Efficient synthesis, fluorescence and DFT studies of different substituted 2-chloroquinoline-4-amines and benzo[g][1,8]naphthyridine derivatives

Article abstract of DOI:10.1016/j.jphotochem.2016.08.014

An efficient and single step strategy for synthesizing new functionalized benzo[b][1,8]naphthyridine derivatives is presented. Benzo[g][1,8]naphthyridines have been synthesized by the condensation of substituted 2-chloroquinoline-3-carbaldehydes with various 2-chloroquinoline-4-amines, 1H-Indazole-6-amine in basic medium. The electro luminescence and photophysical properties of a series of benzo[g][1,8]naphthyridines 5(a–d), 6(a–d) and 2-chloroquinoline-4-amines 3(a–f) are reported and investigated with the aim of arriving at good fluorescent materials. Moreover, the effect of electron donor-acceptor substituent on fluorescence properties of all molecules has been investigated along with their fluorescent quantum yields. Furthermore we analyzed for band gap energy associated with HOMO-LUMO, through density functional (DFT M06-HF) studies. The experimental observations are in close agreement with the theoretical calculation. All the synthesized compounds were identified on the basis of their NMR, Mass spectral data analyses.

Full text of DOI:10.1016/j.jphotochem.2016.08.014

Accepted Manuscript
Title: Efficient synthesis, fluorescence and DFT studies of
different substituted 2-chloroquinoline-4-amines and
benzo[g][1,8]Naphthyridine Derivatives
Author: A.M. Magesh Selva Kumar B.Vijaya Pandiyan
S.Mohana Roopan S.P. Rajendran
PII:
S1010-6030(16)30440-3
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.jphotochem.2016.08.014
JPC 10327
To appear in:
Journal of Photochemistry and Photobiology A: Chemistry
Received date:
Revised date:
Accepted date:
1-6-2016
8-8-2016
8-8-2016
Please cite this article as: A.M.Magesh Selva Kumar, B.Vijaya Pandiyan, S.Mohana
Roopan, S.P.Rajendran, Efficient synthesis, fluorescence and DFT studies of
different substituted 2-chloroquinoline-4-amines and benzo[g][1,8]Naphthyridine
Derivatives, Journal of Photochemistry and Photobiology A: Chemistry
http://dx.doi.org/10.1016/j.jphotochem.2016.08.014
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<AT>Efficient synthesis, fluorescence and DFT studies of different substituted
2-chloroquinoline-4-amines and benzo[g][1,8] Naphthyridine Derivatives
<AU>A. M. Magesh Selva Kumara ##Email##am.organicmagesh@gmail##/Email##, B. Vijaya
Pandiyanb, S. Mohana Roopanc, S. P. Rajendrana*
##Email##rajendransp@yahoo.com##/Email##
<AU>
<AFF>aDepartment of Chemistry, Bharathiar University, Coimbatore 641 046, Tamil Nadu,
India
<AFF>bDepartment of Physics, Bharathiar University, Coimbatore – 641 046, Tamil Nadu, India
<AFF>cChemistry of Heterocycles &Natural Products Research Laboratory, Department of
Chemistry, School of Advanced Sciences, VIT University, Vellore- 632 014, Tamil Nadu, India
<PA>Tel.: +91-9894677335, Fax: 91-422-2425706.
<ABS-Head><ABS-HEAD>Graphical abstract ► RESEARCH HIGHLIGHTS► A unique
and efficient synthesis of novel 2-chloroquinoline-4-amines► and
benzo[g][1,8]naphthyridines.► The major advantage of the protocol is that it does not any
catalyst.► Arrival of products at lesser reaction time.► Influence of electron donor-acceptor
substituent’s on photophysical of► A synthesized compound has been studied.► Photophysical
and theoretical (DFT) studies are in close co-relation.
<ABS-HEAD>ABSTRACT
<ABS-P>An efficient and single step strategy for synthesizing new functionalized
benzo[b][1,8]naphthyridine derivatives is presented. Benzo[g][1,8]naphthyridines have been
synthesized by the condensation of substituted 2-chloroquinoline-3-carbaldehydes with various
2-chloroquinoline-4-amines, 1H-Indazole-6-amine in basic medium. The electro luminescence
and photophysical properties of a series of benzo[g][1,8]naphthyridines 5(a-d), 6(a-d) and 2-
chloroquinoline-4-amines 3(a-f) are reported and investigated with the aim of arriving at good
fluorescent materials. Moreover, the effect of electron donor-acceptor substituent on
fluorescence properties of all molecules has been investigated along with their fluorescent
quantum yields. Furthermore we analyzed for band gap energy associated with HOMO-LUMO,
through density functional (DFT M06-HF) studies. The experimental observations are in close
agreement with the theoretical calculation. All the synthesized compounds were identified on the
basis of their NMR, Mass spectral data analyses.
1

<KWD>Keywords:
2-Chloroquinoline-3-carbaldehydes
2-Chloroquinoline-4-amines
Benzo[g]-1H-Indazolo[5,6-b][1,8]naphthyridines
Benzo[g][3,4-b]-2,6-dichloroquino[1,8]naphthyridines
Fluorescence of benzo[g][1,8]naphthyridines
HOMO-LUMO Energy level diagrams of benzo[g][1,8]naphthyridines.
<H1>1. Introduction
In organic synthesis, functional group transformations have significant importance. The
different substituted heterocyclic compounds have received much interest and attention
especially due to their pharmacological activities [1]. Particularly amino quinolines have
attracted considerable interest because their derivatives display a wide range of pharmacological
activities [2-8]. A recent investigation indicated that new diarylamides and diarylureas 8-amino
(acetamido)quinoline, novel pyrano[3,2-f] quinoline, phenanthroline derivatives display
enhanced activity towards different cancer cell lines,[9,10] and azole-quinoline exhibit excellent
photophysical properties [11]. Keeping all these pharmacological and photo physical/
luminescent profiles in mind we have identified new substituted amino quinolines. The present
work involves the chemical modification of 2-chloro-4-azido quinolines at C4 position to 2-
chloroquinolines-4-amines.
Various naphthyridine derivatives have received considerable attention over the past years
because of their wide range of biological activities [12-16]. In recent literature survey indicates
that various fused angular, linear naphthyridine systems exhibit fluorescence behavior [17-21]
because of the presence of π-π*, σ-π* and n-π* conjugation systems, different electronic states.
Such naphthyridines system exhibit fluorescence activities like benzo[b][1,8] naphthyridines-3-
carbonitrile [22], 5-(3,4Dichlorophenyl)-5,6-dihyrobenzo[b]naphtha[2,1-g][1,8] naphthyridine
[23], 2,5-Diphenylbenzo[h][1,6]naphthyridines [24], Figs 1,2,3. Moreover, we synthesized
different substituted 2-chloroquinoline-4-amine derivatives [25-29] and studied for photo
physical activity in selective organic solvent. A number of angular, linear naphthyridines that
have been prepared in our laboratory were subjected to absorption and emission studies. In
2

present phase of research, we report a new way synthesis of benzo[g][1,8] naphthyridines 5(a-d)
and 6(a-d) starting from 2-chloroquinoline-3-carbaldehydes [30-32]. The photophysical
properties were compared by absorption and emission maxima with reference to donor and
acceptor substitution in it. The substituent effect on the performance of these were studied by
calculating highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital
(LUMO) energies gaps values by Gaussian09 software [33]. The fluorescence properties of 2-
chloroquinoline-4-amines 3(a-f), benzo[g]-1H-Indazolo[5,6-b][1,8]naphthyridines 5(a-d), benzo
[g][3,4-b]2,6-dichloroquino[1,8]naphthyridines 6(a-d) was systematically investigated by
fluorescence spectroscopy.
Some examples of fluorescent active molecules
<H1>2. Experimental sections
<H2>2.1. General
Melting points (mp) were determined on a Mettler FP 51 apparatus (Mettler Instruments,
1
13
Switzerland) and are uncorrected. The H NMR (400 MHz) and C NMR (100 MHz) spectra
were recorded on Bruker AV-400 spectrometer. Chemical shifts were reported in ppm from
internal tetramethylsilane (TMS) internal reference and are given δ-unit. The solvents for NMR
spectra were deuterio-chloroform (CDCl3) and Deuterio-Dimethylsulphoxide (DMSO-d6).
Infrared spectra were taken on Shimadzu FTIR-8201PC (Schimadzu, Japan) instrument in
potassium bromide KBr pellets unless otherwise stated. Absorption spectral measurements were
carried out using JASCO V-630 UV–visible spectrophotometer. Quartz cuvettes of path length 1
cm were used to record the absorption spectra. The emission spectral studies were performed
with JASCO FP-6600 spectrofluorometer equipped with a 1 cm quartz cuvette and exciting the
samples at their absorption maximum wavelength (λabs.max). The concentration of the solute was
maintained at 10-3 M solution in absolute methanol for all experiments. The photophysical
properties of these compounds were determined with respect to the absorption (λabs. max.),
fluorescence maxima (λflu. max.) of these compounds and their quantum yields (ϕf) were calculated
by previous literature methods by using Rhodamine-6G as reference standard (ϕref=0.95 in 0.1 M
CH3OH) [44-46]. UV-visible absorption spectra were recorded in the range of 200 to 600 nm and
3

fluorescence monitored in the range of 400-700nm. The ESI-MS were recorded on a Thermo
Scientific mass spectrometer (mass spectrometer ESI-MS). Microanalyses were performed on a
Vario EL III model CHNS analyzer (Vario, Germany) at the Department of Chemistry,
Bharathiar University, Coimbatore–46, Tamil Nadu, India. Column chromatography was carried
out on silica gel (SD Fine Chemicals, 60–120 mesh). Solutions were concentrated in a rotary
evaporator under reduced pressure. All reactions were monitored by thin layer chromatography
(TLC), carried out on 0.2 mm silica gel 60 F254 (Merck) plates using UV light (254 nm and 366
nm) and Fluorescence light (400 nm and 600 nm) for detection. Common reagents-grade
chemicals were commercially available and were used without further purification or prepared
by standard literature procedures.
Computational details:
All the computations in the present study were performed by DFT theory in the frame work of
M06HF/6-31G (d, p) level of theory which is carried out on all 12 molecules Gaussian09W
programme. Since, Shang et al. [50] clearly reported the M06HF functional gave more
satisfactory results for photochemistry calculations. All these molecules are first optimized with
that level of theories. Then, all the optimized model structures correspond to the minima in the
potential energy surface, because no imaginary frequencies were observed. Molecular orbital
(MO) compositional analyses were carried out by chemissian software.
<H2>2.2. Synthetic procedures
<H3>2.2.1. General procedure for synthesis of 2-chloro-4-azido quinolines 2(a-f)
To a vigorously stirred solution of 2,4-dichloroquinoline 1(a-f) its derivatives ( 9 mmol) in DMF
(20 mL) at 550C, sodium azide (9 mmol) was added slowly for 15 min, the whole reaction was
stirred for 3-4 hrs. After the completion of reaction as it indicated by TLC spot change, the
reaction mixture was poured into crushed ice, filtered, dried and chromatographed over silica gel
using petroleum ether: ethyl acetate (92:8) (v/v) as eluent which yielded yellow/white colored
compound 2(a-f), it was recrystallised from ethyl acetate.
<H4>2.2.1.1. 2-Chloro-4-azidoquinoline (2a)
Yield: 72%; white solid; mp 104-106°C. IR (KBr, cm−1): 1302, 1565, 2126, 2911. 1H NMR (400
MHz, CDCl3): δ 7.13 (s, 1H, Ar-H), 7.56 (t, J = 7.6 Hz, 1H, Ar-H), 7.78 (t, J=7.6 Hz, 1H, Ar-H),
4

8.02 (t, J=8.4 Hz, 1H, Ar-H), 7.96 (s, 1H, Ar-H). 13C NMR (100 MHz, CDCl3): δ 109.38,
120.46, 122.41, 124.22, 126.89, 128.44, 131.66, 148.44, 148.52, 150.48; ESI-MS (m/z): calcd
for [M +H]+ 204.62, found 204.83; Anal. Calcd for C9H5ClN4: C, 52.83; H, 2.46; N, 27.38
Found: C, 52.79; H, 2.44; N, 27.44.
<H4>2.2.1.2. 6-Methyl-2-chloro-4-azidoquinoline (2b)
1
Yield: 82%; yellow solid; mp 98-99°C. IR (KBr, cm−1): 1306, 1567, 2130, 3052. H NMR (400
MHz, CDCl3): δ 2.52 (s, 3H, CH3), 7.08 (s, 1H, Ar-H), 7.57 (d, J = 6.4 Hz, 1H, Ar-H), 7.76 (s,
1H, Ar-H), 7.86 (d, J=6.8 Hz, 1H, Ar-H). 13C NMR (100 MHz, CDCl3): δ 21.71, 109.31, 120.38,
121.31, 124.14, 128.13, 133.80, 137.10, 146.99, 147.77, 149.51. ESI-MS (m/z): calcd for
[M+H]+ 218.04, found 218.01; Anal. Calcd for C10H7ClN4: C, 54.93; H, 3.23; N, 25.62 Found:
C, 54.88; H, 3.26; N, 25.64.
<H4>2.2.1.3. 6-Dichloro-4-azidoquinoline (2c)
Yield: 82%; white solid; mp 103–105°C. IR (KBr, cm−1): 1320, 1562, 2126, 3047. 1H NMR (400
MHz, CDCl3): δ 7.14 (s, 1H, Ar-H), 7.67 (dd, J = 8.8, 1.6 Hz, 1H, Ar-H), 7.91 (d, J=9.2 Hz, 1H,
Ar-H), 7.99 (s, 1H, Ar-H). 13C NMR (100 MHz, CDCl3): δ 110.12, 121.10, 121.62, 130.00,
132.54, 133.00, 146.80, 147.71, 150.79. ESI-MS (m/z): calcd for [M +H]+ 239.06, found 239.21;
for Anal. Calcd for C10H4Cl2N4: C, 45.22; H, 1.69; N, 23.44 Found: C, 45.18; H, 1.74; N, 23.43.
<H4>1.1.1.1. 6-Methoxy-2-chloro-4-azidoquinoline (2d)
Yield: 77%; yellow solid; mp108-109°C. IR (KBr, cm−1): 1312, 1560, 2127, 2918. 1H NMR (400
MHz, CDCl3): δ 3.52 (s, 3H, OCH3), 7.14 (s, 1H, ArH), 7.70 (d, J = 8.8 Hz, 1H, Ar-H), 8.00 (s,
1H, Ar-H), 7.99 (d, J=9.2 Hz, 1H, Ar-H). 13C NMR (100 MHz, CDCl3): δ 41.71, 110.13, 121.10,
121.63, 130.00, 130.55, 133.00, 146.81, 147.72, 150.79, 149.51. ESI-MS (m/z): calcd for [M +
H]+ 234.64, found 234.89; Anal. Calcd for C10H7ClN4O: C, 51.19; H, 3.01; N, 23.88 Found: C,
51.23; H, 2.97; N, 23.86.
<H4>2.2.1.5. 8-Methyl-2-chloro-4-azidoquinoline (2e)
5

Yield: 83%; white solid; mp 98–102°C. IR (KBr, cm−1): 1315, 1567, 2125, 2963. 1H NMR (400
MHz, CDCl3): δ 2.74 (s, 3H, CH3), 7.12 (s, 1H, Ar-H), 7.42 (t, J = 7.2 Hz, 1H, Ar-H), 7.61 (d,
J=7.2 Hz, 1H, Ar-H), 7.87 (d, J=8.4 Hz, 1H, Ar-H). 13C NMR (100 MHz, CDCl3): δ 18.10,
109.18, 120.15, 120.49, 126.52, 131.78, 136.68, 147.69, 148.51, 149.35. ESI-MS (m/z): calcd for
[M + H]+ 218.64, found 218.93; Anal. Calcd for C10H7ClN4: C, 54.93; H, 3.23; N, 25.62 Found:
C, 54.89; H, 3.25; N, 25.64.
<H4>2.2.1.6. Benzo[b]-2-chloro-4-azidoquinoline (2f)
Yield: 87%; white solid; mp 104-106°C. IR (KBr, cm−1): 1317, 1617, 2126, 2923. 1H NMR (400
MHz, CDCl3): δ 7.20 (s, 1H, Ar-H), 7.58-8.04(m, 5H, Ar-H), 9.16 (s, 1H, Ar-H). 13C NMR (100
MHz, CDCl3): δ 110.15, 118.79, 120.41, 122.36, 125.22, 127.80, 127.91, 129.11, 129.35,
130.06, 134.22, 147.38, 149.76. ESI-MS (m/z): calcd for [M + H]+ 254.67, found 254.71; Anal.
Calcd for C13H7ClN4: C, 61.31; H, 2.77; N, 22.00 Found: C, 61.35; H, 2.71; N, 22.02.
<H2>2.3. General procedure Synthesis of 2-chloro quinoline-4-amines 3(a-f)
The 2-chloro-4-azido quinolines (4 mmol) compound 2(a-f) was taken in 20 mL methanol and (4
mmol) of sodium dithionite was added and refluxed for 3-6 hour on water bath. After the
completion of reaction as it indicated by TLC spot change, the reaction mixture was poured into
crushed ice, filtered, dried and chromatographed over silica gel using petroleum ether: ethyl
acetate (80:20) (v/v) as eluent which pure light yellow/white colored needles compound 3(a-f). It
was recrystallised from absolute methanol.
<H3>2.3.1. 2-Chloroquinoline-4-amine (3a)
1
Yield: 91%; white needles; mp 180-183°C. IR (KBr, cm−1): 1643, 2970, 3182, 3312, 3459. H
NMR (400 MHz, DMSO-d6): δ 6.51 (s, 1H, Ar-H), 7.17(s, 2H, NH2), 7.46-7.42 (m, 1H, Ar-H),
7.70-7.63(m, 2H, Ar-H), 8.17 (s, 1H, Ar-H). 13C NMR (100 MHz, DMSO-d6): δ 100.50, 117.63,
122.44, 124.29, 127.89, 130.24, 147.99, 150.55, 154.13. ESI-MS (m/z): calcd for [M + H]+
178.62, found 179.00; Anal. Calcd for C9H7ClN2: C, 60.52; H, 3.95; N, 15.68 Found: C, 60.56;
H, 3.89; N, 15.70.
<H3>2.3.2. 6-Methyl-2-chloroquinoline-4-amine (3b)
1
Yield: 79%; white solid; mp 160-162°C. IR (KBr, cm−1): 1647, 2961, 3181, 3319, 3452. H
NMR (400 MHz, DMSO-d6): δ 2.45 (s, 3H, CH3), 6.48 (s, 1H, Ar-H), 7.05(s, 2H, NH2), 7.50
6

(dd, J=6.8, 2.0 Hz, 1H, Ar-H), 7.59(d, J= 8.8 Hz, 1H, Ar-H), 7.95 (s, 1H, Ar-H). 13C NMR (100
MHz, DMSO-d6): δ 21.14, 100.48, 117.50, 121.41, 127.68, 132.06, 133.65, 146.37, 149.72,
153.60. ESI-MS (m/z): calcd for [M + H]+ 192.64, found 193.01; Anal. Calcd for C10H9ClN2: C,
62.35; H, 4.71; N, 14.54 Found: C, 62.31; H, 4.76; N, 14.53.
<H3>2.3.3. 2,6-Dichloroquinoline-4-amine (3c)
1
Yield: 89%; white needles; mp 240-241°C. IR (KBr, cm−1): 1643, 2970, 3233, 3329, 3465. H
NMR (400 MHz, DMSO-d6): δ 6.60 (s, 1H, Ar-H), 7.33 (s, 2H, NH2), 7.72 (dd, J=9.2, 2.4 Hz,
1H, Ar-H), 7.76(dd, J= 9.2, 2.00 Hz, 1H, Ar-H), 8.37 (s, 1H, Ar-H). 13C NMR (100 MHz,
DMSO-d6): δ 101.23, 118.47, 121.76, 128.80, 130.02, 130.63, 146.55, 151.02, 153.50. ESI-MS
(m/z): calcd for [M + H]+ 213.06, found 212.94; Anal. Calcd for C9H6Cl2N2: C, 50.73; H, 2.84;
N, 13.15 Found: C, 50.68; H, 2.91; N, 13.13.
<H3>2.3.4. 6-Methoxy-2-chloroquinoline-4-amine (3d)
1
Yield: 61%; white needles; mp 139-141°C. IR (KBr, cm−1): 1646, 2970, 3169, 3315, 3453. H
NMR (400 MHz, DMSO-d6): δ 3.91 (s, 3H, OCH3), 4.71 (s, 2H, NH2), 6.59 (s, 1H, Ar-H), 6.92
(s, 1H, Ar-H), 7.33 (d, J=9.2 Hz, 1H, Ar-H), 7.84 (d, J= 9.2 Hz, 1H, Ar-H). 13C NMR (100
MHz, DMSO-d6): δ 41.32, 100.48, 117.50, 121.41, 127.68, 132.06, 133.65, 146.37, 149.72,
153.60. ESI-MS (m/z): calcd for [M + H]+ 208.64, found 209.01; Anal. Calcd for C10H9ClN2O:
C, 57.57; H, 4.35; N, 13.43 Found: C, 57.50; H, 4.37; N, 13.48.
<H3>2.3.5. 8-Methyl-2-chloroquinoline-4-amine (3e)
1
Yield: 96%; white solid; mp 160-162°C. IR (KBr, cm−1): 1628, 2958, 3235, 3392, 3491. H
NMR (400 MHz, DMSO-d6): δ 2.72 (s, 3H, CH3), 4.77 (s, 2H, NH2), 6.59 (s, 1H, Ar-H), 7.32 (d,
13
J=7.2 Hz, 1H, Ar-H), 7.53(d, J= 8.4 Hz, 1H, Ar-H), 7.55 (s, 1H, Ar-H). C NMR (100 MHz,
DMSO-d6): δ 18.49, 103.17, 117.62, 117.84, 124.87, 130.68, 137.25, 147.55, 150.41, 151.62.
ESI-MS (m/z): calcd for [M + H]+ 192.64, found 193.00; Anal. Calcd for C10H9ClN2: C, 62.35;
H, 4.71; N, 14.54 Found: C, 62.32; H, 4.77; N, 14.51.
7

<H3>2.3.6. Benzo[h]-2-chloroquinoline-4-amine (3f)
1
Yield: 89%; white solid; mp 133-136°C. IR (KBr, cm−1): 1624, 2925, 3198, 3982, 3401. H
NMR (400 MHz, DMSO-d6): δ 6.76 (s, 1H, Ar-H), 7.23 (s, 2H, NH2), 7.78-7.71 (m, 2H, Ar-H),
7.88 (d, J=9.2 Hz, 1H, Ar-H), 8.04 (d, J= 6.4 Hz, 1H, Ar-H), 8.14 (d, J= 9.2 Hz, 1H, Ar-H), 9.00
13
(d, J= 6.4 Hz, 1H, Ar-H). C NMR (100 MHz, DMSO-d6): δ 102.84, 113.80, 119.62, 124.27,
124.59, 126.69, 127.65, 128.19, 130.13, 133.58, 145.94, 149.75, 154.39. ESI-MS (m/z): calcd for
[M -H]+ 228.68, found 227.11; Anal. Calcd for C13H9ClN2: C, 68.28; H, 3.97; N, 12.25 Found:
C, 62.33; H, 3.91; N, 12.19.
2.4. General procedure Synthesis of benzo[g]-1H-Indazolo[5,6-b][1,8]naphthyridines 5(a-d).
The 2-chloroquinolines-3-carbaldehyes (2 mmol) compound 4(a-d) was taken in 10 mL
(DMF) and 1H-Indazole-6-amine (2 mmol) was added and refluxed for 2-3 hours 160-1800C on
a mantle. After the completion of reaction as it indicated by TLC spot change, the reaction
mixture was slowly poured in ice water, filtered, dried and chromatographed over silica gel using
Ethyl acetate: Methanol (90:10) (v/v) as eluent which pure orange / green colored solid
compound 5(a-d). It was recrystallised from absolute methanol.
<H3>2.4.1. Benzo[g]-1H-Indazolo[5,6-b][1,8]naphthyridine (5a)
Yield: 60%; light orange solid; mp 282-285°C. IR (KBr, cm−1): 1563, 2926, 3390. 1H NMR (400
MHz, DMSO-d6): δ 7.02 (s, 1H, Ar-H), 7.43 (d, J = 7.6 Hz, 1H, Ar-H), 7.39 (s, 1H, Ar-H), 7.59-
7.65 (m, 5H, Ar-H), 7.70 (d, J=8.8 Hz, 1H, Ar-H), 12.47 (s, 1H, for NH).13C NMR (100 MHz,
DMSO-d6): δ 116.98, 117.73, 118.92, 119.94, 125.66, 126.38, 128.47, 128.57, 128.98, 131.29,
132.07, 133.71, 133.94, 137.15, 146.08, 150.51, 158.71, 165.97. ESI-MS (m/z): calcd for [M +
H]+ 270.29, found 270.21; Anal. Calcd for C17H10N4: C, 75.54; H, 3.73; N, 20.73 Found: C,
75.58; H, 3.69; N, 20.70.
<H3>2.4.2. 8-Methylbenzo[g]-1H-Indazolo[5,6-b][1,8]naphthyridine (5b)
Yield: 54%; orange solid; mp >290°C. IR (KBr, cm−1): 1589, 1626, 2922, 3357. 1H NMR(400
MHz, DMSO-d6): δ 2.71 (s, 3H, CH3), 7.41-7.39(m, 3H, Ar-H), 7.60-7.56(m, 3H, Ar-H), 7.83
(dd, J=8.8,2.4Hz, 1H, Ar-H), 8.08 (d, J=8.8Hz, 1H, Ar-H), 13.53(s, 1H for NH).13C NMR (100
MHz, DMSO-d6): δ 23.31, 124.40, 125.51, 128.50, 128.84, 129.24, 129.38, 130.88, 131.22,
134.35, 143.33, 145.25, 154.38, 168.74. ESI-MS (m/z): calcd for [M +H]+ 284.31, found 284.49;
Anal. Calcd for C18H12N4: C, 76.04; H, 4.25; N, 19.71 Found: C, 75.97; H, 4.23; N, 19.76.
<H3>2.4.3. 8-Methoxybenzo[g]-1H-Indazolo[5,6-b][1,8]naphthyridine (5c)
8

Yield: 47%; orange solid; mp 287-290°C. IR (KBr, cm−1): 1576, 1630, 2922, 3234. 1H NMR(400
MHz, DMSO-d6): δ 3.61 (s, 3H, OCH3), 7.13 (s, 1H, Ar-H), 7.19 (s, 1H, Ar-H), 7.28(s, 1H, Ar-
H), 7.57 (d, J=7.6 Hz, 1H, Ar-H), 7.64 (s, 1H, Ar-H), 7.74 (d, J=7.6 Hz, 1H, Ar-H), 8.03 (s, 1H,
Ar-H), 8.90 (s, 1H, Ar-H), 9.01(bs, s, for NH). ESI-MS (m/z): calcd for [M - H]+ 300.31, found
299.04; Anal. Calcd for C18H12N4O: C, 71.99; H, 4.03; N, 18.66 Found: C, 71.97; H, 43.97; N,
18.69.
<H3>2.4.4. Naphtho[g]-1H-Indazolo[5,6-b][1,8]naphthyridine (5d)
1
Yield: 56%; yellow solid; mp 278-281°C. IR (KBr, cm−1): 1576, 1615, 2925, 3405. H NMR
(400 MHz, DMSO-d6): δ 7.35 (d, J=7.6 Hz, 1H, Ar-H), 7.37 (s, 1H, Ar-H), 7.43 (d, J=8.00 Hz,
1H, Ar-H), 7.63 (t, J=7.2Hz, 1H, Ar-H), 7.80 (d, J=6.8Hz, 1H, Ar-H), 8.22 (d, J=8.8 Hz, 1H,
Ar-H), 8.29(s, 1H, Ar-H), 8.80 (d, J=8.00 Hz,1H, Ar-H), 9.85 (s, 1H, Ar-H), 11.86 (s, 1H, NH).
13C NMR (100 MHz, DMSO-d6): δ 109.78, 101.46, 115.59, 121.34, 121.81, 124.61, 125.35,
125.51, 125.61, 127.81, 127.98, 128.29, 128.76, 129.04, 133.62, 134.19, 137.47, 140.55, 141.77,
155.82. ESI-MS (m/z): calcd for [M -H]+ 320.11, found 319.19; Anal. Calcd for C21H12N4: C,
78.73; H, 3.78; N, 17.49 Found: C, 78.76; H, 3.75; N, 17.45.
<H2>2.5. General procedure Synthesis of benzo[g][3,4-b]-2,6-dichloroquinoline [1,8]
naphthyridines 6(a-d)
The 2-chloroquinolines-3-carbaldehyes (2 mmol) compound 4(a-d) was taken in 10 mL (DMF)
and 2-chloroquinoline-4-amine (2 mmol) derivatives (3c, 3e) were added and refluxed for 2
hours 160-1800C on a mantle. After the completion of reaction as it indicated by TLC spot
change, the reaction mixture was slowly poured in ice water, filtered, dried and chromatographed
over silica gel using Ethyl acetate: Methanol (95:05) (v/v) as eluent which pure green/yellow
colored solid compound 6(a-d). It was recrystallised from absolute methanol.
<H3>2.5.1. 10-Methylbenzo[g][3,4-b]-2,6-dichloroquinoline[1,8]naphthyridine (6a)
Yield: 43%; green solid; mp 243-2450C. IR (KBr, cm−1): 1439, 1516, 1590, 1641. 1H NMR (400
MHz, DMSO-d6): δ 2.51 (s, 3H, CH3), 7.21(d, J=8.4 Hz, 1H, Ar-H), 7.45 (s, 1H, Ar-H), 7.59 (d,
J=8.00 Hz, 1H, Ar-H), 7.85 (d, J=8.8 Hz, 1H, Ar-H), 8.11 (s, 1H, Ar-H), 8.16 (d, J=8.00 Hz, 1H,
Ar-H), 9.00 (s, 1H, Ar-H), 9.14 (s, 1H, Ar-H).13C NMR (100 MHz, DMSO-d6): δ 21.69, 101.33,
115.61, 121.30, 124.91, 126.34, 126.63, 126.75, 129.07, 130.12, 130.39, 133.59, 137.62, 143.17,
9

148.08, 149.47, 155.92. ESI-MS (m/z): calcd for [M + H]+ 363.23, found 363.34; Anal. Calcd
for C20H11Cl2N3: C, 65.95; H, 3.04; N, 11.54 Found: C, 65.89; H, 2.99; N, 11.54.
<H3>2.5.2. 10-Methoxybenzo[g][3,4-b]-2,6-dichloroquinoline[1,8]naphthyridine (6b)
1
Yield: 40%; orange solid; mp 260-262°C. IR (KBr, cm−1): 1464, 1491, 1583, 1516. H NMR
(400 MHz, CDCl3): δ 3.90 (s, 3H, OCH3), 7.02 (s, 1H, Ar-H), 7.19-7.15 (m, 1H,Ar-H), 7.36-7.30
(m, 3H, Ar-H), 7.40 (s, 1H, Ar-H), 7.80 (d, J=9.2 Hz, 1H, Ar-H), 7.86 (d, J=8.8 Hz, 1H, Ar-H).
13C NMR (100 MHz, CDCl3): δ 54.75, 99.33, 100.98, 108.51, 120.38, 121.02, 123.11, 125.33,
128.87, 129.47, 141.07, 143.07, 145.92, 146.03, 146.74, 157.14, 157.95. ESI-MS (m/z): calcd for
[M + H]+ 379.23, found 379.92; Anal. Calcd for C20H11Cl2N3O: C, 63.18; H, 2.92; N, 11.05
Found: C, 63.22; H, 2.90; N, 11.09.
<H3>2.5.3. 12-Methoxybenzo[g][3,4-b]-2,6-dichloroquinoline[1,8]naphthyridine (6c)
1
Yield: 49%; yellow solid; mp 276 °C. IR (KBr, cm−1): 1464, 1583, 1650. H NMR (400 MHz,
CDCl3): δ 3.89 (s, 3H, OCH3), 7.00(s, 1H, Ar-H), 7.19 (s, 1H, Ar-H), 7.32-7.28 (m, 3H, Ar-H),
7.38 (s, 1H, Ar-H), 7.79 (d, J=9.2 Hz, 1H, Ar-H), 7.84 (d, J=9.2 Hz, 1H, Ar-H).13C NMR (100
MHz, CDCl3): δ 54.74, 99.30, 100.96, 108.48, 120.35, 121.00, 123.09, 125.30, 128.84, 129.45,
141.63, 143.04, 143.88, 146.01, 146.71, 157.12, 157.93. ESI-MS (m/z): calcd for [M + H]+
379.03, found 378.65; Anal. Calcd for C20H11Cl2N3O: C, 63.18; H, 2.92; N, 11.05 Found: C,
63.15; H, 2.88; N, 11.09.
<H3>2.5.4. Naphtho[g][3,4-b]-1-Methyl-6-chloroquinoline[1,8]naphthyridine (6d)
Yield: 54%; green solid; mp 267-2690C. IR (KBr, cm−1): 1439, 1515, 1575, 1640. 1H NMR (400
MHz, CDCl3): δ 2.46 (s, 3H, CH3), 6.97 (s, 1H, Ar-H), 7.00 (s, 1H, Ar-H) 7.20-7.18 (m, 2H, Ar-
H), 7.29 (dd, J=8.4, 1.6 Hz, 1H, Ar-H), 7.49 (t, J=8.4 Hz, 1H, Ar-H), 7.51 (s, 1H, Ar-H), 7.66
(s, 1H, Ar-H), 7.74 (d, J=8.4 Hz 1H, Ar-H), 7.81 (d, J=8.4 Hz, 1H, Ar-H), 7.99 (d, J=8.8 Hz, 1H,
13
Ar-H). C NMR (100 MHz, CDCl3): δ 24.39, 108.57, 110.26, 118.41, 119.83, 121.07, 122.03,
123.84, 127.23, 127.55, 128.04, 129.02, 130.01, 130.07, 130.81, 135.35, 142.38, 148.72, 148.78,
10

149.32, 149.81, 150.38, 150.43. ESI-MS (m/z): calcd for [M + H]+ 379.09, found 379.09; Anal.
Calcd for C24H14ClN3: C, 75.89; H, 3.72; N, 11.06 Found: C, 75.85; H, 3.70; N, 11.09.
<H1>3. RESULT AND DISCUSSION
<H2>3.1. Synthesis of 2-chloroquinoline-4-amines (Ortho chloroquinoline Para amines) 3(a-f)
The starting material 2-chloroquinoline-4-amines 3(a-f) required for the synthesis of
1,8-naphthyridines were synthesized by developing a novel route. Recently we have reported 3c
by azidation-reduction procedure by Rajendran et al. [34]. The 2,4,-dichloroquinolines 1(a-f)
were synthesized by literature methods [35,36], which were then reacted with sodium azide in
DMF at 550C stirring for 2-3hrs, furnished 2-Chloro-4-azidoquinolines 2(a-f) in good yields. We
reported here in successfully reduced 2-Chloro-4-azido quinolines 2(a-f) in one step using
sodium dithionite (Na2S2O4) in methanol for refluxing temperature to afford 2-Chloroquinoline-
4-amines 3(a-f) in excellent yields Table 1. The structures of compounds 3(a-f) were assigned
using spectroscopy methods. For instance, IR spectrum of compound 3b showed stretching for
1
C=N, C-H at 1647, 2961cm–1, and NH2 at 3319, 3452 cm–1. The H NMR spectrum of in
(DMSO-d6) showed the resonance at δ 2.45 for methyl protons, two singlet’s at δ 6.48, 8.14
corresponding to C3-H,C5-H protons and two doublets were observed at 7.50 (dd, J=8.4, 2.0 Hz,
1H), 7.59 (d, J= 8.8 Hz, 1H), corresponding to C7-H,C8-H proton respectively, 7.05 were
assignable for NH2 proton respectively. 13C NMR spectra confirmed the presence of 10 carbons.
The ESI-MS spectrum showed the molecular ion peak at m/z 193.01. From these details, the
structure of the compound was confirmed as 6-Methyl-2-chloroquinoline-4-amine 3b. The
reaction sequence was extended to other derivatives of 2-chloroquinoine-4-amines 3(a-f)
Scheme 1. The synthetic procedure is very simple when compared with other previously
reported synthetic methods [25-29]. However, we have modified the workup procedure and
synthesized 3c with better overall yield of 3(a-f), which make this method a simple and
convenient one.
11

<H2>3.2. Synthesis of benzo[g]-1H-Indazolo[5,6-b][1,8]naphthyridines 5(a-d)
Distinguished from classical sequential two-component synthetic procedure,
multicomponent reactions (MCRs) involve the use of three or more synthons for the product
formation [37-41]. To the best of our knowledge, only a few references exist concerning the
synthesis of [1,8] napthyridines [42,43]. K.J.R.Prasad and Co-workers [43] have reported the
synthesis of Indazolo[2,3-b] dibenzo [b,g][1,8]naphthyridines analogues in two steps in
conventional method and single step using micro wave method by varying different metal
catalyst and organic solvents. Now, here in we have reported benzo[g]-1H-Indazolo[5,6-b] [1,8]
naphthyridines 5(a-d) 55-75% yields, a simple efficient method to these heterocycles would be
attractive by under basic solvent conditions no catalyst and short duration of reaction time in
Table 2
Hence equal mole ratio of 2-chloroquinoline-3-carbaldehydes and respective and 1H-
Indazole-6-amine in 10mL of DMF heated with 1600C for 2-3 hrs. The reaction progress was
monitored by various percentages in TLC. After completion of reaction it was noted that the
yielded a single product and no side product, (minor isomer) was obtained. The structure of
compounds 5(a-d) was assigned using spectroscopy and analytical methods. For instance, IR
spectrum of compound 5b showed stretching for C=N at 1589cm–1, and 3357 cm–1 for NH
stretching. The 1H NMR spectrum 5b of in (DMSO-d6) showed that singlet at δ 2.70 corresponds
to C8–CH3 protons respectively, all the aromatic protons multiplet at δ 7.41-7.39 (C3,C4 and C13-
H), δ 7.60-7.56 (C5,C6 and C7-H) except for two protons doublets, which were very much
deshielded δ 7.83 (J =8.8Hz, C9-H) and δ 8.05 (J=8.8Hz, C10-H) one broad singlet was observed
at 13.53 corresponds to Indazolo NH protons and 13C NMR spectra confirmed the presence of 18
carbons. The ESI-MS mass spectrum of reveals a molecular ion peak at m/z 284.49. From these
details, the structure of the compound was confirmed as 8-Methyl benzo[g]-1H-Indazolo[5,6-
12

b][1,8]naphthyridine 5b. The reaction sequence was extended to other derivatives of 5(a-d)
Scheme 2.
<H2>1.2. Synthesis of benzo[g][3,4-b]-2,6-dichloro quinoline[1,8]naphthyridines 6(a-d)
Moreover, we have developed a convenient route for new synthetic derivatives of linear
fused 1,8-naphthyridines for using some of 2-chloroquinoline-4-amine derivatives Table 3.
Hence equal mole ratio of 2-chloroquinoline-3-carbaldehydes 4(a-d) and respective 2-
chloroquinloine-4-amines 3c, 3e in 10mL of DMF heating 1800C for 2hr, after completion of
reaction, yielded a single product indicated thin layer chromatography (TLC). The structures of
compounds 6(a-d) were assigned using spectroscopy methods. For instance, IR spectrum of
compound 6c showed stretching for C=N at 1583cm–1, and 1464 cm–1 for C-N stretching and
1
disappearance of 4c –CHO stretching at 1745cm-1. The H NMR spectrum of in (DMSO-d6)
showed the resonance at δ 3.89 ppm for methoxy protons C12–OCH3, and the remaining aromatic
protons resonance at δ 7.00-7.86 ppm expected chemical shifts and splitting pattern. Both the
sharp singlet at 10.50 ppm corresponding to 4c -CHO and another singlet at δ 6.60 pertaining to
C3-H protons disappeared corresponding to 2,6-dichloroquinoline-4-amine 3c C3-H protons, and
13C NMR spectra confirmed the presence of 20 carbons. The ESI-MS mass spectrum showed the
molecular ion peak at m/z 379.09. From these details, the structure of the compound was
confirmed as 12-Methoxybenzo[g][3,4-b]-2,6-dichloroquinoline[1,8] naphthyridine 6c. The
reaction sequence was extended to other derivatives of benzo[g][3,4-b]-6-chloroquinoline[1,8]
naphthyridines 6(a-d), Scheme 3.
Proposed mechanism for scheme 2 and 3
13

O
O
H
O
H
H
H
..
..
N
Cl
H2N
N
N
H
N
N
H
4a-d
1H-Indazole-6-amine
(or) 2-chloroquinoine
-4-amines 3a-f
H
H
HO
-H2O
N
N
N
N
5a-d & 6a-d
Furthermore, we observed blue light-emission of all synthesized compounds 3(a-f), 5(a-
d) and 6(a-d) with naked eyes under fluorescence wave length (400-600 nm) in methanol; hence
we think these compounds are good conditions for studying their photo physicalproperties. In the
beginning we performed the band gap energy HOMO-LUMO with the DFT calculations.
<H1>4. PHOTOPHYSICAL PROPERTIES
<H2>4.1. Fluorescence properties of 2-chloroquinoline-4-amines 3(a-f), benzo[g]-1H-
Indazolo[5,6-b]
[1,8]naphthyridines
5(a-d)
and
benzo[g][3,4-b]-2,6-
dichloroquino[1,8]naphthyridines 6(a-d)
The UV-Visible absorption and emission spectra of compounds 3(a-f) in polar solvent
(methanol) were studied. Further, the fluorescence quantum yield of each compounds 3(a-f) were
also determined by the standard literature method using Rodamine-6G as a reference standard
(ϕref=0.95 in 0.1 M CH3OH) [44-46]. The concentration of the compounds 3(a-f) were prepared
at 10-3 M in absolute methanol. The UV-Visible absorption and emission spectra of compounds
3(a-f) were studied in the range of 200-400 nm (λabs. max) and 400-700 nm (λf. max.), respectively,
and the results are summarized in Table 4. It can be seen from Table 4 that the 3d, 3f shows
fluorescence maxima at 516 and 487 nm, respectively. Moreover, 3a, 3b, 3e shows emission
maxima at 449, 485, 486 nm. As a whole that fluorescence maxima of compounds 3d, 3f occur
at longer wavelength when compared to that of 3a, 3b, 3c, 3e. This is due to the presence of
strong σ-π*, π-π* electron donor, -OCH3, -CH-CH=CH-CH- groups on ring (A) of 3d, 3f. The
14

lower emission maxima of compounds 3a, 3b, 3e owing to presence of electron withdrawing
groups for CH3 on ring (A) at ortho, para position Fig. 4 due to the +I effect. Another interesting
feature is that chloro substituent molecules 3c have high fluorescence maxima, but less
fluorescence quantum yield compared to compounds 3d, 3f (ϕ= 0.235). This difference may be
attributed the quenching of fluorescence with chlorine atoms as present in ring (A). Comparative
emission spectra of 3(a-f) are represented in Fig. 5.
In the recent past, several literatures have reported that naphthyridines exhibit high
fluorescence properties. The synthesis of novel L-shaped π-extended compounds for
pyrrolo[1,2-a][1,8]naphthyridines systems and their interaction with dichloromethane has
been reported by Tateno et al. [47]. Further, the same authors have well studied the
photophysical studies of pyrrolo[1,2-a] [1,8]naphthyridines as well as frontier MOs and energy
levels of pyrrolo[1,2-a] [1,8] naphthyridines compounds [48]. In our present studies, we have
carried out the absorption and emission properties of newly synthesized benzo[g]-1H-
Indazolo[5,6-b][1,8] naphthyridines 5(a-d) and benzo[g][3,4-b]-2,6-dichloro quinoline
[1,8]naphthyridines 6(a-d). The compounds 5c, 5d, 6b, 6c and 6d show florescence maxima at
542, 532, 552, 554 and 532 nm. However some of 1,8-naphthyridines 5a,5b,6a show less
emission maxima at 492,498,514 nm, respectively. The substituted 1,8-naphthyridines has
showed high fluorescence maxima, mainly, the compounds 5c, 5d, 6b, 6c and 6d exhibit longer
wavelength than that of 5a, 5b, 6a.
This attribute due to the presence of strong π-π*, n-π* electron donor, more conjugation
groups on ring (A) of compounds 5c, 5d, 6b, 6c and 6d (Figs. 6 and 8). The methoxy -OCH3 and
more conjugated compounds showed high quantum yields (ϕf=0.48-0.37) and fluorescent
quantum yield of all the compounds are summarized in Table 4. The emission spectra of
compounds 5(a-d) and 6(a-d) are shown in Figs. 7 and 9.
15

5. DFT study of 2-chloroquinoline-4-amines 3(a-f), benzo[g]-1H-Indazolo[5,6-b][1,8]
naphthyridines 5(a-d) and benzo[g][3,4-b]-2,6-dichloroquino [1,8] naphthyridines 6(a-d)
The HOMO-LUMO band gap is an important phenomena in explaining applications
corresponding to the fluorescence properties and DFT calculation [49]. D.P.Sheler et al. [22]
have earlier approached the synthesis of naphthyridines with HOMO-LUMO energy band gap up
to 7eV which florescence between 400-700 nm that found with applications in OLEDs. To the
best of our knowledge, there is no results in computational literature survey for 2-
chloroquinoline-4-amines 3(a-f) substituted 1,8-naphthyridines 5a, 5b, 5d and 6(b-d), our
research group first explored and analyzed experimentally and theoretically. Hence we calculated
the HOMO-LUMO band gap energy values corresponding to all new molecules through
M06HF/6-31G (d, p) level of theory which is given in Tables 5. The computational calculations
of Table 5 compounds 3d (9.48 eV), 6b (7.49 eV) and 6c (7.58 eV) shows low gap values
compared to other compounds, because methoxy –OCH3, group present in ring (A) as compared
to ring B, C, D and E the 3D images are given in Figs. 4&8 the donor chromaphore –OCH3 on
ring (A) play an important role in increasing electron density and lowering the electron hole gap.
Furthermore compounds 3d, 6b, 6c bearing methoxy –OCH3 group on ring (A) shows low gap
values indicating higher overlapping of HOMO-LUMO orbital’s which shows red shifted
(Bathochromic) in it, fluorescence maxima and high fluorescence quantum yields as compared to
other molecules are briefly discussed in Table 5. When compared parent molecule with
substituent of R = -CH=CH=CH=CH- molecule, There has a contradiction results in
HOMO – LUMO gap. These are deeply discussed in supporting information [51,52]. The
HOMO-LUMO energies for all these compounds are close to each other, the energy level
diagrams of compounds 3(a-f), 5a,5b,5d and 6(b-d) using the Gaussian 09 program package on
Figs. 10-12 are given below.
<H1>6. Conclusion
16

In conclusion, we have developed a direct and efficient approach to the synthesis of
benzo[g][1,8]naphthyridines from simple synthons 2-chloroquinoline-3-carbaldehydes, 1H-
Indazole-6-amine and 2-chloroquinolne-4-amines. The reaction proceed by simple condensation
under basic medium conditions without any catalyst furnishing benzo[g]-1H-Indazolo[5,6-b]
[1,8]naphthyridines 5(a-d), benzo[g][3,4-b]-2,6-dichloroquinoline[1,8]naphthyridines 6(a-d) in
good yields. This method is much more efficient due to short reactions times and easy separation
process. Desired products were obtained in excellent yields. The products synthesized were
subjected to photophysical studies and DFT theoretical evaluation. The emission properties of
methoxy substituted compounds 3d, 6b, 6c established high fluorescence quantum yields
(ϕf=0.25-0.48) compared to all other molecules discussed with Table 5 because of presence of
donor chromophore in ring (A) compared to other (B), (C), (D), (E) rings. The synthesized
compounds were subjected to DFT computational study. It is evident from the computational
studies that HOMO-LUMO energy gap is comparatively low for methoxy substituted
compounds and hence experimentally the methoxy substituted compounds showed relatively
higher emission properties. Finally, all of new compounds were subjected to UV-Vis absorption
and fluorescence emission studies in absolute methanol at ambient temperature and the results
have been interpreted. Further scope of methodology is been exploited and various biological
application studies are currently progressing in our laboratory.
<ACK>Acknowledgements
The authors gratefully acknowledge the Department of Science and Technology (DST),
New Delhi for DST-PURSE fellowships for financial support to this research work. We thank
Prof. Dr. P. Kolandaivel, Professor and Head, Director of Physical Sciences, Department of
Physics, Bharathiar University, Coimbatore – 641 046, Tamil Nadu, India, for voluble
suggestions and computational facilities in the DFT theoretical studies.
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</BIBL>
<Figure>Fig. 1 Benzo [b] [1, 8] naphthyridines-3-carbonitrile [22]
<Figure>Fig. 2 5-(3, 4-Dichlorophenyl)-5, 6-dihyrobenzo[b] naphtha [2, 1-g][1,8] naphthyridine
[23]
<Figure>Fig. 3 2, 5-Diphenylbenzo[h][1,6] naphthyridines [24]
<Figure>Fig. 4 3D picture of 2-choloroquinoline-4-amine 3a
Fig. 5 Fluorescence spectra of 3(a-f) in methanol
<Figure>Fig. 6 3D picture of 8-Methyl benzo [g]-1H Indazolo[5,6-g][1,8]naphthyridine 5b
Fig. 7 Fluorescence spectra of 5(a-d) in methanol
<Figure>Fig. 8 3D picture of 12-Methoxybenzo [g]
[3,4-g]-2,6-dichloro quinoline [1,8] naphthyridine 6c
Fig. 9 Fluorescence spectra of 6(a-d) in methanol
<Figure>Fig. 10 Frontier Molecular Orbital’s (FMO) energy level of 3(a-f)
<Figure>Fig. 11 Frontier Molecular Orbital’s (FMO) energy level of 5a, 5b& 5d
<Figure>Fig. 12 Frontier Molecular Orbital’s (FMO) energy level 6b, 6c, 6d
<Figure>Scheme 1 Synthesis of 2-chloroquinoline-4-amines 3(a-f).
<Figure>Scheme 2 Synthesis of benzo[g]-1H-Indazolo[5,6-b][1,8]naphthyridine 5a-d.
21

<Figure>Scheme 3 Synthesis of benzo[g][3,4-b]-6-chloroquinoline[1,8]naphthyridines 6a-d
<Table>Table 1 Optimization of reaction conditions a,b
Reaction time (h) Yieldc (%)
Substrate 1a-f
Entry
Substrate 2a-f Product 3a-f
Cl
N3
NH2
1
2
3
4
5
3
91
79
89
61
96
N Cl
N Cl
N Cl
Cl
N3
NH2
H3C
Cl
H3C
Cl
H3C
Cl
3
N Cl
Cl
N Cl
N3
N Cl
NH2
N Cl
Cl
N Cl
N3
N Cl
NH2
3.5
H3CO
H3CO
H3CO
N Cl
N Cl
N Cl 4.5
Cl
N3
NH2
4.5
N
Cl
N
Cl
N
Cl
NH2
N
CH3
CH3
CH3
Cl
N3
6
N
Cl
N
Cl
Cl
3
89
aNaN3, DMF, 55 0C, 3h, bNa2S2O4, methanol, cIsolated yields.
<Table>Table 2 Optimization of reaction conditions d
Entry
Product 5(a-d)
Time(h)
Yield (%)e
Substrate 4(a-d)
7
6
5
O
4
3
8
9
H
N2
N
N
N
H
N
Cl
1
13
10 11 12
2.5
2
1
2
3
60
54
47
H3C
O
H3C
N
H
N
N
N
H
N
Cl
H3CO
O
H3CO
N
H
N
N
N
H
N
Cl
3
22

O
N
H
N
N
N
H
N
Cl
2.5
4
56
dDMF, 1600C, 2-3h, eIsolated yields.
<Table>Table 3 Optimization of reaction conditions f
Entry
Product 6(a-d)
Time(h)
1.5
Yield (%)g
Substrate 4(a-d)
O
Cl
9
8
7
6
10
H3C
H3C
5
H
N
1
11
N
Cl
4
3
43
N
13
N
14
12
1
2
Cl
O
Cl
H3CO
H3CO
N
H
2
3
4
2
2
2
40
49
54
N
N
N
H
O
Cl
Cl
Cl
O
N
N
OCH3
N
N
OCH3
Cl
Cl
Cl
N
H
CH3
N
N
N
Cl
fDMF,1800C, 2hr, g Isolated yields.
<Table>Table 4 The photophysical data for electronic absorption (UV λabs.max.), fluorescence
(Em. λflu.max.) and quantum yield (ϕf) of compounds 3(a-f), 5(a-d) and 6(a-d) in absolute
methanol at ambient temperature.
Entry Comps.
R1
H
R2
H
H
H
R3
H
H
H
λabs.CH3OH
299
λflu.CH3OH
449
ϕf
1
2
3
0.136
0.135
0.165
3a
3b
3c
CH3
Cl
306
485
315
487
23

4
5
6
OCH3
H
H
H
H
334
309
260
516
486
0.235
0.059
3d
3e
3f
CH3
-CH CH=CH-CH-
487
0.226
7
H
H
H
H
H
H
H
334
342
352
418
331
363
492
498
542
532
514
552
554
532
0.288
0.318
0.446
0.370
0.254
0.482
0.426
0.278
5a
5b
5c
5d
6a
6b
6c
6d
8
CH3
OCH3
9
10
11
12
13
14
-CH CH=CH-CH-
CH3
OCH3
H
H
H
H
H
H
OCH3 406
426
-CH CH=CH-CH-
<Table>Table 5: The molecular electronic properties (HOMO-LUMO band energy GAP) of the
3a-f, 5a, 5b, 5d and 6b,6c,d) compounds calculated with M06HF/6-31G(d, p) level of theory.
Entry
Comps. R1
R2
H
H
H
H
H
H
R3
H
HOMO (eV) LUMO (eV) GAP(eV)
1
2
3
4
5
6
H
-9.00
-8.89
-9.16
-8.62
-8.87
-8.73
0.84
0.93
0.54
0.85
0.88
0.81
9.84
9.83
9.70
9.48
9.76
9.54
3a
3b
3c
3d
3e
3f
CH3
H
Cl
H
OCH3
H
H
CH3
H
-CH=CH-
CH=CH
24

7
8
9
H
H
H
H
H
H
H
-7.88
-7.83
-7.94
-1.01
-0.94
-0.90
6.86
6.88
7.03
5a
5b
5d
CH3
-CH=CH-
CH=CH-
OCH3
H
10
11
12
H
H
H
H
-8.67
-1.18
-1.10
-0.93
7.49
7.58
7.89
6b
6c
6d
OCH3 -8.68
H -8.82
-CH=CH-
CH=CH-
TDENDOFDOCTD
25