Phosphonate substituted 4,4′-bis(N-carbazolyl)biphenyl with dominant electron injection/transport ability for tuning the single-layer device performance of self-host phosphorescent dendrimer

Article abstract of DOI:10.1039/c2jm35526d

A novel phosphonate substituted 4,4′-bis(N-carbazolyl)biphenyl (CBP), namely PCBP, has been designed and successfully synthesized by an indirect palladium catalyzed Suzuki-Miyaura reaction. X-Ray crystallography analysis from a PCBP single crystal demonstrates that there is a hydrogen bond interaction between the two adjacent molecules due to the presence of phosphonate, which promotes their one-dimensional line arrangement along the c-axis. Compared with the prototype CBP (-5.55 eV), in addition, the highest occupied molecular orbital (HOMO) level of PCBP is reduced to -6.00 eV, leading to a large hole injection barrier. On the other hand, the introduction of phosphonate substitutes can endow PCBP with excellent electron injection/transport ability. As a result, PCBP shows an electron-dominated behaviour observed in single carrier devices, which is different from the hole-dominated one for CBP. Such a transition is then used to tune the single-layer device performance of a self-host phosphorescent dendrimer, and the peak luminous efficiency significantly increases from 1.7 cd A^-1 of CBP to 31.4 cd A ^-1 of PCBP. The Royal Society of Chemistry 2012.

Full text of DOI:10.1039/c2jm35526d

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PAPER
Phosphonate substituted 4,40-bis(N-carbazolyl)biphenyl with dominant
electron injection/transport ability for tuning the single-layer device
performance of self-host phosphorescent dendrimer†
a
a
Bo Chen,ab Junqiao Ding, Lixiang Wang, Xiabin Jinga and Fosong Wanga
*
*
Received 15th August 2012, Accepted 21st September 2012
DOI: 10.1039/c2jm35526d
A novel phosphonate substituted 4,40-bis(N-carbazolyl)biphenyl (CBP), namely PCBP, has been
designed and successfully synthesized by an indirect palladium catalyzed Suzuki–Miyaura reaction.
X-Ray crystallography analysis from a PCBP single crystal demonstrates that there is a hydrogen bond
interaction between the two adjacent molecules due to the presence of phosphonate, which promotes
their one-dimensional line arrangement along the c-axis. Compared with the prototype CBP (ꢀ5.55
eV), in addition, the highest occupied molecular orbital (HOMO) level of PCBP is reduced to ꢀ6.00 eV,
leading to a large hole injection barrier. On the other hand, the introduction of phosphonate substitutes
can endow PCBP with excellent electron injection/transport ability. As a result, PCBP shows an
electron-dominated behaviour observed in single carrier devices, which is different from the hole-
dominated one for CBP. Such a transition is then used to tune the single-layer device performance of a
self-host phosphorescent dendrimer, and the peak luminous efficiency significantly increases from
1.7 cd Aꢀ1 of CBP to 31.4 cd Aꢀ1 of PCBP.
It should be noted that, the introduction of carbazole den-
Introduction
drons endows these SHPhDs with preferential p-type charge
transport characteristic. In order to achieve high efficiency, an
additional electron transport layer must be deposited on the
emitting layer (EML) by vacuum evaporation. This would
inevitably increase the cost and time-consumption of PhOLEDs,
presenting a significant hurdle to commercialization. In view of
this point, a more simplified single-layer structure4 is highly
desirable for such SHPhDs.
Dendrimers are of great importance for their potential applica-
tions in wet-processed organic light-emitting diodes (OLEDs)
because they have the well-defined structure of a small molecule
and the good solution processability of a polymer.1,2 In
comparison to fluorescent ones, much more attention has been
paid to phosphorescent dendrimers owing to their ability to
harvest both singlet and triplet excitons to realize theoretical
100% internal quantum efficiency. Among these developed den-
drimers, interestingly, there is a class of self-host phosphorescent
dendrimers (SHPhDs), which are composed of carbazole-based
dendron and iridium (Ir) complex core. Here the Ir complex core
acts as the emissive dopant, and the dendron plays the same role
as the host. Because of the insensitive doping concentration
dependence of device performance, non-doped electro-
phosphorescent OLEDs (PhOLEDs) are prepared with record
high luminous efficiencies of 23.2 and 34.7 cd Aꢀ1 for the first-
and second-generation green Ir dendrimers with carbazole-based
dendrons (G1 and G2), respectively.3
As for a single-layer device, in principle, hole and electron
fluxes should be balanced to enhance their recombination
possibility. Therefore, appropriate electron transport materials
(ETMs) should be chosen to be blended with SHPhDs to
compose the EML. Through the investigation on literature
reported to date, we find that most of the efficient single-layer
devices are based on the adoption of two oxadiazole deriva-
tives, 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazol (PBD) for
green5,6 and red PhOLEDs,7,8 and 1,3-bis[2-(4-tert-butylphenyl)-
1,3,4-oxadiazol-5-yl]benzene (OXD-7) for blue9,10 and white
PhOLEDs.11,12 This phenomenon is very strange but under-
standable when taking into account that these oxadiazole
derivatives show excellent miscibility with triplet emitters to
form high quality films via wet technologies, whereas other
solution-processable ETMs are scarce. Unfortunately, the rela-
tively low thermal and morphological stability (Tg: 60 ꢁC for
PBD; 77 ꢁC for OXD-7) may hinder their further usage as
ETMs in long-lifetime PhOLEDs.13,14 Therefore, de nova design
of novel efficient ETMs suitable for solution processes should
aState Key Laboratory of Polymer Physics and Chemistry, Changchun
Institute of Applied Chemistry, Chinese Academy of Sciences,
Changchun, P. R. China. E-mail: junqiaod@ciac.jl.cn; lixiang@ciac.jl.cn;
Tel: +86-431-85685653
bGraduate School of Chinese Academy of Sciences, Beijing, P. R. China
† Electronic supplementary information (ESI) available: Thermal
property, OLEDs and crystallographic data. CCDC 884223. For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/c2jm35526d
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be one of the major subjects of considerable research in the
future.
decoration of phosphonate ensures PCBP is soluble in both
nonpolar and polar organic solvents, such as dichloromethane,
toluene, tetrahydrofuran and ethanol. In addition, a high
To this end, one conceivable strategy is to develop soluble
ETMs on the basis of some electron-deficient systems, such as
N-containing heterocyclic aromatic compounds.14–17 However,
the variety of n-type organic semiconductors is not as many as
p-type ones, limiting their prospects. As an alternative, it seems
to be more attractive to modify known p-type ‘‘cores’’ with
strong electron-withdrawing substituents for the construction of
n-type materials. Although this concept has already been used in
n-channel organic thin film transistors (OTFTs), there are few
related reports in the field of OLEDs.18–20
ꢁ
decomposition temperature (5% weight loss) of 316 C is deter-
mined from thermalgravimetric analysis (TGA, Fig. S1†),
indicative of its thermal stability.
A single crystal of PCBP, suitable for X-ray crystallography
analysis, was attained from CH2Cl2–hexane mixed solvents. As
shown in Fig. 1, the two central phenyl rings in PCBP are
virtually coplanar, identical to that in CBP. However, the torsion
between carbazole and biphenyl fragments in crystal state is
found to be strengthened from CBP to PCBP, and the dihedral
angle consequently increases from 46ꢁ to 57ꢁ.23 As can be clearly
seen in Fig. 1, PCBP forms a herringbone packing. Meanwhile,
because the phosphonate group is a good hydrogen bond
acceptor, head-to-tail P–O/H–Cꢁ interactions (O/H distance
In this article, we demonstrate our efforts on the achievement
of such an interesting transition from dominant hole to electron
injection/transport in OLEDs by functionalizing 4,40-bis(N-car-
bazolyl)biphenyl (CBP) with phosphonate substituents. The
design rationale for this new structure (PCBP, Scheme 1) is the
following. CBP is selected as the p-type centre since it is widely
adopted as the host for PhOLEDs where holes are the majority
carriers. Furthermore, as an electron-withdrawing group, phos-
phonate can facilitate effective electron injection/transport from
LiF/Al cathode.21,22 Most importantly, the marriage of phos-
phonate groups with CBP core may not only enable the n-type
character of PCBP, but also improve its solubility in common
organic solvents. Employing SHPhD G1 as the phosphor, highly
efficient single-layer PhOLEDs are fabricated via spin-coating,
and the peak luminous efficiency significantly increases from
1.7 cd Aꢀ1 of CBP to 31.4 cd Aꢀ1 of PCBP. To the best of our
knowledge, this is the first report of hole- to electron-dominated
conversion in OLEDs, which is successfully applied to modulate
the single-layer device performance of SHPhDs.
ꢀ
2.403 A, O/H–C angle: 167.49 ) are observed between the
adjacent molecules,24,25 which further promotes one-dimensional
line arrangement along the c-axis.
Photophysical properties
The room temperature UV/Vis and photoluminescent (PL)
spectra of CBP and PCBP in solutions are shown in Fig. 2, and
the photophysical properties are summarized in Table 1.
Compared with CBP, the absorption of PCBP blue shifts, and
the optical band gap estimated from the absorption onset rises
from 3.52 to 3.57 eV. Correspondingly, an about 4 nm hyp-
sochromic shift of the emission maxima is found from CBP to
PCBP in toluene solutions. According to the literature, when 3
and 6 positions of carbazole are occupied by electron-rich methyl
groups, an opposite bathochromic effect has been reported in a
CBP derivative.26 So it is reasonable to propose that the hyp-
sochromic effect in this case can be ascribed to the electron-
deficient nature of phosphonate moieties, which will be discussed
below in detail. In addition, the PL spectrum of PCBP undergoes
a red shift of 13 nm from solution to film state, indicative of the
existence of aggregation to some degree.
Results and discussion
Synthesis and structure characterization
Unlike CBP, the synthesis of PCBP is not an easy and direct task,
as shown in Scheme 2. Due to the reduced reactivity toward C–N
coupling reaction, initial attempt to use phosphontate func-
tionalized carbazole precursor as the substrate to react with 4,40-
dibromobiphenyl was unsuccessful. To shun this negative effect,
two key intermediates, PCz-Br and PCz-B, were prepared at first,
which were then linked together to afford PCBP with a yield of
60% by palladium catalyzed Suzuki–Miyaura reaction. The
structure of PCBP was fully confirmed by 1H, 13C and 31P NMR
spectroscopy, elemental analysis, and mass spectrometry. The
The phosphorescent spectra of CBP and PCBP were also
measured at 77 K, and the triplet energy was calculated from
n¼0
their maxima of the first vibronic mode (S0
) T1n¼0). As
presented in Fig. S2,† PCBP (2.68 eV) displays a slightly higher
triplet energy than CBP (2.66 eV), which is well consistent with
the fluorescent spectra at room temperature. Moreover, the
triplet energy of PCBP is higher enough than those of green and
red-emitting phosphors to prevent triplet energy back transfer.
That is to say, PCBP can act as an ideal host for green and red
PhOLEDs.
Electrochemical properties and theoretical calculations
To elucidate the effect of the phosphonate groups on the frontier
molecular orbitals, the electrochemical properties of CBP and
PCBP were studied in acetonitrile solutions. Different from the
irreversible oxidation of CBP, a reversible oxidation wave was
detected for PCBP during anodic sweeping (Fig. 3). This is
because the 3- and 6-substitution can prohibit the dimerization of
carbazole units at these positions, and intensify the electro-
chemical stability.27,28 During cathodic sweeping, both CBP and
Scheme 1 Molecular structures of CBP and PCBP.
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Scheme 2 Synthetic route of PCBP.
Fig. 2 The room temperature UV/Vis absorption spectra in dichloro-
methane solutions (10ꢀ5 M), PL spectra in toluene solutions (10ꢀ6 M) of
CBP and PCBP, and PL spectrum in film state of PCBP.
PCBP, the calculated decline in HOMO is 0.54 eV (Table 1),
which is 0.18 eV larger than that in the LUMO. The trend
correlates well with the electrochemical data, and can be
explained by the electron cloud distribution of the frontier
molecular orbitals. As illuminated in Fig. 4, the HOMO is
distributed over the whole molecular p backbone, while the
LUMO is mainly restricted to the central biphenyl unit in CBP.
When phosphonate groups are directly tethered to carbazole
moieties to form PCBP, imaginably, the LUMO will be less
affected by the inductive effect of phosphonate than the HOMO.
This would result in the enhancement of the band gap of PCBP
relative to CBP, in accordance with the aforementioned blue shift
in the absorption and PL spectra.
Fig. 1 (a) Single crystal structure of PCBP with thermal ellipsoid plotted
at 30% probability level. For clarity, CH2Cl2 molecule is omitted; (b) the
packing of PCBP molecules in the crystals; (c) the hydrogen bonds
between two head-to-tail PCBP molecules (viewed along the c axis).
PCBP revealed quasi-reversible reduction processes. By
comparison to CBP, an additional novel reduction wave appears
at a more positive potential for PCBP. With the ferrocene/fer-
rocenium couple as the reference, the highest occupied and
lowest unoccupied molecular orbital (HOMO and LUMO) levels
of PCBP are estimated to be ꢀ6.00 and ꢀ2.30 eV, respectively. It
is worthy noting that, the HOMO level of PCBP behaves more
sensitively to the incorporated phosphonate groups than the
LUMO does. For instance, compared with CBP (HOMO: ꢀ5.55
eV; LUMO: ꢀ2.19 eV), PCBP exhibits a decrease of 0.45 and
0.11 eV for its HOMO and LUMO levels, respectively.
Single carrier devices and electroluminescent properties
Single carrier devices were then fabricated to investigate the
charge injection/transport capability of PCBP compared with
CBP. The structures of electron-only and hole-only devices are
ITO/Al/CBP or PCBP/LiF/Al and ITO/PEDOT/CBP or PCBP/
Au, respectively. Fig. 5 depicts their current density–voltage
characteristics of CBP and PCBP. As for CBP, electron injection
is forbidden by a large mismatch of about 1.9 eV between the
work function of the cathode (ꢀ4.1 eV) and its LUMO level
(ꢀ2.19 eV). Hence the electron current is negligible relative to
the hole one as seen in Fig. 5a, suggesting the dominant hole
injection/transport of CBP. In contrast, PCBP displays an
This discord between HOMO and LUMO level variance can
be further verified by theoretical calculation results. Based on the
molecular geometry from crystal data, density functional theory
(DFT) calculations were performed using B3LYP hybrid func-
tional theory with 6-31G* basis sets. On going from CBP to
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Table 1 Photophysical and electrochemical properties of PCBP and CBP
labs (log x)a [nm]
Eopt [eV]
3.57
lsolc [nm]
363
HOMOe [eV]
ꢀ6.00 (ꢀ5.74)
ꢀ5.55 (ꢀ5.20)
LUMOe [eV]
ꢀ2.30 (ꢀ1.61)
ꢀ2.19 (ꢀ1.25)
b
d
ET [eV]
PCBP
CBP
240(5.0), 249(5.0), 270(4.9), 288(4.6),
308(4.5), 336(4.0)
239(4.9), 293(4.6), 318(4.4), 327(4.4),
341(4.3)
2.68
2.66
3.52
367
a
Measured in CH2Cl2 solution of 10ꢀ5 M at 298 K. b Calculated from the onset of the absorption in CH2Cl2. c Measured in toluene solution of 10ꢀ6 M
d
e
at 298 K. Estimated from the highest energy vibronic band of the phosphorescent spectra at 77 K. The HOMO and LUMO levels are calculated
according to the equations EHOMO ¼ ꢀe [Eox onset + 4.8 V] and ELUMO ¼ ꢀe [Ered onset + 4.8 V], respectively. The theoretical calculation data are
also listed in the parentheses.
Fig. 5 The current density–voltage (J–V) characteristics of electron-only
Fig. 3 The cyclic voltammograms of CBP and PCBP in acetonitrile
(filled squares) and hole-only devices (empty squares) for (a) CBP and (b)
solution, at a scanning rate of 100 mV sꢀ1
.
PCBP.
evaluate the performance of single-layer PhOLEDs. The device
A with a configuration of ITO/PEDOT : PSS/PCBP : G1 (30
wt%)/LiF/Al was fabricated by spin-coating, where the doping
concentration of G1 was optimized to be 30 wt% (Fig. 6). For
comparison, the control device B was prepared at the same time
with CBP as the host instead of PCBP. Their device data are
tabulated in Table 2. As depicted in Fig. S5,† device A gives
green electroluminescence (EL) entirely from G1 with a peak
wavelength of 531 nm and Commission Internationale de
L’Eclairage (CIE) coordinates of (0.38, 0.59).
Fig. 7a and b show the current density–voltage–brightness
characteristics of CBP and PCBP, and their luminous efficiency
as a function of current density, respectively. The turn-on voltage
(defined as the bias at the brightness of 1 cd mꢀ2) decreases from
12.0 V for CBP to 5.8 V for PCBP. Concomitantly, the maximum
Fig. 4 The distribution of HOMO and LUMO density in the molecular
framework, calculated using density functional theory (B3LYP/6-31G*).
electron-dominated behaviour (Fig. 5b), which could be attrib-
uted to two combination factors. On one hand, the presence of
phosphonate can effectively improve the electron injection/
transport arising from a favorable dipole and coordinate effect
between phosphonate and LiF/Al cathode together with a
possible n-doping effect by release of free Li atom under the
thermal vacuum deposition conditions.22,29 On the other hand,
holes can hardly inject from the PEDOT : PSS coated anode
because of the deep HOMO level (ꢀ6.00 eV) of PCBP. Therefore,
from CBP to PCBP, an attractive hole- to electron-dominated
transition is achieved.
Considering the dominant n-type feature of PCBP, we next
dispersed the SHPhD G1 into PCBP to form the EML to
Fig. 6 The energy diagram of light-emitting devices and molecular
structure of G1.
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Table 2 Summary of electroluminescence data for PhOLEDs
Lmax [cd mꢀ2
]
hc max [cd Aꢀ1
]
hp max [lm Wꢀ1
]
EQE [%]
lmax [nm]
CIE (x,y) (at 15 V)
a
Von [V]
PCBP
CBP
5.8
12.0
1.6 ꢂ 104
31.4
1.7
10.3
0.28
9.2
0.5
531
526
(0.38, 0.59)
(0.39, 0.58)
8.2 ꢂ 102
The applied voltage at 1 cd mꢀ2
.
a
LiF/Al cathode is used in place of water and oxygen sensitive
materials, such as Ca and Ba. Additionally, the EML only
consists of two components, different from the commonly used
three-component system. This is a very favorable feature for
solution processed PhOLEDs, because the decrease of the
number of blend components involved in the EML may reduce
the possibility of phase segregation, simplify the device fabrica-
tion process and lower the product cost.
Experimental
General information
All chemicals and reagents were used as received from
commercial sources without further purification. Solvents for
chemical synthesis were purified according to the standard
procedures. 9-(4-bromophenyl)-3,6-diiodo-9H-carbazole32 and
PCz-B33 were prepared according to the literature procedure. 1H,
13C and 31P NMR spectra were recorded at room temperature on
a Bruker Avance 300 NMR spectrometer. Among them, 31P
NMR spectrum was referenced to external 85% H3PO4 (0 ppm).
Elementary analysis was carried out on a Bio-Rad elemental
analysis system. MALDI-TOF mass spectrum was performed on
an AXIMA CFR MS apparatus (COMPACT). UV-Visible
absorption and photoluminescence spectra were recorded on
Perkin-Elmer Lambda 35 UV-vis spectrometer and Perkin-
Elmer LS 50B spectrofluorometer, respectively. Thermal prop-
erties were tested on a Perkin-Elmer-TGA 7 instrument. Cyclic
voltammetry was performed on an EG&G 283 (Princeton
Applied Research) potentiostat–galvanostat system. The
samples were tested in 1 mM solution using the ferrocene/fer-
rocenium couple as the reference. The supporting electrolyte was
0.1 M tetrabutylammonium perchlorate (n-Bu4NClO4). Crystal
data collection was performed on a Bruker Smart APEX
diffractometer. Theoretical calculations were carried out by
density functional theory (DFT) using Gaussian 03.
Fig. 7 (a) The current density–voltage–brightness (J–V–L) and (b)
luminous efficiency–current density (hc–J) characteristics of CBP and
PCBP.
brightness dramatically increases from 820 cd mꢀ2 for CBP to
16 000 cd mꢀ2 for PCBP, regardless of their comparable current
density (Fig. 7a). As indicated in Fig. 7b, the device efficiency has
been greatly improved by the replacement of CBP with PCBP.
The peak luminous efficiency of device A is 31.4 cd Aꢀ1, about 18
times higher than that of device B (1.7 cd Aꢀ1). The salient
improvement in device performance can be interpreted from the
following reason. Due to its shallow HOMO level (ꢀ4.91 eV) and
high doping concentration (30 wt%), G1 can contribute to the
efficient hole injection/transporting for both device A and B
(Fig. 6). However, the electron injection/transport route of device
A is different from that of device B. In device B, it is very difficult
to inject electrons from LiF/Al cathode into CBP molecules.
Therefore, there would be only a small amount of excitons
directly generated on G1 cations (formed through hole injection
into G1 molecules) by Coulomb attracting electrons from the
cathode. Consequently, high current density but low brightness
and poor efficiency are observed for device B. On the contrary, in
device A, besides Coulomb attraction, sufficient electrons can be
easily injected into PCBP molecules, then transferred to G1, and
finally recombine holes to form substantive excitons. As a
consequence, more balanced carrier flux is obtained for device A,
leading to superior device efficiency.
Synthesis of PCz-Br
Under inert atmosphere, a mixture of Pd(OAc)2 (0.14 g,
0.61 mmol), 1,10-bis(diphenylphosphino)ferrocene (dppf, 0.68 g,
1.22 mmol), anhydrous KOAc (0.24 g, 2.44 mmol) and THF
(25 mL) were stirred under reflux for 15 min. A red black solution
was obtained. Then, a THF solution (50 mL) of 9-(4-bromo-
phenyl)-3,6-diiodo-9H-carbazole (7.00 g, 12.2 mmol) and diethyl
phosphite (3.15 mL, 24.4 mmol) was added to the catalytic
solution, and stirred under reflux for 8 hours. After THF was
removed by distillation, dichloromethane was added to dissolve
the residue. The dichloromethane solution was washed with
saturated aqueous sodium chloride. The organic layer was
separated and dried with anhydrous Na2SO4. The solvent was
The state-of-art performance is among the best by solution
processed single-layer PhOLEDs.4,5,30,31 Compared with the
previously reported systems, noticeably, there are two other
advantages here. Firstly, an environmental-friendly and stable
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completely removed by rotatory evaporation. The raw product
was purified by column chromatography on silica gel (200–300
mesh) using ethyl acetate as eluent. The final product was
obtained as a light yellow viscous liquid (4.37 g, 60.2%). 1H
NMR (CDCl3, 300 MHz, d): 8.69 (d, J ¼ 13.1 Hz, 2H), 7.90 (t,
J ¼ 7.9 Hz, 2H), 7.79 (d, J ¼ 8.3 Hz, 2H), 7.40 (d, J ¼ 8.2 Hz,
4H), 4.17 (m, 8H), 1.40 (t, J ¼ 6.8 Hz, 12H).
(100 nm) and ITO/Al (100 nm)/CBP or PCBP (50 nm)/
LiF(1 nm)/Al (100 nm), respectively.
Conclusion
In summary, we have illuminated a hole- to electron-dominated
transition in OLEDs by modifying CBP with phosphonate
groups. Such a conversion is then applied to engineer the single-
layer device performance of SHPhDs. Compared with the
prototype CBP, an about 18-folds improvement of the luminous
efficiency is achieved for PCBP. We believe that, phosphonate
will be an appealing substituent to tune the electronic properties
of p-type semiconductors, and this simple design strategy is
extendable to other p-type ones rather than CBP.
Synthesis of PCBP
PCz-Br (0.52 g, 0.88 mmol), PCz-B (0.55 g, 0.86 mmol) and K2CO3
(0.24 g, 1.8 mmol) were dissolved in 8 mL mixed solvent of
ethylene glycol mono methyl and water (Vethylene glycol mono methyl
:
Vwater ¼ 3 : 1). The solution was added Pd(OAc)2 (1.9 mg, 8.7
mmol) and stirred at room temperature for 7 hours. And the color
of the solution finally turned to dark brown. After the solvent
was removed by vacuum distillation, the residue was purified by
column chromatography on silica gel (200–300 mesh) with ethyl
acetate/methanol (15 : 1) as eluent. Final product was obtained
Acknowledgements
The authors are grateful to the 973 Project (2009CB623601 and
2009CB930603), National Natural Science Foundation of China
(nos. 20923003, 21174144 and 50803062), and Science Fund for
Creative Research Groups (no.20921061) for financial support of
this research. B. Chen also thanks Dr B. Zhang, Dr H. Tian and
Prof. Y. Cheng for their help on the device optimization and
crystal analysis, respectively.
1
as white solid (0.53 g, 60.0%). H NMR (DMSO, 300 MHz, d):
8.89 (d, J ¼ 13.7 Hz, 4H), 8.17 (d, J ¼ 8.5 Hz, 4H), 7.91–7,82 (m,
8H), 7.62 (dd, J ¼ 2.9, 8.5 Hz, 4H), 4.15–4.00 (m, 16H), 1.29 (t, J
¼ 7.0 Hz, 24H). 13C NMR (DMSO, 75 MHz, d): 143.67 (JC–P
2.2 Hz), 140.07, 136.20, 130.78 (JC–P ¼ 11.7 Hz), 129.10 (JC–P
¼
¼
85.3 Hz), 126.39 (JC–P ¼ 11.5 Hz), 123.18 (JC–P ¼ 17.5 Hz),
122.07, 119.55, 111.34 (JC–P ¼ 15.8 Hz), 62.44 (JC–P ¼ 5.2 Hz),
17.11 (JC–P ¼ 5.9 Hz). 31P NMR (DMSO, 121 MHz, d): 22.64.
Anal. Calcd for C52H60N2O12P4: C, 60.70; H, 5.88; N, 2.72;
found: C, 60.57; H, 6.01; N, 2.30%. Calcd mass: 1208.3; MALDI-
TOF found (m/z): 1029.3 [M + H+].
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23686 | J. Mater. Chem., 2012, 22, 23680–23686
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