Effect of donor-acceptor chromophores on photophysical properties of newly synthesized Pyrazolo-Pyrrolo-Pyrimidines (PPP)

Article abstract of DOI:10.1007/s10895-010-0704-3

Novel pyrazolo-pyrrolo-pyrimidine (PPP) derivatives having remarkable photophysical properties are designed with the help of theoretical semiempirical calculations. These compounds then synthesized successfully and studied effect of substituents on its photophysical properties. [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10895-010-0704-3

J Fluoresc (2011) 21:453–459
DOI 10.1007/s10895-010-0704-3
RAPID COMMUNICATION
Effect of Donor-Acceptor Chromophores
on Photophysical Properties of Newly Synthesized
Pyrazolo-Pyrrolo-Pyrimidines (PPP)
Ramhari V. Rote & Deepak P. Shelar & Sandeep R. Patil &
Santosh S. Shinde & Raghunath B. Toche &
Madhukar N. Jachak
Received: 23 March 2010 /Accepted: 19 July 2010 /Published online: 14 August 2010
#
Springer Science+Business Media, LLC 2010
Abstract Novel pyrazolo-pyrrolo-pyrimidine (PPP) deriva-
tives having remarkable photophysical properties are designed
with the help of theoretical semiempirical calculations. These
compounds then synthesized successfully and studied effect
of substituents on its photophysical properties.
role in the photophysics of electron donor-accepter Pi / π
conjugated system. The absorption and emission spectra in
such case significantly depends on the type of substituents
[13, 14]. The heterocycles with high extinction coefficient,
large Stoke’s shift and quantum yield are near to unity are
fluorescent brightners and these three parameters largely
determine both color strength and brightness [15]. Thus, a
suitable blue-emitting material with high brightness, low
hole gap, high quantum yields and good thermal stability still
remain to be developed.
.
Keywords Pyrazolo-pyrrolo-pyrimidine (PPP)
.
.
.
.
.
Cyclic β-ketoester HOMO LUMO UV Fluorescence
Quantum yield
In our earlier communication, synthesis of highly
fluorescent dipyrazolo[3,4-b:3,4-d]pyridines (DPP) [16],
pyrazolo[3,4-b]pyrrolo[2,3-d]pyridines (PPP) [17] and 2,6-
dirayl-4-alkoxypyridine-3-carbonitriles [18] has been
reported. These literature reports and our ongoing interest
in this area prompted us to extend our study in which new
class of heterocycles are synthesized. As theoretically
predicted empirical calculations, HOMO-LUMO, electron
hole gap, ionization potential and heat of formation helps
chemist to design the synthesis of new heterocycles. In the
present communication, we design the synthesis of novel
pyrazolo-pyrrolo-pyrimidine (PPP) derivatives and studied
the effect of substituents on their photophysical properties.
Introduction
Heterocyclic compounds which absorb in the near visible
region and emits lights in the visible region (400–550 nm) are
considered to be fluorophores and can be used as organic light
emitting diodes (OLEDs). Fluorescent compounds are widely
used as markers in biochemical and nucleic acid technologies
and is the subject of intensive investigations [1]. There are
numbers of efficient blue dyes developed in the past several
years [2–8], some of which possess reasonable or high glass
transition temperature [Tg], a property suggested to be
desirable for morphological stability reasons [9–11]. It was
also noted that the heterocyclic compound which are used as
light emitting diodes must have electron hole gap between
2.7 to 3 eV and fluoresces between 400 to 700 nm [12].
Photoinduced intramolecular electron transfer plays a key
Result and Discussion
Semiempirical Study
:
:
:
:
:
R. V. Rote D. P. Shelar S. R. Patil S. S. Shinde R. B. Toche
As a keen interest, atomic contribution on frontier orbital,
we analyzed the three-dimensional HOMO and LUMO
coefficient contribution by the MOPAC-2009 (Version
8.331) [19, 20] and are given in Table 1. From empirical
calculations it is noted that all derivatives of PPP have
M. N. Jachak (*)
Organic Chemistry Research Center, Department of Chemistry, K.
T. H. M. College,
Gangapur Road,
Nashik 422002 MS, India
e-mail: mnjachak@hotmail.com

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J Fluoresc (2011) 21:453–459
Table 1 The molecular electronic properties (HOMO-LUMO energy GAP) of the Compounds 3, 4 and 6a–l at 25 °C
Comp.
Ar
Heat of formation (K Cal.)
Ionization potential (eV)
HOMO(eV)
LUMO (eV)
GAPa (eV)
3
–
80.03
68.07
9.786
9.256
8.686
8.689
8.872
8.887
8.901
8.750
9.218
8.687
8.909
8.879
8.748
8.891
−9.787
−9.257
−8.686
−8.690
−8.873
−8.887
−8.901
−8.751
−9.218
−8.687
−8.909
−8.880
−8.748
−8.891
−1.699
−1.105
−0.855
−0.859
−1.089
−1.082
−1.120
−0.932
−1.802
−0.890
−1.145
−1.083
−0.887
−1.093
8.08
8.15
7.83
7.83
7.78
7.80
7.78
7.81
7.41
7.79
7.76
7.79
7.86
7.79
4
–
6a
6b
6c
6d
6e
6f
6g
6h
6i
p-OCH3-C6H4
p-CH3-C6H4
p-F-C6H4
m-Br-C6H4
P-Br-C6H4
-C6H5
93.28
124.07
86.86
137.06
136.69
134.12
129.49
123.66
86.35
p-NO2-C6H4
m-CH3-C6H4
m-F-C6H4
m-Cl-C6H4
o-CH3-C6H4
p-Cl-C6H4
6j
6k
6l
124.90
125.48
124.74
a GAP = E HOMO−E
LUMO
nearly similar HOMO energies but shows variation in
LUMO energies (i.e., electron affinity ‘EA’ of organic
molecule) corresponds to substituents present on ring D.
The donor chromophore increases the electron density of
rest molecule hence, ultimately electron affinity i.e. LUMO
energy decreases. Similarly acceptor chromophore
decreases the electron density of rest molecule hence,
electron affinity i.e. LUMO energy increases. For instance
compound 6a having donor chromophore (–OCH3) on ring
D shows lower LUMO energy (0.855 eV) and playing
important role in increasing electron density hence
increases stability and reactivity of this molecule. Com-
pound 6g having acceptor chromophore (–NO2) shows
higher LUMO energy (1.802 eV), lower electron density
hence decreases stability and reactivity of this molecule.
The 3D picture (molecular modeling) of representative
compound 6a is shown in Fig. 1. The heat of formation
values indicates that comp. 6a, 6c and 6i are thermodynam-
ically more stable as compared to other compounds (6b, 6d,
6e, 6f, 6g, 6h, 6j, 6k and 6l) (Table 1). From Table 1, It is
clearly observed that; the ionization potential of 6 are in
between 8–9 eV, hence may be used as potential candidates
in the semiconductor [21]. Encouraging from this results, we
undertook the synthesis of pyrazolo-pyrrolo-pyrimidine
(PPP) derivatives 6, starting with precursor 3.
Chemistry
Condensation of α-acetyl-γ-butyrolactone 2 with 2-
aminoheterocycles have been described in literature [17,
22], however this condensation of it with 5-amino-1H-
pyrazole-4-carbonitrile 1 have been little explored. One pot
cyclocondensation of α-acetyl-γ-butyrolactone 2 with 5-
amino-1H-pyrazole-4-carbonitrile 1 furnished a mixture of
two compounds 3 and 4 which are separated by column
chromatography eluting with hexane/ethyl acetate (9:1).
Cyclocondensation of this lactone with 2-aminoheterocycle
under similar reaction condition did not yielded compound
4 [17] (Scheme 1).
Structures of 3 and 4 were assigned by spectroscopic
characterization. For instance 1H NMR of compound 3
shows singlet at 8.83 δ corresponds to aromatic proton of
pyrazole ring, two triplets at 3.90 δ and 3.32 δ corresponds
to protons of aliphatic side chain and singlet at 2.76 δ
corresponds to three protons of methyl group. The mass
spectrum of 3 shows a molecular ion peaks m/z at 255 [M+]
and also peaks at 257 [M+2] and 259 [M+4] due to
presence of two chlorine atom. The sharp band at 2,227 cm−1
in IR spectrum of 3 clearly indicate the presence of –CN
group. The1H NMR Compound 4 shows singlet at 8.72 δ
due to aromatic proton in pyrazole ring and two triplets at
3.79 and 3.50 δ due to four proton of newly annulated furan
Fig. 1 3D-picture of compound 6a

J Fluoresc (2011) 21:453–459
455
Scheme 1 Synthesis of
pyrazolopyrimidines
O
O
Cl
N
H
Cl
+
N
N
N
N
POCl3
N
N
+
NH2
N
Reflux, 4-5 h
O
O
CN
1
CN
CN
2
3
4
ring and the singlet at 2.76 δ corresponds to three proton of
methyl group. The –CN group is observed at 2224 cm−1 in
its IR spectrum. The formation of compound 4 can be
rationalized by following mechanism (Fig. 2). The mecha-
nism proceeds through the formation of Schiff base A which
is isomerized by proton transfer to a more stable transient
intermediate B. The secondary nitrogen of the pyrazole ring
then attack on the lactone carbonyl resulted in the opening of
lactone to form a phosphate ester on the pyrimidine ring C,
which is subsequently displaced during the intramolecular
cyclization to furnish compound 4.
After establishing structure of 3 and 4, the dichloro
compound 3 having two replaceable chlorine groups is fused
with various aniline and /or substituted anilines at 110–120 °
C, for 15–20 min. to afford title compounds 8-aryl-5-methyl-
7,8-dihydro-6H-pyrazolo[1,5-a] pyrrolo[3,2-e]pyrimidine-3-
carbonitriles 6a-l in 73–86% yields (Scheme 2).
quantum yield of each are determined by standard literature
procedure using quinine sulphate as reference standard [23,
24] (Table 2).
The charge is more concentrated on ring D as compare to
ring A, B and C (Fig. 1). The donor/ acceptor chromo-
phores on ring D is playing important role in increasing/
decreasing the electron density. The ring A is having strong
electron withdrawing –CN, which make facile charge
delocalization in the molecules, increases the stability and
reactivity of the molecule and shows high quantum yields
in 6. It is noted that compound 6a having strong donor
chromophore –OCH3 at C4-position of ring D facilitates the
charge delocalization via π→π* and n→π* transition
hence, fluoresces at higher wavelength (457 nm) and shows
highest quantum yield (ФF=0.30), while compound 6g
having strong acceptor chromophore –NO2 at C4-position
of ring D restricts the charge delocalization hence,
fluoresces at lower wavelength (383 nm) and shows lowest
quantum yield (ФF=0.15). All other compounds shows
fluorescence and quantum yield with respect to their
chromophores (ФF=0.15–0.29). The comparative absorp-
tion and emission spectra of 6a and 6g is depicted in Fig. 3.
It is interesting to observe that the −NH2 acted as
2
bidentate nucleophile to give SN and SNAr reaction and
both chlorines in 3 were displaced. Compounds 6 are
characterized by spectroscopic and analytical methods. In
this reaction we have chosen anilines with electron-accepter
and electron-donor groups to study their effect on absorp-
tion and emission in obtained compounds 6a–l.
Thermal Properties
Photophysical Properties
The organic compounds which are to be used in OLEDs and
opto-electronic applications should be thermally and chemi-
cally stable. Thermal analysis of compounds 6a–l, by
differential scanning colorimetry (DSC) revealed that they
The UV absorption and emission of compounds 6a–l are
studied in polar aprotic solvent (DMF). Fluorescence
Fig. 2 Mechanism of
compound 4
POCl3
O
O
O
O
H
O
H
H
N
N
N
N
N
N
+
H
NH2
O
O
N
N
H
CN
CN
CN
A
2
B
1
Cl2OPO
O
O
N
N
N
N
N
H
N
CN
CN
4
C

456
J Fluoresc (2011) 21:453–459
Ar
chromophores on ring D of compound 6 shows higher
LUMO energy, shifts absorption and emission maximum to
blue (Hypsocromic shift) and low quantum yields. Another
interesting feature is that halo-substituted derivative has less
fluorescence quantum yields than that of methoxy substi-
tuted compound. This could be due to quenching of
fluorescence with halogen atom as the substitution. The
efficient photophysical property makes pyrazolo-pyrrolo
pyrimidine (PPP) derivatives a promising family of materi-
als which may be useful in OLEDs [25] and opto-electronic
applications [26, 27].
Cl
N
N
Cl
N
N
Neat Heat
N
N
+
Ar-NH2
N
110-120˚ C
15-20 min.
5a-l
CN
CN
6a-l
Ar
3
5, 6 g-l
Ar
5, 6 a-f
p-OCH3-C6H4
p-CH3-C6H4
p-F-C6H4
g
p-NO2-C6H4
m-CH3-C6H4
m-F-C6H4
a
b
h
c
i
m-Cl-C6H4
j
m-Br-C6H4
p-Br-C6H4
-C6H5
d
e
k
l
o-CH3-C6H4
p-Cl-C6H4
Experimental
f
General
Scheme 2 Synthesis of pyrazolo-pyrrolo-pyrimidines (PPP)
Melting points were determined on a Gallenkamp Melting
Point Apparatus in open capillary tubes and are uncorrected.
The 1H and 13C NMR spectra were recorded on a Varian XL-
300 spectrometer (300 MHz, 75 MHz respectively). Chem-
ical shifts are reported in ppm from internal tetramethylsilane
standard and are given in δ-units. The solvent for NMR
spectra was deuteriochloroform (CDCl3) or DMSO (d6).
Infrared spectra were taken on a Shimadzu IR-408, in
potassium bromide pellets. The mass spectra were recorded
on QP-2010s. UV spectra were recorded on a Shimadzu UV-
1601 UV-VIS Spectrophotometer. Fluorescence spectra were
recorded using RF-5301 PC Spectrofluorophotometer (150-
W Xe lamp), compounds for UV and fluorescence measure-
ments were dissolved in Dimethyl formamide (DMF). UV
and fluorescence scan were recorded from 200 to 600 nm.
Semiempirical molecular orbital calculations were done by
semi empirical PM6 Methods, MOPAC (6, 7) program
package. Determination of quantum yields: emission signals
were set in relation to known area of the emission signal of
quinine sulphate at pH 1. Elemental analyses were performed
on a Hosli CH-Analyzer and are within 0.3 of the
theoretical percentages. All reactions were monitored by
thin layer chromatography, carried out on 0.2 mm silica gel
60 F254 (Merck) plates using UV light (254 and 366 nm) for
detection. Column chromatography was carried out on silica
gel (s.d. Fine Chemicals, 60–120 mesh powder). Starting
materials were obtained from commercial suppliers and used
without further purification. Common grade chemicals and
staring materials are either commercially available and were
used without further purification or prepared by standard
literature procedures.
are thermally stable compounds up to 350 °C and also
possesses high melting points and high crystallization
temperature.
Conclusion
In conclusion, we have successfully synthesized PPP
derivatives having excellent photophysical properties and
are depends upon nature of substituents present on ring D.
For instance, the strong donor chromophores on ring D of
compound 6 shows lower LUMO energy, shifts absorption
and emission maximum to red (Bathochromic shift), hence
shows high quantum yields. Similarly strong acceptor
Table 2 The photophysical data for electronic absorption (UVλMax.),
fluorescence (Em.λMax.) and quantum yield (ФF) of compounds 3, 4
and 6a–l for 0.1 M Conc. in DMF as a solvent at 25 °C
Comp.
Ar
UV λMax. /nm
Em. λMax. /nm
ФF
3
–
322
318
371
364
363
370
371
373
319
377
374
369
330
372
392
387
457
435
433
399
425
424
383
424
408
403
397
427
0.11
0.10
0.30
0.29
0.27
0.18
0.25
0.24
0.15
0.24
0.21
0.20
0.17
0.26
4
–
6a
6b
6c
6d
6e
6f
6g
6h
6i
p-OCH3-C6H4
p-CH3-C6H4
p-F-C6H4
m-Br-C6H4
P-Br-C6H4
-C6H5
p-NO2-C6H4
m-CH3-C6H4
m-F-C6H4
m-Cl-C6H4
o-CH3-C6H4
p-Cl-C6H4
General Procedure for the Synthesis of Compound (3) and (4)
6j
6k
6l
A mixture of 5 amino-1H-pyrazole-4-carbonitrile 1
(0.01 mol, 1.07 g) and α-acetyl -γ-butyrolactone 2

J Fluoresc (2011) 21:453–459
457
Fig. 3 The comparative
absorption (UV λMax.) and
emission (Em λMax.) spectra of
compounds (6a) and (6g)
respectively
(0.01 mol, 1.07 mL) in POCl3 (5 mL) was heated under
reflux for 4–5 h. After completion of reaction (TLC
Check), the reaction mass was allowed to cool, excess
POCl3 was evaporated under reduced pressure, obtained
mass was quenched in ice-cold water (10 ml) to gives
solid precipitate. It contains two compounds according to
TLC analysis (Rf value: 0.92 and 0.69 in hexane/ethyl
acetate = 9:1). This mixture was separated by column
chromatography (Silica-gel: 60–120 mesh, eluent: hex-
ane/ethyl acetate = 9:1).
General Procedure for the Synthesis of Compounds (6a–l)
A mixture of compound 3 (0.01 mol, 2.55 g) and
corresponding anilines 5a–l (0.01 mol) was fused at 110–
120 °C for 15–20 min. After completion of reaction (TLC
Check), the reaction mass was allowed to cool, obtained
crude solid was stirred in cold methanol (10 mL) for 5–
10 min. Filtered the separated solid, dried under high
vacuum and recrystallized from suitable solvent ethanol:
DMF to furnish compounds 6a–l in 73–86% yields.
Chloro-6-(2-chloroethyl)-5-methylpyrazolo [1,5-a]
pyrimidine-3-carbonitrile (3)
8-(4-Methoxyphenyl)-5-methyl-7,8-dihydro-6H-pyrazolo
[1,5-a]pyrrolo[3,2-e] pyrimidine-3-carbonitrile (6a)
Yield: 1.91 g (75%); Colorless prism; mp 268–269 °C;
Yield: 2.34 g (77%); recrystallized from ethanol/DMF (9:1)
to afford colorless needle; mp 278–279 °C; IR (KBr):
3117 w, 3037 w, 2965 w, 2920 m, 2226 m, 1839 m,
1614 m, 1588 m, 1512 m, 1272 w, 1207 w, 1158 m,
IR (KBr): 3427 w, 3107 m, 2227 m, 1614 m, 1541 w,
1
1479 s, 1438 m, 1300 m cm−1; H NMR (DMSO-d6) δ:
2.76 (s, 3H, CH3), 3.32 (t, 2H, J=3.2 Hz, CH2), 3.90 (t,
2H, J=3.2 Hz, CH2), 8.83(s, 1H, Ar-H); 13C NMR
(DMSO-d6) δ: 17.12, 24.18, 48.22, 96.51, 110.42,
122.17, 135.34, 137.01, 159.71, 163.62; MS (70 eV) m/
z (%): 255 [M+] (100), 257 [M+2] (31), 259 [M+4] (16).
Anal. Calcd. for C10H8Cl2N4 (255.11): C, 47.08; H, 3.16;
N, 21.96. Found: C, 47.14; H, 3.11; N, 21.95%.
1
919 m cm−1; H NMR (DMSO-d6) δ: 2.33 (s, 3H, CH3),
2.81 (s, 3H, OCH3), 3.27 (t, 2H, J=9 Hz, CH2), 4.29 (t, 2H,
J=9 Hz, CH2), 7.20 (m, 4H, Ar-H), 8.37 (s,1H, Ar-H); 13C
NMR (DMSO-d6) δ: 18.12, 25.45, 48.78, 59.71, 99.23,
108.25, 118.07 (2 C’s), 121.63 (2 C’s), 127.10, 134.42,
137.58, 144.08, 148.23, 160.41, 169.11; MS (70 eV) m/z
(%): 305 [M+] (100). Anal. Calcd. for C17H15N5O (305.34):
C, 66.87; H, 4.95; N, 22.94. Found: C, 66.85; H, 4.96; N,
22.92%.
5-Methyl-6,7-dihydrofuro[3,2-e]pyrazolo[1,5-a]
pyrimidine-3-carbonitrile (4)
Yield: 0.20 g (10%); Colorless solid; mp 250–251 °C; IR
5-Methyl-8-p-tolyl-7,8-dihydro-6H-pyrazolo[1,5-a]pyrrolo
(KBr): 3238 w, 3105 w, 2920 w, 2224 m, 1780 m, 1612 m,
[3,2-e]pyrimidine-3-carbonitrile (6b)
1
1504 w, 1357 m, 1317 m, 1211 w, 927 s cm−1; H NMR
(DMSO-d6) δ: 2.50 (s, 3H, CH3), 3.50 (t, 2H, J=8.1 Hz,
Yield: 2.25 g (78%); recrystallized from ethanol/DMF (8:2)
to afford white solid; mp 262–263 °C; IR (KBr): 3111 w,
3034 w, 2960 m, 2918 w, 2220 m, 1830 m, 1583 m,
1512 m, 1276 w, 1203 m, 1166 m, 918 m, 817 w,
CH2), 3.79 (t, 2H, J=8.1 Hz, CH2), 8.72 (s, 1H, Ar-H); 13
C
NMR (DMSO-d6) δ: 18.05, 26.23, 76.45, 97.47, 108.53,
125.10, 137.17, 138.21, 158.45, 168.07; MS (70 eV) m/z
(%): 200 [M+] (100). Anal. Calcd. for C10H8N4O (200.20):
C, 60.00; H, 4.03; N, 27.99. Found: C, 60.06; H, 3.99; N,
28.03%.
1
628 m cm−1; H NMR (DMSO-d6) δ: 2.34 (s, 3H, CH3),
3.42 (s, 3H, CH3), 3.24 (t, 2H, J=8.1 Hz, CH2), 4.31 (t, 2H,
J=8.1 Hz, CH2), 7.23 (m, 4H, Ar-H), 8.42 (s, 1H, Ar-H);

458
J Fluoresc (2011) 21:453–459
1
13C NMR (DMSO-d6) δ: 19.08, 24.26, 26.22, 49.45, 98.42,
109.62, 119.17 (2 C’s), 124.08, 126.63, 128.82 (2 C’s),
134.25, 137.91, 142.35, 160.12, 169.36; MS (70 eV) m/z
(%): 289 [M+] (100). Anal. Calcd. for C17H15N5 (289.34):
C, 70.57; H, 5.23; N, 24.20. Found: C, 70.61; H, 5.22; N,
24.22%.
1610 m, 1514 s, 1280 m cm−1. H NMR (DMSO-d6) δ:
2.42 (s, 3H, CH3), 3.28 (t, 2H, J=8.7 Hz, CH2), 4.33 (t, 2H,
J=8.7 Hz, CH2), 7.29–7.38 (m, 5H, Ar-H), 8.38 (s, 1H, Ar-
H); MS (70 eV) m\z (%): 275 [M+] (100). Anal. Calcd. for
C16H13N5 (275.32): C, 69.80; H, 4.76; N, 25.44. Found: C,
69.87; H, 4.71; N, 25.45%.
8-(4-Fluorophenyl)-5-methyl-7,8-dihydro-6H-pyrazolo
5-Methyl-8-(4-nitrophenyl)-7,8-dihydro-6H-pyrazolo[1,5-
[1,5-a]pyrrolo[3,2-e] pyrimidine-3-carbonitrile (6c)
a]pyrrolo[3,2-e] pyrimidine-3-carbonitrile (6g)
Yield: 2.19 g (75%); recrystallized from ethanol/DMF (9:1)
to yield colorless solid; mp 274–275 °C; IR (KBr): 3107 w,
2945 m, 2899 m, 2214 m, 1627 m cm−1; 1H NMR (DMSO-
d6) δ: 2.49 (s, 3H, CH3), 3.30 (t, 2H, J=8.1 Hz, CH2), 4.41
(t, 2H, J=8.1 Hz, CH2), 7.37 (d, 2H, J=8.4 Hz, Ar-H), 7.72
(d, 2H, J=8.4 Hz, Ar-H), 8.53 (s, 1H, Ar-H); MS (70 eV)
m/z (%): 293 [M+] (98). Anal. Calcd. for C16H12FN5
(293.31): C, 65.52; H, 4.12; N, 23.88. Found: C, 65.50; H,
4.11; N, 23.91%.
Yield: 2.49 g (78%); recrystallized from ethanol/DMF (9:1)
to yield white solid; mp 288–289 °C; IR (KBr): 3118 w,
2971 w, 2927 m, 2217 m, 1612 m, 1516 m, 1369 m,
1
1319 m cm−1; H NMR (DMSO-d6) δ: 2.48 (s, 3H, CH3),
3.29 (t, 2H, J=8.1 Hz, CH2), 4.44 (t, 2H, J=8.1 Hz, CH2),
7.62 (d, 2H, J=8.4 Hz, Ar-H), 7.87 (d, 2H, J=8.4 Hz, Ar-
H), 8.72 (s, 1H, Ar-H). MS (70 eV) m\z (%): 320 [M+]
(100). Anal. Calcd. for C16H12N6O2 (320.31): C, 60.00; H,
3.78; N, 26.24. Found: C, 60.07; H, 3.77; N, 26.21%.
8-(3-Bromophenyl)-5-methyl-7,8-dihydro-6H-pyrazolo
5-Methyl-8-m-tolyl-7,8-dihydro-6H-pyrazolo[1,5-a]pyrrolo
[1,5-a]pyrrolo[3,2- e] pyrimidine-3- carbonitrile (6d)
[3,2-e]pyrimidine-3-carbonitrile (6h)
Yield: 2.58 g (73%); recrystallized from ethanol/DMF (7:3)
to afford white solid; mp 269–270 °C; IR (KBr): 2958 w,
2939 w, 2895 w, 2215 m, 1617 m, 1611 m, 1512 m,
Yield: 2.25 g (78%); recrystallized from ethanol/DMF (8:2)
to afford colorless prism; mp 271–272 °C; IR (KBr):
3047 w, 2953 w, 2918 m, 2216 m, 1616 m, 1585 m,
1514 w, 1315 m cm−1; 1H NMR (DMSO-d6) δ: 2.37 (s, 3H,
CH3), 2.82, (s, 3H, CH3), 3.50 (t, 2H, J=8.1 Hz, CH2), 3.81
(t, 2H, J=8.1 Hz, CH2), 7.38 (m, 3H, Ar-H), 7.49 (s, 1H,
Ar-H), 8.42 (s, 1H, Ar-H). MS (70 eV) m\z (%): 289 [M+]
(100). Anal. Calcd. for C17H15N5 (289.34): C, 70.57; H,
5.23; N, 24.20. Found: C, 70.60; H, 5.21; N, 24.23%.
1
1358 m cm−1; H NMR (DMSO-d6) δ: 2.41 (s, 3H, CH3),
3.22 (t, 2H, J=8 Hz, CH2), 4.30 (t, 2H, J=8 Hz, CH2), 7.31
(m, 3H, Ar-H), 7.50 (s, 1H, Ar-H), 8.34 (s, 1H, Ar-H); MS
(70 eV) m\z (%): 354 [M+] (100), 356 [M+2] (36). Anal.
Calcd. for C16H12BrN5 (354.21): C, 54.26; H, 3.41; N,
19.77. Found: C, 54.21; H, 3.39; N, 19.81%.
8-(4-Bromophenyl)-5-methyl-7,8-dihydro-6H-pyrazolo
8-(3-Fluorophenyl)-5-methyl-7,8-dihydro-6H-pyrazolo
[1,5-a]pyrrolo[3,2-e] pyrimidine-3- carbonitrile (6e)
[1,5-a]pyrrolo[3,2-e] pyrimidine-3- carbonitrile (6i)
Yield: 2.79 g (79%); recrystallized from ethanol/DMF (9:1)
to afford colorless solid; mp 258–259 °C; IR (KBr):
3088 m, 2933 w, 2218 m, 1622 m, 1570 m, 1518 m,
Yield: 2.46 g (84%); recrystallized from ethanol/DMF (9:1)
to afford colorless prism; mp 257–258 °C; IR (KBr):
2967 w, 2947 m, 2893 w, 2213 m, 1621 m, 1600 s, 1506 m,
1
1
1487 w cm−1; H NMR (DMSO-d6) δ: 2.43 (s, 3H, CH3),
1362 mcm−1; H NMR (DMSO-d6) δ: 2.46 (s, 3H, CH3),
3.28 (t, 2H, J=9 Hz, CH2), 4.33 (t, 2H, J=9 Hz, CH2), 7.28
(d, 2H, J=8.4 Hz, Ar-H), 7.57 (d, 2H, J=8.4 Hz, Ar-H),
8.42 (s, 1H, Ar-H); MS (70 eV) m\z (%): 354 [M+] (75),
256 [M+2] (93). Anal. Calcd. for C16H12BrN5 (354.31): C,
54.26; H, 3.41; N, 19.77. Found: C, 54.25; H, 3.47; N,
19.75%.
3.29 (t, 2H, J=8.4 Hz, CH2), 4.35 (t, 2H, J=8.4 Hz, CH2),
7.34 (m, 3H, Ar-H), 7.57 (s, 1H, Ar-H), 8.40 (s, 1H, Ar-H).
MS (70 eV) m\z (%): 293 [M+] (100). Anal. Calcd. for
C16H12FN5 (293.31): C, 65.52; H, 4.12; N, 23.88. Found:
C, 65.57; H, 4.09; N, 23.90%.
8-(3-Chlorophenyl)-5-methyl-7,8-dihydro-6H-pyrazolo
5-Methyl-8-phenyl-7,8-dihydro-6H-pyrazolo[1,5-a]pyrrolo
[1,5-a]pyrrolo[3,2-e] pyrimidine-3- carbonitrile (6j)
[3,2-e]pyrimidine-3-carbonitrile (6f)
Yield: 2.65 g (86%); recrystallized from ethanol/DMF (8:2)
to afford colorless needle; mp 276–277 °C; IR (KBr):
2963 w, 2949 w, 2890 w, 2211 m, 1625 m, 1607 m, 1516 s,
Yield: 2.25 g (82%); recrystallized from ethanol/DMF (8:2)
to afford colorless solid; mp 283–284 °C; IR (KBr):
3398 w, 3063 w, 2964 m, 2864 m, 2212 m, 1629 s,
1
1370 m cm−1; H NMR (DMSO-d6) δ: 2.44 (s, 3H, CH3),

J Fluoresc (2011) 21:453–459
459
substituted ter-(phenylene-vinylene) derivative. Appl Phys Lett
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3.27 (t, 2H, J=9 Hz, CH2), 4.34 (t, 2H, J=9 Hz, CH2), 7.32
(m, 3H, Ar-H), 7.55 (s, 1H, Ar-H), 8.39 (s, 1H, Ar-H); MS
(70 eV) m\z (%): 309 [M+] (100), 311 [M+2] (35). Anal.
Calcd. for C16H12ClN5 (309.76): C, 62.04; H, 3.90; N,
22.61. Found: C, 62.07; H, 3.89; N, 22.61%.
5-Methyl-8-o-tolyl-7,8-dihydro-6H-pyrazolo[1,5-a]pyrrolo
[3,2-e]pyrimidine-3- carbonitrile (6k)
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Yield: 2.31 g (80%); recrystallized from ethanol/DMF (9:1)
to afford white needle; mp 283–284 °C; IR (KBr): 3053 w,
2955 w, 2860 w, 2216 m, 1600 m, 1512 s, 1318 m cm−1;
1H NMR (DMSO-d6) δ: 2.49 (s, 3H, CH3), 2.51 (s, 3H,
CH3), 3.39 (t, 2H, J=9 Hz, CH2), 4.42 (t, 2H, J=9 Hz,
CH2), 7.41 (m, 4H, Ar-H), 8.39 (s, 1H, Ar-H). MS (70 eV)
m\z (%): 289 [M+] (100). Anal. Calcd. for C17H15N5
(289.34): C, 70.57; H, 5.23; N, 24.20. Found: C, 70.61;
H, 5.19; N, 24.20%.
8-(4-Chlorophenyl)-5-methyl-7,8-dihydro-6H-pyrazolo
[1,5-a]pyrrolo[3,2-e] pyrimidine-3- carbonitrile (6l)
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derivatives. Spectrochim Acta A 60:3101
Yield: 2.25 g (73%); recrystallized from ethanol/DMF (8:2)
to afford colorless solid; mp 275–276 °C; IR (KBr):
3092 w, 2937 w, 2221 m, 1627 m, 1576 m, 1523 w,
1
1491 m cm−1; H NMR (DMSO-d6) δ: 2.45 (s, 3H, CH3),
3.29 (t, 2H, J=9 Hz, CH2), 4.37 (t, 2H, J=9 Hz, CH2), 7.30
(d, 2H, J=8.1 Hz, Ar-H), 7.59 (d, 2H, J=8.1 Hz, Ar-H),
8.50 (s, 1H, Ar-H). MS (70 eV) m\z (%): 309 [M+] (100),
311 [M+2] (33). Anal. Calcd. for C16H12ClN5 (309.76): C,
62.04; H, 3.90; N, 22.61. Found: C, 62.09; H, 3.87; N,
22.66%.
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Acknowledgements The authors thank to UGC and CSIR, New
Delhi, India, for financial support for this research project. Thank to
Professor D. D. Dhavale, Department of Chemistry, University of
Pune, India, for his valuable cooperation for the measurement of 1H
NMR, 13C NMR, Mass and Fluorescence. Authors also thanks to Dr.
V. B. Gaikwad, Principal. K. R. T. Arts, B. H. Commerce and A. M.
Science College, Nashik - 02, MS, India, for valuable cooperation for
the measurement of IR and UV.
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