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Luminescent Eu3+ and Tb3+ Complexes of a Branched Macrocyclic Ligand Incorporating 2 2-Bipyridine in the Macrocycle and Phosphinate Esters in the Side Arms.

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a ) A . S. Gybin. W. A. Smit. R. Caple. A. L. Veretenov, A. S. Shashkov, L. G.
Vorontsova. M. G. Kurella, V. S. Chertkov, A. A. Carapetyan. A. Y Kosnikov. M . S. Alcxanyan, S. V. Lindeman. V. N . Panov, A. V. Maleev. Y. T.
Struchkov, S. M. Sharpe. J. A m . Chem. Soc. 1992. 114, 5555-5566; b) G . S.
Mikaelian. A. S. Gybin. W. A. Smit, R. Caple, TL/ruhedron L e t / . 1985, 26,
126’1 1272; c ) A. A . Schegolev, W. A . Smit. Y. B. Kalyan, M. Z. Krimer, R.
Caple, hid.1982. 23. 4419- 4422.
W .I Scott. M. R. Pcfia, K. Swird. S. J. Stoessel. J. K. Stille, J. Org Chem. 1985,
50. m - 2 3 n x .
G. T. Crisp. W. J. Scott. J. K Stille. J Am. CIi~rn.Soc 1984, 106. 7500-7506.
E. D. Bergman. D. Ginsburg. R. Pappo, Org. Reuc/. 1959, 10, 179- 555.
1 1 ) S. E. Denmark. K. L. Habermas, G. A. Hite. T. K. Jones, Tetrahrdruri 1986.
42. 2x21 2829; h) M . Ramaiah. Sj~r/iesi.s1984. 529-570; C. Santelli-Rouvier.
M . Santelli. i/nd 1983. 429-442.
Luminescent Eu3+ and Tb3 Complexes of a
Branched Macrocyclic Ligand Incorporating
2,2’-Bipyridine in the Macrocycle and
Phosphinate Esters in the Side Arms**
+
Nanda Sabbatini,” Massimo Guardigli,
Fabrizio Bolletta, Ilse Manet, and Raymond Ziessel*
Lanthanide ions. in particular Eu3+ and Tb3’, are interesting
luminescent species for fluoroimmunoassay (FIA) because of the
long lifetimes of their emitting states, which allow enhancement
of the sensitivity by time-resolved measurements.[’l However,
the Eu3+ and T b 3 + ions are characterized by low absorption
coefficients;”’ consequently, direct excitation of the ion results
only in low luminescence intensity. To overcome this problem,
complexes of these ions with efficient chromophores have been
prepared in order to obtain intense emission after an energy transfer from the excited ligand to the metal ion.
The first type of lanthanide complexes studied for application
in FIA are the Eu3+ chelate~.[~I
These complexes are widely used
in commercial kits, but the procedure is complicated because of
a) the use of two chelates. b) the insolubility of the luminescent
chelate in water, which is the solvent of interest in FIA, and c)
the need to protect the chelated ion from interaction with the
so1ven1.c31
More recently, a different approach to the use of lanthanide
ions in FIA, based on their complexation with cage-type ligands
incorporating chromophoric groups, aims at simplified procedures by using compounds that simultaneously show solubility
and kinetic inertness in water, shielding of the enclosed ion, and
intense metal luminescence. Among the species studied, complexes of branched macrocyclic ligands incorporating the 2,2’bipyridine (bpy) and the 1 .lo-phenanthroline chromophoric
groups have drawn special attention because of their high molar
extinction coefficients and efficient shielding of the enclosed
metal ion.[41For this class of compounds, only the Eu3 complex
of the ligand incorporating two bpy units in the macrocycle and
+
[*] Prof Dr. N . Sahbatini. Dip1 -Chem. M. Guardigli. Prof. Dr. F. Bolletta,
Dipl.-Cliem. 1. Manet
Dipartimmto di Chiinica ”G. Ciamician”, Universiti degli Stud1 di Bologna
Via Selmi 2. 1-40126 Bologna (Italy)
Tclefax: Int. code + (51)259-456
Ecole Europeenne dea Hautes Etudes des Industries Chimiques de Strasbourg
IPCMS. U M R n 46
1. rue Bliiiau Pascal. F-67008, Strasbourg Cedex (France)
[**I This \vork was supported by the Minister0 dell’universiti e della Ricerca
Scientificae Tecnologicd (Italy) and the Centre National de la Recherche Scientilique (France)
two bpy units in the branches shows a luminescence intense
enough to be interesting for application in FIA,14”, but the
complex undergoes decomposition when used in immunological
analyses, most likely because of weak coordination of the ion by
the bpy units in the side arms. Research is therefore directed at
introducing groups into the branches that are known to have
better ligating properties towards lanthanide ions.
In this paper we present the novel. branched
macrocyclic iigand 1,
which contains two bpy
Ph
moieties in the macro\p4
OMe
cycle and phosphinate
ester groups in the
Meo’
branches. The syntheses
of the ligand 1 and the
\ / \
[M 113+
complexes
(M = Eu, Tb, o r Gd) are
reported as well as their
1
photophysical
properties.
Ligand 1 has been synthesized as a mixture of diastereoisomers
in a straightforward manner by treating the bpy . bpy macrocycle[61 (that is, H at the positions of the phosphinate ester
groups) with paraformaldehyde and dimethylphenylphosphonite
under anhydrous conditions, in a procedure adapted from the
method described in the literature[’] (yield 45%, FAB-MS 731
[ M + + H I ) . The [M c l I 3 + complexes (M = Eu. Tb, or G d )
have been prepared as previously described:[*] [Eu c 1]CI, .
3H,O (yield 78%, FAB-MS 953 [ M + - Cl]); [Tb c l]CI, .
2H,O (yield 7 6 % , FAB-MS 959 [ M + - Cl]); [Gd c IICI, .
3 H,O (yield 79 %. FAB-MS 958 [ M - CI]). Interestingly, the
FT-IR spectra of these complexes display a significant shift
(17 cm-’) to lower frequency of the P - 0 stretching frequency
indicating, as expected, strong coordination of this group to the
metaI.[’l
om
yJ$XPh
+
Ph
13+
M (Eu, Tb, or Gd)
-.
=
0
M e 0 /r‘Ph
[Mcl]3+
All the photophysical properties of solutions of the Eu3’,
Tb”. and G d 3 + complexes in water were unchanged for several
days; these complexes are thus kinetically inert in this solvent.
The absorption spectra of the complexes (Fig. 1) are characterized by intense bands in the UV region. By analogy with other
lanthanide complexes of bpy-based l i g a n d ~ , [ ~these
” ] bands are
attributed to bpy z-z* transitions which undergo some red shift
upon complexation (Table 1). The shoulders in the 250-280 nm
region correspond to the weak absorption of the phenyl moiety.
Comparison of the absorption spectrum with the luminescence
excitation spectrum of the metal obtained upon excitation of the
ligand (Fig. 1) indicates that energy transfer from the excited
ligand to the emitting metal ion takes place; the emitting state
D-69451 Winheiin. I994
057U-OX33:94~1414-15013 ifi.OO+ .25!fJ
1501
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EX
t
of the lowest triplet excited state of 21 500 cm- obtained from
the highest energy feature of the phosphorescence of the
[Gd c Il3+ complex (Table I), lies above the Eu3+ 5D, and
Tb3+ 5D, emitting states and below the first excited state of the
G d 3 + ion, the behavior observed is ascribed to deactivation of
the ligand triplet excited state by energy transfer to the Eu3+ or
Tb3 ions. An analogous conclusion was drawn for other Eu3 '
and Tb3+ complexes of ligands containing bpy
Metal luminescence lifetime and quantum yields, obtained
upon ligand excitation under various experimental conditions,
are collated in Table 2. For both the [Tb t lI3+and [Eu c 113'
10
10-3
+
[ M cm-'1
I
I
230
280
L[nrn]
I
I
330
380
Table 2. Luminescence data of the metal ions [a]
Fig. 1. Absoi-ption (-)
and luminescence excitation ( - - ~ ) spectra of the
[Eu c I]" complex in water (similar absorption spectra were obtained for
[Tb c I]' ' and [Gd c Il3 + .and a similar luminescence excitation spectrum for
[Tbcl]").
Lit'ctime [ms] [b]
Complex
[Tb c 11"
.;o:,""
T;i:t
0.43
1.8
0.50
0.62 [d]
2.4
1.2
2.1
2.0
0.53 [d]
[Eu c 1)''
of the metal is clearly populated through absorption by the bpy
unit, while the involvement of the phenyl moiety cannot be
unequivocally assessed.
To study the behavior of the ligand-centered excited states in
the energy transfer, the properties of the lowest singlet and
triplet excited states belonging to the bpy moiety have been
investigated. The lifetimes of the singlet excited state of the
ligand and the fluorescence quantum yields of the ligand in the
Gd3'. Tb3 ', and E u 3 + complexes have been measured
(Table 1 ) . Comparison of the results obtained shows that
[Tb c
and [Eu c ]I3' exhibit fluorescence quantum yields
respectively about two times and fifty times lower than that of
[Gd c
This might imply an energy transfer from the lowest
singlet excited state of the ligand to the E u 3 + and Tb3+ emitting
states. Such a process should take place with a rate constant
greater than lO"s-' and 1 0 1 o s - ' for [ T b c Il3+ and
[Eu c lI3*, respectively (calculated from the fluorescence quantum yield values in Table 1). It is not possible to decide whether
the rate constant values are reasonable, because the only value
available for an analogous process refers to an energy transfer
from the ligand-centered triplet excited state.[''] Finally, it is
worthwhile noting that the lower quantum yield of [Eu c I l 3 +
relative to that of [Tb c lI3' may be due to nonradiative deactivation of the singlet excited state of the ligand to low-lying
metal states (ligand-to-metal charge transfer, LMCT) .[4, ' I
The lowest triplet excited state of the ligand has been investigated by studying the bpy phosphorescence and triplet-triplet
absorption in the [Eu c
[Tb c
and [Gd c lI3' complexes. Both these quantities could be measured for [Gd c lI3*
but not for [Eu c Il3' or [Tb c lI3' (Table 1). Since the energy
0.60
T300K
D:"
.;::
Quantum yield [c]
@A::",
""o: :@;
0.08
0.10 [d]
0.08
0.09
0.11 [d]
0.30
[a] In aerated solution unless otherwise noted. Excitation in the ligand absorption
band at 306nm [b] Experimental error 1 1 0 % . [c] Experimental error -30%.
[d] In deaerated solution.
complexes comparison of the lifetimes and quantum yields in
H,O and D,O solutions indicates that nonradiative deactivation through the 0 - H
occurs. By using the Horrocks and Sudnick
1.3 and 1.4 water molecules are
estimated to coordinate the metal ion in the [Tb c lI3+and
[ELIt lI3' complexes, respectively. In the [Tb c lI3' complex,
the strong temperature dependence of the lifetimes indicates
that an important role in the decay of the T b 3 + emitting state is
played by a thermally activated process. As previously suggested
for Tb3' complexes of other ligands incorporating bpy units,[4a1
such a process most likely involves the bpy lowest triplet excited
state. In fact, as mentioned above. this level lies at 21 500 cmthat is, 1100 cm-' above the Tb3+ emitting level, and therefore
it may be thermally populated at room temperature. Moreover.
the quenching of the Tb3+ luminescence by oxygen ( k , = 1.1 x
1 0 6 ~ - l ~,-obtained
l
from the values in Table 2) suggests that
the Tb3' 'D, level is in equilibrium with the bpy lowest triplet
excited state. In fact, the luminescent states of the lanthanide
ions are not quenched by oxygen;["' thus quenching of the
Tb3 ' luminescence reasonably involves the bpy lowest triplet
excited state. This hypothesis is supported by the observation that
the bpy lowest triplet excited state in [Gd c lI3+is quenched by
oxygen (k, = 5.0 x l o 8 M - ' s - ' , obtained from the lifetime values in Table 1 ) . The same behavior has previously been found
for analogous lanthanide
',
Table I.Abaorption, fluorescence. and phosphorescence data of the ligand 1 and its complexes with lanthanide ions [a]
Compound
Ground state absorption
;.,4r.
c,,, [nm. ~ - ' c i n - ' ]
i,,
[nm]
,
Fluorescence
T [bl [nsl
1 Id1
299.21 200
245. 16100
396
[Gd c lI3+
306. 14200
245. 9800
306. 15 300
353
-1
350
<l
= 360
<l
[Tb c 113 '
Q,
Triplet triplct absorption
T [bl [>I
La,
bml
[c]
T
[bl [sl
360
1 6 x 10-'[e]
47s [f] (445 [g])
1.6 [f]
5x10-'
375
0.36~10~'
1 . 5 l~o - ' [el
493 [h] (465 [g])
495 [el
1x
1.8 x
2x10-J
[I]
[Il
lil
111
1x
4
Phosphorescence
Lx
[nml
10-2
[h]
[el
246, 10 100
[Eu c
307. 15100
246, 9900
:
10-4
[a] In aerilted water at 300 K unless otherwise noted. [b] Experimentalerror 5 10%. [c] Experimentalerror :30%. [d] In aeratedmethanol at 300 K. unless otherwise noted.
[el In deaerated solution. [f] In butyronitrile at 77 K [sJ Highest energy feature in the pliosphorcscence spectrum. [h] At 77 K. [i] Not observed.
1502
('
K ' f I ~ ~ ~ ~ / u * . s ~ e . s r , / /i.i\h~H
l ~,~D-6Y4jl
ifI
U'hlrrim. 1994
US70-0K33:Y4~1414-ISI)
d /O.OO+ .?:a
Aiigebi.
Chein. I n [ . Ed. E q l . 1994. 33. No. 14
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In conclusion, the [Eu c l I 3 and [Tb c l I 3 complexes show
interesting properties for applications in FIA. They are kinetically stable in water, and the metal ions are well protected
against deactivation of the luminescent excited states by water.
Moreover, the luminescence intensity is rather high, in spite of
the relatively low molar extinction coefficients resulting from
the presence in the ligand 1 of only two efficient chromophores.
Substitution of the weakly absorbing phenyl units in the phosphinate groups by efficient chromophores should result in an
even more intense luminescence, if absorption is followed by efficient energy transfer to the metal ion. As mentioned in the discussion of the luminescence excitation spectra of the metal, the
involvement of the phenyl moiety in the energy transfer to the
metal ion cannot be proved. However, for lanthanide complexes
containing phosphinic o r phosphonic groups incorporating
benzyl or phenyl units a quite efficient energy transfer has recently been reported.' 41
+
V. Balzani. I.-M. Lehn, J. van de Loosdrecht. A. Mecati. N. Sabhatini. R.
Ziessel, Angrn.. Clzem. 1991, 103, 186- 187: Angew. Chrm. Inf. Ed. En:nx/.1991,
30. 190-191.
G . R. Newkome, S. Papalardo, V. K. Gupta. F. R. Fronczek. J. Or,q. (%rm.
1983. 48, 4848 -4851. and references therein.
C. J. Broan. E. Cole, K. J. Jankowski, D. Parker. E. Pulukkody. B. A. Boyce.
N. R. A. Beelep, K. Miller, A. T. M i l k a n . Swlhesi.s 1982, 63-68.
V. Balzani. E. Berghmans. J - M . Lehn. N. Sabbatini. R. Terorde, R. Ziessel.
Heh'. Chiin. Arru 1990, 73. 2083 -2089.
A. D.Buss, W. B. Cruse. 0 . Kennard, S.Warren, J. Chpm. Soi.. Prrkin Truns.
1992, 675-681: R. Babecki. A. W G . Platt. J. Fawcett. J. Chmr. S o ( . Ddtori
Truns. 1984. 243-247.
B. Alpha. R. Ballardini. V. Balzani. J.-M. Lehn. S. Perathoner. N . Subhatini.
Phofochmz. Photohiol. 1990. 52, 299 306.
G . Blasse. Slrucr. Bonding /Bcr./in) 1976. 26,43 19.
G.Stein. E. Wurzherg, J. Chem. Phrs. 197562. 208-213: Y. Haas. G . Stein. J.
Phjz. Chenz. 1971. 75. 3677-3681.
W. Dew. Horrocks. D. R. Sudnick. Arc. Chem. Re.\. 1981. 14. 384-392.
M. Murru. D. Parker, G. Williams, A. Beeby. J. CIiwn. Sw. C'him Cummini.
1993, 1116-1118: N. Sato, M. Goto. S. Matsumoto. S. Shinkai. Trrrralzedrron
Lrtt. 1993. 34, 4847-4850.
+
'
E--qwinicntal Procedure
1: A suspension of the bpy . bpy macrocycle (200 mg, 0.51 mmol) and anhydrous
paraformaldehyde (350 mg) in T H F (100 mL) was heated at 60 'C for 2 h. Then,
dded under argon, and the
dimethylphen).lphosphonite (0.24 mL. 1.52 mmol)
mixture was heated at reflux for 24 h in a Soxhlet apparatus containing 3 A molecular sieves ( 1 0 g). After cooling to room temperature the solvent was evaporated,
and the revdue was dissolved in the minimal amount of CH,CI, (about 20 mL).
After filtration over celite. hexane (about 35 nil) was added as a cotinter solvent.
Slow evaporation of the solvent caused the precipitation of the pure, white polymethylenephosphinate ester 1 as a diastereoisomeric mixture (yield 45%). U V N I S
(MeOH)-i,,,,[nm](E) = 299(21200). 245(16100). 'HNMR(200.1 MHz.CDCI,.
25°C): d = 8 3 3 (d, 4H. 'J(H. H) = 8.1 Hz), 7.83 7.41 (m, 14H), 7.23 (d, 4H,
'J(H. H ) =7.5 H r ) , 3.71 (d, 6 H . 'J(P, H) =11.6Hz. OCH,). 3.93 ( s , XH, CH,bpy), 3.03 (d. 4H. "(P. H) = 6.5 Hz. CH,P). 1 3 C ( ' H }N M R (50.3 MHz, CDCI,.
25 C ) :(5 = I 5 6 3 3 (quart. C).151.93 (quart. C),148.76 (CH). 133.30(CH), 132.35
( d . 3 J ( P . C ) = 10Hr.n-Ar). 131.56(CH).130.30(d.'J(P.C)=12OHz,C(Ar)(P)).
129.63 (CH). 128.05 (d. ' J ( P , C ) = 1 3 Hz, o-Ar). 61.73 (CH2-bpy). 59.40 (d.
'J(P, C)= 123 Hz. CHIP), 53.04 (d. *J(P. C) = 7 Hz. OCH,). 3 1 P ( 1 H }N M R
(81.0 MHr. CDCI,, 25 -C): 6 = 41.76 (s). MS (FAB' in m-nitrobenrylalcohol (mNBA) a s matrix): in.': 731 ( M ' + H ) . FT-IR (KBr pellet): i.[cin-'] = 2927. 2857,
1730. 1595. 1577. 1439. 1176 (P=O). 1122. 1035, 796. Anal. Calcd. for
C,,H,,~N,O,Pz ( M r = 730.75).
Lanthanide complexes: To a solution of 1 (30 mg, 0.04 mmol) in CH,CI, (2 mL) an
equimolar quantity of the lanthanide salt (MCI, . 6 H 2 0 . M = Eu, T b or Gd),
dissolved i n methanol (3 mL) was added. After 2 h heating at 60 C, the solvent was
removed under reduced pressure. and the residue was recrystallized twice by slow
diffusion of diethyl ether into a n ethanol solution, [Eu i IICI, . 3 H,O (yield 78%).
UViVIS (H,O): j.,,,[nm] (c) = 307 (lSlOO), 246 (9900). MS (FAB' in m-NBA):
m : z 9 5 3 ( M * C1).918(M' -2CI) FT-IRjKBrpellet): F = 1 1 5 9 c m - ' ( P = O )
3 H,O (Mr = 989.07 + 54.05): [Tb c l]CI,
Anal. Calcd. for C,,H,,,N,O,P,EuCl,
. 2H,O (yield 7 6 % ) . UVIVIS (H,O): >.,,,[nm](~) = 306(15300), 246(10100). MS
(FAB' in ni-NBA): w ; z 959 ( M t - CI). 924 (M' - 2C1). FT-IR (KBr pellet):
i. = 1 1 5 9 c m - ' ( P - 0 ) . Anal. Calcd. for C,,H,,N,O,P,TbCI,~
2H,O ( M r =
996.03 + 36.06): [Gd c 1lC1,. 3H,O (yield 79%). UV,'VIS (H,O): &,,,,[nm]
( t : ) = 306 (14200). 245 (9800). MS (FAB' in m-NBA): nz;z 9% ( M ' - Cl). 923
( M ' - 2 C I ) . FT-IR (KBr pellet): i.=1159cm-' ( P - 0 ) . Anal. Calcd. for
C,,H,,,N,.O,P,CrdCl,
. 3 HIO (Mr = 994.36 t 54.05).
A New Class of Novel Macrocyclic Mesogem**
Peter R. A s h t o n , Detlev Joachimi, Neil Spencer,
J. Fraser Stoddart,* Carsten Tschierske,
Andrew J. P. White, David J. Williams,
and Kerstin Zab
Since Pedersen"] announced his discovery of the crown ethers
in 1967, the amazing ability of these compounds to form complexes with a wide range of species, including alkali metal and
alkaline earth metal cations and ammonium and alkylammonium
ions, has had a widespread influence on the subsequent development of supramolecular chemistry.['] In retrospect. therefore, it
is hardly surprising that crown ethers, and the structurally related aza-crown ethers, have also been used131as building blocks in
liquid crystal chemistry.
More recently we have shownr4"]that nelectron-deficient aromatic dications such as paraquat 1" can be complexed. as its
bis(hexafluor0phosphate) salt, by crown ethers containing nelectron-rich arenes. Indeed, the macrocyclic polyether 2 proved
~
'
Received: December 27, 1993
Revised version: March 18. 1994 [Z 6579 IE]
German version: Angew. Chem. 1994. 106, 1543
[ l ] E. Soini. I . Hemmili, Clin. Chrm. 1979. 25, 353-361: J.-C. G.Bunzli in LanIkunidL, Prohrs in LiJe,Chmiiculand E u r h Scimrrs (Eds. J:C. G . Bunzli. G . R.
Choppin). Elsevier. Amsterdam. 1989. Chap. 7.
[2] B. R. Judd, Plzw. Rev. 1962, (27.750-761 ; G. S. Ofelt, J. Chem. Ph~..s.1962,
37. 511 520.
[3] I. Hemmilii, S. Dakubu, US-B 4565790, 1986: I. Hemmili. A i d . Chenz. 1985,
57. 1676 1681: I. Hemmili. S. Dakubu. V.-M. Mukkala, H. Siitari. T.
LBbgren. A n d . Biochem. 1984. 137. 335-343: T. Taketasu. Tulunra 1982. 29.
397-400: T. Shigematsu, M. Matsui, R. Wake, A d . Chim. Actu 1969, 46,
101 -106.
[4] a ) N Sabbatini, M. Guardigli. J:M. Lehn. Coord. C%mz. Rre. 1993. 123,
201 228. and references therein. b) N. Sabbatini. M. Guardigli, F. Bolletta, I .
Manet. R . Ziessel, N r w J. Cliem. 1993. 17, 323-324: N. Sabbatini, M.
Guardigli, I . Manet, F. Bollettd. R. Ziessel, Inorg. Chem., 1994. 33, 955959.
Angew. Chen?.I n [ . Ed. Engl. 1994, 33. No. 14
C YCH
12+
0
0
0
0
u
o
- uu
2
to be one of the most efficient molecular receptors for bipyridinium dications. These adducts-sustained
by n-n aromatic
stacking and electrostatic interactions, including hydrogen
[*I Prof. J. F. Stoddart, P. R. Ashton. Dr. D. Joachimi, Dr. N . Spencer
School of Chemistry, University of Birmingham
Edgbdston, Birmingham B l 5 2TT (UK)
Telefax: Int. code +@I) 414-3531
Dr. C. Tschierske, K . Tab
Institut fur Organische Cheinie, Martin-Luther-Universitit Halle-Wittenberg
Halle/Saale (FRG)
[**I
Dr. A. J. P. White. Dr. D. J. Williams
Chemical Crystallography Laboratory
Department of Chemistry, Imperial College. London. SW7 2AY (UKI
This work was supported by the German Academic Exchange Service (DAAD)
and by the Science and Engineering Council (SERC) in the United Kingdom.
~rlugsgesellschufrmbH, D-69451 Weinhrin?, 1994
0570-0833/94/1414-1503IF lO.OO+ 2SY1
1503
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luminescence, bipyridine, eu3, tb3, Arms, macrocyclic, complexes, ligand, phosphinate, branches, side, esters, incorporation
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