Synthesis, characterization and evaluation of the photophysical and nonlinear optical behaviour of novel 4-substituted arylidene-2-[5-(2,6- dichlorophenyl)-3-methyl-1,2-oxazol-4-yl]-1,3-oxazol-5-ones

Article abstract of DOI:10.1016/j.dyepig.2013.07.001

Five new 4-substituted arylidene-2-[5-(2,6-dichlorophenyl)-3-methyl-1,2- oxazol-4-yl]-1,3-oxazol-5-ones have been designed and synthesized in order to study their third-order nonlinear optical properties. These novel compounds were characterized by advanced spectroscopic techniques (IR, ¹H, ¹³C NMR, ESI-MS spectroscopy and elemental analyses). In addition, the evaluation of absorption and emission wavelengths of the new 5-oxazolone derivatives was carried out in seven different solvents of varying polarity, which showed intense absorption maxima at 350-480 nm and emission maxima at 390-535 nm respectively. The third-order nonlinear optical properties of the target molecules have been investigated in N,N-dimethylformamide using a single beam Z-scan technique with nanosecond laser pulses at 532 nm. The nonlinear refractive index, nonlinear absorption coefficient, magnitude of third-order susceptibility and molecular two photon absorption cross-sections have been determined. All of the compounds showed excellent optical limiting behaviour at 532 nm, with the best optical limiting behaviour observed with strong electron donor [dimethyl and N,N-diethyl amino] substituents.

Full text of DOI:10.1016/j.dyepig.2013.07.001

Accepted Manuscript
Synthesis, characterization and evaluation of the photophysical and nonlinear optical
behaviour of novel 4-substituted arylidene-2-[5-(2,6-dichlorophenyl)-3-methyl-1,2-
oxazol-4-yl]-1,3-oxazol-5-ones
Y.L.N. Murthy, K.P. Suhasini, V. Veeraiah, G. Umesh, K.B. Manjunatha, V.
Christopher
PII:
S0143-7208(13)00249-0
10.1016/j.dyepig.2013.07.001
DYPI 4006
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 29 April 2013
Revised Date: 29 June 2013
Accepted Date: 1 July 2013
Please cite this article as: Murthy Y, Suhasini K, Veeraiah V, Umesh G, Manjunatha K, Christopher V,
Synthesis, characterization and evaluation of the photophysical and nonlinear optical behaviour of novel
4-substituted arylidene-2-[5-(2,6-dichlorophenyl)-3-methyl-1,2-oxazol-4-yl]-1,3-oxazol-5-ones, Dyes and
Pigments (2013), doi: 10.1016/j.dyepig.2013.07.001.
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Highlights
ꢀ Amongst the oxazolyloxazolones the dialkylamino substituted derivatives exhibited the
highest λmax and λ em in DMF.
ꢀ The nonlinear refractive index is found to be negative and its magnitude is of the order of
10-11 esu.
ꢀ The molecular two photon absorption cross-sections are of the order of 10-46 cm4 s/photon.
ꢀ Values of two photon absorption cross-section are nearly two orders of magnitude larger than
of Rhodamine 6G.
ꢀ Molecules with –NR2 substituents exhibited better optical limiting behavior.

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Synthesis, characterization and evaluation of the photophysical and nonlinear optical
behaviour of novel 4-substituted arylidene-2-[5-(2,6-dichlorophenyl)-3-methyl-1,2-oxazol-4-
yl]-1,3-oxazol-5-ones
Y L N Murthya*, K P Suhasinia*, V Veeraiahb, G Umeshc, K B Manjunathac, V Christophera
aDept. of Organic Chemistry, Andhra University, Visakhapatnam-530003, India.
bDept. of Physics, Andhra University, Visakhapatnam-530003, India.
cOptoelectronics Laboratory, Dept. of Physics, National Institute of Technology Karnataka,
Surathkal, Mangalore- 575025, India.
Email address for correspondence* : murthyyln@gmail.com, suhasini.kl@gmail.com
Telephone and Fax : 91-891-2713813.
Abstract : Five new 4-substituted arylidene-2-[5-(2,6-dichlorophenyl)-3-methyl-1,2-oxazol-4-
yl]-1,3-oxazol-5-ones have been designed and synthesized in order to study their third-order
nonlinear optical properties. These novel compounds were characterized by advanced
1
13
spectroscopic techniques (IR, H, C NMR, ESI-MS spectroscopy and elemental analyses). In
addition, the evaluation of absorption and emission wavelengths of the new 5-oxazolone
derivatives was carried out in seven different solvents of varying polarity, which showed intense
absorption maxima at 350–480 nm and emission maxima at 390-535 nm respectively. The third-
order nonlinear optical properties of the target molecules have been investigated in N,N-
dimethylformamide using a single beam Z-scan technique with nanosecond laser pulses at 532
nm. The nonlinear refractive index, nonlinear absorption coefficient, magnitude of third-order
susceptibility and molecular two photon absorption cross-sections have been determined. All of
the compounds showed excellent optical limiting behaviour at 532 nm, with the best optical

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limiting behaviour observed with strong electron donor [dimethyl and N,N-diethyl amino]
substituents.
Keywords : 5-oxazolones, fluorescent probes, optical properties, third-order nonlinear, optical
limiting, Z-scan.
1. Introduction
Derivatives of 4-arylidene-3-aryl-5-oxazolones have been extensively studied as precursors
of organic molecules, such as amino acids, amides, peptides and a wide range of biologically
active compounds [1-7]. On the other hand, they exhibit interesting photophysical and
photochemical properties, which proved them to be good candidates for semiconductor devices
(electrophotographic photoreceptors), nonlinear optical (NLO) materials, biosensors and wide
variety of dyes [8-15].
Thus, in continuation of our investigations on NLO properties of 5-oxazolones [10], it is
aimed to study the effect of different acceptor and donor groups on the oxazolone moiety and
understand the structure-property relationship on NLO behaviour. In view of this study, a series
of five new 5(4H)-oxazolones (5a-5e) with a novel heterocyclic acceptor group [5-(2,6-
dichlorophenyl)-3-methyl-1,2-oxazole] at the C-2 position and various p-substituted aryl groups
as donors at the C-4 position were designed, synthesized (Scheme-1) and characterized.
The present work describes the synthesis of the title compounds, 4-substituted arylidene-2-
[5-(2,6-dichlorophenyl)-3-methyl-1,2-oxazol-4-yl]-1,3-oxazol-5-ones (5a-5e) and the study of
their third-order nonlinear optical properties in DMF solution by Z-scan technique.
In order to find the suitability of a material for nonlinear applications one needs to study its
photophysical as well as its optical characteristics such as type of nonlinearity, magnitude and
response time [16]. Hence, the photophysical properties of these target molecules were evaluated

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in seven different solvents with a range of polarities (benzene, 1,4-dioxane, tetrahydrofuran
(THF), acetonitrile, 2-proponol, ethanol and N,N-dimethylformamide (DMF)). The influence of
substituted donor/acceptor strength on the third-order NLO properties of the newly synthesized
oxazolones was discussed. The potent optical limiting behaviour exhibited by these molecules is
also demonstrated.
2. Experimental
2.1 Materials and methods
N,N-dimethylformamide (DMF) was vacuum distilled from calcium hydride before being
used for NLO studies. All other organic solvents were commercially available and dried using
standard procedures. The title compounds (5a-5e) were recrystallized twice from hot benzene to
13
enhance the degree of purity for the studies. 1H NMR and C NMR spectra were recorded by a
“Mercury-400” spectrometer using deuteriated chloroform (CDCl3) as solvent and
tetramethylsilane (TMS) as internal standard. IR spectra were obtained on a Perkin-Elmer 1330
infrared spectrophotometer in KBr, UV absorption spectra on a Unicam-540 spectrophotometer
by using quartz cuvette and Fluorescence emission spectra on Horiba Jobinyuon Fluoromax-4
spectrofluorometer with concentration of 10-3 mol/L. The nonlinear transmission of the samples,
with and without the aperture in front of the detector was measured in the far-field using Laser
Probe Rj-7620 Energy Meter with pyroelectric detectors.
Solutions of the title compounds (5a-5e) were prepared using spectroscopic grade N,N-
dimethylformamide (DMF) with concentration 1x10-3 mol/L. Single beam Z-scan technique [17,
18] was employed to measure the third-order optical nonlinearities of the series of novel 5-
oxazolones, which enabled simultaneous measurement of nonlinear refraction (NLR) and
nonlinear absorption (NLA). Basically, in this technique a Gaussian laser beam is focused, using

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a lens on the cuvette containing the liquid sample. The cuvette is translated across the focal
region and changes in the far-field intensity pattern are monitored. The experiments were
performed using a Q-switched, frequency doubled, Nd: YAG laser (Spectra-Physics GCR170)
which produces 7 ns pulses at 532 nm, at a repetition rate of 10 Hz. The laser beam was focused
by using a lens of 25 cm focal length whose beam waist at the focused spot was estimated to be
18.9 µm and the corresponding Rayleigh length at 2.11 mm. The Z-scan measurements with an
input peak intensity of 2.39 GW/cm2 were carried out using a cuvette of 1 mm thickness, which
is less than the Rayleigh length. Hence, the thin sample approximation is valid.
2.2 Synthesis of 5-(2,6-dichlorophenyl)3-methyl-1,2-oxazole-4-carbonylchloride (2)
A mixture of 5-(2,6-dichlorophenyl)-3-methyl-1,2-oxazole-4-carboxylicacid (1) (0.1 mol) in
acetonitrile (30 mL) was added slowly to thionyl chloride (0.3 mol) and the reaction mixture was
heated under reflux for 4 hours under anhydrous conditions. The excess thionyl chloride was
distilled off under reduced pressure and the resultant acid chloride (2) in the form of viscous
liquid, was collected.
2.3 Synthesis of 5-(2,6-dichlorophenyl)3-methyl-1,2-oxazol-4-yl carbonyl aminoacetic acid (3)
Glycine (0.1 mol) was dissolved in NaOH (30 mL, 2N) and stirred vigorously with
mechanical stirrer, until the total solid completely dissolved. This was added dropwise to the
crude acid chloride (2) (0.1 mol) and stirred vigorously for 1 hour. Later it was poured into
crushed ice and concentrated hydrochloric acid was added slowly with stirring, until the mixture
was acidified to Congo red. The obtained crude compound (3) was washed with cold water,
dried and recrystallized from boiling water.
White crystalline powder; Yield : 90%. m.p. : 198°C. IR (KBr, υ, cm-1) : 785, 1191, 1447, 1675,
1
1732. H NMR (400 MHz, DMSO, δ, ppm) : 2.70 (s, CH3, 3H), 3.79 (s, CH2, 2H), 7.53 (m, Ar-

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H, 3H) , 8.19 (s, NH, 1H), 12.68 (br s, COOH, 1H). 13C NMR (100 MHz, DMSO, δ, ppm) : 12.9,
41.1, 113.6, 127.6, 128.6, 132.5, 134.9, 158.4, 160.4, 170.6, 171.2. ESI-MS (m/z) : 329 [M+],
331 [M+2], 333 [M+4]. Anal. Calcd. for C13H10Cl2N2O4 : C, 47.44, H, 3.96 %; Found : C,
47.41, H, 3.98 %.
2.4 Synthesis of 2-[5-(2,6-dichlorophenyl)-3-methyl-1,2-oxazol-4-yl]-4-(4-substituted arylidene)-
1,3-oxazol-5-ones (5a-5e)
A mixture of dry 5-(2,6-dichlorophenyl)-3-methyl-1,2-oxazol-4-yl carbonyl aminoacetic
acid (3) (0.01 mol), substituted aromatic aldehyde (4a-4e) (0.01 mol), powdered anhydrous
sodium acetate (0.01 mol) and high-grade acetic anhydride (0.03 mol) was heated at 110°C on a
hot plate, with constant shaking until the solid gradually liquified to light yellow solution. Then
the reaction mixture was added 4°A molecular sieves (2g) and heated on a water bath for 1 hour
with occasional stirring. The molecular sieves were removed by filtration of the warm reaction
mixture. On cooling, ethanol (10 mL) was added slowly to the reaction mixture and left
overnight at room temperature. The crystalline product thus obtained was filtered under suction
pump, washed with ice cold alcohol, finally with boiling water and dried. The crude 5-
oxazolones obtained (5a-5e) were recrystallized from hot benzene.
2.4.1.
2-[5-(2,6-Dichlorophenyl)-3-methyl-1,2-oxazol-4-yl[-4-(4-arylidene)-1,3-oxazol-5-one
(5a). Pale yellow crystals. Yield : 85%. m.p. : 167°C. IR (KBr, υ, cm-1) : 941, 1143, 1456, 1656,
1765. 1H NMR (400 MHz, CDCl3, δ, ppm) : 2.93 (s, 3H), 7.12 (s, 1H), 7.29 (d, J = 7.6 Hz, 2H).
13
7.38 (d, J = 7.2 Hz, 1H), 7.50 (m, Ar-H, 3H), 7.64 (d, J = 7.6 Hz, 2H), C NMR (100 MHz,
CDCl3, δ, ppm) : 13.8, 105.5, 128.0, 128.1, 128.7, 131.2, 131.3, 131.6, 132.0, 132.5, 133.5,
136.0, 156.7, 158.3, 166.5, 174.3. ESI-MS (m/z) : 399 [M+], 401 [M+2],: 403 [M+4]. Anal.
Calcd. for C20H12Cl2N203 : C, 60.17, H, 3.03, N, 7.02 %; Found : C, 60.15, H, 3.05, N, 6.99 %.

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2.4.2. 2-[5-(2,6-Dichlorophenyl)-3-methyl-1,2-oxazol-4-yl[-4-(4-chloroarylidene)1,3-oxazol-5-
one (5b). Bright yellow crystals. Yield : 82%. m.p. : 163°C. IR (KBr, υ, cm-1) : 784, 960, 1164,
1419, 1667, 1792. 1H NMR (400 MHz, CDCl3, δ, ppm) : 2.92 (s, 3H), 7.04 (s, 1H), 7.23 (d, J =
8.4 Hz, 2H), 7.51 (m, Ar-H, 3H), 7.56 (d, J = 8.4 Hz, 2H). 13C NMR (100 MHz, CDCl3, δ, ppm)
: 13.8, 105.3, 127.8, 128.0, 129.0, 130.3, 131.3, 131.8, 131.9, 133.5, 135.8, 137.4, 156.9, 158.2,
166.2, 174.5. ESI-MS (m/z) : 433 [M+], 435 [M+2], 437 [M+4], 439 [M+6]. Anal. Calcd. for
C20H11Cl3N2O3 : C, 55.39, H, 2.56, N, 6.46 %; Found : C, 55.35, H, 2.59, N, 6.45 %.
2.4.3. 2-[5-(2,6-Dichlorophenyl)-3-methyl-1,2-oxazol-4-yl[-4-(4-methoxyarylidene)1,3-oxazol-5-
one (5c). Yellow crystals. Yield : 88%. m.p. : 179°C. IR (KBr, υ, cm-1) : 773, 959, 1157, 1455,
1668, 1789, 1805. 1H NMR (400 MHz, CDCl3, δ, ppm) : 2.92 (s, 3H), 3.87 (s, 3H), 6.79 (d, J =
13
8.8 Hz, 2H), 7.10 (s, 1H), 7.50 (m, Ar-H, 3H), 7.62 (d, J= 8.8 Hz, 2H); C NMR (100 MHz,
CDCl3, δ, ppm) : 13.7, 55.6, 105.6, 114.3, 126.5, 128.0, 129.3, 131.1, 132.2, 134.6, 135.9, 155.4,
158.2, 162.2, 166.9, 173.8. ESI-MS (m/z) : 429 [M+], 431 [M+2], 433 [M+4]. Anal. Calc. for
C21H14Cl2N2O4 : C, 58.76, H, 3.29, N, 6.53 %; Found : C, 58.73, H, 3.23, N, 6.50 %.
2.4.4. 2-[5-(2,6-Dichlorophenyl)-3-methyl-1,2-oxazol-4-yl[-4-(4-N,N-dimethylaminoarylidine)
1,3-oxazol-5-one (5d). Deep red crystals. Yield : 86%. m.p. : 233°C. IR (KBr, υ, cm-1) : 790,
1
958, 1159, 1377, 1586, 1760, 1787. H NMR (400 MHz, CDCl3, δ, ppm) : 2.91 (s, 3H), 3.10 (s,
6H), 6.53 (d, J = 8.8 Hz, 2H), 7.07 (s, 1H), 7.43-7.51 (m, Ar-H, 3H), 7.59 (d, J = 8.8 Hz, 2H),
13C NMR (100 MHz, CDCl3, δ, ppm) : 13.7, 40.1, 105.9, 111.5, 121.6, 126.5, 128.0, 128.2,
130.9, 133.6, 134.9, 136.0, 152.3, 153.5, 158.1, 167.5, 173.0. ESI-MS (m/z) : 442 [M+], 444
[M+2], 446 [M+4]. Anal. Calcd. for C22H17Cl2N3O3 : C, 59.74, H, 3.87, N, 9.50 %; Found : C,
59.76, H, 3.93, N, 9.47 %.

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2.4.5. 2-[5-(2,6-Dichlorophenyl)-3-methyl-1,2-oxazol-4-yl[-4-(4-N,N-diethylaminoarylidene)1,3-
oxazol-5-one (5e). Orange red crystals. Yield : 83%. m.p.: 245°C. IR (KBr, υ, cm-1) : 791, 957,
1197, 1577, 1664, 1754, 1781. 1H NMR (400 MHz, CDCl3, δ, ppm) : 2.92 (s, 3H), 3.43-3.48 (q,
4H), 6.51 (d, J = 8.8 Hz, 2H), 7.05 (s, 1H), 7.40-7.50 (m, Ar-H, 3H), 7.58 (d, J = 8.8 Hz, 2H).
13C NMR (100 MHz, CDCl3, δ, ppm): 12.7, 13.6, 44.8, 106.0, 111.1, 121.0, 126.0, 128.0, 128.3,
130.8, 133.6, 135.2, 136.0, 150.1, 153.2, 158.1, 167.5, 173.0. ESI-MS (m/z) : 470 [M+], 472
[M+2], 474 [M+4]. Anal. Calcd. for C24H21Cl2N3O3:C, 61.29, H, 4.50, N, 8.93 %; Found : C,
61.25, H, 4.51, N, 8.91 %.
3. Results and discussion
3.1. Synthesis
5-(2,6-Dichlorophenyl)-3-methylisoxazole-4-carboxylic acid (1) in acetonitrile was first
converted to its acid chloride using thionyl chloride and the obtained 5-(2,6-dichlorophenyl)3-
methylisoxazole-4-carbonyl chloride (2) was immediately reacted with glycine (aminoacetic
acid) in presence of sodium hydroxide to give 5-(2,6-dichlorophenyl)3-methyl-1,2-oxazol-4-yl
carbonyl aminoacetic acid (3) in the subsequent step. Finally, the title compounds 4-
(substitutedbenzylidene)-2-[5-(2,6-dichlorophenyl)-3-methylisoxazol-4-yl]oxazol-5(4H)-ones
(5a-5e) with various substituents, were synthesized by the condensation of 3 with different p-
substituted aryl aldehydes (4a-4e) in presence of acetic anhydride and sodium acetate in
excellent yields by using molecular sieves (4A0) as cyclodehydrating agents. The crude
compounds (5a-5e) on purification followed by crystallization formed yellow / reddish
1
crystalline solids and confirmed by IR, H NMR, 13C NMR, ESI mass spectroscopy and
elemental analyses. The detailed experimental procedure is recorded in experimental section
(2.4). The chemistry used to prepare these compounds is illustrated in Scheme 1.

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3.2. Photophysical characterization
The photophysical behaviour of the title compounds (5a-5e) in different solvents of
varying polarity was investigated and presented in Table 1. These compounds exhibited the
excitation and emission wavelengths in the range of 350-480 nm and 390-535 nm respectively in
all the solvents employed.
From the observed data, the influence of different substituents towards their absorption and
fluorescence emission maxima is clearly evidenced (Table 1). With the acceptor remaining
constant throughout the series (5a-5e) at one end, the red shift observed is due to donor strength
of the groups at the other end. Upon formation of the target 5-oxazolone from its reactant
molecules, the transition of an electron from the highest filled molecular orbital (HOMO) of the
donor to the lowest unoccupied molecular orbital (LUMO) of the acceptor takes place forming a
charge transfer complex, where π-electron delocalization takes place from the donor groups to
more or less the carbonyl group in the oxazolone ring (Fig.1).
From Table 1, no considerable changes have been observed in the absorption maxima of
compounds (5a-5e) due to solvent polarity. However, substantial shifts were observed in their
emission maxima, probably due to the interaction of the molecules in their excited states with the
solvent molecules. The compounds 5d and 5e exhibited longest wavelength absorption (λmax) at
471 nm and 479 nm and emission (λem) at 533 nm and 535 nm respectively in DMF (Fig.2).
Consequently, in compounds 5d and 5e, the enhanced π-electron delocalization due to –N(CH3)2
and –N(C2H5)2 groups on the phenyl ring is responsible for these effects.
Furthermore, the molar absorption coefficients (εmax) of 5a-5e were calculated by
recording absorbance values of each compound at a given wavelength in seven different solvents
and listed in Table 1. The Stokes shift values of 5a-5e were also calculated in terms of nm

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(difference in wavelength between the excitation and emission maxima) and cm-1 (the transition
energy between absorption and emission) and presented in Table 1.
The fluorescence quantum yields (φf) were measured using dilute solutions to avoid re-
absorption effect, relative to rhodamine 6G as a reference standard [19]. The quantum yields
observed (Table 1) were low for the series of compounds (5a-5e). A slight increase in these
values was observed in 5d and 5e in all the solvents employed. The low quantum yields
exhibited by oxazolones might be due to an efficient non-radiative deactivation channel of the
excess energy [20]. Finally, these studies reveal that the title compounds have potent
photophysical properties which make them interesting candidates for NLO studies.
3.3. NLO characterization
The nonlinear transmission of compound 5a without aperture (open aperture) was
measured in the far field as the sample was moved through the focal point. This allowed us to
determine the nonlinear absorption β. Here, the transmission is symmetric with respect to focus
(z = 0), where a minimum transmission, showing an intensity dependent absorption effect is
observed. To study the variation in the nonlinear optical parameters with the nature of the
substituent group, Z-scan experiments have been conducted on other samples (5b-5e) of this
series and similar curves have been obtained. The open aperture curves of samples 5c & 5e are
shown in Fig. 3(a) and 4(a). The shape of the open aperture curves suggests that the compounds
exhibit two-photon absorption [21-23]. The normalized transmittance for the open aperture Z-
scan is given by eq. (1) [24]
ln[1+ q0 (z)]
T(z) =
for | q0 (z) | < 1
(1)
q0 (z)
where q0 is a free factor, defined as

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α
L
I0
β
(1− e−
)
q0 (z) =
(2)
(1+ z2 / z2 )
α
0
and α is the linear absorption coefficient, L is the thickness of the sample, I0 is the on axis peak
irradiance at the focus, and z0 is the Rayleigh length.
It is known that nonlinear absorption coefficient β, depends on the number of absorptive centers
in a unit volume. Assuming that this number is N0, in units of cm-3, we have [25, 26],
β
=
σ
2 N0 =
σ
2 NAd ×10−3
(3)
Here, N0 is the molecular density of the sample (in units of 1/cm3), σ2 is the molecular TPA
coefficient (or cross-section) (in units of cm4/GW), d is the concentration of the sample and NA is
the Avogadro number. For known β and d, the value of σ2 can be obtained. Molecular TPA
cross-section (in units of cm4 s/photon) is also defined as [26, 27],
′
σ 2
=
σ
2hυ
,
(4)
Now the nonlinear absorption coefficient β, is related to the imaginary part of third-order
nonlinear optical susceptibility through the equation [24],
(3)
Im
χ
= n02
ε
0cλβ / 2
π
,
(5)
where n0 is the linear refractive index, ε0 is the permittivity of free space and c is velocity of light
in vacuum.
From the open aperture Z-scan data, the measured values of nonlinear absorption
coefficient β, molecular TPA cross-sections σ2 and σ'2 and the imaginary part of third-order
nonlinear optical susceptibility χ(3) of samples (5a-5e) are given in Table 2. The σ'2 value of the
newly synthesized 5-oxazolones (5a-5e) are nearly two orders of magnitude larger than that of
Rhodamine 6G which is 10-48 to 10-50 cm4 s/photon [28]. It is also comparable with values

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obtained in stilbazolium like dyes such as trans-4-[2-(pyrryl)vinyl]-1-methylpyridium iodide
[29].
To determine the sign and magnitude of nonlinear refraction, closed-aperture Z-scan was
performed by placing an aperture in front of the detector. The closed aperture Z-scan curves of
5c & 5e are shown in Fig. 3(b) and 4(b). To obtain the pure nonlinear refraction curve we
adopted the division method [24]. The investigated samples (5a-5e) were found to exhibit peak–
valley characteristics, indicating negative nonlinear refraction or self defocusing effects as shown
in Fig. 3(c) and 4(c) for compounds 5c and 5e.
The nonlinear refractive index γ (m2/W) is given by the formula [24],
∆φ0λ
γ
=
(m2 /W ),
2π Leff I0
(6)
(1−exp−αL
)
Leff =
α
where
and ꢀΦ0 is the on-axis phase change given by the equation,
∆Tp− v
∆φ =
for | ∆φ | ≤ π ,
0
0
0.406(1− S)0.25
(7)
Here ∆Tp−v is the peak to valley transmittance difference and S is the linear aperture
transmittance. Then nonlinear refractive index n2 (in esu) is related to γ (m2/W) by,
n2 (esu) = (cn0 / 40
π
)γ
(m2 / W) ,
(8)
The normalized transmittance for pure nonlinear refraction is given by [24],
4x∆φ0
[(x2 +9)(x2 +1)]
T(Z) =1−
,
(9)
The nonlinear refractive index n2 (esu) is related to the real part of third-order nonlinear optical
susceptibility through equation [24],
(3)
Re
χ
= 2n02
ε
0cn2 (esu),
(10)

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where n0 is the linear refractive index, ε0 is the permittivity of free space and c is velocity of light
in vacuum.
From the pure nonlinear refraction Z-scan data, the real part of third-order nonlinear optical
susceptibility χ(3) and nonlinear refractive index n2, for samples (5a-5e) have been calculated and
tabulated in Table 2.
The nonlinear absorption coefficients (β) of some of the organic compounds and metal
complexes studied previously are listed in Table 3. Azoaromatic compounds such as Disperse
Orange 3, Disperse Red 13, Disperse Red 19 and azobenzene, which are conjugated molecules
with donor/acceptor groups, have large values of β [30]. Similarly, styryl dyes and octupolar
metal complexes are found to have large values [31,32], exceeding that of semiconductors such
as ZnSe, CdS and ZnTe, Cu nanocomposite glasses [33] and bismuth nanorods [34]. The
nonlinear absorption coefficients of the tested samples 5d and 5e are also found to be in the same
range as that of the materials shown in Table 3.
The magnitude of susceptibility (χ(3)) values of the title compounds (5a-5e) were found to
be increasing from 5a to 5e. This can be attributed to the increase in the electron donating
abilities of the donor groups and is pronounced in 5d and 5e [-N(CH3) and -N(C2H5)2]. Thus, the
compounds 5d and 5e, containing the -NR2 substituent groups showed the highest third-order
nonlinear response amongst the title compounds (5a-5e) studied. Thus, the knowledge of
variation of nonlinear response with substituents could be employed to design suitable organic
materials for future specific applications in photonics and other optoelectronics fields.
3.4. Optical limiting
The optical power limiting efficiency of the target molecules (5a-5e) was investigated by
means of nonlinear transmittance measurements as a function of the input fluence, to determine

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the limiting threshold. The optical limiting threshold determines the ability of the limiter and it
is noted that the lower the threshold value, the better the optical limiter [35]. Fig.5 shows the
clear optical limiting behaviour of the tested samples 5a-5e. The optical limiting threshold (the
fluence value at which the transmittance starts decreasing) of the molecules 5a-5e from the Fig.5,
are found to be 2.25x105 J/m2, 8x104 J/m2, 6x104 J/m2, 2x104 J/m2 and 2x104 J/m2 respectively.
The results demonstrated that the molecules 5d and 5e with strong electron donating –N(CH3)2,
–N(C2H5)2 substituents on the phenyl ring, exhibited better optical limiting behaviour with lower
threshold values than all the other molecules tested (5a-5c).
Moreover, the optical limiting parameters of the tested molecules (5a-5e) compare very
well with those of the materials mentioned in Table 3 and are also comparable with those values
for mixed metal clusters [36-39].
4. Conclusion
In conclusion, five novel 5-oxazolones with delocalized π-conjugated systems having
novel acceptor and different donor groups (5a-5e) were synthesized and their third-order
nonlinear optical response was screened using the Z-scan technique in DMF solution. In
addition, the photophysical properties of the title compounds in seven different solvents have
also been determined. The substituent effect on the NLO properties is clearly noticed. The Z-
scan results indicate that the target molecules exhibit good negative nonlinear refractive index
(n2) and nonlinear absorption (NLA). The nonlinear index is found to be negative and its
magnitude is of the order of 10-11 esu. The molecular two-photon absorption cross-section of
these molecules was also measured and is of the order of 10-46 cm4 s/photon which is nearly two
orders of magnitude larger compared to that of Rhodamine dyes. The molecules studied (5a-5e),
exhibit good optical power limiting behaviour of nanosecond laser pulses at 532 nm wavelength.

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A good correlation was found between the theoretical and experimental values, suggesting that
the samples investigated seem to be promising candidates for future photonic and optoelectronic
applications.
Acknowledgements
The authors are grateful to Prof. Nittala S. Sharma, Dept. of PNCO, School of Chemistry and
Prof. N. Someswara Rao, Dept. of Analytical Chemistry, School of Chemistry, Andhra
University, Visakhapatnam, INDIA for providing spectrofluorometer and spectrophotometer to
record the photophysical data.
References
[1]
Lamb J, Robson W. The Erlenmeyer synthesis of amino-acids. Biochem J 1931;25:1231-
1236.
[2]
Park BS, Min Oh C, Chun KH, Lee JO. Photo induced one pot transformation of 2-
phenyl-4-ethylidene-5(4H)-oxazolone and allylic alcohols to γ, δ-unsaturated N-benzoyl
amides. Tetrahedron Lett 1998;39:9711-9714.
[3]
[4]
Matsunaga H, Ishizuka T, Kunieda T. Synthetic utility of five-membered heterocycles-
chiral functionalization and applications. Tetrahedron 2005;61:8073-8094.
Khan KM, Mughal UR, Khan MTH, Ullah Z, Perveen S, Choudhary MI.
Oxazolones:New tyrosinase inhibitors; synthesis and their structure-activity relationships.
Bioorg Med Chem 2006;14:6027-6033.
[5]
Mesaik MA, Rahat S, Khan KM, Ullah Z, Choudhary MI, Murad S, Ismail Z, Rahman A,
Ahmad A. Synthesis and immunomodulatory properties of selected oxazolone
derivatives. Bioorg Med Chem 2004;12:2049-2057.

ACCEPTED MANUSCRIPT
[6]
[7]
[8]
[9]
Pasha MA, Jayashankara VP, Venugopala KN, Rao GK. Zinc oxide (ZnO): An efficient
catalyst for the synthesis of 4-arylmethylidene-2-phenyl-5(4H)-oxazolones having
antimicrobial activity. J Pharmacol Toxicol 2007;2:264-270.
Argade ND, Kalrale BK, Gill CH. Microwave assisted improved method for the
synthesis of pyrazole containing 2,4-disubstitute oxazole-5-one and their antimicrobial
activity. Eur J Chem 2008;5:120-129.
Ozturk G, Alp S, Timur S. Photophysical characterization of fluorescent oxazol-5-one
derivatives in PVC and their application as biosensors in the detection of Ach and AChE
inhibitor:Donepezil. Dyes Pigments 2008;76:792-798.
Ozturk G, Alp S, Ertekin K. Fluorescence emission studies of 4-(2-furylmethylene)-2-
phenyl-5-oxazolone embedded in polymer thin film and detection of Fe3+ ion. Dyes
Pigments 2007;72:150-156.
[10] Murthy YLN, Christopher V, Viplava Prasad U, Bisht PB, Ramanaih DV, Kalanoor BS,
Akbar Ali S. Synthesis and study of nonlinear optical properties of 4-substituted
benzylidene-2-phenyl oxazol-5-ones by Z-scan technique. Synthetic met 2010;160:535-
539.
[11] Bourotte M, Schmitt M, Wund AF, Pigault C, Haiech J, Bourguignon JJ. Fluorophores
related to the green fluorescent protein. Tetrahedron Lett 2004;45:6343-6348.
[12] Jung B, Kim H, Park BS. Photodecarbonylation of 2-phenyl-4-alkylidene-5(4H)-
oxazolones. Tetrahedron Lett 1996;37:4019-4022.
[13] Samieh F, Ahmad MT, Hooshang H, Hojatollah K. A synthesis of some new 4-arylidene-
5(4H)-oxazolone azo dyes and an evaluation of their solvatochromic behaviour.
ARKIVOC 2008; xiv:115-123.

ACCEPTED MANUSCRIPT
[14] Palcut M. Spectral properties of novel 1,3-oxazol-5(4H)-ones with substituted
benzylidene and phenyl rings. Acta Chim Slov 2009;56:362-368.
[15] Ozturk G, Alp S, Ergun Y. Synthesis and spectroscopic properties of new 5-oxazolone
derivatives containing an N-phenyl-aza-15-crown-5 moiety. Tetrahedron Lett
2007;48:7347-7350.
[16] Gayathri C, Ramalingam A. Studies of third-order optical nonlinearities and optical
limiting properties of azo dyes. Spectrochim Acta Part A 2008;69:980-984.
[17] Sheik-Bahae M, Said AA, Wei TH, Hagan DJ, Van Stryland EW. Sensitive measurement
of optical nonlinearities using a single beam. IEEE J Quantum Elec 1990;26:760-769.
[18] Prabhu AN, Upadhyaya V, Jayarama A, Subrahmanya Bhat K. Synthesis, growth and
characterization of π conjugated organic nonlinear optical chalcone derivative. Mater
Chem Phys 2013;138:179-185.
[19] Kubin RF, Fletcher AN. Fluorescence quantum yields of some rhodamine dyes. J Lumin
1982;27:455-462.
[20] Catarina ABR, Ines FAM, Ermelinda MSM, Carlos AMA, Jose MGM. Two-photon
absorption properties of push–pull oxazolones derivatives. Dyes Pigments 2012;95:713-
722.
[21] Ganeev RA, Ryasnyanskii AI, Kodirov MK, Kamalov Sh R, Usmanov T. Optical
limiting in fullerenes, colloidal metal solutions, and semiconductors in the field of pico-
and nanosecond pulses of an Nd:YAG laser. Opt Spectrosc 2002;93:789-796.
[22] Tykwinski, RR. Kamada K, Bykowski D, Hegmann FA, Hinkle RJ. Nonlinear optical
properties of thienyl and bithienyl iodonium salts as measured by the z-scan technique. J
Opt A: Pure Appl Opt 2002;4:S202-206.

ACCEPTED MANUSCRIPT
[23] Yin M, Li HP, Tang SH, Ji W. Determination of nonlinear absorption and refraction by
single Z-scan method. Appl Phys B 2000;70:587-591.
[24] Poornesh P, Ravi K, Umesh G, Hegde PK, Manjunatha MG, Manjunatha KB, Adhikari
AV. 3,3′-Benzene-1,4-diylbis[1-(substituted)phenylprop-2-en-1-one] derivatives: A new
class of materials for third-order nonlinear optical applications. Opt Commun 2010;
283:1519-1527.
[25] He GS, Gvishi R, Prasad PN, Reinhardt BA. Two-photon absorption based optical
limiting and stabilization in organic molecule-doped solid materials. Opt Commun
1995;117:133-136.
[26] He GS, Xu GC, Prasad PN, Reinhardt BA, Bruce AR, Bhatt JC, Dillard AG. Two-photon
absorption and optical-limiting properties of novel organic compounds. Opt Lett
1995;20:435-437.
[27] He GS, Weder C, Smith P, Prasad PN. Optical power limiting and stabilization based on
a novel polymer compound. IEEE J Quantum Elec 1998;34:2279-2285.
[28] Oulianov DA, Tomov IV, Dvornikov AS, Rentzepis PM. Observations on the
measurement of two-photon absorption cross-section. Opt Commun 2001;191:235-243.
[29] Sun W, Lawson CM, Gray GM, Zhan C, Wang D. Degenerate four-wave mixing and Z-
scan measurements of stilbazolium derivatives. Appl Phys Lett 2001;78:1817-1819.
[30] Andrade AA, Yamaki SB, Misoguti L, Zilio SC, Atvars DZ, Oliveira Jr ON, Mendonca
CR. Two-photon absorption in diazobenzene compounds. Opt Mater 2004;27:441-444.
[31] Shettigar S, Umesh G, Poornesh P, Manjunatha KB, Asiri AM. The third-order nonlinear
optical properties of novel styryl dyes. Dyes Pigments 2009;83:207-210.

ACCEPTED MANUSCRIPT
[32] Rudresha BJ, Manjunatha KB, Umesh G, Ramachandra Bhat B. Octupolar metal
complexes for third order nonlinear optical studies. Chem Phys Lett 2012;542:159-163.
[33] Yin M, Li HP, Tang SH, Ji W. Determination of nonlinear absorption and refraction by
single Z-scan method. Appl. Phys. B 2000;70:587-591.
[34] Sivaramakrishnan S, Muthukumar VS, Sivasankara Sai S, Venkataramanaiah K, Reppert
J, Rao AM, Anija M, Philip R, Kuthirummal N. Nonlinear optical scattering and
absorption in bismuth nanorod suspensions. Appl Phys Lett 2007;91:093104-093106.
[35] Yu C, Michael H, Yasuyuki A, Osamu I. Axially modified gallium phthalocyanines and
naphthalocyanines for optical limiting. Chem Soc Rev 2005;34:517-529.
[36] Shi S, Ji W, Tang SH, Lang JP, Xin XQ. Synthesis and Optical Limiting Capability of
Cubane-like Mixed Metal Clusters (n-Bu4N)3[MoAg3BrX3S4] (X = Cl and I). J Am
Chem Soc 1994;116:3615-3616.
[37] Yu H, Zhang WH, Ren ZG, Chen JX, Wang CL, Lang JP, Elim HI, Ji W. Formation of
new organometallic W/Cu/S clusters from reactions of [{(η5-C5Me5)WS3}3 Cu7(MeCN)9]
(PF6)4 with donor ligands. Crystal structures and optical limiting properties of [(η5-
C5Me5)WS3Cu3(Py)6](PF6)2, [(η5-C5Me5)WS3Cu3Br(PPh3)3](PF6), and [(η5-C5Me5)WS3
Cu4(Py)Cl(dppm)2](PF6)2. J Organomet Chem 2005;690:4027-4035.
[38] Marta F, Rosa L, Santiago U, Cristian V, Mark GH, Nigel TL, Marek S, Barry LD. Solid
state synthesis, structure and optical limiting properties of seleno cuboidal clusters
[M3Se4X3(diphosphine)3]+ (M=/Mo, W; X=/Cl, Br). Inorg Chim Acta 2003;349:69-77.
[39] Mark GH, Bryce LG, Marek S, Brian WS, Vicki AT, Allan HW, Adele JW, Brian FY.
Synthesis, structure and optical limiting properties of organoruthenium–chalcogenide
clusters. J Organomet Chem 2005;690:1487–1497.

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Table 1. The absorption and emission maxima of (5a-5e) in different solvents of varying polarity
Table 2. Third-order nonlinear optical parameters of title compounds (5a-5e) in DMF solution at
the concentration of 1x10-3 mol/L.
Table 3. Nonlinear absorption coefficient (β) of various compounds reported in the literature.

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Table 1.
Absorption
Maxima
(λabs in nm)
Molar extension
coefficient
Emission
maxima
(λem in nm)
Stokes shift
Fluorescence
quantum yield
φf
(∆λ)
Compound
Solvent
(εmax (cm-1 M-1))
nm
cm-1
Benzene
1,4-dioxane
Tetrahydrofuran (THF)
Acetonitrile
2-propanol
360
356
357
355
356
356
357
59,000
84,000
52,000
29,000
38,000
75,000
82,000
409
407
399
397
398
399
413
49
51
42
43
43
43
56
3343
3504
2964
3012
2980
3059
3782
0.009
0.008
0.002
0.001
0.004
0.002
0.002
5a
5b
5c
Ethanol
N,N-Dimethylformamide (DMF)
Benzene
1,4-dioxane
Tetrahydrofuran (THF)
Acetonitrile
2-propanol
365
361
361
359
361
360
362
89,000
80,000
70,000
52,000
25,000
78,000
48,000
417
413
414
404
404
405
405
52
52
53
45
43
45
43
3401
3472
3531
3087
3009
3010
2841
0.004
0.003
0.004
0.003
0.006
0.005
0.005
Ethanol
N,N-Dimethylformamide (DMF)
Benzene
1,4-dioxane
Tetrahydrofuran (THF)
Acetonitrile
2-propanol
383
379
382
382
386
386
385
78,000
47,000
99,000
63,000
99,000
92,000
47,000
437
427
432
434
437
435
433
54
48
50
52
51
49
48
3213
2952
3016
3137
3050
2945
2859
0.003
0.002
0.09
0.001
0.001
0.006
0.003
Ethanol
N,N-Dimethylformamide (DMF)

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Benzene
1,4-dioxane
Tetrahydrofuran (THF)
Acetonitrile
2-propanol
463
454
460
464
465
465
471
90,000
62,000
87,000
54,000
69,000
86,000
66,000
497
498
512
528
516
525
533
34
44
52
66
51
60
62
1487
1966
2198
2622
2126
2284
2465
0.06
0.08
0.09
0.14
0.10
0.12
0.18
5d
Ethanol
N,N-Dimethylformamide (DMF)
Benzene
1,4-dioxane
Tetrahydrofuran (THF)
Acetonitrile
2-propanol
470
464
470
471
471
475
479
52,000
62,000
89,000
44,000
36,000
53,000
78,000
500
502
515
530
518
528
535
30
38
45
59
47
53
56
1249
1650
1914
2354
1908
2131
2177
0.05
0.07
0.09
0.12
0.09
0.10
0.15
5e
Ethanol
N,N-Dimethylformamide (DMF)

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Table 2.
n2
σ2
σ'2
β
Re χ(3)
(cm/GW) (x10-13esu)
Im χ(3)
Compound
(x10-11
esu)
(x10-19
(x10-46
(x10-13esu)
cm4/GW) cm4s /photon
-0.4073
-0.6924
-0.7495
-3.0783
-3.2442
0.3219
0.4603
0.9065
9.8652
9.8971
-0.4363
-0.7417
-0.8029
-3.2974
-3.4751
0.0495
0.0708
0.1395
1.5181
1.5230
5.344
7.643
1.993
2.851
5a
5b
5c
5d
5e
15.051
163.792
164.322
5.614
61.094
61.292
Table 3.
Compounds
β (cm/GW)
References
Diazobenzene
Styryl dyes
6.5
[30]
[31]
4.87
Octupolar metal complexes
ZnSe, CdS, and ZnTe
Bismuth nanorods
5.07
[32]
3.6, 4.9 and 4.7
[33]
5.3
9.8
[34]
5-oxazolones (5d & 5e)
Present work

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Scheme 1. Synthetic pathway of title compounds (5a-5e)
Fig. 1. Charge transfer complex of 5-oxazolones (5a-5e)
Fig. 2. (a) Absorption and (b) Emission spectra of title compounds (5a-5e) in DMF
Fig. 3. (a) Open aperture (b) Closed aperture and (c) Pure nonlinear refraction Z-scan curve of 5c
in DMF solution. Solid line is a theoretical fit to the experimental data.
Fig. 4. (a) Open aperture (b) Closed aperture and (c) Pure nonlinear refraction Z-scan curve of 5e
in DMF solution. Solid line is a theoretical fit to the experimental data.
Fig. 5. Optical limiting behaviour of title compounds (5a-5e)

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R in 4a-4e and 5a-5e = (a) H, (b) p-Cl, (c) p-OCH3, (d) p-N(CH3)2, (e) p-N(C2H5)2
Scheme 1.

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Fig. 1.
Fig. 2.

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Fig. 3.
Fig. 4.

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Fig. 5.