Synthesis and optical response to acids and bases of a new styryl—dihydro-benzo[a]phenazine chromophores

Article abstract of DOI:10.1016/j.tet.2016.10.028

Four novel styryl—dihydrobenzo[a]phenazine chromophores have been synthesized and spectroscopically characterized. They respond to acids and bases through changes in absorption resulting in strong bathochromic shift (>437?nm). The emission quantum yields of the dyes were in the range 0.11–0.14. Computational studies have been performed to provide further insights into the nature of electronic transitions for the synthesized dyes. The qualitative trends observed in the optical properties, halochromism and geometrical isomers were supported by density functional theory (DFT) computations.

Full text of DOI:10.1016/j.tet.2016.10.028

Accepted Manuscript
Synthesis and optical response to acids and bases of a new styryl-dihydro-
benzo[a]phenazine chromophores
Sharad R. Patil, Amol S. Choudhary, Nagaiyan Sekar
PII:
S0040-4020(16)31050-X
10.1016/j.tet.2016.10.028
TET 28169
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 11 June 2016
Revised Date: 10 October 2016
Accepted Date: 13 October 2016
Please cite this article as: Patil SR, Choudhary AS, Sekar N, Synthesis and optical response to acids
and bases of a new styryl-dihydro-benzo[a]phenazine chromophores, Tetrahedron (2016), doi: 10.1016/
j.tet.2016.10.028.
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Synthesis and Optical response to Acids and
Bases of new Styryl Dihydro-
Benzo[a]phenazine Chromophores
Leave this area blank for abstract info.
a
–
Sharad R. Patil, Amol S. Choudhary and Nagaiyan Sekar*
Department of Dyestuff Technology, Institute of Chemical Technology, Nathalal Parekh Marg, Matunga, Mumbai - 400 019 (India).
*E-mail: n.sekar@ictmumbai.edu.in, sharad.omd.patil@gmail.com

1
ACCEPTED MANUSCRIPT
Tetrahedron
journal homepage: www.elsevier.com
Synthesis and Optical Response to Acids and Bases of a New Styryl – Dihydro-
Benzo[a]phenazine Chromophores
Sharad R. Patil, Amol S. Choudhary and Nagaiyan Sekar*
Department of Dyestuff Technology, Institute of Chemical Technology, Nathalal Parekh Marg, Matunga, Mumbai
n.sekar@ictmumbai.edu.in, sharad.omd.patil@gmail.com
- 400 019 (India). *E-mail:
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
Four novel styryl – dihydrobenzo[a]phenazine chromophores have been synthesized and
spectroscopically characterized. They respond to acids and bases through changes in absorption
resulting in strong bathochromic shift (> 437 nm). The emission quantum yields of the dyes
were in the range 0.11 – 0.14. Computational studies have been performed to provide further
insights into the nature of electronic transitions for the synthesized dyes. The qualitative trends
observed in the optical properties, halochromism and geometrical isomers were supported by
density functional theory (DFT) computations.
Available online
Keywords:
Dihydrobenzo[a]phenazines
Halochromism
pH sensor
2009 Elsevier Ltd. All rights reserved
.
Stereochemistry
DFT
1. Introduction
system is usually required to separate substantial charges in order
to perturb the receptor. 17
Organic π – conjugated materials are increasingly gaining
attention in many areas of chemistry and functional materials
research.1-7 The organic materials featuring donor – π – bridge –
acceptor architecture have continued to attract wide attention
owing to their potential applications in organic electronics such
as red emitting charge transporters in Organic Light Emitting
Diodes (OLEDs),8 Organic Field Effect Transistors (OFETs),9
sensitizers in excitonic solar cells (DSSCs),10 Organic
Photovoltaics (OPVs),11, 12 and as highly sensitive chromophores
in the area of molecular sensing.13
In this study, we designed and synthesized some new styryl
substituted benzo[a]phenazine derivatives with different electron
– donating abilities except nitro derivative (Scheme 1, chart 1).
The substituent effects on their absorption spectra in solution
were studied. However, to the best of our knowledge, the
dihydrobenzo[a]phenazine
derivatives
containing
naphthoquinone functionality have not been studied in detail for
their optical sensor applications. In order to explore the
feasibility, we have also investigated the sensitivity of these
molecules toward acids and bases which could be considered as
model studies. Both, acidic and basic environment modulate the
intramolecular charge transfer depending on the donor and
acceptor capabilities, resulting in significant changes of the
electronic spectra. These external stimuli can be used to
characterize local environments in artificial and biological
materials, making compounds of this type interesting for sensing
purposes. Chromophores changing color on interaction with acids
18-21 and bases have been studied in detail in recent years owing to
their importance in the sensor industry.
Benzophenazine compounds have electron –deficient
characteristics. Hence, they are used in the design of n – type
organic semiconductors; examples are pyrazinoquinoxaline
derivatives, hexaazatriphenylenes, diquinoxalino, phenazine, and
15
quinoxalino phenanthro phenazine.14,
Prachi Singh et al.
synthesized some acidochromic derivative especially 5-
substituted amino benzo[a]phenazines form 1,
2
–
naphthoquinone and studied their solvatochromism and
acidochromic properties.16 Halochromism is one of the key
parameters that can be used to describe any processes and it
provides valuable information about the progress of such
processes. Indeed the phenazine core, which is highly π –
deficient aromatic heterocycle, can be used as electron
withdrawing part in push – pull structures for intramolecular
charge transfer (ICT). ICT is a key parameter to obtain
luminescent and non – linear optical (NLO) properties. Also, ICT
is useful for the design principle and a push – pull π – electron

2
Tetrahedron
NH2
profiles observed for the dyes (5b and 5d) is suggestive of the
ACCEPTED MANUSCRIPT
O
O
H
NH2
N
involvement of conjugative delocalization. The extended
O
O
OH
EtOH/Piperidine
reflux, 3 h
O
4
conjugation present in the above derivatives may lead to a red-
shifted absorption. On the contrary, the blue – shifted profile
observed for the dyes (5a and 5c) may be attributed to the
retardation of electronic delocalization caused by electron-
withdrawing group. In view of these observations, it may be
argued that the prominent absorption in the naphthoquinone
derived styryl dyes is mainly originating from the π – π*
transition.
Ar
H
N
OH
O
Zn, AcOH / EtOH
80 o C, 30 min.
Ar
5a-d
Ar
3a-d
2a-d
Ar =
1
H3CO
OCH3
N
O2N
2d
2c
2a
2b
Scheme 1. General synthetic scheme employed for the
preparation of the Dyes (5a-d).
O
O
H
N
N
HO
O
R
R
5a, R = -H
3a, R = -H
5b, = -NMe2
3b, = -NMe2
5c,
5d,
= -NO2
= 2, 4 - (OMe)2
3c,
3d,
= -NO2
= 2, 4 - (OMe)2
Figure 1. Absorption spectra of the dyes (5a-d) recorded in THF.
Table 1. Optical data of the dyes 5a-d in THFa
Chart 1. Structures of the Naphthoquinone fused
Dihydrobenzo[a]phenazine Styryl dyes.
ꢀλ(cm-1)
5919
b
Dye
5a
5b
5c
5d
λabs (nm)
429
446
436
log ε
5.92
5.84
5.88
5.94
λem (nm)
575
667
487
φem
0.11
0.14
0.03
0.12
2. Results and discussions
7429
2402
4891
2.1. Synthesis and Characterization
450
577
aAll spectra were recorded at room temperature at C = 1.0 X 10-6 M; λabs(nm)
= Maximum absorption wavelength in nm; λem(nm) = Maximum emission
wavelength in nm; ꢀλ (nm) = Stokes shift in nm. The fluorescence quantum
yield, measured at room temperature using fluorescein in 0.1 M NaOH (φ =
0.79) as a standard.
Synthesis of the dyes were accomplished by a two-step
process as outlined in scheme 1, chart 1. In the first step, 2-
hydroxy, 1, 4-naphthoquinone (Lawsone) (1) was treated with the
corresponding aldehydes (2a-d) in the presence of a catalytic
amount of piperidine and ethanol at reflux temperature to yield 3-
substituted 1, 2, 4-triketo naphthoquinone styryl derivatives (3a-
d). To the best of our knowledge, the reactions of o –
phenylenediamine (OPDA) with 1, 2 – naphthoquinone has not
been explored. The o – phenylenediamine 4 was found to react in
a facile manner with 1, 2 – naphthoquinone (3a-d). The
substituted naphthoquinones were conveniently converted to
dihydrobenzo[a]phenazines (5a-d) by refluxing with o–
phenylenediamine in AcOH/EtOH at 80 oC and subsequently
b
All the dyes displayed moderately intense emission in THF
solutions (Figure 2, Table 1) when excited at their absorption
maximum. The most blue-shifted emission profile was observed
for the nitro derivative (5c) while the N, N – dimethylamino
substituted derivative (5b) displayed a longer wavelength
emission in THF solution. The dyes, 5a and 5d exhibited almost
the same maximum wavelength of absorption in THF. The
quantum yields were measured using fluorescein as reference
standard.22, 23The emission quantum yields of the dyes 5a, 5b
and5d were 0.11, 0.14, 0.12 respectively, which were 4 times
larger than that of dye 5c. The relative fluorescence quantum
yields are summarized for dyes 5a-d in Table 1.
1
reduced by Zn. The dyes were characterized by H and 13C –
NMR, and mass spectral analysis. The dyes are yellow or brown
in the solid state and freely soluble in common organic solvents.
2.2. Optical Properties
The UV-vis spectroscopic data of the dyes (5a-d) measured in
THF solutions are displayed in Figure 1 and the relevant
parameters are compiled in Table 1. All the compounds
exhibited a broad and moderately intense absorption band >400
nm attributable to the electronic transition originating from the π-
molecular orbitals. The peak position of this band assumes a
trend (5a< 5c< 5b< 5d) reflecting the impact of the substituent
on aldehyde segment on the electronic properties. They do not
show solvatochromism and solvatofluorism significantly in the
solvent environment used for measurement. The dyes 5b and 5d
showed red shifted absorption profiles when compared to the
dyes 5a and 5c. These observations cannot be explained by
assuming charge transfer nature for the transition and the trend is
not matching with the donor strength of the substituent on
aldehyde segments (Figure 1). The red-shifted absorption

3
A representative illustration of changes for 5a-d in the
ACCEPTED MANUSCRIPT
absorption profile on incremental addition of TFA and TEA is
shown in Table 2. The halochromic properties of the dyes 5b, 5c
and 5d having similar trend to the dye 5a (Figure S1-S3).As
expected, the dye 5bexhibitsa red shift of their absorption bands
upon protonation due to an increased charge transfer from the
donors to the phenazinium moiety. This color change is fully
reversible by neutralisation with a base triethylamine (TEA).
The red-shifted absorption peak realized for the dyes in the
presence of TFA is attributed to the protonated species. It is
possible that the protonation of phenazine segment occurs in the
presence of TFA and generates a strongly electron-withdrawing
phenazinium segment. Formation of phenazinium ion will trigger
a facile intramolecular charge transfer between the N, N-dimethyl
amino donor group and the phenazinium acceptor segment
(Scheme 2). Addition of an excess TFA (1000 equiv) causes
diprotonation leading to the formation of dictation “D”. The
formation of dictation “D” should completely remove the donor-
acceptor interactions in the molecule and the extinction of charge
transfer transition. Second protonation leading to the species “C”
or “D” for the dyes (5a-d) is unlikely as the remaining nitrogen’s
will become less basic after the monoprotonation due to the
severe push-pull interaction (Scheme 2). The red-shifted
absorption peak realized for the dyes in the presence of TEA is
attributed to the negatively charged species. It is possible that the
deprotonation of phenolic hydrogen occurs in the presence of
TEA and generates a strongly electron-accepting phenazine core.
Formation of phenazine anion will trigger a facile intramolecular
charge transfer between the phenolic donor group and the
phenazine acceptor segment (Scheme 3). The deprotonation of
enolic hydrogen leading to the species “E” for the dyes 5a-d is
the remaining nitrogen atoms will become more basic due to the
severe push-pull interaction (Scheme 3).
Figure 2. Normalized emission spectra of the dyes (5a-d)
recorded in THF.
We demonstrated the ability of the dyes 5a-d to function as
colorimetric and pH sensors due to basic character of nitrogen
atoms of the phenazine ring and acidic character of the enolic
proton. For this reason, we decided to study the effect of
protonation and/or deprotonation on the optical properties of the
synthesised dyes. The absorption spectra of the dyes
bathochromically shifted on addition of trifluoroacetic acid
(TFA) and triethylamine (TEA). The changes in the UV-vis
spectra of 5a upon addition of trifluoroacetic acid (TFA) and
triethylamine (TEA) are illustrated in Figure 3. The spectra show
the progressive attenuation of the charge transfer absorption band
for the neutral compound on increasing the concentration of acid,
whereas a new red-shifted band corresponding to the protonated
species appeared. This bathochromic shift is explained by an
enhancement of the intramolecular charge transfer (ICT) within
the molecule due to the increase in the electron-attracting
character of the phenazine ring by protonation. The same trend
observed, addition of TEA led to a new red-shifted band
appeared (Figure 3). The bathochromic shift is possible that the
deprotonation of phenolic hydrogen occurs in the presence of
TEA and generates a strongly electron-accepting phenazine core.
This color change is fully reversible by neutralisation with acetic
acid. On the basis of the above observations, it is believed that
the dyes exhibit acid-base equilibria as illustrated in scheme 2
and scheme 3. The protonation was completed on the addition of
10 equivalent of TFA (Figure 3). The original color was
regained by the addition of triethylamine which neutralizes the
effect arising due to the addition of TFA. The observation of one
or two isosbestic points suggests the presence of neutral and
protonated forms in equilibrium and the latter being predominant
at higher concentrations of TFA. On the basis of the above
observations, it is believed that the dyes exhibit acid-base
equilibria as illustrated in Scheme 2. Addition of an excess of
TFA (1000 equiv) led to the bleaching of the color for 5a (Figure
3). The absorption pattern of 5c in the presence of excess TFA is
significantly different from that observed for 5c in the absence of
TFA. The appearance of weaker charge transfer transition at the
very high wavelength.
Figure 3. Absorption spectra of the dye 5a measured for THF
solutions with different amounts of TFA and TEA.
Table 2. Halochromic effect of the dyes 5a-d.
c
ꢀλa
(nm) (nm)
ꢀλb
[λabs
]
λabs (nm)
(calc.)
(nm)
Dye
Neutral
(THF)
429
446
436
Acid
Base
(THF+TFA) (THF+TEA)
5a
5b
5c
5d
455
472
437
473
488
523
487
529
+26
+26
+01
+23
+59
+77
+51
+79
538
571
558
552
450
ꢀλa = λabs (THF+TFA) - λabs (THF); ꢀλb = λabs (THF+TEA) - λabs (THF); [λabs]c=
LUMO+1 to HOMO

4
Tetrahedron
ACCEPTED MANUSCRIPT
2.3. Theoretical Calculation
To unravel the structure-electronic property relationship in
these molecules, we have performed DFT calculations as
implemented in Gaussian 09 program package. We optimized the
molecular structure of the dyes in the gas phase as well as in THF
using B3LYP functional and 6-31G (d) basis set without any
symmetry constraints. The optimized geometry was used for the
electronic simulations where at least 10 electronic excitations
were computed for each compound. According to DFT
calculation, the dye 5b was found to exist as ‘E’ isomer (Figure
4). The lowest energy transitions derived from the theoretical
analysis along with their vertical excitations from HOMO to
LUMO+1 are listed in Table 2. According to TD – DFT
calculation, as the protonation on phenazine ring gives red shifted
absorption due to the electronic transition from HOMO to
LUMO+1(Table 2, Figure 6). The electronic distributions in the
HOMO and LUMO+1 for the dye 5b and their protonated and/or
deprotonated forms (A, B, C, D, E) are shown in the Figure 5.
The HOMO of this compound is delocalized over the N, N –
dimethylamine moiety, with maximum components arising from
the nitrogen lone pair and/or from the π framework of the phenyl
groups and is extended along the bridge to the central region of
the molecule. In the LUMO orbital, which also has π – character,
there is no significant contribution from the amine segment and
the
electron
density
has
shifted
toward
the
dihydrobenzo[a]phenazine moiety. In order to identify the effect
of protonation on the optical properties, we have optimized the
geometry of the protonated forms of the dye 5b also. Except for
slight structural variations no significant alternations in the
geometry were observed due to protonation. The HOMO of the
dye 5b protonated forms A and B on protonation has shown a
change in the electron distribution away from the
dihydrobenzo[a]phenazine segment, while in the LUMO of the
dye 5b protonated forms A and B the movement of electron
density toward the dihydrobenzo[a]phenazine segment is noticed.
However, no noteworthy changes in the electron distribution are
observed for the HOMO and LUMO of the form C and D. All
these observations suggest that protonation on the
dihydrobenzo[a]phenazine segment enhances the electron-
accepting ability and drifts the electron – density toward it and
the effect is highly dependent on the donor strength of the N, N –
dimethylamine. Higher wavelength vertical transitions were
predicted for the protonated dyes, which is in agreement with the
observed values. This indicates that the HUMO – LUMO
transitions may be treated as π – π* transitions with prominent
charge transfer contribution.
Scheme 2. Protonation equilibria of the dye 5b in the presence of
TFA.
Figure 4. Optimized geometry of dye 5b.
Scheme 3. Deprotonation Equilibria of the Dye 5b in the
Presence of TEA.

5
LAUMCOCEPTED MANUSCRIPT
Comp
5b
HOMO
5b
Form
A
Figure 6. HOMO – LUMO+1 diagram of the dye 5b protonated
form B.
5b
Form
B
3. Conclusion
In conclusion, we have efficiently synthesised naphthoquinone
fused dihydrobenzo[a]phenazine styryl dyes starting from 2-
hydroxy, 1, 4-naphthoquinone (Lawsone) (1) by employing
simple addition and condensation reactions with the suitable
aldehydes. The styryl dyes displayed rich optical properties in the
ground and excited states. They do not displaysolvatochromism
and solvatofluorism. But, these dyes exhibit halochromism. The
linear absorption of the dyes 5a-d in the neutral, acidic and basic
medium were investigated and they are all sensitive to the
acidic/basic environment. Although the absorption spectra of the
dyes were not influenced by the nature of the solvents, addition
of TFA led to the preferential protonation of the phenazine
segment. This has resulted in an interesting halochromism. The
protonation with TFA and deprotonation with TEA result in
strong bathochromic shifts of the absorption band. The relative
fluorescence quantum yields of compounds were determined by
using fluorescein in 0.1 M NaOH (φ = 0.79) as a standard. Using
DFT computations the red-shifted absorption peak observed for
the dyes were identified to be originating from a π-π* transition
with minor contribution from the charge transfer between the
donor and acceptor fragments. The qualitative trends observed in
the optical properties were supported by the theoretical
computations pointing that the electronic structure in small
molecules with weak donor-acceptor interactions can be
modelled with accuracy using DFT computations. Photophysical
properties of the compounds were supported by DFT and it was
observed that computational results are good agreement with the
5b
Form
C
5b
Form
D
5b
Form
E
1
DFT computations. The compounds were confirmed by IR, H
NMR, 13C NMR and mass spectral analysis. The research work
described herein report naphthoquinone fused dihydrophenazine
styryl derivatives. We hope that the naphthoquinone fused
dihydrobenzo[a]phenazine styryl based fluorescent acid/base
sensors will be developed and applied in sensor industry in the
future.
Figure 5. Electronic distributions observed for the frontier
molecular orbitals of the dye 5b and their protonated forms.
4. Experimental Section
4.1. Physical measurements and Instrumentation
All analytical grade chemicals and reagents were procured
from Sigma Aldrich (India) and were used without further
purification. The reaction was monitored by TLC using 0.25 mm
E – Merck silica gel 60 F254 precoated plates, which were
visualized with UV light.Purifications of all the compounds were

6
Tetrahedron
achieved by recrystallization. Melting points were measured on
The synthesis of 3-benzylidenenaphthalene-1, 2, 4 (3H)-trione
ACCEPTED MANUSCRIPT
standard melting point apparatus from Sunder industrial product
Mumbai, and were uncorrected. The FTIR spectra were recorded
on a JASCO 4100 Fourier Transform IR instrument (ATR
accessories). The nuclear magnetic resonance spectra were
recorded on a Varian 500 MHz instrument using CDCl3 and
DMSO-D6 as a solvent and TMS as an internal standard. The
chemical shift values are expressed in δ ppm. ESI – MS analysis
was performed on Varian mass spectrometer. Hareus rapid
analyser was used for elemental analysis. The UV – Vis spectra
precursor (3a-c)has been described in our previous published
paper. 34
4.3.1. Synthesis
dimethoxybenzylidene)naphthalene-1,2,4(3H)-trione
(3d)
of
3-(2,
4-
A mixture of 2 – hydroxy – 1, 4 – naphthoquinone 1 (10 mmol),
2, 4 – dimethoxybenzaldehyde 2d(10 mmol), and piperidine (2-3
drops) in ethanol was refluxed for 3 h.Progress of the reaction
was monitored by TLC.The reaction mass was then poured into
crushed ice. The precipitate solid obtain was filtered, washed
with water and dried. Further purification was effected by
recrystallization in methanol. Yield = (251 mg, 78%); M.p. =
were performed with
a
Perkin
–
Elmer Lamda-25
spectrophotometer at room temperature. All solutions for energy
transfer studies were prepared at the concentration of 1.0×10−6M
in THF and photophysical measurements were carried out.For the
determination of emission quantum yields φ in THF, fluorescein
in 0.1 M NaOH (φ = 0.79) was used as the reference standard.22,
23The relative quantum yields of the synthesized compounds in
THF solvents were calculated by using the equation (1).
o
1
248-250 C; Rf (30% Hexane/EtOAc) 0.32; H – NMR (CDCl3,
500 MHz) = δ 3.83 (s, 6H, OCH3), 7.68-8.16 (m, 7H, aromatic),
9.75 (s, 1H, vinylic C=C-H); 13C-NMR (DMSO-D6, 125 MHz)
=δ183.5, 180.1, 179.6, 165.7, 160.4, 151.2, 135.4, 134.9, 130.7,
128.5, 126.3, 114.1, 104.4;FT-IR (KBr, cm-1) = 3056 (Ar-H),
1660 (C=O), 1590 (C=C), 1358 (C-O-C); Mass = m/z 322.99.
φx = Φst × (GradX / Gradst) × (η2X / η2 )
(1)
st
Where,
4.3.2. General procedure for Synthesis of (E)-6-
benzylidene-6,
derivatives (5a-d).
12-dihydrobenzo[a]phenazin-5-ol
φx = Quantum yield of compound
Φst = Quantum yield of standard sample
Gradx = Gradient of compound
Gradst = Gradient of standard sample
A solution of (E)-3-benzylidenenaphthalene-1, 2, 4(3H)-trione
(3a-d) (10.0 mmol), o– phenylenediamine 4 (10.0 mmol),
mixture of EtOH/AcOH(50:50) and pinch of Zn powder were
heated at 80 oC. Progress of the reaction was monitored by TLC.
On completion of the reaction, solvent (EtOH/AcOH) was
removed by evaporation under reduced pressure in a rotary
evaporator.The residue was poured into beaker containing
crushed ice (80 mL) and agitated for 10 min. The precipitate
obtainedwas filtered, washed thoroughly with water and dried.
Further purification was effected by recrystallization in aq. DMF.
ꢀ
ꢀ
x = Refractive index of solvent used for synthesized compound
st = Refractive index of solvent used for standard sample
4.2. Computation Methods
The molecular geometries have been optimized using the
Gaussian 09 suite of programs. 24The ground state (S0) geometry
of the dyes were optimized in the gas phase as well as in THF
medium using DFT.25The functional used was B3LYP. The
B3LYP method combines Becke’s three parameter exchange
functional (B3) 26 with the nonlocal correlation functional by Lee,
4.3.2.1. (E)-6-Benzylidene-6,
dihydrobenzo[a]phenazin-5-ol
12-
derivatives
(5a).
Yield = (275 mg, 82%); M.p.= 270-272o C;Rf (30%
Hexane/EtOAc) 0.69;1 H-NMR (DMSO-D6 , 500
MHz) = δ 16.37 (s, 1H, OH), 6.83-8.40 (m, 13H,
aromatic), 6.15 (s, 1H, vinylic C=C-H), 3.80 (s, 1H,
NH); 1 3 C-NMR (DMSO-D6 , 125 MHz) =δ160.1,
134.9, 134.8, 133.6, 132.3, 131.0, 130.9, 126.3,
27
Yang and Parr (LYP). The basis set used for all atoms was 6-
31G (d). The vibrational frequencies at the optimized structures
were computed using the same method to verify that the
optimized structures correspond to local minima on the energy
surface. The vertical excitation energies and oscillator strengths
were obtained for the lowest ten singlet-singlet transitions at the
optimized ground state equilibrium geometries by using the Time
Dependent Density Functional Theory (TD – DFT) with the same
hybrid functional and basis set.28-30 Frequency calculations are
carried out to ensure that each optimized conformation has all
positive frequencies and thus is a minimum on the potential
energy surface. The low-lying first singlet excited states (S1) of
the dyes were relaxed using the TD – DFT to obtain their
minimum energy geometries. We have done TD – DFT of the
optimized first singlet excited state geometries for calculating the
emission. 31 Frequency computations were also carried out on the
excited state geometry of the dyes. All the computations were
carried out initially in gas phase and in acetonitrile solvent using
125.9, 125.8, 111.4;FT-IR (KBr, cm- 1 ) =
3329
(OH), 3250 (NH), 3048 (Ar-H), 1665 (C=N), 1600
(C=C); Mass m/z 336.13.Anal. Calcd for
=
C2 3 H1 6 N2 O (%): Calcd C, 82.12; H, 4.79; N, 8.33;
O, 4.76. Found C, 82.61; H, 4.48; N, 8.35; O, 4.56.
4.3.2.2. (E)-6-(4-(dimethylamino)benzylidene)-6,12-
dihydrobenzo[a]phenazin-5-ol (5b).
Yield = (280 mg,74%); M.p.= 254-256 o C;Rf (30%
Hexane/EtOAc) 0.62;1 H-NMR (DMSO-D6 , 500
MHz) = δ 16.34 (s, 1H, OH), 6.83-8.06 (m, 12H,
aromatic), 6.15 (s, 1H, vinylic C=C-H), 3.84 (s, 1H,
NH), 3.02 (s, 6H, NCH3 ); 1 3 C-NMR (DMSO-D6 ,
125 MHz) =δ156.7, 141.3, 135.1, 133.5, 132.6,
130.3, 128.5, 128.0, 126.4, 125.9, 125.8, 123.5,
48.6; FT-IR (KBr, cm- 1 ) = 3345 (OH), 3252 (NH),
3048 (Ar-H), 1664 (C=N), 1600 (C=C); Mass = m/z
379.33. Anal. Calcd for C2 5 H2 1 N3 O (%): Calcd C,
79.13; H, 5.58; N, 11.07; O, 4.22.Found C, 79.10;
H, 5.48; N, 11.22; O, 4.20.
the Self – Consistent Reaction Field (SCRF) under the
Polarizable Continuum Model (PCM).32,
The electronic
33
absorption spectra, including absorption wavelengths, oscillators
strengths, and main configuration assignment, were
systematically investigated using TD – DFT with PCM model on
the basis of the optimized ground structures.
4.3.2.3. (E)-6-(4-nitrobenzylidene)-6,
12-
dihydrobenzo[a]phenazin-5-ol (5c).
4.3. Synthesis and Characterisation

7
Yield = (289 mg,76% ; M.p.= 260-262 o C; Rf (30%
Yield = (340 mg, 86%); M.p.= 279-281 oC; Rf (30%
ACCEPTED MANUSCRIPT
Hexane/EtOAc) 0.52; 1 H-NMR (CDCl3 , 500 MHz)
11.84 (s, 1H, OH), 6.87-8.02 (m, 12H,
Hexane/EtOAc) 0.59; 1H-NMR (DMSO-D6, 500 MHz) = δ
16.34 (s, 1H, OH), 7.63-8.65 (m, 12H, aromatic), 6.75(s, 1H,
vinylic C=C-H), 4.25 (s, 1H, NH), 3.6 (s, 6H, OCH3); 13C-NMR
(DMSO-D6, 125 MHz) = δ164.8, 146.3, 135.9, 135.4, 134.1,
131.7, 131.2, 128.4, 127.5, 127.2, 126.7, 55.7; FT-IR (KBr, cm-
1) = 3056 (Ar-H), 1660 (C=O), 1590 (C=C), 1247 (C-O-C);
Mass = m/z 395.60. Anal. Calcd for C25H20N2O3 (%): Calcd C,
75.74; H, 5.08; N, 7.07; O, 12.11. Found C, 75.64; H, 5.13; N,
7.11; O, 12.12.
=
δ
aromatic), 6.16 (s, 1H, vinylic C=C-H), 3.42 (s, 1H,
NH); 1 3 C-NMR (DMSO-D6 , 125 MHz) =δ143.6,
139.2, 135.2, 133.6, 132.4, 130.7, 128.3, 126.9,
126.5, 124.8, 124.4, 114.7; FT-IR (KBr, cm- 1 ) =
3378 (OH), 1537, 1420 (N=O), 1665 (C=O), 1600
(C=C);Mass
=
m/z
381.47.Anal. Calcd for
C2 3 H1 5 N3 O3 (%): Calcd C, 72.43; H, 3.96; N, 11.02;
O, 12.59. Found: C, 72.22; H, 3.85; N, 11.51; O,
12.42.
Acknowledgements
Senior Research Fellowship (NET-SRF) of India funded by the
Council of Scientific and Industrial Research (CSIR) and
University Grant Commission (UGC), New Delhi, INDIA to
Sharad Patil is acknowledged.
4.3.2.4. (E)-6-(2,4-dimethoxybenzylidene)-6,12-
dihydrobenzo[a]phenazin-5-ol (5d).
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