Synthesis and photophysical study of novel coumarin based styryl dyes

Article abstract of DOI:10.1016/j.dyepig.2015.04.018

New organic dyes comprising phenothiazine, carbazole, indole, diphenylamine moieties, as the electron donors, and coumarin ring as the electron acceptor through ethylenic π bridge were synthesized and characterized. The reaction of different coumarin-4-acetic acids with phenothiazine-3-carbaldehyde in the presence of piperidine in methanol gives highly fluorescent styryl derivatives having cis configuration of ethylenic double bond. Under similar conditions 7-methylcoumarin-4-acetic acid was condensed with indole-3-carbaldehyde, carbazole-3-carbaldehyde, and diphenyl amine aldehyde to give different styryl derivatives with trans configuration of ethylenic double bond. Synthesized compounds were also studied for photophysical properties and show solvatochromism.

Full text of DOI:10.1016/j.dyepig.2015.04.018

Accepted Manuscript
Synthesis and photophysical study of novel coumarin based styryl dyes
Anita K. Sanap, Kailas K. Sanap, Ganapati S. Shankarling
PII:
S0143-7208(15)00140-0
10.1016/j.dyepig.2015.04.018
DYPI 4740
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 13 January 2015
Revised Date: 5 April 2015
Accepted Date: 10 April 2015
Please cite this article as: Sanap AK, Sanap KK, Shankarling GS, Synthesis and photophysical study of
novel coumarin based styryl dyes, Dyes and Pigments (2015), doi: 10.1016/j.dyepig.2015.04.018.
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ACCEPTED MANUSCRIPT
Graphical Abstract
CH3
CH3
O
O
O
O
O
O
S
S
H
H
H
H
Base, rt
O
1
3
N
N
R , R = H
OH
O
2
Bu
R = CH3
R3
Bu
10
7
H1
+
O
R2
O
S
H2
S
Base, rt
H
R1
R3
N
R
4
N
R
1
O
O
R2
R = H, OH
R = H, CH ,OH, NHCO Et
2
R1
9
3
2
3
8
R = H, Cl,
2
1
3
2
1
3
4
a : R = Me, R & R = H
R = propyl, butyl
9a : R = Me, R & R = H

ACCEPTED MANUSCRIPT
Synthesis and photophysical study of novel coumarin based styryl dyes
a
b
a
Anita K.Sanap , Kailas K. Sanap , Ganapati S. Shankarling *
a
Dyestuff Technology Department, Institute of Chemical Technology, N. P. Marg, Matunga, Mumbai
-
400019, India Tel.: 91-22-33612708, Fax: +91-22-33611020
E-mail: gsshankarling@gmail.com
b
Department of Chemistry, N.B. Mehta Science College, Bordi, Palghar- 401701, Maharashtra, India
Abstract
New organic dyes comprising phenothiazine, carbazole, indole, diphenylamine moieties,
as the electron donors, and coumarin ring as the electron acceptor through ethylenic π
bridge were synthesized and characterized. The reaction of different coumarin-4-acetic
acids with phenothiazine-3-carbaldehyde in the presence of piperidine in methanol gives
highly fluorescent styryl derivatives having cis configuration of ethylenic double bond.
Under similar conditions 7-methylcoumarin-4-acetic acid was condensed with indole-3-
carbaldehyde, carbazole-3-carbaldehyde, and diphenyl amine aldehyde to give different
styryl derivatives with trans configuration of ethylenic double bond. Synthesized
compounds were also studied for photophysical properties and show solvatochromism.
Keywords:
Phenothiazine
Coumarin
Fluorescence
Solvatochromism
1

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1
. Introduction
Organic dyes with donor-π-acceptor (D–π–A) structures have attracted increasing
attention since they can provide photoluminescent materials in molecular electronics,
such as efficient nonlinear optical (NLO) materials [1], organic light-emitting diodes
(OLEDs) [2], and solar cells [3]. So far, many organic D-π-A compounds have been
studied experimentally and theoretically. Various classes, including triarylamines [4],
carbazoles [5], fluorenes [6], and thiophenes [7], have mostly been used as electron-
donating moieties, whereas quinolines [8], quinoxalines [9], oxadiazoles [10],
diarylborons [4], and benzothiadiazoles [11], are commonly used as electron-accepting
moieties. In these compounds, donor moiety facilitates hole injection and transport,
whereas the acceptor moiety facilitates electron injection and transport. Carbazole,
diphenyl amine, and phenothiazine are often adopted as donors, as a result of their good
thermal, electrochemical stability, and electron donating abilities [12]. The UV–Vis
absorption and photoluminescence (PL) of these compounds suggest significant
intramolecular charge transfer (ICT) behavior and solvatochromism. Although
remarkable progress has been made in the organic dyes, further optimization of their
chemical structures is still of great necessity. Their various properties could be finely
tuned by using different donor and acceptor groups.
In 1883, Bernthsen, the father of phenothiazine (PTZ) chemistry, first synthesized
phenothiazine compound. The phenothiazines have wide range of applications. Some
phenothiazine derivatives, notably lauth’s violet and methylene blue were commercially
available as dyes even before the discovery of the parent phenothiazine. Various
phenothiazine derivatives are used in dye sensitized solar cells (DSSCs) [13],
Phenothiazine contains electron-rich sulfur and nitrogen as hetero atoms in the middle
2

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ring exhibits good electrochemical stability and electron-donating ability, and has been
considered as a promising donor moiety in organic dyes. Furthermore, the PTZ ring is
non-planar with a butterfly conformation in the ground state, which can impede the
molecular aggregation and the formation of intermolecular excimers. Therefore, PTZ
based organic dyes have attracted broad interest for synthesis of fluorescent compounds.
On the other hand coumarins have also been widely investigated with regard to
their outstanding optical properties. They constitute the largest class of fluorescent dyes
[
14], and are widely used as emission layers in organic light-emitting diodes (OLED)
15], optical brighteners [16], non-linear optical chromophores [17], fluorescent
[
whiteners [18], fluorescent labels as well as probes for physiological measurement [19].
Typical coumarin based fluorescent compounds normally contain an electron donor
group at the 7-position and an electron acceptor such as benzoxazole, benzimidazole or
benzothiazole ring at the 3-position [20]. There is only one report in which coumarin ring
act as acceptor in organic dyes [21]. If we placed electron donating substituent at proper
position in coumarin ring, coumarin ring act as an acceptor as it involves delocalization
of electron over polar carbonyl group through conjugated 3-4 double bond. Based on
these considerations, we have designed and synthesized a series of styryl dyes containing
phenothiazine as donor and coumarin as an acceptor.
Recently, Samant et al synthesized coumarin based fluorescent compounds in
which one coumarin moiety act as electron donor while other coumarin moiety act as an
electron acceptor through ethylenic bridge [21], [22]. These trans-biscoumarinylethenes
are further studied for photophysical properties. Taking inspiration from this, we have
synthesized phenothiazine based coumarin dyes (PTZ-coumarin ethene) which shows
some comparable and interesting results as compared to trans-biscoumarinylethenes. It
3

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includes 1) in biscoumarinylethenes stereochemistry of ethylenic double bond is trans
while PTZ-coumarin ethene show cis stereochemistry of ethylenic double bond. 2) trans-
Biscoumarinylethenes have good emission value in polar solvent like dimethyl sulfoxide
while PTZ-coumarin ethenes have good emission value in non polar solvent like
chloroform. 3) In addition to this, PTZ-coumarin ethenes show higher Em, λMax, higher
Stokes shift and higher quantum yield as compared to trans-biscoumarinylethenes.
2. Experimental
2
.1. Materials and equipments
Phenothiazine was purchased from commercial suppliers and was used without
further purification. Citric acid, phenols and piperidine were purchased from S. D. Fine
1
13
Chemical Ltd. India. Methanol used in this work was of analytical grade. H and C
NMR spectra were recorded on Bruker Advance NMR spectrometer in CDCl /DMSO-d6
3
with TMS as an internal standard, and the chemical shifts were expressed in δ unit (ppm).
Mass spectral data were obtained with micromass-Q-Tof (YA105) spectrometer.
Elemental analysis was carried out with a Thermo finnigan, Flash EA 1112. All Infrared
spectra were recorded on Jasco-FT/IR 4100 LE ATR PRO450-S spectrometer. All the
melting points reported are in degree centigrade and are uncorrected. Absorption spectra
were recorded on Perkin-Elmer Lamada 25 UV-vis spectrophotometer. Emission spectra
were recorded on a Cary Eclipse fluorescence spectrophotometer. The reactions were
monitored by TLC using 0.25 mm E-Merck silica gel 60 F254 precoated plates, which
were visualized with UV light.
2
.2 Synthesis
4

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2
.2.1 Synthesis of 6,7,8-substituted coumarin-4-acetic acid (4)
All coumarin-4-acetic acids (4) were synthesized using reported methods [23]. A mixture
of anhydrous citric acid (1) (192 g, 1 mol) and conc. H SO (280 mL) was stirred at room
2
4
temperature for 1 h and then slowly heated (rate of heating governed by foaming) to 70
o
C. After 30-35 min at this temperature, with stirring throughout, the evolution of carbon
o
monoxide slackened. The clear solution was rapidly cooled to 0 C. To the cooled
solution, m-cresol (3a) (86.4 g, 0.8 mol) and conc. H SO (112 mL) were added with
2
4
stirring, each in three equal portions, at such a rate that the internal temperature did not
o
exceed 10 C. The resulting mixture was stirred at room temperature for 16 h, poured into
ice and the resulting precipitate was filtered and washed thoroughly with water. The
o
precipitate was stirred with saturated NaHCO solution (1000 mL) for 15 min at 65 C.
3
The solution was filtered and the insoluble material was washed with water. Acidification
with conc. HCl of the combined filtrate gave 110 g, 63% of solid 4a which was used
further without purification.
Using the above procedure different substituted phenols (3) were condensed with acetone
dicarboxylic acid to obtain a series of 6,7,8-substituted coumarin-4-acetic acids (4).
2
.2.2 Synthesis of N-butylphenothiazine (6a)
To a phenothiazine (5) (30 g, 0.15 mol) solution in dry DMF (100 mL), sodium hydride
o
(
10.8 g, 0.45 mol) was slowly added at 0 C for 1 h. Then this reaction mixture was
stirred at room temperature for 1 h. After that 1-bromobutane (0.18 mol) was added drop
o
wise to the reaction mass for 1 h which was then slowly heated to 70 C for 3 h. The
progress of the reaction was monitored by TLC. After complete consumption of
phenothiazine, the reaction mixture was poured into ice cold water and extracted with
5

ACCEPTED MANUSCRIPT
2 4
ethyl acetate. The organic phase was separated and dried over anhydrous Na SO . After
removing the solvent, the residue was purified by column chromatography using hexane
as the eluent to give 35.1 g, 91% of 6a as colourless viscous liquid.
Using above procedure N-propylphenothiazine 6b was synthesied in 87% yiled
2
.2.3 Synthesis of phenothiazine-3-carbaldehyde (8a) and phenothiazine dialdehyde
7a)
a and 8a were synthesied using reported method [12].
(
7
In a three necked 100 mL round bottom flask fitted with a mercury sealed stirrer, addition
dropping funnel topped by calcium chloride guard tube and reflux condenser also topped
by calcium chloride guard tube. N, N-dimethyl formamide (4.58 g, 4.85 mL, 62.7 mmol)
was taken and cooled to 0-5 °C with stirring. To the above solution phosphorous
oxychloride (7.2 g, 4.3 mL, 47 mmol) was added drop wise maintaining the temperature
of the reaction mass at 0-5 °C. The Vilsmeier complex so formed was stirred for further
1
5 min and compound 6a (3.97 g, 15.6 mmol) was added in portion wise (15-25 minutes)
to the complex. The reaction mixture was stirred at 0-5 °C for 3 h and then allowed to
attain room temperature then heated to 75 °C for 8 h. This solution was then cooled to
room temperature, poured into ice water, and neutralized to pH 6-7 by drop wise addition
of saturated aqueous NaHCO
3
solution. The mixture was extracted with dichloromethane.
SO and then concentrated on rotary
The organic layer was dried with anhydrous Na
2
4
evaporator to obtain crude reaction mixture, which was further purified by FCC using
toluene to afforded 7a (0.37 g, 7%) as light brown oil and 8a (2.8 g, 64%) as yellow oil.
Similar way indole-3-carbaldehyde (11), carbazole-3-carbaldehyde (12) were prepared
6

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using reported procedure in the literature [24, 25].
2
.2.4 General procedure for synthesis of styryl dyes
4
a–g (1 mmol) and piperidine (1 mmol) were stirred in methanol (6 mL) for 15 min and
corresponding aldehyde (1 mmol) was added slowly at room temperature. The resulting
reaction mixture was stirred at room temperature for appropriate time as shown in Table
3
. After complete consumption of aldehyde, the precipitated solid was collected by
filtration and washed with small quantity of cold methanol followed by water to remove
traces of piperidine. The products 9 were purified by washing with diethyl ether and the
products 14-16 were purified by FCC using toluene.
2
.3 Spectral data
Z-1(7-Methylcoumarin-4-yl)-2-(10-butyl-10H-phenothiazin-3-yl)ethene (9a)
Yield of 9a: 75%; Red solid; mp: 108-110 °C (ethyl acetate); UV (λmax): 424 nm
(chloroform); Em (λmax): 632 nm (chloroform); Stokes shift: 208 nm; Quantum yield
-1
(Φ
F
): 0.21; FTIR (neat, υ/cm ): 2963 (C-H), 2859 (C-H), 1685 (C=O), 1619 (aromatic
1
C=C), 1469, 1218, 970, and 791; H NMR (300 MHz, CDCl
3
) δ: 0.95 (3H, t, J =7.3Hz,
CH ), 1.45 (2H, sextet, J = 7.3 Hz, CH ), 1.76 (2H, quintet, J = 7.1Hz, CH ), 3.81(2H, t,
3
2
2
J = 7.4 Hz), 2.44 (3H, s, CH ), 6.46 (1H, s, C 'H), 6.74 (1H, d, J = 8.6 Hz, ArH), 6.83
3
3
(
1H, d, J = 8.1 Hz, C 'H), 7.06 –7.17 (7H, m, ArH), 7.28– 7.33 (2H, m, 2H, ArH), 7.64
6
1
3
(
1H, d, J = 8.1 Hz, C 'H ); C NMR (125 MHz, DMSO) δ: 10.9 (CH ), 19.4 (CH ), 20.3
5
3
2
(
CH ), 28.4 (CH ), 48.3 (N-CH ), 107.9 (C ′), 115.6, 116.0, 116.5, 117.7, 118.0 (C '),
3 2 2 3 4a
1
1
4
22.7 (C5a), 122.8, 123.7 (C4a), 124.9, 125.0, 125.7, 127.1, 127.7, 128.5, 130.2, 132.8,
33.6, 136.8 (C ), 143.8 (C9a), 145.6 (C10a), 149.8 (C '), 151.4 (C8a'), 160.1(C '); MS =
40.5 (M+H). Anal. Calcd. for C28 S (439.57): C, 76.51; H, 5.73; N, 3.19 %.
1
4
2
H
25NO
2
7

ACCEPTED MANUSCRIPT
Found: C, 76.38; H, 5.46; N, 3.25 %.
Z-1(6-Methylcoumarin-4-yl)-2-(10-butyl-10H-phenothiazin-3-yl)ethene (9b)
Yield of 9b: 72%; Yellow solid; mp 148-150 °C (ethyl acetate); UV (λmax): 423 nm
(chloroform); Em (λmax): 635 nm (chloroform); Stokes shift: 212 nm; Quantum yield
-1
(
Φ ): 0.70; FTIR (neat, υ/cm ): 2941 (C-H), 1687 (C=O), 1625 (aromatic C=C), 1365 (C-
F
1
N), 1243, 1194, 979, 812 and 745; H NMR (300 MHz, DMSO) δ: 0.88 (3H, t, J =7.5 Hz,
CH
3
), 1.40 (2H, sextet, J = 7.5 Hz, CH
), 3.91 (2H, t, J = 7.5 Hz, N-CH ), 6.72 (1H, s, C
H & C H), 7.15-7.23 (2H, m, C
.1 Hz, C 'H), 7.45 (1H, dd, J = 1.2 & 7.3 Hz, C 'H), 7.57- 7.60 (3H, m, C ′H, C ′H &
2
), 1.68 (2H, quintet, J = 7.5 Hz, CH
'H), 6.96 (1H, t, J = 7.8 Hz, C
H & ArH), 7.30 (1H, d, J =
2
), 2.43 (3H, s,
CH
3
2
3
7
H),
7
8
.05 (2H, d, J = 8.1 Hz, C
6
9
8
8
7
9
10
1
3
ArH ) 7.69 (1H, d, J = 1.5 Hz, C H), 8.05 (1H, s, C 'H); C NMR (125 MHz, DMSO) δ:
4
5
1
1
1
3.6 (CH ), 19.3 (CH ), 20.3 (CH ), 28.2 (CH ), 46.3 (N-CH ), 108.0 (C ′), 115.6, 115.9,
3 2 3 2 2 3
16.4, 117.6, 118.0 (C '), 122.73 (C ), 122.77, 123.7 (C ), 124.9, 125.8, 127.1, 127.7,
4
a
5a
4a
28.3, 130.2, 132.8, 133.6 (C '), 136.7 (C ), 143.9 (C ), 145.6 (C ), 149.8 (C '), 151.4
6
1
9a
10a
4
(C
8a'), 160.3(C
2 2
'); MS = 440.3 (M+H). Anal. Calcd. for C28H25NO S (439.57): C, 76.51;
H, 5.73; N, 3.19 %. Found: C, 76.34; H, 5.54; N, 3.28 %.
Z-1(Coumarin-4-yl)-2-(10-propyl-10H-phenothiazin-3-yl)ethene (9c)
Yield of 9c: 62%; Yellow solid; mp 126-128 °C (ethyl acetate); UV (λmax): 424 nm
(chloroform); Em (λmax): 618 nm (chloroform); Stokes shift: 194 nm; Quantum yield
-1
(
Φ ): 0.50; FTIR (neat, υ/cm ): 2963, 2855, 1695 (C=O), 1680, 1629 (aromatic C=C)
F
1
1
592, 1457, 962, 939 and 744; H NMR (300 MHz, DMSO) δ: 0.94 (3H, t, J =7.3 Hz,
CH
3
), 1.70 (2H, sextet, J = 7.3 Hz, CH
2
), 3.86 (2H, t, J = 6.9 Hz, N-CH
2
), 6.76 (1H, s,
C
3
'H), 6.96 (1H, t, J = 7.3 Hz, C
7
H), 7.03 (2H, d, J = 8.4 Hz, C H & C H), 7.15-7.20 (2H,
6 9
8

ACCEPTED MANUSCRIPT
9
m, ArH), 7.37-7.42 (2H, m, ArH), 7.55-7.59 (3H, m, ArH & C 'H), 7.62 (1H, dt, J = 1.2
1
3
&
7.3 Hz, C 'H), 7.72 (1H, d, J = 1.8 Hz, C H), 8.26 (1H, d, J = 7.3 Hz, C 'H); C NMR
7 4 5
(
125 MHz, DMSO) δ: 10.9 (CH ), 19.4 (CH ), 48.3 (N-CH ), 108.0 (C ′), 115.6, 116.0,
3 2 2 3
1
1
1
5
16.7, 117.6, 118.3 (C '), 122.7 (C ), 122.8, 123.7 (C ), 124.2, 125.4, 125.8, 127.1,
4a 5a 4a
27.7, 128.4, 130.2(C ), 132.0, 137.0, 143.8 (C ), 145.6 (C ), 149.9 (C4'), 153.3 (C '),
3
9a
10a
8a
60.2(C '); MS = 412.5 (M+H). Anal. Calcd. for C H NO S (411.52): C, 75.88; H,
2
26 21
2
.14; N, 3.40 %. Found: C, 75.63; H, 4.96; N, 3.35 %.
Z-1(7-Methylcoumarin-4-yl)-2-(10-propyl-10H-phenothiazin-3-yl)ethene (9d)
Yield of 9d: 75%; Orange solid; mp 160-162 °C (ethyl acetate); UV (λmax): 424 nm
(chloroform); Em (λmax): 631 nm (chloroform); Stokes shift: 207 nm; Quantum yield
-1
(
Φ ): 0.27; FTIR (neat, υ/cm ): 2954, 1695(C=O), 1617 (aromatic C=C) 1465, 1358, 963
F
1
and 734; H NMR (300 MHz, DMSO) δ: 0.94 (3H, t, J =7.3 Hz, CH ), 1.70 (2H, sextet, J
3
=
7.3 Hz, CH ), 2.42 (3H, s, CH ), 3.86 (2H, t, J = 7.3 Hz, N-CH ), 6.68 (1H, s, C 'H),
2 3 2 3
6
.96 (1H, t, J = 7.3 Hz, C H), 7.03 (2H, d, J = 8.4 Hz, C H & C H), 7.14-7.23 (4H, m,
7
6
9
ArH), 7.55-7.58 (3H, m, ArH & C
Hz, C
N, 3.29 %. Found: C, 76.28; H, 5.28; N, 3.17 %.
9
'H), 7.71 (1H, d, J = 1.8 Hz, C
4
H), 8.13 (1H, d, J = 8.1
5
2
'H); MS = 426.7 (M+H). Anal. Calcd. for C27H23NO S (425.54): C, 76.21; H, 5.45;
Z-1(7-Hydroxylcoumarin-4-yl)-2-(10-propyl-10H-phenothiazin-3-yl)ethene (9e)
Yield of 9e: 72%; Red solid; mp 222-223 °C (ethyl acetate); UV (λmax): 422 nm
(chloroform); Em (λmax): 631 nm (chloroform); Stokes shift: 209 nm; Quantum yield
-1
(
Φ ): 0.74; FTIR (neat, υ/cm ): 3237 (O-H), 2959 (C-H), 1680 (C=O), 1615 (aromatic
F
1
C=C), 1540, 1439, 1363, 955 and 854; H NMR (300 MHz, DMSO) δ: 0.94 (3H, t, J =7.2
3 2 3
Hz, CH ), 1.71 (2H, sextet, J = 7.3 Hz, CH ), 2.42 (3H, s, CH ), 3.87 (2H, t, J = 7.5 Hz,
9

ACCEPTED MANUSCRIPT
2 3 8
N-CH ), 6.4 (1H, s, C 'H), 6.73 (1H, d, J = 2.1 Hz, C 'H), 6.81 (1H, dd, J = 2.4 & 8.2 Hz,
C 'H), 6.96 (1H, t, J = 7.2 Hz, C H), 7.03 (2H, d, J = 8.4 Hz, C H & C H), 7.15-7.24 (3H,
6
7
6
9
1
3
m, ArH), 7.53-7.57 (3H, m, ArH), 7.70 (1H, s, C H), 8.08 (1H, d, J = 8.7 Hz, C 'H); C
4
5
NMR (125 MHz, DMSO) δ: 10.9 (CH ), 19.4 (CH ), 48.3 (N-CH ), 102.4 (C '), 103.8
3
2
2
8
(
C ′), 110.6 (C '), 112.7, 115.6, 116.0, 118.1, 119.9, 122.7, 122.8, 125.7, 127.1, 127.7,
3 4a
1
28.3, 130.3, 133.8, 136.5, 138.4, 141.5 (C ), 143.9 (C '), 145.5 (C4'), 150.2 (C '), 161.2
9a 7 8a
(C
2
'); MS = 428.4 (M+H). Anal. Calcd. for C26
3
H21NO S (427.51): C, 73.04; H, 4.95; N,
3
.28 %. Found: C, 72.91; H, 5.01; N, 3.16 %.
Z-1(7,8-Dihydroxylcoumarin-4-yl)-2-(10-propyl-10H-phenothiazin-3-yl)ethene (9f)
Yield of 9f: 78%; Orange solid; mp 185-186 °C (ethyl acetate); UV (λmax): 427 nm
(chloroform); Em (λmax): 643 nm (chloroform); Stokes shift: 216 nm; Quantum yield
-1
(
Φ ): 0.37; FTIR (neat, υ/cm ): 3438 (O-H), 3172 (O-H), 1667 (C=O), 1613 (aromatic
F
1
C=C), 1592, 1461, 960 and 798; H NMR (300 MHz, DMSO) δ: 0.94 (3H, t, J =7.2 Hz,
CH ), 1.70 (2H, sextet, J = 7.2 Hz, CH ), 3.86 (2H, t, J = 7.2 Hz, N-CH ), 6.48 (1H, s,
3
2
2
C
3
'H), 6.80 (1H, d, J = 6.3 Hz, C
8
'H), 6.83 (1H, d, J = 6.3 Hz, C
6
'H), 6.96 (1H, t, J = 7.5
Hz, C
7 6 9
H), 7.03 (2H, d, J = 8.1 Hz, C H & C H), 7.08 (1H, d, J = 8.7 Hz), 7.15-7.23 (2H,
m, ArH), 7.50 (1H, d, J = 2.7 Hz), 7.55 (1H, dd, J = 2.0 & 8.0 Hz, C H), 7.68 (1H, d, J =
2
1
3
1
1
1
.8 Hz, C H); C NMR (125 MHz, DMSO) δ: 11.2 (CH ), 19.4 (CH ), 48.3 (N-CH ),
4 3 2 2
03.7 (C ′), 110.1, 111.4, 111.9, 112.0, 115.4, 115.7, 116.0, 118.4, 123.7, 125.7, 127.1,
3
27.7, 130.3 (C ), 132.4 (C ), 136.2 (C ), 143.9 (C ), 145.5 (C ), 149.4 (C '), 149.5
5
a
4a
1
9a
10a
8
(
C '), 150.6 (C '), 153.8 (C '), 160.6 (C '); MS = 444.7 (M+H). Anal. Calcd. for
7
4
8a
2
C
26
4
H21NO S (443.51): C, 70.41; H, 4.77; N, 3.16%. Found: C, 70.27; H, 4.58; N, 3.14 %.
Z-1(7-Carbamatecoumarin-4-yl)-2-(10-propyl-10H-phenothiazin-3-yl)ethene (9g)
1
0

ACCEPTED MANUSCRIPT
Yield of 9g: 60%; Red solid; mp 208-210 °C (ethyl acetate); UV (λmax): 422 nm
(chloroform); Em (λmax): 635 nm (chloroform); Stokes shift: 213 nm; Quantum yield
-1
(
Φ ): 0.62; FTIR (neat, υ/cm ): 2961, 2869, (C-H), 1686 (C=O), 1593 (aromatic C=C),
F
1
1
1
463, 1215 and 741; H NMR (300 MHz, DMSO,Me Si) δ: 0.94 (3H, t, J =7.2 Hz, CH ),
4
3
.26 (3H, t, J = 6.9 Hz, CH ), 1.70 (2H, sextet, J = 7.3 Hz, CH ), 3.86 (2H, t, J = 7.2 Hz,
3
2
N-CH ), 4.17 (2H, q, J = 6.9 Hz, O-CH ), 6.58 (1H, s, C 'H), 6.95 (1H, t, J = 7.8 Hz,
2
2
3
C
7
6 9
H), 7.02 (2H, d, J = 8 Hz, C H & C H ), 7.05-7.23 (3H, m, ArH) 7.43 (1H, dd, J = 2.4
&
9
7.6 Hz, C
2
H), 7.52-7.56 (3H, m, ArH), 7.69 (1H, d, J = 1.5 Hz, C
4
H), 8.14 (1H, d, J =
), 19.4 (CH ), 48.3
1
3
Hz, C
5
'H); C NMR (125 MHz, DMSO) δ: 11.1 (CH
3
), 14.8 (CH
3
2
(
N-CH ), 60.0 (O-CH ), 104.6 (C ′), 105.3 (C ′), 112.9 (C ′), 114.0, 115.6, 116.0, 117.7,
2 2 3 8 4a
1
1
1
5
22.74 (C ), 122.79, 123.7 (C ), 126.2, 127.1, 127.7, 128.4, 129.3, 130.2 (C ), 136.7,
5a 4a 3
42.9 (C '), 143.8 (C ), 145.6 (C ), 149.7 (C '), 153.3 (C '), 154.3 (CO of NHCO Et),
7
9a
10a
4
8a
2
60.5 (C '); MS = 499.2 (M+H). Anal. Calcd. for C H N O S (498.59): C, 69.86; H,
2
29 26
2
4
.26; N, 5.62 %. Found: C, 69.70; H, 5.18; N, 5.87 %.
Z-1(6-Methylcoumarin-4-yl)-2-(10-propyl-10H-phenothiazin-3-yl)ethene (9h)
Yield of 9h: 62%; Orange solid; mp 152-154 °C (ethyl acetate); UV (λmax): 423 nm
(chloroform); Em (λmax): 637 nm (chloroform); Stokes shift: 214 nm; Quantum yield
-1
(
Φ ): 0.76; FTIR (neat, υ/cm ): 2956 (C-H), 1693 (C=O), 1629 (aromatic C=C), 1588,
F
1
1
466, 1360, 964, 801, and 743; H NMR (300 MHz, DMSO) δ: 0.94 (3H, t, J =7.2 Hz,
CH ), 1.71 (2H, sextet, J = 6.9 Hz, CH ), 2.43 (3H, s, CH ), 3.87 (2H, t, J = 7.2 Hz, N-
3
2
3
CH ), 6.72 (1H, s, C 'H), 6.96 (1H, t, J = 7.5 Hz, C H), 7.04 (2H, d, J = 8.4 Hz, C H &
2
3
7
6
C
9
H), 7.15-7.24 (2H, m, ArH), 7.30 (1H, d, J = 8.4 Hz), 7.45 (1H, dd, J = 1.5 & 8.2 Hz),
.57- 7.60 (3H, m, C ′H, C10′H & ArH ) 7.7 (1H, d, J = 1.5 Hz, C H), 8.05 (1H, s, C 'H);
MS = 426.3 (M+H). Anal. Calcd. for C27 S (425.54): C, 76.21; H, 5.45; N, 3.29
7
9
4
5
H23NO
2
1
1

ACCEPTED MANUSCRIPT
%. Found: C, 75.99; H, 5.35; N, 3.32 %.
Z-1-(6-Chloro-7-methylcoumarin-4-yl)-2-(10-propyl-10H-phenothiazin-3-yl)ethene
9i)
(
Yield of 9i: 74%; Yellow solid; mp 154-155 °C (ethyl acetate); UV (λmax): 432 nm
(
(
(
chloroform); Em (λmax): 648 nm (chloroform); Stokes shift: 216 nm; Quantum yield
-1
Φ ): 0.77; FTIR (neat, υ/cm ): 2959(C-H), 2868, 1729 (C=O), 1687 (C=O), 1615
F
1
aromatic C=C),1573, 1223, 955, and 745; H NMR (300 MHz, DMSO) δ: 0.96 (3H, t, J
=
7.3 Hz, CH ), 1.72 (2H, sextet, J = 7.3 Hz, CH ), 2.43 (3H, s, CH ), 3.88 (2H, t, J = 6.9
3 2 3
Hz, N-CH ), 6.77 (1H, s, C 'H), 6.97 (1H, t, J = 7.4 Hz, C H), 7.05 (2H, d, J = 8.5 Hz,
2
3
7
C H & C H), 7.17 (1H, d, J = 7.5 Hz, C H), 7.22 (1H, t, J = 7.8 Hz), 7.46 (1H, s, C 'H),
6
9
1
8
1
3
7
.59- 7.61 (3H, m, C
9
′H, C10′H & ArH), 7.76 (1H, s, C
4
H), 8.37 (1H, s, C
), 48.3 (N-CH
15.6, 116.0, 117.2, 117.7 119.0 (C4a'), 122.7, 122.8, 124.8 125.9, 127.0, 127.7, 128.7,
29.1 (C ), 130.2 (C ), 137.4, (C ), 140.0, 143.8 (C ), 145.7 (C ), 149.0 (C '), 150.8
5
'H); C NMR
(125 MHz, DMSO) δ: 10.9 (CH
3
), 19.4 (CH
2
), 19.8 (CH
3
2
), 107.7 (C ′),
3
1
1
5
a
4a
1
9a
10a
6
(C '), 151.9 (C '), 159.9 (C '); MS = 460.9 (M+H). Anal. Calcd. for C H ClNO S
4 8a 2 27 22 2
(459.11): C, 70.50; H, 4.82; N, 3.05%. Found: C, 70.34; H, 4.68; N, 2.97 %.
4
-(2-(10-Butyl-7-(2-(7-methyl-coumarin-4-yl)vinyl)-10H-phenothiazin-3-yl)vinyl)-7-
methylcoumarin (10)
Yield of 10: 64%; Brown solid; mp 287-288 °C (ethyl acetate); UV (λmax): 441 nm
(chloroform); Em (λmax): 620 nm (chloroform); Stokes shift: 179 nm; Quantum yield
-1
(
Φ ): 0.83; FTIR (neat, υ/cm ): 2961 (C-H), 2866, 1698 (C=O), 1620 (aromatic C=C),
F
1
1
1
572, 1141, 964 and 798; H NMR (300 MHz, CDCl ) δ: 0.98 (3H, t, J = 7.4 Hz, CH ),
3
3
.50 (2H, d, J = 7.6 Hz, CH
2 2
), 1.83 (2H, quintet, CH ), 2.47 (s, 6H, 2xCH3), 3.91 (2H, t,
J = 7.6 Hz, N-CH
2
), 6.51(s, 2H), 6 89 (2H, d, J = 8.4 Hz), 7.14 (2H, dd, J = 8.1 & 1.1
1
2

ACCEPTED MANUSCRIPT
Hz), 7.18-7.21 (6H, m, ArH), 7.32–7.38 (m, 4H), 7.68 (2H, d, J = 8.1 Hz). Anal. Calcd.
for C H NO S (401.45): C, 77.02; H, 5.33; N, 2.25 %. Found: C, 76.88 H, 5.16; N, 2.18
4
0
33
4
%.
(E)-1-(7-Methylcoumarin-4-yl)-2-(1-butyl-1H-indol-3-yl)ethene (14)
Yield of 14: 60%; Orange solid; mp 136-138 °C (ethyl acetate); UV (λmax): 398 nm
(chloroform); Em (λmax): 474 nm (chloroform); Stokes shift: 118 nm; Quantum yield
-1
(
Φ ): 0.05; FTIR (neat, υ/cm ): 2954 (C-H), 2870, 1682 (C=O), 1618 (aromatic C=C),
F
1
1
520, 1391 (C-N), 1190 and 734; H NMR (300 MHz, DMSO) δ: 0.90 (3H, t, J =7.4 Hz,
CH
3
3
), 1.28 (2H, q, J = 7.4 Hz, CH
2 2
), 1.79 (2H, sextet, J = 7.4 Hz, CH ), 2.43 (3H, s,
CH
), 4.23 (2H, t, J = 7.0 Hz, N-CH
2
), 6.72 (1H, s, C
3
'H), 7.21-7.27 (4H, m, ArH), 7.41
(
1H, d, J = 16 Hz, C ′H), 7.57 (1H, d, J = 8 Hz, C 'H), 7.95 (1H, d, J = 16 Hz, C 'H),
9
5
10
1
3
8
1
1
.07-8.09 (2H, m, ArH), 8.11 (1H, d, J = 7 Hz, ArH); C NMR (125 MHz, DMSO) δ:
3.5 (CH ), 19.4 (CH ), 20.9 (CH ), 31.6 (CH ), 45.5 (N-CH ), 104.4 (C ′), 110.6, 112.7,
3
3
2
2
2
3
13.1 (C '), 117.8, 120.1, 120.7, 122.3, 124.1, 125.2, 131.8, 131.9, 135.9, 138.3, 142.6
4
a
(
C '), 143.2 (C ), 150.5 (C ), 151.1 (C '), (C '), 160.6 (C '); MS = 358.3 (M+H). Anal.
7 9a 10a 4 8a 2
2
Calcd. for C24H23NO (357.44): C, 80.64; H, 6.49; N, 3.92 %. Found: C, 80.58; H, 6.23;
N, 3.99 %.
(E)-1-(7-Methylcoumarin-4-yl)-2-(9-hexyl-9H-carbazol-3-yl)ethene (15)
Yield of 15: 61%; Yellow solid; mp 121-122 °C (ethyl acetate); UV (λmax): 393 nm
(chloroform); Em (λmax): 504 nm (chloroform); Stokes shift: 137 nm; Quantum yield
-1
(
Φ ): 0.38; FTIR (neat, υ/cm ): 2923 (C-H), 2853, 1701 (C=O), 1620 (aromatic C=C),
F
1
1
583, 1379 (C-N), 1325, 1144, 961 and 725; H NMR (300 MHz, DMSO) δ: 0.79 (3H, t,
J =6.8 Hz, CH ), 1.19-1.27 (6H, multiplet, 3 xCH ), 1.77 (2H, quintet, J = 8Hz, CH ),
3
2
2
1
3

ACCEPTED MANUSCRIPT
2
.40 (3H, s, CH
3 2 3
), 4.41 (2H, t, J = 6.8 Hz, N-CH ), 6.75 (1H, s, C 'H), 7.21 (1H, t, J = 7.3
Hz, C H), 7.26 (2H, m, C 'H & C 'H), 7.48 (1H, t, J = 7.3 Hz, C H), 7.62-7.67 (2H, m,
6
6
8
7
ArH), 7.71 (1H, d, J = 16 Hz, C 'H), 7.87 (1H, d, J = 16 Hz, C 'H), 7.93 (1H, d, J = 8
9
10
13
Hz, C H), 8.18-8.21 (2H, m, ArH), 8.67 (1H, s, C H); C NMR (125 MHz, DMSO) δ:
1
4
1
1
1
3.7 (CH ), 21.0 (CH ), 21.9 (CH ), 26.0 (CH ), 28.4 (CH ), 30.9 (CH ), 42.2 (N-CH ),
3 3 2 2 2 2 2
06.2 (C ′), 109.5, 109.7, 113.2 (C '), 116.0, 116.3, 116.8, 119.2, 120.4, 122.1, 125.0,
3
4a
25.3, 126.1, 126.8, 129.6, 138.4, 139.3, 140.9 (C
'), 153.5 (C8a'), 161.7 (C '); MS = 436.3 (M+H). Anal. Calcd. for C30
C, 82.73; H, 6.71; N, 3.22 %. Found: C, 82.55; H, 6.65; N, 3.14 %.
7
'), 142.8 (C9a), 149.3 (C10a), 150.2
(C
4
2
H29NO
2
(435.56):
(E)-4-(4-(Hexyl(phenyl)amino)styryl)-7-methylcoumarin (16)
Yield of 16: 66%; Orange solid; mp 80 °C (ethyl acetate); UV (λmax): 424 nm
(chloroform); Em (λmax): 544 nm (chloroform); Stokes shift: 151 nm; Quantum yield
-1
(
Φ ): 0.05; FTIR (neat, υ/cm ): 2923 (C-H), 2852, 1698 (C=O), 1619 (aromatic C=C),
F
1
1
512, 1379 (C-N), 1183, 978, 803 and 697; H NMR (300 MHz, DMSO) δ: 0.84 (3H, t, J
=
6.4 Hz, CH ), 1.24-1.31 (6H, multiplet, 3 xCH ), 1.58 (2H, quintet, J = 6.4 Hz, CH ),
3
2
2
2
8
1
.42 (3H, s, CH
3
), 3.73 (2H, t, J = 6.4 Hz, N-CH
2
), 6.65 (1H, s, C
3
'H), 6.82 (2H, d, J =
.6 Hz, ArH), 7.15-7.23 (5H, m, ArH) 7.38- 7.44 (3H, m, ArH & C
9
'H), 7.59 (1H, d, J =
1
3
6 Hz, C 'H), 7.64 (2H, d, J = 8.6 Hz, ArH), 8.07 (1H, d, J = 8 Hz, C 'H); C NMR
1
0
5
(
(
(
125 MHz, DMSO) δ: 13.8 (CH ), 20.9 (CH ), 22.0 (CH ), 25.9 (CH ), 26.8 (CH ), 31.0
3 3 2 2 2
CH ), 51.4 (N-CH ), 105.9 (C ′), 115.3, 116.0 (C '), 116.1 (2xC), 116.8, 124.0, 124.6
2
2
3
4a
2xC), 124.8, 125.2, 126.1, 129.4 (2xC), 129.6(2xC), 138.0, 142.6 (C '), 146.3, 148.9,
7
1
50.0 (C '), 153.4 (C '), 160.4 (C '); MS = 438.4 (M+H). Anal. Calcd. for C H NO
4 8a 2 30 31 2
(437.57): C, 82.35; H, 7.14; N, 3.20 %. Found: C, 82.20; H, 6.99; N, 3.23 %.
1
4

ACCEPTED MANUSCRIPT
3
. Results and discussion
3
.1 Synthesis of starting materials
In the initial part coumarin-4-acetic acids (4) and PTZ-3-carbaldehyde (8) were
synthesized using literature methods. In the synthesis of 4, acetone dicarboxylic acid (2),
2 4
was prepared in situ by reacting citric acid (1) with conc. H SO and in next step
substituted phenols (3) were condensed with 2 to obtain substituted coumarin-4-acetic
acids (4) (Scheme 1) [23]. Compounds 3 containing electron-withdrawing groups does
not react adequately with 2 to form the corresponding 4. Thus we were unable to prepare
9
with electron withdrawing group on the acceptor coumarin ring.
R1
O
R2
HO
OH
O
HOOC
HOOC
COOH
R3
COOH
COOH
Conc. H SO4
2
3
R3
O
OH
o
7
0 C 30 min
0 oC to rt
R2
O
R1
1
2
4
Scheme 1 Synthesis of coumarin-4-acetic acids
In the synthesis of 8, firstly phenothiazine (5) was alkylated to give 6, which on
Vilsmeier condition gave 8 with good yield and small amount of dialdehyde (Scheme 2)
[12].
O
O
S
H
H
N
R
S
7
R-Br
S
DMF/POCl3
O
o
N
H
5
0 C to rt 3 h
70 oC 12 h
S
N
R
H
6
N
R
8
6
6
a : R = n-butyl
b : R = n-propyl
When R = n-butyl
Yield of 7a : 7%
Yield of 8a : 64%
When R = n-propyl
Yield of 7b : 2%
Yield of 8b : 70%
Yield of 6a : 91%
87%
Yield of 6b
:
Scheme 2 Synthesis of phenothiazine-3-carbaldehyde (8) and phenothiazine dialdehyde (7)
1
5

ACCEPTED MANUSCRIPT
3
.2 Optimization study for condensation of 7-methylcoumarin-4-acetic acid (4a) and n-
butylphenothiazine-3-carbaldehyde (8a)
Condensation of 4 with 7-diethylaminocoumarin-3-carbaldehyde is known and using this
pathway [21] reaction of 4a with 8a was carried out at room temperature (35 ± 2 °C)
(Scheme 3).
CH3
CH3
O
O
O
O
O
O
S
S
H
H
H
H
Base, rt
O
1
3
N
N
R , R = H
OH
O
2
Bu
R = CH3
R3
Bu
10
7
a
H1
+
O
R2
O
S
H2
S
Base, rt
H
R1
R3
N
R
4
N
R
1
O
O
R2
R = H, OH
2
R = H, CH ,OH, NHCO Et
R1
3
2
9
R3 = H, Cl,
8
2
1
3
2
1
3
4
a : R = Me, R & R = H
8a: R = butyl
9a : R = Me, R & R = H
8b: R = propyl
R = n-butyl
Scheme 3 Condensation of coumarin-4-acetic acids (4) with phenothiazine-3-carbaldehyde (8)/
phenothiazine dialdehyde (7)
The reaction of 4a with 8a was carried out in the presence of different inorganic bases
2 3
such as NaOH, NaH, NaOAc, NaOEt, KOtBu, and K CO at room temperature (Table 1).
In NaOH, instead of condensation, decarboxylation of 4a results into the 4,7-
dimethylcoumarin as by-product (Table 1, entry 1). All other bases such as NaH,
NaOAc, NaOEt, KOtBu, and K CO found to be ineffective and no reaction was
2
3
observed (Table 1, entries 2-6).
1
6

ACCEPTED MANUSCRIPT
a
Table 1 Influence of inorganic bases on styryl formation
Entry
Base
Solvent
Time (h)
Result
Coumarin
decarboxylation
NR
1
NaOH
NaH
Ethanol
48
48
2
3
4
5
6
Tetrahydrofuran
NR
NR
NR
NR
NaOAc
NaOEt
KOtBu
Ethanol
Ethanol
THF
48
48
48
48
K CO3
2
Ethanol
a
Reaction conditions: 8a (1 mmol), 4a (1 mmol), base (1 mmol), solvent: (6 mL), room
temperature (35 ± 2 °C), NR : No reaction
Organic bases such as pyridine, pyrrolidine, piperidine, morpholine, Et N, and DIEPA
3
were also tried for the condensation of 4a with 8a (Table 2). At room temperature
pyridine in methanol gives 60 % yield of 9a while pyrrolidine in ethanol gives 66% yield
of 9a (Table 2, entry 1 & 2). This conversion was also effected with piperidine in
methanol to give 75% yield of 9a at room temperature (Table 2, entry 3), while at reflux
condition in 12 h gave 49% yield (Table 2, entry 4). Here, we have noticed that at reflux
condition in piperidine/methanol, 4a undergoes decarboxylation and hence the less yield
of 9a was observed. Other bases were found to be inefficient (Table 2, entries 5-7).
a
Table 2 Influence of organic bases on styryl formation
c
Entry
Base
Solvent
Time (h)
48
Yield (%)
1
2
3
Pyridine
Methanol
Ethanol
60
66
Pyrrolidine
Piperidine
Piperidine
Morpholine
48
Methanol
Methanol
Ethanol
48
75
b
4
12
49
5
48
NR
1
7

ACCEPTED MANUSCRIPT
6
7
8
9
Triethylamine
DIEPA
Methanol
48
48
48
48
48
NR
NR
NR
NR
NR
Acetonitrile
Choline hydroxide
ChCl: Urea DES
ChCl: glycerol
-
-
-
1
0
a
Reaction conditions: 8a (1 mmol), 4a (1 mmol), base (1 mmol) / DES (5 mL), solvent: (6 mL),
b
c
room temperature (35 ± 2 °C), reflux temp, isolated yield, NR : No reaction.
As our group is more familiar with organic synthesis in deep eutectic solvents (DES) [26-
2
8], consequently we have tried condensation of 4a with 8a in different DES such as
ChCl: urea DES, ChCl: glycerol DES, and choline hydroxide (Table 2, entries 8-10).
There was no formation of desired product at room temperature. At higher temperature
o
(
80 C or more) decarboxylation of 4a is more pronounced than condensation, resulting
in 4,7-dimethyl coumarin as by-product.
3
.3 Synthesis of different styryl dyes
To get series of different fluorescent compounds having coumarin as acceptor moiety,
different 6,7,8-substituted coumarin-4-acetic acids (4) were reacted with phenothiazine-3-
carbaldehyde (8) at room temperature (35 ± 2 °C) (Scheme 3). Similarly phenothiazine
dialdehyde (7) was reacted with 4a to give corresponding distyryl compound (10)
(Scheme 3). Thus compounds 9 were prepared showing cis stereochemistry of ethylenic
1
double bond confirmed by H NMR (J = 8-10 Hz).
Other different aldehydes such as indole-3-carbaldehyde (11), carbazole-3-carbaldehyde
(12), and 4,4’-(hexylimino)bis(benzaldehyde) (13) were condensed with 4a to get
different styryl dyes (14-16) (Scheme 4). Compounds 14, 15 and 16 thus prepared have
1
trans streochemistry of the double bond which was confirmed by H NMR (J = 16 Hz).
1
8

ACCEPTED MANUSCRIPT
These compounds are in resemblance with 1,2-biscoumarinylethenes in trans
stereochemistry of the ethylenic double bond.
H C
3
O
H
14
H
O
O
piperidine, rt
MeOH
H H C
N
3
1
1
N
but
but
H
O
O
H
O
O
O
piperidine, rt
MeOH
OH
O
15
+
H
H
N
CH3
1
2
N
hex
H C
O
hex
3
H
4
a
H
O
piperidine, rt
MeOH
O
N
16
13
N
hex
hex
Scheme 4 Condensation of 7-methylcoumarin-4-acetic acid (4a) with 11, 12, and 13
a
Table 3 Synthesis of tyryl derivatives 9, 10, and 14-16
b
Time
(h)
En
try
Coumarin
(4)
Aldehyde
Product
c
(Yield)
%)
(
O
O
S
N
S
H
OH
1
2
45 (75)
45 (72)
N
O
O
CH
3
8
a
H
3
C
C
O
O
9a
4
4
a
O
O
S
N
S
N
H
OH
O
CH
3
H
3
O
O
8a
O
9b
b
1
9

ACCEPTED MANUSCRIPT
O
O
O
O
O
S
N
S
N
OH
H
H
H
H
3
4
5
6
48 (62)
46 (75)
50 (72)
49 (78)
O
O
O
O
8
b
9c
4
c
O
S
N
S
N
OH
O
O
O
O
O
CH
3
H
3
C
O
8b
9d
4
a
O
S
N
S
N
OH
O
O
OH
OH
HO
HO
O
8b
9e
9f
4
d
O
S
N
S
N
OH
O
O
O
8b
OH
OH
4
e
S
N
O
O
S
N
OH
O
H
7
52 (60)
O
O
2
NHCO Et
9g
EtO
2
CHN
O
8b
4
f
O
O
O
S
N
S
N
OH
O
H
H
CH
3
8
9
H
3
C
48 (62)
46 (74)
O
O
O
O
O
8
b
9h
9i
4
b
O
S
N
S
N
OH
O
Cl
Cl
CH
3
H
3
C
O
8b
4
g
3
H C
O
O
O
O
OH
O
10
H
51 (60)
N
1
1
H
3
C
O
14
but
N
4a
but
2
0

ACCEPTED MANUSCRIPT
CH
3
O
O
OH
H
O
1
1
2
48 (61)
45 (66)
N
O
hex
H
3
C
O
O
1
2
N
1
5
4a
hex
CH
3
O
O
OH
O
H
O
1
N
O
hex
H
3
C
O
13
N
4a
1
6
hex
CH
3
CH
3
O
O
O
OH
O
S
O
O
H
H
13
S
N
58 (64)
O
O
N
H
3
C
O
but
7
4a
1
0
a
Reaction conditions: Aldehyde (1 mmol), 4 (1 mmol), Piperidine (1 mmol), Methanol (6 mL),
Time in hour for total consumption of aldehyde, Temp.: RT (35 ± 2 °C), Isolated yield.
b
c
3
.4 Photophysical properties
The geometry of the optimized structure of 9c is depicted in Fig.1. In 9, the donor
auxochrome N-atom of phenothiazine ring plays an important role in increasing the
electron density in conjugated part and lowering the HOMO-LUMO gap. Due to the
wide-range of π conjugation, compound 9a showed red emission under UV-lamp (365
nm) (Fig. 4). Hence, we thought that the related compounds would be good candidates
for studying their photophysical properties. Using the optimized conditions, series of
compounds were prepared having phenothiazine ring and coumarin ring tethered by
ethylenic link extending the conjugation. Surprisingly all these PTZ styryl derivatives
(9a-9i) show cis stereochemistry of ethylenic double bond.
2
1

ACCEPTED MANUSCRIPT
Fig. 1 Energy optimized structure of 9c
All the compounds are yellow to red in colour and emit in green to red region hence, they
were further studied for photophysical properties. The UV-Visible absorption (Fig. 2)
and emission spectra (Fig. 3) of 9, 10, and 14-16 were recorded in chloroform at room
temperature using 10 ꢀM solutions (emission photograph Fig. 4). 1-(coumarin-4-yl)-2-
(phenothiazine-3-yl)ethene (9) in chloroform absorbs (Visible λMax) in the range of 422 to
4
32 nm while they emit (E λMax) in the range of 618-648 nm. The compounds 9 did not
m
showed good absorption and emission behaviour in polar solvents like acetonitrile,
dimethyl sulfoxide, N,N-dimethyl formamide, methanol. Unlikely, compounds, 14 and 15
show lower range of absorption (393-398 nm) and emission (474-504 nm) in chloroform.
Compound 16 show absorption at 424 nm and emission at 544 nm in chloroform. As
these compounds (14-16) have different orbital characteristic and structural properties
they behave differently in polar solvents (dimethyl sulfoxide, N,N-dimethyl formamide,
methanol) and show good absorption and emission as compared with chloroform.
Compounds 9 show better Stokes shift in the range of 194 to 216 nm. Quantum yields of
2
2

ACCEPTED MANUSCRIPT
all compounds 9, 10 and 14-16 were recorded by using rhodamine 6G (Rhodamine 6G in
ethanol, Φf = 0.95) as a standard in chloroform at room temperature. Among compounds
9
, compound 9i has the lowest HOMO-LUMO gap, as it contains an electron
withdrawing chlorine atom on acceptor coumarin moiety which makes facile charge
transfer and hence absorbs at longer wavelength (432 nm).
Fig. 2 Absorption spectra of 9, 10, and 14-16 in chloroform
Fig. 3 Emission spectra of 9, 10, and 14-16 in chloroform
2
3

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Table 4 Electronic absorption (UV-Visible
yield of 9, 10, 14-16 in chloroform
λ
Max), emission (E
Em (
m
λMax), Stokes shifts, and quantum
UV (
λ
Max
)
λ
Max
)
Stokes shift
(nm)
Quantum
yield
Entry
Compound
(
nm)
(nm)
1
2
3
4
5
6
7
8
9
9a
9b
9c
9d
9e
9f
424
423
424
424
422
427
422
423
432
441
632
208
0.21
635
618
631
631
643
635
637
648
620
212
194
0.70
0.50
0.27
0.74
0.37
0.62
0.76
0.77
0.83
0.05
0.38
0.05
207
209
216
9g
9h
9i
213
214
216
10
10
14
15
16
179
b
b
11
398 (414)
393 (405)
424 (432)
474 (532)
504 (542)
544 (583)
76 (118)
111 (137)
120 (151)
b
b
b
b
1
2
3
1
b
Absorption and emission value in DMSO
2
4

ACCEPTED MANUSCRIPT
spectroscopy. A hypsochromic shift of the UV/VIS absorption band, with increasing
solvent polarity is usually called negative solvatochromism. The corresponding
bathochromic shift, with increasing solvent polarity is termed as positive
solvatochromism. Compounds 9 and 10 showed negative solvatochromism (Fig. 5)
whereas compounds 14, 15 and 16 showed positive solvatochromism (Fig. 6).
Fig. 5 Negative Solvatochromism shown by compound 9a (Hypsochromic shift)
Fig. 6 Positive Solvatochromism shown by compound 16 (Bathochromic shift)
Conclusions
In conclusion, we have successfully designed and synthesized a series of novel styryl
dyes with the different electron-donor and electron-acceptor groups. The coumarin based
2
5

ACCEPTED MANUSCRIPT
styryl dyes 9, 10, 14-16 are valuable as new fluorescent chromophores having long
absorption maxima and emission maxima. The relative strength of fluorescence in 9 was
affected by the substituents on coumarin ring, while in 14-16 it was affected by type of
donor ring. The presence of an electron acceptor group like -Cl on acceptor coumarin
moiety at 6-position caused a pronounced bathochromic shift. Compound 9 and 10 shows
negative solvatochromism while compounds 14-16 shows positive solvatochromism.
Acknowledgements
A.K.S. is thankful to UGC-CAS for providing financial assistance and IIRBS, Mahatma
1
13
Gandhi University, Kottayam for H and C-NMR.
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