Diethyl (biscyclohexano)BODIPY dicarboxylates. Chelation of alkaline-earth metal ions and sensor properties

Article abstract of DOI:10.1134/S1070428014020158

meso-Aryl-substituted (biscyclohexano)bis(ethoxycarbonyl)BODIPY [aryl = phenyl, 3,4-dimethoxyphenyl, and 2,3,5,6,8,9,11,12-octahydro-1,4,7,10,13- benzopentaoxacyclopentadecin-15-yl-(m-{benzo-15-crown-5}-yl)] were synthesized. The effect of alkaline-earth metals on the absorption and fluorescence spectra of these compounds was investigated. In all compounds along with the mechanism of the photoinduced electron transfer (PET), well-known for the crown-containing BODIPY-based sensors, one more response pattern is observed. The large excess of Ca²⁺ and Ba²⁺ ions in the system leads to the changes both in the UV-Vis and emission spectra. The complex formation results in the decrease of emission intensity and in its red shift. Besides, a new longwave absorption band appears in the UV-Vis spectrum of the BODIPY-metal ion complex. The formation constants of the complexes corresponding to this response pattern is about 100 times less than the formation constant of Ca²⁺-crown ether complex. ¹H, ¹³C, ¹¹B, and ¹⁹F NMR spectra, the results of quantum-chemical calculations, and their comparison with the literature data of X-ray diffraction study suggest that the binding of Ca²⁺ and Ba²⁺ ions occurs in the cavity formed by the fluorine atoms and the carbonyl oxygen atoms of the ester groups.

Full text of DOI:10.1134/S1070428014020158

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2014, Vol. 50, No. 2, pp. 229−239. © Pleiades Publishing, Ltd., 2014.
Original English Text © K.V. Tikhomirova, A.V. Khoroshutin, A.V. Anisimov, 2014, published in Zhurnal Organicheskoi Khimii, 2014, Vol. 50, No. 2, pp. 236−246.
Diethyl (Biscyclohexano)BODIPY* Dicarboxylates.
Chelation of Alkaline-Earth Metal Ions and Sensor Properties
K. V. Tikhomirova, A. V. Khoroshutin, and A. V. Anisimov
Lomonosov Moscow State University, Moscow, 119991 Russia
e-mail: khorosh@petrol.chem.msu.ru
Received September 20, 2013
Abstract—meso-Aryl-substituted (biscyclohexano)bis(ethoxycarbonyl)BODIPY [aryl = phenyl,
3,4-dimethoxyphenyl, and 2,3,5,6,8,9,11,12-octahydro-1,4,7,10,13-benzopentaoxacyclopentadecin-15-yl-
(m-{benzo-15-crown-5}-yl)] were synthesized. The effect of alkaline-earth metals on the absorption and
fluorescence spectra of these compounds was investigated. In all compounds along with the mechanism of the
photoinduced electron transfer (PET), well-known for the crown-containing BODIPY-based sensors, one more
response pattern is observed. The large excess of Ca2+ and Ba2+ ions in the system leads to the changes both in
the UV-Vis and emission spectra. The complex formation results in the decrease of emission intensity and in its
red shift. Besides, a new longwave absorption band appears in the UV-Vis spectrum of the BODIPY–metal ion
complex. The formation constants of the complexes corresponding to this response pattern is about 100 times
less than the formation constant of Ca2+-crown ether complex. 1Н, 13С, 11B, and 19F NMR spectra, the results of
quantum-chemical calculations, and their comparison with the literature data of X-ray diffraction study suggest
that the binding of Ca2+ and Ba2+ ions occurs in the cavity formed by the fluorine atoms and the carbonyl oxygen
atoms of the ester groups.
DOI: 10.1134/S1070428014020158
Boron-dipyrrin complexes have been known since presence there of two types of complexing sites: dipyrrin
the late 1960’s [1]. These stable dyes possess a narrow
absorption band in the visible region and are capable
of fluorescence. The photophysical properties of these
substances make it possible to test their applicability,
e.g., as laser dyes [2, 3], markers for biochemistry and
biomedicine [4, 5], as a signal group in versatile chemi-
cal sensors [6–11].
fragment in compounds Iа–Ic and crown ether fragment
in compound Ic. However we found that the dipyrrin
fragment existed in two conformations (cis,syn and
trans,anti), which differ significantly in their complexing
ability thus impeding the application of these compounds
as sensors.
Since this disadvantage is absent in the corresponding
BODIPY dyes, the target of this investigation was their
synthesis and the study of their sensor characteristics.
Several signal mechanisms of optical and fluorescent
sensors based on BODIPY are described in the litera-
ture [6, 9], and the most widely spread among them are
intramolecular photoinduced electron transfer (PET)
and photoinduced charge transfer (ICT). In particular,
large interest is attracted to PET type sensors containing
meso-aryl-substituted BODIPY where the rotation of the
aryl group is hindered either by the substituents in the
backbone of the dye, or in the aryl ring.
BODIPY dyes were obtained from dipyrrins I. The
latter were prepared by the condensation of substi-
tuted benzaldehyde with ethyl 4,5,6,7-tetrahydro-2Н-
isoindolecarboxylate (II) [13, 14] followed by the oxi-
dation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone
(DDQ) (Scheme 1).
The most often in the synthesis of BODIPY the ad-
dition of boron trifluoride etherate to dipyrrin in the
presence of triethylamine or other amines is a standard
practice. In the case of the crown derivative Ic the yield
of its BODIPY-derivative IIIc amounted 46% after the
In the previous article we reported on the synthesis
of dicyclohexano-fused diethyl dipyrrindicarboxylates
I [12], which might exhibit sensor properties due to the
_____________
*
4,4-Difluoro-4-bora-3а,4а-diaza-s-indacene.
229

TIKHOMIROVA et al.
230
Scheme 1.
2
R2
R
R1
R1
R2
.
R1
BF Et O,
3
2
NBu Cl
DDQ
THF
4
+
CH Cl
2
2
EtOOC
N
H
NH
HN
NH
N
CHO
EtOOC
COOEt
EtOOC
COOEt
Ià_Ic
Ia–Ic
II
O
O
O
R1, R2 = H (a), OCH3 (b),
(c).
O
O
purification of the reaction product by column chroma-
tography on silica gel.
also correspond to those found for analogs with ester
groups or for fused dipyrrins. In the spectra in the visible
region a slight solvatochromism was observed.
We failed to isolate compounds IIIa, IIIb under these
conditions. The analysis of the reaction mixtures showed
that the addition of BF3·Et2O is reversible, and the excess
of the base shifts the equilibrium to the starting dipyr-
rin. This behavior of substrate may be attributed to the
increased basicity of the cyclohexanodipyrrins caused
by the out-of-plane deformation of the heterocycle. This
effect was already observed in the cyclohexano-fused
porphyrins [14].
The synthesis and the study of fluorescence of com-
pound IIIа and a number of other cyclohexanodipyrrins
were recently published [17], but the synthesis of crown
derivative IIIc as well as its analog IIIb possessing simi-
lar electronic properties we described for the first time.
The interaction of compounds III with ions of alkaline-
earth metals also has not been studied before.
Optical characteristics of crown-dipyrrin complex
The optimum conditions consisted in using a stronger
base (1,8-diazabicyclo[5.4.0]undec-7-ene, DBU) and
toluene as solvent [15, 16] at the reaction time from 30
to 40 min, for at the longer time the reaction products
suffered decomposition. All three boron complexes
proved to be unstable to the contact with silica gel. The
decomposition products were ketones IVа–IVc. One of
them, IVc, was fully characterized. The use of optimized
procedure made it possible to obtain compounds IIIа–IIIc
in the yields of 72, 42, and 68% respectively (Scheme 2).
IIIc in hexane and acetonitrile and also the changes in its
Table 1. Optical properties of compounds IIIa–IIIc (excitation
wavelength λex 480 nm)
Compound
no.
Absorption, Emission,
Solvent
φfl, %
λmax, nm
λmax, nm
IIIa
IIIb
IIIc
Hexane 259, 429, 541
Toluene 284, 430, 542
CH3OH 260, 427, 535
CH3CN 259, 425, 533
Hexane 281, 419, 541
Toluene 285, 429, 541
CH3OH 259, 409, 535
CH3CN 258, 426, 531
Hexane 259, 419, 541
Toluene 285, 429, 541
CH3OH 258, 421, 535
CH3CN 257, 426, 532
564
37
32
568
563
27
560
31
The absorption and emission spectra of free ligands are
well consistent with the published data on BODIPY dyes
where the rotation of the meso-substituent is hindered
(Table 1). The fluorescence of compounds IIIb, IIIc is
quenched by a mechanism of intramolecular electron
transfer. This phenomenon is favored by the polar en-
vironment stabilizing the final state with the separated
charges. The fluorescence quantum yield (φfl) in nonpolar
solvents is relatively high, and in polar solvents it amounts
to ~1%. The quantum yield measured for compound IIIа
coincided within the limits of experimental error with the
published data [17], the values of φfl for all compounds
561
26
567
34
560
0.21
0.12
37
561
563
568
38
566
0.14
0.13
564
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 50 No. 2 2014

DIETHYL (BISCYCLOHEXANO)BODIPY DICARBOXYLATES.
231
Scheme 2.
We investigated the complex formation of all com-
pounds obtained with Mg
the effect of this process on the optical properties of the
studied substances.
absorption and emission spectra in the presence of sodium
and potassium cations were previously described in the
literature [18–20]. We studied the absorption and emission
spectra and also the quantum yields of fluorescence of
compounds IIIа–IIIc in four different solvents (Table 1).
2+, Ca2+, and Ba2+ cations and
Crown ethers are known to be capable of complexes
formation with cations of alkali and alkaline-earth metals
[23]. Crown ether substituents attached to the BODIPY
molecule yield highly efficient fluorescence sensors of
metal cations [9].
The data obtained show that electron-donor substitu-
ents in the benzene ring in the meso-position insignifi-
cantly affect the position of the absorption and emission
maxima in the spectra of compounds III. However the
quantum yields of fluorescence considerably differ and
strongly depend on the polarity of the solvent. This, as fol-
lows from the published data, is caused by the possibility
to occur in the presence of electron-donor substituents in
the meso-position in compounds IIIb, IIIc of a photo-
induced intramolecular electron transfer (PET) from the
HOMO of the substituent to the HOMO of the excited
fragment of BODIPY. This process results in significant
quenching of the fluorescence in the solvents of high po-
larity [9].Yet in nonpolar solvents (hexane, toluene) this
process is practically absent, therefore the fluorescence
quantum yields remain sufficiently high (25–38%). The
fluorescence quenching is a function of solvent polarity
which favors the stabilization of the charge-separated
state, and of the energy difference between the substitu-
ent’s and the dye’s HOMOs [21]. Evidently in the case
of unsubstituted BODIPY IIIa PET is impossible due
to the low HOMO energy of the unsubstituted phenyl
group. Similar relations were thoroughly studied for
bicyclo[2.2.2]octene-substituted BODIPY containing a
crown ether fragment [22].
In IIIc molecule the substituent in the meso-position is
orthogonal to the dipyrrin plane, therefore it is expectable
that the metal cations complexation should weakly affect
the absorption spectrum, but it should sharply increase the
fluorescence intensity due to suppressing PET. Indeed, in
the case of Mg2+ we observed the changes in the optical
spectra of compound IIIc similar to those described in the
literature at the formation of complexes with Na+ [18]:
addition of Mg2+ excess lead to very small red shift of the
absorption band, and the fluorescence intensity sharply
increased (Fig. 1, Table 2).
Table 2. Effect of magnesium cation on the optical properties
of compounds IIIа–IIIc
Absorption,
λmax (nm)
Emission,
λmax (nm)
Complexа
φfl, %
IIIa + Mg 260, 425, 533
IIIb+ Mg 257, 424, 532
IIIc+ Mg 257, 405, 534
561
561
564
29.35
0.12
29.40
а
Complexes were obtained in situ by adding ~100-fold excess of
Mg(ClO4)2 to a solution of compounds IIIа–IIIc in CH3CN (1 ×
10–5 mol L−1), λex 480 nm.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 50 No. 2 2014

TIKHOMIROVA et al.
232
0.5
0.4
(a)
4 equiv Ba2+
100 equiv Mg2+
0.08
0.07
4 equiv Ba2+
0.06
0.05
0.04
0.03
0.02
0.3
0.2
0.1
0
0 equiv
600
λ, nm
500
550
650
700
100 equiv Ba2+
0.01
0 equiv
0
500
550
600
λ, nm
650
700
Fig. 1. Variation in the fluorescence spectrum of compound IIIc
(1 × 10–4 mol l−1 in CH3CN) at the titration with the solution of
Mg(ClO4)2 in CH3CN. λex 480 nm.
(b)
0 equiv
0.40
0.35
0.30
0.25
The optical properties of compounds IIIa, IIIb lack-
ing the crown ether fragment are virtually insensitive to
the addition of excess Mg2+ (Tables 1,2) confirming the
complexing of magnesium cations only with the crown
ether fragment of IIIc molecule.
Cations Ba2+ also are capable of the formation of
complexes with benzo-15-crown-5, therefore the changes
in the absorption and emission spectra were expectable
similar to those observed for Mg2+. It was observed that
addition of first portions of Ba(ClO4)2 solution to the
solution of compound IIIc resulted in a sharp growth of
the fluorescence intensity, as it was in the previous case.
However on further addition the emission maximum suf-
fered a red shift by 30 nm with simultaneous decrease in
the intensity (Fig. 2а).
0.20
0.15
0.10
160 equiv Ba2+
0.05
0
500 520 540 560 580
600 620 640 660 680
λ, nm
Fig. 2. Variation in the fluorescence spectrum at the titration
with the solution of Ba(ClO4)2 in CH3CN: (a) of compound IIIc
(1 × 10–4 mol L−1); (b) of compound IIIa (1 × 10–4 mol L−1).
λex 480 nm.
Analogous changes in the fluorescence spectrum
were also observed on adding Ba2+ solutions to the solu-
tion of compound IIIа (Fig. 2b). In this case a gradual
quenching of the fluorescence also occurred with the
simultaneous red shift of the emission maximum. The
solution of compound IIIb in acetonitrile possesses a
very weak fluorescence, yet in this case also the red shift
of the spectrum is observed (the figure is not shown).
To account for the observed changes we presumed that
Ba2+ cations get bound to ester fragments of initial dipyr-
rins III. Similar changes (i.e. a considerable red shift of
absorption and emission maxima, partial quenching of flu-
orescence) were described in the literature for molecules
Table 3. Calculated stability constants (log K) of complexes
1 : 1, 2 : 1
Complex
logKcation/ligand
logK11 5.02 ± 0.05
Considerable changes are also observed during the
UV-Vis titration of compounds IIIа–IIIc with Ba2+ solu-
tion: For all three compounds the absorption maximum
at 532 nm gradually decreases, and a new band with the
maximum at 558–561 nm arises (Fig. 3). The red shift is
accompanied with the change in the solution color from
orange-red to crimson.
Mg–IIIc
Ba–IIIа
Ba–IIIb
Ca–IIIa
Ca–IIIc
logK11 2.86 ± 0.07
logK11 2.90 ± 0.02
logK11 2.15 ± 0.10
logK11 4.57 ± 0.22; logK21 6.04 ± 0.22
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 50 No. 2 2014

DIETHYL (BISCYCLOHEXANO)BODIPY DICARBOXYLATES.
233
2.5
904 equiv Ba2+
2.0
1.5
1.0
0 equiv
0.5
0
200 250 300
360 400 450 500 550 600 650
λ, nm
Fig. 3. Variation of EAS of compound IIIа (1 × 10–4 mol L−1) at the spectrophotometric titration with solution of Ba(ClO4)2 in CH3CN.
700
of BODIPYand their analogs when in the complex forma-
tion the electron-acceptor groups were involved being a
part of the the chromophore system [24–26]. However no
published examples exist of complexing of Ca2+ and Ba2+
ions with ester groups of BODIPY, although complexes
are known where the barium atom is coordinated to the
oxygen atom of the other ester groups [27–29].
impeded by the presence of several colored complexes
of various types.
The study of the effect of Ca2+ cations on the optical
spectra of compounds IIIа–IIIc revealed that the Ca2+
ions also cause a red shift of the absorption and emission
maxima and the quenching of fluorescence (Figs. 4, 5).
However, compared to that Ba2+, the addition of Ca2+
solutions leads to more complex shapes of the final spectra
in all cases. I.e. a shoulder is clearly seen at 538–540 nm,
a broad band in the 430–460 nm region also possesses a
dual-band structure, and the main absorption maximum
is shifted further to the red region by 33–36 nm. The
fluorescence spectra also contain two maxima of emission
bands: at 555–560 and 592–599 nm.
The presence of an isosbestic point at 543 nm (Fig. 3)
indicates the formation of a single type of a complex.
The processing of the data of the UV-Vis titration of IIIa
with the Ba(ClO4)2 solution using SPECFIT/32 program
showed that one ligand–metal complex was in this case
formed, i.e. 1 : 1. Compound IIIb is also able to form
a complex at the ester fragment, and its stability con-
stant also has been calculated (Table 3). The accurate
calculation of the constant of complex formation at
ester groups for the crown-containing ligand IIIc was
From the results of the spectrophotometric titration
compound IIIa was shown to form a single complex
(a)
(b)
2.5
3.5
1190 equiv Ca2+
2.0
3.0
50 equiv
50 equiv
0 equiv
1190 equiv Ca2+
2.5
2.0
1.5
1190 equiv
0 equiv
1.5
1.0
0.5
0
1.0
0.5
0
0 equiv
210
310
400
510
610
210
310
400
510
610
λ, nm
λ, nm
Fig. 4. Variation of EAS at the titration with a solution of Ca(ClO4)2 in CH3CN: (a) of compound IIIа (1 × 10–4 mol L−1); (b) of com-
pound IIIc (1 × 10–4 mol L−1).
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 50 No. 2 2014

TIKHOMIROVA et al.
234
1 : 1 like in the case of Ba2+. Compound IIIc formed
complexes with the calcium cation both at the crown ether
and at the ester fragments therefore the spectral changes
at the titration are more complicated (Fig. 4b).
(a)
0.40
0.35
0.30
0.25
0 equiv
UV-Vis titration data were used to calculate the stabil-
ity constants of the corresponding complexes (Table 3).
Similarly using the method of fluorimetric titration we
determined the association constant of IIIc complex with
Mg2+ (Table 3)
The formation of Ca2+ and Ba2+ complexes with the
ester fragments of the studied compounds leads to the de-
crease in the fluorescence quantum yield in contrast to the
increased fluorescence intensity in the Mg2+-IIIc complex
(Tables 1, 2). However it was difficult to estimate quantita-
tively the changes in the fluorescence quantum yields since
the described complexes were obtained in rather concen-
trated solutions. At the strong dilution used for the precise
quantum yield measurement the absorption and emission
maxima broadened and suffered a blue shift evidently due
to the partial decomposition of the complexes.
0.20
0.15
0.10
765 equiv Ca2+
0.05
0
490
540
590
λ, nm
640
690
(b)
2 equiv Ca2+
0.45
2 equiv Ca2+
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0
To confirm the structure of the obtained complexes
we explored the effect of Mg2+, Ca2+, and Ba2+ cations
on the NMR spectra of IIIa, IIIc (Tables 4, 5).
765 equiv Ca2+
650
0 equiv
500
550
600
λ, nm
The data obtained are in good agreement with the
results of optical spectra measurements and with the as-
sumption of the interaction between calcium and barium
cations with the ester groups of the molecules under study.
Fig. 5. Variation of fluorescence spectra of compound IIIа (1 ×
10–4 mol L−1) (a) and IIIc (1 × 10–4 mol L−1) (b) at the titration of
their solutions with a solution of Сa(ClO4)2 in CH3CN. λex 480 nm.
Table 4. Chemical shifts of 1H NMR signals (δ, ppm) in the spectra of compounds IIIа, IIIc and their complexes in CD3CN
(25-fold excess of metal perchlorates)
Compound or complex
ArH
H4
H5
H6
H7
OCH2CH3 OCH2CH3
IIIa
7.35–7.37, 7.55–7.58
7.35–7.37, 7.55–7.58
7.36–7.38, 7.58–7.63
7.35–7.37, 7.58–7.62
2.53
2.53
2.69
2.70
1.57
1.57
1.59
1.58
1.38
1.38
1.38
1.38
1.64
1.64
1.68
1.65
4.36
4.36
4.49
4.49
1.35
1.35
1.41
1.40
IIIa + Mg2+
IIIa + Ca2+
IIIa + Ba2+
H14
6.91
7.21
H16
6.86
7.16
H17
7.06
7.33
H4
H5
H6
H7
OCH2CH3 OCH2CH3
IIIc
IIIc + Mg2+
2.54
2.54
1.60
1.60
1.44
1.44
1.80
1.71
4.36
4.36
1.34
1.34
IIIc + Ca2+
IIIc + Ba2+
7.24
7.12
7.15
7.05
H2'
7.38
7.28
2.71
2.72
1.62
1.61
1.44
1.44
H5',6',8',9'
1.80
1.82
4.50
1.42
4.50
H11'
1.40
H12'
4.05
4.41
4.44
4.34
H3'
IIIc
4.15
4.53
4.52
4.43
3.83
4.15
3.63–3.67
3.92, 3.99
3.97–4.01
3.85–3.97
3.77
IIIc + Mg2+
IIIc + Ca2+
IIIc + Ba2+
4.10
4.10
4.05
3.85–3.97
3.85–3.97
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DIETHYL (BISCYCLOHEXANO)BODIPY DICARBOXYLATES.
235
Table 6. Energy of complexes of model dipyrrin with Ca2+ and
Ba2+ ions (kcal mol−1) of various spatial structures by the data
of quantum-chemical calculations
(a)
Relative energy of com-
plexes, kcal mol−1
Configuration
Ca2+
Ba2+
“Inside cavity” (Fig. 6a)
“Above cavity” (Fig. 6b)
0
0
27.2
25.3
17.4
“At the side of cavity” (not
shown on the figure, see the text)
124.0
The addition of Mg2+ to a solution of compound IIIа
1
has virtually no effect on the position of H signals in
agreement with the absence of the optical response. On
adding Ca2+ or Ba2+ the proton signals of the ethyl group
of the ester fragment significantly shifted downfield,
the greater shift occured in the signals of the methylene
protons (0.13–0.14 ppm). The positions of proton peaks
of the cyclohexane fragment do not practically change
except the signal of H4 that also suffers a significant
downfield shift (0.16–0.18 ppm). These protons are in
close proximity to the ester carbonyl and are affected by
its anisotropic influence. At the formation of the complex
with metal cations apparently changes the spatial position
of the COOEt fragment with respect to the boron-dipyrrin
fragment. The downfield shift of the adjacent groups
evidently indicates that the ester group interacting with
the metal ion is situated in the same plane as the dipyrrin
fragment. The signals of the phenyl group do not visibly
change in the presence of metal cations.
In the 1H NMR spectrum of compound IIIc at adding
cations of Mg2+, Ca2+, and Ba2+ the proton signals of ben-
zocrown ether fragment suffer a considerable downfield
shift (~0.2–0.4 ppm), and the shifts are larger in the case
of Mg2+ and Ca2+, which are known to form stronger com-
plexes with 15-crown-5. Similar changes in NMR spectra
are typical of compounds containing benzocrown ether
fragment at complexing with magnesium and barium cat-
ions [30, 31]. In the signals of protons from the ester and
cyclohexane fragments changes are observed analogous
to the above described for the complex with IIIa ligand.
(b)
Fig. 6. Spatial arrangement of complexes of model compound
analogous to compound IIIb according to the data of ab initio
calculations: (a) the interaction of Ba2+ ion with carbonyl
oxygen atom of ester group and two fluorine atoms inside the
cavity; (b) Ba2+ interacts with carbonyl groups of two COOEt
fragments and one fluorine atom, being located outside of cavity.
Table 5. Chemical shifts of 11B and 19F NMR signals in the
spectra of compounds IIIа, IIIc and their complexes in CD3CN
(25-fold excess of metal perchlorates)
Compound or complex 11B, δ, ppm
19F, δ, ppm
IIIa
0.15
0.15
0.70
0.58
0.16
0.15
0.71
–140.61
–140.52
–138.71
–137.05
–140.45
–140.49
–138.50
IIIa + Mg2+
IIIa + Ca2+
IIIa + Ba2+
IIIc
IIIc + Mg2+
IIIc + Ca2+
11
We also registered the B and 19F NMR spectra of
initial compounds and their complexes (Table 5). IIIа,
IIIc have spectra typical of BODIPY [32–35]. Adding
excess Mg2+ in both cases does not affect the position of
F and B signals. However in the presence of Ca2+ and
Ba2+ both nuclei suffer a downfield shift (0.43–0.55 ppm
for boron atoms and 1.90–3.63 ppm for fluorine). Rao
IIIc + Ba2+
0.60
–136.82
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TIKHOMIROVA et al.
236
et al. [34, 36] observed a downfield shift in the 11B and
19F NMR spectra at the introduction in positions 3, 5 of the
BODIPY molecule of aldehyde or amide groups capable
of forming hydrogen bonds with BF2. Weak (~2–3 ppm)
downfield shifts in 19F NMR spectra were described for
BODIPY and their analogs at the formation of com-
plexes involving interactions BF---Cs+ [37, 38]. A large
downfield shift is characteristic of 3,5-diaryl-substituted
BODIPY as compared with dibromo-substituted [32]. In
our case the observed shifts may be due to the formation
of a complex, where the metal cation is located in the
immediate proximity of BF2 (Fig. 6).
constants, with an accuracy of 0.1 Hz. In the NMR spectra
13С-APT (Attached Proton Test) the signals of secondary
and quaternary carbon atoms are marked with asterisk *.
Mass spectra with laser desorption ionization (LDI-
TOF) were recorded on a Bruker Daltonics Autoflex II
instrument by nitrogen laser irradiation at 337 nm and
19kV accelerating voltage.
Commercial products and solvents were purchased
from Reachim, Aldrich, Acros Organics. The solvents
were distilled before use.
UV-Vis spectra were measured on a spectrophotometer
Agilent-8453, operating range 190–1100 nm. The spec-
trophotometer control, the data collection and processing
was performed using a UV-Visible Chem.Station pro-
gram, Rev. A.10.01. Fluorescence spectra were recorded
on a spectrofluorimeter Flyuorat-02-Panorama, the instru-
ment being controlled with the program Panorama Lite.
Ab initio quantum chemical calculations at the
HF/LANL2MB approximation confirm our assumptions.
For the complex with calcium or barium ions the minima
on the potential energy surface (PES) correspond to the
structures analogous to that shown in Fig. 6a. Other min-
ima on PES were also found. The configuration shown
in Fig. 6b depicts a metal ion located under the dipyrrin
plane and coordinated to two ester groups and a single
fluorine atom. One more minimum corresponds to the
configuration where the cation is coordinated with a
single ester group and it is placed at the side of dipyrrin
molecule (not shown in the figure).
Quantum yields of fluorescence were determined at
room temperature in air-saturated acetonitrile solutions
with respect to the solution of rhodamine 6G in ethanol
used as reference (φfl 0.94) [39]. The fluorescence quan-
tum yield was calculated by the formula [40]
ref
)
,
φexp
ref
φexp
Both for Ca2+ and Ba2+ the structures corresponding
ref
ref
to Fig. 6а are the most favorable by the energy (Table 6).
where S is the integral intensity of the fluorescence, D is
the optical density at the excitation wavelength, n is the
refraction index of the solvent used, φ is the fluorescence
quantum yield.
The stability constants of complexes of dipyrro-
methene ligands with metal cations were determined by
spectrophotometric and fluorimetric titrations at room
temperature in acetonitrile with appropriate metal per-
chlorates. The processing spectrophotometric titration
results and the calculation of the stability constants of
the complexes were carried out using SPECFIT/32 soft-
ware applying the nonlinear least squares method by the
Levenberg–Marquardt algorithm.
Thus we found that the ethoxycarbonyl-substituted
borodipyrrin complexes synthesized in this study exhib-
ited moderate sensing properties to ions of alkaline-earth
metals, calcium and barium. This may be due to the pres-
ence in the studied compounds of a guest cavity formed
of the fluorine atoms of BF2 moiety and the carbonyl
oxygen atoms of the ester group. The sensor effect is
observed in the spectra in UV and visible region and in
the fluorescence spectra. The structure of the complexes
1
was confirmed by the H, 19F NMR spectra and by ab
initio quantum-chemical calculations.
EXPERIMENTAL
Elemental analysis was carried out in the Microanaly-
sis laboratory of the Chemical Department of Lomonosov
Moscow State University.
11
1Н, 13С, and B NMR spectra were registered on a
BrukerAvance 400 spectrometer (400, 100, 128 MHz re-
spectively). Chemical shifts of 11B signals were measured
with respect to external H3BO3 reference. 19F spectra
were recorded on a Bruker АM300 spectrometer at a
frequency 282 M Hz, chemical shifts 19F were measured
with respect to external CFCl3 reference. Chemical shifts
were measured with an accuracy of 0.01 ppm, coupling
Melting points were measured on an instrument Mel-
TempII and were uncorrected.
TLC analyses were carried out on DC-Alufolien Kie-
selgel 60 F254 plates (Merck). For column chromatog-
raphy silica gel Kieselgel 60 0.063–0.200 mm (Merck)
was used.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 50 No. 2 2014

DIETHYL (BISCYCLOHEXANO)BODIPY DICARBOXYLATES.
237
The optimization of the structure of molecules was
performed applying the program GAUSSIAN03 [41]
using the HF/LANL2MB approximation.
(CD3CN), δ, ppm: 0.15 t (1J 27.4 Hz). 19F NMR spec-
trum (CD3CN), δ, ppm: –140.61 q (1J 27.6 Hz). Mass
spectrum (LDI-TOF, 19 kV), m/z (Irel, %): 559.26 (12)
[M + K]+, 543.26 [M + Na]+ (100), 521.21 (15) [M +
H]+, 501.23 (21) [M – F]+. Found, %: C 66.75; H 6.19;
N 5.18. C29H31BF2N2O4. Calculated, %: C 66.93; H 6.00;
N 5.38. M 520.38.
Complexes of bis(ethoxycarbonyl)cyclohexanodi-
pyrrins with BF2 IIIа–IIIc. General procedures. а.
Dipyrrin I (1 equiv) was dissolved in CHCl3, the reac-
tion flask was flushed with argon at stirring, 20 equiv
of triethylamine was added, the mixture was stirred for
30 min, then 30 equiv of freshly distilled BF3·Et2O was
added, and the stirring under an argon atmosphere was
continued (TLC monitoring). On completing the reac-
tion the reaction mixture was washed in succession with
saturated water solution of Na2CO3, water, and brine, and
dried with Na2SO4.
(Ethyl 1-{[3-(ethoxycarbonyl)-4,5,6,7-tetrahydro-
2H-isoindol-1-yl-κN](3,4-dimethoxyphenyl)-
methylene}-4,5,6,7-tetrahydro-1H-isoindole-3-
carboxylato-κN)(difluoro)boron (IIIb). All attempts to
prepare compound IIIb by procedures а, b (varying reac-
tion time, amount of used reagents, temperature) failed.
c. From 0.0384 g (0.072 mmol) of dipyrromethene Ib
in 10 mL of toluene on removing the solvent 0.0399 g
of red solid was obtained consisting (according to NMR
data) of compound IIIb with a slight impurity of initial
dipyrromethene Ib. After adding 10 mL of hexane and
boiling the filtered off insoluble residue contained pure
compound IIIb. Yield 0.0176 g (0.030 mmol, 42%),
mp 136–137°С. UV spectrum (CH3CN), λmax, nm (logε):
258 (4.32), 426 (3.91), 531 (4.39). 1H NMR spectrum
(CDCl3), δ, ppm: 1.41 m (10, OCH2CH3 + H6, 3J 7.0 Hz),
1.55–1.61 m (4H, H5), 1.68–1.73 m (4H, H7), 2.57 m (4H,
H4), 3.85 s (3H, OCH3), 3.96 s (3H, OCH3), 4.42 q (4H,
OCH2CH3, 3J 7.0 Hz), 6.71 d (1H, H14, 4J14,16 1.9 Hz),
6.77 d.d (1H, H16, 4J14,16 1.9, 3J16,17 8.2 Hz), 6.98 d (1H,
b. The synthesis was carried out similarly to proce-
dure а, using instead of triethylamine the corresponding
quantity of N-ethyl-N-diisopropylamine.
c. 1 equiv of dipyrrin I was dissolved in toluene, the
reaction flask was flushed with argon at stirring, 6 equiv
of DBU was added, the stirring continued for 10 min,
then 20 equiv of freshly distilled BF3·Et2O was added,
and the stirring under an argon atmosphere was continued
for 30–40 min. The reaction mixture was washed with
5% water solution of HCl, reaction product was extracted
with CHCl3, the combined organic solutions were washed
with water and brine, dried with Na2SO4.
(Ethyl 1-{[3-(ethoxycarbonyl)-4,5,6,7-tetrahydro-
2H-isoindol-1-yl-κN](phenyl)methylene}-4,5,6,7-
tetrahydro-1H-isoindole-3-carboxylato-κN) )(difluo-
ro)boron IIIa.All attempts to prepare compound IIIa by
procedures а, b (varying reaction time, amount of used
reagents, temperature) failed.
3
H17, J16,17 8.2 Hz). 13С APT NMR spectrum (CDCl3),
δ, ppm: 14.04, 22.09*, 22.36*, 22.70*, 24.58*, 55.93,
56.17, 61.66*, 110.29, 111.75, 119.89, 126.73*, 132.50*,
133.23*, 143.58*, 143.77*, 147.57*, 150.00*, 150.05*,
161.60*. 11B NMR spectrum (CD3CN), δ, ppm: 0.52 t
(1J 27.4 Hz). Mass spectrum (LDI-TOF, 19 kV), m/z
(Irel, %): 619.22 (32) [M + K]+, 603.36 (100) [M + Na]+,
561.32 (18) [M – F]+. Found, %: C 63.96; H 5.88; N
4.64. C31H35BF2N2O6. Calculated, %: C 64.15; H 6.08;
N 4.83. M 580.43.
Ethyl 1-{[3-(ethoxycarbonyl)-4,5,6,7-tetrahydro-
2H-isoindol-1-yl-κN](2,3,5,6,8,9,11,12-octahydro-
1,4,7,10,13-benzopentaoxacyclopentadecin-15-yl)
methylene}-4,5,6,7-tetrahydro-1H-isoindole-3-
carboxylato-κN)(difluoro)boron (IIIc) and ethyl
3-[(2,3,5,6,8,9,11,12-octahydro-1,4,7,10,13benzo-
pentaoxacyclopentadecin-15-yl)carbonyl]-4,5,6,7-
tetrahydro-2H-isoindole-1-carboxylate (IVc). a. The
substance obtained from 0.0334 g (0.0504 mmol) of
dipyrromethene Ic in 5 mL of CHCl3 within 20 h was
purified by column chromatography (silica gel, CHCl3–
c. From 0.0400 g (0.085 mmol) of dipyrromethene Ia
in 8 mL of toluene on removing the solvent 0.0483 g of
solid was obtained consisting (according to NMR data)
of compound IIIa with a slight impurity of initial dipyr-
romethene Ia. After addition 6 mL of hexane and boiling
the filtered off insoluble residue contained pure compound
IIIa. Yield 0.0317 g (0.061 mmol, 72%). Red solid, mp
130–132°С. UV-Vis spectrum (CH3CN), λmax, nm (logε):
1
259 (4.24), 425 (3.80), 533 (4.39). H NMR spectrum
(CDCl3), δ, ppm: 1.41 m (10H, OCH2CH3, H6, 3J 7.0 Hz),
1.53–1.59 m (8H, H5, H7), 2.56 m (4H, H4), 4.43 q (4H,
OCH2CH3, 3J 7.0 Hz), 7.21–7.23 m (2Harom), 7.49–7.52 m
(3Harom). 13СAPT NMR spectrum (CDCl3), δ, ppm: 14.03,
22.02*, 22.33*, 22.62*, 24.41*, 61.67*, 127.18, 127.30,
129.38, 129.48, 129.66, 132.54*, 132.90*, 134.60*,
143.65*, 143.79*, 147.62*, 161.56*. 11B NMR spectrum
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 50 No. 2 2014

TIKHOMIROVA et al.
238
22.70*, 22.92*, 22.98*, 24.37*, 60.59*, 68.58*, 68.85*,
69.12*, 69.20*, 70.15*, 70.21*, 70.98*, 112.10, 113.65,
121.83*, 123.31, 128.88*, 129.04*, 131.72*, 148.77*,
152.58*, 161.04*, 185.71*. Mass spectrum (LDI-TOF,
19 kV), m/z (Irel, %): 525.87 (93) [M + K]+, 509.92 (100)
[M + Na]+, 487.96 (84) [M]+. M 487.54.
EtOH, 30 : 1, later 20 : 1, 10 : 1). Red fractions not con-
taining impurities (TLC) were combined. Yield 0.0163 g
(0.023 mmol, 46%).
b. From 0.0856 g (0.129 mmol) of dipyrromethene Ic
in 25 mL of CHCl3 on removing the solvent we obtained
0.0825 g of red amorphous substance that was subjected
to chromatography (silica gel, CHCl3–EtOH, 50 : 1,
later 20 : 1, 10 : 1). First red fractions not containing
impurities (TLC) were combined. We obtained 0.0133 g
(0.0187 mmol, 14%) of red solid. Fractions containing
another individual compound were combined and from
the sum of spectral data it was identified as the decom-
position product of initial dipyrrin, compound IVc. Yield
0.0178 g (0.0365 mmol, 28%).
ACKNOWLEDGMENTS
The study was carried out under a financial support
of the Russian Foundation for Basic Research (grant
no. 12-03-00260a).
REFERENCES
c. From 0.0802 g (0.121 mmol) of dipyrromethene Ic
in 20 mL toluene after purification by column chroma-
tography (silica gel, CH2Cl2–EtOH, 70 : 1, later 60 : 1,
50 : 1) 0.0582 g (0.082 mmol, 68%) of compound IIIc
was isolated. Red solid, mp 137–138°С (138°С [18]).
UV spectrum (CH3CN), λmax, nm (logε): 257 (4.35), 426
(3.93), 532 (4.38). 1H NMR spectrum (CDCl3), δ, ppm:
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1.40 m (10H, OCH2CH3, H6, J 7.0 Hz), 1.57 m (4H,
H5), 1.70 m (4H, H7), 2.56 m (4H, H4), 3.78–3.79 m
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1
δ, ppm: 1.36 m (3H, OCH2CH3, J 7.2 Hz), 1.60–1.66
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