DTTA-appended 6-phenyl- and 5,6-diphenyl-2,2′-bipyridines as new water soluble ligands for lanthanide cations

Article abstract of DOI:10.1016/j.poly.2017.05.030

By means of “1,2,4-triazine” strategy new DTTA-appended 6-phenyl- and 5,6-diphenyl-2,2′-bipyridines – ligands for lanthanides cations have been synthesized, and their luminescent lanthanides (Sm³⁺, Eu³⁺, Tb³⁺ and Dy³⁺) water-soluble complexes have been prepared. The photophysical properties of new chelates were studied; comparison of quantium yields of fluorescence and lanthanide cation luminescence has been fulfilled. Comparison of characteristics of new complexes with ones of some previously published chelates has been done, for some cases a bathochromic shift in absorption spectra and higher lanthanide luminescence quantum yields were observed.

Full text of DOI:10.1016/j.poly.2017.05.030

Accepted Manuscript
DTTA-appended 6-phenyl-, 5, 6-diphenyl-2, 2′-bipyridines as new water solu-
ble ligands for lanthanide cations
Alexey P. Krinochkin, Dmitry S. Kopchuk, Grigory A. Kim, Ilya N. Ganebnykh,
Igor S. Kovalev, Grigory V. Zyryanov, Fengyu Li, Vladimir L. Rusinov, Oleg
N. Chupakhin
PII:
S0277-5387(17)30378-9
DOI:
http://dx.doi.org/10.1016/j.poly.2017.05.030
POLY 12649
Reference:
To appear in:
Polyhedron
Received Date:
Accepted Date:
28 March 2017
20 May 2017
Please cite this article as: A.P. Krinochkin, D.S. Kopchuk, G.A. Kim, I.N. Ganebnykh, I.S. Kovalev, G.V. Zyryanov,
F. Li, V.L. Rusinov, O.N. Chupakhin, DTTA-appended 6-phenyl-, 5, 6-diphenyl-2, 2′-bipyridines as new water
soluble ligands for lanthanide cations, Polyhedron (2017), doi: http://dx.doi.org/10.1016/j.poly.2017.05.030
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DTTA-appended 6-phenyl- and 5,6-diphenyl-2,2′-bipyridines as new water soluble ligands for
lanthanide cations
a
Alexey P. Krinochkin, Dmitry S. Kopchuk, Grigory A. Kim, Ilya N. Ganebnykh,
a,b∗
a,b
b
a
a,b
c
a,b
Igor S. Kovalev, Grigory V. Zyryanov, Fengyu Li, Vladimir L. Rusinov, Oleg N. Chupakhin
a,b
a
Ural Federal University, 19, Mira St., 620002 Yekaterinburg, Russian Federation
b
Postovsky Institute of Organic Synthesis of RAS (Ural Division), 22/20, S. Kovalevskoy/Akademicheskaya St., 620990
Yekaterinburg, Russian Federation
c
Key Laboratory of Green Printing, Key Lab of Organic Solids, Beijing National Laboratory for Molecular Sciences
(BNLMS), Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 (P.R. China)
Abstract
By means of "1,2,4-triazine" strategy new DTTA-appended 6-phenyl- and 5,6-diphenyl-2,2′-
bipyridines – ligands for lanthanides cations have been synthesized, and their luminescent
3
+
3+
3+
3+
lanthanides (Sm , Eu , Tb and Dy ) water-soluble complexes have been prepared. The
photophysical properties of new chelates were studied; comparison of quantium yields of
fluorescence and lanthanide cation luminescence has been fulfilled. Comparison of characteristics of
new complexes with ones of some previously published chelates has been done, for some cases a
batochromic shift in absorption spectra and higher lanthanide luminescence quantum yields were
observed.
Key words: (Di)aryl-2,2'-bipyridines; luminescence; lanthanide complexes; aza-Diels-Alder
reaction; DTTA.
1
. Introduction
3
+
3+
3+
3+
Water-soluble luminescent lanthanide complexes (i.e. ones of Sm , Eu , Tb and Dy ) are
currently of great interest due to their wide scope of applications [1]. In particular, they are used as
chromophores for phosphorescent labels [2], as chemosensors for metal cations [3], for the
photoluminescent detection of singlet oxygen [4] and nitric oxide [5], as complexes suitable for
usage 'in cellulo' [6] etc.
The common organic ligands for these complexes are composed from the chromophore part,
an “antenna”, which is necessary for efficient absorbing incident light for transferring this excitation
∗Corresponding author. Tel.: +7-343-375-4501; fax: +7-343-374-0458; e-mail: dkopchuk@mail.ru

to the chelated lanthanide ion for the sensitization of the its luminescence, and chelating part for
tightly cation binding (a typical coordination number for the lanthanides is 9). For prevention of
lanthanide cation luminescence quenching it is necessary to avoid the presence of water molecules
in the first coordination sphere of cation since in this case non-radiative decay via vibronic coupling
to vibrational states of O-H bonds occurs. According to the literature, some “antennas” are: the
derivatives of 2,2'-bipyridines [7], 1,10-phenanthrolines [8,9] and 2,2':6',2'' - terpyridines [10].
Among them the terpyridines are the mostly reported in a literature. And the residues of
iminodiacetic acid (IDA) or polyaminocaboxilic acids, for instance, 1,4,7-tris(carboxymethyl)-
1
,4,7,10-tetraazacyclododecane (DO3A) or diethylenetriamine-N,N,N'',N''-tetraacetate (DTTA) are
the common chelates for lanthanide cations. In addition, some macrocycle-based chelating agents
are reported, for instance, oligopyridine- and polyamino-acids-derived cryptands [11].
Previously we reported several Eu(III) complexes based on 5-aryl-2,2′-bipyridines and either
two IDA chelating units or one DTTA (or DO3A) chelating unit respectively. It was shown that for
nine-coordinated Eu(III) complexes the luminescence efficiency depends mostly on aromatic system
and is rather independent of the chelating poly(aminoacetate) structure, while for the eight-
coordinated complexes the luminescence was strongly quenched by water molecule in the Eu(III)
coordination sphere [7]. Therefore, DTTA-or DO3A-based chelating unit is needed in order to
achieve the full occupation of the lanthanide cations coordination sites.
When using the 2,2′-bipyridine units as an antenna the derivatives with an extended
conjugation system are more preferable. In particular, it allows to finely tune the photophysical
properties of a new ligand, for example, due to the bathochromic shift of its absorption maximum,
which allows to use more available light sources for the photoexcitation [12]. In addition, the
aromatic substituents can be used as sites for the possible conjugation with bio-molecules in-vivo or
in-vitro, and the tuning of the photophysical properties of the ligand can be achieved by means of
the proper variation of the functional groups (see for example [7,13]).
It is worthy to mention that similar 2,2′-bipyridine-type ligands are not very common for
obtaining photoluminescent lanthanide cations complexes, the presented examples are shown in Fig.
1
. Thus, there are several examples of ligands and their metal complexes based on 2,2'-bipyridines
[
[
14], 5-aryl-2,2'-bipyridines [7], 7-tert-butyl-2-(pyridin-2-yl)-5H-chromeno[2,3-b]pyridin-5-one
15], 9-methyl-1,10-phenanthroline [16], its 4,7-diphenyl derivative [17], or 10,11,12,13-
tetrahydrodipyrido[3,2- a: 2 ', 3'-c]phenazine [6].

Fig. 1. Previously published chromophores for ligands for lanthanide cations
The main objective of this paper is to study the new antenna ligands for lanthanide cations
based on substituted 2,2'-bipyridine chromophores, modified in α-position of 2,2′-bipyridine core
with DTTA residue via a methylene bridge. In this article we are aiming to study the effectiveness
of 2,2'-bipyridine-based ligands, namely 5,6-diphenyl- and 6-phenyl-2,2'-bipyridines, from the
standpoint of tuning the photophysical properties of their lanthanide chelates, such as emission and
absorption maxima, photoluminescence quantum yield and lifetime, depending on the both type of
the lanthanide cation and the ligand. The open-chain polyaminocarboxylate, namely DTTA, was
selected as a chelating unit, based on the comparable photoluminescent properties of DTTA-based
lanthanide complexes and those derived from less synthetically available cyclic
polyaminocaboxylates (in particular, DO3A) [7]. The structure of the chosen ligands is presented in
Fig. 2.
COOH
HOOC
N
N
R
N
N
COOH
Ph
N
COOH
R = H, Ph
Fig. 2. The structure of the DTTA-appended 6-phenyl- and 5,6-diphenyl-2,2′-bipyridine ligands for
lanthanide cations

2
. Experimental part
All reagents were purchased from commercial sources and used without further purification.
NMR spectra were recorded on a Bruker Avance-400 spectrometer, 298 K, digital resolution ± 0.01
ppm, using TMS as internal standard. UV–Vis spectra were recorded on Lambda 45
spectrophotometer (Perkin Elmer). Luminescence spectra were recorded on a Cary Eclipse
spectrofluorometer (Varian). Mass spectra were recorded on a MicrOTOF-Q II mass spectrometer
(
Bruker Daltonics) with electrospray ionization. Elemental analysis were performed on a РЕ 2400 II
CHN-analyzer (Perkin Elmer). Starting compounds: 3-(6-methylpyridin-2-yl)-5,6-diphenyl-1,2,4-
triazine 6b [18], amidrazone 7 [18], phenylglyoxal [19] and ester of DTTA 4 [20] were synthesized
as described in literature.
2
.1. General method for the obtaining of esters 2
The ester of DTTA 4 (490 mg, 0.88 mmol) was dissolved in dry acetonitrile (40 ml), the
corresponding bromomethylbipyridine 3 (0.8 mmol) and potassium carbonate (550 mg, 4 mmol)
were added and the resulting mixture was stirred under reflux for 8 h in argon atmosphere. Then
solvent was removed under reduced pressure, water (30 ml) was added to the residue, the product
was extracted with DCM (3 x 20 ml). Extract was washed with anhydrous sodium sulfate. Solvent
was removed under reduced pressure. The residue was separated by column chromatography (Silica
gel, eluent: DCM, then ethylacetate).
2
.2. General method for the synthesis of ligands 1
The corresponding ester 2 (0.25 mmol) was dissolved in hydrochloric acid (5N, 10 ml). The
resulting mixture was stirred at room temperature overnight. Then solvent was removed under
reduced pressure. The hydrochloric acid (11N, 7 ml) was added to the residue and the resulting
mixture was stirred at room temperature for 2 h. Undissolved part was filtered off, solvent from the
filtrate was removed under reduced pressure. Dry acetonitrile (7 ml) was added to the residue, the
resulting mixture was stirred at room temperature overnight. The precipitate formed was filtered off,
washed with dry acetonitrile and dried under vacuum.
2
.3. General method for the synthesis of lanthanide complexes 1*Ln
The corresponding ligand 1 (0.05 mmol) was dissolved in water (8 ml). Sodium hydroxide
(
the number of equivalents determined by elemental analysis and additional 4 equivalents (8 mg, 0.2
mmol)). Then the salt of corresponding lanthanide (0.05 mmol) was added, the resulting mixture

was stirred at room temperature for 2 h. Solvent was removed under reduced pressure. The product
was extracted from the residue by hot methanol (3 х 20 ml). Undissolved part was filtered off,
methanol from the filtrate was removed under reduced pressure.
1
a*Eu. Yield 36 mg (0.04 mmol, 80%). Found, %: С 46.45, Н 4.38, N 7.50. Calculated for
-
C
35
H
33EuN
5
O
8
Na*4H
2
O: С 46.78, Н 4.60, N 7.79. ESI-MS, m/z: found 804.16 [M-Na] , required
8
04.15.
1
a*Sm. Yield 32 mg (0.035 mmol, 70%). Found, %: С 45.71, Н 4.53, N 7.42. Calculated for
-
C
35
H33SmN
5
O
8
Na*5H
2
O: С 45.94, Н 4.74, N 7.65. ESI-MS, m/z: found 803.15 [M-Na] , required
8
03.15.
1
a*Tb. Yield 37 mg (0.04 mmol, 80%). Found, %: С 45.23, Н 4.43, N 7.19. Calculated for
-
C
35
H33TbN
5
O
8
Na*5H
2
O: С 45.51, Н 4.69, N 7.58. ESI-MS, m/z: found 810.16 [M-Na] , required
8
10.16.
1
b*Eu. Yield 32 mg (0.0375 mmol, 75%). Found, %: С 41.22, Н 4.42, N 8.11. Calculated
-
for C29
H29EuN
5
O
8
Na*5H
2
O: С 41.44, Н 4.68, N 8.33. ESI-MS, m/z: found 728.12 [M-Na] ,
required 728.12.
1
b*Tb. Yield 29 mg (0.035 mmol, 70%). Found, %: С 41.71, Н 4.27, N 8.19. Calculated for
-
C
29
H29TbN
5
O
8
Na*4H
2
O: С 41.99, Н 4.50, N 8.44. ESI-MS, m/z: found 734.13 [M-Na] , required
7
34.13.
1
b*Dy. Yield 33 mg (0.04 mmol, 80%). Found, %: С 41.55, Н 4.19, N 8.15. Calculated for
-
C
29
H29DyN
5
O
8
Na*4H
2
O: С 41.81, Н 4.48, N 8.41. ESI-MS, m/z: found 739.13 [M-Na] , required
7
39.13.
1
b*Sm. Yield 33 mg (0.04 mmol, 80%). Found, %: С 42.22, Н 4.33, N 8.25. Calculated for
-
C
29
H29SmN
5
O
8
Na*4H
2
O: С 42.43, Н 4.54, N 8.53. ESI-MS, m/z: found 727.12 [M-Na] , required
7
27.12.
The all characterization data for new compounds and complexes can be found in
Supplementary information.
3
. Results and discussion
Regarding to the synthesis of target ligands 1, they can be prepared via the tetra-tert-butyl
esters 2 from the corresponding 6-bromomethyl-2,2'-bipyridines 3 and DTTA ester 4, which can be
prepared by the described previously method [20]. In turn, bromomethyl group was obtained by
radical bromination of the methyl group in the α-position of the corresponding mono- or diaryl-

substituted-2,2′-bipyridines. Thus, the key step for the whole reaction sequence was the efficient
preparation of the aryl-substituted α-metyl-bipyridines 5 accordingly. The "1,2,4-triazine"
methodology is straightforward way for the preparation of substituted 2,2′-bipyridines [21]. In
particular, the preparation of 3-(6-methylpyridin-2-yl)-5,6-diphenyl-1,2,4-triazine 6a, as a key
precursor of compound 5a, by reacting the corresponding amidrazone 7 [18] and benzyl 8a was
reported previously [18]. Therefore this synthetic path was selected for the synthesis of target
ligands (Scheme 1). The monoaryl-substituted α-bromomethyl-2,2′-bipyridine 5b was obtained
similarly, by using the phenylglyoxal 8b [19] as a starting material. The corresponding α-
dibromomethyl-2,2′-bipyridines 9a,b, obtained as side-products of the radical bromination of the
methyl group, were also identified and separated by column chromatography. The alkylation of the
DTTA ester on the central nitrogen atom was carried out in dry acetonitrile under reflux, and 15-
2
0% of the corresponding α-hydroxymethyl-2,2’-bipyridines were observed as side-products.
Therefore, the column chromatography was done at this step for the product purification. As a final
step the removal of the tert-butyl protecting groups was carried out in the concentrated hydrochloric
acid, and the resulting ligands were isolated as hydrochloric salts. The number of HCl and water
molecules in the structure of the target ligands was determined by means of elemental analysis.

NH
N
NH
NH2
R
N
N
R
Ph
R
O
O
N
ii
7
iii
N
N
i
Ph
Ph
N
8a,b
6a,b
5a,b
COOR
COOBut
t
Bu OOC
N
ROOC
N
R
Br
N
H
COOBut
N
4
N
COOBut
R
N
Ph
N
3a,b
iv
N
N
COOR
Ph
N
+
R
COOR
R = But 2a,b
R = H 1a,b
v
N
CHBr2
Ph
N
Ar = Ph (a), H (b)
9a,b
Scheme 1. The preparation of target ligands for lanthanide cations 1. Reagents and
conditions: i) ethanol, 78 ºC, 10 h; ii) 2,5-norbornadiene, o-xylene, 143 ºC, 18 h; iii) NBS, benzoyl
peroxide, CCl , 76 ºC, 8 h; iv) K CO , acetonitrile, 82 ºC, 8 h; v) HCl (5N), r.t., overnight, then HCl
11N), r.t., 2 h, then acetonitrile, r.t., overnight.
4
2
3
(
Lanthanide complexes of the new ligands 1 were prepared according to previously described
procedures (for example, in [7]). Their structures were confirmed based on the elemental analysis as
well as mass spectrometry data (electrospray): in mass spectra the characteristic isotopic
distributions peaks were observed for all complexes (see for details Supplementary information).
The photophysical properties of new complexes as well as some previously reported complexes
(
Fig. 3) are shown in Table 1.

Fig. 3. Structures of previously reported ligands for lanthanide cations

Table 1. Photophysical properties of new complexes 1*Ln and
some previously published lanthanide chelates
a
-3
g
Entry Ligand,
Ref.
Ln
λabs., nm
λ
em.
,
ε, 10
-1
Ф
fluoresc.
,
Ф
Ln
,
τ
H2O
,
τ
D2O
,
q
-
b
-1
e
e
f
nm
191, 225sh, 309 410
M сm
10300
10500
10650
9650
%
%
-
ms
-
ms
-
c
c
c
d
1
2
3
4
1a
1a
1a
1b
Sm
Eu
Tb
Sm
8.7
4.1
4.5
2.8
233sh, 304
217sh, 306
194, 232,
392
400
357
3.2
0.81
2.33
0.67
0.05
-
-
-
-
-
-
-
250sh, 301
c
5
6
7
1b
1b
1b
Eu
Tb
Dy
230sh, 302
360
359
419
9700
9800
9690
3.5
2.9
0.6
27.1
-
1.1
1.27
-
2.415 0.29
d
197, 230, 302
2.18
-
1.13
-
c
205, 225sh
,
18.2
260sh, 305
8
9
1
1
1
1
1
1
1
1
1
1
2
10 [7]
Eu
Eu
Tb
Eu
Tb
Eu
Eu
Tb
Eu
Tb
Eu
Eu
Tb
327
279
279
309
309
341
295
295
295
295
356
347
347
-
-
-
-
-
-
-
-
-
-
-
-
-
12015
-
-
-
-
-
-
-
-
-
-
-
-
-
9.3
24
0.8
1.30
1.88
0.82
1.69
0.64
0.30
1.77
0.32
1.82
-
0.27
0.02
0.01
0.03
0.36
0.15
-0.01
0.2
11 [9]
-
1.25
0.78
1.15
0.59
0.27
1.24
0.31
1.25
-
0
1
2
3
4
5
6
7
8
9
0
11 [9]
-
15
12a [14]
12a [14]
12b [7]
13a [16]
13a [16]
13b [17]
13b [17]
14 [15]
15 [15]
15 [15]
6490
6590
8091
-
17
7
1.1
21
-
11
-
18
0
-
<0.001
14
-
10100
8300
8300
1.00
1.05
1.56
1.35
1.59
1.72
0.01
0.09
0
18
40
a
b
O at room temperature; fluorescence maxima in H
absorbtion maxima in H
2
2
O at room temperature; fluorescence
c
quantium yields were measured in water solution using quinine sulfate [22] or 2-aminopyridine [23] as standard;
d
e
lanthanide cations luminescence quantium yields in water solution were determined using optically matching solutions
e
f
3 2
of [Ru(bpy) ]Cl [24]; lanthanide cation luminescence lifetime in water; lanthanide cation luminescence lifetime in
g
O; the number of coordinated water molecules were calculated using the following formulas:
D
2
q
q
Eu = 1.2*(1/τH2O – 1/τD2O – 0.25) [25]
Tb = 4.2*(1/τH2O – 1/τD2O – 0.06) [26]
As it was expected, according to the photophysical data all new lanthanide chelates exhibited
the bathochromic shifts of the absorption maxima compared to the some of previously reported
complexes, for instance, those having such chromophores as 9-methyl-1,10-phenanthroline and its

4
,7-diphenylsubstituted derivative (although in this case the bathochromic shift was significantly
less). However, in comparison to previously 2,2'-bipyridine-based chelates, for instance complex
2a [14], or 5-aryl-2,2'-bipyridine (complexes 10 [7] and 12b [7]), the herein reported complexes of
1
ligands 1 exhibited the hypsochromic shifts of the absorption maximum. In our opinion, such
significant bathochromic shift for the previously reported 5-aryl-2,2'-bipyridines can be attributed to
the high degree of the conjugation between the β-aromatic substituent and 2,2'-bipyridine core due
to their closed to coplanar orientation.
Next the photoluminescent properties of the new complexes of lanthanides were studied and
compared with the previously reported ones. Unfortunately, in the presence of samarium and
dysprosium complexes exhibited low photoluminescence (less than 1%) while the residual
fluorescence quantum yield values were up to 8.7% in the presence of samarium cation, and up to
1
8.2% in the presence of the dysprosium one. For the dysprosium complex 1b*Dy the bathchromic
shift of fluorescence maximum up to 419 nm compared to the other complexes of ligand 1b was
observed. The europium complexes of the reported herein ligands exhibited the moderate
phosphorescence quantum yields up to 3.2%, which is, however, lower than the phosphorescence
quantum yields reported previously [7, 9, 15, 17] (entries 8-9, 11, 14, 16, 18-19) for other chelates.
At the same time, the herein reported complexes exhibited quite weak residual fluorescence with
quantum yield as low as 3.5% or 4.1%. The phosphorescence lifetime values of 0.81-1.1 ms of
europium complexes reported herein are comparable with that described previously for the most of
chelates (the maximum lifetime values of 1.25 ms were reported only for the chelates 11 [9] (entry
9
) and 13b [17] (entry 16).
As for terbium cation, much attention should be paid to high emission intensity observed for
the terbium complex of ligand 1b substituted with phenyl group in the α-position of 2,2′-bipyridine
core (the phosphorescence quantum yield was as high as 27.1%), despite the presence of one water
molecule in the first coordination sphere of the lanthanide, while the residual fluorescence quantum
yield was very low. It should be noted that among all the systems above, only in case of ligand 15
[
15] (entry 20) the greater value of the phosphorescence quantum yield of 40% was reported for
terbium chalate with the phosphorescence lifetime in water of 1.56 ms vs. 1.27 ms for the herein
reported complex 1b*Tb.
The terbium cation sensitization occurs due to energy transfer from the photoexcited ligand
5
5
4 0
to the higher-energy D level of terbium cation compared to the D level of europium, and, thus,
the extension of the conjugation system of the ligand usually does not contribute much to the
sensitization of the chelated terbium cation (for example, it was reported in the reference [27]). Most

probably, in this case a phenyl substituent at the α-position of one of the pyridine rings lies at a
substantial angle to the plane of 2,2′-bipyridine core, and, thus, the conjugation of the whole aryl-
bipyridine moiety is hampered. Introduction of one more phenyl ring in the β-position of the 2,2’-
bipyridine core (ligand 1a) caused the dramatic quenching of the photoluminescence of the resulting
terbium complex, and neither terbium cation luminescence quantum yield nor luminescence lifetime
could be detected. It worth to mention that in case of terbium complex of previously reported [14]
unsubstituted 2,2′-bipyridine chromophore (ligand 12a) the authors observed a moderate
photoluminescence of the terbium cation (phosphorescence quantum yield of 7%) (entry 12), and
the quantum yield of photoluminescence of the europium cation was much higher (17%) (entry 11).
The luminescence spectra of new chelates of europium cations (1a*Eu and 1b*Eu) and
terbium cations (1a*Tb and 1b*Tb) are presented in Fig. 3-4, the fluorescence spectra of all
chelates are presented in Fig. 5-6. The absorption spectra are presented in Supplemenary
Information (Fig. S1-S2).
350
300
250
200
150
100
1
a*Eu
1b*Eu
50
0
6
00
650
700
Wavelength, nm
Fig. 3. Europium cation luminescence spectra of complexes 1a*Eu and 1b*Eu
in water at room temperature

400
300
200
100
0
1
a*Tb
1b*Tb
4
50
500
550
600
650
700
Wavelength, nm
Fig. 4. Terbium cation luminescence spectra of complexes 1a*Tb and 1b*Tb
in water at room temperature
4
3
3
2
2
1
1
00
50
00
50
00
50
00
3
+
Eu
3+
Tb
3
+
Sm
50
0
350
400
450
500
550
600
Wavelength, nm
Fig. 5. Fluorescence spectra of complexes of ligand 1a in water at room temperature

600
500
400
300
200
100
0
3
+
+
Eu
Dy
Sm
3
3+
+
3
Tb
3
00
350
400
450
500
550
600
Wavelength, nm
Fig. 6. Fluorescence spectra of complexes of ligand 1b in water at room temperature
4
. Conclusion
Thus, in this paper we developed a convenient synthetic approach to the 5,6-diaryl and 6-
aryl-2,2'-bipyridines, substituted at the α-position of 2,2’-bipyridine moiety with the residue of
diethylenetriamine-N,N,N'',N''-tetraacetate (DTTA), as new ligands for lanthanide cations. In case of
the europium cation the obtained lanthanide complexes of new ligands exhibited a moderate
photoluminescence with a quantum yield of 3.2%. In the case of terbium cation the obtained
complex of the 6-phenyl-2,2′-bipyridine-based ligands exhibited quite intense photoluminescence
with a quantum yield of 27.1% and a lifetime of 1.27 ms, which exceeds the values reported
previously for the majority of terbium complexes.
Acknowledgment
This work was supported by the Russian Science Foundation (Grant # 15-13-10033) and the
Council for grants of the President of the Russian Federation (grant no. МК-644.2017.3) (for Dmitry
S. Kopchuk).
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