. / Dyes and Pigments 96 (2013) 45e51
Also, some promising results of NLO based thiazole azo dyes have
recently been published by some of us [21].
mb0
mb0
!
!
mb
¼
¼
!
!
4
l2
eg
u2
u2eg
4
u2
l2eg
l2
Stemmed by this information and in continuation of our interest
on the synthesis and characterization of thiazole azo dyes for
optical applications, it was worthy to synthesize novel thiazole azo
dyes with lateral donor branch and to study their structure and
second order NLO properties.
1 ꢁ
1 ꢁ
u2eg
1 ꢁ
1 ꢁ
l2
where b0 is the intrinsic molecular hyperpolarizability,
excitation frequency (wavelength) of the fundamental beam, ueg
leg) is the transition frequency (wavelength) associated with the
u (l) is the
(
charge transfer band.
2. Experimental
2.2. 4-(4-methoxyphenyl)thiazol-2-amine (2)
2.1. General
A mixture of thiourea (0.53 g, 7 mmol) and 1 (1.6 g, 7 mmol) in
70 ml acetone was stirred overnight at room temperature and
filtered to afford the corresponding hydrobromide salt quantita-
tively. Then, the salt was treated with 5% ammonia solution with
stirring and filtered to give the desired thiazole product 2 as a white
powder. Yield: 94%. Mp 205e206 ꢂC [28]. 1H NMR (600 MHz,
All solvents and reagents were of the highest purity available,
purchased from SigmaeAldrich Company and used as received.
Basic Ethanol solution was made as a fresh stock solution (0.5 ml
piperidine, 1.5 ml glacial acetic acid and 48 ml absolute ethanol) for
the synthesis of dye aec.
1H and 13C NMR spectra were recorded in DMSO-d6 solutions on
a Bruker Avance 600 MHz spectrometer. Infrared spectra were per-
formed on a PerkinElmer spectrum 100 FTIR spectrometer. Mass
spectra were measured on a GCMS-QP1000 EX spectrometer at 70 eV.
HRMS spectra of the chromophores were recorded with a MALDI TOF
DMSO-d6)
d 3.77 (s, 3H, OCH3), 6.84 (s, 1H, 5-H), 6.93 (d, 2H,
J ¼ 4.8 Hz, AreH), 7.04 (s, 2H, NH2), 7.3 (d, 2H, J ¼ 4.8 Hz, AreH). 13
C
NMR (125 MHz, DMSO-d6)
d 55.02, 99.28, 113.76, 126.78, 127.77,
149.59, 158.45, 168. MS m/z (%) 206 (Mþ, 100), 191 (45.8), 149 (43.4),
121 (33.8), 77 (25). IR
n
/cmꢁ1 3438, 3267, 3118, 2965, 1623, 1535,
DE-PRO apparatus on
a matrix of 2,5-dihydroxybenzoic acid.
1492, 1177, 1033, 834, 737, 698. Calcd for C10H10N2OS: C, 58.23%; H,
4.89%; N, 13.58%; S, 15.54. Found: C, 58.45%; H, 4.93%; N, 13.74%; S,
15.04.
Elemental microanalyses were performed at the Taibah University
Microanalytical Center. Melting points were determined in open
capillary tubes in a Stuart Scientific melting point apparatus and are
uncorrected. UV/Vis absorption spectra were recorded with a Jasco
V560spectrophotometer. Thethermalstabilityof thecompoundswas
studied by thermogravimetric analysis (TA SDT 2960, air, 10 K/min).
Single crystals of b and c suitable for X-ray analysis were obtained
at room temperature by slow evaporation of CH2Cl2/heptane solu-
tions. One crystal of b (dark green 0.55 ꢀ 0.50 ꢀ 0.01 mm) and one
crystal of c (dark red 0.60 ꢀ 0.01 ꢀ 0.01 mm) were mounted at 173 K
under N2 flow on a Bruker-Nonius KappaCCD diffractometer equip-
2.3. N-(4-(4-methoxyphenyl)thiazol-2-yl)acetamide (3)
A mixture of 2 (4.12 g, 20 mmol), acetic anhydride (20 ml) and
glacial acetic acid (100 ml) with few drops of conc. H2SO4 was
refluxed for 1 h. The reaction mixture was allowed to cool at room
temperature and then recrystallized from ethanol to afford
compound 3. Yield: 85.7%. Mp 189e190 ꢂC. 1H NMR (600 MHz,
DMSO-d6)
J ¼ 7.14 Hz, AreH), 7.42 (S, 1H, 5-H), 7.82 (d, 2H, J ¼ 7.08 Hz, AreH),
12.2 (S, 1H, NH). 13C NMR (125 MHz, DMSO-d6)
22.63, 55.27,
d 2.16 (S, 3H, COCH3), 3.79 (S, 3H, OCH3), 6.99 (d, 2H,
ped with a graphite monochromated MoKa radiation (
l
¼ 0.71073 Å,
CCD rotation images, thick slices, 4 and scans to fill asymmetric
u
d
unit). Semiempirical absorption correction (SADABS) was applied.
Both the structures were solved by direct methods (SIR97 package
[22]) and refined by the full matrix least-squares method on F2
against all independent measured reflections (SHELXL program of
SHELX97 package [23]). All non-hydrogen atoms were refined
anisotropically. The hydrogen atoms were placed in calculated
positions and refined according to a riding model. The final refine-
ment converged to R1 ¼ 0.0547 and R1 ¼ 0.1265 for b and c, respec-
tively. Crystals of c were poor quality and weakly diffracting and
disordered CH2Cl2 crystallization solvent molecules were found.
Some restrains were introduced in the last stage of refinement to
treat the disorder of CH2Cl2. This may account for the high R values
obtained. Crystal data and refinement details are summarized in
Table 2. CCDC 870850 (b) and 870851 for (c) contain the supple-
mentary crystallographic data for this paper. These data can be ob-
tained free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html
or from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (internat.) þ44-1223/336-033.
105.96, 114.22, 127.12, 127.27, 148.72, 157.94, 159.08, 168.8.
2.4. N-(5-formyl-4-(4-methoxyphenyl)thiazol-2-yl)acetamide (4)
To an ice cooled flask containing N,N-dimethylformamide
(86 ml) was added POCl3 (53.5 ml) dropwise with stirring. After
addition, the solution was stirred at room temperature for 90 min.
Then the flask was cooled again in ice-bath and compound 3
(65 mmol) was added. The reaction mixture was warmed grad-
ually to run at 75 ꢂC for 2 h. Then cooled to room temperature and
poured onto iceewater, basified (sat. aqueous K2CO3 solution)
and extracted with CHCl3 (4 ꢀ 30 ml) washed, dried (MgSO4) and
evaporated. Yield: 75.63%. Mp 124e126 ꢂC. 1H NMR (600 MHz,
CDCl3)
J ¼ 4.8 Hz, AreH), 7.66 (d, 2H, J ¼ 4.8 Hz, AreH), 8.41 (S, 1H, NH),
9.80 (S, 1H, CHO). 13C NMR (125 MHz, CDCl3)
35.41, 55.42,
d 3.16 (S, 3H, COCH3), 3.87 (S, 3H, OCH3), 6.99 (d, 2H,
d
114.02, 126.32, 126.89, 131.21, 156.94, 160.90, 162.99, 179.29,
183.65.
The molecular quadratic optical nonlinearities of chromophores,
in the form of mgb products (mg is the ground state permanent dipole
moment and
b
the first hyperpolarizability of the molecules,
2.5. 2-Amino-4-(4-methoxyphenyl)thiazole-5-carbaldehyde (5)
according to convention B [24,25]), were measured on a standard
Electric Field Induced Second Harmonic Generation (EFISHG) set-up
[26] operating at 1907 nm fundamental wavelength, obtained by
Raman-shifting the emission froma Nd:YAG laser, and which has the
advantage of being far from the absorption bands of the molecules.
The data were also corrected for the dispersion effect on the
basis of the two-level model [27] to obtain static mb0 coefficients,
according to the formula:
A mixture of compound 4 (2.256 g, 8 mmol) and 25% HCl in
methanol was refluxed for 30 min, then cooled to room temper-
ature and poured onto ice-water, basified with 25% ammonia
solution, filtered off and recrystallized from ethanol. yield: 77.48%.
Mp 227e229 ꢂC. 1H NMR (600 MHz, DMSO-d6)
d 3.8 (S, 3H, OCH3),
7.03 (d, 2H, J ¼ 4.8 Hz, AreH), 7.66 (d, 2H, J ¼ 4.8 Hz, AreH), 8.35
(S, 2H, NH2),9.56 (S, 1H, CHO). 13C NMR (125 MHz, DMSO-d6)

R.M. El-Shishtawy et al. / Dyes and Pigments 96 (2013) 45e51
47
d
55.35, 114.08, 121.63, 125.87, 131.05, 160.62, 163.31, 172.55,
2H, AreH), 8.66 (d, 1H, J ¼ 7.8 Hz, AreH), 8.75 (s, 1H, CH]C). 13
C
181.41.
NMR (125 MHz, CDCl3)
d
12.80, 45.42, 55.49, 69.77, 113.90, 114.44,
114.78, 123.85, 125.11, 125.80, 126.01, 132.47, 134.36, 135.15, 136.96,
138.06, 139.94, 143.91, 153.39, 160.77, 161.68, 170.58, 183.00, 188.07.
2.6. 2-((4-(diethylamino)phenyl)diazenyl)-4-(4-methoxyphenyl)
thiazole-5-carbaldehyde (6)
IR n
/cmꢁ1 2211, 1746, 1697, 1595, 1519, 1214, 1102, 1065. HRMS calcd
for C33H26N6O2S: 570.68. Found: 570.95.
NaNO2 (516 mg, 7.48 mmol) was added to 95e98% H2SO4
(5.6 ml) and the mixture was heated at 65 ꢂC until complete
dissolution. After being cooled in an ice-bath (0e5 ꢂC), the nitro-
sylsulphuric acid solution was diluted with AcOH (3.2 ml) over
3 min and then left for 10 min. Following cooling to ꢁ5 ꢂC,
compound 5 (1.0 g, 6.15 mmol) was added portion wise and, once
the addition was complete (15 min), the reaction mixture was
stirred for 2 h at 5 ꢂC. The so formed diazonium salt solution was
added gradually (10 min) to a mixture of N,N-diethylaniline (1.0 ml,
6.29 mmol) in water (62 ml) and 95e98% H2SO4 (1.2 ml), at 0 ꢂC
under vigorous stirring, after which the reaction mixture was left at
rt for 1 h. The resulting solid was then collected by filtration,
washed with water and dried. Column chromatography on silica gel
using CHCl3 as the eluent afforded compound 6 as violet crystals.
Yield: 43.3%. Mp 167e169 ꢂC. 1H NMR (600 MHz, CDCl3) 1.28 (t, 6H,
J ¼ 7.2 Hz, N (CH2CH3)2), 3.53 (q, 4H, J ¼ 7.2 Hz, N(CH2CH3)2), 3.91 (s,
3H, OCH3), 6.76 (d, 2H, J ¼ 9.6 Hz, AreH), 7.05 (d, 2H, J ¼ 7.2 Hz,
AreH), 7.8 (d, 2H, J ¼ 7.2 Hz, AreH), 7.98 (d, 2H, J ¼ 9 Hz, AreH),
3. Results and discussion
3.1. Synthesis
Hantzsch thiazole synthesis in which the reaction proceeds
between a-halocarbonyl compounds and thioureas or thioamides
provides a useful method for the synthesis of thiazoles. Likewise
the synthetic procedure reported earlier for the synthesis of other
thiazole derivatives, compound 2 was obtained quantitatively by
the treatment of 1 with thiourea in acetone at room temperature
after being neutralized with dilute ammonia [29]. It is known
that heteroaromatic compounds undergo VilsmeiereHaack for-
mylations at the electron rich positions [30]. Thus, it is expected
that compound 2 can be easily formylated at the fifth position in the
thiazole ring. For this propose, it was necessary to protect the
amino group by the usual acetylation reaction as indicated in
Scheme 1 to furnish compound 3, which underwent formylation to
produce the formyl product 4 in good yield. Acid catalyzed deace-
tylation of 4 affords the thiazole derivative 5 in good yield.
The common practice of diazotization and coupling was used to
prepare azo dye 6 using thiazole derivative 5 as the diazo compo-
nent and N,N-diethylaniline as the coupling component. Thus,
thiazole derivative 5 was diazotized with nitrosyl sulfuric acid and
then coupled with N,N-diethylaniline dissolved in 0.36 M H2SO4 in
an ice bath to get the corresponding azo dye 6 (Scheme 1) as the
aldehyde precursor for the NLO chromophores (aec). The struc-
tures of compounds 2e6 were confirmed by their analytical and
spectral data.
10.01 (s, 1H, CHO). 13C NMR (125 MHz, CDCl3)
d 12.73, 45.26,
55.44, 111.68, 114.17, 125.98, 130.70, 131.44, 134.87, 142.69, 153.09,
161.10, 162.94, 182.16, 184.90.
2.7. General procedure for the synthesis of NLO chromophores aec
A mixture of dye 6 (1.18 g, 3 mmol) and indandione (0.438 g,
3 mmol) or malononitrile (0.198 g, 3 mmol) or 3-dicyanovinylindan-
1-one (0.582 g, 3 mmol) in basic ethanol solution (7 ml) was stirred
at room temperature overnight, filtered off and purified by column
chromatography on silica gel using CHCl3 as the eluent, affording
dyes a or b or c, respectively.
Knoevenagel condensation [31] of aldehyde 6 with 1H-indene-
1,3(2H)-dione, malononitrile and 2-(3-oxo-2,3-dihydro-1H-inden-
2.7.1. Dye a
Yield: 75%. Mp 185e187 ꢂC. 1H NMR (600 MHz, CDCl3) 1.3 (t, 6H,
J ¼ 7.2 Hz, N(CH2CH3)2), 3.55 (q, 4H, J ¼ 7.2 Hz, N(CH2CH3)), 3.92 (s,
3H, OCH3), 6.78(d, 2H, J ¼ 9 Hz, AreH), 7.08(d, 2H, J ¼ 9 Hz, AreH), 7.6
(d, 2H, J ¼ 9 Hz, AreH), 7.79 (m, 2H, AreH), 7.96 (m, 1H, AreH), 7.99
(m, 1H, AreH), 8.03 (d, 2H, J ¼ 9.6 Hz, AreH), 8.09 (s, 1H, CH]C). 13C
NMR (125 MHz, CDCl3)
d 12.77, 45.28, 55.45, 114.20, 122.88, 122.96,
124.96, 125.36, 126.46, 132.17, 134.86, 135.02, 136.03, 140.45, 142.03,
143.50, 152.97, 161.16, 168.24, 181.88, 189.71, 190.26. IR
n
/cmꢁ1 2924,
1678,1600,1564,1514, 1351, 1292,1245,1213,1140,1014, 986. HRMS
calcd for C30H26N4O3S: 522.63. Found: 522.91.
2.7.2. Dye b
Yield: 59.7%. Mp 158e160 ꢂC. 1H NMR (600 MHz, CDCl3) 1.31 (t,
6H, J ¼ 7.2 Hz, N(CH2CH3)2), 3.56 (q, 4H, J ¼ 7.2 Hz, N(CH2CH3)), 3.9
(s, 3H, OCH3), 6.78 (d, 2H, J ¼ 9 Hz, AreH), 7.07 (d, 2H, J ¼ 9 Hz,
AreH), 7.64 (d, 2H, J ¼ 7.2, AreH), 7.86 (s, 1H, CH]C), 8.00 (m, 2H,
AreH). 13C NMR (125 MHz, CDCl3)
d 12.80, 45.51, 55.53, 113.44,
114.49, 114.89, 123.42, 125.43, 131.73, 143.56, 150.61, 153.81, 161.57,
166.44, 182.41. IR
n
/cmꢁ1 2917, 2211, 1598, 1538, 1412, 1335, 1224,
1195, 1099, 1063. HRMS calcd for C24H22N6OS: 442.55. Found:
442.97.
2.7.3. Dye c
Yield: 66.6%. Mp 208e210 ꢂC. 1H NMR (600 MHz, CDCl3) 1.31 (t,
6H, J ¼ 7.2 Hz, N(CH2CH3)2), 3.56 (q, 4H, J ¼ 7.2 Hz, N(CH2CH3)), 3.92
(s, 3H, OCH3), 6.78 (d, 2H, J ¼ 9.6 Hz, AreH), 7.08 (d, 2H, J ¼ 7.2 Hz,
AreH), 7.76 (m, 4H, AreH), 7.93 (d, 1H, J ¼ 7.2 Hz, AreH), 8.03 (m,
Scheme 1. Synthesis of 2-((4-(diethylamino)phenyl)diazenyl)-4-(4-methoxyphenyl)
thiazole-5-carbaldehyde. Reagents and conditions. (i) thiourea, acetone, rt, 5%
ammonia solution; (ii) Ac2O, reflux; (iii) DMF-POCl3, 0e80 ꢂC; (vi) 25% HCl/MeOH,
reflux; (v) H2SO4, NaNO2, AcOH, ꢁ5e5 ꢂC, N,N-diethylaniline, H2SO4, H2O, ꢂC to rt.

48
R.M. El-Shishtawy et al. / Dyes and Pigments 96 (2013) 45e51
1-ylidene)malononitrile in refluxing ethanol in the presence of
piperidine/acetic acid catalyst affords good yields of the corre-
sponding NLO chromophores a, b, and c, respectively (Scheme 2).
All NLO dyes were fully characterized and their crystal structures
have been solved.
3.2. Optical properties
3.2.1. Linear optical properties
Electronic absorption spectra of NLO chromophores aec in
chloroform solution are shown in Fig. 1. Intense CT absorption
bands are observed in the UVevisible region. The molar absorp-
tivity as well as the position of these bands are affected by the
strength of the acceptor group. This effect is demonstrated by
comparison of the absorption maxima and the molar absorptivity
of dyes a and c in which indandione is less electron acceptor than
dicyanovinyl moieties, respectively. Dye b on the other hand
exhibits a CT absorption band similar to dye a. Furthermore, the
absorption characteristics of such type of dyes can be realized based
on the fact that the electronic absorption of azobenzene derivative
reveals two bands, one weak in the visible and the second strong in
the UV-region, corresponding to ne
presence of strong electron donors and acceptors as in the case of
dyes aec reduce the charge transfer transitional energy of
p* and pep*, respectively. The
pep*
transition and consequently, the stronger the acceptor the higher
the stabilization of LUMO energy and the longer the wavelength of
absorption which overlaps the weak nep* [32]. This structural
feature is beneficial for obtaining high NLO properties as discussed
below.
3.2.2. Nonlinear optical properties
Nonlinearities of the synthesized dyes were evaluated by
measuring the mb coefficients by means of the Electric Field
Induced Second Harmonic Generation (EFISH) technique, at
1907 nm fundamental wavelength. The obtained values are re-
ported in Table 1 and can be considered not affected by resonance
effects, being the second harmonic signal generated from chloro-
form solutions of these dyes (953.5 nm) far beyond the range of
linear absorption, as it can be evinced from UVeVisible spectra.
Results show a and b to have similar nonlinear coefficients whose
difference is lower than the experimental error of the
Fig. 1. UVevisible absorption spectra of dyes aec in chloroform.
measurement. However a more evident difference arises between
the two molecules as far as the values of their figures of merit are
concerned, calculated as the ratio mb0/MW. This evidence suggests
that the dicyanovinyl group has a stronger electron-withdrawing
effect which is responsible for the higher nonlinear response of
molecule b. As expected, the dye c shows the largest mb value,
which results sensibly higher as compared to the dyes a and b. This
performance can be ascribed to the larger extension of the conju-
gated system as well as the increased electron withdrawing
strength of the acceptor group resulting from the combination of
dicyanovinyl and indandione moieties. This marked rise follows
a pronounced batochromic shift of the absorption and therefore is
partially reduced upon correction due to the dispersion effect,
leading to a lower increase of static mb0 coefficient for c with
respect to a and b.
The dye c can be compared with dye c reported in a previous
work [6] based on 4-chlorothiazole, where the only difference in
the conjugated structure is therefore a chlorine atom linked on the
Table 1
Linear and nonlinear optical properties of dyes aec.
Dye
lmax (nm)a
mb (10ꢁ48 esu)b
mb0 (10ꢁ48 esu)b
mb0/MW
a
b
c
623
619
686
1450
1550
4700
740
800
1970
1.42
1.81
3.45
Scheme 2. Synthesis of nonlinear optical dyes aec. Reagents and conditions. (dye a)
1H-Indene-1,3(2H)-dione, piperidine, glacial AcOH, absolute ethanol, rt; (dye b)
Malononitrile and the same as for dye a; (dye c) 2-(3-Oxo-2,3-dihydro-1H-inden-1-
ylidene)malononitrile and the same as for dye a.
a
UVeVis maximum absorption wavelength in chloroform.
Error ꢃ10%.
b

R.M. El-Shishtawy et al. / Dyes and Pigments 96 (2013) 45e51
49
Table 2
fourth position of thiazole instead of a 4-methoxyphenyl group.
The higher activity shown by dye c suggests the methoxyphenyl
ring to significantly affect molecular electronic properties, even if it
results sterically hindered by the acceptor in the crystalline struc-
ture and partially rotated respect to the conjugated backbone, by
effect of the auxiliary donor methoxy group inserted in the middle
of the molecule and/or the relevant lateral extension of the
Crystal data and structure refinement details for b and c.
b
c
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
C24H22N5OS
428.53
173(2) K
0.71073 Å
Monoclinic
P 21/c
C33H26N6O2S $ CH2Cl2
655.58
173(2) K
0.71073 Å
Monoclinic
p-conjugated structure, which makes this molecule an unusual
P 21/c
example of asymmetrical 2D charge transfer chromophore.
Unit cell dimensions
a ¼ 15.855(2) Å
b ¼ 14.666(4) Å
c ¼ 9.442(2) Å
a ¼ 6.225(3) Å
b ¼ 21.279(4) Å
c ¼ 24.312(8) Å
3.3. Thermal stability
a
b
g
¼ 90ꢂ
a
b
g
¼ 90ꢂ
¼ 92.85(1)ꢂ
¼ 90ꢂ
¼ 99.51(3)ꢂ
¼ 90ꢂ
The thermal stability of NLO chromophores is a prerequisite for
their uses in optoelectronics. Fig. 2 shows the thermogravimetric
analysis of dyes aec. All dyes are thermally stable with similar
decomposition temperatures nearby 200 ꢂC.
Volume
Z
Calculated density
Absorption coefficient
2192(8) Å3
4
3176(2) Å3
4
1.340 mg/m3
0.174 mmꢁ1
3.06e27.51ꢂ
928
1.371 mg/m3
0.312 mmꢁ1
3.19e25.03ꢂ
1360
q
range for data collection
F(000)
3.4. Crystal structure studies
Reflections collected/unique 12,906/4866
18,840/5440
[R(int) ¼ 0.1966]
5440/17/418
1.062
R1 ¼ 0.1269,
wR2 ¼ 0.3043
R1 ¼ 0.2708,
wR2 ¼ 0.3985
[R(int) ¼ 0.0836]
Single crystals suitable for X-ray diffraction were obtained for
b and c by evaporation of CH2Cl2/heptane solutions at ambient
temperature. All attempts to obtain crystals of a failed. Compounds
studied are not easy to crystallize. Owing to their bent and Y shape,
voids may be formed during the crystallization, so the presence of
a suitable crystallization solvent seem to be the necessary condition
to form a stable crystalline phase. In particular, the structure
resolution of c showed that, in the crystal, disordered molecules
of CH2Cl2 crystallization solvent are located in channels parallel to
a axis. The molecular structures of b and c are reported in Figs. 3
and 4.
Data/restraints/parameters
4866/0/292
Goodness-of-fit on F2
1.011
Final R indices [I > 2
s(I)]
R1 ¼ 0.0546,
wR2 ¼ 0.0886
R1 ¼ 0.1455,
wR2 ¼ 0.1145
R indices (all data)
Largest diff. peak and hole
0.268 and ꢁ313 eAꢁ3 0.698 and ꢁ0.685 eAꢁ3
Both compounds b and c have similar features. They crystallize
in P 21/c space group, all bond lengths and angles are normal and in
agreement with similar compounds [33,34]. The double bond
character in the azo group is confirmed by N2eN3 bond length and
a conjugated double-bond character is shown by the N1eC7 and
N1eC9 bond lengths. As already found [21], the methyne H atom is
Fig. 3. Molecular structure of b. Up: view perpendicular to the mean plane of mole-
cule. Down: view along the edge of mean plane. Thermal ellipsoids are drawn at 50%
probability level. N2eN3 1.297(3), N1eC7 1.368(3), N1eC9 1.318(3), C7eC8 1.382(4),
C17eC18 1.361(4), S1eC8 1.744(2), S1eC9 1.731(3) Å, C13eN4eC21eC22 ꢁ88.8(3),
C13eN4eC23eC24 ꢁ88.5(3), C3eC4eC7eN1 34.6(4)ꢂ.
Fig. 2. Thermogravimetric analysis of the dyes aec.

50
R.M. El-Shishtawy et al. / Dyes and Pigments 96 (2013) 45e51
Fig. 6. Stacked molecules of c showing the interlayer distance.
direction. In a p-stack (see Fig. 6) the interplanar distance between
molecules is about 3.4 Å and a weak S$$$$p interaction is observed
(S$$$$Cig ¼ 3.472 Å, Cg is the centroid of C10eC15 ring, i ¼ x ꢁ 1, y, z).
4. Conclusions
Fig. 4. Molecular structure of c. Up: perpendicular view to the mean plane of molecule.
Down: view along the edge of mean plane. Thermal ellipsoids are drawn at 30%
probability level.CH2Cl2 solvent molecule is not shown. N2eN3 1.30(1), N1eC7 1.35(1),
N1eC9 1.31(1), C7eC8 1.42(1), C17eC18 1.36(1), S1eC8 1.738(82), S1eC9 1.726(9) Å,
C13eN4eC30eC31 80(1), C13eN4eC32eC33 80(1), C3eC4eC7eN1 ꢁ63(1)ꢂ.
New thiazole based azo dyes with a lateral donor branch have
been synthesized for potential NLO applications. The chromo-
phores aec were obtained by functionalization of the same formyl
azo dye with three different acceptor groups, indandione, malo-
nonitrile and 3-dicyanovinylindan-1-one. All the chromophores
reveal good thermal stability and strong absorption bands, whose
maxima are affected by the strength of the acceptor group. The
chromophores also show large values of mb in chloroform. In this
regard 3-dicyanovinylindan-1-one acceptor gave the major
contribution in the case of dye c, whose mb value (4700 ꢀ 10ꢁ48 esu)
resulted as high as three times that of chromophores
a (1450 ꢀ 10ꢁ48 esu) and b (1550 ꢀ 10ꢁ48 esu). This NLO response
together with the results of crystal study makes these molecules
interesting examples of unusual asymmetrical 2D charge transfer
chromophores. Future synthetic design for NLO chromophores
based on thiazole azo dyes containing different size of lateral
donating groups are in progress.
trans to S atom of thiazole group. The anti disposition of methyne
and azo groups linked to thiazole and the methoxyphenyl group
linked at C7 atom gives the observed bent [35] and Y-shape of
molecules. Both in b and c the molecule is characterized by a quite
overall planarity except for methoxyphenyl and ethyl groups. As
already observed [36] the amino group is planar in both
compounds, thus indicating a degree of conjugation of N atom with
the bonded phenyl ring. The observed planarity of the molecule in
both compounds suggests the possibility of conjugation extended
to the entire molecule. In the crystal packing of b (see Fig. 5) the
molecules are arranged in a parallel way forming sheets of mole-
cules, but no
In the crystal packing of c coplanar molecules are piled up in
a slipped way to form stacked endless columns along (1 0 0)
pep stacking is observed.
Acknowledgments
pep
The authors wish to express their gratitude to the King Abdul
Aziz City for Science and Technology (KACST), Saudi Arabia, for
granting the PhD student Zahra M. Al-amshany a grant number
GSP-17-200. Thanks are also due to “Centro Interdipartimentale di
Metodologie Chimico Fisiche (CIMCF) of the University of Naples
“Federico II” for X-Ray facilities.
References
[1] El-Shishtawy RM. Int J Photoenergy 2009, art. no. 434897. http://dx.doi.org/
10.1155/2009/434897, and references cited therein.
[2] Nalwa HS, Miyata SS. Nonlinear optics of organic molecules and polymers.
Boca Raton: CRC Press; 1997. p. 885.
[3] (a) Zyss DS. Non linear optical properties of organic molecules and crystals,
vols. 1 and 2. Orlando: Academic Press; 1987;
(b) Brosshard C, Sutter K, Petre P, Hulliger J, Florsheimer M, Kaatz M, et al.
Organic non-linear optical materials. Amsterdam: Gordon and Breach Science
Publishers; 1995.
[4] (a) Marder SR, Perry JW, Bourhill G, Gorman CB, Tiemann BG, Mansour K.
Science 1993;261:186;
(b) Marder SR, Cheng LT, Tiemann BG, Friedli AC, Blanchard-Desce M,
Perry JW, et al. Science 1994;263:511;
(c) Marder SR, Gorman CB, Meyers F, Perry JW, Bourhill G, Brédas J-L, et al.
Science 1994;265:632;
Fig. 5. Crystal packing of b viewed along (0 1 0) direction. H atoms are not shown for
clarity.

R.M. El-Shishtawy et al. / Dyes and Pigments 96 (2013) 45e51
51
(d) Bourhill G, Brédas J-L, Cheng LT, Marder SR, Meyers F, Perry JW, et al. J Am
[15] Yen MS, Wang IJ. Dyes Pigm 2004;61:243.
Chem Soc 1994;116:2619;
[16] Towns AD. Dyes Pigm 1999;3:42.
(e) Meyers F, Marder SR, Pierce BM, Brédas J-L. J Am Chem Soc 1994;116:
10703;
[17] Inglot K, Martynski T, Bauman D. Dyes Pigm 2009;80:106.
[18] He M, Zhou Y, Liu R, Dai J, Cui Y, Zhang T. Dyes Pigm 2009;80:6.
(f) Gorman CB, Marder SR. Chem Mater 1995;7:215.
[19] Raposo MMM, Castro MCR, Belsley M, Fonseca AMC. Dyes Pigm 2011;91:454.
[20] Raposo MMM, Fonseca AMC, Castro MCR, Belsley M, Cardoso MFS,
Carvalho LM, et al. Dyes Pigm 2011;91:62.
[21] Borbone F, Carella A, Ricciotti L, Tuzi A, Roviello A, Barsella A. Dyes Pigm 2011;
88:290. and references cited therein.
[22] Altomare A, Burla MC, Camalli M, Cascarano GL, Giacovazzo C, Guagliardi A,
et al. Sir97. J Appl Cryst 1999;32:115.
[23] Sheldrick GM. SHELXL-97. Acta Crystallogr 2008;A64:112.
[24] Willetts A, Rice JE, Burland DM. J Chem Phys 1992;97(10):7590.
[25] Reis H. J Chem Phys 2006;125. 014506.
[5] (a) Lu DQ, Chen GH, Perry JW, Goddard WA. J Am Chem Soc 1994;116:10679;
(b) Chen GH, Lu DQ, Goddard WA. J Chem Phys 1994;101:5860.
[6] Castiglioni C, Del Zoppo M, Zerbi G. Phys Rev B 1996;53:13319.
[7] (a) Plaza P, Laage D, Martin MM, Alain V, Blanchard-Desce M, Thompson WH,
et al. J Phys Chem A 2000;104:2396;
(b) Thompson WH, Blanchard-Desce M, Hynes JT. J Chem Phys A 1998;102:
7712;
(c) Barzoukas M, Runser C, Fort A, Blanchard-Desce M. Chem Phys Lett 1996;
257:531;
(d) Barzoukas M, Fort A, Blanchard-Desce M. Synth Met 1996;83:277.
[8] (a) Dirk CW, Katz HE, Schilling ML, King LA. Chem Mater 1990;2:700;
(b) Rao VP, Jen AK-Y, Wong KY, Drost KJ. Tetrahedron Lett 1993;34:1747;
(c) Jen AK-Y, Rao VP, Wong KY, Drost KJ. J Chem Soc Chem Commun 1993:90;
(d) Rao VP, Jen AK-Y, Wong KY, Drost KJ. J Chem Soc Chem Commun 1993:
1118;
[26] Thami T, Bassoul P, Petit MA, Simon J, Fort A, Barzoukas M, et al. Am Chem Soc
1992;114:915.
[27] Chemla DS, Zyss J. Nonlinear optical effects of organic materials and crystals,
vols. 1 and 2. Orlando, FL: Academic Press; 1994.
[28] Potewar TM, Ingale SA, Srinivasan KV. Tetrahedron 2008;64:5019. and
references cited therein.
(e) Facchetti A, Beverina L, van der Boom ME, Dutta P, Evmenenko G,
Pagani GA, et al. J Am Chem Soc 2006;128:2142. and references cited therein;
(f) Abbotto A, Beverina L, Manfredi N, Pagani GA, Archetti G, Kuball H-G, et al.
Chem Eur J 2009;15:6175.
[29] Zheng W, Nikulin VI, Konkar AA, Vansal SS, Shams G, Feller DR, et al. J Med
Chem 1999;42:2287. and references cited therein.
[30] Wang Z. Comprehensive organic name reactions and reagents. London:
Wiley; 2010. Part 634, p. 2872 and references cited therein.
[31] Tietze LF. The Knoevenagel reaction. In: Trost BM, editor. Comprehensive
organic synthesis, Coll vol. 2. Oxford: Pergamond Press; 1991. p. 358.
[32] Oliva MM, Casado J, Raposo MMM, Fonseca AMC, Hartmann H, Hernandez V,
et al. J Org Chem 2006;71:7509.
[33] Park KM, Yoon I, Lee SS, Choi GC, Lee JS. Anal Sci 2003;9:1219.
[34] Kinnibrugh TL, Salman S, Getmanenko YA, Coropceanu V, Porter WW,
Timofeeva TV, et al. Organometallics 2009;28:1350.
[35] Borbone F, Caruso U, Diana R, Panunzi B, Roviello A, Tingoli M, et al. Org
Electron 2009;10:53.
[36] Borbone F, Caruso U, Centore R, De Maria A, Fort A, Fusco M, et al. Eur J Inorg
Chem 2004:2467.
[9] (a) Varanasi PR, Jen AK-Y, Chandrasekhar J, Namboothiri INN, Rathna A. J Am
Chem Soc 1996;118:12443;
(b) Albert IDL, Marks TJ, Ratner MA. J Am Chem Soc 1997;119:6575;
(c) Breitung EM, Shu C-F, McMahon RJ. J Am Chem Soc 2000;122:1154.
[10] Zollinger H. Color chemistry. Synthesis, properties and aplications of organic
dyes and pigments. 3rd revised ed. Wiley-VCH; 2003.
[11] Hunger K. Industrial dyes, chemistry, properties and applications. 3rd ed.
WILEY-VCH; 2003.
[12] Salvador MA, Almeida P, Reis LV, Santos PF. Dyes Pigm 2009;82:118.
[13] Chen L, Cui Y, Qian G, Wang M. Dyes Pigm 2007;73:338.
[14] Seferoglu Z, Ertan N, Kickelbick G, Hokelek T. Dyes Pigm 2009;82:20.