Carbazole-based conjugated polymer with tethered acetylene groups: Synthesis and characterization

Article abstract of DOI:10.1016/j.dyepig.2012.07.010

A novel carbazole-based conjugated polymer with tethered acetylenes, poly [(9,9-dioctyl)-2,7-fluorene-(N-octyl-3,6-carbazole)]-co-[(9,9-dioctyl)-2, 7-fluorene-(N-4-phenylacetylene)-3,6-carbazole)] (P-2), was successfully synthesized through the desilylati

Full text of DOI:10.1016/j.dyepig.2012.07.010

Dyes and Pigments 96 (2013) 138e147
Contents lists available at SciVerse ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Carbazole-based conjugated polymer with tethered acetylene groups: Synthesis
and characterization
,
,
,
c
,
a,c,
Yanli Lei a c, Qiaoli Niu b, Hongyu Mi a c, Yongli Wang b, Ismayil Nurulla a , Wei Shi
*
*
a Key Laboratory of Petroleum and Gas Fine Chemicals, Educational Ministry of China, School of Chemistry and Chemical Engineering, Xinjiang University, Urumqi 830046, PR China
b Institute of Optoelectronic Materials and Technology, South China Normal University, Guangzhou 510631, PR China
c Key Laboratory of Functional Polymers, Xinjiang University, Urumqi 830046, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel carbazole-based conjugated polymer with tethered acetylenes, poly [(9,9-dioctyl)-2,7-fluorene-(N-
Received 24 January 2012
Received in revised form
9 July 2012
Accepted 13 July 2012
Available online 25 July 2012
octyl-3,6-carbazole)]-co-[(9,9-dioctyl)-2,7-fluorene-(N-4-phenylacetylene)-3,6-carbazole)]
(P-2),
was
successfully synthesized through the desilylation of triisopropylsilyl (TIPS) protected precursor polymer, poly
[(9,9-dioctyl)-2,7-fluorene-(N-octyl-3,6-carbazole)]-co-[(9,9-dioctyl)-2,7-fluorene-(N-4-triisopropylsilyl-
phenylacetylene)-3,6-carbazole)] (P-1). Thermally induced crosslinking between periphery acetylenes
attached on P-2 began to occur when heating temperature above 220 ꢀC, and the solubility of P-2 decreased
significantly after curing. Nanodispersion of P-2 in water was readily prepared by reprecipitation protocol.
Optical properties of P-2 in different states were characterized by UVevis and photoluminescence analyses.
Acceptable quantum efficiency (QE, 0.13) and binding ability with Hg2þ allow P-2’s nanodispersion to act as
optical probe for the detection of Hg2þ in aqueous phase. Primary investigation for the application of P-2 as
hole-transport layer (HTL) in multilayer polymeric light-emitting devices (PLEDs) shown that the device with
the insertion of P-2 between PEDOT:PSS and emissive layeraffords better performance as compared to that of
PEDOT:PSS-based one HTL device.
Keywords:
Conjugated polymer
Carbazole
Acetylene
Hole-transport
Nanoparticle
Probe
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
the excellent hole-transporting capability these carbazole-
derivatives possess, how to realize the retaining of such organic
Conjugated polymers (CPs) have drawn extensive attention in
recent years due to their potential applications in a variety of fields,
such as polymeric light-emitting diodes (PLEDs) [1e4], polymeric
solar cells [5e7], bio-sensors [8e11] and chemosensors [12e15]. In
these CPs, carbazole-based CPs attracted particular attention owing
to their unique properties, such as excellent hole-transporting
capability and high luminescence efficiency [16e19]. The efficient
conjugation length of carbazole-based CPs can be tuned conve-
niently by the alteration of substitution position, i.e., the 3,6- and
2,7-site [19e22]; corresponding optoelectronic properties can be
thus controlled to meet requirements for different usages.
solvent-soluble HTL in multilayer PLEDs is still a challenging
question and needs to be resolved. In the fabrication of multilayer
devices, the solvent-resistivity is an extra requirement for high-
performance HTL, that is, the HTL shouldn’t be erased during the
coating of subsequent emitting layer (EML). One of the efficient
ways to overcome the inter-mixing between HTL and EML is to
prepare cross-linkable HTLs. After post-treatment, these HTLs will
become insoluble without compromising their hole-transport
capability. Two main groups of crosslinkable HTLs have been
reported, which containing thermally (such as organosiloxanes
[26], styrenes [27,28], trifluorovinylethers [29,30], benzocyclobu-
tenes [31]) and photo-crosslinkable (such as cinnamates, chal-
cones [32,33] and oxetanes [34,35]) groups, respectively. With the
introduction of above-mentioned crosslinkable groups into HTLs,
improved performance in solution processed PLEDs can be
obtained by application of them.
A
series of carbazole-based hole-transport polymers
[16,23e25] have been successfully synthesized, and the corre-
sponding device performance improved significantly with the
introduction of these hole-transporting layers (HTLs). Despite of
Acetylene (^H) is an important group of unsaturated compo-
nent and can be crosslinked both with thermal and photo-
treatment. Crosslinking reaction between acetylenes will produce
conjugated double bonds [36] or aromatic ring derivatives [37],
thus the efficient conjugation chain length of acetylene-substituted
* Corresponding authors. Key Laboratory of Functional Polymers, Xinjiang
University, Urumqi 830046, PR China. Tel.: þ86 0991 8583575; fax: þ86 0991
8582809.
E-mail addresses: Ismayilnu@sohu.com (I. Nurulla), xjuwshi@gmail.com (W. Shi).
0143-7208/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2012.07.010

Y. Lei et al. / Dyes and Pigments 96 (2013) 138e147
139
material will be increased after crosslinking. A series of acetylene-
Solutions of Al3þ, Ba2þ, Co2þ, Cu2þ, Kþ, Mg2þ, Naþ, Ni2þ, Sn4þ
,
containing, silole-based CPs have been successfully synthesized
recently and their thermal-crosslinking, photopatterning and sen-
soring properties have been systematically investigated [38]. Lee
et al. [36] have synthesized two kinds of acetylene-containing tri-
phenylamine-based small molecules; these materials can be cured
both by heating and UV irradiation. Improved electroluminescent
efficiency has been obtained after cure treatment of these small-
molecular HTLs as compared to the corresponding device with
un-crosslinked HTL (devices’ structure: ITO/HTL/Alq3/Al). But the
film-forming process of these small-molecular HTLs needs vacuum
deposition, which is tedious and cost-waste relative to spin-coating
process. However, spin-coatable, acetylene-substituted cross-
linkable polymer as hole-transporting material has not been re-
ported by far and will be interesting to be explored.
and Zn2þ were prepared from their chloride salts; Hg2þ, Ca2þ, Pb2þ
were prepared from their acetate salts; Fe3þ and Cd2þ were
prepared from their sulfate salts, and Agþ was prepared from its
nitrate salts. Concentrations of metal solutions were controlled at
10ꢂ1 M in deionized water and were diluted subsequently to
different concentration stocks for next use.
2.2. Measurements and characterization
IR spectra were recorded on an EQUINOX 55 FT-IR spectrometer
with KBr pellets. 1H NMR and 13C NMR spectra were collected on
a VARIAN INOVA-400 spectrometer operating respectively at
400 MHz (for 1H) and 100 MHz (for 13C) in deuterated chloroform
solution with tetramethylsilane as reference. Number-average (Mn)
and weight-average (Mw) molecular weights were determined by
Waters GPC 2410 in tetrahydrofuran (THF) using a calibration curve
of polystyrene standards. UVevis absorption spectra were recorded
on a SHIMADZU UV-2450 UVevis spectrophotometer. PL spectra
were recorded on HITACHIF-4500 spectrophotometer. Cyclic vol-
tammetry was carried out on a CHI660C electrochemical work-
station with platinum electrodes at scan rate of 50 mV/s against
a saturated calomel reference electrode with nitrogen-saturated
Another unique property of acetylene is its binding capability
with some heavy metals [39], this endows acetylene-substituted
materials with potential probing properties toward these metals.
Along with this line, some researchers have synthesized a series of
small molecular optical probes based on acetylene-substituted
materials to realize Hg2þ detection in organic or aqueous envi-
ronment [40e42]. It has been acknowledged that the sensitivity of
CPs is superior to that of small molecules due to their signal-
amplification effect [15]. But to our knowledge, there is no litera-
ture about the application of acetylene-substituted CP to detect
Hg2þ. One of the questions still laid before us is that a majority of
reported mercuric sensors have poor water solubility, and hardly to
be used in pure aqueous environment (which is undoubtedly of
very importance due to the existence of Hg2þ is in water in most
cases). Preparation of water-soluble conjugated polyelectrolytes
[43e45] is a protocol to solve this problem. But the synthesis and
purification of such polyelectrolytes are time-waste and difficult to
realize, and the remaining counter-ions correlated with polymer
backbone may endow unfavorable effect to their photoluminescent
(PL) and detective properties. An alternative way to overcome the
hydrophobic intrinsic of CPs is to transform them into nano-
particles in aqueous phase, in other words, is to take advantage of
their size effect. Various CPs-based nano-sized aqueous dispersions
[46e48] have been readily prepared via simple post-treatment,
such as reprecipitation, with acceptable PL quantum efficiency.
Based on these finding, a kind of water-dispersed fluorescent small
molecular organic nanoparticle [49] has been prepared and was
solution of 0.1
M tetrabutylammonium hexafluorophosphate
(Bu4NPF6) in acetonitrile (CH3CN). Thermogravimetric analysis
(TGA) and differential scanning calorimetric (DSC) analyses were
conducted on a NETZSCH STA 449C and 204F1 at a heating rate of
10 ꢀC/min, respectively. Transmission electron microscope (TEM)
and dynamic light scattering (DLS) were conducted on JEM-2100
(JEOL) and Zetasizer Nano S90, respectively.
2.3. LED fabrication and characterization
PLEDswithP-2 asHTLwereinvestigated. Devices’ structureswere
ITO/(PEDOT:PSS)/(P-2)/emissive
polymer/CsCO3/Al.
Patterned
indium tin oxide (ITO) coated glass substrates were cleaned with
acetone, detergent, distilled water and isopropanol in an ultrasonic
bath, and were treated with oxygen plasma before use. About 1 wt.%
of P-2 was dissolved in toluene, filtered through a 0.45 mm filter and
spin-coated on top of anode inside a dry box. The film thicknesses of
P-2 were around 40 nm, as measured with a profilometry (XP-2).
Emissive material was dissolved in toluene, filtered through
proven to act as efficient sensor for Hg2þ
.
a 0.45 mm filter and spin-coated on top of HTL to form a film of 70 nm.
CsCO3 (2 nm) andAl (100 nm) layerswere vacuum-evaporated on the
top of EML layer in a vacuum of 3 ꢁ 10ꢂ4 Pa. P-2 containing devices
were subjected to thermal treatment at different temperatures
before the spin-coatingof EML. Forcomparative purpose, device with
a structure of ITO/PEDOT:PSS (40 nm)/emissive polymer (70 nm)/
CsCO3/Al was made as reference. In control device, a 40-nm layer of
PEDOTePSS was spin-coated on the cleaned ITO from aqueous
emulsion of PEDOT:PSS (Baytron P, Bayer A.G.) [Poly(3,4-
ethylenedioxythiophene) (PEDOT) doped with poly(styrenesulfonic
acid) (PSS)] followed by drying in a vacuum oven at 90 ꢀC for 8 h. The
current densityevoltageeluminance (JeVeL) characteristics were
measured by a Keithley 2400 source measurement unit and a cali-
brated silicon photodiode which was calibrated for luminance by
a PR-705 SpectraScan Spectrophotometer (Photo Research). The
external EL quantum efficiency (QE) was collected by measuring the
total light output in all directions in an integrating sphere (IS-080,
Labsphere).
In this effort, a kind of novel carbazole-based polymer with
periphery acetylene substituents was successfully synthesized. The
corresponding aqueous nano-suspension of this polymer was
prepared by reprecipitation method and the response to various
metal ions was investigated here. Results show that this polymer
can be act as potential probe for Hg2þ ion, and the lowest detection
of limit is w3.3 ꢁ 10ꢂ6 M. With thermal crosslinking treatment, this
polymer can also be used as solvent-resistant HTL in multilayer
PLEDs. Preliminary analyses indicate that the device with this
material as buffer layer on PEDOT:PSS shows better performance as
compared to that of the PEDOT:PSS-based one HTL device.
2. Experimental section
2.1. Materials
All reagents, unless otherwise specified, were purchased from
Aldrich, Acros and TCI Chemical Co. and used without further puri-
fication. Diisopropylamine, toluene and tetrahydrofuran (THF) were
distilledfromsodium atthepresenceofbenzophenoneanddegassed
before use. 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
9,9-dioctylfluorene was synthesized as the reported literature [20].
2.4. Synthesis
Synthetic route of target polymer is outlined in Scheme 1. 3,6-
dibromo-9-octyl-carbazole (3) and 9-(4-iodophenyl) carbazole (4)

140
Y. Lei et al. / Dyes and Pigments 96 (2013) 138e147
were prepared and purified via similar procedures in reported
literature [50e52].
1104, 1072, 1007, 830, 727. 1H NMR (400 MHz, CDCl3).
d (ppm): 8.18
(d, J ¼ 2.0 Hz, 2H), 7.72e7.70 (d, J ¼ 8.0 Hz, 2H), 7.52e7.49 (dd,
J ¼ 12.0 Hz, 2H), 7.45e7.43 (dd, J ¼ 8.0 Hz, 2H), 7.26e7.23 (t,
J ¼ 12.0 Hz, 2H), 1.18e1.17(s, J ¼ 4.0 Hz, 21H). 13C NMR (100 MHz,
2.4.1. Synthesis of 3,6-dibromo-9-(4-iodophenyl) carbazole (5)
9-(4-iodophenyl) carbazole (4) (0.738 g, 2 mmol) and DMF
(10 mL) were placed in a 50 mL round bottom flask equipped with
a Teflon covered magnetic stir bar. The above mixture was degassed
for several minutes. N-bromo-succinimide (NBS) (0.783 g,
4.4 mmol) was dissolved into DMF (10 mL) and added dropwise
with syringe, and the mixture was stirred overnight at room
temperature under nitrogen atmosphere. The product was purified
by column chromatography using petroleum ether as eluent to give
final product as white solid (0.536 g). Yield: 51%. 1H NMR: 1H NMR
CDCl3).
d (ppm): 139.57, 136.54, 133.77, 129.52, 126.52, 124.08,
123.33, 113.32, 111.40, 105.87, 92.52, 124.08, 123.33.
2.4.3. Synthesis of poly [(9,9-dioctyl)-2,7-fluorene-(N-octyl-3,6-
carbazole)]-co-[(9,9-dioctyl)-2,7-fluorene-(N-4-triisopropylsilyl-
phenylacetylene)-3,6-carbazole] (P-1)
Under nitrogen, 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-
2-yl)-9,9-dioctylfluorene (0.193 g, 0.3 mmol),
3 (0.105 g,
0.24 mmol) and 6 (0.035 g, 0.06 mmol) were added in degassed
toluene (8 mL) and 0.2 M potassium carbonate aqueous solution
(1.5 mL). Pd(OAc)2 (0.003 g, 0.013 mmol) and 3 drops of Aliquat
336 were placed later. The above mixture was degassed for several
times, tricyclohexyl phosphine (0.006 g, 0.021 mmol) was added
afterward. The reaction was refluxed at 90 ꢀC for 72 h before it was
cooled to room temperature. The crude product was purified by
flash column chromatography, using toluene as eluent, then
concentrated to a volume of 3 mL, and reprecipitated into meth-
anol (50 mL). The formed precipitate was recovered by filtration.
The obtained polymer was further purified by washing with
acetone in a Soxhlet apparatus for 24 h to remove oligomers and
catalyst residues and was dried after vacuum drying at 50 ꢀC
overnight (0.090 g). Yield: 44%. FT-IR (KBr, cmꢂ1): 2921, 2850,
2155, 1886, 1602, 1462, 1351, 1268, 1153, 803. 1H NMR (400 MHz,
(400 MHz, CDCl3).
(d, J ¼ 11.2 Hz, 2H), 7.51e7.49 (dd, J ¼ 8.0 Hz, 2H), 7.26e7.21(t,
J ¼ 20.0 Hz, 4H).
d
(ppm): 8.18e8.17 (d, J ¼ 2.0 Hz, 2H), 7.95e7.92
2.4.2. Synthesisof3,6-dibromo-9-(4-triisopropylsilyl-phenylacetylene)
carbazole (6)
3,6-dibromo-9-(4-iodophenyl) carbazole (5) (0.527 g, 1 mmol),
Pd(PPh3)2Cl2 (0.035 g, 0.08 mmol) and CuI (0.019 g, 0.1 mmol) were
added in a 50 mL round bottom flask. After purged with nitrogen
for 5 min, dry toluene (10 mL) and diisopropylamine (5 mL) were
placed via syringe. The mixture was degassed and stirred for 20 min
under nitrogen and triisopropylsilyl acetylene (TIPSA) (0.225 g,
1.2 mmol) was injected. The above mixture was stirred at room
temperature overnight. The crude product was purified by column
chromatography using petroleum ether as eluent to give final
product as white solid (1.664 g). Yield: 83%. FT-IR (KBr, cmꢂ1): 3435,
3064, 2941, 2863, 2721, 2154, 1505, 1466, 1314, 1278, 1228, 1175,
CDCl3).
d (ppm): 8.54e8.52 (m, 1.8H), 8.35e8.32 (m, 0.6H),
7.85e7.33 (m, 10H), 4.40e4.32 (m, eNeCH2e, 1.8H), 2.14e0.76 (m,
alkyl H, 48H).
Scheme 1. Synthetic route of monomers and polymers.

Y. Lei et al. / Dyes and Pigments 96 (2013) 138e147
141
2.4.4. Synthesis of poly [(9,9-dioctyl)-2,7-fluorene-(N-octyl-3,6-
carbazole)]-co-[(9,9-dioctyl)-2,7-fluorene-(N-4-phenylacetylene)-
3,6-carbazole] (P-2)
A solution of P-1 (0.090 g) in anhydrous THF (8 mL) was
vigorously stirred under nitrogen atmosphere in a round-bottom
flask and tetrabutylammoniumfluoride (0.5 mL, 0.5 mmol) was
added to this solution. The mixture was stirred at room tempera-
ture overnight. The crude product was purified by flash column
chromatography, using toluene as an eluent, then concentrated and
reprecipitated in methanol. The final product was obtained after
vacuum drying at 50 ꢀC overnight (0.082 g). Yield: 95%. FT-IR (KBr,
cmꢂ1): 3300 (C^CeH), 3050, 2919, 2849, 2109, 1870, 1581, 1603,
1462, 1351, 1267, 1134, 1005, 802. 1H NMR (400 MHz, CDCl3).
d
(ppm): 8.54e8.51 (m, 1.8H), 8.35e8.32 (m, 0.6H), 7.85e7.33 (m,
10H), 4.40e4.32 (m, eNeCH2e, 1.80H), 3.20 (m, ^CeH, 0.11H),
2.14e0.76 (m, alkyl H, 47H).
2.4.5. Preparation of P-2 nanoparticles in aqueous phase
Fig. 1. FT-IR spectra of P-1 and P-2 (inset is the amplified region from wavenumber of
2200 to 2050 cmꢂ1)
.
Polymer nanoparticles in aqueous phase were prepared follow
procedures in previous literature [46e48]. Briefly, 4 mg of P-2 was
added to a flask containing 100 mL of THF, and keep stirring at room
temperature overnight. 2 mL of above-mentioned solution was
solvents such as THF, chloroform, and toluene at room temperature.
The number-average molecular weight (Mn) of P-2 was measured
by gel permeation chromatography (GPC) analysis using THF as
eluant against polystyrene standards, to be 8200 and with the
polydispersity of 2.1.
filtered via 0.45 mm filter and added to 8 mL of deionized water
with ultrasonic processing (40 kHz) for 20 min. THF was removed
by heating at 60 ꢀC from this mixture to give the final aqueous
dispersion.
Chemical structures of intermediates and polymers were veri-
fied by FT-IR and NMR analyses. Fig. 1 shows FT-IR spectra of
polymers. There is a clear difference in FT-IR spectra between P-1
2.4.6. Fluorescence titration of P-2 nanoparticle with metal ions
Nanoparticles in aqueous phase of P-2 (with concentration of
w1 ꢁ 10ꢂ5 M) were prepared as stated before. Solutions of metal
ions were prepared in deionized water with different concentra-
tions. A stock solution of P-2 (3.0 mL) was placed in a quartz cell
(10.0 mm width). Metal ions solutions were introduced with
micropipette with aimed volumes, and fluorescence intensity
changes (excitation wavelength of 350 nm) and UVevis absorption
were recorded after 3 min with the addition of ions each time.
and P-2. For P-1, a weak absorption signal appeared at w2155 cmꢂ1
,
which corresponds to the C^C stretching vibration, weakened
significantly in the spectrum of P-2 and moved to w2109 cmꢂ1
after the desilylation reaction. New band at w3300 cmꢂ1 is
observed exclusively in the spectrum of P-2, which can be assigned
to the typical stretching absorption signal of ^CeH in P-2.
1H NMR spectra of polymers are shown in Fig. 2. Signals at
4.40e4.32 ppm in both curves can be ascribed to the eCH2e groups
attached directly to the N atoms of carbazole moieties (depicted as
eNeCH2e). By comparison of these two spectra one can find that
a small peak at w3.20 ppm appeared only in the spectrum of P-2,
which can be ascribed to the signal of substituted acetylene. This
result is consistent with the finding in FT-IR analysis, by which one
can conclude that the desilylation reaction successfully realized.
3. Results and discussion
3.1. Synthesis and characterization
The synthetic route of intermediates and target polymer is
shown in Scheme 1.
9-(4-iodophenyl) carbazole (4) was synthesized from carbazole
as the starting material by Ullmann reaction in the presence of
copper and potassium carbonate [52]. Compound 5 was readily
obtained by the bromination of 4 in DMF. Due to the much higher
reactivity of iodide-site as compared to that of bromine-sites
toward Sonogashira reaction, the introduction of TIPS group is
happened exclusively at iodide-site. The attempt to obtain target
polymer, P-2, by using acetylene-substituted dibromo-carbazole
directly as monomer failed after several trials. This might due to the
formation of complexes between acetylene and Pd-catalyst during
polymerization under Suzuki reaction condition. Acetylene groups
can be under good protection with the introduction of TIPS in this
effort. High chemical stability of TIPS endows it with sufficient
tolerance for Suzuki polymerization condition. Along with this line,
P-2 was obtained through two-step reaction (protection and
deprotection). Acetylene proportion in polymer can be tuned by the
alternation of feed ratio of carbazole comonomers, and in this effort
it was controlled at 10%. The obtained TIPS-protected polymer
precursor P-1 was successfully synthesized and purified by
conventional procedure. TIPS in P-1 can be deprotected by the
desilylation of Bu4NF in THF at room temperature to give P-2 with
high yield. Both P-1 and P-2 are readily soluble in common organic
Fig. 2. 1H NMR spectra of P-1 and P-2 in deuterated chloroform (inset is the inte-
gration ratio of protons of eNeCH2e to ^CeH of P-2).

142
Y. Lei et al. / Dyes and Pigments 96 (2013) 138e147
Integration ratio of protons of eNeCH2e against ^CeH (as can be
seen from the inset of NMR spectrum of P-2) in P-2 was evaluated
as w16.4 (1.80/0.11), which is nearly double of the theoretical result
(8.0, as calculated by the feed ratio of monomer 3 and 6), suggesting
that the actual composition ratio of ^CeH groups in whole poly-
mer was w10%. This presumably was brought by the different
reactivity between monomers 3 and 6 in the copolymerization
process. The other alkyl and aromatic protons signals are also
reasonable and match well with their chemical structures.
result was shown in Fig. 3d, which revealed larger average sizes
(w130 nm) of particles than that of TEM result. Similar phenom-
enon was also found in previous literature [53]. After drying,
shrinkage of nanoparticle happened in TEM test while in DLS the
wet environment (may with little residue of THF) may induce the
swollen of particles and gives larger sizes.
3.2. Thermal properties
Nano-dispersion of P-2 in water can be conveniently obtained
by reprecipitation procedure as reported by previous literature
[46e48]. As can be seen from Fig. 3, the corresponding nano-
dispersion is uniform and with good transparency under natural
light (Fig. 3a). It emits bright blue light when excited by UV light
(365 nm, visual photograph was shown in Fig. 3b). Its detailed
optical property will be discussed in following section. Morphology
of the resulted dispersion was characterized by TEM analysis. As
revealed by Fig. 3c, P-2 nanoparticles with shapes approximate to
spherical (with average diameter of w60 nm, as obtained by the
average counting of more than one hundred particles), and with
moderate aggregation. DLS analysis was also conducted and the
Thermal properties of P-2 were examined by thermogravimetric
analysis (TGA) (Fig. 4a) and differential scanning calorimetry (DSC)
(Fig. 4b). As shown in Fig. 4b, the degradation temperature of P-2 is
appeared at w402 ꢀC, which may due to the crack of alkyl attach-
ments. In Fig. 4b, during the first heating scan, P-2 exhibits a glass-
transition temperature (Tg) of w85 ꢀC, and an apparent exothermic
process was revealed at the onset of w220 ꢀC and with the peak at
w270 ꢀC. According to TGA analysis one can conclude that this
process is not due to the degradation of polymer, and this can be
assigned to the crosslinking reaction between acetylene groups on
the periphery of P-2 according to previous report [37,38]. On the
second heating, there is no obvious thermal feature appeared from
Fig. 3. Photograph under natural light (a), ultraviolet light (b), TEM image (c) and DLS analysis (d) of P-2 aqueous dispersion.

Y. Lei et al. / Dyes and Pigments 96 (2013) 138e147
143
Fig. 5. Normalized UVevis spectra of P-2 in THF (4 ꢁ 10ꢂ4 M), aqueous phase
(1 ꢁ 10ꢂ5 M) and as film on glass substrate (a), crosslinked film with and without
washing by a large mount of THF (b).
quantum efficiency (QE, Ff) of P-2 in THF and in aqueous phase was
determined using 9,10-diphenylanthracene (Ff ¼ 0.90 in cyclo-
hexane) as standard, are 0.58 and 0.13, respectively. Although the
QE of P-2 nanoparticle (0.13) is much lower than that in THF
solution (this might due to the quenching effect brought by inter-
chains aggregation), this QE is acceptable in terms of CPs-based
aqueous nanoparticles according to previous reports [54].
Fig. 4. TGA (a) and DSC (b) studies of P-2.
50 to 300 ꢀC, suggesting that all of the acetylene groups have
participated in curing in the first heating.
3.4. Electrochemical properties
Electrochemical property of P-2 was shown in Fig. 7. P-2 shows
one reversible oxidation process, indicative of stable cation radical.
The highest occupied molecular orbital (HOMO) and the lowest
unoccupied molecular orbital (LUMO) levels were calculated
3.3. Optical properties
UVevis absorption properties of P-2 in THF, aqueous dispersion,
and as film were shown in Fig. 5a. From it one can find that there is
apparent red-shift and broaden of absorption curve in aqueous
phase and film as compared to the corresponding one in THF. This
indicates that aggregation of polymer chains happened in nano-
particle and film state. Absorption maxima of P-2 in THF, aqueous
phase and film were found at w347, 351 and 360 nm, respectively.
UV spectra of P-2 film with thermal crosslinking treatment at
240 ꢀC under N2 for 1 h, with and without rinsed by a large amount
of THF, were compared in Fig. 5b. It reveals that the solubility of P-2
decreased dramatically after crosslinking, and w75% of absorption
intensity was preserved after washing.
Fig. 6 shows photoluminescent (PL) properties of P-2 in different
states. Emission maxima of P-2 in THF and in aqueous phase were
found at w420 nm in both cases. The emission peak red-shifts to
451 nm in solid film, suggests stronger intermolecular aggregation
in solid state relative to that in water phase. After thermally
crosslinking, the emission peak red-shifts further to 468 nm and
the emission curve is broader as compared to that of pristine film.
This may be caused by the formation of conjugated linkage
between polymer chains in crosslinked film after the thermally
induced reaction between periphery acetylenes. Fluorescence
Fig. 6. PL spectra of P-2 in different states.

144
Y. Lei et al. / Dyes and Pigments 96 (2013) 138e147
and corresponding spectra were shown in Fig. 9. One can note from
Fig. 9a that upon the presence of incremental amount of Hg2þ, just
tiny alteration of absorption was detected, that is, shapes of
absorption curves of P-2 were scarcely changed and absorbance
intensity was lightly decreased. While for Fe3þ, substantial changes
can be detected when the concentration of Fe3þ exceeding
w9.9 ꢁ 10ꢂ6 M, and curves upturned during succeeding titration.
The combination of PL and UVevis analyses indicated that P-2
possesses discriminating capability for these two ions to some
extent.
Fig. 10a illustrates detailed fluorescence changes of P-2 upon
gradual titration of Hg2þ ion in increasing concentrations. Around
75% of PL intensity of P-2 was quenched when the concentration of
Hg2þ reached 1.3 ꢁ 10ꢂ3 M. The quenching efficiency can be re-
flected by Ksv constant, which can be obtained by the calculation of
the slope of linear region of quenching plot (Fig. 10b) at low
concentration region (with Hg2þ concentration below 10ꢂ5 M), to
be 5.1 ꢁ 104 Mꢂ1 and with the lowest detection limit (LDL) in the
range of w3 ꢁ 10ꢂ6 M.
Fig. 7. Cyclic voltammogram of P-2’s film cast on platinum electrode against standard
calomel electrode (SCE).
Another issue is that what’s the most important moiety in P-2 is
responsible for the quenching toward Hg2þ. As discussed in
Introduction section, complex can be formed between acetylene
derivatives and Hg2þ. In the current case, PL quenching of P-2
toward Hg2þ is also presumable due to the interaction of tethered
acetylene groups in P-2 with Hg2þ. To find some traces for such
according to an empirical formula of EHOMO ¼ ꢂe(Eoxonset þ 4.4)
(eV), and ELUMO ¼ EHOMO ꢂ Eg in which Eg is the optical band gap
(3.08 eV, as calculated by the absorption onset, 403 nm, of P-2’s
film) [55], to be ꢂ5.59 and ꢂ2.51 eV, respectively. Such energy level
fits reasonably with the required electronic levels for hole-
transporting materials.
3.5. Optical response to metal ions by P-2 aqueous nanodispersion
Optical response of P-2 to different metal ions (Agþ, Al3þ, Ba2þ
,
,
Ca2þ, Cd2þ, Co2þ, Cu2þ, Fe3þ, Hg2þ, Kþ, Mg2þ, Naþ, Ni2þ, Pb2þ, Sn4þ
Zn2þ) was detected in aqueous phase. Fig. 8 shows changes of P-2’s
PL intensity with the addition of different metal ions (the concen-
tration of P-2 and each ion were controlled at 1 ꢁ 10ꢂ5 and
3.3 ꢁ 10ꢂ4 M, PL intensity was recorded 3 min later after the
addition of each ion). One can note that compared to other metal
ions, Fe3þ and Hg2þ caused much more pronounced fluorescent
quenching.
In view of the situation, the question laid before us is that
whether the differentiate detection of Hg2þ and Fe3þ can be real-
ized by P-2. UVevis changes of P-2 upon titration of Hg2þ and Fe3þ
were investigated to find some clues for afore-mentioned question,
Fig. 8. Fluorescence intensity changes of P-2 nanoparticle in aqueous phase (with the
concentration of 1 ꢁ 10ꢂ5 M) in the presence of various metal ions (with concentration
of 3.3 ꢁ 10ꢂ4 M). (Excitation wavelength was 350 nm and the slit width was identical
in all cases).
Fig. 9. UVevis spectra of P-2 (with the concentration of 1 ꢁ 10ꢂ5 M) in the presence of
incremental Hg2þ (a) and Fe3þ (b) in deionized water.

Y. Lei et al. / Dyes and Pigments 96 (2013) 138e147
145
Fig. 11. Fluorescence response of P-1 nanoparticle in aqueous phase (1.0 ꢁ 10ꢂ5 M)
upon incremental addition of Hg2þ (0e7.8 ꢁ 10ꢂ4 M). Excitation was 350 nm. Spectra
were recorded 3 min after adding Hg2þ
.
ions in this case brought insignificant effect to the quenching for
the adding of Hg2þ, while Al3þ, Ba2þ, Cu2þ, Mg2þ and Zn2þ had
relatively stronger interference. In all cases the addition of Hg2þ
caused stronger quenching as compared to those only with back-
ground metals. For Fe3þ, additive quenching was detected with the
introduction of Hg2þ. Considering that these spectra were recorded
3 min later with the addition of each ion and Hg2þ without long-
time standing, P-2 might be act as a potential immediacy optical
probe for Hg2þ. Its anti-interference and sensitivity might be
modified by tuning its backbone structure and acetylene compo-
sition, and the relating work is in progress.
Fig. 10. Fluorescence spectra of P-2 nanoparticle (1 ꢁ 10ꢂ5 M) upon incremental
addition of Hg2þ (0e1.78 ꢁ 10ꢂ3 M) in deionized water (a), and the corresponding I0/I
values versus Hg2þ concentration (b) (inset shows the linear region of P-2’s PL
intensity versus Hg2þ (concentration in the range of 1.65e9.9 ꢁ 10ꢂ6 M)). Excitation
3.6. Primary investigation of hole-transporting property of P-2
was controlled at 350 nm, and each spectrum was recorded 3 min after adding Hg2þ
.
It’s well-known that carbazole derivatives have good hole-
transporting capability, and the energy level of P-2 (as evaluated
by its CV and absorption property) seems suitable for the application
speculation, P-1 aqueous nanoparticle suspension (DLS and TEM
spectra of P-1 suspension can be seen in Fig. S1 in supporting
information) was prepared with the same condition as adopted for
P-2, and florescence alteration of P-1 with the incremental amount
of Hg2þ was also investigated to make comparison. The corre-
sponding spectra were shown in Fig. 11. With the introduction of
Hg2þ, against from the pronounced monotonous quenching for P-2,
PL intensity of P-1 altered relatively slightly under the same
circumstance (fluorescence intensity of P-1 increased firstly and
then decreased within a narrow range during the titration process).
Considering the same backbone and alkyl attachments of these two
polymers, and previous report has proven that PL intensity of
carbazole-based compound was not affected by the addition of
Hg2þ [56]. Different responding manner between P-1 and P-2 is
presumably brought by the difference in their acetylene-
substituent. Binding with Hg2þ will quench P-2’s intensity while
for P-1 this effect didn’t work due to the presence of TIPS protecting
groups. Not all of PL intensity of P-2 was quenched and there is
w25% of intensity remained even with w100 eq of Hg2þ. This may
be explained by the possibility that not all of molecular chains in P-
2 contain acetylene groups due to the low ratio of monomer 6
controlled in polymerization process. In other words, some chains
in P-2 might be not attached by acetylene and their intensity
preserved during titration.
Fig. 12. Fluorescence quenching of P-2 nanoparticle in aqueous phase (with concen-
tration of 1.0 ꢁ 10ꢂ5 M) in the presence of various background metal ions (with
Interference of other metal ions for P-2 against Hg2þ was also
investigated. Fig. 12 shows PL responses of P-2 to various back-
ground metal ions before/after the addition of Hg2þ. Majority of
concentration of 3.3 ꢁ 10ꢂ4 M for each ion, from 1 to 16: Agþ, Al3þ, Ba2þ, Ca2þ, Cd2þ
,
Co2þ, Cu2þ, Fe3þ, Kþ, Mg2þ, Naþ, Ni2þ, Pb2þ, Sn4þ, Zn2þ and Hg2þ) and with sequential
addition of Hg2þ (3.3 ꢁ 10ꢂ4 M). The excitation wavelength is 350 nm.

146
Y. Lei et al. / Dyes and Pigments 96 (2013) 138e147
as HTL in multilayer PLEDs. To evaluate the hole-transporting
property of P-2, four parallels of electroluminescence (EL) devices,
with structures of ITO/PEDOT:PSS/Emitting layer (EML)/Cs2CO3/Al
(Device Ⅰ), ITO/P-2/EML/Cs2CO3/Al (Device Ⅱ), ITO/PEDOT:PSS/P-2/
EML/Cs2CO3/Al (270) (Device Ⅲ), ITO/PEDOT:PSS/P-2/EML/Cs2CO3/
Al (240) (Device Ⅳ) were constructed to make comparison. The EML
used here is a kind of fluorene derivative reported previously by our
group [57]. The choice of this polymer is based on its relatively
weaker intrinsic hole-transporting capability as deduced by its
relative higher HOMO level (with w5.8 eV). In Devices Ⅱ and Ⅲ, P-2
was spin-coated onto anode and was thermally annealed at 270 ꢀC
under N2 for 1 h. Device Ⅳ was fabricated under the same condition,
except the heating temperature was controlled at 240 ꢀC. Similar EL
spectra were obtained by these devices, indicating holeeelectron
combination zone was not affected by the insertion of different
HTLs. Devices’ performance curves were shown in Fig. 13. From
Fig.13, one can find that Device Ⅰ shows much higher current density
than the other devices with a given voltage, which may caused by
the high conductivity of PEDOT:PSS. Turn-on voltages of Devices
ⅠeⅣ were at w4.0, 7.5, 9.2 and 4.7 V, respectively, as recorded by
Fig.13b. The maximum brightness of Devices ⅠeⅣ reached w460 (at
7.3 V), 155 (at 11.3 V), 17 (at 12.0 V) and 440 (at 10.3 V) cd/m2,
respectively. As revealed by Fig. 13c, the maximum luminescence
efficiency (LE) of Devices ⅠeⅣ were 0.11 (at 110 mA/cm2), 0.13 (at
18.5 mA/cm2), 0.13 (at 12.0 mA/cm2) and 0.14 (at 76.6 mA/cm2),
respectively. Whole devices’ performance in this effort is inferior to
our previous report [57], which presumably due to the different
cathode structures (Ba/Al in previous work and Cs2CO3/Al in current
case) and different experimental conditions in two cases. The
parallel devices’ performance in this case indicates that type Ⅳ
device shows better performance than those of the others. Type Ⅲ
device shows the poorest performance, which may due to the high
heating temperature (270 ꢀC) treatment during device’s fabrication
process, the underneath PEDOT:PSS film fabricated in previous step
will degraded significantly as reported by previous report [58]. This
will unfavorable to device’s performance and the corresponding
device is tending to breakdown under relatively lower current
density. According to the solubility analysis of P-2 film in previous
section, thermal treatment at 240 ꢀC has endowed it with good
solvent-resistivity. Along with this line, lower curing temperature
was adopted in Device Ⅳ; this temperature will not damage
excessively the applied PEDOT:PSS layer. With this modification, the
corresponding performance was improved as compared to that of
Device Ⅰ, which may due to the hole-transporting and electron-
blocking effect brought by P-2 as revealed by its HOMO and LUMO
energy levels. These primary analyses indicate that P-2 can be used
as potential HTL in multilayer PLEDs. Another merit acetylene-
derivatives possess is that they can also be cured by ultra-violet
radiation. Thermal degradation problem encountered in above-
mentioned discussion might be readily overcome by photo-
crosslinking protocol and the related investigation is underway.
4. Conclusion
In summary,
a crosslinkable conjugated fluorescent poly
(carbazoleefluorene) polymer with tethered acetylenes was
successfully prepared via protectionedeprotection two-step
protocols. Corresponding polymer nanoparticle in aqueous phase
with reasonable QE was prepared and has the potential to be used
as Hg2þ optical probe in pure water phase. Besides, good solvent-
resistivity together with suitable hole-transport and electron-
block capability endows this polymer with the potential to be
used as HTL in multilayer PLEDs.
Acknowledgments
Authors greatly appreciate the financial support from the
National Natural Science Foundation of China (Project No.
50903068,10904042, 21063013), the Natural Science Foundation of
Xinjiang Uygur Autonomous Region (Project No. 2011211A007) and
the Scientific Research Open Project of Key Laboratory of Oil & Gas
Fine Chemicals, Ministry of Education & Xinjiang Uyghur Autono-
mous Region, Xinjiang University (Grant No. XJDX0908-2009-12)
and the Scientific Research Program of the Higher Education
Institution of XinJiang (No. XJEDU2009S17) and the Key Project of
Chinese Ministry of Education (Grant No. 210157).
Appendix A. Supporting information
Supplementary data related to this article can be found online at
http://dx.doi.org/10.1016/j.dyepig.2012.07.010.
References
[1] Friend RH, Gymer RW, Holmes AB, Burroughes JH, Marks RN, Taliani C, et al.
Electroluminescence in conjugated polymers. Nature 1999;397:121e8.
[2] Tonzola CJ, Alam MM, Jenekhe SA. New soluble n-type conjugated copolymer
for light-emitting diodes. Adv Mater 2002;14:1086e90.
Fig. 13. Device characteristics of PLEDs, (a) voltageecurrent density, (b) voltagee
brightness and luminescence efficiencyecurrent density (c) characteristics.

Y. Lei et al. / Dyes and Pigments 96 (2013) 138e147
147
[3] Yang RQ, Wu HB, Cao Y, Bazan GC. Control of cationic conjugated polymer
performance in light emitting diodes by choice of counterion. J Am Chem Soc
2006;128:14422e3.
[4] Liu CH, Chen SH, Chen Y. Synthesis and optical and electrochemical properties
of copolymers containing 9,9-dihexylfluorene and 9-dimethylaminop-
ropylcarbazole chromophores. J Polym Sci A Polym Chem 2006;44:3882e95.
[5] Patra D, Sahu D, Padhy H, Kekuda D, Chu CW, Lin HC. Synthesis and appli-
cations of 2,7-carbazole-based conjugated main-chain copolymers containing
electron deficient bithiazole units for organic solar cells. J Polym Sci A Polym
Chem 2010;48:5479e89.
[6] Liang YY, Xu Z, Xia JB, Tsai ST, Wu Y, Li G, et al. For the bright future-bulk
heterojunction polymer solar cells with power conversion efficiency of 7.4%.
Adv Mater 2010;22:E135e8.
[7] Chen LM, Hong ZR, Li G, Yang Y. Recent progress in polymer solar cells:
manipulation of polymer: fullerene morphology and the formation of efficient
inverted polymer solar cells. Adv Mater 2009;21:1434e49.
[31] Ma BW, Lauterwasser F, Deng L, Zonte CS, Kim BJ, Fréchet JMJ. New thermally
cross-linkable polymer and its application as a hole-transporting layer for
solution processed multilayer organic light emitting diodes. Chem Mater
2007;19:4827e32.
[32] Bellmann E, Shaheen SE, Thayumanavan S, Barlow S, Grubbs RH, Marder SR,
et al. New triarylamine-containing polymers as hole transport materials in
organic light-emitting diodes: effect of polymer structure and cross-linking on
device characteristics. Chem Mater 1998;10:1668e76.
[33] Domercq B, Hreha RD, Zhang YD, Larribeau N, Haddock JN, Schultz C, et al.
Photo-patternable hole-transport polymers for organic light-emitting diodes.
Chem Mater 2003;15:1491e6.
[34] Müller CD, Falcou A, Reckefuss N, Rojahn M, Wiederhirn V, Rudati P, et al.
Multi-colour organic light-emitting displays by solution processing. Nature
2003;421:829e33.
[35] Bacher E, Jungermann S, Rojahn M, Wiederhirn V, Nuyken O. Photopatterning
of crosslinkable hole-conducting materials for application in organic light-
emitting devices. Macromol Rapid Commun 2004;25:1191e6.
[36] Lee CJ, Kang YK, Jung SH, Kim JS, Lee J. Curing and optical properties of thin
films prepared by vacuum deposition of acetylene containing triphenyl-
amines. Opt Mater 2002;21:337e41.
[8] Sun PF, Lu XM, Fan QL, Zhang ZY, Song WL, Li B, et al. Water-soluble
iridium(III)-containing conjugated polyelectrolytes with weakened energy
transfer properties for multicolor protein sensing applications. Macromole-
cules 2011;44:8763e70.
[9] Traina CA, Bakus IIRC, Bazan GC. Design and synthesis of monofunctionalized,
water-soluble conjugated polymers for biosensing and imaging applications.
J Am Chem Soc 2011;133:12600e7.
[10] Liu XF, Fan QL, Huang W. DNA biosensors based on water-soluble conjugated
polymers. Biosens Bioelectron 2011;26:2154e64.
[11] Li K, Liu B. Water-soluble conjugated polymers as the platform for protein
sensors. Polym Chem 2010;1:252e9.
[12] Tang GQ, Chen SSY, Shaw PE, Hegedus K, Wang X, Burn PL, et al. Fluorescent
carbazole dendrimers for the detection of explosives. Polym Chem 2011;2:
2360e8.
[13] Banjoko V, Xu YQ, Mintz E, Pang Y. Synthesis of terpyridine-functionalized
poly(phenylenevinylene)s: the role of meta-phenylene linkage on the Cu2þ
and Zn2þ chemosensors. Polymer 2009;50:2001e9.
[14] Vetrichelvan M, Nagarajan R, Valiyaveettil S. Carbazole-containing conjugated
copolymers as colorimetric/fluorimetric sensor for iodide anion. Macromole-
cules 2006;39:8303e10.
[37] Lee KS, Jeong MH, Lee JP, Lee JS. End-group cross-linked poly(arylene ether)
for proton exchange membranes. Macromolecules 2009;42:584e90.
[38] Liu JZ, Zhong YC, Lam JWY, Lu P, Hong YN, Yu Y, et al. Hyperbranched
conjugated polysiloles: synthesis, structure, aggregation-enhanced emission,
multicolor fluorescent photopatterning, and superamplified detection of
explosives. Macromolecules 2010;43:4921e36.
[39] Liu L, Lam YW, Wong WY. Complexation of 4,40-di(tert-butyl)-5-ethynyl-2,20-
bithiazole with mercury(II) ion: synthesis, structures and analytical applica-
tions. J Organomet Chem 2006;691:1092e100.
[40] Dong M, Wang YW, Peng Y. Highly selective ratiometric fluorescent sensing
for Hg2þ and Au3þ, respectively, in aqueous media. Org Lett 2010;12:5310e3.
[41] Lee DN, Kim GJ, Kim HJ. A fluorescent coumarinylalkyne probe for the selective
detection of mercury(II) ion in water. Tetrahedron Lett 2009;50:4766e8.
[42] Song FL, Watanabe S, Floreancig PE, Koide K. Oxidation-resistant fluorogenic
probe for mercury based on alkyne oxymercuration. J Am Chem Soc 2008;
130:16460e1.
[15] Thomas III SW, Joly GD, Swager TM. Chemical sensors based on amplifying
fluorescent conjugated polymers. Chem Rev 2007;107:1339e86.
[16] Kirkus M, Grazulevicius JV, Grigalevicius S, Gu R, Dehaen W, Jankauskas V.
Hole-transporting glass-forming indolo[3,2-b]carbazole-based diepoxy
monomer and polymers. Eur Polym J 2009;45:410e7.
[17] Michinobu T, Osako H, Shigehara K. Alkyne-linked poly(1,8-carbazole)s:
a novel class of conjugated carbazole polymers. Macromol Rapid Commun
2008;29:111e6.
[43] Kwon NY, Kim D, Son JH, Jang GS, Lee JH, Lee TS. Simultaneous detection and
removal of mercury ions in aqueous solution with fluorescent conjugated
polymer-based sensor ensemble. Macromol Rapid Commun 2011;32:1061e5.
[44] Zhang ZY, Fan QL, Sun PF, Liu LL, Lu XM, Li B, et al. Highly selective anionic
counterion-based fluorescent sensor for Hg2þ by grafted conjugated poly-
electrolytes. Macromol Rapid Commun 2010;31:2160e5.
[45] Qin CJ, Wu XF, Gao BX, Tong H, Wang LX. Amino acid-functionalized poly-
fluorene as a water-soluble Hg2þ chemosensor with high solubility and high
photoluminescence quantum yield. Macromolecules 2009;42:5427e9.
[46] Wu CF, Szymanski C, McNeill J. Preparation and encapsulation of highly
fluorescent conjugated polymer nanoparticles. Langmuir 2006;22:
2956e60.
[47] Andrew TL, Swager TM. Thermally polymerized rylene nanoparticles.
Macromolecules 2011;44:2276e81.
[48] Rahim NAA, McDaniel W, Bardon K, Srinivasan S, Vickerman V, So PTC, et al.
Conjugated polymer nanoparticles for two-photon imaging of endothelial
cells in a tissue model. Adv Mater 2009;21:3492e6.
[18] Wu CS, Chen Y. Copolyfluorenes containing pendant bipolar carbazole and
1,2,4-triazole groups: synthesis, characterization, and optoelectronic appli-
cations. J Polym Sci A Polym Chem 2011;49:3928e38.
[19] Ma ZH, Chen LC, Ding JQ, Wang LX, Jing XB, Wang FS. Green electro-
phosphorescent polymers with poly(3,6-carbazole) as the backbone: a linear
structure does realize high efficiency. Adv Mater 2011;23:3726e9.
[20] Blouin N, Michaud A, Leclerc M. A low-bandgap poly(2,7-carbazole) derivative
for use in high-performance solar cells. Adv Mater 2007;19:2295e300.
[21] Sahu D, Padhy H, Patra D, Huang JH, Chu CW, Lin HC. Synthesis and charac-
terization of novel low-bandgap triphenylamine-based conjugated polymers
with main-chain donors and pendent acceptors for organic photovoltaics.
J Polym Sci A Polym Chem 2010;48:5812e23.
[49] Li HB, Yan HJ. Ratiometric fluorescent mercuric sensor based on thiour-
eaethiadiazoleepyridine linked organic nanoparticles. J Phys Chem C 2009;
113:7526e30.
[22] Lai MH, Tsai JH, Chueh CC, Wang CF, Chen WC. Syntheses of new 3,6-
carbazole-based donor/acceptor conjugated copolymers for optoelectronic
device applications. Macromol Chem Phys 2010;211:2017e25.
[23] Li ZA, Liu YQ, Yu G, Wen YG, Guo YL, Ji L, et al. A new carbazole-constructed
hyperbranched polymer: convenient one-pot synthesis, hole-Transporting
ability, and field-effect transistor properties. Adv Funct Mater 2009;19:2677e83.
[24] Zhao ZJ, Xu XJ, Wang HB, Lu P, Yu G, Liu YQ. Zigzag molecules from pyrene-
modified carbazole oligomers: synthesis, characterization, and application in
OLEDs. J Org Chem 2008;73:594e602.
[50] Wang HY, Chen G, Liu Y, Hu LH, Xu XP, Ji SJ. The synthesis and characterization
of novel dipolar fluorescent materials based on a quinoxaline core. Dyes Pigm
2009;83:269e75.
[51] Cabaj J, Idzik K, So1oducho J, Chyla A. Development in synthesis and electro-
chemical properties of thienyl derivatives of carbazole. Tetrahedron 2006;62:
758e64.
[52] Shao HX, Chen XP, Wang ZX, Lu P. Synthesis and fluorescence properties of
carbazole and fluorene-based compounds. J Lumin 2007;127:349e54.
[53] Zhu LN, Qin JG, Yang CL. Synthesis, photophysical properties, and self-
assembly behavior of amphiphilic polyfluorene: unique dual fluorescence
and its application as a fluorescent probe for the mercury ion. J Phys Chem B
2010;114:14884e9.
[25] Li ZA, Jiang ZQ, Qiu GF, Wu WB, Yu G, Liu YQ, et al. New carbazole-based
hyperbranched conjugated polymer with good hole-transporting properties.
Macromol Chem Phys 2010;211:1820e5.
[26] Yan H, Lee P, Armstrong NR, Graham A, Evmenenko GA, Dutta P, et al. High-
performance hole-transport layers for polymer light-emitting diodes. Imple-
mentation of organosiloxane cross-linking chemistry in polymeric electrolu-
minescent devices. J Am Chem Soc 2005;127:3172e83.
[27] Paul GK, Mwaura J, Argun AA, Taranekar P, Reynolds JR. Cross-linked hyper-
branched arylamine polymers as hole-transporting materials for polymer
LEDs. Macromolecules 2006;39:7789e92.
[28] Niu YH, Liu MS, Ka JW, Bardeker J, Zin MT, Schofield R, et al. Crosslinkable
hole-transport layer on conducting polymer for high-efficiency white poly-
mer light-emitting diodes. Adv Mater 2007;19:300e4.
[54] Wu CF, Bull B, Szymanski C, Christensen K, McNeill J. Multicolor conjugated
polymer dots for biological fluorescence imaging. Am Chem Soc Nano 2008;2:
2415e23.
[55] Zhang K, Chen Z, Zou Y, Yang CL, Qin JG, Cao Y. Synthesis, characterization,
and photophysics of electroluminescent copolymers with a quinoline-based
iridium complex in the main chain: a versatile method for constructing
metal-containing copolymers. Organometallics 2007;26:3699e707.
[56] Zou YP, Wan MX, Sang GY, Ye MF, Li YF. An alternative copolymer of carbazole
and thieno[3,4b]-pyrazine: synthesis and mercury detection. Adv Funct Mater
2008;18:2724e32.
[29] Niu YH, Liu MS, Ka JW, Jen AKY. Thermally crosslinked hole-transporting
layers for cascade hole-injection and effective electron-blocking/exciton-
confinement in phosphorescent polymer light-emitting diodes. Appl Phys
Lett 2006;88. 093505e093505-3.
[30] Lim B, Hwang JT, Kim JY, Ghim J, Vak D, Noh YY, et al. Synthesis of a new
cross-linkable perfluorocyclobutane-based hole-transport material. Org Lett
2006;8:4703e6.
[57] Shi W, Wang L, Zhen HY, Zhu DX, Awut T, Mi HY, et al. Novel luminescent
polymers containing backbone triphenylamine groups and pendant qui-
noxaline groups. Dyes Pigm 2009;83:102e10.
[58] Cheng YJ, Liu MS, Zhang Y, Niu YH, Huang F, Ka JW, et al. Thermally cross-
linkable hole-transporting materials on conducting polymer: synthesis,
characterization, and applications for polymer light-emitting devices. Chem
Mater 2008;20:413e22.