Study on Synthesis and Fluorescence of Novel Benzofused Phenazine π-Conjugated Skeleton with Coumarin and Isophoron Cores

Article abstract of DOI:10.1007/s10895-015-1597-y

The novel benzofused phenazine π-conjugated skeleton with a coumarin and isophoron core was synthesized, characterized, and condensed with suitably substituted active methylene compounds by classical Knoevenagel condensation reaction to obtain novel mono-styryl dyes 6a-6d. These novel styryl dyes have hue varying from yellow to violet. The geometries of the styryl dyes were optimized at B3LYP/6-31G (d) level of theory, and their electronic excitation properties were evaluated using density functional theory.

Full text of DOI:10.1007/s10895-015-1597-y

J Fluoresc
DOI 10.1007/s10895-015-1597-y
ORIGINAL ARTICLE
Study on Synthesis and Fluorescence of Novel Benzofused
Phenazine π-Conjugated Skeleton with Coumarin
and Isophoron Cores
Amol S. Choudhary1 & Sharad R. Patil1 & Nagaiyan Sekar1
Received: 6 February 2015 /Accepted: 15 June 2015
#
Springer Science+Business Media New York 2015
Abstract The novel benzofused phenazine π-conjugated
skeleton with a coumarin and isophoron core was synthesized,
characterized, and condensed with suitably substituted active
methylene compounds by classical Knoevenagel condensa-
tion reaction to obtain novel mono-styryl dyes 6a-6d. These
novel styryl dyes have hue varying from yellow to violet. The
geometries of the styryl dyes were optimized at B3LYP/6-31G
(d) level of theory, and their electronic excitation properties
were evaluated using density functional theory.
π-conjugated molecules and control the solid-state structure to
obtained appropriated intermolecular interaction in an intelli-
gent way.
Consequently, recent advance in exploring π-conjugated
molecules involved the extension of π-conjugation between
the donor (D) motif such as carbazole, biphenyl amine,
quinoxaline or N,N,-diethylamide and acceptor group (A)
such as cyano, nitro or benzimidazole, other heterocycles.
Such kind of analogues gives the excellent photophysical
properties. Conjugated D-π-A materials have important elec-
trical, optical and redox properties that make them outstanding
candidates for integration into electro-optical and light-
emitting devices (LEDs) [5, 6].
.
.
.
.
Keywords Phenazines Isophoron Styryl dyes DFT
.
Fluorescence TDDFT
There have been tremendous research activity in the field
of styryl dyes as they have promising applications in the high
technology areas. One of the reasons for this is the relative
ease of synthesis of such dyes. The styryl dyes have a number
of good properties, like fluorescence and good photo stability
as compared to the cyanine analogous. Styryl dyes with
absorption ranging from UV to near infrared region can
be synthesized by using different substituent on the chromo-
phore [7, 8].
The 2, 5-diamino-3,6-dicynopyrazine derivatives have a
small chromophoric system but have strong fluorescence even
in the solid state [9]. The dicynopyrazine have very strong
electron withdrawing ability, and derivative thereof can be
are expected to have strong intramolecular charge transfer
interaction in their self-assemble aggregates [10].
Introduction
In recent years, the development of organic π-conjugated mol-
ecules for organic electronic, such as organic light emitting
diode (OLEDs) [1], organic field effect transistor (OFETs)
[2], environment-sensitive fluorescence [3] and organic pho-
tovoltaic (OPVs) [4] remain a key objective. Organic mate-
rials have distinct advantage of their structure diversity, which
can be achieved by versatile synthetic protocol in organic
chemistry. It is important to tailor the electronic structure of
Electronic supplementary material The online version of this article
(doi:10.1007/s10895-015-1597-y) contains supplementary material,
which is available to authorized users.
The compounds having an intramolecular charge transfer
properties are one of the most important materials. Such ma-
terials are usually functionalized by electron-donating (D) and
electron-accepting (A) groups through a π-conjugated bridge
which makes it possible to reduce the gap between HOMO
and LUMO orbital of the molecule for increasing the range of
absorption and to study the relationship between the variation
* Nagaiyan Sekar
n.sekar@ictmumbai.edu.in; nethi.sekar@gmail.com
1
Tinctorial Chemistry Group, Department of dyestuff and
intermediate Technology, Institute of Chemical Technology,
Mumbai, Nathalal Parekh Marg, Matunga, Mumbai 400 019, India

J Fluoresc
of donor-acceptor chromophores and their corresponding
photophysical and electrochemical properties [11, 12].
The electron-rich benzo[a]phenazin-5-ol unit is donor moi-
ety of donor-acceptor type of functional molecules. Phenazine
derivatives are important molecules in dye-sensitized solar
cells (DSSCs) [13, 14]. Phenazine π-conjugated skeleton de-
rivatives have also attracted considerable interest in colorimet-
ric and ratiometric near-infrared fluorescent cyanide
chemodosimeter. With these approach, to explore the relation-
ship between chemical structures and various properties of
these compounds, we have designed and synthesized a new
series of intramolecular charge transfer (ICT) compounds by
incorporating the benzo[a]phenazin-5-ol moiety (electron do-
nor) with isophoron bridge or 3-acetylcoumarin groups (elec-
tron acceptor), and studied their absorption and fluorescence
spectroscopy, thermo gravimetric analysis and density func-
tional theory calculations.
hydrazone tautomeric forms [16]. Ground state (S0) geometry
of the dyes in gas and solvent was optimized in their C1
symmetry using DFT [17]. The Becke’s three parameter ex-
change functional (B3) [18] combining with nonlocal correla-
tion functional by Lee, Yang and Parr (LYP) [19] and basis
set6-31G (d)was used for all atom. Same method was used for
vibrational analysis to verify that the optimized structures cor-
respond to local minima on the energy surface. Time
Dependent Density Functional Theory (TD- DFT) computa-
tions were used to obtain the vertical excitation energies and
oscillator strengths at the optimized ground state equilibrium
geometries at the same hybrid functional and basis set
[20–22]. All the computations in solvents of different polari-
ties were carried out using the Self-Consistent Reaction Field
(SCRF) under the Polarizable Continuum Model (PCM) [23].
Synthetic Strategy
Some of these dyes showed fluorescence in the solid state.
The synthesized phenazine π-conjugated dyes have shown
red-shifted absorption properties in comparison with the phen-
azine π-conjugated based dyes reported earlier [10–12].
Density functional theory computations [B3LYP/6-31G (d)]
were carried out to study the geometrical and electronic prop-
erties, and its related properties were computed using B3LYP/
6-31G (d) on the basis of the finite field approach [13–15].
General Method for the Synthesis and Characterization of 3
2-Hydroxy-1, 4-napthaquinone 1 (2 mmol) and substituted o-
phenylenediamine 2 (2 mmol) were stirred in a mixture of
AcOH: EtOH (50:50) (20 ml) at 80 °C for 1–1.5 h.
Completion of the reaction was monitored by TLC. After
completion of the reaction, the reaction mass was poured in
crushed ice and stirred for 30 min at room temperature. The
reaction mass was filtered and the product was purified by
column chromatography using silica gel 100–200 mesh and
ethyl acetate: hexane (50:50) as eluent system.
Experimental
Materials and Instrumentation
General Procedure for the Synthesis of 4a
2-Hydroxy-1, 4-napthaquinone, substituted o-
phenylenediamine, o-aminothiophenol, and malononitrile were
procured from Sigma Aldrich. 2-(3,5,5-trimethylcyclohex-2-
en-1-ylidene)malononitrile and 2-(1-(2-oxo-2 H-chromen-3-
yl)ethylidene) malononitrile were synthesized by the reported
method. The reaction was monitored by TLC using 0.25 mm E-
Merck silica gel 60 F254 percolated plates, which were visual-
ized with UV light. Melting points were measured on standard
melting point apparatus from Sunder industrial product
Mumbai, and are uncorrected. The FTIR spectra were recorded
on a Perkin-Elmer Spectrum 100 FTIR Spectrometer. 1HNMR
spectra were recorded on VXR 300 MHz instrument using
TMS as an internal standard. The visible absorption spectra of
the compounds were recorded on a Spectronic Genesys 2 UV–
Visible spectrophotometer. Emission and excitation spectra of
the compounds are measured on Varian Cary eclipse
spectrofluorimeter.
POCl3 (0.015 mmol) was added to DMF (0.20 mmol) at 0 °C
within 15 min and stirred for 30 min at 0 o C. Naphtho [1,2-
a]phenazin-5-ol 3 (0.01 mmol) dissolved in DMF (5 ml) was
added slowly at 0–5 °C and stirred for 2–3 h at room temper-
ature. The completion of the reaction was monitored by TLC.
The reaction mass was poured in ice and stirred, neutralized
with sodium bicarbonate, filtered and dried. The crude alde-
hyde was recrystallized from ethanol. The product was puri-
fied by column chromatography using silica gel 100–200
mesh and ethyl acetate: hexane (10:90) as eluent system.
Yield = 69 %, Melting point: 163–168 °C FT-IR (KBr,
cm−1): 3100 (−OH), 2930 (COH), 1600 (CO), 1577
(C = N), 1200 (C-O).
Mass: m/z 274 [M + 1].1 H NMR (CDCl3, 300 MHz) = δ
3.67 (t, 4 H, J = 6.9, 4.7 Hz), 3.83 (t, 4 H, J = 7.4, 5.1 Hz), 7.29
(m, 4 H), 8.60 (bs, 1 H), 8.5 (s, 1 H) ppm.
Computational Methods
Procedure for the Synthesis of 4b
Gaussian 09 program package was used to optimize geometry
and to study the synthesized azo dyes in their azo and
POCl3 (0.015 mmol) was added to DMF (0.20 mmol) at 0 °C
within 15 min and stirred for 30 min at 0 °C. Naphtho [1,2-

J Fluoresc
Table 1 Photophysical properties of compound 6b and 6d in different
solvents
a]phenazin-5-ol 17 (0.01 mmol) dissolved in DMF (5 ml) was
added slowly at 0–5 °C and stirred and heated up to 90 0 C for
2–3 h. The completion of the reaction was monitored by TLC.
The reaction mass was poured in ice and stirred, neutralized
with sodium bicarbonate, filtered and dried. The crude alde-
hyde was recrystallized from ethanol. The product was puri-
fied by column chromatography using silica gel 100–200
mesh and hexane as eluent system. Yield = 58 %, Melting
point: 173–178 °C FT-IR (cm−1) = 1701 (C = O), 1586
(C = C, aromatic). Mass = m/z = 292.08, M +
1 = 293.08 M + 2 = 294.08, (M + 1).1 H NMR (CDCl3,
300 MHz) = δ 10.24 (s, 1 H) 7.66–7.80 (m, 4 H), 7.83–7.95
(m, 4 H).
Solvents Dye 6b
Absorption
λnm εmax
Dye 6d
Absorption
λnm εmax
ν cm−1
ν cm−1
ACN
425 0.5615 23,529.4
640 0.3206 15,625
445 0.4424 224,719.1
625 0.1212 160,000
EtOH
415 0.6963 24,096.4
440 0.4180 227,272.8
480 0.5307 208,333.3 630 0.1527 158,730.1
650 0.4647 153,846.1
DMF
420 0.5664 238,095.2 420 0.4962 238,095.2
485 0.4547 206,185.6 625 0.2451 160,000
650 o.4647 153,846.1
DMSO
415 0.5708 24,096.4
485 0.4547 206,185.6 640 0.2070 15,625
650 0.4776 153,846.1
425 0.4284 224,719.1
General Procedure for the Synthesis of 6a-6d
5-Hydroxybenzo[a]phenazine-6-carbaldehyde 4a or 4b
(1.8 mmol) and 2-(3, 5, 5-trimethylcyclohex-2-en-1-ethyli-
dene) malononitrile 5a or 2-(1-(2-oxo-2 H-chromen-3-yl)
ethylene) malononitrile 5b (2.0 mmol) were stirred in ethanol
(20 ml). Catalytic amount of piperidine was added to the
mixture and refluxed for 2 h. Completion of the
reaction was monitored by TLC. The compound precip-
itated out was filtered and purified by column chromatogra-
phy using silica 100–200 mesh and ethyl acetate: hexane
(60:40) as eluent.
O
Scheme 1 Synthesis of
styryl dyes 6a-6d
O
NH2
N
N
i
NH2
OH
OH
1
2
3
N
DMF/POCl3
0 0C - R.T/1 hr
N
3
OH
DMF/POCl3
0 0C -80 0C/3 hr
ii
iii
N
N
N
OH
N
Cl
O
H
O
H
4b
iv
4a
CN
NC
5a
O
O
CN
CN
iv
5a
5b
NC
CN
N
N
N
N
Cl
N
Cl
N
OH
CN
CN
OH
CN
CN
NC
N
O
O
CN
O
O
N
6d
6c
6b
6a
i = ethanol/acetic acid, 80 0C,3 h
ii = POCl3/DMF,0-R.T.
iii = POCl3/DMF 800C
iv = ethanol/ cat. piperiden, 6 h

J Fluoresc
(E)-2-(3-(2-(5-hydroxybenzo[a]phenazin-6-yl)vinyl)-5,5-
dimethylcyclohex-2-en-1-ylidene)malononitrile 6a.
Yield = 54 %; Melting point = 283–285 °C.
FT-IR (cm-1) = 3029 (Ar-H), 3201 (−OH), 2920 (CH3),
1610 (C = C, aromatic), 1558 (C = N), 2110 (−CN).
Mass = m/z = 442.12, M + 2 = 443.6.1 H NMR (CDCl3,
300 MHz) = δ 1.4 (s, 3 H, −CH3) δ 1.7 (s, 3 H, −CH3), δ
2.7 (d, 2 H,-CH2), δ 3.3(s,2 H,-CH2),7.3(s,1 H), δ 7.1(dd,
1 H),7.7(s,1 H) δ 7.9–8.1(m,4 H,Ar), δ 8.2–8.4(m,4 H, Ar),
δ 9.4 (br,s,1 H, −OH).
(E)-2-(3-(5-hydroxybenzo[a]phenazin-6-yl)-1-(2-oxo-2 H-
chromen-3-yl)allylidene) malononitrile 6b.
Fig. 2 Photophysical properties of compound 6b in different solvents
Yield = 64 %; Melting point = 278–281 °C. 73.
FT-IR (cm-1) = 3013 (Ar-H), 3207 (−OH), 2910 (CH3),
1605 (C = C, aromatic), 1545 (C = N), 2210 (−CN).
Mass = m/z = 492.12, M + 2 = 493.6.1 H NMR (CDCl3,
300 MHz) = δ 5.4 (s, 1 H, −OH) δ 6.8 (d, 1 H, =CH), δ 7.2
(d, 1 H,=CH), δ 7.5(s,1 H, pyrano ring proton), δ 7.2–7.4 (m,
4 H, Ar-H), δ 7.5–7.8 (m,4 H, Ar-H), 8.0–8.4 (m,4 H,Ar-H).
(E)-2-(3-(2-(5-chlorobenzo[a]phenazin-6-yl)vinyl)-5,5-
dimethylcyclohex-2-en-1-ylidene)malononitrile 6c.
Result and Discussion
Synthesis Strategy and Characterization
The synthetic plan for the preparation of (E)-2-(3-(5-
hydroxybenzo[a]phenazin-6-yl)-1-(2-oxo-2 H-chromen-3-
yl)allylidene)malononitrile and (E)-2-(3-(5-
chlorobenzo[a]phenazin-6-yl)-1-(2-oxo-2 H-chromen-3-
yl)allylidene)malononitrile 6a-6d is shown in Scheme 1.
Benzo[a]phenazin-5-ol 3 was prepared by condensation of
2-hydroxy-1,4-napthaquinone (Lawson) 1 with 1,2-
diaminobenzene 2 in presences of glacial acetic acid at
60 °C for 60 min. 5-Hydroxybenzo[a]phenazine-6-
carbaldehyde 4a and 5-Chloro[a]phenazine-6-
carbaldehyde 4b were prepared by the Vilsmeier Haack
reaction, which was confirmed by FTIR, 1HNMR, mass spec-
tral analysis and its M + 1 peak was found to be at 274.1. The
compounds 4a or 4b on treatment with 5a or 5b active
methylene compounds, respectively, in the DMSO/ethanol in
presence of catalytic amount of piperidine at reflux tem-
perature (70–80 °C) for 4–5 h gave (E)-2-(3-(5-
hydroxybenzo [a]phenazin-6-yl)-1-(2-oxo-2 H-chromen-
3-yl)allylidene)malononitrile and (E)-2-(3-(5-
Yield = 45 %; Melting point = 278–280 °C.
FT-IR (cm-1) = 3029 (Ar-H), 3201 (−OH), 2920 (CH3), 1610
(C = C, aromatic), 1558 (C = N), 786 (Ar-Cl) 2110 (−CN).
Mass = m/z = 442.12, M + 2 = 443.6.1 H NMR (CDCl3,
300 MHz) = δ 1.4 (s, 3 H, −CH3) δ 1.7 (s, 3 H, −CH3), δ 2.7
(d, 2 H,-CH2), δ 3.3(s,2 H,-CH2),7.3(s,1 H), δ 7.1(dd,1 H),7.
7(s,1 H) δ 7.9–8.1(m,4 H,Ar), δ 8.2–8.4(m,4 H, Ar).
(E)-2-(3-(5-chlorobenzo[a]phenazin-6-yl)-1-(2-oxo-2
H-chromen-3-yl)allylidene)malononitrile 6d.
Yield = 74 %; Melting point = 278–280 °C.
FT-IR (cm-1) = 3013 (Ar-H), 3207 (−OH), 2910 (CH3),
1605 (C = C, aromatic), 1545 (C = N), 2210 (−CN).
Mass = m/z = 492.12, M + 2 = 493.6.1 H NMR (CDCl3,
300 MHz) = δ 6.8 (d, 1 H, =CH), δ 7.2 (d, 1 H,=CH), δ
7.5(s,1 H, pyrano ring proton), δ 7.2–7.4 (m, 4 H, Ar-H), δ
7.5–7.8 (m,4 H, Ar-H), 8.0–8.4 (m,4 H,Ar-H).
Fig. 1 Photophysical properties
of compounds 6a and 6c in
solid state

J Fluoresc
Which illustrates the color of the compounds in different
solvents, in which the respective electronic spectra for 6b and
6d were, recorded (Table 1, Figs. 1 and 2). Form Fig. 2, the dye
6b showed two absorption band in all solvents. The λmax values
of the compound 6b, absorb at 445 and 625 nm for ACN, 440
and 630 nm in EtOH, 420 and 625 nm in DMF, 425 and
640 nm in DMSO, and 624 nm for DMF. While show three
absorption band shown in Fig. 3. From the Fig. 3 the dye 6d in
different solvents were as follows: 425 and 640 nm for ACN,
415,480 and 650 nm in EtOH, 420,485 and 650 nm in DMF,
415,485 and 650 nm in DMSO. The Visible and fluorescence
spectra of dyes 6a and 6c in solid state summarize in Fig. 1. The
excitation wavelength and fluorescence maxima of these dyes
in solid state were observed at 460,465 nm and emission at 552,
550 nm, for dyes 6a and 6c respectively.
It is well known that the fluorescence of coumarins is
strongly dependent on the electron-donating-withdrawing
ability of the substituents at position 7 and 3. Absorption
properties of the synthesized dye 6a-6d. In which benzo phen-
azine π-conjugated skeleton and coumarin couple via C = C
bond. Their photophysical properties depicted (Table 1, Figs
1, 2 and 3). Absorption maxima reveal that the more
conjugated styryl derivatives 6b and 6d are all red-shifted
when compared with the respective isophoron styryl deriva-
tives 6a and 6b.
Fig. 3 Photophysical properties of compound 6d in different solvents
chlorobenzo[a]phenazin-6-yl)-1-(2-oxo-2 H-chromen-3-
yl)allylidene) malononitrile 6a-6d. The synthesized com-
pound 6b and 6d were purified by column chromatography
and confirmed by FTIR, 1HNMR, and mass spectral.
Electronic Spectra
The compounds 6b and 6d are soluble in N, N-
dimethylformamide (DMF), dimethylsulphoxide (DMSO),
methanol (MeOH), ethanol (EtOH), and acetonitrile (ACN).
The compounds 6a and 6c are insoluble in all solvents. The
electronic spectra of the compounds 6b and 6d in solvents of
differing polarity values presented in (Table 1).
Table 2 Calculated electronic absorption spectral data of 6a and 6b molecule
Solvent
Excitation
CI expansion coefficient
Wave length
Calculated
Oscillator strength( f )
Energy
Experimental
ACN
Excited State 1
127 - > 128
Excited State 2
126 - > 128
127 - > 129
Excited State 1
127 - > 128
Excited State 2
126 - > 128
127 - > 129
Excited State 3
126- > 128
0.70032
526.27
421.65
640 (0.3206)
425(0.5615)
0.2611
0.0334
2.3559
2.9404
0.60565
0.35253
EtOH
0.70043
526.86
421.87
650 (0.4647)
480 (0.5307)
0.2628
0.0323
2.3533
2.9389
0.61233
0.34121
−0.34518
418.08
415(0.6963)
0.1296
2.9656
127- > 129
0.59854
DMF
Excited State 1
127- > 128
0.70083
529.48
423.19
650 (0.465)
485 (0.455)
0.2668
0.0252
2.3416
2.9298
Excited State 2
126- > 128
0.64895
0.26749
127- > 129
Excited State 3
126- > 128
−0.26995
418.79
420 (0.566)
0.1471
2.9606
127- > 129
0.63527

J Fluoresc
The TD- DFT is particularly well suited to low energy
valence excited states that can be described by combinations
of single excitations. Electronic transitions determined from
excited state calculations using the TD-DFT method are listed
in Table 2 for the three lowest energy transitions of the mole-
cule. These are identified with the calculated transitions at
526, 421 and 418 nm. In this case the energy transitions are
in reasonable agreement with experimental results.
bridge similarly with benzophenazine core respectively
(Fig. 4).
The optimized ground-state geometries of the studied com-
pound are classified into three categories. The compound in-
cluding the relative linking positioned of coumarin/isophoron
core at one of the end of π-bridge and hydroxy group is
substituted with the chloro group as shown in Fig. 4. The bond
lengths, torsion angle, and dipole moments of 6b and 6d com-
pounds in the ground state are shown in Fig. 4. The presence
of coumarin or isophoron core brings abour appreciable
cahnage in the geometry of the compounds of 6a, 6b, 6c and
6d. For all these compounds, the similar inter link bond length
and different dihedral angle between π-bridge are attentively
observed as shown in the Fig. 4. In the compound 6b,
benzophenazine and coumarin core torsional angle is 270
while the same in 6d 190 which reveals that the presence of
chloro-benzophenazine favors planarity with the π-bridge as
compared to hydroxy benzophenazine. This is because car-
bonyl oxygen of coumarin core and hydroxyl proton of
benzophenazine core come closer to each other with an inter-
atomic distance of 2.12225 A0 while in compound 6a and 6c
chloro group induces steric hindrance. This is because
Optimized Geometries of Dyes 6a-6d
The optimized geometry of all studied compounds calculated
by B3LYP/6-31G d are depicted in Fig. 4 and important struc-
ture parameter of these molecules are shown in Fig. 4. The
optimized structure of the title compounds in the ground state
show the non-planer molecular structure. Since in compound
6a, 6b, 6c and 6d π-bridge and acceptor cyano group is sand-
wich between the hydroxy benzophenazine/chloro
benzophenazine and 3-acetylcoumarin/isophoron subunit. In
the compounds 6b and 6d the connection between the two
adjacent subunit of the molecules relies on single bond, it lead
to elevation torsion angles between the coumarin ring and π-
Fig. 4 Optimized geometry of the consider molecules by DFT/B3LYP/6-31G d

J Fluoresc
HOMO
LUMO
HOMO
LUMO
HOMO-1
HOMO-2
LUMO+1
HOMO-1
LUMO+1
LUMO+2
HOMO-2
LUMO+2
Fig. 5 Molecular orbital plotting (orbital squared) for the mainly
participating molecular orbitals of 6b
Fig. 7 Molecular orbital plotting (orbital squared) for the mainly
participating molecular orbitals of 6a
carbonyl hydroxyl group of benzophenazine core gets in-
volved in conjugation with the π-bridge and acceptor cyano
group.
frontier molecular orbital show π-character. For 6b and 6d
molecules, the HOMO are mainly constrained towards cou-
marin core with largest contributions form planer
benzophenazine, whereas central π-bridge and acceptor cyano
group have dominating contribution to LUMOs. From Fig. 5-
8 the electron density data imply that the benzophenazine unit
serves the electron donating role, and π-bridge and coumarin
serve as electron accepting role and its electron density
strength when the core molecule alter form a coumarin to
isophoron ring. However for 6a molecule, the electronic cloud
Frontier Molecular Orbital and Electronic Properties
The ordering the occupied and virtual orbitals provide a rea-
sonable qualitative indication of the excitation properties. A
sketch of map of the HOMOs and LUMOs as well as other
important orbitals for all synthesized 6a-6d molecules is plot-
ted in (Fig. 5, 6, 7 and 8). The electron density contribution of
each fragment to frontier orbitals has been listed in all the
HOMO
LUMO
HOMO
LUMO
HOMO-1
LUMO+1
HOMO-1
LUMO+1
HOMO-2
LUMO+2
HOMO-2
LUMO+2
Fig. 6 Molecular orbital plotting (orbital squared) for the mainly
participating molecular orbitals of 6d
Fig. 8 Molecular orbital plotting (orbital squared) for the mainly
participating molecular orbitals of 6c

J Fluoresc
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the HOMOs. While for the LUMO, the electronic cloud is
mainly transferred to isophoron bridge core, we have predict-
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delocalization.
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diethyl-1,2,3,4-tetrahydro-6-methoxyquinoxaline. J Heterocyclic
Chem 46:221
In this work, we have developed push-pull chromophores of
A-π-D and A-π-D-π-A types containing benzophenazine,
coumarin and electron withdrawing cyano moieties.
Benzophenazine and coumarin moiety was introduced to the
make the system non-planar. These synthesized fluorophores
1
were confirmed by FT-IR, HNMR and Mass spectral
analysis.
12. Gordo J, Parola AJ, Lima C, Branco PS (2011) Convenient synthe-
sis of 3-vinyl and 3-styryl coumarins. Org Lett 13(19):5112–5115
13. Zhang G, Bala H, Cheng Y, Shi D, Lv X, Yu Q, et al (2009) High
efficiency and stable dye-sensitized solar cells with an organic chro-
mophore featuring a binary pi-conjugated spacer. Chem Commun
(Camb):2198–2200
Acknowledgments The author Amol S. Choudhary is thankful to
University Grants Commission (UGC), New Delhi, India for providing
financial support by way of Junior Research Fellowship (JRF) and Senior
Research Fellowship (SRF) and the Centre of Advanced Studies (CAS),
UGC for the financial support.
14. Zhang X, Zhang J, Xia Y (2008) Molecular design of coumarin
dyes with high efficiency in dye-sensitized solar cells. J
Photochem Photobiol A Chem 194:167–172
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