Chlorine (Cl) - Substituted Carbazole Based A-π-D-π-a Push-Pull Chromophores as Aggregation Enhanced Emission (AEE) Active Viscosity Sensors: Synthesis, DFT and NLO Approach

Article abstract of DOI:10.1007/s10895-019-02396-y

Three new carbazole functionalized A-π-D-π-A extended chromophores 4a, 4b and 4c comprising of different chemical functional groups on C=C bond with the assistance of chlorovinylene group in π-conjugation are synthesized and investigated spectroscopically. We have investigated the effect of different electron acceptors - carboxycyanomethylene, dicyanomethylene and 2-(benzothiazol-2-yl) cyanomethylene, the effect of the insertion of chlorine in π-conjugation on photophysical properties and the effect of double acceptors. The chromophores 4a, 4b and 4c exhibited positive solvatochromism with large Stokes shifts and bright orange to red solid-state fluorescence. Amongst all the three compounds 4c exhibited maximum emission wavelength at 615?nm in DMSO. They presented characteristic twisted intramolecular charge transfer (TICT) emission. Observations exhibited that 4c containing long hexyl group in donor unit and 2-(benzothiazol-2-yl) cyanomethylene as an acceptor group formed an aggregate in the mixture of solvents and exhibited better aggregation enhanced emission (AEE) compared to the other two derivatives. Amongst the three styryls, 4c showed the highest emission intensity 299?a.u. at 90% water:DMF fraction (f_w). Chromophores 4a-4c also exhibited good fluorescence response towards viscosity. Among the three fluorescent molecular rotors (FMR), 4c exhibited excellent viscosity sensitivity with x value = 0.687. The Non-linear (NLO) characters are estimated with the help of solvatochromic and computational methods using the functionals, B3LYP and CAM-B3LYP. The dyes showed large “linear polarizability (α_CT)”, “first order hyperpolarizability” (β) and “second order hyperpolarizability” (γ) values which show that synthesized styryls can be used as a “NLO” material. The α_CT, β and γ for 4c are found to be the maximum amongst the all three dyes which can be ascribed to the smaller band gap apparent from experimental as well as DFT method.

Full text of DOI:10.1007/s10895-019-02396-y

Journal of Fluorescence
https://doi.org/10.1007/s10895-019-02396-y
ORIGINAL ARTICLE
Chlorine (Cl) - Substituted Carbazole Based A-π-D-π-a Push-Pull
Chromophores as Aggregation Enhanced Emission (AEE) Active
Viscosity Sensors: Synthesis, DFT and NLO Approach
1
1
1
1
Prerana K. M. Lokhande & Dinesh S. Patil & Mayuri Kadam & Nagaiyan Sekar
Received: 15 March 2019 /Accepted: 28 May 2019
#
Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
Three new carbazole functionalized A-π-D-π-A extended chromophores 4a, 4b and 4c comprising of different chemical functional
groups on C=C bond with the assistance of chlorovinylene group in π-conjugation are synthesized and investigated spectroscopically.
We have investigated the effect of different electron acceptors - carboxycyanomethylene, dicyanomethylene and 2-(benzothiazol-2-
yl) cyanomethylene, the effect of the insertion of chlorine in π-conjugation on photophysical properties and the effect of double
acceptors. The chromophores 4a, 4b and 4c exhibited positive solvatochromism with large Stokes shifts and bright orange to red
solid-state fluorescence. Amongst all the three compounds 4c exhibited maximum emission wavelength at 615 nm in DMSO. They
presented characteristic twisted intramolecular charge transfer (TICT) emission. Observations exhibited that 4c containing long hexyl
group in donor unit and 2-(benzothiazol-2-yl) cyanomethylene as an acceptor group formed an aggregate in the mixture of solvents
and exhibited better aggregation enhanced emission (AEE) compared to the other two derivatives. Amongst the three styryls, 4c
showed the highest emission intensity 299 a.u. at 90% water:DMF fraction (f ). Chromophores 4a-4c also exhibited good fluores-
w
cence response towards viscosity. Among the three fluorescent molecular rotors (FMR), 4c exhibited excellent viscosity sensitivity
with x value = 0.687. The Non-linear (NLO) characters are estimated with the help of solvatochromic and computational methods
using the functionals, B3LYP and CAM-B3LYP. The dyes showed large Blinear polarizability (αCT)^, Bfirst order
hyperpolarizability^ (β) and Bsecond order hyperpolarizability^ (γ) values which show that synthesized styryls can be used as a
BNLO^ material. The α , β and γ for 4c are found to be the maximum amongst the all three dyes which can be ascribed to the
CT
smaller band gap apparent from experimental as well as DFT method.
.
.
.
.
.
Keywords Extended styryl Solvatochromism AEE FMR DFT NLO
Introduction
with low glass transition temperature (Tg), and by simple
substitution of -NH of carbazole moiety with a long alkyl
chain affords [8–9] solid-state emission, good spectral prop-
erties, and electro-optical properties. Also, the insertion of
electron withdrawing groups at 3 and 6 positions of carbazole
with regard to the bridging nitrogen leads to effective
Intramolecular Charge Transfer (ICT) [10] and it also displays
high thermal, morphological, chemical and environmental sta-
bility [11–13].
Carbazole moiety is considered as a good electron donor to
construct active molecules in numerous fields such as
Borganic light emitting diodes^ (OLED) [1], Bdye-sensitized
solar cells^ (DSSC) [2–3], Bnon-linear optics^ (NLO) [4],
photoconductors [5], Bsolid state lasers^ [6], and Bbio-
imaging^ [7] due to its good charge transporting properties
Electronic supplementary material The online version of this article
BAggregation Enhanced Emission^ (AEE) active moieties
are designed and synthesized to accomplish numerous solid-
state luminescent materials [14]. Two representative AEE-
active molecules are reported in which one comprises strong
ICT states, which assume a twisted geometry in the excited
(https://doi.org/10.1007/s10895-019-02396-y) contains supplementary
material, which is available to authorized users.
*
Nagaiyan Sekar
n.sekar@ictmumbai.edu.in; nethi.sekar@gmail.com
state S in solution [15–16] and other is dependent on
1
1
propeller-shaped Bmolecular rotamers^, displaying active ro-
tation in dilute solution [17–18] due to the formation of H−/J-
Department of Dyestuff Technology, Institute of Chemical
Technology, Matunga, Mumbai 400 019, India

J Fluoresc
aggregates in aggregation state [19], excimer emission [20] or
enhancement through H-bonding [21–24]. Such fluorescent
molecules are effective chromophores due to their typical
ICT characteristics [25]. Fluorescent molecules are extensive-
ly studied by researchers to tune their ICT properties to be
applicable in different fields. They are widely used in many
emergent areas of applications for instance Bfluorescent
probes^ [26–28] Belectroluminescence devices^ [29], BNLO
materials^ [30], Borganic light-emitting diodes (OLEDs)^
which are responsible for the unique J aggregate forma-
tion and leads to enhanced aggregation induced emission
[45–47]. Molecules 4a-4c displays AEE phenomenon
having emission intensity significantly boosted in the ag-
gregation state as well as the solid state. Further, to inves-
tigate the importance of chlorine and structural modifica-
tion of carbazole chromophore on photophysical proper-
ties and AEE characteristics of the molecules, we have
carried out a comparative study [48]. Geometrical optimi-
zations were done using the method, B3LYP/6–31 + G(d)
[49, 50] and DFT computations are used to estimate the
structural, electronic properties of carbazole based mole-
cules and to study the BNLO characteristics^ of new gen-
eration push-pull colorants.
[
31], Bsolid-state lasers^ [32] and BDSSC^ [33]. Though,
making such organic AEE materials with an exceptional re-
versible capacity, and high solid-state fluorescence quantum
yield and to explore the relationship between structure and
AEE properties is still challenging. Conjugated AEE mole-
cules consisting of organic (D-π-A) systems comprise of do-
nor connected to acceptors via π-bridge [34–35]. The pres-
ence of halogen in luminescence phenomena with high quan-
tum yield and good stability can be an essential key factor to
design the AEE molecules [36].
Experimental Section
Materials and Equipment
Organic NLOphoric materials have attracted a great deal of
importance over inorganic materials like lithium niobate due to
its fast response time [37–39]. This difference lies in the fact as
optical properties of organic NLO material is purely electronic in
originwhereas,forinorganicNLOmaterials,itoriginatesthrough
turbulence in structural arrangements of key ions inside the solid-
statecrystallineframework[40–42].Amongsttheseveralorganic
dyes, the carbazole-based ones, the recognized rigid aromatic
dyes, receive great consideration because of their excellent
photophysical characteristics, high molar absorptivity, fluores-
cence quantum yields, and their excellent stability towards
chemicals, heat, and light [43]. The peripheral modification of
carbazole by varying substituents at 2nd, 3rd, 6th, 7th and 9th
position,canenhancetheNLOresponseofpush-pullsystem[44].
Accordingly, herein, we have studied three carbazole medi-
ated A-π-D-π-A type AEE active molecules namely 4a, 4b, and
All the chemicals were procured from BSigma Aldrich^ and
BS. D. Fine Chemicals Pvt. Ltd.^ Pre-coated silica gel alumin-
ium backed TLC plates were used to monitor the reaction. 1H
1
3
and C NMR spectra were obtained on a B500 MHz Varian,
USA instrument^ with TMS as an internal standard.
Absorption spectra were obtained using BPerkin Elmer
Lambda 25 UV-visible spectrophotometer^. BVarian Cary
Eclipse^ fluorescence spectrophotometer was used to record
fluorescence emission spectra using dye solution of 1 X
−6
−1
10 mol L . Fluorescence quantum yield was obtained with
fluorescein as the reference standard (in 0.1 M NaOH) [51].
Computational Strategy
DFT and TD-DFT calculations were applied for comparing
the observed absorption values. The method was applied to
study the structural modification in compounds and to relate
its effect on photophysical properties. DFT method was used
4c. These AEE active chromophores consist of carbazole as a
donor, 1-chlorobuta-1,3-diene as a π-spacer and three different
electron withdrawing groups namely carboxycyanomethylene,
dicyanomethylene and 2-(benzothiazol-2-yl) cyanomethylene
as an acceptor. We have evaluated the effect of structural
modulation of molecules with various acceptors on ICT
characteristics, fluorescent molecular rotor (FMR) proper-
ties, AEE and NLO characteristics of the molecules. We
have tried to extend the conjugation by inserting an extra
π-bond in charge transfer system to configure their effect
on photophysical properties and have introduced addition-
al electron withdrawing chlorine atom in π-spacer to in-
crease the accepting capacity of chromophore as it is ob-
served that ICT stabilizes the π-orbitals facilitating the
ionization of electrons from the orbitals of the unshared
pairs of chlorine. Also, the presence of halogen atom (−X)
in a molecule can give an enhancement in the emission
intensity as it shows interactions of C–H——Cl (halogen)
for geometry optimization in ground state (S ). All the calcu-
0
lations were achieved with BGaussian 09 package^ [52]. The
hybrid functional namely BB3LYP (Becke3-Lee-Yang-Parr
hybrid functional)^ was used. B3LYP [53] method used for
the vibration frequency of each compound computed using
TD-DFT calculation at 6–31 + G(d) basis set. The TD-DFT
calculation used for the optimization of the structure at first
singlet excited state (S ) of each molecule with its minimum
1
energy geometry [54–57]. The BPolarizable Continuum
Model^ (PCM) [58, 59] was applied for S and S state ge-
0
1
ometry optimization in solvent. The solvents used were tolu-
ene, chloroform (CHCl ), ethanol (EtOH), dimethyl sulfoxide
3
(DMSO).
The NLO characters of chromophores were estimated by
solvatochromic as well as computational methods. The

J Fluoresc
Bpolarizability parameter^ a , Bfirst hyperpolarizability
After cooling to 0 °C, 0.67 mL of acetyl chloride (0.74 g,
9.48 mmol) in 10 mL of chloroform was added dropwise over
10 min under vigorous stirring and stirring continued for 3–4 h
at ambient temperature. The reaction mixture was neutralized
and then extracted with DCM twice, washed by 1 M NaHCO3
and water. The organic phase was dried over anhydrous
CT
parameter^ βCT and Bsecond hyperpolarizability^ γ were cal-
culated by solvatochromic two level microscopic model and
DFT method.TD-DFT functionals namely, BB3LYP and
CAM-B3LYP^ were used to calculate NLO parameters.
Synthesis and Characterization
MgSO . The organic layer was completely removed under
4
reduced pressure and the crude solid obtained was then puri-
fied by column chromatography using petroleum ether and
ethyl acetate (9:1) as eluent to give the desired compound
The synthetic route of intermediates 1,2,3, and target com-
pounds 4a,4b and 4c are showed in Scheme 1.
(
0.7 g, 80%).
1
9-Hexyl-Carbazole (1)
H NMR (500 MHz, CDCl ) δ 8.77 (d, J = 1.6 Hz, 2H),
3
8.16 (dd, J = 8.6, 1.7 Hz, 2H), 7.44 (d, J = 8.7 Hz, 2H), 4.32 (t,
To a solution of 9-H-carbazole (1 g, 5.9 mmol) in acetone
20 mL) was added KOH (0.66 g, 11 mmol) and stirred the
mixture for 2 h at room temperature. 0.83 mL of 1-
bromohexane (0.98 g, 59 mmol) was then added to the above
mixture and refluxed it for 24 h. After the complete consump-
tion of starting material (confirmed by TLC), the solvent was
J = 7.3 Hz, 2H), 2.73 (s, 6H), 1.84–1.90 (m, 2H), 1.39–1.24
(m, 6H), 0.84 (t, J = 7.1 Hz, 3H).
C NMR (125 MHz, CDCl ) δ 197.48, 143.87, 129.66,
3
126.98, 122.86, 122.00, 108.97, 43.61, 31.44, 28.88, 26.84,
26.68, 22.47, 13.96.
(
1
3
removed under reduced pressure. 50 mL H O was then added
3-Chloro-3-(6–1-Chloro-3-Oxoprop-1-en-1-Yl)
2
to the solution and obtained solid was filtered followed by
recrystallization using EtOH and water to give colourless solid
-9-Hexyl-9H-Carbazol-3-Yl)Acrylaldehyde (3)
(
0.8 g, yield 80.0%).
To anhydrous DMF in a round bottom flask, phosphorus
oxychloride (POCl , 4.4 mmol) was added dropwise at 0 °C
3
3
,6-Diacetyl-9-Hexyl-Carbazole (2)
and stirring continued for another 30 min then added solution
of compound 2 (0.5 g, 1.49 mmol) in anhydrous DMF. Then
the mixture was heated to 70 °C for 2 h. The solution was then
rapidly transferred into cold water and neutralized with
To a solution of 9-hexyl-carbazole (0.8 g, 3.1 mmol) in chlo-
roform (10 mL) was slowly added anhydrous AlCl (1.27 g,
3
9
.56 mmol) with constant stirring under cooling condition.
NaHCO followed by extraction with ethyl acetate (20 mL)
3
Scheme 1 Synthetic pathway for the synthesis of molecules 4a-4c

J Fluoresc
and the organic layer was then dried over anhydrous MgSO4.
The organic layer was concentrated and the crude solid ob-
tained was purified by column chromatography (neutral alu-
mina; ethyl acetate/petroleum ether,1/10, v/v) to provide a
yellow solid (0.42 g, yield: 85%).
5,5′-(9-Hexyl-9H-Carbazole-3,6-Diyl) Bis(2-(Benzo[d]
Thiazol-2-Yl)-5-Chloropenta-2,4-Dienenitrile) (4c)
To a solution of intermediate 3 (0.2 g, 0.46 mmol) in 10 mL
MeOH, was added 2-(benzothiazol-2-yl) acetonitrile (0.085 g,
1
mmol), ammonium acetate (0.03 g). Acetic acid was added
5
-(6–4-Carboxy-1-Chloro-4-Cyanobuta-1,3-Dien-1-Yl)
to the solution in catalytic amount (1–2 drops). The solution
was refluxed for 18 h. After cooled down to room tempera-
ture, the solvent was removed by rotary evaporation. The
product was obtained by silica gel chromatography (CH Cl :
-
-
9-Hexyl-9H-Carbazol-3-Yl)
5-Chloro-2-Cyanopenta-2,4-Dienoic Acid (4a)
2
2
To a solution of intermediate 3 (0.2 g, 0.46 mmol) in 10 mL
MeOH, was added cyanoacetic acid (0.087 g, 1 mmol), am-
monium acetate (0.03 g). Acetic acid was added to the solu-
tion in catalytic amount (1–2 drops). The solution was
refluxed for 18 h. After cooling down to room temperature,
the solvent was removed by rotary evaporation. The crude
product was obtained by silica gel chromatography (CH Cl :
MeOH, 95:5 as eluent) as a dark red solid. Yield: 84%.
1
H NMR (600 MHz, DMSO) δ 8.25 (d, J = 7.8 Hz, 9H),
7.98 (s, 5H), 7.65 (d, J = 8.3 Hz, 8H), 7.56–7.49 (m, 13H),
7.28–7.24 (m, 8H), 7.18 (d, J = 7.5 Hz, 7H), 6.71–6.66 (m,
10H), 6.44 (d, J = 8 Hz, 10H), 6.34 (d, J = 7.9 Hz, 9H), 6.24–
6.18 (m, 11H).
CHN analysis: Calculated: C, 68.10; H, 4.22; N, 9.45.
Found: C, 68.13; H, 4.23; N, 9.46%.
2
2
MeOH, 95:5 as eluent) as a dark red solid. Yield: 77%.
1
H NMR (500 MHz, DMSO) δ 8.90 (d, J = 1.8 Hz, 1H),
.16 (d, J = 11.4 Hz, 1H), 7.97 (dd, J = 8.8, 1.8 Hz, 1H), 7.76
8
(
6
6
d, J = 8.9 Hz, 1H), 7.33 (d, J = 11.4 Hz, 1H), 4.45 (t, J =
Results and Discussions
.6 Hz, 2H), 1.76 (dd, J = 12.8, 6.0 Hz, 2H), 1.35–1.09 (m,
H), 0.78 (t, J = 7.1 Hz, 3H).
Design and Synthesis
13
C NMR (125 MHz, DMSO) δ 172.43, 163.40, 146.34,
42.77, 127.74, 126.31, 122.87, 121.58, 119.24, 116.94,
1
1
To further explore the application of AEE molecules, we have
synthesized three new AEE styryls through a multistep reac-
tion route. All the molecules were synthesized in the multi-
step synthetic pathway as shown in Scheme 1. Carbazole was
first alkylated using n-bromohexane in acetone and KOH, to
give N-hexyl carbazole 1. Further, N-hexyl carbazole was
acylated by BFriedel Craft acylation^ using acetyl chloride
10.88, 43.31, 31.34, 28.93, 26.44, 22.41, 14.28.
CHN analysis: Calculated C, 64.06; H, 4.48; Cl, 12.61;
N, 7.47; Found C, 64.07; H, 4.4; N, 7.47%.
2
,2′-(9-Pentyl-9H-Carbazole-3,6-Diyl)
Bis(3-Chloroprop-2-en-3-Yl-1-Ylidene))Dimalononitrile (4b)
and AlCl to give compound 2. Acylated compound 2 after
3
To a solution of intermediate 3 (0.2 g, 0.46 mmol) in 10 mL
MeOH, was added malononitrile (0.077 g, 1 mmol), ammo-
nium acetate (0.03 g). Acetic acid was added to the solution in
catalytic amount (1–2 drops). The solution was refluxed for
BVilsmeier–Haack formylation^ gave compound 3 which fi-
nally subjected to BKnoevenagel condensation^ with various
active methylene derivatives, in the presence of NH OAc and
4
CH COOH to produce styryl dyes 4a-4c in good yields.
3
1
8 h. After cooling down to room temperature, the solvent
Molecular structures of the styryls 4a-4c are represented in
Fig. 1 where highlighted part shows different functionalities
introduced on the designed molecule.
was removed by rotary evaporation. The product was obtained
by silica gel chromatography (CH Cl : MeOH, 95:5 as eluent)
2
2
as a dark red solid. Yield: 80%.
1
H NMR (500 MHz, CDCl ) δ 8.66 (d, J = 0.7 Hz, 1H),
Photophysical Properties
3
8
7
.15 (dd, J = 11.5, 1.0 Hz, 1H), 8.00 (dd, J = 8.3, 1.3 Hz, 1H),
.51 (d, J = 8.8 Hz, 1H), 7.42 (dd, J = 11.5, 0.9 Hz, 1H), 4.39
Styryls 4a, 4b, and 4c possess the molecular structures with
(
(
t, J = 7.1 Hz, 1H), 1.92 (dt, J = 14.6, 7.2 Hz, 1H), 1.43–1.26
m, 4H), 0.88 (t, J = 6.8 Hz, 2H).
different electron withdrawing groups as an acceptor. The op-
−6
−1
tical properties of 1 × 10 mol L solution of 4a-4c in sol-
vents of different polarities were studied and the correspond-
ing photophysical data are listed in Table 1 and Table S1
(ESI). We have investigated the spectroscopic properties in
seven organic solvents of different polarity and proticity: tol-
C 68.72, H 4.43, N 13.36.
13
C NMR (125 MHz, CDCl ) δ 155.74, 155.28, 155.01,
3
1
1
51.88, 143.54, 142.92, 128.40, 127.31, 127.12, 126.74,
26.57, 123.19, 122.98, 122.85, 122.77, 121.75, 117.90,
117.84, 113.73, 112.10, 110.05, 83.32, 43.93, 31.42, 28.96,
uene (TOL), ethyl acetate (EA), chloroform (CHCl ), ethanol
3
2
6.85, 22.47, 13.96.
CHN analysis: Calculated: C, 68.71; H, 4.42; N, 13.35%.
(EtOH), acetonitrile (CAN), dimethylformamide (DMF) and
dimethyl sulfoxide (DMSO). Typical absorption spectra of
compound 4c in several solvents is represented in Fig. 2(a)
Found: C, 68.72; H, 4.43; N, 13.36%.

J Fluoresc
Fig. 1 Molecular structures of chromophores 4a-4c
and data are recorded in Table 1. Absorption and emission
graphs of 4a and 4b are presented in Fig. S1 and data are
provided in Table S1. Absorption graphs of compounds 4a-
which might be because of conjugation from both the sides of
3 and 6 positions of carbazole. Styryls 4a and 4b exhibited
higher absorption maxima at 412 nm and 456 nm respectively
in DMSO and lower absorption maxima at 387 nm and
435 nm respectively in toluene. From toluene, the absorption
maxima of 4c located at 425 nm start shifting gradually with
increasing solvent polarity, and finally reaches 439 nm in
DMSO (Fig. 2a, Table 1). Similar observations were seen in
4
c presented shorter maxima at around 300–380 nm arising
from the π-π* transition and longer and broad maxima at
around 400–450 nm owing to ICT between the donor carba-
zole unit and the electron withdrawing acceptor units. These
graphs also showed a shoulder peak at around 460–540 nm,
Table 1 Photophysical data of 4c in several solvents
a
b
c
d
e
f
g
h
Dye
Solvent
λ
abs
λ
emi
Stokes shift (Δv)
ε
max
Φ
f
FWHM
cm−1
σ
(
μ
ge
10^-19)
nm
cm−
1
cm
2
Debye
Toluene
EA
425
426
435
429
432
433
439
535
540
565
585
578
600
615
111
114
130
156
146
167
176
4861
4967
5479
6216
5856
6428
6518
38,595
38,518
36,408
38,945
51,202
42,349
43,203
0.324
0.088
0.084
0.076
0.089
0.091
0.092
1.34
1.35
1.19
1.43
1.83
1.54
1.59
15,782
15,783
14,969
14,924
15,010
15,306
15,512
1.47
1.47
1.39
1.48
1.95
1.61
1.65
8.03
8.04
7.5
4
c
CHCl3
Ethanol
ACN
8.45
9.99
8.92
9.19
DMF
DMSO
a
b
c
d
e
f
BMaximum absorption wavelength^ in nm
BMaximum emission wavelength^ in nm
BMolar extinction coefficient^ in Lmol−1 cm−1
BFluorescence quantum yield^ (estimated using fluorescein as the standard in 0.1 M NaOH)
BOscillator strength^ experimental
BFull width half maxima^ of the absorption band
g
h
BMolar absorption cross section^ in (10−19 cm2 )
BTransition dipole moment^

J Fluoresc
Fig. 2 a Typical absorption spectra of 4c in several solvents. b Typical emission spectra of 4c in several solvents
the case of 4a and 4b. The Bmolar absorptivity (ε)^ of 4a-4c in
of compounds. For instance, we compared the photophysical
properties of 4c with previously reported Dye R1 (Fig. S2),
where R1 with ethyl group on a donor carbazole exhibited
(λabs) at 420 nm and (λemi) at 505 nm in DMF whereas syn-
thesized 4c with hexyl group on carbazole, additional π-bond
in conjugation and electron withdrawing chlorine group
showed λabs at 433 nm and λemi at 600 nm in DMF due to
the elongation of conjugate chain and increased electron do-
nating and accepting capacity of molecule. The designed syn-
thetic strategy furnished a red shift of about 13 nm in absorp-
tion maxima and 95 nm in emission maxima. Stokes shift also
−
1
−1
DMSO were found to be 39,235 Lmol cm , 28,298
Lmol− cm and 43,203 Lmol cm respectively.
1
−1
−1
−1
Compared to absorption wavelength, the emission wave-
lengths (λemi) exhibited significant red-shift with the rising
polarity of solvents. For example, λemi of 4c is 615 nm in polar
DMSO, which is red shifted by about 80 nm from that in non-
polar toluene (535 nm) (Table 1) (as represented in Fig. 2b).
Similarly, λemi of 4b slowly red-shifted from non-polar tolu-
ene (506 nm) to polar DMSO (570 nm) and the λemi of 4a red
shifted from (511 nm) toluene to DMSO (564 nm) (Table S1).
Amongst all three styryls 4a-4c, styryl 4c exhibited highest
emission maxima at 615 nm in DMSO owing to the existence
of stronger electron withdrawing group 2-(benzothiazol-2-yl)
cyanomethylene. With the increasing electron withdrawing
capacity, emission wavelength red shifted as following order
−1
−1
showed an increment from 4008 cm (R1) to 6428 cm (4c)
Table S2(a). So, the presence of chlorine with an additional π-
bond helped to increase the conjugation length and the
accepting capacity of chromophore and facilitates the ioniza-
tion of electrons from the orbitals of the unshared pairs of
chlorine which can be responsible for a bathochromic shift
in absorption along with the emission wavelength. Further,
we investigated the importance of double acceptors by com-
paring with R2 (single acceptor) (Fig. S2 Table S2(a)), where
R2 showed (λabs) at 430 nm and λemi at 591 nm in DMF
whereas an enhancement was observed in case of 4c due to
the presence of double acceptors and increased conjugation
length Table S2(a). We have also compared the results of 4c
with other similar reported analogues [105, 106] Table S2(b),
where compound 4 with -NO as an acceptor showed λ at
4
a < 4b < 4c in DMSO. With the increase in solvent polarity,
Stokes shift of 4c showed an increasing tendency from toluene
−1
−1
(
4861 cm ) to DMSO (6518 cm ) (Table 1). Similar results
were obtained for compounds 4a and 4b (Table S1). The
Stokes shifts are maximum in the polar solvent and can be
ascribed to the more stabilized excited state in a polar solvent
than non-polar solvents which is responsible for charge trans-
fer. All the compounds 4a-4c showed positive
solvatochromism.
To figure out the basis of the red shifted emission wave-
length of 4c, we further compared the results with the similar
derivatives (Table S2, ESI) considering following points: (1)
comparison with the similar analogue R1 with ethyl chain in a
donor [48] to investigate the donating capacity of the mole-
cule; (2) comparison with the molecule R1 [48] without
chlorovinylene group to verify the importance of the presence
of -Cl substituent; (3) comparison with R2 having single ac-
ceptor (D-π-A) (synthesis is provided in ESI) instead of dou-
ble acceptors to study the effect of double electron withdraw-
ing groups on the emission. Generally, the extension of π-
conjugation and the increased capacity of donor and acceptor
groups are effective in enhancing the photophysical properties
2
abs
363 nm and λemi at 585 nm, compound 5 showed λabs at
301 nm and λemi at 397 nm and CS3 showed λabs = 434 nm,
λemi = 504 nm in chloroform while the designed strategy of
the present paper resulted in longer absorption and emission
wavelength (for 4c, λabs = 425 nm, λemi = 535 nm) due to the
presence of hexyl group in a donor, chlorine group with an
additional π-bond in the conjugation and stronger withdraw-
ing acceptor group.
All three compounds exhibited solid-state emission around
450–700 nm represented in Fig. 3. 4a-4c showed a
bathochromic shift in solid state absorption and emission
wavelength compared to their absorption and emission in the

J Fluoresc
in transition dipole moment with increasing oscillator strength
Table 1. The styryls showed a range of transition dipole mo-
ment as follows: 4a (6.88–7.68 D), 4b (6.41–7.91 D) and 4c
(7.50–9.99 D) which conclude that styryl 4c exhibits better
charge transfer than other two derivatives owing to the stron-
ger electron acceptor in 4c.
Polarity Plots and Dipole Moment Ratio
We have examined the photophysical character of the A-π-
D-π-A carbazole styryls to investigate the role of strong elec-
tron accepting groups and the effect of extended conjugation
on the ground and excited-state characteristics. Dyes 4a-4c
showed red shifts in CT absorption band by varying solvent
polarity from toluene to a DMSO solvent, signifying the high-
ly stabilized S than the S state. Further, dipole moment ratios
Fig. 3 Solid-state emission graph of 4a-4c
solution state. The compounds 4a, 4b and 4c exhibited in-
creased emission intensity in a solid state which is around 95
a.u, 589 a.u and 685a.u respectively. Also, 4a-4c showed red
shifted emission wavelength in a solid state because of the
aggregate formation in the solid state. With the increase in
solvent polarity, fluorescence quantum yield decreases from
non-polar solvent to polar solvent [60–63]. The extended
styryl 4c gave ϕ = 0.324 and ϕ = 0.076 in toluene and ethanol
respectively Table 1. 4b showed similar results, where it ex-
hibited maximum quantum yield in toluene (ϕ = 0.298) and
minimum quantum yield in ethanol (0.061) (quantum yields
are measured using quinine sulfate as a standard [61–63])
Table S1.
Above discussion indicates that 2-(benzothiazol-2-yl)
cyanomethylene can be a better acceptor compared to the
other two electron withdrawing groups. Further the designed
strategy of increasing the conjugation length, increasing the
electron donating and accepting capacity by substituting ethyl
with hexyl group in a donor, using double acceptors and
inserting chlorine group with an additional π-bond in the con-
jugation between donor and acceptor furnished bathochromic
shift in the solution and the solid-state emission both.
1
0
were estimated using Bilot-Kawski [64, 65] and Bakhshiev
[66–68] functions plots for 4a-4c and are presented in
Table S3. The increase in Stokes shift for compounds 4a-4c
with rising solvent polarity is ascribed to the polarized excited
state (S ) in the polar microenvironments. The ratio of μ /μ
1
e
g
for dyes 4a-4c is found to be more than unity representing
higher polarity of the S state dipole moment than the S state
1
0
dipole moment, resulting in the charge transfer in the S state.
1
A change in a solvent polarity, dielectric constant and polar-
izability of the medium affects the ground and excited state.
We plotted graph of Stokes shifts Vs the Bsolvent orienta-
tion polarizability^, the respective BLippert-Mataga plots^
[69] are shown in Fig. 4. The observed linearity proposed that
a single S state was present on excitation. The slope of the
1
BLippert-Mataga plots^ of all the three dyes proposed a higher
contribution of the S dipole moment than the dipole moment
1
in S . The upgraded form of BLippert-Mataga model^ i.e.
0
−1
BMcRae [70] function (fMcRae)^ vs Stokes shift in cm was
plotted which gave a linear relationship with a good regression
coefficient for 4a-4c (Fig. S3). Hence, the difference in the
dipole moment of S and S states evaluates the CT character-
1
0
istic of the compounds [71, 72].
Oscillator Strength and Transition State Dipole
Moment
BOscillator strength^ explains about the probability of spectral
characteristics in energy levels. It provides information about
intramolecular charge transfer. It can be estimated using the
following Eq. 1
−9
f ¼ 4:32 Â 10 ε ðvÞ dv
ð1Þ
From the value of Bf^, transition dipole moment can be
estimated, which is the difference in electric charge distribu-
tion between the S and S state of the compound [64, 65].
0
1
The increase in the oscillator strength results into increased
transition dipole moment. Styryl 4c exhibited an enhancement
Fig. 4 Lippert-Mataga plots of 4a-4c

J Fluoresc
BWeller equation^ can be used to get a more quantifiable
investigation of the fluorescence solvatochromism [73].
BWeller equation^ is an upgraded form of the BLippert-
Mataga equation^, helps to calculate the dipole moment of
the S state (μ ). In the BWeller plot^ [Fig. S4], the observed
intensity but with the further increase in water fraction from
50% onwards, 4a-4c showed dramatic increment in the fluo-
rescence intensity showing bright orange luminescence under
UV radiation. Figure 5(a) and Fig. S6 reveals that dyes 4a-4c
display higher fluorescence intensity at water fraction (fw)
90%. It is remarkable that with steady addition of water frac-
tion to the solution of dye 4c in DMF, the emission wave-
0
e
regression coefficients are 0.5754, 0.8606 and 0.9059 for the
dyes 4a-4c respectively this shows that the molecules exhibit
more CT properties in the S state. To understand more about
length was red shifted to 632 nm when f was between 50
1
w
the S state that whether 4a-4c are showing ICTcharacteristics
and 90 vol%.
1
−1
or TICT, we used BRettig equation^, a plot of Δῡemi (cm ) vs
BRettig function^ [74, 75] [Fig. S5]. All the molecules 4a-4c
exhibited a linear relationship from non-polar to polar solvents
and the regression coefficients were obtained as 0.5806,
Similar observations were noticed for the 4a and 4b styryls.
The emission intensity of styryl 4c found to be the highest
when water fractions (f ) was 90%. In the case of 4b, emis-
sion wavelength increased gradually and showed dramatic red
shit after 70% water fraction. Similarly, emission intensity
also showed maximum enhancement after 70% water fraction.
4b exhibited highest emission wavelength and fluorescence
w
0
.8604 and 0.9090 for 4a-4c respectively. From the observa-
tions, it can be confirmed that all the molecules show more or
less TICT but 4c has the highest regression coefficient than 4a
and 4b and it shows more TICT properties.
intensity at water fraction (f ) 90%. Amongst the three styryls,
w
4c showed the highest emission intensity 299 a.u. at 632 nm.
Aggregation Enhanced Emission (AEE)
So, dyes 4a-4c are found to be AEE active which is advanta-
geous to find an application in the Bfluorescent probe Band in
Belectroluminescent devices^. The red shifted emission peaks
of styryls 4a-4c with rising water fraction may be the result of
strong electronic interaction through the π-stacking in aggre-
gate formation and supramolecular interactions of C–H——
Cl (halogen) resulting into J aggregate formation [45–47].
The BAEE^ characteristics of the styryls 4a, 4b and 4c were
examined in a mixture of DMF and H O (Fig. 5 (a-b)). All the
2
three styryls 4a-4c were well-dispersed in DMF and presented
fluorescence emission with weak intensity in their solution
state. To examine the AEE activity of 4a-4c, emission graph
of dyes was investigated in a sequence of mixtures of H O–
2
DMF with different water fractions (f ). As H O is the anti-
Fluorescent Molecular Rotor (FMR) Properties
w
2
solvent for the dyes, the increase in H O fraction changes the
2
solution form into aggregated particles in the mixture of DMF
The effects on the emission intensity with the change in vis-
cosity of solvent for synthesized FMRs 4a-4c was studied.
Thus, these molecules were solubilized in EtOH and viscosity
was increased using polyethylene glycol 400 (PEG:400). As
the viscosity of the solvent was increased, it resulted in en-
hanced emission intensities. The effect of the change in
and H O. The concentration was maintained at 1 ×
2
−
6
−1
1
0
mol L . We observed the transition in the λemi and
fluorescence intensity by gradually adding water fractions
fw) of 0–90% to the pure DMF solutions. Till the water frac-
tion 40%, the only slight increase was observed in fluorescent
(
2
Fig. 5 (a) Emission spectra of 4c in DMF and different H O–DMF mixtures. (b) Plot of water fraction versus ratio metric fluorescence intensity of 4c in
DMF and water–DMF mixtures

J Fluoresc
viscosity of solvent on emission intensity of FMR can be
explained by using BForster-Hoffmann^ Eq. (2).
same experiment was carried out in DMSO: Glycerol system
but no changes were observed. So, we can say that this change
in fluorescent intensity is due to the change in viscosity of the
mixture and not due to change in a polarity of the solvent.
log I ¼ C þ x log η
ð2Þ
where.
Geometry Optimization
I
x
η
emission intensity of FMR
sensitivity towards viscosity
viscosity of the mixture
DFT and TD-DFT calculations were applied to compare the
observed absorption and emission values. The method was
applied to study the structural modification in dyes and to
relate its effect on photophysical properties. DFT method
In a low viscous medium the molecules show free move-
ments along the carbon-carbon single and double bond but
with an increase in viscosity, free movements along the bonds
get prohibited. In a medium of low viscosity, molecules ex-
was applied for the S geometry optimization. The TD-DFT
0
calculation at B3LYP/6–31 + G(d) and CAM B3LYP/6–31 +
G(d) basis set used for the optimization of the structure at first
hibit S state relaxation via Bnon-radiative pathway^ [76, 77]
1
singlet S state of each molecule with its minimum energy
due to the free movements. While in a medium of high vis-
cosity molecules show Brestriction of rotation^ (RIR) [78] and
relaxation proceeds by improved fluorescence emission. The
FMRs 4a-4c exhibited a red shift in emission wavelength as
well as emission intensity. With the gradual increase in vis-
cosity of the mixture, the FMRs showed a hyperchromic shift
in emission intensity. Figure 6 (a) shows emission graph of 4c
in the mixture of EtOH and PEG 400. Amongst all the FMRs,
1
geometry [79]. Figure 7 shows the optimized molecular ge-
ometries of 4a-4c. The observed bond length and bond angles
are presented in Table 2 and Table S4-S5. C-H bond lengths
increases from 1.085 A° to 1.095A°. The C-C bond lengths
increased from 1.428 to 1.466A°. The O-H, N-C and N ≡ C
bond lengths showed values of 0.975 A°, 1.386 A° and 1.163
A° respectively. As per the geometry optimization using
B3LYP/6-31G+(d), the dihedral angles indicate that the car-
bazole and acceptor are planar.
4
c exhibited a drastic change in emission intensity after 10%
PEG 400 and ethanol mixture. Maximum emission intensity
for 4c is 680 a.u. at 90% PEG 400 and ethanol mixture. We
have plotted a graph of log I vs log η to calculate the value of x
for 4c [Fig. 6 (b)]. Higher the value of x, higher is the sensi-
tivity of FMR towards viscosity.
BVertical Excitation^, BFrontier molecular orbitals^
(FMOs), Bglobal reactivity descriptors^
and Bmolecular electrostatic potential^ (MEP)
The FMRs 4a, 4b and 4c have x values 0.22, 0.23 and 0.68
respectively. The extended styryls dye 4c show better im-
provement in the emission intensity with the rising viscosity
as compared to FMR 4a and 4b. Emission graphs of 4a and 4b
in the mixture of EtOH and PEG 400 and graph of log I vs log
η of 4a and 4b are provided in Fig. S7(a-b) [SI]. The com-
pound 4c showed good FMR properties than 4a and 4b. The
Electronic Spectra
TD-B3LYP/6–31 + G(d) and CAM-TD-B3LYP/6–31 + G(d)
were employed for vertical excitations of the S state geome-
tries of carbazole dyes (4a-4c) in solvents of different polari-
ties. All parameters obtained from the computational study are
0
Fig. 6 a Emission graph of 4c in mixture of EtOH and PEG 400. b Emission intensity Vs viscosity of solvent for 4c

J Fluoresc
Fig. 7 Optimized geometry of 4a-4c front view and side view
summarized in Table S6. Dyes 4a-4c exhibited one shorter
wavelength owing to aromatic π-π* transitions. All the dyes
exhibited longer absorption peak having higher oscillator
strength which can be contributed to the ICT characteristic
of dyes. The CT band for 4a-4c are primarily owing to the
transition of an electron from H to L of dyes. From TD-
B3LYP/6–31 + G(d) basis set, the smaller experimental λabs
for dye 4c was observed in toluene (425 nm) and maximum in
DMSO (439 nm) solvent while the computed smallest vertical
excitation is in toluene was (507.86 nm) and highest in DMSO
HOMO→LUMO transitions and oscillator strength of the
compound. Among all the three compounds, 4c exhibited a
maximum oscillator strength and maximum H-L transition
contribution.
Homo-LUMO
Usually, the BHOMO^ levels are dispersed over donor while
the BLUMO^ levels are localized on the acceptor. Figure 8
indicates that the BHOMO^ levels of 4a-4c are distributed
on carbazole core, and in disparity, the LUMO levels are dis-
persed on the electron withdrawing unit 2-cyanoacrylic acid,
dicyano vinylene and 2-(benzothiazol-2-yl) cyanomethylene.
On excitation, electron density population shifts from the car-
bazole unit to the acceptor moiety. This signifies ICT between
donor carbazole and acceptor groups. BHOMO–LUMO gaps^
in 4a, 4b, and 4c are found as 2.82, 2.77 and 2.72 eV
(
(
539.11 nm). For dye 4a experimental λabs in toluene
387 nm) and maximum in DMSO (411 nm) solvent however
the computed vertical excitation is lowest in toluene
499.06 nm) and maximum in DMSO (520.67 nm). Similar
(
solvatochromism results were obtained for 4b. Conjugation
length is directly proportional to ICT between HOMO and
LUMO and the vertical excitations are connected with the

J Fluoresc
Table 2 Optimized geometrical
parameters of 4c by DFT B3LYP/
Bond Length
Values A°
Bond angle
Values (deg)
Dihedral angle
Values (deg)
6–31 + G(d)
N29-C30
N29-C11
C13-C27
C27-Cl28
C19-C21
C49-C61
C61-N62
C49-C56
C56-N63
C56-S64
C12-H16
C19-H20
C30-H31
1.4584
1.3867
1.4665
1.7668
1.4280
1.4347
1.1636
1.4592
1.3001
1.7894
1.0842
1.0859
1.0959
C11-N29-C30
Cl28-C27-C13
S64-C56-C49
N63-C56-C49
C56-C49-C61
125.70
119.42
121.77
122.95
116.17
H22-C21-C19-H20
S64-C56-C49-C61
N63-C56-C49-C21
N29-C30-C33-C36
179.85
179.79
179.39
180.00
respectively in Fig. 9. The smallest energy gap values
2.72 eV) of 4c, in comparison with 4a and 4b, mainly owing
to the reduced LUMO energy as the result of the insertion of
-(benzothiazol-2-yl) cyanomethylene as an electron acceptor.
The results indicate that increasing the electron-accepting ca-
pacity of the acceptors can reduce the band gaps.
G(d) optimized geometry of 4a-4c (Fig. 8). The charge distri-
butions helps to understand the dye interaction with another
one which is valuable to describe the sites of Belectrophilicity^
and nucleophilic reactions [80, 81]. The potential values de-
fined by different colours reduces as follows: blue> orange>
red [82]. Negative – low potentials in MEPs represent the
abundance of electrons while positive – high potentials repre-
sent an absence of electrons. A deep red colour was used to
denote the negative – low potentials and the positive – high
potentials was represented by a deep blue colour. The negative
(red) low potentials are found noticeably in the region of the
(
2
Molecular Electrostatic Potential Surface (MEPs)
The effect of D-A groups was examined by observing the
various H and L levels and the MEPs at the B3LYP/6–31 +
Fig. 8 Frontier molecular orbitals and MEP diagram of 4a-4c obtained at B3LYP/6–31 + G(d) level

J Fluoresc
Fig. 9 HOMO-LUMO band gap
diagram of 4a-4c in chloroform
anchoring group and the positive (blue) high potentials in the
donor carbazole and hexyl regions. In the case of 4c, blue
colour is spread over carbazole showing positive low potential
and the red colour is mainly dispersed on 2-(benzothiazol-2-
yl) cyanomethylene unit showing negative low potential.
Similar observations were seen in the case of 4a and 4b.
From MEPS plots with total SCF density [isovalue =
related to the CT from higher to a lower chemical potential
system [86].
A molecule with higher softness value gives lower value of
η which shows more reactivity The chemical hardness of the
molecule is related to the stability of the molecules [88]. The
electrophilicity index estimates the energy lowering of a sub-
stance owing to the electron transfer from D to A [87].
The H-L energies give an idea about the electron donating
and withdrawing capacity of the molecule which is convenient
to evaluate molecular electronic properties. All the equations
for calculating global reactivity parameters are given in the
supporting information.
0
.0004 a.u.;(mapped with ESP)] represented total densities
for 4a-4c as ±0.103, ±0.092 and ± 0.111 a.u. respectively.
Global Reactivity Descriptors
The global reactivity parameters electronegativity (χ), hard-
ness (η), softness (S) [83] and electrophilicity index (ω) [84,
NLO Properties
8
5] were estimated using DFT method with the help of H-L
Conjugated D-π-A compounds design are recognized to pos-
sess high Bfirst hyperpolarizability (β)^ value. BSophisticated
and expensive electric Field Induced Second Harmonic
Generation^ (EFISH) technique is usually used to evaluate
the experimental NLO characters [89]. Apart from this, exper-
imental method and DFT computational method are primarily
used to furnish a primary understanding of NLO characteris-
tics from spectroscopic and computations data. In view of this,
we have used the spectroscopic method and computational
method to study the NLO characters of synthesized dyes.
Urea is used as a reference for comparison of NLO response
of the molecule [90, 91].
gap and all the values are given in Table 3.
Chemical hardness value helps to understand chemical
softness of the molecule.
Larger HOMO-LUMO gap signifies the more hardness of
the molecule. It can be established that smaller H– > L energy
gap results into more softness. Chemical potential (μ) is
Table 3 Chemical reactivity description (eV) for dye 4a-4c
a
b
c
d
Dye HOMO
LUMO
μ
η
ω
S
4a
4b
4c
−6.1364 −3.3129 −4.7247 1.4117 7.9062 0.7083
−6.2050 −3.4335 −4.8192 1.3857 8.3801 0.7216
−6.2567 −3.5312 −4.8939 1.3627 8.7877 0.7338
NLO Properties Obtained from Experimental Solvatochromic
Method
a
b
c
d
Chemical potential
hardness of molecule
Global electrophilicity index
Softness of molecule
BMean polarizability^ (α ), Bstatic first hyperpolarizability^
CT
(β) and Bsecond hyperpolarizability^ (γ) for the dyes 4a-4c
were estimated using the equations given in the SI [92–100]

J Fluoresc
Fig. 10 Solvatochromic β value
of 4a-4c in solvents
and are recorded in Table S7. Among dyes 4a-4c,
hyperpolarizability value rises with the increasing strength of
relative donor and acceptor chromophore. Dyes 4a-4c showed
maximum αCT in polar solvent DMSO and minimum αCT in
4a. β value is found to be maximum in polar solvents for dyes
4 a - 4 c . T h e s e m o l e c u l e s e x h i b i t e d h i g h e r
Bhyperpolarizability^ (β) values than urea (0.371 ×
−30
10
esu). The Bthree-level model^ is applied to calculate
non-polar solvent toluene. 4c exhibited higher α values in
Bsecond order hyperpolarizability^ (γ) at molecular level ini-
tiating from the electronic polarization [103, 104]. The value
of 〈γ〉 for 4b and 4c is larger than 4a which suggest the higher
electron accepting capacity of dicyanovinyl and benzthiazole
group.
CT
−24
DMSO (44.44 × 10 esu). Similar observations were obtain-
ed for 4a-4c (Table S7). The order of αCT for the synthesized
styryl is as 4c > 4b > 4a. The trend gives an idea about the
strength of acceptors and the length of π-delocalization in
styryl molecules. The hyperpolarizability (β) was estimated
using Btwo-level microscopic model^ based on Oudar [101,
NLO Values Obtained from Computational Methods
1
1
02] equation in different solvents. β value for 4a (16.74 ×
−30
−30
−30
0
esu), 4b (20.93 × 10 esu) and 4c (56.22 × 10 esu)
Theoretical method was also used to study the NLO proper-
−
30
respectively in toluene while 4a (24.81 × 10
esu), 4b
esu) respectively in
DMSO. The order of β value for dyes is found as 4c > 4b >
ties. The, a , β , γ for 4a, 4b, and 4c was calculated using
0
ο
29.45 × 10− esu) 4c (74.74 × 10
30
−30
(
B3LYP/6–31 + G (d) and CAM- B3LYP/6–31 + G (d) basis
set (Table S8). It is clear from the observations that a and β
,
0
0
0 ο
Fig. 11 Computational a , β , γ values of 4a-4c in different solvents

J Fluoresc
values for 4a-4c are smaller in a non-polar solvent whereas
design of a molecule. So, the present research may provide
suitable enlightenment for the future design of FMR material
and AEE active molecules. DFT and TD-DFT computations
were done to find out the computed vertical excitation which
showed consistency with the experimental values. The NLO
character are studied using solvatochromic and computational
methods, global hybrid BB3LYP^ and range separated
BCAM-B3LYP^ method where, CAM-B3LYP results are
found to be more consistent. Thus, the synthesized push-pull
chromophores based on carbazole dyes can be served as a
higher in a polar solvent. 4c exhibited a smaller value of α at
0
−
24
(
1
(
103.58 × 10
esu) in toluene and higher at (125.19 ×
−24
0
esu) in DMSO by using B3LYP basis set and α at
0
99.34 × 10− esu) in toluene and (119.95 × 10−24 esu) in
24
DMSO by CAM-B3LYP basis set. The computed β of 4c
0
−30
using CAM-B3LYP basis set is (242.46 × 10 esu) in tolu-
−30
ene and (439.62 × 10 esu in DMSO) and computed β of
0
4
b (224.23 × 10− esu) in toluene and (404.79 × 10 esu in
30
−30
DMSO). The higher value of β in polar solvent shows strong
0
solute-solvent interaction. γ values using CAM-B3LYP for 4c
in toluene is (215.42 × 10 esu) and (464.62 × 10 esu) in
good candidate of NLO material with good β values.
o
−36
−36
Acknowledgments The author, Prerana Kumar Lokhande is thankful to
University Grants Commission (Greentech), New Delhi (India) for the
award of Junior and Senior Research fellowships.
DMSO. Similar results were given by 4a and 4b. These values
−36
are larger as compared to urea (0.68 × 10
esu). NLO re-
sponse can be associated with the H-L energy gap. The calcu-
lated energy gaps were observed between 2.72–2.82 eV which
is smaller as compared to urea (ΔE = 6.7063 eV).
Compliance with Ethical Standards
The trend of a β and γ value is found to be as 4c > 4b >
0
,
0
Conflict of Interest There are no conflicts to declare.
4
a. Overall calculations of NLO parameters shows that 4c
possess better strength of acceptors and the length of π-
delocalization compared to 4a and 4b. The long range-
separated hybrid CAM-B3LYP performed well compared
to B3LYP for NLO properties and results are found to be
in good contract with experimental results. From the spec-
troscopic and DFT observations, it can be concluded that
accepting capacity of anchoring group and extended π-
conjugation are the key points to increase NLO properties
of the dyes (Figs. 10 and 11).
References
1
.
Brunner K, van Dijken A, B€orner H, Bastiaansen JJ, Kiggen
NMM, Langeveld BMW (2004) J Am Chem Soc 126:6035–6042
2. Chu H-C, Sahu D, Hsu Y-C, Padhy H, Patra D, Lin J-T (2012)
Structural planarity and conjugation effects of novel symmetrical
acceptor–donor–acceptor organic sensitizers on dye-sensitized so-
lar cells. Dyes Pigments 93:1488–1497
3.
4.
5.
Ning Z, Zhang Q, Wu W, Pei H, Liu B, Tian H (2008) Starburst
Triarylamine Based Dyes for Efficient Dye-Sensitized Solar Cells.
J Org Chem 73:3791–3797
Yoon KR, Ko S-O, Lee SM, Lee H (2007) Synthesis and charac-
terization of carbazole derived nonlinear optical dyes. Dyes
Pigments 75:567–573
Pacansky J, Waltman RJ (1992) X-ray photoelectron and optical
absorption spectroscopic studies on the dye chlorodiane blue, used
as a carrier generation molecule in organic photoconductors. J Am
Chem Soc 114:5813–5839
Conclusion
In summary, we have reported a series of A-π-D-π-A mole-
cules using carbazole as a donor and three different acceptors
of varying withdrawing capacity. Solvatochromism data
showed that the synthesized styryl 4c show slightly red shifted
emission compared to 4a, 4b, R2 and reported carbazole
styryls (R1) owing to the strong acceptor, extended π-
conjugation and assistance of extra electron withdrawing
chlorine group in conjugation. The chemical structure of dyes
with extended π-delocalization in the molecules are responsi-
ble for FMRs which leads to enhanced emission intensity.
Compounds 4a-4c were found to show viscosity dependent
properties in which 4c showed a higher response. This shows
that reported styryls can be used as excellent FMRs for the
viscosity measurements.
6
.
Mor GK, Basham J, Paulose M, Kim S, Varghese OK, Vaish A
(2010) High-Efficiency Förster Resonance Energy Transfer in
Solid-State Dye Sensitized Solar Cells. Nano Lett 10:2387–2394
7. Yang Z, Zhao N, Sun Y, Miao F, Liu Y, Liu X (2012) Highly
selective red- and green-emitting two-photon fluorescent probes
for cysteine detection and their bio-imaging in living cells. Chem
CommunCamb 48:3442–3444
8
.
Meerholz K, Volodin BL, Sandalphon N, Kippelen K,
Peyghambarian N (1994) A photorefractive polymer with high
optical gain and diffraction efficiency near 100%. Nature 371:
4
97–500
Cox AM, Blackburn RD, West DP, King TA, Wade FA, Leigh DA
1996) Crystallization‐resistant photorefractive polymer compos-
9
.
(
Further, we have studied the AEE phenomenon of 4a-4c.
ite with high diffraction efficiency and reproducibility. Appl Phys
All the three dyes were found to be AEE-active in DMF-H O
Lett 68:2801–2803
2
mixture and emit bright orange luminescence under UV light.
From the investigation, we confirm that optical properties of
molecules can be modified by extending conjugation, intro-
ducing longer alkyl chain, inserting electronegative groups
like chlorine and varying electron accepting groups in the
10. Gupta VD, Padalkar VS, Phatangare KR, Patil VS, Umape PG,
Sekar N (2011) The synthesis and photo-physical properties of
extended styryl fluorescent derivatives of N-ethyl carbazole.
Dyes Pigments 88:378–384
11. Gupta VD, Tathe AB, Padalkar VS, Umape PG, Sekar N (2013)
Red emitting solid state fluorescent triphenylamine dyes:

J Fluoresc
Synthesis, photo-physical property and DFTstudy. Dyes Pigments
7:429–439
2. Law KY (1993) Organic photoconductive materials: recent trends
and developments. Chem Rev 93:449–486
3. Yang MJ, Tsutsui T (2000) Jpn J Appl Phys 39:1828
4. Luo J, Xie Z, Lam JWY, Cheng L, Chen H, Qiu C, Kwok HS,
Zhan X, Liu Y, Zhu D, Tang BZ (2001) Aggregation-induced
emission of 1-methyl-1,2,3,4,5-pentaphenylsilole. Chem
Commun:1740–1741
5. Yang Z, Qin W, Lam JWY, Chen S, Sung HHY, Williams ID, Tang
BZ (2013) Fluorescent pH sensor constructed from a heteroatom-
containing luminogen with tunable AIE and ICT characteristics.
Chem Sci 4:3725
6. Roy S, Stollberg P, Herbst-Irmer R, Stalke D, Andrada DM,
Frenking G, Roesky HW (2015) Carbene-Dichlorosilylene
Stabilized Phosphinidenes Exhibiting Strong Intramolecular
Charge Transfer Transition. J Am Chem Soc 137:150–153
7. Hong Y, Lam JW, Tang BZ (2011) Aggregation-induced emission.
Chem Soc Rev 40:5361–5388
8. Sharma S, Dhir A, Pradeep CP (2014) ESIPTinduced AIEE active
material for recognition of 2-thiobarbituric acid. Sens Actuators B
Chem 191:445–449
9. An BK, Kwon SK, Jung SD, Park SY (2002) Enhanced Emission
and Its Switching in Fluorescent Organic Nanoparticles.
J.Am.Chem.Soc. 124:14410–14415
0. Hu R, Lager E, Aguilar Aguilar A, Liu J, Lam JWY, Sung HHY,
Williams ID, Zhong Y, Wong KS, Peña-Cabrera E, Tang BZ
32. Carda-Moreno I, Costela A, Mantin V, Pintado-Sierra M, Sastre R
(2009) Materials for a Reliable Solid-State Dye Laser at the Red
Spectral Edge. Adv Funct Mater 19:2547–254752
33. Patel DG, Bastianon NM, Tongwa P, Leger JM, Timofeeva TV,
Bartholomew GP (2011) Modification of nonlinear optical dyes
for dye sensitized solar cells: a new use for a familiar acceptor. J
Mater Chem 21:4242
34. Slama-Schwok MB-DA, Lehn J-M (1990) Intramolecular charge
transfer in donor-acceptor molecules. J Phys Chem 94:3894–3902
35. Han F, Zhang R, Zhang Z, Su J, Ni Z (2016) A new TICT and
AIE-active tetraphenylethene-based Schiff base with reversible
piezofluorochromism. RSC Adv 6:68178–68184
36. Zhang Y, Wang J-H, Zheng J, Li D (2015) A Br-substituted
phenanthroimidazole derivative with aggregation induced emis-
sion from intermolecular halogen–hydrogen interactions. Chem
Commun 51:6350–6353
37. Dalton LR, Benight SJ, Johnson LE, Knorr DB, Kosilkin I,
Eichinger BE (2011) Systematic Nanoengineering of Soft Matter
Organic Electro-optic Materials†. Chem Mater 23:430–445
38. Lupo D (1995) Molecular nonlinear optics: materials, physics, and
devices. Edited by J. Zyss, academic press, San Diego. CA 1994,
XIII, 478 pp., hardcover, ISBN 0-12- 784450-3. Adv Mater 7:
248–249
39. Dalton LR, Sullivan PA, Bale DH (2010) Electric Field Poled
Organic Electro-optic Materials: State of the Art and Future
Prospects. Chem Rev 110:25–25
40. Cole JM (2003) Organic materials for second-harmonic genera-
tion: advances in relating structure to function. Trans Roy Soc A:
Math Phys Eng Sci 361:2751–2770
41. Kanis DR, Ratner MA, Marks TJ (1994) Design and construction
of molecular assemblies with large second-order optical nonline-
arities. Quantum chemical aspects. Chem Rev 94:195–242
42. S.R. Forrest. M.E (2007) Introduction: Organic Electronics and
Optoelectronics. Chem Rev 107:923–925
9
1
1
1
1
1
1
1
1
2
(
2009) Twisted Intramolecular Charge Transfer and
Aggregation-Induced Emission of BODIPY Derivatives. J Phys
Chem C 113:15845–15853
2
2
1. Liu Y, Tao X, Wang F, Shi J, Sun J, Yu W, Ren Y, Zou D, Jiang M
(2007) J Phys Chem C111:6544
2. Wu QY, Peng Q, Niu YL, Gao X, Shuai ZG (2012) Theoretical
Insights into the Aggregation-Induced Emission by Hydrogen
Bonding: A QM/MM Study. J.Phys.Chem. A116 116:3881–3888
3. Xiao S, Zou Y, Wu J, Zhou Y, Yi T, Li F, Huang CJ (2007)
Hydrogen bonding assisted switchable fluorescence in self-
assembled complexes containing diarylethene: controllable fluo-
rescent emission in the solid state. Mater.Chem. 17:2483
4. Zhou T, Li F, Fan Y, Song W, Mu X, Zhang H, Wang Y (2009)
Hydrogen-bonded dimer stacking induced emission of
aminobenzoic acid compounds. Chem.Commun.:3199–3201
5. Deligeorgiev T, Vasilev A (2010) Chemistry F. ColorTechnol:55–
43. Thomas KRJ, Lin JT, Tao Y-T, Ko C-W (2000) Novel Green
Light-Emitting Carbazole Derivatives: Potential
Electroluminescent Materials. Adv Mater 12:1949–1951
44. Ciorba S, Galiazzo G, Mazzucato U, Spalletti A (2010)
Photobehavior of the Geometrical Isomers of Two 1,4-
Distyrylbenzene Analogues with Side Groups of Different
Electron Donor/Acceptor Character. J Phys Chem A 114:
10761–10768
2
2
2
2
45. Sagara Y, Kato T (2009) Nat Chem 1:1605
8
0
46. Sagara Y, Kato T (2011) Angew Chem 123:9294
47. Nagura K, Saito S, Yusa H, Yamawaki H, Fujihisa H, Sato H,
Yamaguchi YS aS (2013) Distinct Responses to Mechanical
Grinding and Hydrostatic Pressure in Luminescent Chromism of
Tetrathiazolylthiophene. J Am Chem Soc 135:10322–10325
48. Kumbhar HS, Deshpande SS, Shankarling GS (2016) Chemistry
Select 1:2058–2064
49. Thorat KG, Kamble P, Mallah R, Ray AK, Sekar N (2015)
Congeners of Pyrromethene-567 Dye: Perspectives from
Synthesis, Photophysics, Photostability, Laser, and TD-DFT
Theory. J Org Chem 80:6152–6164
50. Thorat KG, Bhakhoa H, Ramasami P, Sekar N (2015) NIR-
Emitting Boradiazaindacene Fluorophores -TD-DFT Studies on
Electronic Structure and Photophysical Properties. J Fluoresc 25:
69–78
51. Shen J, Snook RD (1989) Thermal lens measurement of absolute
quantum yields using quenched fluorescent samples as references.
Chem Phys Lett 155:583–586
6. Tokar VP, Losytskyy MY, Ohulchanskyy TY (2010) Styryl Dyes
as Two-Photon Excited Fluorescent Probes for DNA Detection
and Two-Photon Laser Scanning Fluorescence Microscopy of
Living Cells. J Fluoresc 20:865–872
7. Wandelt B, Mielniczak A, Turkewitsch P, Darling GD, Stranix
BRS (2003) Substituted 4-[4-(dimethylamino)styryl]pyridinium
salt as a fluorescent probe for cell microviscosity.
BiosensBioelectron 18:465–471
2
2
2
8. Ismail L (2012) Photophysical properties of a surfactive long-
chain styryl merocyanine dye as fluorescent probe. F MJ Lumin
32:2512–2520
9. Horiguchi E, Kitaguchi T, Matsui M (2006) Substituent effects of
,3-dicyano-5-[4-(diethylamino)styryl]-7-methyl-6H-1,4-
1
2
diazepines on their use as red dopants in single-layer organic elec-
troluminescence devices. Dyes Pigments 70:43–47
3
3
0. Rodrigues CAB, Mariz IFA, Maçoas EMS, Afonso CAM,
Martinho JMG (2012) Two-photon absorption properties of
push–pull oxazolones derivatives. Dyes Pigments 95:713–722
1. Chan CYK, Lam JWY, Zhao Z, Chen S, Lu P, Sung HHY (2014)
Aggregation-induced emission, mechanochromism and blue elec-
troluminescence of carbazole and triphenylamine-substituted eth-
enes. J Mater Chem C 2:4320–4327
52. Ooyama Y, Nagano T, Inoue S, Imae I, Komaguchi K, Ohshita J,
Harima Y (2011) Dye-Sensitized Solar Cells Based on Donor-π-
Acceptor Fluorescent Dyes with a Pyridine Ring as an Electron-
Withdrawing-Injecting Anchoring Group. Chem-Eur J 17:14837–
14843

J Fluoresc
5
3. Zhao J, Yang X, Cheng M, Li S, Sun L (2013) Molecular Design
and Performance of Hydroxylpyridium Sensitizers for Dye-
Sensitized Solar Cells. ACS Appl Mater Interfaces 5:5227–5231
4. Sacconi L (1966) Tetrahedral complexes of nickel(II) and
copper(II) with schiff bases. Coord Chem Rev 1:126–132
5. Yamada S (1966) Recent aspects of the stereochemistry of schiff-
base-metal complexes. Coord Chem Rev 1:415–437
73. Coe BJ, Harris JA, Asselberghs I, Clays K, Olbrechts G, Persoons
A (2002) Quadratic Nonlinear Optical Properties ofN-Aryl
Stilbazolium Dyes. Adv Funct Mater 12:110–116
74. Beens H, Knibbe H, Weller A (1967) Dipolar nature of molecular
complexes formedin the excited state. J Chem Phys 47:1183–1184
75. Zheng J, Kang YK, Therien MJ, Beratan DN (2005) Generalized
Mulliken−Hush Analysis of Electronic Coupling Interactions in
Compressed π-Stacked Porphyrin−Bridge−Quinone Systems. J
Am Chem Soc 127:11303–11310
5
5
5
6. Mehrotra C, Srivastva G, Saraswat BS (1982) Rev Silicon,
Germanium, Tin, Lead Compd 6:171
5
5
7. Nath M, Goyal S (1995) Main Group Met Chem 19:75
8. Siddiqui HL, Iqbal A, Ahmad S, Weaver GW (2006) Synthesis
and Spectroscopic Studies of New Schiff Bases. Molecules 11:
76. Zheng J, Kang YK, Therien MJ, Beratan DN (2005) Generalized
Mulliken−Hush Analysis of Electronic Coupling Interactions in
Compressed π-Stacked Porphyrin−Bridge−Quinone Systems. J
Am Chem Soc 127:11303–11310
2
06–211
5
9. G.E.M.J.F.G.W.T. H. B. Schlegel, G.A.S.M.A.R.J.R.C.G.S.V.B.
B. Mennucci, J.P.H.N.M.C.X.L.H.P.H. A. F. Izmaylov,
J . B . G . Z . J . L . S . M . H . M . E . K . T . R . F u k u d a ,
J . A . H . M . I . T . N . Y. H . O . K . H . N . T . V r e v e n ,
K . N . M . J . J . E . P. F. O . M . B . J . J . H . E . B r o t h e r s ,
J . K . V . N . S . R . K . J . N . K . R . A . R e n d e l l ,
J . E . C . B . S . S . I . J . T. M . C . N . R . J . M . M . M . K l e n e ,
R . E . S . K . J . B . C . V. B . C . A . J . J . R . G o m p e r t s ,
K . O . Y. A . J . A . R . C . C . P. J . W. O . R . L . M a r t i n ,
S . M . V. G . Z . G . A . V. P. S . J . J . D a n n e n b e r g , a n d
D.D.A.D.D.O.F.J.B.F.J.V.O. J. Cioslowski, W.C.J.F.G. Inc.,
Gaussian 09, Revision A.1, (n.d.)
77. Kadam MML, Patil DS, Sekar N (2019) Red emitting coumarin
based 4, 6-disubstituted-3-cyano-2-pyridones dyes – Synthesis,
solvatochromism, linear and non-linear optical properties. J Mol
Liq 276:385–398
78. Li J, Zhang Y, Mei J, Lam JWY, Hao J, Tang BZ (2015)
Aggregation-Induced Emission Rotors: Rational Design and
Tunable Stimuli Response. Chem - A Eur J 21:907–914
79. Zhao Z, Lam JWY, Tang BZ (2012) Tetraphenylethene: a versatile
AIE building block for the construction of efficient luminescent
materials for organic light-emitting diodes. J Mater Chem 22:
23726
80. Alam MJ, Ahmad S (2012) Anharmonic vibrational studies of l-
aspartic acid using HF and DFT calculations. Spectrochim Acta -
Part A Mol Biomol Spectrosc 96:992–1004
81. Uludağ N, Serdaroğlu G, Yinanc A (2018) A novel synthesis of
octahydropyrido[3,2- ]carbazole framework of aspidospermidine
alkaloids and a combined computational, FT-IR, NMR, NBO,
NLO, FMO, MEP study of the cis-4a-Ethyl-1-(2hydroxyethyl)-
2,3,4,4a,5,6,7,11c-octahydro-1H-pyrido[3,2-c]carbazole. J Mol
Struct 1161:152–168
6
0. Gao BR, Wang HY, Hao YW, Fu LM, Fang HH, Jiang Y, Wang L,
Chen QD, Xia H, Pan LY, Ma YG, Sun HB (2010) Time-Resolved
Fluorescence Study of Aggregation-Induced Emission
Enhancement by Restriction of Intramolecular Charge Transfer
State. J Phys Chem B 114:128–134
6
6
1. Al-Sabtl KEA (1983) M J Phys Chem 87:446
2. Lai C-T, Hong J-L (2010) Aggregation-Induced Emission in
Tetraphenylthiophene-Derived Organic Molecules and Vinyl
Polymer. J Phys Chem B 114:10302–10310
82. Thul P, Gupta VP, Ram VJ (2010) Structural and spectroscopic
studies on 2-pyranones. P Tandon Spectrochim Acta - Part A Mol
Biomol Spectrosc 75:251–260
83. Yang W, Parr RG (1985) Hardness, softness, and the fukui func-
tion in the electronic theory of metals and catalysis. Proc Natl
Acad Sci 82:6723–6726
6
6
3. Chen M, Li L, Nie H, Tong J, Yan L, Xu B, Sun JZ, Tian W, Zhao
Z, Qin A, Tang BZ (2015) Tetraphenylpyrazine-based AIEgens:
facile preparation and tunable light emission. Chem Sci 6:1932–
1
937
4. Bruni S, Cariati E, Cariati F, Porta FA, Quici S, Roberto D (2001)
Determination of the quadratic hyperpolarizability of trans-4-[4-
84. Parr RG, Szentpály LV, Liu S (1999) Electrophilicity Index. J Am
Chem Soc 121:1922–1924
(
dimethylamino)styryl]pyridine and 5-dimethylamino-1,10-
phenanthroline from solvatochromism of absorption and fluores-
cence spectra: a comparison with the electric-field-induced
second-harmonic generation technique. Spectrochim Acta Part A
Mol BiomolSpectrosc 57:1417–1426
85. Koopmans T (1934) Über die Zuordnung von Wellenfunktionen
und Eigenwerten zu den Einzelnen Elektronen Eines Atoms.
Physica. 1:104–113
86. Parr RG, Pearson RG (1983) Absolute hardness: companion pa-
rameter to absolute electronegativity. J Am Chem Soc 105:7512–
7516
87. Rezende MC, Dominguez M, Aracena A, Millán D (2011)
Solvatochromism and electrophilicity. Chem Phys Lett 514:267–
273
88. Pearson RG (1985) Absolute electronegativity and absolute hard-
ness of Lewis acids and bases. J Am Chem Soc 107:6801–6806
89. Jiao Z (2011) N, Huang, K W, Wang, P, Wu J Org Lett 13:3652–
3655
90. Katariya S, Rhyman L, Alswaidan IA, Ramasami P, Sekar N
(2017) Triphenylamine-Based Fluorescent Styryl Dyes: DFT,
TD-DFT and Non-Linear Optical Property Study. J Fluoresc 27:
993–1007
91. Margar SN, Sekar N (2016) Nonlinear optical properties of
curcumin: solvatochromism-based approach and computational
study. Mol Phys 114:1867–1879
92. Cho MJ, Choi DH, Sullivan PA, Akelaitis AJP, Dalton LR (2008)
Recent progress in second-order nonlinear optical polymers and
dendrimers. Prog Polym Sci 33:1013–1058
6
5. Coe BJ, Harris JA, Asselberghs I, Clays K, Olbrechts G, Persoons
A (2002) Quadratic Nonlinear Optical Properties ofN-Aryl
Stilbazolium Dyes. Adv Funct Mater 12:110–116
6
6
6
6
6. Kawski A (2002) Zeitschrift Fur Naturforsch - Sect A. J Phys Sci
5
7:255–262
7. Chamma A, Viallet PCR (1970) Acad Sci Paris Ser C 270:1901–
904
1
8. Kawski A (1964) Dipolmomenteeiniger Naphtholeim Grundund
Anregungszust and. Naturwissenschaften. 51:82–83
9. Rettig W (1986) Ladungstrennung in angeregten Zuständen
entkoppelter Systeme – TICT-Verbindungen und Implikationen
für die Entwicklung neuer Laserfarbstoffe sowie für den
Primärprozeß von Sehvorgang und Photosynthese.
AngewChem. 98:969–986
0. Valeur B (2001) Related titles from WILEY-VCH analytical atom-
ic spectrometry with flames and plasmas handbook of analytical
techniques single-molecule detection in solution. Methods and
Applications 8
7
7
7
1. McRae EG (1954) J Phys Chem 6:1957
2. Eisenthal KB, Rieckhoff KE (1971) Polarizability of Molecules in
Excited Electronic States. J Chem Phys 55:3317–3327
93. Tayade RP, Sekar N (2016) Benzimidazole-thiazole based
NLOphoric styryl dyes with solid state emission – Synthesis,

J Fluoresc
photophysical, hyperpolarizability and TD-DFT studies. Dyes
101. Oudar JL (1977) Optical nonlinearities of conjugated molecules.
Stilbene derivatives and highly polar aromatic compounds. J
Chem Phys 67:446–457
102. Margar SN, Rhyman L, Ramasami P, Sekar N (2016) Fluorescent
difluoroboron-curcumin analogs: An investigation of the electron-
ic structures and photophysical properties. Spectrochim Acta Part
A Mol Biomol Spectrosc 152:241–251
Pigments 128:111–123
9
9
9
4. Jenekhe SA, Osaheni JA, Meth JS, Vanherzeele H (1992)
N o n l i n e a r o p t i c a l p r o p e r t i e s o f p o l y ( p -
phenylenebenzobisoxazole). Chem Mater 4:683–687
5. Oudar JL, Chemla DS (1977) Hyperpolarizabilities of the
nitroanilines and their relations to the excited state dipole moment.
J Chem Phys 66:2664–2668
6. Momicchioli F, Ponterini G, Vanossi D (2008) First- and Second-
Order Polarizabilities of Simple Merocyanines. An Experimental
and Theoretical Reassessment of the Two-Level Model. J Phys
Chem A 112:11861–11872
1
03. Champagne B, Perpete EA, Andre J, Kirtman B (1997) Analysis
of the vibrational static and dynamic second hyperpolarizabilities
of polyacetylene chains. Syn Metals 85:1047–1050
1
04. Parr RG, Yang W Density-functional theory of atoms and mole-
cules. Oxford University Press, New York, p 19
1
05. Kremser G, Hofmann OT, Sax S, Kappaun S, List EJW, Zojer E,
Slugovc C (2008) Synthesis and Photophysical Properties of 3,6-
Diphenyl-9-hexyl-9H-carbazole Derivatives Bearing Electron
Withdrawing Groups. Monatsh Chem 139:223–231
9
7. Meyers F, Marder SR, Pierce BM, Bredas JL (1994) Electric Field
Modulated Nonlinear Optical Properties of Donor-Acceptor
Polyenes: Sum-Over-States Investigation of the Relationship be-
tween Molecular Polarizabilities (.alpha., .beta., and .gamma.) and
Bond Length Alternation. J Am Chem Soc 116:10703–10714
8. S.K. Lanke, N. Sekar, J. Fluoresc. 25(2015)1469–1480. J.L.
Oudar, D.S. Chemla, J. Chem. Phys. 66, (1977), 2664–2668
9. Abbotto A, Beverina L, Bradamante S, Facchetti A, Klein C,
Pagani GA et al (2003) Chem Eur J 9:991–2007
1
06. Lanke SK, Sekar N (2016) Novel NLOphoric 2-methoxy carba-
zole-based push pull chromophores: Synthesis, photophysical
properties and TD-DFT Study. J Photochem Photobiol A Chem
9
9
3
21:63–71
Publisher’s NoteSpringer Nature remains neutral with regard to
jurisdictional claims in published maps and institutional affiliations.
1
00. Momicchioli F, Ponterini G, Vanossi D (2008) First- and second-
order polarizabilities of simple merocyanines. J Phys Chem A 112:
11861–11872