Benzothiazole-pyridone and benzothiazole-pyrazole clubbed emissive azo dyes and dyeing application on polyester fabric: UPF, biological, photophysical and fastness properties with correlative computational assessments

Article abstract of DOI:10.1016/j.saa.2020.118064

Positional isomers of benzothiazole-pyridone and benzothiazole-pyrazole containing disperse azo dyes are reported. These heterocyclic azo dyes are decorated with ‘separate ESIPT core’ and show emission in seven solvents of different polarity. After applic

Full text of DOI:10.1016/j.saa.2020.118064

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Benzothiazole-pyridone and benzothiazole-pyrazole clubbed
emissive azo dyes and dyeing application on polyester fabric:
UPF, biological, photophysical and fastness properties with
correlative computational assessments
Chaitannya W. Ghanavatkar, Virendra R. Mishra, Nagaiyan Sekar
PII:
S1386-1425(20)30041-X
https://doi.org/10.1016/j.saa.2020.118064
SAA 118064
DOI:
Reference:
Spectrochimica Acta Part A: Molecular and Biomolecular
Spectroscopy
To appear in:
Received date: 30 August 2019
Revised date:
7 January 2020
10 January 2020
Accepted
date:
Please cite this article as: C.W. Ghanavatkar, V.R. Mishra and N. Sekar, Benzothiazole-
pyridone and benzothiazole-pyrazole clubbed emissive azo dyes and dyeing application
on polyester fabric: UPF, biological, photophysical and fastness properties with correlative
computational assessments, Spectrochimica Acta Part A: Molecular and Biomolecular
Spectroscopy(2020), https://doi.org/10.1016/j.saa.2020.118064
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Benzothiazole-Pyridone and Benzothiazole-Pyrazole clubbed Emissive Azo Dyes and
Dyeing application on Polyester fabric: UPF, Biological, Photophysical and Fastness
properties with Correlative Computational assessments.
Chaitannya W. Ghanavatkar a, Virendra R. Mishra a, Nagaiyan Sekar a,*
a Chaitannya W. Ghanavatkar -ORCID ID- https://orcid.org/0000-0003-0821-1083
a Virendra R. Mishra -ORCID ID- https://orcid.org/0000-0003-0070-4705
a; a,*Department of Dyestuff Technology, Institute of Chemical Technology, Matunga (E),
Mumbai, Maharashtra, India, PIN: 400 019.
a,* E-mail: nethi.sekar@gmail.com; n.sekar@ictmumbai.edu.in
ORCID ID- https://orcid.org/0000-0001-7568-5129
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Graphical abstract
Abstract
Positional isomers of benzothiazole-pyridone and benzothiazole-pyrazole containing disperse azo
dyes are reported. These heterocyclic azo dyes are decorated with ‘separate ESIPT core’ and show
emission in seven solvents of different polarity. After application on polyester fabric, “very good to
excellent” light and washing fastness properties were observed. Thermal stability of ‘dyed fabric’ was
analysed by sublimation fastness test- and found ‘very good to excellent’ ratings at 210 °C. Ultraviolet
Protection Factor (UPF) analysis of four ‘dyed fabric’ indicates the blocking 96-97 % of UV
radiation. Dyes were found effective on gram positive and negative bacteria by agar diffusion method
and all the ‘dyed fabrics’ also showed more than 92% or 94% reduction of S. aureus or K.
pneumoniae respectively by ‘AATCC 100’ method. Structures of the dyes were optimized using
Density Functional Theory (DFT) to deduce stable tautomeric form. Calculated HOMO-LUMO gap is
then compared with antibacterial activities. Electrophilicity index and lightfastness property were also
compared and found to have very good correlation.
Keywords: Bi-Heterocyclic emissive azo dyes, polyester dyeing, Fastness properties, UPF, DFT,
Antibacterial studies
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1. Introduction
Azo dyes are most important class of industrial colorants [1] due to widespread applications
in several fields, such as non-linear optical materials (NLO) [2–5], dye-sensitized solar cells (DSSC)
[6], printing [7], cosmetics and medicines [8–10]. Particularly, dyes containing Sulfur and Nitrogen (S
and N) hetero atomic moieties, namely thiazole and benzothiazole are utilized in the production of
disperse dyes [1,11–14]. Borai and co-workers [15] utilised thiazole-pyridine hybrids in azo dyes and
reported ‘good light fastness ratings’, but ‘moderate’ biological activities. Yahyazadeh et al [16]
observed ‘potent antibacterial activities’, but ‘moderate to fairly good light fastness’ properties for the
dyes containing benzothiazole scaffold- compared to pyridine or triazole analogue. Mohammadi et al
[8] reported that thiazole or benzothiazole containing azo dyes showed ‘moderate to better light
fastness’ ratings than triazole analogue. Replacement of phenyl ring by benzothiazole unit in disperse
azo dyes is also reported with better fastness properties [14]. Hence, benzothiazole is a good
candidate when incorporated in azo dyes for effective biological activities. Moreover, various fastness
properties can be further improved by structural modifications.
On the other hand, N-substituted pyridone containing disperse dyes shows good color
strength, excellent light fastness properties, bright hues, luminous colors as well as they possess
pharmacological activities and also utilized in the dye industry [12,17–20]. Dyes containing hydroxyl
group adjacent to the azo bridge are reported and showed very good light fastness properties
[15,21,22]. Incorporation of such couplers with benzothiazole can be effective strategy for the
improved properties.
Furthermore, azo dyes are generally-weakly fluorescent or non-emissive because of eximer
or exiplex formation and the azo linkage which undergo photoisomerization [23,24]. Azo dyes are
weakly fluorescent because they exist in ‘hydrazone form’ in solution and decreases the population of
‘azo form’ thereby restricts photoisomerization [14,25]. Molecules containing in-built Excited State
Intramolecular Proton Transfer (ESIPT) unit or N-B linkage are also reported to develop emissive azo
dyes [26,27]. In our previous work, we have reported emissive azo dyes with benzothiazole scaffold
connected to ESIPT core, but they showed emission only in highly polar solvents (DMF, DMSO)
[28], and ‘moderate light fastness ratings’[14,28].
We hypothesize that, benzothiazole-pyridone or benzothiazole-pyrazole containing disperse
azo dyes can be utilised as effective candidates to improve diverse properties such as photostability,
fastness properties, UPF, biological activities and thermal stabilities. Further, such heterocyclic azo
dyes decorated with ‘separate ESIPT core’ (Figure A) can be emerge as emissive azo dyes having
versatile properties [29]. Hence, design and development of such azo dyes is still an active research
area (Table 6) [28]
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Figure A: Structural highlights of azo dyes (This work).
In this regard, we now extend our work with recently reported six bi-heterocyclic monoazo
dyes [30]. Two isomers of benzothiazole clubbed- substituted aromatic primary amines are diazotized
and then coupled with substituted pyridone or pyrazole coupling component to produce dyes 5(a-c)
and 9(a-c). Absorption and emission maxima recorded in seven different solvents. All the synthesized
azo dyes are applied on a polyester substrate. Different fastness properties and Ultraviolet Protection
Factor (UPF) of dyed fabric is measured. Density Functional Theory (DFT) is used to deduce stable
tautomeric form. Electrophilicity index is then calculated by DFT method and compared with
practically measured lightfastness values. Antibacterial activities of all the dyes and dyed fabric
studied against ‘gram positive (S. aureus)’ and ‘gram-negative (K. pneumoniae)’ bacteria by well
diffusion and AATCC 100.
2. Experimental
2.1 General dyeing procedure
Newly synthesized azo disperse dyes 5(a-c) and 9(a-c) were applied on polyester fabric using high-
temperature high pressure (HTHP) method by using Rossari Labtech Flexi Dyer machine. 1% stock
solution of all the dyes prepared by dispersing a dye in water using a dispersing agent (Saracen SO).
The polyester fabric was dyed using 3 % dye (calculated on the wt. of the fabric). Material: liquor
ratio was kept 1:30. 2 g/l dispersing agent (Saracen SO) and 2 g/l levelling agent (Supergen KDF)
then subsequently added to the dye bath. pH of the dye bath was maintained at 4-5 by the addition of
glacial acetic acid. The dye bath temperature was kept at 130 °C for 45 minutes (by maintaining the
heating rate of 2 °C/min) and then allowed to cool at 27°C (room temperature). Dyed fabric samples
thoroughly washed with cold water and then with hot water. These fabric samples then treated for
reduction clearing, in a solution of sodium hydrosulfite (2 g/l) and sodium hydroxide (2 g/l ) at 70 °C
for 20 min. Treated fabric samples again rinsed with cold water and then finally dried in open air [31].
2.2 Fastness to washing
‘Dyed polyester fabric’ was stitched between pieces having equal length of ‘undyed cotton fabric’ and
‘undyed polyester’. These stitched fabrics were washed together in lauder-o-meter in a solution of 3
g/l Na2CO3 and 1 g/l NaOH at 60°C, for 30 minutes. Fabrics unstitched from each other after washing
with cold water. Then, change in color of ‘dyed fabric’ as well as, the staining on the adjacent
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‘undyed fabric’ was measured according to SDC grayscale (Ratings: ‘1 for poor’ and ‘5 for
excellent’) [32].
2.3 Fastness to light
Evaluation of Lightfastness carried out by exposing dyed fabric to Xenon lamp for 24 h, in which half
part of the fabric was exposed to light; while half part was covered i.e. not exposed to light. The
change in the color assessed using standard blue wool scale (‘1 for poor’ and ‘8 for outstanding’) [32].
2.4 Fastness to sublimation
Sublimation fastness property was analysed using sublimation fastness analyser. Dyed polyester
fabric was stitched between two pieces of fabric (one ‘undyed polyester fabric’ and other ‘undyed
cotton fabric’ of equal length). These stitched fabric samples then treated on the previously heated
plates at 150 °C, 180 °C and 210 °C for the 30 seconds. Any ‘staining on undyed adjacent fabric’ or
‘change in tone on the dyed fabric’ measured by referring the ‘international geometric Greyscale’
(Ratings: ‘1 for poor and 5 for excellent’) [32].
2.5 Color assessment
The color coordinates of dyed polyester fabric were analysed on Rayscan-Spectrascan 5100+
instrument equipped with reflectance accessories. ‘Color values’ expressed by using ‘CIELAB Colour
Space method’. L* denotes for lightness (100 represents white and 0 for black), a* denotes for red-
green coordinate (redness and greenness represents positive and negative value respectively), b*
denotes for yellow–blue coordinate (yellowness and blueness represents positive and negative value
respectively), c* denotes for chroma; ho denotes hue angle in the range of “0° to 360°”. The ‘K/S’
value is directly related with the dye concentration on polyester fabrics.
‘K/S’ values were determined using the formula:
2
(
)
퐾
푆
1 − 푅
=
2푅
Where, R = reflectance at complete opacity; K = Absorption coefficient; S = Scattering coefficient
2.6 Spectrophotometer measurements
UV-visible studies and Fluorescence emission measurements of synthesised azo dyes were carried out
by using Perkin Elmer UV Vis spectrophotometer and Cary Eclipse fluorescence spectrophotometer
(Varian, Australia) respectively- with 1 cm quartz cells. The concentration used was 10μM to measure
absorbance and emission spectra in various solvents.
2.7 Ultraviolet protection factor (UPF)
UV-protection efficiency of a dyed fabric was measured by its Ultraviolet Protection Factor (UPF).
Fabric’s protection level is high when higher UPF ratings observed. Australian or New Zealand
standard classification systems was the very first and utilized among the existing systems [31,33]. It’s
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an established grouping system for fabric according to their sun protection properties as presented in
Table 1.
UPF rating
% UV radiation
transmitted
6.7–4.2
Ratings for
Protection efficiency
Good
15-24
25-39
4.1–2.6
≤ 2.5
Very Good
Excellent
40-50+
Table 1: Standard UPF ratings.
2.8 Antibacterial activities
Antibacterial activity checked against two strains of Klebsiella pneumoniae (Strain No. - “AATCC
4352”, Gram-negative) and Staphylococcus aureus (Strain No. - “AATCC 6538”, Gram-positive).
The antimicrobial activity of solid samples was carried out using agar well diffusion method[34].
Dyed fabric can also play an important role by protecting human skin from bacteria or microbes. So,
quantitatively effective antimicrobial activity was carried out using standard “AATCC 100” test
method [34,35].
In AATCC 100 test method, percentage reduction of microorganisms (R) calculated using the
following formula
퐵 − 퐴
(
)
푅 = 100 푋
퐵
Where R represents percent (%) reduction, A represents No. of bacteria colonies which were
recovered after 18 h, B represent the number of bacteria colonies present at 0 h [34].
2.9 Computational Method
Structures of all the compounds were optimized to the ground state, using Density Functional Theory
(DFT). Gaussian 09 package [36] and popular hybrid functional B3LYP was used. The B3LYP
functional is a combination of Becke’s three parameter exchange functional (B3) [37] with the
nonlocal correlation functional of Lee, Yang, and Parr (LYP) [38]. The basis sets used for all atoms
were the popular Pople’s split-valence basis sets. The B3LYP functional is used with the triple zeta
basis set 6-311+G (d) for optimization of stable tautomeric form in the gas phase. Theoretical
investigation about has been performed based on DFT and TDDFT methods with PCM model to
study ESIPT process.
2.2 Synthesis
Intermediates (3, 7) [39] and (C1, C2) [40] were synthesized as reported. (C3) used as it is received
from a commercial source. Dyes 5 (a-c) and 9 (a-c) are synthesized as reported [30] and synthesis
scheme is also mentioned in Figure B.
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Figure B: Synthesis scheme of Heterocyclic Azo Dyes [30].
3. Results and discussions
3.1 Photophysical properties
The absorption and emission spectra were measured in seven different organic solvents with different
polarity indexes. UV-visible spectra of 5(a-c) or 9(a-c) were measured at a concentration of 10 µM; in
the wavelength range of 350-700 nm. The absorption maxima (λmax) values are observed in the range
of 412-467 nm. It is observed that solvent polarity does not affect the absorption maxima extensively.
The shorter wavelength band observed in the region of 300-350 nm is ascribed mainly to the π-π*
transition of the aromatic system present in the azo dyes [41]. The major broad-band observed in the
region of 307–540 nm is assigned to n–π* transition which ascribes the considerable charge-transfer
character [41]. Moreover, all the azo dyes are emissive in the wavelength range of 485-568 nm and
stokes shift in the range of 79-129 nm. Fluorescence emission spectra have no specific relevance with
solvent polarity. We observe no any consistence effect on Stokes shift according to solvent polarity
change. All the data are summarized in Table 2-3 and graphically represented in Figure 1-2.
Pyrazole containing compounds (5c and 9c) have showed lower emission intensities than pyridone
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compounds (5a, 5b, 9a, 9b) in highly polar solvents like DMF. Also, there is no substantial red or
blue shift observed in between 5a-9a; 5b-9b; 5c-9c dyes; except dye 5b-which showed blue shift in
DMF.
Large stokes shift and broad emission spectra can be due to ESIPT core present in the dye structure
[29].
Figure 1: Absorption spectra of “5(a-c) and 9(a-c)” in various solvents
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Figure 2: Emission spectra of Dyes ‘5(a-c) and 9(a-c)’ in various solvents.
Dye
5a
Solvent
Toluene
Absorbance
(nm)
ε
Emission
(nm)
Stoke's shift
(nm)
L mol-1 cm-1
456
456
459
455
457
456
455
59591
59591
73425
68784
69655
30427
55468
556
557
561
559
567
570
542
100
101
102
104
110
114
87
ACN
THF
EtAc
CHCl3
MEOH
DMF
466
462
459
457
467
461
406
65592
54674
69293
68891
79375
65560
53781
556
552
556
551
563
559
535
90
90
5b
Toluene
ACN
97
THF
94
EtAc
96
CHCl3
MEOH
DMF
98
129
420
412
414
414
24439
33698
24917
26305
486
486
485
486
66
74
71
72
5c
Toluene
ACN
THF
EtAc
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419
414
421
28022
29457
24752
488
494
500
69
80
79
CHCl3
MEOH
DMF
Table 2: Absorption and emission spectral data for 5(a-c)
Dye
9a
Solvent
Toluene
Absorbance
(nm)
ε
Emission
Stoke's shift
L mol-1 cm-1 (nm)
44133
(nm)
465
457
460
457
465
459
457
556
561
561
558
568
548
567
91
62841
104
101
101
103
89
ACN
THF
55896
60818
EtAc
64171
CHCl3
MEOH
DMF
40839
48168
110
465
457
459
456
466
456
454
44133
62841
55896
60818
64171
40839
48168
557
560
561
573
574
547
559
92
9b
Toluene
ACN
103
102
117
108
91
THF
EtAc
CHCl3
MEOH
DMF
105
430
420
426
421
428
420
432
48853
66481
57613
52863
60831
51864
44368
494
495
493
495
502
495
491
64
75
67
74
74
75
59
9c
Toluene
ACN
THF
EtAc
CHCl3
MEOH
DMF
Table 3: Absorption and emission spectral data for 9(a-c)
3.2 ‘Dyeing and fastness properties’ of 5(a-c) and 9(a-c) dyes on polyester fabric
Synthesized azo disperse dyes were insoluble in water and hence prepared for application on the
polyester fibre by dispersing in water [12] to avoid loss of dye. These readily dispersible dyes 5(a-c)
and 9(a-c) were applied on hydrophobic fibres (polyester fabric) at 3% shade by using ‘High-
Temperature High Pressure technique’ (HTHP). These dyes gave reddish yellow or yellowish shades
on polyester fabric with admirable uniformity. We observe different color shades for dyed fabric 5(a-
c) and 9(a-c) under visible light and also under long and short UV light region; images are gathered
in Figure 3. Dyed fabrics were then evaluated for their fastness properties. Light, wash, sublimation
fastness properties of all the ‘dyed polyester fabric’ were evaluated and the ratings are arranged in
Table 4 and Table 5.
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Figure 3: Color shades of dyed polyester fabric visualized under visible light, long and short UV
light. A represents 5(a-c) and B for 9(a-c) series.
3.2.1 Fastness to light
Lightfastness is known as, the degree to which a dye resists fading when a dyed fabric is exposed to
light. ‘Very good to excellent’ ratings observed for all the dyes. Evaluation of ‘Lightfastness’ was
carried out by exposing dyed fabric to Xenon lamp for 24 h [31]. Among all six dyes, 9(a-c) series
shown excellent ratings compared to 5(a-c) as mentioned in Table 4.
3.2.2 Fastness to washing
All the synthesized disperse azo dyes 5(a-c) and 9(a-c) showed very good to excellent ratings (Table
Dyes
Light fastness1
Washing fastness2
Change in color
Staining on stitched
of dyed fabric
fabric
6
6
5
5
5
5
4
5
5
4
5a
5b
5c
9a
9b
9c
3-4
6-7
6-7
6
4‒5
5
5
5
4) for ‘wash fastness properties’ according to the ‘international geometric grey scale’ [31].
Table 4: Light and washing fastness ratings for dyes 5(a-c) and 9(a-c)
(1 for poor and 8 for outstanding) 1 and (1 for poor and 5 for excellent)2
3.2.3 Fastness to sublimation
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“Fastness to sublimation” is also the essential criterion of dyed polyester fabric; as the migration of
dye on polyester fabric is totally depended on heat treatment [31,42]. The ratings for sublimation
fastness properties are mentioned in Table 5. All the fabric samples 5(a-c) and 9(a-c) showed
excellent ratings at 150 °C and 180 °C; at 210 °C. Dyed fabrics as well as stitched fabrics (undyed
polyester and cotton fabric) showed “very good to excellent” ratings for sublimation fastness. This
indicates that all the dyed fabric are thermally stable upto 210oC
Sublimation fastness3
o
o
o
150 C
180 C
210 C
Dyes
Staining on fabric
Staining on fabric
Staining on fabric
Cotton
Polyester
Cotton
Polyester
Cotton
Polyester
5
5
5
5
5
5
5
5
5
5
5
5
5
5
4-5
5
4-5
5
5a
5b
5c
9a
9b
9c
5
5
5
5
5
5
4-5
5
4-5
4-5
5
4
4-5
5
5
5
4
4
Table 5: Sublimation fastness ratings for dyes 5(a-c) and 9(a-c). (1 for poor and 5 for excellent)3.
Finally, the various fastness properties are compared with some reported molecules and representative
dyes 9a, 9b (Table 6) showed improved results.
Fastness Properties
Dye
A
Dye
Reference
Light
Wash Sublimation
4-5
4
4
[14]
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B
3
4-5
3-4
4-5
5
[28]
9a
9b
6-7
6-7
5
This work
This work
5
Table 6: Comparison of azo dyes containing “Benzothiazole-ESIPT core”
3.2.4 Color assessment
‘Colorimetric parameters’ of all the dyed polyester fabrics were recorded on a Spectrascan 5100+
instrument. Color values of dyes 5(a-c) and 9(a-c) on polyester fabric were analysed by using CIE
1976 Color Space method represented by L*, a* and b*; and are gathered in Table 7. All the dyes
showed good affinity on polyester fabric and exhibits reddish yellow to yellowish shades. The values
of a* and b* color coordinate represents that color hues are shifted towards the reddish direction (on
the red-green axis) and yellowish direction (on yellow-blue axis) respectively. K/S values are in the
*
*
*
*
Dyes
h°
K/S
L
a
b
c
71.059
65.173
69.908
68.687
75.886
66.054
24.074
26.284
10.083
28.067
20.011
19.634
58.538
50.977
60.459
54.395
48.981
63.702
63.295
57.354
61.294
61.209
52.911
66.659
67.618
62.699
80.499
62.682
67.75
5.7802
5.9139
7.0697
4.9615
2.3384
9.7208
5a
5b
5c
9a
9b
9c
72.841
range of 2.33-9.72
Table 7: K/S values for dyes 5(a-c) and 9(a-c)
3.3 UPF studies
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The fabric has property to ‘absorb, reflect or scatter’ the harmful UV rays. Textile clothing or Dyed
fabric may act as a guard from these harmful UV radiations and it can be measured in terms of
Ultraviolet Protection Factor (UPF) [28,42]. Observed UPF values are mentioned in Table 8.
According to Table 1, protection efficiency is ‘good’ for 9b, as it has UPF value in the range of 15-
24. For 5a, 5c, 9c- UPF values are in the range of 25-39 which indicates that the transmittance of 4.1-
2.6 % (i.e. Blocking 95.9-97.4%) of ‘UV radiation’, which conveys the ‘very good’ ultraviolet
protection property. Figure 4 is the Graphical comparative representation of UPF values of dyed
fabric.
Dyed fabric
UPF value
25.11
5a
5b
5c
9a
9b
9c
14.18
33.45
13.57
22.35
27.87
Table 8: UPF values for dyes 5(a-c) and 9(a-c)
Figure 4: Graphical representation of UPF values of dyed fabric.
3.4 Antimicrobial study
Six azo dyes 5(a-c) and 9(a-c) were tested for antibacterial activity against S. aureus (gram-positive
bacteria) and K. pneumoniae (gram-negative bacteria). Activities were measured by using ‘agar well
diffusion method’; and reported in terms of diameter of the ‘zone of inhibition (cm)’. By referring to
the activity index, agar well diffusion results showed that all six azo dyes shown “good to
intermediate” antimicrobial activity for both bacteria. (Table 9).
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Agar gel diffusion method images for 9b are given in Figure 5. It is observed that both dye series 5
(a-c) and 9 (a-c) series follows a similar trend for antimicrobial activities and it is graphically
represented in Figure 6.
Zone of inhibition (cm)
Dyes
5a
S.aureus
1.8
K. pneumoniae
1.7
1.7
1.8
1.9
1.9
1.5
1.7
5b
5c
1.9
1.9
9a
2.1
9b
9c
1.6
Table 9: Zone of inhibition (in cm) for dyes by agar gel diffusion method
Figure 5: Agar gel diffusion method for 9b against both gram-positive and negative bacteria
Figure 6: Graphical representation of Zone of inhibition (cm) for dyes 5(a-c) and 9(a-c)
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Then, dyed fabric samples 5(a-c) and 9(a-c) initially tested for antibacterial analysis as per AATCC
147 method. Results showed that there was no zone of inhibition recorded. However, there was no
bacterial growth of gram-positive and negative bacteria below the fabric observed. Hence, the dyed
fabric samples 5(a-c) and 9(a-c) possess antibacterial activity (bacteriostatic activity) when analysed
as per ‘AATCC 147’ [28]. Figure 7 displays representative AATCC 147 method image the of 5a
against S. aureus (gram-positive) bacteria
Figure 7: AATCC 147 method for 5a against gram-positive bacteria (S. aureus)
The six dyed fabric samples 5(a-c) and 9(a-c) were then tested for antibacterial property as per
AATCC 100 method and all the samples showed more than 92% of antibacterial activity; Among all
the dyed fabric samples, sample 9b showed maximum reduction (98%) against S.aureus bacteria
(Table 10) and hence found most potent in the series. Figure 8 is represents AATCC 100 test result
for 9b.
Figure 8: Antibacterial study by AATCC 100 method of Dyed fabric 9b
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Dyed fabric
Test Culture
No. of colonies
No. of colonies
Reduction of
recovered at ‘0’ h recovered at ‘24’ h Microorganisms
[B] x 105
2.04
2.24
1.88
1.96
1.96
2.02
2.04
2.06
1.52
1.76
1.92
2.08
[A] x 104
5.0 x 103
1.1 x 104
7.0 x 103
1.10 x 104
1.10 x 104
1.5 x 104
1.2 x 104
1.2 x 104
3.0 x 103
4.0 x 103
5.0 x 103
1.2 x 104
[R]
97.54%
95.08%
96.27%
94.38%
94.38%
92.57%
94.11%
94.17%
98.02%
97.72%
97.39%
95.67%
5a
5b
5c
9a
9b
9c
S.aureus
K. pneumoniae
S.aureus
K. pneumoniae
S.aureus
K. pneumoniae
S.aureus
K. pneumoniae
S.aureus
K. pneumoniae
S.aureus
K. pneumoniae
Table 10: Antibacterial study by AATCC 100 method of Dyed fabric
3.5 Computational studies
3.5.1 Tautomeric structures and ESIPT phenomenon
Dyes 5(a-c) and 9(a-c) can exist in different tautomeric forms as mentioned in Figure 9, and Figure
S13 respectively. All the possible tautomeric forms are optimized at B3LYP/6-31g (d) level of theory
in the gas phase to determine the stable conformers [43]. The relative ground state energies (E) of
stable tautomeric forms are listed in Table S2. It is observed that all the dyes 5(a-c) and 9(a-c) have
less energy value for their “hydrazone enol” form and hence concluded that, all the dyes are stable in
hydrazone enol form (HE). This HE form then further optimised and used for various DFT
calculations.
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Figure 9: Tautomeric structures of 5(a-c) dyes.
Furthermore, in order to study the ESIPT process, theoretical calculations were performed[44] for
both the electronic ground state (S0) and excited state (S1) of all the dyes by using DFT/TD-DFT
method [45,46]. Relatively non-polar solvent and polar solvent phase [47] (toluene and DCM) was
used, by means of the CPCM method [29]. Generally, in the ground state the HE (enol form) is stable
because the phenolic proton is not acidic sufficiently to be deprotonated, and HE to HK
tautomerization does not occur in the ground state [48]. During photo-excitation process, the proton
transfer from the ‘excited enol’ is converted to ‘excited keto’ tautomer [48]. It is reported that, in the
ESIPT phenomenon, the tautomeric form HE show an increase in the phenolic (O-H) bond length;
while lowering of the N-H bond length in excited states [29,48]. In case of our 5(a-c) and 9(a-c) dyes,
the similar trend in the used solvent; i.e. increase in the phenolic (O-H) bond length while lowering of
heterocyclic N-H bond length in the excited state is observed. Which supports an ESIPT mechanism
[29,48] (General ESIPT mechanism and observed bond lengths are mentioned in SI)
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3.5.2 Electrophilicity Index
The experimentally observed results are correlated with theoretical parameters like Global Reactivity
Descriptors (GRD). By using these GRD, Quantitative Structure-Activity Relation (QSAR) or
Quantitative Structure-Property Relation (QSPR) can be developed [49]. The flow of electron from
donor to acceptor i.e. from ‘HOMO- Highest occupied molecular orbital’ to ‘LUMO- Lowest
Unoccupied Molecular Orbital’ results lowering of energy, from which electrophilicity index
produced.
So, we exploited electrophilicity index (ω) and correlated with photostability of dyes. According to
Parr et al [50], electrophilicity index measures the propensity of the moiety to absorb electrons and its
formulated as [51]:
휇2
휔 =
2휂
Where, ω=electrophilicity index, μ=chemical potential, η=chemical hardness.
By using conceptual density functional theory (CDFT) containing these (ω, μ, η) descriptors, we can
also predict biological properties [51]. Electrophilicity index (ω) is important CDFT descriptor co-
related to study photostability and lightfastness. Electrophilicity index (ω) is related to energy
stabilization phenomena, which related to transfer of an electron from the environment to the
molecular system. When the value of ‘ω’ is more, the system is more stabilized and hence shows
higher lightfastness ratings [42,52]. A linear or direct relation is observed when electrophilicity index
and light fastness ratings compare as mentioned in Table S1 and displayed in Figure 10.
Figure 10: Lightfastness values compared with electrophilicity.
3.5.3 HOMO–LUMO theory and (FMO approach)
Stable tautomeric form (HE) of all the compounds 5(a-c) and 9(a-c) further optimized at B3LYP/6-
311+ g (d,p) and CAM-B3LYP/6-311+ g (d,p) level in gas phase, ethyl acetate and DMSO. Highest
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Occupied Molecular Orbital- i.e. HOMO and Lowest Unoccupied Molecular Orbital- i.e. LUMO are
most important orbitals in molecule. High chemical reactivity and low kinetic stability of a molecule
is generally accomplice with a small energy gap between frontier orbitals. A molecule when
energized, it easily loses an electron, as ‘HOMO energy’ is directly related to ionization potential.
Conversely, ‘LUMO energy’ directly related with electron affinity, as it accepts an electron. HOMO–
LUMO theory is used to compare with biological activities of newly synthesized dyes 5(a-c) and 9(a-
c). So, calculation of Energy gap (ELUMO – EHOMO) is important, as these values are related to the
reactivity of molecule [53,54]. The HOMO-LUMO gap are calculated in gas phase as well as in ethyl
acetate and DMSO solvents in two different functionals. (ELUMO – EHOMO) are gathered in Table 11
and also presented in Figure 11. From the Table 11, and Table S3 it is observed that, (ELUMO
–
EHOMO) follows the same trend in “B3LYP or CAM-B3LYP” functional in gas phase or solvent phase.
Series 9(a-c) has less HOMO-LUMO gap compared to 5(a-c) series in both the functionals (in gas or
solvent conditions).
Moreover, CAM-B3LYP gave higher (overestimated) results compared to B3LYP functional. The
observations using CAM-B3LYP functional gives higher orbital energies is can be attributed to the
Hartree-Fock exchange composition in long-range correction.
We tried this theory to compare with biological activities [53]. 9(a-c) should exhibit better
biological properties compared to 5(a-c) [53]. This is valid when results of the zone of inhibition
compared in between 5a-9a and 5b-9b pairs against both the gram positive and negative bacteria i.e.
inverse relation of (ELUMO – EHOMO) with antibacterial activity. But, surprisingly opposite trend
observed for 5c-9c pair.
B3LYP/6-311+ G(d,p)
HOMO Energy
Hartree eV
LUMO Energy
Hartree eV
E(LUMO-HOMO)
eV
Dyes
5a
5b
5c
9a
9b
9c
-0.2278 -6.2003 -0.1158 -3.1502
-0.2279 -6.2017 -0.1176 -3.2003
-0.2180 -5.9402 -0.1004 -2.7331
-0.2326 -6.3315 -0.1258 -3.4229
-0.2326 -6.3315 -0.1258 -3.4223
-0.2238 -6.0912 -0.1096 -2.9815
3.0501
3.0014
3.2071
2.9086
2.9091
3.1097
Gas phase
5a
5b
5c
9a
9b
9c
-0.2252 -6.1266 -0.1160 -3.1554
-0.2259 -6.1471 -0.1171 -3.1856
-0.2201 -5.9881 -0.1022 -2.7821
-0.2291 -6.2344 -0.1237 -3.3650
-0.2297 -6.2505 -0.1247 -3.3930
-0.2252 -6.1277 -0.1104 -3.0033
2.9712
2.9614
3.2060
2.8694
2.8575
3.1244
Ethyl acetate
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CAM-B3LYP/6-311+ G(d,p)
5a
5b
5c
9a
9b
9c
-0.2722 -7.4069 -0.0753 -2.0498
-0.2722 -7.4064 -0.0752 -2.0449
-0.2674 -7.2766 -0.0558 -1.5195
-0.2774 -7.5495 -0.0837 -2.2787
-0.2774 -7.5482 -0.0835 -2.2719
-0.2711 -7.3781 -0.0654 -1.7791
5.3571
5.3615
5.7571
5.2708
5.2763
5.5990
Gas phase
5a
5b
5c
9a
9b
9c
-0.2695 -7.3343 -0.0733 -1.9954
-0.2703 -7.3552 -0.0743 -2.0221
-0.2661 -7.2418 -0.0575 -1.5652
-0.2740 -7.4557 -0.0815 -2.2175
-0.2746 -7.4720 -0.0824 -2.2417
-0.2715 -7.3884 -0.0663 -1.8041
5.3389
5.3332
5.6766
5.2382
5.2303
5.5843
Ethyl acetate
Table 11: HOMO-LUMO energy gap of dyes- 5(a-c) and 9(a-c) after optimization in the gas phase at
B3LYP/6-311+g (d) and CAM- B3LYP/6-311+g (d) level of theory.
Figure 11: Graphical representation of “HOMO-LUMO energy gap” for- 5(a-c) and 9(a-c) at
B3LYP/6-311+g (d)” level of theory.
4. Conclusion:
We report six monoazo bi-heterocyclic disperse dyes for dyeing, UPF and antimicrobial applications.
Dyes are emissive in solvents of different polarity with Stokes shift in the range of 79-129 nm. After
application on polyester fabric, ‘Very good to excellent’ ratings are observed for light and washing
fastness properties. Among all dyes, 9(a-c) series shown excellent ratings compared to 5(a-c). For
sublimation fastness property, all the dyes showed ‘excellent’ ratings at 150 °C, 180 °C. At 210 °C,
‘very good to excellent ratings’ were observed. Dyed fabrics are also found effective against harmful
UV rays. UPF values for four dyed fabric showed ‘good to very good’ ratings. ‘Dyes’- as well as
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‘dyed fabrics’ are tested against S. aureus (gram-positive bacteria) and K. pneumoniae (gram-negative
bacteria); All six azo dyes showed excellent to intermediate antimicrobial activity on both bacteria
when tested by agar gel diffusion method. Among all the dyed fabric samples, 9b shown a maximum
reduction (98%) against S.aureus bacteria. All dyes fabrics showed more than 92% or 94% reduction
of microorganism S. aureus or K. pneumoniae respectively by AATCC 100 method. We also tried to
correlate HOMO-LUMO gap and antimicrobial activity found good relation with exceptions
Computational studies were also performed to optimize the structure and to deduce stable tautomeric
form. Electrophilicity index correlated with light fastness property and both the theoretical and
practically observed values directly related with each other.
Acknowledgments
Authors CWG and VRM are thankful to Principle Scientific Advisor (PSA) India, for financial
support. We are also thankful to Sujal Warik-Kansare and Shailesh Kansare; Ashitosh Pawar (Dept.
of Textiles, ICT, Mumbai); Dr. Nerurkar (Calantha Biotech, Mumbai) for their support, dyeing and
antibacterial studies respectively.
References:
[1]
A.D. Towns, Developments in azo disperse dyes derived from heterocyclic diazo components,
Dye. Pigment. 42 (1999) 3–28. doi:10.1016/S0143-7208(99)00005-4.
[2]
M.C. Sreenath, I. Hubert Joe, V.K. Rastogi, Experimental and theoretical investigation of
third-order nonlinear optical properties of azo dye 1-(2, 5-Dimethoxy-phenylazo)-naphthalen-
2-ol by Z-scan technique and quantum chemical computations, Dye. Pigment. 157 (2018) 163–
178. doi:10.1016/j.dyepig.2018.04.044.
[3]
[4]
[5]
B. Çatikkaş, E. Aktan, E. Yalçin, Vibrational and electronic investigations, NLO, FMO
analysis on a hetarylazoindole disperse dye by density functional theory, J. Mol. Struct. 1117
(2016) 218–226. doi:10.1016/j.molstruc.2016.03.074.
Y. Cui, G. Qian, L. Chen, Z. Wang, M. Wang, Synthesis and nonlinear optical properties of a
series of azo chromophore functionalized alkoxysilanes, Dye. Pigment. 77 (2008) 217–222.
doi:10.1016/j.dyepig.2007.05.005.
C.W. Ghanavatkar, V.R. Mishra, N. Sekar, E. Mathew, S.S. Thomas, I.H. Joe, Benzothiazole
pyrazole containing emissive azo dyes decorated with ESIPT core: Linear and non linear
optical properties, Z scan, optical limiting, laser damage threshold with comparative DFT
studies, J. Mol. Struct. 1203 (2019) 127401. doi:10.1016/j.molstruc.2019.127401.
P. Prajongtat, S. Suramitr, S. Nokbin, K. Nakajima, K. Mitsuke, S. Hannongbua, Density
functional theory study of adsorption geometries and electronic structures of azo-dye-based
molecules on anatase TiO2 surface for dye-sensitized solar cell applications, J. Mol. Graph.
Model. 76 (2017) 551–561. doi:10.1016/j.jmgm.2017.06.002.
[6]
22

Journal Pre-proof
[7]
[8]
K.M. Al-Zaydi, R.M. Borik, M.H. Elnagdi, Studies with arylhydrazonopyridinones: Synthesis
of new arylhydrazono thieno[3,4-c]pyridinones as novel D2T2 dye class; classical verse green
methodologies, Ultrason. Sonochem. 16 (2009) 660–668. doi:10.1016/j.ultsonch.2008.11.004.
A. Mohammadi, B. Khalili, M. Tahavor, Novel push-pull heterocyclic azo disperse dyes
containing piperazine moiety: Synthesis, spectral properties, antioxidant activity and dyeing
performance on polyester fibers, Spectrochim. Acta - Part A Mol. Biomol. Spectrosc. 150
(2015) 799–805. doi:10.1016/j.saa.2015.06.024.
[9]
N. Hassan, A.Z. El-sonbati, M.G. El-desouky, Synthesis , characterization , molecular docking
and DNA binding studies of Cu ( II ), Ni ( II ), Zn ( II ) and Mn ( II ) complexes, J. Mol. Liq.
242 (2017) 293–307. doi:10.1016/j.molliq.2017.07.019.
[10] W.H. Mahmoud, F.N. Sayed, G.G. Mohamed, Synthesis, characterization and in vitro
antimicrobial and anti-breast cancer activity studies of metal complexes of novel pentadentate
azo dye ligand, Appl. Organomet. Chem. 30 (2016) 959–973. doi:10.1002/aoc.3529.
[11] M.A. Weaver, L. Shuttleworth, Heterocyclic diazo components, Dye. Pigment. 3 (1982) 81–
121. doi:10.1016/0143-7208(82)80016-8.
[12] M.A. Metwally, E. Abdel-Galil, A. Metwally, F.A. Amer, New azodisperse dyes with thiazole,
thiophene, pyridone and pyrazolone moiety for dyeing polyester fabrics, Dye. Pigment. 92
(2012) 902–908. doi:10.1016/j.dyepig.2011.07.009.
[13] G. Hallas, Synthesis and spectral properties of azo dyes derived from 2-aminothiophenes and
2-aminothiazoles, Dye. Pigment. 42 (2002) 249–265. doi:10.1016/s0143-7208(99)00031-5.
[14] M.A. Satam, R.K. Raut, N. Sekar, Dyes and Pigments and comparison with 2-naphthol
analogs, Dye. Pigment. 96 (2013) 92–103. doi:10.1016/j.dyepig.2012.07.019.
[15] M.A. El-Borai, H.F. Rizk, G.B. El-Hefnawy, H.F. El-Sayed, S.A. Ibrahim, Dyeing, color
fastness and antimicrobial properties of some mono and disazo disperse dyes derived from
thiazole moiety, Fibers Polym. 14 (2013) 2061–2068. doi:10.1007/s12221-013-2061-8.
[16] H. Yousefi, A. Yahyazadeh, E.O.M. Rufchahi, M. Rassa, Synthesis, spectral properties,
biological activity and application of new 4-(benzyloxy)phenol derived azo dyes for polyester
fiber dyeing, J. Mol. Liq. 180 (2013) 51–58. doi:10.1016/j.molliq.2012.12.030.
[17] A. Al, M. Ahmed, E. Apasery, H. Mahmoud, N. Al, new azo pyridone disperse dyes on
polyester fabric, 5 (2014). doi:10.5155/eurjchem.5.2.321.
[18] S.M. Ashkar, M.A. El-Apasery, M.M. Touma, M.H. Elnagdi, Synthesis of some novel
biologically active disperse dyes derived from 4-methyl-2,6-dioxo-1-propyl-1,2,5,6-
tetrahydropyridine- 3-carbonitrile as coupling component and their colour assessment on
polyester fabrics, Molecules. 17 (2012) 8822–8831. doi:10.3390/molecules17088822.
[19] S. Rasapalli, Y. Fan, M. Yu, C. Rees, J.T. Harris, J.A. Golen, J.P. Jasinski, A.L. Rheingold,
S.M. Kwasny, T.J. Opperman, Detour of prenostodione synthesis towards pyrazolones for
antibacterial activity, Bioorganic Med. Chem. Lett. 23 (2013) 3235–3238.
23

Journal Pre-proof
doi:10.1016/j.bmcl.2013.03.123.
[20] D. Renck, P. Machado, A.A. Souto, L.A. Rosado, T. Erig, M.M. Campos, C.B. Farias, R.
Roesler, L.F.S.M. Timmers, O.N. De Souza, D.S. Santos, L.A. Basso, Design of Novel Potent
Inhibitors of Human Uridine Phosphorylase- 1: Synthesis, Inhibition Studies,
Thermodynamics, and in Vitro In fl uence on 5 ‑ Fluorouracil Cytotoxicity, 56 (2013) 8892–
8902. doi:10.1021/jm401389u.
[21] H. Langhals, Color Chemistry. Synthesis, Properties and Applications of Organic Dyes and
Pigments. 3rd revised edition. By Heinrich Zollinger., Angew. Chemie Int. Ed. 43 (2004)
5291–5292. doi:10.1002/anie.200385122.
[22] J. Qiu, J. Xiao, B. Tang, B. Ju, S. Zhang, Facile synthesis of novel disperse azo dyes with
aromatic hydroxyl group, Dye. Pigment. 160 (2019) 524–529.
doi:10.1016/j.dyepig.2018.08.052.
[23] L.M.B.J.W. Andrei, FLUORESCENCE QUENCHINGAZO DYES, THER METHODS OF
PREPARATION AND USE, US 2005/0112673 A1, 2005.
[24] L.M.B.J.W. Andrei, FLUORESCENCE QUENCHINGAZO DYES, THER METHODS OF
PREPARATION AND USE, US 2009/0053821 A1, 2009.
[25] P.P. Kasture, Y.A. Sonawane, R.N. Rajule, G.S. Shankarling, Synthesis and characterisation of
benzothiazole-based solid-state fluorescent azo dyes, Color. Technol. 126 (2010) 348–352.
doi:10.1111/j.1478-4408.2010.00268.x.
[26] J. Jayabharathi, V. Thanikachalam, M. Venkatesh Perumal, N. Srinivasan, A physiochemical
study of azo dyes: DFT based ESIPT process, Spectrochim. Acta - Part A Mol. Biomol.
Spectrosc. 83 (2011) 200–206. doi:10.1016/j.saa.2011.08.017.
[27] J. Yoshino, N. Kano, T. Kawashima, Fluorescent azobenzenes and aromatic aldimines
featuring an N-B interaction, Dalt. Trans. 42 (2013) 15826–15834. doi:10.1039/c3dt51689j.
[28] V.R. Mishra, C.W. Ghanavatkar, N. Sekar, UV protective heterocyclic disperse azo dyes:
Spectral properties, dyeing, potent antibacterial activity on dyed fabric and comparative
computational study, Spectrochim. Acta - Part A Mol. Biomol. Spectrosc. 223 (2019).
doi:10.1016/j.saa.2019.117353.
[29] J.F. Berbigier, L.G.T.A. Duarte, J.M. Perez, R.A. Mendes, E. Zapp, T.D.Z. Atvars, A.G. Dal-
Bó, F.S. Rodembusch, Excited state intramolecular proton transfer process in benzazole
fluorophores tailored by polymeric matrix: A combined theoretical and experimental study, J.
Mol. Liq. 295 (2019) 111710. doi:10.1016/j.molliq.2019.111710.
[30] C.W. Ghanavatkar, V.R. Mishra, H.K. Chaudhari, N. Sekar, Synthesis , bioactivities , DFT and
in-silico appraisal of azo clubbed benzothiazole derivatives, J. Mol. Struct. 1192 (2019) 162–
171. doi:10.1016/j.molstruc.2019.04.123.
[31] A.B. Pawar, S.P. More, R. V. Adivarekar, Dyeing of Polyester and Nylon with Semi-synthetic
Azo Dye by Chemical Modification of Natural Source Areca Nut, Nat. Products Bioprospect.
24

Journal Pre-proof
8 (2017) 23–29. doi:10.1007/s13659-017-0144-8.
[32] H.R. Maradiya, Synthesis of azobenzo[b]thiophene derivatives and their dyeing performance
on polyester fibre, Turkish J. Chem. 25 (2001) 441–450.
[33] A. Riva, I. Algaba, M. Pepió, R. Prieto, Modeling the effects of color on the UV protection
provided by cotton woven fabrics dyed with azo dyestuffs, Ind. Eng. Chem. Res. 48 (2009)
9817–9822. doi:10.1021/ie9006694.
[34] K. Erdem, S. Yurudu, The Evaluation of Antibacterial Activity of Fabrics Impregnated with
Dimethyltetradecyl ( 3- ( Trimethoxysilyl ) Propyl ) Ammonium Chloride, J. Biol. 67 (2008)
115–122. http://dergipark.gov.tr/download/article-file/95572.
[35] M. Balouiri, M. Sadiki, S.K. Ibnsouda, Methods for in vitro evaluating antimicrobial activity:
A review, J. Pharm. Anal. 6 (2016) 71–79. doi:10.1016/j.jpha.2015.11.005.
[36] G. M. J. Frisch, W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, G.
Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H.P.
Hratchian, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg, Gaussian 09, Revision C.01,
Inc. Wallingford, CT. (2009) 2009–2009.
[37] A.D. Becke, A new mixing of Hartree–Fock and local density-functional theories, J. Chem.
Phys. 98 (1993) 1372. doi:10.1063/1.464304.
[38] C. Lee, W. Yang, R.G. Parr, Development of the Colic-Salvetti correlation-energy into a
functional of the electron density formula Chengteh, Phys. Rev. B. 37 (1988) 785–789.
doi:10.1103/PhysRevB.37.785.
[39] M.G. Holler, L.F. Campo, A. Brandelli, V. Stefani, Synthesis and spectroscopic
characterisation of 2-(2′-hydroxyphenyl)benzazole isothiocyanates as new fluorescent probes
for proteins, J. Photochem. Photobiol. A Chem. 149 (2002) 217–225. doi:10.1016/S1010-
6030(02)00008-4.
[40] C.C. Chen, I.J. Wang, Synthesis of some pyridone azo dyes from 1-substituted 2-hydroxy-6-
pyridone derivatives and their colour assessment, Dye. Pigment. 15 (1991) 69–82.
doi:10.1016/0143-7208(91)87008-B.
[41] M.S. Masoud, R.M.I. Elsamra, S.S. Hemdan, Solvent, substituents and pH effects towards the
spectral shifts of some highly coloured indicators, J. Serbian Chem. Soc. 82 (2017) 851–864.
doi:10.2298/JSC170204032M.
[42] N.N. Ayare, S.H. Ramugade, N. Sekar, Photostable coumarin containing azo dyes with
multifunctional property, Dye. Pigment. 163 (2019) 692–699.
doi:10.1016/j.dyepig.2018.12.050.
[43] R. Bhide, A.G. Jadhav, N. Sekar, Light fast monoazo dyes with an inbuilt photostabilizing
unit: Synthesis and computational studies, Fibers Polym. 17 (2016) 349–357.
doi:10.1007/s12221-016-5717-3.
[44] J. Zhao, Y. Yang, Excited state proton transfer coupled with twisted intermolecular charge
25

Journal Pre-proof
transfer for N,N-dimethylanilino-1,3-diketone in high polar acetonitrile solvent, J. Mol. Liq.
220 (2016) 735–741. doi:10.1016/j.molliq.2016.05.029.
[45] Y. Yang, Y. Ding, W. Shi, F. Ma, Y. Li, The effects of amino group meta- and para-
substitution on ESIPT mechanisms of amino 2-(2’-hydroxyphenyl) benzazole derivatives, J.
Lumin. 218 (2020) 116836. doi:10.1016/j.jlumin.2019.116836.
[46] Y. Yang, Y. Chen, Y. Zhao, W. Shi, F. Ma, Y. Li, Under different solvents excited-state
intramolecular proton transfer mechanism and solvatochromic effect of 2-(2-hydroxyphenyl)
benzothiazole molecule, J. Lumin. 206 (2019) 326–334. doi:10.1016/j.jlumin.2018.10.077.
[47] Z. Tang, M. Lu, K. Liu, Y. Zhao, Y. Qi, Y. Wang, P. Zhang, P. Zhou, Solvation effect on the
ESIPT mechanism of 2-(4′-amino-2′-hydroxyphenyl)-1H-imidazo-[4,5-c]pyridine, J.
Photochem. Photobiol. A Chem. 367 (2018) 261–269. doi:10.1016/j.jphotochem.2018.08.028.
[48] C. Li, C. Ma, D. Li, Y. Liu, Excited state intramolecular proton transfer ( ESIPT ) of 6-amino-
2- ( 2 0 -hydroxyphenyl ) benzoxazole in dichloromethane and methanolꢀ: A TD-DFT quantum
chemical study, J. Lumin. 172 (2016) 29–33. doi:10.1016/j.jlumin.2015.11.026.
[49] R. Vijayaraj, V. Subramanian, P.K. Chattaraj, Comparison of global reactivity descriptors
calculated using various density functionals: A QSAR perspective, J. Chem. Theory Comput. 5
(2009) 2744–2753. doi:10.1021/ct900347f.
[50] R.G. Parr, L. V. Szentpály, S. Liu, Electrophilicity index, J. Am. Chem. Soc. 121 (1999)
1922–1924. doi:10.1021/ja983494x.
[51] D.R. Roy, R. Parthasarathi, B. Maiti, V. Subramanian, P.K. Chattaraj, Electrophilicity as a
possible descriptor for toxicity prediction, Bioorganic Med. Chem. 13 (2005) 3405–3412.
doi:10.1016/j.bmc.2005.03.011.
[52] V.R. Mishra, N. Sekar, Photostability of Coumarin Laser Dyes - a Mechanistic Study Using
Global and Local Reactivity Descriptors, J. Fluoresc. 27 (2017) 1101–1108.
doi:10.1007/s10895-017-2045-y.
[53] P.M. Chauhan, S.N. Thummar, K.H. Chikhalia, Design, synthesis, bioactivity, and
computational studies of some morpholine-clubbed coumarinyl acetamide and cinnamide
derivatives, J. Iran. Chem. Soc. 15 (2018) 1261–1277. doi:10.1007/s13738-018-1324-0.
[54] V.R. Mishra, C.W. Ghanavatkar, S.I. Qureshi, H.K. Chaudhari, N. Sekar, Design, Synthesis,
antimicrobial activity and computational studies of novel azo linked substituted
benzimidazole, benzoxazole and benzothiazole derivatives, Comput. Biol. Chem. 78 (2019)
330–337. doi:10.1016/j.compbiolchem.2019.01.003.
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Author contribution
“All the authors are aware of this submission”
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Declaration of Interest
“The authors declare no conflict of interest”
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Highlights

Six monoazo bi-heterocyclic, emissive azo disperse dyes having separate ESIPT-
benzothiazole core are utilised for dyeing on polyester fabric, then different fastness
properties and Ultraviolet Protecting Factor (UPF) were analysed.

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Antibacterial studies of “dyes” and “dyed fabric” carried out by agar gel diffusion and
AATCC 147, AATCC 100 respectively.
Electrophilicity index calculated using DFT and correlated with light fastness ratings;
Also, HOMO-LUMO gap compared with antibacterial activity.
Improved fastness properties were obtained compared to dyes having similar scaffolds.
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