Clicked dipicolinic antennae for lanthanide luminescent probes

Article abstract of DOI:10.1039/c002982c

4-Triazolyl-dipicolinic acids, prepared efficiently by CuAAC, proved to act as efficient antennae for optical lanthanide probes containing Eu³⁺ or Tb³⁺, under linear and non linear excitations (one, two and three photons provided by

Full text of DOI:10.1039/c002982c

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Clicked dipicolinic antennae for lanthanide luminescent probes†
Zein El Abidine Chamas,a Xianmin Guo,b Jean-Louis Canet,*c,d Arnaud Gautier,a,d Damien Boyer*e, f and
Rachid Mahioub, f
Received 12th February 2010, Accepted 12th May 2010
First published as an Advance Article on the web 25th June 2010
DOI: 10.1039/c002982c
4-Triazolyl-dipicolinic acids, prepared efficiently by CuAAC, proved to act as efficient antennae for
optical lanthanide probes containing Eu3+ or Tb3+, under linear and non linear excitations (one, two and
three photons provided by laser induced luminescence). The versatility offered by the substitution of
the triazole subunit is, in addition, useful for covalent linkage to slide glass providing luminescent films.
Introduction
The recent emergence of “click chemistry” as a new way of catego-
rizing organic reactions has facilitated an extraordinary expansion
in the number of molecules available for medicinal chemistry,
biology and material sciences.1 Among “click” synthetic tools, the
copper(I)-catalyzed azide alkyne cycloaddition (CuAAC) has re-
ceived unrivalled attention and has been found to be of paramount
importance to attach fluorescent probes to films, nanoparticles and
biomaterials.2 Fluorescent lanthanide complexes present several
advantages3 compared to regular organic dyes: insensitivity, to
oxygen and moderate warming, and to the local environment,
narrow electronic transitions with large Stokes shifts, long excited-
state lifetimes and high luminescence intensities induced by
Fig. 1 Representative DPA-based antennae.
These ligands are classically synthesized by palladium coupling
(1–3), however, their synthesis is not straightforward, especially if
further functionalizations are envisaged.6 Moreover, the absorp-
tion wavelength depends on the attached group. Changing the
absorption range, if needed, would require additional synthetic
work. To circumvent the aforementioned efforts, we assumed that
a 1–4 subsituted 1,2,3-triazole moiety could serve as relevant and
adjustable antenna, allowing good triplet sensitizing properties on
a large absorption domain (Fig. 2).7
increasing significantly the absorption cross-section (in these
systems, energy is absorbed by the ligand and efficiently transferred
to the emitting metal ion via the so-called antenna effect or
Absorption-Transfer-Emission – ATE – mechanism). All these
characteristics explain that considerable attention is presently
devoted to the design of Light Conversion Molecular Devices
based on lanthanides for bioimaging applications.4 Pyridines and
terpyridines subunits are by far the most common chromophores
used for luminescent lanthanide complexes, as these chemical
antennae enjoy strong light absorption and triplet sensitizing
properties. A wide range of conjugated dipicolinic acid (DPA)
derivatives (Fig. 1), recently synthesized, exhibit a high absorption
coefficient, broad excitation range, and efficient energy transfer
giving rise to significant improvements in detection sensitivity.5
aClermont Universite´, Universite´ Blaise Pascal, Laboratoire SEESIB, BP
10448, F-63000, Clermont-Ferrand, France
bClermont Universite´, Universite´ Blaise Pascal, Laboratoire des Mate´riaux
Inorganiques, BP 10448, F-63000, Clermont-Ferrand, France
Fig. 2 Click strategy to construct new antennae and materials.
cClermont Universite´, ENSCCF, Laboratoire SEESIB, BP 10448, F-63000,
Clermont-Ferrand, France. E-mail: j-louis.canet@univ-bpclermont.fr;
Fax: +33 (0)4 73 40 77 17; Tel: +33 (0)4 73 40 70 32
We then decided to synthesise a set of 4-triazolyl-DPA, contain-
ing electron withdrawing and electron donating groups in order
to study the electronic influence on the luminescence properties of
corresponding Tb(III) and Eu(III) chelates.
To allow for their use as chromophores in fluorescence based
bioassays or as biomarkers for medical imaging, these Ln com-
plexes should be covalently grafted to solid supports. Further-
more, these fluorescent materials must withstand the heating
temperature upon light radiations. To fulfil such requirements,
dCNRS, UMR 6504, SEESIB, F-63177, Aubie`re, France
eClermont Universite´, ENSCCF, Laboratoire des Mate´riaux Inorganiques,
BP 10448, F-63000, Clermont-Ferrand, France. E-mail: damien.boyer@
univ-bpclermont.fr; Fax: +33 (0)4 73 40 71 08; Tel: +33 (0)4 73 40 76
47
f
CNRS, UMR 6002, LMI, F-63177, Aubie`re, France
† Electronic supplementary information (ESI) available: photolumines-
cence spectra, decay curves, films preparation and characterization. See
DOI: 10.1039/c002982c
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Table 1 Yields of 7a–d
organic-inorganic hybrids have been achieved by a sol-gel process
from Ln complexes bearing an alkoxysilane moiety. The sol-gel
process is a common way to make such materials due to its mild
conditions.5b,d The optical properties are provided by the Ln-doped
organic moiety while the shaping as well as the mechanical and
thermal resistances are brought by the silica network. In this paper
are reported preliminary investigations undertaken to prepare
strongly fluorescent films, based on lanthanide activated hybrid
materials coated onto glass substrates.
Entry Alkyne
Cu(I)/THPTA
Cu(I)/NHC
1
2
3
4
6a phenylacetylene
94%
94%
98%
100%
90%
6b 4-methoxyphenylacetylene 95%
6c 4-nitrophenylacetylene
6d propargyl alcohol
93%
92%
Results and discussion
Ligand synthesis
The 4-azido DPA derivative 4a was synthesized in high yield
from dimethyl 4-chlorodipocolinate8 by an aromatic nucleophilic
substitution with sodium azide, in DMF at 50 ◦C during 24 h. The
pure and stable product 4a, prone to precipitate in water, is easily
obtained by a simple filtration, making this procedure amenable
on a multigram scale (Scheme 1).
Fig. 3 General synthesis of 1,2,3-triazoles.
Scheme 1 Synthesis of dimethyl 4-azidodipicolinate.
The CuAAC reaction was firstly tested with CuSO4 (30 mol %)
and ascorbic acid (60 mol %). Unfortunately, this reaction proved
to be too slow (48 h) and yields were disappointing, probably
because of a competitive chelation with the pyridyl substrate.
To circumvent this matter, we turned our attention to ligands
known to bind copper(I) and displaying strong rate acceleration
effects. Indeed, several nitrogen containing ligands were
considered, such as TBAT (tris-(benzyltriazolylmethyl)amine),
Fig. 4 Saponification of clicked dipicolinate esters.
THPTA
(tris(3-hydroxypropyltriazolylmethyl)amine)
and
(BimC4A)3, all of them requiring the presence of a sacrificial
reducing agent.9 Newly reported catalytic systems, to allow a
CuAAC reaction in reducing agent free conditions, were also
considered, (namely: [Cu(C186tren)]Br, tris(triazolyl)methanol
copper(I), (Aminoarenethiolato) copper(I) and the copper(I)
N-heterocyclic carbenes [CuBr(SIMes)], [CuCl(Phen)(SIMes)],
Complex synthesis
Corresponding solid lanthanide complexes 9a–d and 10a–d were
prepared using, respectively, europium chloride and terbium
nitrate, following Andraud and Maury’s procedure.11 Accordingly,
complexes 9–10 were obtained within a few minutes by addition of
the lanthanide to an aqueous solution of 8a–d guanidinium salts,
and were quantitatively isolated by simple filtration (Scheme 2).
Overall, the synthesis of the ligands and the complexes were
conducted without any tedious purification.
[CuCl(SIMes)(4,7-dichloro-1,10-phenanthroline)]).10
Among
these possibilities, THPTA and [CuCl(SIMes)(4,7-dichloro-1,10-
phenanthroline)] were tested. To our delight, the triazoles 7a–d
formed in a very efficient manner from 4a using both catalysts.
The reactions proceed very efficiently and extremely fast as
completion is reached in approximately 30 min for the former and
10 min for the latter (Fig. 3).
Luminescence properties
It has to be noticed that the reactions are conducted in an open
vessel and, in most cases, the products precipitate at completion of
the process, satisfying the Click criteria.1b The exception is ligand
7d that contains an alcohol function for which a simple extraction
may be necessary. The yields for the CuAAC reactions are gathered
in Table 1.
Finally, targeted DPA derivatives 8a–d were obtained quantita-
tively, cleanly and without purification, by saponification of diester
7a–d followed by acidification (Fig. 4).
All the measurements were performed on solid state samples.
Each complex exhibits an excitation spectrum featuring a
broad absorption band within the near-UV range, with a shift
of the maximum depending on the substituting groups on the
triazole subunit. This signal was assigned to an S0→S1 absorption
transition within the organic chromophore. On the basis of
excitation spectra and for any rare earth ion, the presence of
electron withdrawing groups results in a redshift of the maximum
absorption. For both types of lanthanide complexes, the maximum
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Table 2 Maximum excitation wavelengths for lanthanide complexes
Europium complexes
Terbium complexes
9a : 341 nm
9b : 374 nm
9c : 387 nm
9d : 301 nm
10a : 340 nm
10b : 370 nm
10c : weak fluorescence
10d : 340 nm
Tb3+ transitions. Samples 9a–d, 10a–b, and 10d exhibit remarkable
fluorescence confirming that a very efficient ATE mechanism takes
place. Very weak fluorescence was observed for compound 10c.
This feature is probably due to the strong electron withdrawing
effect of the nitro group that stabilizes the singlet and triplet states
of the ligand. Thus, the triplet state probably lies too low for
5
Scheme 2 Synthesis of clicked DPA complexes.
an efficient electron transfer to the D4 level of the terbium. The
decays for complexes 9a–d and 10a–d are given in Table 3.
excitation wavelengths are gathered in Table 2 while excitation and
emission spectra of compounds 9a–d are presented in Fig. 5 (for
10 see ESI†).
Despite the fact that quantum yields are not reported (due to
absence of specific device), two complexes demonstrate promising
properties with fluorescence intensities much stronger than other
samples i.e. complexes 9b and 10d. They were retained to
measure fluorescence properties upon pulsed OPE (One Photon
Excitation), TPE (Two Photon Excitation) and THPE (Three
Photon Excitation) regimes. Linear (OPE) and non-linear (TPE
Emission spectra were recorded within the visible range upon
excitation at the maximum absorption wavelength for europium
and terbium complexes. They consist, respectively, of characteris-
7
7
tic 5D0→ FJ (J = 1–2) and 5D4→ FJ (J=6–3) emission bands of Eu3+ and
Fig. 5 (a) Excitation and (b) emission spectra recorded at RT from europium complexes. (c) Excitation and (d) emission spectra recorded at RT from
terbium complexes. Emission spectra were recorded upon excitation at wavelengths given in Table 2.
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Table 3 Constants of decay times for europium and terbium complexes
Table 4 Maximum excitation wavelengths and constants of decay times
recorded from samples 9b and 10d upon OPE, TPE and THPE conditions
Europium complexes
Terbium complexes
9b (lem.= 616 nm) Decay/ms 10d (lem.= 554 nm) Decay/ms
9a : 0.87 ms
9b : 0.84 ms
9c : 0.85 ms
9d : 1.12 ms
10a : 0.28 ms
10b : 0.04 ms
10c : no signal
10d : 0.67 ms
1 photon 374 nm
2 photons 762 nm
3 photons 990 nm
0.84a
1.09b
N.D.c
340 nm
757 nm
996 nm
0.67a
0.58b
N.D.c
a Excitation at 337 nm. b Excitation at 762 nm. c Not determined.
and THPE) time resolved emission spectra are consistent with the
characteristic optical features of Eu3+ and Tb3+ ions embedded in
9b and 10d complexes respectively (see ESI†).
7
The decay curves of the Tb3+ 5D4→ F5 transition (547 nm)
indicate an approximately single exponential profile with lifetime
around 0.6 ms under OPE or TPE regimes. To the contrary
The TPE and THPE processes are unambiguously confirmed
7
by the quadratic and cubic dependence of the 5D0→ F2 (616 nm)
the decay curve resulting from the Eu3+ 5D0→ F2 transition
7
5
7
and D4→ F5 (554 nm) emissions with the laser power (TPE:
lexc = 760 nm; THPE: lexc = 957 nm) as shown in Fig. 6 for
compound 9b. The same quadratic and cubic dependences are
observed for these anti-Stokes emissions under the experimental
conditions employed for both samples. The TPE and THPE
maximum wavelengths fit quite perfectly with those recorded by
OPE, indicating that the excited states reached by such processes
are the same and the ATE mechanism occurs. Such results are very
promising for future biphotonic or multiphotonic applications.12
is bi-exponential in OPE conditions while exhibiting a single
exponential shape with a time constant of 0.97 ms in the case
of TPE conditions (see ESI†). These results are presently not
totally explained but may be due to differences in the selection
rules between OPE and TPE regimes and the possible existence of
two sites for the Eu3+ ion.13 All the data are gathered in Table 4.
Grafting on solid support
The first application of these new lanthanide complexes consisted
of the preparation of luminescent films, covalently fixed on glass
slides. For this purpose, functionalizable ligand 7d was treated with
isocyanate 11 to afford the carbamate 12 (Scheme 3).
Scheme 3 Method for glass surface coating.
To our pleasure, deposition from an ethanol solution of (3 : 1)
12 : Ln3+ onto a glass substrate by the spin-coating method led
to transparent, smooth and homogeneous films with a thickness
close to half a micrometre as demonstrated by scanning electron
microscopy and profilometry analyses, respectively (see ESI†). In
Fig. 7, pictures of the resulting films are shown without and with
UV excitation (365 nm). The strong luminescence resulting from
these samples emphasizes the outstanding capabilities of these
rare earth ion doped hybrids to be used as advanced phosphors
in biolabelling applications. Detailed emission spectra recorded at
room temperature upon 365 nm excitation are presented in the
ESI†.
7
Fig. 6 (a) quadratic and (b) cubic dependence of the 5D0→ F2 (616 nm)
emission with the laser power (TPE: lexc = 760 nm; THPE: lexc = 957 nm)
in compound 9b. The straight line corresponds to the linear fit of the
experimental data.
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General procedure for 7a–d (CuAAC reactions)
Method A (Cu(I)/THPTA). Azide 4a (236 mg, 1 mmol,
1.0 eq.) is suspended in 20 mL of methanol and the appropriate
alkyne (1.5 mmol, 1.5 eq.) is added. Then, 200 mL of copper
complex (0.1 M in aqueous stock solution, 0.02 mmol, 2 mol %)
followed by 600 mL of ascorbic acid (0.1 M in aqueous solution,
0.06 mmol, 6 mol %) are added. The solution turns from green
to yellow. After 10–20 min the solution returns to green and,
if necessary, an additional 600 mL of ascorbic acid is added. In
the cases of 7a–c the product deposits during the reaction. In
these cases the products are obtained pure after a simple filtration
followed by washing with cold methanol and ether. In the case of
compound 7d, the reaction is evaporated to 1/3 of the volume.
20 mL of water is added and the solution is extracted with
3 ¥ 30 mL of CHCl3. Combined organic extracts are dried over
MgSO4, filtered and then evaporated to furnish pure compound.
Fig. 7 Pictures of coatings achieved from compounds 13a (terbium
complex) and 13b (europium complex) without (left) and with (right)
excitation by UV light at 365 nm displaying respectively green and red
emission.
Conclusion
In this report, we have disclosed an elegant, practical and straight-
forward synthesis of adjustable antennae for DPA lanthanide-
based probes. Complexes exhibit one, two and three photon
excitation properties that are of great interest for biomedical
applications. Finally, coating these luminescent complexes on
glass support using a sol-gel process paves the way for future
applications. For this purpose the grafting of modified “clicked”
lanthanide complexes onto silica nanoparticles is currently under
study. Resulting core-shell type luminescent nanohybrids will be
then evaluated as new bio-imaging sensors.
Method
B [CuCl(SIMes)(4,7-dichloro-1,10-phenanthroline)].
Azide 4a (236 mg, 1 mmol, 1.0 eq.) is suspended in 20 mL of
methanol and the appropriate alkyne (1.5 mmol, 1.5 eq.) is added.
Then, copper complex (13 mg, 2 mol %) is added in one portion.
In cases of 7a–c the product deposits during the reaction. In
these cases the products are obtained pure after a simple filtration
followed by washing with cold methanol and ether. In the case of
compound 7d, the reaction is evaporated to 1/3 of the volume.
20 mL of water are added and the solution is extracted with
3 ¥ 30 mL of CHCl3. Combined organic extracts are dried over
MgSO4, filtered and then evaporated to furnish pure compound.
Experimental
General procedure for 4b, 8a–d
Chemistry
To a 5 mL suspension of diester (1 mmol) in water is added 4 mL
of aqueous NaOH (1 M). The reaction mixture is heated at 50 ◦C
until total disappearance of the starting material after which the
temperature is maintained for an additional 2 h. After cooling to
room temperature, HCl (3 M) is added dropwise until pH = 3. The
desired diacid precipitates, and is isolated after simple filtration
followed by washing with water and drying under vacuum.
NMR spectra were recorded in Fourier Transform mode with
a Bruker AVANCE 500 spectrometer (1H at 500 MHz) or a
Bruker AVANCE 400 spectrometer (1H at 400 MHz, 13C at 100
MHz), at 298 K. Data are reported as chemical shifts (d) in ppm.
Residual solvent signals were used as internal references (1H, 13C).
Electrospray (positive mode) high-resolution mass spectra were
recorded on a Q-TOF micro spectrometer (Waters), using an
internal lock mass (H3PO4) and an external lock mass (leucine-
enkephalin [M + H]+: m/z = 556.2766). IR spectra were recorded
on a Shimadzu Fourier Transform Infrared Spectrophotometer
FTIR-8400S.
Dimethyl 4-(4-phenyl-1H-1,2,3-triazol-1-yl)pyridine-2,6-
dicarboxylate (7a)
Pale yellow solid. Mp: 240 ◦C, Rf : 0.35 (ethyl acetate–cyclohexane:
1 : 1).1H NMR (400 MHz, DMSO-d6) d (ppm): 9.84 (1H, s), 8.81
(2H, s), 7.99 (2H, d, J = 8 Hz), 7.53 (2H, dd, J = 7 and 8 Hz), 7.43
(1H, t, J = 7 Hz), 3.99 (6H, s).13C NMR (100 MHz, DMSO-d6) d
(ppm): 163.8, 149.6, 148.0, 144.7, 129.4, 129.0, 128.6, 125.3, 119.9,
116.8, 52.9. IR (KBr) n/cm-1: 3125, 2957, 1750, 1717, 1599, 1446,
1251, 1223, 1153, 1119, 1047, 1019, 987, 947, 892, 782, 756, 692.
HR-ESI-MS calculated for C17H14N4O4Na [M + Na]+: 361.0913,
found: 361.0899.
Synthesis of dimethyl 4-azidopyridine-2,6-dicarboxylate (4a)
A mixture of dimethyl 4-chloropyridine-2,6-dicarboxylate (2.2 g,
9.56 mmol, prepared according to reference 8) and sodium azide
(6 g, 10 eq.) in DMF (30 mL) is heated at 50 ◦C overnight.
The yellow reaction mixture is cooled down to room temperature
and poured onto 80 mL of cold water under vigourous stirring.
Compound 4a precipitates immediately and a filtration affords
2.0 g (90 %) of a pale yellow solid. Mp: 160 ◦C. Rf : 0.35 (AcOEt–
Cyclohexane = 1 : 1). 1H NMR (400 MHz, CDCl3) d (ppm): 7.93
(2H, s), 4.03 (6H, s). 13C NMR (100 MHz, CDCl3) d (ppm): 164.5,
151.7, 149.9, 118.0, 53.4. IR (KBr) n/cm-1: 3075, 2960, 2122, 1753,
1718, 1594, 1445, 1351, 1273, 1250, 1190, 1158. Anal. Calcd for
C9H8N4O4: C, 45.77; H, 3.41; N, 23.72. Found: C, 45.19; H, 3.41;
N, 23.75.
Dimethyl 4-[4-(4-methoxyphenyl)-1H-1,2,3-triazol-1-yl]pyridine-
2,6-dicarboxylate (7b)
Pale yellow solid. Mp: 260.4 ◦C. Rf : 0.21 (ethyl acetate–
cyclohexane: 1 : 1). 1H NMR (400 MHz, DMSO-d6) d (ppm): 9.73
(1H, s), 8.80 (2H, s), 7.91 (2H, d, J = 9 Hz), 7.10 (2H, d, J =
9 Hz), 3.99 (6H, s), 3.82 (3H, s). 13C NMR (100 MHz, DMSO-
d6) d (ppm): 163.8, 159.5, 147.9, 144.7, 126.8, 121.9, 118.9, 116.8,
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114.4, 55.1, 52.9. IR (KBr) n/cm-1: 3143, 2954, 1748, 1716, 1597,
1479, 1438, 1360, 1323, 1249, 1186, 1156, 1124, 1050, 1030, 956,
846, 752. HR-ESI-MS calculated for C18H16N4O5Na [M + Na]+:
391.1018, found: 391.1000.
4-[4-(Hydroxymethyl)-1H-1,2,3-triazol-1-yl]pyridine-2,6-
dicarboxylic acid (8d)
◦
1
White solid. Mp: 225 C. H NMR (400 MHz, D2O) d (ppm):
9.20 (1H, s), 8.73 (2H, s), 4.63 (2H, s). 13C NMR (400 MHz,
D2O + NaOH): 171.2, 155.1, 150.7, 144.8, 121.4, 115.3, 54.9. IR
(KBr) n/cm-1: 3575, 3160, 1726, 1599, 1482, 1430, 1149, 1230,
1166, 1048, 1007, 964, 904, 823, 759, 723, 677. HR-ESI-MS
calculated for C9H7N4O3 [M - CO2]+: 219.0518, found: 219.0524.
Dimethyl 4-[4-(4-nitrophenyl)-1H-1,2,3-triazol-1-yl]pyridine-2,6-
dicarboxylate (7c)
Pale yellow solid. Mp: 263.7 ◦C. Rf : 0.19 (ethyl acetate). 1H NMR
(400 MHz, DMSO-d6) d (ppm): 10.11 (1H, s), 8.83 (2H, s), 8.43
(2H, d, J = 8 Hz), 8.25 (2H, d, J = 8 Hz), 4.00 (6H, s). 13C
NMR: compound not soluble enough in common NMR solvents.
IR (KBr) n/cm-1: 3142, 3103, 3062, 2956, 1748, 1711, 1597, 1519,
1476, 1444, 1339, 1259, 1205, 1160, 1124, 1048, 1008, 864, 756.
HR-ESI-MS calculated for C17H13N5O6Na [M + Na]+: 406.0764,
found: 406.0745.
Preparation of lanthanide complexes 9–10
To a suspension of 0.2 mmol (3 equivalents) of diacid hydrochlo-
ride 4b or 8a–d (prepared as described above) in 5 mL of
water is added, under stirring, 4.5 equivalents of guanidinium
carbonate. To the resulting solution is added 1 equivalent of
europium(III) chloride hexahydrate or 1 equivalent of terbium(III)
nitrate hexahydrate. The resulting complex 9 or 10 precipitates
almost immediately. After 1 h of stirring, the lanthanide com-
plex is isolated by filtration, washed with water and finally
dried in vacuo. LnL3 stoichiometry of complexes prepared was
checked through elemental analysis of 10a, calculated (%) for
C48H42N21O12Tb·6H2O: C 42.02, N 21.44, Tb 11.58; found C 42.10,
N 21.52, Tb 11.78.
Complex 9d: 1H NMR (500 MHz, D2O) d (ppm): 7.44 (1H, br
s), 4.37 (2H, br s), last signal (2 aromatic H) masked by solvent
residual peak. Complex 10d: 1H NMR (500 MHz, D2O) d (ppm):
41.45 (2H, br s), 24.38 (1H, br s), 10.94 (2H, br s). Other complexes
were insoluble in common NMR solvents.
Dimethyl 4-[4-(hydroxymethyl)-1H-1,2,3-triazol-1-yl]pyridine-2,6-
dicarboxylate (7d)
White solid. Mp: 188 ◦C. Rf : 0.22 (ethyl acetate–cyclohexane:
1 : 1). 1H NMR (400 MHz, DMSO-d6) d (ppm): 9.23 (1H, s), 8.79
(2H, s), 5.54 (1H, t, J = 5.5 Hz), 4.65 (2H, d, J = 5.5 Hz), 3.98
(6H, s). 13C NMR (400 MHz, DMSO-d6) d (ppm): 163.9, 151.0,
149.7, 144.9, 121.6, 117.0, 54.8, 53.0. IR (KBr) n/cm-1: 3310, 3144,
3080, 2961, 1720, 1599, 1473, 1437, 1425, 1363, 1317, 1288, 1250,
1234, 1213, 1198, 1151, 1122, 1064, 1024, 1010, 989, 924, 891, 835,
821, 785, 767, 744, 734. HR-ESI-MS calculated for C12H12N4O5Na
[M + Na]+: 315.0705, found: 315.0696.
4-(4-Phenyl)-1H-1,2,3-triazol-1-yl)pyridine-2,6-dicarboxylic acid
(8a)
Synthesis and analytical data for compound 12
Triethylamine (50 mL, 0.35 mmol, 1.0 eq.) and 3-(triethoxysilyl)-
propyl isocyanate (130 mL, 0.53 mmol, 1.5 eq.) were added under
argon to a solution of 7d (102 mg, 0.35 mmol) in anhydrous CHCl3
(18 mL). The mixture was heated under reflux for 24 h. After
cooling to room temperature, the mixture was added dropwise
into petroleum ether under stirring by glass rod. The resulting
white precipitate was isolated by filtration, washed for 4 times
with petroleum ether and dried in vacuo for 10 h, to give cleanly
and quantitatively trialkoxysilane 12. 1H NMR (400 MHz, CDCl3)
d (ppm): 8.72 (2H, s), 8.35 (1H, s), 5.29 (2H, s), 5.09 (1H, br s),
4.08 (6H, s), 3.80 (6H, q, J = 7 Hz), 3.20 (2H, q, J = 7 Hz),
1.63 (2H, m), 1.21 (9H, t, J = 7 Hz), 0.62 (2H, t, J = 7.5 Hz).
This compound was immediately engaged in the next step, without
further purification.
◦
1
White solid. Mp: >290 C. H NMR (400 MHz, DMSO-d6) d
(ppm): 9.82 (1H, s), 8.76 (2H, s), 7.99 (2H, d, J = 8 Hz), 7.52 (2H,
d, J = 8 Hz), 7.41 (1H, t, J = 8 Hz). 13C NMR: compound not
soluble enough in common NMR solvents. IR (KBr)n/cm-1: 3144,
3062, 1728, 1647, 1603, 1480, 1450, 1359, 1279, 1238, 1216, 1202,
1170, 1128, 1050, 1011, 907, 762, 690. HR-ESI-MS calculated for
C14H9N4O2 [M - CO2]+: 265.0726, found: 265.0717.
4-[4-(4-Methoxyphenyl)-1H-1,2,3-triazol-1-yl]pyridine-2,6-
dicarboxylic acid (8b)
◦
1
Pale yellow solid. Mp: 286 C. H NMR (400 MHz, DMSO-d6)
d (ppm): 9.73 (1H, s), 8.76 (2H, s), 7.92 (2H, d, J = 9 Hz), 7.08
(2H, d, J = 9 Hz), 3.82 (3H, s). 13C NMR: compound not soluble
enough in common NMR solvents. IR (KBr) n/cm-1: 3140, 3080,
2359, 1727, 1646, 1603, 1481, 1359, 1306, 1253, 1213, 1170, 1128,
1052, 1016, 906, 798. HR-ESI-MS calculated for C15H11N4O3 [M -
CO2]+: 295.0831, found: 295.0842.
Coatings preparation
Coatings were prepared with Laurell WS-400-6NPP-LITE spin-
coater. The hybrid films were prepared from the solution of Ln(12)3
(Ln = Eu, Tb) in ethanol. Typically, the detailed procedure for the
spin-coating is as follows: compound 12 (152 mg, 0.28 mmol, 3 eq.)
and Ln(NO3)3·6H2O (0.094 mmol, 1 eq.) were dissolved, under
argon and at room temperature, in 3 mL of anhydrous ethanol.
After stirring for 10 h, the solution was carefully dropped into
the middle of the clean glass substrate. The transparent films were
obtained with a rotation speed of 5000 rpm for 2 min, and after
drying at 80 ◦C in an oven for 2 h. Micrographs were recorded
by means of a ZEISS Supra 55VP scanning electron microscope
operating in high vacuum at 1 kV, using secondary electron
4-[4-(4-Nitrophenyl)-1H-1,2,3-triazol-1-yl]pyridine-2,6-
dicarboxylic acid (8c)
Pale yellow solid. Mp: 272 ◦C (dec.). 1H NMR (400 MHz, DMSO-
d6) d (ppm): 10.09 (1H, s), 8.28 (2H, s), 8.42 (2H, d, J = 9 Hz),
8.25 (2H, d, J = 9 Hz). 13C NMR: compound not soluble enough
in common NMR solvents. IR (KBr) n/cm-1: 3581, 3504, 3098,
1710, 1596, 1504, 1476, 1434, 1339, 1275, 1242, 1106, 1048, 1016,
910, 872, 783. HR-ESI-MS calculated for C14H8N5O4 [M - CO2]+:
310.0576, found: 310.0572.
7096 | Dalton Trans., 2010, 39, 7091–7097
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detector (Everhart–Thornley detector). Thickness of coatings was
measured by using a KLA-Tencor Alpha-Step IQ Profilometer.
Notes and references
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Luminescence
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The cw photoluminescence spectra were collected using, as exci-
tation source, a 450 W xenon lamp continuous wave monochro-
matized (TRIAX 180 from Jobin-Yvon/Horriba) and analyzed
by a TRIAX 550 Jobin-Yvon/Horriba monochromator equipped
with either a R928 Hamamatsu photomultiplier or a nitrogen-
cooled CCD camera as detector. Cw excitation and emission
spectra were obtained by monitoring the detector response
while scanning the appropriate monochromator. One Photon
Excited (OPE) luminescence intensity dependence and decays
were obtained by pulsed excitation using a Jobin-Yvon LA-04
Nitrogen Laser (337.1 nm, 8 ns pulse, 25 Hz) and analyzed
6 For key references concerning the functionalization of dipicolinic
derivatives through palladium coupling, see: (a) A. D’Aleo, A. Picot,
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through a Jobin-Yvon HR 1000 monochromator (focal length:
-1
1 m, 1200 groove mm-1 grating and band-pass of 8 A mm
˚
slits). The detector was a R1104 Hamamatsu photomultiplier
tube. Fluorescence decays were measured with a Lecroy 9310A
- 400 MHz digital oscilloscope. The Two Photon Excited (TPE)
luminescence measurements were performed using a pulsed dye
laser (Continuum ND60) pumped by a Continuum Surelite
I-SL10 doubled Nd:YAG laser (10 ns pulse, 0.1 cm-1 band width,
10 Hz repetition rate). The dye laser was equipped with a hydrogen
Raman-shifter cell. Mixing of Rhodamines 590 and 610 used as
dye solution provides energy up to 4 mJ in the selected infrared
region. The Stokes-1 Raman shifted beam (shift of 4155 cm-1) is
spatially isolated from the other Stokes and anti-Stokes beams
generated in the H2-Raman cell by two Pellin-Brocca prisms
associated with an iris diaphragm. In addition a set of IR Schott
filter RG 750 and green-red transmission coloured filters are
used to blocks any parasitic laser radiation and to select the
overall visible fluorescence of Tb3+ and Eu3+ embedded in the
complexes. Thanks to the high efficiency of the TPE processes,
the emitted photons are collected with the previous experimental
set-up consisting of the HR-1000 monochromator and R1104
photomultiplier associated with an EG&G PAR Boxcar Averager
Model 162/164 ensuring a good signal/noise ratio. The TPE
excitation spectra were recorded from the whole spectral response
of the dye and corrected for its intensity distribution. The emission
intensity dependence on the excitation beam power is analyzed
by interposition of a set of neutral density filters (transmission
varying between 2 % and 100 %) on the optical pathway. Moreover,
using LDS 690 as the dye solution allows tuning the laser excitation
in the 0.9–1.1 mm IR range, by using the Stokes-1 Raman shifted
beam, which is consistent with a Three Photon Excitation (THPE)
induced luminescence process. Images of the luminescent films are
obtained with a digital camera after excitation provided by the
350 nm selected-radiation of a Hg lamp.
7 It has to be noticed that click chemistry has been previously employed
to link lanthanides and chromophores for FRET; 1,2,3-triazoles have
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10 (a) for [Cu(C186tren)]Br, see: N. Candelon, D. Laste´coue`res, A. Khadri
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The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 7091–7097 | 7097
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