Luminescent Thin Films Composed of Nanosized Europium Coordination Polymers on Glass Electrodes

Article abstract of DOI:10.1002/cplu.201500382

Luminescent thin films composed of thermostable lanthanide coordination polymers on glass electrodes were prepared using a novel combination of micelle reactions and electrochemical deposition techniques. The micelle-encapsulated luminescent polymers were

Full text of DOI:10.1002/cplu.201500382

DOI: 10.1002/cplu.201500382
Full Papers
Luminescent Thin Films Composed of Nanosized Europium
Coordination Polymers on Glass Electrodes
Yasuchika Hasegawa,*[a] Takeshi Sugawara,[a] Takayuki Nakanishi,[a] Yuichi Kitagawa,[a]
Makoto Takada,[b] Akitsugu Niwa,[b] Hiroyoshi Naito,[b] and Koji Fushimi[a]
Luminescent thin films composed of thermostable lanthanide
coordination polymers on glass electrodes were prepared
using a novel combination of micelle reactions and electro-
chemical deposition techniques. The micelle-encapsulated lu-
minescent polymers were obtained by the polymerization of
[Eu(hfa)3] (hfa=hexafluoroacetylacetonate) with bridging phos-
phine oxide ligands in micelles using a redox-active ferrocenyl-
containing surfactant in water. Films were electrochemically
deposited on indium tin oxide coated glass electrodes by po-
tentiostatic polarization of micelle-encapsulated EuIII coordina-
tion polymers. The luminescence properties of the electro-
chemically deposited films were characterized by measuring
their emission spectra, emission lifetimes and emission quan-
tum yields.
Introduction
Lanthanide complexes are regarded as attractive luminescent
materials because of their characteristic narrow emission
bands (full width at half-maximum, FWHM<10 nm), wide
emission area (UV/Vis/near-IR) and long emission lifetimes (t>
ms). In general, the luminescence properties of lanthanide com-
plexes arise from 4f–4f transitions. The 4f–4f emission of EuIII
and TbIII complexes plays an important role in the design of
monochromatic red and green luminescent materials, respec-
tively, for display devices.[1–3] The near-IR 4f–4f luminescence of
NdIII, ErIII and YbIII complexes with long emission lifetimes is
useful in bioimaging applications.[4] Many types of luminescent
lanthanide complexes have been reported.[5] In this paper, we
focus on the luminescent thin films of lanthanide complexes
on glass electrodes. Such films, either on glass electrodes or
semiconductor crystals, are expected to be useful for applica-
tions in display devices such as those that are organo-electro-
luminescent (EL) or electrochemically luminescent, light-emit-
ting diode (LED) tip-devices, and photovoltaic polymer memo-
ries.[1–3] de Bettencourt-Dias has written a review of lanthanide-
based emitting materials in the field of LEDs.[2] Luminescent
thin film devices containing lanthanide complexes have been
also studied recently.[6] Thin films composed of luminescent
lanthanide complexes are expected to open up new areas of
material science.
Lanthanide-complex emitting layers are required to be
stable at temperatures around 2508C in order to be useful in
molding and solder dissolution processes—modern industrial
processes that are used for the manufacture of electronic devi-
ces. Accordingly, luminescent lanthanide coordination poly-
mers have recently received attention as thermally stable lumi-
nescent materials. Lanthanide coordination polymers are com-
posed of repeating lanthanide-complex-bridged organic coor-
dination units.[7] The polymer structures are associated with
chemical bonding such as CH–p and CH–F interactions. The
periodic structure leads to improved thermal stability with the
suppression of thermal relaxation at high temperatures. We
have recently reported thermostable lanthanide coordination
polymers with high emission quantum yields.[8,9] These lantha-
nide coordination polymers are composed of hexafluoroacetyl-
acetonate (hfa) ligands for suppression of vibrational relaxation
and bidentate phosphine oxide ligands for the formation of
asymmetric coordination structures. The emission quantum
yield and decomposition point of EuIII coordination polymers
appended with 4,4’-bis(diphenylphosphoryl)biphenyl (dpbp),
[Eu(hfa)3(dpbp)]n, are found to be greater than 70% and
3088C, respectively. The three-dimensional network structure
provides thermostable and favorable luminescent properties.[8]
Strong luminescence and thermostable thin films composed
of lanthanide coordination polymers on substrates have not
yet been prepared because lanthanide coordination polymers
with network structures are not readily dissolved in common
organic solvents and polymer matrices, although layer-by-layer
fabrication of transition-metal–organic frameworks has been
reported.[10] In particular, the thermostable luminescent EuIII co-
ordination polymer [Eu(hfa)3(dpbp)]n is insoluble in common
organic solvents (e.g., chloroform, dichloromethane, toluene,
acetone, methanol, THF, DMSO, DMF) and water.[8] The key
[a] Prof. Dr. Y. Hasegawa, T. Sugawara, Dr. T. Nakanishi, Dr. Y. Kitagawa,
Prof. Dr. K. Fushimi
Faculty of Engineering
Hokkaido University
N13 W8, Kita-ku, Sapporo
Hokkaido 060-8628 (Japan)
E-mail: hasegaway@eng.hokudai.ac.jp
[b] M. Takada, A. Niwa, Prof. Dr. H. Naito
Department of Physics and Electronics
Graduate School of Engineering
Osaka Prefecture University
1-1 Gakuen-cho, Naka-ku, Sakai, 1-2 Osaka 59908531 (Japan)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cplu.201500382.
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factor for the fabrication of thin films based on lanthanide co-
ordination polymers with network structures on a substrate is
solubility. In this study, we attempted to use luminescent
nanoparticles composed of lanthanide coordination polymers
for the preparation of a thin film on a glass electrode. The
nanoparticles were homogeneously dispersed in liquid media.
Kimizuka et al. have reported the preparation of lanthanide-co-
ordinated nanoparticles using supramolecular networks.[11] We
have also prepared lanthanide-coordinated nanoparticles using
micelle reaction techniques in aqueous solution.[12] The use of
micelle reaction techniques ensures automatic polymerization
of the coordination complexes in micellar capsules. Nanoparti-
cles composed of lanthanide coordination polymers retain the
favorable luminescent properties and good thermal stability of
their bulk powders.
Using micelle reactions and electrochemical deposition tech-
niques, we prepared and characterized luminescent thin films
composed of micelle-encapsulated EuIII coordination polymers
on indium tin oxide (ITO) glass electrodes for the first time.
The lanthanide coordination polymers [Eu(hfa)3(dpbp)]n and
[Eu(ntfa)3(dppcz)]n [ntfa=3-(2-naphthoyl)-1,1,1-trifluoroacetone,
dppcz=3,6-bis(diphenylphosphoryl)-9-phenylcarbazole] were
obtained by the polymerization of EuIII complexes ([Eu-
(hfa)3(H2O)2] and [Eu(ntfa)3(H2O)2] with shared dpbp and
dppcz[13] ligands in micellar capsules in water. Their particle
sizes were controlled using ferrocenyl surfactants (FcPEG=1,1-
ferrocenylundecylpolyoxyethylene glycol[14]) in water (Figure 1
and Scheme 1). The sizes of the prepared micelles were mea-
sured using dynamic light scattering (DLS) techniques.
Results and Discussion
Size distributions of micelle-encapsulated EuIII coordination
polymers
The bulk powders of lanthanide coordination polymers cannot
be dispersed using various types of surfactants in water. In this
study, we attempted to prepare nanosized EuIII coordination
polymers using micelle reaction techniques.[12]First, precursor
micelles (0.04 mmol) of [Eu(hfa)3] and dpbp ligand were pre-
pared in water (20 mL containing 1 mm FePEG and 0.1m LiBr).
The precursor micelles were characterized using DLS measure-
ments and the size distributions are shown in Figure 2a and b.
The average number distributions of micelles with EuIII com-
plex and bridging ligand were calculated to be 102 and
112 nm, respectively. The particle size was dependent on the
Figure 1. Formation of EuIII coordination polymer thin films on glass electro-
des.
Figure 2. Size distributions of a) [Eu(hfa)3(H2O)2] micelles, b) dpbp micelles,
c) [Eu(hfa)3(dpbp)]n micelles, and d) [Eu(ntfa)3(dppcz)]n micelles with FcPEG,
measured using DLS.
Scheme 1. Structures of the coordination polymers [Eu(hfa)3(dpbp)]n and
[Eu(ntfa)3(dppcz)]n, and the ferrocenyl surfactant FcPEG.
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concentration of [Eu(hfa)3] and dpbp ligand and independent
of the concentration of FePEG. In contrast, the average size de-
pended on the concentration of precursor [Eu(hfa)3] complex.
A lower concentration of [Eu(hfa)3] complex (0.08 mmol in
20 mL) gave rise to larger micelles (average size 300 nm). We
also found that higher concentrations (>0.02 mmol in 20 mL)
did not lead to the formation of micelles in water. The average
number distributions were larger than those of previously re-
ported micelles containing EuIII complexes[12] [sodium dodecyl
sulfate and [Eu(hfa)3(H2O)2], average size=14 nm; also trime-
thyloctylammonium bromide and the bridging ligand dpbp,
average size=10 nm]. The distribution of large-sized micelles
formed using FcPEG is due to the high hydrophilicity of the
polyoxyethylene groups. The mixed micelles for the prepara-
tion of [Eu(hfa)3(dpbp)]n nanoparticles were obtained by addi-
tion of a solution containing EuIII-complex micelles into one
containing dpbp micelles. The mixed-micelle solution showed
a mono-dispersed distribution in water (Figure 2c). The aver-
age size was approximately 170 nm (Figure 2c and Table 1).
bromide) and redox-active sites (the ferrocenyl moiety in
FcPEG). These solutions were used for electrochemical deposi-
tion of thin films directly on a glass electrode.
Preparation of thin films using electrochemical deposition
A redox-active surfactant in micelles, FcPEG shows a reversible
oxidation peak at E1/2 =0.49 V (vs. SHE) in water (see Figure S1
in the Supporting Information). This indicates that FcPEG de-
composes on the electrode surface at potentials higher than
E1/2. We attempted to prepare an EuIII coordination nanoparti-
cle thin film on an ITO-coated glass electrode by potentiostatic
polarization at 1.0 V (vs. SHE), which is high enough to oxidize
FcPEG. The ferrocenyl group is reversibly redox active and also
acts as a hydrophobic moiety in the FcPEG surfactant. Under
potentiostatic polarization at 1.0 V, the ferrocenyl group is ion-
ized to a ferrocenyl cation of hydrophilic character, resulting in
the decomposition of micelles containing the FcPEG surfactant.
The decomposition of micelles leads to deposition of EuIII-coor-
dinated nanoparticles on the glass electrode. The time transi-
ent of the current during polarization is shown in Figure 3a
and b. A relatively large anodic current flowed at the initial
Table 1. Performance of thin films on glass electrodes.
Complex
Thin film
Size
[nm][a] under
polarization [C][b]
Electric charge
Film
thickness [nm]
[Eu(hfa)3(dpbp)]n deposition 170
0.097
100–600
130–150
90
film
[Eu(ntfa)3(dppcz)]n deposition 199
film
0.114
–
[Eu(ntfa)3(dppcz)]n spin-coated
film
–
[a] Micelle size measured using DLS. [b] Working electrode: ITO-coated
glass plate (75 mm”25 mm, 8–12 W); counter electrode: platinum plate,
reference electrode: platinum wire. Potentiostatic polarization at À1.0 V
(SHE) for 5000 s.
The larger sizes of the mixed micelles might have been caused
by reconstruction of micelle shells composed of FcPEG. The re-
construction of micelle shells led to the effective formation of
[Eu(hfa)3(dpbp)]n in the mixed micelle sample.
By contrast, synthesized [Eu(ntfa)3(dppcz)]n was dissolved in
a
range of organic solvents. We speculated that [Eu-
(ntfa)3(dppcz)]n might be covered with the polyoxyethylene
units of FcPEG, resulting in the ready formation of micelles
that include [Eu(ntfa)3(dppcz)]n nanoparticles. The micelle con-
taining [Eu(ntfa)3(dppcz)]n nanoparticles for electrochemical
deposition were obtained by simply mixing FcPEG, lithium bro-
mide and [Eu(ntfa)3(dppcz)]n powder for 24 h in water. The size
distribution of micelles was determined using DLS measure-
ments (Figure 2d and Table 1). The average size was estimated
to be 199 nm. The size distribution of [Eu(ntfa)3(dppcz)]n mi-
celles was much narrower than that of [Eu(hfa)3(dpbp)]n mixed
micelles. The narrow size distribution of [Eu(ntfa)3(dppcz)]n mi-
celles might be caused by the removal of larger and smaller
micelles during the filtration process.
Figure 3. The time transient of current during polarization of a) [Eu-
(hfa)3(dpbp)]n mixed-micelle solution (0.097 C) and b) [Eu(hfa)3(dppcz)]n
mixed-micelles solution (0.114 C). SEM laser scanning microscopic images of
c,d) [Eu(hfa)3(dpbp)]n deposition film, and e,f) [Eu(ntfa)3(dppcz)]n deposition
film on the glass electrode.
stage. However, the current decreased gradually and was con-
stant after 4000 s, indicating that decomposition of FcPEG on
the ITO electrode proceeded at a steady state. The electric
charges consumed for 5000 s polarization were approximately
0.1 C (Table 1), suggesting that there is no difference between
the [Eu(hfa)3(dpbp)]n mixed-micelle solution (0.097 C) and the
[Eu(hfa)3(dppcz)]n mixed-micelle solution (0.114 C).
The prepared solutions of [Eu(hfa)3(dpbp)]n mixed micelles
and [Eu(ntfa)3(dppcz)]n micelles include an electrolyte (lithium
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After potentiostatic polarization, the presence of white-col-
ored compounds deposited uniformly on the ITO-coated glass
electrodes was observed. SEM and laser scanning microscopic
images of the deposits from the [Eu(hfa)3(dpbp)]n mixed-mi-
celle solution are shown in Figure 3c and d, respectively. A
rugged surface composed of nanoparticles, the average size of
which was approximately 150 nm, was observed. The size of
these nanoparticles was similar to that of [Eu(hfa)3(dpbp)]n
mixed micelles (average size=170 nm), indicating that a [Eu-
(hfa)3(dpbp)]n film had formed on the glass electrode. The film
thickness, measured using a laser scanning microscope, was
found to be 100–600 nm. Similarly, by using SEM and laser
scanning microscopy, the formation of [Eu(ntfa)3(dppcz)]n dep-
osition film was confirmed (Figure 3e and f). However, the
deposition film using [Eu(hfa)3(dppcz)]n micelles had a smoother
surface, and the film thickness was found to be 130–150 nm.
We consider that this smooth surface might be caused by ho-
mogenous micelle particles having a narrow size distribution.
These film thicknesses were approximately constant in each
experiment because of their fixed currents (ꢀ0.10 C) under
static polarization.
Figure 4. Emission spectra of thin films composed of EuIII-coordinated nano-
particles on glass electrodes. a) Bulk [Eu(hfa)3(dpbp)]n powder, [Eu-
(hfa)3(dpbp)]n deposition film, and bulk [Eu(hfa)3(H2O)2] powder. b) Bulk [Eu-
(ntfa)3(dppcz)]n powder, [Eu(ntfa)3(dppcz)]n deposition film, and spin-coated
[Eu(ntfa)3(dppcz)]n film. c) Emission decay profiles of [Eu(hfa)3(dpbp)]n and
[Eu(hfa)3(dppcz)]n thin films on glass electrodes. Inset in (d) is a photolumi-
nescence image of [Eu(hfa)3(dppcz)]n thin films on a glass electrode.
Emission properties of electrochemically deposited films
The emission spectra of electrochemically deposited films com-
posed of EuIII coordination polymers on glass electrodes are
shown in Figure 4a and b. Emission bands for the EuIII coordi-
nation polymers were observed at 578, 592, 613, 650, and
Table 2. Photophysical properties of bulk EuIII coordination polymers,
nanoparticle deposition films and a spin-coated film at room tempera-
ture.
5
698 nm and are attributed to the 4f–4f transitions of D0–7FJ,
[a]
Complex
Form
Ire
tobsd [ms][b]
F [%][c]
where J=0, 1, 2, 3, and 4, respectively. The spectra were nor-
malized with respect to the magnetic dipole transition intensi-
ties at 592 nm (EuIII: 5D0–7F1), which are known to be insensitive
to the environment surrounding the lanthanide ions. The
branching ratio of the electric dipole transition band, Irel, is
given by Equation (1)
[Eu(hfa)3(dpbp)]n
[Eu(hfa)3(dpbp)]n
[Eu(ntfa)3(dppcz)]n
[Eu(ntfa)3(dppcz)]n
[Eu(ntfa)3(dppcz)]n
bulk powder
deposition film
bulk powder
deposition film
spin-coated film
18.3
18.2
15.4
15.0
9.3
0.85
0.85
0.37
0.34, 0.09
0.46, 0.12
72
72
32
30[d]
25[d]
[a] Branching ratio of the electric dipole transition in emission spectra,
rel =IED/IMD [Eq. (1)]. [b] Emission lifetimes (tobsd) of the lanthanide com-
I
plexes were measured by excitation at 355 nm (Nd:YAG 3w). [c] Emission
quantum yields for EuIII complexes were determined by comparison with
the integrated emission signal (550–750 nm) of [Eu(hfa)3(biphepo)] as
F=0.60, with excitation at 465 nm. [d] Collected emission quantum
yields were estimated using calculation based on the emission lifetimes
(longer lifetime components) and radiative rate constants from the
branching ratio of the electric dipole transition.
Irel ¼ IED=IMD
ð1Þ
where IED and IMD are the intensity of the electric dipole transi-
tion at around 610 nm and magnetic dipole transition at
around 592 nm in emission spectra, respectively. The ratiomet-
ric analysis of EuIII complexes has been reported by Parker and
co-workers.[15] The Irel values are summarized in Table 2. The Irel
value for [Eu(hfa)3(dpbp)]n on the electrode was 18.2, which is
similar to that of [Eu(hfa)3(dpbp)]n bulk powders (Irel =18.3).
This result indicates that the coordination geometry of lantha-
nide coordination nanoparticles is consistent with that of bulk
lanthanide coordination polymers. We also found that the
branching ratio for the [Eu(hfa)3(dppcz)]n thin film on the elec-
trode is the same as that of bulk [Eu(hfa)3(dppcz)]n powder.
However, the Irel value of the spin-coated [Eu(hfa)3(dppcz)]n
thin film is smaller than that of bulk [Eu(hfa)3(dppcz)]n powder.
We note that the spin-coated [Eu(hfa)3(dppcz)]n thin film was
prepared from a solution of [Eu(hfa)3(dppcz)]n in chloroform;
the network structure of [Eu(hfa)3(dppcz)]n might be broken
down in this solvent. These results suggest that the electro-
chemical deposition method involving EuIII-coordinated nano-
particle micelles provides a route to stable thin films on a glass
electrode.
In order to quantitatively analyze the photophysical proper-
ties of these materials, we measured their emission lifetimes.
The emission decay profiles of [Eu(hfa)3(dpbp)]n and [Eu-
(hfa)3(dppcz)]n thin films on a glass electrode are shown in Fig-
ure 4c and d. The emission lifetimes were determined from
the slopes of the logarithmic plots of the decay profiles. The
emission lifetimes of [Eu(hfa)3(dpbp)]n bulk powder were found
to be 0.85 ms. The emission lifetime of nanosized [Eu-
(hfa)3(dpbp)]n on a glass electrode (0.85 ms) are consistent
with this value. These results indicate that the [Eu(hfa)3(dpbp)]n
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on the electrode is composed of [Eu(hfa)3(dpbp)]n nanoparti-
cles. The calculated emission quantum yield of an electrochem-
ically deposited film of [Eu(hfa)3(dpbp)]n on the electrode was
found to be 72%. The emission lifetime of nanosized [Eu-
(ntfa)3(dppcz)]n on a glass electrode is the sum of two compo-
nents—0.34 ms (longer component: 35%) and 0.09 ms (shorter
component: 65%). The longer component is similar to the
emission lifetime of bulk [Eu(ntfa)3(dppcz)]n powder (0.37 ms).
The calculated emission quantum yield based on the longer
emission lifetime component and radiative rate constant[16]
was estimated to be 30%, which is similar to that of bulk [Eu-
(ntfa)3(dppcz)]n powder (32%). The origin of the shorter com-
ponent is unclear. In contrast, the emission lifetime of the spin-
coated [Eu(hfa)3(dppcz)]n thin film (longer component:
0.46 ms) was different to that of [Eu(ntfa)3(dppcz)]n powder
and nanosized [Eu(ntfa)3(dppcz)]n on a glass electrode. In gen-
eral, the decomposition of an asymmetric eight-coordinate
structure of a lanthanide coordination compound leads to 1) a
decrease of the Irel value, 2) a decrease of the radiative rate
constant, and 3) an increase in the emission lifetime.[17] The
larger emission lifetime of the spin-coated [Eu(hfa)3(dppcz)]n
thin film might be due to decomposition of the coordination
structure. The calculated emission quantum yield of the spin-
coated [Eu(hfa)3(dppcz)]n thin film was estimated to be 25%,
which is smaller than those of bulk and thin films of [Eu-
(hfa)3(dppcz)]n. These results indicate that the luminescence
properties of the electrochemically deposited films are similar
to those of bulk lanthanide coordination polymers.
Experimental Section
Materials
Europium acetate monohydrate (99.9%) was purchased from Wako
Pure Chemical Industries Ltd. 1,1,1,5,5,5-Hexafluoro-2,4-pentane-
dione was obtained from Tokyo Kasei Organic Chemicals and
Sigma–Aldrich. All other chemicals and solvents were reagent
grade and used without further purification.
Apparatus
1H NMR (400 MHz) spectra were recorded on a JEOL ECS400 spec-
trometer. Chemical shifts are reported in d [ppm] and are refer-
enced to an internal tetramethylsilane standard. IR spectra were
measured using a Jasco FT/IR-350 spectrometer. Elemental analyses
were performed using a Yanaco CHN Corder MT-6 analyzer. Mass
spectra were acquired on a JEOL JMS-T100LP spectrometer. Size
distributions were measured with a Beckman Coulter DelsaNa-
no HC analyzer. The thicknesses of the nanoparticle thin films were
measured using a Keyence VK-8710 color 3D laser-scanning micro-
scope. SEM was performed with a JEOL JSM-6500F electron micro-
scope (acceleration voltage 10 kV).
Preparation of tris(hexafluoroacetylacetonato)europium di-
hydrate [Eu(hfa)3(H2O)2]
Europium acetate monohydrate (5.0 g, 13 mmol) was dissolved in
distilled water (20 mL) in a 100 mL flask. A solution of 1,1,1,5,5,5-
hexafluoro-2,4-pentanedione (7.0 g, 34 mmol) was added dropwise
to the solution. A white yellow precipitate formed after the reac-
tion mixture had been stirred for 3 h at room temperature. The re-
action mixture was filtered, and the resulting powder was recrystal-
lized from methanol/water to afford the title compound as color-
less crystalline needles (9.6 g, 95%). IR (KBr): n˜ =1650 (s, C=O),
1145–1258 cmÀ1 (s, CÀF); elemental analysis calcd (%) for
C15H7EuF18O8 (809.91): C 22.27, H 0.87; found: C 22.12, H 1.01.
Conclusion
Luminescent thin films composed of thermostable lanthanide
coordination polymers on glass electrodes were prepared
using a novel combination of micelle reactions and electro-
chemical deposition techniques. Electrochemical deposition of
[Eu(ntfa)3(dppcz)]n micelles provides homogenous and smooth
thin film on a glass electrode. We also demonstrated that
a simple thin film device composed of Al/[Eu(ntfa)3(dppcz)]n/
ITO/glass multilayers could be fabricated for evaluation of I–V
performance (Figure S2). A dramatic increase in current at
around 6 V was observed, which is not an ohmic response for
Preparation of 4,4’-bis(diphenylphosphoryl)biphenyl (dpbp)
4,4’-Bis-(diphenylphosphoryl)biphenyl was synthesized according
to a published procedure.[8,9] A solution of nBuLi (1.6m in hexane,
9.3 mL, 15 mmol) was added dropwise to a solution of 4,4’-dibro-
mobiphenyl (1.9 g, 6.0 mmol) in dry THF (30 mL) at À808C. The ad-
dition was complete in approximately 15 min during which time
a yellow precipitate formed. The mixture was stirred for 3 h at
À18C, after which time PPh2Cl (2.7 mL, 15 mmol) was added drop-
wise at À808C. The mixture was gradually warmed to room tem-
perature and stirred for 14 h. The product was extracted with ethyl
acetate, and the extracts were washed with brine three times and
dried over anhydrous MgSO4. The solvent was evaporated, and the
resulting residue was washed with acetone and ethanol several
times. The obtained white solid and dichloromethane (ꢀ40 mL)
were placed in a flask. The solution was cooled to 08C and then
30% aq H2O2 (5 mL) was added. The reaction mixture was stirred
for 2 h. The product was extracted with dichloromethane, and the
extracts were washed with brine three times and dried over anhy-
drous MgSO4. The solvent was evaporated to afford a white
powder. Recrystallization from dichloromethane gave the title com-
pound as white crystals (1.1 g, 33%). 1H NMR (400 MHz, CDCl3,
258C): d=7.66–7.81 (m, 16H), 7.45–7.60 ppm (m, 12H); IR (KBr):
n˜ =1120 cmÀ1 (s, P=O); MS (ESI): m/z: 555.2 [M+H]+; elemental
a
short current circuit. The network structure of [Eu-
(ntfa)3(dppcz)]n coordination nanoparticle thin film also pro-
vides thermostable properties with high decomposition tem-
perature (decomposition point>2808C), which is higher than
those
of
previous
EuIII
complexes
(decomposition
pointffi2208C).[18] Currently, we are trying to fabricate and eval-
uate a sandwich-type EL device composed of a lanthanide-co-
ordination nanoparticle thin film with holes and electron trans-
port layers. The optimum ligands for the EL device are also
being studied. Thermostable EuIII coordination polymer thin
films on electrodes are expected to be parts of a new field of
inorganic, material, electrochemical, and colloid science and
technology.
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Preparation of micelles with EuIII complexes, bridging li-
gands and micelle-encapsulated EuIII coordination polymers
analysis calcd (%) for C36H28O2P2: C 77.97, H 5.09, found: C 77.49, H,
5.20.
A solution of [Eu(hfa)3(H2O)2] (32.4 mg, 0.04 mmol) in diethyl ether
(2 mL) was added to a solution of FcPEG (1 mm) and lithium bro-
mide (0.1m) in distilled water (20 mL) in a 100 mL flask at room
temperature, resulting in the formation of micelles composed of
FCPEG, lithium bromide and [Eu(hfa)3(H2O)2]. Separately, a solution
of dpbp (22.2 mg, 0.04 mmol) in dichloromethane (2 mL) was
added to a solution of FcPEG (1 mm) and lithium bromide (0.1m)
in water (20 mL) at room temperature, resulting in the formation
of micelles composed of FcPEG, lithium bromide and dpbp. The
mixed micelles for the preparation of [Eu(hfa)3(dpbp)]n nanoparti-
cles were obtained by adding of solution containing EuIII-complex
micelles (1 mL) into a solution containing dpbp micelles (20 mL).
The micelles of [Eu(ntfa)3(dppcz)]n nanoparticles were obtained by
stirring water (20 mL) containing FcPEG (1 mm), lithium bromide
(0.1m) and [Eu(ntfa)3(dppcz)]n powder (2 mg) for 24 h at room tem-
perature. The water solution containing micelles was filtered using
a micro-filter (CS080AS, Advantec).
Preparation of 3,6-bis(diphenylphosphoryl)-9-phenylcarba-
zole (dppcz)
3,6-Bis(diphenylphosphoryl)-9-phenylcarbazole was synthesized ac-
cording to a published procedure.[8] A solution of nBuLi (1.6m in
hexane, 8.8 mL, 14 mmol) was added dropwise to a solution of 3,6-
dibromo-9-phenylcarbazole (2.4 g, 6.0 mmol) in dry THF (30 mL) at
À808C. The addition was completed within approximately 10 min,
during which time a white yellow precipitate formed. The mixture
was stirred for 2 h at À108C, after which time PPh2Cl (2.6 mL,
14 mmol) was added dropwise at À808C. The mixture was gradual-
ly warmed to room temperature, and stirred for 18 h to give
a white precipitate. The precipitate was filtered, washed with
methanol several times, and dried in vacuo. The obtained white
powder and dichloromethane (ꢀ40 mL) were placed in a flask.
The solution was cooled to 08C and then 30% aq H2O2 (8 mL) was
added. The reaction mixture was stirred for 2 h. The product was
extracted with dichloromethane, and the extracts were washed
with brine three times and dried over anhydrous MgSO4. The sol-
vent was evaporated to afford a white powder. Recrystallization
from dichloromethane/hexane gave the title compound as color-
Electrochemical measurements and deposition of a thin film
on a glass electrode
The water solution prepared above, containing micelle-encapsulat-
ed EuIII coordination polymers, was placed in a three-electrode
electrochemical cell and bubbled with pure argon gas to remove
dissolved oxygen. An ITO-coated glass plate (sheet resistance: 8–
12 W) with an area of 75 mm”25 mm was used as a working elec-
trode and a platinum plate and wire were used as the counter
electrode and quasi-reference electrode, respectively. The quasi-ref-
erence electrode potential was calibrated with the standard hydro-
gen electrode (SHE) potential by measuring a redox potential of
ferrocene (E0 =0.554 V vs. SHE) before and after polarization. A po-
tentiostat (Hokuto HA-151) and a function generator (Hokuto HB-
104) were used for the following two modes of polarization: cyclic
voltammetry in the potential range 0–1.3 V (vs. SHE) at a scan rate
of 5 mVsÀ1 was performed to survey the electrochemical activity of
FcPEG, and potentiostatic polarization at 1.0 V (vs. SHE) for 5000 s
was also conducted to electrochemically deposit nanoparticles on
the electrode surface.
1
less crystals (2.0 g, 53%). H NMR (400 MHz, CDCl3, 258C) d=8.43–
8.47 (d, J=12.0 Hz, 2H), 7.63–7.76 (m, 11 H), 7.43–7.60 ppm (m,
18H); IR (KBr): n˜ =1122 cmÀ1 (s, P=O); MS (ESI): m/z: 644.2 [M+H]+;
elemental analysis calcd (%) for C42H31NO2P2: C 78.37, H 4.85, N
2.18; found: C 78.42, H 5.00, N 2.18.
Preparation of [Eu(hfa)3(dpbp)]n coordination polymer
The dpbp ligand (1 equiv) and [Eu(hfa)3(H2O)2] (1 equiv) were dis-
solved in chloroform (20 mL). The solution was heated at reflux
with stirring for 8 h, and then the reaction mixture was concentrat-
ed to dryness. A single crystal suitable for X-ray structural determi-
nation of the EuIII coordination polymer was obtained by the diffu-
sion method from methanol/chloroform solution at room tempera-
ture. Yield: 98 mg (67% for monomer); IR (KBr): n˜ =1653 (s, C=O),
1255–1145 (s, CÀF), 1127 cmÀ1 (s, P=O); MS (ESI): m/z: 1120.08 [Eu-
(hfa)2(dpbp)]+, 2447.15 [Eu2(hfa)5(dpbp)2]+; elemental analysis
calcd (%) for [C51H31EuF18O8P2]n: C 46.14, H 2.35; found: C 45.59, H
2.49; decomposition temperature: 3088C.
Preparation of a spin-coated thin film on a glass electrode
The spin-coated thin film was prepared as a reference using
a Nanbu Mechatro Co. Ltd spin coater (2000 rpm, 60 s) with
Preparation of [Eu(ntfa)3(dppcz)]n coordination polymer
a
chloroform solution containing [Eu(ntfa)3(dppcz)]n powder
(1 mm). After spin-coating, the thin film was sintered at 608C for
30 min to evaporate chloroform.
Europium chloride hexahydrate (0.54 g, 1.5 mmol) was dissolved in
ethanol (10 mL) in a 100 mL flask. A solution of 3-(2-naphthoyl)-
1,1,1-trifluoroacetone (ntfa; 1.2 g, 4.5 mmol) in ethanol (40 mL) and
triethylamine (0.6 mL, 4.5 mmol) was added dropwise to the flask. A
white/yellow precipitate formed after stirring for 2 h at room tem-
perature. The reaction mixture was filtered, and the resulting solid
was recrystallized from methanol/water. A solution of the phos-
phine oxide ligand (dppcz, 0.2 g, 0.31 mmol) in chloroform (3 mL)
was added to a solution of [Eu(ntfa)3(H2O)2] (0.34 g, 34 mmol) in
ethanol (5 mL). The solution was stirred at room temperature for
4 h to give a white precipitate. The precipitate was filtered, washed
with ethanol and hexane several times, and dried in vacuo. Yield:
0.34 g (63%). MS (ESI): m/z: 1326.2 [Eu(ntfa)2(dppcz)]+, 1969.38 [Eu-
(ntfa)2(dppcz)2]+, 2917.4 [Eu2(ntfa)2(dppcz)]+; elemental analysis
calcd (%) for C84H55EuF9NO8P2: C 63.40, H 3.48, N 0.88; found: C
64.64, H 3.67, N 1.05; decomposition temperature: 2808C.
Optical measurements
Absorption and emission spectra of the lanthanide complexes
were measured with JASCO V-670, JASCO F-6300-H and Horiba Flu-
oroLog spectrometers, which were used to correct for the response
of the lamp, mirrors, gratings, and photomultiplier detector
system. The emission quantum yields of solutions of lanthanide
complexes (10 mm in [D6]acetone), degassed with argon, were ob-
tained by comparison with the integrated emission signal (550–
750 nm) of a reference solution of [Eu(hfa)3(TPPO)2] (50 mm in
[D6]acetone, F=0.60). EuIII complexes were excited at 465 nm
(direct excitation). Emission lifetimes of lanthanide complexes
(10 mm in [D6]acetone) were measured using the third harmonics
ChemPlusChem 2016, 81, 187 – 193
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Manuscript received: August 25, 2015
Accepted Article published: September 30, 2015
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