Synthesis of novel diphenylamine-based fluorescent styryl colorants and study of their thermal, photophysical, and electrochemical properties

Article abstract of DOI:10.1007/s00706-010-0365-6

Three novel "Y"-shaped acceptor-π-donor-π-acceptor-type compounds were synthesized from 4,4′-(hexylimino)bis(benzaldehyde) as a donor and 2-methylthiazolo[4,5-b]quinoxaline derivatives as strong electron acceptors condensed by classical Knoevenagel condensation. Their absorption, emission, and thermal properties and electrochemical stability were investigated. It was found that the strong electron acceptor-donor chromophoric system of these compounds showed high Stokes shift, excellent thermal stability, and electrochemical reversibility. The solvatochromic behavior of these colorants was studied by using various solvents such as toluene, chloroform, ethyl acetate, tetrahydrofuran, methanol, and N,N-dimethylformamide in increasing order of polarity. The dyes were characterized by means of elemental analysis, ¹H NMR, and mass spectrometry. Springer-Verlag 2010.

Full text of DOI:10.1007/s00706-010-0365-6

Monatsh Chem (2010) 141:1145–1151
DOI 10.1007/s00706-010-0365-6
ORIGINAL PAPER
Synthesis of novel diphenylamine-based fluorescent styryl
colorants and study of their thermal, photophysical,
and electrochemical properties
•
Yogesh A. Sonawane Rajkumar N. Rajule
•
Ganapati S. Shankarling
Received: 17 November 2009 / Accepted: 29 June 2010 / Published online: 5 August 2010
Ó Springer-Verlag 2010
Abstract Three novel ‘‘Y’’-shaped acceptor–p-donor–
p-acceptor-type compounds were synthesized from
photovoltaic cells [4], and in traditional textile and polymer
fields [5].
Electron donors like triphenylamine and diphenylamine
4,40-(hexylimino)bis(benzaldehyde) as
a
donor and
2-methylthiazolo[4,5-b]quinoxaline derivatives as strong
electron acceptors condensed by classical Knoevenagel
condensation. Their absorption, emission, and thermal
properties and electrochemical stability were investigated.
It was found that the strong electron acceptor–donor
chromophoric system of these compounds showed high
Stokes shift, excellent thermal stability, and electrochem-
ical reversibility. The solvatochromic behavior of these
colorants was studied by using various solvents such as
toluene, chloroform, ethyl acetate, tetrahydrofuran, meth-
anol, and N,N-dimethylformamide in increasing order of
polarity. The dyes were characterized by means of ele-
with high electron mobility and thermal and photochemical
stability are commonly used as hole-transporting materials
or light-emitting materials for balanced charge injection.
Recently triphenylamine derivatives have been widely
investigated [6]. N-Alkyldiphenylamines have not been
exploited much in the past, but attract increasing interest as
they exhibit better solubility in common organic solvents,
excellent thermal and electrochemical stability, electron-
donating ability, and optoelectronic properties [7]. The
rigidity and non-planar structure of N-alkyldiphenylamines
offer a sterically well-hindered feature. The presence of
two electron acceptor moieties increases the electron
affinity of the compounds [8]. From the viewpoint of
molecular design, structural features such as the long p
conjugation style, the molecular planarity, and the length of
the conjugated bridge play important roles in functional
chromophores, which are highly promising for electronic
applications like photonics materials [9, 10], holographic
optical data storage [11], and organic photorefractive
materials. It has been demonstrated that diarylamine- and
triarylamine-based chromophores have extremely high
electro-optic properties [12]. Exploitation of electron
acceptor fused quinoxaline systems as fluorescent styryl
dyes is of interest because of their strong fluorescence
[13, 14] and their versatile applications [15, 16]. Quinox-
alines are in general easy to prepare [17–19].
1
mental analysis, H NMR, and mass spectrometry.
Keywords Dyes ꢀ Absorption spectra ꢀ
Fluorescent colorants ꢀ Cyclic voltammetry ꢀ
Knoevenagel condensation
Introduction
Electron transfer (ET) is one of the most fundamental
phenomena in chemistry and biology [1]. Organic fluo-
rescent heterocyclic chromophores have a wide range of
applications in biochemistry and electronics such as
molecular probes [2], organic light-emitting diodes [3],
In this research work, our interest was to design and
develop novel heterocycle-based chromophores with
excellent photophysical and thermal properties. We report
the synthesis and study of new chromophores based on
4,40-(hexylimino)bis(benzaldehyde) (11). We have espe-
cially focused on the condensation and synthesis of two
Y. A. Sonawane ꢀ R. N. Rajule ꢀ G. S. Shankarling (&)
Department of Dyestuff Technology,
Institute of Chemical Technology,
N. P. Marg, Matunga, Mumbai 400019, India
e-mail: gss@udct.org; gsshankarling@gmail.com
123

1146
Y. A. Sonawane et al.
excellent molecular moieties, 2-methylthiazolo[4,5-b]-
quinoxaline (6) and 4,40-(hexylimino)bis(benzaldehyde)
(11). Rangnekar et al. [20] reported the synthesis and study
of quinoxaline-based styryl dyes for polyester applications.
We have exploited that earlier work and now report the
synthesis and study of novel quinoxaline-based styryl dyes
for functional applications with improved photophysical
properties.
solvents such as chloroform, dichloromethane, 1,2-dichlo-
roethane, acetonitrile, tetrahydrofuran (THF), and N,N-
dimethylformamide (DMF) due to introduction of the long
hexyl chain in the compounds. All intermediates and final
compounds were characterized by 1H NMR, 13C NMR
spectroscopy, mass spectrometry, and elemental analysis.
The coupling constant (J = 16.2 Hz) of olefinic protons in
purified chromophores 12a–12c indicates that the reaction
afforded the trans isomer [25]. There are chances of for-
mation of isomeric compounds but these may get removed
during recrystallization. No isomer was detected in the
synthesis of colorant 12c as proven by NMR spectra.
In order to investigate photophysical properties the
absorption and photoluminescence spectra of 12a–12c in
chloroform solution (1 9 10-4 M) were recorded. The
absorption maxima and fluorescence were in the range of
447–516 nm and 570–610 nm, respectively. These dyes
showed high molar extinction coefficients and their Stokes
shifts were in the range of 74–163 nm (Tables 2, 3). The
electron-donating groups in 12a–12c generate the batho-
chromic shifts due to their long conjugation. Extended
chromophores displayed dramatic enhancement in absorp-
tion and fluorescence properties and Stokes shift.
Results and discussion
Most of organic dyes have limited applications because of
some disadvantages such as lack of photophysical and
thermal stability [21]. In order to overcome these problems,
‘‘Y’’-shaped dyes were designed and synthesized. The
linear long alkyl chain was introduced via the 4,40-
(hexylimino)bis(benzaldehyde) moiety to improve the
solubility of the resulting fluorescent compounds in com-
mon organic solvents. The photophysical, thermal, and
electrochemical properties of these dyes were studied
(Table 1).
2,3-Dimercaptoquinoxaline (4) was synthesized from
benzene-1,2-diamine in three steps. The advantages of this
method include good yields, short reaction times, and
simple procedures and, in most cases, the product is pre-
cipitated from the reaction media. Partial ammonolysis of
compound 4 using alcoholic ammonia yielded the crystal-
line compound 5. An optimum condition for this
temperature-sensitive reaction is 100–120 °C for 3 h,
which gave 70% yield. Electron acceptors 2-methylthiaz-
olo[4,5-b]quinoxaline (6) and 2,6-dimethylthiazolo[4,5-b]-
quinoxaline (7) were synthesized by condensation reaction
of 2,3-dichloroquinoxaline with sodium hydrogen sulfide,
followed by subsequent reaction with ammonia and acetic
anhydride (Scheme 1) [22, 23]. Key intermediate 11 was
synthesized by N-hexylation of diphenylamine, followed
by Vilsmeier–Haack formylation (Scheme 2) [24]. Chro-
mophores 12a–12c were synthesized by the classical
Knoevenagel condensation of 4,40-(hexylimino)bis(benz-
aldehyde) with electron acceptors 6 and 7 (Scheme 3).
Chromophores 12a–12c are soluble in common organic
Absorption and emission maxima of chromophores
12a–12c were compared with reported quinoxaline-based
styryl dyes 12d and 12e [22] (Table 2). Absorption and
Reflux
N
N
R
OH
OH
R
NH2
NH2
OH
O
O
4N HCl
OH 93%
+
1a
: R = H
1b: R = CH3
2a
: R = H
2b: R = CH3
Reflux
POCl3 / PCl5
85%
Ethanol
NaSH
N
N
R
Cl
Cl
R
N
N
SH
SH
86%
4a
: R = H
3a
3b
: R = H
: R = CH3
4b
: R = CH3
72% NH3
Table 1 Thermal and electrochemical properties of 12a–12c
Compound
TGAa (°C)
DSCb (°C)
Eox (V)
Ered (V)
R
N
N
NH2
SH
R
N
N
12a
12b
12c
a
312
317
325
149
218
208
1.32
1.34
-1.04
-1.08
N
S
Acetic anhydride
74%
Thermogravimetric analysis (TGA), decomposition temperature of
the respective compounds
5a: R = H
5b: R = CH3
6: R = H
7: R = CH3
b
Differential scanning calorimetry (DSC), transition temperature of
the respective compounds
Scheme 1
123

Synthesis of diphenylamine-based novel fluorescent styryl colorants
1147
The compounds 12a–12c exhibit absorption maxima at
459, 507, and 498 nm, respectively (Fig. 1). Emission
maxima of 12a–12c were observed at 570, 592, and
594 nm, respectively (Fig. 2). Absorption and emission
maxima of 12b and 12c are significantly higher than those
of chromophore 12a, and the fluorescence intensity of 12c
is higher than that of 12a and 12b.
Br
+
N
H
9
8
TBAB, Reflux
61%
Toluene, Na2CO3
Solvatochromism [26] was studied by using various
solvents such as toluene, chloroform, ethyl acetate, tetra-
hydrofuron, methanol, and N,N-dimethylformamide in
increasing order of polarity. The data collected in Table 3
clearly indicate that absorption, emission maxima, and
Stokes shift in DMF are higher than in toluene because of
the higher solvatochromic effect of the polar solvent DMF.
Chromophores 12b and 12c showed higher absorption
maxima than 12a because of the long extended conjuga-
tion. The higher Stokes shift of compound 12a reveals that
only one electron-withdrawing group is responsible for this
change.
N
10
80 °C, 14h
65%
DMF/POCl3
O
O
H
Thermal properties of dyes 12a–12c were explored.
Phase transitions of compounds 12a–12c are displayed in
Fig. 3. Heat stability of compounds 12a–12c is shown in
Fig. 4 and tabulated in Table 1.
H
N
Compounds 12a–12c were subjected to thermogravi-
metric analysis to investigate their thermal stability.
Stepwise isothermal ramping up to 600 °C at 10 °C/min
was performed in a nitrogen atmosphere. The change in
weight of the colorants was measured as a function of
temperature. Thermogravimetric analysis of compound
12c showed the highest decomposition temperature, 98%
of the weight composition was stable up to 325 °C and
underwent rapid thermal decomposition thereafter.
Compound 12b was 97% stable up to 317 °C and 12a
was 95% stable up to 312 °C. Phase transition of the
chromophores 12a–12c measured by differential scanning
11
Scheme 2
emission maxima of 12d and 12e are 515, 593 and 505, 586,
respectively, which is not much different from 12a to 12c.
Stokes shifts of chromophores 12a–12c are higher than 12d
and 12e. Two electron-withdrawing groups increase the
hyperpolarizability in compounds 12a–12c.
Scheme 3
N
N
N
S
R
N
N
N
S
11
+
11
+
2
6
6
: R = H
7: R = CH3
Piperidine
Ethanol
55%
Piperidine
Ethanol
70%
R
R
N
N
H
N
N
N
S
O
N
N
N
N
N
S
S
N
12a
12b
: R = H
12c: R = CH3
123

1148
Y. A. Sonawane et al.
The dyes show a strong fluorescence at long UV. Pho-
tographs of dyes in daylight and under long UV (365 nm)
are presented in Fig. 7.
Table 2 Comparison of the spectral properties of the dyes 12a–12c
with those of 12d–12e in chloroform
kmax (nm) kem (nm) Stokes shift e (dm3 mol-1 cm-1
)
12a 459
12b 507
12c 498
12d 515
12e 505
570
592
594
593
586
111
85
96
78
81
50,000
68,261
77,440
–
Conclusion
We have successfully designed and synthesized novel
‘‘Y’’-shaped organic chromophores by using 4,40-(hexyl-
imino)bis(benzaldehyde) (11) as electron donor center and
2-methyl- (6) and 2,6-dimethylthiazolo[4,5-b]quinoxaline
(7) as electron-withdrawing groups. Compounds 12a–12c
exhibited high thermal stability and excellent electro-
chemical reversibility. These compounds showed solva-
tochromism in different solvents. The dyes 12a–12c
displayed excellent photoluminescent properties and high
molar extinction coefficient and Stokes shift.
–
N
N
N
N
N
N
S
S
O
O
N
N
12d
12e
calorimetry showed sharp transitions. Compounds 12c
(217 °C) and 12b (208 °C) showed higher phase transi-
tion temperatures than 12a (149 °C). These data indicate
that all of these chromophores have good thermal sta-
bility and are therefore applicable for polymers requiring
higher extrusion temperature ranges.
Experimental
Materials and equipments
All solvents and chemicals were procured from sd fine
chemicals (India) and were used without further purifica-
tion. The reactions were monitored by TLC using 0.25 mm
E-Merck silica gel 60 F254 precoated plates, which were
visualized with UV light. Melting points were measured on
a standard melting point apparatus from Sunder Industrial
Products, Mumbai. UV–Vis absorption spectra were
recorded on a Spectronic GENEYSIS 2 spectrophotometer
instrument from dye solutions (*10-4 M) in chloroform.
The fluorescence maxima were recorded on a Jasco FP-
1520 fluorimeter from dye solutions in chloroform. The 1H
NMR and 13C NMR spectra were recorded at 400 and
The electrochemical properties of the compounds were
studied and showed reversible redox potential. Cyclic
voltammetry (CV) experiments were performed in
dichloromethane solutions containing Bu4NPF6 as the
supporting electrolyte. Voltammograms of *10-4
M
solutions of chromophores 12a–12c were recorded and
Eox and Ered for each compound were determined from
each data set and tabulated in Table 1. Cyclic voltam-
metric traces recorded for 12a and 12b are shown in
Figs. 5 and 6.
Table 3 Spectral properties of the dyes 12a–12c in different solvents
Dye Toluene
no.
Chloroform
Ethyl acetate
kmax kem Stokes
(nm) (nm) shift
e
kmax kem
(nm) (nm) shift
Stokes
e
kmax kem
(nm) (nm) shift
Stokes
e
(dm3 mol-1 cm-1
)
(dm3 mol-1 cm-1
)
(dm3 mol-1 cm-1
)
12a 450
12b 489
12c 510
576
606
584
126
117
74
24,108
39,875
42,240
459
507
498
570
592
594
111
85
50,000
68,261
77,440
447
516
486
610
592
580
163
76
35,424
47,310
47,168
96
94
Dye THF
no.
Methanol
DMF
kmax kem Stokes
(nm) (nm) shift
e
kmax kem
(nm) (nm) shift
Stokes
e
kmax kem
(nm) (nm) shift
Stokes
e
(dm3 mol-1 cm-1
)
(dm3 mol-1 cm-1
)
(dm3 mol-1 cm-1
)
12a 462
12b 498
12c 516
594
596
594
132
98
34,440
50,689
57,024
456
510
504
604
622
610
148
112
106
34,064
51,703
41,606
459
513
510
602
610
608
143
97
36,424
48,710
47,268
78
98
123

Synthesis of diphenylamine-based novel fluorescent styryl colorants
1149
2.5
2.0
1.5
1.0
0.5
0.0
12a
12b
12c
217.89°C
1.353W/g
149.34°C
1.376W/g
208.05°C
0.6312W/g
0
100
200
300
400
500
600
Temperature / °C
Fig. 3 Differential scanning calorimetry of compounds 12a–12c
Fig. 1 UV–Vis spectra of 12a–12c (10-4 M) in chloroform
120
12a
12b
12c
100
80
60
40
20
0
100
200
300
400
500
600
Temperature / °C
Fig. 2 Fluorescence spectra of 12a–12c (10-4 M) in chloroform
Fig. 4 Thermogravimetric analysis of the dyes 12a–12c
100 MHz, respectively, on a Varian Mercury Plus spec-
trometer. Chemical shifts are expressed in d (ppm) using
TMS as an internal standard. Mass spectral data were
obtained with a Micromass Q-Tof (YA105) spectrometer.
Elemental analysis was done on a Harieus rapid analyzer.
Thermogravimetric analysis was carried out on an SDT
Q600 v8.2 Build 100 model of TA instruments. Cyclic
voltammetric analyses were recorded on a l Autolab type-
III 663 VAstand X Metrohm.
J = 8.9 Hz, 2H), 7.47 (d, J = 16.2 Hz, 2H, olefinic), 7.66
(d, J = 8.16 Hz, 2H), 7.74 (d, J = 8.8 Hz, 2H), 7.82 (dd,
J = 8.8 Hz, 2H), 7.82 (dd, J = 2.4 Hz, 1H), 8.14 (dd,
J = 2.1 Hz, 1H), 9.83 (s, 1H, aldehyde) ppm; 13C NMR
(100 MHz, CDCl3): d = 14.1, 22.7, 26.8, 27.6, 31.6, 52.7,
77.5, 76.9, 117.4, 121.3, 124.5, 128.3, 129.8, 129.9, 129.9,
130.1, 130.4, 131.8, 140.9, 141.8, 148.6, 152.5, 153.9, 158.1,
174.1, 190.5 ppm; TOF–MS (ES?): m/z = 493.2 (M ? 1).
N-Hexyl-4-[(E)-2-(thiazolo[4,5-b]quinoxalin-2-yl)-
ethenyl]-N-[4-[(E)-2-(thiazolo[4,5-b]quinoxalin-2-yl)-
ethenyl]phenyl]benzenamine (12b, C40H33N7S2)
4-[N-Hexyl-N-[4-[(E)-2-(thiazolo[4,5-b]quinoxalin-2-
yl)ethenyl]phenyl]amino]benzaldehyde
(12a, C30H28N4OS)
A mixture of 1 g 11 (3.1 mmol), 1.20 g 6 (6.2 mmol), and
piperidine (3–4 drops) in 25 cm3 absolute ethanol was
stirred at reflux for 6 h. The precipitated solid was filtered,
washed with ethanol, dried, and purified by column
chromatography (toluene, 100–200 mesh silica gel). Yield
1.52 g (70%) red crystals; m.p.: 204–206 °C; 1H NMR
(400 MHz, CDCl3): d = 0.90 (t, J = 7.2 Hz, 3H), 1.32 (m,
4H), 1.58 (m, 2H), 1.73 (m, 2H), 3.84 (t, 2H), 7.14 (d,
J = 8.86 Hz, 4H), 7.40 (d, J = 16.2 Hz, 2H, olefinic), 7.84
A mixture of 1 g 11 (3.1 mmol), 0.63 g 6 (3.1 mmol), and
piperidine (2–3 drops) in 15 cm3 absolute ethanol was stirred
at reflux for 6 h. The precipitated solid was filtered, washed
with ethanol, dried, and purified by column chromatography
(toluene, 100–200 mesh silica gel) to obtain orange crystals,
yield 0.9 g (55%); m.p.: 146–148 °C; 1H NMR (400 MHz,
CDCl3): d = 0.89 (t, 3H), 1.32 (m, 4H), 1.58 (m, 2H), 1.72
(m, 2H), 3.83 (t, 2H), 7.01 (d, J = 9.47 Hz, 2H), 7.25 (d,
123

1150
Y. A. Sonawane et al.
chromatography (toluene, 100–200 mesh silica gel). Yield
1.26 g (60%) red crystals; m.p.: 208–210 °C; 1H NMR
(400 MHz, CDCl3): d = 0.89 (t, J = 7.02 Hz, 3H),
1.32–1.36 (m, 4H), 1.59 (m, 2H), 1.73 (m, 2H), 2.64 (s,
6H), 3.83 (t, 2H), 7.12 (d, J = 7.94 Hz, 4H), 7.36 (d,
J = 14.65 Hz, 2H, olefinic), 7.82 (d, 2H, olefinic),
7.61–7.64 (d, J = 7.02 Hz, 4H), 7.78 (d, J = 7.9 Hz,
2H), 8.02 (d, J = 7.02 Hz, 2H), 8.12 (d, J = 2.2 Hz, 2H)
ppm; 13C NMR (100 MHz, CDCl3): d = 14.2, 22.1, 22.8,
26.8, 27.7, 31.7, 52.6, 120.2, 121.2, 127.1, 127.7, 128.3,
128.6, 129.4, 130.0, 132.1, 139.4, 140.2, 140.3, 140.4,
140.9, 141.8, 141.9, 149.2, 152.9, 157.8, 158.3, 173.5,
173.9 ppm; TOF–MS (ES?): m/z = 704.37 (M ? 1).
Fig. 5 Cyclic voltammogram of 12a recorded in dichloromethane
using tetrabutylammonium hexafluorophosphate as supporting
electrolyte
Acknowledgments Authors are thankful to SAIF IIT-Mumbai for
1
recording H NMR, 13C NMR, mass spectra, and elemental analysis,
and are also thankful to Chemical Engineering Department, Institute
of Chemical Technology, Matunga, Mumbai for cyclic voltammetry
analysis of the compounds.
References
1. Fox MA (1992) Chem Rev 92:365
Fig. 6 Cyclic voltammogram of 12b recorded in dichloromethane
using tetrabutylammonium hexafluorophosphate as supporting elec-
trolyte
2. Lakowicz JR (1994) Probe design and chemical sensing. In:
Lakowicz JR (ed) Topics in fluorescence spectroscopy, vol 4.
Plenum, New York, p 501
3. Balaganesan B, Wen S-W, Chen CH (2003) Tetrahedron Lett
44:145
4. Yu G, Gao J, Hummelen JC, Wudl F, Heeger A (1995) J Polym
Sci 270:1789
5. Gold H (1971) In: Venkataraman H (ed) The chemistry of syn-
thetic dyes. Academic, New York, p 535
6. Shirota Y (2000) J Mater Chem 10:1
7. Shirota Y (2005) J Mater Chem 15:75
8. Greenham NC, Moratti SC, Bradley DDC, Friend RH, Holmes
AB (1993) Nature 365:628
9. Albota M, Beljonne D, Bredas JL, Ehrlich JE, Heikal AA, Hess
SE, Kogej T, Levin MD, Marder SRM, McCord-Maughon D,
Perry JW, Rockel H, Rumi M, Subramaniam G, Webb WW,
Wu XL, Xu C (1998) Science 281:1653
Fig. 7 Photographs of dyes 12a–12c (left to right) in daylight (left)
and long UV (365 nm) (right)
10. Cheng YJ, Luo J, Hau SDM, Kim T-D, Shi Z, Lao DB, Tocker
NN, Tian Y, Dalton LR, Reid PJ, Jen AKY (2007) Chem Mater
19:1154
11. Sochova SL, Akella A, Hesselink L (1997) Optic Lett 22:919
12. Van Steenwinckl D, Hendrichs E, Persoons A (2001) J Chem
Phys 114:9557
13. Belgodere E, Bossio R, Chimichi S, Parrini V, Pepino R (1983)
Dyes Pigm 4:59
14. Juang J, Matsuoka M, Fukunishi K (1996) Dyes Pigm 31:141
15. Sabnis RW, Rangnekar DW (1990) J Chem Technol Biotechnol
47:39
(d, 2H, olefinic), 7.60–7.63 (d, J = 8.5 Hz, 4H), 7.79–7.81
(m, J = 3.0 Hz, 4H), 8.15 (dd, J = 1.53 Hz, 2H), 8.25 (dd,
J = 2.13 Hz, 2H) ppm; 13C NMR (100 MHz, CDCl3):
d = 14.2, 22.8, 26.9, 27.7, 31.7, 52.6, 120.2, 121.3, 128.3,
129.6, 129.8, 129.9, 130.1, 140.8, 141.8, 142.3, 149.4,
154.1, 158.3, 174.4 ppm; TOF–MS (ES?): m/z = 676.44
(M ? 1).
16. Rangnekar DW, Mavlankar SV (1992) Dyes Pigm 19:259
17. Rao KV, Rock CP (1996) J Heterocycl Chem 33:447
18. Satam VS, Rajule RN, Bendre SR, Bineesh P, Kanetkar VR
(2009) J Heterocycl Chem 46:221
N-Hexyl-4-[(E)-2-(6-methylthiazolo[4,5-b]quinoxalin-2-
yl)ethenyl]-N-[4-[(E)-2-(6-methylthiazolo[4,5-b]-
quinoxalin-2-yl)ethenyl]phenyl]benzenamine
(12c, C42H37N7S2)
19. Jagtap AR, Satam VS, Rajule RN, Kanetkar VR (2009) Dyes
Pigm 82:82
20. Rangnekar DW, Sonawane ND, Sabnis RW (1998) J Heterocycl
Chem 35:1353
21. Gvishi R, Narang H, Ruland G, Kumar DN, Prasad PN (1997)
Appl Organomet Chem 11:107
A mixture of 1 g 11 (3.1 mmol), 1.33 g 7 (6.2 mmol), and
piperidine (3–4 drops) in 25 cm3 absolute ethanol was
stirred at reflux for 6 h. The precipitated solid was filtered,
washed with ethanol, dried, and purified by column
123

Synthesis of diphenylamine-based novel fluorescent styryl colorants
1151
22. Rangnekar DW, Sonawane ND (2000) Dyes Pigm 45:87
23. Lemke R (1970) Chem Ber 103:1894
24. Park JH, Cho NS, Jung YK, Cho HJ, Shim HK, Kim H, Lee YS
(2007) Organ Electron 8:272
26. Zollinger H (2003) Color chemistry: synthesis, properties, and
applications of organic dyes and pigments, 3rd edn. Wiley-VCH,
Weinheim, Germany, p 42
25. He F, Xia H, Tang S, Duan Y, Zeng M, Liu L, Li M, Zhang H,
Yang B, Ma S, Liu S, Shen J (2004) J Mater Chem 14:2735
123