Dipyrenylcarbazole derivatives for blue organic light-emitting diodes

Article abstract of DOI:10.1002/asia.201000304

Blue moon: Three new light-emitting materials, comprising highly fluorescent pyrenes with holetransporting carbazole units, have high thermal stabilities and optoelectronic properties that are suitable for application in electroluminescent devices. A devi

Full text of DOI:10.1002/asia.201000304

COMMUNICATION
DOI: 10.1002/asia.201000304
Dipyrenylcarbazole Derivatives for Blue Organic Light-Emitting Diodes
Trakool Kumchoo,[a] Vinich Promarak,[b] Taweesak Sudyoadsuk,[b]
Mongkol Sukwattanasinitt,[a] and Paitoon Rashatasakhon*[a]
The use of p-conjugated organic compounds as electrolu-
minescent materials in diode devices was pioneered by van
Slyke and co-workers over two decades ago.[1] Since then,
the development of new polymeric or small molecular p-
conjugated compounds with superior physical, optical, ther-
mal, and electrochemical properties has become one of the
most thriving research areas.[2–4] This research is driven in-
part by the recent growing demands for organic light-emit-
ting diodes (OLEDs)[5] in high-performance electrolumines-
cent materials that have applications in full-color, flat panel,
and flexible displays. The simplest configuration of OLEDs,
which are composed of a layer of emissive material sand-
wiched between a cathode and an anode, usually fails to
provide satisfactory efficiency and stability for long-term
use.[6] To circumvent these problems, double- or multi-layer
devices have been constructed by incorporating charge-
transporting layers, that is, hole-transport and electron-
transport layers, into the device. In order to simplify the
manufacturing process of material coating, organic com-
pounds that have both light-emitting and charge-transport-
ing properties are therefore highly desirable. A number of
polymers or small molecules containing carbazoles are com-
mercially available and have been used as amorphous hole-
transporting materials, such as poly(vinylcarbazole) (PVK),
tris(4-carbazoyl-9-ylphenyl)amine (TCTA), and 4,4’-di(9H-
carbazol-9-yl)biphenyl (CBP). These compounds are known
for their high glass transition temperatures and good ther-
mal stabilities. Several other examples, such as carbazole de-
rivatives containing diarylamine peripheries[7] and triaryla-
mine–carbazole end-capped oligofluorenes[8] have also been
reported. Recent development in emissive materials has fo-
cused on the blue electroluminescence (EL)[9] as a number
of new fluorescent blue light-emitting materials, such as tri-
phenylfluoranthene,[10] oligoquinoline,[11] triarylamine,[12] flu-
orene,[13] and pyrene derivatives[14] have been reported.
However, pyrene derivatives are more attractive to us owing
to their strong fluorescence, high quantum efficiency, carrier
mobility, and hole-transporting ability.[14a,15]
Our design for new electroluminescent materials involved
a combination of a hole-transporting carbazole unit and a
highly fluorescent pyrene moiety to incorporate desirable
physical, optical, and electronic properties. Herein, we
report a detailed synthesis of compounds 1–3 and their opti-
cal, thermal, and electrochemical properties (Scheme 1). A
preliminary investigation of OLED device fabrication is also
reported. We began with a regioselective diiodination of car-
bazole using KI/KIO3 in refluxing acetic acid, followed by a
Suzuki coupling with the commercially available pyrene-1-
boronic acid to afford dipyrenylcarbazole 5 in 67% yield
(Scheme 2). The nitrogen atom was then substituted with a
para-tolyl group by reacting with 4-iodotoluene under the
À
copper-catalyzed C N coupling conditions developed by
Buchwald and co-workers.[16] After a purification by column
chromatography on silica gel, compound 1 was obtained in a
fair yield of 56%. However, we found that 1 had low solu-
bility in most organic solvents, which is considered to be an
undesirable property of materials for solvent-casting tech-
niques. Therefore, we decided to substitute the nitrogen
atom in 5 with a flexible glycolic chain. Along this line, it
would be interesting to see the effect of a combination of
multiple units of 5 into a single molecule. Upon treatment
of 5 with K2CO3 and 1,2-bis(chloroacetoxy)ethane,[17] we ob-
tained diester 2 in 42% yield. This compound is highly solu-
ble in most organic solvents, such as ethyl acetate, dichloro-
methane, and tetrahydrofuran. We also opted to incorporate
a triphenylamine group into the molecule as it is well-
[a] T. Kumchoo, Prof. M. Sukwattanasinitt, Prof. P. Rashatasakhon
Organic Synthesis Research Unit, Department of Chemistry
Faculty of Science, Chulalongkorn University
Payathai Road, Pathumwan District, Bangkok 10330 (Thailand)
Fax : (+66)2-2187598
E-mail: paitoon.r@chula.ac.th
[b] Prof. V. Promarak, Prof. T. Sudyoadsuk
Advanced Organic Materials and Devices Laboratory
Department of Chemistry, Faculty of Science
Ubon Ratchathani University
Warinchumrap, Ubon Ratchathani, 34190 (Thailand)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201000304.
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Chem. Asian J. 2010, 5, 2162 – 2167

À
copper-catalyzed C N coupling with 5 to give 3 in 70%
yield.
The photophysical properties of 1, 2, and 3 (0.1 mm in di-
chloromethane) were investigated and the results were sum-
marized in Table 1. The absorption spectra of all three com-
pounds appeared to be very similar, showing bands at 250,
280, and 350 nm. Although these absorption bands were in
the same region as the free carbazole and pyrene, their rela-
tively broader shapes indicated a strong electronic coupling
between these two p-conjugated units. This electronic com-
munication was also evident from the fact that the emission
wavelengths of 1–3 were significantly longer than that of
pyrene.[14a,19] Compound 2, which contained two dipyrenyl-
carbazole units connected with a flexible glycolic chain,
showed an emission shoulder at 470 nm that corresponded
to the pyrene excimer.[20] For compound 3, which contained
a triphenylamine group, the maximum emission peak ap-
peared at a longer wavelength (465 nm), while its absorption
band appeared in the same location as 1 and 2. These obser-
vations suggest that the incorporation of a triphenylamine
moiety promotes the electron–vibration coupling in the elec-
tronic excited state of 3, thereby resulting in a geometrically
relaxed exciton with lower energy.
Scheme 1. Structures of dipyrenylcarbazole derivatives (1–3).
The solid-phase absorption spectra of the thin films of all
three compounds (obtained by spin-casting techniques) ex-
hibited significant bathochromic shifts, thus indicating better
p-electron delocalization in the conjugated systems and
greater planarity between the carbazole and pyrene units
caused by solid-state packing.[21] Subsequently, the emission
spectra of 1 and 2 also showed substantial bathochromic
shifts. As both the absorption and emission spectra of the
three compounds in the solid state were very similar in
shape and wavelength, it may be assumed that the dipyre-
nylcarbazole is the photoactive module in these compounds,
regardless of the substituent on the nitrogen atom. Interest-
ingly, the solid-state emission spectrum of 3 exhibited a hyp-
sochromic shift compared to the solution-phase spectrum.
This result may also be attributed to the aforementioned
solid-state packing force which precludes the electron-vibra-
tion coupling between the triphenylamine substituent and
the photoactive unit.
Next, the thermal properties of 1–3 were examined by dif-
ferential scanning calorimetry (DSC) and thermogravimetric
analysis (TGA) under a nitrogen atmosphere (for thermo-
grams, see the Supporting Information). Those results sug-
gested that all three compounds were thermally stable, with
5% weight-loss temperatures (Td5%) well above 3908C.
During the first heating cycle in the DSC experiments, there
were sharp endothermic peaks for 1 and 2, representing
their melting temperatures (Tm) at 256 and 2208C, respec-
tively. In the second heating cycle, compound 1 showed an
endothermic baseline shift owing to glass transition (Tg) at
1658C. Further heating of this sample resulted in exothermic
peaks at 294 and 3578C, corresponding to the crystallization
temperature (Tc) and Tm, respectively. For compound 2,
only a Tg at 1998C was observed and there were no signals
for crystallization or melting upon further heating. For com-
Scheme 2. Synthesis of dipyrenylcarbazole derivatives (1–3). DMF=N,N-
dimethylformamide, DMSO=dimethyl sulfoxide.
known for its hole-transporting properties. 4-Bromo-N,N-di-
phenylaniline, pre-prepared from reacting triphenylamine
with N-bromosuccinimide,[18] successfully underwent
a
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Rashatasakhon et al.
COMMUNICATION
Table 1. Photophysical, thermal, and electronic properties of 1–3.
[d]
Cmpd
Absorption
Emission[c]
FF
Tg [8C][e] Ts% [8C][f]
E1/2/V
Eg [eV][h] HOMO [eV][i] LUMO [eV][j]
AHCTUNGTRENNUNG
lmax [nm] (log e)
lmax [nm]
lmax [nm]
Solution[a]
Thin film[b] Solution Thin film
1
2
3
347 (4.87)
347 (5.15)
345 (4.94)
359
360
356
427
425
465
456
460
453
0.79
0.79
0.73
165
199
166
459
414
398
1.09 (1.06)
1.03 (1.00)
0.91 (0.85)
3.06
3.06
2.73
À5.50
À5.44
À5.29
À2.44
À2.38
À2.56
[a] Measured in a dilute CH2Cl2 solution. [b] Measured on a spin-cast film. [c] Excited at 345 nm. [d] Quinine sulfate as a standard in CH2Cl2. [e] Ob-
tained from DSC measurements on the second heating cycle with a heating rate of 108CminÀ1 under N2. [f] Obtained from TGA measurements with a
heating rate of 108CminÀ1 under N2. [g] Measured using a platinum disk as a working electrode, a platinum rod as a counter electrode, and a SCE as a
reference electrode in CH2Cl2 containing 0.1m nBu4NPF6 as a supporting electrolyte at a scan rate of 50 mVsÀ1 under an argon atmosphere. [h] Estimat-
ed from the electronic absorption edge (Eg =1240/ledge eV). [i] Calculated by the empirical equation: HOMO=À(4.44+Eonset), where Eonset is the onset
potential of the oxidation peak.[j] Calculated from LUMO=HOMOÀEg.
pound 3, the endothermic peak was not observed in the first
and second heating cycles, but a Tg of 1668C was observed.
These results suggested that the amorphous compounds 2
and 3 have the ability to form molecular glass with a high
Tg.
The electrochemical properties of the compounds were
studied by cyclic and differential pulse voltammetric tech-
niques and their redox potentials are shown in Table 1. The
HOMO energy levels of 1–3 were calculated from the onset
potential of the oxidation (Eonset). The energy band gaps
(Eg) were estimated from the electronic absorption band
edges which were used for determination of the LUMO
energy levels. The results suggested that the HOMO–
LUMO energy gaps for 1 and 2 are of a similar size
(3.06 eV), although the HOMO of 1 is slightly lower
(0.06 eV). Of the three compounds, 3 possessed the highest
HOMO, lowest LUMO, and narrowest energy gap of
2.73 eV. In addition, the electrochemical stability of these
compounds was tested by seven subsequent redox cycles
Scheme 3. Band diagrams for devices I–IV.
(voltammograms are available in the Supporting Informa-
tion). Compounds 1 and 3, which have aromatic substituents
on their carbazole nitrogens, were electrochemically unsta-
ble. For compound 1, the oxidation may first take place at
the nitrogen atom. Delocalization of the unpaired electron
Table 2. EL performance of devices with 1–3 as EM without HTM (devi-
ces I–III) and a device with 3 as EM and PEDOT:PSS as HTM (device
and a loss of hydrogen radical would lead to a benzylic radi-
cal-cation that could undergo a dimerization. In the case of
3, oxidative coupling at the para position of the phenyl rings
in the triphenylamine moiety probably led to electro-poly-
merization. The observation of these oxidative couplings
was in good agreement with results previously reported for
the other compounds containing the triphenylamine frag-
ment.[22] Multiple cyclic voltammetry scans revealed that 2
had good electrochemical stability.
IV).
[a]
[b]
[c]
[d]
Device EM Von
Lmax
hlum
hex
J[e]
CIE[f]
I
II
III
IV
1
2
3
3
5.4
6.9
4.8
3.8
670 (12.0) 0.41
1200 (11.6) 0.48
1450 (9.8)
1600 (8.8)
0.07
0.07
0.15
0.40
440 (0.18,0.25)
770 (0.21,0.33)
820 (0.18,0.17)
660 (0.17,0.15)
0.50
1.50
[a] Turn-on voltage (V). [b] Maximum luminance (cdmÀ2) at the applied
potential (V). [c] Luminance efficiency (cdAÀ1). [d] External efficiency
(%). [e] Current density (mAmÀ2). [f] Commission International d’Eclair-
age coordinates (x, y).
The high photoluminescence (PL) quantum yields of 1–3
encouraged us to investigate the use of these compounds as
emissive material (EM) for OLEDs. We used indium tin
oxide (ITO; 4.80 eV) as the anode and LiF (3.5 eV) coated
with aluminium as the cathode. Single-layer devices of struc-
Table 3. EL performance of devices with 1–3 as HTM.
[a]
[b]
[c]
[d]
Device
HTM
Von
Lmax
hlum
hex
J[e]
V
VI
VII
1
2
3
4.7
4.8
4.2
1600 (8.8)
6900 (9.6)
9300 (8.8)
0.65
2.50
2.00
0.03
0.10
0.10
1950
1342
1555
ture ITO/EMACHTUNGTRENNUNG(10 nm)/LiFACHTUNRTEGG(NNUN 0.5 nm)/AlACHTGUNTREN(NUGN 120 nm) were made
using 1–3 as the EM (Scheme 3). The voltage/luminance and
voltage/current-density characteristics of the devices are
shown in Table 2 and Figure 2. Device III was found to have
the best external efficiency of 0.15 with a maximum lumi-
[a] Turn-on voltage (V). [b] Maximum luminance (cdmÀ2) at the applied
potential (V). [c] Luminance efficiency (cdAÀ1). [d] External efficiency
(%). [e] Current density (mAmÀ2).
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Dipyrenylcarbazole Derivatives for Blue Organic Light-Emitting Diodes
nance of 1,450 cdmÀ2 and a turn-on voltage at 4.8 V
(Table 2, entry 3). As the most-promising result was ob-
tained from device III, 3 was used in the fabrication of a
double-layer device (device IV), which incorporated conduc-
tive polymers PEDOT:PSS as hole-transporting materials
(HTM). We found that the incorporation of PEDOT:PSS
not only increased the maximum luminance to 1600 cdmÀ2
but also decreased the turn-on voltage from 4.8 to 3.8 V,
which is considered to be one of the lowest turn-on voltages
for a blue OLED (Table 2, entry 4). The device also emitted
the desirable blue light at CIE coordinate of (0.17, 0.15)
along with a significantly improved luminance efficiency and
a better external efficiency.
Interestingly, we also observed spectral shifts in the solid
phase PL and the device EL for the three emissive com-
pounds (compare Figure 3 with Figure 1, bottom). As device
IV emitted light at similar wavelengths to device III, these
Figure 2. The I-V-L curve of devices with 1–3 as EM without HTM (ITO/
EM/LiF/Al) (devices I–III) and with HTM (ITO/PEDOT:PSS/3/LiF/Al;
devices IV).
Figure 3. EL spectra of devices I–III (insets are cropped photographs of
the working devices).
Figure 1. Absorption and emission spectra of 1–3 in CH2Cl2 solution
(top) and thin film (bottom).
pothesis, double-layer devices of configuration ITO/HTM-
AHCTUNGTERNN(GUN 10 nm)/Alq3CAHUTGTNREN(UNG 10 nm)/LiFAHCNUTGERTG(NNUN 0.5 nm)/AlACHTNUGRTEN(NUGN 120 nm) were fabricat-
shifts between the solid phase PL and the device EL were ir-
relevant to the presence of the hole-transporting material,
PEDOT:PSS. Notably, the maximum emission wavelenghts
for 1 and 2 shifted bathochromically, whilst that of 3 shifted
hypsochromically. Therefore, we reasoned that the exciton
formation in device III may occur closer to the cathode,
where the injected electron has less chance to relax, owing
to the greater hole-transporting ability of 3. It is important
to emphasize that this blue shift in the EL device is a very
welcome property for a blue-light-emitting material.
ed using 1–3 as the HTM and Alq3 as the EM (devices V–
VII; Scheme 4). The voltage/luminance and voltage/current-
density characteristics of these green-light-emitting devices
are shown in Table 3 and Figure 4. These results clearly
demonstrate the hole-transporting ability of 1–3. Device VII
exhibited the best performance with a moderate maximum
luminance of 9,300 cd/m2 for green OLEDs at 8.8 V and a
low turn-on voltage of 4.2 V. Therefore, 3 has the best hole
transporting ability among these three materials.
In conclusion, we successfully synthesized three new de-
rivatives of 3,6-dipyrenylcarbazole with the combined char-
acteristics of blue light-emitting and hole-transporting mate-
rials. These fluorescent compounds showed emission in the
As the HOMO levels of 1–3 lie between the work func-
tion of ITO (4.80 eV) and HOMO of Alq3 (5.70 eV), these
compounds may potentially serve as HTM. To test this hy-
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Rashatasakhon et al.
COMMUNICATION
DI-TOF) Calcd for C51H31N: 657.2.
Found: 657.1. Anal. Calcd for
C51H31N: C 93.12, H 4.75, N 2.13.
Found: C 93.22, H 4.81, N 1.93.
Characterization data for 2: 1H NMR
(CDCl3): d=8.38 (s, 4H), 8.10–8.14
(m, 8H), 7.88–8.00 (m, 24H), 7.73 (d,
J=9.32 Hz, 4H), 7.67 (d, J=8.36 Hz,
4H), 7.44 (d, J=8.40 Hz, 4H), 5.11 (s,
4H), 4.55 ppm (s, 4H). 13C NMR
(CDCl3): d=168.5, 140.3, 138.0, 133.2,
131.4, 130.8, 130.2, 129.1, 128.6, 128.0,
127.3, 127.2, 127.1, 125.8, 125.3, 124.8,
Scheme 4. Band diagrams for devices V–VII.
124.6, 124.5, 123.6, 122.6, 108.4, 62.9,
44.8 ppm. MS(MALDI-TOF) Calcd
for C94H56N2O4: 1277.5 Found: 1277.6. Anal. Calcd for C94H56N2O4:
C 88.38, H 4.42, N 2.19. Found: C 88.58, H 3.96, N 2.11.
Characterization data for 3: 1H NMR (CDCl3): d=8.44 (s, 2H), 8.32 (d,
J=9.10 Hz, 2H), 8.26 (d, J=7.54 Hz, 2H), 8.23–8.07 (m, 10H), 8.06–7.95
(m, 4H), 7.73 (dd, J=22.42, 8.33 Hz, 4H), 7.61 (d, J=7.79 Hz, 1H),
7.45–7.06 ppm (m, 12H). 13C NMR (CDCl3): d=147.6, 147.4, 141.0, 138.5,
133.2, 131.6, 131.3, 131.1, 130.4, 129.4, 129.0, 128.9, 128.2, 127.9, 127.5,
127.4, 127.2, 126.0, 125.7, 125.1, 125.0, 124.9, 124.7, 124.7, 124.1, 123.6,
122.7, 122.4, 109.9 ppm. MS(MALDI-TOF) Calcd for C62H38N2: 810.1.
Found: 810.4. Anal. Calcd for C62H38N2: C 91.82, H 4.72, N 3.45. Found:
C 91.51, H 4.51, N 3.53.
Acknowledgements
This work is financially supported by the Thailand Research Fund (TFR-
MRG5080197), a research grant (NN-B-22-FN9–10–52–06) from the Na-
tional Nanotechnology Center, and the Faculty of Science, Chulalong-
korn University. T.K. thanks the Center for Petroleum, Petrochemicals
and Advanced Material, Chulalongkorn University for a scholarship. P.R.
thanks Prof. Thawatchai Tuntulani for valuable advice and information.
Keywords: carbazole · electroluminescence · fluorescence ·
organic light emitting diodes · pyrenes
Figure 4. The I-V-L curve of devices V–VII with 1–3 as hole-transporting
materials (ITO/HTM/Alq3/LiF/Al).
[1] a) C. W. Tang, S. A. van Slyke, Appl. Phys. Lett. 1987, 51, 913–915;
b) S. A. Van Slyke, C. H. Chen, C. W. Tang, Appl. Phys. Lett. 1996,
69, 2160–2162.
[2] a) A. O. Patil, A. J. Heeger, F. Wudl. , Chem. Rev. 1988, 88, 183–
200; b) J. Pei, W.-L. Yu, W. Huang, A. J. Heeger, Macromolecules
2000, 33, 2462–2471; c) D. Vak, J. Jo, J. Ghim, C. Chun, B. Lim,
A. J. Heeger, D.-Y. Kim, Macromolecules 2006, 39, 6433–6439;
d) A. J. Heeger, Chem. Soc. Rev. 2010, DOI:10.1039/b914956m.
[3] a) J. H. Burroughes, D. D. C. Bradley, A. R. Brown, R. N. Marks, K.
Mackay, R. H. Friend, P. L. Burn, A. B. Holmes, Nature 1990, 347,
539–541; b) N. C. Greenham, R. H. Friend, Solid State Phys. 1996,
49, 1–149; c) J. Morgado, F. Cacialli, J. Grꢁner, N. C. Greenham,
R. H. Friend, J. Appl. Phys. 1999, 85, 1784–1791.
blue to green region with high quantum efficiencies of over
70% in the solution phase, and strong luminescence in the
solid-phase thin film. All of these compounds were thermal-
ly stable and possessed high glass-transition temperatures,
well above 1608C. Most importantly, these compounds
showed promising potential as either blue-light-emitting ma-
terials or hole-transporting materials for Alq3-based
OLEDs. Further studies on multi-layered device and device
optimization are currently underway.
[4] a) S. R. Forrest, M. E. Thompson, Chem. Rev. 2007, 107, 923–925;
b) S.-C. Lo, P. L. Burn, Chem. Rev. 2007, 107, 1097–1116; c) A. C.
Grimsdale, K. L. Chan, R. E. Martin, P. G. Jokisz, A. B. Holmes,
Chem. Rev. 2009, 109, 897–1091.
[5] K. Mꢁllen, U. Scherf in Organic Light Emitting Devices: Synthesis
Properties and Applications, Wiley-VCH, Weinheim 2006.
[6] a) S. W. Cha, J.-I. Jin, Synth. Met. 2004, 143, 97–101; b) G. Y. Zhong,
Z. Xu, J. He, S. T. Zhang, Y. Q. Zhan, X. J. Wang, Z. H. Xiong,
H. Z. Shi, X. M. Ding, W. Huang, X. Y. Hou, Appl. Phys. Lett. 2002,
81, 1122–1124.
Experimental Section
Characterization data for 1: 1H NMR (CDCl3): d=8.37 (s, 2H), 8.25 (d,
J=9.2 Hz, 2H), 8.18 (d, J=7.6 Hz, 2H), 8.02–8.13 (m, 10H), 7.91–7.96
(m, 4H), 7.44 (d, J=8.40 Hz, 2H), 7.56–7.60 (m, 4H), 7.45 (d, J=8.0 Hz
4H), 2.49 ppm (s, 3H). 13C NMR (CDCl3): d=140.9, 138.5, 137.7, 133.1,
131.6, 131.1, 130.7, 130.4, 129.0, 128.2, 127.5, 127.4, 127.2, 127.1, 125.9,
125.7, 125.0, 124.7, 124.6, 123.5, 122.4, 120.4, 109.9, 21.3 ppm. MS(MAL-
[7] K. R. J. Thomas, J. T. Lin, Y.-T. Tao, C.-W. Ko, J. Am. Chem. Soc.
2001, 123, 9404–9411.
2166
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Dipyrenylcarbazole Derivatives for Blue Organic Light-Emitting Diodes
[8] V. Promarak, M. Ichikawa, D. Meunmart, T. Sudyoadsuk, S. Saeng-
suwan, T. Keawin, Tetrahedron Lett. 2006, 47, 8949–8952.
[9] X. Ren, J. Li, R. J. Holmes, P. I. Djurovich, S. R. Forrest, M. E.
Thompson, Chem. Mater. 2004, 16, 4743–4747.
[10] R. C. Chiechi, R. J. Tseng, F. Marchioni, Y. Yang, F. Wudl, Adv.
Mater. 2006, 18, 325–328.
[11] C. J. Tonzola, A. P. Kukarni, A. P. Gifford, W. Kaminsky, S. A.
Jenekhe, Adv. Funct. Mater. 2007, 17, 863–874; Kaminsky, S. A.
Jenekhe, Adv. Funct. Mater. 2007, 17, 863–874.
[12] Q. D. Liu, J. Lu, J. Ding, M. Day, Y. Tao, P. Barrios, J. Stupak, K.
Chan, J. Li, Y. Chi, Adv. Funct. Mater. 2007, 17, 1028–1036.
[13] K. T. Wong, R. T. Chen, F. C. Fang, C. C. Wu, Y. T Lin, Org. Lett.
2005, 7, 1979–1982.
[14] a) C. Tang, F. Liu, Y.-J. Xia, L.-H. Xie, A. Wie, S.-B. Li, Q.-L. Fan,
W. Huang, J. Mater. Chem. 2006, 16, 4074–4080; b) J. N. Moorthy, P.
Natarajan, P. Venkatakrishnan, D.-F. Huang, T. J. Chow, Org. Lett.
2007, 9, 5215–5218; c) F. Liu, C. Tang, Q.-Q. Chen, F.-F. Shi, H.-B.
Wu, L.-H. Xie, B. Peng, W. Wei, Y. Cao, W. Huang, J. Phys. Chem.
A 2009, 113, 4641–4647; d) K.-R. Wee, H.-C. Ahn, H.-J. Son, W.-S.
Han, J.-E. Kim, D. W. Cho, S. O. Kang, J. Org. Chem. 2009, 74,
8472–8475.
[16] a) A. Klapars, X. Huang, S. L. Buchwald, J. Am. Chem. Soc. 2002,
124, 7421–7428; b) A. Klapars, C. J. Antilla, X. Huang, S. L. Buch-
wald, J. Am. Chem. Soc. 2001, 123, 7727–7729.
[17] A. Kimoto, J.-S. Cho, M. Higushi, K. Yamamoto, Macromolecules
2004, 37, 5531–5537.
[18] E. Bacher, M. Bayerl, P. Rudati, N. Reckefuss, D. Mꢁller, K. Meer-
holz, O. Nuyken, Macromolecules 2005, 38, 1640–1647.
[19] a) H. Du, R. A. Fuh, J. Li, A. Corkan, J. S. Lindsey, Photochem.
Photobiol. 1998, 68, 141–142; b) J.-H. Lee, E. R. Carraway, J. Hur,
S. Yim. M. A. Schlautman, J. Photochem. Photobiol. A 2007, 185,
57–61.
[20] O. A. Khakhel, V. V. Nekrasov, T. V. Sakhno, N. N. Barashkov, R. N.
Nurmukhametov, J. Appl. Spectrosc. 1994, 60, 66–70.
[21] a) J.-F. Pan, S.-J. Chua, W. Huang, Chem. Phys. Lett. 2002, 363, 18–
24; b) C. P. Brock, R. P. Minton, J. Am. Chem. Soc. 1989, 111, 4586–
4593.
[22] a) C. C. Chiang, H.-C. Chen, C.-S. Lee, M.-K. Leung, K.-R. Lin, K.-
H. Hsieh, Chem. Mater. 2008, 20, 540–552; b) K. Sreenath, C. V. Su-
neesh, V. R. K. Kumar, K. R. Gopidas, J. Org. Chem. 2008, 73,
3245–3251.
[15] B. Valeur, Molecular Fluorescence: Principles and Applications,
Wiley-VCH, New York, 2002.
Received: April 26, 2010
Published online: August 16, 2010
Chem. Asian J. 2010, 5, 2162 – 2167
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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