A Luminescent Dinuclear EuIII/TbIII Complex with LMCT Band as a Single-Molecular Thermosensor

Article abstract of DOI:10.1002/chem.201705021

Temperature-dependent luminescence of a dinuclear Eu^III/Tb^III complex with a seven-coordinate structure is demonstrated. The dinuclear complex is composed of two lanthanide ions, six tetramethylheptanedionate ligands, and a bidentate phosphine oxide linker ligand. The dinuclear structure of the complex was characterized by single-crystal XRD. Intrinsic 4f–4f emission quantum yields of the dinuclear Eu^III and Tb^III complexes were 66 and 61 %, respectively. The luminescence color of the dinuclear Eu^III/Tb^III complex changed from red to green with increasing temperature. The thermosensing range based on the ratio of luminescence intensity (A_Eu/A_Tb) was 100–450 K. The temperature-dependent luminescence is due to the presence of a ligand-to-metal charge-transfer state.

Full text of DOI:10.1002/chem.201705021

A Journal of
Accepted Article
Title: A Luminescent Dinuclear EuIII/TbIII Complex with LMCT Band for
Single-molecular Thermosensor
Authors: Kei Yanagisawa, Yuichi Kitagawa, Takayuki Nakanishi,
Tomohiro Seki, Koji Fushimi, Hajime Ito, and Yasuchika
Hasegawa
This manuscript has been accepted after peer review and appears as an
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of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.201705021
Link to VoR: http://dx.doi.org/10.1002/chem.201705021
Supported by

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FULL PAPER
III
III
A Luminescent Dinuclear Eu /Tb Complex with LMCT Band for
Single-molecular Thermosensor
[b]
[a]
[a]
[a]
[a]
Kei Yanagisawa, Yuichi Kitagawa, Takayuki Nakanishi, Tomohiro Seki, Koji Fushimi, Hajime
[
a]
[a]
Ito, and Yasuchika Hasegawa*
Abstract: Temperature-dependent luminescence of a dinuclear
Thermosensing materials constructed from lanthanide
complexes have been increasingly studied due to the narrow
fwhm of emission bands.[ The narrow bandwidths originate
from 4f-4f transitions because of little change in the electronic
structures between ground and excited states. Since the
emission wavelength of 4f-4f transitions is independent of the
surrounding environment, the emission color can be controlled
III
III
Eu /Tb complex with a seven-coordinate structure is demonstrated.
The dinuclear complex is composed of two lanthanide ions, six
tetramethylheptanedionate ligands, and a bidentate phosphine oxide
linker ligand. The dinuclear structure of the complex was
characterized by single-crystal X-ray analysis. Intrinsic 4f-4f
7]
III
III
emission quantum yields of the dinuclear Eu and Tb complexes
III
III
III
were found to be 66% and 61%, respectively. The luminescence
by selection of lanthanide ions (Eu : red, Tb : green, and Yb :
near-infrared). Carlos pioneered luminescence thermometry
III
III
color of the dinuclear Eu /Tb complex changed unusually from red
to green with increasing temperature. The thermosensing range
using the ratio of luminescence intensity (AEu/ATb) was 100-450 K.
The temperature-dependent luminescence is caused by the
presence of a ligand-to-metal charge transfer state.
III
III
based on dual-emission of Eu /Tb hybridized organosilica on
6]
Fe
2
O
3
nanoparticles (sensing range: 10-350 K).[
Qian
demonstrated the first example of a luminescent metal organic
framework (MOF) including EuIII and TbIII for a ratiometric
thermometer (sensing range: 10-300 K).[8] Our research group
also reported
‘
thermostability (sensing range: 200-500 K).
Temperature-dependent luminescence
a
luminescent coordination polymer named
chameleon luminophore’ containing Eu and TbIII with high
III
Introduction
[9]
III
III
of
Eu /Tb
Temperature-sensitive luminescent nano compounds have
potential applications as thermometric materials in the field of
microelectronics and microfluidics due to their fast responses,
noninvasive operations, and nano-scale high resolutions.[1]
Various luminescent nano materials including boron-based
complexes are attributed to 1) energy gap dependence: back
5
configuration of TbIII to the excited
energy transfer from the D
4
) of organic ligands[10] and/or 2) activation energy
dependence: phonon-assisted energy transfer from Tb to
triplet state (T
1
III
III [11]
Eu .
These dependences concerned with thermo-sensitivity
organic molecules,[2] gold nanoclusters,[3] semiconductor
induce typical emission color change (green to red) with
increasing temperature. Here, we have attempted to utilize
ligand-to-metal charge transfer (LMCT) transition of lanthanide
complexes for effective thermosensing properties. The LMCT
quantum-dots,[
4]
and
lanthanide-doped
upconverting
nanoparticles[ have been reported as thermosensing materials.
In these materials, photophysical parameters such as emission
lifetime, emission wavelength, and emission intensity have been
utilized for thermosensing performance. Recently, thermometric
methods using the ratio of luminescent intensities from multiple
emission centers have been developed for accurate
5]
III
band is observed in Eu -tetramethylheptanedionate (tmh)
complexes and promotes non-radiative relaxation.[12-14] The
quenching mechanism by LMCT band has been also proposed
[15]
theoretically.
The fast relaxation process through the LMCT
[6]
thermosensing measurements. Dual-emissive thermometry is
not affected by excitation intensity of the light source,
concentration of the emitter, and/or sensitivity of the optical
detector. In terms of accurate measurements, narrow full-width
at half-maximum (fwhm) of each emission band is useful for
calculation of the ratio of luminescence intensity.
band is expected to produce unprecedented thermo-sensitive
luminescence properties.
In this study, we synthesized new seven-coordinate
dinuclear complexes composed of two lanthanide ions, six tmh
ligands, and
a
4,4’-bis(diphenylphosphoryl)biphenyl (dpbp)
dpbp], [Tb (tmh) dpbp], and [EuTb(tmh) dpbp]
ligand {[Eu (tmh)
2
6
2
6
6
in Figure 1a} for introduction of a LMCT band into dual-emissive
thermometry. The dinuclear structures were determined by
single-crystal X-ray diffraction analysis. Photophysical properties
of the dinuclear complexes were evaluated using absorption,
emission, and excitation spectra. Radiative and non-radiative
[
a]
Y. Kitagawa, T. Nakanishi, T. Seki, K. Fushimi, H. Ito, Y. Hasegawa
Faculty of Engineering
Hokkaido University
Kita-13 Jo, Nishi-8 Chome, Kita-ku, Sapporo, Hokkaido, 060-8628
(Japan)
rate constants (k
r
and knr) were calculated using emission
) and 4f-4f emission quantum yields (Φff).
E-mail: hasegaway@eng.hokudai.ac.jp
K. Yanagisawa
Graduate School of Chemical Sciences and Engineering
Hokkaido University
lifetimes (τobs
Unexpectedly,
[
b]
III
III
the
dinuclear
Eu /Tb
complex,
6
[EuTb(tmh) dpbp], showed gradual emission color change from
Kita-13 Jo, Nishi-8 Chome, Kita-ku, Sapporo, Hokkaido 060-8628
red to green with increasing temperature (Figure 1b). The
thermosensing range using the ratio of luminescence intensity
(AEu/ATb) was found to be 100-450 K. We also found that the
thermosensing ability is based on the presence of a LMCT band,
(Japan)
Supporting information for this article is given via a link at the end of
the document.
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FULL PAPER
Table 1. Crystallographic data of [EuTb(tmh)
6
dpbp], [Eu
dpbp]
Tb
2
(tmh)
6
dpbp], [Tb
2
(tmh)
6
dpbp], and [Gd
2
(tmh)
6
dpbp].
[
EuTb(tmh)
6
[Eu (tmh)
2
6
dpbp]
[Tb
2
(tmh)
6
dpbp]
Tb
2 6
[Gd (tmh) dpbp]
chemical formula
formula weight
crystal system
space group
a [Å]
C
102
H
142EuO14
P
2
C
102
H
142Eu
O
2 14
P
2
C
102
H
O
142 14
P
2
2
102 2 14 2
C H142Gd O P
1964.97
1958.01
1971.93
monoclinic
P 2 /n
1968.61
monoclinic
P 2 /n
monoclinic
monoclinic
P 2
1
/n
1
P 2 /n
1
1
22.2487 (8)
12.9155 (5)
35.9989 (14)
95.331 (7)
10299.6 (7)
4
22.2843 (5)
12.9376 (4)
36.0342 (7)
95.2528 (7)
10345.2 (4)
4
22.2894 (6)
12.9348 (3)
36.0983 (7)
95.372 (1)
10361.7 (4)
4
22.2685 (5)
12.9311 (3)
36.0097 (7)
95.402 (1)
10323.2 (4)
4
b [Å]
c [Å]
β [º]
V [Å3]
Z
-
1
d
calcd [g cm ]
1.267
1.257
1.264
1.267
T [K]
R[a]
123
123
123
123
0.0641
0.0507
0.0372
0.0563
wR[b]
0.1396
0.1264
0.0888
0.1297
0 c 0 0 c 0
a] R = Σ||F |—|F || / Σ|F |. [b] wR = [(Σw(|F |—|F .
|)2 / ΣwF 2)]1/2
[
by Arrhenius analysis of the emission lifetime. The characteristic
temperature-dependent luminescence of the dinuclear Eu /Tb
distorted monocapped-octahedron (see supporting information,
Tables S1 and S2).[17,18] TG-DTA analysis revealed that the
III
III
complex including a LMCT band is demonstrated as a single-
molecular thermosensor.
decomposition temperature of [Eu
(Figure S1).
2 6
(tmh) dpbp] was 495 K
Results and Discussion
Structural and photophysical analyses
Dinuclear
lanthanide
complexes
2 6
{[Eu (tmh) dpbp],
[
Tb
2
(tmh) dpbp], and [EuTb(tmh)
6
6
dpbp]} were synthesized by
the reaction of a precursor complex [Ln(tmh)
3
(MeOH)
2
] (Ln =
EuIII and/or Tb ) with dpbp in methanol under reflux for 6 h. A
III
dinuclear GdIII complex, [Gd
estimation of the energy level of T
(tmh)
dpbp], was also prepared for
of the organic ligands. Single
2
6
1
crystals of all of the dinuclear complexes were obtained from
recrystallization from methanol at room temperature. The
crystallographic data for [EuTb(tmh)
Tb (tmh) dpbp], and [Gd (tmh) dpbp] is shown in Table 1. The
lattice constants in a monoclinic system of [EuTb(tmh) dpbp]
were similar to those of [Eu (tmh) dpbp], [Gd (tmh) dpbp], and
Tb (tmh) dpbp]. The ORTEP view of [Eu (tmh) dpbp] is shown
in Figure 2. In this dinuclear structure, two units of [Eu(tmh) ] are
6 2 6
dpbp], [Eu (tmh) dpbp],
[
2
6
2
6
6
2
6
2
6
[
2
6
2
6
3
connected with a dpbp ligand. Average bond lengths between
Eu and O atoms in tmh and dpbp ligands were 2.33 and 2.35 Å,
respectively. These relatively short distances are similar to those
of previously reported seven-coordinate EuIII complexes.[14,16]
We carried out shape-factor calculation based on the crystal
2 6
Figure 1. a) Chemical structure of [Ln (tmh) dpbp] and b) the luminescence
color at 100-300K.
III
structure to estimate the coordination geometry around Eu . The
2 6
geometrical structure of [Eu (tmh) dpbp] was categorized as a
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The magnitudes of k
These photophysical
Tb (tmh) dpbp], and [EuTb(tmh)
. The value of Φtot for [Eu (tmh)
6
r
and knr were calculated using τobs and Φff
properties of [Eu (tmh) dpbp],
dpbp] are summarized in Table
dpbp] was 0.5%, which is due
.
2
6
[
2
2
6
6
2
to thermal relaxation from the LMCT state before
III [12-15]
photosensitized energy transfer from T
1
to Eu .
On the
other hand, [Tb (tmh) dpbp] exhibited relatively high Φtot (56%).
2
6
The high value is comparable to previously reported emission
quantum yields of the TbIII complexes with efficient
luminescence.[23-25] The large energy gap between T
and D
5
in
1
4
[
2 6
Tb (tmh) dpbp] (Figure S6) provides inefficient back-energy
2 6
Figure 2. ORTEP drawing of [Eu (tmh) dpbp]. Hydrogen atoms are omitted for
clarity. Thermal ellipsoids are shown at the 50% probability.
Table 2. Photophysical properties of [Eu
2
(tmh)
6 2 6
dpbp], [Tb (tmh) dpbp], and
[
EuTb(tmh) dpbp].
6
[
a]
[b]
ff
[c]
[d]
[e]
2
τ
[
obs
Φ
Φ
[%]
tot
k
r
k
nr
[10 s ]
complex
3
-1
-1
Figure 3a shows absorption, excitation, and emission
ms]
[%]
[10 s ]
2 6
spectra of [Eu (tmh) dpbp] in the solid state at room temperature.
[
[
Eu
2
(tmh)
6
dpbp]
0.62
0.96
66±3
0.5±0.1
1.1
5.2
The absorption band at around 320 nm is attributed to singlet π-
π* and/or σ-π* transitions of the tmh ligands.[14] Additionally, the
Tb
2
(tmh)
6
dpbp]
>61±1
56±2
>0.6
<4.6
III
shoulder band at around 370 nm is based on LMCT (tmh→Eu )
transition. The LMCT band in the EuIII complex was
experimentally confirmed by comparison with absorption
[EuTb(tmh) dpbp]
0.76
—
—
—
—
6
5
→7F
(
D
0
2
)
2 6
spectrum of [Gd (tmh)
dpbp] (Figure S2).[19] In contrast, we
[
EuTb(tmh)
6
dpbp]
0.90
—
—
—
—
5
→7F
cannot observe an effective excitation band in the UV region,
due to inefficient photosensitized energy transfer from the
( D
4
5
)
III
ligands to Eu . The excitation spectrum shows distinguishable
[a] Emission lifetime was measured excited at 355 nm (Nd:YAG laser, third
harmonics). [b] Emission quantum yield of 4f-4f transition for Eu and Tb was
III
III
5
5
4
3
f-4f absorption bands in the visible region [ L
6
and D
)← F In the case of absorption spectrum for
6
(tmh) dpbp] (Figure 3b), π-π* and/or σ-π* bands without a
J
(J = 0-
5
7
measured with an integrating-sphere unit excited at 464 nm ( D
2
← F
), respectively. [c] Total emission quantum yield was also
measured using an integrating-sphere unit excited at 330 nm. [d] Radiative
rate constant was estimated from k = Φff /τobs. [e] Non-radiative rate constant
was calculated from knr = (1/τobs)-k
0
) and
7
[20]
J
(J = 0,1)].
5
7
4
83 nm ( D ← F
4 6
[
Tb
2
LMCT band are observed in the UV region. The excitation
spectrum clearly shows intense bands based on photosensitized
luminescence at around 330 nm. The shoulder band at
r
r
.
transfer, resulting in relatively high Φtot
.
III
5
←7F
).[21]
approximately 380 nm is 4f-4f transition of Tb ( D
The emission spectra of [Eu (tmh)
(tmh) dpbp] exhibit typical 4f-4f transitions [Eu : D
0-4) and Tb : D
shapes with wide Stark splitting of [Eu
and [Tb (tmh)
3
6
2
6
III
dpbp]
and
→7F
(J
(J = 6-0)]. The characteristic spectral
(tmh) dpbp] (Figure S3a)
6
dpbp] (Figure S3b) are similar to those of
5
[
=
Tb
2
6
0
J
III
5
7
4
→ F
J
2
6
2
previously reported EuIII and TbIII complexes with low-
symmetrical seven-coordinate structures.[14, 22]
The τobs values of [Eu
EuTb(tmh) dpbp] were
luminescence decay profiles (Figure S4 and S5). The emission
profiles for [EuTb(tmh) dpbp] was single-exponential decay
curves. Therefore, the luminescence properties for
EuTb(tmh) dpbp] is expected to be mainly due to heterometallic
dinuclear complex. The τobs for [EuTb(tmh) dpbp] monitored at
) were 0.90 ms and
2
(tmh)
6
dpbp], [Tb
2
(tmh)
6
dpbp], and
[
6
obtained
from
time-resolved
6
[
6
6
5
7
5
7
5
4 5 0 2
48 nm ( D → F ) and 611 nm ( D → F
0
.76 ms, respectively. The values were different from those for
III
homometallic complexes. The decrease in lifetime of Tb
emission is attributed to energy transfer to Eu . The increase in
that of Eu emission is assumed to be due to suppression of
concentration quenching between EuIII ions.
III
III
Total emission quantum yields (Φtot) excited at 330 nm
were directly measured with an integrating-sphere unit. The
III
values of Φff (excited at 464 nm for Eu and excited at 483 nm
III
for Tb ) were also estimated by the same method as that for Φtot
.
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Figure 3. Diffuse reflection (broken line), excitation (dotted line), and emission
Figure 4. a) Emission spectra of [EuTb(tmh)
6
dpbp] at 100-400 K. b) The ratio
of emission spectral area of 5
D
→ F
7
(AEu) to 5
D
→ F
7
(ATb) at 100-450 K for
(
solid line) spectra of a) [Eu
2
(tmh)
6
dpbp] and b) [Tb
2
(tmh)
6
dpbp] in the solid
0
2
4
5
state at room temperature.
[EuTb(tmh)
6 3
dpbp] (circle) and the mixture of [Ln(tmh) tppo] (square).
Temperature-dependent luminescence
Emission spectra of [EuTb(tmh) dpbp] in the solid state at
00-400 K are shown in Figure 4a. The luminescence intensity
In accordance with previous reports by Brites et al., the
relative thermal sensitivity (S ) and temperature uncertainty (δT)
were calculated.[29] The values were summarized in Table S3,
and the values of S
and δT at 88 K were 2.2 % K-1 and 0.01 K,
respectively. The sensor reproducibility (R) was also estimated
from 10 consecutive measurements for the ratio of
luminescence integrated intensities (Figure S8), and the value of
R was found to be 99.4%.
6
r
1
5
→7F
5
→7F
of D
transition (548 nm) at 100 K and decreased with increasing
temperature. The luminescence color of [EuTb(tmh) dpbp]
0
2
transition (611 nm) was larger than that of D
4
5
r
6
gradually changed from red to green with increasing
temperature (Figure 1b), being different from the luminescence
III
III
behavior of previously reported Eu /Tb MOFs and coordination
polymers (color change: green to red).[6,8,9,26-28] We considered
that the unexpected color change is induced by the presence of
An energy diagram for energy transfer processes of
[EuTb(tmh)
the tmh ligand is excited to a singlet state, S
undergoes intersystem crossing to T
large spin-orbit interaction of the Tb -tmh unit. The triplet state
6
dpbp] are proposed in Figure 5. Under irradiation,
-1
1
(30,300 cm ), and
(25,600 cm ) owing to the
-1
a LMCT band in [EuTb(tmh)
emission spectra of the mixture of [Eu(tmh)
Tb(tmh)
tppo][15] were also evaluated to confirm the effect of the
6
dpbp]. Temperature-dependent
1
III
3
tppo] and
5
III
[
3
of tmh ligands (Ttmh
photosensitized energy transfer, which is obviously shown by
the excitation spectrum. Energy transfer from S also
to 5
occurs although the rate constant is generally smaller than that
)
generates excited
D
4
of Tb by
dinuclear structure on the luminescent color-changing
phenomenon (Figure S7). The mixture also showed red-to-green
color change with increasing temperature. Figure 4b shows the
1
D
4
ratio of the emission spectral area of 5
D
0
→ F
7
(AEu) to that of
from T
to D
5
[30]
2
1
4
.
1 1
Energy transfer from S and T of tmh ligand to
5D
of AEu/ATb for [EuTb(tmh)
mixture below 300 K. We assume that the enhanced emission at
→7F
(ATb) for [EuTb(tmh)
dpbp] and the mixture. The value
EuIII is not efficient because of the presence of LMCT state that
is main deactivation process. According to previous reports for
temperature-dependent luminescence of the ‘chameleon
4
5
6
6
dpbp] was higher than those for the
III
III
III
6
11 nm resulted from Tb -to-Eu energy transfer through dpbp
luminophore’, the combination of Tb with dpbp induces energy
ligand.
transfer from 5 to the triplet state of dpbp (Tdpbp).[9,11] The
D
4
-1
energy level of Tdpbp (22,100 cm ) was higher than the emitting
levels of TbIII ( D
5
: 20,500 cm ) and Eu ( D : 17,300 cm ). This
-1
III
5
-1
4
0
energy balance with activation energy provides temperature-
dependent energy transfer from TbIII to Eu . Excitation spectrum
III
5
→7F
of [EuTb(tmh)
6
dpbp] monitored at 611 nm ( D
0
2
) shows
photosensitized band in the UV region (Figure S9). In addition,
an emission spectrum of [EuTb(tmh)
6
dpbp] excited at 484 nm
(5
D
4
← F
7
5
→7F
transition
6
) exhibited emission band based on D
0
2
III
of Eu (Figure S10).
According to the previous reports, energy transfer through
III [9,31]
III
III
dpbp promotes effective emission from Eu .
In the Eu /Tb
mixed complexes, the energy transfer efficiency increased with
increasing temperature, resulting in gradual color change from
green to red (Figure S11). The temperature-dependent energy
transfer rate constants (kEnT) of [EuTb(tmh)
calculated using emission lifetimes of [Tb
EuTb(tmh)
dpbp] (Figure S12a).[32] Recently, Rodrigues and co-
workers calculated rate constants of energy transfer ( D
6
dpbp] were also
2
(tmh) dpbp] and
6
[
6
5
5
4
→ D
4 1
D → D
) using multipolar and exchange mechanism.[33] In
0
5
5
and
our system, the relatively long distance between lanthanide ions
in the crystal structure (the minimum is 10.2 Å) indicates that the
contribution of exchange mechanism is not much effective.
Calculated value of kEnT increased with increasing temperature
above 350 K. The Arrhenius plot of
EuTb(tmh) dpbp] presented temperature-dependent energy
transfer with activation energy (Figure S12b). The Arrhenius
kEnT indicated that
[
6
-1
analysis also suggests that the activation energy (3,700 cm ) is
5
attributed to back energy transfer from D to T
4
dpbp
rather than
that to Ttmh. In this study, unexpected red-to-green luminescence
color change of [EuTb(tmh) dpbp] was observed despite the
6
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temperature-dependent energy transfer from TbIII to Eu . We
III
were purchased from Wako Pure Chemical Industries Ltd.
Chlorodiphenylphosphine (PPh Cl), 2,2,6,6-tetramethylheptane-3,5-dion,
2
n-BuLi (in n-hexane, 1.6 M), and 4,4’-dibromobiphenyl were obtained
from Tokyo Kasei Organic Chemicals. All other chemicals and solvents
were reagent-grade and were used without further purification.
consider that the color change is caused by the state transitions
5
from D
0
to LMCT.
A state transition from 5D
previous studies.[12,14] The emission lifetime of [Eu
to LMCT has been found in
(tmh) dpbp]
0
2
6
at 100-400 K was measured for investigation of the state
transition (Figure S13). The values of τobs in the range of 100-
Apparatus: Elemental analyses were performed with an Exeter
Analytical CE440. IR spectra were recorded using a JASCO FT/IR-4600
spectrometer. 1H NMR (400MHz) spectra were measured by JEOL
300 K were approximately constant and decreased with
increasing temperature above 300 K. The temperature-
ECS400. Chemical shifts were reported in δ ppm, which is referenced to
an internal tetramethylsilane (TMS) standard. Mass-spectroscopy was
carried out by use of a Thermo Scientific Exactive (ESI-MS). TG-DTA
measurements were performed with a Seiko Instruments Inc. EXSTAR
6000 (TG-DTA 6300) in a nitrogen atmosphere at a heating rate of 1 ºC
III
dependent τobs for [Eu
tmh complexes in our previous study. The decrease in τobs is
based on the state transition from 5D
2
(tmh)
6
dpbp] is similar to those for Eu -
[
14]
0
to LMCT because the
-
1
activation energy (2,900 cm ) is smaller than the energy gap
-
1
min .
5
between D
0
and Tdpbp. We consider that the unexpected color
dpbp] is caused by the state transition
process. The quenching process related to the LMCT state in
EuTb(tmh) dpbp] provide unexpected thermosensitive
change of [EuTb(tmh)
6
Preparation of 4,4’-bis(diphenylphophoryl)biphenyl (dpbp):[34] 4,4’-
Dibromobiphenyl (1.9 g, 6.0 mmol) was dissolved in anhydrous THF
under argon and cooled to -78 ºC. A total of 2.1 equivalent of n-BuLi (7.9
mL, 12.6 mmol) was added dropwise. The temperature was not allowed
to rise above -60 ºC during the addition. Stirring was continued for 3 h at
[
6
luminescence and a wide sensing range (100-450 K) compared
with that in our previous study.
-
2
10 ºC, after which PPh Cl (2.3 mL, 12.6 mmol) was added at -78 ºC.
The mixture was gradually brought room temperature, and stirred for 6 h.
The mixture was quenched with 2 mL of methanol. The product was
extracted with ethyl acetate, and then the extract was washed with brine
for 3 times and dried over anhydrous MgSO . Volatiles were removed
4
under reduced pressure to give an off-white solid that was filtered. The
solid was dissolved in dichloromethane and cooled to 0 ºC and then 30%
H O aqueous solution (5 mL) was added to it. The reaction mixture was
2 2
stirred for 2 h. The product was extracted with dichloromethane, the
extracts washed with brine for three times and dried over anhydrous
4
MgSO . Recrystallization from dichloromethane gave colorless crystals of
the titled compound. Yield 1.7 g (54%), 1H NMR (400 MHz, CDCl
3
, 25
ºC): δ 7.67-7.80 (m, 16H), 7.45-7.60 (m, 12H) ppm.
Preparation
Tb (tmh) dpbp]: The precursor complexes, [Eu(tmh)
[Gd(tmh) (MeOH) ], and [Tb(tmh) (MeOH) ], were synthesized by the
same method as a previous report. Europium chloride hexahydrate,
gadolinium chloride hexahydrate, or terbium chloride pentahydrate (1.0 g,
.7 mmol) was dissolved in distilled water (5 mL) in a 100 mL flask. An
of
[Eu
2
(tmh)
6
dpbp],
[Gd
2
(tmh)
6
dpbp],
and
[
2
6
3 2
(MeOH) ],
Figure 5. Energy diagram for [EuTb(tmh)
6
dpbp].
3
2
3
2
[
16]
2
Conclusions
ethanol solution (20 mL) of tmh (1.46 g, 8.1 mmol) was added to the
aqueous solution. An ammonia solution was added dropwise to the flask
until pH 7. After stirring at room temperature for 6 h, the reaction mixture
was poured into cold water (300 mL) in a conical flask. The produced
III
III
We successfully synthesized a dinuclear Eu /Tb complex
with a seven-coordinate structure by means of binding two units
of lanthanide-tetramethylheptanedionate through a bidentate
phosphine oxide linker ligand. The observed luminescence color
change (red to green) with increasing temperature is based on
the presence of a LMCT state in combination with EuIII and tmh
2 6 2 6 2 6
(tmh) ], [Gd (tmh) ], or [Tb (tmh)
][12,13] was filtered, and
precipitate, [Eu
the resulting powder was recrystallized from methanol to afford colorless
block crystals of [Eu(tmh) (MeOH) ], [Gd(tmh) (MeOH) ], or
[Tb(tmh) (MeOH) ]. Each of the precursor complexes (1.0 g, 1.4 mmol)
and dpbp (0.39 g, 0.7 mmol) were dissolved with methanol (30 mL) in a
00 mL flask. The solution was heated under reflux while stirring for 6 h.
The reaction mixture was recrystallized in methanol to afford colorless
crystals of titled compounds. [Eu (tmh) dpbp]: Yield 1.1 g (79%). IR
(ATR) ˜ν = 2,865-2,955 (m, C-H), 1,570 (s, C=O), 1,172 cm (s, P=O).
3
2
3
2
3
2
5
ligands. The LMCT state induces the state transition from D
0
to
1
LMCT. The presence of a LMCT band in the lanthanide
luminophore is effective for thermosensing measurements in a
wide range. This study provides significant thermosensing ability
and new aspects for an energy transfer process in the field of
luminescent lanthanide complexes.
2
6
-
1
102 2 14 2
C H142Eu O P calcd. (%): C 62.57, H 7.31; found C 62.06, H 7.25.
[
1
6
Tb
2
(tmh)
6
dpbp]: Yield 1.1 g (81%). IR (ATR) ˜ν = 2,865-2,955 (m, C-H),
,572 (s, C=O), 1,173 cm- (s, P=O). C102
1
142 14 2 2
H O P Tb calcd. (%): C
2.12, H 7.26; found C 61.66, H 7.21. [Gd
2
(tmh)
6
dpbp]: Yield 1.1 g (79%).
-
1
IR (ATR) ˜ν = 2,865-2,955 (m, C-H), 1,570 (s, C=O), 1,172 cm (s, P=O).
calcd. (%): C 62.23, H 7.27; found C 61.89, H 7.25.
Experimental Section
C
102 2 14 2
H142Gd O P
Materials: Europium chloride hexahydrate (99.9%), terbium chloride
pentahydrate (99.9%), and gadolinium chloride hexahydrate (99.9%),
ammonia aqueous solution (28%) and H O aqueous solution (30%)
2 2
Preparation of [EuTb(tmh)
g, 0.7 mmol) and [Tb(tmh) (MeOH)
methanol (30 mL). The dpbp ligand (0.39 g, 0.7 mmol) was added to it.
6
dpbp]: A Mixture of [Eu(tmh)
3 2
(MeOH) ] (0.5
3
2
] (0.5 g, 0.7 mmol) was dissolved in
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Chemistry - A European Journal
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After reflux for 6 h, recrystallization from methanol provided colorless
crystals of titled compound. IR (ATR) ˜ν = 2,865-2,955 (m, C-H), 1,572 (s,
[4]
[5]
G. W. Walker, V. C. Sundar, C. M. Rudzinski, A. W. Wun, M. G.
Bawendi, D. G. Nocera, Appl. Phys. Lett. 2003, 83, 3555–3557.
B. Dong, B. Cao, Y. He, Z. Liu, Z. Li, Z. Feng, Adv. Mater. 2012, 24,
1987–1993.
C=O), 1,173 cm-1 (s, P=O). C102
.28; found C 62.60, H 7.20.
2
H142EuO14P Tb calcd. (%): C 62.34, H
7
[
[
[
[
[
[
6]
7]
8]
9]
C. D. S. Brites, P. P. Lima, N. J. O. Silva, A. Millán, V. S. Amaral, F.
Palacio, L. D. Carlos, Adv. Mater. 2010, 22, 4499–4504.
a) K. Binnemans, Chem. Rev. 2009, 109, 4283–4374. b) S. V Eliseeva,
J.-C. G. Bünzli, Chem. Soc. Rev. 2010, 39, 189–227.
Crystallography: Single crystals of lanthanide complexes were mounted
on micromesh (MiTeGen M3-L19-25L) using paraffin oil. All
a
measurements were carried out using a RIGAKU R-AXIS RAPID imaging
plate area detector with graphite monochromated Mo-Kα. Non-hydrogen
atoms were refined anisotoropically. All calculations were performed with
crystal-structure crystallographic software package. The quality of CIF
data was validated by the checkCIF/PLATON service. The CIF data is
presented in supporting information, and the data can be also obtained
from The Cambridge Crystallographic Data Centre (CCDC 1575443,
Y. Cui, H. Xu, Y. Yue, Z. Guo, J. Yu, Z. Chen, J. Gao, Y. Yang, G. Qian,
B. Chen, J. Am. Chem. Soc. 2012, 134, 3979−3982.
K. Miyata, Y. Konno, T. Nakanishi, A. Kobayashi, M. Kato, K. Fushimi,
Y. Hasegawa, Angew. Chem. Int. Ed. 2013, 52, 6413–6416.
10] S. Katagiri, Y. Hasegawa, Y. Wada, S. Yanagida, Chem. Lett. 2004, 33,
438–1439.
1
11] M. Hatanaka, Y. Hirai, Y. Kitagawa, T. Nakanishi, Y. Hasegawa, K.
Morokuma, Chem. Sci. 2017, 8, 423–429.
1575444, 1575445, 1584058 for [Eu
2 6 2 6
(tmh) dpbp], [Gd (tmh) dpbp],
[
Tb (tmh) dpbp], and [EuTb(tmh) dpbp], respectively).
2
6
6
[
[
12] M. T. Berry, P. S. May, H. Xu, J. Phys. Chem. 1996, 100, 9216–9222.
13] Y. C. Miranda, L. L. A. L. Pereira, J. H. P. Barbosa, H. F. Brito, M. C. F.
C. Felinto, O. L. Malta, W. M. Faustino, E. E. S. Teotonio, Eur. J. Inorg.
Chem. 2015, 3019–3027.
Optical measurements: Emission and excitation spectra were
measured with a spectrofluorometer (HORIBA Fluorolog-3). Emission
quantum yields were estimated using a spectrofluorometer (JASCO FP-
[
14] K. Yanagisawa, Y. Kitagawa, T. Nakanishi, T. Akama, M. Kobayashi, T.
Seki, K. Fushimi, H. Ito, T. Taketsugu, Y. Hasegawa, Eur. J. Inorg.
Chem. 2017, 3843-3848.
6300) with an integrating sphere unit (JASCO ILF-533). The wavelength
dependence of the detector response and beam intensity of the Xe light
source for each spectrum were calibrated using a standard light source.
Emission lifetimes were measured using the third harmonic (355 nm) of a
Q-switched Nd:YAG laser (Spectra-Physics, INDI-50, fwhm = 5 ns, λ =
[
[
15] W. M. Faustino, O. L. Malta, G. F. de Sá, J. Chem. Phys. 2005, 122,
054109.
16] K. Yanagisawa, Y. Kitagawa, T. Nakanishi, T. Akama, M. Kobayashi, T.
Seki, K. Fushimi, H. Ito, T. Taketsugu, Y. Hasegawa, Eur. J. Inorg.
Chem. 2015, 4769-4774.
1064 nm) and a photomultiplier (Hamamatsu Photonics, R-5108,
response time < 1.1 ns). The Nd:YAG laser response was monitored with
a digital oscilloscope (Sony Tektonics, TDS3052, 500 MHz) synchronized
to single pulse excitation. Emission lifetimes were determined from the
slopes of logarithmic plots of decay profiles. Temperature-dependent
emission spectra and emission lifetimes were measured using a cryostat
[
[
[
[
[
17] I. Baxter, S. R. Drake, M. B. Hursthouse, J. K. M. A. Malik, J. McAleese,
D. J. Otway, J. C. Plakatouras, Inorg. Chem. 1995, 34, 1384–1394.
18] J. Xu, E. Radkov, M. Ziegler, K. N. Raymond, Inorg. Chem. 2000, 39,
4156–4164.
(
(
Thermal Block Company SA-SB245T) and a temperature controller
Oxford Instruments ITC-502S). Diffuse reflection spectra were recorded
19] L. D. Carlos, J. A. Fernandes, R. A. Sá Ferreira, O. L. Malta, I. S.
Gonçalves, P. Ribeiro-Claro, Chem. Phys. Lett. 2005, 413, 22–24.
using a spectrophotometer (JASCO V-670) with an integrating sphere
unit (JASCO ISN-723).
20] W. T. Carnall, P. R. Fields, K. Rajnak, J. Chem. Phys. 1968, 49, 4450-
4
455.
21] W. T. Carnall, P. R. Fields, K. Rajnak, J. Chem. Phys. 1968, 49, 4447-
449.
[22] K. Binemans, Coord. Chem. Rev. 2015, 295, 1–45.
4
Acknowledgements
[
[
[
23] C. Tedeschi, C. Picard, J. Aze´ma, B. Donnadieu, P. Tisnès, New J.
Chem. 2000, 24, 735–737.
This work was supported by a Grant-in-Aid for Scientific
Research on Innovative Area of “New Polymeric Materials
Based on Element-Blocks” from the Ministry of Education,
Culture, Sports, Science and Technology (MEXT) (Japan; grant
number 2401). K. Y. was supported by the Ministry of Education,
Culture, Sports, Science and Technology through a Program for
Leading Graduate Schools (Hokkaido University “Ambitious
Leader’s Program”).
24] L. Benisvy, P. Gamez, W. T. Fu, H. Kooijman, A. L. Spek, A. Meijerink,
J. Reedijk, Dalton Trans. 2008, 3147–3149.
25] A. P. S. Samuel, J. Xu, K. N. Raymond, Inorg. Chem. 2009, 48, 687–
698.
[26] Y. Zhou, B. Yan, F. Lei, Chem. Commun. 2014, 50, 15235–15238.
[27] Y. Wei, R. Sa, Q. Li, K. Wu, Dalton Trans. 2015, 44, 3067–3074.
[
28] Q. Xu, Z. Li, Y. Wang, H. Li, Photochem. Photobiol. Sci. 2016, 15, 405–
11.
4
[
29] a) C. D. S. Brites, P. P. Lima, N. J. O. Silva, A. Millán, V. S. Amaral, F.
Palacio, L. D. Carlos, Nanoscale 2012, 4, 4799–4829; b) C. D. S. Brites,
A. Millán, L. D. Carlos, Handbook on the Physics and Chemistry of
Rare Earths, Vol. 49, (Eds.: J.-C. G. Bünzli, V. K. Pecharsky), Elsevier
Science, B. V., Amsterdam, 2016, pp. 339–427.
Keywords: Lanthanides • Luminescence • Charge transfer •
Thermochemistry • Sensors
[
[
[
[
30] W. M. Faustino, L. A. Nunes, I. A. A. Terra, M. C. F. C. Felinto, H. F.
Brito, O. L. Malta, J. Lumin. 2013, 137, 269–273.
References
31] Y. Hirai, T. Nakanishi, K. Miyata, K. Fushimi, Y. Hasegawa, Mater. Lett.
2014, 130, 91-93.
[
[
[
1]
2]
3]
L. H. Fischer, G. S. Harms, O. S. Wolfbeis, Angew. Chem. Int. Ed. 2011,
0, 4546–4551.
32] C. Piguet, J.-C. G. Bünzli, G. Bernardinelli, G. Hopfgartner, A. F.
Williams, J. Am. Chem. Soc. 1993, 115, 8197-8206.
5
J. Feng, K. Tian, D. Hu, S. Wang, S. Li, Y. Zeng, Y. Li, G. Yang, Angew.
Chem. Int. Ed. 2011, 50, 8072–8076.
33] C. V Rodrigues, L. L. Luz, J. D. L. Dutra, S. a Junior, O. L. Malta, C. C.
Gatto, H. C. Streit, R. O. Freire, C. Wickleder, M. O. Rodrigues, Phys.
Chem. Chem. Phys. 2014, 16, 14858–66.
L. Shang, F. Stockmar, N. Azadfar, G. U. Nienhaus, Angew. Chem. Int.
Ed. 2013, 52, 11154–11157.
[
34] K. Miyata, T. Ohba, A. Kobayashi, M. Kato, T. Nakanishi, K. Fushimi, Y.
Hasegawa,
ChemPlusChem
2012,
77,
277-280.
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201705021
FULL PAPER
FULL PAPER
Temperature-dependent
Lanthanide Luminescence
luminescence of the dinuclear
Kei Yanagisawa, Yuichi Kitagawa,
Takayuki Nakanishi, Tomohiro Seki,
Koji Fushimi, Hajime Ito, Yasuchika
Hasegawa*
III
III
Eu /Tb complex is demonstrated.
The unexpected luminescence color
change from red to green with
increasing temperature was
observed in the dinuclear complex.
The temperature-dependent
luminescence properties including
LMCT state are discussed.
Page No. – Page No.
III
III
A Luminescent Dinuclear Eu /Tb
Complex with LMCT Band for
Single-molecular Thermosensor
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