Synthesis and properties of fluorene or carbazole-based and dicyanovinyl-capped n-type organic semiconductors

Article abstract of DOI:10.1039/b715920j

Dicyanovinyl-substituted compounds as electron transport materials are rarely studied, especially oligomers. A new series of fluorene or carbazole-based and dicyanovinyl-capped oligomers consisting of benzene or thiophene segments were synthesized using t

Full text of DOI:10.1039/b715920j

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www.rsc.org/materials | Journal of Materials Chemistry
Synthesis and properties of fluorene or carbazole-based and
dicyanovinyl-capped n-type organic semiconductors†‡
a
Ting Qi,ab Yunqi Liu, Wenfeng Qiu,a Hengjun Zhang,ab Xike Gao,ab Ying Liu,ab Kun Lu,ab
*
Chunyan Du,ab Gui Yua and Daoben Zhua
Received 15th October 2007, Accepted 3rd January 2008
First published as an Advance Article on the web 30th January 2008
DOI: 10.1039/b715920j
Dicyanovinyl-substituted compounds as electron transport materials are rarely studied, especially
oligomers. A new series of fluorene or carbazole-based and dicyanovinyl-capped oligomers consisting
of benzene or thiophene segments were synthesized using the Stille coupling reaction and their physical
properties were investigated. Optical spectra show that the introduction of electron-accepting groups
induces an intramolecular charge transfer, resulting in a shift of the absorption onset toward longer
wavelengths. Moreover, the optical spectra of their films show intermolecular interactions, leading to
bathochromic shifts with respect to the spectra in solution. Cyclic voltammetry indicates that they have
suitable HOMO and LUMO energy levels, and the oligomers containing thiophene segments show
lower LUMO levels. The X-ray crystallography of compound FTCN shows that the compound
exhibits extended p stacking of the molecules. Thermal analysis reveals that they are thermally stable
and no phase transition was observed at low temperatures.
synthesized highly soluble dicyanomethylene-substituted oligo-
thiophenes with high electron mobilities (up to 0.16 cm2 Vꢀ1 sꢀ1
1. Introduction
,
Organic semiconductors are intensively investigated from the
viewpoints of their fundamental optoelectronic properties and
their potential applications in organic field-effect transistors
(OFETs),1 organic light-emitting diodes,2 and photovoltaic
cells.3 Most conjugated organic systems have inherently low
electron affinities and therefore behave as p-type semiconductors
and as hole-transport materials.4 Recent advances in p-type
organic semiconductors have fulfilled many of the requirements
for use in diverse applications. However, n-type materials needed
for complementary circuits present a challenge for chemists. New
n-type organic semiconductors should have a suitable electron
affinity larger than oxygen (1.46 eV),5 excellent electron-trans-
porting properties, and good solubility in organic solvents. The
long-term exploration of this subject has shown the difficulty
in fulfilling all of these desired properties simultaneously.6
One strategy to obtain air stable n-type organic semiconduc-
tors is modifying a conjugated core with strong electron-
withdrawing substituents to lower its LUMO energy level so
that the electron charge carriers are less susceptible to oxidation.7
The most frequently used side groups sofar are fluoro/fluoroalkyl8
and cyano/dicyanomethylene9 substituents. Dicyanomethylene-
substituted quinoidal oligothiophene showed superior n-type
characteristics.9a,10 Recently, Takimiya and co-workers have
Ion/Ioff
z
1ꢁ103).11 However, dicyanovinyl-substituted
compounds as electron-transport materials are rarely studied,12
especially oligomers. To date, Uhrich et al. have synthesized
dicyanovinyl-substituted oligothiophenes reaching open circuit
voltages of up to 1.04 V for solar cells (power conversion efficien-
cies of up to 1.6%).12b Here, we selected the dicyanovinyl group as
the substituent because it has the following advantages: (i) the
double bond can participate in the conjugation of the whole
p-system and lead to efficient intermolecular interactions; (ii)
the cyano groups have strong electron-accepting properties and
may be useful for electron injection as suggested for a compound
possessing pentafluorobenzene groups;8c (iii) the substituent can
be easily introduced at the aromatic ring to control the HOMO–
LUMO energy gap and the molecular packing. The fluorene
and carbazole cores were chosen because they can increase the
air stability of materials by lowering the HOMO energy level13
and are suitable materials for OFETs.14,15 Furthermore, the long
alkyl chains can be easily introduced in the 9-position of the
fluorene and carbazole rings, which may increase the solubility
of the compounds and benefit the fabrication of devices. The hexyl
side chain is optimum for charge transport due to its better
self-organization.1c,16
In this paper, we report the synthesis and characterization of
the dicyanovinyl-capped and fluorene or carbazole-based
oligomers FBCN, FTCN, CBCN and CTCN. The introduction
of benzene or thiophene rings is to extend p-conjugated systems.
To the best of our knowledge, this series of compounds has
not been reported. They would be promising electron transport
materials as n-type organic semiconductors. The target com-
pounds are characterized in detail, and their electronic properties
are studied by UV-vis/fluorescence spectroscopy and cyclic
voltammetry. The solid state structure of FTCN has been
investigated (Fig. 1).
aBeijing National Laboratory for Molecular Sciences, Organic Solids
Laboratory, Institute of Chemistry, Chinese Academy of Sciences,
Beijing 100080, China
bGraduate School of Chinese Academy of Sciences, Beijing 100080, China.
E-mail: liuyq@mail.iccas.ac.cn
† CCDC reference number 659317. For crystallographic data in CIF or
other electronic format see DOI: 10.1039/b715920j
‡ Electronic supplementary information (ESI) available: X-Ray
diffraction measurements, crystal structure and packing of FTCN,
optical properties of 7 and 8 and electrochemical measurements for
FTCN, FBCN, CBCN, CTCN, 7 and 8. See DOI: 10.1039/b715920j
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Fig. 1 Chemical structures of the target compounds.
red cuboid single crystals of FTCN by slow diffusion of 2 : 1
hexane–ethyl acetate. Unfortunately, the single crystals of other
target compounds FBCN, CBCN and CTCN have not been
obtained. An X-ray diffraction study was performed on the
crystal of FTCN to determine its solid state structure (see
ESI‡). As shown in Fig. 2, the molecular backbone is nearly
planar (excluding the hexyl groups), and has a very slight twist
along its long axis. The two dicyanovinyl end groups both
deviated only 4ꢂ from the plane. The S atoms of thiophenes
and the bridging carbon atom of the fluorene segment all face
the same side. The two substituted alkyl chains are asymmetric.
One is nearly perpendicular to the conjugate plane (ꢃ90ꢂ), and
the other is reclined to 126ꢂ with respect to the plane.
2. Results and discussion
2.1. Synthesis and characterization
The target compounds FBCN, FTCN, CBCN and CTCN were
synthesized via the Stille coupling reaction as illustrated in
Scheme 1. Two types of cores of dialkylfluorene and alkylcarba-
zole were used. The alkyl substituents would increase the solu-
bility of the target molecules in common organic solvents.
2,7-Dibromodialkylfluorene (2) was obtained by brominating
with Br2 solution directly from dialkylfluorene in high yield.
2,7-Dibromodialkylcarbazole (6) was prepared from alkylation
of 2,7-dibromocarbazole (5) in high yield, and 5 was achieved
by an efficient two-step synthesis according to the literature.17
In this study, we use 2,7-dibromocarbazole because the 2,7-
substituted carbazole is more favorable to the conjugation of
the whole system relative to a 3,6-substituted one.18 The synthetic
methods for 319 and 420 were both reported in the literature under
different reaction conditions. Here, we synthesized them under
the same conditions via a Knoevenagel reaction.21 In this reac-
tion, malononitrile was condensed under Knoevenagel conditions
(basic Al2O3 in dry toluene) with an aldehyde functionality to
form the dicyanovinyl substituent. The corresponding
compounds 3 and 4 were isolated in 71% and 72% yields. In the
next step, dibromofluorene (2) and dibromocarbazole (6) were
treated with n-BuLi and tri-n-butyltin chloride to afford the
stannylated fluorene and carbazole. The organostannane was
used directly in the next step without further purification. Stanny-
lated fluorene reacted with 2 equiv. of compound 3 or 4 to afford
the target products FBCN and FTCN in 51% and 53% yields,
respectively. Similarly, stannylated carbazole was reacted with 2
equiv. of compound 3 or 4 to afford the target products CBCN
and CTCN in 46% and 45% yields, respectively. As a general
procedure, the reaction was performed using PdCl2(PPh3)2 as
a catalyst in toluene. For comparison, 7 and 8 were prepared
under Suzuki cross-coupling conditions, and 7 has been reported
in the literature.22 Product 8 was isolated in reasonable yield
(58%). The target molecules FBCN and FTCN are soluble in
most common organic solvents, and the solubility of molecules
CBCN and CTCN are moderate and inferior to FBCN and
Another peculiar structural feature of the compound concerns
its molecular packing. The conjugate planes stack in an arrange-
ment with a honeycomb, graphite structure (Fig. S3‡). For the
fluorene–thiophene co-oligomers, such a kind of packing struc-
ture is rarely reported in the literature.13b The crystal structure
is characterized by a ‘‘layer-by-layer’’ stacking mode viewed
down the b-axis (Fig. 3), and the molecular arrangement is inter-
digitated and has parallel layers like a ‘‘bricklayer’’ structure.
The unit cell contains four layers along the c-axis. Molecules
pack in such a way that nearest neighbor molecules in the central
two layers have the fluorene ring pointing in opposite directions.
˚
The mean distance between layers is 3.5 A. The central two layers
˚
demonstrate a C–S short contact of 3.57 A, and the side two
˚
˚
layers demonstrate C–C short contacts of 3.39 A and 3.55 A.
These data are indicated with dashed lines in Fig. 3. These
distances are close to the van der Waals radii of sulfur–carbon
(3.45–3.5 A) and carbon–carbon (3.3–3.4 A) atom pairs.9b These
obviously indicate that p–p interactions exists between layers.
However, due to the steric hindrance that the two asymmetric
alkyl chains impose, the adjacent molecules between layers are
interdigitated and oriented to form a ring (Fig. S2‡). Endless
p–p stacking of the molecules’ conjugated backbones results in
infinite columns of porous structure with alkyl chains lying in
the middle of rings (Fig. S3‡). This structure resembles a honey-
comb graphite structure. Through packing of columns of rings, it
extends the p stacking of the aromatic rings, leading to efficient
electron transport in well-ordered thin films.
˚
˚
FTCN. Their structures were confirmed by HNMR, 13CNMR,
1
EI-MS, and HRMS spectrometric methods.
2.3. Optical properties
2.2. Solid state structure of compound FTCN
The electronic spectra of oligomers FBCN, FTCN, CBCN and
CTCN were recorded in a CH2Cl2 solution and as thin films
on quartz substrates (Table 1). 7 and 8 were studied under the
The solubility of compound FTCN is the best in this series of tar-
get compounds, and it can form crystals very easily. We obtained
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Scheme 1 Synthetic route to the target compounds.
same conditions to allow proper comparisons between dicyano-
vinyl-substituted and unsubstituted analogues.
The different cores (fluorene or carbazole) cannot bring obvious
shifts of the absorption maxima in solution, but the introduction
of different aromatic rings (thiophene or benzene) results in
obvious bathochromic shifts. The compound containing
thiophene segments FTCN (or CTCN) produces more than
50 nm bathochromic shift of the absorption maximum, much
larger than one containing benzene segments FBCN (or
CBCN). The results indicate that thiophene moieties enhance
the charge transfer from the electron-rich moieties to electron-
withdrawing groups. Their absorption spectra reveal similar
trends in the solid state as shown in Fig. 5. Films were easily
formed by spin coating from THF (1 mg mlꢀ1, quartz substrate).
Optical band gaps (Table 1) in solution and solid state were
approximated by extrapolation of the low-energy side of the
absorption spectra to the baseline.25 As expected, the energy
The absorption spectra of the target compounds in solution
exhibit three absorption bands, the absorption band at 289–
308 nm is assigned to the p–p* transition (Fig. 4). Compared
with 7 and 8, respectively, FTCN and CTCN exhibit a large
bathochromic shift (114 nm and 122 nm) of the absorption
maximum (Fig. S4‡), which is attributed to the dicyanovinyl
group taking part in the conjugation and the great stabilization
of the LUMO by the electron-withdrawing groups.23 Meanwhile,
the introduction of electron-withdrawing groups produces the
emergence of a new band at 400–550 nm assigned to an intra-
molecular charge transfer (ICT) between the aromatic ring
donor part and the acceptor end groups.24 The absorption bands
of FBCN and CBCN are similar to those of FTCN and CTCN.
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Fig. 4 Optical properties of the target compounds measured in CH2Cl2
solution.
Fig. 2 Crystal structure of the molecule FTCN. (Top) top view.
(Bottom) side view.
Fig. 3 View down the b-axis in crystals of FTCN, hydrogen atoms and
alkyl groups are removed for clarity and all values are in angstroms.
band gaps of compounds decrease in the order, 7 > 8 > FBCN >
CBCN > FTCN > CTCN, either in solution or in the solid state.
The fluorescence spectra of the target compounds in solution
cover the visible spectrum from yellow to orange assigned to
the pAr / p*CV ICT excited state.24b The phenomenon of
bathochromic shifts of the emission maxima is not identical to
the optical absorption. The emission maxima increase is in the
order, FBCN < FTCN < CBCN < CTCN (Table 1), and the
peak of FTCN almost overlaps with that of CBCN. Further-
more, the gradually increasing trend is more clearly observed
in the solid state (Fig. 5). The emission spectrum of FTCN
exhibits a blue shift relative to CBCN opposite to their absorp-
tion spectrum. This is clearly supported by the Stokes shifts
between the fluorescence emission and the absorption maxima.
Fig. 5 Optical properties for films of the target compounds.
The Stokes shifts of the target compounds are relatively large,
ranging from 70 to 121 nm in solution and from 88 to 148 nm
in the solid state. In both states, FTCN has the smallest Stokes
shift and CBCN has the largest one. The reason could be that
the dipole moment of CBCN is larger than that of FTCN, and
the emitting state of the former would be more stabilized by
the ICT.26 The fluorescence spectra of 7 and 8 in solution exhibit
obvious blue shifts of the emission maxima with photolumine-
scence in the blue with respect to FTCN and CTCN, consistent
with the absorption spectra (Fig. S4‡). The fluorescence spectra
Table 1 Optical data for compounds FBCN, FTCN, CBCN, CTCN, 7 and 8
Solution
Filmd
Stokes
Stokes
Compd labs /nm (logea/dm3 molꢀ1 cmꢀ1
)
llum /nm shift /nm lonseta/nm (Egc/eV) labs /nm llum /nm shift /nm lonset /nm (Egc/eV)
a
b
e
b
FBCN
FTCN
CBCN
CTCN
7
227, 296, 415(4.84)
228, 289, 467(4.86)
264, 302, 418(4.79)
264, 308, 475(4.86)
229, 353(4.59)
517
537
539
545
102
70
121
70
53
59
467 (2.65)
526 (2.36)
477 (2.60)
534 (2.32)
392 (3.16)
397 (3.12)
430
483
446
500
357
349
527
571, 719
594
635, 741
442, 467
445, 470
97
88
148
135
85
502 (2.47)
557 (2.23)
539 (2.30)
595 (2.08)
404 (3.07)
407 (3.05)
386, 406
394, 412
8
270, 353(4.64)
96
a
Measured in a dilute CH2Cl2 solution (ꢃ1ꢁ10ꢀ5 M). b Excited at the absorption maxima. c Estimated from the onset of absorption (Eg ¼ 1240/lonset).
d
e
Films were drop cast from THF (1 mg mlꢀ1, quartz substrate). Reported values are the absorption maxima.
1134 | J. Mater. Chem., 2008, 18, 1131–1138
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of FTCN and CTCN in the solid state present broader
bandwidths with respective to those in solution.
both lowered to a certain extent. Compared with unsubstituted
compounds 7 and 8, HOMO energy levels of FTCN and
CTCN are stabilized by 0.27 eV and 0.28 eV, respectively. For
the four target compounds, fluorene-based compounds display
lower HOMO energy levels with respect to carbazole-based
compounds. The HOMO energy level is mainly attributed to
the contribution of the core (fluorene or carbazole) which leads
to a stable energy level. The low HOMO levels may bring the
target compounds good air stability. In the reduction processes,
oligomers containing thiophene segments show lower LUMO
energy levels with respect to ones containing benzene segments,
indicating that thiophene segments shows larger contribution
to n-type behavior. Electrochemical band gaps (Table 2) were
calculated from the onset potentials of the anodic and cathodic
processes and coincide with the calculated optical band gaps.
Our results indicate that the target compounds would be ideal
n-type materials.
From the solution to the solid state, the absorption and
fluorescence spectra of the target compounds are red-shifted
(see Table 1), due to the presence of stronger interactions between
molecules (packing effect) in the solid state.27 As shown in the
single crystal structure (Fig. 3 and S3‡), FTCN has good p–p
stacking in the solid state. The bathochromic shift of the
UV-vis absorption observed in the solid state also can be
explained by the crystal structure of FTCN that shows the
J-aggregate conformation (Fig. 3). For the four target com-
pounds, the bathochromic shifts of the absorption and emission
maxima obviously show that the carbazole-based compounds
shift to longer wavelengths relative to the fluorene-based
compounds (Table 1). The difference in the molecular structure
gives rise to the change in spectrum. The presence of two hexyl
chains in the 9-position of the fluorene ring increases the inter-
molecular distances and thereby prevents better p stacking of
the molecules,28 which can be also confirmed by the crystal
structure of FTCN (Fig. S2‡). The alkyl effect is reduced by the
carbazole ring with one hexyl chain at the N atom, leading to
stronger p stacking of the carbazole-based molecules.27 When
comparing dicyanovinyl-substituted compounds (FTCN and
CTCN) with unsubstituted compounds (7 and 8), the absorption
maxima of 7 and 8 are nearly invariant, but the introduction of
dicyanovinyl groups strengthens intermolecular interactions in
the solid state and results in the red-shift of the absorption
maxima from the solution to solid state (Table 1).
2.5. Thermal properties
The thermal properties of the target compounds were evaluated
by thermal gravimetric analysis (TGA) and differential scanning
calorimetry (DSC). TGA revealed the onset decomposition
temperꢂatures oꢂf compounds FBCN, FTCN, CBCN and CTCN
ꢂ
ꢂ
at 374 C, 371 C, 382 C, and 372 C, respectively. The results
indicate their good thermal stability. As shown in Fig. 6, the
heating and cooling DSC scans of the target compounds show
no glass transitions up to 270–300 ꢂC, due to the dense molecular
packing.29 Carbazole-based compounds CBCN and CTCN were
both highly crystalline, exhibiting reversible thermal transitions
and only a sharp melting point at 252 ꢂC and 280 ꢂC, respec-
tively. In contrast, fluorene-based compounds behave totally
differently. FBCN exhibited a sharp melting point at 216 ꢂC
lower than CBCN in the heating segment, and formed an amor-
phous state in the cooling segment. FTCN formed an amorphous
state basically during the heating and cooling, and exhibited
a broad and weak exothermic peak around 175 ꢂC. These results
further confirm the aforementioned alkyl effect where the
molecules of carbazole-based compounds containing one hexyl
chain are packed more tightly than those of fluorene-based
compounds containing two hexyl chains. No phase transition
2.4. Electrochemical properties
In order to investigate the electrochemical behaviors of oligo-
mers FBCN, FTCN, CBCN, CTCN, 7 and 8, cyclic voltammetry
(CV) measurements were performed in CH2Cl2 containing 0.1 M
n-Bu4NPF6 as a supporting electrolyte. The electrochemical
potentials are summarized in Table 2. The CV of FBCN,
FTCN, CBCN and CTCN displayed irreversible oxidative and
reduction processes, while the CV of 7 and 8 only displayed
irreversible oxidative processes under the same experimental
conditions. Because of the introduction of the dicyanovinyl
groups, the HOMO and LUMO energy levels of molecules are
Table 2 Electrochemical properties of p-conjugated compounds
Compd Eox /V Ereda/V HOMOb/eV LUMOc/eV 6Ed/eV Egopt/eV
a
FBCN 1.76
FTCN 1.64
ꢀ1.11 ꢀ6.00
ꢀ1.08, ꢀ5.86
ꢀ1.64
ꢀ3.45
ꢀ3.56
2.55
2.30
2.65
2.36
CBCN 1.43
CTCN 1.58
ꢀ1.21 ꢀ5.79
ꢀ1.08, ꢀ5.78
ꢀ1.65
ꢀ3.46
2.33
2.20
2.60
2.32
ꢀ3.58
7
8
1.31
1.34
nde
nde
ꢀ5.63
ꢀ5.50
nde
nde
a
b
c
Calculated from the potential at peak of oxidation and reduction.
Calculated using the empirical equation: HOMO ¼ ꢀ(4.44 + Eoxonset).
d
Calculated from LUMO ¼ ꢀ(4.44 + Eredonset). Measured using
a glassy carbon electrode as a working electrode, a platinum rod as
a counter electrode, and Ag/Ag+ as a reference electrode in CH2Cl2
containing 0.1 M n-Bu4NPF6 as a supporting electrolyte at a scan rate of
100 mV sꢀ1 under an argon atmosphere. Not determined.
e
Fig. 6 DSC images of the target compounds with a heating and cooling
rate of 10 ꢂC minꢀ1 under N2.
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at low temperatures indicates the series of compounds are highly
desirable for application in devices.
4.2. Synthetic procedures
4.2.1. 4-Bromobenzylidenemalononitrile (3). 5-Bromothio-
phene-2-carboxaldehyde (1 g, 5.40 mmol), malononitrile (0.71
g, 10.80 mmol), and basic aluminum oxide (2.55 g) were stirred
in toluene (50 ml) for 8 h at 70 ꢂC. After cooling to room
temperature, the reaction solution was diluted with toluene
and filtered through a pad of silica gel, and the solvent of the
filtrate was removed in vacuo. The crude product was purified
by recrystallization from ethanol to give light yellow crystals 3
3. Conclusions
A new series of fluorene or carbazole-based and dicyanovinyl-
capped oligomers consisting of benzene or thiophene segments
FBCN, FTCN, CBCN and CTCN have been synthesized and
characterized. Optical spectra of these materials suggest that
the introduction of electron-accepting groups induces an intra-
molecular charge transfer, resulting in a shift of the absorption
onset towards longer wavelengths. Moreover, the optical spectra
of their films show intermolecular interactions, leading to bath-
ochromic shifts with respect to the spectra in solution. Coupled
with thermal properties, the molecules of carbazole-based
compounds are packed more tightly than those of fluorene-based
compounds due to the alkyl effect. The crystal structure of
FTCN also displays extended p stacking of molecules in the solid
state. In addition, this class of materials shows suitable HOMO
and LUMO energy levels, and the compounds attaching
thiophene segments show lower LUMO energy levels. They
also exhibited good thermal stability and no phase transition
at low temperature. These behaviors make them promising
candidates for n-channel semiconductors. Experiments are
underway to test this hypothesis.
1
(889 mg, 71%): HNMR (400 MHz, CDCl3): d (ppm) 7.78 (d,
J ¼ 8.62 Hz, 2 H), 7.71 (d, J ¼ 6.48 Hz, 2 H), 7.68 (s, 1 H).
13CNMR (100 MHz, CDCl3): d (ppm) 158.5, 133.2, 131.9, 130.0,
129.8, 113.6, 112.4, 83.6. EI-MS: m/z (%) ¼ 232 (M+, 100%).
4.2.2. 5-Bromo-2-dicyanovinylthiophene (4). This compound
was prepared from 4-bromobenzaldehyde according to the
1
procedure for 3 to give yellow crystals 4 in 72% yield: HNMR
(400 MHz, CDCl3): d (ppm) 7.74 (s, 1 H), 7.50 (d, J ¼ 4.08
Hz, 1 H), 7.24 (d, J ¼ 4.16 Hz, 1 H). 13CNMR (100 MHz,
CDCl3): d (ppm) 150.1, 138.9, 136.9, 132.1, 126.6, 113.6, 113.0,
78.7. EI-MS: m/z (%) ¼ 240 (M+, 100%).
4.2.3. General procedure for the Stille coupling reactions.
2.5 M n-BuLi (1.6 ml, 4.00 mmol) was added dropwise to a solu-
tion of 2 (or 6) (885 mg, 1.80 mmol) in anhydrous THF (40 ml) at
ꢂ
ꢀ78 C under nitrogen with stirring. A deep pink precipitation
was formed. After stirring for 1 h at ꢀ78 ꢂC, tri-n-butyltin
chloride (1.1 ml, 4.06 mmol) was added. The reaction mixture
was then warmed to room temperature and stirred overnight.
The clear solution was diluted with diethyl ether and washed
with aqueous sodium bicarbonate solution (5%), and water.
The organic layer was dried over MgSO4, and the solvents
were concentrated on a rotavap.
4. Experimental
4.1. General procedures
Chemicals were purchased from Aldrich, Alfa Aesar and used as
received. Solvents and other common reagents were obtained
from the Beijing Chemical Plant. THF and Toluene were dried
and distilled immediately prior to use. 1HNMR (400 MHz)
and 13CNMR (75 and 100 MHz) spectra were obtained on
a Bruker DMX-300 and DMX-400 NMR Spectrometer using
tetramethylsilane as the internal standard. High-resolution
mass spectra (HRMS) and EI MS were both recorded on a
Micromass GCT-MS spectrometer. Electronic absorption
spectra were measured on a Jasco V570 UV-vis spectrophoto-
meter. Emission spectra were recorded on a Hitachi F-4500
fluorescence spectrometer. TGA measurements were carried
out on a TA SDT 2960 instrument under a dry nitrogen flow,
The above residue (1.48 g, 1.62 mmol), 3 (or 4) (902 mg,
3.89 mmol), and PdCl2(PPh3)2 (137 mg, 0.20 mmol) mixed in
anhydrous toluene (40 ml) were heated at reflux under nitrogen
for 36 h. The reaction mixture was allowed to cool to room
temperature, poured into aqueous KF solution, and stirred at
room temperature for 3 h. The resulting suspension was diluted
with CH2Cl2 and filtered to remove polymeric tributyltin
fluoride. The organic phase was separated, and the aqueous
phase was extracted with CH2Cl2. The combined organic phase
was washed with brine, dried with MgSO4, and concentrated.
2,7-Bis[4-(1,1-dicyanovinyl)benzyl]-9,9-di-n-hexylfluorene
(FBCN)
ꢂ
heating from room temperature (RT) to 500 C, with a heating
rate of 10 ꢂC minꢀ1. DSC analyses were performed on a TA
DSC 2010 instrument under a dry N2 flow, heating from ꢀ85
ꢂC to 270–300 ꢂC and cooling from 270–300 ꢂC to ꢀ85 ꢂC at
The crude product was separated by chromatography on silica
gel (toluene) to give FBCN (527 mg, 51%). An analytical sample
was purified by recrystallization from acetonitrile to give golden
crystals: 1HNMR (400 MHz, CDCl3): d (ppm) 8.04 (s, 2 H,
CH]C(CN)2), 8.02 (s, 2 H, Ph–H), 7.86–7.81 (m, 8 H, Ph–H),
7.69 (dd, J ¼ 7.88 Hz, J ¼ 1.54 Hz, 2 H, Ph–H), 7.63 (d, J ¼
1.30 Hz, 2 H, Ph–H), 2.09–2.00 (m, 4 H, CH2), 1.13–1.01 (m,
12 H, CH2), 0.75 (t, J ¼ 6.96 Hz, 6 H, CH3), 0.70–0.66 (m, 4
H, CH2). 13CNMR (75 MHz, CDCl3): d (ppm) 159.2, 152.4,
147.7, 141.4, 138.4, 131.6, 129.9, 128.2, 126.7, 121.7, 120.9,
114.1, 113.0, 82.0, 55.7, 40.4, 31.5, 29.7, 23.9, 22.6, 14.1.
EI-MS: m/z (%) ¼ 638 (M+, 100%). HRMS (EI): calcd for
C45H42N4, 638.3409; found 638.3416.
a rate of 10 C minꢀ1. Cyclic voltammetric measurements were
ꢂ
carried out in a conventional three-electrode cell using Pt button
working electrodes of 2 mm diameter, a platinum wire counter
electrode, and a Ag/AgCl reference electrode on a computer-
controlled CHI660C instruments at RT. X-Ray diffraction
(XRD) measurements were carried out in the reflection mode
at RT using a Rigaku MM-007 X-ray diffraction system
˚
(Mo Ka radiation, l ¼ 0.71073 A). 9,9-Bis-n-hexylfluorene
(1),30 2,7-dibromo-9,9-bis-n-hexylfluorene (2),30 2,7-dibromo-
carbazole (5),17 2,7-dibromo-9-(2-hexyl)carbazole (6),15a and
2,7-Bis(thiophene-2-yl)-9,9-bis-n-hexylfluorene (7)22 were synthe-
sized according to literature or slightly modified procedures.
1136 | J. Mater. Chem., 2008, 18, 1131–1138
This journal is ª The Royal Society of Chemistry 2008

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2,7-Bis[5-(1,1-dicyanovinyl)thiophen-2-yl]-9,9-di-n-
hexylfluorene (FTCN)
Hz, 2 H), 7.32 (d, J ¼ 5.01 Hz, 2 H), 7.14 (dd, J ¼ 4.83 Hz, J ¼
3.74 Hz, 2 H), 4.35 (t, J ¼ 7.23 Hz, 2 H), 1.94–1.88 (m, 2 H),
1.48–1.28 (m, 6 H), 0.88 (t, J ¼ 7.01 Hz. 3 H). 13CNMR (100
MHz, CDCl3): d (ppm) 145.8, 141.6, 132.3, 128.2, 124.7, 123.2,
122.4, 120.8, 118.0, 106.1, 43.1, 31.7, 29.1, 27.1, 22.7, 14.2.
EI-MS: m/z (%) ¼ 415 (M+, 100%). HRMS (EI): calcd. for
C26H25NS2, 415.1428; found 415.1430.
The crude product was separated by chromatography on silica
gel (toluene) to give FTCN (558 mg, 53%). An analytical sample
was purified by recrystallization from acetonitrile to give red
crystals: 1HNMR (400 MHz, CDCl3): d (ppm) 7.81 [s, 2 H,
CH]C(CN)2], 7.78 (s, 2 H, Ph–H), 7.76–7.72 (m, 4 H, Ph–H),
7.64 (d, J ¼ 1.27 Hz, 2 H, Ar–H), 7.54 (d, J ¼ 4.08 Hz, 2 H,
Ar–H), 2.10–2.04 (m, 4 H, CH2), 1.13–1.00 (m, 12 H, CH2),
0.74 (t, J ¼ 6.98 Hz, 6 H, CH3), 0.65–0.61 (m, 4 H, CH2).
13CNMR (75 MHz, CDCl3): d (ppm) 157.4, 153.0, 151.0, 142.6,
140.7, 134.6, 132.2, 126.6, 125.2, 121.5, 121.2, 114.7, 113.9,
56.2, 40.6, 31.8, 29.9, 24.2, 22.9, 14.4. EI-MS: m/z (%) ¼ 650
(M+, 100%). HRMS (EI): calcd. for C41H38N4S2, 650.2538;
found 650.2544.
5. Acknowledgements
The present research was financially supported by the National
Natural Science Foundation (20421101, 60671047, 50673093,
60736004), the Major State Basic Research Development
Program (2006CB806203, 2006CB932103) and the Chinese
Academy of Sciences.
2,7-Bis[4-(1,1-dicyanovinyl)benzyl]-9-(2-hexyl)carbazole
(CBCN)
6. References
The crude product was separated by chromatography on silica
gel (1 : 1 toluene–CH2Cl2) to give CBCN (414 mg, 46%). An
analytical sample was purified by recrystallization from aceto-
nitrile to give orange crystals: 1HNMR (400 MHz, CDCl3):
d (ppm) 8.23 [dd, J ¼ 8.01 Hz, J ¼ 4.16 Hz, 2 H, CH]C(CN)2],
8.06 (d, J ¼ 8.34 Hz, 4 H, Ph–H), 7.93–7.90 (m, 4 H, Ph–H),
7.81–7.72 (m, 2 H, Ph–H), 7.65–7.63 (m, 2 H), 7.56 (dd, J ¼
8.16 Hz, J ¼ 0.78 Hz, 2 H, Ph–H), 4.47–4.41 (m, 2 H, CH2),
2.00–1.93 (m, 2 H, CH2), 1.46–1.27 (m, 6 H, CH2), 0.89–0.85
(m, 3 H, CH3). 13CNMR (100 MHz, CDCl3): d (ppm) 159.2,
148.3, 141.9, 137.3, 131.6, 129.8, 128.5, 123.1, 121.5, 119.0,
114.1, 113.0, 107.7, 82.0, 43.4, 31.7, 29.2, 27.1, 22.7, 14.1.
EI-MS: m/z (%) ¼ 555 (M+, 100%). HRMS (EI): calcd. for
C38H29N5, 555.2423; found 555.2431.
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nitrile to give deep red crystals: HNMR (400 MHz, CDCl3):
d (ppm) 8.15 (d, J ¼ 8.16 Hz, 2 H, CH]C(CN)2), 7.83 (s, 2 H,
Ph–H), 7.78 (d, J ¼ 4.02 Hz, 2 H, Ph–H), 7.69 (s, 2 H, Ph–H),
7.62 (d, J ¼ 8.11 Hz, 2 H, Ar–H), 7.58 (d, J ¼ 4.06 Hz, 2 H,
Ar–H), 4.42 (t, J ¼ 7.09 Hz, 2 H, CH2), 1.96–1.92 (m, 2 H,
CH2), 1.46–1.26 (m, 6 H, CH2), 0.87 (t, J ¼ 6.96 Hz, 3 H,
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567.1551; found 567.1558.
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1138 | J. Mater. Chem., 2008, 18, 1131–1138
This journal is ª The Royal Society of Chemistry 2008