The structural criteria of hydrolytic stability in series of dioxaborine polymethine dyes

Article abstract of DOI:10.1016/j.dyepig.2010.09.007

The structural criteria that affect stability to the alkaline hydrolysis of dioxaborine dyes were analyzed. Dyes with different electron-donor and electron-withdrawing groups conjugated with dioxaborine cycle, and also having some steric effects were analyzed. For this purpose, some new dioxaborine dyes were synthesized. It was shown that electron-donor substituents, unlike electron-withdrawing ones, increase the hydrolytic stability of the dioxaborine dyes. The possible way of the basic hydrolysis of dioxaborine dyes was suggested. The products of the partial hydrolysis of the symmetrical dioxaborine dyes were first obtained.

Full text of DOI:10.1016/j.dyepig.2010.09.007

Dyes and Pigments 89 (2011) 76e85
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
The structural criteria of hydrolytic stability in series of dioxaborine
polymethine dyes
*
Andrii O. Gerasov, Konstantin V. Zyabrev, Mykola P. Shandura, Yuriy P. Kovtun
Institute of Organic Chemistry, National Academy of Sciences of Ukraine, 5 Murmanska str., 02660 Kyiv, Ukraine
a r t i c l e i n f o
a b s t r a c t
Article history:
The structural criteria that affect stability to the alkaline hydrolysis of dioxaborine dyes were analyzed.
Dyes with different electron-donor and electron-withdrawing groups conjugated with dioxaborine cycle,
and also having some steric effects were analyzed. For this purpose, some new dioxaborine dyes were
synthesized. It was shown that electron-donor substituents, unlike electron-withdrawing ones, increase
the hydrolytic stability of the dioxaborine dyes. The possible way of the basic hydrolysis of dioxaborine
dyes was suggested. The products of the partial hydrolysis of the symmetrical dioxaborine dyes were first
obtained.
Received 10 June 2010
Received in revised form
14 September 2010
Accepted 19 September 2010
Available online 29 September 2010
Keywords:
Dye
Ó 2010 Elsevier Ltd. All rights reserved.
Dioxaborine
Hydrolysis
Pigment
Absorption
1. Introduction
comparison with the unsubstituted analogues [10,11]. Improved
hydrolytic stability the former dyes was explained by electron-
Polymethine dyes based on 2,2-difluoro-1,3,2(2H)-dioxaborine
(DOB-dyes, structure A, Fig. 1) are noted for their deep colour and
intense luminescence [1e15], effective two-photon absorption
cross-section [6,16], as well as large second- [2] and third-order [3]
hyperpolarizabilities. However, a significant drawback of DOB-dyes
on the way to expand their practical applications exists, which are
not always acceptable stability and particularly low stability
towards hydrolysis of dioxaborine cycle. Notably, the stability of
luminophors in alkaline medium (pH w 8e9) is an important
characteristic of the dyes that are used in biological studies, for
example for fluorescent labels of biomolecules. Therefore, it was
important to identify and examine the factors that affect the
resistance of DOB-dyes to alkaline hydrolysis. In this work we
investigated hydrolytic stability for both: new and described in the
literature DOB-dyes.
withdrawing properties of DOB-fragment. For better under-
standing of these factors, which affect the stability, it was our
intention to expand the above dye series with some new
representatives.
The electron-donor properties are increasing on changing from
diethylaminophenyl (type-B dyes) to julolidine fragment (deriva-
tive 2, Scheme 1) due to rigidifying of the dialkylamino substituent,
and hence increasing the positive mesomeric effect. Dioxaborine 2
was obtained in one step by the acetylation of coumarin 1 [17] with
acetic anhydride in the presence of BF3- etherate (Scheme 1).
The electron-withdrawing properties of type-B DOB-fragment
are decreased on replacing the coumarin oxygen atom with the less
electronegative quinolone nitrogen atom. As the direct introduc-
tion of the acetyl group into 3 position of the quinolone 3 [18] did
not succeed, dioxaborine 6 was obtained in several steps analo-
gously to published procedure [19] (Scheme 2).
Symmetrical anionic dyes and indolenine merocyanines were
synthesized from compounds 2 and 6 by conventional methods
(Scheme 3, structures in the Tables 1 and 2).
To estimate the influence of the lactone and lactam fragments
on the hydrolytic stability of DOB-dyes based on 4-hydrox-
ycoumarin (dyes 7e10) and 4-hydroxyquinolone (11a,b) we also
analyzed benzoylacetone-based DOB-dyes (12e14, 20, Tables 1 and
2). For this purpose new merocyanines 13b and 14b were synthe-
sized (Table 2).
2. Results and discussion
We have recently shown that the introduction of dialkylamino
groups to the coumarin nucleus gives rise to the dramatic increase
of the absorption, fluorescence intensities and the hydrolytic
stability of the DOB-based dyes (B and C-type structures) [11,12] in
* Corresponding author. Tel.: þ380 44 5510682; fax: þ380 44 5732643.
E-mail address: kovtun@ioch.kiev.ua (Y.P. Kovtun).
0143-7208/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2010.09.007

A.O. Gerasov et al. / Dyes and Pigments 89 (2011) 76e85
77
methylene bridge in the case of benzoylacetone derivatives (dye
13a) leads to a decrease of electron-withdrawing properties of
DOB-fragment (compared with 12a). The reason for this is
strengthening of the conjugation between the phenyl nucleus and
the DOB-cycle, and the introduction of electron-donating methy-
lene group at the position 5. At the same time, the introduction of
the ethylene bridge (dye 14a) hardly changes electron-donor effect
of the substituent at the position 5 of DOB-cycle, but the conjuga-
tion with the phenyl fragment distinctly disrupts, because of the
distortion of the planarity [7]. Such trends in the electron-with-
drawing properties of DOB-fragment are in good agreement with
the hydrolytic stability of these dyes, which increases in the series:
12a < 14a < 13a.
On comparison of coumarin dye 7a with benzoylacetone
derivative 12a, one can see that the formation of the lactone cycle
drastically (by more than two orders of magnitude) reduces the
hydrolytic stability of these dyes due to the electron-withdrawing
effect of the ester group at the position 5 of DOB-cycle. The elec-
tron-withdrawing properties of the DOB-fragment are decreased
on replacing the lactone fragment (dyes 8a, 15a) with the lactam
(dyes 11a, 16a), which results in the higher hydrolytic stability of
the dyes. Introduction of electron-donating dialkylamino groups
into the coumarin nucleus (dyes 8a, 9a, 10a) leads to a subsequent
increase in the stability to the alkaline hydrolysis (half-lifetime
(t0.5) is 410 s, 870 s and 26660 s respectively). Thus, the highest
stability is reached for the dipyrrolidylcoumarin-based dye (10a).
The additional factor that affects the stability of this dye could be
the steric hindrance (from the second pyrrolidyl-group) to attack at
the DOB-cycle by the hydroxyl anion.
For all investigated symmetrical (7ae16a) and indolenin-type
merocyanine dyes (7be16b), (except for 7a, 7b and 15a, 15b dyes)
we noticed the higher stability of symmetrical dyes, caused by the
anionic character of the chromophore (Tables 1 and 2). A chro-
mophore charge (positive or negative) significantly affects the
resistance to alkaline hydrolysis. This phenomenon is very well
exemplified by the conventional cationic (18, t0.5 ¼ 116 s) and
anionic (17, t0.5 ¼ 7750 s) symmetrical dyes. In addition, the devi-
ation from the symmetrical distribution of electron density, typical
of merocyanines, could also be the reason of their lower hydrolytic
stability. However, within the dye pairs 7ae7b, and 15ae15b with
the strong electron-withdrawing DOB-nucleus, asymmetrical
electronic structure of the merocyanines (7b and 15b) results in
increasing their hydrolytic stability, compared to their symmetrical
analogs (7a and 15a), due to the strong shift of the electron density
towards the DOB-cycle.
Fig. 1. General types of DOB-dyes.
The methyl group in dioxaborine 19 [20] derived from
4-dimethylaminobenzoylacetone has the very low reactivity in
cyanine condensations, so that we were able to synthesize only one
non-bridged merocyanine dye 20 (Scheme 4) in addition to 12b [4].
The hydrolytic stability of pyranone 15a,b and pyridone 16a,b
dyes [13] was also investigated. For comparison, we measured the
resistance to alkaline hydrolysis of known polymethine anionic 17
and cationic dyes 18 (Table 1).
In the reports [14,21] triethylamine and sodium acetate aqueous
solutions were used for the study of the hydrolysis of some diox-
aborine dyes. In our case, these reagents proved to be inconvenient
due to the relatively high stability of the most dyes in these
conditions. Consequently, using stronger bases, such as DBU,
allowed to reduce the experiment time significantly. In our study
a large excess of DBU (1:10000) was used in the acetonitrile-water
(9:1) mixture, so that the measurements would only depend on the
dye concentration. On the addition of DBU to an aqueous-aceto-
nitrile dye solution the series of the absorption spectra, depending
on the reaction time, was obtained (Fig. 2a). The subsequent
measurement of the optical density (D) led to kinetic curve (D as
function of time), which after the transformation gave the linear
dependence shown in Fig. 2b, which allowed for the hydrolytic
stability constants of the dyes to be investigated (Tables 1 and 2).
Analysis of the hydrolytic rate constants of the symmetrical
DOB-dyes shows that weakening of electron-withdrawing proper-
ties of DOB-nucleus significantly increases their stability (Table 1).
For example, rigidifying of the chromophore part with the
Scheme 1. Synthesis of boron difluoride complex 2.
Scheme 2. Synthesis of boron difluoride complex 6.
Scheme 3. General method for the DOB-dyes synthesis: a) anionic symmetrical dyes; b) indolenine-based merocyanines (Table 1).

78
A.O. Gerasov et al. / Dyes and Pigments 89 (2011) 76e85
Table 1
Spectral properties and hydrolytic stability parameters of symmetric polymethine dyes.
Dye
Structure
labs(MeCN), nm (
3
∙10ꢀ5, Mꢀ1 cmꢀ1
)
lem(MeCN), nm (
4)
t0.5, s
k, sꢀ1
F
F
F
F
B
B
O
O
O
O
7a
572 (2.15)
581(0.04)
13
5.36∙10ꢀ2
+
O
O
Et3NH
O
O
F
F
F
F
B
B
O
O
O
O
8a
8c
615 (2.52)
712 (3.00)
636 (0.86)
732 (0.66)
410
1.69∙10ꢀ3
+
N
O
B
O
O
O
B
N
Bu3NH
F
F
F
F
O
O
O
O
1.15∙10ꢀ2
+
60
Et3NH
N
O
O
O
O
N
F
F
F
F
B
B
O
O
O
O
9a
663 (2.73)
666 (0.11)
870
7.98∙10ꢀ4
+
N
O
F
O
O
B
O
N
Et3NH
F
F
F
B
N+
N
O
O
O
O
N
10a
11a
12a
13a
14a
633 (3.00)
617 (1.96)
597 (1.14)
606 (2.11)
619 (2.14)
661 (0.29)
631 (0.31)
618 (0.25)c
621 (0.50)c
636 (0.30)c
26660
2040
2330
11950
4680
2.60∙10ꢀ5
3.40∙10ꢀ4
2.98∙10ꢀ4
5.80∙10ꢀ5
1.48∙10ꢀ4
N
O
O
O
O
N
F
F
F
F
B
B
O
O
O
O
+
N
N
O
O
N
N
Et3NH
F
F
F
F
B
B
O
O
O
O
+
Et3NH
F
F
F
F
B
B
B
O
O
O
O
+
Et3NH
F
F
F
F
B
O
O
O
O
+
Et3NH
F
F
F
F
B
B
O
O
O
O
15a
554 (1.55)
560 (0.12)
112
6.19∙10ꢀ3
+
Et3NH
O
O
O
O

A.O. Gerasov et al. / Dyes and Pigments 89 (2011) 76e85
79
Table 1 (continued )
Dye
Structure
labs(MeCN), nm (
3
∙10ꢀ5, Mꢀ1 cmꢀ1
)
lem(MeCN), nm (
4)
t0.5, s
k, sꢀ1
F
F
F
F
B
B
O
O
O
O
16a
5.68 (1.47)
575 (0.20)
260
2.67∙10ꢀ3
+
N
O
O
O
N
Et3NH
O
N
O
N
O
N
+
Et3NH
17
18
495 (1.13)a
e
7750
116
8.94∙10ꢀ5
O
O
O
N
O
N+
N
542 (1.38)
568 (0.03)b
5.96∙10ꢀ3
-
ClO4
t0.5 e half lifetime. k e hydrolytic rate constant.
a
In CHCl3.
In EtOH.
In CH2Cl2.
b
c
Merocyanine dye 20 derived from 4-dimetylaminobenzoylace-
tone shows one of the highest values of the hydrolytic stability
(t0.5 ¼ 11890 s) within the merocyanine series. However, such
a decrease of the electron-withdrawing properties of the DOB-
fragment has its drawback: the methyl group in dioxaborine 19
reactivity is considerably decreased, which limits the synthetic
versatility of the initial complex.
For diethylaminocoumarin-based merocyanines (8b, 8e and 8f),
the increase in the electron-donor ability of the second heterocyclic
residue, gives rise to the increased hydrolytic stability of the dyes.
Thus, in passing from indolenine merocyanine 8b (t0.5 ¼ 300 s) to
benzothiazole 8e (t0.5 ¼ 1050 s), and quinoline derivatives 8f
(t0.5 ¼ 4310 s) the hydrolytic stability increases by more than an
order of magnitude, which significantly exceeds the respective
characteristic for symmetrical dye 8a (t0.5 ¼ 410 s). This could be
explained in terms of the increased electron-donor ability of the
heterocyclic residue and hence shifted electron density towards the
DOB-cycle.
The influence of the polymethine chain length on the hydro-
lytic stability of the dyes could be examplified by the vinylogue
dyes 8a (t0.5 ¼ 410 s) and 8c (t0.5 ¼ 60 s), as well as 8b (t0.5 ¼ 300s)
and 8d (t0.5 ¼ 42 s). On passing from trimethine- to pentam-
ethinecyanine system, the hydrolytic stability is significantly
decreased (Tables 1 and 2). For the heptamethinecyanine dye, the
solution decolorized immediately after the addition of the base
(DBU). Similar conclusions on the influence of the polymethine
chain length on the hydrolytic stability of DOB-dyes were drawn
in the literature [14].
nonequivalent protons from the heterocyclic residues and the
chain, which clearly proves the asymmetric character of the
molecule (Fig. 3). Elemental analysis of the compound is in good
agreement with the proposed structure. Treating of compound 21
with BF3-etherate in the presence of triethylamine results in the
initial dye 8a (confirmed by the absorption spectrum) (Scheme 2).
The stability of dye 21 to the further hydrolysis could be explained
in terms of the greater negative charge, localized on the DOB-cycle,
than in case of 8a.
The absorption maximum of dye 21 is only 39 nm higher than
that of corresponding dye 8a, with the significantly lower absorp-
tion intensity (Fig. 4). The noticeable broadening of the absorption
band could be the result of the asymmetrical distribution of the
electron density.
The partial hydrolysis products of the symmetrical dyes 7a and
12a were obtained similarly to 8a. In the case of the large excess of
base and more drastic hydrolysis conditions, only products of the
complete destruction were observed, and 1,3,7,9-tetracarbonyl
derivatives were not obtained.
We assume that the initial step of the reaction of DOB-dye A
with base is the addition of the hydroxyl anion to the meso-atom of
the polymethine chain with the formation of intermediate D
(Scheme 7), accompanied by breaking of the conjugation and hence
a loss of the resonance stabilization of the DOB-cycle. Subsequently,
the DOB-cycle undergoes the further hydrolysis with the formation
of the intermediate E. Upon of the acidification of the reaction
mixture, dye A absorption band appears, as well as that of the
hydrolyzed product F in the electronic spectrum. Thus, the partial
regeneration of the initial dye A through the elimination of the
hydroxyl group from intermediate D confirms the suggested
mechanism.
It is known that merocyanines with DOB-nuclei are hydrolyzed
to the corresponding 1,3-dicarbonyl compounds (Scheme 5)
[8,11,22,23].
In the case of the symmetrical trimethine DOB-dyes it was
expected that the products of hydrolysis would be 1,3,7,9-tetra-
carbonyl derivatives. But on treating compound 8a with tetrabu-
tylammonium hydroxide only partially hydrolyzed anionic dye 21
was isolated (Scheme 6).
3. Experiment
Electronic absorption spectra were recorded on a Shimadzu UV-
3100 spectrophotometer.
NMR spectra were obtained with a Varian VXR-300 instrument
(300 MHz) at 25 ꢁC using tetramethylsilane as an internal standard
for 1H NMR and CFCl3 for 19F NMR.
The singlet at ꢀ144 ppm in 19F NMR spectrum of the reaction
product confirms the presence of the remaining non-hydrolyzed
DOB-cycle. The 1H NMR spectrum of dye 21 reveals the presence of

80
A.O. Gerasov et al. / Dyes and Pigments 89 (2011) 76e85
Table 2
Spectral properties and hydrolytic stability parameters of merocyanine dyes.
Dye
Structure
labs(MeCN), nm (
3
∙10ꢀ5, Mꢀ1 cmꢀ1
)
lem(MeCN), nm (
590 (<0.005)
4
)
t0.5, s
k, sꢀ1
F
F
B
O
O
1.40∙10ꢀ2
N
7b
568 (0.79)
50
O
O
F
F
B
O
O
N
8b
584 (1.95)
607 (0.125)
300
2.33∙10ꢀ3
N
O
B
O
F
F
O
O
N
8d
678 (2.31)
701 (0.52)
42
1.64∙10ꢀ2
N
O
O
F
F
B
O
O
N
9b
593 (1.83)
621 (0.05)
340
2.04∙10ꢀ3
N
O
O
F
F
B
N
O
O
N
10b
588 (1.81)
607 (0.1)
7330
9.46∙10ꢀ5
N
O
O
F
F
B
O
O
N
11b
12b
583 (1.85)
605 (0.18)
2240
3.09∙10ꢀ4
N
N
O
F
F
B
O
O
562 (1.25)a
890
7.80∙10ꢀ4
b
N
F
F
B
O
O
b
13b
14b
567 (1.32)
576 (1.21)
700
330
9.87∙10ꢀ4
N
F
F
B
O
O
b
2.12∙10ꢀ3
N

A.O. Gerasov et al. / Dyes and Pigments 89 (2011) 76e85
81
Table 2 (continued )
Dye
Structure
labs(MeCN), nm (
3
∙10ꢀ5, Mꢀ1 cmꢀ1
)
lem(MeCN), nm (
4
)
t0.5, s
k, sꢀ1
F
F
B
O
O
5.20∙10ꢀ3
N
15b
554 (0.88)
566 (0.013)
113
O
O
F
F
B
O
O
N
16b
558 (1.29)
575 (0.021)
175
3.96∙10ꢀ3
N
O
B
O
F
F
O
O
N
20
581 (1.34)
590 (1.71)
646 (1.26)
620 (0.28)
608 (0.105)
670 (0.05)
11890
1050
4310
5.83∙10ꢀ5
6.61∙10ꢀ4
1.61∙10ꢀ4
N
F
F
B
O
O
S
N
8e
N
O
B
O
F
F
O
O
N
8f
N
O
O
a
In CH2Cl2.
Emission spectra were not recorded.
b
3.1. Measuring of the hydrolytic stability constants
0.1 ml DBU 10 ml was added to the stirred aqueous-acetonitrile
(9:1) dye solution with optical density w1 (molar ratio Dye:DBU e
1:10000), and the series of the absorption spectra, depending on
the reaction time, were recorded. The kinetic curve was plotted
based on the changing of optical density of the absorption
Scheme 4. Synthesis of merocyanine 20.
Fig. 2. a) absorption spectra of water-acetonitrile (1:9) solution of 8a (0.6∙10ꢀ5 M) with DBU (1∙104 eq.) depending on time; b) kinetic curve in the coordinates lnD-t.

82
A.O. Gerasov et al. / Dyes and Pigments 89 (2011) 76e85
2,5
2,0
1,5
1,0
0,5
0,0
Scheme 5. Hydrolysis of DOB-dyes.
Scheme 6. Partial hydrolysis of symmetrical anionic dye 8a.
400
500
600
700
λ
, нм
maximum (Fig. 2b). In all cases the rate of hydrolysis was first order
with respect to the dye concentration.
Fig. 4. Absorption spectra of dyes 8a (d) and 21 (e) in acetonitrile (1∙10ꢀ5 M).
Synthesis of dyes 7a, 8a, 8c, 7b, 8b, 8d, 8e and 8f was described
in literature [11]; 10a and 10b [12]; 12a and 12b [4]; 13a and 14a
[7]; 15a, 15b, 16a and 16b [13].
3.3. 8-(Dimethylamino)-4-hydroxy-6-methyl-(6H)-pyrano[3,2-c]
quinolino-2,5-dion (4)
A mixture of quinolone 3 (3.75 g, 17 mmol) and di-(2,4,6-tri-
chlorophenyl) malonate (8.0 g, 17 mmol) was heated at 190 ꢁC for
15 min. The melt was triturated with acetone and compound 4 was
filtered off. Yield: 3.7 g (75%); m.p. >300 ꢁC; elemental analysis
calcd (%) for C15H14N2O4: C 62.93, H 4.93, N 9.79; found: C 62.76, H
5.03, N 9.89.
3.2. 2,2-Difluoro-4-methyl-5-oxo-(5H)-(2,3,4,6,7,8-
hexahydroquinolyzine)[9,10,1-g,h]chromeno[4,3-d]-1,3,2-(2H)-
dioxaborine (2)
A mixture of coumarin 1 (1.3 g, 5 mmol) and BF3-etherate (1.0 g,
7 mmol) in acetic anhydride (5 ml) was refluxed for 10 min. The
mixture was cooled, the product was filtered off and washed with
ether. Yield: 1.62 g (93%); m.p. 249e251 ꢁC (dec.); 1H NMR (CDCl3):
3.4. 3-Acetyl-7-(dimethylamino)-4-hydroxy-1-methylquinolin-2
(1H)-on (5)
d
¼ 1.88 (m, 4 H, CH2), 2,76 (m, 4 H, CH2), 2.81 (s, 3 H, CH3), 3.44 (m,
4 H, NCH2), 7.46 (s, 1 H, Ar-H); labs 449 nm (CHCl3); elemental
analysis calcd (%) for C17H16BF2NO4: C 58.79, H 4.61, N 4.03; found:
C 58.66, H 4.58, N 3.97.
A mixture of compound 4 (4.45 g, 16 mmol), sodium hydroxide
(8.9 g, 223 mmol), water (12 ml) and ethylene glycol (77 ml) was
refluxed for 1.5 h. The mixture was cooled and neutralized with
Fig. 3. 1H NMR spectrum of dye 21 in DMSO-d6.

A.O. Gerasov et al. / Dyes and Pigments 89 (2011) 76e85
83
Scheme 7. Proposed mechanism for DOB-dyes hydrolysis.
hydrochloric acid. The product was filtered off and washed with
water. Yield: 2.2 g (53%); m.p. 244e245 ꢁC (DMF); 1H NMR (DMSO-
d6):
(s,1 H, 8-H), 6.74 (d, J ¼ 9.3 Hz,1 H, 6-H), 7.85 (d, J ¼ 9.3 Hz,1 H, 5-H),
16.93 (s, 1 H, OH); labs 386 nm (CHCl3); elemental analysis calcd (%)
for C14H16N2O3: C 64.60, H 6.20, N 10.76; found: C 64.63, H 6.25,
N 10.71.
3.9. Dyes 9b and 11b
d
¼ 2.66 (s, 3 H, CH3), 3.13 (s, 6 H, NCH3), 3.50 (s, 3 H, NCH3), 6.32
A mixture of the corresponding dioxaborine (1 mmol), (1,3,3-tri-
methyl-1,3-dihydroindol-2-ylidene)acetaldehyde (Fisher’ aldehyde)
(1.05 mmol) in acetic anhydride was refluxed for 5 min. The mixture
was allowed to stand for 12 h and the product was filtered off.
3.10. 2,2-Difluoro-4-[3-(1,3,3-trimethylindolin-2-ylidene)-
1-propenyl]-5-oxo-(5H)-(2,3,4,6,7,8- hexahydroquinolyzine)
[9,10,1-g,h]chromeno[4,3-d]-1,3,2-(2H)-dioxaborine (9b)
3.5. 2,2-Difluoro-4,6-dimethyl-5-oxo-(5H)-
8-dimethylaminoquinolino[4,3-d]-1,3,2-(2H)-dioxaborine (6)
Yield: 94%; m.p. >300 ꢁC; 1H NMR (DMSO-d6):
CH3), 1.85 (m, 4 H, CH2), 2.70 (m, 4 H, CH2), 3.30 (m, 4 H, NCH2), 3.61
d
¼ 1.61 (s, 6 H,
A mixture of quinolone 5 (400 mg, 1.54 mmol), BF3-etherate
(280 mg, 1.97 mmol), acetic anhydride (370 mg, 3.6 mmol) in dry
acetonitrile (3 ml) was refluxed for 15 min. The mixture was
allowed to stand for 12 h and the product was filtered off. Yield:
(s, 3 H, NCH3), 6.38 (d, J ¼ 14.4 Hz,1 H,
a
0-H), 7.24 (m, 1 H, 50-H), 7.38
(m, 4 H, 10-H, 60-H, 70-H,
a
-H), 7.57 (d, J ¼ 7.5 Hz, 1 H, 40-H), 8.52
(t, J ¼ 13.5 Hz, 1 H,
b-H); elemental analysis calcd (%) for
430 mg (90%); m.p. 294e295 ꢁC; 1H NMR (DMSO-d6):
d
¼ 2.79 (s, 3
C30H29BF2N2O4: C 67.92, H 5.47, N 5.28; found: C 67.95, H 5.45, N 5.31.
H, CH3), 3.21 (s, 6 H, NCH3), 3.50 (s, 3 H, NCH3), 6.30 (s, 1 H, 7-H),
6.83 (d, J ¼ 9.3 Hz, 1 H, 9-H), 7.90 (d, J ¼ 9.3 Hz, 1 H, 10-H); labs
425 nm (MeCN); elemental analysis calcd (%) for C14H15BF4N2O3:
C 54.55, H 4.87, N 9.09; found: C 54.67, H 4.94, N 9.14.
3.11. 2,2-Difluoro-4-[3-(1,3,3-trimethylindolin-2-ylidene)-1-
propenyl]-5-oxo-(5H)-6-methyl-8-dimethylamino-quinolino
[4,3-d]-1,3,2-(2H)-dioxaborine (11b)
Yield: 26%; m.p. >300 ꢁC (DMF); 1H NMR (DMSO-d6):
H, CH3), 3.16 (s, 6 H, NCH3), 3.57 (s, 3 H, NCH3), 3.62 (s, 3 H, NCH3),
d
¼ 1.66 (s, 6
3.6. Dyes 9a and 11a
6.34 (m, 2 H, 7-H,
a
0-H), 6.79 (d, J ¼ 9.6 Hz,1 H, 9-H), 7.25 (t, J ¼ 6.9 Hz,
1 H, 50-H), 7.40 (m, 2 H, 60-H, 70-H), 7.61 (d, J ¼ 6.9 Hz,1 H, 40-H), 7.80
A mixture of the corresponding dioxaborine (1 mmol), ethyl-
isoformanilide (0.5 mmol) and triethylamine (1.5 mmol) in acetic
anhydride (5 ml) was stirred at room temperature for 24 h. The
product was filtered off.
(d, J ¼ 12.6 Hz, 1 H,
a-H), 7.88 (d, J ¼ 9.6 Hz, 1 H, 10-H), 8.57
(t, J ¼ 13.8 Hz, 1 H,
b-H); elemental analysis calcd (%) for
C27H28BF2N3O3: C 66.00, H 5.74, N 8.55; found: C 65.96, H 5.76,
N 8.55.
3.12. Dyes 13b, 14b
3.7. Thiethylammonium 2,2-difluoro-4-[3-(2,2-difluoro-5-oxo-
(5H)-(2,3,4,6,7,8-hexahydroquinolyzine)[9,10,1-g,h]chromeno
[4,3-d]-1,3,2-(2H)-dioxaborin-4-ylidene)-1-propenyl]-5-oxo-(5H)-
(2,3,4,6,7,8-hexahydroquinolyzine)[9,10,1-g,h]chromeno[4,3-d]-
1,3,2-(2H)-dioxaborinate (9a)
A mixture of the corresponding dioxaborine [24] (1mmol),
(1,3,3-trimethyl-1,3-dihydroindol-2-ylidene)acetaldehyde (Fisher’
aldehyde) (1 mmol) in acetic anhydride (1.2 ml) was heated at
100ꢁC for 1 h and cooled to room temperature. The resulting solid
was suspended in diethyl ether (25 ml), and the mixture was
allowed to stand for 2 h. The precipitate was filtered off and washed
with diethyl ether.
Yield: 56%; m.p. >300 ꢁC (MeCN); 1H NMR (DMSO-d6):
(t, J ¼ 7.3 Hz, 9 H, CH3), 1.89 (m, 8 H, CH2), 2.74 (m, 8 H, CH2), 3.11
(m, 6 H, NCH2), 3.36 (m, 8 H, NCH2), 7.28 (d, J ¼ 13.5 Hz, 2 H, -H),
-H), 8.88 (br.s,1 H, NþH);
d
¼ 1.19
a
7.37 (s, 2 H,10-H), 8.64 (t, J ¼ 13.5 Hz, 2 H,
b
elemental analysis calcd (%) for C41H45B2F4N3O8: C 61.12, H 5.59,
N 5.22; found: C 61.21, H 5.66, N 5.25.
3.13. 2,2-Difluoro-4-[3-(1,3,3-trimethyl-(1H,3H)indol-2-ylidene)-
propenyl]-5H-indeno-[2,1-e]-1,3,2(2H)-dioxaborine (13b)
Yield: 0.16 g (39 %); m.p. 213e214 ꢁC (MeCN); 1H NMR CDCl3,
TMS:
d
¼ 1.68 (s, 6H, 2 ꢂ CH3), 3.39 (s, 3H, NCH3), 3.61 (s, 2H, CH2),
3.8. Thiethylammonium 2,2-difluoro-4-[3-(2,2-difluoro-5-oxo-
(5H)-6-methyl-8-(dimethylamino)-quinolino[4,3-d]-1,3,2-(2H)-
dioxaborin-4-ylidene)-1-propenyl]-5-oxo-(5H)-6-methyl-8-
dimethylamino-quinolino[4,3-d]-1,3,2-(2H)-dioxaborinate (11a)
5.68 (d, J ¼ 13.6 Hz, 1H, CHg), 5.97 (d, J ¼ 13.6 Hz, 1H, CHa), 6.91
(d, J ¼ 8 Hz, 1H, HAr), 7.11 (t, J ¼ 7.6 Hz, 1H, HAr), 7.26e7.35 (m, 4H,
HAr), 7.43 (m, 1 H, HAr), 7.85(d, J ¼ 7.6 Hz, 1H, HAr), 8.47
(t, J ¼ 13.6 Hz, 1 H, CHb); elemental analysis calcd (%) for
C24H22BF2NO2: C 71.13, H 5.47, N 3.46; found C 71.02, H 5.50, N 3.42.
Yield: 75%; m.p. >300 ꢁC (MeCNeCH2Cl2); 1H NMR (DMSO-d6):
d
¼ 1.17 (m, 9 H, CH3), 3.10 (m, 6 H, NCH2), 3.14 (s, 6 H, NCH3), 3.35
(s, 12 H, NCH3), 6.34 (s, 2 H, 7-H), 6.77 (d, J ¼ 9.4 Hz, 2 H, 9-H), 7.67
(d, J ¼ 13.8 Hz, 2 H, -H), 7.86 (d, J ¼ 9.4 Hz, 2 H, 10-H), 8.72
-H), 8.84 (br.s, 1 H, NþH); elemental analysis
calcd (%) for C35H43B2F4N5O6: C 57.77, H 5.91, N 9.63; found: C 57.93,
H 6.07, N 9.55.
3.14. 2,2-Difluoro-4-[3-(1,3,3-trimethyl-(1H,3H)indol-2-ylidene)-
propenyl]-5H,6H-naphtho-[2,1-e]- 1,3,2(2H)-dioxaborine (14b)
a
(t, J ¼ 13.8 Hz, 2 H,
b
Yield: 0.22 g (52%); m.p. 187e188 ꢁC (AcOH); 1H NMR DMSO:
d
¼ 1.64 (s, 6H, CH3), 2.66 (m, 2H, CH2), 2.92 (m, 2H, CH2), 3.56

84
A.O. Gerasov et al. / Dyes and Pigments 89 (2011) 76e85
Fig. 5.
(s, 3H, NCH3), 6.28 (d, J ¼ 13.0 Hz,
a
-H), 7.23 (m, 1H, HAr), 7.39
8.84 (m, 1 H); labs 551 nm (MeCN); elemental analysis calcd (%) for
C39H48BF2NO8: C 66.20, H 6.84, N 1.98; found: C 65.93, H 6.79,
N 1.90.
(m, 4H,
g
-H, HAr), 7.49 (m,2H, HAr), 7.58 (d, J ¼ 7.5 Hz, HAr), 7.81
(d, J ¼ 7.5 Hz, HAr), 8.42 (t, J ¼ 12.5 Hz,
b-H); elemental analysis
calcd (%) for C25H24BF2NO2: C 71.62, H 5.77, N 3.34; found C 71.79, H
5.84, N 3.37.
3.19. Tetrabutylammonium 2,2-difluoro-4-(4-oxo-6-hydroxy-6-
phenylhexa-2,5-dien-1-ylidene)-5-phenyl-1,3,2-(2H)-dioxaborinate
3.15. 2,2-Difluoro-4-[3-(1,3,3-trimethylindolin-2-ylidene)-1-
From 12a. Yield: 61 %; m.p. 135e138 ꢁC (i-PrOH); 1H NMR
propenyl]-6-(4-dimethylaminophenyl)-1,3,2-(2H)-dioxaborine (20)
(DMSO-d6):
d
¼ 0.93 (m, 12 H, CH3), 1.30 (m, 8 H, CH2), 1.55 (m, 8 H,
A mixture of compound 19 (50 mg, 0.2 mmol), (1,3,3-trimethyl-
CH2), 3.15 (m, 8 H, NCH2), 5.30 (d, J ¼ 10.5 Hz, 1 H), 5.75 (d,
J ¼ 13.8 Hz, 1 H), 6.12 (s, 1 H), 6.33 (s, 1 H), 7.40e7.52 (m, 6 H),
7.77e8.03 (m, 5 H); 19F NMR (DMSO-d6): ꢀ142.50 (BF2). labs
525 nm (MeCN); elemental analysis calcd (%) for C37H52BF2NO4:
C 71.26, H 8.40, N 2.25; found: C 71.03, H 8.34, N 2.31.
1,3-dihydroindol-2-ylidene)acetaldehyde
(Fisher’
aldehyde)
(40 mg, 0.2 mmol) and triethylamine (40 mg, 0.4 mmol) in acetic
anhydride was refluxed for 45 min. The mixture was cooled and
allowed to stand for 12 h to crystallize. The product was filtered off,
and washed with i-PrOH. Yield: 54 mg (63%); m.p. 263e265 ꢁC; 1H
NMR (DMSO-d6):
d
¼ 1.60 (s, 6 H, CH3), 3.07 (s, 3 H, NCH3), 3.41 (s, 6
4. Conclusion
H, NCH3), 6.16 (m, 2 H,
a-H, a
0-H), 6.61 (s, 1 H, 5-H), 6.80 (d,
J ¼ 6.6 Hz, 2 H, 30-H, 50-H), 7.08e7.48 (m, 4 H, CH), 7.89 (d, J ¼ 6.6 Hz,
It was shown that the hydrolytic stability within the symmet-
rical DOB-dye series is increased as the electron-withdrawing
properties of the DOB-fragment weaken (Fig. 5).
2 H, 20-H, 60-H), 8.16 (m, 1 H,
b-H); elemental analysis calcd (%) for
C25H27BF2N2O2: C 68.81, H 6.19, N 6.42; found: C 68.76, H 6.16,
N 6.43.
The DOB-based merocyanine dyes with the higher basicity of
the second heterocyclic residue are characterized by the higher
hydrolytic stability. Hydrolytic stability of DOB-dyes decreases by
order of magnitude with lengthening of polymethine chain by each
vinylen group. The mechanism of the DOB-dyes alkaline hydrolysis
was suggested. The products of the partial hydrolysis of the
symmetrical dioxaborine dyes were first obtained.
3.16. Method of symmetrical dyes partial hydrolysis
A solution of the corresponding dye (1 mmol) and 25%-solution
of tetrabutylammonium hydroxide in methanol (10 mmol) was
allowed to stand at room temperature for 24 h. Acetic acid
(10 mmol) was added to the mixture and the product was precip-
itated by the addition of water and filtered off.
Acknowledgements
3.17. Tetrabutylammonium 2,2-difluoro-4-[4-(2-oxo-(2H)-4-
hydroxy-7-(diethylamino)-chromen-3-il)-4-oxobut-2-en-1-
ylidene]-5-oxo-(5H)-8-(diethylamino)-chromeno[4,3-d]-1,3,2-(2H)-
dioxaborinate (21)
We thank Dr. Eugene Poronik and Dr. Simon Kosinski for their
help in preparation of the manuscript.
References
From 8a.Yield: 77%; m.p. 145e148 ꢁC (EtOH); 1H NMR (DMSO-
d6):
d
¼ 0.93 (m, 12 H, CH3), 1.15 (m, 12 H, CH3), 1.32 (m, 8 H, CH2),
[1] Van Allen JA, Reynolds GA. The reactions of 2,2-difluoro-4-methylnaphtho
[l,2-e] -1,3,2-dioxaborin and Its [2,1-e] Isomer with Carbonyl compounds and
with Aniline. J Het Chem 1969;6:29e35.
[2] Kammler R, Bourhill G, Jin Y, Bräuchle C, Görlitz G. H Hartmann. Second-order
optical non-linearity of new 1,3,2(2H)-dioxaborine dyes. J Chem Soc Faraday
Trans 1996;92:945e7.
[3] Hales JW, Zheng S, Barlow S, Marder SR, Perry JW. Bisdioxaborine Poly-
methines with Large Third-Order Nonlinearities for All-Optical Signal Pro-
cessing. J Am Chem Soc 2006;128:11362e3.
1.56 (m, 8 H, CH2), 3.16 (m, 8 H, NCH2), 3.46 (m, 8 H, NCH2), 6.41 (s, 1
H), 6.47 (s, 1 H), 6.73 (m, 2 H), 7.00 (d, J ¼ 12.3 Hz, 1 H), 7.37 (d,
19
J ¼ 14.1 Hz,1 H), 7.69 (m, 2 H), 8.50 (m, 1 H), 15.50 (br.s, 1 H, OH);
F
NMR (DMSO-d6): ꢀ144.01 (BF2); labs 576 nm,
e
10.1∙104 Mꢀ1 cmꢀ1
(MeCN); lem 600 nm, 0.105 (MeCN); elemental analysis calcd (%)
4
for C47H66BF2N3O8: C 66.43, H 7.77, N 4.95; found: C 65.13, H 7.70,
N 4.83.
[4] Makin VS, Abramenko PI, Boiko II
. Polymethine dyes derivatives of
organic boron complexes. Zh Vses Khim Obshch 1984;29:457e9 [Chem Abstr
1984;101:231932a].
3.18. Tetrabutylammonium 2,2-difluoro-4-[4-(2-oxo-(2H)-4-
hydroxychromen-3-il)-4-oxobut-2-en-1-ylidene]-5-oxo-(5H)-
chromeno[4,3-d]-1,3,2-(2H)-dioxaborinate
[5] Halik M, Hartmann H. Synthesis and characterization of new long-wave-
length-absorbing oxonol dyes from the 2,2-difluoro-1,3,2-dioxaborine type.
Chem Eur J 1999;5:2511e7.
[6] Halik M, Wenseleers W, Grasso C, Stellacci F, Zojer E, Barlow S, et al. Bis
(dioxaborine) compounds with large two-photon cross sections, and their use
in the photodeposition of silver. Chem Commun 2003;13:1490e1.
[7] Zyabrev KV, AYa Il’chenko, YuL Slominskii, Romanov NN, Tolmachev AI. Pol-
ymethine dyes derived from 2,2-difluoro-3,1,2(2H)-oxaoxoniaboratines with
polymethylene bridge groups in the chromophore. Dyes Pigm 2006;71:
199e206.
From 7a. Yield: 56%; m.p. 202e204 ꢁC (EtOH); 1H NMR (CDCl3):
d
¼ 0.98 (m, 12 H, CH3), 1.43 (m, 8 H, CH2), 1.66 (m, 8 H, CH2), 3.20
(m, 8 H, NCH2), 7.22e7.36 (m, 5 H), 7.54e7.60 (m, 2 H), 7.65
(d, J ¼ 14.4 Hz, 1 H), 8.03 (d, J ¼ 8.4 Hz, 1 H), 8.10 (d, J ¼ 8.1 Hz, 1 H),

A.O. Gerasov et al. / Dyes and Pigments 89 (2011) 76e85
85
[8] Zyabrev KV, AYa Il’chenko, YuL Slominskii, Tolmachev AI. Polymethine dyes
based on 2,2-difluoro-1,3,2-dioxaborine complex, synthesized from 2-ace-
tyldimedone. Ukr Khim Zh (Russ. Ed.) 2006;72(5):56e63.
[15] Matichak JD, Hales JM, Ohira S, Barlow S, Jang SH, Jen AKY, et al. Using end
groups to tune the linear and nonlinear optical properties of bis(dioxaborine)-
terminated polymethine dyes. ChemPhysChem 2010;11:130e8.
[9] Zyabrev K, Doroshenko A, Mikitenko E, Yu Slominskii, Tolmachev A. Design,
synthesis, and spectral luminescent properties of a novel polycarbocyanine
series based on the 2,2-difluoro-1,3,2-dioxaborine nucleus. Eur J Org Chem;
2008:1550e8.
[10] Traven VF, Chibisova TA, Manaev AV. Polymethine dyes derived from 2,2-
difluoro-3,1,2(2H)-oxaoxoniaboratines with polymethylene bridge groups in
the chromophore. Dyes Pigments 2003;58:41e6.
[16] Padilha LA, Webster S, Przhonska OV, Hu H, Peceli D, Gerasov AO, et al.
Nonlinear absorption in a series of donore
peacceptor cyanines with different
conjugation lengths. J Mater Chem 2009;19:7503e13.
[17] Coleman RS, Madaras ML. Synthesis of a novel coumarin C-riboside as a pho-
tophysical probe of oligonucleotide dynamics. J Org Chem 1998;63:5700e3.
[18] Harnisch H, Brack A. Über 4-chlor-7-dimethylamino-1-methyl-chinolon-(2)-
aldehyd-(30). I. Liebigs Ann Chem 1970;740:164e8.
[11] Gerasov AO, Shandura MP, Kovtun YP. Series of polymethine dyes derived
from 2,2-difluoro-1,3,2-(2H)-dioxaborine of 3-acetyl-7-diethylamino-4-
hydroxycoumarin. Dyes Pigments 2008;77:598e607.
[12] Gerasov AO, Shandura MP, Kovtun YP. Polymethine dyes derived from the
boron difluoride complex of 3-acetyl-5,7-di(pyrrolidin-1-yl)-4-hydrox-
ycoumarin. Dyes Pigments 2008;79:252e8.
[13] Gerasov AO, Shandura MP, Kovtun YP, Vlasenko YuG, Gorchev VF. 1,3,2-(2 H)-
dioxaborine polymethine dyes on the base of dehydroacetic acid e effective
fluorescent amine probes. J Heterocycl Chem 2008;45:1665e72.
[14] Halik M. 2,2-Difluor-1,3,2-(2H)-dioxaborine als Bausteine zur Darstellung von
[19] Khattab AF. Ring closure of 4-azido-3-formyl-(or acetyl-)2-pyridones to iso-
xazolo[4,3-c]pyridones. Liebigs Ann Chem 1996;3:393e5.
[20] Görlitz G, Hartmann. On the formation and solvolysis of 4-aryl-2,2-difluoro-6-
methyl-1,3,2-(2H)-dioxaborines. Heteroatom Chem 1997;8:147e55.
[21] Rohde D. Darstellung und Eigenschaftsuntersuchungen an 1,3,2-Dioxaborinen
mit variablen Coliganden am Boratom. Ph D Thesis, University of Halle/Saale;
2002.
[22] Manaev AV, Tambov KV, Traven VF. Synthesis and reactions of dehydracetic
acid difluoroborane complex. Russ J Org Chem 2008;44:1054e60.
[23] Manaev AV, Chibisova TA, Traven VF. Synthesis and structures of boron
complexes of acyl hydroxy coumarins. Russ Chem Bull 2006;55:2226e32.
[24] U.S. Pat. 3862144 (1975); Chem. Abstr., 1975, 82, 170668j.
langwellig absorbierenden Methinfarbstoffen. Ph
Halle/Saale; 1998.
D Thesis, University of