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PAPER
www.rsc.org/materials | Journal of Materials Chemistry
Luminescent terbium and europium probes for lifetime based sensing of
temperature between 0 and 70 C†
Jiangbo Yu,‡x*a Lining Sun,‡ab Hongshang Pengac and Matthias I. J. Sticha
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Published on 09 July 2010 on http://pubs.rsc.org | doi:10.1039/C0JM01069C
Received 16th April 2010, Accepted 8th June 2010
DOI: 10.1039/c0jm01069c
Organic europium (III) and terbium (III) complexes (refered to as Eu1, Eu2, and Tb-L1, Tb-L2,
respectively) have been synthesized that display bright emission and small bandwidth. Tb-L1 and TbL2 show lifetimes in the order of almost 1 ms at room temperature, good color purity, and high relative
photoluminescence quantum yields. This makes them excellent probes for sensing temperature via
measurement of luminescence lifetime. Probes Eu1, Eu2, Tb-L1 and Tb-L2 were incorporated into
various polymer matrices to give sensor films for use as temperature-sensitive paints (TSPs). Eu (III)
complexes have the advantage of being effectively excited by purple light-emitting diodes with their
peak wavelengths of 405 nm. All TSPs based on these europium and terbium probes display good
sensitivities to temperature, in particular, TSP based on Tb-L1 and Tb-L2 can show temperaturelifetime sensitivities of 13.8 ms per C and 9.2 ms per C, respectively. Assuming a precision of 1 ms
in the determination of lifetime, this will enable temperature to be determined with a precision of
around 0.1 C. This temperature dependence is the highest one reported so far for lanthanide
complexes.
1. Introduction
Luminescent probes for sensing temperature (T) have advantages
over other methods and have been used in marine research,1,2
underground geochemistry,3 diagnosis,4 biotechnology,5 micro
air vehicles,6 wind tunnels,7–9 aircraft and car industries.8,10,11
Generally, luminescent materials for sensing T are made of
inorganic phosphors (like chromium (ruby12) and lanthanum
oxysulfides13–15), or from organic fluorophores (like some dyes16–18
or metal–ligand complexes6,19–23). Inorganic phosphors cannot be
easily doped into polymer films, so that sensor films, referred to as
‘‘T-sensitive paint’’ (TSP),24 have a high degree of heterogeneity.
TSP represents an attractive alternative to IR-based thermography.9 For TSP, the indicator dye is incorporated into a polymer
binder, both being dissolved in an appropriate solvent. Then the
paint can be sprayed onto the surface and map the surface
distribution of T of aircrafts. The luminescence of the indicator in
TSP can be thermally quenched. It is also well known TSP has
a higher spatial resolution than the conventional method of
thermocouples. Usually, in TSP system organic dyes such as
a
Institute of Analytical Chemistry, Chemo- and Biosensors, University of
Regensburg, D-93040 Regensburg, Germany. E-mail: yujiangbo75@
yahoo.com
b
Research Center of Nano Science and Technology, Shanghai University,
200444 Shanghai, P. R. China
c
Key Laboratory of Luminescence and Optical Information,Ministry of
Education, Institute of Optoelectronic Technology, Beijing Jiaotong
University, 100044 Beijing, P. R. China
† Electronic supplementary information (ESI) available: Electro
supplementary information (ESI) available: TGA of Tb-L1 and Tb-L2,
photostability curves of Tb-L1_TSP1 and Tb-L2_TSP1, synthetic
protocols and characterization, and photophyscial properties of Tb-L3.
See DOI: 10.1039/c0jm01069c
‡ These authors contributed equally.
x Current address: Department of Chemistry, Clemson University,
Clemson, SC 29634, USA.
This journal is ª The Royal Society of Chemistry 2010
rhodamine B, Coumarine and pyrene, metal complexes such as
Ru(II) and Eu(III) complexes are used as indicators and incorporated into polymers.
Lanthanide complexes are promising in terms of sensing and
imaging of T because they show strong and sharp emission
bands, and lifetimes from several hundred microseconds (ms) to
several milliseconds (ms). In addition, their luminescence is
hardly quenched by oxygen.6,25,26 Complexes of Eu (III) have
been used fairly often in TSPs.6,27,28 Their excitation maxima
usually are located in the UV, but recently were shifted to around
400 nm by using proper antenna ligands.20,29–31 Complexes of
Tb (III) have rarely been used in TSPs,32–35 and intensity
was mainly measured.36–38 Unfortunately, such measurements
are compromised by drifts in the opto-electronic system (lamps
and detectors), and by variations of the optical properties of the
sensor layer including probe concentration, turbidity, thickness,
intrinsic coloration, and changes in refractive index.20,29,39
Measurement of the decay time, in contrast, is free from these
drawbacks. We therefore hypothesized that complexes of
Tb (III) with their luminescence lifetimes in the order of ms
represent attractive alternatives for sensing T.
We are reporting here (a) the synthesis of new organic
complexes of Tb (III) and Eu (III), (b) their T-dependent
photoluminescence (PL), and (c) their applications in TSPs. The
results show that the Eu (III) complexes (which can be excited at
around 400 nm) have moderate T sensitivity, whilst the terbium
complexes need to be excited in the UV but exhibit high sensitivity to T, both in terms of decay time and intensity.
2. Results and discussion
2.1 Spectral properties of lanthanide complexes
Fig. 1 shows the chemical structures of the lanthanide complexes
studied for T indictors. It is well known that organic ligand plays
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Fig. 1 Chemical structures of the Eu (III) and Tb (III) complexes used for T probes.
the important role in sensing emission of central lanthanide ion.
For Eu1, we selected dinaphthoylmethane (DNM) as the sensing
ligand because its absorption spectrum extends into the visible
region40 and trioctylphosphine oxide ligand as the neutral ligand
because it can increase the luminescence quantum yield of the
complex by strengthening the ligand-to-metal energy transfer
and decreasing that of the nonradiative decay of the 5D0 electronic state.41 Eu1 was prepared in complete analogy to the
reported procedure.40,41 Eu2 has been proved that it is a high
luminescent complex excited by the visible light source42 and it
can be applied as the T indictor.20,30,31 Tb-L1 has been reported
by Wong group,43,44 which shows excellent luminescence and
upconversion fluorescence. However, the potential of Tb-L1 as
a temperature indicator was not recognized. Usually, subtle
changes in ligand-molecular structures can dramatically tune the
photoluminescence properties of the lanthanide complexes.45–47
Therefore, using the similar procedure of synthesizing Tb-L1, we
have synthesized Tb-L2 and Tb-L3 (shown in the supporting
information (SI)) by adding different branch groups on the
phenyl of the ligand backbone to investigate how the photophysical properties of Tb (III)-complex indicators are influenced
by the groups of the corresponding ligands (discussed details
shown in SI).
The absorption and emission spectra of the probes are shown
in Fig. 2. The Eu (III) complexes have absorption peaks at 375
and 402 nm,20 respectively. The emission spectra show a typical
radiation emission of the 5D0 excited state (5D0 / 7FJ, J ¼ 0, 1,
2, 3, corresponding to the peaks at 579, 592, 612 and 653 nm,
respectively.) of Eu3+ ion due to the ‘‘antenna effect’’, i.e. the
energy transferred from the chromophores (ligands) to the
excited states of Eu3+ ion. The absorption spectra of ligands and
Tb (III) complexes show some differences between them each
other because the different groups appear in the benzene ring of
the ligands. The ligand L2 exhibits a little blue shift absorption in
comparison with the ligand L1. Accordingly, the excitation
spectrum of Tb-L2 shows a little blue shift compared with that of
Tb-L1. With the excitation light at around 330 nm, the two Tb
(III) complexes show the same f-f transition emission bands
peaking at 488, 545, 584, and 619 nm, respectively, which are
assigned to the transitions from the 5D4 excited states to the other
lower states 7FJ (J ¼ 6, 5, 4, 3) (shown in Fig. 2B and 2C). In the
fluorescence emission spectra of these two Tb complexes, there
are much weaker broad emission bands being compared to the
emission bands of Tb3+ ions (cantered at 545 nm), which are
centred at 420 nm and originated from the ligands. Usually, the
6976 | J. Mater. Chem., 2010, 20, 6975–6981
luminescent mechanism of the Tb (III) complexes is the same as
Eu1. Therefore, the aforementioned phenomenon suggests that
the energy gap between the triplet state (T1) of the ligand and the
resonant excited state of Tb3+ ion (5D4) is some small and results
in the back energy transfer process from the later to the former.
The T-sensitivity of the lanthanide complex works by means of
the T-quenching, to which the deactivation of the luminescent
excited states of lanthanide ions mainly contributes.6 So the small
energy gap and the resulted back energy transfer may play an
important role on the later discussed results that increasing the
temperature can cause the large decrease of both luminescence
intensity and especially of lifetime.6,24 Actually, among these
emission bands, the 5D4 / 7F5 transition gives the strongest
band centres at 545 nm and has a full-width at half-maximum
(fwhm) < 10 nm, which enables Tb (III) complexes to have high
green colour purity. This is of particular significance with respect
to multiplex (multi-signal based) sensing. All detailed photophysical properties of Eu (III) and Tb (III) complexes are displayed in Table 1. The luminescence lifetimes at room
temperature (RT) of Tb-L1 and Tb-L2 are close to 1 ms, which
are longer than that of Eu (III) complexes, especially much
longer than that of Eu1. It is noted that Eu1 has a very short
lifetime in toluene solution, however, when it is doped into
polymer film, the lifetime can be increased by 6 times more. The
details will be discussed in detail in later.
2.2.
Effects of T on the luminescence of the probes
The probes Tb-L1 and Tb-L2 show long luminescence lifetimes
of almost 1 ms. In DMSO solution, both Tb-L1 and Tb-L2 show
very strong T-dependence of their emission intensities and
lifetimes. The results are given in Fig. 3 and show that the
T-dependence is linear. The sensitivity of the luminescence intensity of Tb-L1 is 1.13%/ C and lifetime drops by 10.9 ms/ C.
The respective values for Tb-L2 are 1.23%/ C and 8.4 ms/ C
(shown in Table 2). Since Tb (III) complexes have longer decay
times, their T-lifetime sensitivities (around 10 ms/ C) are higher
than those of Eu (III) complexes,6,20,29,30 which is a quite attractive
feature for Tb (III) complexes used as the T probes. Both the
intensity and decay times of Tb-L1 and Tb-L2 drop by around 50%
from 20 C to 65 C. The effect most likely is based on the deactivation of the 5D4 state of Tb3+ ion mainly through the back
energy transfer from the 5D4 state to the triplet excited state of the
antenna chromophore of the ligand.29,34
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Table 1 Photophysical properties of Eu (III) and Tb (III) complexes
Complex
Eu1
Eu2
Tb-L1
Tb-L2
labs/nma
lexc/nmb
s/msc
QY/%d
374
406
57
—
402
410
600
39
308
334
902
13
306
329
881
15
a
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Absorption (labs) and excitation (lexc) peaks in solution for Eu1 and
Eu2 (10 mM in toluene) and Tb (III) complexes (0.1 mM in
acetonitrile). b Excitation (lex) peaks for Eu (III) complexes (10 mM in
toluene) and Tb (III) complexes (40 mM in acetonitrile). c Decay time
measured for the transmission of 5D0 / 7F2 of Eu (III) complex, or of
5
D4 / 7F5 of Tb (III) complexes. d Relative quantum yield measured,
for Eu2 in toluene,42 for Tb (III) complexes in DMSO solution.
Fig. 3 T-dependence of the luminescence of Tb-L1 and Tb-L2 (0.1 mM
in DMSO): (A) the luminescence lifetime_T curves of Tb-L1 (solid
square, and fitting line: solid) and Tb-L2 (hollow square, and fitting line:
dash) complexes; (B) intensity_T plots of Tb-L1 (solid circle, and fitting
line: solid) and Tb-L2 (hollow circle, and fitting line: dash).
Table 2 T sensitivity of Eu (III) complexes (in polymer) and Tb (III)
complexes (in solution and in polymer) and the corresponding parameters of the fitting of the T-lifetime dependence curves
SLLb
k0
k1
DE
SLIa
(%/ C) (ms/ C) (s1) (103s1) (kJmol1)
Probe and TSP
Eu1_TSP
Eu2_TSP
Tb-L1
Tb-L1_TSP1
Fig. 2 Spectra of the lanthanide complexes at RT. Graph A, plot 1
(——): absorption spectrum; plot 2 (//): excitation spectrum; plot 3
(—
—): emission spectrum of the Eu1 complex (10 mM in toluene). Graph B,
plot 4 (——): absorption spectrum of ligand L1 (0.1 mM in acetonitrile);
plot 5 (//): absorption spectrum; plot 6 ($-$-$-): excitation spectrum;
plot 7 (—
—): emission spectrum of the Tb-L1 complex (40 mM in acetonitrile). Graph C, plot 8 (——): absorption spectrum of ligand L2
(0.1 mM in acetonitrile); plot 9 (//): absorption spectrum; plot 10
($-$-$-): excitation spectrum; plot 11 (—
—): emission spectrum of the Tb-L2
complex (40 mM in acetonitrile).
2.3.
T-senstive paints made from Eu (III) complexes
Usually, TSP is obtained by doping a T-indicator into a polymer
matrix. Poly(methyl methacrylate) (PMMA) is a very good
optical matrix for TSP because it is transparent to light from
This journal is ª The Royal Society of Chemistry 2010
Tb-L1_TSP2
Tb-L2
Tb-L2_TSP1
Tb-L2_TSP2
50 mbar
1000 mbar
1950 mbar
50 mbar
500 mbar
1750 mbar
DMSO
Solution
3 wt% in
PMMA
3wt% in
PAN
DMSO
Solution
5 wt% in
PMMA
5 wt% in
PAN
—
—
—
—
—
—
1.13
1.8
1.6
1.9
7.1
6.9
7.0
10.9
2.34
2.32
2.39
1.11
1.25
1.35
—
5.34
1.67
3.24
0.65
4.99
42.9
—
23.5
20.0
21.6
17.1
22.4
27.8
—
0.67
13.8
0.45 12.6
24.6
—
8.7
0.83 10.2
24.9
1.23
8.4
—
—
0.73
7.8
0.95 1121.8
40.6
—
9.2
0.93 72.3
30.1
a
Sensitivity of luminescence intensity.
lifetime.
b
—
Sensitivity of luminescence
300 nm to 2800 nm. Also, PMMA has excellent environmental
stability compared to other plastics such as polycarbonate, and
can be easily processed and of low cost. It also acts as a good
solvent for Eu1. The sensor layer was obtained by dissolving
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PMMA and Eu1 in toluene, spreading this solution onto
a polymer support, and evaporating the solvent to give a sensor
film (Eu1_TSP) of 10 mm thickness (preparing details shown in
Experimental section).
The T-dependence of Eu1_TSP at different pressures was
investigated by using the rapid lifetime determination (RLD)
method.30,48 In Fig. 4A, the Eu1_TSP shows a 6 times longer
luminescence lifetime (360 ms) than that of the toluene solution
(57 ms). A similar phenomenon has been observed for another Eu
(III) complex which has the same b-diketone ligand (DNM) to
Eu1.40 It is presumed that the rise of the luminescence decay time
due to the f-shell transitions that are parity forbidden, which also
indicates the Eu3+ ion is shielded from most quenching mechanisms.40 Therefore, Eu1_TSP shows high T-sensitivity at each
different air pressure (shown in Fig. 4A). From Table 2 and
Fig. 4A, it is observed that the Eu1_TSP shows the lifetimesensitivities at different air pressures being of 2 ms/ C.
The Eu2_TSP was made from the polymer poly(vinyl chloride)
(PVC) which acts as a gas-blocking polymer. This is necessary
because the luminescence of Eu2 is quenched by oxygen.30 The
T-dependence of Eu2_TSP at different pressures was also
investigated by using the RLD method. From Fig. 4, it can be
known that the T-dependence of the luminescence of Eu2_TSP is
more expressed than that of the Eu1_TSP. Fig. 4B shows that
lifetime-sensitivity of Eu2_TSP is around 7ms/ C. The lifetimeT plot generally can be fitted by an Arrhenius-type equation:
1
DE
¼ k0 þ k1 exp (1)
s
RT
than that in lower temperature.23,30 In Fig. 4, at the T of 274 K,
the luminescence lifetime of Eu1_TSP drops from 0.397 to
0.379 ms, decreasing by 4.5% when pressure is increased from
50 to 1950 mbar, which drops from 0.304 to 0.283 ms at 327 K
(from 50 to 1950 mbar), decreasing by 6.9%. This means that
the maximum cross-sensitivity of the Eu1_TSP towards
oxygen quenching is between 4.5% and 6.9%, and the oxygen
diffusion is more obvious at higher temperatures. For Eu2_TSP,
the maximum cross-sensitivity towards oxygen quenching is
between 5.1% (at 274 K) and 6.0% (at 309 K), under air pressure
from 50 to 1750 mbar. These values are satisfactory for these
probes with decaytimes of several hundred microseconds, which
can be fabricated with other pressure or oxygen probes with
decay times of several microseconds as the dual sensor.23,30,31 The
lifetime-sensitivities and the maximum cross-sensitivities of the
Eu1_TSP and Eu2_TSP towards oxygen quenching show that
the two TSPs are also promising for the potential application as
T sensors.
2.4 TSPs made from Tb (III) complexes
where s is the luminescence lifetime, k0 is the T-independent
decay rate for the deactivation of the excited state, k1 is the
preexponential factor, DE is the energy gap between the emitting
level and the higher excited state, R is the gas constant and T is
the absolute T.19,20,30,49 The T-dependence of the Eu1_TSP and
Eu2_TSP can be fitted using the parameters at different air
pressures shown in Table 2 with the correlation coefficients (r2)
being higher than 0.99.
The cross-sensitivities of Eu1_TSP and Eu2_TSP towards
oxygen quenching have been also studied to check how much the
pressure (due to the oxygen quenching) influences the T-sensitivities because the oxygen is another quencher besides the
thermal quenching on the luminescence especially at higher
temperature the collisional quenching by oxygen becomes higher
These TSPs of Tb-L1 and Tb-L2 were made by the method
described above and using PMMA as the matrix. It is found that
the concentration of the complex does affect T sensitivity.6 The
results of a respective study are shown in Fig. 5. The concentration of the probes was changed from 1 wt% to 7 wt%. In case
of Tb-L1, the best linearity between T and intensity is obtained at
the concentration of Tb-L1 of 3 wt%, and the T-intensity sensitivity is 0.67%/ C. The best concentration of probe Tb-L2 is
5 wt%, which gives a T-intensity sensitivity of 0.73%/ C.
According to these results, 3 wt% and 5 wt% doping concentrations were selected to study the T-lifetime sensitivity characteristics of Tb-L1 and Tb-L2, respectively.
Fig. 6A shows the T-dependence of the luminescence lifetimes
of the two TSPs (Tb-L1_TSP1: 3 wt% Tb-L1 in PMMA; TbL2_TSP1: 5 wt% Tb-L2 in PMMA) at atmospheric pressure.
Both exhibit very high lifetime sensitivities (13.8 ms/ C for
Tb-L1_TSP1 and 7.8 ms/ C for Tb-L2_TSP1), which are the
highest lifetime sensitivities reported for TSPs based on lanthanide complexes so far.6,20,29,30,33,50 The corresponding plots of
Tb-L1_TSP1 and Tb-L2_TSP1 can be fitted by an Arrheniustype equation. The parameters are shown in Table 2, and the
correlation coefficients (r2) are > 0.99.
Fig. 4 T-dependence of the luminescence lifetime of the Eu (III)
complexes-based TSPs at different air pressures: (A) Eu1_TSP, 50 mbar
(square, and fitting line: solid), 1000 mbar (triangle, and fitting line:
dash), 1950 mbar (circle, and fitting line: dot); (B) Eu2_TSP, 50 mbar
(square, and fitting line: solid), 500 mbar (triangle, and fitting line: dash),
1750 mbar (circle, and fitting line: dot).
Fig. 5 T-intensity sensitivity plots of TSPs based on different Tb (III)
complexes doped into PMMA matrix at different concentrations. A: TbL1, 1 wt% (square), 3 wt% (circle), 5 wt% (triangle); B: Tb-L2, 3 wt%
(square), 5 wt% (circle), 7 wt% (triangle).
6978 | J. Mater. Chem., 2010, 20, 6975–6981
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and 20% over a period of 2 h, respectively. This shows both two
TSPs show fairly good photostability. The Tb-L2_TSP1 has
a slightly better photostability than the Tb-L1_TSP1. The polymer matrix is known to have a large effect on the photodegradation.6,29
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2.8 Thermal stability of Tb (III) complexes
Fig. 6 T-dependence of the luminescence lifetime of TSPs at atmospheric pressure, A: Tb-L1_TSP1 (square) and Tb-L2_TSP1 (circle)
doped into PMMA matrix; B: Tb-L1_TSP2 (square) and Tb-L2_TSP2
(circle) doped into PAN matrix. The fits were obtained using the
Arrhenius equation.
2.5 Variation of polymer matrix
Different polymers were examined with respect to their suitability as matrices for TSPs. Polyacrylonitrile (PAN) was found
to be best suited, not the least because it is stable, optically
transparent, and capable of shielding oxygen. The results
reported in the following refer to a TSP based on PAN. The
T-dependence of the luminescence lifetimes of the two TSPs
(Tb-L1_TSP2: 3 wt% Tb-L1 in PAN; Tb-L2_TSP2: 5 wt% Tb-L2
in PAN) at atmosphere is shown in Fig. 6B, which can be also
fitted by an Arrhenius equation. From this figure and Table 2, it
is well known that both TSPs of Tb-L1 and Tb-L2 doped into
PAN, respectively, also show very high lifetime sensitivity, 8.7
ms/ C of Tb-L1_TSP2 and 9.2 ms/ C of Tb-L2_TSP2. By
comparison of the T-dependence of different TSPs with different
polymer matrixes, it can be easily known that the T-dependence
of the luminescence lifetime is influenced by the polymer matrix.
This phenomenon has also been reported in other published
papers.6,29
2.6 Effect of oxygen
The quenching by oxygen of the luminescence lifetime of TSPs
with PMMA as the matrix was investigated. Compared to the
luminescence lifetimes under N2 environment, at air atmosphere
by oxygen quenching the lifetimes are reduced by 6.5% and 2.8%
for Tb-L1_TSP1 and Tb-L2_TSP1, respectively. Therefore, the
quenching effect for TSPs can be neglected in many cases. Since
there is no UV excitation source (wavelength around 330 nm) for
Tb (III) complexes in the experimental setup used in the RLD
method which was used to measure the T_lifetime sensitivity of
TSPs based on Eu (III) complexes at different air pressures
above,30 the luminescence lifetimes of the TSPs based on Tb (III)
complexes were measured only at atmospheric pressure.
2.7 Photostability of TSPs based on Tb (III) complexes
The photostability of TSP is another key figure of merit for it
used as the T probe and particularly for the long-term sensor.
The photodegradation curves of Tb (III) complexes_TSPs (in
PMMA matrix) were recorded by continuous illumination with
UV light of Xenon lamp at a power of 1.0 mW (shown in
Figure S4). It is observed that the emission intensity of TbL1_TSP1 and Tb-L2_TSP1 is decreased by approximately 28%
This journal is ª The Royal Society of Chemistry 2010
Thermal stability is also critically important for fluorescent
probes applied as T sensor. The thermal stabilities of Tb-L1 and
Tb-L2 have been investigated by the TGA-DSC technology.
Figure S5 shows the TGA-DSC curves belong to Tb-L1 and TbL2, from which it is observed that they show melting points
around 170 C, 164 C for Tb-L1 and 171 C for Tb-L2,
respectively. The two complexes show the same decomposition T
(307 C). Both the two complexes have a thermal stability good
enough to be used as the T sensors when doped into different
polymer-matrix.
3. Experimental
Materials and syntheses
Tb(NO3)3$6H2O, ethyl salicylate, ethyl 4-ethoxy-2-hydroxybenzoate, triethylenetetramine, poly(vinyl chloride) (PVA, high
molecular weight), poly(methyl methacrylate) (PMMA, Mw:
120,000), polyacrylonitrile (PAN, average Mw 150,000), and
Quinine hemisulfate monohydrate were purchased from SigmaAldrich (www.sigma-aldrich.com). All solvents and chemicals were
used directly without further purification. Eu1 and Eu2 were
synthesized according to the literatures.20,40,42,50 All the ligands and
their Tb (III) complexes were synthesized according the literature
methods.43,51
1,8-bis(2-hydroxy-benzamido)3,6dioxaoctane
(L1), 1,8-bis(4-ethoxy-2-hydroxy-benzamido)3,6dioxaoctane
(L2) were synthesized using very similar procedures, and details are
given as the following: ethyl salicylate (or its derivatives) and triethylenetetramine mixed together and heated at 100 C on an oil
bath under stirring for 24 h. The mass was then crystallized from
a 1:l (in volume) ethanol-water mixture, affording a white solid.
L1
1
H NMR (300 MHz, Chloroform-d, d): 2.77 (s, 4H, 4,5-CH2),
2.85 (t, J ¼ 5.21 Hz, 4H, 3,6-CH2), 3.53 (t, J ¼ 4.80 Hz, 4H, 2,7CH2), 5.88 (s br, 4H, 3,6-(CH2)-NH and Ar-OH), 6.76
(t, J ¼ 7.34 Hz, 2H, ArH), 6.94 (d, J ¼ 8.23 Hz, 2H, ArH), 7.30
(t, J ¼ 7.14 Hz, 2H, ArH), 7.53 (d, J ¼ 7.96 Hz, 2H, ArH), 7.80 (s
br, 2H, 2,7-CH2-NH). 13C NMR (300 MHz, Chloroform-d, d):
38.97 (C4,5), 48.11(C3,6), 48.40 (C4,5), 115.26 (Ar), 118.27 (Ar),
118.64 (Ar), 126.80 (Ar), 133.93 (Ar), 160.85 (ArCOH), 169.77
(C ¼ O). ES-MS (m/z (%)):387.0 (100.0) [M + H]+, 388.0 (23.3)
[M + 2H]+, 389.1 (3.3) [M + 3H]+. Anal. Calcd for C20H26N4O4:
C 62.16, H 6.78, N 16.56; found: C 62.07, H 6.68, N 16.43.
L2
1
H NMR (300 MHz, Chloroform-d, d): 1.38 (t, J ¼ 7.00 Hz, 6H,
Ar-OCH2CH3), 2.75 (s, 4H, 4,5-CH2), 2.84 (t, J ¼ 5.63 Hz, 4H,
3,6-CH2), 3.48 (t, J ¼ 5.49 Hz, 4H, 2,7-CH2), 3.99 (q, J ¼ 7.04
Hz, 4H, Ar-OCH2CH3), 6.33 (d, J ¼ 11.25 Hz, 2H, ArH), 6.40
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(d, J ¼ 2.47 Hz, 2H, ArH), 6.95 (s br, 4H, 3,6-(CH2)-NH and ArOH), 7.22 (s br, 2,7-(CH2)-NH), 7.34 (d, J ¼ 8.78 Hz, 2H, ArH).
13
C NMR (300 MHz, Chloroform-d, d): 14.61 (Ar-OCH2CH3),
38.89 (C2,7), 48.23 (C3,6), 48.23 (C4,7), 63.64 (Ar-OCH2),
102.12 (Ar), 106.71 (Ar), 107.67 (Ar), 127.35 (Ar), 137.07 (Ar),
163.29 (ArCOH), 169.80 (C ¼ O). EI-MS (m/z (%)): 475.2 (100.0)
[M + H]+, 476.2 (26.6) [M + 2H]+, 476.2 (4.9) [M + 3H]+. Anal.
Calcd for C24H34N4O6: C 60.74, H 7.22, N 11.81; found: C 60.47,
H 7.32, N 11.73.
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Published on 09 July 2010 on http://pubs.rsc.org | doi:10.1039/C0JM01069C
Tb-L1
0.5 g (1.3 mmol) Ln(NO3)3 $ 6H2O was dissolved in 15 mL
acetonitrile and then was added to the solution of L1 (0.5 g, 1.3
mmol) in MeCN (15 mL). After stirring at RT for 2 days, the
mixture was then filtered and washed with MeCN several times
to obtain the raw product. Further purification was processed by
several turns of recrystallization from the MeCN solution. Anal.
calcd: C 20.95, H 2.81; N 12.22%; found for C20H32N10O26Tb2: C
20.88, H 2.82, N 12.30%.
Tb-L2
This complex was synthesized by using the same procedure to
Tb-L1. Anal. calcd: C, 23.35; H, 3.27; N, 11.35%; found for
C24H40N10O28Tb2: C, 23.27; H, 3.31; N, 11.27%.
Preparation of the T-sensitive paints
The lanthanide complexes and the doped polymers were mixed
together with a certain ratio and then dissolved in the solvent
with 5 wt% ratio (polymer/solvent in weight). For Eu1/PMMA
(2 wt%), toluene was used as the solvent; Eu2/PV (4 wt%), tetrahydrofurane was used; Tb (III) complexes/PMMA, dimethylformamide was used. The ‘‘cocktail’’ was knife-coated onto
a 100 mm thick poly(ethylene terephthalate) support foil to give
a sensor film 10 mm thickness after solvent evaporation at
room temperature (for Tb (III) complexes using a heating at
50 C).
Instruments
The 1H and 13C NMR spectra were acquired on an Avance
300 MHz NMR Spectrometer (Bruker-BioSpin GmbH,
www.bruker-biospin.com). The ESI-MS mass spectrometry was
performed on a Bruker Daltonics Esquire 3000 plus (Bremen,
Germany) ion trap mass spectrometer. The TGA and DSC
measurement were obtained by TGA-7 and DSC-7 of Perkin
Elmer Corp., Norwalk, Connecticut, USA. About 5 mg of
sample were heated in synthetic air atmosphere with 10 C/min to
a maximum T of 500 C (DSC) and 700 C (TGA). DSC
measurement: A baseline (two aluminium pans heated without
sample in an individual run) was subtracted from each sample
measurement to reduce the slope of the curves.
luminescence spectrometer (Thermo Scientific Inc., Waltham,
MA, USA, www.thermo.com) with a 150 W continuous wave
lamp, repectively. For Eu (III) complexes based TSPs, the timeresolved measurements were performed with a PCO SensiCam 12
bit b/w CCD camera (PCO, Kelheim, Germany, www.pco.de)
equipped with a Schneider-Kreuznach Xenon 0.95/17 lens (Jos.
Schneider Optische Werke, Bad Kreuznach, Germany,
www.schneiderkreuznach.com) and a 4056660 405nm LED
sold by Roithner Lasertechnik (Vienna, Austria, www.roithnerlaser.com). The excitation light was focused by a PCX 18 18
MgF2 TS lens from Edmund Optics (Karlsruhe, Germany,
www.edmundoptics.com) and fell onto the sensor through
an angle of approximately 20 . It was filtered through a BG 12
filter (Schott, Mainz, Germany, www.schott.-com) with a
thickness of 2 mm. Emission was detected after passing a D610/
60M band pass filter (Chroma, Rockingham, VT, USA,
www.chroma.com).
For Tb (III) complexes based TSPs, time-resolved fluorescence
spectra at different Ts were recorded on the same Aminco AB 2
luminescence spectrometer above with a Xenon flash lamp and
with a thermometer control part to make T being accurate to
0.1 C using water as the heating medium. Relative quantum
yield (QY) was determined by the relative comparison procedure,
using Quinine Sulfate in 0.1 M H2SO4 as the standard. For the QY
measurement, the used solution of 0.1 M H2SO4 and DMSO are
O2-degassed by using high pure N2 flow. Both the solution of
quinine sulfate in 0.1 M H2SO4 and the solution of Tb (III)
complexes in DMSO were adjusted to have the same absorbance
being less than 0.05 at 350 nm. The method has been reported in the
literature using quinine sulfate as a standard (QYref ¼ 0.58). 52–54
4. Conclusions
In conclusion, a series of Eu (III) complexes and Tb (III)
complexes have been synthesized. Their high luminescence
brightness, high luminescence quantum yields, and long luminescence lifetimes and high color purities enable them to be good
indicators for TSPs. The Eu (III)_TSPs can be efficiently excited
upon visible light emitting diode (405 nm) and show good lifetime sensitivity. The Tb (III) complexes also have good T
sensitivities (intensity sensitivity and lifetime sensitivity), which
endows them to be applied as sensitive T probes. The Tb
(III)_TSPs show the highest lifetime sensitivities reported for
TSPs so far such as 13.8 ms/ C (Tb-L1_TSP1) and 9.2 ms/ C
(Tb-L2_TSP2). Therefore, the T-sensitivities can be determined
with a precision of around 0.1 C. Such good resolution makes
the TSPs for sensing and imaging of physiological temperatures.
The different polymer matrixes also have effects on the T-sensitivities of the Tb (III)_TSPs. All the Tb (III) complexes possess
good thermal stabilities and their TSPs possess good photostability, which is adequate for their most applications. All these
TSPs have been demonstrated to be viable probes for sensing T.
Acquisition of spectra and experimental setup
Absorption and fluorescence spectra were recorded on
a Lambda 14 p Perkin-Elmer UV-vis spectrophotometer (Waltham, MA, USA, www.perkinelmer.-com) and an Aminco AB 2
6980 | J. Mater. Chem., 2010, 20, 6975–6981
Acknowledgements
Financial support by the German Aerospace Center (DLR) in
G€
ottingen is gratefully acknowledged.
This journal is ª The Royal Society of Chemistry 2010
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Published on 09 July 2010 on http://pubs.rsc.org | doi:10.1039/C0JM01069C
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