Synthesis and properties of diphenylcarbazole triphenylethylene derivatives with aggregation-induced emission, blue light emission and high thermal stability

Article abstract of DOI:10.1007/s10895-010-0732-z

New aggregation-induced emission materials derived from diphenylcarbazole triphenylethylene were prepared. The thermal, photophysical, electrochemical and aggregation-induced emissive properties were investigated. All the compounds had strong blue light e

Full text of DOI:10.1007/s10895-010-0732-z

J Fluoresc (2011) 21:433–441
DOI 10.1007/s10895-010-0732-z
ORIGINAL PAPER
Synthesis and Properties of Diphenylcarbazole
Triphenylethylene Derivatives with Aggregation-Induced
Emission, Blue Light Emission and High Thermal Stability
Bing-jia Xu & Zhen-guo Chi & Xiao-fang Li & Hai-yin Li &
Wei Zhou & Xi-qi Zhang & Cheng-cheng Wang &
Yi Zhang & Si-wei Liu & Jia-rui Xu
Received: 10 June 2010 /Accepted: 28 September 2010 /Published online: 30 October 2010
#
Springer Science+Business Media, LLC 2010
Abstract New aggregation-induced emission materials
derived from diphenylcarbazole triphenylethylene were
prepared. The thermal, photophysical, electrochemical and
aggregation-induced emissive properties were investigated.
All the compounds had strong blue light emission capability
and excellent thermal stability. Their maximum fluorescence
emission wavelengths were between 450 to 460 nm in TLC
plates, while their glass transition temperatures ranged from
162.2 to 182.4 °C. The decomposition temperatures of the
synthesized compounds were all well over 500 °C. The
synthesized compounds possessed aggregation-induced
emission (AIE) properties, which exhibited enhanced
fluorescence emissions in aggregation states or in solid
states. The HOMO energy levels estimated from the
oxidation potentials were found in the range from 5.49
to5.52 eV. The lowest unoccupied molecular orbital/high-
est occupied molecular orbital (LUMO/HOMO) energy
gaps (ΔEg) for the compounds were estimated from the
onset absorption wavelengths of UVabsorption spectra and
ranged from 3.04 to 3.20 eV.
Introduction
Most luminescent materials, such as thin films of organic
light-emitting diodes [1–5], are used in the solid state.
However, the efficiency of solid-state luminescent materials
is unsatisfactory due to quenching caused by aggregation.
This quenching is due mainly to both strong π–π stacking
interactions and non-radiative decay [6–9], thereby hinder-
ing many scientists from finding luminescent materials that
could be used in a wide variety of applications.
Recently, several types of electroluminescent materials,
including siloles and 1-cyanotrans-1,2-bis-(4-methylbiphenyl)
ethylene, were found by Tang and Park to possess abnormal
luminescent properties, in which light emission is enhanced
from an aggregated or solid state [10–14]. This interesting
luminescent property has been named aggregation-induced
emission (AIE) [10] or aggregation-induced emission en-
hancement (AIEE) [11]. Currently, more and more AIE
materials have been found, such as tetraphenylethene (TPE)
derivatives, among others, for potential application as active
layers in organic light emitting diodes (OLEDs) or fluores-
cent diagnostic kits [15–17].
.
.
Keywords Triphenylethylene Blue light emission High
.
.
thermal stability Synthesis Aggregation-induced emission
Triphenylethylene carbazole derivatives, a new kind of
AIE-active molecules with excellent thermal properties and
blue light emission capabilities, were first found in our
laboratory. The twisted configuration of triphenylethylene,
the core of the derivative, is assumed to have made it AIE
active and that the functional groups around triphenyl-
ethylene enhanced this phenomenon [18].
Further research on the triphenylethylene system was
performed by our team. As a result, diphenylcarbazole
triphenylethylene derivatives, which are AIE active and
have much better thermal properties as well as stronger blue
light emission, were successfully synthesized.
:
:
:
:
:
B.-j. Xu Z.-g. Chi (*) X.-f. Li H.-y. Li W. Zhou
:
:
:
:
X.-q. Zhang C.-c. Wang Y. Zhang S.-w. Liu J.-r. Xu (*)
PCFM Lab, DSAPM Lab, FCM Institute,
State Key Laboratory of Optoelectronic Materials and Technologies,
School of Chemistry and Chemical Engineering,
Sun Yat-sen University,
Guangzhou 510275, China
e-mail: chizhg@mail.sysu.edu.cn
J.-r. Xu
e-mail: xjr@mail.sysu.edu.cn

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J Fluoresc (2011) 21:433–441
Experimental
Synthesis of Compound P2CTs
Materials and Methods
3,6-diiodo-9-tosyl-9H-carbazole (1.92 g, 3.4 mmol) and
phenylboronic acid (0.90 g, 7.4 mmol) were dissolved in
toluene (30 mL), and then 2 M aqueous K2CO3 solution
(4.0 mL) and 5 drops of aliquat 336 were added. The
mixture was stirred for 45 min under an argon atmosphere
at room temperature. Then the Pd(PPh3)4 catalyst (catalytic
amount) was added and the reaction mixture was stirred at
85 °C for 16 h. After cooling to room temperature, the
product was concentrated and purified by silica gel column
chromatography using dichloromethane/n-hexane (v/v=3/5)
All reagents and chemicals purchased from Alfa Aesar
were used as received. Tetrahydrofuran (THF) was distilled
from sodium/benzophenone. Ultra-pure water was used in
the experiments. All other solvents were purchased as
analytical grade from Guangzhou Dongzheng Company
and used without further purification. H-NMR and 13C-
1
NMR was measured on a Mercury-Plus 300 spectrometer
with chemical shifts reported as ppm (in CDCl3, TMS as
internal standard). Mass spectra were measured with
Thermo spectrometers (MAT95XP-HRMS). Fluorescence
spectra were determined with a Shimadzu RF-5301PC
spectrometer and the slit widths were 1.5 nm for both
excitation and emission. The fluorescence spectra at low
temperature were done with an Endinburgh Instruments
Ltd spectrometer (FLSP920). The Differential scanning
calorimetry (DSC) curves were obtained with a
NETZSCH thermal analyzer (DSC 204) at a heating rate
of 10 °C/min under a N2 atmosphere. Thermogravimetric
analyses (TGA) were performed with a TA thermal
analyzer (Q50) under a N2 atmosphere with a heating rate
of 20 °C/min. The fluorescence quantum yield (ϕFL) of all
the compounds in THF or THF/water mixture was
evaluated using 9,10-diphenylanthracene as the reference
[19].
The THF-water mixtures with different water fractions
were prepared by adding Ultra-pure water slowly into the
THF solution of samples under ultrasound at room
temperature. For example, a 70% water fraction mixture
was prepared by adding 7 mL Ultra-pure water into
3 mL of an appropriate concentration THF solution of
sample in a 10-mL volumetric flask. The concentrations
of all samples were adjusted to 10 μM after adding
Ultra-pure water.
1
as eluent to yield 1.17 g of a white solid (yield 74%). H
NMR (300 MHz, CDCl3) δ(ppm): 8.37(d, 2H); 8.13
(s,2H); 7.73(t,4H); 7.65(d,4H); 7.46(t,4H); 7.36(t,2H);
7.12(d,2H); 2.27(s,3H). MS (EI), m/z: 473([M]+, calcd
for C31H23NO2S, 473); Anal. Calc. for C31H23NO2S: C,
78.62; H, 4.90; N, 2.96; S, 6.77 Found: C, 78.56; H, 4.94;
N, 3.01; S, 6.69.
Synthesis of the Compound P2C
The P2CTs (1.10 g, 2.3 mmol) was dissolved in the mixture
of THF (13.8 ml) and DMSO (6.9 ml). Then H2O (2.3 ml)
and KOH (5.15 g, 92.0 mmol) were added and the reaction
mixture was stirred at 80 °C for 4 h. After cooling to room
temperature, the reaction mixture was neutralized with the
solution of hydrochloric acid and a yellow solid was
obtained. The crude product was purified by silica gel
column chromatography using dichloromethane/n-hexane
(v/v=1/1) as eluent to yield 0.70 g of a white solid (yield
95%). 1H NMR (300 MHz, CDCl3) δ: 8.32(s,2H); 8.11
(s,1H); 7.70(t,6H); 7.46(t,6H); 7.32(t,3H). MS (EI), m/z:
319([M]+, calcd for C24H17N, 319); Anal. Calc. for
C24H17N: C, 90.25; H, 5.36; N, 4.39 Found: C, 90.16; H,
5.41; N, 4.32.
Cyclic voltammetry (CV) measurement was carried out
on a Shanghai Chenhua electrochemical workstations
CHI660C in a three-electrode cell with a Pt disk working
electrode, a Ag/AgCl reference electrode, and a glassy
carbon counter electrode. All CV measurements were
performed under an inert argon atmosphere with supporting
electrolyte of 0.1 M tetrabutylammonium perchlorate
(n-Bu4NClO4) in dichloromethane at scan rate of 100 mV/s
using ferrocene (Fc) as standard. The HOMO energy
levels were obtained using the onset oxidation potential
from the CV curves. The lowest unoccupied molecular
orbital/highest occupied molecular orbital (LUMO/HO-
MO) energy gaps ΔEg for the compounds were estimated
from the absorption edge of UV-vis absorption spectra.
The 3,6-diiodo-9-tosyl-9H-carbazole was prepared accord-
ing to the literature [20].
Synthesis of the Compound (PBC)2-PBr
A mixture of P2C (1.50 g, 4.7 mmol) and Postassium tert-
butoxide (1.05 g, 9.4 mmol) were stirred in DMF (20 mL)
at room temperature for 30 min. Bis(4-fluorophenyl)
methanone (0.46 g, 2.1 mmol) was then added to the
mixture and a yellow precipitate appeared after stirring at
70 °C for 6 h. The yellow precipitate was filtrated and dried
without further purification due to the slightly solubility.
The crude product and diethyl-4-bromobenzylphosphonate
(0.78 g, 2.5 mmol) were added to the anhydrous tetrahy-
drofuran (30 ml) and the mixture was stirred under a N2
atmosphere at room temperature. Then the Postassium tert-
butoxide (2.2 g, 20 mmol) was added quickly and the
mixture was stirred continuously for 2 h. The reaction
mixture was precipitated with ethanol and the crude product

J Fluoresc (2011) 21:433–441
435
was collected. Further purification can be accomplished by
silica gel column chromatography with dichloromethane/
n-hexane (v/v=3/5) as eluent. A yellowish green powder
was abtained with a total yield of 49%. 1H NMR
(300 MHz, CDCl3) δ: 8.40(s,4H); 7.76-7.62.(m,18H);
7.59-7.44(m,14H); 7.36(q,6H); 7.12(s,1H); 7.04(d,2H).
13C NMR (125 MHz, CDCl3) δ(ppm): 141.98, 141.95,
140.77, 138.97, 137.53, 137.45, 136.16, 134.05, 132.22,
131.61, 131.40, 129.30, 129.05, 128.52, 127.54, 127.43,
126.90, 125.97, 124.41, 121.47, 119.19, 110.48, 110.41.
FT-IR (KBr) υ (cm−1): 3029 (Ar and =C–H stretching),
1600, 1514, 1457, 1266, 815, 760, 700, 650. MS (EI), m/z:
970([M]+, calcd for C68H45BrN2, 970); Anal. Calc. for
C68H45BrN2: C, 84.20; H, 4.68; N, 2.89; Br, 8.24 Found: C,
84.16; H, 4.62; N, 2.92; Br, 8.20.
129.86, 129.53, 129.30, 129.05, 128.60, 128.02, 127.54,
127.15, 126.90, 126.38, 125.99, 125.65, 124.38, 119.19,
110.54, 110.42. FT-IR (KBr) υ (cm−1): 3029 (Ar and =C–H
stretching), 2961, 2866, 1607, 1497, 1459, 1260, 1113,
822. MS (FAB), m/z: 1017([M]+, calcd for C78H52N2,
1017); Anal. Calc. for C78H52N2: C, 92.09; H, 5.15; N,
2.75 Found: C, 92.01; H, 5.12; N, 2.69.
(PBC)2-P
1H NMR (300 MHz, CDCl3) δ: 8.40(d,4H); 8.24-8.16
(m,3H); 8.14-8.05(m,3H); 8.04-7.94(m,3H);7.80-7.62
(m,20H); 7.62-7.54(m,5H); 7.53(s,1H); 7.51-7.39(m,8H);
7.39-7.28(m,7H). 13C NMR (75 MHz, CDCl3) δ(ppm):
142.03, 141.93, 141.39, 140.84, 140.40, 139.59, 137.40,
137.30, 136.25, 134.03, 132.41, 131.69, 131.13, 130.88,
130.69, 129.96, 129.54, 129.30, 129.02, 128.65, 127.85,
127.71, 127.54, 127.48, 126.88, 126.26, 125.99, 125.42,
125.25, 125.13, 124.93, 124.41, 119.16, 110.53, 110.40.
FT-IR (KBr) υ (cm-1): 3034 (Ar and =C–H stretching),
1600, 1512, 1457, 1269, 815, 760, 700. MS (FAB), m/z:
1091([M]+, calcd for C84H54N2, 1091); Anal. Calc. for
C78H54N2: C, 92.45; H, 4.99; N, 2.57 Found: C, 92.39; H,
4.91; N, 2.48.
General Procedure for the Synthesis of Compounds
(PBC)2-TB, (PBC)2-N and (PBC)2-P
(PBC)2-PBr (0.40, 0.4 mmol) and the corresponding boric
acid (0.5 mmol) were dissolved in toluene (25 mL), and
then 2 M aqueous K2CO3 solution (0.5 mL) and 3 drops
of aliquat 336 were added. The mixture was stirred for
45 min under an argon atmosphere at room temperature.
Then the Pd(Pph3)4 catalyst (catalytic amount) was added
and the reaction mixture was stirred at 85°C for 16 h.
After cooling to room temperature, the product was
concentrated and purified by silica gel column chroma-
tography using dichloromethane/n-hexane (v/v=1/2) as
eluent. Yields of products: (PBC)2-TB 73%; (PBC)2-N
60%; (PBC)2-P 54%.
Results and Discussion
Synthesis
The synthetic routes of this new series of diphenylcarbazole
triphenylethylene derivatives are outlined in Scheme 1, and
the chemical structures of reference compounds 5,7 and
8 are shown in Scheme 2. The modification of carbazole, as
already known, is possible with high reactivity and
selectivity at positions 3 and 6. The functional group
benzene was selected and introduced to carbazole in
consideration of its solubility, thermal stability and increase
in π–π conjugation, all of which are assumed to benefit
light emission enhancement. (PBC)2-PBr, the key precur-
sor, was synthesized from bis(4-(3,6-dipenyl-9H-carbazol-
9-yl)phenyl) methanone [(PBC)2-one] and diethyl
4-bromobenzyl-phosphonate through the Wittig-Horner
reaction with a yield of 49.4% for the slight solubility of
the (PBC)2 -one. The desired compounds were obtained
through cross-coupling of (PBC)2-PBr with several aryl-
boronic acids under Pd-catalyzed Suzuki reactions. The
yields ranged from 54 to 73%.
(PBC)2-TB
1H NMR (300 MHz, CDCl3) δ: 8.40(s,4H), 7.76-7.64
(m,18H); 7.64-7.54(m,8H); 7.54-7.42(m,14H); 7.34(t,4H);
7.24(s,1H); 1.36(s,9H). 13C NMR (75 MHz, CDCl3)
δ(ppm): 150.72, 142.25, 142.03, 140.84, 140.00, 139.56,
137.68, 137.28, 135.95, 134.02, 132.34, 130.33, 129.25,
127.53, 126.87, 126.00, 124.40, 119.17, 110.46, 34.95,
31.74. FT-IR (KBr) υ (cm−1): 3029 (Ar and =C–H
stretching), 2962, 2866, 1600, 1512, 1457, 1264, 817,
760, 697. MS (EI), m/z: 1023([M]+, calcd for C78H58N2
1023); Anal. Calc. for C78H58N2: C, 91.55; H, 5.71; N,
2.74 Found: C, 91.48; H, 5.69; N, 2.66.
(PBC)2-N
1H NMR (300 MHz, CDCl3) δ: 8.40(s,4H); 7.82-7.98
(m,3H); 7.78-7.62(q,20H); 7.59(t,5H); 7.52-7.38
(m,13H);7.38-7.26(m,7H). 13C NMR (75 MHz, CDCl3)
δ(ppm): 142.17, 142.01, 141.20, 140.79, 139.95, 139.85,
139.54, 137.33, 136.19, 133.99, 132.36, 131.63, 130.19,
The structural information of the compounds was
obtained with proton nuclear magnetic resonance imaging
(1H NMR), carbon nuclear magnetic resonance imaging
(13C NMR), Fourier transform infrared spectroscopy (FT-IR),
and high-resolution mass spectroscopy (MS).

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J Fluoresc (2011) 21:433–441
CH3
CH3
B(OH)2
DMSO / THF
KOH/H2O
O
S O
N
O
S O
N
Pd(Pph3)4 / Toluene
Aliquat 336 / K2CO3(2M)
I
I
P2CTS
O
Η
O
N
F
F
N
N
DMF/t-BuOK
P2C
(PBC)2-one
Ar
Br
N
N
CH2PO(OC2H5)2
THF/t-BuOK
Br
(PBC)2-X
(PBC)2-TB
(PBC)2-N
Ar =
N
N
Ar =
Ar =
(PBC)2-PBr
(PBC)2-P
Scheme 1 Synthetic routes for the new compounds
Thermal Properties
We measured the decomposition temperatures (Td) of
(PBC)2-TB, (PBC)2-N, and (PBC)2-P, which were deter-
mined from the point of 5% weight loss during heating in
nitrogen. These were found to be 501, 540 and 549 °C,
respectively. The TGA curves of each compound are
presented in Fig. 1. The figure shows that all the
Thermogravimetric analysis (TGA) and differential scan-
ning calorimetry (DSC) were utilized to investigate the
thermal properties of all target compounds. The test results
are summarized in Table 1.

J Fluoresc (2011) 21:433–441
437
Ar
100
80
N
N
(PBC)2-N
(PBC)2-P
(PBC)2-TB
60
Ar =
5
7
Ar =
8
Ar =
40
Scheme 2 The chemical structures of compounds 5,7 and 8 as
references
0
200
400
600
800
1000
o
Temperature / C
compounds are highly stable. Their Td values were much
higher than MPPS (309 °C) and HPS (351 °C), both of which
are typical AIE-active molecules reported in the literature
[21]. They were also higher than all the triphenylethylene
carbazole derivatives of compounds 4 to 8 (453 to 488 °C)
[18]. Due to the substituents of benzene attached to the
carbazole core, the heighten of Td value of the derivatives
approached 100 °C. (PBC)2-P, which is a diphenylcarbazole
triphenylethylene derivative functionalized by the fused ring
of a pyrenyl group, had the highest Td value, and (PBC)2-N,
which is functionalized by the fused ring of a naphthyl
group, was most similar to it. In contrast, (PBC)2-TB, which
does not contain a fused ring, had a Td value that was about
39 to 48 °C lower. This indicates that the introduction of a
fused ring is beneficial in enhancing the thermal properties of
the derivatives.
Fig. 1 TGA curves of the compounds
As can be seen from Fig. 2, the DSC curves of the
derivatives show no crystallization or melting peaks but
only glass transition peaks. The results from these thermal
behaviors are expected to yield better electroluminescent
properties for minimal crystal formation when cooling from
the melted state.
Optical Properties
The optical properties of the diphenylcarbazole triphenyl-
ethylene derivatives were investigated both in tetrahydrofuran
(THF) solution and TLC thin films at room temperature. The
results of this analysis are summarized in Table 2.
The maximum absorption wavelengths of (PBC)2-TB,
(PBC)2-N and (PBC)2-P were found to be 343, 341, and
358 nm, respectively. Compared with the corresponding
triphenylethylene carbazole derivatives of compounds 7
The glass transition temperatures (Tg) of the compounds
were measured by DSC, and the second heating curves,
running at a scan rate of 10 °C/min in a nitrogen atmosphere,
are shown in Fig. 2. The results of the investigation indicate
that all the compounds exhibited glass transition peaks, with
Tg values ranging from 168.2 to 182.4 °C. The Tg values are
about three times those of MPPS(54 °C) and HPS(65 °C)
[21]. Furthermore, (PBC)2-N and (PBC)2-P were 45 and
31 °C higher, respectively, than the corresponding triphenyl-
ethylene carbazole derivatives of compounds 7 and 5 (126.6
and 151.1 °C, respectively). This is due to the benzene
substituents attached to the carbazole core [18]. The Tg of
(PBC)2-P was the highest (182.4 °C), and this can be
attributed to its significant increase in molecular weight and
bulky pyrenyl group substituent.
1.
2.
(PBC)2-TB
(PBC)2-N
3. (PBC)2-P
1.
2.
3.
Table 1 Thermal properties of the compounds
Sample
Tg (°C)
Tm (°C)
Td (°C)
0
100
200
300
400
500
(PBC)2-TB
(PBC)2-N
(PBC)2-P
168.2
171.2
182.4
N/A
N/A
N/A
501
540
549
Temperature / oC
Fig. 2 DSC curves for the compounds at a scan rate of 10°C/min
(second heating scan)

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J Fluoresc (2011) 21:433–441
Table 2 Optical properties of the compounds
and similar to the corresponding triphenylethylene carbazole
derivative of compound 5 [16], the planarity of the pyrenyl
group caused (PBC)2-P to exhibit an opposite phenomenon,
resulting in red-shift of the PL spectrum caused by the strong
intermolecular interaction between the pyrenyl groups.
The quantum yields (ΦFL) of all the derivatives in THF
with 9,10-diphenylanthracene as standard (ΦFL=90%)
ranged from 2.2 to 8.7%. However, the ΦFL determined in
cyclohexane was in the range of 32.2 to 69.4%, 8- and 18-
fold increased in ΦFL when compared to those of THF
solutions and cyclohexane solutions, respectively.
abs
max
em
max
l
ðnmÞ
l
ðnmÞ
fFLð%Þ
Sample
a
b
c
d
e
(PBC)2-TB
(PBC)2-N
(PBC)2-P
343
341
358
465
459
2.2
2.1
8.7
40.0
457
466
450
470
32.2
69.4
a
b
c
In THF; InTHF; in TLC thin film; Fluorescence quantum yields
d
e
were measured in THF solution and cyclohexane solution using
9,10-diphenyl- anthracene as standard.
and 5 (at 343 and 360 nm, respectively), the introduction of
four benzene rings to the carbazole cores did not cause the
maximum absorption wavelengths of the compounds to
red-shift. Rather, slight blue-shifts were found [18]. This
could be attributed to the effect of the benzenes rings linked
to the carbazoles. An increase in volume and enhancement
of the twisted configuration could decrease the π–π
conjugation of the molecule.
The photoluminescent spectra of the compounds
(PBC)2-TB, (PBC)2-N and (PBC)2-P in THF solution
showed maxima at 465, 457, and 466 nm, respectively,
while the maxima in solid thin films were found to be 459,
450 and 470 nm, respectively. These indicate that all the
compounds exhibit blue light emission in both THF
solution and solid thin films.
AIE Properties
AIE behavior is commonly proven by the emission
enhancement resulting from fluorescent nanoparticle for-
mation [10, 11, 22]. We measured the fluorescent emission
of all the compounds in aqueous THF at different water/
THF ratios, and the corresponding emission spectra of
(PBC)2-TB are shown in Fig. 3. As can be seen from the
figure, the PL signals of the compound in a dilute solution
of THF are quite weak, and they remained almost
unchanged when up to 50% (v/v) water was added. This
phenomenon may be attributed to the fact that the
intramolecular rotation of (PBC)2-TB, which serves as the
relaxation channel for the excited state to decay, is active
[14]. When the water fraction reached 60% (v/v), however,
the PL intensity was boosted to 192. The highest PL
intensity value of 245 was obtained at the water fraction of
90%(v/v) while in pure THF the highest PL intensity value
obtained was only 16. This dramatic enhancement in
As compared to the THF solution, the compounds
(PBC)2-TB and (PBC)2-N were blue-shifted in the case of
solid thin films due to the more significantly twisted
configuration of the molecules in the solid state. In contrast
Fig. 3 PL spectra of (PBC)2-
TB in various water/THF
300
300
mixtures. The inset depicts the
250
changes in PL peak intensity
0
10
250
200
30
150
50
60
200
150
100
50
100
70
50
80
0
90
0
20
40
60
80
100
Water fraction / vol%
0
350
400
450
500
550
600
650
700
Wavelength / nm

J Fluoresc (2011) 21:433–441
439
2.0
1.5
1.0
0.5
0.0
luminescence indicates that the nanoparticles are formed in
the proportion of 60:10 (v/v) water/THF, and that intramolec-
ular rotation is restricted due to physical constraint [14]. When
the water fraction was higher than 60%, the PL intensity
showed no regularity. We suggest this because solute
molecules may aggregate into crystal and amorphous
particles. The former leads to an enhancement in the
intensity of photoluminescent emission, while the latter leads
to its reduction. Thus, the measured photoluminescent
intensity often shows no regularity for the uncontrollable
formation of the nanoparticles in solutions with high water
content. Similar effects were observed for the other
compounds. The emission images of (PBC)2-TB in pure
THF, 90:10 (v/v) water/THF and a TLC solid thin film under
UV light (365 nm) illumination at room temperature are
shown in Fig. 4. Clearly, (PBC)2-TB in both water fraction
of 90%(v/v) water/THF and the solid thin film exhibited very
strong fluorescence, while the same compound showed weak
fluorescence in THF solution.
Different absorption behaviors are seen as the water
fractions in the solutions increased. These difference were
observed by investigating the UV absorption spectra of
(PBC)2-TB in different ratios of water and THF (Fig. 5).
The absorption intensities of (PBC)2-TB were virtually
unchanged from water fractions of 0% to 50%(v/v) water/
THF. However, when the water fraction of the water/THF
mixture increased to 60% (v/v), the entire spectrum began
to rise and showed a long-wavelength absorption tail. This
is due to light-scattering effects in the solution, which
suggests the formation of aggregates that effectively
decrease light transmission through the mixtures [23]. The
abrupt increase in absorbance in the 60% water fraction
corresponds to the sudden jump in PL intensity and
quantum yield as shown in Fig. 3 and Table 3.
Water fraction / %
0
10
30
50
60
70
80
90
300
400
500
600
700
800
Wavelength / nm
Fig. 5 UV absorption spectra of (PBC)2-TB in water/THF mixtures
with different volume fractions of water
The photoluminescent quantum yields (ΦFL) of all
compounds, estimated in different ratios of water and
THF mixtures relative to 9,10-diphenyl-anthracene (DPA),
are summarized in Table 3. As can be seen, the aggregates
in aqueous mixtures exhibited fluorescence quantum yields
ranging from 20 to 46%, which are much higher than those
of the solutions in pure THF (2.0 to 8.5%). The changes in
ΦFL values agree well with the observed behaviors of
absorption and photoluminescence, both of which showed
abrupt increases when the water fraction reached 60% (v/v).
Similar to the changes in PL peak intensity, the quantum
yields showed no regularity when the water fraction was
higher than 60%, suggesting that different and uncontrol-
lable proportions of crystal and amorphous particles are
formed in high water content solutions. The above results
indicate that the compound molecules start to aggregate
significantly when the volume fraction of water is around
60%. Moreover, the results prove the existence of AIE
properties in all the derivatives.
The effects of temperature on the PL relative peak
intensity of the compounds and DPA in dilute THF
solutions (10 μM) were also investigated, and the
corresponding curves are shown in Fig. 6. When the
temperature increased from 77 K, the relative peak intensity
of the new compounds decreased dramatically near the
melting point of THF (Tm, ~165 K), while that of DPA
Table 3 PL quantum yields (ΦFL) of the compounds in various ratios
of water and THF
H2O (v %)
0
10
30
50
60
70
80
90
(PBC)2-TB
(PBC)2-N
(PBC)2-P
2.1
2.0
8.5
2.4
2.4
9.6
2.8
2.9
11
3.3
3.6
13
18
17
46
14
15
44
5.6
9.5
28
20
25
39
Fig. 4 Emission images of (PBC)2-TB in (a) pure THF (10 μM), (b)
90% water/THF solution (v/v), and (b) TLC thin film under UV light
(365 nm) illumination at room temperature

440
J Fluoresc (2011) 21:433–441
-40
-20
0
DPA
(PBC)2-TB
20
15
10
5
(PBC)2-N
(PBC)2-P
1.52V
E onset =1.22V
1.34V
1.26V
20
40
60
0
50
100
150
200
250
300
-2
-1
0
1
2
Temperature / K
Potential / V
Fig. 6 Effect of temperature on the PL relative peak intensity of the
new compounds and DPA in THF
Fig. 8 CV curve of (PBC)2-TB in CH2Cl2
each compound. The relative peak intensity of (PBC)2-P
shows slow drop in all the time.
remained almost unchanged. This implies that when a
molecule is frozen in THF, similar to the effects of
aggregation in liquids, the intramolecular rotation, which
serves as a relaxation channel for the excited state to decay,
is blocked, and the PL intensity exhibits a dramatic
increase. As compared to the carbazole triphenylethylene
derivative of compound 7 [18], in which the extent of the
decrease was about 40-fold and two times lager than that of
(PBC)2-N (20-fold), the extent of decrease seems closely
related to the volume of the substituent, as smaller
substituents rotate with more ease than larger ones because
of smaller steric effects. From Fig. 6, it can also be seen that
the extent of the decrease and the trend are not the same for
AIE materials possess the on/off fluorescence switching
property in some organic vapors, it was suggested that this
could be one of the most important potential applications in
the photoswitch field as a chemical vapor sensor [14]. The
on/off fluorescence switch effect was investigated with a
spot of (PBC)2-N on the thin-layer chromatography (TLC)
plate (Fig. 7). Under UV light illumination (wavelength
365 nm) at room temperature, the spot showed bright blue
fluorescence, which was switched off (very weak fluores-
cence) reversibly in an atmosphere of dichloromethane
vapor. It is a probable explanation that solvation of the
vapor of good solvent releases interaction of solid mole-
cules to great extent and cause free rotation of single bonds
of the AIE molecules and lead to nonemission.
Electrochemical Properties
The highest occupied molecular orbital (HOMO) and
lowest unoccupied molecular orbital (LUMO) are two
important parameters for electroluminescence materials
due to their relationship with the hole-/electron-injecting
capability of OLEDs. To test the electrochemical properties
of all the derivertives, cyclic voltammetry (CV) studies
were performed in CH2Cl2 solution, using tetrabutylammo-
nium perchlorate (n-Bu4NClO4, 0.1 M) as the supporting
Table 4 Energy levels of the molecular orbitals and band gaps of the
compounds
Sample
HOMO (eV)
LUMO (eV)
ΔEg (eV)
(PBC)2-TB
(PBC)2-N
(PBC)2-P
5.49
5.49
5.52
2.31
2.29
2.48
3.18
3.20
3.04
Fig. 7 On/off fluorescence switching of compound (PBC)2-N on
TLC plates without vapor (a) and in CH2Cl2 vapor (b) under UV light
(365 nm) illumination at room temperature

J Fluoresc (2011) 21:433–441
441
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electrolyte. Figure 8 shows the cyclic voltammogram of
(PBC)2-TB. The energy band gaps (ΔEg) of the deriver-
tives were estimated from the onset wavelength of their UV
absorptions. The HOMO energy levels were obtained using
the onset oxidation potential. The LUMO energy levels are
computed from the difference between HOMO energy and
the energy band gap (ΔEg=HOMO−LUMO). The HOMO,
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(PBC)2-P were found to be 3.18, 3.20, and 3.04 eV,
respectively. The LUMO values of the compounds ranged
from 2.29 to 2.31 eV, with (PBC)2-N possessing the lowest
and (PBC)2-P possessing the highest LUMO levels. The
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Conclusions
We have synthesized a new series of diphenylcarbazole
triphenylethylene derivatives, all of which are AIE active.
All the compounds exhibited strong blue light emission
both in the aggregated state and in TLC solid thin films.
The maximum fluorescence emission wavelengths ranged
from 450 to 470 nm. The derivatives exhibited excellent
thermal properties, with glass transition temperatures ranging
from 168.2 to 182.4 °C and decomposition temperatures
(5% weight loss) ranging from 501 to 549 °C. Both of these
temperature ranges are much higher than those reported in
the literature for silole and carbazole triphenylethylene
derivatives which were the focus of our previous work.
These new derivatives are suggested as potential materials
for blue light emitters in OLEDs.
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Acknowledgements The authors gratefully acknowledge the finan-
cial support from the National Natural Science Foundation of China
(Grant numbers: 50773096, 50473020), the Start-up Fund for
Recruiting Professionals from “985 Project” of SYSU, the Science
and Technology Planning Project of Guangdong Province, China
(Grant numbers: 2007A010500001-2), Construction Project for
University-Industry cooperation platform for Flat Panel Display from
The Commission of Economy and Informatization of Guangdong
Province (Grant numbers: 20081203), and the Open Research Fund of
State Key Laboratory of Optoelectronic Materials and Technologies.
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