Synthesis of new efficient laser dyes of red spectral range, the DCM analogs, based on 2-aryl-6-methyl-4H-pyrone

Article abstract of DOI:10.1134/S1070363211110156

A new method was developed for the synthesis of 2-aryl-6-methyl-4H-pyrones by the condensation of arylmethylketones with the acetoacetic ester ethylene ketal in the presence of sodium alkoxylate. New laser merocyanine dyes, the analogues of 4-dicyanomethylene-2-methyl-6-[(4-dimethylamino)styryl]-4H-pyran (DCM), were obtained based on the synthesized 2-aryl-4-pyrones. The dyes are characterized by high generation efficiency in the red spectral range.

Full text of DOI:10.1134/S1070363211110156

ISSN 1070-3632, Russian Journal of General Chemistry, 2011, Vol. 81, No. 11, pp. 2310–2315. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © O.V. Ponomareva, A.P. Lugovskii, A.A. Lugovskii, M.P. Males, I.V. Komlev, E.E. Nifant’ev, 2011, published in Zhurnal Obshchei
Khimii, 2011, Vol. 81, No. 11, pp. 1859–1864.
Synthesis of New Efficient Laser Dyes
of Red Spectral Range, the DCM Analogs,
Based on 2-Aryl-6-methyl-4H-pyrone
O. V. Ponomarevaa, A. P. Lugovskiib, A. A. Lugovskiib,
M. P. Malesb, I. V. Komleva, and E. E. Nifant’eva
a Moscow State Pedagogical University, Nesvizhskii per. 3, Moscow, 119021 Russia
e-mail: chemdept@mtu-net.ru
b Shevchenko Research Institute of Applied Physical Problems, Minsk, Belarus
e-mail: chemdept@mtu-net.ru
Received December 9, 2010
Abstract—A new method was developed for the synthesis of 2-aryl-6-methyl-4H-pyrones by the condensation
of arylmethylketones with the acetoacetic ester ethylene ketal in the presence of sodium alkoxylate. New laser
merocyanine dyes, the analogues of 4-dicyanomethylene-2-methyl-6-[(4-dimethylamino)styryl]-4H-pyran
(DCM), were obtained based on the synthesized 2-aryl-4-pyrones. The dyes are characterized by high
generation efficiency in the red spectral range.
DOI: 10.1134/S1070363211110156
DCM (4-dicyanomethylene-2-methyl-6-[(4-dimethyl-
amino)styryl]-4H-pyran) and its derivatives are highly
efficient laser dyes for the red spectral range [1]. Their
implementation as working substances in electro-
luminescent devices [2], using a two-photon techno-
logies [3] and solar concentrators [4] has been
reported. The synthesis of new derivatives of these dye
merocyanines, development and improvement of methods
for obtaining the fluorophores of this type is very relevant.
Usually, the synthesis of DCM II, the basic dye of
this series, is performed by condensation of 4-dimethyl-
aminobenzaldehyde with the synthetically accessible 4-
dicyanomethylene-2,6-dimethyl-4H-pyran (I).
NC
CN
CHO
NC
CN
+
H3C
O
H3C
O
CH3
N(CH3)2
N(CH3)2
I
II
NC
CN
+
O
(H3C)2N
N(CH3)2
III
2310

SYNTHESIS OF NEW EFFICIENT LASER DYES
2311
However, preparation of the desired laser dye of
spectral purity is complicated considerably by the
necessity to remove a deeply colored product III of
condensation the aldehyde at the second methyl group
identical in terms of reactivity with the first methyl
group of the pyran fragment, which is formed even at
the stoichiometric ratio of initial reagents. The
purification increases the product cost.
More accessible method for the synthesis of the 4-
pyrone 2-aryl derivatives that has been tested by us [6]
is the condensation of acetylacetone dianion with
carboxylic acid esters followed by the cyclization of
obtained 1,3,5-triketones [7]. This method, however,
involves the use of unsafe and expensive sodium
hydride. In addition, the yield of the desired product
does not exceed 20%.
Replacing one methyl group by a substituent not
containing active methylene component allows to
avoid the formation of the condensation by-product.
Such a substituent may be an aryl group.
In this paper we propose a method for the synthesis
of 2-aryl-4-pyrone based on the condensation of
arylmethylketones IV with the acetoacetic ester
ethylene ketal V. The ethylene ketal protector of the
acetoacetic ester carbonyl group prevents enolization
of the latter by blocking sterically the α-methylene
center for nucleophilic reactions. This allows the use
of ethylene ketal V as the ester component in the
condensation with ketones IV.
A method for producing 2-aryl-6-methyl-4-pyrones
by the condensation of arylacethylenecarboxylic esters
with acetone in 48–50% yield has been described [5].
Its drawback is inaccessibility of the arylacethylene-
carboxylic esters, particularly those containing
different substituents in the aryl ring.
O
Ar
OH
O
ClO4−
CH3
O
H3C
O
OEt
NaO
O
HClO4
NaHCO3
i-PrONa
+
Ar
O
+
O
O
Ar
Ar
O
CH3
CH3
CH3
O
VIIa−VIId
IV
V
VI
R = Ph (a), 4-EtO-C6H4 (b), 1-C10H7 (c), 2-C10H7 (d).
Condensation reaction was carried out in toluene as
a solvent, in the presence of sodium ethoxide or isoprop-
oxide. The optimum molar ratio of reactants (ketone–
ethylene ketal–alkoxylate) was found equal to 1:1.5:1.
Dibenzo-18-crown-6 added to the reaction mixture in
an amount of 0.5–1 mol % increases the final product
yield (Table 1). Replacement of sodium isopropoxide
by sodium ethoxide had no effect on the pyrone yield.
A similar situation observed at the use of sodium
hydride in monoglime or toluene. 4-Etoxyaceto-
phenone and 2-naphthylmethylketone give higher yield
of respective arylpyrones.
It should be noted that application of this method to
α-tetralone resulted in the arylpyrone VIIe with
annelated hydroaromatic fragment, not synthesised
previously.
O
O
H3C
OEt
O
O
+
O
O
CH3
V
VIIe
Cyclization with simultaneous removal of the ketal
protection requires two equivalents of perchloric acid:
one equivalent is consumed for the formation of
sodium perchlorate, and the second serves to the
formation of 4-hydroxypyrilium perchlorate VI. The
latter is soluble in hot water phase and crystallizes at
cooling the solution. Separation of the desired product
from resinous by-products was carried out by
treatment of the filtered off salt VI with a sodium
hydrocarbonate solution.
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2312
PONOMAREVA et al.
Malononitrile derivatives VIII were prepared using
The presence of one reaction center has allowed to
carry out the condensation of dicyanomethylenepyrans
VIIIa–VIIIe with 4-dimethylaminobenzaldehyde in
the pyridine–piperidine system by a single route. The
DCM derivatives of high purity crystallized from the
reaction medium after cooling.
a procedure similar to that given in [8, 9]: by boiling 2-
arylpyrones VIIa–VIIe in acetic anhydride with
equimolar amount of malonic dinitrile.
NC
CN
CN
CN
Ac2O
Structures of the DCM aryl analogues IXa–IXe
thus obtained are shown below, yields and main physico-
chemical characteristics of the new merocyanine dyes
and their intermediates are listed in Tables 1–3.
VIIа−VIIe
+ H2C
Ar
O
CH3
VIIIа−VIIIe
NC
CN
NC
CN
O
O
EtO
N(CH3)2
N(CH3)2
IXа
IXb
NC
CN
NC
CN
O
O
N(CH3)2
N(CH3)2
NC
IXc
IXd
CN
O
N(CH3)2
IXe
Replacement of the methyl group in DCM by
phenyl (compound IXa) containing conjugated π-
electron system, practically did not change the band
position and shape in the electron absorption spectra.
The synthesized merocyanine dyes IXa–IXe are
characterized by a slight solvatochromism, like DCM
(Table 2).
scence quantum yield (φf) in polar solvents, associated
apparently with the rotational-vibrational relaxation of
the energy of the 2-phenyl substituent excited state.
The higher value of the Stokes shift for the analyzed
compounds is due, in our opinion, to the high content
of the pyrilium tautomeric forms.
Two cyano groups withdraw strongly the electron
density from the 4-methylene substituent, thus con-
tributing to increased negative charge. At the same
time the energetically favorable pyrilium structure
Stronger difference is seen in the luminescence
spectra. For the 2-aryl compounds is typical a higher
value of the Stokes shift and lower value of fluore-
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SYNTHESIS OF NEW EFFICIENT LASER DYES
2313
Table 1. Physicochemical characteristics of 2-aryl-6-methyl-4H-pyrones, 4-dicyanomethylene merocyanine derivatives and
dyes based on them
Found, %
Calculated, %
Comp. no.
Yield, %
mp, °С
Formula
C
H
N
C
H
N
53
52а
50b
58
44
59
49
60
62
59
62
67
91
88
87
90
90
82–83
77.13
5.27
C12H10O2
77.40
5.41
VIIа
78–79
72.81
80.63
80.58
77.57
75.98
73.25
80.06
79.87
78.21
78.81
74.98
80.78
80.69
79.21
6.05
5.01
5.03
5.41
4.11
5.03
4.11
4.03
4.27
5.07
5.60
5.03
5.02
5.20
C14H14O3
73.03
81.34
81.34
77.76
76.91
73.37
80.27
80.27
78.45
78.88
75.26
80.94
80.94
79.77
6.13
5.12
5.12
5.59
4.30
5.07
4.25
4.25
4.64
5.24
5.66
5.09
5.09
5.41
VIIb
VIIc
VIId
VIIe
VIIIа
VIIIb
VIIIc
VIIId
VIIIe
IXа
87–88
C16H12O2
91–92
C16H12O2
101–102
184–186
169–170
171–172
175–176
191–192
274–275
233–234
229–230
232–233
276–277
C14H12O2
11.83
9.94
C15H10N2O
C17H14N2O2
C19H12N2O
C19H12N2O
C17H12N2O
C24H19N3O
C26H23N3O2
C28H21N3O
C28H21N3O
C26H21N3O
11.96
10.06
9.85
9.46
9.51
9.85
10.70
11.31
9.94
10.76
11.50
10.26
10.11
10.11
10.73
IXb
10.01
10.02
10.03
IXc
IXd
IXe
a The catalyst is sodium hydride in toluene (method b). b The catalyst is sodium hydride in monoglime (method b).
Table 2. Comparative spectral-luminescent and geberation characteristics of compounds IXa–IXe and the DCM dye
Dye
Sovent
λabsorb, nm
λfluor, nm
φf
ηgener, %
Δλgener, nm
DCM
Dioxane
ma4x 66
462
472
488
475
481
482
480
472
487
485
480
495
500
497
500
500
503
m5ax60
563
582
628
638
640
660
582
565
595
673
676
700
711
693
690
730
736
0.01
0.01
0.02
0.14
0.308
0.45
0.59
0.45
0.04
0.55
0.14
0.05
0.02
0.02
0.05
–
–
–
Toluene
Dichloromethane
Acetone
Ethanol
–
–
–
–
–
–
25
28
27
47
47
40
47
47
43
42
38
–
605–672
DMF
607–690
DMSO
611–712
Dioxane
Toluene
Dichloromethane
Acetone
Ethanol
–
IXа
–
607–674
–
–
DMF
647–735
675–810
620–800
–
DMSO
DMSO
IXb
IXc
IXd
IXe
DMSO
DMSO
–
–
–
DMSO
0.06
42
670–850
contributes to appearance of a positive charge on the
oxygen. An increase in the solvent polarity also
contributes to the shift of the equilibrium toward the
more polar pyrilium form. Interaction of π-electron
system of the aryl substituent with the π-electron
system of the pyrane ring results in a bathochromic
shift in the fluorescence spectra. The introduction of
donor substituents in the phenyl ring reduces this effect
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 11 2011

2314
PONOMAREVA et al.
Table 3. 1H NMR spectral characteristics of the synthesized
intermediates VII, VIII and IX of merotsianinovyh dyes
At the testsing the laser activity of the synthesized
merocyanine dyes we found (Table 2) that they are
effectively generating compounds for the red spectral
region (generating efficiency is up to 47%) with wide
tuning range, and can be recommended for practical
use as components of active medium in liquid and
polymer lasers.
Comp.
δ, ppm
no.
2.06 s (3Н, СН3), 5.83, 6.22 s (2Н, –СН=), 6.98, 7.37 m
(5Н, Нphenyl
1.35 t (3Н, СН3), 2.06 s (3Н, СН3), 4.12 q (2Н, СН2),
5.82, 6.22 s (2Н, –СН=), 6.87, 7.37 m (4Н, Нphenyl
2.05 s (3Н, СН3), 5.83, 6.24 s (2Н, –СН=), 7.15, 8.17 m
(7Н, Нnaphtyl
2.04 s (3Н, СН3), 5.83, 6.24 s (2Н, –СН=), 7.12, 7.86 m
(7Н, Нnaphtyl
2.09 s (3Н, СН3), 2.94, 3.23 m (4Н, СН2), 5.43 s (1Н,
3Нpyran), 7.22, 7.45 m (4Н, Нphenyl
2.13 s (3Н, СН3), 6.5, 7.02 s (2Н, –СН=), 7.02, 7.51 m
(5Н, Нphenyl
1.35 t (3Н, СН3), 2.06 s (3Н, СН3), 4.13 q (2Н, СН2),
6.62, 7.11 s (2Н, –СН=), 6.99, 7.47 m (4Н, Нphenyl
2.14 s (3Н, СН3), 6.51, 7.12 s (2Н, –СН=), 7.15, 8.17 m
(7Н, Нnaphtyl
2.14 s (3Н, СН3), 6.51, 7.12 s (2Н, –СН=), 7.15, 8.17 m
(7Н, Нnaphtyl
2.15 s (3Н, СН3), 2.86, 3.20 m (4Н, СН2), 5.91 s (1Н,
3Нpyran), 7.25, 7.44 m (4Н, Нphenyl
VIIа
VIIb
VIIc
)
)
EXPERIMENTAL
1H NMR spectra were taken from 5% solutions of
compounds on a Bruker AW 200 spectrometer at the
operating frequency 200 MHz, internal reference TMS.
The absorption spectra were recorded using a Solar
PV-1251 spectrophotometer, fluorescence spectra
using Spex Fluorolog fluorimeter.
)
VIId
VIIe
)
)
VIIIа
VIIIb
VIIIc
VIIId
VIIIe
IXа
)
At the measuring the generation parameters of dye
solutions, their concentrations were optimized to
maximize the energy generation. For pumping was
used the second harmonic of the Q-switched yttrium–
aluminum garnet laser with the following parameters:
single pulse energy E = 0.1 J, τ = 20 ns, λ = 532 nm.
The spectral tuning range was determined from the
level of 0.5 Emax of the generation in a selective
resonator.
)
)
)
)
3.07 s (6Н, СН3), 6.55, 7.46 d (2Н, –СН=, J 16 Hz),
6.66 s (1Н, 5Нpyran), 7.06 s (1Н, 3Нpyran), 6.73, 7.87 d
The DCM dye was synthesized by us earlier [10],
the acetoacetic ester ethylene ketal V was prepared as
described in [11] using a 60% dispersion of sodium
hydride in mineral oil from Aldrich.
(4Н, Нphenylene), 7.05, 7.57 m (5Н, Нphenyl
)
1.35 t (3Н, СН3), 3.07 s (6Н, СН3), 4.12 q (2Н, СН2),
6.54, 7.42 d (2Н, –СН=, J 16 Hz), 6.68 s (1Н, 5Нpyran),
7.07 s (1Н, 3Нpyran), 6.73, 7.87 d (4Н, Нphenylene), 7.05,
IXb
Synthesis of aryl derivatives of 4H-pyrone
(VIIa–VIIe). a. In a three-necked 0.5 l flask equipped
with mechanical stirrer, reflux condenser, dropping
funnel and inert gas inlet was placed 200 ml of water-
free toluene and 11.5 g (0.5 mol) of sodium metal.
Solution was heated to boil, and while vigorously
stirring strived the sodium pulverization. Then while
stirring and maintaining the temperature in the flask
30–40°C was added dropwise 30 ml (0.5 mol) of
isopropyl alcohol. After dissolution of sodium, 1.5 g
(2.8 mmol) of dibenzo-18-crown-6 was added, the
reaction mixture was heated to 100–105°C and a
mixture of 0.5 mol of aromatic ketone and 133.5 g
(0.75 mol) of acetoacetic ester ethylene ketal V was
added dropwise, while the mixture of ethyl and
isopropyl alcohols evolved in the reaction course was
distilled off. Then the cooled reaction mixture was
treated with 150 ml of 57% perchloric acid and 150 ml
of water. The organic layer was distilled off with
steam, the hot water fraction was cooled to room
temperature. The precipitated perchlorate VI was
7.57 m (4Н, 6Нphenylene
)
3.07 s (6Н, СН3), 6.56, 7.48 d (2Н, –СН=, J 16 Hz),
6.66 s (1Н, 5Нpyran), 7.06 s (1Н, 3Нpyran), 6.72, 7.86 d
IXc
IXd
IXe
(4Н, Нphenylene), 7.15, 8.17 m (7Н, Нnaphtyl
)
3.07 s (6Н, СН3), 6.56, 7.48 d (2Н, –СН=, J 16 Hz),
6.66 s (1Н, 5Нpyran), 7.06 s (1Н, 3Нpyran), 6.73, 7.87 d
(4Н, Нphenylene), 7.15, 8.17 m (7Н, Нnaphtyl
)
2.96, 3.25 m (4Н, СН2), 3.07 s (6Н, СН3), 6.53, 7.44 d
(2Н, –СН=, J 16 Hz), 6.71 s (1Н, 5Нpyran), 6.71, 7.87 d
(4Н, Нphenylene), 7.25, 7.39 m (4Н, Нphenyl
)
(compound IXb). This is evidenced additionally by the
comparison of the spectra of α- and β-naphthyl
derivatives IXc and IXd, in which the electron density
of the pyran ring is increased or decreased,
respectively, and this effect is reflected by their
luminescence spectra (Table 2).
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SYNTHESIS OF NEW EFFICIENT LASER DYES
2315
filtered off and washed with diethyl ether. After
treatment with 5% aqueous solution of sodium
hydrocarbonate the precipitate was filtered off, washed
with water, and dried in a vacuum. The isolated 2-aryl-
6-methyl-4H-pyrones were of sufficiently high purity
and could be used without further recrystallization in
the following steps.
water. After drying, the compounds were further
crystallized from cyclohexane.
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sodium hydride in oil and 200 ml of monoglyme, and
while stirring and boiling was added dropwise 0.5 mol
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was added 133.5 g (0.75 mol) of the ethylene ketal V
and the mixture was refluxed for 2 h. Further
processing is analogous to the method a.
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(VIII). A mixture of 0.1 mol of pyrone VII, 7.26 g
(0.11 mol) of malonodinitrile and 80 ml of acetic
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4-dicyanomethylene-2-aryl-6-methyl-4H-pyran VIII,
16.39 g (0.11 mol) of 4-dimethylaminobenzaldehyde,
80 ml of pyridine and 8 ml of piperidine was refluxed
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RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 11 2011