Synthesis and fluorescence investigation of differently substituted Benzo[b][1,8]Naphthyridines: Interaction with different solvents and bovine serum albumin (BSA)

Article abstract of DOI:10.1007/s10895-010-0783-1

A series of benzo[b][1, 8]naphthyridines has been synthesized by Friedlaender condensation of 2-aminoquinoline-3-carbaldehyde 1 (o-aminoaldehyde) with active methylenes in basic medium. The fluorescence spectroscopic properties of some representative comp

Full text of DOI:10.1007/s10895-010-0783-1

J Fluoresc (2011) 21:1033–1047
DOI 10.1007/s10895-010-0783-1
RAPID COMMUNICATION
Synthesis and Fluorescence Investigation of Differently
Substituted Benzo[b][1,8]Naphthyridines: Interaction
with Different Solvents and Bovine Serum Albumin (BSA)
Deepak P. Shelar & Sandeep R. Patil & Ramhari V. Rote &
Raghunath B. Toche & Madhukar N. Jachak
Received: 2 September 2010 /Accepted: 25 November 2010 /Published online: 9 December 2010
#
Springer Science+Business Media, LLC 2010
Abstract A series of benzo[b][1, 8]naphthyridines has
been synthesized by Friedländer condensation of 2-
aminoquinoline-3-carbaldehyde 1 (o-aminoaldehyde) with
active methylenes in basic medium. The fluorescence
spectroscopic properties of some representative compounds
has been studied in different organic solvents; moreover
interaction with bovine serum albumin (BSA) in phosphate
buffer was examined by UV–vis and fluorescence spec-
troscopy. The effect of electron donor-acceptor substituents
on fluorescence properties of benzo[b][1, 8]naphthyridines
13(a-n) has been investigated along with their fluorescent
quantum yields.
during past decade. Recently, several donor and/or acceptor
substituted compounds related to carbazoles, acridines etc.
were synthesized and photoinduced charged separation has
been intensively studied [20–22]. The 4-N,N-dimethylami-
nophenyl derivatives of bis-pyrazolo[3,4-b;4’3’-e]pyridine
and pyrazolo[3,4-b]quinoline are further representatives of
bulky π-electron donor-acceptor compounds and were
recently investigated in some detail both experimentally
[23–28] as well as semiempirically [26, 29–31]. These are
highly emissive in non-polar solvents and shows charge
separation and dual fluorescence in polar protic solvents.
The donor-acceptor diphenylpolyenes capable of fluoresc-
ing from their charge-transfer excited states and were
studied for microenvironment of micelles and proteins
[32–35]. From literature, it was observed that the photo-
physical properties of heterocyclic compounds in different
organic solvents were little explored. Prompted with these
literature reports, we undertook the synthesis and study
photophysical properties of benzonaphthyridines obtained
from 2-aminoquinoline-3-carbaldehyde (o-aminoaldehyde)
1. The construction of ring structures from orthoaminoal-
dehyde as a starting material has wide applicability for the
annulation of various heterocyclic systems [36–56].
In our earlier communications [57–61], we have reported
the synthetic utility of heterocyclic o-aminoaldehyde in
which annulation of heterocyclic system on pyrazole and
pyrazolopyridine nucleus were performed and recently [62]
synthesis of fluorescent benzo[b][1, 8]naphthyridine-3-
carbonitrile using 1 has been reported. In this communica-
tion, we extend the work towards the synthesis of several
linear polycyclic heterocycles from 1 and studied their
photophysical properties. We also studied the effect of
specific solvent-fluorophore interaction on absorption and
emission of flurophore 13k, 15b as well as fluorescence
properties of 13d, 13k, 15a and 15b in aqueous buffer and
.
.
Keywords Fluorophore Solvatochromic effect Bovine
.
.
serum albumin (BSA) Phosphate buffer HOMO- LUMO
Introduction
In recent years, carbon rich organic compounds with a high
degree of π-conjugation has received much attention
because of their unique property as an ideal materials for
advanced electronic and photonic applications, such as
organic light-emitting diodes (OLEDs), liquid-crystal dis-
plays, thin-film transistors, solar cell and optical storage
devices [1–19]. Large π-electron donor-acceptor com-
pounds like ADMS, 9-(4-N,N-dimethylaminophenyl)-an-
thracene, has been the subject of intensive investigations
:
:
:
:
D. P. Shelar S. R. Patil R. V. Rote R. B. Toche
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

1034
J Fluoresc (2011) 21:1033–1047
in bovine serum albumin (BSA) (a well known protein
responsible for transport of a variety of ligands [63]) are
studied. Photophysical properties of 13(a-n) are also
studied and compared absorption and emission maxima
with reference to donor and acceptor substituents on D ring
(Fig. 1). The substituent effect on the performance of 13(a-
n) and 15(a-d) are studied by calculating HOMO, LUMO
energies and electron hole gap by using MOPAC-2009 to
investigate the fluorescence properties of 13 and 15.
ingly, ester functionality in 7(c-d) and 9(a-b) remains intact
in the product, under basic reaction condition. Cyclo-
condensation of 1a or 1b with aliphatic ketones 10(a-b)
and substituted acetophenones 12(a-g) under similar reac-
tion condition smoothly yielded benzo[b][1, 8]naphthyr-
idine 11(a-d) and 13(a-n) respectively in excellent yield.
Reactions of o-aminoaldehyde 1 (2-aminoquinoline-3-
carbaldehyde) with cyclic ketones are especially valuable
for the construction of polycondensed heterocyclic rings.
The synthesis of pentacyclic linear heterocycles can be
achieved by condensation of 1a or 1b with indanone 14(a-
b). However, this condensation was unsuccessful under
mild base such as piperidine, hence; this cyclocondensation
was achieved by using strong base such as ethanolic KOH.
Thus, condensation of 1a or 1b with indanone 14(a-b)
yielded 9,10-dimethoxy-7H-benzo[b]indeno[1,2-g][1, 8]
naphthyridine 15(a-d) in 80–89% yield (Scheme 1). Sub-
stituents of 13(a-n) and 15(a-d) are summarized in Tables 1
and 4. Synthesised compounds were characterized by spectro-
scopic and analytical methods. The spectroscopic data of 15b is
Result and Discussion
In continuation of our efforts to explore the synthetic
applicability of o-aminoaldehyde 1 [62], we report herein
condensation of 1 with different reactive methylenes to
obtained polycyclic heterocycles. Thus, Friedländer con-
densation of 1a or 1b with active methylene nitriles such as
malononitrile/cyanoacetamide in ethanol using piperidine
as a base under reflux yielded 2-aminobenzo[b][1, 8]
naphthyridine-3-carbonitrile 3(a-b) and 2-aminobenzo[b]
[1, 8]naphthyridine-3-carboxymide 5(a-b) respectively in
83-87% yield. In this cyclization, the reactive methylene
undergoes Aldol condensation with carbonyl of 1 then
intramolecular attack of amino on nitrile to yield 3 or 5.
However, the course of reaction of 1 with cyanoacetic ester
6a or diethyl malonate 6b is different under similar reaction
conditions in which Aldol type condensation of aldehyde
carbonyl of 1 with active methylene, then SN2 attack of –
NH2 functionality on to ester, displacing ethoxy group. This
cyclocondensation furnished tricyclic benzo[b][1, 8]naph-
thyridine derivatives 7(a-d) in good yield. It was interesting
to observe that when condensation partner of 1 is aceto-
acetic ester 8 then Friedländer condensation occur via
usual combined Schiff base formation and then Aldol
condensation to furnished 9(a-b) in 83-84% yield. Surpris-
1
discussed here. The H NMR of 15b shows three singlet at
3.88, 3.96 and 4.05 ppm corresponds to protons of three
methoxy groups, singlet at 3.75 ppm corresponds to methy-
lene protons. All aromatic protons shows expected chemical
shifts and splitting patterns which resembles with the structure
of 15b. The mass spectrum of 15b reveals a molecular ion
peak m/z at 358. The 13C NMR spectrum of this compound
in agreement with the structure proposed. (Scheme 1)
Semi-empirical study of Benzo[b][1, 8]naphthyridine
13(a-n) and 2,9,10-trimethoxy-7H-benzo[b]indeno[1,2-g]
[1, 8]naphthyridine 15(a-d)
The heterocycles which are useful as Organic Light
Emitting Diodes (OLED) should fluoresces between 400–
700 nm and HOMO/LUMO or ‘electron-hole’ gap in the
Fig. 1 3D picture of benzo[b]
[1, 8]naphthyridine 13(a-g) and
13(h-n)

J Fluoresc (2011) 21:1033–1047
1035
O
R
CN
R
NH2
NH2
N
5(a-b)
N
N
3(a-b)
N
NH2
O
CN
O
EtOH, Piperidine
reflux, 2 h
EtOH, Piperidine
reflux, 1 h
OCH2CH3
6(a-b)
NH2
CN
2
R'
O
R
CN
R'
4
Ethanol, Piperidine
reflux, 2 h
N
N
H
O
O
7(a-d)
R''
R
R
10(a-b)
7a; R=H, R'=CN,
7b; R=OCH3, R'=CN,
7c; R=H, R'= -COOCH2CH3,
R''
H
Ethanol, Piperidine
reflux, 1 h
CH3
N
N
N
NH2
7d; R=OCH3, R'= -COOCH2CH3
1(a-b)
11(a-d)
O
11a; R=H, R''= -COCH3,
11b; R=OCH3, R''= -COCH3,
11c; R=H, R''=H,
R''
R
8
R''
O
Ethanol, Piperidine
reflux, 1 h
11d; R=OCH3, R''= H
R1
R2
CH3
N
9(a-b)
N
EtOH, Piperidine
reflux, 2 h
Ethanol, aq. KOH,
reflux, 1 h
ArCOCH3
9a; R=H, R''= -COOCH2CH3,
9b; R=OCH3, R''= -COOCH2CH3,
12(a-g)
14(a-b)
R
R2
R1
R1
R
R2
R3
N
N
N
N
15(a-d)
13(a-n)
R4
Scheme 1 Synthesis of Benzo[b][1,8]naphthyridines
Table 1 The molecular electronic properties (HOMO-LUMO energy, GAP) of the 2-(4-Bromophenyl)benzo[b][1, 8]naphthyridine 13(a-n) and
9,10-dimethoxy-7H-benzo[b]indeno[1,2-g][1, 8]naphthyridine 15(a-d)
Comp.
R
R1
R2
R3
R4
HOMO (eV)
LUMO (eV)
GAP (eV)
13a
13b
13c
13d
13e
13f
H
H
H
Br
H
H
CF3
H
H
H
H
H
H
CF3
H
H
H
H
–
-9.116
-9.156
-9.616
-8.672
-8.401
-8.848
-10.288
-9.187
-9.079
-8.987
-8.513
-8.247
-8.527
-8.994
-8.329
-8.234
-8.849
-8.787
-1.601
-1.556
-2.987
-1.369
-1.408
-1.387
-2.587
-1.572
-1.580
-1.750
-1.330
-1.368
-1.342
-1.311
-1.315
-1.289
-1.366
-1.327
7.515
7.600
6.629
7.303
6.993
7.461
7.701
7.615
7.499
7.237
7.183
6.879
7.185
7.683
7.014
6.945
7.483
7.460
H
H
H
Cl
H
H
CF3
H
H
H
H
OCH3
OCH3
CH3
NO2
Br
H
H
OCH3
H
H
H
13g
13h
13i
H
H
H
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
H
H
H
H
H
Cl
13j
H
CF3
H
H
13k
13l
H
OCH3
OCH3
CH3
NO2
–
H
OCH3
H
13m
13n
15a
15b
15c
15d
H
H
H
OCH3
OCH3
H
OCH3
OCH3
H
OCH3
H
–
–
–
–
OCH3
H
H
–
–
GAP = ELUMO-EHOMO

1036
J Fluoresc (2011) 21:1033–1047
range 2.7–3.0 eV i.e. low gap [64]. Prompted with these
quotations, we have calculated HOMO-LUMO energies,
electron hole gap of compounds 13 and 15 by using
MOPAC-2009 (Version 8.331) [65, 66] and are summarized
in Table 1. The charge is more concentrated on ring D as
compared to ring A, B and C (Fig. 1). The donor
chromophores (-CF3,-OCH3 groups) on ring D plays an
important role in increasing the electron density and
lowering electron hole gap. Compounds 13c, 13d, 13e,
13j, 13k, 13l and 13m shows low GAP values indicating
higher overlapping of HOMO or LUMO orbitals which
shows red shift and high quantum yields. On the other
hand, HOMO-LUMO energies of compound 13g and 13n
shows increase in GAP values due to presence of
inductively and mesomerically electron withdrawing chro-
mophore (-NO2) i.e. lower overlapping of atomic orbitals,
this shows blue shift and low quantum yields. Among 15,
methoxy substituted derivatives 15a and 15b shows low
GAP values, it fluoresces at longer wavelength and high
quantum yields as compared to 15c and 15d. (Table 1)
spectra of fluorophore are depends both on orientation
polarizability of the solvent and chemical structure of
fluorophore and solvent. Therefore solvent effect can cause
large change in emission of fluorophore and hence more
easily observed spectral shifts. The solvent-fluorophore
interactions can be studied by examining the UV/vis and
fluorescence spectra of fluorophore in variety of solvents.
Thus, absorption and emission spectra of 13k and 15b were
undertaken in variety of solvents such as non-polar aprotic
(n-Hexane), polar aprotic (THF, DMF, acetonitrile, acetone)
and polar protic (Methanol, Ethanol) at room temperature at
same concentration i.e. 1.0×10-3 M. The absorption and
fluorescence spectral data of 13k and 15b in different
organic solvents are summarized in Table 2 and graphically
represented in Fig. 2. The fluorescence maxima of these
compounds are greatly affected by the solvent polarity. Such a
behavior indicates that the fluorescent state is not the same as
the initially populated locally excited state (LE state), but it is a
polar state with a charge transfer character. We observed that as
the solvent polarity is increased further, the emission spectra
continue to shift to longer wavelength and each monomer
shows a certain solvatochromism in both the absorption
and the emission spectrum. The λabs. max. and λem. max. of
fluorophore 13k and 15b are significantly red-shifted as the
solvent polarity is increased from n-Hexane to acetonitrile. In
non-polar aprotic solvents (such as n-Hexane), the fluores-
cence intensities are weak as well as a shift of the emission
spectrum to shorter wavelength. It has been reported that in
nitrogen heterocycles (e.g. quinoline, isoquinoline and acri-
Photophysical Properties
Effect of Solvent
The effects of solvents on fluorescence spectra are the result
of specific interactions between the solvent and the
fluorophore. Specific interactions are produced by one or
a few neighboring molecules and are determined by
specific chemical properties of both the fluorophore and
the solvent [67, 68]. Specific effects can be due to hydrogen
bonding, acid–base chemistry or charge-transfer interac-
tions, to name a few of the possible origins. The emission
1
dine) there is a nπ* state very close to the π-π* state [69,
70]. In fact, in hydrocarbon solvents, the lowest excited
1
singlet state in these molecules is of n, π* type. Most of
these nitrogen heterocycles are weakly or non-fluorescent in
non-polar and aprotic solvents. However, in polar-aprotic and
Table 2 Absorption maximum (λabs. max.), fluorescence emission
maximum (λem. max.) and fluorescence quantum yield (fF) of 7-
Methoxy-2-(4-methoxyphenyl)benzo[b][1, 8]- naphthyridine 13k and
2,9,10-trimethoxy-7H-benzo[b]indeno[1,2-g][1, 8]naphthyridine 15b
in various solvents (ca 10-3) at room tempa
Solvent
13k
15b
λabs. max. [nm]a
λem. max. [nm]b
fF
λabs. max. [nm]a
λem. max. [nm]b
fF
c
c
Hexane
THF
388
391
402
399
396
398
444
464
472
480
478
484
486
550
0.25
0.27
0.29
0.28
0.32
0.33
0.44
373
376
379
380
387
381
398
469
475
479
481
489
489
525
0.29
0.31
0.33
0.34
0.36
0.37
0.42
Methanol
Ethanol
Acetonitrile
DMF
Acetone
All measurements were performed under degassed conditions
a λabs. is the absorption band at about 10-3 M in the different solvents
b λem. is the fluorescence band at about 10-3 M in the different solvents
c Fluorescence quantum yields; the values ( 0.01-0.03) are relative to that of quinine sulphate (0.57 in 10-3 M H2SO4)

J Fluoresc (2011) 21:1033–1047
1037
Fig. 2 UV–vis absorption
(λabs. max.) and fluorescence
(λem. max.) spectra of 13k
in solvents of different polarity
protic solvents, they become strongly fluorescent due to a
reversal of n, π* and π, π* states [69, 70]. Thus, π- π* is the
lowest energy transition in these molecules in protic solvents.
noted that emission corresponding to only the monomer at
476 nm of 13k (Fig. 3). We observed that, emission is
maximum in acetone because of acetone have keto-enol
tautomerism due to this, conjugation increases as a result
fluorophore may be fluoresces to longer wavelength in acetone.
Thus UV/vis and fluorescence spectra of compounds 3(a-b), 5
(a-b), 7(a-d), 9(a-b), 11(a-d), 13(a-n) and 15(a-d) are taken in
acetone. Fluorescence quantum yield of each were determined
by standard literature procedure using quinine sulphate as a
reference standard [71, 72] and are given in Tables 2, 3 and 4.
1
In protic solvents, the energy gap between 1n, π* and π, π*
(lowest excited singlet state) is probably very small. In
general, in the emission spectra, the emission bands are found
to be similar in acetonitrile and DMF. On the other hand, in
ethanol and methanol, the emission band shifts to the blue it
may be due to intramolecular hydrogen bond interaction
between solvent and fluorophore. As the absorption band
shifts to the blue, the emission band also shifts to the local
emission from the hydrogen bonded clusters. Thus, intramo-
lecular hydrogen bonding between solvent-fluorophore inter-
action can often be identified by examining the emission
spectra in different concentration of methanol. We thought
that, fluorescence may increases as solvent polarity increases
by increasing % of water, but surprisingly, we observed that
intensity of this emission band to gradually increases and we
Table 3 Absorption maximum (λabs. max.), fluorescence emission
maximum (λem. max.) and fluorescence quantum yield (fF) of 2-
aminobenzo[b][1, 8]naphthyridine-3-carbonitrile 3 (a-b), 2-
aminobenzo[b][1, 8]naphthyridine-3-carboxymide 5(a-b), 1,2-dihy-
dro-2-oxobenzo[b][1, 8]naphthyridine-3-carbonitrile 7(a-d), Ethyl-2-
methylbenzo[b][1, 8]- naphthyridine-3-carboxylate 9(a-b) and 1-(2-
methylbenzo[b][1, 8]naphthyridin-3-yl)- ethanone 11(a-d) in acetone
as the solvent (ca.10-3) at room temperature
λabs. max. [nm]a
λem. max. [nm]b
fF
c
Comp.
3a
387
401
392
415
392
398
377
382
362
370
372
375
368
371
483
499
491
510
476
485
465
483
468
476
470
482
480
487
0.34
0.38
0.36
0.40
0.30
0.32
0.26
0.32
0.26
0.29
0.28
0.35
0.33
0.36
3b
5a
5b
7a
7b
7c
7d
9a
9b
11a
11b
11c
11d
All measurements were performed under degassed conditions
a λabs. is the absorption band at about 10-3 M in acetone
b λem. is the fluorescence band at about 10-3 M in acetone
Fig. 3 Fluorescence emission spectra of 13k in methanol to which
water was added. The % of water in the solvent were 1) 10% 2) 20%
3) 30% 4) 40%
c Fluorescence quantum yields; the values ( 0.01-0.03) are relative to that
of quinine sulphate (0.57 in 10-3 M H2SO4)

1038
J Fluoresc (2011) 21:1033–1047
Table 4 Absorption maximum (λabs. max.), fluorescence emission
maximum (λem. max.) and fluorescence quantum yield (fF) of 2-(4-
Bromophenyl)benzo[b][1, 8]naphthyridine 13(a-n) and 9,10-dime-
thoxy-7H-benzo[b]indeno[1,2-g][1, 8]naphthyridine 15(a-d) in ace-
[a]
tone as the solvent (ca. 10-3) at room temperature
R1
R2
R3
R4
λabs. max. [nm][b]
λem. max. [nm][c]
fF
[d]
Comp.
R
13a
13b
13c
13d
13e
13f
H
H
H
H
H
H
Br
Cl
H
H
398
392
378
426
382
388
383
414
403
384
444
401
397
394
370
398
371
373
469
474
484
566
483
480
441
480
481
504
550
498
491
449
484
525
476
483
0.29
0.31
0.35
0.47
0.35
0.34
0.18
0.33
0.34
0.40
0.44
0.39
0.38
0.19
0.35
0.42
0.31
0.34
H
H
CF3
H
H
CF3
H
H
H
OCH3
OCH3
CH3
NO2
Br
H
H
OCH3
H
H
H
H
H
13g
13h
13i
H
H
H
H
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
H
H
H
H
H
H
Cl
H
13j
H
CF3
H
H
CF3
H
13k
13l
H
OCH3
OCH3
CH3
NO2
–
H
OCH3
H
H
13m
13n
15a
15b
15c
15d
H
H
H
H
H
OCH3
OCH3
H
OCH3
OCH3
H
–
OCH3
H
–
–
–
–
OCH3
H
H
–
–
[a] All measurements were performed under degassed conditions. [b] λabs. is the absorption band at about 10-3 M in acetone. [c] λem. is the fluorescence
band at about 10-3 M in acetone. [d] Fluorescence quantum yields; the values ( 0.01-0.03) are relative to that of quinine sulphate (0.57 in 10-3 M H2SO4)
Effect of Concentration
(Fig. 4, line 4), we observed that intensity of this emission
band to gradually increases, and we noted that the emission
corresponding to only the monomer at 550 nm (Fig. 4).
We also examined the effect of concentration on the
fluorescence emission of 13k in acetone. By increasing the
concentration from 1.0×10-7 M (Fig. 4, line 1) to 1.0×10-3 M
Effect of Electron Donor-Acceptor Substituents
From the Table 4, it was observed that fluorescence maxima
of the compound 13(h-n) are larger than 13(a-g) may be due
to presence of strong π-electron donor group i.e. -OCH3 on
the A ring except 13d (Fig. 1). The 3D picture of the
benzonaphthyridines 13(a-n) is depicted in Fig. 1. From the
Table 4, it was noted that compound 13c, 13d, 13e, 13j, 13k
and 13l shows fluorescence band appearing at longer
wavelength was substantially bathochromically shifted, we
ascribe to the increased π-electron density on the D ring,
arising from the electron donating nature of -CF3 group (σ-π
electron donor) at C3 & C5 position (13c, 13j) and -OCH3
group (π-electron donor) at para position (13d, 13k), at C3 &
C4 position (13e, 13l) respectively. Among 13, the 13d and
13k displayed the largest bathochromic shift of absorption
and fluorescence bands, which could be attributed to the
methoxy group at para position on ring D having strongest
electron donating ability having different substituents. On
the other hand, blue shift was observed in 13g and 13n due
to presence of electron acceptor group i.e. -NO2 group at
para position on ring D. Another interesting feature was that
Fig. 4 Effect of concentration on the fluorescence emission spectra of
13k recorded in acetone at room temperature (1) 1.0×10-7 M, (2) 1.0×
10-6 M, (3) 1.0×10-5 M, (4) 1.0×10-3

J Fluoresc (2011) 21:1033–1047
1039
Table 5 Absorption maximum (λabs. max.), fluorescence emission
maximum (λem. max.) and fluorescence quantum yield (fF) of benzo[b]
[1, 8]naphthyridine (13d, 13k) and 9,10-dimethoxy-7H-benzo[b]
indeno[1,2-g][1, 8]naphthyridine (15a, 15b) in phosphate buffer (pH,
7.4) and BSA (5.0×10-6 mol L-1)
halo substituted molecules (compounds 13a, 13b, 13h and
13i) shows less fluorescence, quantum yield than methoxy
substituted compounds (φF=0.39-0.44). This may be due to
the quenching of fluorescence with halogen atoms as the
substitution. The comparative absorption and emission spectra
of compounds 13j, 13k and 13n are graphically presented in
Fig. 5. We also noted that among 15, the methoxy substituted
compounds i.e. 15(a-b) shows more fluorescence and
quantum yields as compare to 15(c-d) may be due to presence
of -OCH3 group in 15(a-b) [R1=R2=OCH3] (Table 4).
Compound
λabs. max. (nm)
λem. max. (nm)
fF ( 0.002)
Buffer
BSA
Buffer
BSA
Buffer
BSA
13d
13k
15a
15b
390
397
386
393
391
398
388
392
572
560
488
533
504
496
440
472
0.42
0.40
0.33
0.39
0.46
0.45
0.38
0.42
The Effect of BSA on the Fluorescence Emission
of Compounds 13d, 13k, 15a and 15b in Phosphate Buffer
In order to examine the interaction of 13d, 13k, 15a and
15b with bovine serum albumin (BSA), the fluorescence
titrations with BSA, was carried out in phosphate buffer of
pH 7.4. The absorption and fluorescent spectral data of 13d,
13k, 15a and 15b are collected in Table 5 and λem. max. is
graphically presented in Fig. 6. We observed the blue shift
of λem. max. for 13d, 13k, 15a and 15b. We also examined
the effect of increasing BSA concentration on fluorescence
emission and noted that gradually increase in the concen-
tration of BSA in the solutions of 13k in phosphate buffer
results in an enhancement of the fluorescence emission and
quantum yield (fF) (Fig. 7). The blue shift in the λem. max.
suggests that the polarities of the protein environments in
which the benzo[b][1, 8]naphthyridines are located are less
that the polarity of the bulk aqueous phase since similar blue
shifts are observed in less polar organic solvents. This shows
the binding of the probes to a hydrophobic site of the protein.
activemethylene nitrile, active methylene and cyclic ketone
such as indanone with 1. Our methods have several
additional advantages such as milder reaction condition,
shorter reaction time, scalable and lack of side product.
UV–vis absorption and emission spectroscopic studies
of 13k and 15b have been done in three types of solvents
i.e. non-polar aprotic, polar aprotic, polar protic and it
exhibit solvatochromic fluorescence emission in organic
solvents. The interaction of 13d, 13k, 15a and 15b with
BSA have been investigated by UV–vis absorption and
fluorescence spectroscopy and observed that the λem. max.
gets blue-shifted upon binding with BSA. However the
fluorescence intensity enhancement is linear with the
increasing in BSA concentration (13k). The fluorescence
properties of benzo[b][1, 8]naphthyridines 13(a-n) depend
upon the nature of substituents present on ring D. Thus,
benzo[b][1, 8]naphthyridines 13(a-n) bearing electron-
releasing group i.e. substituents like di-CF3 and -OMe
(Compound 13c, 13j, 13d, 13e, 13k and 13l) on ring D
(Fig. 1) fluoresces at longer wavelength as compared
with the electron-withdrawing group like -NO2 (Com-
pound 13g, 13n) on ring D (Fig. 1) at the para position.
From empirical calculations, we revels that benzo[b][1, 8]
Conclusion
In summary, the tetracyclic and pentacyclic linear hetero-
cycles are synthesized by Friedländer condensation of
Fig. 5 The comparative absorp-
tion (UV λMax.) and fluores-
cence (Em λMax.) spectra of
compounds 13j, 13k and 13n
respectively

1040
J Fluoresc (2011) 21:1033–1047
Fig. 6 Comparative fluores-
cence (Em λMax.) spectra of
13d, 13k, 15a and 15b: A] In
Phosphate Buffer, B] In BSA
naphthyridines (13a-n and 15a-d) which shows low electron
hole gap values (e.g. 13c, 13d, 13e, 13j, 13k, 13l, 13m,
15a and 15b) are fluoresces at longer wavelength and have
high quantum yields, while compounds with higher
electron hole gap (e.g. 13b, 13g, 13h and 13n) are
fluoresces at shorter wavelength with low quantum yields
and are in agreement with theoretical observations. This
study has brought out interesting substituent and solvent-
dependent fluorescence properties of benzonaphthyri-
dines. The efficient blue light emission and physical and
chemical stability makes these benzonaphthyridine deriv-
atives as a promising family of materials which may be
useful in photophysical applications. All these synthesized
compounds are addition to the library of new heterocyclic
compounds.
Experimental
General
Bovine serum albumin (BSA) and Quinine sulphate was
purchased from HiMedia Laboratories Pvt. Ltd. Mumbai
(India) and Research-Lab Fine Chem Industries, Mumbai
(India) respectively. All other chemicals, reagents and
solvents were obtained from LOBA Chemie. Pvt. Ltd.,
Mumbai (India), Spectrochem, Mumbai (India) and E.
Merck (India). All AR-grade organic solvents were dried
and freshly distilled prior to use. The UV-grade solvents
were used for spectral studies. Melting points were
determined on a Gallenkamp melting point apparatus,
Mod. MFB595 in open capillary tubes and are uncorrected.
Fourier transform infrared (FTIR) spectra in KBr disk were
1
measured on a Shimadzu FTIR-408 spectrophotometer. H
NMR and 13C NMR spectra were recorded on a Varian XL-
300 MHz spectrometer using tetramethylsilane (TMS) as
internal standard and solvents are deuterio-chloroform
(CDCl3) and deuterio-dimethylsulphoxide (DMSO-d6).
Chemical shifts are reported in ppm from internal tetrame-
thylsilane standard and are given in δ-units. High-resolution
mass spectra are obtained with a Mat 112 Varian Mat
Bremen (70 eV) mass spectrometer. Elemental analyses are
performed on a Hosli CH-Analyzer and are within 0.3 of
the theoretical percentage. The absorption spectra were
measured using a Shimadzu UV-1601 UV–VIS spectro-
photometer. The fluorescence spectra were recorded on a
RF-5301 PC spectrofluorophotometer by exciting the
samples at their absorption maximum (λabs. max.). Com-
pounds for UV and fluorescence measurements are dis-
solved in acetone, UV and fluorescence scan are recorded
from 200 to 600 nm. The Фf relative to quinine sulphate in
1.0×10-3 mol L-1 H2SO4 (Фf=0.57) was measured at room
temperature by standard literature procedure [73–75]. Both
Fig. 7 Fluorescence emission spectra of 13k with increasing BSA
concentration; curves a-e correspond to [BSA] 1.0, 2.0, 3.0, 4.0 and
5.0 (x 10-6 mol L-1), respectively

J Fluoresc (2011) 21:1033–1047
1041
samples and standard were excited at the same excitation
wavelength and the optical density (OD) of the standard
and the sample was adjusted to be nearly equal. For all
electronic spectroscopic studies (absorption, fluorescence
excitation and emission) 1.0×10-3 mol L-1 solutions of the
compounds were used. All reactions are monitored by thin
layer chromatography, carried out on 0.2 mm silica gel
60 F254 (Merck) plates using UV light (250 and 400 nm)
and Fluorescence light (400 and 600 nm) for detection. For
fluorescence quenching studies, the required amount of BSA
solution (in phosphate buffer) and the required amount of
benzo[b][1, 8]naphthyridines solution in dimethylsulphoxide
(DMSO) (1.0×10-4 mol L-1) were taken in a 5 ml volumetric
flask. Since the benzo[b][1, 8]naphthyridines are sparingly
soluble in water, their stock solutions were prepared in
DMSO, which is used as a solvent for interaction studies of
serum albumins [76].
156.34, 158.74, 159.63. MS (70 eV) m/z (%): 250 [M+]
(79), 223 (44), 207 (49), 130 (51), 69 (28), 44 (61), 32 (74).
Anal. Calcd. for C14H10N4O (250.26): C, 67.20; H, 4.00;
N, 22.40% Found: C, 67.18; H, 3.98; N, 22.38%
Synthesis of 2-Aminobenzo[b][1, 8]Naphthyridine-3-Car-
boxymide (5a, b) A mixture of 2-aminoquinoline-3-carbal-
dehyde (1a-b) (0.01 mol) & cyanoacetamide 4 (0.01 mol)
in ethanol (10 mL) containing catalytic amount of piperi-
dine was refluxed for 2 h. After completion of reaction
(TLC checked), reaction mixture was cooled to room
temperature. The separated solid product was collected by
suction filtration, washed with cold methanol (10 mL),
dried under vacuum and recrystallized from Ethanol: DMF
(70: 30) (v: v).
2-Aminobenzo[b][1, 8]Naphthyridine-3-Carboxymide (5a)
Yield 0.204 g (85%), recrystallised from Ethanol: DMF (70:
30) to afford yellow solid; M.p. 289–292 °C, IR (KBr):
3,440 m, 3,410 m, 3,245 m, 3,197 m, 2,929 m, 1,671 s,
Synthesis
1
Synthesis of 2-Aminobenzo[b][1, 8]Naphthyridine-3-Car-
bonitrile (3a, b) A mixture of 2-aminoquinoline-3-carbalde-
hyde (1a-b) (0.01 mol) & malononitrile 2 (0.01 mol) in
ethanol (10 mL) containing catalytic amount of piperidine
was refluxed for 1 h. After completion of reaction (TLC
checked), reaction mixture was cooled to room temperature.
The separated solid product was collected by suction
filtration, washed with cold methanol (10 mL), dried under
vacuum and recrystallized from Ethanol: DMF (90:10) (v: v).
1,613 scm-1, H NMR (300 MHz DMSO-d6) δ: 7.15 (dd,
1 H, J=7.9 & 8.2 Hz, Ar-H), 7.46 (bs, 2 H, NH), 7.89 (dd,
1 H, J=8.2 & 8.6 Hz, Ar-H), 8.04 (d, 1 H, J=7.9 Hz, Ar-H),
8.17 (d, 1 H, J=8.6 Hz, Ar-H), 8.40 (bs, 2 H, NH), 8.82 (s,
1 H, Ar-H), 8.96 (s,1 H, Ar-H). MS (70 eV) m/z (%): 238
[M+] (78), 221 (31), 194 (76), 166 (62), 139 (59), 110 (45),
77 (67). Anal. Calcd. for C13H10N4O (238.24): C, 65.54; H,
4.20; N, 23.52% Found: C, 65.55; H, 4.21; N, 23.55%
2-Amino-7-Methoxybenzo[b][1, 8]Naphthyridine-3-Car-
boxymide (5b) Yield 0.232 g (86%), recrystallised from
Ethanol: DMF (80:20) to afford yellow prism, M.p. 283–
285 °C. IR (KBr): 3,448 m, 3,419 m, 3,266 m, 3,207 m,
2,955 s, 1,675 s, 1,612 s, 1,022 mcm-1. 1H NMR
(300 MHz DMSO-d6) δ: 4.01 (s, 3 H, OCH3), 7.10 (d,
1 H, J=8.7 Hz, Ar- H), 7.21 (s, 1 H, Ar-H), 7.72 (bs, 2 H,
NH), 7.98 (d, 1 H, J=8.7 Hz, Ar-H), 8.34 (bs, 2 H, NH),
8.61 (s, 1 H, Ar-H), 8.65 (s, 1 H, Ar-H). 13C NMR
(75 MHz DMSO-d6) δ: 55.47, 105.04, 114.51, 115.62,
118.23, 120.37, 130.19, 138.19, 139.98, 152.95, 155.91,
159.36, 161.94, 169.00. MS (70 eV) m/z (%): 268 [M+]
(77), 251 (41), 225 (73), 196 (29), 181 (33), 44 (49), 32
(71). Anal. Calcd. for C14H12N4O2 (268.27): C, 62.68; H,
4.47; N, 20.89%. Found: C, 62.66; H, 4.48; N, 20.88%.
2-Aminobenzo[b][1, 8]Naphthyridine-3-Carbonitrile (3a)
Yield: 0.184 g (83%), recrystallized from Ethanol: DMF
(90:10) to afford yellow solid; M.p. 283–286 °C, IR (KBr):
1
3,413 m, 3,375 m, 2,911 s, 2,219 s, 1,633 scm-1. H NMR
(300 MHz DMSO-d6) δ: 7.39 (dd, 1 H, J=8.2 & 8.5 Hz,
Ar-H), 7.53 (bs, 2 H, NH), 7.77 (dd, 1 H, J=8.5 & 8.1 Hz,
Ar-H), 7.92 (d, 1 H, J=8.2 Hz, Ar-H), 8.08 (d, 1 H, J=
8.1 Hz, Ar-H), 8.66 (s, 1 H, Ar-H), 8.78 (s, 1 H, Ar-H). MS
(70 eV) m/z (%): 220 [M+] (20), 193 (30), 150 (20), 136
(60), 105 (40), 77 (40). Anal. Calcd. for C13H8N4 (220.23):
C, 70.90; H, 3.63; N, 25.45% Found: C, 70.93; H, 3.60; N,
25.46%
7-Methoxy-2-Amino[b][1, 8]Naphthyridine-3-Carbonitrile
(3b) Yield: 0.218 g (87%), recrystalized from Ethanol:
DMF (80: 20) to afford yellow needles; M.p. 278–281 °C.
IR (KBr): 3,442 m, 3,378 m, 2,914 s, 2,230 s, 1,621 s,
1,019 mcm-1.1H NMR (300 MHz DMSO-d6) δ: 3.93 (s,
3 H, OCH3), 6.99 (bs, 2 H, NH), 7.43 (d, 1 H, J=9.0 Hz,
Ar-H), 7.51 (s, 1 H, Ar-H), 8.24 (d, 1 H, J=9.0 Hz, Ar-H),
9.21 (s, 1 H, Ar-H), 9.44 (s, 1 H, Ar-H). 13C NMR
(75 MHz DMSO-d6) δ: 58.32, 98.26, 108.11, 112.44,
122.78, 123.36, 128.21, 132.66, 133.43, 146.53, 148.27,
Synthesis of 1,2-Dihydro-2-Oxobenzo[b][1, 8]Naphthyri-
dine-3-Carbonitrile (7 a-d) A mixture of 2-aminoquinoline-
3-carbaldehyde (1a-b) (0.01 mol) & ethylcyanoacetate (6a)
(0.01 mol) in ethanol (10 mL) containing catalytic amount of
piperidine was refluxed for 2 h. After completion of reaction
(TLC checked), reaction mixture was cooled to room
temperature. The separated solid product was collected by
suction filtration, washed with cold methanol or pet-ether,

1042
J Fluoresc (2011) 21:1033–1047
dried under suction and recrystallized from Ethanol: DMF
(80: 20) (v: v) or Ethanol.
Ar-H), 9.20 (s, 1 H, Ar-H), 9.40 (s, 1 H, Ar-H). 13C NMR
(75 MHz DMSO-d6) δ: 19.22, 55.89, 66.72, 104.22,
120.51, 121.20, 121.88, 122.26, 126.47, 132.77, 135.24,
141.02, 152.13, 161.23, 162.88, 167.34. MS (70 eV) m/z
(%): 298 [M+] (76), 253 (68), 226 (91), 198 (79), 183 (51),
127 (52), 44 (31). Anal. Calcd. for C16H14N2O4 (298.29):
C, 64.42; H, 4.69; N, 9.39% Found: C, 64.43; H, 4.71; N,
9.37%
1,2-Dihydro-2-Oxobenzo[b][1, 8]Naphthyridine-3-Carbon-
itrile (7a) Yield: 0.179 g (80%), recrystalized from Etha-
nol: DMF (80: 20) to afford pale yellow crystal; M.p. 261–
264 °C. IR (KBr): 3,240 m, 2,912 m, 2,244 s, 1,674 s,
1
1,601 scm-1. H NMR (300 MHz DMSO-d6) δ: 7.22 (bs,
1 H, NH), 7.84 (dd, 1 H, J=8.2 & 8.6 Hz, Ar-H), 7.97 (dd,
1 H, J=8.6 & 8.0 Hz, Ar-H), 8.09 (d, 1 H, J=8.2 Hz, Ar-
H), 8.39 (d, 1 H, J=8.0 Hz, Ar-H), 9.02 (s, 1 H, Ar-H),
9.13 (s, 1 H, Ar-H). MS (70 eV) m/z (%): 221 [M+] (85),
193 (96), 178 (87), 150 (61), 127 (67), 96 (54), 77 (42), 44
(64). Anal. Calcd. for C13H7N3O (221.21): C, 70.58; H,
3.16; N, 19.00%. Found: C, 70.56; H, 3.18; N, 18.98%.
Synthesis of Ethyl-2-Methylbenzo[b][1, 8]Naphthyridine-3-
Carboxylate (9 a-b) A mixture of 2-aminoquinoline-3-
carbaldehyde (1a-b) (0.01 mol) & ethylacetoacetate (8)
(0.01 mol) in ethanol (10 mL) containing 2-3 drops of
piperidine was refluxed for 1 h. After completion of
reaction (TLC checked), reaction mass dumped over ice-
crushed water (20 mL) and stirred for the 30 mins.,
separated solid was filtered by suction, washed with cold
n-hexane (20 mL), dried under vacuum and recrystallized
from Ethanol or Toluene.
1,2-Dihydro-7-Methoxy-2-Oxobenzo[b][1, 8]Naphthyri-
dine-3-Carbonitrile (7b) Yield: 0.218 g (86%), recrystalized
from Ethanol: DMF (70: 30) to afford yellow needles; M.p.
256–258 °C. IR (KBr): 3,256 m, 2,902 m, 2,239 s, 1,669 s,
1,598 s, 1,027 mcm-1.1H NMR (300 MHz DMSO-d6) δ:
4.03 (s, 3 H, OCH3), 6.92 (bs, 1 H, NH), 7.25 (d, 1 H, J=
8.6 Hz, Ar-H), 7.47 (s, 1 H, Ar-H), 8.12 (d, 1 H, J=8.6 Hz,
Ar-H), 9.31 (s, 1 H, Ar-H), 9.49 (s, 1 H, Ar-H). 13C NMR
(75 MHz DMSO-d6) δ: 58.13, 98.47, 107.46, 109.11,
114.45, 123.65, 124.73, 126.88, 129.40, 135.29, 145.73,
154.32, 158.23, 166.30. MS (70 eV) m/z (%): 251 [M+] (72),
223 (67), 208 (51), 193 (38), 180 (89), 153 (62), 126 (60),
44 (81). Anal. Calcd. for C14H9N3O2 (251.24): C, 66.93; H,
3.58; N, 16.73% Found: C, 66.96; H, 3.60; N, 16.71%
Ethyl-2-Methylbenzo[b][1, 8]Naphthyridine-3-Carboxylate
(9a) Yield: 0.222 g (83%), recrystalized from ethanol to
afford yellow crystal; M.p. 264-267 °C. IR (KBr): 2,945 m,
1
1,738 s, 1,612 s, 1,018 mcm-1. H NMR (300 MHz CDCl3)
δ: 1.69 (t, 3 H, J=5.9 Hz, CH3), 2.79 (s, 3 H, CH3), 4.33 (q,
2 H, J=5.9 Hz, CH2), 7.34 (dd, 1 H, J=8.2 & 8.7 Hz, Ar-H),
7.79 (dd, 1 H, J=8.7 & 8.1 Hz, Ar-H), 8.09 (d, 1 H, J=
8.2 Hz, Ar-H), 8.36 (d, 1 H, J=8.1 Hz, Ar-H), 8.78 (s, 1 H,
Ar-H), 9.19 (s, 1 H, Ar-H). MS (70 eV) m/z (%): 266 [M+]
(95), 251 (89), 213 (85), 197 (64), 158 (80), 77 (71), 69 (47),
53 (38). Anal. Calcd. for C16H14N2O2 (266.29): C, 72.18; H,
5.26; N, 10.52% Found: C, 72.15; H, 5.24; N, 10.50%
Ethyl-1,2-Dihydro-2-Oxobenzo[b][1, 8]Naphthyridine-3-
Carboxylate (7c) Yield: 0.232 g (86%), recrystalized from
ethanol to afford pale yellow solid; M.p. 195–198 °C. IR
(KBr): 3,221 m, 2,901 s, 1,738 s, 1,669 s, 1,618 s, 1,022 m
cm-1. 1H NMR (300 MHz CDCl3) δ: 1.77 (t, 3 H, J=
5.3 Hz, CH3), 4.34 (q, 2 H, J=5.3 Hz, CH2), 7.18 (bs, 1 H,
NH), 7.29 (dd, 1 H, J=7.7 & 8.1 Hz, Ar-H), 7.57 (dd, 1 H,
J=8.1 & 8.4 Hz, Ar-H), 7.92 (d, 1 H, J=7.7 Hz, Ar-H),
8.32 (d, 1 H, J=8.4 Hz, Ar-H), 9.12 (s, 1 H, Ar-H), 9.23 (s,
1 H, Ar-H). MS (70 eV) m/z (%): 268 [M+] (79), 223 (66),
195 (76), 166 (59), 122 (64), 77 (48), 45 (34). Anal. Calcd.
for C15H12N2O3 (268.27): C, 67.16; H, 4.47; N, 10.44%
Found: C, 67.18; H, 4.45; N, 10.42%
Ethyl-7-Methoxy-2-Methylbenzo[b][1, 8]Naphthyridine-3-
Carboxylate (9b) Yield: 0.249 g (84%), recrystalized from
ethanol to afford yellow needles; M.p. 257-260 °C. IR
(KBr): 2,940 m, 1,740, 1,619 s, 1,024 mcm-1.1H NMR
(300 MHz CDCl3) δ: 1.72 (t, 3 H, J=4.8 Hz, CH3), 2.66 (s,
3 H, CH3), 3.96 (s, 3 H, OCH3), 4.43 (q, 2 H, J=4.8 Hz,
CH2), 7.43 (d, 1 H, J=8.8 Hz, Ar-H), 7.56 (s, 1 H, Ar-H),
8.24 (d, 1 H, J=8.8 Hz, Ar-H), 9.21 (s, 1 H, Ar-H), 9.44 (s,
1 H, Ar-H). 13C NMR (75 MHz CDCl3) δ: 19.24, 26.72,
59.33, 68.45, 110.21, 121.47, 123.57, 126.94, 129.78,
132.43, 137.44, 138.73, 147.87, 154.27, 158.94, 159.64,
169.09. MS (70 eV) m/z (%): 296 [M+] (69), 277 (94), 253
(74), 224 (41), 182 (57), 152 (59), 127 (49), 77 (64), 44
(88). Anal. Calcd. for C17H16N2O3 (296.32): C, 68.91; H,
5.40; N, 9.45%. Found: C, 68.90; H, 5.42; N, 9.47%.
Ethyl-1,2-Dihydro-7-Methoxy-2-Oxobenzo[b][1, 8]Naph-
thyridine-3-Carboxylate (7d) Yield: 0.260 g (87%), recrys-
talized from ethanol to afford yellow needles; M.p. 185–
188 °C. IR (KBr): 3,249 m, 2,912 s, 1,737 s, 1,674 m,
1,601 s, 1,027 scm-1.1H NMR (300 MHz CDCl3) δ: 1.88
(t, 3 H, J=5.2 Hz, CH3), 3.98 (s, 3 H, OCH3), 4.28 (q, 2 H,
J=5.2 Hz, CH2), 6.28 (bs, 1 H, NH), 7.31 (d, 1 H, J=
8.6 Hz, Ar-H), 7.61 (s, 1 H, Ar-H), 8.29 (d, 1 H, J=8.6 Hz,
Synthesis of 1-(2-Methylbenzo[b][1, 8]Naphthyridin-3-yl)
Ethanone (11 a-d) A mixture of 2-aminoquinoline-3-car-
baldehyde (1a-b) (0.01 mol) & acetyl acetone (10a)
(0.01 mol) in ethanol (10 mL) containing 2-3 drops of

J Fluoresc (2011) 21:1033–1047
1043
piperidine was refluxed for 1 h. After completion of
reaction (TLC checked), reaction mass dumped over ice-
crushed water (20 mL) and stirred for the 30 mins.,
separated solid was filtered by suction, washed with cold
n-hexane (20 mL), dried under vacuum and recrystallized
from Ethanol or Toluene.
7.48 (d, 1 H, J=9.0 Hz, Ar-H), 7.56 (s, 1 H, Ar-H), 8.31 (d,
1 H, J=9.0 Hz, Ar-H), 8.57 (d, 1 H, J=8.2 Hz, Ar-H), 9.37
(s, 1 H, Ar-H). MS (70 eV) m/z (%): 224 [M+] (82), 201
(77), 181 (64), 152 (47), 77 (87), 51 (78). Anal. Calcd. for
C14H12N2O (224.26): C, 75.00; H, 5.35; N, 12.50% Found:
C, 75.02; H, 5.37; N, 12.48%
1-(2-Methylbenzo[b][1, 8]Naphthyridin-3-yl)Ethanone
(11a) Yield: 0.201 g (85%), recrystalized from ethanol to
afford faint yellow solid; M.p. 204-206 °C. IR (KBr): 2,945 s,
1,705 s, 1,632 scm-1. 1H NMR (300 MHz CDCl3) δ: 2.55 (s,
3 H, CH3), 2.89 (s, 3 H, CH3), 7.46 (dd, 1 H, J=7.8 &
8.4 Hz, Ar-H), 7.83 (dd, 1 H, J=8.4 & 8.3 Hz, Ar-H), 8.17
(d, 1 H, J=7.8 Hz, Ar-H), 8.29 (d, 1 H, J=8.3 Hz, Ar-H),
8.78 (s, 1 H, Ar-H), 9.19 (s, 1 H, Ar-H). MS (70 eV) m/z
(%): 236 [M+] (79), 221 (74), 205 (67), 193 (47), 190 (69),
152 (39), 121 (49), 77 (64), 44 (81), 31 (64). Anal. Calcd.
for C15H12N2O (236.27): C, 76.27; H, 5.08; N, 11.86%
Found: C, 76.28; H, 5.10; N, 11.88%
Syntesis of 2-(4-Bromophenyl)Benzo[b][1, 8]Naphthyridine
(13 a-n) A solution of 1a-b (0.001 mol) and p-
bromoacetophenone (12a) (0.001 mol) in ethanol (10 mL)
containing catalytic amount of piperidine was refluxed for
2 h. Completion of the reaction was monitored by thin layer
chromatography (TLC). The mixture was then cooled to
room temperature; the separated solid product was collected
by suction filtration, washed with pet-ether, dried and
recrystallized from ethanol.
2-(4-Bromophenyl)Benzo[b][1, 8]Naphthyridine (13a)
Yield: 0.301 g (90%), recrystalized from ethanol to afford
faint yellow solid; M.p. 95-98 °C. IR (KBr): 3,018 m,
1,640 scm-1. 1H NMR (300 MHz CDCl3) δ: 7.46 (dd, 1 H,
J=8.2 & 8.6 Hz, Ar-H), 7.52 (d, 2 H, J=8.3 Hz, Ar-H),
7.77 (dd, 1 H, J=8.6 & 8.1 Hz, Ar-H), 7.92 (d, 1 H, J=
8.2 Hz, Ar-H), 8.02 (d, 1 H, J=8.1 Hz, Ar H), 8.12 (d, 1 H,
J=7.8 Hz, Ar-H), 8.22 (d, 2 H, J=8.3 Hz, Ar-H), 8.42 (d,
1 H, J=7.8 Hz, Ar-H), 9.23 (s, 1 H, Ar-H). MS (70 eV) m/z
(%): 334 [M+] (84), 336 [M+2] (80), 255 (89), 212 (68),
207 (59), 179 (63), 77 (78). Anal. Calcd. for C18H11N2Br
(335.20): C, 64.67; H, 3.29; N, 8.38% Found: C, 64.65; H,
3.30; N, 8.39%
1-(7-Methoxy-2-Methylbenzo[b][1, 8]Naphthyridin-3-yl)
Ethanone (11b) Yield: 0.230 g (86%), recrystalized from
ethanol to afford pale yellow needles; M.p. 214-217 °C. IR
(KBr): 2,959 m, 1,712 s, 1,620 s, 1,024 scm-1.1H NMR
(300 MHz CDCl3) δ: 2.44 (s, 3 H, CH3), 2.72 (s, 3 H,
CH3), 4.09 (s, 3 H, OCH3), 7.31 (d, 1 H, J=8.8 Hz, Ar-H),
7.46 (s, 1 H, Ar-H), 8.18 (d, 1 H, J=8.8 Hz, Ar-H), 9.11 (s,
1 H, Ar-H), 9.39 (s, 1 H, Ar-H). 13C NMR (75 MHz
CDCl3) δ: 18.24, 28.76, 59.84, 109.44, 124.31, 125.74,
129.16, 133.43, 135.24, 136.37, 138.47, 147.89, 156.74,
159.21, 161.47, 187.20. MS (70 eV) m/z (%): 266 [M+]
(100), 251 (94), 223 (32), 182 (95), 139 (46), 44 (51). Anal.
Calcd. for C16H14N2O2 (266.29): C, 72.18; H, 5.26; N,
10.52%. Found: C, 72.19; H, 5.29; N, 10.50%.
2-(4-Chlorophenyl)Benzo[b][1, 8]Naphthyridine (13b)
Yield: 0.233 g (80%), recrystalized from ethanol to afford
faint brown solid; M.p. 120-123 °C. IR (KBr): 3,030 m,
1,646 scm-1. 1H NMR (300 MHz CDCl3) δ: 7.29 (dd, 1 H,
J=8.1 & 8.4 Hz, Ar-H), 7.42 (d, 2 H, J=8.3 Hz, Ar-H),
7.57 (dd, 1 H, J=8.4 & 8.5 Hz, Ar-H), 7.79 (d, 1 H, J=
8.1 Hz, Ar-H), 8.10 (d, 1 H, J=8.5 Hz, Ar H), 8.22 (d, 1 H,
J=7.8 Hz, Ar-H), 8.36 (d, 2 H, J=8.3 Hz, Ar-H), 8.51 (d,
1 H, J=7.8 Hz, Ar-H), 9.03 (s, 1 H, Ar-H). Anal. Calcd. for
C18H11N2Cl (290.75): C, 74.48; H, 3.79; N, 9.65% Found:
C, 74.52; H, 3.77; N, 9.68%
2-Methylbenzo[b][1, 8]Naphthyridine (11c) Yield: 0.155 g
(79%), recrystalized from toluene to afford faint yellow solid;
M.p. 90-93 °C. IR (KBr): 2,978 s, 1,626 scm-1. 1H NMR
(300 MHz CDCl3) δ: 2.92 (s, 3 H, CH3), 7.22 (dd, 1 H, J=
7.9 & 8.7 Hz, Ar-H), 7.37 (d, 1 H, J=8.5 Hz, Ar-H), 7.67
(dd, 1 H, J=8.7 & 8.3 Hz, Ar-H), 8.14 (d, 1 H, J=7.9 Hz,
Ar-H), 8.25 (d, 1 H, J=8.3 Hz, Ar-H), 8.48 (d, 1 H, J=
8.5 Hz, Ar-H), 9.25 (s, 1 H, Ar-H). 13C NMR (75 MHz
CDCl3) δ: 24.11, 121.55, 123.47, 126.74, 127.41, 127.94,
128.56, 129.47, 135.67, 138.66, 148.72, 153.48, 157.49.
Anal. Calcd. for C13H10N2 (194.23): C, 80.41; H, 5.15; N,
14.43% Found: C, 80.43; H, 5.17; N, 14.49%
2-(3,5-Bis(trifluoromethyl)Phenyl)Benzo[b][1, 8]
Naphthyridine (13c) Yield: 0.344 g (87%), recrystalized
from ethanol to afford yellow solid; M.p. 102-105 °C. IR
1
(KBr): 3,028 m, 1,649 scm-1. H NMR (300 MHz CDCl3)
δ: 7.38 (dd, 1 H, J=8.3 & 8.7 Hz, Ar-H), 7.60 (dd, 1 H, J=
8.7 & 8.5 Hz, Ar-H), 7.84 (d, 1 H, J=8.3 Hz, Ar-H), 7.93
(d, 1 H, J=7.9 Hz, Ar-H), 8.18 (d, 1 H, J=8.5 Hz, Ar-H),
8.34 (d, 1 H, J=7.9 Hz, Ar-H), 8.42 (s, 1 H, Ar-H), 9.24 (s,
2 H, Ar-H), 9.47 (s, 1 H, Ar-H). MS (70 eV) m/z (%): 392
[M+] (59), 351 (78), 323 (80), 254 (66), 254 (56), 213 (47), 179
7-Methoxy-2-Methylbenzo[b][1, 8]Naphthyridine (11d)
Yield: 0.187 g (83%), recrystalized from toulene to afford
green needles; M.p. 84-86 °C. IR (KBr): 2,968 s, 1,618 s,
1,025 mcm-1.1H NMR (300 MHz CDCl3) δ: 3.12 (s, 3 H,
CH3), 4.02 (s, 3 H, OCH3), 7.29 (d, 1 H, J=8.2 Hz, Ar-H),

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J Fluoresc (2011) 21:1033–1047
(79). Anal. Calcd. for C20H10N2F6 (392.30): C, 61.22; H, 2.55;
N, 7.14% Found: C, 61.23; H, 2.56; N, 7.12%
7.9 Hz, Ar-H), 8.22 (d, 1 H, J=8.0 Hz, Ar-H), 8.36 (d, 1 H,
J=8.9 Hz, Ar-H), 8.43 (d, 1 H, J=8.9 Hz, Ar-H), 8.56 (d,
2 H, J=8.8 Hz, Ar-H), 9.18 (s, 1 H, Ar-H). MS (70 eV) m/z
(%): 301 [M+] (88), 255 (82), 179 (55), 77 (68). Anal.
Calcd. for C18H11N3O2 (301.30): C, 71.76; H, 3.65; N,
13.95% Found: C, 71.77; H, 3.66; N, 13.97%
2-(4-Methoxyphenyl)Benzo[b][1, 8]Naphthyridine (13d)
Yield: 0.252 g (88%), recrystalized from ethanol to afford
pale yellow needles; M.p. 114-117 °C. IR (KBr): 3,031 m,
1,649 s, 1,027 mcm-1. 1H NMR (300 MHz CDCl3) δ: 3.98
(s, 3 H, OCH3), 7.10 (d, 2 H, J=9.2 Hz, Ar-H), 7.46 (dd,
1 H, J=8.0 & 8.4 Hz, Ar-H), 7.67 (dd, 1 H, J=8.4 &
8.3 Hz, Ar-H), 7.88 (d, 1 H, J=8.0 Hz, Ar-H), 7.94 (d, 2 H,
J=9.2 Hz, Ar-H), 8.02 (d, 1 H, J=7.7 Hz, Ar-H), 8.19 (d,
1 H, J=8.3 Hz, Ar-H), 8.28 (d, 1 H, J=7.7 Hz, Ar-H), 9.25
(s, 1 H, Ar-H). MS (70 eV) m/z (%): 286 [M+] (100), 271
(68), 255 (35), 242 (42), 121 (29), 63 (32), 39 (22). Anal.
Calcd. for C19H14N2O (286.33): C, 79.72; H, 4.89; N,
9.79% Found: C, 79.73; H, 4.90; N, 9.77%
2-(4-Bromophenyl)-7-Methoxybenzo[b][1, 8]Naphthyridine
(13 h) Yield: 0.312 g (85%), recrystalized from ethanol to
afford yellow solid; M.p. 248-249 °C. IR (KBr): 3,010 m,
1
1,642 s, 1,040 mcm-1. H NMR (300 MHz CDCl3) δ: 4.07
(s, 3 H, OCH3), 7.34 (d, 1 H, J=9.3 Hz, Ar-H), 7.46 (s, 1 H,
Ar-H), 7.89 (d, 2 H, J=8.1 Hz, Ar- H), 8.04 (d, 1 H, J=
7.8 Hz, Ar-H), 8.19 (d, 2 H, J=8.1 Hz, Ar-H), 8.35 (d, 1 H,
J=9.3 Hz, Ar-H), 9.05 (d, 1 H, J=7.8 Hz, Ar-H), 9.46 (s,
1 H, Ar-H). 13C NMR (75 MHz CDCl3) δ: 57.21, 109.42,
122.74, 123.24, 123.66, 126.47, 127.89, 129.30 (2 C’s),
131.51, 133.46 (2 C’s), 135.66, 136.94, 138.40, 145.55,
153.26, 156.19, 158.74. MS (70 eV) m/z (%): 364 [M+]
(89), 366 [M+2] (88), 285 (45), 242 (57), 142 (32), 121
(51). Anal. Calcd. for C19H13N2BrO (365.23): C, 62.63; H,
3.57; N, 7.69% Found: C, 62.64; H, 3.56; N, 7.70%
2-(2,3-Dimethoxyphenyl)Benzo[b][1, 8]Naphthyridine
(13e) Yield: 0.275 g (87%), recrystalized from ethanol to
afford yellow crystal; M.p. 119-122 °C. IR (KBr): 3,029 m,
1
1,646 s, 1,022 mcm-1. H NMR (300 MHz CDCl3) δ: 3.60
(s, 6 H, 2×OCH3), 7.08 (d, 1 H, J=8.7 Hz, Ar-H), 7.26 (dd,
1 H, J=2.5 & 8.7 Hz, Ar-H), 7.38 (d, 1 H, J=2.5 Hz, Ar-H),
7.49 (dd, 1 H, J=8.1 & 8.8 Hz, Ar-H), 7.83 (dd, 1 H, J=8.8
& 7.9 Hz, Ar-H), 7.96 (d, 1 H, J=8.1 Hz, Ar-H), 8.16 (d,
1 H, J=7.8 Hz, Ar-H), 8.20 (d, 1 H, J=7.9 Hz, Ar-H), 8.29
(d, 1 H, J=7.8 Hz, Ar-H), 9.12 (s, 1 H, Ar-H). 13C NMR
(75 MHz CDCl3) δ: 57.43, 56.79, 115.20, 117.47, 120.12,
121.47, 125.33, 127.12, 127.49, 128.32, 128.78, 129.28,
129.82, 135.43, 137.77, 145.64, 149.74, 152.64, 156.57,
159.71. Anal. Calcd. for C20H16N2O2 (316.35): C, 75.94; H,
5.06; N, 8.86% Found: C, 75.92; H, 5.08; N, 8.88%
2-(4-Chlorophenyl)-7-Methoxybenzo[b][1, 8]Naphthyri-
dine (13i) Yield: 0.267 g (83%), recrystalized from ethanol
to afford yellow crystals; M.p. 254-257 °C. IR (KBr): 3,026 m,
1
1,635 s, 1,038 mcm-1. H NMR (300 MHz CDCl3) δ: 4.02
(s, 3 H, OCH3), 7.18 (d, 1 H, J=9.1 Hz, Ar-H), 7.33 (s, 1 H,
Ar-H), 7.74 (d, 2 H, J=8.3 Hz, Ar- H), 7.93 (d, 1 H, J=
7.5 Hz, Ar-H), 8.12 (d, 2 H, J=8.3 Hz, Ar-H), 8.43 (d, 1 H,
J=9.1 Hz, Ar-H), 9.17 (d, 1 H, J=7.5 Hz, Ar-H), 9.33 (s, 1 H,
Ar-H). Anal. Calcd. for C19H13N2ClO (320.77): C, 71.25; H,
4.06; N, 8.75% Found: C, 71.22; H, 4.09; N, 8.77%
2-p-Tolylbenzo[b][1, 8]Naphthyridine (13f) Yield: 0.237 g
(87%), recrystalized from ethanol to afford yellow solid;
M.p. 92-95 °C. IR (KBr): 3,004 m, 1,640 scm-1. 1H
NMR (300 MHz CDCl3) δ: 2.48 (s, 3 H, CH3), 7.44 (d,
2 H, J=8.7 Hz, Ar-H), 7.60 (dd, 1 H, J=8.2 & 8.5 Hz, Ar-
H), 7.98 (dd, 1 H, J=8.5 & 8.1 Hz, Ar-H), 8.07 (d, 1 H, J
=8.2 Hz, Ar-H), 8.29 (d, 2 H, J=8.7 Hz, Ar-H), 8.42 (d,
1 H, J=7.9 Hz, Ar-H), 8.59 (d, 1 H, J=8.1 Hz, Ar-H), 8.68
(d, 1 H, J=7.9 Hz, Ar-H), 8.97 (s, 1 H, Ar-H). MS (70 eV)
m/z (%): 270 [M+] (81), 255 (62), 241 (32), 152 (29), 134
(61), 89 (32). Anal. Calcd. for C19H14N2 (270.33): C,
84.44; H, 5.18; N, 10.37% Found: C, 84.45; H, 5.17; N,
10.35%
2-(3,5-Bis(Trifluoromethyl)Phenyl)-7-Methoxybenzo[b][1,
8]Naphthyridine (13j) Yield: 0.359 g (85%), recrystalized
from ethanol to afford faint green solid; M.p. 199-202 °C.
IR (KBr): 3,024 m, 1,642 s, 1,032 mcm-1. 1H NMR
(300 MHz CDCl3) δ: 4.05 (s, 3 H, OCH3), 7.39 (d, 1 H, J=
9.1 Hz, Ar-H), 7.57 (s, 1 H, Ar-H), 8.08 (d, 1 H, J=7.9 Hz,
Ar-H), 8.27 (d, 1 H, J=9.1 Hz, Ar-H), 8.43 (s, 1 H, Ar-H),
8.78 (s, 2 H, Ar-H), 8.91 (d, 1 H, J=7.9 Hz, Ar-H), 9.52 (s,
1 H, Ar-H). MS (70 eV) m/z (%): 423 [M+1] (100), 380
(69), 354 (74), 310 (18), 285 (64). Anal. Calcd. for
C21H12N2F6O (422.32): C, 59.71; H, 2.84; N, 6.63%
Found: C, 59.70; H, 2.85; N, 6.64%
2-(4-Nitrophenyl)Benzo[b][1, 8]Naphthyridine (13 g)
Yield: 0.239 g (79%), recrystalized from ethanol to afford
brown solid; M.p. 115-118 °C. IR (KBr): 3,033 m, 1,540 m,
1,372 mcm-1. 1H NMR (300 MHz CDCl3) δ: 7.45 (dd, 1 H,
J=7.9 & 7.8 Hz, Ar-H), 7.54 (d, 2 H, J=8.8 Hz, Ar-H),
7.68 (dd, 1 H, J=7.8 & 8.0 Hz, Ar-H), 8.02 (d, 1 H, J=
7-Methoxy-2-(4-Methoxyphenyl)Benzo[b][1, 8]Naphthyri-
dine (13k) Yield: 0.272 g (86%), recrystalized from ethanol
to afford yellow solid; M.p. 229-232 °C. IR (KBr): 3,021 m,
1
1,639 s, 1,036 mcm-1. H NMR (300 MHz DMSO-d6) δ:
3.89 (s, 3 H, OCH3), 4.02 (s, 3 H, OCH3), 7.21 (d, 2 H, J=
8.5 Hz, Ar-H), 7.39 (d, 1 H, J=8.2 Hz, Ar-H), 7.50 (s, 1 H,

J Fluoresc (2011) 21:1033–1047
1045
Ar-H), 7.64 (d, 2 H, J=8.5 Hz, Ar-H), 8.12 (d, 1 H, J=
8.1 Hz, Ar-H), 8.22 (d, 1 H, J=8.2 Hz, Ar-H), 8.84 (d, 1 H,
J=8.1 Hz, Ar-H), 9.38 (s, 1 H, Ar-H). 13C NMR (75 MHz
CDCl3) δ: 55.39, 55.62, 105.80, 114.13 (2 C’s), 117.76,
118.57, 121.45, 122.95, 129.05, 129.68 (2 C’s), 131.20,
136.62, 137.75, 153.01, 155.26, 161.18, 161.70, 162.10. MS
(70 eV) m/z (%): 316 [M+] (100), 301 (32), 230 (19), 158
(15), 115 (12). Anal. Calcd. for C20H16N2O2 (316.35): C,
75.94; H, 5.06; N, 8.86% Found: C, 75.95; H, 5.08; N, 8.87%
(0.01 mol) in ethanolic potassium hydroxide solution
(10 mL, 2%) was refluxed for 1 h. Completion of the
reaction was monitored by Thin Layer Chromatography
(TLC). The mixture was then dumped over ice-crushed
water (20 mL) and stirred for the 30 mins. The separated
solid product was collected by suction filtration, washed
with pet-ether, dried and recrystallized from Methanol.
9,10-Dimethoxy-7H-Benzo[b]Indeno[1,2-g][1, 8]Naph-
thyridine (15a) Yield: 0.281 g (85%), recrystalized from
Methanol to afford yellow solid; M.p. 269-272 °C. IR (KBr):
2,997 m, 2,968 m, 1,618 s, 1,024 mcm-1. 1H NMR (300 MHz
CDCl3) δ: 3.89 (s, 2 H, CH2), 3.95 (s, 3 H, OCH3), 4.01 (s,
3 H, OCH3), 6.78 (s, 1 H, Ar-H), 7.34 (dd, 1 H, J=7.8 &
8.7 Hz, Ar-H), 7.55 (s, 1 H, Ar-H), 7.79 (dd, 1 H, J=8.7 &
8.1 Hz, Ar-H), 8.09 (d, 1 H, J=7.8 Hz, Ar-H), 8.36 (d, 1 H,
J=8.1 Hz, Ar-H), 8.78 (s, 1 H, Ar-H), 9.19 (s, 1 H, Ar-H).
Anal. Calcd. for C21H16N2O2 (328.36): C, 76.82; H, 4.87; N,
8.53% Found: C, 76.84; H, 4.88; N, 8.55%
7-Methoxy-2-(2,3-Dimethoxyphenyl)Benzo[b][1, 8]Naph-
thyridine (13 l) Yield: 0.307 g (88%), recrystalized from
ethanol to afford yellow crystals; M.p. 238-241 °C. IR
(KBr): 3,026 m, 1,635 s, 1,038 mcm-1. 1H NMR
(300 MHz DMSO-d6) δ: 3.80 (s, 6 H, 2×OCH3), 4.04
(s, 3 H, OCH3), 7.10 (d, 1 H, J=9.2 Hz, Ar-H), 7.18 (dd,
1 H, J=2.4 & 9.2 Hz, Ar-H), 7.29 (d, 1 H, J=2.4 Hz, Ar-
H), 7.41 (d, 1 H, J=8.6 Hz, Ar-H), 7.52 (s, 1 H, Ar-H),
7.97 (d, 1 H, J=8.2 Hz, Ar-H), 8.25 (d, 1 H, J=8.6 Hz,
Ar-H), 8.95 (d, 1 H, J=8.2 Hz, Ar-H), 9.32 (s, 1 H, Ar-H).
MS (70 eV) m/z (%): 345 [M-1] (100), 331 (49), 315 (42),
300 (41), 286 (19), 151 (19), 108 (12). Anal. Calcd. for
C21H18N2O3 (346.38): C, 72.83; H, 5.20; N, 8.09%
Found: C, 72.85; H, 5.21; N, 8.10%
2,9,10-Trimethoxy-7H-Benzo[b]Indeno[1,2-g][1, 8]Naph-
thyridine (15b) Yield: 0.319 g (89%), recrystalized from
Methanol to afford yellow needles; M.p. 231-233 °C. IR
(KBr): 3,012 s, 2,977 m, 1,607 s, 1,011 mcm-1.1H NMR
(300 MHz CDCl3) δ: 3.75 (s, 2 H, CH2), 3.88 (s, 3 H,
OCH3), 3.96 (s, 3 H, OCH3), 4.05 (s, 3 H, OCH3), 6.87 (s,
1 H, Ar-H), 7.43 (d, 1 H, J=8.8 Hz, Ar-H), 7.51 (s, 1 H,
Ar-H), 7.67 (s, 1 H, Ar-H), 8.94 (d, 1 H, J=8.8 Hz, Ar-H),
9.21 (s, 1 H, Ar-H), 9.44 (s, 1 H, Ar-H). 13C NMR
(75 MHz CDCl3) δ: 33.47, 55.55, 56.16, 56.38, 104.87,
105.77, 107.41, 113.81, 118.60, 120.77, 122.48, 128.86,
130.57, 132.14, 134.45, 136.43, 149.77, 151.94, 152.73,
155.69, 161.68, 166.94. MS (70 eV) m/z (%): 358 [M+]
(58), 327 (51), 288 (56), 207 (57), 189 (50), 175 (62), 164
(82), 150 (87), 131 (74), 118 (70), 91 (68), 63 (42). Anal.
Calcd. for C22H18N2O3 (358.39): C, 73.74; H, 5.02; N,
7.82%. Found: C, 73.75; H, 5.04; N, 7.84%.
7-Methoxy-2-p-Tolylbenzo[b][1, 8]Naphthyridine (13 m)
Yield: 0.261 g (87%), recrystalized from ethanol to afford
yellow prism; M.p. 208-211 °C. IR (KBr): 3,035 m, 1,625 s,
1
1,026 mcm-1. H NMR (300 MHz CDCl3) δ: 2.47 (s, 3 H,
CH3), 3.98 (s, 3 H, OCH3), 7.35 (d, 1 H, J=8.7 Hz, Ar-H),
7.49 (d, 2 H, J=8.5 Hz, Ar-H), 7.59 (s, 1 H, Ar- H), 7.95 (d,
2 H, J=8.5 Hz, Ar-H), 8.12 (d, 1 H, J=7.9 Hz, Ar-H), 8.25
(d, 1 H, J=8.7 Hz, Ar-H), 8.49 (d, 1 H, J=7.9 Hz, Ar-H),
8.83 (s, 1 H, Ar-H). MS (70 eV) m/z (%): 300 [M+] (97),
285 (92), 209 (77), 77 (89). Anal. Calcd. for C20H16N2O
(300.35): C, 80.00; H, 5.33; N, 9.33% Found: C, 79.98; H,
5.32; N, 9.35%
7-Methoxy-2-(4-Nitrophenyl)Benzo[b][1, 8]Naphthyridine
(13n) Yield: 0.265 g (80%), recrystalized from ethanol to
afford yellow solid; M.p. 191-194 °C, IR (KBr): 3,020 m,
1,642 s, 1,559 m, 1,367 m, 1,045 mcm-1. 1H NMR
(300 MHz DMSO-d6) δ: 4.03 (s, 3 H, OCH3), 7.32 (d,
2 H, J=8.3 Hz, Ar-H), 7.48 (d, 1 H, J=8.5 Hz, Ar-H), 7.52
(s, 1 H, Ar-H), 8.01 (d, 1 H, J=7.7 Hz, Ar-H), 8.19 (d, 1 H,
J=8.5 Hz, Ar-H), 8.30 (d, 2 H, J=8.3 Hz, Ar-H), 8.98 (d,
1 H, J=7.7 Hz, Ar-H), 9.37 (s, 1 H, Ar-H). Anal. Calcd. for
C19H13N3O3 (331.33): C, 68.88; H, 3.92; N, 12.68%
Found: C, 68.89; H, 3.94; N, 12.70%
7H-Benzo[b]Indeno[1,2-g][1, 8]Naphthyridine (15c)
Yield: 0.217 g (80%), recrystalized from Methanol to
afford yellow solid; M.p. 277-280 °C. IR (KBr): 3,014 m,
2,968 m, 1,618 scm-1. 1H NMR (300 MHz CDCl3) δ: 3.94
(s, 2 H, CH2), 7.24-7.32 (m, 4 H, Ar-H), 7.42 (dd, 1 H, J=
8.2 & 8.4 Hz, Ar-H), 7.79 (dd, 1 H, J=8.4 & 8.1 Hz, Ar-H),
8.09 (d, 1 H, J=8.2 Hz, Ar-H), 8.36 (d, 1 H, J=8.1 Hz, Ar-
H), 8.78 (s, 1 H, Ar-H), 9.19 (s, 1 H, Ar-H). Anal. Calcd.
for C19H12N2 (268.31): C, 85.07; H, 4.47; N, 10.44%.
Found: C, 85.10; H, 4.48; N, 10.45%.
2-Methoxy-7H-Benzo[b]indeno[1,2-g][1, 8]Naphthyridine
(15d) Yield: 0.259 g (86%), recrystalized from Methanol
to afford yellow needles; M.p. 252-255 °C. IR (KBr):
3,012 m, 2,968 m, 1,611 s, 1,011 mcm-1.1H NMR
Synthesis of 9,10-Dimethoxy-7H-Benzo[b]Indeno[1,2-g][1, 8]
Naphthyridine (15 a-d) The mixture of 2-aminoquinoline-3-
carbaldehyde (1a-b) (0.01 mol) & indanone (14a-b)

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J Fluoresc (2011) 21:1033–1047
(300 MHz CDCl3) δ: 3.82 (s, 2 H, CH2), 4.05 (s, 3 H,
OCH3), 7.09-7.38 (m, 4 H, Ar-H), 7.43 (d, 1 H, J=8.6 Hz,
Ar-H), 7.51 (s, 1 H, Ar-H), 8.24 (d, 1 H, J=8.6 Hz, Ar-H),
9.21 (s, 1 H, Ar-H), 9.44 (s, 1 H, Ar-H). MS (70 eV) m/z
(%): 298 [M+] (100), 277 (32), 255 (64), 227 (32), 149
(38), 128 (45), 114 (18), 77 (13). Anal. Calcd. for
C20H14N2O (298.34): C, 80.53; H, 4.69; N, 9.39%. Found:
C, 80.55; H, 4.70; N, 9.40%.
15. Seminario JM (2005) Molecular electronics: approaching reality.
Nat Mater 4:111–113
16. Hughes G, Bryce MR (2005) Electron-transporting materials for
organic electroluminescent and electrophosphoresc-ent devices. J
Mater Chem 15:94–107
17. Van der Auweraer M, De Schryver FC (2004) Organic electronics:
supra solutions. Nat Mater 3:507–508
18. Special Issue on Organic Electronics (2004) Chem Mater
16:4381–4846
19. Simpson CD, Wu J, Watson MD, Műllen K (2004) From graphite
molecules to columnar superstructures-an excercise in nano-
science. J Mater Chem 14:494–504
20. Kapturkiewicz A, Herbich J, Nowacki J (1997) Highly efficient
electrochemical generation of fluorescent intramolecular charge-
transfer states. Chem Phys Lett 275:355
21. Herbich J, Kapturkiewicz A (1997) Electronic and molecular
structure of charge transfer singlet states: 4-(9-anthryl)julolidine
and 4-(9-acridyl)julolidine. Chem Phys Lett 273:8
22. Herbich J, Kapturkiewicz A, Nowacki J (1996) Phosphorescent
intramolecular charge transfer triplet states. Chem Phys Lett 262:633
23. Rechthaler K, Schamschule R, Parusel ABJ, Rotkiewicz K, Piorun
D, Kőhler G (1999) Fluorescence properties of an electron
acceptor substituted bis-pyrazolo-pyridine derivative: NO2-DMPP.
Acta Phys Polon A 95:321
Acknowledgement The authors thank to CSIR, New Delhi, India,
for financial support for this research project. We thank Professor D.
D. Dhavale, Department of Chemistry, University of Pune, Pune,
India, for his valuable cooperation for the measurement of 1H NMR,
13C NMR, Mass and Elemental Analysis. 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, UV and Fluorescence spectra.
References
1. Meijere A de (1998) In topics in current chemistry, carbon-rich
compounds, I, (Ed.) Springer, Berlin, Germany, vol 196
2. Meijere A de (1999) In topics in current chemistry, carbon-rich
compounds, II, (Ed.) Springer, Berlin, Germany, vol 201
3. Diederich F, Stang PJ, Tykwinski RR (2005) In acetylene
chemistry: chemistry, biology and material science, (Eds.)
Wiley-VCH, Weinheim, Germany
4. Haley MM, Tykwinski RR (2006) In carbon-rich compounds:
from molecules to materials, (Eds.) Wiely-VCH, Weinheim,
Germany
5. Műllen K, Scherf U (2006) In organic light emitting devices:
synthesis properties and applications (Eds.): Wiely-VCH, Wein-
heim, Germany
6. Chen J, Reed MA, Dirk SM, Price DW, Rawlett AM, Tour JM,
Grubisha DS, Bennett DW (2003) In NATO science series II,
mathematics, physics, chemistry (Molecular Electronics: Bio-
Sensors and Bio-Computers) (Eds.): Plenum, New York, Vol.
96: pp 59-195
24. Miyasaka H, Itaya A, Rotkiewicz K, Rechthaler K (1999)
Picosecond laser photolysis studies of DMA–DMPP in solution.
Chem Phys Lett 307:121
25. Piorun D, Parusel ABJ, Rechthaler K, Rotkiewicz K, Kőhler G
(1999) Acid–base properties of bis-pyrazolopyridine derivatives in
nonaqueous solutions. J Photochem Photobiol A:Chem 129:33
26. Parusel ABJ, Rechthaler K, Piorun D, Danel A, Khatchatryan K,
Rotkiewicz K, Kőhler G (1998) Fluorescence properties of donor–
acceptor-substituted pyrazoloquinolines. J Fluoresc 8:375
27. Khatchatryan K, Rotkiewicz K, Kőhler G, Danel A, Tomasik P,
Khatchatryan K (1997) Emissive properties and intramolecular
charge transfer of pyrazoloquinoline derivatives. J Fluoresc 7:301
28. Rotkiewicz K, Rechthaler K, Puchala A, Rasala D, Styrcz S,
Kőhler G (1996) Dual fluorescence and intramolecular charge
transfer in a bulky electron donor-acceptor system. N, N-
Dimethylanilino-bis-pyrazolopyridine. J Photochem Photobiol A:
Chem 98:15–19
29. Parusel ABJ, Schamschule R, Kőhler G (1998) Theoretical
description of solvent effects on fluorescence spectra of bulky
charge transfer compound DMA-DMPP. J Comput Chem 19:1584
30. Parusel ABJ, Schamschule R, Kőhler G (1997) A semiempirical
study of the fluorescence properties of large charge-transfer
compounds. N, N-dimethylanilino-bis-pyrazolopyridine. Ber Bun-
senges Phys Chem 101:1836–1843
7. Domerco B, Hreha RD, Zhang YD, Haldi A, Barlow S, Marder
SR, Kippelen B (2003) Organic light-emitting diodes with
multiple photocrosslinkable hole-transport layers. J Polym Sci
Part B: Polym Phys 41(21):2726–2732
8. Shirota Y (2000) Organic materials for electronic and optoelec-
tronic devices. J Mater Chem 10:1–25
9. Schwab PFH, Levin MD, Michl J (1999) Molecular rods. 1.
Simple axial rods. Chem Rev 99:1863–1933
10. Műllen K, Wehner G (1998) In electronic materials: the oligomer
approach, (Eds.) Wiely-VCH, Weinheim, Germany
31. Parusel ABJ, Schamschule R, Piorun D, Rechthaler K, Puchala A,
Rasala D, Rotkiewicz K, Kőhler G (1997) Semiempirical
characterization of substituted bis-pyrazolopyridines as new bulky
electron donor-acceptor systems in their electronic ground state. J
Mol Struct (Theochem) 419:63–76
32. Singh AK, Kanvah S (2000) Effect of micro heterogeneous media
on fluorescence and fluorescence probe properties of diary-
lpolyenes. New J Chem 24:639–646
33. Singh AK, Manjula D, Kanvah S (2000) α, ω-diphenylpolyenes
cabable of exhibiting twisted intramolecular charge transfer
fluorescence: a fluorescence and fluorescence probe study of
nitro- and nitrocyano-substituted 1, 4-diphenyl butadienes. J Phys
Chem A 104:464–471
34. Singh AK, Krishna TSR (1997) Photophysical and optical probe
properties of 1-(p-N, N-Dimethylaminophenyl)-4-Phenyl-2-Meth-
yl-1E, 3E-Butadiene. J Photosci 4:1–5
11. Nalwa HS, Miyata S (1997) In nonlinear optics of organic
molecules and polymers (Eds.) CRC Press, Boca Raton, FL
12. Kang H, Evrenenko G, Dutta P, Clays K, Song K, Marks TJ
(2006) X-shaped electro-optic chromophore with remarkably
blue-shifted optical absorption. synthesis, characterization, linear/
nonlinear optical properties, self-assembly, and thin film micro-
structural characteristics. J Am Chem Soc 128:6194–6205
13. Knox JE, Halls MD, Hratchian HP, Schlegel HB (2006) Chemical
failure modes of Alq3-based OLEDs: Alq3 hydrolysis. Phys
Chem Chem Phys 8:1371–1377
14. Shukla VK, Kumar S, Deva D (2006) Light induced effects on the
morphology and optical properties of tris-(8-hydroxyquinoline)
aluminium (Alq3) small molecular thin film. Synth Met 156:387–
391
35. Singh AK, Darshi M (2004) A fluorescence study of (4-{(1E, 3E)-
4-[4-(dimethyl-amino)phenyl]- buta-1, 3-dienyl}phenyl)methanol

J Fluoresc (2011) 21:1033–1047
1047
and its bioconjugates with bovine and human serum albumins.
New J Chem 28:120–126
56. Godard A, Queguiner G (1982) Synthesis of Benzonaphthyr-
idines. J Heterocyclic Chem 19:1279
36. Caluwe P (1980) Heteroannelations with o-aminoaldehydes.
Tetrahedron 36:2359
37. Fehnel EA (1966) Friedländer syntheses with o-aminoaryl ketones. I.
Acid-catalyzed condensations of o-aminobenzophenone with
ketones. J Org Chem 31:2899
57. Jachak MN, Avhale AB, Tantak CD, Toche RB (2005) Fried-
länder condensation of 5-Aminopyrazole-4-carbaldehydes with
reactive α-methylene ketones: synthesis of pyrazolo[3, 4-b]
pyridines. J Heterocyclic Chem 42:1311–1319
58. Jachak MN, Avhale AB, Tantak CD, Toche RB (2006) A
convenient route for the synthesis of pyrazolo[3, 4-d]pyrimidine,
pyrazolo[3, 4-b][1, 6]naphthyridine and pyrazolo[3, 4-b]quinoline
derivatives. J Heterocyclic Chem 43:1169–1175
59. Jachak MN, Avhale AB, Toche RB, Sabnis RW (2007) Synthesis
of pyrazolo-annelated heterocyclic ring compounds such as
pyrazolo[3, 4-b]pyridines and pyrazolo[4′, 3′:5, 6]-pyrido[2, 3-d]
pyrimidines. J Heterocyclic Chem 44:343–347
60. Jachak MN, Bagul SM, Kazi MA, Toche RB (2009) Facile
synthesis of novel pyrazolo[3, 4-h][1, 6]naphthyridines deriva-
tives from new 4-amino-pyrazolo[3, 4-b] pyridine-5-
carbaldehyde. J Heterocyclic Chem 46:343
61. Toche RB, Bhavsar DC, Kazi MA, Bagul SM, Jachak MN (2010)
Synthesis of pyrazolopyridine 3-carboxylates by Friedlander
condensation. J Heterocyclic Chem 47:287–291
62. Shelar DP, Birari DR, Rote RV, Patil SR, Toche RB, Jachak MN
(2010) Novel Synthesis of 2-aminoquinoline-3-carbaldehyde,
benzo[b][1, 8] naphthyridines and study of their fluorescence
behavior. J Phys Org Chem. doi:10.1002/poc.1727
63. Peters T (1985) Serum albumin. Jr Advan Prot Chem 37:161–245
64. Zollinger H (2003) Color Chemistry, 3rd ed., Switzerland, Page
No.479
38. Boekelheide V, Nottke JE (1969) Novel cyclization reaction of
acetylene derivatives. J Org Chem 34(12):4134–4136
39. Liao TK, Nyberg WH, Cheng CC (1971) Total synthesis of
camptotheein. I. Synthesis of ethyl 8-(α-chlorobutyryloxymethyl)-
7,9-dioxo-7,8,9,11-tetrahydro indolizino [1,2-a]quinoline-8-carbox-
ylate and related tetracyclic compounds. J Heterocyclic Chem 8:373
40. Zalkow LH, Nabors JB, French K, Bisarya SC (1971) Studies in the
synthesis of Camptothecin. An efficient synthesis of 2,3-dihydro-1H-
pyrazolo[3,4-b]quinoline. J Chem Soc (C):3551-3554.
41. Borch RF, Grudzinskas CV, Peterson DA, Weber LD (1972) New
synthesis of substituted 2(1 H)-pyridones. Synthesis of a potential
camptothecin intermediate. J Org Chem 37(8):1141–1145
42. Croisy A, Jacqquignon P, Fravolini A (1974) Sur quelques analogues
fluores des [1] benzothiopyrano[4, 3-b]indoles et des 6 H[1]
benzothiopyrano[4, 3-b]quinoleines. J Heterocyclic Chem 11:113
43. Cliff GR, Jones G, Woollard J McK (1974) Intramolecular nitrene
insertions into aromatic and heteroaromatic systems. Part II.
Insertions into thiophen rings. J Chem Soc Perkin I:2072–2076
44. Sugasawa T, Toyoda T, Sasakura K (1974) Experiments on the
synthesis of dl-camptothecin. III. Total synthesis of dl-
camptothecin. Chem Pharm Bull 22:771–781
45. Tang CSF, Morrow CJ, Rapoport H (1975) Total synthesis of dl-
camptothecin. J Am Chem Soc 97:159
65. Stewart JJP (1990) J Comput-Aided Mol Des 4:1
66. Stewart JJP. QCPE Bull. (1989), 9, 10. QCPE program no. 455
67. Perov AN (1980) Energy of intermediate pair interactions as a
characteristics of their nature. Theory of the solvate (Fluoro)
Chromism of three-component solutions. Opt Spectrosc 49:371–374
68. Neporent BS, Bakhshiev NG (1960) On the role of universal and
specific intermolecular interactions in the influence of the solvent
on the electronic spectra of molecules. Opt Spectrosc 8:408–413
69. Dey JK, Warner IM (1998) Charge-transfer effects on the
fluorescence spectra of 9-aminocamptothecin steady-state and
time-resolved fluorescence studies. J Photochem Photobiol A:
Chem 116:27
70. Biswas A, Dey JK (2001) Ground and excited state ionization
behavior of 9-aminocamptothecin: an absorption and fluorescence
study. Indian J Chem 40A:1143–1148
71. Lakowicz JR (1999) In principals of fluorescence spectroscopy,
2nd ed., New York
72. Fletecher AN (1969) Quinine sulfate as a fluorescence quantum
yield standard. Phot Chem Photo Biol 9(5):439–444
73. Eastman JW (1967) Quantitative spectrofluorimetry-the fluores-
cence quantum yield of quinine sulfate. Photo Chem Photo Biol 6
(1):55–72
74. Adams MJ, Highfield JG, Kirkbright GF (1977) Determination of
absolute fluorescence quantum efficiency of quinine bisulfate in
aqueous medium by optoacoustic spectrometry. Anal Chem 49
(12):1850–1852
75. Meech SR, Phillips D (1983) Photophysics of some common
fluorescence standards. J Photochem 23:193–217
46. Da SA, Primofiore G, Livo O, Ferrarini PL, Spinelli S (1979)
Synthesis of some 3-substituted quino[3, 2-c][1, 8]naphtyridines.
A new heterocyclic ring system. J Heterocyclic Chem 16:169
47. Hawes EM, Wibberley DG (1966) 1,8-Naphthyridines. J Chem
Soc:315-321
48. Majewicz TG, Caluwe P (1975) Chemistry of o-aminoaldehydes.
Reactions of 2-aminonicotinaldehyde and cyclohexanediones. J
Org Chem 40(23):3407–3410
49. Hawes EM, Wibberley DG (1967) 1,8-Naphthyridines. Part II.
Preparation and some reactions of 2-substituted derivatives. J
Chem Soc (C):1564-1568.
50. Hawes EM, Gorecki DKJ, Gedir RG (1977) 2, 3-Disubstituted 1,
8-naphthyridines as potential diuretic agents. 2. 5, 7-Dimethyl
derivatives. J Med Chem 20(6):838–841
51. Haufel J, Breitmaier E (1974) Synthesis of pyrazolo heteroar-
omatic compounds by means of 5-amino-3-methyl-1-phenylpyr-
azole-4-carbaldehyde. Angew Chem Internat Edit 13(9):604
52. Simay A, Takacs K, Toth L (1982) Aminopyrazoles, II. Synthesis
of pyrazolo[3, 4-b] pyridines via Vilsmeier-Haack reaction of 5-
acetaminopyrazoles. Acta Chim Acad Sci Hung 109:175–187
53. Ahluwalia VK, Dahiya A (1996) Synthesis of pyrazolo[3’, 4’: 5,
6]pyrido[2, 3-d] pyrimidines. Indian J Chemistry 35B:1208–1210
54. Ahluwalia VK, Dahiya A, Garg VK (1997) Reaction of 5- amino-
4-formyl-3-methyl (or phenyl)-1-phenyl-1 H-prazoles with com-
pounds containing active methylene group: synthesis of fused
heterocyclic rings. Indian J Chemistry 36B:88–90
55. Godard A, Queguiner G (1980) Sur les orthoamino formyl
quinoleines, nouveaux synthons heterocycliques. J Heterocyclic
Chem 17:465
76. Papadopoulou A, Green RJ, Frazier A (2005) Interaction of
flavonoids with bovine serum albumin: a fluorescence quenching
study. J Agric Food Chem 53:158–163