Synthesis, characterization and fluorescent property evaluation of 1,3,5-triaryl-2-pyrazolines

Article abstract of DOI:10.3390/molecules16097789

A series of 1,3,5-triaryl-2-pyrazolines was synthesized by dissolving the corresponding 4-alkoxychalcones in glacial acetic acid containing a few drops of concentrated hydrochloric acid. This step was followed by the addition of (3,4-dimethylphenyl) hydrazaine hydrochloride. Finally the target compounds were precipitated by pouring the reaction mixture onto crushed ice. The structures of the synthesized compounds were established by physicochemical and spectroscopic methods. The 1,3,5-triaryl-2-pyrazolines bearing homologous alkoxy groups were found to possess fluorescence properties in the blue region of the visible spectrum when irradiated with ultraviolet radiation. The fluorescent behavior of these compounds was studied by UV-Vis and emission spectroscopy, performed at room temperature.

Full text of DOI:10.3390/molecules16097789

Molecules 2011, 16, 7789-7802; doi:10.3390/molecules16097789
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Synthesis, Characterization and Fluorescent Property
Evaluation of 1,3,5-Triaryl-2-pyrazolines
Aurangzeb Hasan 1,*, Asghar Abbas 2 and Muhammed Nadeem Akhtar 3
1
Department of Chemistry, Faculty of Science, University of Malaya, Kuala Lumpur-50603,
Malaysia
2
Department of Chemistry, Faculty of Science, Quaid-i-Azam University, Islamabad 45320,
Pakistan
3
Laboratory of Natural Products, Institute of Bioscience, University Putra Malaysia,
Kuala Lumpur 43400, Malaysia
* Author to whom correspondence should be addressed; E-Mail: flavonoids@hotmail.com;
Tel.: +603-7967-5165; Fax: +603-7967-4193.
Received: 12 July 2011; in revised form: 3 August 2011 / Accepted: 10 August 2011 /
Published: 13 September 2011
Abstract: A series of 1,3,5-triaryl-2-pyrazolines was synthesized by dissolving the
corresponding 4-alkoxychalcones in glacial acetic acid containing a few drops of
concentrated hydrochloric acid. This step was followed by the addition of
(3,4-dimethylphenyl) hydrazaine hydrochloride. Finally the target compounds were
precipitated by pouring the reaction mixture onto crushed ice. The structures of the
synthesized compounds were established by physicochemical and spectroscopic methods.
The 1,3,5-triaryl-2-pyrazolines bearing homologous alkoxy groups were found to possess
fluorescence properties in the blue region of the visible spectrum when irradiated with
ultraviolet radiation. The fluorescent behavior of these compounds was studied by UV-Vis
and emission spectroscopy, performed at room temperature.
Keywords: triarylpyrazolines; alkoxychalcones; synthesis; fluorescence

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1. Introduction
Due to the interesting properties of substituted pyrazolines as biological agents and optical
materials, considerable attention has been focused on the study of this class of compounds. They have
pharmaceutical importance as these can be effectively utilized as potential therapeutic agents against a
variety of major ailments, due to their antibacterial and antifungal [1], antimicrobial [2,3] cytotoxic [4]
anticancer [5] anti-inflammatory [6] and platelet aggregation inhibiting [7] properties. 1,3,5-Triaryl-2-
pyrazolines constitute an important class of conjugated nitrogen-containing fluorescent compounds
emitting a blue fluorescence with high quantum yield [8-11] and have been found to act as hole
transporting media in photoconductive as well as emitting materials [12-16] and in organic
electroluminescent devices (OELDs) [17-20]. Organic electroluminescent devices find potential use in
various displays [21-23], and have many advantages over inorganic ones, such as high luminous
efficiency, low cost, wide range of emission colors via specialized molecular design of organic
compounds, and easy processing. 1,3,5-Triaryl-2-pyrazolines are also utilized as optical brightening
agents for textiles, fabrics, plastics, papers [24] fluorescent switches [25] and as fluorescent probes in
many chemosensors [26].
In this work we report the synthesis of some new 1,3,5-triaryl-2-pyrazolines 1h-12h by converting
benzaldehyde into the corresponding 4-alkoxybenzaldehydes 1a-12a by treatment with appropriate
alkyl halides. The 4-alkoxybenzaldehydes yielded 4-alkoxychalcones 1b-12b on reaction with
acetophenones in the presence of sodium hydroxide, water and ethanol. The target compounds were
finally obtained by the reaction of 4-alkoxychalcones with (3,4-dimethylphenyl) hydrazaine
hydrochloride (Scheme 1).
Scheme 1. Synthesis of 1,3,5-triaryl-2-pyrazolines.
O
O
K CO MEK
Refl ux 5- 8 hour s
H
H
2
3
+
R- Br
O
OH
+
OR
1a- 12a
O
O
Na OH/ H OC H OH
2
5
Stirri ng 5- 82hour s
CH
H
3
OR
1b- 12b
OR
CH
3
CH
3
Gl aci al CH CO H
3
2
CH
3
Conc. HCl, Refl ux
5- 8 hours
H N
N
H
CH
3
2
2
1
N
N
H
3
5
H
4
H
OR
1h- 12h
R= CH, C H, C H, C H, C H , C H
3
3
7
9
5
11
6
C H , 2C5H , C H 4, C H , C H1,3 C H
7
15
8
17
9
19
10 21
11 23
12 25
2. Results and Discussion
Twelve alkoxybenzaldehydes were synthesized by refluxing 4-hydroxybenzaldehyde with twelve
alkyl bromides (CH3-Br – C12H25-Br) in the presence of potassium carbonate and butanone. The

Molecules 2011, 16
7791
resulting 4-alkoxybenzaldehydes 1a-12a were reacted with acetophenone in the presence of sodium
hydroxide and ethanol to yield corresponding 4-alkoxychalcones 1b-12b. 4-Alkoxychalcones were
dissolved in glacial acetic acid containing a few drops of concentrated hydrochloric acid. This step was
followed by the addition of (3,4-dimethylphenyl)hydrazaine hydrochloride. Finally the target
compounds 1h-12h were precipitated by pouring the reaction mixture onto crushed ice as outlined in
Scheme 1.
The FT−IR spectra of synthesized 4-alkoxybenzaldehydes 1a−12a showed two strong bands at
stretching frequencies in the range of 1260–1245 cm−1 and 1050–1035 cm−1, which are characteristic
of Ar−O−R groups. No peak appeared in the range of 3400–3300 cm−1, which indicated the
disappearance of the –OH group of the 4-hydroxybenzaldehyde. A strong carbonyl group (C=O) band
appeared in the 1700–1660 cm−1 range.
The 4-alkoxychalcones 1b−12b were synthesized by base catalysed Claisen−Schmidt aldol
condensation and were obtained as pale yellow crystalline solids. The FT-IR spectra of all the
synthesized 4-alkoxychalcones showed absorption bands in the range of 1700–1675 cm−1 for carbonyl
groups (C=O) and 1644–1617 cm−1 for olefinic double bonds (−CH=CH−). In addition the two strong
characteristic Ar−O−R group bands were observed.
Two prominent doublets δ = 7.37–7.43 ppm, J = 15.6 Hz and δ =7.80–7.81 ppm, J = 15.6 Hz
1
appeared in the H-NMR spectra of 4-alkoxychalcones, which corresponds to the α- and β-hydrogen
atoms, respectively, attached to the olefinic double bond of the α,β-unsaturated carbonyl system.
The chemical shifts of doublets corresponding to the α-hydrogen atoms were found to be
7.37–7.43 ppm, with coupling constants of 15.6 Hz. The chemical shifts of doublets corresponding to
the β-hydrogen atoms appeared at 7.80–7.81 ppm, with coupling constants of 15.6 Hz. The large
coupling constant values confirmed that the 4-alkoxychalcones possess trans (E)-configurations. The
aromatic protons of the 4-alkoxychalcones appeared downfield between 6.90 and 8.00 ppm in the
aromatic region of the spectrum. The methylene protons (Ar−O−CH2−) of the alkoxy group adjacent
to the oxygen atom appeared as a triplet. The chemical shifts of these protons were found between
3.90–4.10 ppm for all 4-alkoxychalcones, confirming the presence of ether (Ar−O−R) linkages. The
chemical shifts of other aliphatic protons of the alkoxy group were found in the range of 0−2.0 ppm
according to their respective splitting pattern.
The 13C-NMR of 4-alkoxychalcones 1b−12b revealed carbonyl carbon peaks at 187–192 ppm.
Aromatic carbon atom chemical shifts appeared in the range of 112–140 ppm. The aromatic carbon
resonances of the compounds were assigned on the basis of signal intensities and comparison with the
reported values. The Cα and Cβ of the 4-alkoxychalcones were observed in the range of 118–121 ppm
and 144–146 ppm, respectively. The methylene carbons attached to the oxygen atom of aromatic ring
(ArO−CH2−) were found in the range of 60–70 ppm.
Gas chromatograms (GC) displayed single peaks with different retention times for every compound,
confirming the purity of the compounds. Mass Spectrometry (MS) was used to determine the
molecular weights of these compounds. A molecular ion peak (M+) was observed for the
4-alkoxychalcones 1b−12b, in their respective mass spectra. The fragmentation pattern of synthesized
compounds matched the typical pattern of chalcone fragmentation, further confirming the structures of
the compounds.

Molecules 2011, 16
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The FT-IR spectra of the 1,3,5-triaryl-2-pyrazoline compounds 1h−12h, showed absorption bands
in the range of 1690–1640 cm−1 confirming the presence of carbon-nitrogen (C=N) double bonds, and
at 1350–1000 cm−1 for carbon-nitrogen single bonds (C-N). A strong band for arylcarbon-alkylcarbon
(Ar-R) appeared in the 1500–1490 cm−1 range. Two strong bands at stretching frequencies in the range
of 1260–1245 cm−1 and 1050–1035 cm−1 were also observed, which confirmed the presence of
Ar−O−R groups.
The formation of the five membered pyrazoline cycle was confirmed by the presence of two
1
methylene protons (Ha and Hb) and one methine proton (Hx) for the pyrazoline ring. The H-NMR
spectra of the compounds 1h−12h showed three doublet of doublets corresponding to the Ha, Hb and
Hx atoms of the pyrazoline ring, respectively.
Figure 1. Mass fragmentation pattern for 1-(3,4-dimethylphenyl)-3-phenyl-5-(4-
hexyloxyphenyl)-2-pyrazoline (6h).
N
NH
CH3
CH3
OC6H13
m/z = 178
C6H13
H
H
OH
m/z = 238
N
H
N
N
NH
H
PhOC6H13
N
NH
H
H
H
m/z = 325
OC6H13
H
m/z = 321
m/z = 145
N
NH
H
H3C
H3C
CH3
CH3
H
OC6H13
CH3
CH3
N
H
N
H
H
m/z = 249
m/z = 222
N
H
N
H
OC6H13
H
CH3
CH3
OC6H13
+
m/z = 426
NH
[M ]
N
N
m/z = 77
CH3
CH3
N
H
H
C4H9
CH3
m/z = 104
C6H13
CH3
O
Ph
CH3
N
CH3
OC6H13
N
N
H
H
H
H
H
H
O
m/z = 238
.
OC6H13
m/z = 323
m/z = 222
+
H3C
H3C
CH3
H
CH3
OC6H13
N
H
N
CH3
H
H
CH3
.
H
m/z = 239
+ .
H
OH
N
m/z = 119
H
H3C
H3C
H
- HCN
N
m/z = 77
m/z = 222
OH
H
H
H
H
OH
H
m/z = 91
m/z = 120
m/z = 103
H
H
O
m/z = 119

Molecules 2011, 16
7793
The chemical shifts of a doublet of doublets for Ha of the compounds 1h−12h were observed at
3.11 ppm, with coupling constants in the range of 7.5–7.8 Hz and 16.8–17.1 Hz. The chemical shifts of
a doublet of doublets for Hb of the compounds 1h−12h were observed at 3.80 ppm with coupling
constants in the range of 12.0–12.6 Hz and 16.8–17.1 Hz. The chemical shifts of a doublet of doublets
for Hx of the compounds 1h–12h were observed at 5.20 ppm, with coupling constants in the range of
7.0–7.8, 12.0–12.6 Hz. The aromatic protons appeared downfield between 6.70 and 8.00 ppm with
multiplicity according to the aromatic ring substitution pattern. The methylene protons (Ar−O−CH2−)
of the alkoxy group adjacent to the oxygen atom appeared as a triplet. The chemical shifts for these
protons are found around 3.90–4.10 ppm for all pyrazolines, confirming the presence of ether
(Ar−O−C−) linkages. The chemical shifts of other aliphatic protons of the alkoxy groups were
observed in the range of 0–2.0 ppm. The protons of methyl groups at the 3 and 4 positions of the
aromatic ring directly attached to the nitrogen of the pyrazoline cycle in compounds 1h−12h appeared
as singlet in the range of 2.20–2.22 ppm and 2.16–2.17 ppm, respectively.
The proton-decoupled 13C-NMR spectra for all the synthesized 2-pyrazolines 1h−12h were
recorded at 75 MHz in CDCl3 and peak assignments were made on the basis of calculated and reported
values [27,28]. The aromatic carbon resonances of the compounds are assigned on the basis of signal
intensities and comparing with the calculated values. The methylene carbons attached to the oxygen
atom of aromatic ring (ArO−CH2−) were observed around 60–70 ppm. In compounds 1h−12h, the
methylene carbon (−CH2−) and methine carbon (−CH−) of the five membered pyrazoline rings were
assigned chemical shift values in the range of 41–44 ppm and 55–65 ppm, respectively.
A molecular ion peak (M+) which was also the base peak was observed for all the synthesized
2-pyrazolines in their respective mass spectra. The fragmentation pattern of the synthesized compounds
(exemplified by that of compound 6h) matched the typical pattern of pyrazoline fragmentation [29]
(Figure 1), confirming the structure of compounds. On the basis of the combined physical and spectral
data, compounds 1,3,5-triaryl-2-pyrazolines were assigned the structures shown in Figure 2.
Figure 2. Structures of 1,3,5-triaryl-2-pyrazolines.
CH
3
CH
3
2
1
N
N
H
3
5
H
4
H
OR
1h- 12h
R= CH, C H, C H, C H, C H , C H
3
3
7
9
5
11
6
C H , 2C5H , C H4, C10 H , C H1,3 C12 H
7
15
8
17
9
19
21
11 23
25
The synthesized 1,3,5-triaryl-2-pyrazolines 1h−12h bearing homologous alkoxy groups were found
to possess fluorescence properties in the blue region of the visible spectrum when irradiated with ultra-
violet radiation. The fluorescence behavior of these compounds was studied by UV-Vis and emission
spectroscopy performed at room temperature.

Molecules 2011, 16
7794
The UV-Vis spectra (Figure 3) of 1,3,5-triaryl-2-pyrazolines 1h−12h exhibit an intense absorption
band which is attributed to the π − π* transition of the conjugated backbone. In case of absorption
spectra of compounds 1h−12h, the absorption maxima (λmaxabs) wavelength was observed in the range
of 367−377 nm (Table 1) with the corresponding absorbance. The absorption spectra of the
1,3,5-triaryl-2-pyrazolines 1h−12h showed that the spectral shapes are very similar because all these
compounds possess the same (1,3,5-triaryl)-2-pyrazoline central nucleus. The difference of absorption
wavelengths and absorption intensities is due to the effect of the presence of 4-alkoxyphenyl groups at
the 5-position of the 2-pyrazoline moiety. In the emission spectra of 2-pyrazolines 1h−12h (Figure 3)
it was observed that all these compounds exhibited blue emission with variable emission intensity at
constant concentration. The emission maxima (λmaxem) wavelengths of all the synthesized compounds
lie in the blue region of visible spectrum and therefore show blue fluorescence.
Figure 3. The UV-Vis absorption and emission spectra of 1h-12h.
Table 1. Absorption and fluorescence wavelengths of compounds 1h−12h.
Compound
γmaxabs nm
377
γmaxem (nm)
469
1h
2h
371
459
3h
371
460
4h
367
459
5h
367
460
6h
371
460
7h
371
460
8h
372
462
9h
370
461
10h
11h
12h
370
371
370
460
459
459
The geometry of the 1,3,5-triaryl-2-pyrazoline nucleus has a configuration such that the aryl groups
at the 1 and 3 positions are in conjugation with the pyrazoline ring. However, the aryl group at position
5 is not part of the conjugated moiety of the 2-pyrazoline nucleus. The alkoxy substitution at the aryl

Molecules 2011, 16
7795
group at the 5 position can be expected to have some effect on the physico-chemical properties due to
its electron donating nature. From emission spectra of the reported compounds, it can be concluded
that the introduction of electron-donating 4-alkoxyphenyl groups at the 5-position strongly affects the
emission intensity without causing any major blue- or red-shift in the emission wavelength.
3. Experimental
3.1. General
Melting points of the synthesized compounds were recorded on a MFB-595-101M Gallenkamp
digital melting point apparatus in open-end capillary tubes and are uncorrected. Thin layer
chromatography was carried out on pre-coated silica gel plates (0.2 mm, E. Merck, 20 × 20 cm,
60F254). FT-IR spectra were recorded on a Bio-Red Merlin Spectrophotometer using KBr discs.
1H- NMR (300 MHz) and 13C-NMR (75.43 MHz) spectra were recorded on a Bruker AM-300
spectrometer in DMSO and CDCl3 solutions using TMS as internal standard. EIMS were recorded on
a GCMS Agilent VG: 70 SE Mass Spectrometer. Purity of the synthesized compounds was also
monitored by the same instrument.
3.2. Procedure for the Preparation of 4-Alkoxybenzaldehydes 1a–12a
4-Hydroxybenzaldehyde (0.1 mole, 12.2 g) and anhydrous K2CO3 (0.1 mole, 13.8 g) were added to
2-butanone (150 mL) in a 250 mL two neck round bottom flask. The reaction mixture was heated
gently at 60–65 °C for 30 minutes, then 1-bromoalkane (Br-CH3 to Br-C12H25, 0.1 mole) was added
drop wise and the reaction mixture was heated to reflux for 5–8 hours. The progress of the reaction
was monitored by TLC. After completion of the reaction, the solvent was evaporated under reduced
pressure on a rotary evaporator. The reaction mixture was transferred to a 1 L separatory funnel and
diethyl ether (250 mL) was added. The K2CO3 was removed by washing the reaction mixture
repeatedly with distilled water. Traces of unreacted 4-hydroxybenzaldehyde were removed by washing
the ether layer with 5% NaOH solution (25 mL). The ether layer was washed with distilled water till it
became neutral to pH paper and was dried on anhydrous MgSO4. The diethyl ether was evaporated to
give the 4-alkoxybenzaldehydes 1a−12a as transparent pale yellow liquids.
3.2. Procedure for the Preparation of 4-Alkoxychalcones 1b–12b
In a 500 mL beaker acetophenone (0.1 mole, 12.0 g) was dissolved in ethanol (20 mL). To this
mixture, ice cold 10% NaOH solution (200 mL) was added and the mixture stirred for 30 minutes at
room temperature. Then 4-alkoxybenzaldehyde 1a–12a (0.1 mole) was added to the reaction mixture
that was further stirred for 5–8 hours till pale yellow precipitates appeared. Crushed ice was added to
the solid mass and the reaction mixture was neutralized with dilute HCl. The products 1b–12b were
obtained as yellow solids, which were filtered and recrystallized from ethanol.

Molecules 2011, 16
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3.3. Procedure for the Preparation of 1-(3,4-Dimethylphenyl)-3-Phenyl-5-(4-Alkoxyphenyl)-2-
Pyrazolines 1h–12h
Synthesis of 1-(3,4-dimethylphenyl)-3-phenyl-5-(4-alkoxyphenyl)-2-pyrazolines was carried out
by dissolving the 4-alkoxychalcones 1b–12b (0.01 moles) in glacial acetic acid (25 mL) containing
a few drops of concentrated hydrochloric acid and were heated to 60–65 °C for 30 minutes.
(3,4-Dimethylphenyl)hydrazaine hydrochloride (0.02 mole, 3.45 g) was added to the reaction flask
and the resulting mixture heated to reflux for 5–8 hours. The reaction mixture was cooled to room
temperature and poured onto crushed ice to obtain the products. The precipitates obtained were
filtered, washed with distilled water and dried in a desicator and were purified by column
chromatography using silica gel and petroleum ether/ethyl acetate (4:1) as mobile phase. Purification
of all the synthesized compounds was achieved by recrystallization and purity of each compound was
monitored by thin layer (tlc) and gas (gc) chromatography.
1-(3,4-Dimethylphenyl)-3-phenyl-5-(4-methoxyphenyl)-2-pyrazoline (1h). 3-(4-Methoxyphenyl)-1-
phenylprop-2-en-1-one (2.38 g, 10 mmol) and (3,4-dimethylphenyl) hydrazaine (2.72 g, 20 mmol)
were reacted according to the general procedure. Color pale yellow solid; yield 80% (1.90 g); m.p.
120–124 °C; Rf = 0.88 (petroleum ether-ethyl acetate, 4:1), FT-IR (KBr, cm−1): 1682, 1292, 1497,
1257, 1047, 1H-NMR (300 MHz, CDCl3) δ 2.17 (s, 3H, N-Ar-4-CH3), 2.22 (s, 3H, N-Ar-3-CH3), 3.11
(dd, 1H, J = 7.8, 17.1 Hz, Ha), 3.75 (s, 3H, -O-CH3), 3.80 (dd, 1H, J = 12.3, 16.8 Hz, Hb), 5.20 (dd,
1H, J = 7.5, 12.3 Hz, Hx), 6.71 (d, 1H, J = 8.4 Hz, N-ArHh), 6.87 (d, 2H, J = 8.7 Hz, ArHc=c'), 6.93
(d, 1H, J = 8.4 Hz, N-ArHi), 7.06 (s, 1H, N-ArHj), 7.27 (d, 2H, J = 8.7 Hz, ArHd=d'), 7.33−7.43 (m,
13
3H, ArHf=f', g), 7.74(d, 2H, J = 8.4 Hz, ArHe=e'), C-NMR (75 MHz, CDCl3) δ 18.8, 20.2, 43.5,
55.2, 64.2, 110.7, 114.4 (2C), 115.1, 125.6 (2C), 127.0 (2C), 128.3, 128.5 (2C), 129.8, 132.9, 134.9,
137.0, 143.1, 146.1, 158.8, 162.6 EIMS: m/z 356 (M+, base peak). Anal. Calcd. For C24H24N2O (Mol.
Wt. 356): C, 80.87; H, 6.79; N, 7.86; Found: C, 80.81; H, 6.73; N, 7.92%.
1-(3,4-Dimethylphenyl)-3-phenyl-5-(4-ethoxyphenyl)-2-pyrazoline (2h). 3-(4-Ethoxyphenyl)-1-phenyl-
prop-2-en-1-one (2.52 g, 10 mmol) and (3,4-dimethylphenyl) hydrazaine (2.72 g, 20 mmol) were
reacted according to the general procedure. Color pale yellow solid; yield 85% (2.14 g); m.p. 102–106 °C;
Rf = 0.85 (petroleum ether-ethyl acetate, 4:1), FT-IR (KBr, cm−1): 1685, 1297, 1495, 1255, 1043,
1H-NMR (300 MHz, CDCl3) δ 1.42 (t, 3H, J = 7.0 Hz, −O−CH2−CH3), 2.17 (s, 3H, N- Ar-4-CH3),
2.22 (s, 3H, N-Ar-3-CH3), 3.11 (dd, 1H, J = 7.8, 17.1 Hz, Ha), 3.80 (dd, 1H, J = 12.3, 16.8 Hz, Hb),
4.02 (q, 2H, J = 7.2 Hz, −O−CH2−), 5.20 (dd, 1H, J = 7.5, 12.3 Hz, Hx), 6.72 (d, 1H, J = 8.4 Hz, N-ArHh),
6.87 (d, 2H, J = 8.7 Hz, ArHc=c’), 6.93 (d, 1H, J = 8.4 Hz, N- ArHi), 7.06 (s, 1H, N-ArHj), 7.25 (d, 2H,
13
J = 8.7 Hz, ArHd=d’), 7.31-7.43 (m, 3H, ArHf=f’, g), 7.75(d, 2H, J = 8.4 Hz, ArHe=e’), C-NMR (75
MHz, CDCl3) δ 14.8, 18.8, 20.2, 43.5, 63.4, 64.3, 110.7, 114.9, 115.1, 125.6 (2C), 127.0 (2C), 127.1,
128.3, 128.5, 129.8, 133.0, 134.8, 137.4, 143.2, 146.1, 158.2, EIMS: m/z 370 (M+, base peak). Anal.
Calcd. For C25H26N2O (Mol. Wt. 370): C, 81.05; H, 7.07; N, 7.56; Found: C, 81.01; H, 7.02; N, 7.64%.
1-(3,4-Dimethylphenyl)-3-phenyl-5-(4-propyloxyphenyl)-2-pyrazoline (3h). 3-(4-Propyloxyphenyl)-1-
phenylprop-2-en-1-one (2.66 g, 10 mmol) and (3,4-dimethylphenyl) hydrazaine (2.72 g; 20 mmol)
were reacted according to the general procedure. Color pale yellow solid; yield 81% (2.15 g); m.p.

Molecules 2011, 16
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126–130 °C; Rf = 0.87 (petroleum ether-ethyl acetate, 4:1), FT-IR (KBr, cm−1): 1687, 1299, 1493,
1254, 1042, 1H-NMR (300 MHz, CDCl3) δ 1.04 (t, 3H, J = 7.2 Hz, −O−CH2−CH2−CH3), 1.81 (sextet,
2H, J = 7.2 Hz, −O−CH2−CH2−CH3), 2.17 (s, 3H, N-Ar-4-CH3), 2.22 (s, 3H, N-Ar-3-CH3), 3.11 (dd,
1H, J = 7.5, 16.8 Hz, Ha), 3.80 (dd, 1H, J = 12.3, 16.8 Hz, Hb), 3.90 (t, 2H, J = 6.6 Hz, −O−CH2−),
5.20 (dd, 1H, J = 7.5, 12.3 Hz, Hx), 6.72 (d, 1H, J = 8.4 Hz, N-ArHh), 6.87 (d, 2H, J = 8.7 Hz,
ArHc=c'), 6.93 (d, 1H, J = 8.4 Hz, N-ArHi), 7.06 (s, 1H, N-ArHj), 7.25 (d, 2H, J = 8.7 Hz, ArHd=d'),
13
7.33-7.43 (m, 3H, ArHf= f', g), 7.74(d, 2H, J = 8.4 Hz, ArHe=e'); C-NMR (75 MHz, CDCl3) δ 10.5,
18.8, 20.2, 22.6, 43.6, 64.3, 69.4, 110.7, 114.9 (2C), 115.1, 125.6 (2C), 127.0 (2C), 127.1, 128.3, 128.5
(2C), 129.8, 133.0, 134.7, 137.0, 143.1, 146.1, 158.4, EIMS: m/z 384 (M+, base peak). Anal. Calcd.
For C26H28N2O (Mol. Wt. 384): C, 81.21; H, 7.34; N, 7.29; Found: C, 81.16; H, 7.31; N, 7.37%.
1-(3,4-Dimethylphenyl)-3-phenyl-5-(4-butyloxyphenyl)-2-pyrazoline (4h). 3-(4-Butyloxyphenyl)-1-
phenylprop-2-en-1-one (2.80 g, 10 mmol) and (3,4-dimethylphenyl) hydrazaine (2.72 g, 20 mmol)
were reacted according to the general procedure. Color pale yellow solid; yield 86% (2.40 g); m.p.
122–125 °C; Rf = 0.87 (petroleum ether-ethyl acetate, 4:1), FT-IR (KBr, cm−1): 1680, 1294, 1494,
1
1258, 1052, H-NMR (300 MHz, CDCl3) δ 0.99 (t, 3H, J = 7.2 Hz, −O−(CH2)3−CH3), 1.50 (sextet,
2H, J = 7.8 Hz, −O−CH2−CH2−CH2− CH3), 1.77 (qn, 2H, J = 8.0 Hz, −O−CH2−CH2−C2H5), 2.17 (s,
3H, N-Ar-4-CH3), 2.22 (s, 3H, N-Ar-3-CH3), 3.11 (dd, 1H, J = 7.5, 16.8 Hz, Ha), 3.80 (dd, 1H, J = 12.3,
16.8 Hz, Hb), 3.95 (t, 2H, J = 6.6 Hz, −O−CH2−), 5.20 (dd, 1H, J = 7.5, 12.3 Hz, Hx), 6.72 (d, 1H,
J = 8.0 Hz, N-ArHh), 6.87 (d, 2H, J = 8.7 Hz, ArHc=c'), 6.93 (d, 1H, J = 8.1 Hz, N-ArHi), 7.06 (s, 1H,
N-ArHj), 7.25 (d, 2H, J = 8.7 Hz, ArHd=d'), 7.33-7.43 (m, 3H, ArHf=f', g), 7.75(d, 2H, J = 8.4 Hz,
13
ArHe=e'); C-NMR (75 MHz, CDCl3) δ 13.9, 18.8, 19.2, 20.2, 31.3, 43.60, 64.3, 67.6, 110.7, 114.9
(2C), 115.1, 125.6 (2C), 127.0 (2C), 127.1, 128.3, 128.5 (2C), 129.8, 133.0, 134.7, 137.0, 143.1, 146.1,
158.4; EIMS: m/z 398 (M+, base peak). Anal. Calcd. For C27H30N2O (Mol. Wt. 398): C, 81.37; H,
7.59; N, 7.03; Found: C, 81.31; H, 7.55; N, 7.13%.
1-(3,4-Dimethylphenyl)-3-phenyl-5-(4-pentyloxyphenyl)-2-pyrazoline (5h). 3-(4-Pentyloxyphenyl)-1-
phenylprop-2-en-1-one (2.94 g, 10 mmol) and (3,4-dimethylphenyl) hydrazaine (2.72 g, 20 mmol)
were reacted according to the general procedure. Color pale yellow solid; yield 84% (2.46 g); m.p.
121–125 °C; Rf = 0.89 (petroleum ether-ethyl acetate, 4:1), FT-IR (KBr, cm−1): 1686, 1296, 1491,
1256, 1054, 1H-NMR (300 MHz, CDCl3) δ 0.94 (t, 3H, J = 7.2 Hz, −O−(CH2)4−CH3), 1.38−1.46 (m,
−O−CH2−CH2−(CH2)2− CH3), 1.78 (qn, 2H, J = 7.2 Hz, −O−CH2−CH2−C3H7), 2.17 (s, 3H, N-Ar-4-
CH3), 2.22 (s, 3H, N-Ar-3-CH3) , 3.11 (dd, 1H, J = 7.8, 17.1 Hz, Ha), 3.80 (dd, 1H, J = 12.3, 17.1 Hz,
Hb), 3.94 (t, 2H, J = 6.6 Hz, −O−CH2−), 5.20 (dd, 1H, J = 7.5, 12.3 Hz, Hx), 6.72 (d, 1H, J = 8.1 Hz,
N-ArHh), 6.86 (d, 2H, J = 8.7 Hz, ArHc=c'), 6.93 (d, 1H, J = 8.1 Hz, N-ArHi), 7.06 (s, 1H, N-ArHj),
7.25 (d, 2H, J = 8.7 Hz, ArHd=d'), 7.32-7.43 (m, 3H, ArHf=f', g), 7.74(d, 2H, J = 8.1 Hz, ArHe=e');
13C-NMR (75 MHz, CDCl3) δ 14.0, 18.8, 20.2, 22.4, 28.2, 28.9, 43.6, 64.3, 67.9, 110.7, 114.9, 115.1,
125.6, 127.0, 127.1, 128.3, 128.5, 129.8, 133.0, 134.7, 137.0, 143.1, 146.1, 158.4; EIMS: m/z 412 (M+,
base peak). Anal. Calcd. For C28H32N2O (Mol. Wt. 412): C, 81.51; H, 7.82; N, 6.79; Found: C, 81.48;
H, 7.79; N, 6.85%.

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1-(3,4-Dimethylphenyl)-3-phenyl-5-(4-hexyloxyphenyl)-2-pyrazoline (6h). 3-(4-Hexyloxyphenyl)-1-
phenylprop-2-en-1-one (3.08 g, 10 mmol) and (3,4-dimethylphenyl) hydrazaine (2.72 g, 20 mmol)
were reacted according to the general procedure. Color pale yellow solid; yield 87% (2.67 g); m.p.
88–93 °C Rf = 0.87 (petroleum ether-ethyl acetate, 4:1), FT- IR (KBr, cm−1): 1679, 1292, 1497, 1258,
1
1048, H-NMR (300 MHz, CDCl3) δ 0.92 (t, 3H, J = 7.2 Hz, −O−(CH2)5−CH3), 1.32−1.48 (m, 6H,
−O−CH2−CH2−(CH2)3− CH3), 1.78 (qn, 2H, J = 7.2 Hz, −O−CH2−CH2−C4H9), 2.16 (s, 3H, N-Ar-4-
CH3), 2.22 (s, 3H, N-Ar-3-CH3), 3.11 (dd, 1H, J = 7.5, 16.8 Hz, Ha), 3.80 (dd, 1H, J = 12.3, 17.1 Hz,
Hb), 3.93 (t, 2H, J = 6.6 Hz, −O−CH2−), 5.20 (dd, 1H, J = 7.0, 12.0 Hz, Hx), 6.71 (d, 1H, J = 8.1 Hz,
N- ArHh), 6.86 (d, 2H, J = 8.7 Hz, ArHc=c'), 6.93 (d, 1H, J = 8.1 Hz, N-ArHi), 7.06 (s, 1H, N-ArHj),
7.25 (d, 2H, J = 8.7 Hz, ArHd=d'), 7.32-7.43 (m, 3H, ArHf=f', g), 7.74(d, 2H, J = 8.1 Hz, ArHe=e');
13C-NMR (75 MHz, CDCl3) δ 14.0, 18.8, 20.2, 22.6, 25.7, 29.2, 31.6, 43.6, 64.3, 68.0, 110.7, 114.9,
115.1, 125.6, 127.0, 127.1, 128.3, 128.5, 129.8, 133.0, 134.7, 137.0, 143.1, 146.1, 158.4; EIMS: m/z
426 (M+, base peak). Anal. Calcd. For C29H34N2O (Mol. Wt. 426): C, 81.65; H, 8.03; N, 6.57; Found:
C, 81.65; H, 8.03; N, 6.57%.
1-(3, 4-Dimethylphenyl)-3-phenyl-5-(4-heptyloxyphenyl)-2-pyrazoline (7h). 3-(4-Heptyloxyphenyl)-1-
phenylprop-2-en-1-one (3.22 g, 10 mmol) and (3,4-dimethylphenyl) hydrazaine (2.72 g, 20 mmol)
were reacted according to the general procedure. Color pale yellow solid; yield 83% (2.67 g); m.p.
93–97 °C; Rf = 0.85 (petroleum ether-ethyl acetate, 4:1), FT-IR (KBr, cm−1): 1677, 1294, 1488, 1257,
1
1043, H-NMR (300 MHz, CDCl3) δ 0.91 (t, 3H, J = 7.2 Hz, −O−(CH2)6−CH3), 1.31−1.48 (m, 8H,
−O−CH2−CH2−(CH2)4− CH3), 1.77 (qn, 2H, J = 7.8 Hz, −O−CH2−CH2−C5H11), 2.16 (s, 3H, N-Ar-4-
CH3), 2.21 (s, 3H, N-Ar-3-CH3), 3.11 (dd, 1H, J = 7.8, 17.1 Hz, Ha), 3.80 (dd, 1H, J = 12.3, 17.1 Hz,
Hb), 3.93 (t, 2H, J = 6.6 Hz, −O−CH2−), 5.20 (dd, 1H, J = 7.5, 12.3 Hz, Hx), 6.71 (d, 1H, J = 8.4 Hz,
N-ArHh), 6.86 (d, 2H, J = 8.7 Hz, ArHc=c'), 6.92 (d, 1H, J = 8.1 Hz, N-ArHi), 7.05 (s, 1H, N-ArHj),
7.24 (d, 2H, J = 8.7 Hz, ArHd=d'), 7.32-7.42 (m, 3H, ArHf=f', g), 7.74(d, 2H, J = 8.1 Hz, ArHe=e');
13C-NMR (75 MHz, CDCl3) δ 14.1, 18.8, 20.1, 22.6, 26.0, 29.2, 31.7, 34.7, 43.5, 64.3, 68.0, 110.7,
114.9, 115.1, 125.6, 127.0, 127.1, 128.3, 128.5, 129.8, 133.0, 134.7, 137.0, 143.1, 146.1, 158.4; EIMS:
m/z 440 (M+, base peak). Anal. Calcd. For C30H36N2O (Mol. Wt. 440): C, 81.78; H, 8.24; N, 6.36;
Found: C, 81.72; H, 8.18; N, 6.43%.
1-(3,4-Dimethylphenyl)-3-phenyl-5-(4-octyloxyphenyl)-2-pyrazoline (8h). 3-(4-Octyloxyphenyl)-1-
phenylprop-2-en-1-one (3.36 g, 10 mmol) and (3,4-dimethylphenyl) hydrazaine (2.72 g, 20 mmol)
were reacted according to the general procedure. Color pale yellow solid; yield 86% (2.88 g); m.p.
96–99 °C; Rf = 0.87 (petroleum ether-ethyl acetate, 4:1), FT-IR (KBr, cm−1): 1685, 1298, 1491, 1253,
1
1057, H-NMR (300 MHz, CDCl3) δ 0.91 (t, 3H, J = 7.2 Hz, −O−(CH2)7−CH3), 1.30−1.45 (m, 10H,
−O−CH2−CH2−(CH2)5− CH3), 1.78 (qn, 2H, J = 8.0 Hz, −O−CH2−CH2−C6H13), 2.16 (s, 3H, N-Ar-4-
CH3), 2.21 (s, 3H, N-Ar-3-CH3), 3.11 (dd, 1H, J = 7.8, 17.1 Hz, Ha), 3.80 (dd, 1H, J = 12.3, 17.1 Hz,
Hb), 3.93 (t, 2H, J = 6.6 Hz, −O−CH2−), 5.20 (dd, 1H, J = 7.5, 12.0 Hz, Hx), 6.71 (d, 1H, J = 8.1 Hz,
N-ArHh), 6.86 (d, 2H, J = 8.7 Hz, ArHc=c'), 6.93 (d, 1H, J = 8.1 Hz, N-ArHi), 7.06 (s, 1H, N-ArHj),
7.25 (d, 2H, J = 8.7 Hz, ArHd=d'), 7.32–7.45 (m, 3H, ArHf=f', g), 7.74(d, 2H, J = 8.4 Hz, ArHe=e'); 13C-
NMR (CDCl3) δ 14.1, 18.8, 20.2, 22.6, 26.0, 29.2, 29.3, 31.8, 35.5, 43.5, 64.3, 67.9, 110.7, 114.9 (2C),
115.1, 125.6 (2C), 127.0 (2C), 127.1, 128.3, 128.5 (2C), 129.8, 132.9, 134.7, 137.0, 143.1, 146.1,

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158.4; EIMS: m/z 454 (M+, base peak). Anal. Calcd. For C31H38N2O (Mol. Wt. 454): C, 81.89; H,
8.42; N, 6.16; Found: C, 81.85; H, 8.38; N, 6.25%.
1-(3,4-Dimethylphenyl)-3-phenyl-5-(4-nonyloxyphenyl)-2-pyrazoline (9h). 3-(4-Nonyloxyphenyl)-1-
phenylprop-2-en-1-one (3.50 g, 10 mmol) and (3,4-dimethylphenyl) hydrazaine (2.72 g, 20 mmol)
were reacted according to the general procedure. Color pale yellow solid; yield 85% (2.97 g); m.p.
101–103 °C; Rf = 0.85 (petroleum ether-ethyl acetate, 4:1), FT-IR (KBr, cm−1): 1679, 1292, 1493,
1254, 1055, 1H-NMR (300 MHz, CDCl3) δ 0.90 (t, 3H, J = 7.2 Hz, −O−(CH2)8−CH3), 1.30−1.47 (m,
12H, −O−CH2−CH2−(CH2)6− CH3), 1.78 (qn, 2H, J = 7.8 Hz, −O−CH2−CH2−C7H15), 2.17 (s, 3H,
N-Ar-4- CH3), 2.22 (s, 3H, N-Ar-3-CH3), 3.11 (dd, 1H, J = 7.5, 16.8 Hz, Ha), 3.80 (dd, 1H, J = 12.3,
17.1 Hz, Hb), 3.93 (t, 2H, J = 6.6 Hz, −O−CH2−), 5.20 (dd, 1H, J = 7.5, 12.3 Hz, Hx), 6.71 (d, 1H,
J = 8.1 Hz, N-ArHh), 6.87 (d, 2H, J = 8.7 Hz, ArHc=c'), 6.93 (d, 1H, J = 8.1 Hz, N-ArHi), 7.06 (s, 1H,
N-ArHj), 7.25 (d, 2H, J = 8.7 Hz, ArHd=d'), 7.33-7.43 (m, 3H, ArHf=f', g), 7.75(d, 2H, J = 8.4 Hz,
13
ArHe=e'); C-NMR (75 MHz, CDCl3) δ 14.1, 18.8, 20.2, 22.7, 26.0, 29.3 (2C), 29.4, 29.5, 31.9, 43.6,
64.3, 67.9, 110.7, 114.9, 115.1, 125.6, 127.0, 127.1, 128.3, 128.5, 129.8, 133.0, 134.7, 137.0, 143.1,
146.1, 158.4; EIMS: m/z 468 (M+, base peak). Anal. Calcd. For C32H40N2O (Mol. Wt. 468): C, 82.01;
H, 8.60; N, 5.98; Found: C, 81.97; H, 8.57; N, 6.05%.
1-(3,4-Dimethylphenyl)-3-phenyl-5-(4-decyloxyphenyl)-2-pyrazoline (10h). 3-(4-Decyloxyphenyl)-1-
phenylprop-2-en-1-one (3.64 g, 10 mmol) and (3,4-dimethylphenyl) hydrazaine (2.72 g, 20 mmol)
were reacted according to the general procedure. Color pale yellow solid; yield 81% (2.94 g); m.p.
85–87 °C; Rf = 0.86 (petroleum ether-ethyl acetate, 4:1), FT-IR (KBr, cm−1): 1687, 1297, 1498, 1259,
1049, 1H-NMR (300 MHz, CDCl3) δ 0.90 (t, 3H, J = 7.2 Hz, −O−(CH2)9−CH3), 1.30−1.47 (m, 14H,
−O−CH2−CH2−(CH2)7− CH3), 1.78 (qn, 2H, J = 7.2 Hz, −O−CH2−CH2−C8H17), 2.16 (s, 3H, N-Ar-4-
CH3), 2.20 (s, 3H, N-Ar-3-CH3), 3.11 (dd, 1H, J = 7.5, 17.1 Hz, Ha), 3.80 (dd, 1H, J = 12.3, 17.1 Hz,
Hb), 3.93 (t, 2H, J = 6.6 Hz, −O−CH2−), 5.20 (dd, 1H, J = 7.5, 12.0 Hz, Hx), 6.71 (d, 1H, J = 8.1 Hz,
N-ArHh), 6.86 (d, 2H, J = 8.7 Hz, ArHc=c'), 6.92 (d, 1H, J = 8.1 Hz, N-ArHi), 7.06 (s, 1H, N-ArHj),
7.25 (d, 2H, J = 8.7 Hz, ArHd=d'), 7.32-7.47 (m, 3H, ArHf=f', g), 7.74(d, 2H, J = 8.4 Hz, ArHe=e’); 13C-
NMR (75 MHz, CDCl3) δ 14.1, 18.8, 20.2, 22.7, 26.0, 29.2, 29.3, 29.4, 29.5, 29.6, 31.9, 43.5, 64.3,
68.0, 110.7, 114.9 (2C), 115.1, 125.6 (2C), 127.0, 127.1, 128.3, 128.5 (2C), 129.8, 133.0, 134.7, 137.0,
143.1, 146.1, 158.4; EIMS: m/z 482 (M+, base peak). Anal. Calcd. For C33H42N2O (Mol. Wt. 482): C,
82.11; H, 8.77; N, 5.80; Found: C, 82.09; H, 8.74; N, 5.88%.
1-(3,4-Dimethylphenyl)-3-phenyl-5-(4-undecyloxyphenyl)-2-pyrazoline (11h). 3-(4-Unecyloxyphenyl)-
1-phenylprop-2-en-1-one (3.76 g, 10 mmol) and (3,4-dimethylphenyl) hydrazaine (2.72 g, 20 mmol)
were reacted according to the general procedure. Color pale yellow solid; yield 87% (3.27 g); m.p.
88–92 °C; Rf = 0.85 (petroleum ether-ethyl acetate, 4:1), FT-IR (KBr, cm−1): 1689, 1295, 1494, 1256,
1054, 1H-NMR (300 MHz, CDCl3) δ 0.90 (t, 3H, J = 7.2 Hz, −O−(CH2)10−CH3), 1.29−1.47 (m, 16H,
−O−CH2−CH2−(CH2)8− CH3), 1.78 (qn, 2H, J = 8.0 Hz, −O−CH2−CH2−C9H19), 2.17 (s, 3H, N-Ar-4-
CH3), 2.22 (s, 3H, N-Ar-3-CH3), 3.11 (dd, 1H, J = 7.8, 17.1 Hz, Ha), 3.80 (dd, 1H, J = 12.3, 17.1 Hz,
Hb), 3.93 (t, 2H, J = 6.6 Hz, −O−CH2−), 5.20 (dd, 1H, J = 7.5, 12.3 Hz, Hx), 6.71 (d, 1H, J = 8.1 Hz,
N-ArHh), 6.86 (d, 2H, J = 8.7 Hz, ArHc=c'), 6.93 (d, 1H, J = 8.1 Hz, N-ArHi), 7.06 (s, 1H, N-ArHj),

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13
7.25 (d, 2H, J = 8.7 Hz, ArHd=d'), 7.32-7.45 (m, 3H, ArHf=f', g), 7.74(d, 2H, J = 7.8 Hz, ArHe=e'); C-
NMR (75 MHz, CDCl3) δ 14.1, 18.8, 20.2, 22.7, 26.0, 29.3, 29.3, 29.4, 29.6, 29.7, 31.9, 43.6, 64.3,
67.9, 110.7, 114.3, 114.9 (2C), 115.1, 125.6 (2C), 127.0 (2C), 127.1, 128.3, 128.5, (2C), 129.8, 132.9,
134.7, 137.0, 143.1, 146.1, 158.4; EIMS: m/z 496 (M+, base peak). Anal. Calcd. For C34H44N2O (Mol.
Wt. 496): C, 82.21; H, 8.93; N, 5.64; Found: C, 82.17; H, 8.89; N, 5.71%.
1-(3,4-Dimethylphenyl)-3-phenyl-5-(4-dodecyloxyphenyl)-2-pyrazoline(12h). 3-(4-Dodecyloxyphenyl)
-1-phenylprop-2-en-1-one (3.90 g, 10 mmol) and (3,4-dimethylphenyl) hydrazaine (2.72 g, 20 mmol)
were reacted according to the general procedure. Color pale yellow solid; yield 84% (3.27 g); m.p.
86–88 °C; Rf = 0.87 (petroleum ether-ethyl acetate, 4:1), FT-IR (KBr, cm−1): 1684, 1293, 1493, 1253,
1052, 1H-NMR (300 MHz, CDCl3) δ 0.90 (t, 3H, J = 7.2 Hz, −O−(CH2)11−CH3), 1.29−1.47 (m, 18H,
−O−CH2−CH2−(CH2)9− CH3), 1.78 (qn, 2H, J = 7.8 Hz, −O−CH2−CH2−C10H21), 2.17 (s, 3H, N-Ar-4-
CH3), 2.22 (s, 3H, N-Ar-3-CH3), 3.11 (dd, 1H, J = 7.5, 16.8 Hz, Ha), 3.80 (dd, 1H, J = 12.3, 17.1 Hz,
Hb), 3.93 (t, 2H, J = 6.6 Hz, –O–CH2–), 5.20 (dd, 1H, J = 7.8, 12.3 Hz, Hx), 6.72 (d, 1H, J = 8.1 Hz,
N-ArHh), 6.87 (d, 2H, J = 8.7 Hz, ArHc=c'), 6.93 (d, 1H, J = 8.1 Hz, N-ArHi), 7.06 (s, 1H, N- ArHj),
7.25 (d, 2H, J = 8.7 Hz, ArHd=d'), 7.32-7.43 (m, 3H, ArHf=f', g), 7.74(d, 2H, J = 8.4 Hz, ArHe=e');
13C-NMR (75 MHz, CDCl3) δ 14.1, 18.8, 20.2, 26.0, 29.3, 29.3, 29.4, 29.6, 29.6, 29.6, 29.6, 31.9, 43.6,
64.3, 68.0, 110.7, 114.9 (2C), 115.1, 125.6 (2C), 127.0 (2C), 127.1, 128.3, 128.5 (2C), 129.8, 133.0,
134.7, 137.0, 143.1, 146.1, 158.4; EIMS: m/z 510 (M+, base peak). Anal. Calcd. For C35H46N2O (Mol.
Wt. 510): C, 82.30; H, 9.08; N, 5.48; Found: C, 82.24; H, 9.01; N, 5.54%.
3.4. Fluorescence Properties of 1,3,5-Triaryl-2-pyrazolines
The fluorescent behavior of these compounds was studied by UV-Vis and emission spectroscopy,
performed at room temperature (298 K). The UV-Vis and the emission spectra of 1,3,5-triaryl-2-
pyrazolines 1h−12h, were recorded in N,N-dimethylformamide-water (3:7) solution at a concentration
of 1 × 10−5 mol L−1 and 1 × 10−7 mol L−1, respectively.
4. Conclusions
A series of twelve 1,3,5-triaryl-2-pyrazolines 1h-12h containing homologous alkoxy groups (CH3-
C12H25) were synthesized by converting benzaldehyde into 4-alkoxybenzaldehydes with the
corresponding alkyl halides. The 4-alkoxybenzaldehydes yielded 4-alkoxychalcones on reaction with
acetophenone. The target compounds were finally obtained by the reaction of the 4-alkoxychalcones
1
with (3,4-dimethylphenyl) hydrazaine hydrochloride. Their structures were confirmed by IR, H- and
13C–NMR, mass spectrometric and elemental analysis. The synthesized 1,3,5-triaryl-2-pyrazolines
were found to possess fluorescence properties in the blue region of the visible spectrum when
irradiated with ultraviolet radiation. The comparison of emission intensities of pyrazoline derivatives
revealed that the alkoxy chains have remarkable effect on emission intensity of the 1,3,5-triaryl-2-
pyrazolines. The absorption intensities of 6h, 10h 11h, 12h and 8h are much higher than other
derivatives. Approximately, it was the same case in emission intensities. It can thus be concluded that
variation in alkoxy chains can be used to tune the emission intensity that can find potential applications

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in controlling/optimizing the optoelectronic and luminescence properties of Organic Light Emitting
Diodes (OLEDs) based on such types of fluorescent compounds.
Acknowledgements
The financial support for the research project No. RG095/10AFR from the Universiti Malaya
Research Grant (UMRG), University of Malaya is highly appreciated.
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Sample Availability: Samples of the compounds are available from the authors.
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