Synthesis and Computational Studies on Optoelectronically Important Novel Acridin-Isoindoline-1,3-Dione Derivatives

Article abstract of DOI:10.1007/s10895-019-02376-2

A series of novel 2-(4-(acridin-9-ylamino)phenyl)isoindoline-1,3-dione derivatives were designed and synthesized namely 2-(4-(4-methoxyacridin-9-ylamino)phenyl)isoindoline-1,3-dione [S1], 2-(4-(3-chloroacridin-9ylamino)phenyl)isoindoline-1,3-dione [S2], 2-(4-(2-fluor oacridin-9ylamino)phenyl)isoindoline-1,3-dione [S3], 2-(4-(1,4-dichloroacridin-9ylamino) phenyl)isoindoline-1,3-dione [S4]. The photophysical, thermal properties of these compounds were characterized by the spectroscopic and thermographic method. The absorbance and fluorescence spectra of these derivatives were recorded in different solvents to understand the role of solute and solvent interaction. The compounds showed high thermal stability with thermal decomposition temperatures at 5% weight loss in a range of 250–287?°C. Compared with these compounds, donor groups containing derivatives exhibited excellent properties as fluorescent compounds. Computational studies were done using DFT (Density Functional Theory) G09 software (B3LYP/6-311G++V(d,p)) basis sets in order to calculate the optical band gap and FMO (Frontier Molecular Orbital) energies. The chemical stability of the four derivatives was determined by means of chemical hardness (η) using HOMO-LUMO energies.

Full text of DOI:10.1007/s10895-019-02376-2

Journal of Fluorescence
https://doi.org/10.1007/s10895-019-02376-2
ORIGINAL ARTICLE
Synthesis and Computational Studies on Optoelectronically
Important Novel Acridin-Isoindoline-1,3-Dione Derivatives
1
1
2
Smita Mane & Kariyappa Katagi & Raveendra Melavanki
Received: 18 September 2018 /Accepted: 3 April 2019
#
Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
A series of novel 2-(4-(acridin-9-ylamino)phenyl)isoindoline-1,3-dione derivatives were designed and synthesized namely 2-(4-(4-
methoxyacridin-9-ylamino)phenyl)isoindoline-1,3-dione [S1], 2-(4-(3-chloroacridin-9ylamino)phenyl)isoindoline-1,3-dione [S2],
2-(4-(2-fluor oacridin-9ylamino)phenyl)isoindoline-1,3-dione [S3], 2-(4-(1,4-dichloroacridin-9ylamino) phenyl)isoindoline-1,3-
dione [S4]. The photophysical, thermal properties of these compounds were characterized by the spectroscopic and thermographic
method. The absorbance and fluorescence spectra of these derivatives were recorded in different solvents to understand the role of
solute and solvent interaction. The compounds showed high thermal stability with thermal decomposition temperatures at 5%
weight loss in a range of 250–287 °C. Compared with these compounds, donor groups containing derivatives exhibited excellent
properties as fluorescent compounds. Computational studies were done using DFT (Density Functional Theory) G09 software
(B3LYP/6-311G++V(d,p)) basis sets in order to calculate the optical band gap and FMO (Frontier Molecular Orbital) energies. The
chemical stability of the four derivatives was determined by means of chemical hardness (η) using HOMO-LUMO energies.
.
.
Keywords Acridine derivatives DFT HOMO-LUMO
Introduction
(ESP) of compounds S1-S4. The thermal stability of the de-
rivatives was determined by TGA.
In this study, four acridin-phthalimide derivatives 2-(4-(4-
methoxyacridin-9-ylamino) phenyl)isoindoline-1,3-dione
Fluorescence applications have been widely used in mate-
rial science and biological chemistry because of its selectivity,
susceptibility, rapid response, and high spatial resolution via
microscopic imaging [1]. The design and synthesis of func-
tional fluorescent dyes have attracted tremendous interest in
chemist because of their extensive applications. An ideal fluo-
rescent dye often possesses a high absorption coefficient and
quantum yield, a large Stokes shift, high chemical stability,
tuneable absorption, and emission profiles and good solubility
for practical applications [2].
The effect of solvent on the absorption and fluorescence
emission characteristics of organic compounds has been a
subject of interesting investigation [3]. Dissolved substances
are greatly influenced by solvent parameters like bipolarity,
hydrogen bond donating and accepting ability which consti-
tute solute-solvent interactions [4]. The solvatochromic meth-
od is based on the shift of absorption and fluorescence maxi-
ma in different solvents of varying polarity [5]. Depending on
the polarity of the solvent, position, intensity, and shape of the
absorption band can vary. Several studies of photophysical
properties of organic donor-acceptor molecules suggest
intra-molecular charge transfer (ICT) and give access to sin-
glet excited state characteristics, which allows one to design
[
S1], 2-(4-(3-chloroacridin-9ylamino)phenyl)isoindoline-1,3-
d i o n e [ S 2 ] , 2 - ( 4 - ( 2 - f l u o r o a c r i d i n -
ylamino)phenyl)isoindoline-1,3-dione [S3], 2-(4-(1,4-
9
dichloroacridin-9ylamino)phenyl)isoindoline-1,3-dione [S4].
Substituted electron donating and withdrawing groups vary-
ing in positions were investigated spectrally in various polar
solvents to examine their Solvatochromism luminescent prop-
erty. As a result, absorbance and fluorescence spectra of the
derivative were recorded. Electrochemical properties
(
HOMO-LUMO) of the acridine derivatives are determined
using cyclic voltammetry (CV). DFT is used to calculate
HOMO–LUMO energy gap and electrostatic potential map
*
Kariyappa Katagi
kskatagi69@gmail.com
1
2
Department of Chemistry, Karnatak Science College,
Dharwad 580001, India
Department of Physics, M S Ramaiah Institute of Technology,
Bangalore, Karnataka 560054, India

J Fluoresc
new molecules and perform in specific applications. These
properties include quantum yield, fluorescence decay time,
absorption and fluorescence spectral shift [6].
DMSO, δ ppm): 55.9, 106.8, 107.9, 113.2, 116.4, 116.4,
122.3, 122.4, 122.4, 122.8, 125.4, 127.0, 127.9, 127.9,
128.2, 128.9, 129.9, 132.3, 132.3, 132.6, 132.6, 138.7,
1
39.5, 148.2, 149.0, 155.8, 167.1, 167.1; GC-MS: m/z 445
+
(M ).
Experimental
Synthesis of 2-(4-(3-Chloroacridin-9ylamino)Phenyl)
Isoindoline-1,3-Dione[S2]
Synthesis of 9-Chloroacridine
A mixture of 2-(phenylamino) benzoic acid (0.024 mol) and
phosphorus oxychloride (5 mL) was heated on a water bath for
Yield: 75%; brown solid; MP = 160–162 °C IR (KBr)
(Vmax/cm ): 3444.0, 1721.6, 1629.6, 1524.2 cm ; H NMR
−1
−1 1
1
5–20 min. at 80–90 °C and then the reaction mixture was
(400 MHz, DMSO-d , δ ppm): 7.20–7.19 (d, 2H, J = 6.4 Hz),
6
placed in an oil bath at 150 °C for 2 h, the excess of oxychloride
was removed by distillation. The cooled reaction mixture was
poured in to water and made alkaline with ammonia solution.
The product was filtered and washed with hot water [7].
7.48–7.30 (m, 2H), 7.61–7.51 (m, 5H), 7.69–7.67 (d, 2H, J =
13
7.6 Hz), 7.74 (s, 3H), 8.19–8.14 (m, 1H), 11.47 (s, 1H, -NH); C
NMR (100 MHz, DMSO, δ ppm): 108.3, 116.5, 116.5, 119.7,
122.4, 122.4, 122.5, 122.8, 127.0, 127.0, 127.6, 127.6, 128.3,
1
29.0, 129.3, 129.4, 129.9, 132.8, 132.8, 132.9, 134.9, 138.7,
+
148.2, 149.5, 150.2, 167.1, 167.1; GC-MS: m/z 450 (M ).
Synthesis of 2-(4-(Acridin-9ylamino) Phenyl)
Isoindoline-1, 3-Dione (6a-6j) Derivatives
Synthesis of 2-(4-(2-Fluoroacridin-9ylamino)Phenyl)
Isoindoline-1,3-Dione [S3]
An equimolar mixture of 9-chloroacridine (0.02 mol) and p-
phenylene diamine (0.024 mol) was dissolved in 20 mL of
methanol and refluxed for 4 h at 70 °C. After the completion
of reaction monitored by TLC then it was cooled and poured
into diethyl ether the compound starts separation. The product
was filtered and recrystallised from ethanol.
Yield: 70%; brown solid; MP = 208–210 °C IR (KBr)
−
1
−1 1
(Vmax/cm ): 3443.6, 1694.8, 1657.1, 1546.5 cm ; H
NMR (400 MHz, DMSO-d , δ ppm): 6.52–6.50 (d, 2H, J =
6
8 Hz), 7.44–6.91 (m, 3H), 7.55 (s, 1H), 7.79–7.57 (m, 4H),
1
3
The substituted 9-aminoacridine (0.011 mol) and
8.10–7.89 (m, 5H), 11.36 (s, 1H, -NH); C NMR (100 MHz,
DMSO, δ ppm): 102.8, 109.2, 116.5, 116.5, 119.6, 122.6,
122.6, 122.6, 122.6, 126.9, 127.0, 127.6, 128.5, 129.0,
(0.016 mol) pthalic anhydride was refluxed with acetic acid
for 5–6 h at 110 °C. The product was filtered and recrystallised.
The synthesized compounds S1-S4 outlined in Scheme 1.
129.9, 131.6, 132.2, 132.2, 132.3, 132.3, 138.9, 144.7,
+
148.4, 149.5, 159.7, 167.6, 167.6; GC-MS: m/z 433 (M ).
Synthesis of 2-(4-(4-Methoxyacridin-9ylamino)Phenyl)
Isoindoline-1,3-Dione[S1]
Synthesis of 2-(4-(1,4-Dichloroacridin-9ylamino)Phenyl)
Isoindoline-1,3-Dione[S4]
Yield: 75%; dark brown solid; MP =200–202 °C IR (KBr)
−
1
−1 1
(
Vmax/cm ): 3340.6, 1716.7, 1635.5, 1532.1 cm ; H
Yield: 85%; dark brown solid; MP = 190–192 °C IR (KBr)
(Vmax/cm ): 3445.4, 1742.2, 1622.8, 1516.0 cm ; H
−
1
−1 1
NMR (400 MHz, DMSO-d , δ ppm): 3.56 (s, 3H, -0CH ),
6
3
6
3
8
.44–6.42 (d, 2H, J = 10.4 Hz), 6.89 (s, 1H), 7.39–7.31 (m,
NMR (400 MHz, DMSO-d , δ ppm): 6.44–6.41 (d, 2H, J =
6
H), 7.73–7.68 (m, 3H), 8.24–8.22 (d, 2H, J = 6.4 Hz), 8.50–
8.8 Hz), 7.41–7.32 (m, 3H), 7.72–7.57 (m, 6H), 8.04 (s, 1H),
1
3
13
.39 (m, 4H), 11.55 (s, 1H, -NH); C NMR (100 MHz,
8.14–8.12 (d, 2H, J = 8 Hz), 11.36 (s, 1H, -NH); C NMR
ii
Scheme 1 Synthesis of acridine
derivatives S1-S4
O
O
NH
2
O
N
H
2
N
O
O
HN
N
i. MeOH/70 0C, reflux 4h.
ii. AcOH/110 0C, reflux 5h.
i
Cl
N
R
R
R: -OCH3, F, Cl, di-Cl

J Fluoresc
S1
S2
(
ppm). Mass spectra were recorded using Shimadzu
O
O
GCMSQP2010S. The absorption spectra, emission spec-
tra and fluorescence lifetimes were recorded using
Carry-100 UV-Visible spectrophotometer, Hitachi F-
7000 spectrofluorometer and ISS Chronos BH time-
correlated single photon counting (TCS PC) spectrome-
ter respectively. Thermogravimetric Analysis (TGA) and
Cyclic Voltammetry (CV) spectra are recorded using
SDT Q600 V20.9 Build 20 and Electrochemical analyz-
er CHI7772C 20 V AC 1.0 A CH Instruments respec-
tively. The DFT method is widely used for finding the
energetic and geometric properties of atoms or mole-
cules [8, 9]. In order to determine the HOMO–LUMO
energy gap and electrostatic potential map (ESP) of
compounds S1-S4. DFT calculations were performed
using G09 software (B3LYP/6-311G++V(d, p)) basis
sets and using Gaussview 5 visualization program com-
pounds were built and analyzed [10].
N
N
O
O
HN
HN
N
N
Cl
OCH3
S3
S4
O
O
N
N
O
O
HN
Cl
Cl
HN
N
F
N
Fig. 1 Molecular structure of acridine derivatives S1, S2, S3 and S4
Result and Discussion
Synthesis of Acridine Derivatives
(
100 MHz, DMSO, δ ppm): 111.9, 114.6, 116.4, 116.4, 120.4,
1
1
1
20.4, 122.7, 126.5, 126.9, 127.0, 127.6, 127.6, 128.2, 128.9,
29.8, 130.3, 132.1, 132.1, 132.3, 132.3, 132.6, 138.6, 144.3,
45.6, 153.1, 167.1, 167.1; GC-MS: m/z 484 (M ).
9-chloroacridine (1) was prepared according to the literature
[7] to this by treatment with a p-phenylene diamine to get
amine derivatives (2). Further the target compound (3) 2-(4-
acridine-9-yl-aminophenyl)isoindoline-1,3-dione was easily
achieved by the reaction of N -(acridine-9-yl)benzene-1,4-di-
amine (2) and phthalic anhydride at 110 °C with acetic acid.
+
All the chemicals were purchased from the SD fine
1
and TCI, Mumbai, India. Melting points were deter-
mined with an open capillary method on a Buchi appa-
ratus. The IR spectra were recorded on a Nicolet 5700
FT-IR Spectrometer in KBr tablets. H and C NMR
spectra were recorded on Bruker 400 MHz Spectrometer
using DMSO-d6 as solvent and TMS as an internal
standard. All chemical shifts were reported as δ values
1
13
Spectroscopic Properties
In order to understand the role of solute-solvent interac-
tions, the effects of solvents on absorption and emission
Table 1 Absorption and Emission data of acridine derivatives in different solvents
Solvents
S1
S2
S3
S4
a
max
b
max
a
max
b
max
a
max
b
max
a
max
b
max
λ
λ
λ
λ
λ
λ
λ
λ
CH
318
333
335
338
339
342
345
346
347
349
432
439
443
445
445
446
449
452
453
453
332
332
334
336
338
339
340
341
341
342
411
412
432
433
435
437
440
443
444
445
338
339
339
341
342
344
346
346
347
348
430
438
440
447
447
451
451
453
455
456
321
322
324
325
325
326
329
330
331
333
397
398
421
425
432
435
435
438
439
441
TL
BZ
THF
BL
DX
ML
AN
DMF
DMSO

J Fluoresc
Table 2 Optical properties of acridine derivatives S1-S4 in methanol
a
max
b
max
Compounds
λ
λ
ϕ
s
S1
S2
S3
S4
345
340
346
329
449
440
451
435
0.56
0.47
0.61
0.66
spectra of each compound were investigated as shown
in Fig 1. The absorption and emission spectra of acri-
dine derivatives S1-S4 is carried in ten different polarity
solvents such as benzene (BZ), toluene (TL), tetrahydro-
furan (THF), butanol (BL), methanol (ML), acetonitrile
Figures 2 and 3 shows the absorption and emission spectra
of the compounds S1 to S4 along with standard dye POPOP in
methanol. From Fig. 2, maximum absorption wavelength
bands were observed at 345, 340, 346 and 329 nm for the
acridine derivative S1-S4 in methanol respectively. Figure 3,
shows the emission maxima for the compounds S1 and S2 at
449 nm and 440 nm whereas, S3 and S4 have shown at
451 nm and 435 nm respectively.
(
(
(
AN), N, N-dimethyl formamide (DMF), 1,4-dioxane
DX), cyclohexane (CH), and dimethyl sulphoxide
DMSO) and is listed in Table 1. The absorption bands
of compounds S1-S4 in different solvents have shown
bathochraomic shift. This may be due to a solvent sol-
ute change of the electronic excited state structure in
non-polar solvents to polar solvents with increasing sol-
vent polarity. From Table 1 it is observed that emission
spectra of compounds in different solvents with varying
solvent polarity have shown bathochromic shift (red
shift) is due to a π-π* transitions. This may be the
indication that substituents are playing a major role in
the absorption and emission spectra. Further, on increas-
ing the solvent polarity, the stoke shift value also in-
creases, which may be an indication for intramolecular
charge transfer [11]. The Stoke shift (Δλ), indicating
All these absorption spectra (near UV region) were corre-
sponding to the π-π* electron transition [12]. Optical band
gaps (Eopt) of these compounds were calculated using Eq.
(1) from the onset of the low energy side of the absorption
spectra (λ) to the baseline and are shown in Table 2.
1
240
Eopt ¼
ð1Þ
λ
From the data it is clear that the band gap goes on increas-
ing from S1-S2, it reveals that the synthesised acridine deriv-
atives can be applicable in organic solar cells (OLEDs) [13].
the extent of the bathochromic shift of the emission
Quantum Yield
emi
maximum (λ
) compared to the absorption maxima
max
abs
(
λ
), there was a substantial increment in Stoke shift
Quantum yield provides important quantum efficiency of the
acridine derivatives like excited electronic states, radiationless
max
from S1 to S4 as depicted in Table 2.
Fig. 2 Absorption spectra of acridine derivative S1-S4
Fig. 3 Emission spectra of acridine derivative S1-S4

J Fluoresc
transitions, and coupling of electronic to vibronic states. The
the derivatives are recorded with respect to that of their
excitation wavelengths which were obtained from the
absorption maxima and each sample was scanned for
the 50s. Fluorescence lifetime measurements are the
most sensitive measurements to understand the lifetime
of the material. Therefore, the decay profile is fitted
relative quantum yields (ϕ ) of acridine derivatives were cal-
s
culated using comparative method POPOP (ϕ = 0.98) in
s
methanol using as Eq. (2) [14].
ISODRn2
S
ΦS ¼ ΦR
ð2Þ
IRODSn2
2
R
with tri-exponential function with a χ value close to
unity.
Where I is the intensity of the standard, ODR is the
optical density of the reference, n is the refractive index
I ¼ ðA τ þ A τ þ A τ Þ
1
1
2
2
3 3
ð3Þ
standard, IR is the intensity of the reference, n is the
s
refractive index of the solvent, OD is the optical density
S
Where τ , τ and τ represented the shorter, longer
of the solvent and n is the refractive index of the refer-
1
2,
3
R
and longest lifetime components with their normalized
amplitude components A , A and A respectively and
ence of the fluorophore of known quantum yield. The
quantum yields of all the compounds are in the range of
1
2,
3
lifetime value are given in Table 3. From Table 3 it is
0
.47 to 0.66. From Table 2, it is noted that the quantum
2
observed that the values of χ are close to unity and
yield is highest for S4 (0.66) and lowest for S3 (0.47).
The quantum yield maxima in case of compound S4 is
due to chloro group attached to C1 and C4 position of
acridine molecule respectively. Similarly, the quantum
yield minima in case of compound S2 is due to fluoro
group at the C3 position of the acridine derivatives.
The possible movements of the electron in the acridine are
shown in the resonance structure in Fig. 4.
also these illustrate the accuracy of fluorescence life-
time. Fluorescence lifetime measurement results that
compound S1 has higher lifetime 7.88 ns and S2 has
the lowest lifetime 6.83 ns.
These may prove that these derivatives are useful for
characterization of biological assays such as scanning of
tissue surfaces, DNA chip analysis, skin imaging, as
well as in optoelectronics like sensors and tuning of
dye laser etc.
Fluorescence Lifetime
The fluorescence lifetime of the compound S1-S4 was
recorded using time-correlated single photon counting
technique (TCSPC) in methanol and the average lifetime
are given in Table 3. The fluorescence lifetime of all
Determination of HOMO-LUMO Energy States
Cyclic voltammetry (CV) instrument and cyclic volt-
ammogram were used to determine the electrochemical
O
O
N
N
O
O
HN
N
HN
R
R
N
O
O
O
EDG
N
N
N
O
O
O
HN
N
HN
N
HN
N
R
R
R
EWG
Fig. 4 Possible resonance structure of the S1-S4 acridine derivatives

J Fluoresc
Table 3 Fluorescence lifetime of
acridine derivatives S1-S4 in
methanol
2
Compounds
λ
exc
τ
1
(ns)
τ
2
(ns)
τ
3
(ns)
A
1
A
2
A
3
Average lifetime (τ) ns
χ
S1
S2
S3
S4
340
334
342
325
0.99
0.48
0.48
0.02
2.54
1.62
2.62
1.57
10.60
8.72
7.90
9.82
0.09
0.09
0.09
0.07
0.19
0.15
0.15
0.17
0.69
0.75
7.90
0.74
7.88
6.83
7.15
7.58
1.06
1.09
1.09
1.07
λexc – excitation wavelength; τ- average lifetime; Α- pre-exponential value; χ- chi square value
properties (HOMO and LUMO) of the acridine deriva-
tives (S1-S4), and are shown in Fig. 5. HOMO
Determination of HOMO-LUMO Energy Gap
(
highest occupied molecular orbital) and LUMO (low-
Spatial distribution of molecular orbitals, mainly those
of HOMO and LUMO are luminous indicators of
electron transport in molecular systems [16].
Generally, if the energy gap between the HOMO and
LUMO decreases, it is easier for the electrons of the
HOMO to be excited. The lowering of the HOMO–
LUMO gap is fundamentally a consequence of the
large stabilization of the LUMO due to the strong
electron-accepting ability of the electron-acceptor
group [17].
est unoccupied molecular orbital) energy levels were
calculated by using Eq.4–5 respectively [15] and are
given in Table 4.
Â
Ã
onset
ox
HOMO ¼ – E
þ 4:44 ðeVÞ
ð4Þ
ð5Þ
Â
Ã
LUMO ¼ HOMO þ Eopt ðeVÞ
onset
The difference between HOMO and LUMO energy
values gives the HOMO–LUMO energy gap. By using
these HOMO–LUMO energy values, the important
property like chemical hardness (η) of the chemical
compound can be calculated. In the simplest terms,
the hardness of a species (atom, ion, or molecule) is
a qualitative indication of how polarizable it is, in
another way how much its electron cloud is distorted
in an electric field. The hardness and softness were
suggested in the literature [18–20] to denote resis-
tance to deformation by mechanical force. Molecules
with large HOMO–LUMO gap is hard which implies
higher stability and opposing charge transfer since
they oppose changes in their electron density and dis-
tribution. On the contrary, molecules which require a
small energy gap for its excitation are also termed as
soft molecules. Hence, they are highly polarizable in
nature [21].
Where,Eox is onset oxidation potential and remaining
notation have their usual meaning.
The HOMO energy levels of the compounds were
determined and found to be in the range of 5.123 to
.397 eV (vs. Ag/AgCl). From Table 4 it is observed
that the values of HOMO increase with the change in a
substituent which is attached to the acridine moiety.
Lower values of HOMO for compound S1 may be due to
5
the presence of electron donating group (-OCH ) at the C4
position of acridine ring.
3
In terms of chemical change, soft molecules are more reac-
tive than hard molecules. The chemical hardness (η) can be
observed by using Eq. (6) [22].
½
EL−EHŠ
η ¼
ð6Þ
2
Where, E is the energy of HOMO and E is the energy of
H
L
LUMO.
The chemical hardness (η) estimated for all the four
molecules are given in Table 5. It is observed that
chemical hardness is higher for S4 (η =1.4998 eV)
Fig. 5 Cyclic voltammogram curves of compounds S1-S4 were
4 6
measured in methanol in the presence of nBu NPF at a scan rate of
1
1
00 mV s−

J Fluoresc
Table 4 HOMO LUMO properties of acridine derivatives S1-S4
onset ðaÞ
(b)
(c)
Compounds
E
HOMO (eV)
LUMO (eV)
ox
S1
S2
S3
S4
0.683
0.701
0.824
0.957
−5.123
−5.141
−5.264
−5.397
−1.793
−1.631
−1.894
−2.177
(
a)
(b)
Oxidation potential relative to Ag/AgCl electrode. Calculated HOMO from the onset oxidation potentials of the compounds using Eq.(4) (eV).
Estimated LUMO using empirical Eq.(5)
(c)
and least for S1 (η =1.3601 eV). This indicates that the
separation of molecules S1-S4 discloses their strong
intramolecular charge transfer property, which leads to
controllable green color emission. The computationally
calculated HOMO energy values are in the range of
−5.4141 eV to −5.7660 eV and LUMO energy values
are in the range of −2.6938 eV to −2.8196 eV respec-
tively. Optical band gaps obtained from absorption
thresholds are in the range of 2.71 to 2.85 eV which
are in good agreement with the band gaps 3.22 eV to
3.515 eV obtained using DFT. The energy level dia-
gram of the frontier orbitals is shown in Fig. 7. The
presence of strong electron deficient (amino-
phenyl)isoindoline-1,3-dione moiety results in the low-
ering of the LUMO level, which leads to a significant
bathochromic shift in the electronic absorption.
To know the reactive sites and hydrogen bonding
interaction of the acridine derivatives the electrostatic
potential maps (ESP). The MEP of the compound is
in use to figure out the reactive sites for electrophilic
and nucleophilic attacks and is also useful in biological
detection and hydrogen bonding interactions studies [23,
24]. In addition, the MEP is based on the molecular
size, shape as well as positive, negative and neutral
electrostatic potential region in terms of color grading.
The different values of the electrostatic potential at the
surface are represented by different colors; red repre-
sents regions of most negative electrostatic potential,
blue represents regions of most positive electrostatic po-
tential and [25]. It also provides an understanding of the
relative polarity of the molecule. The molecular struc-
ture with its physicochemical property can be
recognized.
soft molecules require very less energy for excitation.
The small difference between η and HOMO-LUMO en-
ergy gaps reflects that all molecules under study result-
ed in soft molecules.
The ground state optimized molecular structures;
HOMO and LUMO of all compounds are shown in
Fig. 6. The value HOMO, LUMO, and energy band
gap (E ) are given in Table 5. From the Fig. 6 it is
g
observed that the electron clouds of HOMO energy
1
levels are all mainly located on the N -(acridine-
9
yl)benzene-1,4-diamine region of acridine molecules
and this data strongly counts for good electron donat-
ing property of acridine-diamine unit and LUMO ener-
gy levels are mainly concentrated on the (amino-
phenyl)isoindoline-1,3-dione unit, except the compound
S4. Compared with a all three compounds (S1, S2 and
S3) the compound S4 has shown different locality,
which is due to the reduction of the energy level of
HOMO was higher than that of LUMO because of the
introduction of electron withdrawing (Dichloro) group.
From the Fig. 7 it is clear that the energy gap between
HOMO LUMO is increased in S4. This confirms that
introduction of more electron withdrawing group is su-
perior way to increase the energy gap, which is useful
in the application of OLEDs due to increase in the
enhancement of electron transfer (23). From the
Table 5, it is observed that, among the four com-
pounds, S4 which bears the electron-withdrawing
dichloro-acridine derivative has shown highest HOMO
level compared to others and these results are in good
agreement with CV calculations. The partial charge
Table 5 DFT calculations for the
acridine derivatives S1-S4
a
Compouds
HOMO (eV)
LUMO (eV)
ΔE (eV)
Eopt(eV)
η
S1
S2
S3
S4
−5.414
−5. 754
−5.684
−5. 766
−2.693
−2.819
−2.752
−2.769
2.720
2.941
2.931
2.999
3.33 (372 nm)
3.51 (353 nm)
3.37 (367 nm)
3.22 (385 nm)
1.3601
1.4705
1.4658
1.4998
a
ΔE - Energy band gap; Eopt – optical band gap; η- chemical hardness

J Fluoresc
Compounds
Optimized geometry
HOMO
LUMO
S1
-
5.4141eV
-2.6938eV
S2
-
5.7548eV
-2.8196eV
S3
S4
-
5.6846eV
-2.7529eV
-
5.7660eV
-
2.7695eV
Fig. 6 Molecular orbital amplitude plots of HOMO and LUMO levels and optimized molecular structures of acridine derivative S1-S4 calculated using
DFT method
In order to know the charge interrelated properties of the
newly synthesised acridine derivative, electrostatic potential
maps (ESP) were plotted and are given in Fig. 8. ESP provides
visualization of the electron delocalization in a molecule in
which acridine derivative shows negative phases around the
Thermogravimetric Analysis (TGA)
The ability of a material to form morphologically stable films
is an important requirement for the successful operation of
OLEDs. The thermal stabilities of the compounds were stud-
ied by thermogravimetric analysis (TGA) under a nitrogen
atmosphere, the thermal and morphological stabilities of de-
rivatives of acridine molecules (S1-S4) are summarized
Table 6.
-
OCH which consists of an oxygen molecule at the C4 posi-
3
tion of the substituted acridine moiety and a carbonyl group,
whereas, positive phases around the nitrogen group present in
the acridine-isoindoline moiety and all hydrogen atoms.

J Fluoresc
atmosphere (50 mL/min). The TG and Derivative TG
grap represented in Fig. 9 and the data are depicted in
Table 6. The TGA results reveals that first degrada-
tion is observed in all compounds (S1-S4) are in the
range of 35–60 °C with minor weight loss (5%) is
due to the evaporation of moisture content in the
compounds. The major weight loss is observed (S1-
S4) in the range of 250–287 °C. It is confirmed that
all the compounds shows good thermal stability.
Conclusion
From the above discussion of all the four acridine
derivatives, absorption and emission spectra it can
be concluded that by increasing the polarity of the
solvent, the stoke shift also increases which leads to
intramolecular charge transfer. The acridine deriva-
tives S1-S4 have shown bathochromic shift π-π* due
to the presence of different substituted electron with-
drawing and electron donating groups at a different
Fig. 7 Energy diagram of the frontier orbitals of acridine derivatives S1-
S4 estimated by theoretical (DFT) calculations
Compounds S1-S4 was subjected to thermogravi-
metric analysis (TGA). The temperatures ranged from
room temperature to 400 °C under nitrogen
Fig. 8 Molecular electrostatic
potential map of acridine
derivatives (a) S1, (b) S2, (c) S3
and (d) S4
(a)
(b)
(
c)
(d)

J Fluoresc
Table 6 Thermal and
morphological stabilities of
acridine derivatives (S1-S4)
Compounds
S1
I-Degradation % wt loss
41.0 to47.57 °C
II-Degradation % wt loss
III-Degradation % wt loss
–
241.60 to 276.64 °C
55.59
6
.70
36.44 to 39.60 °C
.43
48.44 to 63.43 °C
.92
39.44 to 42.60 °C
.12
S2
S3
S4
135.87 to 189.48 °C
5.21
267 to 286.02 °C
17.50
2
170.72 to 194.03 °C
4.96
246.68 to 283.25 °C
15.39
6
128.58 to 190.33 °C
4.12
259 to 287.02 °C
16.78
3
position of the acridine derivatives. From the fluores-
cence lifetime, the compound S1 has a higher lifetime
energy gap, the chemical hardness of the molecules
of the acridine derivatives is calculated, which reveal
that the compounds are soft in nature due to the pres-
ence of small η values. From the TGA studies it can
be concluded that all the acridine derivatives are ther-
mally stable.
(
7.88 ns) and S3 has least (6.83 ns) lifetime and
hence these may be useful for characterization of the
biological assay and can be used in optoelectronics
like sensors and OLEDs. From the HOMO-LUMO
110
0.35
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
S3
1
00
S1
105
0
.30
.25
100
0
8
6
4
2
0
0
0
0
95
0.20
90
85
0.15
0.10
0.05
0.00
8
0
5
7
70
50
100
150
200
250
300
0
50
100
150
200
0
250
300
o
Temperature ( C)
Temperature ( c)
Fig. 9 TGA/Derivative TGA thermograms of the acridine derivatives S1, S2, S3 and S4 measured at a heating rate of 10 °C min−1 under Nitrogen
atmosphere

J Fluoresc
Acknowledgments Authors are very much thankful to Department of
Chemistry, Karnataka University’s Karnataka Science College,
Dharwad, for providing necessary Research facilities. Further, Smita. G.
Mane and Dr. Kariyappa. S. Katagi highly acknowledges to UGC New
Delhi, India for providing Rajiv Gandhi National Fellowship (RGNF)
12. Roquet S, Cravino A, Leriche P, Aleveque O, Frere P, Roncali J
(2006) Triphenylamine-thienylenevinylene hybrid systems with in-
ternal charge transfer as donor materials for heterojunction solar
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13. Marzena GZ, Michal F, Lukasz S, Jacek G, Eric DG, Helmut N,
Ewa SB (2012) Thermal, optical, electrochemical, and
electrochromic characteristics of novel polyimides bearing the
Acridine yellow moiety. Mater Chem Phys 137:221–234
(
F117.1/ 2016-17/ RGNF-2015-17-SC-MAH-26074 /(SAIII/Website)
and UGC-SWRO, Bangalore for granting research project No. F.2070-
MRP/15-16/KAKA056/UGC-SWRO respectively.
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