Red emitting solid state fluorescent triphenylamine dyes: Synthesis, photo-physical property and DFT study

Article abstract of DOI:10.1016/j.dyepig.2012.12.024

In this work, four red-emitting push-pull chromophoric dyes containing triphenylamine are reported. The synthesis and solvatochromic behavior of novel triphenylamine based Y-shaped dyes obtained by the condensation of 4-(diphenylamino) benzaldehyde and 4,4′-diformyltriphenylamine with (1-phenylethylidene) propanedinitrile and ethyl-2-cyano-3-phenyl-2-butenoate are reported. The UV-Visible absorption and fluorescence emission spectra of these dyes were studied in solvents of different polarities. The photophysical behavior and the relation between structure and properties of the chromophores were investigated experimentally. These dyes exhibited positive solvatochromism and solvatofluorism in solution. The dyes were characterized by FT-IR, ¹H NMR and Mass spectral analysis. Thermal analysis showed that, these dyes are thermally stable up to 300 °C. Density Functional Theory [B3LYP/6-31G(d)] computations have been used to have more understanding of structural, molecular, electronic and photophysical parameters of push-pull dyes. The absorption wavelength values are found to be in good agreement with the experimental results. Non-linear properties (β_o) were calculated by theoretical method and found in the range of 196.45 × 10^-30 to 222.18 × 10^-30 e.s.u.

Full text of DOI:10.1016/j.dyepig.2012.12.024

Dyes and Pigments 97 (2013) 429e439
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Red emitting solid state fluorescent triphenylamine dyes: Synthesis,
photo-physical property and DFT study
*
Vinod D. Gupta, Abhinav B. Tathe, Vikas S. Padalkar, Prashant G. Umape, Nagaiyan Sekar
Tinctorial Chemistry Group, Department of Dyestuff Technology, Institute of Chemical Technology, N. P. Marg, Matunga, Mumbai 400 019, Maharashtra, India
a r t i c l e i n f o
a b s t r a c t
Article history:
In this work, four red-emitting pushepull chromophoric dyes containing triphenylamine are reported. The
synthesis and solvatochromic behavior of novel triphenylamine based Y-shaped dyes obtained by the
condensation of 4-(diphenylamino) benzaldehyde and 4,40-diformyltriphenylamine with (1-phenylethyl-
idene) propanedinitrile and ethyl-2-cyano-3-phenyl-2-butenoate are reported. The UVeVisible absorption
and fluorescence emission spectra of these dyes were studied in solvents of different polarities. The
photophysical behavior and the relation between structure and properties of the chromophores were
investigated experimentally. These dyes exhibited positive solvatochromism and solvatofluorism in so-
lution. The dyes were characterized by FT-IR, 1H NMR and Mass spectral analysis. Thermal analysis showed
that, these dyes are thermally stable up to 300 ꢀC. Density Functional Theory [B3LYP/6-31G(d)] compu-
tations have been used to have more understanding of structural, molecular, electronic and photophysical
parameters of pushepull dyes. The absorption wavelength values are found to be in good agreement with
the experimental results. Non-linear properties (bo) were calculated by theoretical method and found in
the range of 196.45 ꢁ 10ꢂ30 to 222.18 ꢁ 10ꢂ30 e.s.u.
Received 7 September 2012
Received in revised form
13 December 2012
Accepted 21 December 2012
Available online 24 January 2013
Keywords:
Red emitting dyes
Solid state fluorescent dyes
Triphenylamine
Solvatochromism
Thermally stable dyes
Dipole moment
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
numerous dye-sensitized solar cells (DSSCs) due to the non-
coplanarity of the three phenyl substituent’s, strong electron-
In the field of functional materials design and development of
innovative molecules have been progressing remarkably in recent
years due to their potential applications in the optoelectronic de-
vices, such as electroluminescence devices [1], organic light emit-
ting devices (OLED) [2], photoconductors [3], non-linear optics [4],
thin film transistors [5], solid-state lasers [6], photovoltaics [7], and
bio-sensing fluorescence technology [8].
donating nature, high light-to-electrical energy-conversion effi-
ciencies and good hole-transporting capability and organic electro-
luminescence materials [10b,11]. p-Aryl-substituted triphenylamine
derivatives have also attracted considerable interest due to their
wide range of applications in DSSCs, organic field-effect transistors,
and organic light-emitting diodes (OLEDs), as well as second order
nonlinear optical devices [12].
Compounds having an intramolecular charge transfer properties
are one of the most important materials. Such materials are usually
functionalized by electron-donating (D) and electron-accepting (A)
With these approach, to explore the relationship between
chemical structures and various properties of these compounds, we
have designed and synthesized a new series of twisted-intramole-
cular charge transfer (TICT) compounds by incorporating the tri-
phenylamine moiety (electron donor) with multiple cyano groups
(electron acceptor) for comparison (Fig. 1).
Properties of triphenylamine based derivatives were investigated
using absorption and fluorescence spectroscopy, thermogravimetric
analysis and density functional theory calculations. These dyes
showed fluorescence in solution as well as in the solid state. The
ground and excited electronic states of such chromophores can
be shown by linear combinations of neutral and zwitterionic states
(DeA) and (DþeAꢂ), respectively. These triphenylamine dyes have
shown red-shifted absorption and emission properties in compari-
son with the carbazole based fluorescent dyes reported in the earlier
paper [13]. The broader and red-shifted absorption and fluorescence
groups through a
p-conjugated bridge which makes it possible to
reduce the gap between HOMO and LUMO orbital of the molecule
for broadening the range of absorption and to study the relationship
between the variation of donor/acceptor chromophores and their
corresponding photophysical and electrochemical properties [9].
The electron-rich triphenylamine unit is one of the promising
donor moiety of donoreacceptor type of functional molecules
because of its good electron-donating and high hole mobility prop-
erties [10]. Triphenylamine derivatives are important molecules in
* Corresponding author. Tel.: þ91 22 3361 2707; fax: þ91 22 3361 1020.
E-mail addresses: n.sekar@ictmumbai.edu.in, nethi.sekar@gmail.com (N. Sekar).
0143-7208/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2012.12.024

430
V.D. Gupta et al. / Dyes and Pigments 97 (2013) 429e439
Fig. 1. Structures of the dyes TMS1, TMS2, TDS1 and TDS2.
bands with higher quantum yields is due to twisted-intramolecular
charge transfer (TICT) bands which showed positive sol-
vatochromism and solvatofluorism by recording in different sol-
constant. Relative quantum yields of the dyes in different solvents
were calculated by using equation (1).
a
!
ꢀ
ꢁ
hX2
h2Std
GradX
GradStd
vents. This combination of the non-planar triphenylamine core with
FX
¼
FStd
(1)
a linear
materials with good solution processability, decreasing the inter-
molecular stacking and reducing luminance quenching by
p-conjugated branch could lead to amorphous conjugated
Where,
pep
aggregation [12g,14].
FX
¼ Quantum yield of dye sample
FStd ¼ Quantum yield of standard sample
GradX ¼ Gradient of dye sample
GradStd ¼ Gradient of standard sample
hX
Density functional theory computations [B3LYP/6-31G(d)] were
carried out to study the geometrical and electronic properties of the
synthesized molecules. The static first hyperpolarizability (bo) and
its related properties were calculated using B3LYP/6-31G(d) on the
basis of the finite field approach [15].
¼ Refractive index of solvent used for synthesized compound
hStd ¼ Refractive index of solvent used for standard sample
2. Experimental section
2.2. Synthetic strategy
2.1. Materials and equipments
Four different kinds of red-emitting, solid state fluorescent
pushepull DepeA chromophoric dyes have been successfully
All commercial reagents were purchased from Aldrich and Sd
Fine Chemical Limited and used without purification and all sol-
vents were reagent grade. The reaction was monitored by TLC using
on 0.25 mm E-Merck silica gel 60 F254 precoated plates, which were
visualized with UV light. Melting points were measured on stan-
dard melting point apparatus from Sunder Industrial Product
Mumbai and are uncorrected. The FT-IR spectra were recorded on
a Jasco 4100 Fourier Transform IR instrument (ATR accessories). 1H
(300 MHz) and 13C (100 MHz) NMR spectra were recorded on
a Varian Cary Eclipse Australia, USA instrument using TMS as an
internal standard. Mass spectra were recorded on Finnigan Mass
spectrometer. The absorption spectra of the compounds were
recorded on a Spectronic Genesys 2 UVevisible spectropho-
tometer; fluorescence emission spectra were recorded on Varian
Cary Eclipse fluorescence spectrophotometer using freshly pre-
pared solutions at the concentration 1 ꢁ 10ꢂ6 mol Lꢂ1 solution.
DSCeTGA measurements were performed out on SDT Q600 v8.2
Build 100 model of TA instruments Waters (India) Pvt. Ltd. Fluo-
rescence quantum yields were determined in different solvents by
synthesized. These dyes contain triphenylamine as an electron
donor, cyano/carbethoxy group as electron acceptors conjugated
through a
p-bridge. They were synthesized by classical Knoeve-
nagel condensation of 4-(diphenylamino)benzaldehyde 2a and
4,40-diformyltriphenylamine 2b with active methylene compounds
3a and 3b as shown in Scheme 1. In the first step, triphenylamine 1
was mono or bis-formylated at 4 or 4 and 40 positions by
VilsmeiereHaack formylation reaction to obtain compounds 2a and
2b respectively. Finally, aldehyde 2a or 2b and suitable active
methylene compound 3a or 3b were refluxed in absolute ethanol
containing a catalytic amount of piperidine to yield desired fluo-
rescent extended styryl dyes TMS1, TMS2, TDS1 and TDS2.
The structures of the dyes were confirmed by FT-IR, 1H NMR, and
Mass spectral analysis. The 1H NMR spectra of dye TMS1 showed
doublet peaks at
d 6.78 and 7.42 having trans vicinal coupling
constant (J ¼ 15.4 Hz) which indicates the ethylenic protons at
styryl group are in transform and also showed a strong peak in FTIR
at 980 cmꢂ1 (CꢂH trans vicinal). Similarly, the geometry of other
three dyes were also confirmed by the presence of trans vicinal
using Rhodamine B (
F
¼ 0.97 in ethanol) [16] as a reference stan-
coupling in NMR spectra for ethylenic protons on p-bridge. The FT-
dard using the comparative method. The emission spectra of the
dyes and standard were measured at the absorbance below 0.05 to
minimize the inner filter and re-absorption effect. Emission in-
tensity values were plotted against absorbance values and linear
plots were obtained. Gradients were calculated for each dye in each
solvent and for the standard. All the measurements were done by
keeping the parameters constant such as solvent and slit width
IR spectra of these dyes showed presence of cyano and carbonyl
ester group stretching near about 2210 and 1710 cmꢂ1 respectively.
Absorption and emission spectra were measured to investigate its
photophysical properties and also the solvatochromism and solvato-
fluorism behaviors of the molecule were studied by measuring elec-
tronic absorption and emission spectra in solvents. Solvatochromic
data was used to determine the ground and excited state dipole

V.D. Gupta et al. / Dyes and Pigments 97 (2013) 429e439
431
Scheme 1. Synthesis of extended styryl mono- and bis-styryl triphenylamine dyes TMS1, TMS2, TDS1 and TDS2.
moments of the synthesized dyes by using LipperteMataga, Bakh-
shiev and KawskieChammaeViallet correlations.
dissolved in absolute ethanol (25 mL). Piperidine was added in
catalytic amount (0.1 mL) and the reaction mixture was refluxed for
6 h. The bright red crystals obtained were filtered, washed with
ethanol. The dye TMS1 obtained was purified by column chroma-
tography using silica gel 100e200 mesh and toluene as eluent
system.
2.3. Computational methods
All computations were performed using the Gaussian 09 package
[17]. Thegroundstate(S0)geometryofthesynthesizeddyesintheirC1
symmetry was optimized in the gas phase using DFT [18]. The func-
tional used was B3LYP. The B3LYP method combines Becke’s three
parameterexchangefunctional(B3)[19]withthenonlocalcorrelation
functional by Lee, Yang and Parr (LYP) [20]. The basis set used for all
atoms was 6-31G(d). The vibrational analysis was performed using
the same method to verify that the optimized structures correspond
to local minima on the energysurface. The vertical excitation energies
and oscillator strengths were obtained for the lowest 10 singlete
singlet transitions at the optimized ground state equilibrium geom-
etries by using TDDFTat the same hybrid functional and basis set [21].
The low-lying first singlet excited states (S1) of only one dye TMS1
was relaxed using TDDFT to obtain its minimum energy geometry.
The difference between the energies of the optimized geometries at
first singlet excited state and ground state was used to calculate the
emission [22]. Frequency computations were also carried out on
FrankeCondon excited state of the dyes. All the computations in
solvents of different polarities were carried out using the Self-
Consistent Reaction Field (SCRF) under the Polarizable Continuum
Model (PCM) [23]. Vertical electronic excitation spectra, including
wavelengths, oscillators strengths, and main configuration assign-
ment, were systematically investigated using TDDFT with PCM
model on the basis of the optimized ground state structures.
Yield: 68%, Melting point ¼ 222e224 ꢀC.
1H NMR (CDCl3, 300 MHz):
d
6.78 (d, J ¼ 15.4 Hz, 1H), 7.42 (d,
J ¼ 15.4 Hz, 1H), 6.95 (d, J ¼ 8.8 Hz, 2H), 7.32e7.34 (m, 6H), 7.48e
7.59 (m, 5H), 7.37 (d, J ¼ 8.1 Hz, 2H), 7.30 (d, J ¼ 7.7 Hz, 2H), 7.13
(t, J ¼ 8.1 Hz, 2H) ppm.
13C NMR (CDCl3, 100 MHz): 79.5, 113.4, 114.0, 120.5, 121.5, 124.9,
125.9, 126.8, 128.9, 129.6, 130.4, 130.8, 133.5, 146.2, 148.9, 151.3,
171.3 ppm.
Mass: m/z 424.2 (M þ 1).
FT-IR (cmꢂ1): 2214 (C^N), 1574 (Ar), 1280 (CꢂN), 980 (CꢂH
trans-vicinal).
2.4.4. Synthesis of ethyl-2-cyano-5-(4-triphenylamino)-3-phenyl-
penta-2,4-dienoate (TMS2)
4-(Diphenylamino)benzaldehyde (1.092 g, 4 mmol) 2a and
ethyl-2-cyano-3-phenyl-2-butenoate (0.864 g, 4 mmol) 3b were
dissolved in absolute ethanol (25 mL). Piperidine was added in
catalytic amount (0.1 mL) and the reaction mixture was refluxed for
6 h. The solvent was removed under reduced pressure. The red
colored dye TMS2 obtained was purified by column chromatogra-
phy using silica gel 100e200 mesh and toluene as eluent system.
Yield: 56%, Melting point: 104e106 ꢀC.
1H NMR (CDCl3, 300 MHz):
d
6.58 (d, J ¼ 15.8 Hz, 1H), 8.54 (d,
J ¼ 15.8 Hz, 1H), 6.95 (d, J ¼ 8.8 Hz, 2H), 7.12 (d, J ¼ 8.4 Hz, 8H), 7.32
(t, J ¼ 8.7 Hz, 4H), 7.44e7.52, (m, 5H), 1.39 (t, J ¼ 7.3 Hz, 3H), 4.35 (q,
J ¼ 7.3 Hz, 2H) ppm.
2.4. Synthesis and characterization
13C NMR (CDCl3, 100 MHz): 14.2, 61.7, 100.5, 117.3, 121.3, 123.3,
124.4, 125.5, 128.0, 128.5, 128.9, 129.5, 129.7, 129.9, 136.7, 146.6,
147.4, 150.3, 162.9, 168.1 ppm.
2.4.1. Synthesis of 4-(diphenylamino)benzaldehyde (2a) and
4,40-diformyltriphenylamine (2b)
The compounds 2a and 2b were prepared by the reported
method [24].
Mass: m/z 471.1 (M þ 1).
FT-IR (cmꢂ1): 2211 (C^N), 1709 (C]O), 1579 (Ar), 1279 (CꢂN),
1232 (CeO), 970 (CꢂH trans-vicinal).
2.4.2. Synthesis of (1-phenylethylidene) propanedinitrile (3a) and
ethyl-2-cyano-3-phenyl-2-butenoate (3b)
The compounds 3a and 3b were prepared by the reported
method [25].
2.4.5. Synthesis of 4,40-bis[4-(1,1-dicyano-2-phenyl)buta-1,3-dienyl]
triphenylamine (TDS1)
4,40-Diformyltriphenylamine (0.602 g,
2 mmol) 2b and
2.4.3. Synthesis of 4-[4-(1,1-dicyano-2-phenyl)buta-1,3-dienyl]
tri-phenylamine (TMS1)
4-(Diphenylamino)benzaldehyde (1.092 g, 4 mmol) 2a and (1-
phenylethylidene) propanedinitrile (0.672 g, 4 mmol) 3a were
(1-phenylethylidene) propanedinitrile (0.84 g, 5 mmol) 3a were
dissolved in absolute ethanol (30 mL). Piperidine was added in
catalytic amount (0.1 mL) and the reaction mixture was refluxed for
8 h. The dark red product thus obtained was filtered, washed

432
V.D. Gupta et al. / Dyes and Pigments 97 (2013) 429e439
with ethanol. The dye TDS1 obtained was purified by column
chromatography using silica gel 100e200 mesh and toluene as
eluent system.
through
wavelength ranging from 300 to 550 nm in solution as shown in
Fig. 2. These red-shifted absorptions are due to the extended
conjugation framework present in these dyes. The first peak near
300 nm is due to the * transition of the dye and the second
peak near 500 nm due to the twisted-intramolecular charge
transfer transition (TICT) between donor group and acceptor
moiety.
p-bonding exhibited strong red-shifted absorption in
p
-
Yield: 52%, Melting point: 268e270 ꢀC.
1H NMR (CDCl3, 300 MHz):
d
6.80 (d, J ¼ 15.4 Hz, 2H), 7.48 (d,
pep
J ¼ 15.4 Hz, 2H), 7.06 (d, J ¼ 8.4 Hz, 4H), 7.13 (d, J ¼ 8.4 Hz, 4H), 7.21
(d, J ¼ 9.2 Hz, 2H), 7.34 (t, J ¼ 9.2 Hz, 4H), 7.40 (d, J ¼ 8.8 Hz, 6H),
7.55 (t, J ¼ 7.3 Hz, 3H) ppm.
13C NMR (CDCl3, 100 MHz): 80.9, 113.1, 113.7, 122.9, 123.2, 126.0,
126.6, 128.9, 129.0, 130.0, 130.3, 131.0, 133.3, 145.4, 148.2, 149.7,
171.1 ppm.
The absorption spectra of dye TMS1 showed red shift with the
increase in the solvent polarity and showed shorter wavelength
absorption maxima in ethyl acetate at 478 nm and longer wave-
length in chloroform at 502 nm (Table 1 and Fig. 2). Similarly, dyes
TMS2 and TDS1 showed short wavelength absorption maxima in
ethyl acetate and dichloromethane at 454 and 505 nm and long
wavelength absorption band in chloroform at 475 and 523 nm
(Table 1 and Fig. 2). TDS2 showed short wavelength absorption
maxima in 1,4-dioxane at 474 nm and long wavelength absorption
in chloroform at 502 nm (Table 1 and Fig. 2). Both the dyes TMS1
and TMS2 have shown maximum 21 nm shift in the absorption
maxima when measured in different solvents of varying polarities.
In comparison with TMS1 (502 nm), the absorption maxima of
TMS2 is at 475 nm in chloroform. The red shift of TICT band of TMS1
indicates that dicyanovinyl moiety present in TMS1 has stronger
electron withdrawing effect than cyano carbethoxy vinyl unit
(present in TMS2) increasing the charge transfer between donors
and acceptors. Bis-styryl dyes (TDS1 and TDS2) have shown red-
shifted absorption bands when compared to mono-styryl dyes
(TMS1 and TMS2). Red-shifted absorption is due to presence of one
additional electron withdrawing group present in the bis-styryl
molecules which leads to decrease in the band gap energy.
In the previous report, the four dyes contain carbazole unit in
place of triphenylamine (Fig. 3) as reported in this paper [13]. Tri-
phenylamine dyes were found to have red-shifted absorption as
compared to each of the corresponding system similar to carbazole
(Table 2). TMS1 and TMS2 have 36 nm shift in comparison with
carbazole dyes (5a and 5b respectively) whereas the dyes TDS1 and
TDS2 have 42 and 40 nm longer absorption as compared to dyes 6a
and 6b of carbazole dyes. Unlike triphenylamine, carbazole system
is rigid and the two phenyl rings are fused to a middle pyrrole ring
whereas triphenylamine contains three phenyl rings attached to
a single nitrogen atom. These phenyl rings present on triphenyl-
amine can freely rotate and alter the optical properties of the tri-
phenylamine derivatives.
Mass: m/z 602.2 (M þ 1).
FT-IR (cmꢂ1): 2217 (C^N), 1578 (Ar), 1261 (CꢂN), 971 (CꢂH
trans-vicinal).
2.4.6. Synthesisof4-[5-(ethyl-2-cyano-3-phenyl) penta-2,4-dienoate]
triphenylamine (TDS2)
4,40-Diformyltriphenylamine (1.26 g, 5 mmol) 2b and ethyl-2-
cyano-3-phenyl-2-butenoate (2.16 g, 10 mmol) 4b were dissolved
in absolute ethanol (15 mL). Piperidine was added in catalytic
amount (0.1 mL) and the reaction mixture was refluxed for 8 h. The
bright red crystals thus obtained were filtered, washed with etha-
nol. The dye TDS2 obtained was purified by column chromatogra-
phy using silica gel 100e200 mesh and toluene as eluent system.
Yield: 45%, Melting point: 140e142 ꢀC.
1H NMR (CDCl3, 300 MHz):
d
6.58 (d, J ¼ 15.8 Hz, 2H), 8.57 (d,
J ¼ 15.8 Hz, 2H), 7.00 (d, J ¼ 8.8 Hz, 4H), 7.09 (d, J ¼ 7.3 Hz, 4H), 7.16
(t, J ¼ 7.0 Hz, 2H), 7.32 (m, 8H), 7.48 (t, J ¼ 6.6 Hz, 5H), 1.39 (t,
J ¼ 7.3 Hz, 6H), 4.35 (q, J ¼ 7.3 Hz, 4H) ppm.
13C NMR (CDCl3, 100 MHz): 14.2, 61.8, 101.3, 117.1, 123.2, 124.3,
126.2, 127.9, 128.1, 128.6, 128.9, 129.8, 129.9, 136.5, 145.9, 146.5,
146.8, 149.0, 162.8, 167.8 ppm.
Mass: m/z 718.4 (M þ Naþ).
FT-IR (cmꢂ1): 2209 (C^N), 1712 (C]O), 1588 (Ar), 1268 (CꢂN),
1232 (CꢂO), 970 (CꢂH trans-vicinal).
3. Results and discussion
3.1. Photo-physical properties
The UVeVis absorption and fluorescence emission spectra of
extended styryl triphenylamine dyes TMS1, TMS2, TDS1 and TDS2
in solvents of varying polarities are reported in Table 1. These tri-
phenylamine dyes have shown red-shifted absorption maxima
(about 40 nm shift) as compared to its styryl analogues reported in
literature [26]. These newly synthesized triphenylamine derivatives
with DepeA (TMS1 and TMS2) and AepeDepeA (TDS1 and
TDS2) system consist of an electron-donating triphenylamine unit
and electron-withdrawing cyano or carbethoxy groups conjugated
A strong solvatofluorism was shown by triphenylamine dyes
and they emit in the red region (Table 1 and Fig. 4, S1eS4) (see
electronic supplementary material). These four dyes showed
a blue-shifted fluorescence emission maxima in non-polar solvent
(toluene) and red-shifted longer fluorescence emission maxima in
polar solvent (acetonitrile and DMF) indicating that the charge
Table 1
Absorption maxima wavelength (labs, nm), molar extinction coefficient (ε Mꢂ1 cmꢂ1), fluorescence emission maxima wavelength (lems, nm); fluorescence quantum yield (Ff
)
and Stokes shift (cmꢂ1) of extended styryl triphenylamine dyes in different solvents.
Solvent
TMS1
TMS2
TDS1
TDS2
labs (ε)
lems
(
Ff)
Stokes labs (ε)
shift
lems
(
Ff
)
Stokes labs (ε)
shift
lems
(Ff)
Stokes labs (ε)
shift
lems
(
Ff)
Stokes
shift
Toluene
487 (24859) 574 (0.1322) 3112
463 (25457) 560 (0.0218) 3741
459 (30116) 590 (0.0299) 4837
454 (29975) 581 (0.0270) 4815
475 (29645) 608 (0.0383) 4605
454 (28845) 599 (0.0262) 5332
457 (46162) 630 (0.0065) 6009
463 (44703) 625 (0.0014) 5598
466 (35245) 619 (0.0041) 5304
457 (36139) 644 (0.0011) 6354
466 (25646) 642 (0.0026) 5883
508 (50000) 570 (0.3730) 2141
507 (44886) 601 (0.3347) 3085
505 (41517) 588 (0.1453) 2795
523 (43863) 604 (0.4419) 2564
505 (43923) 615 (0.1174) 3542
508 (43021) 643 (0.0023) 4133
490 (49545) 562 (0.4296) 2615
474 (52606) 589 (0.5263) 4119
481 (61304) 577 (0.3285) 3459
502 (55668) 604 (0.5663) 3364
481 (52398) 602 (0.3368) 4179
484 (53859) 634 (0.0301) 4888
493 (55877) 628 (0.0085) 4360
493 (56781) 619 (0.0355) 4129
487 (52398) 643 (0.0082) 4982
496 (52954) 640 (0.0129) 4536
1,4-Dioxane 480 (31932) 610 (0.1050) 4440
DCM
Chloroform
481 (35108) 599 (0.0644) 4096
502 (33795) 619 (0.2063) 3765
Ethyl acetate 478 (38242) 620 (0.0878) 4791
Acetone
Methanol
Ethanol
Acetonitrile
DMF
481(44129) 652 (0.0031) 5453
484 (35701) 631 (0.0008) 4813
490 (41503) 630 (0.0035) 4535
481 (50312) 659 (0.0006) 5616
490 (36294) 654 (0.0016) 5118
511 (8363)
514 (7461)
627 (0.0005) 3621
633 (0.0028) 3657
508 (39712) 652 (0.0001) 4348
520 (37004) 653 (0.0021) 3917

V.D. Gupta et al. / Dyes and Pigments 97 (2013) 429e439
433
TMS2
fluorescence maxima at 630, 625, 665 and 649 nm (Figs. 4 and 6).
Bright red fluorescence shown by dye TDS2 in solid state powder
form (Figure S5).
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
466 nm
TDS2
496 nm
TDS1
520 nm
TMS1
490 nm
3.2. Quantum yields of the dyes
The fluorescence quantum yields of the synthesized dyes were
determined in different solvents and tabulated in Table 1. The flu-
orescence quantum yields of the dyes largely depend on both the
nature of the substituent and the solvent polarity. Here, decrease in
the solvent polarity strongly enhances the fluorescence quantum
yields of TMS1, TMS2, TDS1 and TDS2 as shown in Table 1. The four
dyes showed higher quantum efficiencies in non-polar solvents
whereas in polar solvents the quantum yield values were invariably
found to be very low. These dyes showed highest quantum yield in
chloroform in the increasing order: TMS2 (0.0383) < TMS1
(0.2063) < TDS1 (0.4419) < TDS2 (0.5663). The quantum yield
values were the lowest in acetonitrile in the decreasing order: TDS2
(0.0082) > TMS2 (0.0011) > TMS1 (0.0006) > TDS1 (0.0001). These
dyes showed very less emission intensity in acetonitrile and DMF
showing an obvious positive solvatokinetic behavior suggesting
that a highly polar excited-state population charge transfer state
and a non-radiative decay was prominent in these dyes [28].
These fluorescent materials are bright red to dark red in color
and soluble in most of the organic solvents. In less polar solvents
such as toluene, all the dyes emit orange to yellow light of moderate
intensity. On increasing the solvent polarity the emission band also
shifts bathochromatically and in DMF it emits red light. Fig. S5 that
the daylight and fluorescence emission photographs of dye TMS1 in
different solvents and the difference in the emission color can be
easily observed by naked eyes. These dyes showed very less
emission intensity in acetonitrile and DMF solvents, which is in
accordance with the low fluorescence quantum yield observed
250
300
350
400
450
500
550
600
Wavelength (nm)
Fig. 2. Absorption spectra of dyes TMS1, TMS2, TDS1 and TDS2 (in DMF).
separation increases in the excited state which results in a larger
dipole moment than that in the ground state and explains the
sensitivity of the fluorescence emission spectra of these pushepull
dipolar dyes to solvent polarities. The effect of solvent polarities on
emission behavior of the dye TMS1 is shown in Fig. 5 and S1. Also,
dye TMS1 showed higher fluorescence intensity in non-polar sol-
vents and less in the polar solvents (Fig. S1). Similarly, red shift of
84, 83 and 81 nm for the dyes TMS2, TDS1 and TDS2 respectively as
the solvent polarity increases from non-polar to polar medium
(Table 1 and Figs. S2eS4).
In comparison with the carbazole dyes (5a, 5b, 6a and 6b), tri-
phenylamine dyes have shown red-shifted fluorescence maxima
(Table 2). TMS1 (652 nm) and TMS2 (644 nm) have shown 94 and
84 nm shift in fluorescence maxima comparison with respect to
carbazole dyes (5a (558 nm) and 5b (560 nm) respectively)
whereas the dyes TDS1 and TDS2 have 75 and 82 nm longer ab-
sorption as compared to dyes 6a and 6b. Here, triphenylamine
extends the conjugation and acts a strong electron donor, thus re-
sults in longer absorption and emission than that of carbazole dyes.
The Stokes shift increases with the increase in the solvent po-
larity which indicates an extensive structural re-organization in the
excited state [27]. This shows that these dyes have polar excited
state and it is more stabilized in the polar solvent. This confirms the
twisted intramolecular charge transfer characteristics of these
pushepull dyes. Compared with fluorescence spectra in solution,
four dyes in solid state have a slight red-shifted fluorescence band
(Table 1). Pushepull charge transfer mechanism in De
chromophore is illustrated in Fig. S8 and AepeDepeA type
chromophore in Fig. S9.
peA type
3.3. Thermal stability of dyes
The dye molecules should have strong intermolecular in-
teractions and form compact aggregates to possess high thermal
stability [29]. In order to give more insight into the thermal prop-
erties of the dyes TMS1, TMS2, TDS1 and TDS2, the thermal studies
revealing intermolecular
solid state. TMS1, TMS2, TDS1 and TDS2 showed solid state
pep interaction and aggregation in the
Fig. 3. Structures of previously reported dyes 5a, 5b, 6a and 6b [13].

434
V.D. Gupta et al. / Dyes and Pigments 97 (2013) 429e439
Table 2
Comparative photo-physical properties of the triphenylamine and carbazole (given in bracket) based dyes in different solvents.
Solvent
TMS1 (5a)
labs, nm
TMS2 (5b)
labs, nm
TDS1 (6a)
labs, nm
TDS2 (6b)
labs, nm
lems, nm
lems, nm
lems, nm
lems, nm
Toluene
1,4-Dioxane
DCM
Chloroform
Ethyl acetate
Acetone
Methanol
Ethanol
487 (453)
480 (444)
481 (456)
502 (ꢂ)
574 (530)
610 (534)
599 (552)
619 (ꢂ)
463 (429)
459 (426)
454 (429)
475 (ꢂ)
560 (522)
590 (528)
581 (547)
608 (ꢂ)
508 (474)
507 (465)
505 (477)
523 (ꢂ)
570 (526)
601 (536)
588 (553)
604 (ꢂ)
490 (450)
474 (447)
481 (457)
502 (ꢂ)
562 (524)
589 (530)
577 (554)
604 (ꢂ)
478 (447)
481(450)
484 (453)
490 (ꢂ)
620 (548)
652 (558)
631 (572)
630 (ꢂ)
454 (426)
457 (429)
463 (429)
466 (ꢂ)
599 (534)
630 (548)
625 (560)
619 (ꢂ)
505 (468)
508 (474)
511 (474)
514 (ꢂ)
615 (550)
643 (568)
627 (578)
633 (ꢂ)
481 (448)
484 (451)
493 (457)
493 (ꢂ)
602 (546)
634 (552)
628 (570)
619 (ꢂ)
Acetonitrile
DMF
481 (450)
490 (457)
659 (570)
654 (574)
457 (429)
466 (430)
644 (560)
642 (560)
508 (471)
520 (484)
652 (578)
653 (584)
487 (450)
496 (459)
643 (572)
640 (574)
*(ꢂ) indicated not reported.
have been carried out using thermal gravimetric techniques (TGA).
The thermogravimetric studies have been carried out in the tem-
perature range 50e600 ꢀC under nitrogen gas at a heating rate of
10 ꢀC minꢂ1. The TGA results indicated that the synthesized dyes
are stable up to 300 ꢀC which indicates that the presence of tri-
phenylamine conjugated framework imparts thermal stability. TGA
revealed the onset decomposition temperature (Td) of dyes TMS1,
TMS2, TDS1 and TDS2 are 306 ꢀC (93%), 323 ꢀC (96%), 324 ꢀC (93%)
and 328 ꢀC (96%), respectively (Fig. S7) which indicate that the
decomposition temperatures increase with the increase of con-
jugation length and electron rich substituent effect.
present at the end. The resulting optimized geometry of dye TMS1
is such that it has a small twist dihedral angle along C6eC1eC39e
N52 is 13.1ꢀ (Fig. 7) but bis-styryl dye TDS1 showed little lower
twist of 15.3ꢀ (Fig. S10). Dye TDS1 did not possess a vertical plane of
symmetry (CS) in the molecule. Therefore, bonds of either-side of
middle triphenylamine moiety have different bonds lengths.
The optimized geometry of dye TMS2 is such that it has also
a small twist dihedral angle of 15.3ꢀ along C6eC1eC39eO54 angle
between the phenyl ring of triphenylamine and terminal carbe-
thoxy units (Fig. S11). The dye TDS2 showed highest twist angle
among the four dyes of angle 23.5ꢀ (Fig. S12). Also one of the two
carbonyl groups is facing away from triphenylamine ring whereas
second carbonyl ring is pointing inwards. But, in dye TMS2, car-
bonyl group is pointing towards triphenylamine ring. The pending
In general the backbones of these dyes are stable up to 300 ꢀC
and above 300 ꢀC the thermogravimetric curve of these dyes
showed a major loss in weight. The comparisons of the Td
(decomposition temperature) show that the thermal stability of
the TMS1, TMS2, TDS1 and TDS2 decreases in the order
TDS2 > TDS1 > TMS2 > TMS1. The results showed that synthesized
dyes have good thermal stability. Dyes TMS1 and TMS2 showed
a sharp decomposition after temperature 306 ꢀC and 323 ꢀC
respectively and completely decomposed beyond 550 ꢀC. However,
dyes TDS1 and TDS2 showed sluggish decomposition characteris-
tics and completely decomposed beyond 600 ꢀC. The high molec-
ular weight and polar substituents of the synthesized dyes are
beneficial for intermolecular interactions, such as van der Waals
force and dipoleedipole interaction to increase the thermal
stability.
phenyl ring on C30 atom of
p-bridge was twisted with a dihedral
angle 57.4ꢀ, 64.4ꢀ for the dyes TMS1 and TMS2 and in case of dyes
TDS1 and TDS2, it is 57.3ꢀ and 61.8ꢀ on one side of extended con-
jugation and for other side it is 57.0ꢀ and 65.2ꢀ.
Dye TMS1 was optimized in the excited state and major bond
lengthening was observed between the bonds C4eN33, C22eN33
,
C11eN33, C34eC35, C35eC38, C38eC39, C39eC53, C39eC51, C51eN52
and C53eN44 by 0.054, 0.031, 0.031, 0.017, 0.010, 0.040, 0.012,
ꢀ
0.012, 0.006 and 0.006 A and bond length shortened for the bonds
ꢀ
C
29eC30, C31eC32, C31eC33 with 0.012, 0.011, 0.023 A (Fig. 7 and
S13). Also, the three phenyl ring present on triphenylamine are
orthogonal to each other by ꢂ62.9 and ꢂ64.6ꢀ and more twisting is
being observed in the excited state as shown in Fig. 7 and S13. Also
the bond angles between three rings on triphenylamine are not
same and decreases from 121.1 to 118.5ꢀ along the angle C4eN33e
C11 and 121.2 to 118.6ꢀ along the bond angle C4eN33eC22
whereas bond angle increases from 117.7 to 122.9ꢀ along the
bond angle C11eN33eC22. Such lengthening and shortening of the
bonds i.e. the bond length alteration were due to the effect of donor
and acceptor groups present in the molecules. Similarly for dyes
3.4. Optimized geometries of dyes TMS1, TMS2, TDS1 and TDS2
Ground state geometries of the dyes were having planar
arrangement with one of the phenyl ring present on the triphe-
nylamine moiety, p-bridge and acceptor cyano or carbethoxy group
10
TMS2
642 nm
9
8
7
6
5
4
3
2
1
0
Toluene
TMS1
TMS2
TDS1
TDS2
600
DCM
659 nm
574 nm
TMS1
654 nm
Chloroform
TDS2
640 nm
Ethyl acetate
500
Acetone
Methanol
Ethanol
400
Acetonitrile
DMF
300
200
100
0
TDS1
653 nm
515
565
615
665
715
765
520
570
620
670
720
770
Wavelength (nm)
Wavelength (nm)
Fig. 4. Fluorescence emission spectra of dyes TMS1, TMS2, TDS1 and TDS2 (in DMF).
Fig. 5. Normalized fluorescence emission spectra of dye TMS1 in different solvents.

V.D. Gupta et al. / Dyes and Pigments 97 (2013) 429e439
435
TDS2
Table 3
TDS1
TMS1
TMS2
649 nm
665 nm
630 nm
200
150
100
50
Mulliken charge (e) distribution for dyes TMS1, TMS2, TDS1 and TDS2 in the ground
state (GS) optimized geometry [excited state (ES) for TMS1] in DMF.
625 nm
TMS1
TMS2
TDS1
TDS2
Atom no.
TMS1
GS
TMS2
Atom no.
TDS1
TDS2
ES
N33
C4
C11
C22
C1
C34
C35
C38
C39
C51
C53
N52
N54/O54
H36
H37
O55
ꢂ0.644
0.336
0.252
0.253
0.160
ꢂ0.175
ꢂ0.208
0.165
0.020
0.300
0.286
ꢂ0.545
ꢂ0.541
0.174
0.167
e
ꢂ0.644
0.212
0.300
0.303
0.169
ꢂ0.166
ꢂ0.202
0.176
0.025
0.301
0.293
ꢂ0.543
ꢂ0.540
0.185
0.172
e
ꢂ0.645
0.331
0.253
0.256
0.161
ꢂ0.178
ꢂ0.199
0.103
N33
C4
C11
C21
C1
C33
C34
C37
C38
C50
C52/C81
N51/N52
N53/O82
H35
ꢂ0.642
0.311
0.309
0.232
0.163
ꢂ0.172
ꢂ0.201
0.166
0.028
0.304
0.291
ꢂ0.540
ꢂ0.537
0.178
0.171
e
ꢂ0.643
0.307
0.305
0.238
0.165
ꢂ0.177
ꢂ0.193
0.102
0
550
600
650
700
750
ꢂ0.043
ꢂ0.038
Wavelength (nm)
0.26
0.264
0.664
0.667
Fig. 6. Solid-state fluorescence spectra (normalized) of dyes TMS1, TMS2, TDS1 and
TDS2 in powder form.
ꢂ0.559
ꢂ0.534
0.168
0.187
ꢂ0.489
ꢂ0.555
ꢂ0.531
0.171
0.191
ꢂ0.487
H36
O83
TMS2, TDS1 and TDS2 the ground state geometry is shown in the
Figs. S11eS13.
The Mulliken charge distribution in ground state (DMF solvent)
on selected atoms of the dyes TMS1, TMS2, TDS1 and TDS2 are
shown in Table 3 and Fig. 8 and S14eS17. In the excited state, the
dye TMS1 showed increase in the positive charge on atom C22 and
C11; and decrease on C4 which suggest charge delocalization in the
molecule from triphenylamine donor moiety to dicyanovinyl
acceptor moiety. These atoms are also engaged in bond lengthening
at the excited state. The charge on nitrogen atom present as
a central atom in the triphenylamine moiety did not show any
change in the charge (Fig. S14). The charge on the C4 atom was
found to be nearly same in dyes TMS2, TDS1 and TDS2 in the
ground state. The atom C39 (in dyes TMS1 and TMS2) and C38 (in
dyes TDS1 and TDS2) to which cyano and carbethoxy groups are
attached possess positive charge 0.020 and 0.028 in the dyes TMS1
and TDS1 whereas it is negative ꢂ0.043 and ꢂ0.038 in the dyes
TMS2 and TDS2 (Table 3). Fig. 8 and S13eS16 represent Mulliken
charge distribution on atoms in the molecule. Structures indicating
charge distribution on the dyes were visualized using GaussView
5.0 software [30].
3.5. Electronic vertical excitation spectra (TDDFT)
Electronic vertical excitations were calculated using TD-B3LYP/
6-31G(d) method. Computed vertical excitation spectra associated
with their oscillator strengths, composition, and their assignments
of the chromophores as well as corresponding experimental ab-
sorption wavelengths of the dyes TMS1, TMS2, TDS1 and TDS2 are
reported in supporting material in Tables S1eS4. As discussed
earlier in the Section 3.1, absorption maxima did not show much
solvatochromism, while Stokes shift increases progressively with
the increase in solvent polarity for all four dyes. These observations
are in accordance with the higher stabilization in increasingly polar
solvents. The absorption band occurring with higher oscillator
strength at lower energy is due to intramolecular charge transfer
(ICT) characteristic of donorepeacceptor pushepull dyes
(Tables S1eS4). These ICT bands for all four dyes were mainly due to
the electronic transition from highest occupied molecular orbital
(HOMO) to lowest unoccupied molecular orbital (LUMO).
ꢀ
Fig. 7. Optimized geometry parameters of dye TMS1 in DMF solvent in the ground state and excited state (bond length are in A, dihedral angles are in degree).

436
V.D. Gupta et al. / Dyes and Pigments 97 (2013) 429e439
3.6. Frontier molecular orbitals
The different frontier molecular orbitals were studied to un-
derstand the electronic transition and charge delocalization within
these pushepull chromophores. The comparative increase and
decrease in the energy of the occupied (HOMO’s) and virtual or-
bitals (LUMO’s) gives a qualitative idea of the excitation properties
and the ability of hole or electron injection. First allowed and the
strongest electron transitions with largest oscillator strength usu-
ally correspond almost exclusively to the transfer of an electron
from HOMO / LUMO. Table S5 shows the energies of different
molecular orbitals involved in the electronic transitions of these
pushepull dyes in different solvents. It was observed that elec-
tronic transition in each case included HOMO / LUMO transition.
In the case of mono-styryl De
peA dye TMS1, the energy gap of
HOMO and LUMO orbitals were lowered as the solvent polarity was
increased. But the extent of decrease in energy levels was found to
be more in the case of LUMO by 0.057 eV and the increase in HOMO
by 0.019 eV as we move from 1,4-dioxane to DMF. This indicates
that the LUMO is more relaxed in the polar solvent (Table S5).
Whereas in case of TMS2, both HOMO and LUMO were relaxed as
the solvent polarity was increased. The extent of decrease of LUMO
(0.128 eV) was greater than HOMO (0.042 eV).
Fig. 8. Graph of Mulliken charge distribution on the dye TMS1 in the ground and
excited state optimized geometry in DMF.
Dye TMS1 showed the lower experimental absorption maxima
in 1,4-dioxane (480 nm) and red-sifted absorption band in DMF
(490 nm). The computed vertical excitations for dye TMS1 were
found low in 1,4-dioxane (516 nm) and high in chloroform
(502 nm). Similar, solvatochromism results were obtained for the
other three dyes TMS2, TDS1 and TDS2. The largest wavelength
difference between the experimental absorption maxima and
computed vertical excitation is 45 nm (DCM) for dye TMS1. On
moving from toluene to DMF, 13 nm shift in the absorption band
was observed for dye TMS1 and similar 14 nm shift was observed in
the computed vertical excitation spectra. The largest wavelength
difference between experimental absorption maxima and com-
puted vertical excitation was 65 (acetone), 78 and 87 nm (DCM) for
dyes TMS2, TDS1 and TDS2.
But, in case of bis-styryl AepeDepeA dye TDS1, energy of both
the orbitals was increased as a function of solvent polarity. The
energy of HOMO was highly increased by 0.124 eV, while the en-
ergy of LUMO was increased to lesser extent by 0.026 eV (Table S6).
For the dye TDS2, energy of HOMO was increased by 0.058 eV and
that of LUMO was lowered by 0.051 eV as the solvent polarity
increased. Normally, all these dyes have shown decrease in the
band gap (HOMOeLUMO) as polarity of the solvent increased.
Molecular orbital plots for these dyes are shown in Figs. 9
and 10. From the pictorial diagram, it was found that HOMO and
LUMO orbitals of the dyes are fully delocalized on the donor tri-
phenylamine moiety, phenyl ring and acceptor cyano or carbethoxy
TMS1 was optimized in the first excited state to calculate the
fluorescence. Experimentally obtained fluorescence emission
spectral data and emission computed from TD-B3LYP/6-31G(d)
computations are shown in Table 4. The computational results
obtained by using TD-B3LYP/6-31G(d) were not able to reproduce
the solvatofluorism behavior of the dye TMS1 and shown almost
nearly same value of emission energy. The experimental emission
wavelength and emission computed by TD-B3LYP/6-31G(d)
showed a largest difference of 58 nm in toluene and showed
a closest difference of 4 and 5 nm in methanol and ethanol. A graph
plotted (Fig. S18) represents correlation between experimentally
recorded emissions against the emissions computed from TD-
B3LYP/6-31G(d) for the dye TMS1.
group through
p-bond conjugation. Electron densities in the HO-
MOs of all these four dyes were largely located on donor triphe-
nylamine moiety, and electron densities on the LUMOs were
found localized on acceptor through p-bridge. The excitation from
HOMO to LUMO mostly consists of charge transfer from triphe-
nylamine moiety on the donor to the acceptor end. Energy gap of
HOMO / LUMO explains the charge transfer interactions within
the dye, which also influences non-linear properties of dyes. Fig. 9
contains FMO of dye TMS1 in the excited state, which shows that
electron densities are located on the donor triphenylamine moiety
in the HOMO and these electron densities were fully transferred on
the acceptor moiety in the LUMO.
3.7. Static second-order nonlinear optical (NLO) properties
Table 4
Pushepull chromophores are likely to have good non-linear
properties and their first hyperpolarizability (bo) value can be
enhanced due to their relative orientation. Thus, pushepull chro-
mophores have been studied due to their good linear and nonlinear
optical properties.
Experimental UVeVisible emission and computed emission from TD-B3LYP/6-
31G(d) computations for dye TMS1 in different solvents.
Solvents
Experimentala
lems (nm)
TD-B3LYP/6-31G(d)
emission (nm)b
1,4-Dioxane
Toluene
Ethyl acetate
DCM
Chloroform
Acetone
Methanol
Ethanol
574
610
620
599
619
652
631
630
659
654
632
632
633
633
633
635
635
635
635
636
Second-order NLO properties of the triphenylamine De
peA and
Ae
p
eDe eA chromophores were calculated by using density
p
functional theory (DFT). The static first hyperpolarizability (bo) and
its related properties for dyes TMS1, TMS2, TDS1 and TDS2 were
calculated using B3LYP/6-31G(d) on the basis of the finite field
approach [15].
The computed b-tensors are given in Table 5. The computed first
Acetonitrile
DMF
hyperpolarizability bo, of dyes was found to be ranging from 196.45,
222.18, 216.24 and 221.65 ꢁ 10ꢂ30 e.s.u. for dyes TMS1, TMS2, TDS1
and TDS2 respectively. These values are greater than urea (0.38 ꢁ
a
Experimentally recorded emission maxima.
Emission computed using TD-B3LYP/6-31G(d) level.
b

V.D. Gupta et al. / Dyes and Pigments 97 (2013) 429e439
437
Fig. 9. Frontier molecular orbitals of dye TMS1 in the ground and excited state.
Fig. 10. Frontier molecular orbitals of dyes TMS2, TDS1 and TDS2 in the ground state.
10ꢂ30 e.s.u.) by 516, 583, 568 and 582 times. As expected, these dyes
have shown a large hyperpolarizability, suggesting considerable
charge transfer characteristics of the first excited state which is
further supported by the large difference in the dipole moments
between the ground and excited states from the solvatochromism
studies. These dyes can be used as a promising candidate in the
field of non-linear optics.
4. Conclusion
Table 5
Static first hyperpolarizability and its
TDS2 (all values in e.s.u.).
b-components of dyes TMS1, TMS2, TDS1 and
In this paper, we have developed pushepull chromophores of
AepeD and AepeDepeA types containing triphenylamine as
b
-tensors TMS1
TMS2
TDS1
1.25 ꢁ 10ꢂ29
TDS2
ꢂ5.76 ꢁ 10ꢂ29
bxxx
bxxy
bxyy
byyy
bxxz
byyz
bxzz
byzz
bzzz
bo
ꢂ1.03 ꢁ 10ꢂ28 2.30 ꢁ 10ꢂ28
electron donor and electron withdrawing cyano/carbethoxy moi-
eties. Triphenylamine moiety was introduced to the make the
system non-planar. These synthesized fluorophores were con-
firmed by FT-IR, 1H NMR and Mass spectral analysis. The optical
properties of these dyes were studied in solvents of different po-
larities. The resultant solvatochromism data showed that these
dyes have a high Stokes shift ranging from 2141 to 6354 cmꢂ1
which increases with the solvent polarity. Solvatochromism studies
have shown large increase in the dipole moment in the first excited
ꢂ2.86 ꢁ 10ꢂ30 ꢂ2.15 ꢁ 10ꢂ29 ꢂ2.04 ꢁ 10ꢂ28 ꢂ2.04 ꢁ 10ꢂ28
8.06 ꢁ 10ꢂ31
1.10 ꢁ 10ꢂ31
ꢂ7.46 ꢁ 10ꢂ30 ꢂ2.52 ꢁ 10ꢂ29 2.14 ꢁ 10ꢂ29
6.67 ꢁ 10ꢂ30
ꢂ1.23 ꢁ 10ꢂ29 ꢂ1.58 ꢁ 10ꢂ29
ꢂ8.26 ꢁ 10ꢂ29 ꢂ5.66 ꢁ 10ꢂ32 ꢂ1.26 ꢁ 10ꢂ29 ꢂ4.04 ꢁ 10ꢂ30
9.52 ꢁ 10ꢂ31
ꢂ3.95 ꢁ 10ꢂ31 ꢂ2.58 ꢁ 10ꢂ30 ꢂ3.38 ꢁ 10ꢂ30
ꢂ5.72 ꢁ 10ꢂ29 ꢂ5.75 ꢁ 10ꢂ31 ꢂ4.18 ꢁ 10ꢂ31 5.76 ꢁ 10ꢂ31
1.52 ꢁ 10ꢂ30
ꢂ6.21 ꢁ 10ꢂ32 9.22 ꢁ 10ꢂ31
1.32 ꢁ 10ꢂ30
ꢂ3.36 ꢁ 10ꢂ29 ꢂ5.00 ꢁ 10ꢂ32 6.13 ꢁ 10ꢂ31
ꢂ4.37 ꢁ 10ꢂ31
196.45 ꢁ 10ꢂ30 222.18 ꢁ 10ꢂ30 216.24 ꢁ 10ꢂ30 221.65 ꢁ 10ꢂ30

438
V.D. Gupta et al. / Dyes and Pigments 97 (2013) 429e439
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molecular orbital plots have displayed that majority of electron
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transfer. The TGA results show that they possess a good thermal
stability.
In summary, this paper describes the synthesis, character-
ization, photo-physical, thermal properties and DFT study of these
twisted pushepull styryl dyes. In conclusion, these dyes can be
used promising candidate for various applications in nonlinear
optics (NLO), electronic and photonic devices, and organic light e
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Acknowledgements
Vinod Gupta is greatly thankful to University Grant Commission
(UGC), New Delhi, India for providing financial support. Abhinav
Tathe is grateful to UGC for research support under Major Research
Project as well as UGC-CSIR fellowship. Vikas Padalkar is thankful
for postdoctoral fellowship from the Principal Scientific Adviser
(PSA), Govt. of India. Prashant Umape is thankful to UGC-CAS for
providing research fellowship under Special Assistance Programme
(SAP).
(b) Roquet S, Cravino A, Leriche P, Alévêque O, Frère P, Roncali J. Triphenyl-
amineethienylenevinylene hybrid systems with internal charge transfer as
donor materials for heterojunction solar cells. J Am Chem Soc 2006;128:
3459e66;
(c) Ning ZJ, Tian H. Triarylamine: a promising core unit for efficient photo-
voltaic materials. Chem Commun 2009;37:5483e95.
Appendix A. Supplementary data
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Supplementary data related to this article can be found at
http://dx.doi.org/10.1016/j.dyepig.2012.12.024.
(b) Tian H-N, Yang X-C, Pan J-X, Chen R-K, Liu M, Zhang Q-Y, et al.
A triphenylamine dye model for the study of intramolecular energy transfer
and charge transfer in dye-sensitized solar cells. Adv Funct Mater 2008;18:
3461e8;
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