Synthesis, optical and nonlinear optical properties of new pyrazoline derivatives

Article abstract of DOI:10.1016/j.dyepig.2013.10.027

We report on synthesis and optical properties of new organic compounds based on substituted pyrazole ring. The investigated pyrazoline derivatives (PRDs) exhibit efficient broadband photoluminescence which covers nearly whole visible spectrum. The experimental results are compared to quantum chemical calculations. Amplified spontaneous emission and photodegradation measurements were performed for hybrid systems based on selected PRDs doped into poly(methyl methacrylate) matrix proving the potential utility of such systems in lasing applications. Two-photon absorption (TPA) properties were characterized by the femtosecond Z-scan technique.

Full text of DOI:10.1016/j.dyepig.2013.10.027

Dyes and Pigments 102 (2014) 63e70
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Synthesis, optical and nonlinear optical properties of new pyrazoline
derivatives
J. Mysliwiec a , A. Szukalski , L. Sznitko , A. Miniewicz , K. Haupa , K. Zygadlo ,
,
a
a
a
b
c
*
a
a
a
K. Matczyszyn , J. Olesiak-Banska , M. Samoc
Institute of Physical and Theoretical Chemistry, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland
Faculty of Chemistry, University of Wroclaw, F. Joliot-Curie 14, 50-383 Wroclaw, Poland
a
b
c
Wroclaw Research Centre EITþ, Stablowicka 147, 54-066 Wroclaw, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 21 June 2013
Received in revised form
We report on synthesis and optical properties of new organic compounds based on substituted pyrazole
ring. The investigated pyrazoline derivatives (PRDs) exhibit efficient broadband photoluminescence
which covers nearly whole visible spectrum. The experimental results are compared to quantum
chemical calculations. Amplified spontaneous emission and photodegradation measurements were
performed for hybrid systems based on selected PRDs doped into poly(methyl methacrylate) matrix
proving the potential utility of such systems in lasing applications. Two-photon absorption (TPA)
properties were characterized by the femtosecond Z-scan technique.
26 September 2013
Accepted 18 October 2013
Available online 28 October 2013
Keywords:
Pyrazoline
Ó 2013 Elsevier Ltd. All rights reserved.
Amplified spontaneous emission
Luminescence
Two-photon absorption (TPA)
Nonlinear optics
Pushepull molecules
1. Introduction
yield, thermal, and photochemical stability make this class of com-
pounds promising for organic thin film laser applications.
Multifunctional materials, which can be used in modern tech-
nology applications are nowadays one of the main research topics
in materials science. Modern photonics requires effective materials,
which among others can exhibit sizable nonlinear optical effects
making them suitable for applications involving in numerous
multidisciplinary areas, such as photodynamic cancer therapy [1],
multiphoton fluorescence and biological imaging [2], optical power
limiting [3], in construction of organic light-emitting diodes [4] or
two-photon microfabrication [5]. The materials intended for
various applications should also possess other properties, like e.g.
good photostability or high efficiency of performing the intended
function, e.g. high yield of singlet oxygen production, efficient
fluorescence, etc.
In this paper we present studies of a group of newly synthesized
pyrazoline derivatives, with respect to their luminescent properties
and possible applications in devices fabrication exploiting ampli-
fied spontaneous emission/lasing phenomena and two-photon
absorption.
The new synthesized derivatives of pyrazoline due to presence
of
p-conjugated bonds can exhibit high values of dipole moment
and hyperpolarizability, which are desired attributes for nonlinear
optics and luminescent chromophores. The strategy of its proper-
ties modification during molecular design and synthesis is based on
structural changes like surrounding electron-donor and acceptor
group position manipulation and its capability of effective charge
transfer.
We have been interested in synthesis, luminescent and nonlinear
optical properties of newderivatives of pyrazoline. Nonlinearoptical
properties of some pyrazoline derivatives have been already
investigated and, in particular, their efficient two- and three
photon absorption (2PA and 3PA) together with their potential for
lasing [6e10] have been demonstrated. High fluorescence quantum
2. Materials synthesis and methods
We present here the particular steps of synthesis for the
investigated pyrazoline derivatives. An intermediate, 1-phenyl-4,5-
dihydro-1H-pyrazole, was synthesized by the method of Knoeve-
nagel and Fischer [11]: phenylhydrazine (100 g, 0.92 mol) was
3
ꢀ
dissolved in ether (500 cm ) and cooled down to about 5 C. So-
*
Corresponding author.
3
E-mail address: jaroslaw.mysliwiec@pwr.wroc.pl (J. Mysliwiec).
lution of propenal (40 g, 0.71 mol) in ether (100 cm ) was added
0143-7208/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2013.10.027

64
J. Mysliwiec et al. / Dyes and Pigments 102 (2014) 63e70
drop wise within 30 min with stirring. The reaction mixture was
stirred for the next 48 h. The ether was evaporated and 600 cm of
The residue was chromatographed on silica gel with DCM as eluent.
Only the first fraction was collected. The yield of reaction was 25 g
(57%). According to the following procedure final compound e (E)-
2-(2-(1-phenyl-4,5-dihydro-1H-pyrazol-3-yl)vinyl)benzonitrile
was obtained. The 2-(bromomethyl)benzonitrile from the first step
of synthesis described above (0.4 g, 2 mmol) and triphenylphos-
phine (0.524 g, 2 mmol) were dissolved and boiled in dry benzene
overnight. The resulting salt was filtered, washed with hot benzene
and used without further purification. To the suspension of phos-
3
7
1
% sulfuric acid was added. Subsequently it was steam distilled. The
-phenyl-4,5-dihydro-1H-pyrazole was collected as yellow oil then
it solidified and was filtered. Crystallization from petroleum ether
gave 17 g (0.097 mol) of 1-phenyl-4,5-dihydro-1H-pyrazole with
reaction yield equal to 12.6%. The next step of synthesis was to
receive the 1-phenyl-4,5-dihydro-1H-pyrazole-3-carbaldehyde
(
4
Fig. 1.) as intermediate for other pyrazoline derivatives (Figs. 2e
3
3
). POCl
3
(32 g, 0.21 mol) was added to DMF (120 cm ) at room
phonium salt in dry THF (25 cm ), under inert atmosphere at room
temperature. Next, the entire solution of 1-phenyl-4,5-dihydro-1H-
temperature, sodium ethanolate (0.108 g, 2 mmol) was added. The
color of the mixture became deep red and after that the solution
was stirred for another 30 min. After that time the solution of 1-
3
pyrazole in DMF (20 cm ) was added to the previously prepared
ꢀ
mixture. The whole mixture was heated to 90 C and kept at this
temperature for 30 min and then poured onto water with ice and
the product separated overnight as yellow needles. It was filtered
and crystallized from a small amount of ethanol. Filtration gave
phenyl-4,5-dihydro-1H-pyrazole-3-carbaldehyde
(0.348
g,
3
2 mmol) in dry THF (10 cm ) was added drop wise and was stirred
ꢀ
overnight at 50 C. Next the solvent was evaporated and DCM was
7
.5 g (37%) of 1-phenyl-4,5-dihydro-1H-pyrazole-3-carbaldehyde.
The synthesis procedure for the (E)-2-(4-(2-(1-phenyl-4,5-
dihydro-1H-pyrazol-3-yl)vinyl)benzylidene)malononitrile was
added to the orange residue until it became homogenous. The
product was purified on silica gel with DCM as eluent. It was
crystallized from heptane with yield of reaction 0.325 g (59.5%). To
obtain e (E)-2-(1-cyano-2-(1-phenyl-4,5-dihydro-1H-pyrazol-3-yl)
vinyl)benzonitrile, which is a derivative of PY-oCN, it was necessary
to synthesize another intermediate. The 2-(bromomethyl)benzo-
nitrile (5 g, 25.5 mmol), which was obtained before, was dissolved
in a mixture of ethanol (50 cm ) and water (10 cm ). Potassium
cyanide (2.6 g, 40 mmol) was added to this solution. Then it was
refluxed for 1.5 hand subsequently poured onto ice. Deep green-
blue solution was extracted with DCM. The extract was dried
performed by the following steps (Fig. 2). At first 2-(4-(bromo-
methyl)benzylidene)malononitrile was prepared. Then 4-
methylbenzaldehyde (30 g, 0.25 mol) and malononitirile (16.5 g,
0
acetate was added (0.5 g, 0.006 mol). The reaction mixture was
heated under reflux for 4 h. The dark-brown solution was poured
onto water with ice and gray precipitate was filtered and dried. The
final compound was crystallized twice from ethanol. The yield of
this step was 33 g (78.5%). Dry compound was suspended in
3
.25 mol) were dissolved in 300 cm of dry ethanol and sodium
3
3
4
with MgSO and passed on alumina(neutral) in DCM to give
anhydrous CCl
4
with equimolar amount of NBS (35 g, 0.19 mol) and
yellowish solution. The eluent was evaporated and the residue
crystallized from methanol. The yield of the intermediate was 1.2 g
(33%). The last step of (E)-2-(1-cyano-2-(1-phenyl-4,5-dihydro-1H-
pyrazol-3-yl)vinyl)benzonitrilesynthesis was as follows (cf. Fig. 3).
Anhydrous sodium acetate was added (0.05 g) to the solution of 2-
(cyanomethyl)benzonitrile (0.4 g, 2.8 mmol) and 1-phenyl-4,5-
dihydro-1H-pyrazole-3-carbaldehyde (0.490 g, 2.8 mmol), in dry
ethanol. Then it was stirred and refluxed overnight. The solvent was
evaporated and oily residue was chromatographed on silica gel
with DCM as eluent. After evaporation of DCM the oil was dissolved
0
.3 g of AIBN as initiator. The reaction flask was heated to the
boiling temperature and stirred for 24 h. Colorless succinimide was
filtered off and the solvent was evaporated. The residue was crys-
tallized from ethanol. The yield of 2-(4-(bromomethyl)benzyli-
dene)malononitrile synthesis was 32 g (66%). Product from the last
step (0.5 g, 2 mmol) and triphenylphosphine (0.524 g, 2 mmol)
were dissolved and boiled in dry benzene overnight. Resulting salt
was filtered, washed with hot benzene and used without further
purification. Sodium ethanolate (0.108 g, 2 mmol) was added to the
3
ꢀ
suspension of phosphonium salt in dry THF (25 cm ), under inert
in boiling heptane. After cooling below 0 C the orange solid
atmosphere at room temperature. The color of the solution became
deep red and then the solution was stirred for another 30 min. After
that time the solution of 1-phenyl-4,5-dihydro-1H-pyrazole-3-
precipitated from the solution and then it was filtered. The yield of
this synthesis was 0.216 g (efficiency: 26%).
The intermediates: 2-(4-nitrophenyl)acetonitrile and 2-(4-
nitrophenyl)acetic acid were synthesized by known procedures.
3
carbaldehyde (0.348 g, 2 mmol) in dry THF (10 cm ) was added
ꢀ
drop wise. It was stirred overnight at 50 C. The solvent was
Compound
(E)-3-(4-nitrostyryl)-1-phenyl-4,5-dihydro-1H-pyr-
evaporated and to the dark red residue DCM was added, until it
became homogenous. The product was purified on silica gel with
DCM as eluent and crystallized from ethanol. The yield of synthesis
of (E)-2-(4-(2-(1-phenyl-4,5-dihydro-1H-pyrazol-3-yl)vinyl)ben-
zylidene)malononitrile was 0.318 g (48.5%).
The synthesis procedure of (E)-2-(2-(1-phenyl-4,5-dihydro-1H-
pyrazol-3-yl)vinyl)benzonitrile (PY-oCN) was performed by the
following steps (Fig. 3). At first 2-(bromomethyl)benzonitrile was
synthesized also as an intermediate for the next pyrazoline deriv-
azole(PY-pNO
2
) was made as follows (c.f. Fig. 4). A few drops of
piperidine were added to the solution of 2-(4-nitrophenyl)acetic
(0.4 g, 2.2 mmol) and 1-phenyl-4,5-dihydro-1H-pyrazole-3-
carbaldehyde (0.384 g, 2.2 mmol) in dry ethanol. The whole
mixture was mixed and refluxed overnight. The day after, the sol-
vent was evaporated and the residue was dissolved in DCM until
the solvent became homogenous. The whole solution was then
purified by column chromatography (silica, DCM) and red solid was
crystallized from heptane. The yield of this synthesis was 0.110 g
(17%). The scheme of (E)-2-(4-nitrophenyl)-3-(1-phenyl-4,5-
ative (PY-oCNCN). First 2-methylbenzonitrile (25 g, 0.21 mol) was
3
dissolved in 150 cm of CCl
4
. Equimolar amount of NBS and 0.3 g of
dihydro-1H-pyrazol-3-yl)acrylonitrile(PY-oCNNO
presented in Fig. 4. The second step is similar to synthesis of PY-
pNO compound. A few drops of piperidine were added to the
2
)
synthesis is
AIBN were added. The reaction mixture was refluxed for 5 h and
ꢀ
after cooling to 40 C it was filtered and the solvent was evaporated.
2
Fig. 1. Steps of synthesis of 1-phenyl-4,5-dihydro-1H-pyrazole-3-carbaldehyde.

J. Mysliwiec et al. / Dyes and Pigments 102 (2014) 63e70
65
Fig. 2. Steps of synthesis (E)-2-(4-(2-(1-phenyl-4,5-dihydro-1H-pyrazol-3-yl)vinyl)benzylidene)malononitrile (PirazFPHdiCN).
solution of 2-(4-nitrophenyl)acetonitrile (0.4 g, 2.4 mmol) and 1-
phenyl-4,5-dihydro-1H-pyrazole-3-carbaldehyde (0.429 g,
.4 mmol) in dry ethanol and the whole mixture was refluxed with
stirring overnight. The next day the solvent was evaporated, the
residue was dissolved in DCM until it was homogenous and purified
by column chromatography (silica, DCM). Dark red solid was
crystallized from heptane. 0.110 g of the product was obtained
Strong stretch band of C]C aliphatic group can be used for
confirming the presence of eCN group in position R . Com-
pounds 5, 7 and 8 give C]C stretch vibration at higher fre-
1
2
ꢁ1
quency (1653, 1653, 1630 cm ). In the case when C]C is linked
ꢁ
1
with nitryl group the bond is lower (1610e1595 cm ) and
overlaps with deformation bands of the ring and C]N stretch-
ing region.
(
yield of the reaction was 17%).
The structure was confirmed by infrared spectroscopy. FTIR
The C^N stretching band is observed in the case of compounds
ꢁ ꢁ1 ꢁ1
1
4 (2251 cm AreC^N, 2226 cm ReC^N), 5 (2218 cm ), 6
ꢁ1
ꢁ1
ꢁ1
spectra were recorded in range 4000e400 cm using KBr discs on
a Bruker Vertex 70 spectrometer.
In spectra of all examined compounds presented in Table 1, the
vibrations characteristic for pyrazoline derivatives (CeH aromatic,
CeH aliphatic, CeN, C]N) are observed.
(2211 cm ) and 7 (2228 cm ).
Compounds 6 and 8 contain a nitro group. The stretch bands Are
ꢁ
ꢁ
1
ꢁ1
2
NO are found 1500 cm (asymmetric), 1350 cm (symmetric) for
1
ꢁ1
compound 6 and 1498 cm (asymmetric) and 1327 cm (symmetric).
CN
CN
CN
NBS, AIBN
CCl4,reflux
KCN, EtOH, H2O
reflux, 1.5h
CN
Br
1
. PPh , benzene
3
EtOH, CH COONa
3
2
. CH ONa and
3
N
N
N
N
O
O
CN
NC
N
N
N
N
CN
Fig. 3. Steps of synthesis (E)-2-(2-(1-phenyl-4,5-dihydro-1H-pyrazol-3-yl)vinyl)benzonitrile (PY-oCN) e left panel, and (Z)-2-(1-cyano-2-(1-phenyl-4,5-dihydro-1H-pyrazol-3-yl)
vinyl)benzonitrile (PY-oCNCN) e right panel.

66
J. Mysliwiec et al. / Dyes and Pigments 102 (2014) 63e70
–O
–O
O
H SO ,HNO
H2SO4, H2O
reflux, 1h
2
4
3
N+
N+
5
-10°C
CN
O
CN
OH
O
EtOH, pip eridine
EtOH, piperidine
N
N
N
N
O
O
O–
N+
O
N+
O
O–
N
N
N
N
CN
Fig. 4. Steps of synthesis (E)-2-(4-nitrophenyl)-3-(1-phenyl-4,5-dihydro-1H-pyrazol-3-yl)acrylonitrile (PY-oCNNO2) e left panel, and (E)-3-(4-nitrostyryl)-1-phenyl-4,5-dihydro-
H-pyrazole (PY-pNO2) e right panel.
1
Table 1
1
231, 1164, 1124, 1112, 1074, 1037, 1002, 977, 959, 898, 851, 827,
The chemical structure of studied compounds.
774, 748, 692, 660, 527, 516, 505, 481, 403.
2
2
.4. Compound 7
IR (KBr)
(cmꢁ1): 3412, 3028, 2927, 2228, 1656, 1599, 1578, 1546,
n
1
1
6
531, 1500, 1456, 1421, 1374, 1350, 1315, 1299, 1288, 1222, 1183,
154, 1134, 1072, 1034, 1014, 954, 876, 855, 815, 751, 728, 691,
61, 616, 592, 546, 506, 460.
No.
Compound
R
1
R
2
R
3
.5. Compound 8
(cmꢁ1): 3402, 3080, 3043, 2956, 2908, 2879, 2815,
4
5
6
7
8
PY-oCNCN
PY-oCN
eCN
eH
eCN
eH
eH
eH
eNO
2
eH]C(CN)
eH
eCN
eCN
eH
eH
eNO
2
IR (KBr) n
PY-oCNNO
2
1616, 1599, 1589, 1534, 1498, 1473, 1454, 1437, 1421, 1401, 1351,
PirazFPHdiCN
2
1327, 1298, 1260, 1226, 1205, 1179, 1131, 1106, 1067, 1034, 1017,
PY-pNO
2
eH
9
6
96, 967, 946, 878, 871, 861, 849, 833, 758, 744, 723, 694, 688,
64, 645, 631, 535, 522, 506, 475, 450, 411.
The peaks in OeH stretching region are observed as well (4:
3
. Results and discussion
ꢁ ꢁ1 ꢁ1 ꢁ1
1
3
3
400 cm , 5: 3422 cm , 6: 3430 cm , 7: 3412 cm , and 8:
ꢁ1
402 cm ). It is due to stretching mode of OeH from water of
3.1. Quantum chemical calculations
crystallization.
The spectra and complete list of vibrations is presented below:
The quantum chemical calculations have been performed for
2
five pyrazoline derivatives (PY-oCN, PY-oCNNO , PY-oCNCN,
2.1. Compound 4
PirazFPHdiCN, PY-pNO ) using the Gaussian 09 software [12]. Ge-
2
ometry optimization and harmonic IR frequency calculations for
(cm 1): 3430, 3070, 2974, 2927, 2909, 2251, 2226,
ꢁ
IR (KBr)
2
1
7
n
compounds in the gas phase were carried out using DFT level of
theory with Becke’s three parameter exchange function and Leee
YangeParr correlation function functional (B3LYP) with 6-
311þþG(2d,2p) basis set without any symmetry restrictions.
Structures in dichloromethane (DCM) solutions were obtained us-
ing the Polarizable Continuum Model (PCM). For all optimized ge-
ometries the frequency analyses have been performed and stability
202, 1956, 1630, 1598, 1581, 1500 1484, 1454, 1445, 1410, 1359,
328, 1297, 1230, 1207, 1173, 1093, 1051, 963, 949, 882, 862, 809,
66, 752, 704, 691, 665, 631, 561, 453, 418.
2
.2. Compound 5
(cm 1): 3422, 3061, 2940, 2873, 2824, 2218,1653,1598,
ꢁ
IR (KBr)
n
of wave function has been checked. Calculations of lmax(maxima of
1
1
7
529, 1501, 1474, 1459, 1445, 1431, 1404, 1348, 1287, 1259, 1219,
150, 1129, 1070, 1034, 1011, 995, 962, 953, 874, 846, 773, 749,
27, 687, 661, 616, 604, 561, 527, 505, 479.
absorption) in the UVeVis spectrum were obtained using the TD-
DFT/B3LYP method with the same basis set and semi-empirical
Zerner’s Intermediate Neglect of Differential Overlap (ZINDO)
method. Optimized chemical structures in DCM solution of the five
2
.3. Compound 6
synthesized and studied trans isomers of PY-oCN (a), PY-oCNNO
b), PY-oCNCN (c), PirazFPHdiCN (d) and PY-pNO (e) are presented
below in Fig. 5. In Table 2 we present results of their calculated
dipole moments.
2
(
2
ꢁ
IR (KBr)
n
(cm 1): 3430, 3120, 3085, 2925, 2211, 1598, 1562, 1511,
1486, 1473, 1454, 1425, 1400, 1378, 1358, 1338, 1297, 1283, 1252,

J. Mysliwiec et al. / Dyes and Pigments 102 (2014) 63e70
67
Fig. 5. Optimized chemical structures in DCM solution of the synthesized trans isomers of PY-oCN (a), PY-oCNNO2 (b), PY-oCNCN (c), PirazFPHdiCN (d) and PY-pNO2 (e).
3
.2. Spectroscopy measurements
silica glass plates by simple drop-casting technique and dried for
h at room temperature. The thickness of the thin polymeric layers
amounted to 4 m. In Fig. 6a and b we show the normalized ab-
3
Prior to the amplified spontaneous emission measurements, the
m
emissive and absorptive properties of PRDs in tetrahydrofur-
an(THF)were studied. The photoluminescence measurements were
carried out using a Hitachi F-4500 fluorescence spectrophotometer
within the range of 350e800 nm at room temperature. The spectral
resolution was maintained at 1 nm for both excitation and emission
spectra. For the experimental UVeVIS spectroscopic measurements
we have prepared 0.004% solutions by weight of PRD in THF. For
amplified spontaneous emission measurements of dye properties
in polymer matrix we have used commercially available PMMA
sorption and emission luminescence spectra of the 0.004% PRD-THF
solutions, respectively. A broad luminescence band for all com-
pounds is observed within the range of 500 nme700 nm charac-
terized with 70e100 nm full width at half maximum (FWHM). The
excitation spectra are slightly broader, with maxima in the range of
420 nme540 nm. Maxima of fluorescence are observed for PY-oCN
2 2
at 506 nm, PY-oCNCN at 542 nm, PY-oCNNO at 587 nm, PY-pNO at
623 nm and PirazFPHdiCN at 674 nm which is related with the
molecular HOMO-LUMO gap and correlated with the values of
permanent molecular dipole moments of the studied compounds
(cf. Table 2).
For investigation of amplified spontaneous emission (ASE) we
have chosen two compounds with the highest calculated dipole
(
Sigma Aldrich, M
w
¼ 996 000) of 5% by weight dissolved in THF.
Then we have prepared 0.1% by weight solution of a PRD in THF and
mixed it with PMMA solution in order to obtain 2% PRD in PMMA
w/w in the dry mass. The PRD-PMMA solutions were applied onto
moments and absorption coefficients (at
l
¼ 532 nm excitation
wavelength) namely, PY-oCNNO and PirazFPHdiCN. To induce and
2
Table 2
measure the ASE phenomenon we have used an experimental set-
up which is schematically shown in Fig. 7.
Molecular dipole moments calculated for pyrazoline derivatives in gas phase as well
as in dichloromethane (DCM) solution.
For the sample excitation we used linearly polarized light of the
Compound
Dipole moment
Gas phase
m [D]
wavelength
l
¼ 532 nm, which was the second harmonic of a Q-
CH
2
Cl
2
solution
switched nanosecond neodymium doped yttrium aluminum
garnet (Nd:YAG) laser (6 ns pulse duration, 10 Hz maximum
repetition rate). The excitation light incident normally onto the
sample generated intense luminescence of the investigated film.
Light which was emitted from the edges of the sample was
collected by an optical fiber and analyzed with an Ocean Optics
PY-oCN
PY-oCNCN
PY-pNO
PY-oCNNO
PirazFPHdiCN
2.1
2.5
7.8
8.5
11.2
2.4
3.6
10.4
12.0
14.6
2
2

68
J. Mysliwiec et al. / Dyes and Pigments 102 (2014) 63e70
a) 1.2
a)4000
PY-oCN
3
6 mJ/cm
PY-oCNCN
PY-oCNNO2
33 mJ/cm
30 mJ/cm
20 mJ/cm
6 mJ/cm
1
0
0
0
0
0
.0
.8
.6
.4
.2
.0
PY-pNO2
3000
PY-oCNNO2
PirazFPHdiCN
2000
1000
0
3
00 350 400 450 500 550 600 650 700
500
550
600
650
700
750
800
Wavelength [nm]
Wavelength, λ [nm]
b) 40
b) 1.2
PY-oCNNO2
PY-oCN
PY-oCNCN
PY-oCNNO
PirazFPHdiCN
ρ =20mJ/cm
1
0
0
0
0
0
.0
.8
.6
.4
.2
.0
36
PY-pNO2
3
2
28
2
4
1
5
20
25
30
35
40
Energy density [mJ/cm ]
3
50 400 450 500 550 600 650 700 750 800
Wavelength, λ [nm]
Fig. 8. Luminescence spectrum changes for 2% PY-oCNNO
2
/PMMA sample a) excited
by the nanosecond pulsed laser, with characteristic signature of ASE and full width at
Fig. 6. Normalized absorption (a) and emission (b) spectra of the studied compounds
in 0.004% THF solutions.
half maximum (FWHM) changes, (b) as a function of excitation energy density.
2
r
th ¼ 20 mJ/cm e the threshold energy density for ASE process.
(
USB 2000) CCD array spectrometer coupled to a computer for data
acquisition. Fig. 8a shows luminescence spectra changes for 2% PY-
oCNNO /PMMA sample excited by the nanosecond pulsed laser
dominating the luminescence spectrum. Results of full width at half
maximum (FWHM) changes as a function of excitation energy
density are presented in Fig. 8b. For the reported PY-oCNNO /
2
PMMA sample, we could observe changes in luminescence band-
width from DlFWHM z 36 nm for the lower excitation energy
density and below the ASE threshold, down to DlFWHM z 25 nm.
2
with the different excitation energy densities. One can clearly see
the characteristic signature of ASE, i.e. significant narrowing of the
broad fluorescence spectrum to
a relatively narrow band
Fig. 7. Experimental set-up for the amplified spontaneous emission and photostability measurements.

J. Mysliwiec et al. / Dyes and Pigments 102 (2014) 63e70
69
From the plot shown in Fig. 8b, the threshold energy density for the
2
ASE process was estimated to be
r
th ¼ 20 mJ/cm .
Similar measurements were performed for the PirazFPHdiCN/
PMMA. Fig. 9a and b shows luminescence spectra changes of 2%
PirazFPHdiCN/PMMA sample excited by the nanosecond pulsed laser
in function of excitation energy density and results of full width at
half maximum (FWHM) as a function of excitation energy density.
For the reported 2% PirazFPHdiCN/PMMA sample, we could observe
changes in luminescence bandwidth from DlFWHM z 55 nm for the
low excitation energy density and below the ASE threshold, down to
2
DlFWHM z 20 nm at higher energy density of 25 mJ/cm . From the
plot shown in Fig. 9b, the threshold energy density for the ASE
2
process was estimated to
r
th ¼ 18 mJ/cm .
3.3. Nonlinear spectroscopy
Two-photon absorption measurements were performed using a
typical Z-scan setup shown in Fig. 10. The tunable excitation was
achieved by using the beam from a Quantronix Integra Ti:Sapphire
regenerative amplifier (output wavelength 800 nm, pulse duration
Fig. 10. Setup used for Z-scan measurements [13].
1
30 fs, repetition rate 1 kHz) to pump an optical parametric
manner along the z-direction, and a beam splitter (BS2) was used to
divide the beam after the sample to obtain the open and closed-
aperture signals in a single run. The open-aperture signal, sensi-
tive to nonlinear absorption, was obtained by focusing the splitted
part of the beam with a large diameter lens (L2) onto PD3, while the
closed-aperture signal, sensitive to both nonlinear absorption and
to intensity dependent refractive index changes was collected by
the PD2 photodiode, placed behind an aperture of reasonably small
transmittance. The beam power was adjusted in such a way that the
amplifier (OPA, a Quantronix Palitra). After suitable filtering to
reject unwanted wavelengths and attenuation a part of the Palitra
beam was used as a reference signal (detected by the PD1 photo-
diode), the main beam being directed through a lens (L1) to create a
focus in the middle of the Z-scan range (z ¼ 0). The measurements
were performed as the samples were moved in the stepwise
a) 4000
nonlinear phase shift
0
D4 for a 4 mm thick silica plate used as a
2
5 mJ/cm
24 mJ/cm
8 mJ/cm
16 mJ/cm
1 mJ/cm
PirazFPHdiCN
reference did not exceed 1.5 rad.
1
The wide wavelength tunability of the OPA provides the op-
portunity of obtaining extensive spectral information on nonlinear
refraction (related to the real part of the cubic hyperpolarizability
3
2
1
000
000
000
0
1
g
), not discussed by us here, and nonlinear absorption (related to
the imaginary part of and usually quantified as the two-photon
absorption cross section ), the current study being carried out
g
s
2
with a resolution of 25 nm, which is fair to follow the most
important spectral features, taking into account both broad ab-
sorption bands in the investigated substances and the natural line
width of a femtosecond laser. It should be noted that performing
the Z-scan measurements over a broad spectral range makes this
study much more thorough compared with the Z-scan experiments
conducted to date on this class of compounds, which were often
limited to a single excitation wavelength.
6
00
650
700
750
800
Wavelength [nm]
b) 60
All theoretical Z-scan calculations needed for fitting the exper-
imental curves were performed under the assumption of working
in the “thin” sample regime. For satisfying this condition, the
Rayleigh length was therefore always adjusted by selection of the
focal length of L1 and the input beam geometric parameters to be
larger than the sum of the cell path length (1 mm) and the thick-
ness of glass walls (1 mm each).
PirazFPHdiCN
5
4
3
2
1
0
0
0
0
0
2
ρth=18mJ/cm
in GM units (1 GM ¼ 1 ꢂ10ꢁ cm s photon
50
4
ꢁ1
)
The spectra of
for PY-oCNNO
s
2
2
and PirazFPHdiCN are shown in Fig. 11 together
with the corresponding linear absorption in THF solution. For both
compounds the TPA is the most significant in the short wavelength
region (
s
2
vs.
l peaking at around 700 nm and 650 nm for PY-
oCNNO
2
and PirazFPHdiCN, respectively), whereas the second peak
4
8
12
16
20
24
28
at around 850 nm is less intense. The latter peak is considerably
blue shifted compared with the positions of the peaks in one-
photon absorption spectra plotted against the doubled wave-
length. Such disagreement between the one-photon and two-
photon absorption spectra is typical for centrosymmetric com-
pounds (it results from the mutual exclusion selection rule) but is
2
Energy density [mJ/cm ]
Fig. 9. Luminescence spectrum changes for 2% PirazFPHdiCN/PMMA sample a) excited
by the nanosecond pulsed laser, with characteristic signature of ASE and full width at
half maximum (FWHM) changes (b) as
a function of excitation energy density.
2
r
th ¼ 18 mJ/cm e the threshold energy density for ASE process.

70
J. Mysliwiec et al. / Dyes and Pigments 102 (2014) 63e70
and two-photon absorption properties. The quantum chemical
DFT based calculations indicate that those which are substituted
with highly polar end-groups present large dipole moments what
could be beneficial for obtaining large ordering under electric
poling procedure of thin polymeric films containing these chro-
mophores for second order NLO properties. For two of such
compounds we performed measurements of the ASE phenome-
non. The dyes doped into the PMMA matrix exhibited the light
amplification property and spectral narrowing of their lumines-
cence spectra. The properties of these new dyes with respect to
the ASE threshold energy density are comparable with other
organic luminescent dyes in PMMA matrix [17e21]. Such prop-
erties together with their nonlinear optical properties showing
considerable two-photon absorption cross-sections make this
particular group of molecules attractive compounds for various
photonic applications.
Acknowledgments
This work was financially supported by Polish National Science
Centre, (Dec-2011/01/B/ST5/00773), Iuventus Plus grant IP2012
0
04172, the Foundation for Polish Science (under the “Welcome”
program) and Wroclaw University of Technology. A grant of com-
puter time from the Wroclaw Center for Networking and Super-
computing is gratefully acknowledged.
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. Conclusions
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