Novel fluorescent phenazines: Synthesis, characterization, photophysical properties and DFT calculations

Article abstract of DOI:10.1007/s10895-015-1631-0

The organic compounds with donor-π-bridge-acceptor type of architecture are of great interest for application as semiconductors. The synthesized compounds are obtained from 4-morpholino naphthalene-1,2-dione and 4-(4-(diethylamino) phenyl)naphthalene-1,2-dione and mono substituted ortho-phenylene diamines by condensation reaction. The donor groups are morpholinyl and N,N-diethylamino phenyl moieties, whereas acceptors are substituted phenazines. The synthesized molecules were characterized by spectral analysis. The effect of the substitution has been studied on the basis of photophysical properties of the molecules. The halochromism behaviour of the molecule shows that at low to moderate acidity they respond differently with two types of donors. DFT computations were used in conjunction with NMR analysis to determine the ratio of the positional isomers.

Full text of DOI:10.1007/s10895-015-1631-0

J Fluoresc
DOI 10.1007/s10895-015-1631-0
ORIGINAL ARTICLE
Novel Fluorescent Phenazines : Synthesis, Characterization,
Photophysical Properties and DFT Calculations
1
1
Abhinav B. Tathe & Nagaiyan Sekar
Received: 22 May 2015 /Accepted: 26 July 2015
Springer Science+Business Media New York 2015
#
Abstract The organic compounds with donor-π-bridge-
acceptor type of architecture are of great interest for ap-
plication as semiconductors. The synthesized compounds
are obtained from 4-morpholino naphthalene-1,2-dione
and 4-(4-(diethylamino) phenyl)naphthalene-1,2-dione
and mono substituted ortho-phenylene diamines by con-
densation reaction. The donor groups are morpholinyl
and N,N-diethylamino phenyl moieties, whereas accep-
tors are substituted phenazines. The synthesized mole-
cules were characterized by spectral analysis.. The effect
of the substitution has been studied on the basis of
photophysical properties of the molecules. The
halochromism behaviour of the molecule shows that at
low to moderate acidity they respond differently with
two types of donors. DFT computations were used in
conjunction with NMR analysis to determine the ratio
of the positional isomers.
Introduction
The organic molecules with donor-π-bridge-acceptor type of
architecture are of great interest for the application as semicon-
ductors in TFT (Thin Film Transistors) [1], as sensitizers or light
harvesting materials in DSSC (Dye-sensitized Solar Cells) [2]
and as sensors in many applications[3–6]. The ability of these
molecules to produce red emission has sought application in the
field of OLEDs (Organic Light Emitting Diodes) [7, 8]. The red
emission complements green [9, 10] and blue [11, 12] emission
in OLEDs to create white light and covers visible spectrum for
OLEDs. The placement of donor and acceptor groups affects the
photophysical properties of the compounds. The π-bridge facil-
itates the interaction of donor and acceptors. Designing the mol-
ecule with proper placement of donor and acceptor separated by
a π-bridge can modulate the properties to a great extent. The
typical donors employed are triarylamines [13], carbazole [14],
phenothiazine [15] and aliphatic amines [16], which are consid-
ered to be strong donors. The popular acceptor fragments are
cyanoacrylic acid [17], dicyanovinyl [18], oxadiazole [19],
benzothiadiazole [20], phenazine/quinoxaline and their analogs
.
.
.
.
Keywords Phenazines DFT TD-DFT Verticalexcitation
NMR
[21–23]. The substitution on the acceptor fragment also alters the
signalling of the molecule [24].
In present paper, the intermediates 4-morpholinonaphthalene-
1,2-dione (2) and 4-(4-(diethylamino)phenyl)naphthalene-1,2-
dione (3) have been synthesized from β-naphthol deriva-
tives. These intermediates were reacted with ortho ami-
no aromatics to obtain desired phenazines. The donor
groups are morpholinyl and N,N-diethylamino phenyl
moieties, whereas acceptors are substituted phenazine/
quinoxaline derivatives. The effect of substitution on
photophysical properties were studied in solvents of dif-
ferent polarities. The experimental photophysical proper-
ties were compared with theoretical photophysical prop-
erties computed by DFT.
Electronic supplementary material The online version of this article
(doi:10.1007/s10895-015-1631-0) contains supplementary material,
which is available to authorized users.
*
Nagaiyan Sekar
n.sekar@ictmumbai.edu.in
1
Tinctorial Chemistry Group, Department of Dyestuff Technology,
Institute of Chemical Technology, N. P. Marg, Matunga (East),
Mumbai, MH, India 400019

J Fluoresc
Materials and Methods
Density Functional Theory (DFT) [26] has been used
for ground state optimisations and Time Dependent-
Density Functional Theory (TD-DFT) has been used for
calculations of vertical excitations. Twenty lowest excita-
tions were estimated. The functional used is B3LYP [27,
28], which is a hybrid functionals. The solvents consid-
ered were DCM, toluene DMF, acetonitrile, methanol, n-
hexane and n-heptane. Solvation model used here is PCM
(Polarizable Continuum Model) [29]. The Pople’s basis set
6-311+G(d), was used for all atoms with added polariza-
tion function [30, 31]. Optimized structures were local
minima on potential energy surface and were confirmed
by vibrational analysis and show no imaginary frequen-
cies. NMR calculated in chloroform for the protons was
normalized with the calculated values of TMS
(Tetramethyl silane) protons at the same level. All compu-
tations were performed with Gaussian 09 W package [32].
All the reagents were purchased from Sigma Aldrich
and S.D. Fine Ltd., Mumbai (India) and used without
further purification. Solvents used were of spectroscopic
grade purchased from Rankem Ltd. Mumbai. Mass anal-
yses were carried out with electron spray ionisation
(
(
ESI) on 410 Prostar mass spectrometer of Varian Inc.
USA). H-NMR analyses were done using CDCl3 as
1
solvent on 500 MHz Varian Inc. The chemical shifts
are expressed in δppm. Absorption spectrum was mea-
sured in standard 3.5 mL quartz cuvette with 1 cm path
length using Perkin Elmer Lambda 25 spectrophotome-
ter. Fluorescence was measured using Cary Eclipse
spectrofluorometer from Varian Inc. (USA). Relative
quantum yields were measured using rhodamine-6G in
ethanol as standard [25].
Fig. 1 Synthesis of phenazines

J Fluoresc
a
3
3
2
2
1
1
50
00
50
00
50
00
DCM
DCM
1
1
1
4000
2000
0000
Toluene
DMF
Toluene
DMF
CH3CN
MeOH
n-Hex
n-Hept
CH3CN
MeOH
n-Hex
n-Hept
8
000
000
000
000
0
6
4
2
5
0
0
3
20
370
420
470
520
400
500
600
700
Wavelength (nm)
Wavelength (nm)
b
3
3
2
2
1
1
5000
0000
5000
0000
5000
0000
DCM
DCM
Toluene
DMF
Toluene
DMF
180
1
1
1
1
60
40
20
00
CH3CN
MeOH
n-Hex
n-Hept
CH3CN
MeOH
n-Hex
n-Hept
80
60
4
2
0
0
5
000
0
0
3
20
420
520
400
500
600
700
Wavelength (nm)
Wavelength (nm)
c
DCM
Toluene
DMF
CH3CN
MeOH
n-Hex
n-Hept
DCM
Toluene
DMF
CH3CN
MeOH
n-Hex
n-Hept
3
2
2
1
1
0000
5000
0000
5000
0000
400
3
50
300
50
200
2
1
1
50
00
5
000
0
5
0
0
3
20
420
520
400
500
600
700
Wavelength (nm)
Wavelength (nm)
d
3
3
50
00
DCM
Toluene
DMF
CH3CN
MeOH
n-Hex
n-Hept
DCM
Toluene
DMF
CH3CN
MeOH
n-Hex
n-Hept
2
2
1
1
5000
0000
5000
0000
250
2
1
1
00
50
00
5
000
50
0
0
3
20
420
Wavelength (nm)
Fig. 2 UV-visible absorption and fluorescence spectra of 2a-2d in various solvents
520
620
400
500
600
700
Wavelength (nm)

J Fluoresc
Results and Discussion
core has been altered by the electron donating (−Me) as
well as electron withdrawing group (−NO ). The ab-
sorption of these molecules have been changed by
2
Synthesis and Characterization
around 80 nm with a change in the donor group and
Commercially available 1,2,4-acid was used for the synthesis
of diketones. The 1,2,4-acid was converted to 1,2-diketo
naphthalene 4-sulphonic acid potassium salt 1 as per reported
method Fig. 1 [33].
the introduction of –NO group.
2
The emission characteristics of the molecules 2a-2d and
3a-3d are given in Table 1. The Stoke’s shifts exhibited by
2a-2d are constantly higher than the compound 3a-3d. The
Compound 1,2-diketo naphthalene 4-sulphonic acid
potassium salt 1 was reacted with morpholine at 0 °C
and with water as solvent to obtain brick red coloured
compound 2 [34], which was used without further puri-
fication. The (N,N-diethylamino)phenyl derivative 3 was
synthesized as per reported procedure [35]. The
diketones 2 and 3 were condensed with substituted
ortho phenylene diamines in ethanol at reflux tempera-
ture to obtain phenazines 2a-2d and 3a-3d. The mole-
cules possessed different groups on the other side of
phenazine core (considered to be an acceptor) and al-
tered the electron withdrawing ability of the phenazine
core. The synthesized molecules showed a bright yellow
to brownish color.
compound with –NO substitution (2b) showed lowest Stokes
2
−1
shift of 3445 cm in acetonitrile as against the highest of
−1
5671 cm in dichloromethane. Stokes shift in studied sol-
vents were summarised in Table 1. The compound 2c with –
Me substitution showed Stoke’s shifts from 4652 to
−1
6358 cm in studied solvents. In non-polar solvents the com-
pound with electron donating group 2c and non-substituted
compound 2a showed a lower Stoke’s shift. A reverse trend
was observed for the compound with electron withdrawing
group 2b. It shows that the electron withdrawing group has
enhanced the charge transfer and the polar solvent has stabi-
lized the excited state. The electron donating group supplies
electron to the acceptor (phenazine), so the molecule is less
polarised and hence less affected by the polar solvents. The
non-substituted compound 2a showed the highest Stokes
−1
−1
Photophysical Study
shifts ranging from 4705 cm in toluene to 6471 cm in
acetonitrile among all the synthesized molecules. The com-
pounds 2a-2d and 3a-3d show higher quantum yields in non-
polar solvents. The quantum yields are low in polar solvents.
The interaction of the polar solvents with the solute has
lowered the quantum yields [36]. The compound with –NO2
substitution shows lower quantum yields as the nitro group is
known to quench the fluorescence [37–39].
Absorption and emission spectra were obtained in solvents of
different polarities. The absorption and emission spectra are
shown in Figs. 2 and 3. The absorption wavelength is inde-
pendent on solvent polarity but significant effect was observed
on molar extinction coefficient Table 1. Compounds showed
higher molar extinction coefficients in non-polar solvents as
compared to polar solvents. This may be attributed to the
interaction of solvent dipoles with the molecules thus nega-
tively affecting the charge transfer efficiency. Higher absorp-
tion intensities were observed in the solvent dichloromethane.
The donor group variation between two series i.e. 2a-2d and
The solvatochromic behaviour of the molecules 2a-2d and
3a-3d was studied with the help of Lippert [40], Weller [41]
and Rettig’s [41] plots. Lippert’s plot is the plot of Stokes shift
−1
in cm v/s orientation polarizability and is given in Eq. 1.
Lippert function is constituted of polarity function f (ε) and
polarizability function f (η)
3
a-3d has been clearly reflected in their absorption behaviour.
The series 3a-d compounds showed a red shift of 22 to 61 nm
with respect to the corresponding 2a-d compounds. The
length of π-conjugation plays an important role for
bathochromic shift for 3a-3d as compared to 2a-2d.
ꢀ
ꢁ
2
2
μe−μg
hca3
0
ϑss ¼
f 1 þ ϑss
ð1Þ
In both the type of compounds nitro substitution on
the acceptor phenazine showed a red shifted absorption
as compared to the –Me, −Cl, and the unsubstituted
molecules. Compound 2c was not significantly red
shifted as compared to the red shift exhibited by com-
pound 3c. Compound 3c showed red shifted absorption
by 8 to 12 nm. In case of molecule 3d the –Cl substi-
tution showed a blue shifted absorption of 2 to 5 nm in
all the solvents, whereas molecule 2d showed a red
shifted absorption of 6 to 9 nm. The effect of –Cl sub-
stitution is not expressed in the absorption characteris-
tics of the molecules. The acceptor ability of phenazine
Where,
Planks constant
ℎ
c
ϑ
ϑ
velocity of light in vacuum
Stokes shift in solvent
Stokes shift in vacuum
ss
0
ss
f1
polarity function and is described in Eq. 2 below
2
ε−1
n −1
f 1ðε; nÞ ¼
2ε þ 1 − 2n þ 1
ð2Þ
2

J Fluoresc
a
3
3
2
50
00
50
DCM
Toluene
DMF
CH3CN
MeOH
n-Hex
n-Hept
DCM
Toluene
DMF
CH3CN
MeOH
n-Hex
n-Hept
2
2
1
1
5000
0000
5000
0000
200
1
1
50
00
5
000
0
5
0
0
3
20
420
520
700 620
400
500
600
700
Wavelength (nm)
Wavelength(nm)
b
DCM
Toluene
DMF
CH3CN
MeOH
n-Hex
n-Hept
DCM
Toluene
DMF
CH3CN
MeOH
n-Hex
n-Hept
3
0
2
2
1
1
5000
25
0000
5000
0000
20
1
5
0
5
0
1
5
000
0
3
20
420
520
400
500
600
700
Wavelength(nm)
Wavelength (nm)
c 2
0000
8000
6000
4000
2000
0000
3
3
2
50
00
50
DCM
Toluene
DMF
CH3CN
MeOH
n-Hex
n-Hept
DCM
Toluene
DMF
CH3CN
MeOH
n-Hex
1
1
1
1
1
200
50
100
n-Hept
1
8
000
000
000
000
0
6
4
2
5
0
0
3
30
430
530
630
400
500
600
700
Wavelength (nm)
Wavelength (nm)
1
1
80
60
d
DCM
Toluene
DMF
CH3CN
MeOH
n-Hex
n-Hept
DCM
Toluene
DMF
CH3CN
MeOH
n-Hex
1
1
1
4000
2000
0000
140
1
1
20
00
n-Hept
8
000
000
000
000
0
8
0
0
0
6
4
2
6
4
20
0
3
30
430
Wavelength (nm)
Fig. 3 UV-visible absorption and fluorescence spectra of 3a-3d in various solvents
530
630
400
500
600
700
Wavelength (nm)

J Fluoresc
The Wellers equation which considers only shift in emis-
sion is given as follows,
−H > −NO
~100 nm.
2
. The red shifts induced were in the order of
On the other hand the protonation of 4-(N,N-
diethylamino)-phenyl substituted series of compounds 3a-3d
show different trend. The N,N-diethylamino group gets pro-
tonated first and induces a blue shift in the absorption spec-
trum by interrupting the electron donation by the group.
Similar trend continues till the complete protonation of
diethylamino group takes place, but at higher concentration
of acid the phenazine nitrogen also gets protonated and gives a
red shift in absorption. In this case the order of induced red
shift is ~30–40 nm. This is due to the fact that in the case of
morpholino substituted compounds there is no protonation of
donor nitrogen, hence a better conjugation is achieved.
2
2
ðμ Þ
e
ϑf ¼
f 2 þ constant
ð3Þ
ð4Þ
3
hca
2
ε−1
n −1
f 2ðε; nÞ ¼ 2
−
;
2
ε þ 1 4n þ 2
Neglecting the ground state dipole moment with respect to
that of the excited state and approximating the solute polariz-
.
3
ability to a
the following formula is obtained as in Eq. 5,
2
2
2
ðμ Þ
f 3 þ constant
3
e
ϑ ¼
f
ð5Þ
hca
Where solvent polarity function f (Rettig equation )is giv-
DFT Computations
3
en as follows,
DFT computations were performed in solution phase to un-
derstand the photophysical behaviour of the molecules
Tables 3 and 4. A red shift is always observed when the sub-
stitution changes from morpholine 2a-2d to N,N-
diethylaminophenyl 3a-3d and is also observed in theoretical
calculations of the vertical excitations. The deviation in the
experimental and computational data was found to be 1.0 %
for 2c in toluene whereas highest deviation was observed in
2
ε−1
n −1
f 3ðε; nÞ ¼
−
ð6Þ
2
ε þ 2 2n þ 4
Lippert plots for compound 2a, 2b and 2d are linear and
showed a regression factor ≥0.800 indicating the charge trans-
fer by local excitation (LE) occurring in these molecules. This
indicates there is a good linearity and the molecules show
solvtochromism in emission as the absorption is less sensitive
to solvent polarity. But in the case of compound 2b, where –
2b in acetonitrile(%?). The deviation in series 3a-3d remain
mostly on negative side; however compound 3b shows a pos-
itive deviation. For series 3a-3d the vertical excitation energy
is overestimated. It was observed that for the compounds 2b
and 3b the computed values are higher than the other deriva-
tives in the same series. There waslittle change in the vertical
excitation energies calculated with respect to the solvent po-
larity. Similarly the absorption values measured experimental-
ly were too less sensitive to the solvent polarity.
NO is present as a strong donor and makes molecule less
sensitive to the solvent environment, the regression factor is
2
≤0.400. It is thus indicative that charge transfer by LE in not
important in this molecule. In similar way when morpholine
donor is replaced by a stronger donor N, N-
diethylaminophenyl the molecules are not responsive to sol-
vent polarity and the regression factors are very low for 3a-3d
series (Table 2).
NMR : Theoretical and Experimental
Halochromism
The comparison of calculated and experimental NMR pro-
vides an easy tool to distinguish between the closely related
molecules, which could be a cumbersome task if performed
otherwise. The reactions involved in the synthesis of phena-
zines 2b-2d and 3b-3d involve use of substituted asymmetric
The effect of acidity on photophysical properties of the com-
pounds 2a-2d (Fig. 4) and 3a-3d (Fig. 5) were studied by
addition of trifluoroacetic acid. The halochromism data of
the dye 2a is reported to show a red shift in the absorption
maxima due to the protonation of nitrogen atom of the phen-
azine core [42–44]. The protonation of the aromatic nitrogen
of phenazine enhances the charge transfer from the donor
o-phenylene diamines (substitution include –NO , −Cl,
2
−CH ). The reaction products obtained are expected to have
3
two positional isomers depending upon the position of sub-
stitution. The possible structures are shown in Fig. 1. The
assignment of the proton NMR signals to the specific struc-
ture is difficult with such complicated and closely related
structures. DFT has been used since a period to calculate
NMR prediction of organic molecules [45–48]. The normal-
ized calculated values give an insight into the observed NMR
spectrum and based on this the assignment of major isomer
has been done (Table 5).
(
morpholine) to acceptor (protonated Phenazine), and hence
imparts a red shift in absorption. A similar trend was observed
in all substituted phenazines 2a-2d, irrespective of their sub-
stitution. The electron releasing –CH group in 2c enhances
3
the protonation more than the acceptor –NO group in 2b,
2
while non-substituted compound 2a remained intermediate.
The compound 2b needed very high concentration of acid to
induced red shift. The order of protonation was –CH > −Cl >
3

J Fluoresc
The major isomers predicted are 2b’, 3b’, 2c, 3c, 2d and
d. The –Me substitution on compounds 2c-2c’ and 3c-3c’
does not have much effect on selectivity of the product for-
ammonium and potassium salts [33]. Compound 1 was then
reacted with morpholine and N,N-diethyl aniline in different
conditions to give compound 2 and 3 respectively.
3
mation. The –NO group drives the product formation at ex-
2
actly reverse than the –CH , and –Cl substitution. The map of
the protons used for the comparison is given in Fig. 6.
3
Synthesis of Phenazines
General Procedure The diketo compound (2 or 3) (1 mmol)
was suspended in absolute ethanol (10 mL). The substituted
diamines (1 mmol) were added in one portion and the mixture
was heated to reflux for 2 h. The color changed to yellow
(from brick red for compound 2 and bfor compound 3). The
reaction was monitored by TLC. After completion of reaction
Experimental
The synthesis of compound 1 was achieved by oxidation of 4-
amino-3-hydroxynaphthalene-1-sulfonic acid (1,2,4 acid) to
1
,2-diquinone sulphonic acid and further converting it to
Table 1 Photophysical properties in various solvents for compounds 2a-2d and 3a-3d
Solvent
2a
3a
2b
3b
2c
3c
2d
3d
Acetonitrile
λabs
ε L mol− cm−1
418
451
441
502
420
463
427
449
1
11400
569
8360
515
11400
598
6248
567
16960
562
9600
499
12800
578
4460
508
λem
Φ
0.4235
6349
422
0.0065
2755
454
0.0099
5953
446
0.0038
2284
503
0.4980
6016
420
0.0065
1558
462
0.4001
6118
427
0.0089
2587
447
−1
Stokes shift (cm )
Dichloromethane
N,N-dimethyl formamide
Methanol
λabs
ε L mol− cm−1
1
8996
544
8400
641
13360
593
8360
557
12480
538
8800
535
8052
553
5183
632
λem
Φ
0.8985
5314
422
0.0799
6426
451
0.1497
5558
449
0.0292
1927
507
0.7569
5222
419
0.0125
2953
462
0.9326
5336
428
0.0939
6549
447
−
1
Stokes shift (cm )
λabs
ε L mol− cm−1
1
10080
569
7440
493
14000
572
5228
590
12800
569
6572
–
12000
591
3959
–
λem
Φ
0.4443
6122
418
0.0119
1889
452
0.0223
4789
446
0.0072
2775
507
0.6805
6292
420
–
0.2826
6444
429
–
−1
Stokes shift (cm )
–
–
λabs
ε L mol− cm−1
464
450
1
11880
596
9280
504
12400
561
7384
578
17360
584
8160
505
16800
597
11676
503
λem
Φ
0.0660
7145
421
0.0087
2283
452
0.0081
4596
445
0.0030
2423
502
0.5012
6686
420
0.0094
1750
462
0.0352
6560
427
0.0034
2342
447
−1
Stokes shift (cm )
Toluene
λabs
ε L mol− cm−1
1
8720
523
12480
548
11960
576
8012
640
15600
522
7208
568
12000
545
11352
546
λem
Φ
0.6612
4633
407
0.7464
3876
430
0.2248
5111
437
0.0788
4295
479
0.5826
4652
414
0.6305
4039
439
0.7660
5071
421
0.4020
4056
430
−1
Stokes shift (cm )
n-hexane
λabs
ε L mol− cm−1
1
8320
513
12160
491
8432
534
7443
563
13520
483
7920
496
11200
494
4920
478
λem
Φ
0.3576
5077
407
0.4342
2889
432
0.4697
4157
436
0.1119
3115
471
0.2337
3451
413
0.6773
2618
441
0.3250
3510
421
0.4958
2335
427
−1
Stokes shift (cm )
n-heptane
λabs
ε L mol− cm−1
1
11040
486
10640
491
6752
528
9736
541
14948
483
8104
498
12200
497
6264
481
λem
Φ
0.1475
3994
0.4786
2782
0.4672
3996
0.0514
2747
0.1449
3509
0.5117
2595
0.2191
3632
0.4512
2629
−1
Stokes shift (cm )

J Fluoresc
2
Table 2 Regression factor (R )
values for various solvent polarity
Lippert (ε, η)
Polarity (ε)
Polarizability (η)
Weller (ε, η)
Rettig (ε, η)
plots for compound 2a-2d and
2
2
2
2
3
3
3
3
a
b
c
d
a
b
c
d
0.8150
0.3255
0.8950
0.8385
0.0157
0.4668
0.4802
0.0043
0.7509
0.3847
0.9175
0.8851
0.0034
0.3966
0.3553
0.0315
0.3138
0.0200
0.0612
0.0214
0.2530
0.2932
0.9173
0.4753
0.8702
0.4845
0.8952
0.8485
0.0217
0.0003
0.0156
0.1075
0.8900
0.0446
0.8384
0.7197
0.0946
0.2756
0.4211
0.0755
3
a-3d
the separated solid was filtered and washed with cold ethanol
to obtain phenazines.
CHN Analysis : Calculated: C 76.17, H 5.43, N 13.32, O
5.07 Observed: C 76.11, H 5.39, N 13.3, O 5.01.
Compound 2b
Compound 2a
M.P: 160 °C; Yield: 83 %
M.P: 190 °C; Yield: 72 %
1
1
H-NMR (CDCl , 500 MHz , δ ppm): δ 9.47–9.44 (m,
H-NMR (CDCl , 500 MHz , δ ppm): δ 9.42 (d, J=
3
3
1
1
4
H), 8.36–8.32 (m, 1H), 8.24–8.20 (m, 2H), 7.85 (dt, J=3.2,
.6 Hz, 1H), 7.81 (ddd, J=9.4, 5.4, 2.1 Hz, 3H), 7.46 (s, 1H),
.07–4.04 (t, 4H), 3.32 (t, 4H).
8.9 Hz, 1H), 9.07 (d, J=2.2 Hz, 1H), 8.50 (dd, J=9.3,
2.3 Hz, 1H), 8.40 (d, J=9.2 Hz, 1H), 8.23–8.18 (m, 1H),
7.90–7.80 (m, 1H), 7.40 (s, 1H), 4.15 (t, 4H), 3.35 (t, 4H).
13
13
C-NMR (CDCl , 125 MHz , δ ppm): δ 153.3, 144.6,
C-NMR (CDCl , 125 MHz , δ ppm): δ 152.1, 144.2,
3
3
1
1
42.4, 141.4, 141.2, 132.2, 130.4, 130.0, 129.7, 129.5, 128.9,
28.6, 128.0, 126.1, 124.3, 112.8, 67.1, 53.0.
Mass (ESI): 316.2 (M+1)
143.7, 142.7, 141.8, 141.5, 140.6, 139.9, 139.4, 132.8, 132.1,
131.6, 130.3, 129.4, 127.4, 125.6, 123.6, 113.5, 68.3, 54.5.
Mass (ESI): 361.1 (M+1)
Fig. 4 Halochromism shown by
compound 2a-2d in toluene and
TFA
2
a0.120
2b
0.120
0
0
0
0
0
0
.100
.080
.060
.040
.020
.000
Toluene
Toluene
0
.100
1
2
3
0µL 1% TFA in Toluene
0µL 1% TFA in Toluene
0µL 1% TFA in Toluene
10µL 1% TFA in Toluene
20µL 1% TFA in Toluene
30µL 1% TFA in Toluene
Excess TFA in Toluene
0.080
0
0
0
.060
.040
.020
Excess TFA in Toluene
0.000
300
3
00
400
500
600
700
400
500
600
700
Wavelength (nm)
Wavelength (nm)
2
c0
2d0
.120
.100
.080
.060
.040
.020
.000
.120
0.100
0.080
0.060
0.040
0.020
0.000
0
0
0
0
0
0
Toluene
Toluene
1
2
3
0µL 1% TFA in Toluene
0µL 1% TFA in Toluene
0µL 1% TFA in Toluene
10µL 1% TFA in Toluene
20µL 1% TFA in Toluene
30µL 1% TFA in Toluene
Excess TFA in Toluene
Excess TFA in Toluene
3
00
400
500
600
700
300
400
500
600
700
Wavelength (nm)
Wavelength (nm)

J Fluoresc
CHN Analysis : Calculated: C 66.66, H 4.48, N 15.55, O
3.32 Observed: C 66.61, H 4.47, N 15.50, O 13.29.
131.8, 130.8, 130.5, 129.90, 129.7, 128.2, 127.2, 126.0,
124.3, 112.4, 67.0, 53.0
1
Compound 2c
Mass (ESI): 350.2 (M+1)
M.P: 157 °C; Yield: 68 %
CHN Analysis : Calculated: C 68.67, H 4.61, Cl 10.13, N
12.01, O 4.57 Observed: C 68. 62, H 4.57, Cl 10.11, N 12.00
Compound 3a
1
H-NMR (CDCl , 500 MHz , δ ppm): δ 9.42 (ddd, J=
3
6
.9, 5.1, 2.0 Hz, 1H), 8.21 (td, J=6.8, 4.0 Hz, 1H), 8.15–8.05
(
(
m, 1H), 7.95 (s, 1H), 7.78 (ddd, J=6.3, 4.8, 1.9 Hz, 2H), 7.65
ddd, J=14.5, 8.7, 1.7 Hz, 1H), 7.43 (d, J=2.7 Hz, 1H), 4.10–
M.P: 172 °C; Yield: 80 %
1
H-NMR (CDCl , 500 MHz , δ ppm): δ 9.54 (d, J=
3
4
.00 (t, 4H), 3.29 (t, 4H), 2.66 (s, 3H).
8.0 Hz, 1H), 8.38 (dd, J=6.6, 3.2 Hz, 1H), 8.27 (dd, J=6.6,
3.2 Hz, 1H), 8.15 (d, J=7.9 Hz, 1H), 7.92 (s, 1H), 7.87–7.84
(m, 1H), 7.81 (t, J=7.6 Hz, 1H), 7.74 (t, J=7.5 Hz, 1H), 7.53
(d, J=8.5 Hz, 2H), 6.86 (d, J=5.8 Hz, 2H), 3.48 (q, J=7.0 Hz,
4H), 1.44–1.10 (t , J=7.0, 6H).
13
C-NMR (CDCl , 125 MHz , δ ppm): δ 153.0, 152.7,
3
1
1
1
44.5, 143.9, 143.0, 141.5, 141.3, 140.6, 139.9, 139.4, 132.6,
32.2, 132.2, 131.6, 130.4, 129.4, 128.1, 127.9, 127.1, 125.9,
24.2, 124.2, 113.0, 67.1, 53.0, 22.2.
1
3
Mass (ESI): 330.2 (M+1)
C-NMR (CDCl , 125 MHz , δ ppm): δ 145.7, 143.7,
3
CHN Analysis : Calculated: C 76.57, H 5.81, N 12.76, O
.86 Observed: C 76.57, H 5.79, N 12.71, O 4.86.
Compound 2d
143.1, 142.3, 141.7, 133.2, 131.6, 130.9, 129.8, 129.7, 129.4,
129.3, 129.0, 127.5, 127.3, 126.2, 125.7, 111.4, 44.4, 12.7.
Mass (ESI): 378.3 (M+1)
4
M.P:168 °C; Yield: 79 %
CHN Analysis : Calculated: C 82.73, H 6.14, N 11.13
Observed: C 82.70, H 6.09, N 11.11.
1
H-NMR (CDCl , 500 MHz , δ ppm): δ 9.40–9.35 (m,
3
1
9
7
H), 8.29 (d, J=2.1 Hz, 1H), 8.24–8.14 (m, 2H), 8.10 (d, J=
.0 Hz, 1H), 7.82–7.76 (m, 2H), 7.74 (dd, J=9.1, 2.3 Hz, 1H),
.38 (d, J=3.9 Hz, 1H), 4.04 (t, 4H), 3.30 (t, 4H).
Compound 3b
M.P: 182 °C; Yield: 78 %
1
H-NMR (CDCl , 500 MHz , δ ppm): δ 9.50 (d, J=
3
13
C-NMR (CDCl , 125 MHz , δ ppm): δ 153.9, 153.5,
7.7 Hz, 1H), 9.16 (d, J=2.3 Hz, 1H), 8.55 (dd, J=9.2,
2.5 Hz, 1H), 8.46 (d, J=9.3 Hz, 1H), 8.17 (d, J=7.5 Hz,
3
1
45.1, 144.6, 143.0, 141.8, 141.3, 141.1, 139.5, 135.7, 134.5,
Fig. 5 Halochromism shown by
compound 3a-3d in toluene and
TFA
3
a
3b0.120
0
0
0
0
0
0
0
.120
.100
.080
.060
.040
.020
.000
Toluene
0µL 1% TFA in Toluene
20µL 1% TFA in Toluene
0µL 1% TFA in Toluene
Excess TFA in Toluene
Toluene
0
0
0
0
0
.100
.080
.060
.040
.020
1
10µL 1% TFA in Toluene
20µL 1% TFA in Toluene
30µL 1% TFA in Toluene
Excess TFA in Toluene
3
0.000
300
3
00
400
500
600
400
500
600
Wavelength (nm)
Wavelength
3
c0
3d
.120
.100
.080
.060
.040
.020
.000
0
.120
0.100
.080
Toluene
Toluene
0
0
0
0
0
0
1
2
0µL 1% TFA in Toluene
0µL 1% TFA in Toluene
10µL 1% TFA in Toluene
20µL 1% TFA in Toluene
30µL 1% TFA in Toluene
Excess TFA in Toluene
30µL 1% TFA in Toluene
Excess TFA in Toluene
0
0.060
0.040
0.020
0
.000
300
400
500
600
3
00
400
500
600
Wavelength (nm)
Wavelength (nm)

J Fluoresc
Table 3 Photophysical
properties of compounds 2a-2d in
various solvents
Phase /solvent
Energy (Hartree)
Dipole moment (Debye)
λmax (nm)
Experimental
Theoretical
%D
2a
2b
2c
2d
ACN
DCM
DMF
MeOH
TOL
−1011.7332
−1011.7318
−1011.7333
−1011.7332
−1011.7276
−1216.2955
−1216.2936
−1216.2956
−1216.2955
−1216.2880
−1051.0393
−1051.0376
−1051.0393
−1051.0393
−1051.0330
−1471.3742
−1471.3726
−1471.3742
−1471.3741
−1471.3683
1.66
1.60
1.67
1.66
1.44
6.99
6.81
7.00
6.99
6.23
1.02
0.95
1.02
1.02
0.80
4.60
4.39
4.60
4.59
3.84
418
422
422
418
421
441
446
449
446
445
420
420
419
420
420
427
428
428
428
427
453
450
453
453
443
466
462
467
466
449
431
429
432
431
424
445
443
446
444
436
8.4
6.7
7.4
8.4
5.3
5.7
3.6
4.0
4.5
0.9
2.6
2.2
3.1
2.6
1.0
4.3
3.6
4.3
3.8
2.2
ACN
DCM
DMF
MeOH
TOL
ACN
DCM
DMF
MeOH
TOL
ACN
DCM
DMF
MeOH
TOL
ACN Acetonitrile, DCM Dichloromethane, DMF N,N-dimethyl formamide, MeOH Methanol, TOL Toluene
Table 4 Photophysical
properties of compounds 3a-3d in
various solvents
Phase /solvent Energy (Hartree) Dipole moment (Debye) λmax (nm)
Experimental Theoretical %D
3a
3b
3c
3d
ACN
DCM
DMF
MeOH
TOL
−1168.4593
−1168.4581
−1168.4593
−1168.4593
−1168.4549
−1372.9570
−1372.9555
−1372.9570
−1372.9569
−1372.9512
−1207.7491
−1207.7478
−1207.7491
−1207.7490
−1207.7445
−1628.0629
−1628.0618
−1628.0629
−1628.0629
−1628.0587
1.2358
1.0829
1.2370
1.2325
0.953
451
449
450
450
450
506
501
503
502
501
463
458
469
464
457
446
445
446
446
446
420
418
421
420
416
510
506
510
510
492
413
413
414
413
410
425
423
425
424
419
−7.4
−7.4
−6.9
−7.2
−8.1
1.0
ACN
DCM
DMF
MeOH
TOL
8.7900
8.5746
8.7926
8.7839
7.9551
1.1388
1.0286
1.1406
1.1348
0.8037
3.8054
3.6948
3.8076
3.8010
3.4033
1.2
1.7
1.9
−2.2
−12.0
−10.8
−13.2
−12.2
−11.2
−5.0
−5.3
−5.0
−5.3
−6.5
ACN
DCM
DMF
MeOH
TOL
ACN
DCM
DMF
MeOH
TOL
ACN Acetonitrile, DCM Dichloromethane, DMF N,N-dimethyl formamide, MeOH Methanol, TOL Toluene

J Fluoresc
Table 5 Calculated and experimental δ ppm values for selected protons in compounds 2b-2d, 2b’-2d’, 3b-3d and 3b’-3d’
Positional isomer 1
Positional isomer 2
Proton number (δ calculated/δ experimental)
Integration
Proton number (δ calculated/δ experimental)
Integration
Ratio
Major isomer
2
b
2b’
2b’
H23(9.558/9.201)
0.15
3.00
H22(9.453/9.074)
0.78
2.22
0.19
1.35
2
c
2c’
2c
H41,42,43(2.930/2.662)
H42,43,44(2.891/2.657)
2
d
2d’
2d
H7(8.095/7.745)
0.64
0.63
H7 (8.090/7.702)’
0.35
0.32
1.82
1.96
H12(8.088/7.727)
H12(8.076/7.696)
3
b
3b’
3b’
3c
H23(9.656/9.261)
0.22
3.00
1.00
H22(9.529/9.157)
1.00
2.83
0.32
0.22
1.06
3.12
3
c
3c’
H53,54,55(3.027/2.696)
H53,54,55(3.006/2.682)
3
d
3d’
3d
H8(9.993/9.472)
H8(9.984/9.426)
1
6
7
H), 7.89 (s, 1H), 7.85–7.75 (m, 2H), 7.52 (d, J=8.6 Hz, 2H),
.86 (d, J=8.2 Hz, 2H), 3.48 (q, J=7.0 Hz, 4H), 1.28 (t, J=
.0 Hz, 6H).
2H), 8.03 (s, 1H), 7.91 (s, 1H), 7.81 (t, J=7.6 Hz, 1H), 7.77–
7.64 (m, 2H), 7.53 (d, J=7.3 Hz, 2H), 3.49 (q, J=7.0 Hz, 4H),
2.69 (d, J=7.1 Hz, 3H), 1.28 (t, J=7.0 Hz, 6H).
13
13
C-NMR (CDCl , 125 MHz , δ ppm): δ 147.5, 145.3,
C-NMR (CDCl , 125 MHz , δ ppm): δ 142.7, 141.7,
3
3
1
1
44.3, 143.3, 141.4, 133.8, 131.2, 130.9, 130.9, 130.6, 130.4,
28.0, 127.6, 126.3, 125.6, 125.5, 122.0, 111.3, , 44.4, 12.7.
Mass (ESI): 423.3(M+1)
131.7, 131.6, 131.0, 129.2, 128.5, 128.2, 127.5, 127.1, 125.6,
44.4, 22.1, 12.4.
Mass (ESI): 392.3 (M+1)
CHN Analysis : Calculated: C 73.92, H 5.25, N 13.26 O,
.57 Observed: C 73.90, H 5.24, N 13.22, O 7.55.
Compound 3c
CHN Analysis : Calculated: C 82.83 H 6.44 N 10.73
Observed: C 82.80, H 6.41, N 10.70.
Compound 3d
7
M.P:164 °C; Yield: 63 %
M.P: 178 °C; Yield: 72 %
1
1
H-NMR (CDCl , 500 MHz , δ ppm): δ 9.52 (dd, J=7.5,
H-NMR (CDCl , 500 MHz , δ ppm): δ 9.47 (d, J=
3
3
5
.1 Hz, 1H), 8.27 (d, J=8.7 Hz, 1H), 8.15 (dd, J=16.8, 8.5 Hz,
8.0 Hz, 1H), 8.37–8.22 (m, 2H), 8.17 (dd, J=21.5, 8.5 Hz,
Fig. 6 Protons considered for
estimation of the positional
isomers

J Fluoresc
transfer of donor—acceptor systems. Sensors Actuators B Chem
2
8
3
H), 7.87 (s, 2H), 7.84–7.78 (m, 1H), 7.75 (dd, J=12.4,
.4 Hz, 3H), 7.51 (d, J=7.2 Hz, 2H), 6.96–6.81 (m, 3H),
.48 (dd, J=13.9, 6.9 Hz, 4H), 1.28 (t, J=7.0 Hz, 6H).
1
50:798–805. doi:10.1016/j.snb.2010.07.025
5
.
Liu X, Shu X, Zhou X et al (2010) Ultra-sensitive fluorescent sen-
sor for Hg2+ based on a donor-acceptor-donor framework. J Phys
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C-NMR (CDCl , 125 MHz , δ ppm): δ 147.4, 145.2,
3
1
1
44.2, 143.3, 141.5, 140.8, 134.5, 131.4, 128.9, 127.6, 126.7,
25.1, 122.7, 121.3, 111.7, 43.3, 11.9.
Mass (ESI): 412.3 (M+1)
CHN Analysis : Calculated : C 75.81 H 5.38 Cl 8.61 N
0.20 Observed : C 75.55, H 5.32, Cl 8.60, N 10.15.
6. Basurto S, Riant O, Moreno D et al (2007) Colorimetric detection
of Cu[II] cation and acetate, benzoate, and cyanide anions by co-
operative receptor binding in new alpha, alpha’-bis-substituted
donor-acceptor ferrocene sensors. J Org Chem 72:4673–4688.
doi:10.1021/jo0702589
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Conclusion
The phenazine molecules with different donor and acceptor
units were synthesized and their photophysical properties were
studied. The molecules with either donor i.e. morpholino or N,
N-(diethylamino)phenyl, do not show solvatochromism. The
two series with different donors behave differently in acidic
environment. Compounds 2a-2d showed red shifted absorption
and with increase in the absorption intensity of red shifted band
with increasing acidity. The N,N-diethylamino(phenyl)
substituted 3a-3d compounds show a blue shift in the absorp-
9. Kim S-J, Zhang Y, Zuniga C et al (2011) Efficient green OLED
devices with an emissive layer comprised of phosphor-doped
carbazole/bis-oxadiazole side-chain polymer blends. Org Electron
1
2:492–496
1
0. Ni YR, Su HQ, Huang W et al (2013) A spiro [fluorene-9, 9′-xan-
thene]-based host material for efficient green and blue phosphores-
cent OLED. Appl Mech Mater 331:503–507
1
1. Sun Q, Li D, Dong G et al (2013) Improved organic optocouplers
based on a deep blue fluorescent OLED and an optimized bilayer
heterojunction photosensor. Sensors Actuators B Chem 188:879–
885
tion spectrum, it is due to the protonation of –NEt nitrogen.
12. Kessler F, Watanabe Y, Sasabe H et al (2013) High-performance
pure blue phosphorescent OLED using a novel bis-heteroleptic
iridium(iii) complex with fluorinated bipyridyl ligands. J Mater
Chem C 1:1070. doi:10.1039/c2tc00836j
2
Which hinders the group to take part in conjugation. But excess
of acid can protonate phenazine nitrogen to impart a red shift to
these molecules also. Interestingly the series 2a, 2c and 2d
show linear solvent polarity parameter plots of their
photophysical property while the molecule 2b remains an ex-
ception. The combination of either a stronger donor-acceptor as
in 3a-3d and in compound 2b remains less responsive to the
solvent environment. The fluorescence of the molecules 2a, 2b
and 2c show response to solvent polarity. Theoretical and prac-
tical NMR in combination was useful in obtaining the compo-
sition of positional isomers.
1
3. Wang L, Shi Y, Zhao Y et al (2014) BPush–pull^ 1,8-naphthalic
anhydride with multiple triphenylamine groups as electron donor.
J Mol Struct 1056–1057:339–346. doi:10.1016/j.molstruc.2013.10.
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4. Sudyoadsuk T, Pansay S, Morada S et al (2013) Synthesis and
characterization of D-D-π-A-type organic dyes bearing carbazole-
carbazole as a donor moiety (D-D) for efficient dye-sensitized solar
cells. Eur J Org Chem 2013:5051–5063. doi:10.1002/ejoc.
2
01300373
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5. Hua Y, Chang S, Wang H et al (2013) New phenothiazine-based
dyes for efficient dye-sensitized solar cells: positioning effect of a
donor group on the cell performance. J Power Sources 243:253–
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Acknowledgments Abhinav Tathe is thankful to University Grants
Commission, New Delhi for JRF and SRF fellowship.
16. Jamorski CJ, Casida ME (2004) Time-dependent density-functional
theory investigation of the fluorescence behavior as a function of
alkyl chain size for the 4-( N, N -dimethylamino)benzonitrile-like
donor−acceptor systems 4-( N, N -diethylamino)benzonitrile and 4-
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