Triphenylamine derived coumarin chalcones and their red emitting OBO difluoride complexes: Synthesis, photophysical and NLO property study

Article abstract of DOI:10.1016/j.dyepig.2017.09.045

The auxiliary methoxy aided triphenylamine donors derived coumarin chalcones and their OBO complexes with branched donor-pi-acceptor systems are synthesized and characterized. Their photophysical properties are extensively studied in solvents of different polarity. They show strong emission solvatochromism and have quantum yields up to 0.87. The BF₂-complexation of coumarin chalcones enhanced the quantum efficiency by approximately 1.4 times compared to the uncomplexed chalcones. Frontier molecular orbital analysis and Generalised Mulliken Hush analysis revealed a strong intramolecular charge transfer character of these chromophores. The first, second and third order polarizability of these chromophores are evaluated by the solvatochromic method and supported by Density Functional Theory calculations using CAM-B3LYP/6-31g(d) method. The third order nonlinear optical susceptibilities of these chromophores obtained by Z-scan analysis showed very less values of the imaginary part. Replacement of N-ethyl donors by aryl amine groups provided branched push-pull systems with enhanced thermal stability and nonlinear optical response.

Full text of DOI:10.1016/j.dyepig.2017.09.045

Dyes and Pigments 148 (2018) 474e491
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Triphenylamine derived coumarin chalcones and their red emitting
OBO difluoride complexes: Synthesis, photophysical and NLO property
study
a
a
b
Yogesh Erande , Shantaram Kothavale , Mavila C. Sreenath ,
b
b,
**
, Nagaiyan Sekar a
, *
Subramaniyan Chitrambalam , Isaac H. Joe
Department of Dyestuff Technology, Institute of Chemical Technology, N. P. Marg, Matunga, Mumbai, MH 400019, India
a
b
Centre for Molecular and Biophysics Research, Department of Physics, Mar Ivanios College, Thiruananthapuram, Kerala 695015, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 June 2017
Received in revised form
The auxiliary methoxy aided triphenylamine donors derived coumarin chalcones and their OBO com-
plexes with branched donor-pi-acceptor systems are synthesized and characterized. Their photophysical
properties are extensively studied in solvents of different polarity. They show strong emission sol-
17 September 2017
2
vatochromism and have quantum yields up to 0.87. The BF -complexation of coumarin chalcones
Accepted 18 September 2017
enhanced the quantum efficiency by approximately 1.4 times compared to the uncomplexed chalcones.
Frontier molecular orbital analysis and Generalised Mulliken Hush analysis revealed a strong intra-
molecular charge transfer character of these chromophores. The first, second and third order polariz-
ability of these chromophores are evaluated by the solvatochromic method and supported by Density
Functional Theory calculations using CAM-B3LYP/6-31g(d) method. The third order nonlinear optical
susceptibilities of these chromophores obtained by Z-scan analysis showed very less values of the
imaginary part. Replacement of N-ethyl donors by aryl amine groups provided branched push-pull
systems with enhanced thermal stability and nonlinear optical response.
Available online 21 September 2017
Keywords:
Charge transfer
Coumarin chalcones
BF complex
2
Triphenylamine
Nonlinear optical
©
2017 Elsevier Ltd. All rights reserved.
1. Introduction
integrated optical circuits for telecommunications, optical
computing, optical poling, phase modulators of optical signal and
Since a photon has replaced the electron as information carrier
the field of design of nonlinear optical (NLO) materials, investiga-
tion of their properties and application are tremendously growing
devices for frequency mixing processes [5,7e9]. The organic p-
conjugated systems have widely been investigated as efficient NLO
materials due to strong charge transfer in the system as these
compounds generally show a high degree of nonlinearity, faster
optical response high damage resistance and high nonlinear optical
susceptibilities compared to conventional materials [10e14].
Among the organic NLOphores, the chalcones are the promising
ones with good NLO efficiency and transparency [15]. By virtue of
their design, NLOphoric structures are largely of the push-pull type
[1]. Inorganic materials are relatively more stable than the organic
materials but usually accompanied with poor amplitudes of
hyperpolarizability [2]. Inorganic materials are also associated with
difficulties in obtaining high purity crystals and in device fabrica-
tion [2]. Organic NLOphores provide a diversity of structures, ease
of fabrication and low synthetic cost combined with large ampli-
tudes of hyperpolarizability [3,4]. As far as the quadratic hyper-
polarizability is concerned, organic molecules are versatile
NLOphores [4e6]. Organic NLO materials are widely used for NLO
devices and applications like optical switches, optical sensors,
with donor and acceptor groups separated by
p-conjugated
framework [16e19]. The bulk nonlinear properties of such systems
are crucially dependent on the molecular hyperpolarizability and
dipole moment of the molecule [11,20]. Several amino substituted
coumarins with the donor-acceptor framework and styryl couma-
rins have been emphasized for their NLO properties using different
methods [21,22]. Understanding the molecular origins of the NLO
properties of chromophores provides rational guidelines to syn-
thesize better-performing architecture [23]. Oudar's two level
*
Corresponding author.
** Corresponding author.
E-mail addresses: hubertjoe@gmail.com (I.H. Joe), n.sekar@ictmumbai.edu.in,
nethi.sekar@gmail.com (N. Sekar).
https://doi.org/10.1016/j.dyepig.2017.09.045
0143-7208/© 2017 Elsevier Ltd. All rights reserved.

Y. Erande et al. / Dyes and Pigments 148 (2018) 474e491
475
model (eq. (1)) is the tool to provide the basis for designing organic
closely with the direction of the ICT from the 7 position to lactone
carbonyl [38]. To exhibit such a strong ICT, 7 position is substituted
with N, N-diethyl donor group and 3 position by an acetyl group.
The formation of intramolecular hydrogen bonding with the
acceptor unit in D-A compounds is an effective way to lower the
bandgap. In that context, OH group is deployed at 4 position of
coumarin moiety for betterment of NLO response. The acetyl
moiety is further extended to a chalcone by substituting with
differently substituted phenyl and triphenylamine as strong donors
by Claisen-Schimidt condensation to achieve highly efficient D-A-D
NLO molecules with large first order hyperpolarizability (
b
) [24,25].
(
see Fig. 1)
m Dm
ge
ge
3
b
f
(1)
ꢀ
ꢁ
DE
eg
The first order hyperpolarizability
b is proportional to the
product of excess dipole moment (Dmge), the difference in dipole
moments between the ground ( ) and excited states ( ) and the
transition dipole moment ( ge). Also, is inversely proportional to
eg) between these two states. Increase in the
m
g
m
e
(D-p-A-p-D) NLOphoric system. The electronic property of the
m
b
substituents on the aromatic compounds can greatly affect the
electronic state of the entire molecule [39] hence phenyl and tri-
phenylamine donor part of coumarin chalcones are substituted
with methoxy group as an auxiliary donors which further helps to
improve solubility. This overall design strategy makes the coumarin
the energy gap (
DE
value of product
ge
m .Dmge and a decrease in
D
Eeg value lead to
maximization of the
b
value. Highly delocalized acentric p
-electron
systems interacting with suitably substituted electron donor and
electron acceptor group are known to exhibit a large value of the
chalcones as a rich
p-conjugated system with asymmetric distri-
first hyperpolarizability (
Thus NLO properties of organic molecules can be engineered by
tuning their HOMO-LUMO energy gap (HLG. For a -conjugated
b) and second hyperpolarizability (g) [26].
bution of electronic charge to realize large molecular hyper-
polarizability values. The further red shift in absorption may lead to
manifestation of enhanced hyperpolarizability characteristics
p
system like chalcones, an extension of the conjugation can lead to a
decrease in the HLG to a certain extent [27]. Considering the un-
desirable degradation of most of the organic molecules when
excited by high energy optical beams, chalcones are the better
candidates to enhance the NLO responses to avoid possible damage
of matrix [28e34]. Some simple coumarins are reported to show
significant NLO properties [11,26,35]. Further solid state emissive
D-A-D coumarin chalcones are reported to possess promising NLO
characteristics [33,36]. So in this study, we have investigated the
solvatochromism and NLO properties of newly designed D-A-D
which can be achieved by BF
40e42]. BF complexation of coumarin and dipyrromethane
moiety is often utilised to enhance its fluorescence characteristics
and photochemical stability [43e47]. Also BF complexation of
such type of ligands results into red shifted absorption and emissive
entities with enhanced NLO responses [42,48e50]. OBO difluoride
complexes are known to possess good solvatochromic properties
2
complexation of coumarin chalcones
[
2
2
[45,51e53]. The crucial role of the B(III) is to stabilize the ligand by
coordination and to make the -system planar to enhance the
p
conjugation and charge transfer along the molecular axis. This is
expected to furnish more efficient ICT for enhancement of NLO
properties of D-A-D coumarins. Thus synthesized chalcones and
type coumarin chalcones. From Oudar's formula, it is clear that
b is
intrinsically related to the charge-transfer excited states i.e ICT [4].
In coumarin chalcones, the ICTcan be assisted by lowering HLG [37]
which can be achieved by electron donating group at the 7 position
and/or an electron withdrawing group either at the 3 position via
resonance and inductive effects [38]. A donor at 7 position and
acceptor at 3 position resulting in the “push-pull” effect align more
2
their red shifted BF complexes were studied for their NLO prop-
erties by solvatochromic measurement and computations. Theo-
retical investigation of ground and excited state geometries and
energies, dipole moment, polarizability and hyperpolarizability are
Fig. 1. Structures of dyes 1 to 3 and 1a to 4a.

476
Y. Erande et al. / Dyes and Pigments 148 (2018) 474e491
performed using density functional theory (DFT). Red shifted ab-
sorption and emission maxima of BF complexes and better NLO
chemical computations while results were visualized with Gauss
View 5.0 [57]. The ground state (S ) geometry of all the compounds
2
0
characteristics than hydroxy chalcones of coumarin justify the
design approach.
To study the substituent effects on solvatochromic and NLO
2
properties, the hydroxyl chalcones and respective BF complexes
are differently substituted. Triphenylamines with auxiliary
methoxy donors are employed as stronger donors. 1a has ortho
methoxy and para N, N-diethylamino donors on phenyl ring in
addition to N, N-diethylamino group at 7 position while in 2a the
para nitrogen is substituted with two phenyl rings. In 3a and 4a the
donor capacity of these phenyl rings is further strengthened by
putting one and two methoxy groups at ortho positions respec-
was optimized in the gas phase using Density Functional Theory
(DFT) [58]. The popular hybrid functional B3LYP was used, which
combines Becke's three parameter exchange functional (B3) [59]
with the nonlocal correlation functional by Lee, Yang and Parr
(LYP) [60]. All the atoms were treated with 6e31g(d) basis set. The
validity of the structures as local minima on potential energy sur-
face was verified with vibrational analysis and confirmed that they
are with no imaginary frequencies. All the solvent phase optimi-
sations were carried out using the Polarizable Continuum Model
(PCM) [61] as implemented in Gaussian 09. Molecular hyper-
polarizability calculations of coumarins by quantum mechanical
approach were performed by using the same basis set 6e31g(d).
The CAM-B3LYP functional (range separated-generalised gradient
approximation (GGA)) has 19%e65% HartreeꢁFock exchange which
performs well for hyperpolarizability computations as compared to
B3LYP and BHandHLYP [62,63]. Hence CAM-B3LYP/6-31g(d)
2
tively. Compound 4 i.e. BF complex of 4a was not obtained in pure
form. All the coumarin chalcones 1a to 4a are solid and solution
state emissive mostly in non polar to mid polar media while their
BF
2
analogues exhibit comparatively intense red shifted fluid
emission, however, 1 to 3 are non emissive in the solid state.
method was used for the calculation of dipole moment(
izability( and hyperpolarizability characteristics of
coumarins.
m), polar-
2
. Experimental
a
)
(b, g)
2.1. Material and methods
2.4. Synthesis procedures
All the reagents were procured from SD Fine Chemicals
(
Mumbai) and were used without further purification. Laboratory
The chalcones were prepared by Claisen-Schmidt reaction be-
reagent grade solvents were purchased from Rankem, Mumbai. The
reactions were monitored by TLC using on 0.25 mm EMerck silica
gel 60 F254 precoated plates, which were visualized using UV light
tween aldehydes and 3-acetyl, 4-hydroxy, 7-N, N-diethyl coumarin.
2.4.1. Synthesis of (E)-8-(diethylamino)-4-(4-(diethylamino)-2-
methoxystyryl)-2,2-difluoro-5-oxo-2,5-dihydro-[1,3,2]
dioxaborinino[5,4-c]chromen-3-ium-2-uide; (dye 1)
(
254 nm and 344 nm). Melting points were measured on standard
melting point apparatus from Sunder Industrial Products, Mumbai
1
13 11
19
and are uncorrected. H, C, B and F [54,55] NMR spectra were
recorded on Varian 500 MHz instrument using TMS as an internal
standard. The absorption spectra of the compounds were recorded
on a Perkin-Elmer Lambda 25 UV-Visible spectrophotometer and
emission spectra were recorded on Varian Inc. Cary Eclipse
spectrofluorometer.
2
0.2 ml n-BuNH was added to the mixture of compound-8 (0.2 g,
0.96 mmol), compound 7 (0.4 g, 1.25 mmol) and dry toluene (20 ml)
under nitrogen atmosphere and resulting mixture was then
ꢀ
maintained at 100 C for 18 h. Completion of the reaction was
confirmed by TLC and then concentrated residue was purified by
column chromatography using chloroform: hexane (2.5:7.5) eluent
ꢀ
Cyclic voltammetric data were measured on a Autolab instru-
ment using a conventional three electrode cell with Pt metal as the
working electrode, Pt gauze as the counter-electrode, and Ag/
to afford pure solid (0.25 g, yield ¼ 51%). m. p. ¼ 260 C.
1
H NMR (500 MHz, CDCl
3
)
d
8.74 (d, J ¼ 14.9 Hz, 1H), 8.29 (d,
J ¼ 14.9 Hz, 1H), 7.94 (d, J ¼ 9.2 Hz, 1H), 7.69 (d, J ¼ 9.1 Hz, 1H), 6.62
AgNO
3
as the reference electrode at a scan rate of 100 mV/s. The
PF ) in
(dd, J ¼ 9.2, 2.3 Hz, 1H), 6.39e6.32 (m, 2H), 6.04 (s, 1H), 3.94 (s, 3H),
13
0
.1 M tetrabutylammonium hexa-fluorophosphate (NBu
4
6
3.53e3.43 (m, 8H), 1.26 (td, J ¼ 7.1, 4.8 Hz, 12H). C NMR (125 MHz,
dichloromethane was used as the electrolyte. The TGA was carried
3
CDCl ) d 179.1, 172.4, 163.4, 160.1, 157.9, 154.5, 154.2, 149.1, 133.7,
out using Perkin Elmer STA 6000 instrument with a heating rate of
128.2, 113.3, 111.8, 109.6, 105.9, 103.5, 96.6, 96.3, 92.8, 55.3, 45.2,
ꢀ
11
19
10 C/min under the nitrogen atmosphere.
12.7, 12.5. B NMR
d
¼ 0.24. F NMR
d
¼ ꢁ145.3 [54,55]. CHN
analysis: Expected: C-63.29, H-6.10, N-5.47. Results: C-63.27, H-
2.2. Z-scan experimental
6.11, N-4.48.
The nonlinear absorption coefficient (
index (n ) were simultaneously measured by the Z-scan technique
2
b
) and nonlinear refractive
2.4.2. Synthesis of (E)-8-(diethylamino)-4-(4-(diphenylamino)-2-
methoxystyryl)-2,2-difluoro-5-oxo-2,5-dihydro-[1,3,2]
dioxaborinino[5,4-c]chromen-3-ium-2-uide; (dye 2)
for dyes 1 to 3 and 1a to 4a. Samples were liquid solutions of DMSO
and acetone. In the Z-scan experiment, a laser beam was focused to
a minimum waist at the focal point which corresponds to the value
of Z ¼ 0 (Z is the beam propagation direction i.e. Z axis). A sample
was then moved along the path of the beam, by varying incident
beam intensity. The resulting distortion and changes in trans-
mittance of the beam were probed by two detectors, open-aperture
and closed-aperture detectors. For all the dyes, 0.3 mM solutions
were used for the Z-scan measurement which was performed by
using 532 nm Nd:YAG laser having 5ns pulses at a repetition rate of
2
0.2 ml n-BuNH was added to the mixture of compound 9 (0.2 g,
0.66 mmol), compound 7 (0.26 g, 0.8 mmol) and dry toluene
(20 ml) under nitrogen atmosphere and mixture was maintained at
ꢀ
100 C for 12 h. Reaction completion was confirmed by TLC and
then pure solid was obtained by filtration at room temperature
ꢀ
followed by toluene wash (0.2 g, yield ¼ 50%). m. p. ¼ 278 C.
1
H NMR (500 MHz, CDCl
3
)
d
8.68 (d, J ¼ 15.2 Hz, 1H), 8.40 (d,
J ¼ 15.2 Hz, 1H), 7.95 (d, J ¼ 9.2 Hz, 1H), 7.61 (d, J ¼ 8.7 Hz, 1H), 7.37
(t, J ¼ 7.6 Hz, 4H), 7.21 (d, J ¼ 7.1 Hz, 6H), 6.64 (d, J ¼ 10.7 Hz, 1H),
1
0 Hz. The results were used to evaluate the values of microscopic
6.55 (d, J ¼ 8.6 Hz, 1H), 6.43 (s, 1H), 6.37 (s, 1H), 3.73 (s, 3H), 3.49 (q,
(
3)
13
parameters
b
, n
2
and X of the dyes.
J ¼ 6.9 Hz, 4H), 1.27 (d, J ¼ 14.0 Hz, 6H). C NMR (125 MHz, CDCl
3
)
d
181.4, 173.3, 161.3, 159.6, 158.5, 158.4, 155.4, 152.1, 146.7, 145.0,
2
.3. Computational details
131.9, 130.0, 128.8, 127.2, 126.6, 119.2, 117.6, 116.0, 110.1, 105.5, 103.1,
11
19
97.6, 96.4, 55.7, 45.4, 12.5. B NMR
d
¼ 0.27. F NMR
d
¼ ꢁ144.39.
Gaussian 09 program [56] was used for all the quantum
CHN analysis: Expected: C-69.09, H-5.14, N-4.60,; Results: C-69.08,

Y. Erande et al. / Dyes and Pigments 148 (2018) 474e491
477
0
H-5.14, N-4.61.
2.4.6. Synthesis of 3,3'-((2E,2 E)-3,3'-((phenylazanediyl)bis(2-
methoxy-4,1-phenylene)) bis (acryloyl))bis(7-(diethylamino)-4-
hydroxy-2H-chromen-2-one); (dye 3a)
0
2
4
.4.3. Synthesis of 4,4'-((1E,1 E)-((phenylazanediyl)bis(2-methoxy-
,1-phenylene))bis(ethene-2,1-diyl))bis(8-(diethylamino)-2,2-
0
.1 ml of piperidine was added to the mixture of compound 10
0.1 g, 0.28 mmol), compound 6 (0.153 g, 0.56 mmol) and absolute
(
difluoro-5-oxo-2,5-dihydro-[1,3,2]dioxaborinino[5,4-c]chromen-3-
ium-2-uide); (dye 3)
ethanol (10 ml) under nitrogen atmosphere and mixture was
maintained at reflux for 12 h. Reaction completion was confirmed
by TLC and then residue was filtered at room temperature to afford
crude solid which was purified by column chromatography using
chloroform: hexane (4:6) as an eluent to afford pure red solid
0
.2 ml n-BuNH
2
was added to the mixture of compound 10
(
0.1 g, 0.28 mmol), compound 7 (0.268 g, 0.83 mmol) and dry
toluene (20 ml) under nitrogen atmosphere and the mixture was
maintained at 100 C for 16 h. Reaction completion was confirmed
by TLC and then residue was filtered to afford crude solid which
was purified by recrystalization from ethyl acetate (0.08 g,
ꢀ
(
0.17 g, yield ¼ 72%).
1
H NMR (500 MHz, CDCl
3
)
d
8.35 (q, J ¼ 15.8 Hz, 2H), 7.84 (d,
J ¼ 9.1 Hz, 1H), 7.61 (d, J ¼ 8.7 Hz, 1H), 7.32 (t, J ¼ 7.9 Hz, 4H), 7.17 (d,
ꢀ
yield ¼ 29.7%). m. p. ¼ 306e310 C.
J ¼ 7.5 Hz, 4H), 7.13 (t, J ¼ 7.4 Hz, 2H), 6.59 (dd, J ¼ 8.7, 1.9 Hz, 2H),
1
H NMR (500 MHz, CDCl
3
)
d
8.66 (d, J ¼ 15.4 Hz, 2H), 8.48 (d,
6
.52 (d, J ¼ 2.1 Hz, 1H), 6.37 (d, J ¼ 2.4 Hz, 1H), 3.72 (s, 3H), 3.45 (q,
J ¼ 15.4 Hz, 2H), 7.97 (d, J ¼ 9.2 Hz, 2H), 7.70 (d, J ¼ 8.6 Hz, 2H), 7.43
13
J ¼ 7.1 Hz, 4H), 1.24 (t, J ¼ 7.1 Hz, 6H). C NMR (125 MHz, CDCl
190.9, 180.6, 161.4, 160.2, 157.1, 153.5, 152.1, 146.6, 140.8, 130.4,
29.4, 127.1, 125.8, 124.4, 119.9, 117.5, 113.8, 108.8, 104.7, 103.5, 98.1,
3
)
(
(
3
t, J ¼ 7.7 Hz, 2H), 7.30 (d, J ¼ 7.4 Hz,1H), 7.23 (d, J ¼ 8.2 Hz, 2H), 6.73
d, J ¼ 8.6 Hz, 2H), 6.65 (d, J ¼ 8.5 Hz, 4H), 6.38 (s, 2H), 3.81 (s, 6H),
d
1
9
4
13
.50 (q, J ¼ 7.0 Hz, 8H), 1.28 (t, J ¼ 7.1 Hz, 12H). C NMR (125 MHz,
6.4, 55.4, 44.9, 12.4. CHN analysis: Expected: C-71.30, H-5.64, N-
.80,; Results: C-71.28, H-5.63, N-4.81.
3
CDCl ) d 173.3, 161.3, 159.6, 158.5, 155.3, 152.0, 146.7, 146.5, 144.9,
1
5
31.9, 130.1, 128.9, 127.2, 126.6, 119.2, 117.6, 115.9, 110.1, 105.5, 97.7,
5.9, 45.4,12.5. 11B NMR
d
¼ 0.26, ꢁ0.99. F NMR
19
d
¼ ꢁ144.13. CHN
analysis: Expected: C-64.28, H-4.88, N- 4.33; Results: C-64.27, H-
0
00
0
00
0
00
4
.88, N-4.33.
2.4.7. Synthesis of 3,3 ,3 -((2E,2 E,2 E)-3,3 ,3 -(nitrilotris(2-
methoxybenzene-4,1-diyl))tris(acryloyl))tris(7-(diethylamino)-4-
hydroxy-2H-chromen-2-one); (dye 4a)
.1 ml of piperidine was added to the mixture of compound 11
0.1 g, 0.24 mmol), compound 6 (0.2 g, 0.72 mmol) and absolute
ethanol (10 ml) under nitrogen atmosphere and mixture was
maintained at reflux for 15 h. Reaction completion was confirmed
by TLC and then residue was filtered at room temperature to afford
crude solid which was purified by recrystalization from ethanol to
2.4.4. Synthesis of (E)-7-(diethylamino)-3-(3-(4-(diethylamino)-2-
0
methoxyphenyl)acryloyl)-4-hydroxy-2H-chromen-2-one; (dye 1a)
.1 ml of piperidine was added to the mixture of compound-8
0.2 g, 0.97 mmol), compound 6 (0.27 g, 0.97 mmol) and absolute
(
0
(
ethanol (12 ml) under nitrogen atmosphere and mixture was
maintained at reflux for 12 h. Reaction completion was confirmed
by TLC and then residue filtered at room temperature to afford
crude solid which was further purified by recrystalization from
ꢀ
afford pure red solid (0.16 g, yield ¼ 56%). m. p. ¼ 186 C.
1
H NMR (500 MHz, CDCl
3
)
d
8.45 (d, J ¼ 15.7 Hz, 1H), 8.32 (d,
ethyl acetate: hexane (1:2) and then ethanol (0.28 g, yield ¼ 62%).
J ¼ 15.9 Hz, 1H), 7.85 (d, J ¼ 9.1 Hz, 1H), 7.71 (d, J ¼ 8.5 Hz, 1H), 6.78
1
H NMR (500 MHz, CDCl
3
)
d
8.42 (d, J ¼ 15.8 Hz, 2H), 8.32 (d,
(
3
d, J ¼ 7.6 Hz, 1H), 6.70 (s, 1H), 6.60 (d, J ¼ 8.9 Hz, 1H), 6.38 (s, 1H),
J ¼ 15.8 Hz, 2H), 7.84 (d, J ¼ 9.1 Hz, 2H), 7.67 (d, J ¼ 8.6 Hz, 2H), 7.37
t, J ¼ 7.9 Hz, 2H), 7.20 (d, J ¼ 9.1 Hz, 3H), 6.70 (dd, J ¼ 8.5, 1.9 Hz,
H), 6.65 (d, J ¼ 2.0 Hz, 2H), 6.60 (dd, J ¼ 9.1, 2.4 Hz, 2H), 6.37 (d,
J ¼ 2.3 Hz, 2H), 3.77 (s, 6H), 3.44 (d, J ¼ 7.1 Hz, 8H), 1.24 (t, J ¼ 7.1 Hz,
3H). 13C NMR (125 MHz, CDCl
191.1, 180.3, 161.4, 159.9, 157.2,
53.5, 150.7, 145.8, 140.1, 130.5, 129.7, 127.2, 126.5, 125.4, 121.3,
19.22, 115.9, 108.8, 105.9, 104.4, 98.1, 96.4, 55.6, 44.8, 12.2. CHN
analysis: Expected: C-69.81, H- 6.94, N-6.03; Results: C-69.79, H-
13
.81 (s, 3H), 3.46 (d, J ¼ 7.0 Hz, 4H), 1.24 (t, J ¼ 7.0 Hz, 6H). C NMR
(
2
(
125 MHz, CDCl 191.1, 180.3, 161.4, 159.9, 157.2, 153.4, 149.7,
3
) d
1
5
39.7, 130.5, 127.1, 122.1, 120.1, 116.93, 108.9, 107.0, 104.4, 98.1, 96.2,
5.8, 44.8, 12.4. CHN analysis: Expected: C-69.57, H-5.58, N-4.70;
Results: C-69.55, H-5.57, N-4.71.
1
1
1
3
) d
6
.93, N-6.04.
2.5. Synthesis of 7-(diethylamino)-4-hydroxy-2H-chromen-2-one
(compound 5)
2
2
2
.4.5. Synthesis of (E)-7-(diethylamino)-3-(3-(4-(diphenylamino)-
-methoxyphenyl)acryloyl)-4-hydroxy-2H-chromen-2-one; (dye
a)
Compound 5 was synthesized according to reported method
64].
[
0
.1 ml of piperidine was added to the mixture of compound 9
(
0.15 g, 0.49 mmol), compound 6 (0.136 g, 0.49 mmol) and absolute
ethanol (8 ml) under nitrogen atmosphere and mixture was
maintained at reflux for 12 h. Reaction completion was confirmed
by TLC and residue was filtered at room temperature to afford crude
solid which was purified by column chromatography using ethyl
acetate: hexane (2:8) as an eluent to afford pure red solid (0.22 g,
2.6. Synthesis of 3-acetyl-7-(diethylamino)-4-hydroxy-2H-
chromen-2-one; (compound 6)
A mixture of compound 5 (6 g, 25.7 mmol), acetic anhydride
ꢀ
(5 g) and pyridine (10.4 ml) was maintained at reflux (125 C) under
ꢀ
yield ¼ 79%). m. p. ¼ 224 C.
nitrogen for 2.5 h. Completion of the reaction was confirmed by
TLC. Brown crystals were obtained from mixture on 12 h standing
at room temperature, and the solution was then diluted with water
(25 ml). The residue was filtered and washed with isopropyl alcohol
1
H NMR (500 MHz, CDCl
3
)
d
8.76 (d, J ¼ 15.9 Hz, 1H), 8.49 (d,
J ¼ 15.9 Hz, 1H), 7.84 (d, J ¼ 9.1 Hz, 1H), 6.58 (d, J ¼ 9.1 Hz, 1H), 6.35
(
d, J ¼ 2.4 Hz, 1H), 6.13 (s, 2H), 3.95 (s, 6H), 3.85 (s, 3H), 3.44 (q,
1
3
ꢀ
J ¼ 7.1 Hz, 4H), 1.23 (t, J ¼ 7.1 Hz, 6H). C NMR (125 MHz, CDCl
3
)
(7 ml) to afford pure solid (5.5 g, yield ¼ 78%). m. p. ¼ 140 C.
1
d
192.0, 180.7, 163.8, 162.1, 161.5, 157.1, 153.4, 137.2, 127.1, 122.2,
3
H NMR (500 MHz, CDCl ) d 7.72(s, 1H), 6.53 (s, 1H), 6.30 (s, 1H),
13
108.7, 107.2, 104.9, 98.3, 96.4, 90.4, 55.8, 55.4, 44.9, 12.4. CHN
3.39 (s, 4H), 2.64 (s, 3H), 1.18 (s, 6H). C NMR (125 MHz, CDCl
204.4, 177.7, 161.2, 157.4, 153.8, 127.0, 109.1, 102.7, 98.4, 96.4, 45.0,
29.76, 12.4.
3
)
analysis: Expected: C-74.98, H-5.75, N-5.00; Results: C-74.95, H-
d
5
.74, N-5.02.

478
Y. Erande et al. / Dyes and Pigments 148 (2018) 474e491
2
2
.7. Synthesis of 8-(diethylamino)-2,2-difluoro-4-methyl-5-oxo-
,5-dihydro-[1,3,2]dioxaborinino [5,4-c]chromen-3-ium-2-uide;
pure compound as yellow solid (yield ¼ 85%).
1
H NMR (500 MHz, CDCl
3
)
d
10.11 (s,1H), 7.68 (dd, J ¼ 8.9, 2.8 Hz,
(
compound 7)
1H), 6.26 (d, J ¼ 8.8 Hz, 1H), 6.02 (s, 1H), 3.87 (s, 3H), 3.41 (dd,
J ¼ 6.9, 2.7 Hz, 4H), 1.21 (t, J ¼ 5.4 Hz, 6H).
13
A mixture of compound 6 (4 g, mmol), acetic anhydride (2.5 g)
3
C NMR (125 MHz, CDCl ) d: 187.1, 164.1, 153.8, 130.7, 114.2,
ꢀ
and acetonitrile (20 ml) was maintained at 70 C for 10 min under
104.2, 92.4, 55.2, 44.7, 12.5 (see Fig. 2).
3 2
nitrogen atmosphere. Then after adding F B:OEt (2.2 ml) mixture
was maintained at reflux for 5 min and then allow to stand at room
temperature for 12 h. The residue was filtered and washed with
3. Results & discussion
acetonitrile (3 ml) and hexane (5 ml) to afford pure yellow crystals
ꢀ
3.1. Optical properties
(
4.5 g, yield ¼ 95%). m. p. ¼ 210e213 C.
1
H NMR (500 MHz, CDCl
3
)
d
7.92 (dd, J ¼ 9.3, 2.6 Hz, 1H), 6.65 (d,
Absorption and emission properties of the chalcones and their
J ¼ 7.2 Hz, 1H), 6.35 (s, 1H), 3.51 (dd, J ¼ 7.0, 2.5 Hz, 4H), 2.83 (s, 3H),
.27 (t, 6H). 13C NMR (125 MHz, CDCl
196.2, 173.1, 159.2, 159.1,
56.2, 129.3, 110.5, 101.9, 99.2, 96.5, 45.5, 26.3, 12.4.
BF complexes were extensively studied in ten solvents of varying
2
1
1
3
) d
polarity ranging from non polar toluene to highly polar DMSO. As a
representative absorption and emission plots in ten solvents for dye
Compound 8, 9, 10 and 11 were synthesized according to re-
ported procedure [65,66].
2a and 2 are presented in Fig. 3. Absorption and emission plots for
dye 1a, 3a, 4a, 1 and 3 are presented in supporting information
(Figs. S1 and S2).
2
8
.8. Synthesis of 4-(diethylamino)-2-methoxybenzaldehyde; (comp
)
Coumarin chalcones do not show notable absorption sol-
vatochromism. In case of coumarin chalcones from 1a to 4a, as size
and branching in the chromophores increases the max of absorp-
tion show only little red shift. But in case of their BF complex
analogues the max of absorption show bathochromic shift from dye
1 to 3 and show absorption solvatochromism in the tested solvents.
As compared to the chalcones the corresponding BF analogues
show red shifted absorption and the red shift increases from
toluene to DMSO. In toluene, dyes 3a and 3 have absorption
498 nm and 594 nm respectively while in DMSO dye 3a and3 have
max of absorption ¼ 517 nm and 627 nm respectively.
l
A mixture of 4-diethylamino-2-hydroxy benzaldehyde (5.8 g,
2
3
0 mmol), KOH (2 g, 35 mol) and K
2
CO
3
(8.3 g, 60 mmol) in
l
ꢀ
acetonitrile (30 ml) was heated for 10 min at 80 C. MeI (3.5 ml,
5
continued for another 2 h at 80 C. The reaction mixture was then
cooled to room temperature filtered. The filtrate was concentrated
under reduced pressure and chromatographed on silica gel column
6 mmol) was added to this alkaline mixture and stirring was
2
ꢀ
lmax of
(
mesh sizee120-200) eluting with EtOAc/hexane in 1:3 ratio to get
l
Fig. 2. Scheme-1: a) Acetic anhydride, pyridine, reflux; b) Acetic anhydride, acetonitrile, F3B:OEt2; c) nBuNH2, chloroform/toluene, heat; d) Piperidine, absolute ethanol, heat.

Y. Erande et al. / Dyes and Pigments 148 (2018) 474e491
479
All the four coumarin chalcones exhibit high molar absorptivity
values in studied solvents. The molar absorptivities were further
enhanced in their BF complexed analogues, dye 1 to 3. Dye 3
possesses maximum molar absorptivity as it has more branched
system as compared to the dyes 1 and 2. Same trend was observed
for the dyes 1a to 4a series. Absorption and emission data for the
dyes 1 to 3 and 1a to 4a are summarised in Tables 1 and 2
3.2. Charge transfer characteristics
2
The transition dipole moment associated with excitation from
ground to excited state. The charge transfer character of these
chromophores was evaluated from transition dipole moment (
Transition dipole moment for absorption is a measure of the
probability of * a transition from ground to excited state and it
meg).
p-p
respectively. Here both the coumarin chalcones and BF
2
com-
has been calculated for all dyes in ten solvents using the eq. (2) [67].
plexed chalcones show strong emission solvatochromism in the
examined solvents. The polarity driven red shift in emission max-
ima from toluene to DMSO for coumarin chalcones are as follows:
f
2
m
¼
(2)
eg
ꢁ7
4
:72X 10 X v
The values of transition dipole moment for dyes 1 to 3 and 1a to
a are listed in Tables 3 and 4 respectively. The eg goes on
increasing from 1a to 4a as branching increases in coumarin chal-
cones, while the corresponding BF analogues 1 to 3 exhibit higher
eg values than the dyes 1a to 3a.
The charge transfer properties of push-pull chromophores
depend on the solute-solvent interactions. Hence the photophysical
properties studied in the solvents of different polarity is important
to determine charge transfer characteristics of these chromo-
phores. The dipole moment difference between ground and excited
state (Dmeg) which is also known as excess dipole moment of charge
transfer is obtained by modified McRae equation developed by the
Suppan [68,69]. Suppan equation for the difference in frequency of
emission for two different solvents 1 and 2 is as below,
dyes 1a/49 nm, 2a/60 nm, 3a/66 nm, 4a/41 nm and for BF
plexed chalcones are as dye 1/52 nm, 2/52 nm, 3/90 nm. These
chromophores are D- -A type push-pull systems, and hence the
2
com-
4
m
p
resulting dipoles undergo polarity driven increase in solvent sta-
bilisation moving from toluene to DMSO. This polarity driven sta-
bilisation utilises the excited state energy, which is the maximum
in highly polar solvents hence emission maxima is red shifted with
increased polarity. Increased loss of excitation energy with
increasing polarity of solvents resulted in reduced fluorescence
quantum yields and in highly polar solvents like acetone, methanol,
acetonitrile, DMF and DMSO all coumarins are non emissive. In
remaining solvents they show good fluorescence quantum yields
which is accounted on the scale of radiative rate constant (Kr) ob-
tained by Strickler Berg equation (presented in supp. info. eq. (S1)
and the values are presented in Tables 1 and 2. Emission quan-
tum yields were obtained by using Rhodamine-6G (ɸ ¼ 0.94 in
ethanol) as reference. The Stokes shift values are also increased
from toluene to DMSO for coumarin chalcones and further from dye
2
m
2
2
m
egDmge
hca3
m
ꢁ
m
e
g
ꢁDn1
¼
D
½ fðε
s
Þ ꢁ fðn Þꢂ1ꢁ2 þ
s
ꢁ2
3
hca
1
a to 3a. A compared to chalcones the BF
2
complexed chromo-
ꢁ
D
fðn
s
Þ 1ꢁ2
(3)
phores show reduced Stokes shift, but increasing trend was same.
where, n is the corresponding solution phase frequency of emission,
Fig. 3. Absorption and emission plots of dye 2a and 2.

480
Y. Erande et al. / Dyes and Pigments 148 (2018) 474e491
Table 1
Absorption and emission data of dyes 1, 2 and 3.
a
εb
fwhmc
f d
e
emf
g
Kr x (108)h
Knr x (108)i
Ʈsj
Solvent
l
abs
l
em
Stokes shift
F
m
ge
(Lmol 1cmꢁ1
ꢁ
)
(cm
ꢁ1
)
(nm)
(nm)
(cm
ꢁ1
)
(Debye)
(S
ꢁ1
)
(S
ꢁ1
)
(ns)
(
nm)
1
Toluene
THF
EtOAc
DCM
566
578
573
588
582
588
587
593
604
612
81666
1580
1584
1628
1515
1459
1595
1720
1588
1621
1560
0.49
0.85
0.98
0.88
0.91
1.02
1.03
0.90
0.98
0.98
596
612
610
626
617
626
628
632
640
648
30
34
37
38
35
38
41
39
36
36
889
961
1059
1032
975
1032
1112
1041
931
0.87
0.71
0.28
0.16
0.74
7.68
1.94
2.78
3.04
2.81
3.09
2.98
2.86
2.52
3.05
3.17
0.28
1.14
8.01
14.75
1.06
4.50
2.55
0.90
0.57
2.41
131819
146069
139754
148410
154315
146951
130218
146069
149546
10.23
10.92
10.49
10.64
11.31
11.37
10.69
11.20
11.31
CHCl
3
Acetone
MeOH
ACN
DMF
DMSO
2
908
Toluene
THF
EtOAc
DCM
564
572
566
583
580
579
577
581
595
597
73337
63709
49771
71455
76455
71223
64078
75450
71223
55525
1953
1841
1606
2241
2068
2309
2168
2004
2159
1856
0.57
0.42
0.29
0.65
0.61
0.69
0.58
0.61
0.62
0.44
611
635
630
659
645
650
646
648
654
663
47
63
64
76
65
71
69
67
59
66
1364
1734
1795
1978
1738
1887
1851
1780
1516
1667
0.80
0.65
0.23
0.08
0.63
8.27
7.12
5.93
8.99
8.67
9.22
8.48
8.71
8.87
7.52
1.96
1.20
0.80
1.59
1.74
1.76
1.74
0.12
0.82
1.00
0.48
0.64
2.66
19.32
1.03
4.09
5.42
2.89
0.48
3.61
CHCl
3
Acetone
MeOH
ACN
DMF
DMSO
3
Toluene
THF
EtOAc
DCM
594
601
597
616
613
612
606
612
611
627
82078
151414
98593
172217
150480
128593
128986
124143
120363
74205
5455
3607
4351
2718
2950
3419
4130
3710
2919
5257
7.73
3.94
4.48
2.41
2.55
3.29
4.56
4.00
1.65
5.53
635
661
658
680
665
677
41
60
61
64
52
65
1087
1510
1553
1528
1276
1569
0.79
0.69
0.19
0.12
0.65
31.27
22.44
23.87
17.77
18.24
20.71
24.25
22.85
14.67
27.17
2.01
8.10
6.47
5.39
5.31
7.10
0.00
3.65
4.13
10.95
0.54
3.61
28.52
40.64
2.81
3.92
0.85
0.29
0.22
1.23
CHCl
3
Acetone
MeOH
ACN
DMF
DMSO
709
704
725
97
93
98
2235
2162
2156
a
Experimental absorption maxima.
b
c
d
e
f
ꢁ1
ꢁ1
.
Molar extinction coefficient at absorption maxima L.M .cm
Full width at half absorption maxima.
Oscillator strength.
Experimental emission maxima.
Fluorescence quantum yields.
Transition dipole moment.
Radiative rate constant.
Non radiative rate constant.
Fluorescence lifetime.
g
h
i
j
f(n
s
) and f(ε
s
) are the refractive index and dielectric medium
3.3. Generalised Mulliken Hush (GMH) analysis
functions of solvent, h and c are Planck's constant and velocity of
light respectively, a is the Onsager cavity radius. and are the
and Dmge are
m
me
g
e
m
g
The charge transfer properties of the synthesized chromophores
were further studied by using Generalised Mulliken Hush analysis
(GMH). The eq. (5) for two state GMH analysis which accounts the
intramolecular charge transfer (ICT) character of molecule is as
follows [70],
ground and excited state dipole moments,
mentioned earlier.
Eq. (3) was presented by Ayachit et al. in the following format
69],
[
2
ab
2
2
Dm
¼
Dm þ 4
ge
m
(5)
ge
X
C1
Y
C2
þ
¼ 1
(4)
2
2
The Dm and
m
terms are obtained from Suppan equation and
ge
ge
absorption plots respectively and are listed in Tables 3 and 4 for all
the chromophores. GMH analysis states that the electronic coupling
between donor (D) and acceptor (A) group is an important factor in
controlling the charge transfer of D-A systems [71]. Hence in order
to understand the behaviour of long distance charge transfer, the
electronic coupling matrix elements (Hab) is crucial parameter,
where a and b refer to the initial and final diabatic states and the
3
¼ hca3/(m2
m2
where C
1
¼ hca /(
m
g
Dmg-e) and C
and C
2
e
ꢁ
g
).
The values of C
1
2
are obtained using least square fit
method. Onsager radii and ground state dipole moment were ob-
tained from the DFT optimized geometries. Using these values the
Dmge values are calculated and summarised in Tables 3 and 4. The
Dmeg values presented as DmCT which increases from the dye 1 to 3
and 1a to 3a as branching increases. Thus increased branching
strengthens the ICT character of chromophores, which is desirable
to obtain higher NLO response. These values are further utilised for
hyperpolarizability calculations by the solvatochromic method.
Hab in adiabatic state of D-p-A systems can be denoted as HDA
which was calculated by using eq. (6). The degree of delocalization
2
b
or fractional degree of localization (C ) of the excess charge for the
diabatic states was obtained by eq. (7),

Y. Erande et al. / Dyes and Pigments 148 (2018) 474e491
481
Table 2
Absorption and emission data of dyes 1a, 2a, 3a and 4a.
a
εb
fwhmc
f d
e
emf
g
Kr x (108)h
Knr x (108)i
Ʈsj
Solvent
l
abs
l
em
Stokes shift
F
m
ge
(Lmol 1cmꢁ1
ꢁ
)
(cm
ꢁ1
)
(nm)
(nm)
(cm
ꢁ1
)
(Debye)
(S
ꢁ1
)
(S
ꢁ1
)
(ns)
(
nm)
1a
Toluene
THF
EtOAc
DCM
485
496
490
504
503
502
502
503
514
524
52258
62870
59818
61662
64877
74205
63260
62870
68662
71455
2986
3013
3242
3252
3053
3145
3664
3288
3164
3201
0.70
0.84
0.90
0.94
0.90
1.06
1.07
0.95
0.97
1.06
546
564
559
576
568
578
578
583
589
595
61
68
69
72
65
76
76
80
75
71
2304
0.39
0.44
0.48
0.39
0.41
8.51
9.39
9.69
10.06
9.79
10.67
10.71
10.07
10.35
10.88
2.91
2.86
2.92
3.05
3.17
3.21
2.93
2.72
3.13
3.50
4.55
3.68
3.14
4.75
4.54
1.34
1.53
1.65
1.28
1.30
2431
2519
2480
2275
2619
2619
2728
2477
2277
CHCl
3
Acetone
MeOH
ACN
DMF
DMSO
2a
Toluene
THF
EtOAc
DCM
481
475
475
481
484
478
29631
31300
31230
31927
28427
34574
3397
3205
3563
3682
3384
3541
0.41
0.36
0.46
0.50
0.40
0.52
554
578
576
602
590
603
73
2739
3752
3692
4179
3712
4337
0.48
0.54
0.49
0.66
0.73
6.52
6.01
6.81
7.17
6.39
7.29
0.00
6.14
5.82
6.91
1.56
1.17
1.35
1.42
1.25
1.38
0.00
0.87
0.89
1.41
1.69
0.99
1.38
0.72
0.47
3.08
4.63
3.67
4.66
5.83
103
101
121
106
125
CHCl
3
Acetone
MeOH
ACN
DMF
DMSO
485
484
493
22889
22310
28981
3768
4057
3746
0.36
0.33
0.45
610
617
614
125
133
121
4225
4454
3997
3a
Toluene
THF
EtOAc
DCM
498
502
496
508
510
502
490
501
439
517
70240
81013
77215
80740
61866
79155
41039
77967
48493
71444
5641
5338
5273
5778
5946
5410
7378
5656
1.77
1.84
1.74
2.04
1.59
1.86
1.51
2.00
1.65
1.66
568
595
590
611
599
615
599
618
519
634
70
93
94
103
89
113
109
117
80
2475
3114
3212
3318
2913
3660
3714
3779
3511
3569
0.51
0.23
0.21
0.29
0.39
13.69
14.01
13.58
14.87
13.13
14.11
12.53
14.61
39.23
13.51
5.40
4.58
4.24
4.71
3.83
3.86
2.23
3.65
47.16
4.08
5.16
0.95
0.50
0.50
0.62
1.02
15.52
15.65
11.37
5.93
CHCl
3
Acetone
MeOH
ACN
DMF
DMSO
21302
5318
117
4a
Toluene
THF
EtOAc
DCM
493
494
491
498
499
495
196592
216573
218000
229643
207791
246483
4423
4391
4535
4753
4764
4514
3.50
3.82
4.09
4.44
3.95
4.54
595
598
595
614
603
624
102
104
104
116
104
129
3477
3521
3560
3794
3456
4176
0.59
0.38
0.32
0.42
0.53
19.16
20.05
20.69
21.71
20.49
21.88
0.00
0.00
111.36
23.44
9.48
9.88
9.62
10.17
9.90
9.54
0.00
0.00
21.00
10.14
6.48
0.63
0.38
0.33
0.41
0.54
16.12
20.91
14.33
8.78
CHCl
3
Acetone
MeOH
ACN
DMF
DMSO
454
507
136058
223108
28111
5144
1.28
5.09
543
636
89
129
3610
4001
a
Experimental absorption maxima.
b
c
d
e
f
ꢁ1
ꢁ1
.
Molar extinction coefficient at absorption maxima L.M .cm
Full width at half absorption maxima.
Oscillator strength.
Experimental emission maxima.
Fluorescence quantum yields.
Transition dipole moment.
Radiative rate constant.
Non radiative rate constant.
Fluorescence lifetime.
g
h
i
j
D
E
ge
·
mge
D
E
ge·mge
ge
DE ·m
ge
HDA
¼
(6)
HDA
¼
(8)
¼ qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
Dmab
Dm
D
2
2
ge
Dm þ 4
m
ge
ge
0
vffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1
u
u
t
Dmge
2
The charge separation distance in the charge transfer process
from D to A in coumarin chalcones and BF
determined by the eq. (9) [73,74],
1
2
2
b
@
A
C ¼
1 ꢁ
(7)
2
complexes can be
2
2
Dm þ 4
m
ge
ge
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
Within two level approximation in eq. (6), the HDA is correlated
ge
DE εmaxDn
1=2
with the vertical excitation energy (
the adiabatic dipole moments of the ground and excited states
Dmge), and the difference in diabatic state dipole moments (Dm ge
DE
ge), the difference between
RDA ¼ 2:06 ꢃ 10ꢁ
2
(9)
H
DA
D
)
and the transition dipole moments by the GMH model [71e73] is
correlated as eq. (8),
where RDA is the distance between the centroids of the donor and
acceptor orbitals (Å), DEge is vertical excitation energy (cm ), εmax
ꢁ
1

482
Y. Erande et al. / Dyes and Pigments 148 (2018) 474e491
is molar absorptivity (L.M 1.cmꢁ1), Dn1/2 is bandwidth (cm ) and
ꢁ
ꢁ1
demonstrates that the electron density is effectively moved from
donor to acceptor and also spread over the -conjugation path.
Such efficient delocalization of electron density over D- -A
ꢁ
1
H
DA is donor acceptor electronic coupling matrix (cm ). The values
of C , HDA and RDA were calculated using eqs. (7)e(9) for dyes 1 to 3
p
2
p
b
framework is an important aspect of ICT which is responsible for
significant NLO response of the molecule [4,75]. The Same type of
electronic arrangement was observed in dyes 1a to 4a in Table S1
and 1a to 4a are summarised in Tables 3 and 4 respectively. When
the value of C2 is zero then it is considered as total delocalization
b
of charges over the D-p-A framework and when it is unity then it is
(supp.info.).
total localization of the charge. The values of C b2 for all coumarin
chromophores in all solvents are far less than unity and
approaching towards the zero which signify the high degree of
delocalization. This suggests the strong ICT character of these
chromophores.
3.4. Electrochemical analysis
Electrochemical properties of the coumarin chromophores were
studied by cyclic voltammetry (CV) measurements. The CV mea-
surements were conducted in degassed anhydrous dichloro-
methane solutions and 0.1 mol/L tetrabutylammonium
Usually, the ICT from donor to acceptor in a molecular system is
characterized by the excitation of an electron from HOMO to LUMO.
Hence to see the nature ICT in the designed coumarin systems, we
have plotted the FMOs from DFT geometry optimized structures of
the chromophores using B3LYP/6-31g(d) method. Table 5 and
Table S1 (supp.info.) shows the HOMO and LUMO level frontier
molecular orbital (FMO) diagrams of dyes 1 to 3 and 1a to 4a.
HOMO for dyes 1 to 3 show that electron density is located on N, N-
diethylamino and N-arylamino part of the molecule as well as the
hexafluorophosphate (NBu
The CV plots for dye 1 to 3 and 1a to 4a are shown in Fig. S3
supp.info.).
4 6
PF ) used as a supporting electrolyte.
(
ꢂ
ꢃ
oxd
EHOMO ¼ ꢁ E
þ 4:8 eV
(10)
(11)
onset
ꢂ
ꢃ
over the
p-linker framework, while in LUMO the electron density is
red
ELUMO ¼ ꢁ E
þ 4:8 eV
onset
located on OBO core along with
p-linker framework. This
optical
g
1240
¼ l
E
(12)
Table 3
onset
Charge transfer characteristics data of dyes 1 to 3.
The HOMO and LUMO energies of the chromophores were
Solvent aa x10ꢁ8 IACb x108
m
c
DmCTd
D e
Dmge
C
2f
H
g
R
DA
h
ge
b
DA
calculated from their corresponding oxidation and reduction po-
tentials using eqs. (10) and (11) respectively [76]. Difference be-
tween their values provides the HOMO-LUMO energy difference
ꢁ1
ꢁ2
ꢁ1
cm
cm
M
cm
Debye Debye Debye
Å
1
Toluene 6.22
1.13
1.97
2.26
2.03
2.12
2.37
2.39
2.09
2.26
2.27
7.68
9.46
18.04 0.24 7522 4.13
22.07 0.31 8017 4.88
23.66 0.31 8056 5.21
22.71 0.31 7854 4.98
22.99 0.31 7953 5.00
23.97 0.33 8027 5.25
24.16 0.33 8013 5.33
22.71 0.33 7935 4.85
23.63 0.34 7848 5.20
23.99 0.33 7703 5.22
D
E/BG (CV). Optical BG for all chromophores was calculated using
THF
EtOAc
DCM
6.26
6.41
6.39
6.26
10.23 8.29
10.92 9.09
10.49 8.70
10.64 8.70
11.31 7.91
11.37 8.20
10.69 7.68
11.20 7.52
11.31 8.00
eq. (12), where onset was measured in long wave direction in ab-
l
sorption spectra. The HOMO, LUMO and corresponding BG were
obtained from DFT calculations for coumarin dyes. All the CV, op-
tical DFT values of HOMO, LUMO and BG energies are summarised
CHCl
3
Acetone 6.30
MeOH
ACN
DMF
DMSO
2
6.35
6.25
6.20
6.34
2
in Table 6 for all the coumarin chalcones and BF complexes. As
shown in Table 6 it is observed that oxidation potential was lowered
as branching increases. This decrease of oxidation potential was
also attributed to the increased donor strength with auxiliary
methoxy donors. The trend observed in CV values of oxidation
potential was followed by the values obtained from DFT. However,
the same trend between CV and DFT values was not observed in
case of reduction potential and BG. Further, the optical BG was
reduced from dye1 to 3 and 1a to 4a as branching increases and the
same trend was reproduced by corresponding DFT values.
Toluene 6.57
1.32
0.96
0.67
1.51
1.41
1.60
1.35
1.42
1.44
1.03
8.27
7.12
5.93
8.99
8.67
9.22
8.48
8.71
8.87
7.52
15.58 22.72 0.16 6452 5.09
13.22 19.42 0.16 6405 4.61
13.70 18.11 0.12 5777 4.24
12.82 22.07 0.21 6982 4.89
14.31 22.48 0.18 6649 5.12
12.60 22.33 0.22 7129 4.87
13.19 21.48 0.19 6838 4.67
12.52 21.45 0.21 6989 4.75
12.51 21.71 0.21 6867 4.82
12.07 19.28 0.19 6531 4.14
THF
EtOAc
DCM
6.56
6.60
6.52
6.62
CHCl
3
Acetone 6.60
MeOH
ACN
DMF
DMSO
3
6.68
6.59
6.59
6.52
3.5. Thermal stability study
Toluene 7.53
17.89
9.11
10.37
5.57
5.90
7.61
10.55
9.27
3.83
31.27 23.62 66.84 0.32 7874 7.18
22.44 19.97 49.12 0.30 7601 8.17
23.87 21.47 52.33 0.29 7638 7.23
17.77 18.78 40.18 0.27 7176 7.91
18.24 21.52 42.34 0.25 7025 7.89
20.71 19.03 45.57 0.29 7423 7.44
24.25 18.91 52.04 0.32 7687 7.95
22.85 16.87 48.69 0.33 7664 7.37
14.67 18.78 34.83 0.23 6891 7.17
27.17 20.07 57.91 0.33 7480 6.87
Thermal stability is a very important aspect of NLO materials for
THF
EtOAc
DCM
7.46
7.60
7.34
7.54
their applications in devices [77]. During device operations, NLO
molecules exhibit particular orientation under the influence of
optical poling or static electric field. For enduring device efficiency,
the stability of such induced alignment of NLO molecules is
important. Thus to withstand the poling and fabrication processes
the thermal stability of the NLOphore is crucial. In this context, the
replacement of dialkylamino donors by diaryamino donors has
shown a remarkable improvement in thermal stability of NLO-
phores [78]. Also in case of NLOphores with bulky triphenylamine
substituted group embedded in the small free volume of poling
matrix, the stability of the poling induced alignment may poten-
tially get improved after heat treatment [79]. Hence replacement of
N-ethyl groups in dye 1a/a by phenyl groups by use of triphenyl-
amine core with auxiliary methoxy donors in dyes 2a/2, 3a/3 and 4
is worth to design the thermally stable NLOphores. The thermal
CHCl
3
Acetone 7.49
MeOH
ACN
DMF
7.44
7.19
7.46
7.63
DMSO
12.79
a
Onsager radius.
Integrated area of absorption coefficient.
Oscillator strength.
Transition dipole moment.
Difference between ground and excited state dipole moments evaluated using
b
c
d
e
Lippert-Mataga solvent polarity parameter.
f
Dipole moment change between the diabatic states.
Degree of delocalization.
Electronic coupling matrix/Strength of electronic coupling between the ground
g
h
(
S
0
) and charge transfer excited states.
2
stabilities of the coumarin chalcones and BF complexes were

Y. Erande et al. / Dyes and Pigments 148 (2018) 474e491
483
Table 4
Charge transfer characteristics data of dyes 1a to 4a.
aa x10ꢁ8
IACb x108
m
c
DmCTd
D e
Dmge
C
2f
H
DA
g
R
DA
h
Solvent
ge
ꢁ1
ꢁ2
ꢁ1
cm
cm
M
cm
Debye
Debye
Debye
Å
1a
Toluene
THF
EtOAc
DCM
6.30
6.23
6.17
6.10
6.27
6.09
6.27
6.05
6.30
6.10
1.62
1.93
2.08
2.18
2.07
2.46
2.48
2.19
2.25
2.46
8.51
9.39
9.69
10.06
9.79
10.67
10.71
10.07
10.35
10.88
32.11
26.37
26.25
24.42
28.32
22.89
25.33
22.43
25.29
22.85
36.34
32.38
32.62
31.63
34.43
31.29
33.16
30.14
32.64
31.55
0.06
0.09
0.10
0.11
0.09
0.13
0.12
0.13
0.11
0.14
4827
5848
6060
6306
5652
6789
6428
6639
6148
6581
7.65
6.88
6.76
6.52
7.23
6.54
6.89
6.29
6.89
6.54
CHCl
3
Acetone
MeOH
ACN
DMF
DMSO
2a
Toluene
THF
EtOAc
DCM
6.40
6.62
6.47
6.47
6.43
6.60
6.56
6.51
6.58
6.45
0.96
0.83
1.06
1.16
0.92
1.21
6.52
6.01
6.81
7.17
6.39
7.29
76.85
68.43
65.72
62.81
67.00
61.55
77.95
69.47
67.11
64.43
68.21
63.25
0.01
0.01
0.01
0.01
0.01
0.01
1737
1821
2137
2312
1934
2410
17.15
16.44
14.76
13.93
15.01
13.68
CHCl
3
Acetone
MeOH
ACN
DMF
DMSO
0.84
0.76
1.05
6.14
5.82
6.91
58.91
60.88
57.10
60.17
61.98
58.75
0.01
0.01
0.01
2103
1939
2385
13.06
14.53
12.82
3a
Toluene
THF
EtOAc
DCM
7.32
7.35
7.52
7.39
7.30
7.66
7.33
7.39
7.35
7.62
4.09
4.25
4.04
4.73
3.67
4.31
3.48
4.63
13.69
14.01
13.58
14.87
13.13
14.11
12.53
14.61
39.23
13.51
180.42
153.76
168.73
153.88
158.80
159.41
142.02
142.75
140.15
155.59
182.49
156.29
170.90
156.72
160.96
161.89
144.21
145.71
160.61
157.91
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.06
0.01
1506
1786
1601
1867
1599
1735
1773
2000
5563
1654
38.58
33.86
36.86
33.44
34.60
34.67
28.88
30.55
17.96
33.77
CHCl
3
Acetone
MeOH
ACN
DMF
DMSO
38.10
3.83
4a
Toluene
THF
EtOAc
DCM
8.05
8.15
8.19
8.15
8.17
8.14
8.29
8.39
8.12
8.22
8.09
8.84
9.48
10.28
9.15
10.51
19.16
20.05
20.69
21.71
20.49
21.88
64.37
61.09
62.49
60.62
63.08
58.55
74.91
73.07
74.94
74.56
75.22
73.09
0.07
0.08
0.08
0.09
0.08
0.10
5187
5553
5621
5845
5459
6047
16.68
16.28
16.45
16.50
16.81
16.15
CHCl
3
Acetone
MeOH
ACN
DMF
DMSO
296.85
11.78
111.36
23.44
58.01
60.06
230.08
76.18
0.37
0.11
10657
6066
17.74
16.16
a
Onsager radius.
Integrated area of absorption coefficient.
Oscillator strength.
b
c
d
e
f
Transition dipole moment.
Difference between ground and excited state dipole moments evaluated using Lippert-Mataga solvent polarity parameter.
Dipole moment change between the diabatic states.
Degree of delocalization.
g
h
0
Electronic coupling matrix/Strength of electronic coupling between the ground (S ) and charge transfer excited states.
investigated by thermogravimetric analysis (TGA) and the plots are
shown in Fig. 4. Further, the chalcones can withstand the high
energy optical beams hence proposed to be an effective optical
material to enhance the efficiency of polymer matrix [29,30]. The
3.6. Nonlinear optical property study
We have designed the branched D-p-A system to achieve
enhanced NLO response through highly efficient ICT framework.
Owing to its strong electron donating ability the triphenylamine is
utilised as a donor as well as a source of branching. Triphenylamine
derived chromophores possesses very good NLO response attrib-
uted to their multifunctional properties [80,81] Also the hydroxyl
d
thermal stability on the scale of decomposition temperature (T ;
temperature at 5% weight loss) of coumarin chalcones was
increased with substitution of N-ethyl groups by triphenylamine
ꢀ
ꢀ
ꢀ
ꢀ
groups as: dye 1a/240 C, 2a/280 C, 3a/280 C and 4a/290 C. Same
trend was observed for BF
2
complexes coumarin chalcones as: dye
2
chalcones of coumarin and their BF complexes are proved to be
ꢀ
ꢀ
ꢀ
1
/250 C, 2/300 C, 3/310 C and attributed to their OBO
efficient NLO molecules [42], and hence we have extensively
studied the linear and non linear optical properties of the synthe-
sized coumarin chromophores. The synthesized molecules are
sensitive to the solvent polarity, and hence the solvatochromic
property is used to determine their NLO properties. The sol-
complexation dyes 1 to 3 are thermally more stable than chalcones
analogues. In this background, the branched D- -A coumarin
chalcones and BF complexed chromophores are showing good
p
2
thermal stability and attractive NLO materials for device
applications.
vatochromic and theoretical values of
a (linear polarizability), b

484
Y. Erande et al. / Dyes and Pigments 148 (2018) 474e491
Table 5
FMO diagrams of dyes 1 to 3 in chloroform.
Electron density distribution of frontier molecular orbitals of dyes 1e3 in chloroform, calculated by B3LYP/6 -31g(d) level of theory. (The orbital diagrams are plotted with the
contour value of 0.02 a. u.).
Table 6
Cyclic voltametric analysis results and comparison data for dye 1 to 3 and 1a to 4a.
Dye
l
onseta
nm)
Egb
HOMOc
(eV)
LUMOc
(eV)
B.G.c
(eV)
HOMOd
(eV)
LUMOd
(eV)
B.G.d
(eV)
(
(eV)
1
2
3
635
652
685
576
582
590
592
1.953
1.902
1.81
2.153
2.131
2.102
2.095
ꢁ5.742
ꢁ5.871
ꢁ5.942
ꢁ5.613
ꢁ5.776
ꢁ5.879
ꢁ5.964
ꢁ3.661
ꢁ3.39
2.081
2.481
2.588
2.432
2.407
2.352
2.521
ꢁ5.262
ꢁ5.285
ꢁ5.365
ꢁ5.119
ꢁ5.175
ꢁ5.228
ꢁ5.251
ꢁ2.534
ꢁ2.672
ꢁ2.925
ꢁ2.212
ꢁ2.372
ꢁ2.606
ꢁ2.637
2.726
2.613
2.439
2.907
2.802
2.622
2.614
ꢁ3.354
ꢁ3.181
ꢁ3.369
ꢁ3.527
ꢁ3.443
1a
2a
3a
4a
a
b
c
l
onset values are from absorption plot in DCM.
Optical band gap calculated from absorption onset/edge using the eq. (12).
HOMO, LUMO and BG values obtained from CV using Eqs. (10) and (11).
Theoretically calculated HOMO, LUMO and BG values from DFT calculations.
d
Fig. 4. TGA plots for dyes 1 to 3 and 1a to 4a.
(
first hyperpolarizability) and
g
(second hyperpolarizability) for
presented in supp. info. The obtained values for dyes 1 to 3 and 1a
to 4a are summarised in Tables 7 and 8 respectively.
dyes 1 to 3 and 1a to 4a are determined in toluene, chloroform,
methanol and DMSO. The theoretical values are determined by
TDDFT calculations using CAM-B3LYP/6-31g(d) method as dis-
cussed in the section-computational details. The corresponding
equations for solvatochromic and theoretical methods are
3.7. Calculation of
a
CT from the solvatochromic data
CT was evaluated by a solvatochromic
The linear polarizability
a

Y. Erande et al. / Dyes and Pigments 148 (2018) 474e491
485
Table 7
Linear and nonlinear optical property data for dyes 1 to 3.
ma
a
b
a
c
Dad
b
e
b
f
<g
>g
gh
Solv
CT
0
CT
0
ꢁ
18
ꢁ24
ꢁ24
ꢁ24
ꢁ30
ꢁ30
ꢁ36
ꢁ36
/10
/10
/10
/10
/10
/10
/10
/10
e.s.u
e.s.u
e.s.u
e.s.u
e.s.u
e.s.u
e.s.u
e.s.u
1
Toluene
CHCl3
MeOH
DMSO
2
8.33
9.24
10.37
10.32
33.6
66.3
76.2
78.7
45.6
49.3
54.2
54.0
82719
67.8
175.6
226.9
297.9
304.0
41.5
663.3
892.9
1233.8
1248.0
102504
131509
130111
126.5
138.3
145.2
ꢁ106.6
ꢁ205.4
ꢁ238.1
Toluene
CHCl3
MeOH
DMSO
3
6.15
7.18
8.02
8.06
38.7
43.8
41.7
33.9
75.6
91.7
102.0
102.7
57817
84848
102668
103913
128.4
137.2
119.6
92.2
230.9
328.0
431.4
438.1
271.6
241.5
179.3
136.4
1084.3
1775.2
2507.4
2557.7
Toluene
CHCl3
MeOH
DMSO
11.46
11.92
13.10
13.17
583.7
204.9
358.2
465.1
133.1
129.9
141.2
141.9
193016
189112
222826
224970
3088.6
1019.3
1547.6
2206.5
327.5
369.5
474.4
481.4
ꢁ10908.7
1269.7
3976.7
4395.9
5916.1
6021.0
ꢁ3826.3
ꢁ7741.8
a
Total static dipole moment by DFT.
Experimental first order polarizability.
First order polarizability by DFT.
Polarization anisotropy by DFT.
Experimental first order hyperpolarizability.
First order hyperpolarizability by DFT.
b
c
d
e
f
g
h
Solvatochromic descriptor of second order hyperpolarizability.
Second order hyperpolarizability by DFT.
Table 8
Linear and nonlinear optical property data for dyes 1a to 4a.
ma
a
b
a
c
Dad
b
e
b
0
f
<g
>g
gh
Solv
CT
0
CT
ꢁ18
ꢁ24
ꢁ24
ꢁ24
ꢁ30
ꢁ30
ꢁ36
ꢁ36
/10
/10
/10
/10
/10
/10
/10
/10
e.s.u
e.s.u
e.s.u
e.s.u
e.s.u
e.s.u
e.s.u
e.s.u
1a
Toluene
CHCl3
MeOH
DMSO
4.64
5.16
5.82
5.86
35.3
48.5
57.8
62.4
34.1
36.8
40.1
40.4
99013
207.2
260.4
277.2
281.6
147.8
191.1
251.9
256.0
1005.6
1094.9
970.9
498.3
663.4
901.4
917.5
115704
137737
139162
873.5
2a
Toluene
CHCl3
MeOH
DMSO
1.92
2.21
2.58
2.61
20.5
19.8
46.8
50.6
54.9
55.2
117225
133241
154244
155614
286.1
242.7
184.3
233.0
298.4
302.7
3518.8
2613.9
893.4
1171.4
1565.1
1591.5
23.7
251.1
2334.7
3a
Toluene
CHCl3
MeOH
DMSO
1.24
1.38
1.57
1.58
93.8
88.3
77.3
94.8
105.6
112.0
120.1
120.6
140856
159870
183811
185297
3178.7
2697.4
2029.5
2874.6
209.7
256.9
319.6
323.7
95178.4
72723.1
46969.3
76917.5
2512.4
3135.1
3989.2
4045.7
4a
Toluene
CHCl3
MeOH
DMSO
3.62
3.82
4.03
4.04
181.9
210.6
122.9
129.5
138.1
138.7
325332
368751
422791
426273
2176.8
2499.5
124.7
146.2
173.9
175.8
21102.6
23586.2
3609.0
4409.2
5492.7
5564.7
279.88
3213.88
27812.24
a
Total static dipole moment by DFT.
Experimental first order polarizability.
First order polarizability by DFT.
Polarization anisotropy by DFT.
Experimental first order hyperpolarizability.
First order hyperpolarizability by DFT.
b
c
d
e
f
g
h
Solvatochromic descriptor of second order hyperpolarizability.
Second order hyperpolarizability by DFT.
method for synthesized coumarins. The values were obtained by
two level model using UV-vis absorption/emission spectroscopy.
All these NLOphores have a donor and acceptor groups linked
component of first order polarizability/isotropic polarizability is
often referred as CT [82]. (eq. (S4), supp. info.) The CT are sol-
vatochromic values, which are compared with theoretically ob-
tained xx as shown in Tables 7 and 8. Maximum value is
obtained for the dye 3, 3a and 4a.
a
a
through a
p
conjugated system, hence, the first excited state is
a
o/
a
a
frequently a low lying charge transfer state. Therefore the dominant

486
Y. Erande et al. / Dyes and Pigments 148 (2018) 474e491
Fig. 5. Open aperture Z-scan curves for dye 1, 2 and 3 in DMSO.
Fig. 6. Open aperture Z-scan curves for dye 1a to 4a in DMSO.

Y. Erande et al. / Dyes and Pigments 148 (2018) 474e491
487
Table 9
Third order nonlinear susceptibility parameters for dyes 1 to 3 and 1a to 4a.
(
Re
3)
(3)
Im
c(3)
Solvent
b
n
2
c
c
ꢃ10ꢁ (m/W)
12
ꢃ10ꢁ19 (m /W)
2
ꢃ10ꢁ13 (e.s.u)
ꢃ10ꢁ13 (e.s.u)
ꢃ10ꢁ13 (e.s.u)
1
DMSO
Acetone
2
ꢁ2.62
ꢁ2.95
4.83
3.59
1.11
0.82
ꢁ0.25
ꢁ0.28
1.14
0.87
DMSO
Acetone
3
ꢁ6.3
5
3.53
1.61
1.13
ꢁ0.86
ꢁ0.4
1.83
1.2
ꢁ2.99
DMSO
Acetone
ꢁ2.57
ꢁ2.12
3.65
4.39
0.68
1.58
ꢁ0.2
0.71
1.61
ꢁ0.32
1a
DMSO
Acetone
ꢁ6.71
ꢁ7.5
6.39
2.13
3.17
1.06
ꢁ1.41
ꢁ1.58
3.46
1.9
2a
DMSO
Acetone
ꢁ4.8
3.56
3.02
1.14
0.97
ꢁ0.65
ꢁ0.45
1.31
1.07
ꢁ3.29
3a
DMSO
Acetone
ꢁ6.45
ꢁ3.92
7.09
3.28
2.28
1.07
ꢁ0.88
ꢁ0.54
2.44
1.2
4a
DMSO
Acetone
ꢁ4.46
ꢁ5.44
6.55
4.06
3.42
2.12
ꢁ0.99
ꢁ1.2
3.56
2.43
Fig. 7. Closed aperture Z-scan curves for dye 1, 2 and 3 in DMSO.
3.8. Calculation of
b
CT from solvatochromic shifts
As compared to the other expensive techniques with tedious
experimental setup the approximate estimation of CT values are
b
The first hyperpolarizability values obtained by the sol-
advantages in order to understand the trend. The Oudars two level
vatochromic method are based on numerous assumptions and
hence allow to estimate the approximate dominant tensor of total
hyperpolarizability along the direction of charge transfer. This
tensor is the major contributor to the total first hyperpolarizability.
simplified model for the first order hyperpolarizability is presented
in supp. info. (eq. (S5)) [11,83]. Static first hyperpolarizability (b )
0
was calculated using CAM-B3LYP/6-31g(d) method on the basis of
the finite field approach. Both the theoretical and solvatochromic

488
Y. Erande et al. / Dyes and Pigments 148 (2018) 474e491
Fig. 8. Closed aperture Z-scan curves for dye 1a to 4a in DMSO.
values of the first hyperpolarizability for all chromophores are
summarised in Tables 7 and 8. The values increase as branching
increases from dye 1 to 3 and 1a to 3a, while in case of 4a it gets
lowered which may be because of the symmetric arrangement.
Increased ICT character with increased branching seems to enhance
the first hyperpolarizability values of coumarin NLOphores.
nonlinear absorption effect was evaluated from open aperture Z-
scan measurements [88]. The equations used are presented in
supporting information- S13, S15 [89].
Figs. 5 and 6 show the open aperture Z-scan curves for dyes 1 to
3 and 1a to 4a in DMSO. (The open aperture Z-scan curves for dyes 1
to 3 and 1a to 4a in acetone are presented in supp. info. Figs. S4 and
S6). For all the NLOphores the measured transmittance forms a
peak which is known as saturable absorption and it gives the
b
0
3.9. Calculation of <g> from solvatochromic shifts
negative type of absorption nonlinearity hence the values of
negative as shown in Table 9. Further, the calculated values
contribute to the imaginary part (eq. (S17), supp. info.) of the third
b are
b
The second order hyperpolarizability known as “solvatochromic
descriptor” > SD at molecular level. The > SD originates
<
g
< g
(
3)
order nonlinear susceptibility (
c ).
from the electronic polarization in the non-resonant region and
obtained by the quasi-two-level model in place of three level model
using the density matrix formalism to a simpler format. (eq. (S6),
supp. info.) [84,85]. The individual component of the second order
In nonlinear refraction phenomenon the refractive index of
medium varies under the influence of high intensity laser beam.
(3)
The n
2
values contribute to the real part of
c
(eq. (S16)) and are
evaluated using close aperture Z-scan measurement results. The
close aperture Z-scan curves for dyes 1 to 3and 1a to 4a in DMSO
are shown in Figs. 7 and 8 respectively. (The close aperture Z-scan
curves for dyes 1 to 3and 1a to 4a in acetone are presented in supp.
info. Figs. S5 and S7 respectively). For all chromophores, the curves
produce the prefocal transmittance minimum (valley) followed by
post focal transmittance maximum (peak). This is significance of
positive nonlinear refractive index which is a result of self focusing.
static hyperpolarizability
values are proportional to the solvatochromic descriptor <
second order hyperpolarizability in case of dyes 1, 2 and 3.
g
was obtained computationally. The
g>of the
3.10. Z-scan analysis
To get more insight into the third order nonlinear optical
property of these chromophores, we evaluated the third order
(
3)
Therefore all the chromophores shows þ ve n
2
values as summar-
nonlinear susceptibility (
macroscopic parameter. The Z-scan analysis simultaneously pro-
vides the magnitude of nonlinear absorption coefficient ( ) and the
sign and magnitude of nonlinear refraction (n ) [86,87]. From and
the microscopic parameter like third order nonlinear suscepti-
c , which is a wavelength dependent
ised in Table 9. The overall third order nonlinear susceptibility was
calculated by eq. (13) and the corresponding values are summar-
ised in Table 9.
b
2
b
n
2
(
3)
ð3Þ
ð3Þ
ð3Þ
bility (
c
) can be determined. The closed aperture Z-scan mea-
c
¼
c
þ i
c
(13)
Re
Im
surement provided the nonlinear refractive index, while the

Y. Erande et al. / Dyes and Pigments 148 (2018) 474e491
489
The nonlinear refractive index contribute to the real part of the
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Acknowledgement
[
Author Yogesh Erande gratefully acknowledges the financial
support from the UGC, New Delhi, Govt. of India for SRF fellowship,
file number F.4-1/2006(BSR)/8-10/2007(BSR). Shantaram Kothavale
thanks the UGC, New Delhi, Govt. of India for SRF fellowship. I.
Hubert Joe thanks the Defence Research and Development Orga-
nisation (DRDO), New Delhi, India for the financial support (No.
ERIP/ER/1204694/M/01/1518).
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Appendix A. Supplementary data
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