Molecular properties of 5-(1H-Benzo[D]Oxa, thia, imid azole-2-Yl)-2-methyl quinazolin-4-ol fluorescent brighteners: Theoretical and experimental approach

Article abstract of DOI:10.1016/j.molstruc.2019.126984

A series of seven new fluorescent brighteners 5-(1H-benzo[d]oxazole, thiazole, imidazole-2-yl)-2-methyl quinazolin-4-ol were synthesized by chemical reaction of 2-Methyl-4-oxo-3,4-dihydroquinazoline-5-carboxylic acid and derivatives of 2-aminophenol/2-ami

Full text of DOI:10.1016/j.molstruc.2019.126984

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Molecular Properties of 5-(1H-Benzo[D]Oxa, Thia, Imid azole-2-Yl)-2-Methyl
Quinazolin-4-ol Fluorescent Brighteners: Theoretical And Experimental Approach
Vikas Patil, Nagaiyan Sekar, Vikas S. Padalkar, Jamatsing Rajput, Sharad R.
Patil, Satish V. Patil
PII:
S0022-2860(19)31081-6
https://doi.org/10.1016/j.molstruc.2019.126984
126984
DOI:
Article Number:
Reference:
MOLSTR 126984
To appear in:
Journal of Molecular Structure
Received Date:
Accepted Date:
25 June 2019
24 August 2019
Please cite this article as: Vikas Patil, Nagaiyan Sekar, Vikas S. Padalkar, Jamatsing Rajput,
Sharad R. Patil, Satish V. Patil, Molecular Properties of 5-(1H-Benzo[D]Oxa, Thia, Imid azole-2-Yl)
-2-Methyl Quinazolin-4-ol Fluorescent Brighteners: Theoretical And Experimental Approach,
Journal of Molecular Structure (2019), https://doi.org/10.1016/j.molstruc.2019.126984
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Quinazoline linked substituted Benzimidazole, Benzoxazole, Benzothiazole Fluorescent Brightening Agents: Theoretical and
Experimental approach for Molecular Properties
Vikas Patil*, Nagaiyan Sekar, Vikas S. Padalkar, Jamatsing Rajput, Sharad R. Patil, Satish V Patil,
A series of novel oxazole, thiazole, imidazole substituted quinazoline representing fluorescent brightening agents and photophysics of
fluorescence was optimised by experimental DFT computational.

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Molecular Properties of 5-(1H-Benzo[D]Oxa, Thia, Imid azole-2-Yl)-2-Methyl Quinazolin-4-ol
Fluorescent Brighteners: Theoretical And Experimental Approach
ab
b
b
c
d
c
Vikas Patil *, Nagaiyan Sekar Vikas S. Padalkar Jamatsing Rajput Sharad R. Patil , Satish V. Patil
,
,
,
a) University Institute of Chemical Technology, North Maharashtra University, Jalgaon-425001 (India)
Email: vikasudct@gmail.com
b) Department of Intermediate and Dyestuff technology, Institute of Chemical Technology, Mumbai-
4
00019 (India)
c) School of Life Sciences, North Maharashtra University, Jalgaon 425001(India)
d) SPDM Arts, Commerce, Science College Shirpur-425405 (India)
Abstract:
A series of seven new fluorescent brighteners 5-(1H-benzo[d]oxazole, thiazole, imidazole-2-yl)-2-
methyl quinazolin-4-ol were synthesized by chemical reaction of 2-Methyl-4-oxo-3,4-
dihydroquinazoline-5-carboxylic acid and derivatives of 2-aminophenol/2-aminothiophenol/1,2-
phenylenediamine attributes to its computational and experimental comparison. Density Functional
Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT) calculations was performed
by PCM model maintaining C symmetry in ground state both in gas and DMF solvent. The electronic
1
distribution over the molecules has built up strong relationship with its fluorescence quantum
efficiency. HOMO and LUMO energies defined electron donor acceptor relationship and shows two
distinct plane which are less responsive towards the π-π electronic transition and has inductive
electronic effect control their fluorescence properties. The fluorescent brighteners 6a-6g exhibits 0.6 -
2
2% and 0.6 - 7.4% deviation for UV-absorption and fluorescence emission respectively. The
theoretical and experimental results for absorption and emission are in well agreement that certainly
believe to perform theoretical calculations before experimental setup. The thermally stable
fluorescent brightening agents have been systematically investigated. The color space method was
used to evaluate the brightening values on polyester fabrics in terms of L*, a* and b*.
Keywords: Benzimidazole, Benzoxazole, Benzothiazole, Quinazoline, DFT, Vertical excitation.
Introduction:
Thermally stable quinazoline based dyes are reported for coloring man-made fabrics due to
excellent dyeing and optical brightening nature because of low sublimation nature [1]. While the base
structure of quinazoline is utilized to carry chromophoric diazo as well as water solubilizing sulphonyl
acid group [2-4]. The hybrid combination of bifunctional active compounds brings the synergistic
effect and multiply the activity of quinazoline centric benzazole motif, where it found to be active
1

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against the 60-tumour cell line panel and act as anticancer agent against leukemia, colon, melanoma,
renal, breast cancer cell lines [5-7]. Computational structure-activity relationship (SAR) efficiently
determines in vitro and in vivo cancer activities where in vitro activity against Versus Aurora was
significantly noticed [8,9]. Substituent groups at different position has significant role on activity
where this information is useful as future templates to investigate potential active molecules in
-
medical science [10,11]. Where the chelating ability was utilized as chemical sensor against -CN and
2
+
Pb with high selectivity 0.05 µM lowest detection limit [11]. The fluorescent activity performance
2
+
on-off’ switch was designed for high Cu ion selectivity and enhanced fluorescence was found for in
2
+
situ generated Cu complex as cyanide ion sensor [12]. Photophysical-electrooptical-optoelectronics
properties are invented in electronics to obtain low turn on voltage efficient of red-light
phosphorescent emitter with high external current, quantum and power efficiencies [13]. Quinazoline
being active component in optics, medicinal, dyes, electronics and high-tech application the interest is
focused to investigation of new infringing roots [14, 15, 16]. The structural analysis and molecular
properties are investigated as predetermine strategy with the help of DFT computation. Where X-ray
diffraction of regioselective system [17] and molecular vibrational spectroscopic analysis was
performed [18,19]. This report is in continuation of our interest in quinazoline as well as new
benzimidazole, benzoxazole and benzothiazole chemistry [22-26]. Summarized a complimentary
relationship of theoretical results with respect to synthesis, photophysical properties by experimental.
The new class of multifunctional heterocyclic azole-quinazoline system was introduced to obtain
comparative discussion between actual and theoretical measures. The effects of various substituent
groups significantly influence absorption and emission properties of structure in DMF solvent. The
trends in vertical excitations obtained from Time Dependent Density Functional Theory calculations
are in good agreement with the experimental absorptions.
Experimental
Materials and Methods
The materials and solvents used in the present work were pure and laboratory prepared. All the
commercial chemical reagents and spectroscopic grade solvents were procured from S. D. Fine
chemicals private limited Mumbai. The solvents and reagents were used as received without further
purification. The reactions were monitored on silica gel aluminium based plates kisel gel 60 F254
Merck, India. The synthesized FBA’s were purified by column chromatography technique. Spectronic
Genesys 2 UV-Visible spectrophotometer was used for UV-Vis absorption spectra and emission
spectra were recorded on Varian Cary Eclipse fluorescence spectrophotometer. 110-6 mol L-1
concentration of freshly prepared solution was used for measurement. Absorption maxima from
experimental and DFT was used as excitation wavelength in fluorescence measurement. Perkin-Elmer
Spectrum 100 FTIR spectrometer was used for IR spectral analysis and VXR 300 MHz NMR was used
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1
for H NMR with TMS as internal standard. Finnigan mass spectrometer was used for mass spectra
analysis and technique used was Electro Ionisation (EI) technique for low molecular weight.
Fluorescent brightening agent application was performed using Rossari Labtech Flexi Dyer dyeing
machine.
Relative Fluorescence Quantum Yield Calculations:
Comparative method of fluorescence quantum yield was used for evaluating the fluorescence quantum
efficiency in DMF solvent. The internal standard anthracene was used and absorption and emission of
five difference concentration was determined at 1 to 5 ppm. Slit width of emission measurement was
kept constant at 2.5 unit. The phasor representation of absorption (X-axis) vs emission (Y-axis) was
graphed for anthracene as well as new synthetic compounds i. e. 6a-6g. Phasor was evaluated for the
gradient calculation and these gradients were used in given formula (1). The terminal calculation gives
the value of fluorescence quantum yield in given solvent at standard conditions [20,21, 23, 24].
2
Gradx x
Gradst st
x   

(1)
st
2
Where: Φ = Fluorescence quantum yield of compound
= Fluorescence quantum yield of standard sample
x
Φst
Grad = Gradient from the plot of integrated fluorescence intensity against
x
absorbance of the studied compound
Grad = Gradient of standard sample
st
ηx
ηst
= Refractive index of solvent used for synthesized compound
= Refractive index of solvent used for standard sample
Synthesis
Ethyl 2-methyl-4-oxo-3, 4-dihydroquinoline-5-carboxylate 4
Ethyl ester of 3-nitrophtallic acid (5g) was prepared at refluxed in 15 mL of ethanol in catalytic
amount of p-toluene sulphonic acid (0.1 g) to drive dehydration. After 2 hours of reflux separation of
3
-nitrobenzene-1,2-dicarboxylate in ethyl acetate was obtained and un-esterified 3-nitrophtallic acid
was drain in water by treatment of Na CO . Reduction of 3-Nitrobenzene-1,2-dicarboxylate in 5%
2
3
2
Pd/C was performed under hydrogen gas pressure at 5 Kg/cm in methanol gives diethyl 3-
aminobenzene-1,2-dicarboxylate. HCl gas purging reaction of 3-aminobenzene-1,2-dicarboxylate (2.5
g) in acetonitrile (100 mL) was performed to yield intermediate ethyl 2-methyl-4-oxo-3,4-
dihydroquinoline -5-carboxylate (4) separated by quenching in cold water under continuous stirring.
o
o
Yield: 58 %, Melting point = 212 C (Lit 212 C) [21, 25].
3

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FTIR (KBr): 2978 (CH Out of plane), 2910 (-CH methylene), 1739 (-C=O ester), 1674 (-C=O Amide),
3
2
1
1
613 (C=N), 1590 (C=C Aromatic), 1503 (C=C Aromatic), 1468 (C-C-O), 1380 (-CH First overtone),
3
322 (C-H ion phase), 1273 (-CH ), 1180, 1024, 873, 779, 678 (C-O-C sting) cm .
2
-1
1
H-NMR (CD ) SO: δ = 1.41 (t, 3H, -CH ), 2.55 (s, 3H, -CH ), 4.40 (q, 2H, -CH2), 7.42 (d, 1H, J = 8.4 Hz,
3
2
3
3
Ar-H), 7.7 (d, 2H, J = 9.9 Hz, Ar-H), 11.88 (s, 1H, NH).
Mass: m/z 235 (M+1).
Synthesis of 2-methyl-4-oxo-3,4-dihydroquinazoline-5-carboxylic acid 5
A mixture of ethyl-2-methyl-4-oxo-3,4-dihydroquinazoline-5-carboxylate 4 (5 g, 0.021 moles) and 4N
HCl (20 mL) was stirred at room temperature for 4 hrs. The reaction mixture was poured onto
crushed ice (500 g) whereby a white colored solid separated out. The solid was filtered, washed
separately with ice-cold water to remove the trace of acid and dried to yield the crude product 5. The
compound 5 was crystallized from ethanol to get 2-methyl-4-oxo-3,4-dihydroquinazoline-5-carboxylic
acid.
o
Yield: 4 g, 90 % m.p > 300 C.
Synthesis of 5-(1H-benzo[d]oxazole, thiazole, imidazole-2-yl)-2 methylquinazolin-4-ol derivatives
(
2
6a-6g)
-Methyl-4-oxo-3,4-dihydroquinazoline-5-carboxylic acid 5 (2.45 mmol) and different 2-
aminophenol/2-aminothiophenol/1,2-phenylenediamine (2.45 mmol) were mixed in polyphosphoric
o
acid. The mixture was heated to 150 C for the appropriate time (3-7 hrs). After completion of the
reaction (monitored by TLC) the reaction mixture was cooled to room temperature and made neutral
with liquor ammonia (30 %). The separated product was collected by filtration and recrystallized
from DMF 6a-6g.
Synthesis of 5-(1,3-Benzoxazol-2-yl)-2-methylquinazolin-4(3H)-one 6a
o
Reaction time: 7h, Yield: 64 %, Melting point = 271 C.
FT-IR (KBr): 3048 (-CH Out of plane), 2981 (C-H benzoxazole), 2898, 1674 (C=O), 1610 (C=O amide),
3
1
1
588 (C=C aromatic), 1471, 1406 (N-H amide), 1322, 1277 (C-O aromatic), 1235 (N-N oxadiazole),
015, 1031, 960, 824, 743 (C-O oxazole), 685 cm .
-1
1
H-NMR (CD ) SO: δ 2.19 (s, 3H, -CH ), 7.12 (d, 2H, J = 9.1 Hz, Ar-H), 7.59 (d, 2H, J = 9.1 Hz, Ar-H), 7.78
3
2
3
(
d, 1H, J = 7.8 Hz, Ar-H), 7.93 (dd, 1H, J = 7.1 Hz, Ar-H), 8.13 (d, 1H, J = 7.8 Hz, Ar-H), 11.13 (s, 1H, NH-
amide).
Mass: m/z 278 (M+1).
Synthesis of 5-(6-chloro-1,3-benzoxazol-2-yl)-2-methylquinazolin-4(3H)-one 6b
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o
Reaction time: 3h, Yield: 71 %, Melting point = 282 C.
FT-IR (KBr): 3018 (-CH Out of plane), 1676, 1618 (C=O amide), 1434 (N-H amide), 1176 (N-N
3
-
1
oxadiazole), 1034, 898, 726 (C-O oxazole)., 711 cm
.
1
H-NMR (CD ) SO: δ 1.91 (s, 3H, -CH ), 7.26 (s, 1H, Ar-H), 7.40 (dd, 2H, J = 6.1, 8.4 Hz, Ar-H), 7.6 (s, 1H,
3
2
3
Ar-H), 7.81 (dd, 2H, J = 11.4, 8.5 Hz, Ar-H), 12.03 (s, 1H, NH-amide).
Mass: m/z 312 (M+1).
Synthesis of 2-methyl-5-(5-methyl-1,3-benzoxazol-2-yl)quinazolin-4(3H)-one 6c
o
Reaction time: 4h, Yield: 51 %, Melting point = 302 C.
FT-IR (KBr): 3025 (-CH Out of plane), 1672 (C=O), 1626 (C=O amide), 1467 (N-H amide), 1198 (N-N
3
-
1
oxadiazole), 1034, 911, 734 (C-O oxazole)., 656 cm
.
1
H-NMR (CD ) SO: δ 1.78 (s, 3H, -CH ), 1.98 (s, 3H, Ar-CH ), 7.41 (s, 1H, Ar-H), 7.59 (d, 2H, J = 8.5 Hz,
3
2
3
3
Ar-H), 7.75 (s, 1H, Ar-H), 7.83 (s, 1H, Ar-H), 7.98 (d, 2H, J = 9.8 Hz, Ar-H), 12.31 (s, 1H, -NH amide)
Mass: m/z 292 (M+1).
Synthesis of 5-(1,3-benzothiazol-2-yl)-2-methylquinazolin-4(3H)-one 6d
Reaction time: 6h, Yield: 73 %, Melting point = 248 oC
FT-IR (KBr): 3024 (-CH Out of plane), 1670, 1621 (C=O amide), 1465 (N-H amide), 1180 (N-N
3
-
1
oxadiazole), 1035, 913, 734, 656 (S-O thiazole) cm
.
1
H-NMR (CD ) SO: δ 1.8 (s, 3H), 7.44 (s, 1H, Ar-H), 7.56 (dd, 2H, J = 8.5, 9.9 Hz, Ar-H), 7.79 (d, 2H, J =
3
2
6
.9 Hz, Ar-H), 8.10 (dd, 2H, J = 8.0, 8.1 Hz, Ar-H), 12.08 (s, 1H, -NH amide).
Mass: m/z 294 (M+1).
Synthesis of 5-(1H-benzimidazol-2-yl)-2-methylquinazolin-4(3H)-one 6e
o
Reaction time: 4h, Yield: 61 %, Melting point = 298-300 C.
FT-IR (KBr): 3014 (-CH Out of plane), 1675, 1633 (C=O amide), 1543 (C=C aromatic), 1167 (N-N
3
-
1
oxadiazole), 1056, 943, 786 (C-N imidazole), 666 cm
.
1
H-NMR (CD ) SO: δ 2.11 (s, 3H, -CH ), 7.12 (d, 2H, J = 9.1 Hz, Ar-H), 7.59 (d, 2H, J = 9.1 Hz, Ar-H), 7.78
3
2
3
(
d, 1H, J = 7.8 Hz, Ar-H), 7.93 (dd, 1H, J = 7.1 Hz, Ar-H), 8.13 (d, 1H, J = 7.8 Hz, Ar-H), 11.13 (s, 1H, -NH
amide).
Mass: m/z 277 (M+1).
Synthesis of 2-methyl-5-(6-methyl-1H-benzimidazol-2-yl)quinazolin-4(3H)-one 6f
o
Reaction time: 3h, Yield: 67 %, Melting point = 266 C.
FT-IR (KBr): 3028 (-CH Out of plane), 1678, 1623 (C=O amide), 1523 (C=C aromatic), 1345 (N-H
3
-1
amide), 1239, 1078 (N-N oxadiazole), 878, 773 (C-N imidazole). cm .
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1
H-NMR (CD ) SO: δ 2.42 (s, 3H, -CH ), 2.59 (s, 3H, Ar-CH ), 7.22 (dd, 2H, J = 11.4, 8.4 Hz, Ar-H), 7.5 (s,
3
2
3
3
1
H, Ar-H), 7.65 (dd, 2H, J = 14.7, 12.2 Hz, Ar-H), 7.85 (s, 1H, Ar-H), 8.7 (s, 1H, Ar-H), 12.31 (s, 1H, NH-
amide).
Mass: m/z 291 (M+1).
Synthesis of 2-methyl-5-(6-nitro-1H-benzimidazol-2-yl) quinazolin-4(3H)-one 6g
o
Reaction time: 3h, Yield: 59 %, Melting point = 302 C.
FT-IR (KBr): 3024 (-CH Out of plane), 1678, 1619 (C=O amide), 1534 (C=C aromatic), 1353 (N-H
3
-1
amide), 1218 (C-O aromatic), 1048 (N-N oxadiazole), 878, 771 (C-N imidazole). cm .
1
H-NMR (CD ) SO: δ 2.59 (s, 3H, -CH ), 7.6 (s, 2H, Ar-H), 7.9-8.1 (m, 3H, J = 9.6, 14.6 Hz, Ar-H), 8.24 (s,
3
2
3
1
H, Ar-H), 8.75 (s, 1H, Ar-H), 9.14 (s, 1H, Ar-H).
Mass: m/z 322 (M+1).
Computational Details:
The effect of heteroatom and substituent was studied as function of photophysical properties,
electronic state and energy level with respect to capacity as electron donor-acceptor. The density
functional theory (DFT) calculations was performed at ground state C symmetry fixed parameter in
1
gas phase and DMF. In DMF Polarizable Continuum Model (PCM) solvation model was used [27]. The
B3LYP function was used which is complementary combination of Becke’s three parameter exchange
functional (B3) [28,29] with the nonlocal correlation functional by Lee, Yang, and Parr (LYP) [30]. The
6
-31G(d) basic set was computed to determines the vibrational frequencies of the optimized
structures [31-34] corresponds to the local minima of potential energy surface verified by the
optimized structures. The electronic conduction π-π system creates donor-acceptor continuous
electron flow back and forth has no fused ring. The synergy was maintain between theoretical and
excited computation level optimized in the framework of PCM model which has its own implications
[34-37]. However, the general trend in the experimentally observed vertical excitations and emissions
(
in the same series of generic structures) was considered as an assess to the simple and traditional
computational strategy. The ground-state vertical excitation energies in equilibrium geometries were
calculated as TD-DFT function [38]. Using TD-DFT minimum energy and geometry was computed at
less energetic first singlet excited state (S ) of each tautomer. The vertical excitations equivalence to
1
theoretical emission was obtained as energy difference between the ground state and first singlet
excited state [39, 40]. Gaussian 09 program has additional function of calculation of theoretical
emission [40]. As depicted in Figure 1 ground state geometry computationally optimized minimum
stereochemical interactions of compound 6a shows two distinct planes for quinazoline and
substituted benz-azoles. The two distinct planes imply maximum inductive effect and minimum π- π
6

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electron transfer over quinazoline core controlling the absorption and emission properties and
fluorescence quantum efficiency of structure.
Figure 1: Molecular structure of substituted Quinazoline 6a extracted from DFT optimization.
General procedure of fluorescent brightening application on polyester fiber:
High temperature-high pressure dying method was used in fluorescent brightening agent application
with liquor ratio of 1:20. Comparing to weight of fabric 2 wt % fluorescent material was used initially
solubilize in DMF and diluted to 15 mL by sodium acetate and acetic acid buffered solution of pH 5
prepared in water. Dispersing agent Metamol was used and further solution was ultra-sonicated for
°
-
1
1
5 to 20 minutes to obtain a high dispersion. Temperature was gradually raised at the rate of 3 C min
°
to 130 C continued for next 60 minutes and cooled down to room temperature. The treated fabric
was washed with cool water and allow to dry in open air [21, 40].
Results and Discussion:
The intermediate ethyl-2-methyl-4-oxo-3,4-dihydroquinazoline-5-carboxylate 4 was prepared from 3-
nitrophthalic acid by esterification, reduction and followed by cyclisation reaction Scheme 1 [25].
This intermediate was used for the synthesis of novel heterocyclic quinazolinone compounds by
different strategy presented in Scheme 1.
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COOH
COOH
COOEt
H2
COOEt
COOEt
EtOH
PTSA
Dry HCl gas
CH CN
Pd/C
3
COOEt
NO2
NO2
NH2
1
2
3
R
N
H N
2
COOH
O
X
COOEt
R
O
6a: X = O, R = H
4N HCl
X
6b: X = O, R =m-Cl
O
N
NH
6c, X = O, R =m-Me
Reflux 4 hour
N
NH
6d, X=S, R=H
N
NH
6
e, X= N, R= H
CH3
CH3
6f, X= N, R= m-Me
g, X= N, R= m-NO2
CH3
6
6
a-6g
5
4
Scheme1. Synthesis of 5-(1H-benzo[d]oxazole, thiazole, imidazole-2-yl)-2 methylquinazoline-4-ol
derivatives 6a-6g.
5
-(1H-Benzo[d]oxazole (6a-6c), thiazole (6d) and imidazole (6e-6f)-2-yl)-2-methyl quinazolin-4-ol
derivatives were synthesized from 2-methyl-4-oxo-3,4-dihydroquinazoline-5-carboxylic acid (5) by
condensation reaction with different o-amino phenols or o-amino thiophenols or 1,2-
phenylenediamine in polyphosphoric acid. The intermediate 2-methyl-4-oxo-3,4-dihydroquinazoline-
5
-carboxylic acid 5 was synthesized by acid hydrolysis of ethyl-2-methyl-4-oxo-3, 4-
dihydroquinazoline-5-carboxylate 4. The synthetic details for 6a-6g are shown in Scheme 1.
Photophysical Properties of Fluorescent Brightening Agents (FBA) (6a-6g):
The absorption and emission properties of all the compounds 6a-6g were studied in the solvent
dimethylformamide (DMF). All the absorption-emission studies were performed at room temperature
-6
using solutions of concentration 1x10 M. The synthesized compounds are fluorescent in solution
under irradiation of UV light. The effect of electron donor and electron acceptor groups on the
absorption and the emission properties of the compounds were studied. The absorption and emission
spectra of all the compounds are shown in Figure 2.
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Figure 2: Absorption and Emission spectra of compounds 6a-6g in DMF
The two distinct planes of quinazoline-azole have less significant effect in absorption wavelength
which was found in similar range for benzoxazole (6a-6c), benzothiazole (6d), and benzimidazole
(
6e-6g) derivatives. However, benzimidazole derivatives (6e-6g) uniformly emit at longer
wavelengths compared to the benzoxazoles (6a-6c). The compounds 6e-6g containing the imidazole
core showed a redshift as compared to the compounds containing thiazole 6d and oxazole 6a-6c
cores. A large Stokes shift was observed for imidazole quinazolones (6e-6g) 127 nm, 109 nm, 140 nm
respectively as compared to the thiazole (6d) 97 nm and oxazole (6a-6c) 88 nm, 89 nm and 100 nm
respectively. As there is not momentous difference in absorption of the compounds while change in
substituents plays important role in emission spectra. The absorption spectra occurs in the range of
3
10-322 nm range. Where 322 nm absorbance observed for methyl substituted benzimidazole (6f).
While 310 nm absorption was given for all oxazole derivatives (6a-6c) and nitro substituted imidazole
compound (6g). Benzthiazole substituent (6d) compound shows 319 nm absorption. The emission
spectra arise through the excitation at particular absorption are ranging from 398 nm to 450 nm. The
long-range emission 450 nm was observed for nitro substituted imidazole (6g) rather methyl
substituted benzimidazole (6f) gives 431 nm and methyl substituted oxazole (6c) gives 410 nm
emission. While unsubstituted benzoxazole, benzthiazole and benzimidazole gives emission to the 398
nm, 416 nm, 441 nm respectively. This suggest that emission is increasing from oxazole to thiazole to
imidazole from 398 nm to 450 nm range. Fluorescence quantum yields of the compounds were
evaluated in DMF using anthracene (Fluorescence quantum yield = 0.270) as the standard [20, 21, 23,
2
4]. Since the vertical excitation is govern by the only inductive effect which has significant effect on
emission and fluorescence properties. The fluorescence quantum yield values of the compounds 6a
(
(
0.392), 6b (0.275) and 6d (0.202) are much higher as compared to the other synthesized compounds
6c = 0.076, 6e = 0.0887, 6f = 0.0363, 6g = 0.017) (Table 1). The fluorescence quantum efficiency is a
9

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measure of its capacity to transfer the electrons in excited state is counted as its oxidation potential in
excited state [20]. Fluorescence quantum yield of the compound 6c is less as even having methyl
substituent as compared to its analogy 6a and 6b. The fluorescence quantum yield is an intrinsic
phenomenon of molecule which is truly controlled by the capacity to photoinduced electron transfer
from ground state i. e. photo excitation oxidation potential which is higher for methyl substituent 6c
and secondary process of fluorescence emission from higher energy state to ground state. Even there
is more excitation due to the methyl substituent in 6c the capacity to accommodate that excited
electrons (while returning to the ground state) i. e. reduction potential is lower due to high electron
density due to methyl group. This is responsible for quantum yield which is balanced process of the
oxidation potential in ground state and reduction potential in excited state of molecule [20, 41].
Figure 3 depicts the transition of electrons in ground and excited state. Amongst imidazole
substituents 6e to 6g compound 6g has less quantum efficiency (0.017) due to less oxidation potential
being nitro substituent.
Figure. 3. Predicted electron Shifting mechanism in quinazoline-benzazole derivatives during
excitation and emission.
Computational Study
In azole series, the compounds absorb in the UV region between 310-322 nm and emit in the visible
region 398-450 nm with good Stokes shift value in DMF (88-140 nm) as the difference in HOMO
energy and LUMO energy was significantly large (Figure 4). The absorption and emission properties
of the compounds 6a-6g in DMF were correlated with the computed vertical excitations obtained from
DFT and emission from TD-DFT and the results are summarized in Table 1. The large difference
between the observed absorption and the vertical excitation is observed in (HOMO-LUMO) DMF (71
nm) for the compound 6g where % deviation was maximum amongst all. Maximum populations of
vertical excitation are from HOMO-LUMO (approximately 70%). Maximum % deviation between the
experimental absorption and vertical excitation is 22 % for compound 6g which was due to the
presence of -NO group on the imidazole core. The nitro group is likely to have increased electron
2
withdrawing capacity causing a red shift in imidazole core. The computed emission using TD-DFT was
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in close agreement with the observed emission Table 1, while there was some deviation in the case of
vertical excitation and observed absorption. The maximum difference between the observed emission
and the emission obtained by the TD-DFT computation is 28 nm and 31 nm for 6a and 6b respectively.
The difference in experimental and theoretical emission are well in agreement and are acceptable
level at the initial stage of calculation. Further refining of calculation tends to reach exact values by
TD-DFT and experimental. The absorption wavelength and vertical excitations are precisely closed for
6a, 6b, 6c and 6d % deviation was in the range of 0.6 to 3.5 %. While for 6e, 6f and 6g was 14, 14 and
2
2 % respectively. These results are highly promising and genuine efforts to optimize the large
molecular weight fluorescent compounds to its optimized absorption and emission value by
computational analysis.
Table 1: Observed UV-visible absorption, emission and computed vertical excitation and emission of
compounds 6a -6g in DMF.
a
b

exp
Stokes shift, Quantum yield, f Oscillator strength, Analyses were carried out at room temperature (25 C); λ
푬풙풑풕
bϕ
흀푬풎 aStoke
%
D
Vertical
Excitation
%
D
TD-DFT
λEm (nm)
(
nm)
f
Task
Shift
(nm)
-1
nm
eV
(cm )
H→L
0.6857)
H→L
0.6882)
H→L
0.6930)
H→L
0.6857)
H→L
0.6991)
H→L
0.7009)
H→L
6.7
7.4
4.3
2.4
0.6
4.8
1.3
0.392
0.275
0.076
0.202
0.088
0.036
0.017
6
a
310 308
310 308
310 314
319 308
313 359
322 370
310 381
4.017
0.343
0.390
0.321
0.343
0.598
0.629
0.725
0.6
0.6
1.2
3.5
14
398
401
410
416
441
431
450
7132
426
432
428
426
438
452
444
(
(
(
(
(
(
6
b
4.014
3.938
4.016
3.448
3.349
3.248
7320
7867
7309
9273
7854
10003
6
c
6
d
6
e
6
f
14
6
g
22
(
0.6995)
experimentally absorption and emission, %D-% Deviation between vertical excitation and experimental
absorption and experimental emission and computed (TD-DFT) emission.
The frontier molecular orbitals and their energies were obtained from DMF. The HOMO and LUMO
orbital diagrams with their energies are summarized in Table 2 for the compounds 6a-6g. In all the
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molecules (except 6b), the electron density is distributed across the molecule in the ground state
(
HOMO) as well as in the excited state (LUMO). In case of the molecule 6b the electron density is
surrounded on the benzioxazole core in the ground state (HOMO) and it acts as a donor and the
quinazoline core acts as an electron acceptor, while in the excited state (LUMO), the electron density is
localized along the quinazol-4-ol unit of the molecule. In the case of 6a-6d the excited state is more
planar as compared to ground state, but in the case of 6e-6g the ground as well as an excited state are
planar and the dihedral angle between azole core and quinazoline core is zero-degree Table 3.
Figure 4: HOMO-LUMO Energy level diagram of compounds 6a-6g in DMF
Table 2. HOMO-LUMO Orbital diagram of compound 6a-6g in DMF with their energy.
HOMO
LUMO
HOMO
LUMO
6
a
c
6b
6d
6
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6
e
g
6f
6
Table 3: The dihedral angle of 6a-6g between quinazolinone and azole ring in ground and
excited state calculated by TD and TD-DFT
FBA’s
Dihedral Angle
Dihedral Angle G
Dihedral Angle E Quantum Yie
%)
(
6
a
C -C -C -O
60.07
12.91
13.27
14.00
12.00
0.00
39.2
27.5
7.6
20.2
8.8
2
5
12
13
6
b
61.33
60.12
60.00
0.00
6
c
6
d
6
e
C -C -C -N
2 5 12
32
6
f
0.00
0.00
3.6
6
g
0.00
0.00
1.7
Thermogravimetric Analysis:
In order to give more insight into the dyes 6a-6g, the thermal studies of the compounds have been
carried out using thermal gravimetric techniques (TGA). The thermogravimetric studies have been
o
o
-1
carried out in the temperature range 50-600 C under nitrogen gas at a heating rate of 10 C min . The
TG curves of the compounds are shown in Figure 5. The TG results indicate that the frame works of
0
0
the synthesized compounds are stable up to 300 C (80%). Above 300 C the thermogravimetric
o
curves of the synthesized compounds show a loss in weight, but up to 600 C compounds are not
decomposes completely. The comparisons of the T (decomposition temperature) showed that
d
compound 6g is thermally not stable and shows continuous weight loss as compare to other
compounds from the series. Thermal stability and their plausible degradation scheme were presented
in Figure 5.
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Figure 5: Thermo gravimetric analysis of compounds 6a-6g.
Fluorescent Brightening Study
The colorimetric parameters of the whitened polyester fabrics using synthesized fluorescent
molecules 6a-6g were recorded on a reflectance spectrophotometer CE-7000A Gretag-Macbeth [21,
4
6
2]. CIE 1976 Color Space method was used to evaluate the color values of synthesized compounds
a-6g on polyester fabrics in terms of L*, a* and b* (Tables 4). All the compounds have a good affinity
towards the polyester fabrics at high temperature and gave whitening with a blue tinge on polyester
fabrics. The whiteness index values of the fabrics dyed with compounds 6a-6g are summarized in
Table 4. The colorfastness properties of these dyes were correlated with commercially used
whitening agents.
Table 4: Color values of fluorescent dyes 6a-6g polyester fabric and commercially used optical
whiteners.
Parameters
Blank P6a
6b
6c
6d
6e
6f
6g
LeucophoSera whi Sera Wh Hostalux
BSB
PB
PN
ESR50
X
48.0
50.8
54.1
76.5
51.2
60.1
61.4
53.7
82.6
52.8
55.8
56.3
79.5
48.2 49.7 57.7 56.1 74.6
50.9 52.7 60.2 59.1 80.1
54.8 55.0 55.8 56.5 83.1
76.6 77.7 81.9 81.3 91.7
73.9
77.7
105.7
90.6
71.2
75.0
96.8
89.4
75.4
79.9
105.4
91.6
Y
53.5
55.0
78.2
Z
L*
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a*
-0.3
0.4
0.5
1.2
2.3
2.6
4.7
-0.2
3.4
-0.0 -0.7
-0.1 1.5
1.5
8.1
8.2
0.3
6.4
6.4
-28.2
2.1
1.1
0.6
-0.1
b*
C*
ho
11.2
12.1
66.9
0.63
63.2
-16.1
16.1
274.0
0.26
142.4
-12.2
12.2
273.2
0.07
128.0
-14.0
14.0
3.4
0.1
1.7
3.5
133.6 63.0
93.8
0.42
68.5
240 114.8 79.0 87.2 142.5
0.30 0.30 0.71 0.82 0.04
76.8 70.9 62.0 38.1 0.5
269.4
0.09
K/S
0.25
0.39
74.7
Stensbay
134.0
Whiteness
Taube Whitene
59.4
30.6
57.6
66.6 61.8 42.3 48.5 92.1
189.7
162.3
181.8
Conclusion:
The novel synthetic compound has good response towards its computational B3LYP calculations with
basic set of 6-31GD methods adapted in DFT as well as TD-DFT functions. The distribution of electron
density over the molecules were obtained by HOMO and LUMO which was accredited to restricted
electron transfer due to the bi-planer structure. Hence π-π electronic transition has relatively lower
stake as compare to inductive transition defining the fluorescence properties of molecules. The
vertical excitations of absorption were found a difference of only 2 nm for 1a and 1b compound with
respect to its experimental values. In case of emission only 3 nm difference was observed for
compound 6e shows close resembles in theoretical and experimental results. The quantum efficiency
was in lowest amount for 6g (0.017) compound being nitro (-NO ) substituent at benzimidazole
2
terminal reducing oxidation potential to electronic transition in excited state. The compounds were
enough thermally stable to apply as fluorescent brightening agent and color space method gives L*, a*
and b* values are in comparison with commercially available brightening agents on polyester fabric.
The DFT and TD-DFT computation is theoretical technique has certainty of results in very close
proximity with the experimental results. In near future the molecular chemist must adapt trend to
obtain theoretical calculation before the experimental set-up and properties must be verified as an
application point of view.
Acknowledgments: Vikas Patil and Vikas Padalkar are thankful to the Institute of Chemical
Technology, Mumbai. Vikas Patil is thankful to University Grant Commission (UGC) New Delhi for UGC-
FRP and Science and Engineering Research Board (SERB), Department of Science and Technology
(
DST) New Delhi for young scientist fastrack scheme (SB/FT/CS-106/2014).
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Table and Figure captions
Table 1: Observed UV-visible absorption, emission and computed vertical excitation and emission of
compounds 6a -6g in DMF.
Table 2: HOMO-LUMO Orbital diagram of compound 6a -6g in DMF with their energy
Table 3: The dihedral angle of 6a -6g between quinazolinone and azole ring in ground and excited state
calculated by TD and TD-DFT
Table 4: Colour values of fluorescent dyes 6a -6g polyester fabric and commercially used optical whiteners.
Figure 1: Molecular structure of substituted quinazoline 6a-6g extracted from DFT optimization.
Figure 2: Emission spectra of compounds 6a -6g in DMF.
Figure. 3. Predicted electron Shifting mechanism in quinazoline-benzazole derivatives during
excitation and emission.
Figure 4: HOMO-LUMO Energy level diagram of compounds 6a -6g in DMF
Figure 5: Thermo gravimetric analysis of compounds 6a-6g.
Scheme1. Synthesis of 5-(1H-benzo[d]oxazole, thiazole, imidazole-2-yl)-2 methylquinazoline-4-ol
derivatives 6a -6g.
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



PCM model C symmetry molecular DFT-TDDFT optimisation.
1
Two distinct planes has large resistance to the π-π electronic transition.
Inductive electronic effect of molecules controls fluorescence properties.
Future prospectus to reduce laboratory work rather to perform by computational.