Imidazolium ionic liquids in OLEDs: synthesis and improved electroluminescence of an 'ionophilic' diphenylanthracene

Article abstract of DOI:10.1016/j.tet.2008.04.112

A 9,10-diarylanthracene having two ionophilic imidazolium tags on peripheral positions has been synthesized through a radical chain addition of 1,2-dimethyl-3-(3-mercaptopropyl)imidazolium to 9,10-distyrylanthracene. OLED cells prepared with this derivative exhibits 13.6-fold efficiency enhancement as compared to that prepared with 9,10-diphenylanthracene at the same concentration. Based on electrical conductivity measurements, this efficiency enhancement has been attributed to the blocking of spurious current flow due to ion relocation near the electrodes. The advantage of covalent attachment compared to physical mixtures of 9,10-diphenylanthracene and 1,2-dimethyl-3-(3-mercaptopropyl)imidazolium ionic liquid derives from the experimental difficulty of having an active layer with the target anthracene-to-ionic liquid ratio due to the remarkable differences in viscosity of the two components of the mixture.

Full text of DOI:10.1016/j.tet.2008.04.112

Tetrahedron 64 (2008) 6270–6274
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Imidazolium ionic liquids in OLEDs: synthesis and improved electroluminescence
of an ‘ionophilic’ diphenylanthracene
´
*
Roberto Mart ı´ n, Laura Teruel, Carmela Aprile, Jose F. Cabeza, Mercedes Alvaro, Hermenegildo Garc ı´ a
Instituto de Tecnolog ´ı a Qu ´ı mica CSIC-UPV and Departamento de Qu ´ı mica, Universidad Polit e´ cnica de Valencia, Av. De los Naranjos s/n, 46022 Valencia, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
A 9,10-diarylanthracene having two ionophilic imidazolium tags on peripheral positions has been syn-
thesized through a radical chain addition of 1,2-dimethyl-3-(3-mercaptopropyl)imidazolium to 9,10-
distyrylanthracene. OLED cells prepared with this derivative exhibits 13.6-fold efficiency enhancement as
compared to that prepared with 9,10-diphenylanthracene at the same concentration. Based on electrical
conductivity measurements, this efficiency enhancement has been attributed to the blocking of spurious
current flow due to ion relocation near the electrodes. The advantage of covalent attachment compared
to physical mixtures of 9,10-diphenylanthracene and 1,2-dimethyl-3-(3-mercaptopropyl)imidazolium
ionic liquid derives from the experimental difficulty of having an active layer with the target anthracene-
to-ionic liquid ratio due to the remarkable differences in viscosity of the two components of the mixture.
Ó 2008 Elsevier Ltd. All rights reserved.
Received 21 March 2008
Received in revised form 24 April 2008
Accepted 28 April 2008
Available online 1 May 2008
1. Introduction
to increase the solubility in perfluorinated solvents.31–35 In the case
of ionic liquids, we and others have reported that the affinity of
Ionic liquids, particularly those with imidazolium type, have
a catalyst for these solvents can be increased by attaching imida-
zolium units far from the active metal center.
1
–4
36–39
emerged as novel green solvents in catalysis.
Due to the re-
markable physicochemical properties of ionic liquids, particularly
the electrical conductivity and electrochemical stability, these
Inspired by this work on catalysis and considering the pre-
cedents suggesting that the presence of ionic liquids can enhance
the performance of OLEDs, in the present work we describe the
synthesis and electroluminescent properties of an ‘ionophilic’ 9,10-
diphenylanthracene (DPA). DPA is an organic compound that ex-
5
–7
compounds have also found application in electrochemistry
and
as components for solar cells and organic electroluminescent
diodes (OLEDs).5
,8–14
Specifically, the low volatility of ionic liquids
4
0–42
and their ionic conductivity can be used to replace advantageously
aqueous electrolytes in fuel cells and dye synthesized solar cells,
prolonging the service lifetime of these photovoltaic devices.11–22
One general problem in OLEDs is charge transport from the
external electrodes through the organic layer in which electron and
hibits electroluminescence.
We will show that the covalent
attachment of imidazolium tags renders a product that combines
the electroluminescent properties imparted by the 9,10-diaryl-
anthracene with the ionic liquid characteristics of the imidazolium
moieties. The resulting ionophilic derivative exhibits improved
electroluminescent properties with respect to cells based on 9,10-
diarylanthracene or even a mixtures of the polycyclic aromatic
compound and imidazolium ionic liquid.
hole recombination must generate the electronically excited state
that eventually will originate light emission.2
3–29
In this context,
it has been recently reported that the presence of ionic liquids can
enhance the efficiency of OLED emission by one or two orders of
magnitude.5
,7,8,10,13,16
The positive influence of ionic liquids has
2. Results and discussion
been attributed to accumulation of ions near the electrodes
that leads to high interfacial fields favoring the tunneling of
electrons.1
2.1. Synthesis of ionophilic diarylanthracene
0,16
One general strategy in catalysis to increase the affinity of
a successful catalyst for a particular medium is to modify the active
species by introducing in peripheral position a tag that increases
In order to implement the properties of ionic liquids on DPA, we
designed an ionophilic diarylanthracene having two imidazolium
rings in peripheral positions. The actual compound 9,10-bis[4-(3-
(1,2-dimethyl imidazoliumyl)propylthioethyl)phenyl]anthracene
bishexafluorophosphate (compound 7) was synthesized as in-
dicated in Scheme 1.
3
0
the affinity for this solvent. Analogous strategy has been applied
*
Corresponding author.
E-mail address: hgarcia@qim.upv.es (H. Garc ı´ a).
The starting compound in the synthesis is 1,10-dis-
tyrylanthracene (3) that was in turn obtained by the palladium
0
040-4020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.04.112

R. Mart ´ı n et al. / Tetrahedron 64 (2008) 6270–6274
6271
Cl
S
S
Br
Pd(dba)2
Na2CO3
HSCH2CH2Cl
+
2
Dioxane/Water
AIBN/N atm
Toluene/reflux
2
Reflux
Br
B
HO
OH
1
2
3
4
Cl
N
S
S
N
N
X
N
5
6
X
X
= Cl
1
,2-dimethyl-1H-imidazole
NH4PF6
Toluene reflux
7
= PF6
X
N
N
Scheme 1. Synthesis of the ionophilic derivative of 9,10-diarylanthracene having two imidazolium units.
catalyzed Suzuki cross-coupling between commercially available
,10-dibromoanthracene and 4-styrylboronic acid. This styrylan-
diarylanthracene derivative on the electrode. Since the active layer
was prepared by spin coating, it was difficult to reproduce exactly
the concentration of anthracene luminophore in the film from cells
prepared with different anthracene derivatives. Actually, the con-
centration of the active anthracene units prepared at the same
speed varied in each cell depending on the viscosity of the com-
pound. More viscous ionophilic anthracene derivative 7 tends to
give more concentrated films than less viscous DPA or DPA/imi-
dazolium mixtures. For this reason, the spinning speed was ad-
justed for each sample to obtain films with matched optical
absorbance for anthracene, thus allowing drawing conclusions
about the relative light emission efficiency for films with identical
anthracene concentrations. To illustrate this point, Figure 1 shows
the transmission optical spectra of three representative films of
DPA and compound 7. In this figure, it can be seen that by adjusting
the spin coating parameters it was possible to prepare optically
matched films for DPA and compound 7. This figure also shows that
it is possible to quantify the relative concentration of anthracenyl
chromophore by measuring the optical density at 380 or 410 nm. In
9
thracene 3 was reacted with 3-chloropropanethiol using AIBN as
radical initiator in the absence of oxygen. Radical addition of thiols
to electron rich carbon–carbon double bonds is a reaction that
occurs in high yields under mild conditions compatible with the
4
3
presence of a large variety of functional groups. The last step in
the synthesis was the nucleophilic substitution of primary chlorine
atom by the nucleophilic nitrogen of N-methylimidazol. Finally, ion
ꢀ
ꢀ
6
renders the hexafluorophosphate salt of
metathesis of Cl by PF
bisimidazolium 7.
The target ionophilic diarylanthracene 7 and the synthetic in-
termediates were characterized by their spectroscopic properties.
4
4
Compound 3 had been previously reported in the literature and
1
its transformation into 4 is accompanied by the disappearance in H
NMR of the signals corresponding to vinylic hydrogens and the
concurrent appearance of the two triplets at 3.11 and 2.99 ppm due
to the methylene groups attached to sulfur.
On the other hand, the introduction of the 1,2-dimethylimid-
azolium units by substitution of the two terminal chloride atoms in
compound 4 is accompanied by the presence of the signals corre-
sponding to the quasi-equivalent four imidazoliumyl hydrogen
atoms at low field in the aromatic region. A complete set of spec-
troscopic data for compound 7 and its synthetic intermediates are
given in Section 4.
0.15
a
0.10
2
.2. Electroluminescence study
b
9
,10-Diphenylanthracene has a fluorescence quantum yield of
0
.98. This high photoluminescence efficiency is in part responsible
0.05
for the use of these compounds in OLEDs. In order to evaluate the
influence of the presence of imidazolium tags on the electrolumi-
nescence performance of compound 7, three series of OLED cells
were prepared on transparent ITO electrodes previously treated to
deposit a nanometric PEDOT–PSS layer. The series of cells contained
as active layer DPA, mixtures of DPA and 1,2-dimethyl-3-(3-mer-
captopropyl)imidazolium hexafluorophosphate ionic liquid
c
0.00
400
500
Wavelength (nm)
(
DMPIM), or compound 7. The construction of the cells was com-
Figure 1. Transmission optical spectrum of ITO/PEDOT–PSS electrode containing a film
at two different concentrations: DPA (spectra a and b) or a film of the ionophilic an-
thracene 7 (spectrum c). The broad band spanning from 435 to 600 nm and peaking at
pleted by sublimation of aluminum as back electrode. The config-
uration of the cells was ITO/PEDOT–PSS/luminophore/Al.
Transmission optical spectroscopy of the ITO/PEDOT–PSS/
luminophore allowed quantifying the actual amount of
480 nm is due to PEDOT–PSS. The spectra show the vibrational structure characteristic
of anthracene chromophore with relative maxima at 345, 380 and 410 nm.

6272
R. Mart ´ı n et al. / Tetrahedron 64 (2008) 6270–6274
this way, the electroluminescence efficiency of the different cells
with optically matched anthracene absorbance could be compared
directly.
60
9000
60
d
a
Using the ITO/PEDOT–PSS/DPA or ITO/PEDOT–PSS/7 as anodes,
two electroluminescent cells were prepared and the corresponding
emission measured. No light emission was observed at low DC
voltages, but the ITO/PEDOT–PSS/7 cell started to emit above 6 V.
The positive influence of the imidazolium tags favoring the effi-
ciency of the cell was clearly demonstrated by the fact that the cell
containing DPA at the same concentration as compound 7 does not
emit at all in this voltage range. Actually, working at voltages below
b
0
0
10
0
5
V (v)
c
8
V DC we observed emission from the cell containing DPA at the
b
concentration shown in plot ‘a’ of Figure 1 that is higher than that of
luminophore in the cell constructed with compound 7. However, as
Figure 2 shows, the intensity of the cell containing higher DPA
concentration was still much lower than that of the ITO/PEDOT–
PSS/7 electrode despite that the last cell contains 2.1 times lower
chromophore concentration. Thus, the results shown in Figure 2
nicely exemplify the beneficial influence of the imidazolium tags
boosting the emission inherent to the DPA electroluminophore.
One point of interest is to disclose whether or not the effect of
the imidazolium ionic liquid is also observed for physical mixtures
of DPA and DMPIM ionic liquid not covalently bonded. In other
words, an interesting issue is to assess the role of the covalent at-
tachment between the electroluminophore unit and the imidazo-
lium tag. This point was addressed by preparing a third cell in
which the active layer was a mixture of DPA and DMPIM in a 1:2 M
ratio. DMPIM imidazolium ionic liquid has the same structure as
the ionophilic tag unit present in compound 7. The cell preparation
and, particularly, the spinning rate were again adjusted to obtain
films with optically matched absorbance for the anthracene lumi-
nophore. However, also for this ITO/PEDOT–PSS/DPA–DMPIM/Al
cell, no electroluminescence was observed for voltages below 8 V
DC. This control shows again the benefits of the covalent linkage
occurring in compound 7 as compared to a physical mixture of two
analogous components. Among the reasons for this different be-
havior, the simplest one is the different relative concentration of
DPA versus imidazolium ionic liquid in the initial solution (1:2) and
in the film. In this regard we note that, as commented before, due to
differences in viscosity, the film becomes more concentrated on the
ionic liquid than the initial mixture.
0
0
6
Voltage (V)
12
Figure 3. Current density versus the DC voltage applied: (a) ITO/PEDOT–PSS/DPA/Al;
(b) ITO/PEDOT–PSS/7/Al, and (c) ITO/PEDOT–PSS/DPA–DMPIM/Al. Inset: Light emission
intensity (I, plot d) and current density (J, plot b) versus the DC voltage applied (V) for
the ITO/PEDOT–PSS/7/Al cell.
were carried out. Figure 3 shows the current density flowing
through the cell versus the DC voltage applied for two of the cells
shown in Figures 1 and 2 as well as a third cell prepared with the
1:2 physical mixture of DPA and DMPIM.
As it can be seen in this figure the cell prepared with compound
7 is the one that exhibits the minimum current flow. Particularly, at
the voltage at which the electroluminescence shown in Figure 2
was measured (8 V DC), the current density of the cell prepared
with 7 as active layer was 6.1 times smaller than that of the cell
prepared with DPA. These values allowed estimating that the effi-
ciency of the cell prepared with compound 7 is 13.7 times higher
than that of DPA, again reinforcing the positive influence of
attaching the ionophilic tags on the electroluminophore unit. Ac-
tually, this influence of the ionic liquid on the efficiency of elec-
troluminescence cells had been previously reported although not
10,16
for compounds having covalent linkage.
It is interesting to note
that also for the sample prepared using a mechanical mixture of
DPA and DMPIM the same effect, i.e., a decrease of the current in-
tensity as compared to the cell with DPA lacking ionic liquid, was
observed (see Fig. 3, plot ‘c’). According to the precedents in the
literature, this effect of the ionic liquid on the conductivity using DC
can be explained by the creation of a double layer in contact with
the electrodes due to the relocation of the ions. Due to the elec-
trostatic fields, a gradient of ions in the film will occur, the con-
centration of mobile PF
In order to gain understanding on the origin of the beneficial
influence of imidazolium substituents on the electroluminescent
emission, measurements of the electrical conductivity of the cells
10
10000
c
ꢀ
6
anions being higher near the cathode and
lower near the anode. Thus, a barrier in the electrode–film interface
will block the spurious current flow. Also in our case, the expla-
nation proposed in the literature would apply and will be sup-
ported by the lower current flow when imidazolium ions are
present in the active layer.
5000
Concerning the measurements of the electrical conductivity in
the film prepared with a physical mixture of DPA and DMPIM, it is
interesting to comment that the reports in the literature used
typically a luminophore-to-ionic liquid molar ratio of 1:0.5, i.e.,
about 4 times less than the initial concentration of our mixture.
Moreover, as commented earlier, in the spin coating process
a concentration in DMPIM ionic liquid occurs when there is no
covalent bonding and, therefore, the film prepared with the DPA–
DMPIM mixture contains a DPA/DMPIM ratio lower than 1:2. Thus,
it has to be noted that the precedents in the literature focused on
the optimization of the OLED cell are using much less concentration
in ionic liquid than in our case that deals on the positive influence
of the covalent binding of an ionophilic tag on an
b
a
0
400
500
Wavelength (nm)
600
700
Figure 2. Light emission from OLED cells recorded: (a) ITO/PEDOT–PSS/7/Al at 0 V, (b)
ITO/PEDOT–PSS/DPA (2.1 times more concentrated)/Al at 8 V DC, and (c) ITO/PEDOT–
PSS/7/Al at 8 V DC.

R. Mart ´ı n et al. / Tetrahedron 64 (2008) 6270–6274
6273
electroluminescent molecules. However, we consider that the ini-
4.1.3. 9,10-Bis[4-(2-(3-(N-1,2-dimethylimidazoliumyl)propylthio)-
tial molar ratio of the mixture employed here is more relevant to
the present study in which compound 7 has two imidazolium units
per diarylanthracenyl core. Thus, in a simplistic manner, the ad-
vantage of the covalent attachment is to ensure a fixed lumino-
phore ionic liquid ratio avoiding viscosity effects and problems
associated with the active layer preparation.
ethyl)phenyl]anthracene bischloride (6)
A solution of 9,10-bis[4-(2-(3-chloropropylthio)ethyl)phenyl]-
anthracene (4) (80 mg, 0.133 mmol) and 1,2-dimethylimidazole (5)
(24 ml, 0.266 mmol) in dry toluene (5 ml) was heated at reflux
temperature under Ar atmosphere for 48 h. After removal of the
solvent, diethyl ether was added and the evolved solid filtered to
obtain 9,10-bis(4-(2-(3-(N-1,2-dimethylimidazoliumyl)propylth-
3
. Conclusion
io)ethyl)phenyl)anthracene bischloride (6) (95 mg, 93.1%) as
1
a brown material. H NMR (300 MHz, CDCl
3
):
d
(ppm)¼7.80–7.35
Analogously to the precedents reporting the beneficial in-
(m, 16H; arom. H), 6.96þ6.84 (sþs, 1þ1H, –CH]CH–), 3.68 (t,
J¼6.3 Hz, 2ꢂ2H; N–CH ), 3.61 (s, 3H, N–CH ), 3.11 (t, J¼7.9 Hz,
), 2.82 (t, J¼6.0 Hz,
), 2.19 (q, J¼6.1 Hz,
(300 MHz, CDCl ):
fluence of ionic liquids on the efficiency of electroluminescent
cells, herein we have observed that a molecule derived from DPA
containing two peripheral imidazolium units exhibits over one
order of magnitude efficiency enhancement as compared to the
parent molecule. This effect seems to arise from the blocking of
spurious current flow and a more efficient charge injection into
the active layer. Compared to mixtures of luminophore and ionic
liquid, the covalent attachment presents the advantage of film
preparation, ensuring the fixed luminophore-to-ionic liquid ratio.
Overall, our report illustrates the benefits of applying the concept
of ionophilicity to OLED cells.
2
3
2ꢂ2H; CH
2ꢂ2H; Ar–CH
2ꢂ2H; CH –CH
2
–S), 2.97 (t, J¼7.2 Hz, 2ꢂ2H; S–CH
2
2
–CH
2
), 2.45 (s, 3H, C–CH
3
13
2
2
–CH
2
);
C
NMR
3
d
(ppm)¼133.92, 131.41, 129.83, 128.55, 126.88, 125.91, 124.89,
120.34, 53.95, 49.23, 43.48, 36.19, 32.17, 29.61, 29.21, 26.71; IR
ꢀ
1
(KBr):
n
(cm )¼3045, 2939, 2864, 2232, 1716, 1684, 1606, 1513,
1441, 1399, 1310, 1263, 1098, 1025, 941, 813, 771, 670, 544. ESI-
2
þ
2þ
364.1, found m/z 413
MS: Calcd for C46
H
56
N
4
S
2
(MþH)
ꢀ
ꢀ 2þ
2
)
(MHþAcO þHCO
.
4
.1.4. 9,10-Bis(4-(2-(3-(N-1,2-dimethylimidazolyl)propylthio)-
ethyl)phenyl)anthracene bishexafluorophosphate 7
saturated aqueous solution of ammonium hexa-
4
4
4
. Experimental section
A
.1. Synthesis of organic compounds
fluorophosphate was mixed with 9,10-bis(4-(2-(3-(N-1,2-dime-
thylimidazoliumyl)propylthio)ethyl)phenyl)anthracene bischloride
(6) (90 mg, 0.117 mmol) by ultrasonication for 12 h until appear-
ance of an orange solid corresponding to 9,10-bis(4-(2-(3-(N-1,
.1.1. Synthesis of 9,10-bis-(4-vinylphenyl)anthracene (3)
9
,10-Distyrylanthracene was prepared according to the method
4
4,45
reported in the literature.
9,10-Dibromoanthracene (6.04 g,
2-dimethylimidazolyl)propylthio)ethyl)phenyl)anthracene bishex-
1
18 mmol), 4-vinylphenylboronic acid (7.98 g, 54 mmol), ground
afluorophosphate (7) (110 mg, >95%). H NMR (300 MHz, CDCl
3
):
t
potassium carbonate (8.292 g, 108 mmol) and Pd
2
(dba)
3
/Pd(P Bu
3
)
2
d
(ppm)¼7.80–7.3 (m, 16H; arom. H), 7.20þ6.95 (sþs, 1þ1H,
–CH]CH–), 3.74 (s, 3H, N–CH ),
), 3.64 (t, J¼6.3 Hz, 2ꢂ2H; N–CH
3.13 (t, J¼7.4 Hz, 2ꢂ2H; S–CH ), 2.93 (t, J¼7.2 Hz, 2ꢂ2H; CH –S),
2.81 (t, J¼6.9 Hz, 2ꢂ2H; Ar–CH –CH ), 2.74 (s, 3H, C](N)C–CH ),
2.13 (q, J¼6.3 Hz, 2ꢂ2H; CH –CH ); C NMR (300 MHz,
CDCl ):
(ppm)¼132.09, 131.72, 130.17, 128.93, 128.85, 127.25,
125.35, 125.28, 54.32, 49.78, 43.86, 34.03, 31.79, 29.60, 27.10, 26.15;
(
108.8:30.6 mg, 0.12:0.06 mmol, 1 mol Pd%) in dry toluene (300 ml)
3
2
ꢁ
were stirred magnetically in a pre-heated oil bath at 110 C for 48 h
under nitrogen atmosphere. After this time, the suspension was
filtered while hot under vacuum and the solvent was evaporated
under vacuum, allowing a further evaporation to remove any sty-
rene formed. The crude was submitted to partition in CH
the organic phase was collected, dried and CH Cl evaporated un-
der reduced pressure to obtain a bright yellow solid (6.28 g,
2
2
2
2
3
13
2
2 2
–CH
3
d
2 2
Cl /water,
ꢀ
1
2
2
IR (KBr):
n
(cm )¼3046, 2944, 2862, 2238, 1689, 1604, 1512,
1446, 1408, 1393, 1313, 1263, 1023, 913, 843, 815, 770, 740, 670, 644,
549. ESI-MS: Calcd for C46
ꢀ1
þ
16.4 mmol, 91%). IR (KBr)
n
(cm ): 1668, 1627, 1508, 1438, 1392,
H
56
N
4
S
2
, 724.9, found 759 (100)
1
ꢀ
ꢀ þ
þ
1110, 1029, 991, 941, 908, 875, 829; H NMR (300 MHz, CDCl
3
)
(MHþCl ), 761 (33) (MHþCl ) ; ESI-MS/MS for the (MHþCl) peak
þ
ꢀ
ꢃ
þ
ꢀ
d
(ppm): 7.75 (4H, dd, J¼4 Hz, 7 Hz), 7.65 (4H, d, J¼8 Hz), 7.45 (4H, d,
m/z: 759 (MHþCl) , 661 (MHþCl ꢀC
5
H
10
N
2
) , 563 (MHþCl ꢀ2ꢂ
ꢃ
þ
5 10 2
C H N ) .
J¼8 Hz), 7.30 (4H, dd, J¼4 Hz, 7 Hz), 6.90 (2H, dd, J¼11 Hz, 18 Hz),
13
5
.90 (2H, d, J¼18 Hz), 5.40 (2H, d, J¼11 Hz); C NMR (300 MHz,
CDCl (ppm): 136.7 (2C), 134.9, 134.8, 129.7, 128.0, 125.1, 124.4,
3
) d
123.2, 112.3. MS: m/z 382.
4.2. Preparation of light emitting cells
4
.1.2. 9,10-Bis(4-(2-(3-chloropropylthio)ethyl)phenyl)anthracene (4)
-Chloropropanethiol (51 l, 0.523 mmol) was added to a solu-
tion of 9,10-distyrylanthracene (3) (100 mg, 0.262 mmol) and AIBN
Commercial ITO transparent electrode (OC50 on 175
ester, 40–60 U/sqr, 85% transmittance) was rinsed with Alcanox
m
m poly-
Ò
3
m
then with MilliQ water, dried and submitted to deep UV irradiation
for 15 min. Recently clean ITOs were spin coated with an aqueous
solution of PEDOT–PSS {Aldrich, poly(styrenesulfonate)/poly(2,3-
dihydrothieno[3,4-b]-1,4-dioxin), 1,3 wt % dispersion in water} at
2000 rpm. After drying the film in a laminar flux hood, the elec-
(
10 mg) in dry toluene (5 ml). The solution was exhaustively
ꢁ
degassed for 30 min before heating at 110 C for 24 h. The reaction
mixture was stirred magnetically while heated. After the required
time, the solvent was removed in vacuum and 9,10-bis(4-(2-(3-
chloropropylthio)ethyl)phenyl)anthracene (4) (98 mg, 95%) was
2 2
trode was submitted again to spin coating with a CH Cl solution of
1
obtained as
a
yellow solid.
H
NMR (300 MHz, CDCl
3
):
DPA (2.5 mg/ml), ionophilic compound 7 (7.5 mg/ml) or a mixture of
DPA and 1,2-dimethyl-3-(3-mercaptopropyl)imidazolium (DMPIM)
hexafluorophosphate (2.5:4.8 mg/ml, respectively, in a 1:1 AcN/
d
(ppm)¼7.85–7.30 (m, 16H; arom. H), 3.73 (t, J¼6.3 Hz, 2ꢂ2H; CH
Cl), 3.11 (t, J¼8.1 Hz, 2ꢂ2H; ArCH CH –S), 2.99 (t, J¼8.1 Hz, 2ꢂ2H;
ClCH CH CH –CH ), 2.14 (q,
–S), 2.81 (t, J¼6.9 Hz, 2ꢂ2H; Ar–CH
J¼6.3 Hz, 2ꢂ2H; CH C NMR (300 MHz, CDCl ):
(ppm)¼139.97, 137.36, 137.19, 132.11, 130.18, 128.69, 127.28,
2
–
2
2
2
2
2
2
2
2 2
CH Cl solution). The speed of the spin coater was adjusted be-
1
3
2
–CH
2
–CH
2
);
3
tween 1500 and 2500 rpm. After drying, the concentration of an-
thracene units was determined by transmission optical
spectroscopy of the transparent electrode using a Cary 5 Varian SG
spectrophotometer. Finally, the counter electrode was deposited by
subliming aluminum in a chemical vapor deposition chamber
d
ꢀ
1
1
2
25.86, 43.64, 36.60, 33.87, 32.86, 29.63; IR (KBr):
n
(cm )¼3043,
932, 2850, 2232, 1699, 1603, 1514, 1440, 1392, 1306, 1270, 1207,
1
2 2
101, 1021, 998, 890, 769, 673, 539. ESI-MS: Calcd for C36H36Cl S
þ
þ
ꢀ6
(
MH) 603, found m/z 610 (MHꢀLi) .
(Edwards) operating at 10 mbar.

6274
R. Mart ´ı n et al. / Tetrahedron 64 (2008) 6270–6274
4
.3. Electroluminescent measurements
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(
Microbeam) by using colloidal silver and clamps. The cell was
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1
1
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1
9
6
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