Synthesis of 6-(4-diethylamino)phenyl-2-oxo-2H-pyran-3-carbonitorile derivatives and their fluorescence in solid state and in solutions

Article abstract of DOI:10.1016/j.dyepig.2011.05.014

One-pot synthesis of a new 2-pyrone dye (3a) by the reaction of 4-diethylamino-acetophenone (1) with methyl 2-cyano-3,3-bis(methylsulfanyl) acrylate (2) in the presence of sodium hydroxide as the base was carried out in DMSO. Compound 4a was synthesized by the replacement of methylsulfanyl group of 3a with dimethylamine at 4-position of pyrone ring. Similarly, compound 5a was prepared via the reaction of 3a with diethyl malonate. Compounds 3a-5a exhibited the following fluorescence in the solid state: red (3a), green (4a), and orange (5a). In addition, it was revealed that 2-pyrone dyes exhibit fluorescence in various solvents and show positive solvatochromism. Compounds 3a and 5a exhibited intense fluorescence in chloroform and dichloromethane (fluorescence quantum yield Φ: 0.94-0.95). In contrast, compound 4a exhibited intense fluorescence in polar solvents (methanol: Φ = 0.92). These 2-pyrone dyes have the potential for applications in various fields.

Full text of DOI:10.1016/j.dyepig.2011.05.014

Dyes and Pigments 92 (2012) 1069e1074
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Synthesis of 6-(4-diethylamino)phenyl-2-oxo-2H-pyran-3-carbonitorile
derivatives and their fluorescence in solid state and in solutions
Masayori Hagimori a, Naoko Mizuyama b, Kenichirou Yokota c, Yasuhisa Nishimura c, Mika Suzuta c,
,
d
d
d
Chen-Kuen Tai d, Bo-Cheng Wang d , San-Lang Wang , Tzenge-Lien Shih , Kuen-Da Wu ,
*
Zhi-Shuan Huang d, Shih-Chun Tseng d, Chieh-Yu Chen d, Jian-Wei Lu d, Ho-Hsiang Wei d,
Keisuke Kawashima e, Shinich Kawashima e, Yoshinori Tominaga c
,d,
**
a Faculty of Pharmaceutical Sciences, Nagasaki International University, 2825-7 Huis Ten Bosch, Sasebo 859-3298, Japan
b Department of Pharmacy, Saga University Hospital, 5-1-1 Nabeshima, Saga 849-8521, Japan
c Faculty of Environmental Studies, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852-8521, Japan
d Department of Chemistry, Tamkang University, Tamsui 251, Taiwan
e Harima Chemical, Inc., 671-4 Noguchi-machi, Kakogawa 675-0019, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
One-pot synthesis of a new 2-pyrone dye (3a) by the reaction of 4-diethylamino-acetophenone (1) with
methyl 2-cyano-3,3-bis(methylsulfanyl)acrylate (2) in the presence of sodium hydroxide as the base was
carried out in DMSO. Compound 4a was synthesized by the replacement of methylsulfanyl group of 3a
with dimethylamine at 4-position of pyrone ring. Similarly, compound 5a was prepared via the reaction
of 3a with diethyl malonate. Compounds 3ae5a exhibited the following fluorescence in the solid state:
red (3a), green (4a), and orange (5a). In addition, it was revealed that 2-pyrone dyes exhibit fluorescence
in various solvents and show positive solvatochromism. Compounds 3a and 5a exhibited intense fluo-
Received 4 March 2011
Received in revised form
12 May 2011
Accepted 17 May 2011
Available online 12 July 2011
Keywords:
rescence in chloroform and dichloromethane (fluorescence quantum yield
compound 4a exhibited intense fluorescence in polar solvents (methanol:
dyes have the potential for applications in various fields.
F
: 0.94e0.95). In contrast,
¼ 0.92). These 2-pyrone
2-Pyrone dyes
One-pot synthesis
Ketene dithioacetal
Fluorescence
F
Ó 2011 Elsevier Ltd. All rights reserved.
Solvatochromism
Solid state
1. Introduction
generally the molecular aggregation in the solid state causes fluo-
rescence quenching. The 2-pyrone derivatives synthesized previ-
ously showed almost no fluorescence in solution; however we
recently reported the synthesis of 2-pyrone derivatives that
exhibited light emission in the range of 400e626 nm in the solid
state and 511e516 nm when dissolved in CHCl3 [13e15]. The pattern
of substitution of the groups in the pyrone ring has a considerable
influence on the fluorescence properties of these 2-pyrone deriva-
tives. In particular, the presence of aryl groups such as the phenyl
group at the 6-position of the pyrone ring has a significant effect on
the fluorescence properties. Furthermore, the introduction of
electron-donating groups such as a diethylamino moiety in the aryl
group affects the fluorescence and emission, and can cause a bath-
ochromic shift. The presence of electron-withdrawing substituents
such as cyano, ester, and sulfonyl groups are necessary at the
3-position of the pyrone ring [13e15]. It has been observed that in
the solid state, 2-pyrone derivatives synthesized using ketene
dithioacetals emit light. The strongest fluorescence properties were
observed in the case of 2-pyrones having a 4-diethylaminophenyl
Fluorescent dyes are currently attracting considerable interest
owing to their wide range of applications in various fields, e.g., for
preparing emitters for electroluminescence devices in copy-
preventing, materials for collecting solar energy, fluorescent films
for greenhouses, and fluorescent colorants [1e8]. Recently, we have
reported that 2-pyrone-type compounds having very strong fluo-
rescence properties can be synthesized using sulfonyl ketene
dithioacetals [9e12] and active methyl compounds in the presence
of an appropriate base [13e15]. There are very few dyes that exhibit
fluorescence both in the solid state and in solutions because
* Corresponding author. Tel.: þ886 2 26215656.
** Corresponding author. Faculty of Environmental Studies, Nagasaki University,
1-14 Bunkyo-machi, Nagasaki 852-8521, Japan. Tel.: þ81 958192713; fax: þ81
958192716.
E-mail addresses: mhagimori@niu.ac.jp (M. Hagimori), bcw@mail.tku.edu.tw
(B.-C. Wang), ytomi@nagasaki-u.ac.jp (Y. Tominaga).
0143-7208/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2011.05.014

1070
M. Hagimori et al. / Dyes and Pigments 92 (2012) 1069e1074
SMe
compounds were reagent grade and used without further purifi-
cation unless otherwise specified.
CN
O
O
MeS
MeS
CN
NaOH
H2O
CH3
O
+
Et
in DMSO
Et
N
COOMe
2.1. Materials
N
Et
Et
1
3a 36%
2
All chemicals were reagent grade and used without further
purification unless otherwise specified. All the solvents were of
analytic grade and used as received.
Scheme 1.
2.2. Synthesis of 6-(4-diethylamino)phenyl-4-methylsulfanyl-2-
oxo-2H-pyran-3-carbonitrile (3a)
group at the 6-position of the 2-pyrone ring. We continue our
previous studies on heterocyclic compounds, and in this study, we
synthesize
6-(4-diethylamino)-phenyl-2-oxo-2H-pyran-3-
A mixture of 4-(diethylamino)phenylacetophenone (1) (0.96 g,
5.0 mmol), methyl 2-cyano-3,3-bis(methylsulfanyl)acrylate (2)
(1.01 g, 5.0 mmol), a powdered sodium hydroxide (0.8 g, 2.0 mmol)
and 20 ml of DMSO and this solution was maintained at 10e15 ꢀC.
This mixture was stirred for 5 h at the same temperature. The
reaction mixture was poured into 300 ml of ice-water and then
allowed to stand for 30 min. The resulting precipitate was collected
by filtration and washed several times with water. After air-drying,
the product was recrystallized from toluene to give red needles
(0.56 g, 1.78 mmol, 36% yield), mp 245e246 ꢀC. The pure compound
was recrystallized from toluene to give red needles, mp
carbonitorile derivatives (3ae5a) using 4-diethylaminoaceto-phe-
none (1) and ketene dithioacetal (2) [16e18] in the presence of an
appropriate base. These novel 2-pyrone derivative compounds have
a diethylamino group, instead of a dimethylamino group, as the
electron-donating group. It is expected that because of the dieth-
ylamino group, the molecular aggregation is lower and that as
a result, strong fluorescence emission is induced. We compare the
fluorescence properties of these derivatives with those of dime-
thylamino derivatives (3be5b) [13] in solid state and in solutions. In
addition, we investigated the solvatochromic behavior of 3ae5a in
various solvents.
246e247 ꢀC. IR (KBr, cmꢁ1
1469, 1346. UV (EtOH) lmax nm (log
400 MHz)
)
n
: 2969, 2924, 2366 (CN), 1697, 1572,
3
): 469(4,33). 1H-NMR (CDCl3,
d
: 1.23 (6H, t, J ¼ 7.3 Hz, CH2eCH3), 2.65 (3H, s, SMe), 3.45
2. Experimental
(4H, q, J ¼ 7.3 Hz, 2 ꢂ NeCH2e), 6.47 (1H, s, 5H), 6.67 (2H, d,
J ¼ 9.3 Hz, 30, 50-H), 7.74 (2H, d, J ¼ 9.3 Hz, 20, 60-H). 13C-NMR (CDCl6,
Synthesis and characterization of compounds were carried out
using general procedures employing the following equipment. All
melting points were determined using a Mitamura Riken Kogyo
Mel-Temp apparatus or a Laboratory Devices Mel-Temp II appa-
ratus and were uncorrected. IR spectra were recorded in potassium
bromide pellets on a Jasco 810 or Shimadzu IR-460 spectrometer.
UV absorption spectra were determined in 95% ethanol on a Hitachi
323 spectrometer. Fluorescence spectra were recorded on a Shi-
madzu RF-5300pc. NMR spectra were obtained on Gemini 300NMR
(300 MHz), Varian Unityplus 500NMR (500 MHz), and Bruker
(600 MHz) spectrometers using tetramethylsilane as the internal
standard. Mass spectroscopy was performed using JEOL DX-303
mass spectrometers. Microanalyses were performed by K. Tsuda
100 MHz) d: 12.51 (2), 14.63, 44.70 (2), 94.14, 111.29 (3), 114.33,
115.16, 129.05 (2), 151.23, 158.31, 163.39, 168.89. Ms (Bruker, TOF/
TOF) m/z: 313.164 (Mþ ꢁ 1). Anal. Calcd for C17H18NSO2 ¼ 314.1089:
C, 64.94; H, 5.77; N, 8.91%. Found: C, 64.92; H, 5.71; N, 8.92%.
2.3. Synthesis of 6-(4-diethylamino)phenyl-4-dimethylamino-2-
oxo-2H-pyran-3-carbonitrile (4a)
A mixture of 3a (0.63 g, 2.0 mmol), 50% dimethylamine (2.50 g,
27.8 mmol), and 30 ml of methanol was refluxed for 2 h. The excess
dimethylamine and methanol were completely removed under
reduced pressure on a rotary evaporator. The residue was recrys-
tallized from methanol to give yellow leaflets (4a) (0.38 g,
on
a PerkineElmer instrument at Nagasaki University. All
Me
Me
Me
S
N
O
N
Me
C
Me
N
C
N
H
O
O
O
Et
Et
N
N
Et
Et
4a
61%
3a
Me
COO
MeOOC
N
C
O
O
K
2CO3
Me
Me
COO
3a
+
t
E
N
COO
in DM
SO
Et
5a
90%
Scheme 2.

M. Hagimori et al. / Dyes and Pigments 92 (2012) 1069e1074
1071
Table 1
UV and fluorescence data for 2-pyrones in CHCI3 and solid state.
Compounds
Dissolved in CHCI3
Solid
lmax (nm)a
Emmax (nm)b
Fc
Emmax (nm)b
Fc
a: R ¼ Et
474
466
540
534
0.95
0.60
624
675
0.34
0.11
3
4
5
b: R ¼ Me
a: R ¼ Et
406
398
490
486
0.47
0.17
525
525
0.22
0.58
b: R ¼ Me
a: R ¼ Et
498
490
542
536
0.94
0.84
606
643
0.05
0.06
b: R ¼ Me
a
b
c
Concentration: 10e5 M.
Each emission was measured using excitation wavelengths.
This quantum yields were determined by using Absolute PL Quantum Yield Measurement System (C9920-01) of Hamamastu Photonics.
1.22 mmol, 61% yield), mp 257e258 ꢀC. IR (KBr, cmꢁ1
2198 (CN), 1686 (C]O), 1597, 1547, 1519, 1473, 1204, 793. 1H-NMR
(CDCl3, 400 MHz)
)
n
: 2972, 2930,
cmꢁ1
1598, 1507, 1211, 1200. 1H-NMR (CDCl3, 400 MHz)
)
n
: 2974, 2956, 2216 (CN), 1748 (C]O), 1731 (C]O), 1607,
: 1.23 (6H, t,
d
d
: 1.19 (6H, t, J ¼ 7.1 Hz, eCH2eCH3), 3.32 (6H, s,
J ¼ 7.1 Hz, NeCH2eCH3), 3.45 (4H, q, J ¼ 7.1 Hz, NeCH2e), 3.84 (6H,
s, OMe), 4.98 (1H, s, eCHe), 6.66 (2H, d, J ¼ 9.3 Hz, 30, 50-H), 6.86
(1H, s, 5-H), 7.76 (2H, d, J ¼ 9.3 Hz, 20, 60-H). 13C-NMR (CDCl3,
NMe2), 3.40 (4H, q, J ¼ 7.1 Hz, 2 ꢂ NeCH2e), 6.19 (1H, s, 5-H), 6.66
(2H, br s, 30, 50-H), 7.66 (2H, d, J ¼ 8.4 Hz, 20, 60-H). 13C-NMR (DMSO-
d6, 100 MHz)
d
: 12.35 (2), 42.38 (2), 44.58 (2), 69.80, 89.67, 111.08,
100 MHz) d: 12.46, 12.55, 44.74 (2), 53.69, 53.77, 55.23, 55.46, 93.91,
118.44, 128.08 (4), 161.16, 163.05. Ms m/z: 312 (Mþ þ 1, 17), 311 (Mþ,
81), 297 (20), 296 (100), 176 (22), 132 (7). Anal. Calcd for
C18H21N3O2 ¼ 311.1634: C, 69.43; H, 6.80; N, 13.49%. Found: C,
69.13; H, 6.90; N, 13.41%.
98.56,111.31 (2),114.11,115.33,129.39,129.48, 151.42,156.31,158.97,
165.51, 165.77. Ms m/z: 399 (Mþ þ 1, 24), 398 (Mþ, 99), 384 (23),
383 (100), 351 (11), 296 (12), 176 (15), 132 (10). Anal. Calcd for
C21H23N2O4 ¼ 398.4092: C, 63.31; H, 5.57; N, 7.03%. Found: C, 63.39;
H, 5.58; N, 7.09%.
2.4. Synthesis of dimethyl 3-cyano-6-(4-diethylamino)phenyl-2-
oxo-2H-pyran-4-ylmalonate (5a)
2.5. Fluorescence measurements
A mixture of of 3a (0.31 g,1.0 mmol), dimethyl malonate (0.53 g,
4.0 mmol), potassium carbonate (1.38 g, 10.0 mmol), and 15 ml of
DMSO was stirred for 1 h at room temperature. After the reaction,
the reaction mixture was poured into 100 ml of water and then
acidified with 10% hydrochricacid. The resulting precipitate that
appeared was collected by filtration and washed with water. After
air-drying, the product was recrystallized from methanol to give
red needles (0.37 g, 0.90 mmol, 90% yield), mp 209e210 ꢀC. IR (KBr,
(a) Solid state: A powder sample of the subject compound was
heaped on a tray. After covering the sample with a quartz plate,
the tray was fixed in the fluorescence spectrometer. After
setting the fluorescence wavelength, the excitation spectrum
was determined by scanning at the fluorescence wavelength.
Similarly, the fluorescence spectrum was obtained by scanning
at the excitation wavelength. The excitation wavelength was
determined and the fluorescence spectrum was measured.
Fig. 1. Solid-state fluorescence of 2-pyrones irradiated with black light (365 nm).

1072
M. Hagimori et al. / Dyes and Pigments 92 (2012) 1069e1074
Table 2
UVeVis absorption properties of 3ae5b in various solvents.a
Solvent
Absorption maximum (nm) (log e)
3a
3b
4a
4b
5a
5b
benzenze
466 (4.75)
462 (4.79)
474 (4.79)
472 (4.83)
466 (4.73)
466 (4.79)
476 (4.75)
470 (4.75)
460 (4.73)
454 (4.67)
466 (4.69)
464 (4.74)
458 (4.66)
460 (4.67)
470 (4.67)
465 (4.65)
398 (4.63)
396 (4.67)
406 (4.68)
400 (4.71)
398 (4.65)
398 (4.67)
400 (4.64)
400 (4.64)
394 (4.61)
392 (4.65)
398 (4.64)
400 (4.71)
396 (4.67)
394 (4.62)
398 (4.61)
396 (4.62)
490 (4.75)
482 (4.77)
498 (4.83)
496 (4.89)
488 (4.64)
382 (4.75)
388 (4.72)
392 (4.72)
482 (4.65)
474 (4.66)
490 (4.73)
486 (4.79)
480 (4.72)
376 (4.69)
382 (4.66)
484 (4.68)
diethyl ether
chloroform
dichloromethane
acetone
acetonitrile
DMSO
ethanol
a
Measured 1 ꢂ 10ꢁ5 mol/L.
Quantum yields were obtained by using Absolute PL Quantum
Yield Measurement System (C9920-01) of Hamamastu
Photonics.
The development of materials with high quantum efficiency and
fluorescence quantum yield ( ) is important in order to assess the
F
potential applications of these fluorescent compounds. Recently,
the synthesis of fluorescent 2-pyrone derivatives that emit fluo-
rescence (red, green, and blue) in the solid state has been reported.
We previously reported the synthesis of N-methyl compounds,
6-(4-dimethylamino)phenyl-2-oxo-2H-pyran-3-carbonitriles
(3be5b) by a convenient one-pot reaction involving ketene
dithioacetals [14]. We analyzed the room-temperature fluores-
cence emission spectra of N-ethyl compounds (3ae5a) and
N-methyl compounds (3be5b) in their solid states (the analysis
results are listed in Table 1). The fluorescence maximum of 3a in
CHCl3 was observed at 543 nm and of solid 3a was observed at
624 nm. The fluorescence maximum wavelength of 3a was slightly
longer than that of 3b, however 3a dissolved in CHCl3 exhibited
(b) Solution state: Quantum yields were obtained by using Abso-
lute PL Quantum Yield Measurement System (C9920-01) of
Hamamastu Photonics. The concentrations of the measured
samples in the excitation wavelength region were adjusted
using a molar absorption coefficient of 0.05. The solution
fluorescence spectra were obtained in a manner similar to that
described for measurement in the solid state. The emissions
were measured using each excitation wavelength.
3. Results and discussion
Scheme 1 shows the synthesis of compound (3a). Reaction of 1
with 2 in the presence of powdered sodium hydroxide in dimethyl
sulfoxide (DMSO) for 10 h at room temperature and subsequent
treatment with cold water yields 3a (mp: 245e246 ꢀC) and the
yield was 36%.
intense fluorescence (
¼ 0.60). The fluorescence of solid 3a exhibited a hypsochromic
shift of 51 nm compared to that of 3b, and red fluorescence was
observed (Fig. 1). The value of solid 3a was about 3 times higher
F
¼ 0.95), which was higher than that of 3b
(F
F
Dramatic changes in the fluorescence colors can be observed
when the methylsulfanyl group at the 4-position of the pyrone ring
is substituted with either an amino moiety or a malonyl substituent.
Then, if the abovementioned substitutions can be achieved, it would
be possible to prepare a compound possessing the desired color
fluorescence color property. The synthesis of 4-amino-6-aryl-2-
oxo-2H-pyran-3-carbonitriles by a displacement reaction of 4-
methylsulfanyl-2H-pyran- 3-carbonitriles with various amines in
methanol under reflux has been reported. Therefore, 3a was reacted
with amines to yield 6-(4-diethylamino)phenyl-4-dimethylamino-
2-oxo-2H-pyran-3-carbonitrile (4a). As shown in Scheme 2,
compound 4a in the form of yellow needles was formed by the
reaction of 3a with dimethylamine in refluxing methanol (mp
257e258 ꢀC), and the yield was 61%. Compound 5a was synthesized
by the reaction of 3a with dimethyl malonate in the presence of
sodium hydroxide (base) in DMSO at room temperature. This
compound was obtained in the form of red needles with 90% yield
and mp of 209e210 ꢀC.
than that of solid 3b. We speculated that the molecular stacking
might weaken in the presence of an ethyl group and result in
increased fluorescence intensity. The compounds 4a and 4b
exhibited highly hypsochromic shift compared to 3a and 3b in
solution and solid state. The fluorescence maximum wavelength of
4a was longer than that of 4b in CHCl3 and the
F value of 4a in
CHCl3 was 2.8 times higher than that of 4b. These phenomena in
CHCl3 were similar to the results for 3a and 3b. However, it is
interesting to note that compound 4b exhibited strong green
fluorescence in solid state (
F
¼ 0.58) (Fig. 1), the
F value of 4b was
2.6 times higher than that of 4a and was considerably higher than
that of other 2-pyrone derivatives. It was considered that the
molecular arrangement and orientation in the solid sate resulted in
the high fluorescence intensity of 4b. In a previous study, X-ray
crystallographic analysis revealed that compound 4b was almost
plane with small torsion angles (15ꢀ) and that this small torsional
angles caused strong molecular stacking; the molecular packing
diagram of 4b clearly showed short molecular distances (ca 3.12 Å)
Table 3
Fluorescence properties of 3ae5b in various solvents.
Solvent
Emission maximum (nm) (F)
3a
3b
4a
4b
5a
5b
benzene
524 (0.50)
532 (0.13)
540 (0.95)
540 (0.95)
540 (0.39)
546 (0.09)
552 (0.13)
548 (0.01)
522 (0.28)
532 (0.23)
534 (0.60)
536 (0.63)
542 (0.16)
544 (0.04)
554 (0.04)
546 (0.04)
482 (0.04)
490 (0.03)
490 (0.47)
494 (0.66)
500 (0.38)
504 (0.68)
512 (0.89)
504 (0.92)
478 (0.02)
488 (0.01)
486 (0.17)
492 (0.28)
500 (0.16)
504 (0.35)
514 (0.69)
504 (0.63)
524 (0.75)
534 (0.78)
542 (0.94)
548 (0.93)
556 (0.32)
ea
522 (0.48)
532 (0.39)
538 (0.84)
546 (0.69)
556 (0.16)
ea
diethyl ether
chloroform
dichloromethane
acetone
acetonitrile
DMSO
ea
ea
ethanol
ea
ea
a
No fluorescence was observed.

M. Hagimori et al. / Dyes and Pigments 92 (2012) 1069e1074
1073
a
b
benzen
diethyl ether
chloroform
dichloromethan
aceton
3000
2000
1000
0
acetonitril
DMSO
ethanol
500
550
600
650
700
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
wavelength (nm)
Δ f = (ε -1)/(2ε +1)-(n2-1)/(2n2+1)
c
d
benzen
benzen
diethyl ether
chloroform
dichloromethan
aceton
diethyl ether
chloroform
dichloromethan
aceton
acetonitril
DMSO
acetonitril
DMSO
ethanol
ethanol
450
500
550
600
650
450
500
550
600
650
wavelength (nm)
wavelength (nm)
Fig. 2. (a) Lippert-Mataga plot of 3a in benzene, chloroform, diethylether, dichloromethane, DMSO, acetone, ethanol, acetonitril (1 ꢂ 10ꢁ5 M).
3: dielectric constant, n: refractive
index. (b) Fluorescence spectra of 3a in various solvents. (c) Fluorescence spectra of 4a in various solvents. (d) Fluorescence spectra of 5a in various solvents.
[13]. The properties of compounds 5a and 5b in CHCl3 were similar;
the fluorescence maximum wavelength of 5a was longer than that
of 5b, and the intensity of the fluorescence of 5a in CHCl3 was
higher than that of 5b in CHCL3. The absorption data for 5a and 5b
indicated that the absorption of these compounds bathochromi-
group present at the 4-position of pyrone ring have a significant
effect on fluorescent properties. The solvatochromic effect has been
estimated by using a Lippert-Mataga plot (Fig. 2a) [19e21]. The plot
of Stokes shifts versus the polarity function
Df of compound 3a
shows the good correlation between Stokes shifts and solvent
polarity. This result indicated that the dipole moment of molecules
changes upon excitation due to intramolecular charge transfer.
In addition, it was observed that the fluorescence quantum yield
significantly depend on the solvent molecules. The polarity of
a solvent will generally influence the fluorescence-emission spectra
cally shifted from the absorption of 3b by 24e32 nm. The
F values
of 5a and 5b were 0.94 and 0.84, respectively. The compounds 5a
and 5b in the solid state exhibited weak orangeered fluorescence,
and the
(Fig. 1).
F values of 5a and 5b were 0.05 and 0.06, respectively
It was observed that the new 2-pyrone derivatives 3ae5a that
have a diethylamino group at 4-position of the phenyl group
showed a bathochromic shift of absorption and fluorescence and
also showed a high fluorescence quantum yield when dissolved in
CHCl3. Therefore, we also investigated the solvatochromic proper-
ties of 3e5 in various solvents. Table 2 lists the absorption data, and
Table 3 lists the fluorescence data for 3e5. The replacement of
of fluorophores. The
was high; in particular, fluorescence quantum yields of 3a in
chloroform ( : 0.95) and dichloromethane ( : 0.95) were very high
(Fig. 2b). In contrast, 4a and 4b emitted both in polar and non-polar
solvents except for benzene and diethyl ether ( : 0.17e0.92). In
DMSO and ethanol, the fluorescence quantum yield of 4a was very
high (Fig. 2c). Compounds 5a and 5b, like 3a and 3b, showed strong
fluorescence in non-polar solvents (Fig. 2d). The fluorescence
quantum yield of the synthesized 2-pyrone derivatives increased
when the amino group of 4-position of phenyl group and 4-position
of pyrone ring in solution was changed; this suggest that it is
possible to use fluorophores for various purposes.
F values of 3a and 3b in non-polar solvents
F
F
F
a
dimethylamino group with a diethylamino group induced
a bathochromic shift in the absorption, while a slight bathochromic
shift in the fluorescence of 3e5 was observed by the replacement of
a dimethylamino group with a diethylamino group. The emission
maximum of 3e5 was dependent on the dielectric constant of the
solvent, and as a result the Stokes shift became larger with an
increase in the polarity of the solvent used. Quenching of the
fluorescence of 5a and 5b was observed in high-permittivity
solvents (ethanol, DMSO, acetonitril). However, the bathochromic
shift in the case of acetone was larger than the bathochromic shift
in the case of benzene. These results suggest that the malonic ester
4. Conclusion
The strongly fluorescent dye 3a with an electron-donating 6-(4-
diethylamino)phenyl group and an electron-withdrawing cyano
group was synthesized by a convenient one-pot reaction of ketene

1074
M. Hagimori et al. / Dyes and Pigments 92 (2012) 1069e1074
[9] Tominaga Y, Matsuda Y. Synthesis of heterocyclic compounds using nitro
ketene dithioacetal. J Heterocycl Chem 1985;22:937e49.
[10] Tominaga Y, Matsuda Y. Synthesis of indolizine derivatives and their related
dithioacetal (2) with 4-diethylaminoacetophenone (1) in the
presence of sodium hydroxide as the base in DMSO. The
compounds 4a and 5a were synthesized by replacing of the
methylsulfanyl group of 3a in good yield. The novel 2H-pyrone
derivatives (3ae5a) exhibited fluorescence in the solid state (red
(3a), green (4a), and orange (5a)), and they also exhibited positive
solvatochromism in various solvents. The fluorescence of 3ae5a in
solutions showed a bathochromic shift and intense fluorescence
from the fluorescence of the previously reported 2H-pyrone
derivatives (3be5b) in solution. It is anticipated that these mate-
rials will find applications in various fields.
compounds using ketene dithioacetals.
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