Synthesis and characterization of triphenylethylene derivatives with aggregation-induced emission characteristics

Article abstract of DOI:10.1007/s10895-011-0896-1

New aggregation-induced emission (AIE) compounds derived from triphenylethylene were synthesized. The thermal, photophysical, electrochemical and aggregation-induced emissive properties were investigated. All the compounds had strong blue light emission c

Full text of DOI:10.1007/s10895-011-0896-1

J Fluoresc (2011) 21:1969–1977
DOI 10.1007/s10895-011-0896-1
ORIGINAL PAPER
Synthesis and Characterization of Triphenylethylene
Derivatives with Aggregation-Induced Emission
Characteristics
Xiao-Fang Li & Zhen-Guo Chi & Bing-Jia Xu &
Hai-Yin Li & Xi-Qi Zhang & Wei Zhou & Yi Zhang &
Si-Wei Liu & Jia-Rui Xu
Received: 26 September 2010 /Accepted: 2 May 2011 /Published online: 21 May 2011
#
Springer Science+Business Media, LLC 2011
Abstract New aggregation-induced emission (AIE) com-
pounds derived from triphenylethylene were synthesized.
The thermal, photophysical, electrochemical and
aggregation-induced emissive properties were investigated.
All the compounds had strong blue light emission capabil-
ity and good thermal stability. Their maximum fluorescence
emission wavelengths were between 443 to 461 nm in solid
states, while their glass transition temperatures ranged from
86 to 129 °C. The decomposition temperatures of the
synthesized compounds were in the range of 432–534 °C.
The synthesized compounds possessed aggregation-induced
emission properties, namely exhibited enhanced fluores-
cence emission in aggregated states. The highest occupied
molecular orbital (HOMO) energy levels estimated from the
oxidation potentials were between 5.61 and 5.66 eV and the
lowest unoccupied molecular orbital/highest occupied mo-
lecular orbital (LUMO/HOMO) energy gap values were
found to be in the range of 3.18–3.22 eV. The compounds
4-(4-(2,2-bis(4-(naphthalen-1-yl)phenyl)vinyl)phenyl)
dibenzothiophene [(BN)2Bt] and 4-(4-(2,2-di(biphenyl-4-
yl)vinyl)phenyl) dibenzothiophene [(BB)2Bt] exhibited
vibronic fine-structure photoluminescence spectra when
the water fraction was less than 70%.
.
.
Keywords Triphenylethylene Blue light emission
.
.
Thermal property stability Synthesis Aggregation-induced
emission
Introduction
Organic luminescent materials with aggregation-induced emis-
sion (AIE) properties have attracted considerable attention
because of their potential application in electroluminescence
devices and chemosensors [1, 2]. Since the first AIE
compound 1-methyl-1,2,3,4,5-pentaphenylsilole was reported
in 2001 by Tang’s group [3], aggregation-caused quenching
(ACQ) is no longer the almost insurmountable obstacle in the
fabrication of efficient electroluminescent (EL) devices it once
was. Since then, some AIE compounds have been developed
by various research groups, examples of which include silole,
1,1,2,2-tetraphenylethene (TPE) and 1-cyanotrans-1,2-bis-(4-
methylbiphenyl) ethylene (CN-MBE) derivatives [4–11].
However, the AIE materials are still limited in number due
to complicated and difficult preparation. Recently, a series of
triphenylethylene carbazole and triphenylethylene derivatives
with strong light emission, high thermal stability, and AIE
characteristics were facilely synthesized via Wittig-Horner
and Suzuki reactions in our laboratory [12–21]. The twisted
configuration of the three phenyl rings in triphenylethylene,
due to the bulky aryl substituents, is considered as one of the
possible reasons for the AIE effect.
Electronic supplementary material The online version of this article
(doi:10.1007/s10895-011-0896-1) contains supplementary material,
which is available to authorized users.
:
:
:
:
:
X.-F. Li Z.-G. Chi (*) B.-J. Xu H.-Y. Li X.-Q. Zhang
:
:
:
W. Zhou Y. Zhang S.-W. Liu J.-R. Xu (*)
PCFM Lab, DSAPM Lab, KLGHEI of Environment and Energy
Chemistry, 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
In this article, we report a new class of triphenylethylene
derivatives with strong blue light emission in solid state and
AIE characteristics. The derivatives were easily prepared by
J.-R. Xu
e-mail: xjr@mail.sysu.edu.cn

1970
J Fluoresc (2011) 21:1969–1977
a three-step reaction, including the Suzuki and Wittig–
Horner reactions. The thermal, photophysical, and AIE
properties were preliminarily evaluated.
The water/THF mixtures with different water fractions
were prepared by slowly adding ultra-pure water into the THF
solution of samples under ultrasound at room temperature. For
example, a 70% water fraction mixture was prepared in a
volumetric flask by adding 7 mL ultra-pure water into 3 mL
THF solution of the sample. The concentrations of all samples
were adjusted to 10 μM after adding ultra-pure water.
Experimental
Materials and Methods
General Procedure for the Synthesis of Ketone
Bis(4-bromophenyl)methanone, 4,4′-diphenylbenzophe-
none, phenylboronic acid, naphthalen-1-ylboronic acid,
dibenzothiophene-4-boronic acid, dibenzofuran-4-boronic
acid, diethyl 4-bromobenzylphosphonate, tetrakis(triphenyl-
phosphine) palladium(0), tetrabutylammonium bromide
(TBAB), potassium tert-butyloxide and tetrabutylammo-
nium perchlorate (n-Bu4NClO4, electrochemical grade)
purchased from Alfa Aesar were used as received. All
other reagents and solvents were purchased as analytical
grade from Guangzhou Dongzheng Company (China) and
used without further purification. Anhydrous tetrahydrofu-
ran (THF) was distilled from sodium/benzophenone. Ultra-
pure water was used in the experiments.
Intermediates (Ar1)2-one
Bis(4-bromophenyl)methanone (4.6 mmol) and arylboronic
acid (11.0 mmol) were dissolved in the mixture of toluene
(30 mL), TBAB (0.5 g) and 2 M potassium carbonate
aqueous solution (8 mL). The mixture was stirred at room
temperature for 0.5 h under argon followed adding Pd
(PPh3)4 (0.01 g) and then heated to 85 °C for 16 h. After
that the mixture was poured into water and extracted three
times with ethyl acetate. The organic layer was dried over
anhydrous sodium sulfate. After removing the solvent
under reduced pressure, the residue was chromatographed
on a silica gel column with n-hexane-CH2Cl2 mixed solvent
as eluent to give (Ar1)2-one. Note: in this paper, Ar1 and
Ar2 represent aryl groups and are identified in Scheme 1.
1H NMR and 13C NMR spectra were measured on a
Mercury-Plus 300 spectrometer [CDCl3 as solvent and
tetramethylsilane (TMS) as the internal standard]. The
Fourier transform infrared (FTIR) spectra were recorded on
a Nicolet Nexus 670 spectrometer in the region of 3000–
400 cm−1. Mass spectra (MS) were measured on a Thermo
DSQ MS spectrometer. Elemental analyses (EA) were
performed with an Elementar Vario EL elemental analyzer.
Fluorescence spectra were measured on a Shimadzu RF-
5301pc spectrometer with a slit width of 1.5 nm for
excitation and 3.0 nm for emission. Differential scanning
calorimetry (DSC) curves were obtained with a NETZSCH
thermal analyzer (DSC 204F1) at heating and cooling rates
of 10 °C/min under nitrogen atmosphere. Thermogravimetric
analyses (TGA) were performed with a thermal analyzer
(Shimadzu, TGA-50H) under nitrogen atmosphere with a
heating rate of 20 °C/min. The fluorescence quantum yields
(ФFL) of all the compounds in different solvents and THF/
water mixtures were evaluated using 9,10-diphenylanthra-
cene as the reference [22]. Cyclic voltammetry (CV)
measurements were carried out on Shanghai Chenhua
electrochemical workstations CHI660C in a three-electrode
cell with a Pt disk counter electrode, an Ag/AgCl reference
electrode, and a glassy carbon working electrode. All CV
measurements were performed under an inert argon atmo-
sphere with supporting electrolyte of 0.1 M n-Bu4NClO4 in
dichloromethane at scan rate of 100 mV/s using ferrocene as
standard. The lowest unoccupied molecular orbital/highest
occupied molecular orbital (LUMO/HOMO) energy gaps
ΔEg for the compounds were estimated from the absorption
edge of UV–vis absorption spectra.
1
(BN)2-one White powder, yield 90%. H NMR (300 MHz,
CDCl3) δ(ppm) : 8.13-8.01 (d, 4H), 8.00-7.82 (t, 6H), 7.73-
7.62 (d, 4H),7.62-7.35 (m, 8H); 13C NMR (75 MHz,
CDCl3) δ (ppm): 145.43, 139.36, 136.79, 134.09, 131.55,
130.36, 128.66, 127.25, 126.64, 126.25, 125.90, 125.61;
MS (EI), m/z : 434 ([M]+, calcd for C33H22O, 434); FTIR
(KBr) ν(cm−1): 3047, 1654, 1599, 1507, 1393, 1311, 1279,
1180, 929, 779, 690; Anal. calc. for C33H22O: C 91.21, H
5.10, O 3.68; Found: C 91.16, H 5.13.
(BFu)2-one White powder, yield 80%. 1H NMR (300 MHz,
CDCl3) δ (ppm): 8.09 (S, 8H), 8.04-7.96 (d, 4H), 7.73-7.60
(dd, 4H), 7.54-7.44 (dd, 4H), 7.43-7.34 (t, 2H); 13C NMR
(75 MHz, CDCl3) δ (ppm): 195.93, 156.34, 153.54, 140.75,
136.93, 130.69, 128.86, 127.65, 127.07, 125.41, 124.23,
123.55, 123.18, 120.96, 120.79, 112.11; MS (EI), m/z: 514
([M]+, calcd for C37H22O3, 514); FTIR (KBr) ν (cm−1):
3048, 1652, 1604, 1448, 1393, 1280, 1185, 930, 865, 746,
685; Anal. calc. for C37H22O3: C 86.36, H 4.31, O 9.33;
Found: C 86.32, H 4.35.
General Procedure for the Synthesis of Bromide
Intermediates (Ar1)2Br
A solution of compound (Ar1)2-one (1.84 mmol) and
diethyl 4-bromobenzylphosphonate (3.68 mmol) in anhy-
drous tetrahydrofuran (50 mL) was stirred under an argon

J Fluoresc (2011) 21:1969–1977
1971
Scheme 1 Synthetic routes to
the compounds
O
O
Ar1-B(OH)2
Pd(PPh3)4, K2CO3 (aq. 2M)
TBAB,Toluene, 85oC, 16h
Br
Br
Ar1
Ar1
(Ar1)2-one
Br
Ar2
Br
CH2P(O)(OC2H5)2
Ar2-B(OH)2
Pd(PPh3)4, K2CO3 (aq. 2M)
TBAB,Toluene, 85oC, 16h
t-BuOK, THF, 2h
Ar1
Ar1
Ar1
Ar1
(Ar1)2Br
Target compound
(Ar1)2Br:
(BB)2Br:
(Ar1)2-one:
Ar1=
Ar1=
Ar1=
(BN)2 -one:
O
(BN)2Br:
(BFu)2-one: Ar1=
O
(BFu)2Br:
Ar1=
Target compound:
(BFu)2Bt:
S
O
,
Ar2=
Ar1=
Ar1=
O
O
(BFu)2N:
,
,
Ar2=
Ar2=
(BFu)2B: Ar1=
S
S
(BB)2Bt:
(BN)2Bt:
Ar1=
Ar1=
,
,
Ar2=
Ar2=
1
atmosphere at room temperature. Potassium tert-butyloxide
(5.54 mmol) was added quickly and the mixture was stirred
continuously for 2 h at room temperature. The reaction
mixture was precipitated into ethanol, the crude product
was collected, and washed with ethanol three times. The
crude product was recrystallized from dichloromethane/
ethanol (1:20, v/v) to obtain white powder (Ar1)2Br.
(BN)2Br White powder, yield 92%. H NMR (300 MHz,
CDCl3) δ (ppm): 8.04-7.85 (m, 6H), 7.60-7.46 (m, 14H),
7.43-7.38 (d, 2H), 7.38-7.31 (d, 2H), 7.11-7.04 (d, 2H),
7.02 (s, 1H); 13C NMR (75 MHz, CDCl3) δ (ppm): 143.11,
142.03, 140.55, 140.38, 139.98, 139.03, 136.63, 134.07,
132.07, 131.75, 131.40, 130.79, 130.49, 130.31, 128.61,
128.21, 128.04, 127.73, 127.41, 127.23, 127.14, 126.77,
126.38, 126.31, 126.20, 126.05, 125.63, 120.96; MS (EI),
m/z: 586 ([M]+, calcd for C40H27Br, 586); FTIR (KBr) ν
(cm−1): 3035, 1587, 1507, 1397, 1249, 1070, 1014, 959,
842, 804, 779, 658; Anal. calc. for C40H27Br: C 81.77, H
4.63, Br 13.60; Found: C 81.73, H 4.66.
1
(BB)2Br White powder, yield 80%. H NMR (300 MHz,
CDCl3) δ(ppm): 7.70-7.59 (m, 6H), 7.59-7.55 (d, 2H),
7.51-7.46 (d, 2H), 7.46-7.40 (d, 4H), 7.40-7.34 (m, 2H),
7.32-7.26 (m, 4H), 7.00-6.96 (d, 2H), 6 .95 (s, 1H); 13C
NMR (75 MHz, CDCl3) δ (ppm): 142.82, 142.20, 140.76,
140.65, 140.54, 139.01, 136.51, 133.32, 132.05, 131.37,
131.30, 130.98, 129.02, 128.28, 127.58, 127.18, 120.87;
MS(EI), m/z: 486 ([M]+, calcd for C32H23Br, 486); FTIR
(KBr) ν (cm−1): 3026, 1551, 1517, 1488, 1225, 1075,
1005, 839, 766, 743, 697; Anal. calc. for C32H23Br: C
78.85, H 4.76, Br 16.39; Found: C 78.87, H 4.73.
1
(BFu)2Br White powder, yield 77%. H NMR (300 MHz,
CDCl3) δ (ppm) : 8.01-7.88 (m, 8H), 7.70-7.62 (t, 2H), 62–
7.54 (t, 4H), 7.50-7.44 (m, 2H), 7.44-7.39 (m, 4H), 7.38-
7.32 (m, 2H), 7.31-7.26 (d, 2H), 7.03 (s, 2H), 7.00 (s, 1H);
13C NMR (75 MHz, CDCl3) δ (ppm): 155.89, 153.13,
142.57, 142.23, 139.04, 136.11, 135.64, 135.55, 131.02,

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J Fluoresc (2011) 21:1969–1977
130.46, 128.86, 128.44, 127.79, 127.05, 126.47, 125.14,
125.01, 124.87, 124.79, 123.96, 123.04, 122.60, 120.47,
119.62, 119.56, 111.70; MS(EI), m/z: 666 ([M]+, calcd for
C44H27BrO2, 666); FTIR (KBr) ν(cm−1): 3032, 2359, 1587,
1513, 1481, 1450, 1393, 1260, 1190, 1067, 1011, 874, 842,
795, 750; Anal. calc. for C44H27BrO2: C 79.16, H 4.08, Br
11.97, O 4.79; Found: C 79.13, H 4.12.
(BFu)2Bt Light green powder, yield 30%. 1H NMR
(300 MHz, CDCl3) δ (ppm): 8.16-8.07 (m, 2H), 8.05-7.89
(m, 8H), 7.80-7.75 (dd, 1H), 7.73-7.69 (d, 1H), 7.65-7.62
(d, 2H), 7.61-7.57 (t, 4H), 7.55-7.39 (m, 10H), 7.38-7.29
(m, 4H),7.23 (s, 1H),7.20 (s, 1H); 13C NMR (75 MHz,
CDCl3) δ (ppm): 156.34, 153.58, 142.94, 142.64, 139.88,
139.73, 139.17, 138.56, 137.32, 136.77, 136.44, 135.93,
131.01, 130.28, 129.31, 128.86, 128.25, 128.15, 127.44,
126.94, 125.64, 125.27, 124.53, 124.40, 123.45, 122.99,
122.79, 121.88, 120.60, 119.95, 112.13; MS(EI), m/z: 770
([M]+, calcd for C56H34O2S, 770); FTIR (KBr) ν (cm−1):
3059, 1584, 1517, 1451, 1394, 1257, 1190, 1013, 874, 842,
798, 750; Anal. calc. for C56H34O2S: C 87.24, H 4.45, O
4.15, S 4.16; Found: C 87.21, H 4.46, S 4.18.
General Procedure for the Synthesis of the Target
Compounds
To a solution of (Ar1)2Br (0.75 mmol), corresponding boric
acid (0.90 mmol) and TBAB (0.5 g) in toluene (35 mL),
2 M aqueous K2CO3 solution (1.5 mL) was added and the
mixture was stirred for 30 min under an argon atmosphere.
Then, the Pd(PPh3)4 catalyst (0.01 g) was added all at once
to the mixture. The reaction mixture was stirred at 85 °C for
16 h. After cooling, the product was extracted with
dichloromethane/water. The organic layers were collected
and dried under anhydrous sodium sulfate. The concentrat-
ed product was purified by silica gel column chromatogra-
phy (dichloromethane-n-hexane mixed solvent as eluent) to
obtain target products.
1
(BN)2Bt White powder, yield 50%. H NMR (300 MHz,
CDCl3) δ (ppm): 8.18-8.09 (m, 2H), 8.06-7.97 (t, 2H),
7.93-7.83 (dd, 4H), 7.80-7.75 (m, 1H), 7.64-7.40 (m, 22H),
7.33-7.27(d, 2H), 7.24-7.22 (d, 1H); 13C NMR (75 MHz,
CDCl3) δ (ppm): 142.80, 142.27, 141.94, 140.42, 140.29,
140.14, 140.07, 139.76, 139.43, 139.20, 138.63, 137.43,
136.81, 136.48, 135.98, 134.25, 134.07, 131.81, 130.78,
130.61, 130.29, 128.54, 128.24, 128.11, 127.95, 127.74,
127.21, 127.13, 126.98, 126.38, 126.27, 126.15, 126.02,
125.62, 125.30, 124.57, 122.80, 121.92, 120.65, 109.98;
MS(EI), m/z: 690 ([M]+, calcd for C52H34S, 690); FTIR
(KBr) ν (cm−1): 3054, 1587, 1507, 1439, 1390, 1241, 1187,
1107, 1020, 960, 845, 797, 748; Anal. calc. for C52H34S: C
90.40, H 4.96, S 4.64; Found: C 90.38, H 4.98, S 4.62.
1
(BFu)2B White powder, yield 30%. H NMR (300 MHz,
CDCl3) δ (ppm): 8.04-7.98 (t, 4H), 7.98-7.93 (m, 4H), 74–
7.71 (d, 1H), 7.67-7.65 (d, 1H), 7.64-7.56 (m, 6H), 7.54-7.39
(m, 11H), 7.38-7.34 (d, 2H), 7.33-7.27 (t, 2H), 7.18 (s, 1H);
13C NMR (75 MHz, CDCl3) δ (ppm): 155.89, 153.13,
142.54, 141.77, 140.31, 139.54, 139.20, 136.19, 135.40,
135.34, 130.55, 129.87, 128.82, 128.47, 128.40, 127.95,
127.76, 127.00, 126.61, 126.47, 125.21, 125.13, 124.84,
124.76, 123.96, 123.01, 122.55, 120.44, 119.47, 111.66; MS
(EI), m/z: 664 ([M]+, calcd for C50H32O2, 664); FTIR(KBr)
ν (cm−1): 3029, 2370, 1590, 1517, 1483, 1448, 1394, 1264,
1190, 1008, 875, 840, 751, 696; Anal. calc. for C50H32O2: C
90.33, H 4.85, O 4.81; Found: C 90.30, H 4.88.
1
(BB)2Bt White powder, yield 50%. H NMR (300 MHz,
CDCl3) δ (ppm): 8.16-8.06 (m, 2H), 7.82-7.75 (t, 1H),
7.69-7.63 (d, 3H), 7.63-7.56 (t, 4H), 7.56-7.51 (d,3H),
7.50-7.37 (m, 11H), 7.37-7.28 (t, 3H), 7.26-7.22 (d, 2H),
7.10 (s, 1H); 13C NMR (75 MHz, CDCl3) δ (ppm): 142.51,
140.83, 140.64, 140.45, 139.72, 139.44, 139.11, 138.54,
137.29, 136.74, 136.44, 135.93, 131.10, 130.20, 129.02,
128.33, 128.10, 128.00, 127.62, 127.22, 126.97, 125.28,
124.56, 122.79, 121.91, 120.62; MS(EI), m/z: 590 ([M]+,
calcd for C44H30S, 590); FTIR (KBr) ν (cm−1): 3026, 2353,
1602, 1481, 1441, 1380, 1249, 1107, 1003, 897, 840, 745,
695; Anal. calc. for C44H30S: C 89.45, H 5.12, S 5.43;
Found: C 89.41, H 5.15, S 5.40.
1
(BFu)2N White powder, yield 37%. H NMR (300 MHz,
CDCl3) δ (ppm) : 8.05-7.96 (t, 4H), 7.96-7.92 (m, 4H), 7.88-
7.83 (d, 1H), 7.83-7.78 (d, 1H), 7.72-7.68 (d, 1H), 7.66-7.63
(d, 2H), 7.62-7.58 (d, 3H), 7.56-7.51 (d, 2H), 7.51-7.34 (m,
11H), 7.34-7.28 (t, 4H),7.22 (s, 1H); 13C NMR (75 MHz,
CDCl3) δ (ppm): 155.93, 153.17, 142.61, 141.88, 139.63,
139.10, 136.14, 135.46, 133.60, 131.25, 130.58, 129.67,
129.36, 128.89, 128.45, 128.06, 127.80, 127.38, 127.02,
126.65, 126.51, 125.77, 125.51, 125.24, 125.15, 124.86,
123.99, 123.04, 122.58, 120.47, 119.53, 111.69; MS(EI), m/
z: 714 ([M]+, calcd for C54H34O2, 714); FTIR (KBr) ν
(cm−1): 3059, 1583, 1557, 1539, 1519, 1450, 1393, 1260,
1190, 869, 841, 794, 774, 748; Anal. calc. for C54H34O2: C
90.73, H 4.79, O 4.48; Found: C 90.76, H 4.77.
Results and Discussion
Synthesis
Our strategy for the synthesis of the new class of
triphenylethylene derivatives is outlined in Scheme 1. The
target compounds were synthesized by the palladium-

J Fluoresc (2011) 21:1969–1977
1973
100
80
60
40
20
0
catalyzed Suzuki coupling reactions of aryl bromide
intermediates [(Ar1)2Br] with arylboronic acids in moder-
ate yields (30–50%). The (Ar1)2Br were synthesized
through simple Wittig-Horner reaction of the ylide reagent
diethyl 4-bromobenzylphosphonate with ketone intermedi-
ates [(Ar1)2-one] in high yields (77–92%). The (Ar1)2-one
were also prepared by the Suzuki coupling reactions of bis(4-
bromophenyl)methanone (4.6 mmol) and the corresponding
arylboronic acids with high yields (66–90%). The products
were purified by recrystallization or column chromatography
on silica gel using dichloromethane-n-hexane as eluent. Their
(BB)2Bt
(BN)2Bt
(BFu)2B
(BFu)2N
(BFu)2Bt
0
200
400
600
800
1000
Temperature / o
C
1
molecular structures were confirmed with H-NMR, 13C-
Fig. 2 TGA curves of the compounds
NMR, MS and FTIR and EA.
For the comparison purposes, the five target compounds
were divided into two classes. In one class, the Ar1 was
dibenzofuran ring and the Ar2 were phenyl, naphthalene
and dibenzothiophene rings with increasing size of substit-
uent [Class I: (BFu)2B, (BFu)2N, and (BFu)2Bt]. In the
other class, the Ar2 was the same (dibenzothiophene ring)
and the Ar1 were different. The Ar1 were changed
according to the increasing size of substituent: phenyl,
naphthalene and dibenzofuran rings [Class II: (BB)2Bt,
(BN)2Bt and (BFu)2Bt].
summarized in Table 1. The Tg values of (BFu)2B,
(BFu)2N, (BFu)2Bt, (BN)2Bt and (BB)2Bt are 110, 117,
129, 108 and 86 °C, which are higher than those of the two
typical AIE compounds reported, 1-methyl-1,2,3,4,5-penta-
phenylsilole (MPPS, 54 °C) and 1,1,2,3,4,5-hexaphenyl
silole (HPS, 65 °C) [23]. As expected, Tg values of either
Class I compounds or Class II compounds increased with
the increasing size of substituent. For example, in Class II,
the Tg of (BFu)2Bt with the largest substituent dibenzofuran
ring is 43 °C higher than that of (BB)2Bt with the smallest
substituent phenyl ring. Thus the incorporation of a bulky
substituent in molecular structure can greatly improve
glassy-state durability.
From Fig. 1, it can be seen that the DSC curve of each
compound in second heating run exhibits only a glass
transition. This indicates that the compounds have an
extremely low tendency toward crystallization from their
melts. No melting peak could be detected in the second
heating runs, which was ascribed to the non-planar and
propeller-like chemical structure of substituent triphenyl-
ethylene making it difficult for them to assume a dense
packing structure.
Thermal Properties
The thermal stability of organic materials is crucial for EL
device stability and lifetime. The thermal instability or low
glass transition temperature (Tg) of the amorphous organic
materials may result in the degradation of EL device due to
morphological changes during the device operation. Hence,
a relatively high Tg is essential for emissive materials used
in optoelectronic applications.
Thermal properties of the compounds were investigated
by differential scanning calorimetry (DSC) and thermal
gravimetric analysis (TGA). Their DSC and TGA curves
are shown in Figs. 1 and 2, respectively, and the data are
The decomposition temperatures with 5% weight loss
under nitrogen atmosphere (Td) of (BFu)2B, (BFu)2N,
(BFu)2Bt, (BN)2Bt and (BB)2Bt are 505, 505, 534, 484
and 432 °C, respectively. The Td values, as expected, also
increase with the increasing size of the substituent, similar
to the change of Tg.
1 - (BB)2Bt
2 - (BN)2Bt
3 - (BFu)2B
4 - (BFu)2N
5 - (BFu)2Bt
1
2
3
Table 1 The thermal properties of the compounds
4
5
Tg/°C
Td/°C(weight loss 5%)
(BFu)2B
(BFu)2N
(BFu)2Bt
(BN)2Bt
(BB)2Bt
110
117
129
108
86
505
505
534
484
432
100
200
300
400
500
Temperature / oC
Fig. 1 DSC curves for the compounds at a scan rate of 10 °C/min
(second heating scan)

1974
J Fluoresc (2011) 21:1969–1977
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
-0.1
800
700
600
500
400
300
200
100
0
(BB)2Bt
(BN)2Bt
(BFu)2Bt
(BFu)2N
(BFu)2B
(BB)2Bt
(BN)2Bt
(BFu)2Bt
(BFu)2N
(BFu)2B
300
400
500
600
700
800
350 400 450 500 550 600 650 700
Wavelength / nm
Wavelength / nm
Fig. 3 UV absorption spectra of the compounds in THF (10 μM)
Fig. 5 Photoluminescence emission spectra of the compounds in solid
powders upon excitation at 365 nm
Photophysical and Electrochemical Properties
due to more twisted conformation caused by the effect of
steric hindrance of naphthalene ring.
As shown in Fig. 3, the Class I compounds containing
dibenzofuran rings, (BFu)2B, (BFu)2N and (BFu)2Bt, can
exhibit three absorption bands centered at 289, 322 and
∼340 nm, respectively. The fact that the former two bands
remain unchanged indicates that the two absorption bands
correspond to the absorption of dibenzofuran rings. The
absorption band at ∼340 nm is ascribed to the π-π*
transition of the whole conjugated π-electron system. There
are two main absorption bands in the compounds (BN)2Bt
and (BB)2Bt: one located at about 284 nm could be assigned
to the absorption of the dibenzothiophene ring, and the other
located at about 340 nm is also attributed to the π-π*
transition of the whole conjugated π-electron system. It is
interesting to note that the two compounds (BFu)2N in Class
I and (BN)2Bt in Class II containing naphthalene ring have
shorter absorption of the π-π* transition of the whole
conjugated π-electron system. This indicates that, although
naphthalene ring [in (BFu)2N and (BN)2Bt] has longer
conjugation than phenyl ring [in (BFu)2B and (BB)2Bt], the
naphthalene ring substituents cannot improve the molecular
π- conjugation extents, however, they shorten π-conjugation
Surprisingly, the photoluminescence (PL) spectra
(Fig. 4) of the three compounds containing dibenzofuran
rings are very similar, and the maximum emission wave-
em
max
lengths ðl Þ are found at about 464 nm. This strongly
suggests that the Ar2 substituents do not affect the electron
transition energy from excited state to the ground state.
However, the compounds (BN)2Bt and (BB)2Bt exhibit
vibronic fine-structure PL spectra and significant blue-shift
in the emission spectra. At the same concentration (10 μM),
(BN)2Bt shows the strongest PL intensity among the
compounds, and (BB)2Bt is the weakest one.
The PL spectra of the compounds in solid powder states are
em
max
shown in Fig. 5. The l
values of (BFu)2B, (BFu)2N,
(BFu)2Bt, (BN)2Bt and (BB)2Bt are 452, 450, 461, 454 and
em
max
443 nm, respectively. In Class I, comparing the l
values
of the compounds, it can found that the Ar2 substituents
em
max
affect the l
values. Compared with (BFu)2Bt, the lemmax of
(BFu)2B and (BFu)2N with smaller substituents exhibit
significant blue-shift by 9 and 11 nm, respectively. However,
Table 2 Optical properties of the compounds
λabs/nm
λem/nm
Φ
FL/%
120
90
60
30
0
(BFu)2B
(BFu)2N
(BFu)2Bt
(BN)2Bt
(BB)2Bt
a
b
c
d
(BFu)2B
(BFu)2N
(BFu)2Bt
(BN)2Bt
(BB)2Bt
289,322,341
289,322,338
289,322,346
284,342
465
464
464
415
448
452
450
461
454
443
1.0
1.5
1.1
3.8
0.9
284,345
a In THF
400
500
600
700
b In THF
Wavelength / nm
c Solid powder
d Fluorescence quantum yields measured in THF solution
Fig. 4 Photoluminescence emission spectra of the compounds in THF
(10 μM) upon excitation at 365 nm

J Fluoresc (2011) 21:1969–1977
1975
18
16
14
12
10
8
Table 3 Energy levels of the compounds
(BFu)2Bt
(BFu)2N
(BFu)2B
(BB)2Bt
(BN)2Bt
HOMO/eV
LUMO/eV
ΔEg/eV
(BFu)2B
(BFu)2N
(BFu)2Bt
(BN)2Bt
(BB)2Bt
5.61
5.63
5.64
5.66
5.64
2.41
2.41
2.46
2.44
2.44
3.20
3.22
3.18
3.22
3.20
6
4
2
0
0
20
40
60
80
100
Water fraction / %
in Class II compared with (BFu)2Bt, the (BN)2Bt shows a
Fig. 7 Photoluminescence quantum yields of the compounds in
water/THF mixtures with water fraction (10 μM)
7 nm blue-shift and (BB)2Bt shows a 18 nm blue-shift.
em
Comparing the l
values of the compounds in THF
max
solutions and in the solid states, the compounds (BFu)2B
and (BFu)2N exhibit significant blue-shift by 13 and 14 nm,
respectively. However, the (BN)2Bt shows a 39 nm red-
shift and (BB)2Bt shows a 5 nm blue-shift. This indicates
that different substituting groups and their sites affect the
intermolecular interaction and molecular packing which
strongly affect their solid emission.
Similar to other reported AIE materials, the synthesized
compounds exhibit weak emission when dissolved as
dispersed molecules in good solvents, as can be seen from
low PL intensity and low fluorescence quantum yield
(ΦFL). For example, the 10 μM THF solutions of the
compounds show low ΦFL values less than 3.8% (Table 2).
The highest occupied molecular orbital (HOMO), lowest
unoccupied molecular orbital (LUMO) and energy band
gaps (ΔEg) are three important parameters for electrolumi-
nescent materials. By cyclic voltammetry (CV) analyses
and UV absorption spectra, the HOMO energy levels and
ΔEg were obtained using the onset oxidation potential in
the CV curve (Fig. S1) and from the onset wavelength of
their UV absorption spectra, respectively. Then, the LUMO
energy levels were obtained from the HOMO energy and
energy band gap (ΔEg=HOMO−LUMO). Table 3 shows
that the energy levels of the compounds are very close to
each other. The HOMO levels of these compounds are
between 5.61 and 5.66 eV. This suggests that the
synthesized compounds have potential as a hole trans-
porting materials. The ΔEg values of the compounds were
found to be in the range of 3.18–3.22 eV. The LUMO
values ranged from 2.41 to 2.46 eV.
1000
(BFu)2Bt
900
Water fraction / %
800
0
10
700
20
30
600
500
400
300
200
100
0
40
50
60
70
80
90
350 400 450 500 550 600 650 700
Wavelength / nm
600
500
400
300
200
100
0
(BN)2Bt
Water fraction / %
0
10
20
30
40
50
60
70
80
90
350 400 450 500 550 600 650 700
Wavelength / nm
Fig. 6 Photoluminescence spectra of (BFu)2Bt and (BN)2Bt in water/
THF mixtures (10 μM) with different volume fractions of water upon
excitation at 365 nm
Fig. 8 Emission images of the compounds in pure THF (10 μM) and
in water/THF mixture with 90% water fraction under UV light
(365 nm) illumination

1976
J Fluoresc (2011) 21:1969–1977
AIE Properties
534 °C, both of which are higher than those silole
derivatives ever reported in the literature. The HOMO
levels of these compounds are between 5.61 and 5.66 eV
and the ΔEg values were found to be in the range of 3.18–
3.22 eV. The compounds (BN)2Bt and (BB)2Bt exhibited
vibronic fine-structure PL spectra when the water fraction
was less than 70%.
To determine whether or not these compounds are AIE
active, the UV absorption and PL emission behaviors of
their diluted mixtures were studied in a mixture of water/
THF with different water fractions. Since the compounds
were insoluble in water, increasing the water fraction in the
mixed solvent could thus change their existing forms from
a solution or well-dispersed state in pure THF to aggregated
particles in the mixtures with high water content, which
results in changes in the UV and PL spectra.
The PL spectra of 10 μM of (BFu)2Bt and (BN)2Bt in
water/THF mixtures with different water contents are
shown in Fig. 6 as examples (the others are shown in Fig.
S2). For (BFu)2Bt in pure THF and in the mixtures with
water fraction <60% exhibited very weak PL intensity.
However, the fluorescent intensity was significantly en-
hanced when the water fraction exceeded 60%, and when
the water fraction was up from 70% to 80%, the PL
intensity exhibited a decrease. Similar effects were ob-
served for the compounds (BFu)2N and (BFu)2B (Fig. 7).
This phenomenon was often observed in some compounds
with AIE properties, but the reasons remain unclear.
Although the PL intensities of the Class I compounds
changed with the increase of water fraction, the position of
peaks showed almost no change.
However, the compounds (BN)2Bt and (BB)2Bt
exhibited vibronic fine-structure PL spectra when the water
fraction was less than 70%. When the water fraction was up
to 70%, the PL spectrum had a significant change with the
disappearance of the fine-structure, and the maximum
emission wavelength exhibited a significant red-shift. The
difference was also reflected in PL quantum yields (Fig. 7).
The emission images of the compounds in pure THF and
in water/THF mixture with 90% water fraction under UV
light (365 nm) illumination at room temperature are shown
in Fig. 8. Clearly, THF solutions of the compounds showed
very weak fluorescence. However, the compounds in high
water fractions of water/THF mixtures exhibited very
strong fluorescence confirming that the emission enhance-
ments were induced by the aggregation of the molecules.
Acknowledgments The authors gratefully acknowledge the financial
support from the National Natural Science Foundation of China (Grant
numbers: 50773096 and 51073177), 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, 2008B090500196), Construction Project for
University-Industry cooperation platform for Flat Panel Display from
the Commission of Economy and Informatization of Guangdong
Province (Grant numbers: 20081203), the Fundamental Research Funds
for the Central Universities, the Opening Fund of Laboratory Sun
Yat-sen University (KF201026), and the Fund for Innovative Chemical
Experiment and Research of School of Chemistry and Chemical
Engineering.
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