Anionic, cationic and merocyanine polymethine dyes based on dipyrromethene core

Article abstract of DOI:10.1016/j.dyepig.2013.02.004

Both symmetrical anionic polymethine dye which is derived from the boron difluoride form of the dipyrromethene (BODIPY) and the corresponding symmetrical cationic dye derived from the cationic form of the dipyrromethene have been obtained on the identical atomic framework. Their spectral properties and π-electronic structure suggest that these long-wavelength absorbing dyes are closely related. On the contrary, the non-symmetrical compounds belong to the different types of dyes, namely merocyanines in the case of boron dipyrromethene complexes, and non-symmetrical cationic dyes for salt-like compounds. Each of these types possesses a distinct complex of spectral properties.

Full text of DOI:10.1016/j.dyepig.2013.02.004

Accepted Manuscript
Anionic, cationic and merocyanine polymethine dyes based on dipyrromethene core
Mykola P. Shandura, Viktor P. Yakubovskyi, Yuriy V. Zatsikha, Olexiy D. Kachkovsky,
Yevgen M. Poronik, Yuriy P. Kovtun
PII:
S0143-7208(13)00052-1
10.1016/j.dyepig.2013.02.004
DYPI 3849
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 25 December 2012
Revised Date: 30 January 2013
Accepted Date: 2 February 2013
Please cite this article as: Shandura MP, Yakubovskyi VP, Zatsikha YV, Kachkovsky OD, Poronik YM,
Kovtun YP, Anionic, cationic and merocyanine polymethine dyes based on dipyrromethene core, Dyes
and Pigments (2013), doi: 10.1016/j.dyepig.2013.02.004.
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ACCEPTED MANUSCRIPT
Mykola P. Shanduraa, Viktor P. Yakubovskyia, Yuriy V. Zatsikhaa, Olexiy D. Kachkovskya,
Yevgen M. Poronika,b, Yuriy P. Kovtuna*
a) Institute of Organic Chemistry, National Academy of Sciences of Ukraine, 5 Murmanska Street, 02660 Kyiv
(Ukraine)
b) Institute of Organic Chemistry of the Polish Academy of Sciences, 44/52 Kasprzaka Str., 01-224 Warsaw
(Poland)
Anionic, cationic and merocyanine polymethine dyes based on dipyrromethene core
Both symmetrical anionic polymethine dye which is derived from the boron difluoride form of
the dipyrromethene (BODIPY) and the corresponding symmetrical cationic dye derived from the
cationic form of the dipyrromethene have been obtained on the identical atomic framework.
Their spectral properties and π-electronic structure suggest that these long-wavelength absorbing
dyes are closely related. On the contrary, the non-symmetrical compounds belong to the different
types of dyes, namely merocyanines in the case of boron dipyrromethene complexes, and non-
symmetrical cationic dyes for salt-like compounds. Each of these types possesses a distinct
complex of spectral properties.
Keywords: BODIPY compounds, Polymethine dyes, Dipyrromethene compounds, Long-
wavelength dyes, Merocyanine
1. Introduction
Dyes derived from boron dipyrromethene (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene,
BODIPY, BDP) have been attracting considerable attention over the past two decades. The ever-
increasing interest in this type of compound stems from their excellent thermal, chemical, and
photochemical stability, high molar absorption coefficients, high fluorescence quantum yields,
general insensitivity to both solvent polarity and pH, large two-photon cross-section for
multiphoton excitation, the lack of ionic charge and good solubility [1-6].
-
H
OH
N
+
N
H
N
H
+
-
+
N
N
N
-
NH HN
N
HN
X
HN
B
B
NH
Cat
X
F
F
F F
A
B
C
D
E
Scheme 1. A number of possible forms of dipyrromethenes
The fundamentals of BODIPY chemistry were established by Alfred Treibs in the 50's and 60's
of the 20th century [7-10]. In spite of facilities available 60 years ago, notably those works
(though sometimes not clear enough) showed a large variety of possible dipyrromethene forms,
such as free bases (A), salts (B-type cations), boron dipyrromethenes (C) and its derivatives
anionic (D) and cationic (E) forms (Scheme 1). In our recent reports we were able to enhance the
concept of
_________________________
* Corresponding author:
E-mail address: kovtun@ioch.kiev.ua

ACCEPTED MANUSCRIPT
-
Ph
Ph
N
+
N
Et3NH
F
F
B
F
B
N
N
1,4
1,2
1,0
0,8
0,6
0,4
0,2
0,0
F
Ph
Ph
+
N
Ph
Ph
N
H
H
-
HN
NH
Ph
TsO
Ph
300
400
500
600
700
800
900
Wavelenght (nm)

ACCEPTED MANUSCRIPT
► The symmetrical anionic dye derived from BODIPY core was synthesized.
► Symmetrical cationic dye derived from the cationic form of dipyrromethene was obtained.
► Both dyes have absorption maxima around 800 nm.

ACCEPTED MANUSCRIPT
Mykola P. Shandura, Viktor P. Yakubovskyi, Yuriy V. Zatsikha, Olexiy D. Kachkovsky,
Yevgen M. Poronik, Yuriy P. Kovtun
Anionic, cationic and merocyanine polymethine dyes based on dipyrromethene core
Both symmetrical anionic polymethine dye which is derived from the boron difluoride form of the
dipyrromethene (BODIPY) and the corresponding symmetrical cationic dye derived from the
cationic form of the dipyrromethene have been obtained on the identical atomic framework. Their
spectral properties and π-electronic structure suggest that these long-wavelength absorbing dyes are
closely related. On the contrary, the non-symmetrical compounds belong to the different types of
dyes, namely merocyanines in the case of boron dipyrromethene complexes, and non-symmetrical
cationic dyes for salt-like compounds. Each of these types possesses a distinct complex of spectral
properties.
Keywords: BODIPY compounds, Polymethine dyes, Dipyrromethene compounds, Long-wavelength
dyes, Merocyanine
1. Introduction
Dyes derived from boron dipyrromethene (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene,
BODIPY, BDP) have been attracting considerable attention over the past two decades. The ever-
increasing interest in this type of compound stems from their excellent thermal, chemical, and
photochemical stability, high molar absorption coefficients, high fluorescence quantum yields,
general insensitivity to both solvent polarity and pH, large two-photon cross-section for multiphoton
excitation, the lack of ionic charge and good solubility [1-6].
-
H
OH
N
+
N
H
N
H
+
-
+
N
N
N
-
NH HN
N
HN
X
HN
B
B
NH
Cat
X
F
F
F F
A
B
C
D
E
Scheme 1. A number of possible forms of dipyrromethenes
The fundamentals of BODIPY chemistry were established by Alfred Treibs in the 50's and
60's of the 20th century [7-10]. In spite of facilities available 60 years ago, notably those works
(though sometimes not clear enough) showed a large variety of possible dipyrromethene forms, such
as free bases (A), salts (B-type cations), boron dipyrromethenes (C) and its derivatives anionic (D)
and cationic (E) forms (Scheme 1). In our recent reports we were able to enhance the concept of

ACCEPTED MANUSCRIPT
2
possible dipyrromethene forms. A number of meso- [11,12] and α-BODIPY-derived [13]
polymethine dyes of merocyanine type were obtained. In these cases, BODIPY core behaves as
electron-withdrawing end group in the donor-acceptor merocyanine chromophore system, i.e. brings
partial negative charge, whereas in classical dipyrromethene dyes partial positive charge is
delocalized within BODIPY chromophore. There is a set of indirect evidences in favor of this claim,
but only synthesis can clearly prove the existence of the anionic form of BODIPY. This work is
addressed to the synthetic corroboration of the above-mentioned hypothesis. Moreover, compounds
of this family could be long-wavelength dyes that are of interest for various applications ranging
from materials science to biology and medicine [14-21].
2. Results and Discussion
In our previous work [11] we failed to synthesize dye a 2a, particularly under conditions
mentioned in Scheme 2 (acetic anhydride in the presence of triethylamine). The reason appears to be
the following: the reaction was carried out at the increased temperature (the usual conditions for
cyanine condensations) [22-26]. Probably, during the heating in acetic anhydride the fluorine atoms
of BODIPY undergo the substitution with the acetate anion, exemplified in the report [27].
Acetyloxy groups decrease the stability of the BODIPY, resulting in the cleavage of the complex
that was demonstrated on the other examples [11]. While carrying out the condensation of
compound 1a with its anilidovinyl derivative at room temperature, it gave rise to dye 2a in a high
yield (Scheme 2). The merocyanine dyes 3a-6a described in our previous report [11] are also shown
in Scheme 2.

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3
Ph
HN
-
N
N
B
Ph
Ph
F
F
Ph
Ph
N
+
N
Et3NH
F
N
N
B
F
B
B
N
N
Ac2O / Et3N
F
Ph
Ph
F
F
F
Ph
Ph
1a
2a
ref.11
ref.11
X
N
N
Bu
N
N
B
N
N
B
Ph
Ph
F
F
Ph
Ph
F
F
3a - 5a
X = C(CH3)2 (3a), S (4a), CH=CH (5a)
6a
Scheme 2. Synthetic route to dyes 2a–6a.
Evidently, the most general form of dye 2a representation is the form shown in Scheme 2.
Nevertheless, the anionic part of this dye can be described with a set of mesomeric forms; some of
them are shown in Scheme 3. The last resulting form, though roughly, depicts the end nucleus which
is typical for cyanine dyes chemistry. In this sense, the latter helps to consider the boron
dipyrromethene fragment as the entire terminal group of the polymethine chromophore system.
-
Ph
Ph
Ph
-
-
N
B
Ph
Ph
N
B
N
Ph
Ph
N
B
N
B
Ph
F
N
B
N
B
F
N
B
B
-
N
F
F
N
N
F
F
F
N
N
F
F
N
F
N
F
F
F
N
F
F
F
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Scheme 3.
In addition, the alternative series of dyes 2b-6b were obtained from dipyrromethene salt 1b
(Scheme 4). The symmetrical dye 2b was synthesized analogously to the work of Treibs [10] by the
condensation of the dipyrromethene 1b with triethylorthoformate. Other non-symmetrical cationic
dyes 3b-6b have been obtained by the reaction of compound 1b with corresponding hemicyanines in
the conditions typical for cyanine condensations [22-26]. The absorption spectra of the dyes 2a-5a
are shown in Fig. 1, dyes 2b-5b in Fig. 2, and their spectral characteristics in Tab. 1, respectively. It
is worth mentioning that the dyes 2b-6b undergo the dissociation in dilute solutions and

ACCEPTED MANUSCRIPT
4
subsequently decompose. By this reason, quantitative spectra of these dyes were measured with the
addition of 5% acetic acid.
Some of the cationic dyes can be transformed into to the corresponding merocyanines. For
example, the formation of free base 3c can be observed on treating salt 3b solutions with bases,
however, the compound 3c cannot be isolated due to its instability. On the other hand, the treating
with the base in the presence of borontrifluoride etherate gives rise to the formation of merocyanine.
The stability of free bases tends to decrease on the increase of electron-donor properties of the
second end moiety, making it more difficult to undergo such a reaction. Most of all, this is related to
the symmetrical dyes. There were no traces of dye 2a observed on treating the compound 2b with
bases in the presence of boron trifluoride etherate due to the decomposition of the free
base.
+
Ph
Ph
N
N
+
H
H
NH HN
-
HN
NH
Ph
TsO
Ph
Ph
-
TsO
1b
Ph
2b
Et3N
Ph
-
X
X
ClO4
N
-
N
An
N
N
-
Ph
N
HO
N
N
Bu
BF3
Bu
ClO4
3a
-
-
NH HN
An
Et3N
Ph
Ph
+
NH HN
+
N
HN
1c
NH HN
Ph
Ph
Ph
Ph
Ph
Ph
3b - 5b
3b X = C(CH3)2, An = TsO- ,
3c
6b
-
4b X = S, An = ClO4
,
5b X = CH=CH, TsO-
Scheme 4. Synthetic route to dyes 2b–6b.
1,4
4a
2a
5a
1,2
3a
1,0
0,8
0,6
0,4
0,2
0,0
300
400
500
600
700
800
900
λ
nm

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5
Figure 1. Absorption spectra of compounds 2а – 5а in acetonitrile (C = 1 x 10–5 M)
One can see the similarity of the absorption spectra of the dyes 2a and 2b. Both have quite
intense long-wavelength bands with the absorption maxima around 800 nm and the weak absorption
bands with maxima around 600 nm. The quantum-chemical analysis was carried out in order to
estimate their spectral properties. The quantum-chemical calculations were performed with the
Gaussian 03 program package [28]. The ground state geometry was optimized by the DFT/6-
31(d,p)/B3LYP method. The TD-SCF-AM1 method was employed to obtain the characteristics of
the electron transitions. We could not use the “spectroscopic” ZINDO method owing to the absence
of the boron atom parameters.
1,0
2b
3b
0,8
0,6
0,4
0,2
0,0
5b
4b
300
400
500
600
700
800
900
λ nm
Figure 2. Absorption spectra of compounds 2b – 5b in acetonitrile containing 5% of acetic acid
(C = 1 x 10–5 M)
As shown by the optimized geometry of the symmetrical anionic dye 2a and the cationic dye
2b, both molecules are not planar due to spatial hindrances. The calculations show that atoms of the
polymethine chain in both cases are set approximately at 5о torsion angles. Phenyl substituents in the
cationic dye 2b are turned out of the dipyrromethene framework plane at an angle of 20о, but in the
anionic dye 2a they are set at 32о angle due to the additional spatial hindrance of the BF2 bridge.
The end groups as the entire molecular fragment in the dye 2b are turned out of the plane of the
polymethine chain at an angle of 16о.
The performed calculations show that the transition from the cationic dye 2b to its anionic
analogue 2a hardly alters the C-C bond length in the chromophores of symmetrical dyes The
optimized C-C bond lengths (lν) along the conjugated system ranging from the meso-position atom
of the polymethine chain, through C-atoms of the pyrrole and benzene rings to the atom at the p-

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6
position of the phenyl substituent are shown in Figure 3a (for convenience, an average value of lν
was taken for the equivalent positions in the branched part of end groups). As one can see, the
alteration of the average charge hardly changes C-C bond lengths in the polymethine chain or in the
end moieties, namely in the π-electronic system of the dye chromophore. Analogously, in the
chromophore systems of the dyes 2a and 2b charges of the atoms qµ appeared to be almost equal,
although they differ in total charge. The calculated charges of C-atoms are presented in Fig. 3b. The
analysis of calculations suggests the significant alternation of the electron density along the
chromophore chain which is typical for polymethine dyes not being affected by the sign of the total
charge. The amplitude of the alternation is almost equal. The additional information about the
similarity of the electronic structures of the cationic 2b and anionic dyes 2a can be obtained from
diagrams of the electron density redistribution upon the transition to the excited state. The diagram
0
of the change of electron density upon the excitation is shown in Fig. 3c: ∆qµ = qµ* - qµ , where the
0
superscripts * and denote the excited and the ground states respectively. The analysis shows that
the values of the parameter ∆qµ are really close, especially for atoms of the polymethine chain.
Table 1 Optical properties of the prepared compounds
CH3CN
ε, М–1· cm–1
Dye
λabs,
fwhm*, cm–1
nm
2a
2b
3a ([11])
3b
4a ([11])
4b
5a ([11])
5b
6a ([11])
6b
810
805
671
663
683
606
705
607
752
768
138 000
94 000
111 000
82 000
116 000
49 000
117 000
52 000
74 000
115 000
1348
1074
1656
2575
1595
4065
1403
3833
2184
1099
*fwhm = full width at half-maximum height.
1,48
1,43
1,38
l, Å
ν
1
2
3
4
5
6
7
8
9
10 11 12 13 14
a

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7
0,3
0,15
0
q, e.u.
µ
1
2
3
4
5
6
7
8
9
10
11
12
13
-0,15
-0,3
b
q, e.u.
∆
0,4
0,2
0
µ
1
2
3
4
5
6
7
8
9
10
11
12
13
-0,2
-0,4
c
Figure 3. Bond CC-lengths (a), charges in ground state (b) and charge changes upon excitation (c)
at carbon atoms in chromophore of dyes 2a ( - - - -) and 2b (____).
It is worth saying that signs of alteration of the electron density also match, and this means
that the transition occurs between the orbitals of the same symmetry. Fig. 4 shows, that the shapes of
the frontier and adjacent to them molecular orbitals of the cationic and anionic dyes 2b and 2a are
also in good agreement. In particular, the HOMO-1 and HOMO orbitals are practically degenerated
and can be considered as local orbitals extended only within the terminal groups. They have their
nodes at the carbon atoms connected with open polymethine chain. As the result, these local MOs of
both terminal groups cannot interact with each other in symmetrical molecules 2a and 2b.

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8
Figure 4 Positions of electron levels and electron transitions in symmetrical cationic (2b) and
anionic (2a) dyes
Fig. 4 clearly demonstrates that the main difference between symmetrical dyes 2a and 2b is
the dramatic shift of molecular levels upwards during the change of the total charge from positive to
negative. The peculiar localization of molecular levels on an energy scale of the anionic
polymethine dyes has already been noticed by us for dioxaborines [29]. Meanwhile, the above-
mentioned shift of the frontier and adjacent to them levels does not affect the nature of the highest
electronic transitions (Fig. 4). For the pair of symmetrical dyes the calculations demonstrate
comparable values of wavelengths and dipole moments for the corresponding electronic transitions,
which are in good agreement with the spectral data. Therefore, the highest transitions in cationic and
anionic dyes involve the same MOs, and the calculated absorption spectra well match with the
experimental spectra. Evidently, π-systems of the cationic and anionic dyes 2b and 2a possess the
similar electronic structure and differ only in total charge.
Thus, the long-wavelength absorption bands in the spectra of both cationic and anionic
symmetrical dyes are connected with the first electron transitions involved frontier orbitals:
HOMO→LUMO>. These MOs have the opposite symmetry, the S0→S1> transition is polarized
along the polymethine chromophore; its oscillator strength is quite large, that is in agreement with
high intensity of the first spectral band. The next spectral band, weakly intense for both symmetric
dyes, corresponds to two practically degenerated electron transitions from two local orbitals to
LUMO. The splitting of the S0→S2> and S0→S3> is negligible (3-5 nm) although the oscillator
strengths f2 and f3 differ significantly. Also, the fourth transition involves the delocalized highest

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9
occupied level and the next vacant level; these orbitals have equal symmetry and, as the result, this
transition has very low dipole moment that explains weak absorption in the spectral region around
400 nm.
1,2
5a
6b
6a
1,0
0,8
0,6
0,4
0,2
0,0
5b
300
400
500
600
700
800
900
λ nm
Figure 5. Absorption spectra of compounds 5a – 6a in acetonitrile and of compounds 5b – 6b in
acetonitrile containing 5% of acetic acid (C = 1 x 10–5 M)
In contrast to symmetrical dyes, each type of non-symmetrical derivatives possesses a
distinct complex of spectral properties. In the first case, there is a set of merocyanines with BODIPY
as the weak electron-withdrawing end nucleus, which gives rise to certain spectral consequences,
thoroughly analyzed [11-13]. The derivatives of b-type are non-symmetrical cationic polymethine
dyes with the dipyrromethene fragment acting as the weak electron-donor end nucleus. Therefore,
dye 3b, containing the weak electron-donor indoline end nucleus exhibits the most intense and the
narrowest long-wavelength band (Figure 2). This means that the structure of this dye is the most
electron-symmetrical within 3b-5b series.
The difference between the dyes of a and b series can be well illustrated by spectral
properties of dyes consisting of end nuclei of distinct electron donor-acceptor ability (Fig. 5). In the
case of dye 6a, a derivative of the weak electron-donor benz[c,d]indole end nucleus, the broad and
weak absorption band is observed, hence, the structure somewhat loses the cyanine character and
gains that of polyene, while dye 6b demonstrates the narrow and intense long-wavelength
absorption, suggesting its electron-symmetrical state. In the case of dyes with the electron rich
quinoline nucleus, the opposite spectral effects are observed. The merocyanine 5a shows narrow and
intense absorption, whereas the absorption of the cationic dye 5b is broad and weak which suggests
the significant electronic asymmetry.

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10
3. Conclusions
In conclusion, for the first time we have obtained a very unusual structure – the symmetrical
anionic dye derived from BODIPY core. The possibility of existence of the anionic dipyrromethene
form has been predicted in the basic works of Treibs, but later this idea was not further developed.
The symmetrical cationic dye derived from the cationic form of dipyrromethene also has been
obtained. The spectral properties and parameters resulted from the quantum-chemical analysis
suggest that this dye is closely related to the anionic analogue, based on the same framework. The
only difference between the symmetrical dyes of both types is the energy of the molecular orbitals
which is higher for the anionic dye. This case is of theoretical interest, as first cationic and anionic
polymethine dyes on the same framework were compared. Moreover, these compounds are intensive
long-wavelength dyes.
Unsymmetrical dyes synthesized belong to completely different types merocyanines in the case
of boron dipyrromethene complexes, and non-symmetrical cationic dyes for salt-like compounds.
The dipyrromethene end moiety in the former case behaves as the weak electron-acceptor fragment,
while in the latter case as the weak electron-donor which in both cases gives rise to its own set of
spectral properties and regularities.
All dyes synthesized are practically not fluorescent.
4. Experimental
1
General: The absorption spectra were recorded with a Shimadzu UV-3100 spectrophotometer. H
spectra were recorded with a Varian VXR-300 spectrometer and 13C NMR spectra were obtained on
a Bruker Avance 500 spectrometer. Chemical shifts are given in ppm and were referenced using
residual signals of the solvent as internal standard (1H: CHCl3, 7.26 ppm and [D5]DMSO, 2.50 ppm.
13C: [D6]-DMSO, 39.5 ppm). LC–MS measurements were performed with a liquid
chromatography–mass spectrometric system consisting of an Agilent 1100 Series HPLC instrument
equipped with a diode matrix detector and an Agilent LC/MSD SL mass-selective detector. The
atmospheric pressure chemical ionization (APCI) technique with detection of positive ions was
used.
Dye 2a
Compound 1a (0.18 g, 0.5 mmol) and 4,4-difluoro-3,5-diphenyl-8-(2-N-phenylaminoethen-1-yl)- 4-
bora-3a,4a-diaza-s-indacene [11] (0.23 g, 0.5 mmol) was added to mixture of Ac2O (1 mL) and
triethylamine (1 mL). The reaction mixture was stirred for 2 h at room temperature. Then reaction
mixture was diluted with i-PrOH and stirred additionally 15 min. Crude product was filtered,

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11
1
washed with i-PrOH and recrystallized from i-PrOH. Yield 0.23 g, 56%; m.p. > 250 °C. H NMR
+
([D6]DMSO): δ = 8.83 (br. s, 1 H, NH), 8.43 (t, J = 13.2 Hz, 1 H, CH), 7.69 (d, J = 6.8 Hz, 8 H,
ArH), 7.42 (d, J = 13.2 Hz, 2 H, CH), 7.36 (t, J = 6.8 Hz, 8 H, ArH), 7.28 (t, J = 6.8 Hz, 4 H, ArH),
7.18 (d, J = 3.6 Hz, 4 H, pyrrole H), 6.53 (d, J = 3.6 Hz, 4 H, pyrrole H), 3.08 (q, J = 7.6 Hz, 6 H,
CH2), 1.16 (t, J = 7.6 Hz, 9 H, CH3) ppm. 13C NMR ([D6]DMSO): δ = 9.2, 46.3, 116.6, 119.4,
119.5, 120.2, 120.3, 127.7, 128.2, 129.0, 133.9, 135.1, 139.9, 147.0, 148.1 ppm. Anal. calcd. for
C51H47B2F4N5. C, 74.02; H, 5.72; N, 8.46. Found C, 74.21; H, 5.79; N, 8.51.
Dye 2b
Triethyl orthoformate (0.25 g, 1.69 mmol) was added to suspension of compound 1b (0.25 g, 0.5
mmol) in Ac2O (2 mL) and the reaction mixture was heated at 100 °C for 30 min. After cooling to
room temperature, the product was filtered and washed with Ac2O. Yield 0.11 g, 52 %; m.p. > 250
°C. 1H NMR ([D6]DMSO): δ = 12.24 (s, 4 H, NH), 8.05 (t, J = 13.2 Hz, 1 H, CH), 7.92 (d, J = 6.6
Hz, 8 H, ArH), 7.60 (d, J = 13.2 Hz, 2 H, CH), 7.35-7.53 (m, 18 H, 14 ArH, 4 pyrrole H), 6.99-7.13
13
(m, 6 H, 2 ArH, 4 pyrrole H), 2.28 (s, 3 H, CH3) ppm. C NMR ([D6]DMSO): δ = 21.3, 112.3,
126.0, 128.7, 129.0, 129.4, 130.5, 130.8, 131.1, 133.2, 134.5,135.1, 136.7, 138.6, 142.3, 145.5 ppm.
Anal. calcd. for C52H42N4O3S. C, 77.78; H, 5.27; N, 6.98. Found C, 77.89; H, 5.35; N, 7.07
Dye 3a
To the suspension of dye 3b (0.22 g, 0.33 mmol) in BF3•Et2O (2 mL) Et3N (0.33 g, 3.3 mmol) was
added, the reaction mixture was refluxed for 5 min and then was cooled to room temperature,
diluted with EtOH and precipitate was filtered. Yield 0.04 g, 23 %. All characteristics are identical
to those from ref. [11].
General Procedure for the Synthesis of Dyes 3b – 6b:
Compound 1b (0.5 mmol) was added to the corresponding hemicyanine (0.55 mmol) in Ac2O
(2 mL) and the reaction mixture was heated at reflux for 2–3 min. After cooling to room
temperature, the crude product was filtered and washed with HOAc.
Dye 3b
Yield 0.18 g, 54 %; m.p. > 250 °C. 1H NMR ([D6]DMSO): δ = 12.09 (s, 2 H, NH), 8.26 (t, J = 13
Hz, 1 H, CH), 7.95 (d, J = 6.6 Hz, 4 H, ArH), 7.34-7.64 (m, 13H), 7.11 (d, J = 3.8 Hz, 2 H, pyrrole
H), 6.94-6.6.99 (m, 3 H, 2 ArH, 1 CH), 6.81 (d, J = 3.8 Hz, 2 H, pyrrole H), 3.83 (s, 3 H, NCH3),
2.29 (s, 3 H, CH3), 1.60 (s, 6 H, CH3) ppm. 13C NMR ([D6]DMSO): δ = 21.3, 27.1, 32.8, 50.3,
109.8, 113.3, 119.8, 120.9, 121.2, 123.0, 125.2, 126.0, 127.2, 128.6, 129.4, 132.5, 138.1, 139.6,
140.6, 141.9, 142.0, 142.9, 146.2, 153.5, 177.3 ppm.
Dye 4b
Yield 0.17 g, 53 %; m.p. > 250 °C. 1H NMR ([D6]DMSO): δ = 11.95 (s, 2 H, NH), 8.18 (d, J = 8.1
Hz, 1 H, ArH), 8.04 (d, J = 8.4 Hz, 1 H, ArH), 7.85-7.98 (m, 5 H, 4 H, ArH, 1 CH), 7.75 (t, J = 8.1
Hz, 1 H, ArH), 7.62 (t, J = 8.4 Hz, 1 H, ArH), 7.42-7.50 (m, 4 H, ArH), 7.25-7.36 (m, 3 H, 2 ArH, 1
CH), 7.16 (d, J = 11.7 Hz, 1 H, CH), 6.88 (d, J = 3.8 Hz, 2 H, pyrrole H), 6.65 (d, J = 3.8 Hz, 2 H,
pyrrole H), 4.12 (s, 3 H, NCH3) ppm. 13C NMR ([D6]DMSO): δ = 35.4, 109.4, 110.4, 110.9, 116.0,

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118.8, 119.5, 120.5, 125.3, 126.2, 127.5, 128.2, 129.4, 131.7, 132.2, 137.7, 139.2, 142.5, 149.4,
169.8 ppm.
Dye 5b
Yield 0.18 g, 53 %; m.p. > 250 °C. 1H NMR ([D6]DMSO): δ = 11.83 (s, 2 H, NH), 8.63 (d, J = 9.3
Hz, 1 H, ArH), 8.35 (d, J = 8.7 Hz, 1 H, ArH), 8.13 (d, J = 8.1 Hz, 2 H, ArH), 8.08 (t, J = 8.1 Hz, 1
H, ArH) 7.78-7.92 (m, 5 H), 7.40-7.50 (m, 6 H), 7.24-7.34 (m, 5 H), 7.10 (d, J = 8.1 Hz, 2 H, ArH),
6.87 (d, J = 3.7 Hz, 2 H, pyrrole H), 6.54 (d, J = 3.7 Hz, 2 H, pyrrole H), 4.36 (s, 3 H, NCH3), 2.29
(s, 3 H, CH3) ppm. 13C NMR ([D6]DMSO): δ = 21.3, 44.4, 108.6, 109.7, 114.3, 116.7, 117.7, 119.5,
120.1, 122.0, 125.3, 126.0, 127.5, 128.5, 129.1, 130.0, 132.2, 134.6, 135.3, 135.8, 137.5, 138.1,
139.3, 143.9, 146.3, 147.0, 152.4 ppm.
Dye 6b
Yield 0.26 g, 73 %; m.p. > 250 °C. 1H NMR ([D6]DMSO): δ = 12.32 (s, 2 H, NH), 8.61 (t, J = 13.2
Hz, 1 H, CH), 8.30 (d, J = 8.1 Hz, 1 H, ArH), 8.12 (d, J = 7.5 Hz, 1 H, ArH), 8.00 (d, J = 4.5 Hz, 4
H, ArH), 7.89-7.93 (m, 2 H, ArH), 7.74-7.82 (m, 3 H, ArH, 1 CH), 7.39-7.60 (m, 6 H), 7.24 (d, J =
13.2 Hz, 1 H, CH), 7.14 (J = 3.7 Hz, 2 H, pyrrole H), 7.03 (d, J = 3.7 Hz, 2 H, pyrrole H), 4.50 (q, J
= 7.8 Hz, 2 H, CH2), 1.87 (q, J = 7.8 Hz, 2 H, CH2), 1.47 (q, J = 7.8 Hz, 2 H, CH2), 0.98 (t, J = 7.8
Hz, 2 H, CH3) ppm. 13C NMR ([D6]DMSO): δ = 14.2, 21.3, 31.5, 44.6, 112.2, 112.4, 123.5, 124.7,
126.2, 127.7, 128.3, 129.5, 129.9, 130.2, 130.3, 131.2, 132.1, 132.9,133.5, 134.2, 136.0, 137.7,
139.1, 141.2, 142.5, 152.5, 156.2 ppm.
Acknowledgment
This work was partially financially supported by the NATO “Science for Peace” program, project
NUKR.SFPP 984189.
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► The symmetrical anionic dye derived from BODIPY core was synthesized.
► Symmetrical cationic dye derived from the cationic form of dipyrromethene also has been
obtained.
► Both dyes have quite intense long-wavelength bands with the absorption maxima around 800
nm.
► The only difference between the symmetrical dyes of both types is the energy of the
molecular orbitals, which is higher for the anionic dye.