White organic light-emitting diodes based on quench-resistant fluorescent organophosphorus dopants

Article abstract of DOI:10.1002/adfm.201102005

The control of the doping ratio of a blue-emitting matrix by an orange emitter with high accuracy still remains very challenging in the development of reproducible white organic light-emitting diodes (WOLEDs). In this work, the development of an organophosphorus dopant that presents a high doping rate in order to reach white emission is reported. The increase of the doping rate has a small impact on the CIE co-ordinates and on the EQE. These results are very appealing towards the development of "easy-to-make" WOLEDS.

Full text of DOI:10.1002/adfm.201102005

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White Organic Light-Emitting Diodes Based on Quench-
Resistant Fluorescent Organophosphorus Dopants
Damien Joly, Denis Tondelier, Valérie Deborde, Wylliam Delaunay, Anup Thomas,
Kotamarthi Bhanuprakash, Bernard Geffroy, Muriel Hissler,* and Régis Réau*
the use of a single chromophore that can
combine emission from both monomeric
(blue) and aggregate (orange) forms.[3a,b,4]
However, the most-general approaches
of obtaining white emission are through
combining different organic components
emitting: i) three primary colors (red
(R), green (G) and blue (B)),[3,5] or ii) two
complementary colors.[3a,6] This latter
approach is more suitable from a prac-
tical point of view, since it simply involves
the coevaporation of a matrix (generally a
The control of the doping ratio of a blue-emitting matrix by an orange emitter
with high accuracy still remains very challenging in the development of repro-
ducible white organic light-emitting diodes (WOLEDs). In this work, the devel-
opment of an organophosphorus dopant that presents a high doping rate in
order to reach white emission is reported. The increase of the doping rate has
a small impact on the CIE co-ordinates and on the EQE. These results are very
appealing towards the development of “easy-to-make” WOLEDS.
1. Introduction
blue-emitter) with a suitable dopant.
The emissive materials used in WOLEDs can be fluorescent
and/or phosphorescent chromophores. Up to now, efficient
blue-emitting materials have been most-exclusively fluores-
cent derivatives, due the short operational lifetimes of blue
phosphors.[7] In contrast, phosphors are the most-investigated
dopants, since they can achieve high internal quantum effi-
ciency by employing the participation of the triplet emission.[8]
However, WOLEDs using phosphorescent dopants typically
suffer from color-stability problems associated with signifi-
cant roll-off at high brightness (i.e., high current density) due
to strong triplet-triplet or triplet-charge annihilation.[8d,9] At the
moment, the most-widely used phosphorescent emitters are
metal complexes of iridium and platinum ions. These precious
metals are quite rare and already widely used for many other
important industrial applications including homogeneous/het-
erogeneous catalysis and electronics. Therefore, considering
their rarity and their quite-confined geographic localization,
the price of these precious metals is continuously increasing
(+100% within the last year for Pt and Ir). Indeed, the price and
availability of these metal-based phosphors can be a limitation
for the long-term mass production of WOLEDs since it seems
technologically difficult to recycle these dopants. Therefore, the
development of fluorescent WOLEDs is still important for “low-
cost” applications, although they are intrinsically less efficient
than WOLEDs incorporating phosphorescent dopants.
The field of organic optoelectronics has witnessed tremendous
progress since the first report on organic light-emitting diodes
(OLEDs) by Tang and VanSlyke in 1987.[1] Taking advantage of
the optical/semiconducting properties of π-conjugated organic
materials, and also of their lightness and flexible behavior, inno-
vative devices including OLEDs (full-color flat-panel displays)
and photovoltaic cells have recently been commercialized.[2]
Among all of the possible applications of organic devices, white
organic light-emitting diodes (WOLEDs) have received con-
siderable interest due to their potential for replacing conven-
tional lighting sources for display backlighting and solid-state
lighting.[3] In particular, WOLEDs have the potential to save a
significant amount of energy, compared with typical incan-
descent or fluorescent light bulbs, and therefore are attractive
devices in the frame of “sustainable development”.[3a–c] To realize
white emission with chromaticity Commission Internationale
de l’Eclairage (CIE) co-ordinates close to (0.313, 0.329), various
strategies have been developed.[2a,3] An appealing approach is
D. Joly, V. Deborde, W. Delaunay, Prof. M. Hissler, Prof. R. Réau,
Sciences Chimiques de Rennes
UMR6226 CNRS-Université de Rennes 1
Campus de Beaulieu, 35042 Rennes Cedex, France
E-mail: mhissler@univ-rennes1.fr; regis.reau@univ-rennes1.fr
D. Tondelier
Considering the most-simple device configuration for
WOLEDs (i.e., a blue-emitting matrix doped with a fluorescent
compound), one of the most-critical parameters to optimize is
the doping rate (DR). In practice, the effective DR required to
obtain white emission is usually very low (0.2–2%) and has to
be precisely controlled (±0.1%).[10] Furthermore, besides emis-
sion-color modification, small DR variations usually induce
dramatic modifications of the device performance, and espe-
cially important, a decrease of the external quantum efficiency
(EQE).[10] Controlling these rather-low DRs with a high accuracy
Laboratoire de Physique des Interfaces et Couches Minces
CNRS UMR 7647, Ecole Polytechnique, 91128 Palaiseau, France
A. Thomas, Prof. K. Bhanuprakash
Inorganic and Physical Chemistry Division
Indian Institute of Chemical Technology
Habsiguda, Hyderabad-500 607, A.P., India
B. Geffroy
Laboratoire de Chimie des Surfaces et Interfaces
CEA Saclay, IRAMIS, SPCSI, 91191 Gif-sur-Yvette, Cedex, France
DOI: 10.1002/adfm.201102005
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N
N
N
N
N
N
N
N
Cu
N
N
N
N
H3C
CH3
CuPc
NPB
BCP
N
O
O
O
N
Al
N
S
P
S
S
DPVBi
Alq3
A
Figure 1. Chemical structures of the OLED components and dopant A.
is very challenging from an experimental point of view, espe-
cially in an industrial process, making matrix doping by no
means a trivial task. This severe drawback can strongly limit
the repeatability of devices that have identical performances
in mass production. Therefore, the design of new, advanced
dopants affording WOLEDs presenting a very-small sensitivity
to concentration variations is of considerable importance. Mate-
rials exhibiting this appealing property are extremely rare for
OLEDs[11] and totally unknown for WOLED applications.
In order to tackle this problem, we decided to exploit the flex-
ibility available for fine-tuning of the optical and electrochem-
ical properties of phosphole-based conjugated systems through
manipulation of their chemical structure for the preparation of
tailored white-light-emitting devices. We recently showed that
bis(2-(5-methyl)thienyl)thioxophosphole, A, (Figure 1) is an effi-
cient fluorescent dopant for 4,4′-bis(2,2′-diphenylvinyl)biphenyl
(DPVBi) (Figure 1) in the construction of WOLEDs that have
simplified structures.[12] These single-emitting layered devices are
easily obtained by coevaporation of the two compounds. As usu-
ally observed with this general approach, a drawback is that the
DRs for obtaining white emission with these phosphole-based
molecules are low (approximately 0.1%), and therefore they are
quite difficult to control and reproduce within the coevaporation
process. Therefore, molecular engineering around the phosphole
building block was undertaken, with the preparation of new,
advanced, mixed thiophene-phosphole-fluorene dopants.
In this paper, we report on the synthesis and characterization
of mixed thiophene-phosphole-fluorene derivatives that can be
used as dopants for DPVBi (Figure 1), a widely used blue-emit-
ting matrix. Their chemical structures were elucidated using
1H-NMR and 13C-NMR spectroscopy and mass spectrometry.
Their photophysical, thermal and electrochemical properties
were determined using UV–vis and photoluminescence spec-
troscopy, cyclic voltammetry, thermogravimetric analysis (TGA)
and DSC. A series of OLEDs including these phosphole deriva-
tives emitting different colors were developed, displaying similar
EQEs with DRs varying from 1% to 50%. Furthermore, white-
emission was obtained for DRs varying in quite a large range.
These unprecedented properties make these thiophene-phosp-
hole-fluorene derivatives appealing dopants for the tailoring of
OLEDs, including WOLEDs that are easy to reproduce.
2. Results and Discussion
2.1. Synthesis
The novel, phosphole-based π-conjugated systems 4a and 4b
(Scheme 1) were readily obtained in good yields according to
R
R
R
S
S
S
i
ii
I
H
H
H
(CH2)4
(CH2)4
(CH2)4
+
2a,b
3a,b
a
: R = H
1a,b
b
: R = CH3
iii
S
S
R
iv
R
P
P
Ph
Ph
S
5a,b
4a,b
Scheme 1. Synthetic route to the thioxophosphole-based dopants 5a and 5b. Reactions and conditions: i) Pd(PPh3)2Cl2 (5 mol%) CuI (5 mol%), di-
isopropylamine, room temperature (RT); ii) 9,9-(dimethyl)-2-bromofluorene, Pd(PPh3)2Cl2 (5 mol%) CuI (5 mol%), di-isopropylamine, tetrahydrofuran
(THF), RT; iii) (a) Cp2ZrCl2, n-BuLi (2 equiv), THF, −78 °C–RT, 12h; (b) PhPBr2, THF, −78 °C–RT, 4h; iv) S8, CH2Cl2, RT, 24h.
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Figure 2. Structures and packing of the thio-oxophospholes 5a and 5b in the solid state.
the Fagan–Nugent route[13] using the mixed diynes 3a and 3b,
which were available on a gram scale using Sonogashira coup-
ling.[14] A terminal methyl group was introduced in 4b in order
to enhance the electrochemical stability of these thienyl-capped
derivatives (vide infra). They were transformed into their thioxo
derivatives, 5a and 5b, (Scheme 1) to increase their thermal sta-
bility, since σ3,λ3-phospholes are generally not stable enough
to undergo vacuum sublimation for device fabrication.[15] The
multinuclear NMR spectra were as expected for unsymmetrical
thioxophosphole compounds[15,16] and the proposed structures
were confirmed by mass spectrometry and X-ray diffraction
studies (Figure 2). The metric data of these new derivatives
are very similar to those of symmetrical phosphole derivatives
bearing 2-thienyl or 2-fluorenyl substituents;[12,16,17] for example,
the phosphorus center adopts a distorted tetrahedral geometry
with the usual endocyclic P–C bond lengths (5a, 1.814(4) Å; 5b,
1.820(3) Å). For both derivatives, the phosphole and thiophene
moieties were almost coplanar (twist angles: 5a, 17.7°; 5b, 1.2°)
and the fluorenyl substituents exhibited a large rotational dis-
order (twist angles: 5a, 56.6°; 5b, 56.0°). It is interesting to com-
pare the packing diagrams of these two related derivatives to
probe their ability to aggregate in the solid state. The unit cell
of 5a contains 8 molecules, two neighboring molecules being
in close contact (3.3–3.6 Å) via intermolecular π–π interac-
tions involving a P-phenyl ring and a fluorene group (Figure 2,
right). In addition, a short contact between the H-atom at the
7-position of one fluorene group and the fluorenyl group of a
neighboring molecule (2.6 Å) was observed (Figure 2). In the
case of 5b, which features terminal methyl groups (Scheme 1),
only 4 molecules are present in the unit cell, indicating a less-
congested environment favoring a single-molecule behavior in
the solid state (vide infra). The fluorene moieties of two neigh-
boring molecules are π-stacked (π–π distance, 3.6 Å) with a
parallel displaced arrangement (Figure 2). These π-dimers are
in mutual interaction via CH-π interactions (2.8 Å) involving a
P-phenyl H-atom and a fluorenyl moiety (Figure 2, right). The
comparison of these packing patterns shows that a tiny mole-
cular variation (Scheme 1: 5a R = H; 5b, R = CH3) has a profound
impact on the supramolecular organization of these mixed flu-
orene-phosphole-thiophene derivatives in the solid state.
2.2. Optical Properties
In order to further establish the structure-property relation-
ship for this novel series of phosphole-based,π-conjugated
systems, their UV–vis absorption and fluorescence spectra
were measured, both in CH2Cl2 and in thin films. In solution,
the two phosphole derivatives 5a and 5b exhibited an intense
band in the UV–visible region, attributed to π–π* transitions
of the extended conjugated system, and broad emissions in
the visible region (Table 1). The replacement of one of the
Table 1. Optical (solution and in thin films), electrochemical and thermal data for the organophosphorus compounds 5a and 5b, and A.
e)
f)
b)
c)
d)
maxa)
ε
λ ema)
[nm]
Φ f
λ em
ϕ f
g)
g)
g)
Eo1x
Eo2x
Er1ed
Compound
T TGA
T m
λ
[nm]
447
413
420
[mol−1 L cm−1
]
[%]
0.5
5.6
0.5
[nm]
549
543
560
[%]
70
54
55
[°C]
[°C]
[V]
[V]
[V]
A
29 320
13 400
14 400
575
558
578
-
-
+0.95
+1.24h)
+1.13
+1.28
+1.41
+1.36
−1.61
−1.58
−1.61
5a
5b
361
355
209
171
a)Measured in CH2Cl2; b)Fluorescence quantum yields determined using fluorescein as standard, ±15%; c)Dispersed in PMMA (2 wt%); d)Measured in integrating sphere;
e)Onset weight-loss temperature estimated using TGA under air; f)Melting point measured by DSC under He; g)All potentials were obtained during cyclic-voltammetry
investigations in 0.2 m Bu4NPF6 in CH2Cl2. Platinum-electrode diameter = 1 mm, sweep rate = 200 mV s−1. All of the reported potentials are referenced to a saturated
calomel electrode (SCE); h)Irreversible processes.
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methylthiophene substituents on the reference molecule A
with a fluorene atom induced a blue shift of the absorption
maximum, and the emission maximum was weakly affected
(5b/A; Δλmax = 27 nm, Δλem = 3 nm, Table 1). Moreover, the
introduction of the methyl group (5a → 5b) resulted in a slight
red-shift of the value of λem (Δλem = 20 nm). It is noteworthy
that the photoluminescence (PL) quantum yields (QYs) in solu-
tion were low and the PL quantum yield of 5a (5.6%) was much
higher than that of 5b (0.5%). Since these compounds were
being developed as dopants for OLEDs, it was of interest to
investigate their PL properties in a poly(methyl methacrylate)
(PMMA) matrix. The values of λem in PMMA (doping rate =
2 wt%) were slightly blue-shifted compared with those recorded
in solution (Table 1). Of great interest, the PL QYs of 5a and 5b
in a PMMA matrix reached 54–55%, values considerably higher
than those observed in solution (Table 1). This behavior, which
is very appealing towards the development of the phosphole
derivatives, 5a and 5b, as dopants in OLEDs, can be attributed
to a rotational restriction in the solid state and to the steric pro-
tection provided by the tetrahedral P-center, the endocyclic cylo-
hexane, the bulkiness of the fluorene substituent of complexes
5a and 5b preventing the formation of strong aggregates in the
solid state.[12,15]
the glass-transition temperature resulted in no further crystal-
lization or melting behaviors. These results indicate that these
materials present good morphological and thermal stabilities,
two critical issues for device stability and lifetime.
2.5. Device Performance/Development of WOLEDs
Since the derivatives 5a and 5b are thermally stable and emis-
sive compounds, they could be used as the emitting layer
(EML) in the multilayer OLEDs B0 and C0 (Table 2), having
an indium tin oxide (ITO) (Asahi)/copper phthalocyanine
(CuPc) (10 nm)/N,N′-diphenyl-N,N′-bis(1-naphthylphenyl)-1,1′-
biphenyl-4,4′-diamine (α-NPB) (50 nm)/EML (15 nm)/DPVBi
(35 nm)/bathocuproine (BCP) (10 nm)/tris(8-hydroxyquino-
linato)aluminium (Alq3) (10 nm)/LiF (1.2 nm)/Al (100 nm)
configuration (Figure S1, Supporting Information). The elec-
troluminescence (EL) spectra of devices B0 (λmax,EL = 548 nm)
and C0 (λmax,EL = 572 nm) resemble the thin-film PL spectra
of the thio-oxophosphole derivatives 5a (λem = 543 nm) and 5b
(λem = 560 nm) (Figure S2 and S3, Supporting Information),
respectively, showing that the EL emission bands were from
these P-luminophores.
The coevaporation of DPVBi and the phosphole-based dopant
5b was firstly explored in order to construct devices with an ITO
(PG&O)/CuPc (10 nm)/α-NPB (50 nm)/doped-DPVBi (50 nm)/
BCP (10 nm)/Alq3 (10 nm)/LiF (1.2 nm)/Al (100 nm) structure.
For a DR of 1%, the EL spectrum consisted of the dual emission
of the DPVBi (λ = 460 nm) and of the dopant 5b (λ = 560 nm)
(Figure 3). It is very striking to note that the DPVBi matrix still
contributed to the EL spectra of the OLEDs for doping ratios up
to 25% (devices C4–C12, Figure 3). In fact, the emission of the
DPVBi matrix was predominant for DRs between 1% and 3.2%
(devices C4–C6), and the contribution of the DPVBi emission
decreased (devices C7–C9) and became weak when the DR level
reached 25% (device C10, Figure 3). Moreover, the impact of the
DRs on the OLED performances was also very intriguing. The
external quantum efficiency (EQE) remained stable (2.4 ± 0.1%)
for DRs varying between 1% and 50% (Table 2, Figure 4). Note
that a “doping rate” of 50% is meaningless, since, in this case,
the EML was a 1/1 mixture of two semiconducting electrolu-
minescent derivatives (i.e., DPVBi and 5b). In fact, the EQE
recorded for DRs ranging from 1% to 50% was similar to that
of the device A2, in which the EML was pure DPVBi (Table 2).
This very-unusual behavior, which shows that 5b is a quench-
resistant dopant, resulted in a very-progressive modification of
the device CIE co-ordinates upon increasing the DR (Table 2,
devices C4–C12). The relationship defining the EQE involves
the singlet/triplet ratio (ρS/T), the extraction yield (ηextraction),
the recombination rate (β) and the photoluminescent quantum
yield (ηPL) of the EML.[18,6g] For diodes A2 and C4−C11 (Table 2),
the first two factors (ρS/T, ηextraction) were constant. Therefore, the
fact that the EQE did not vary implies that the recombination
rate (β) and the photoluminescence quantum yields (ηPL) of the
DPBVi/5b EML were either constant or offset each other for DR
values ranging from 0% to 50%. PL measurements conducted
on DPVBi films doped with 5b revealed that the photolumines-
cence quantum yield was stable (21%) when the DRs ranged
from 1% to 40%.
2.3. Electrochemical Properties
The redox properties of these novel, phosphole-based
π-conjugated systems 5a and 5b were determined by cyclic vol-
tammetry (CV), recorded in CH2Cl2 using Bu4NPF6 as an elec-
trolyte. The nature of the substituents in positions 2 and 5 on
the phosphole ring affected the oxidation potentials, while the
reduction potentials were not modified (Table 1). For example,
the reference molecule A (Figure 1) presents a lower oxida-
tion potential than the fluorene-phosphole-methylthiophene
system 5b, which displays a lower oxidation potential than 5a
(Table 1).[12] These data indicate that the lowest-unoccupied-
molecular-orbital (LUMO) level was unchanged and the
highest-occupied-molecular-orbital (HOMO) level was gradually
stabilized going from compounds A and 5b to 5a. Furthermore,
reversible reduction and oxidation processes took place for com-
pound 5b, whereas, for 5a, only the reduction was reversible. It
is likely that the presence of the methyl group at the α-position
of the S-atom stabilized the thiophene radical cation and also
prevented electropolymerization taking place.[16a,c]
2.4. Thermal Properties
The thermal behaviors of these thiooxophole derivatives 5a and
5b were investigated, since a high thermal stability is a key prop-
erty for device fabrication (sublimation of the organic materials
under vacuum) and also for getting a stable device operation.
The decomposition temperatures (Td) established by TGA were
above 350 °C (Table 1). This high thermal stability will allow 5a
and 5b to be used in “small-molecule” OLED technology. The
melting points (Tm) were in the range of 170–209 °C (Table 1).
The formation of a glassy state of these derivatives after melting
and cooling was evidenced (Tg ≈ 80 °C). Further heating above
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Table 2. EL performance of the devices as a function of the device structure and of the doping rate.
Devicea)
EML Doping rate
(doping ratio [wt,%])
V on
V 20
B 20
Power efficiencyd) Current efficiencyd) CIE co-ordinatesd)
c)
d)
d)
d)
λ max EL
[nm]
η 20
[V]
[V]
ITO Asahi
10.9
[cd m−2
]
[lm W−1
]
[cd A−1
]
[%]
x
y
A1
DPVBi (0)
5a
448
548
5.4
4.7
4.7
4.4
5.9
5.8
5.3
5.3
479
705
832
810
509
840
898
1158
2.4
1.1
2.1
1.5
0.9
2.3
2.1
2.5
0.7
1.1
1.3
1.2
0.7
1.2
1.3
3.3
2.4
3.3
4.3
4.2
2.5
4.1
4.8
5.5
0.16
0.39
0.27
0.38
0.44
0.25
0.29
0.31
x
0.13
0.55
0.33
0.51
0.48
0.30
0.35
0.37
y
b)
B0
10.4
B1
B2
DPVBi: 5a (0.3)
DPVBi: 5a (1.4)
5b
448/550
552
10.8
10.7
b)
C0
572
11.92
11.3
C1
C2
C3
DPVBi: 5b (2.1)
DPVBi: 5b (3.2)
DPVBi: 5b (3.8)
464
460/556
460/552
12.0
11.7
ITO PG&O
A2
DPVBi (0)
460
460
5.3
5.6
5.8
5.6
4.9
5.0
5.0
4.7
5.3
5.4
11.8
11.8
11.8
11.5
11.3
11.8
11.4
10.8
11.2
12.
660
968
2.4
2.5
2.3
2.3
2.4
2.3
2.4
2.3
2.3
1.9
0.9
1.4
1.2
1.6
1.7
1.2
1.8
2.0
1.9
1.6
2.7
4.9
4.5
5.4
5.9
7.8
7.2
6.2
6.5
5.4
0.16
0.24
0.26
0.32
0.34
0.35
0.36
0.40
0.42
0.44
0.20
0.31
0.32
0.40
0.43
0.44
0.48
0.50
0.51
0.51
C4
DPVBi: 5b (1)
DPVBi: 5b (2)
DPVBi: 5b (3.2)
DPVBi: 5b (5. 3)
DPVBi: 5b (6)
DPVBi: 5b (12)
DPVBi: 5b (25)
DPVBi: 5b (50)
DPVBi: 5b (80)
C5
460
851
C6
460/530
464/556
560
1061
1210
1099
1380
1035
1273
11.16
C7
C8
C9
560
C10
C11
C12
560
564
568
a)Device configuration (thickness): ITO/CuPc (10 nm)/α-NPB (50 nm)/doped-DPVBi (50 nm)/BCP (10 nm)/Alq3 (10 nm)/LiF (1.2 nm)/Al (100 nm); b)Device configuration
(thickness): ITO/CuPc (10 nm)/α-NPB (50 nm)/EML (15 nm)/DPVBi (35 nm)/BCP (10 nm)/Alq3 (10 nm)/LiF (1.2 nm)/Al (100 nm) configuration; c)Turn-on voltage at
which emission becomes detectable (0.1 cd m−2); d)Measured at 20 mA cm−2
.
These data therefore suggest that the recombination rate
should be constant to account for the stable EQEs observed for
the C4–C11 OLEDs. It is difficult to propose a rational expla-
nation to account for this unusual phenomenon, but it seems
that the recombination taking place in the DPVBi, the efficient
energy transfer between the DPVBi and the dopant and the spa-
tial arrangement of the DPVBi and the dopant 5b in the doped
layer could be responsible. Effectively, a resonant energy transfer
between the two chromophores can be considered since the
emission spectrum of the DPVBi and the absorption spectrum
of the dopant 5b present some overlap. The calculated Förster
radius (3 nm) (see Supporting Information) was much higher
than the spatial separation of the DPVBi and the dopant 5b
inside the doped layer, leading to a high Förster energy-transfer
rate. As a consequence, the energy transfer from DPVBi to 5b
was almost complete. Since the kinetic rate constant for the flu-
orescence process was high and the energy transfer was almost
complete, the photoluminescence quantum yield of the DPVBi
films doped with 5b can be expected to be stable for different
doping ranges. In order to understand the charge-recombina-
tion processes, calculations (at the B2PLYP-D/6-31G(d)//B97-
D/6-31G(d) level (see Supporting Information for details)) of
1.0% (C4)
0.8
0.7
0.6
1.0
0.8
0.6
0.4
0.2
0.0
2.0% (C5)
3.2% (C6)
5.3% (C7)
6.0% (C8)
0.5
0.4
0.3
0.2
0.1
0
White
12.0% (C9)
25.0% (C10)
50.0% (C11)
80.0% (C12)
380
430
480
530
580
630
680
730
780
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
< /nm
Figure 3. Normalized electroluminescent spectra and CIE chromaticity co-ordinates of devices C4 – C12 (Table 2), recorded at 30 mA cm−2.
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not observed with 5a because the optical properties, the fron-
tiers orbital and the solid-state arrangement were different to
those of the dopant 5b. Indeed, the derivative 5b appears to
be a unique dopant for DPVBi, due to a combination of elec-
tronic and structural properties, making the P-derivatives very
attractive from a technical point of view for the development
of WOLEDs, since small DR variations had almost no impact,
neither on the CIE co-ordinates nor on the EQE.
3
2
None of the C4–C12 OLEDs exhibited a pure-white emission
(the best CIE co-ordinates being obtained for DR = 3.2%: device
C6, Table 2) due to the fact that dopant 5b did not emit the
exact complementary colour of the DPVBi matrix (Figure 3).
However, it appears that replacing PG&O ITO with Asahi ITO
modified the EL emission of the DPVBi matrix. For the same
general device structure (Table 2), the EL spectrum of the diode
A1 (Asahi ITO-coated glass) substrate was blue-shifted (Δλ =
12 nm) compared with that of the A2 device (PG&O ITO-coated
glass). This tiny change is very important, since the derivatives
5a and 5b exhibit emission colors that are complementary to
that of this novel device A1. This modification is likely to be
due to a small difference of the ITO thickness inducing a cavity
phenomenon.[19]
The mixed fluorene-phosphole-thiophene derivative 5a was
firstly investigated using an Asahi ITO coated glass substrate.
The corresponding devices, B1 and B2, exhibited a dual EL
emission from DPVBi (448 nm) and the phosphole dopant
(550 nm). As classically observed, a small variation of the DR
had a large impact, both on the CIE co-ordinates and on the
EQE of the devices (Table 2, devices B1/B2).[12] A well-balanced
emission from DPVBi and 5a was obtained for a doping rate of
0.3%, affording the OLED B1, which displayed CIE co-ordinates
(0.27, 0.33) that are close to pure-white emission. The turn-on
voltage of device B1 was quite low (4.7 V) and it exhibited an
EQE of 2.1%, a brightness of 832 cd m−2 at 20 mA cm−2 and a
power efficiency of 1.3 lm W−1 (Table 2). These data show that
the mixed fluorene-phosphole-thiophene derivative 5a is an
efficient dopant for DPVBi towards the development of efficient
WOLEDs. However, the required low DR value (approximately
0.3%) to reach white emission was quite dif-
0
0
50
100
Doping rate /wt %
Figure 4. Influence of the doping rate on the external quantum efficiency
for devices C4 – C12 and C0 (Table 2).
the heterodimer (DPVBi-dopant 5b) interaction energy were
performed. A few possible potential-energy surface minima
for this heterodimer were obtained by optimizing the various
initial spatial arrangements of the DPVBi and 5b. The dimer
having the largest interaction energy (ΔEAB = −26.84 kcal mol−1
(Figure 5)) presented a π–π interaction (3.5 Å), but the π-systems
of the DPVBi and 5b didn’t overlap strongly, preventing the
formation of strong aggregates in the solid state. The frontier
molecular orbitals of the dimer (Figure 5) show that the elec-
tron density was mostly located on the DPVBi in the HOMO
and on the compound 5b in the HOMO-1. Since the difference
in energy between the HOMO and the HOMO-1 was small, a
hole could be injected to the HOMO levels of each component
and be subsequently trapped to the HOMO level of the DPVBi
before forming an exciton by recombination with the electron
that was mainly located on the DPVBi due to the structure of
the OLEDs (Figure S1, Supporting Information). Since the
structure (layer thicknesses) of the OLED was not modified,
all of these data suggest that the rate of recombination can be
constant when the doping rate increases. This behaviour was
ficult to control and reproduce within the
coevaporation process, since a rather-small
variation of the doping rate resulted in an
important modification of the device CIE
co-ordinates (Table 2). Of great interest, the
very-appealing quench properties of dopant
5b, resulting in small variations of the CIE
co-ordinates and EQEs upon DR modifica-
tion, were retained using this novel glass
substrate (Asahi ITO). Indeed, the EQE of
the C1–C3 OLEDs were almost unchanged
(2.3 ± 0.2%) for DRs increasing from 2.1% to
3.8% and a WOLED having CIE co-ordinates
close to white emission (0.29, 0.35) could
be obtained using a DR of 3.2% (device C2,
Table 2). The performance of this WOLED
was very satisfying, with a brightness of
898cdm−2at20mAcm−2(Table2).Moreover,the
brightness increased regularly with the cur-
rent density (see Supporting Information),
Figure 5. Optimized spatial arrangement of DPVBi and 5b, frontier molecular orbitals of dimer
DPVBi - 5b and eigenvalues calculated at B3LYP/6-31G(d,p)//B97-D/6-31G(d) level of theory.
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Cyclic-Voltammetry Measurements: The electrochemical studies
were carried out under argon using an Eco Chemie Autolab PGSTAT
30 potentiostat for cyclic voltammetry with the three-electrode
showing the good stability of this WOLED, despite the rather
high DR. These data show that the mixed fluorene-phosphole-
thiophene derivative 5b is also an efficient dopant for DPVBi
towards the development of efficient WOLEDs. In this case,
the DR value (approximately 3.2%) to reach white emission
was quite easy to control and reproduce within the coevapora-
tion process since: i) it was rather high, and ii) it could vary
without a dramatic modification of the device CIE co-ordinates
and the EQE.
configuration: the working electrode was
a platinum disk, the
reference electrode was a saturated calomel electrode (SCE), and the
counterelectrode was a platinum wire. All of the potentials were internally
referenced to the ferrocene/ferrocenium couple. For the measurements,
concentrations of 10−3 m samples of the electroactive species were used
in freshly distilled and degassed dichloromethane (Lichrosolv) (Merck)
and 0.2 m tetrabutylammonium hexafluorophosphate (TBAHFP) (Fluka),
which was twice recrystallized from ethanol and dried under vacuum
prior to use.
Device Fabrication and Characterization: The EL devices, based on a
multilayer structure, were fabricated on patterned ITO-coated-glass
substrates from Asahi (sheet resistance 10 Ω m−1) or PGO CEC020S
(thickness: 100 nm and sheet resistance: less than 20 Ω m−1). The
organic materials (from Aldrich and Syntec) were deposited onto the
ITO anode by sublimation under high vacuum (<10−6 Torr) at a rate
of 0.2–0.3 nm s−1. The common structure of all the devices was the
following: a thin layer (10 nm thick) of CuPc was used as the hole-injection
layer (HIL) and 50 nm of α-NPB was used as the hole-transporting layer
(HTL). The emitting layer consisted of a 15 nm-thick film of one of the
pure phosphole derivatives or the DPVBi-doped phosphole derivatives.
The doped layer was obtained by coevaporation of the two compounds
and the doping rate was controlled by tuning the evaporation rate of
each material. A thin layer of BCP (10 nm) was used as the hole-blocking
layer. Alq3 (10 nm) was used as electron-transporting layer (ETL). Finally,
a cathode consisting of 1.2 nm of LiF capped with 100 nm of Al was
deposited onto the organic stack. The entire device was fabricated in the
same run without breaking the vacuum. In this study, the thicknesses of
the different organic layers were kept constant for all of the devices. The
active area of the devices defined by the overlap of the ITO anode and
the metallic cathode was 0.3 cm2.
3. Conclusions
In conclusion, two phosphole-based dopants 5a and 5b, which
have very-similar structures (Scheme 1), exhibited very-different
doping properties. The doping rate used to reach white emis-
sion was much higher with 5b (3.2%) than with 5a (0.3%) and,
in contrast to what was observed with 5a, increasing the doping
rate (2.1→ 3.8%) of 5b had a small impact on the CIE co-ordi-
nates. Moreover, no modification of the EQE was observed by
increasing the doping rate. These two properties make 5b a
very-appealing dopant for the DPVBi matrix towards the devel-
opment of “easy-to-make” WOLEDs.
4. Experimental Section
General Procedures: All of the experiments were performed under an
atmosphere of dry argon using standard Schlenk techniques. The column
chromatography was performed in air, unless stated in the text. The
solvents were freshly distilled under argon from sodium/benzophenone
(tetrahydrofuran (THF), diethyl ether) or from phosphorus pentoxide
The current–voltage–luminance (I–V–L) characteristics of the devices
were measured using a regulated power supply (Laboratory Power
Supply EA-PS 3032-10B) combined with a multimeter and a 1 cm2-area
silicon calibrated photodiode (Hamamatsu). The spectral emissions
were recorded using a SpectraScan PR650 spectrophotometer. All of
the measurements were performed at room temperature and under an
ambient atmosphere with no further encapsulation of devices.
(pentane,
dichloromethane).
Bis(cyclopentadienyl)zirconium
dichloride (Cp2ZrCl2) was obtained from Alfa Aesar Chem. Co.
Bis(triphenylphosphine)palladium(II) dichloride (PdCl2(PPh3)2), CuI,
1,7-octadiyne, n-butyl-lithium (n-BuLi), di-isopropylamine and S8 were
obtained from Acros Chem. Co. All of the compounds were used
as received without further purification. dibromophenylphosphine
(PPhBr2),[20] 9,9’-dimethyl-2-bromofluorene[21] and 2-thienyl-octa-1,7-
diyne[16]a] were prepared as described in the literature. Preparative
separations were performed by gravity-column chromatography
on basic alumina (Aldrich, Type 5016A, 150 mesh, 58 Å) or silica gel
Details of the X-Ray Crystallography Study: Single-crystal data collection
was performed at 100 K using an APEX II Bruker-AXS (Centre de
Diffractométrie, Université de Rennes 1, France) with Mo K radiation
(λ = 0.71073 Å). The reflections were indexed, Lorentz polarization
corrected and integrated using the DENZO program of the KappaCCD
software package. The data-merging process was performed using the
SCALEPACK program.[23] Structure determinations were performed by
direct methods using the SIR97 solving program,[24] which revealed
all the non-hydrogen atoms. The SHELXL program (G. M. Sheldrick,
SHELX97, Program for the Refinement of Crystal Structures, University
of Göttingen, Germany, 1997) was used to refine the structures by
full-matrix least-squares based on F2. All of the non-hydrogen atoms
were refined with anisotropic displacement parameters. The hydrogen
atoms were included in idealized positions and refined with isotropic
displacement parameters. Atomic scattering factors for all of the atoms
were taken from International Tables for X-Ray Crystallography.[25] Details
of the crystal data and structural refinements are provided (Table S2,
Supporting Information).
Crystallographic Data: Crystallographic data (excluding structure
factors) for the structures reported in this paper have been deposited
with the Cambridge Crystallographic Data Centre as supplementary
publication nos. CCDC-804759 for 5a and CCDC-804760 for 5b. Copies
of the data can be obtained free of charge from http://www.ccdc.cam.
ac.uk/conts/retrieving.html.
Calculations of the Interaction Energy of the Heterodimers: The
optimization of the spatial arrangements of the DPVBi and 5b was
carried out using Grimme’s specially designed semilocal density
functional augmented with dispersion corrections (B97-D), especially
(Merck Geduran 60, 0.063–0.200 mm) in 3.5–20 cm columns. H-, 13C-
1
and 31P-NMR spectra were recorded using a Bruker AM300 or DPX200
instrument. The 1H- and 13C-NMR-spectroscopy chemical shifts are
reported in parts per million (ppm), relative to Si(CH3)4 as an external
standard. The 31P-NMR-spectroscopy downfield chemical shifts are
expressed with a positive sign, in ppm, relative to external 85% H3PO4.
The assignment of the proton atoms was based on a correlation-
spectroscopy (COSY) experiment. The assignment of the carbon
atoms was based on heteronuclear-multiple-bond-correlation (HMBC),
heteronuclear-multiple-quantum-coherence (HMQC) and distortionless-
enhancement-by-polarization-transfer (DEPT-135) experiments. The
high-resolution mass spectra were obtained using Varian MAT 311,
Waters Q-TOF 2 or ZabSpec TOF Micromass instruments at the Centre
Régional de Mesures Physiques de l’Ouest (CRMPO), University of
Rennes 1. The elemental analyses were performed by the CRMPO,
University of Rennes 1.
Determination of Optical Data: The UV–vis spectra were recorded at
room temperature using a UVIKON 942 spectrophotometer and the
luminescence spectra were recorded in freshly distilled solvents at room
temperature using a PTI spectrofluorimeter (PTI-814 PDS, MD 5020, LPS
220B) with a xenon lamp. The quantum yields were calculated relative to
fluorescein (Φ = 0.90 in 0.1 n NaOH).[22]
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recommended for van der Waals complexes.[26] Due to the large size
of the system, we used only a moderate Pople’s split valence 6-31G(d)
basis set. The interaction (association) energy, ΔE, was obtained from
a single-point calculation using the dispersion-corrected double-hybrid
functional, B2PLYP-D, and a moderate basis set, 6-31G(d,p), using B97-
D/6-31G(d) minimized structures,[26] by Equation 1:
Rf = 0.4) the product was obtained as a yellow oil (yield 26%, 146 mg,
1
0.36 mmol). H NMR (300 MHz, CDCl3, δ): 7.72 (m, 1H, Hfluorenyl) 7.66
(d, 3J(H,H) = 7.8 Hz, 1H, Hfluorenyl), 7.49 (s, 1H, Hfluorenyl), 7.46–7.39
(m, 2H, Hfluorenyl), 7.37–7.32 (m, 2H, Hfluorenyl), 6.77 (AB system,
3J(H,H) = 3.0 Hz, Δυ = 104.5 Hz, 2H, Hthienyl), 2.54 (m, 4H, CH2–C≡C),
2.47 (s, 3H, CH3thienyl), 1.84 (m, 4H, CH2), 1.51 (s, 6H, CH3fluorenyl); 13C
NMR (75 MHz, CDCl3, δ): 153.8 (s, Cfluorenyl), 153.5 (s, Cfluorenyl), 140.6 (s,
(1)
EAB = EAB − EA − EB
Cthienyl), 138.8 (s, Cfluorenyl), 138.7 (s, Cfluorenyl), 131.2 (s, CHthienyl), 130.6 (s,
In Equation 1, EAB is the total energy of the optimized dimer and EA
and EB are the single-point energies of the isolated monomers A and
B extracted from the optimized dimer. The HOMO and LUMO orbital
energies were estimated at the B3LYP/6-31G(d,p) level using the B97-
D/6-31G(d) optimized geometries. All of the computations were done
using G09 software.[27]
CHfluorenyl), 127.5 (s, CHfluorenyl), 127.1 (s, CHfluorenyl), 125.9 (s, CHfluorenyl),
125.0 (s, CHthienyl), 122.6 (s, CHfluorenyl), 122.5 (s, Cfluorenyl), 121.7 (s,
Cthienyl), 120.2 (s, CHfluorenyl), 119.8 (s, CHfluorenyl), 93.0 (s, C≡C–Cthienyl),
89.8 (s, C≡C–Cfluorenyl), 81.7 (s, C≡C–Cfluorenyl), 74.4 (s, C≡C–Cthienyl), 46.8
(s, Cfluorenyl), 28.0 (s, C≡CCH2), 27.9 (s, C≡CCH2), 27.1 (s, CH3fluorenyl),
19.4 (s, CH2), 19.1 (s, CH2), 15.3 (s, CH3thienyl); HRMS (ESI, m/z): [M +
Na]+ calcd for C28H26SNa, 417.16529; found, 417.1653. Anal. calcd for
C28H26S: C 85.23, H 6.64, S 8.13; found: C 83.62, H 6.89, S 8.45.
Synthesis of 1-(5-Methyl-2-thienyl)octa-1,7-diyne (2b): Catalytic amounts
of [PdCl2(PPh3)2] (104 mg, 0.37 mmol) and CuI (28 mg, 0.37 mmol)
were added to a solution of octa-1,7-diyne (1.6 ml, 12 mmol) and
2-methyl-5-iodothiophene (0.9 ml, 7.4 mmol) in di-isopropylamine
(25 ml). The heterogeneous, brown mixture was stirred overnight at
room temperature. All volatile materials were removed in vacuo and the
residue was extracted using diethyl ether (3 × 20 ml). After purification by
column chromatography on silica gel (n-heptane/ethyl acetate, 95:5, v:v,
Rf = 0.64) and by vacuum distillation, the product was obtained as a
Synthesis of 1-Phenyl-2-(9,9’-dimethylfluoren-2-yl)-5-(2-thienyl)thio-
oxophosphole (5a): A hexane solution of n-BuLi (2.5 m, 0.8 ml, 2.05 mmol)
was added dropwise (approximately 1 min) at −78 °C to a THF solution
(10 ml) of Cp2ZrCl2 (286 mg, 1.00 mmol) and 1-(9,9’-dimethylfluoren-
2-yl)-8-(2-thienyl)-1,7-octadiyne 3a (366 mg, 1.00 mmol). The solution
was warmed to room temperature and stirred overnight. Freshly distilled
PhPBr2 (0.22 ml, 1.05 mmol) at −78 °C was added to this solution.
The solution was allowed to warm to room temperature and stirred for
30 h. The solution was filtered on basic alumina (THF) and any volatile
materials were removed in vacuo. The yellow precipitate containing the
phosphole 4a (31P–{1H} NMR (80 MHz, CDCl3): δ = 11.3) was dissolved
in CH2Cl2 (20 ml) and elemental sulfur (32 mg, 0.12 mmol) was added
to this solution. The solution was stirred for 4 d at room temperature
and chromatographed on silica gel (eluent n-heptane/ethyl acetate, 8/2
v/v, Rf = 0.5). 5a was obtained as a yellow-orange solid (yield = 70%,
1
yellow oil (yield 30%, 450 mg, 2.22 mmol). H NMR (300 MHz, CDCl3,
δ): 6.93 (d, 3J(H,H) = 3.6 Hz, 1H, Hthienyl), 6.59 (dd, 3J(H,H) = 3.6 Hz,
4J(H,H) = 0.9 Hz, 1H, Hthienyl), 2.43 (m, 5H, CH2C≡Cthienyl and CH3),
2.26 (m, 2H, CH2C≡CH), 1.98 (t, 3J(H,H) = 2.7 Hz, 1H, C≡CH), 1.71
(m, 4H, CH2); 13C NMR (75 MHz, CDCl3, δ): = 140.6 (s, CHthienyl), 131.2
(s, CHthienyl), 125.0 (s, CHthienyl), 121.6 (s, Cthienyl), 92.8 (s, CH2C≡Cthienyl),
84.1 (s, CH2C≡CH), 74.4 (s, CH2C≡Cthienyl), 68.6 (s, C≡CH), 27.6 (s,
CH2), 19.2 (s, CH2C≡CH), 18.0 (s, CH2C≡Cthienyl), 15.3 (s, CH3); HRMS
(EI, m/z): [M + Na]+ calcd for C13H14S, 225.07139; found, 225.0717.
Anal. Calcd for C13H14S: C 77.18, H 6.97, S 15.85; found: C 77.69, H 7.21,
S 14.64.
1
0.7 mmol, 364 mg). TTGA,10% = 376°C; H NMR (300 MHz, CDCl3, δ):
7.90 (dd, 4J(H,H) = 1.6 Hz, 3J(H,H) = 7.1 Hz, 3J(P,H) = 13.8 Hz, 2H,
H
ortho), 7.67 (m, 1H, Hfluorenyl), 7.62 (d, 3J(H,H) = 7.9 Hz, 1 H, Hfluorenyl),
Synthesis of 1-(2-Thienyl)-8-(9,9’-dimethylfluoren-2-yl)-1,7-octadiyne
(3a): Catalytic amounts of [PdCl2(PPh3)2] (101 mg, 0.14 mmol) and
CuI (27 mg, 0.14 mmol) were added to a solution of 1-(2-thienyl)octa-
1,7-diyne (545 mg, 2.9 mmol) and 9,9’-dimethyl-2-bromofluorene (799
mg, 2.9 mmol) in THF (30 ml) and di-isopropylamine (30 ml). The
heterogeneous, brown mixture was stirred for 1 d at 55 °C. All volatile
materials were removed in vacuo and the residue was extracted using
diethyl ether (3 × 20 ml). After purification by column chromatography
on silica gel (heptane, Rf = 0.2), the product was obtained as a yellow
oil (yield 77%, 852 mg, 2.2 mmol). 1H NMR (300 MHz, CDCl3, δ):
7.77 (m, 1H, Hfluorenyl), 7.72 (d, 3J(H,H) = 7.8 Hz, 1H, Hfluorenyl), 7.62
(s, 1H, Hfluorenyl), 7.54–7.49 (m, 2H, Hfluorenyl), 7.44–7.39 (m, 2H, Hfluorenyl),
7.24 (d, 3J(H,H) = 5.1 Hz, 1H, Hthienyl), 7.23 (dd, 3J(H,H) = 3.6 Hz,
4J(H,H) = 1.2 Hz, 1H, Hthienyl), 7.00 (dd, 3J(H,H) = 3.6 Hz, 3J(H,H) =
5.1 Hz, 1H, Hthienyl), 2.61 (m, 4H, C≡CCH2), 1.91 (m, 4H, CH2), 1.58 (s,
6H, CH3); 13C–{1H} NMR (75 MHz, CDCl3, δ): 153.9 (s, Cfluorenyl), 153.6
(s, Cfluorenyl), 138.8 (s, Cfluorenyl), 138.7 (s, Cfluorenyl), 131.1 (s, CHthienyl),
130.8 (s, CHfluorenyl), 127.6 (s, CHfluorenyl), 127.2 (s, CHfluorenyl), 126.9 (s,
CHthienyl), 126.0 (s, Cthienyl), 125.9 (s, CHfluorenyl), 124.3 (s, Cthienyl), 122.7
(s, CHfluorenyl), 122.6 (s, Cfluorenyl), 120.3 (s, CHfluorenyl), 119.9 (s, CHfluorenyl),
94.0 (s, C≡C–Cthienyl), 89.8 (s, C≡C–Cfluorenyl), 81.9 (s, C≡C–Cfluorenyl), 74.3
(s, C≡C–Cthienyl), 46.8 (s, Cflurorenyl), 28.1 (s, C≡CCH2), 27.9 (s, C≡CCH2),
27.1 (s, CH3fluorenyl), 19.4 (s, CH2), 19.2 (s, CH2). HRMS (ESI, m/z): [M.]+
calcd for C27H24S, 380.45987; found, 380.1614. Anal. calcd for C27H24S: C
85.22, H 6.36, S 8.43; found: C 85.66, H 6.50, S 8.38.
7.55–7.40 (m, 7 H, 2 Hfluorenyl, 2 Hthienyl, 2 Hmeta, Hpara), 7.34 (m, 2H,
fluorenyl), 7.29 (d, 3J(H,H) = 8.0 Hz, 1 H, Hfluorenyl), 7.05 (dd, 3J(H,H)
H
= 3.8 Hz, 3J(H,H) = 5.1 Hz, 1H, Hthienyl), 3.04 (s, 4H, C=CCH2), 2.88
(s, 4H, C=CCH2), 1.97 (m, 4H, CH2), 1.81 (m, 4H, CH2), 1.42 (s, 6H,
CH3). 13C NMR (50 MHz, CDCl3, δ): 153.9 (s, Cfluorenyl) 153.5 (s, Cfluorenyl),
2
2
148.5 (d, J(P,C) = 22.0 Hz, Cβ), 145.2 (d, J(P,C) = 22.3 Hz, Cβ), 138.8
(s, Cfluorenyl), 138.6 (s, Cfluorenyl), 135.1 (d, 2J(P,C) = 17.1 Hz, Cthienyl), 135.2
(d, J(P,C) = 81.7 Hz, Cipso), 131.9 (d, 4J(P,C) = 3.0 Hz, CHpara), 131.4
1
2
3
(d, J(P,C) = 22.0 Hz, CHfluorenyl), 130.6 (d, J(P,C) = 11.5 Hz, CHorhto),
1
3
129.1 (d, J(P,C) = 73.1 Hz, Cα), 128.8 (d, J(P,C) = 12.3 Hz, CHmeta),
128 (d, 3J(P,C) = 5.8 Hz, CHfluorenyl), 127.8 (d, 2J(P,C) = 5.3 Hz, CHthienyl),
127.5 (s, CHfluorenyl), 127.2 (s, CHthienyl), 127.0 (s, CHfluorenyl), 126.8 (s,
CHthienyl), 123.4 (d, 2J(P,C) = 5.5 Hz, CHfluorenyl), 122.6 (s, CHfluorenyl),
120.1 (s, CHfluorenyl), 119.7 (s, CHfluorenyl), 46.7 (s, Cfluorenyl), 28.9 (d, 3J(P,C)
= 13.2 Hz, C=CCH2), 28.8 (d, 3J(P,C) = 13.2 Hz, C=CCH2), 26.8 (s, CH3),
26.7 (s, CH3), 22.7 (s, CH2), 22.6 (s, CH2); 31P–{1H} NMR (121.5 MHz,
CDCl3, δ): 53.0 (s). HRMS (ESI, m/z): [M + Na]+ calcd for C33H29PS2Na,
543.1346; found, 543.1343; [M + H]+ calcd for C33H30PS2, 521.152658;
found, 521.1525. Anal. calcd for C33H29PS2: C 76.12, H 5.61, S 12.32;
found: C 76.66, H 5.78, S 12.56.
Synthesis
of
1-Phenyl-2-(9,9’-dimethylfluoren-2-yl)-5-(5-methyl-2-
thienyl)thio-oxophosphole (5b): A hexane solution of n-BuLi (2.5 m,
0.8 ml, 2.05 mmol) was added dropwise (approximately 1 min) at
−78 °C to a THF solution (10 ml) of Cp2ZrCl2 (286 mg, 1.00 mmol)
and 1-(9,9’-dimethylfluoren-2-yl)-8-(5-methyl-2-thienyl)-1,7-octadiyne 3b
(395 mg, 1.00 mmol). The solution was warmed to room temperature
and stirred over night. Freshly distilled PhPBr2 (0.22 ml, 1.05 mmol)was
added to this solution at −78 °C. The solution was allowed to warm to
room temperature and was stirred for 30 h. The solution was filtered
on basic alumina (THF) and the volatile materials were removed under
vacuum. The yellow precipitate containing the phosphole 4b (31P–{1H}
NMR (80 MHz, CDCl3): δ = 13.0) was dissolved in CH2Cl2 (20 ml) and
elemental sulfur (32 mg, 0.12 mmol) was added to this solution. The
solution was stirred for 1 d at room temperature and chromatographed
Synthesis
of
1-(5-Methyl-2-thienyl)-8-(9,9’-dimethylfluoren-2-yl)-
1,7-octadiyne (3b): Catalytic amounts of [PdCl2(PPh3)2] (20 mg,
0.03 mmol) and CuI (5 mg, 0.03 mmol) were added to a solution
of 1-(2-methylthiophene)octa-1,7-diyne (292 mg, 1.4 mmol) and
9,9’-dimethyl-2-bromofluorene (414 mg, 1.5 mmol) in THF (20 ml) and
di-isopropylamine (5 ml). The heterogeneous, brown mixture was stirred
for 1 d at 55 °C. All volatile materials were removed in vacuo and the
residue was extracted with diethyl ether (3 × 20 ml). After purification by
column chromatography on silica gel (heptane/ethyl acetate, 95/5 v/v,
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on silica gel (eluent: heptane/ethyl acetate, 95/5 v/v, Rf = 0.4). 5b was
obtained as a yellow-orange solid (yield = 70%, 0.7 mmol, 374 mg).
1
TTGA,10% = 365 °C; H NMR (300 MHz, CD2Cl2, δ): 7.74 (ddd, 4J(H,H)
= 1.5 Hz, 3J(H,H) = 6.9 Hz, 3J(P,H) = 13.8 Hz, 2H, Hortho), 7.58 (m, 1H,
H
H
fluorenyl), 7.51 (d, 3J(H,H) = 7.8 Hz, 1H, Hfluorenyl), 7.41–7.31 (m, 4H, 2
meta, Hpara, Hfluorenyl) 7.28 (s, 1H, Hfluorenyl) 7.23–7.20 (m, 2H, Hfluorenyl),
7.16 (d, J(H,H) = 7.8 Hz, 1H, Hfluorenyl) 7.08 (AB system, 3J(H,H) =
3.6 Hz, Δυ = 150.1 Hz, 2H, Hthienyl), 2.87 (m, 2H, C=CCH2), 2.74 (m,
2H, C=CCH2), 2.38 (s, 3H, CH3thienyl), 1.64 (m, 4H, CH2), 1.29 (s, 6H,
CH3fluorenyl); 13C NMR (75 MHz, CD2Cl2, δ): 154.3 (s, Cfluorenyl), 153.9 (s,
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Cfluorenyl), 148.9 (d, 2J(P,C) = 22.1 Hz, Cβ), 143.9 (d, 2J(P,C) = 22.4 Hz, Cβ),
142.5 (s, Cthienyl), 139.1 (s, Cfluorenyl), 139.0 (s, Cfluorenyl), 133.4 (d, 1J(P,C)
= 82.0 Hz, Cipso), 133.3 (d, 2J(P,C) = 17.1 Hz, Cthienyl), 132.2 (d, 4J(P,C) =
2.9 Hz, CHpara), 131.8 (d, 2J(P,C) = 12.3 Hz, Cfluorenyl), 130.9 (d, 2J(P,C)
= 11.5 Hz, CHortho), 130.1 (d, 1J(P,C) = 72.0 Hz, Cα), 129.1 (d, 3J(P,C)
= 12.3 Hz, CHmeta), 129.0 (d, 1J(P,C) = 81.7 Hz, Cα), 128.6 (d, 4J(P,C)
= 5.7 Hz, CHthienyl), 128.4 (d, 3J(P,C) = 5.8 Hz, CHfluorenyl), 127.8 (s,
CHfluorenyl), 127.4 (s, CHfluorenyl), 126.0 (s, CHthienyl), 123.7 (d, 3J(P,C) =
5.5 Hz, CHfluorenyl), 123.0 (s, CHfluorenyl), 120.4 (s, CHfluorenyl), 120.0 (s,
CHfluorenyl), 47.1 (s, CH3fluorenyl), 29.3 (s, C=CCH2), 29.1 (s, C=CCH2), 27.2
(s, CH3fluorenyl), 27.1 (s, CH3fluorenyl), 23.2 (s, CH2), 23.0 (s, CH2), 15.4 (s,
CH3thienyl); 31P NMR (121 MHz, CD2Cl2, δ): 52.5 (s); HRMS (ESI, m/z):
[M + H]+ calcd for C34H32PS2, 535.16831; found, 535.1701. Anal. calcd for
C34H31PS2: C 76.37, H 5.84, S 11.99; found: C 76.28, H 6.02, S 12.05.
Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
Acknowledgements
This work was supported by the Ministère de la Recherche et de
l’Enseignement Supérieur, the Institut Universitaire de France, the CNRS,
the Région Bretagne, the ANR PSICO, Indo-French “Joint Laboratory
for Sustainable Chemistry at the Interfaces” and COST CM0802
(Phoscinet). The authors are grateful to D. Aldakov for the PL thin-film
measurements, to Dr. S. Forget (LPL, University Paris 13) for the Förster
radius calculation and to C. Lescop for the X-ray diffraction studies.
Received: August 24, 2011
Published online: December 5, 2011
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