Synthesis, photophysical and electrochemical properties and theoretical studies on three novel indolo[3,2-b]carbazole derivatives containing benzothiazole units

Article abstract of DOI:10.1016/j.tet.2012.09.012

Three novel indolo[3,2-b]carbazoles derivatives were successfully synthesized by condensation reaction and structurally characterized by elemental analysis, mass spectrometry and proton nuclear magnetic resonance spectroscopy methods, which belong to dono

Full text of DOI:10.1016/j.tet.2012.09.012

Tetrahedron 68 (2012) 9788e9794
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis, photophysical and electrochemical properties and theoretical studies
on three novel indolo[3,2-b]carbazole derivatives containing benzothiazole units
,
a
a
a
a
a
a
He-ping Shi a , Li-wen Shi , Jian-xin Dai , Lei Xu , Mei-hua Wang , Xiao-huan Wu , Li Fang ,
*
Chuan Dong a , Martin M.F. Choi
,
b,
*
*
a School of Chemistry and Chemical Engineering, Shanxi University, Taiyuan 030006, PR China
b Department of Chemistry, Hong Kong Baptist University, 224 Waterloo Road, Kowloon Tong, Hong Kong SAR, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 19 June 2012
Received in revised form 24 August 2012
Accepted 4 September 2012
Available online 10 September 2012
Three novel indolo[3,2-b]carbazoles derivatives were successfully synthesized by condensation reaction
and structurally characterized by elemental analysis, mass spectrometry and proton nuclear magnetic
resonance spectroscopy methods, which belong to donor-p-acceptor systems comprising an indolo[3,2-
b]carbazole group as an electron donor and two benzothiazole rings as electron acceptors. The thermal,
electrochemical and photophysical properties of the compounds were characterized by thermogravi-
metric analysis combined with electrochemistry, UVevis absorption spectroscopy and fluorescence
spectroscopy. On the other hand, the geometries, molecular orbitals, charge-injection and transport
properties were determined by quantum chemical calculations. The results show that the compounds
synthesized exhibit good thermal stability and high fluorescence quantum yields, indicating the potential
application as optoelectronic materials.
Keywords:
Indolo[3,2-b]carbazoles
Benzothiazole
Donor-p-acceptor
Photophysical properties
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
organic field-effect transistor (OFET) using 5,11-dioctyl-6,12-
dimethylindolo[3,2-b]carbazole as an active layer in 2004.12 Ong
Since Tang and Van Slyke demonstrated the use of hole-trans-
porting layers (HTLs) for hole injection from the anodes into the
light-emitting layer provides the significant improvement of the
organic light-emitting diode (OLED) device performance,1,2 much
attention has been paid to OLED due to their potential applications
in high-efficiency flat-panel displays and solid-state lighting.3e7 To
date, many types of high-performance materials have been fab-
ricated.8e10 Among them, indolo[3,2-b]carbazole and its de-
rivatives are the most popular ones because these compounds
comprise the large planar and rigid conjugated structures allowing
efficient charge-injection and transfer with their proper molecular
arrangement. In addition, the properties of this type of compounds
can be greatly improved by derivatization with other functional-
ities. In 1999, Hu et al. reported the first indolo[3,2-b]carbazole
derivative, 5,11-dihydro-5,11-di-1-naphthylindolo[3,2-b]carbazole,
showing an unusual atropisomerism and excellent hole-transport
properties in OLED.11 Since then, the design and synthesis of
novel derivatives based on indolo[3,2-b]carbazole have been
booming. Wakim et al. successfully fabricated the first
et al. developed N,N-disubstituted indolo[3,2-b]carbazoles and
polyindolo[3,2-b]carbazoles as new classes of high-performance p-
channel semiconductors, and these indolo[3,2-b]carbazole de-
rivatives could be used to fabricate high-mobility organic thin-film
transistor (OTFT).13e15 Tao et al. synthesized three compounds
based on indolo[3,2-b]carbazole, 2,8-bis(4-diphenylaminophenyl)-
5,11-di-n-octylindolo[3,2-b]carbazole (BTOICZ), 2,8-bis(9,90-di-n-
butylfluorenyl)-5,11-di-n-octylindolo[3,2-b]carbazole (BFOICZ) and
2,8-bis [N-(n-butyl)carbazolyl]-5,11-di-n-octylindolo[3,2-b]carba-
zole (BCOICZ) by Suzuki coupling reaction, these indolo[3,2-b]car-
bazole derivatives could be used as hole-transporting materials.16
Recently, the study of new indolo[3,2-b]carbazole derivatives
continues to grow steadily. For instance, Lengvinaite et al. synthe-
sized indolo[3,2-b]carbazole derivatives containing reactive oxe-
tanyl groups, which could be used for preparation of cross-linked
hole-transporting layers by photoinduced polymerization.17 Pierre-
Luc et al. synthesized new soluble materials based on the indolo
[3,2-b]carbazole framework, which were particularly suitable for p-
channel OFET.18 Liu et al. developed a series of indolo[3,2-b]car-
bazole derivatives with donor-p-acceptor (D-p
-A) systems.19
In view of the great potential applications in many fields of
indolo[3,2-b]carbazole derivatives, the molecular design and syn-
* Corresponding authors. Tel.: þ86 351 7018094; fax: þ86 351 7011011 (H.-p.S.);
tel.: þ86 351 7018094; fax: þ86 351 7011011 (C.D.); tel.: þ852 34117839; fax: þ852
34117348 (M.M.F.C.); e-mail addresses: hepingshi@sxu.edu.cn (H.-ping Shi), dc@
sxu.edu.cn (C. Dong), mfchoi@hkbu.edu.hk (M.M.F. Choi).
thesis of novel indolo[3,2-b]carbazole derivatives with D-
p-A
structure need to be further developed in order to improve their
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2012.09.012

H.-ping Shi et al. / Tetrahedron 68 (2012) 9788e9794
9789
properties. In the present work, we synthesized three new indolo
[3,2-b]carbazole derivatives by introducing different benzothiazole
units to the 2,8-positions of indolo[3,2-b]carbazole, which contain
an indolo[3,2-b]carbazole group as an electron donor and two
benzothiazole rings as electron acceptors, namely 2,8-
dibenzothiazolyl-5,11-dibutylindolo[3,2-b]carbazole (DDICZ), 2,8-
bis((E)-2-(benzothiazolyl)vinyl)-5,11-dibutylindolo[3,2-b]carba-
zole (BBDICZ) and 2,8-bis((E)-2-(4-(benzothiazolyl)phenyl)vinyl)-
5,11-dibutylindolo[3,2-b]carbazole (BBPDICZ). The structures of
these derivatives were determined by elemental analysis, 1H NMR,
13C NMR and mass spectrometry. Their thermal, electrochemical
and photophysical properties were characterized by thermogravi-
metric analysis combined with electrochemistry, UVevis absorp-
tion spectroscopy and fluorescence spectroscopy. Their geometries,
molecular orbitals, charge-injection and transport properties were
determined by quantum chemical calculations.
by bromination of 2-p-tolylbenzothiazole with NBS followed by
reaction with PPh3 in CCl4. BBPDICZ was obtained as a greenish
solid in an overall yield of 35%. All synthesized compounds were
fully characterized by mass spectrometry and NMR methods. De-
tails are given in experimental section.
2.2. Thermal stability
The thermal properties of three indolo[3,2-b]carbazole de-
rivatives were determined by TGA, as shown in Supplementary data
Fig. S1. DDICZ presents an onset degradation temperature (Td) for 5%
weight loss as high as 418 ꢀC. Degradation temperature of BBDICZ
and BBPDICZ is 331 ꢀC and 390 ꢀC, respectively. For comparison, the
Td data are listed in Table 1. Obviously, these derivatives exhibit good
thermal stability, implying that incorporation of indolo[3,2-b]car-
bazole and benzothiazole units into the indolo[3,2-b]carbazole de-
rivative is favorable to enhance the thermal stability. Furthermore,
the different conjugate connection of benzothiazole units and indolo
[3,2-b]carbazole has a significant effect on their thermal stability.
Thus DDICZ has best thermal stability among these derivatives.
2. Results and discussion
2.1. Synthesis
The molecular structures of three indolo[3,2-b]carbazole de-
rivatives are shown in Fig. 1. As illustrated in Scheme 1, we carried
out the synthesis of the key intermediate 4 for the whole procedure
via a four-step reaction. The target compound DDICZ was formed by
condensation reaction of 4 with 2-aminothiophenol in DMSO so-
lution with 83% yield as light yellow solid. To gain BBDICZ, a two-
step synthesis was carried out by lithiation of 2-
methylbenzothiazole with n-butyllithium in THF solution fol-
lowed by reaction with 4, and then dehydration of the obtained
product. BBDICZ was obtained as a greenish solid in an overall yield
of 43%. To form the more extended conjugation molecule of
BBPDICZ, a three-step synthesis was carried out by Wittig reaction
of 4 with the corresponding phosphonium salt, which was obtained
2.3. Quantum calculation
To understand the geometries and the electronic properties of
DDICZ, BBDICZ and BBPDICZ, quantum chemical calculations were
performed using the DFT/B3LYP/6-31G (d,p) method.
2.3.1. The geometries and frontier molecular orbitals. The optimized
structures of the derivatives reveal that these molecules adopt pla-
nar conformations. Such structural characteristics can influence their
electronic and physical properties as a result of an extension of the
conjugation. Fig. 2 illustrates the highest occupied molecular orbitals
(HOMOs) and the lowest unoccupied molecular orbitals (LUMOs) of
the obtained compounds. The election density of the HOMO of
DDICZ is mostly localized on the central indolo[3,2-b]carbazole
moiety, while that of LUMO is delocalized over indolo[3,2-b]carba-
zole core and benzothiazole terminals. Similar distribution of the
election density of HOMO could be observed in BBDICZ and BBPDICZ
as well, while the election density of LUMO of BBDICZ is mostly lo-
calized on vinyl linker segments and benzothiazoles and that of
LUMO of BBPDICZ is mostly localized on styryl linker segments and
benzothiazoles. The electron transitions of these derivatives from the
ground to excited states are mainly from the indolo[3,2-b]carbazole
ring to the benzothiazole rings, belonging to the intramolecular
charge transfer (ICT) from electron donor to electron acceptors. The
HOMOeLUMO energy gaps (Eg calcd) are calculated and presented
in Table 1. The calculated values slightly deviate from those obtained
from the experimental results (ca. 0.05e0.09 eV).
N
N
S
N
N
S
DDICZ
N
N
S
N
2.3.2. Charge-injection and transport properties. In order to un-
derstand the charge-injection and transport properties, the ioni-
zation potential (IP), electronic affinity (EA) and hole/electron
reorganization energy of DDICZ, BBDICZ and BBPDICZ are calcu-
lated and displayed in Supplementary data Table S1. In general, the
lower the IP, the easier the entrance of holes from ITO to hole-
transport layer (HTL). The higher the EA, the easier the entrance
of electrons from cathode to electron-transport layer (ETL). Fur-
thermore, the charge transport rate can be represented by the
Marcus electron-transfer theory,20 and the charge transport rate is
mainly decided by hole/electron reorganization energy according
to this theory.21 The calculated results show that DDICZ, BBDICZ
and BBPDICZ have almost the same ionization potential but dif-
ferent electronic affinity and a small hole reorganization energy
compared with electron reorganization energy, inferring their po-
tential application as hole-transport materials.
N
S
BBDICZ
N
S
N
N
N
S
BBPDICZ
Fig. 1. The molecular structures of three indolo[3,2-b]carbazole derivatives.

9790
H.-ping Shi et al. / Tetrahedron 68 (2012) 9788e9794
H
N
Br
O
O
Br
b
a
Br
N
NH
N
N
NH
Br
+
N
H
Br
NHNH2
( 1 )
( 2 )
N
Br
OHC
d
c
CHO
Br
N
N
N
( 4 )
( 3 )
e
N
S
N
N
S
DDICZ
N
N
OH
g
N
N
f
S
S
N
N
HO
N
N
S
S
BBDICZ
( 5 )
N
S
h
N
N
N
S
BBPDICZ
Scheme 1. The synthetic route of three indolo[3,2-b]carbazole derivatives.
Table 1
Experimental and theoretical data of three indolo[3,2-b]carbazole derivatives
Compounds
labs [nm]/
3
lemb [nm]
Fd
(
f)
Eox [V]
EHOMO [eV] (EHOMOh [eV])
ELUMO [eV] (ELUMOh eV])
Eg [eV] (Egh [eV])
f
a
c
Td [ꢀC]
e
g
g
max
DDICZ
BBDICZ
BBPDICZ
352 (65,300)
405 (32,320)
408 (38,110)
435, 465
507
517
418
331
390
0.38
0.17
0.11
0.88
0.77
0.64
ꢂ5.28 (ꢂ5.01)
ꢂ5.17 (ꢂ4.95)
ꢂ5.04 (ꢂ4.81)
ꢂ1.99 (ꢂ1.67)
ꢂ2.03 (ꢂ1.71)
ꢂ2.14 (ꢂ1.82)
3.29 (3.34)
3.18 (3.24)
2.90 (2.99)
a
Measured in a dilute THF solution (10ꢂ5 M).
Excited at the absorption maxima.
b
c
Obtained from TGA measurements with a heating rate of 10 ꢀC/min under N2.
d
e
Fluorescence quantum yields (
f
) in a dilute THF solution (10ꢂ6 M).
ox
E
¼onset oxidation potential; measured using a three-electrode system fitted with a glassy carbon working electrode, a platinum rod counter electrode, and Ag/AgCl
onset
reference electrode in degassed CH3CN containing 0.1 M n-Bu4NClO4 as a supporting electrolyte at a scan rate of 50 mV/s.
f
Estimated according to the oxidation potential and the onset of the absorption spectra (Eg¼1240/lonset).
g
Calculated using the empirical equation: HOMO¼(4.4þEonset) and LUMO¼HOMOþEg.
h
Obtained from quantum chemical calculation using DFT/B3LYP/6-31G (d,p).
2.4. Photophysical properties
The pertinent data are summarized in Table 1. All the derivatives
exhibit two similar absorption bands, a high-energy absorption
band at 300e370 nm and a low-energy absorption band at
370e480 nm, in which the high-energy absorption band is
The UVevis absorption spectra of the indolo[3,2-b]carbazole
derivatives in several solvents (1ꢁ10ꢂ5 M) are illustrated in Fig. 3.

H.-ping Shi et al. / Tetrahedron 68 (2012) 9788e9794
9791
Fig. 2. The contour plots of HOMOs and LUMOs of three indolo[3,2-b]carbazole derivatives in the ground state.
attributed to
p
e
p
*
transition of the indolo[3,2-b]carbazole back-
carbazole unit in DDICZ raises the fluorescence quantum yield and
the fluorescence quantum yields are reduced with the increase of
the elongation of the conjugated length of BBDICZ and BBPDICZ as
these two molecules become more planar and then the fluores-
bone and the low-energy absorption band is attributed to
pep
*
transition of the intramolecular charge transfer (ICT) from the
indolo[3,2-b]carbazole unit to the benzothiazole units. In addition,
DDICZ, BBDICZ and BBPDICZ exhibit different maximum absorption
wavelengths, varying from 355 nm to 363 nm and increasing with
the elongation of the conjugated length of these molecules. Their
HOMOeLUMO energy gaps (Eg) estimated from the onset of the
absorption spectra are 2.96 eV for DDICZ, 2.89 eV for BBDICZ and
2.85 eV for BBPDICZ, respectively.
The normalized fluorescence spectra of the indolo[3,2-b]carba-
zole derivatives in several solvents (1ꢁ10ꢂ5 M) are illustrated in
Fig. 4, respectively. The relevant data are also summarized in Table
1. DDICZ displays two emission bands, a high-energy emission band
at 410e450 nm and a low-energy emission band at 450e650 nm in
different solvents, in which the low-energy emission band is orig-
cence of them is reduced by intermolecular pep stacking.
2.5. Electrochemical properties
In order to investigate the redox properties of the indolo[3,2-b]
carbazole derivatives and their HOMO and LUMO energy levels,
cyclic voltammetry (CV) analysis was performed. The measure-
ments were carried out in CH3CN solution containing 0.1 M n-
Bu4NClO4 as supporting electrolyte, using three-electrode systems
under an argon atmosphere. The reference electrode was Ag/Agþ.
The results are shown in Supplementary data Fig. S2 and summa-
rized in Table 1. The CV curves of these derivatives remain un-
changed under successive oxidation, indicating their excellent
stability against electrochemical oxidation. The onset oxidation
potentials of DDICZ, BBDICZ and BBPDICZ are 0.88 V, 0.70 V and
0.64 V, respectively. The HOMO energy levels can be calculated by
using the empirical equation EHOMO¼ꢂ(Eoxþ4.40) eV, where Eox is
the onset potentials for oxidation.23 Therefore, the HOMO levels of
DDICZ, BBDICZ and BBPDICZ are ꢂ5.28 eV, ꢂ5.17 eV and ꢂ5.04 eV,
respectively. The LUMO energy levels can be calculated by using the
equation ELUMO¼EHOMOꢂEg, where energy gap (Eg) is estimated
from the onset of the absorption spectra for DDICZ, BBDICZ and
BBPDICZ, respectively. The HOMO levels of the compounds increase
whereas the LUMO levels of the compounds decrease with the
extended conjugation. The HOMO levels are available to facilitate
hole injection and transport from ITO (4.80 eV) to the emissive Alq3
(5.80 eV), while the LUMO levels are available to facilitate electron
injection and transport from cathode to the emissive Alq3
inated from
(ICT) from the indolo[3,2-b]carbazole unit to the benzothiazole
units, and the high-energy emission band is related to tran-
pep transition of the intramolecular charge transfer
*
pep
*
sition of DDICZ skeleton. BBDICZ and BBPDICZ exhibit mainly
a broad emission band in several solvents except that hexane owe
* *
to overlap of pep transition of their skeletons and pep transition
of the intramolecular charge transfer (ICT) from the indolo[3,2-b]
carbazole unit to the benzothiazole units.
In order to further understand the emission property of these
indolo[3,2-b]carbazole derivatives, their fluorescence quantum
yields were measured in THF solvent (1ꢁ10ꢂ6 M) using quinine
sulfate in 0.01 M H2SO4 solution as a standard at room temperature
based on the literature.22 The results are summarized in Table 1.
Fluorescence quantum yields of DDICZ, BBDICZ and BBPDICZ are
0.38, 0.17 and 0.11, respectively. The results indicate that the direct
attachment of the benzothiazole units to the indolo[3,2-b]

9792
H.-ping Shi et al. / Tetrahedron 68 (2012) 9788e9794
0.8
0.6
0.4
0.2
0.0
1.0
DDICZ
Hex
Hex
DDICZ
THF
THF
CHCl
Chloroform
0.8
Acetone
3
DMSO
Acetone
DMSO
0.6
0.4
0.2
0.0
350 400 450 500 550 600 650
Wavelength(nm)
350
400
450
500
Wavelength(nm)
BBDICZ
Hex
0.4
0.3
0.2
0.1
0.0
1.0
THF
CHCl
Hex
BBDICZ
THF
3
Chloroform
Acetone
DMSO
Acetone
DMSO
0.8
0.6
0.4
0.2
0.0
350
400
450
500
400 450 500 550 600 650 700
Wavelength(nm)
Wavelength(nm)
0.4
BBPDICZ
Hex
THF
BBPDICZ
Hex
1.0
0.8
0.6
0.4
0.2
0.0
Chloroform
THF
Acetone
DMSO
CHCl
3
0.3
0.2
0.1
0.0
Acetone
DMSO
400 450 500 550 600 650 700
Wavelength(nm)
350
400
450
500
Wavelength(nm)
Fig. 4. The normalized fluorescence spectra of three indolo[3,2-b]carbazole derivatives
in several solvents.
Fig. 3. UVevis spectra of three indolo[3,2-b]carbazole derivatives in several solvents.
(5.80 eV).24 The high-lying HOMO energy levels can be good and
stable hole-transport and injection materials for fabrication of
OLEDs. Therefore, incorporating both hole-transporting indole[3,2-
b]carbazole unit and electron-transporting benzothiazole units into
a structure can significantly tune electrochemical and transporting
properties of the derivatives.
thermal stability and high fluorescence quantum yields indicating
the potential applications as optoelectronic materials.
4. Experimental
4.1. General procedure
3. Conclusions
The reagents, including 2-aminothiophenol, 4-bromophenylh-
ydrazine hydrochloride, 1,4-cyclohexanedione, 2-methylbenzoth-
iazole and 2-p-tolylbenzothiazole, were purchased from Alfa Aesar
(Ward Hill, MA, USA) and used without further purification. All other
reagents of analytical reagent grade or above from Beijing Chemical
Plant (Beijing, China) were used as received. The solvents such as
carbon tetrachloride, diethyl ether (Et2O), N,N-dimethylformamide
(DMF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), toluene,
acetone and acetonitrile were treated according to the standard
methods.
In this work, three novel compounds, namely 2,8-dibenzot-
hiazolyl-5,11-dibutylindolo[3,2-b]carbazole(DDICZ), 2,8-bis((E)-2-
(benzothiazolyl)vinyl)-5,11-dibutylindolo[3,2-b]carbazole (BBDICZ)
and 2,8-bis((E)-2-(4-(benzothiazolyl)phenyl)vinyl)-5,11-dibutylin-
dolo[3,2-b]carbazole (BBPDICZ), were successfully synthesized and
structurally characterized by elemental analysis, NMR and MS
methods. These compounds belong to donor-p-acceptor systems
comprising an indolo[3,2-b]carbazole group as an electron donor
and two benzothiazole rings as electron acceptors. Their properties
were studied by the combination of experimental and theoretical
methods. The results show that these compounds exhibit good
Elemental analyses were conducted on a PerkinElmer elemental
analyzer (PerkinElmer. USA). 1H and 13C nuclear magnetic

H.-ping Shi et al. / Tetrahedron 68 (2012) 9788e9794
9793
resonance (NMR) spectra were recorded on a Bruker Avance
600 MHz NMR spectrometer (Bremen, Germany) with CDCl3 or
DMSO-d6 as solvent. Mass spectra were recorded with the LCeMS
system consisted of a Waters 1525 pump and a Micromass ZQ4000
single quadrupole mass spectrometer. UVevis absorption spectra
were conducted on a Shimadzu UV-2450 spectrophotometers.
Fluorescence spectra were acquired on a Hitachi F-4500 spectro-
fluorometer (Tokyo, Japan). Fluorescence quantum yield was de-
termined using the standard actinometric method. Quinine sulfate
was the reference with a fluorescence quantum yield of 0.55 in
0.01 M H2SO4 and the sample was excited at 350 nm. The fluores-
cence quantum yield was calculated according to the following
equation.
heated to 50 ꢀC, and thereafter, the temperature was allowed to
cool to 0 ꢀC. A precipitate was filtered off, washed carefully with
water to give 1 (yield 66%).
4.2.2. Synthesis of 2,8-dibromoindolo[3,2-b]carbazole (2). Compound
1 (10 g, 22 mmol) was added to a mixture of acetic acid (AcOH)
(130 mL) and H2SO4 (32 mL) at 0 ꢀC and stirred for 5 min. Afterward,
the reaction mixture was stirred at 30 ꢀC for 1 h. Thereafter, the
mixture was further warmed up to 60e70 ꢀC and stirred for 1 h.
Subsequently cool down to room temperature and pour into ice
water with stirring. The greenish solid was filtered off. Wash it with
water and EtOH to neutral pH. Dried and pure 2,8-dibromoindolo
[3,2-b]carbazole (2) (4.88 g, yield 52.8%) was obtained. Melting
point (Mp) >300 ꢀC. 1H NMR (DMSO-d6)
7.1e8.24 (8H, m, AreH).
d 11.14 (2H, s, NeH),
ꢀ
ꢁ
2
Fs Ar nr
fs
¼
fr
Fr As ns
4.2.3. Synthesis of 2,8-dibromo-5,11-dibutylindolo[3,2-b]carbazole
(3). Compound 2 (2.0 g, 4.8 mmol) was added to a suspension of
NaH (0.35 g, 14 mmol) in THF (50 mL) under nitrogen flow. There-
after, the mixture was stirred for 2 h at room temperature, and then
the temperature was increased slowly to 50 ꢀC. Keep at the uniform
temperature for 4 h and cool to room temperature. 1-Bromobutane
(1.91 g, 14 mmol) was added dropwise to the mixture with stirring
continued for 50 min, and then the mixture was heated at 50 ꢀC and
maintained at this temperature for 24 h. Afterward, the solvent was
evaporated and solid left. The solid was washed with water and two
or three times each with acetone to afford the desired 3 (2.01 g,
where
4 is the fluorescence quantum yield, F is the integration of
the emission intensity, n is the index of refraction of the solution
and A is the absorbance at the excitation wavelength, the sub-
scripts ‘r’ and ‘s’ denote the reference and sample, respectively.
The time-resolved photoluminescence measurements were per-
formed on an Edinburgh FLS920 fluorescence lifetime spectrom-
eter (Livingston, UK) operating in the time-correlated single
photon counting mode. Differential scanning calorimetry (DSC)
analysis and thermogravimetry analysis (TGA) were performed on
a TA Instruments TGA 2050 thermogravimetric analyzer (New
Castle, DE, USA) under nitrogen atmosphere at a heating rate of
10 ꢀC/min from room temperature to 600 ꢀC. Cyclic voltammetry
experiments were performed on a CHI-600C electrochemical an-
alyzer (Austin, TX, USA) using a three-electrode system compris-
ing a glassy carbon working electrode, a platinum counter
electrode and a Ag/AgCl reference electrode at a scan rate of
50 mV/s in acetonitrile under argon atmosphere. The concentra-
tions of an analytical material and supporting electrolyte tetra-
butyl ammonium hexafluorophosphate (n-Bu4NPF6) were 10ꢂ3 M
and 0.1 M, respectively.
The ground state geometries of three derivatives and their ionic
were fully optimized using density functional theory (DFT) at B3LYP
level with 6-31G(d,p) basis set and 6-31Gþ(d,p), respectively.25e27
The frontier molecular orbital characteristics were analyzed on the
optimized neutral structures. The ionization potential (IP), electron
affinity (EA) and reorganization energy of three compounds DDICZ,
BBDICZ and BBPDICZ were calculated based on the optimized ge-
ometries of the neutral and ionic molecules. Solvent effect was also
taken into account by using the polarized continuum model
(PCM).28,29 All calculations were carried out with the Gaussian 03
program package.30 All the calculations were performed in super-
computing center of computer network information center of
Chinese Academy of Sciences.
yield 79.5%). Mp: 271e274 ꢀC. 1H NMR (CDCl3)
d 7.572e8.547 (8H,
m, AreH), 4.359e4.383 (4H, t, eNCH2e, J¼7.2 Hz),1.900e1.925 (4H,
t, eCH2e, J¼7.5 Hz), 1.440e1.453 (4H, m, eCH2e), 0.965e0.990 (6H,
t, eCH3, J¼7.5 Hz).
4.2.4. Synthesis of 5,11-dibutylindolo[3,2-b]carbazole-2,8-dicarbalde-
hyde (4). To a well-stirred suspension of 3 (1.6 g, 3 mmol) in 80 mL
of absolute ether under a nitrogen atmosphere at ꢂ78 ꢀC was added
3.03 mL of a 2.5 mol solution of n-butyllithium. The resulting sus-
pension was stirred for 4 h before adding dimethylformamide (DMF)
(2.35 mL) at ꢂ78 ꢀC. The mixture was allowed to warm to room
temperature with stirring for 8 h and was then poured into ice water.
After addition of a 10% aqueous hydrochloric acid solution to neutral
pH, the precipitated solid was collected by filtration. The solid from
the filtrate was separated, washed with water, ether and dried.
Yellow crystals 4 was given (0.85 g, yield 67%). Mp: 282e284 ꢀC. 1H
NMR (CDCl3)
d 10.107 (2H, s, eCHO), 7.461e8.725 (8H, m, AreH),
4.400e4.448(4H, t, eNCH2e, J¼7.2 Hz), 1.928e1.978 (4H, t, eCH2e,
J¼7.5 Hz), 1.428e1.903 (4H, m, eCH2e), 0.965e1.013 (6H, t, eCH3,
J¼7.2 Hz).
4.2.5. Synthesis of 2,8-dibenzothiazolyl-5,11-dibutylindolo[3,2-b]
carbazole (DDICZ). A mixture of 2-aminobenzenethiol (300 mg,
2.4 mmol) and 4 (424 mg, 1 mmol) in 30 mL DMSO was refluxed
at 195 ꢀC for 2 h. Ice water was added after the mixture was
cooled. The solid was filtered and added to acetic acid and water
(50 mL, 1:4). The precipitate was filtered and washed with water
and dilute NaHCO3 solution. Recrystallized in ethanol to give
384 mg of DDICZ (yield 60.5%). Mp >300 ꢀC. 1H NMR (CDCl3)
4.2. Synthesis and characterization
The synthesis of compounds cyclohexane-1,4-dione-bis(p-
bromophenyl)-hydrazone (1), 2,8-dibromoindolo[3,2-b]carbazole
(2) and 2,8-dibromo-5,11-dibutylindolo[3,2-b]carbazole (3) were
performed according to or slightly modified literature
procedures.31
d
7.436e8.744 (16H, m, AreH), 4.557e4.605 (4H, t, eNCH2e,
J¼7.2 Hz), 1.891e1.940 (4H, t, eCH2e, J¼7.3 Hz), 1.324e1.428 (4H,
m, eCH2e), 0.925e0.973 (6H, t, eCH3, J¼7.2 Hz). MS (m/z):
634.9213 (Mþ). Anal. Calcd for C40H34N4S2: C, 75.68%; H, 5.40%;
N, 8.83%; S, 10.10%. Found: C, 75.30%; H, 5.45%; N, 8.72%; S,
10.03%.
4.2.1. Synthesis of cyclohexane-1,4-dione-bis (p-bromophenyl)-hy-
drazone (1). 1,4-Cyclohexanedione (5.62 g, 50 mmol) dissolved in
absolute ethanol (EtOH) (100 mL) was added with stirring to
a mixture of powdered 4-bromophenylhydrazine hydrochloride
(22.4 g, 100 mmol), sodium acetate (8.2 g, 100 mmol) and absolute
ethanol (200 mL) at room temperature. The mixture was quickly
4.2.6. Synthesis of 2,8-di(2-(benzothiazolyl)ethanolyl)-5,11-
dibutylindolo[3,2-b] carbazole (5). Under nitrogen, to a solution of
2-methylbenzothiazole (0.32 mL, 2.4 mmol) in 10 mL of anhydrous

9794
H.-ping Shi et al. / Tetrahedron 68 (2012) 9788e9794
THF at ꢂ78 ꢀC was added dropwise, 2.5 M n-BuLi in hexane
(0.56 mL, 1.4 mmol). The mixture was stirred at ꢂ78 ꢀC for 30 min,
then 4 (0.424 g, 1.0 mmol) in 15 mL of anhydrous THF was added
dropwise. The reaction mixture was stirred at ꢂ78 ꢀC for 1 h, then
allowed to warm to ambient temperature and stirred overnight.
Next, 0.20 mL of acetic acid was added, and the mixture was diluted
with 50 mL of CH2Cl2. The solution was dried over MgSO4, filtered
and concentrated in vacuum. A yellow powder was obtained by
recrystallization from ethanol (0.38 g, yield 53%). Mp 203e205 ꢀC.
Anal. Calcd for C56H46N4S2: C, 80.16%; H, 5.53%; N, 6.68%; S, 7.64%.
Found: C, 80.46%; H, 5.41%; N, 6.39%; S, 7.40%.
Acknowledgements
This work was supported by the Hundred Talent Programme of
Shanxi Province, National Science Foundation of China (21175086),
Fund of Key Laboratory of Optoelectronic Materials Chemistry and
Physics, Chinese Academy of Sciences (2011KL004), HKBU Faculty
ResearchGrant (FRG2/10-11/112)andTheInternationalScientific and
Technological Cooperation Projects of Shanxi Province (2011081017).
We would express our sincere thanks to the Supercomputing Center
of Computer Network Information Center of Chinese Academy of
Sciences for conducting all the theoretical calculations.
1H NMR (CDCl3)
d 7.258e8.341 (16H, m, AreH), 5.521e5.532 (2H, d,
eCHe, J¼6.6 Hz), 4.419e4.445 (4H, t, eNCH2e, J¼7.8 Hz),
3.622e3.654 (4H, t, eCH2e, J¼9.6 Hz), 1.994e2.018 (4H, t, CH2e,
J¼7.2 Hz), 1.476e1.502 (4H, m, eCH2e), 0.979e1.003 (6H, t, eCH3,
J¼7.2 Hz).
4.2.7. Synthesis of 2,8-bis((E)-2-(benzothiazolyl)vinyl)-5,11-
dibutylindolo[3,2-b] carbazole (BBDICZ). A mixture of 5 (0.29 g,
0.40 mmol) and p-toluenesulfonic acid monohydrate (0.304 g, 1.6
mmol) was added to 20 mL of toluene. The reaction mixture was
heated at reflux for 3 h, then cooled to ambient temperature and
concentrated in vacuum. The crude product was recrystallized from
ethanol to give a yellow powder BBDICZ (0.125 g, yield 46%). Mp
Supplementary data
Supplementary data associated with this article can be found in
the online version, at doi:10.1016/j.tet.2012.09.012. These data in-
clude MOL files and InChIKeys of the most important compounds
described in this article.
>300 ꢀC. 1H NMR (CDCl3)
d 7.285e8.459 (20H, m, AreH),
References and notes
4.437e4.463 (4H, t, eNCH2e, J¼7.8 Hz), 2.022e2.048 (4H, t, eCH2e,
J¼7.8 Hz), 1.476e1.545 (4H, m, eCH2e), 0.982e1.007 (6H, t, eCH3,
J¼7.5 Hz). MS (m/z): 686.9402 (Mþ). Anal. Calcd for C44H38N4S2: C,
76.93%; H, 5.58%; N, 8.16%; S, 9.34%. Found: C, 76.68%; H, 5.65%; N,
8.27%; S, 9.40%.
1. Tang, C. W.; Van Slyke, S. A. Appl. Phys. Lett. 1987, 51, 913e915.
2. Yasuhiko, S. J. Mater. Chem. 2000, 10, 1e25.
3. Van Slyke, S. A.; Chen, C. H.; Tang, C. W. Appl. Phys. Lett. 1996, 69, 2160e2162.
4. Tullo, A. H. Chem. Eng. News 2000, 78, 11e12.
5. Tullo, A. H. Chem. Eng. News 2001, 79, 22e24.
6. Hung, L. S.; Tang, C. W. Appl. Phys. Lett. 1997, 70, 152e154.
7. Zhao, H. P.; Wang, F. Z.; Yuan, C. X.; Tao, X. T.; Sun, J. L.; Zou, D. C.; Jiang, M. H.
Org. Electron. 2009, 10, 925e931.
8. Zhang, Q.; Chen, J.; Chen, Y.; Wang, L.; Ma, D.; Jing, X.; Wang, F. J. Mater. Chem.
2004, 14, 895e900.
4.2.8. Synthesis of 2,8-bis((E)-2-(4-(benzothiazolyl)phenyl)vinyl)-
5,11-dibutylindolo[3,2-b] carbazole (BBPDICZ)
4.2.8.1. 2-(4-(Bromomethyl)phenyl)benzothiazole. 2-p-Tolylbenzo-
thiazole (2.71 g, 12 mmol) and N-bromosuccinimide (NBS) (2.14 g,
12 mmol) were dissolved in 50 mL of CCl4. The solution was refluxed
for 4 h. The precipitated succinimide was filtered, and the solvent was
evaporated from the solution. The remaining gray oil was recrystal-
lized from ethanol. The obtained white crystalline powder was dried
in vacuum (3.43 g, yield 94%). Mp: 132e133 ꢀC. 1H NMR (CDCl3)
9. Li, J.; Ma, C.; Tang, J.; Lee, C. S.; Lee, S. Chem. Mater. 2005, 17, 615e619.
10. Li, J.; Liu, D.; Li, Y.; Lee, C. S.; Kwong, H.; Lee, S. Chem. Mater. 2005, 17,
1208e1212.
11. Hu, N. X.; Xie, S.; Popovic, Z.; Ong, B. S.; Hor, A. M. J. Am. Chem. Soc. 1999, 121,
5097e5098.
12. Wakim, S.; Bouchard, J.; Simard, M.; Drolet, N.; Tao, Y.; Leclerc, M. Chem. Mater.
2004, 16, 4386e4388.
13. Wu, Y. L.; Li, Y. N.; Gardner, S.; Ong, B. S. J. Am. Chem. Soc. 2005, 127, 614e618.
14. Li, Y. N.; Wu, Y. L.; Gardner, S.; Ong, B. S. Adv. Mater. 2005, 17, 849e853.
15. Li, Y. N.; Wu, Y. L.; Ong, B. S. Macromolecules 2006, 39, 6521e6527.
16. Zhao, H. P.; Tao, X. T.; Wang, P.; Ren, Y.; Yang, J. X.; Yan, Y. X.; Yuan, C. X.; Liu, H.
J.; Zou, D. C.; Jiang, M. H. Org. Electron. 2007, 8, 673e682.
17. Lengvinaite, S.; Grazulevicius, J. V.; Grigalevicius, S.; Gu, R.; Dehaen, W.; Jan-
kauskas, V.; Zhang, B.; Xie, Z. Dyes Pigments 2010, 85, 183e188.
18. Boudreault, P. T.; Virkar, A. A.; Bao, Z.; Leclerc, M. Org. Electron. 2010, 11,
1649e1659.
d
7.928e8.132 (m, 8H, AreH), 4.550e4.622 (s, 2H, eCH2e).
4.2.8.2. 4-(2-Benzothiazolyl)-benzyl triphenyl phosphonium
bromide. A mixture of 2-(4-(bromomethyl)phenyl)benzothiazole
(3.04 g, 10 mmol) and triphenylphosphine (2.62 g, 10 mmol) was
added to CHCl3 (50 mL) under N2 flow. The mixture was heated up
slowly to 60 ꢀC and kept for 24 h. After that, it was cooled to room
temperature, the solvent was removed under reduced pressure.
The residue was recrystallized from Et2O to give the white solid
19. Liu, Z.; Cao, D.; Chen, Y.; Fang, Q. Dyes Pigments 2010, 86, 63e67.
20. Marcus, R. A. Rev. Mod. Phys. 1993, 65, 599e610.
ꢀ
21. Coropceanu, V.; Cornil, J.; Demetrio, A.; Olivier, Y.; Silbey, R.; Bredas, J. L. Chem.
Rev. 2007, 107, 926e952.
22. Dmas, J. N.; Crobys, G. A. J. Phys. Chem. 1971, 75, 991e1024.
(4.98 g, yield 88%). Mp 295e297 ꢀC. 1H NMR (CDCl3)
(m, 23H), 5.721e5.770 (s, 2H, eCH2e).
d 7.264e8.082
ꢀ
23. Bredas, J. L.; Silbey, R.; Boudreaux, D. S.; Chance, R. R. J. Am. Chem. Soc. 1983, 105,
6555e6559.
24. Promaraka, V.; Ruchirawat, S. Tetrahedron 2007, 63, 1602e1609.
25. Hohenberg, P.; Kohn, W. Phys. Rev. B 1964, 136, 864e871.
4.2.8.3. 2,8-Bis((E)-2-(4-(benzothiazolyl)phenyl)vinyl)-5,11-
dibutylindolo[3,2-b]carbazole (BBPDICZ). Under nitrogen atmo-
sphere, a stirred slurry of 4-(2-benzothiazolyl)-benzyl triphenyl
phosphonium bromide (0.566 g, 1 mmol) in 30 mL anhydrous THF
was cooled to ꢂ78 ꢀC, 0.40 mL of 2.5 M n-BuLi in hexane (1 mmol)
was added and the mixture was warmed to room temperature over
2 h. Then a solution of compound 4 (0.21 g, 1.77 mmol) in 10 mL
THF was added dropwise with vigorous stirring at ꢂ78 ꢀC. The re-
action mixture was warmed to room temperature and stirred for
12 h. Then the THF was evaporated at reduced pressure and the
residue was separated by column chromatography (petroleum
ether/methylene chloride 1:3) to give a yellow powder BBPDICZ
26. Kohn, W.; Sham, L. J. Phys. Rev. A 1965, 140, 1133e1138.
27. Foresman, J. B.; Gordon, M. H.; Pople, J. A.; Frisch, M. J. J. Phys. Chem. 1992, 96,
135e149.
28. Cossi, M.; Rega, N.; Scalmani, G.; Barone, V. J. Chem. Phys. 2001, 114, 5691e5701.
29. Cossi, M.; Scalmani, G.; Rega, N.; Barone, V. J. Chem. Phys. 2002, 117, 43e54.
30. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman,
J. R.; Montgomery, J. A.; Vreven, T., Jr.; Kudin, K. N.; Burant, J. C.; Millam, J. M.;
Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, B.; Rega, G.
N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li,
X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo, C.; Jaramillo, J.; Gomperts, R.;
Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.;
Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski,
V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A.
D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.;
Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;
Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.;
Pople, J. A. Gaussian 03. Gaussian: Pittsburgh PA, 2003.
(0.16 g, yield 38%). Mp >300 ꢀC. 1H NMR (CDCl3)
d 7.372e8.393
(28H, m, AreH), 4.422e4.447 (4H, t, eNCH2e, J¼7.5 Hz),
1.966e1.988 (4H, t, eCH2e, J¼6.6 Hz), 1.256e1.450 (4H, m, eCH2e),
0.961e0.986 (6H, t, eCH3, J¼7.5 Hz). MS (m/z): 839.2037 (Mþ).
31. Yudina, L. N.; Bergman, J. Tetrahedron 2003, 59, 1265e1275.