New 9-fluorene-type trispirocyclic compounds for thermally stable hole transport materials in OLEDs

Article abstract of DOI:10.1039/b502268a

A novel trispirocyclic hydrocarbon having three 9-fluorene moieties around the core of truxene (5) was prepared readily via coupling of truxenone with 2-bromobiphenyl; 5 was a high melting (>500°C) solid. For the application of 5 to an effective hole tran

Full text of DOI:10.1039/b502268a

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/materials | Journal of Materials Chemistry
New 9-fluorene-type trispirocyclic compounds for thermally stable hole
transport materials in OLEDs
Makoto Kimura,*a Seiichi Kuwano,a Yasuhiko Sawaki,a Hisayoshi Fujikawa,b Koji Noda,b Yasunori Taga*b
and Katsuhiko Takagi*a
Received 14th February 2005, Accepted 19th April 2005
First published as an Advance Article on the web 4th May 2005
DOI: 10.1039/b502268a
A novel trispirocyclic hydrocarbon having three 9-fluorene moieties around the core of truxene (5)
was prepared readily via coupling of truxenone with 2-bromobiphenyl; 5 was a high melting
(.500 uC) solid. For the application of 5 to an effective hole transport material (HTM) in the
OLED, a triphenylamine derivative carrying six diphenylamino groups at the 2- and 7-positions
of each 9-fluorene moiety (6) was designed in order to get high thermal stability as an improved
material of the TPD type HTM. The synthesis of 6 was easily achieved using
4,49-bis(diphenylamino)-2-bromobiphenyl (9). The trispirocyclic 6 was found to show a glass
transition temperature as high as 170 uC. It effects the formation of its stable cation radical upon
electrooxidation in solution, and amorphous thin films in solid. A multi-layered EL device for 6 as
an HTM using Alq3 as an electron transporting emitter showed good EL characteristics such as
the maximum luminance of 37 000 cd m22 at 14 V. Thus, the hexakis(diphenylamino)substituted
trispirocycle 6 (TX-F6S) can be used as an efficient and thermally stable HTM in OLEDs.
extended into materials chemistry.27–29 Since spirobi-9-fluor-
Introduction
ene looking like double fluorene has been used as the thermally
stable framework of various materials30–34 including HTMs
Highly thermally durable and amorphous thin-film materials
have recently been actively developed in organic light emitting
diodes (OLEDs) with the aim of long-life and full-color flat
panel displays.1–4 Since Tang’s pioneering work, typical multi-
layered devices involving appropriate organic substances have
been fabricated on a transparent anode, like an indium tin
oxide (ITO) glass substrate, by successive vapor deposition of
a hole transport material (HTM), a light emitting and electron
transport material (that is, tris(8-quinolinolato) aluminium(III)
(Alq3)) and finally a metallic cathode.5 Various triphenyl-
amine derivatives have been prepared for the effective HTM,
for example: (1) diamine TCTA,5 (2) N,N,N9,N9-tetraphenyl-
benzidine family such as TPD6 (1, Fig. 1), a-NPD or NPB7 (2),
CPB8 etc.,9 (3) Shirota’s starburst molecules with various
core1,10,11 and shells,12 (4) linear oligomeric amines,13 (5) spiro-
linked or spirocyclic benzidines,14,15 (6) 9,9-diphenylfluor-
enes,16,17 (7) tetrahedral aromatic amines18,19 and (8) others
including dibenzo[g,p]chrysene20 and indolocarvazoles,21 and
so on.22
A representative HTM, i.e., TPD 1, is known to effect quite
excellent elcctroluminescence (EL). However, 1 has a problem
with thermal stability as shown by its low glass transition
temperature (Tg) of 62 uC.23 Therefore, the modified a-NPD 2
possessing a higher Tg of 95 uC24 is used as the incipient
commercial HTM in mono-color displays. On the other hand,
the 9-fluorene framework has recently been utilized in OLED
materials as the molecular core14–17 or shell12 as well as
numerous macromolecular poly(9-fluorenes).25 Truxene (3)26
has a structure of threefold 9-fluorene (see Fig. 1). It is only
recently that the chemistry of the old known 3 has been
Fig. 1 Chemical structures of compounds for 1–6 and 13.
J. Mater. Chem., 2005, 15, 2393–2398 | 2393
*ktakagi@apchem.nagoya-u.ac.jp (Makoto Kimura)
This journal is ß The Royal Society of Chemistry 2005

View Article Online
(for example 4),14,15 a new trispirocyclic hydrocarbon 5 can be
designed as the threefold spirobifluorene. Its hexakis(diphenyl-
amino) substituted derivative 6 can be expected not only to
retain the excellence in EL characteristics due to the TPD
moiety, but also to exhibit an enhanced Tg leading to thermal
stability in devices over the previous spirobifluorene deriva-
tive.14 We report here the preparation of hydrocarbon 5 and its
HTM derivative 6. Thermal and electrochemical properties of
6 are also described. Conventional devices using 6 as an HTM
were fabricated and EL characteristics of 6 (named here as TX-
F6S) were obtained in detail.
Scheme 2
Results and discussion
since the monoketonic dispirocyclic compound was isolated as
major side product.
Synthesis
The method for the preparation of threefold spirobifluorene 5
is the use of truxenone (7, truxenequinone)29 and its coupling
with 2-lithiobiphenyl, followed by acid-catalyzed cyclization of
the resulting alcohol to a spirocycle (Scheme 1). The coupling
of 7 with 2-bromobiphenyl took place smoothly in THF using
toluene as co-solvent. The resulting triol 8 was probably a
mixture of two isomers (a,a,a- and a,a,b-), and underwent the
expected spirocyclization quantitatively. The aromatic hydro-
carbon 535,36 was a colorless solid, sparingly soluble in common
organic solvents, and did not melt up to 500 uC.
For the synthesis of 6, 4,49-hexakis(diphenylamino) sub-
stituted 2-bromobiphenyl compound 9 was prepared in several
steps (Scheme 2). 2-Aminobiphenyl turned out as a good
starting material for the key material synthesis of 9. Classical
nitration of it fortunately gave rise to di-functionalization
at the 4- and 49-positions cleanly; attempts to brominate
selectively appropriate biphenyl compounds as the starting
materials were in vain to give inseparable mixtures. The
product 2-amino-4,49-dinitrobiphenyl (10)37 was easily purified
by recrystallization, and obtained in a good yield, in turn being
converted into dinitrobromide 11.38 Reduction of dinitro
compound 11 with iron powder and hydrochloric acid gave
2-bromobenzidine (12). Desired 9 was obtained after reaction
of 12 with an excessive amount of iodobenzene under the tri-
tert-butylphosphine palladium catalysis.15
Properties
The hexakis(diphenylamino)substituted trispirocycle 6 being
of molecular weight of 1796 g mol21 is a high melting colorless
solid, mp 427–430 uC. Differential scanning calorimetry (DSC)
analysis showed that the Tg of 6 was as high as 170 uC; the
value considerably exceeds Tg’s of common polymers such as
poly(methyl methacrylate) (125 uC) and poly(Bisphenol A
carbonate) (149 uC). The Tg’s of monospiro-bifluorene
analogues like 4 are reported to be 111–133 uC.14,15 In the
study on the oligomeric triphenylamine series, it is shown that
the Tg of HTM increases with increasing molecular weights;
for instance, the TPTE (13, see Fig. 1) as a linear dimeric
derivative of TPD has 140 uC of Tg.13 Thus, the higher Tg of
trispirocycle 6 can be ascribed to an effect of its high molecular
weight. Moreover, we propose that a contribution of the high
melting nature of 6 is derived from that of the parent
hydrocarbon 5. Since light-emitting Alq3 is known to have
175 uC of Tg,23,41 the trispirocycle 6 can be compatible with
Alq3 when they are used in a device working at such high
temperatures without crystallization causing dark spots.
The hexakis(diphenylamino) substituted 6 can form trans-
parent and glassy thin films, judging from an X-ray diffraction
(XRD) analysis. Although a powder sample of 6 showed
several peaks indicative of a poly-crystalline structure, the
film obtained by evaporating chloroform showed only a
hollow curve. As for the molecular structure of 6, six bulky
diphenylamino groups attached at the fringes of 9-fluorene
moieties can undergo free rotation in three dimensions,
apart from the rigid trispirocyclic core. Accordingly, such an
arrangement of diphenylamino groups can contribute to the
glassy nature, whereas the rigid core of trispirocycle establishes
a high Tg.
The coupling component 9 was lithiated with t-BuLi in ether
and then allowed to react with less than one-third equiv of tri-
ketone 7. The resulting crude triol was treated with methane-
sulfonic acid as catalyst to afford the desired trispirocyclic
compound 4 albeit in 23% yield. Such a low yield is pre-
sumably due to the low solubility of the intermediary product,
UV and visible absorption spectra of 6 in chloroform
were recorded using N,N,N9,N9-tetraphenylbenzidine and 2,7-
bis(diphenylamino)-9-fluorene as the standard compounds.
The latter two samples showed their absorption maxima at 354
and 362 nm with extinction coefficients e of 4.1 6 104 and
4.3 6 104, respectively. On the other hand, trispirocycle 6
exhibited two absorption maxima at 365 (e 5 9.6 6 104) and
380 (e 5 9.3 6 104) nm, being not simply a triplicate of the
monomeric fluorene derivative. One reason for such absorp-
tion of 6 may result from possible contribution of the spiro-
conjugation.42 For the application to device design, the
Scheme 1
2394 | J. Mater. Chem., 2005, 15, 2393–2398
This journal is ß The Royal Society of Chemistry 2005

View Article Online
HOMO–LUMO energy band gap of 6 can be roughly
estimated to be smaller by 0.2–0.3 eV than that of TPD on
the basis of their absorption onsets. Cyclic voltammetry (CV)
of 6 was carried out in dichloromethane using tetrabutyl-
ammonium perchlorate as an electrolyte (Fig. 2). Notably,
three reversible waves for 6 were observed, being in contrast to
the result of popular two waves for TPD. This may be due to
possible interaction among free rotating diphenylamino
groups present at each fluorene shell. The standard TPD
shows two peaks at 0.63 (oxidation potential, the average of
anodic and cathodic peak potentials) and 0.91 (anodic peak
potential) V vs. Ag–AgCl electrode, suggesting a successive
formation of the cation radical and then dication species of
TPD molecule. In the case of 6, the first, second and third peak
oxidation peaks appeared at 0.60 (oxidation potential), 0.88
(peak potential) and 1.07 (peak potential) V vs. Ag–AgCl, in
Fig. 2, appeared at 420, 650 and 860 mV, respectively. From
the first peak, the oxidation potentials of 6 can be regarded
as almost equal to that of TPD. The stability of the hole,
Fig. 3 Luminance–applied voltage characteristics of 6 (#) and TPTE
(m). As for the device structure, ITO/HTM (6 or TPTE) 60 nm/Alq3
60 nm/LiF 0.5 nm–Al 150 nm.
i.e., cation radicals generated, can be deduced by the ratio
43
of cathodic and anodic peak current ipc/ipa
.
In fact, the
6 and TPD,
measured ratios were 0.92 and 0.95 for
respectively. These results indicate that 6 can form stable
cation radicals in its tetraphenylbenzidine moieties like TPD.
In case of the device design,44 the HOMO level of 6 is nearly
the same as that of TPD family compounds. On the basis of
the results of the absorption spectra and electrochemical CV, 6
may undergo a sort of space interaction among three
electrophores, i.e., TPD moieties at its activated state.
Generally, the present HTM 6 shows excellent EL charac-
teristics, being equivalent to those of TPTE. In the luminance-
applied voltage characteristics (Fig. 3), the emission for both 6
and TPTE starts at a voltage lower than 3 V, passes through
the practical use level of 200–300 cd m22 at about 5 V, and
finally reaches the maximum of 37 000 cd m22 at 14 V. The
current density–voltage characteristics in Fig. 4 show that the
present 6 has almost the same or slightly better efficiency in
hole injection and transport ability as compared with TPTE.
The luminance–current density characteristics in Fig. 5 show
a similar situation; the photometric efficiencies of 6 and
TPTE were 3.4 and 3.3 cd A21, respectively. These values are
remarkably high among fluorescence-based devices using Alq3
as electron transporting emitter. This new HTM 6 (TX-F6S)
EL devices
A conventional multi-layered device for 6 (nicknamed TX-
F6S) was fabricated by successive vapor deposition onto an
ITO transparent glass substrate in the order of ITO cathode/
HTM 6 60 nm/Alq3 60 nm/LiF 0.5 nm–Al 150 nm. Upon
application of direct current voltage, the device emitted green
light due to Alq3 with a peak wavelength around 530 nm.
Figs. 3–6 show various EL characteristics of 6 including those
of the former developed TPTE (13)13 for comparison.
Fig. 2 Cyclic voltammogram of trispirocycle 6 measured in CH2Cl2
containing Bu4ClO4. The potential is recoded here vs. the ferrocene
electrode after corrected potentials.
Fig. 4 Current density–applied voltage characteristics of 6 (#) and
TPTE (m). The device structure is shown in the caption of Fig. 3.
This journal is ß The Royal Society of Chemistry 2005
J. Mater. Chem., 2005, 15, 2393–2398 | 2395

View Article Online
Recently, Shirota et al. have illustrated that the Tg of HTM
can be enhanced by the introduction of rigid groups like
9,9-dimethylfluorene into starburst molecules around those
shell parts.12 The reverse approach is our design using rigid
spiro-linked molecules in the core. The thermal stability
represented by high Tg is emphasized in our case, whereas
glassy materials are stressed in Shirota’s study. The glassy
nature of 6 can be ascribed to the presence of six free rotating
diphenylamino groups attached on the three-dimensional core
hydrocarbon.
In conclusion, a unique trispirocyclic hydrocarbon C63H36
as a threefold molecule of spirobi-9H-fluorene was prepared
favorably from truxenone and 2-bromobiphenyl. We prepared
its hexakis(diphenylamino) substituted derivative 6 (TX-F6S)
by employing the requisite 2-bromobiphenyl derivative as
the coupling and spirocyclizing agent. The amine 6 exhibited
a high Tg of 170 uC. According to our molecular design, this
allows 6 to be used as a thermally durable HTM in com-
bination with Alq3 at high temperatures. The EL character-
istics of 6 as HTM proved to be like or better than the
representative TPD. Therefore, the trispirocyclic amine 6 can
be applied to advanced full-color EL displays.
Fig. 5 Luminance–current density characteristics of 6 (#) and (m)
TPTE. See Fig. 3.
Experimental
General
Commercially available reagents including dry solvents were
used as received. NMR spectra were recorded on a 200 MHz
spectrometer using TMS as an internal standard. XRD data
were collected on a Rigaku Rint 2100 model using Cu Ka
radiation with 60 kV and 50 mA. CV measurements were
carried out on a BAS-50w electrochemical analyzer with 10 mL
of dichloromethane solutions (0.01 M) containing tetrabutyl-
ammonium perchlorate (0.1 M) under nitrogen atmosphere.
The scan rate was 0.2 V s21. The electrode potential was
corrected using ferrocene as a standard (Fig. 2).
Materials
Trispirocyclic hydrocarbon 5. A solution of t-butyllithium in
hexane (1.6 M, 11.3 mL, 18 mmol) was added dropwise into a
cooled solution of 2-bromobiphenyl (2.1 g, 9 mmol) in ether
(6 mL) at 210 uC with stirring. The reaction mixture was
kept stirring for 2 h. Then a mixture of truxenone29 (0.768 g,
2 mmol), prepared previously from indane-1,3-dione in conc.
sulfuric acid, and toluene (10 mL) was treated with the
resultant solution of 2-lithiobiphenyl at room temperature for
1 h. The reaction mixture was poured into water (50 mL) and
benzene (80 mL) and neutralized with dilute hydrochloric
acid. Extraction with benzene and subsequent work-up gave a
brownish solid of the resulting triols. To the material acetic
acid (25 mL) and methanesulfonic acid (60 mg) as catalyst
were added and then heated at 90 uC for 1 h. After cooling,
the precipitated solid was filtered and washed repeatedly with
acetic acid , water, methanol and benzene. There was obtained
pale-yellow powder of 5 (0.92 g, 58%), sufficiently pure; mp .
Fig. 6 Life times for devices of 6 (#) and TPTE (m). The relative
luminance L/L0 is plotted, initial luminance L0 being 3100 cd m22
.
was examined with respect to the lifetime (Fig. 5). The half
luminance of 6 was several tens of times longer than that of
TPTE in an accelerated examination. At the practical use level
of 200–300 cd m22, the value of 6 can be regarded to work
about several hundred to thousand hours.20 Since over ten
thousand hours is necessary for full-color displays, the value
is still insufficient. But, suitable design for thin-film con-
figuration should enhance the durability. Hence, the new
trispirocyclic HTM 6 can give better performance in device
driving than the previously developed TPTE.
The present results provide a clue how to design the HTM
molecule possessing a high Tg. A decade ago, the amorphous
thin film was associated with a symmetric globular structure
with large molecular weight and small intermolecular cohe-
sion.23 The statement fairly falls in the tetrahedral-type
HTM.18,19 The design also holds true in the HTM 6.
1
500 uC, H NMR (CDCl3) d 6.35 (d, J 5 7 Hz, 3H), 6.52 (d,
J 5 7 Hz, 3H), 6.60 (t-like, J 5 7 Hz, 3H), 6.73 (t, J 5 7 Hz,
3H), 6.85 (d, J 5 7 Hz, 6H), 7.18 (t-like, J 5 7 Hz, 6H), 7.40
2396 | J. Mater. Chem., 2005, 15, 2393–2398
This journal is ß The Royal Society of Chemistry 2005

View Article Online
(t, J 5 7 Hz, 6H), 7.91 (d, J 5 2 Hz, 6H). FAB-MS m/z 5
792.61 (M+). HR-MS for C63H36 (+H), calced, 793.2886,
found 793.2915.
Devices
An ITO-coated glass substrate was treated by r.f. plasma of
argon and oxygen gas for 60 s at a pressure of 2 6 1022 Torr
for cleaning of the surface. A hole transport layer of 60 nm and
then an Alq3 layer of 60 nm were formed under a vacuum of
5 6 1027 Torr onto the ITO anode substrate. Finally, a 0.5 nm
thick LiF layer and a 150 nm thick Al layer were deposited as
the cathode. The emission area of the device was 0.09 cm2.
The luminance–current–voltage characteristics (Fig. 3–6)
were measured using a source meter (Keithley 2400) and a
luminance meter (Minolta LS-110).
Spirocycle-coupling component 9. 2-Amino 4,49-dinitro-
biphenyl (10) was prepared according to literature37 mp 207–
209 uC (lit.37 206 uC). This amine was converted by the
Sandmeyer reaction to 2-bromo-4,49-dinitrobiphenly (11)38 in
73% yield, mp 144–146 uC (lit. 148–149 uC).
Reduction of dinitro compound 11 to diamine 12 as follows:
To a solution of 11 (4.83 g, 15 mmol) in THF (50 mL) and
ethanol (40 mL) and conc. HCl (90 mL), iron powder (55.9 g,
0.24 g-atm) was added in small portions for 2 h. The mixture
was allowed to react at 75 uC overnight. After cooling and
concentration, water and benzene were added and phases were
separated. When the aqueous layer was made alkaline, the
resulting insoluble material was filtered off and washed with
benzene. The collected benzene layer was dried and removal of
the solvent gave a viscous liquid of crude 12,39 2.4 g, 61%,
being deteriorated on standing.
Acknowledgements
This study was supported financially in part by a Grant-in-Aid
for Scientific Research on Basic Research and Priority Areas
(417) from The Ministry of Education, Culture, Sports,
Science and Technology of Japan. We are grateful to Dr
S. Tokito, now NHK Broadcasting Corporation, for his
contribution to the EL device performance.
A mixture of 2- bromobenzidine (12 2.67 g, 10 mmol),
sodium t-butoxide (4.8 g, 50 mmol), iodobenzene (26.5 g,
0.13 mol) and o-xylene (12 mL), to which a solution of
palladium acetate and tri-t-butylphosphine40 (1 : 4 mol ratio,
Pd cat. 0.05 mmol) was added under nitrogen atmosphere, was
heated to reflux at 120 uC and kept stirring for 20 h. The
reaction mixture was poured onto ice water and acidified with
dilute hydrochloric acid. Extractive work-up with chloroform
and solvent evaporation gave a brown residue. Isolation of 9
after column chromatography on silica gel using benzene–
hexane (1 : 2) as eluent, followed by recrystallization from
benzene, gave white crystals (4.01 g, 71% yield), mp 191–2 uC,
Makoto Kimura,*a Seiichi Kuwano,a Yasuhiko Sawaki,a
Hisayoshi Fujikawa,b Koji Noda,b Yasunori Taga*b and
Katsuhiko Takagi*a
aDepartment of Applied Chemistry and Crystalline Materials Science,
Graduate School of Engineering, Nagoya University, Chikusa, Nagoya,
464-8603, Japan. E-mail: ktakagi@apchem.nagoya-u.ac.jp
bToyota Central Research and Development Laboratories, Inc.,
Nagakute, Aichi, 480-1192, Japan
References
1 Y. Shirota, J. Mater. Chem., 2000, 10, 1.
2 U. Mitschke and P. Bauerle, J. Mater. Chem., 2000, 10, 1471.
3 P. Strohriegel and J. V. Grazulcicius, Adv. Mater., 2002, 14, 1439.
4 J. Kido and Y. Okamoto, Chem. Rev., 2002, 102, 2357.
5 C. W. Tang and S. A. VanSlyke, Appl. Phys. Lett., 1987, 51, 913.
6 C. Adachi, S. Tokito, T. Tsutsui and S. Saito, Jpn. J. Appl. Phys.,
1988, 27, L269; C. Adachi, K. Nagai and N. Tamoto, Appl. Phys.
Lett., 1995, 66, 2679.
m/e 567 and 569 (M + 1), 1H NMR (CDCl3), d 6.9–7.5 (m), 13
C
NMR, 122.01, 122.62, 122.91, 123.14, 123.67, 124.79, 124.92,
127.11, 129.44, 129.61, 130.42, 131.62, 134.70, 135.78, 137.66,
147.14, 147.38, 148.87, 147.97. Anal. calcd for C36H27BrN, C
76.19, H 4.99, N 4.94. Found, C 76.63, H 4.93, N 4.28.
7 S. A. Van Slyke, C. H. Chen and C. W. Tang, Appl. Phys. Lett.,
1996, 69, 2160.
Hexakis(diphenylamino) substituted spirocycle 6 (TX-F6S).
To a solution of ortho-bromide 9 (3.1 g, 5.5 mmol) in ether
(30 mL) was added a hexane solution of t-butyllithium (1.6 M,
6.9 mL, 11 mmol) at 210 uC under nitrogen, and the mixture
was kept stirring for 3 h. A suspension of truxenone (0.58 g,
1.5 mmol) in toluene (15 mL) was added and the reaction
mixture was allowed to react for 1 h at room temperature. The
resulting orange red solution was diluted with benzene and
acidified with dilute hydrochloric acid. Usual workup gave the
adduct triol as an orange–red glassy solid. This material was
admixed with acetic acid (25 mL) containing methanesulfonic
acid (0.5 mL) and heated at 100 uC for 2 h. After extractive
workup using chloroform, an orange-colored solid was
obtained. Careful addition of acetonitrile to the chloroform
solution caused precipitation of pale yellow crystals of 6,
mp 427–430 uC. The analytical sample depended on further
8 M. A. Baldo, S. Lamansky, P. E. Burrowa, M. E. Thomoson and
S. R. Forrest, Appl. Phys. Lett., 1999, 75, 4.
9 D. E. Loy, B. E. Koene and M. E. Thompson, Adv. Funct. Mater.,
2002, 12, 245.
10 J. Louie, J. F. Hartwig and A. J. Fry, J. Am. Chem. Soc., 1997, 119,
11695.
11 J.-P. Chen, H. Tanabe, X.-C. Li, T. Thomas, Y. Okamura and
K. Ueno, Synth. Met., 2003, 132, 173.
12 K. Okumoto and Y. Shirota, Chem. Lett., 2000, 1034; Y. Shirota,
M. Kinoshita, T. Noda, K. Okumoto and T. Ohara, J. Am. Chem.
Soc., 2000, 122, 11021.
13 H. Tanaka, S. Tokito, Y. Taga and A. Okada, Chem. Commun.,
1996, 2175; S. Tokito, H. Tanaka, A. Okada and Y. Taga, Appl.
Phys. Lett., 1996, 69, 878.
14 N. Johansson, J. Salbeck, J. Bauer, F. Weissoertel, P. Broems,
A. Anderson and W. R. Salaneck, Adv. Mater., 1998, 10, 1136;
J. Salbeck, N. Yu, J. Bauer, F. Weissoertel and H. Bestgen, Synth.
Met., 1997, 91, 209; J. Salbeck, F. Weissoertel and J. Bauer,
Macromol. Symp., 1997, 125, 121.
15 M. Kimura, S. Inoue, K. Shimada, S. Tokito, N. Noda, Y. Taga
and Y. Sawaki, Chem. Lett., 2000, 192.
purification by vacuum sublimation. FAB-MS m/z
5
1796 (M+), 13C NMR 119.60, 120.30, 121.94, 124.88, 126.29,
126.85, 128.32, 137.61, 138.80, 140.89, 148.72. Anal. calcd for
C135H90N6, C 90.27, H 5.05, N 4.68. Found, C 90.61, H 4.91,
N 4.48.
16 S. Okutsu, T. Onikubo, M. Tamano and T. Enokida, IEEE Trans.
Electron Devices, 1997, 44, 1302.
17 K.-T. Wong, Z.-J. Wang, Y.-Y. Chien and C.-L. Wang, Org. Lett.,
2001, 3, 2285; C. Ego, A. C. Grimsdale, F. Uckert, G. Yu,
G. Sradanov and K. Muellen, Adv. Mater., 2002, 14, 809.
This journal is ß The Royal Society of Chemistry 2005
J. Mater. Chem., 2005, 15, 2393–2398 | 2397

View Article Online
18 H. Zhao, C. Tanjuto and S. Thayumanavan, Tetrahedron
Lett., 2001, 42, 4421; See also, S. Wang, W. J. Oldham, Jr.,
R. A. Hudack, Jr. and G. C. Bazan, J. Am. Chem. Soc., 2000, 122,
5695.
19 L.-H. Chen, R.-H. Lee, C.-F. Hieh, H.-C. Yeh and C.-T. Chen,
J. Am. Chem. Soc., 2002, 124, 6419.
20 S. Tokito, K. Noda, H. Fujikawa, Y. Taga, M. Kimura,
K. Shimada and Y. Sawaki, Appl. Phys. Lett., 2000, 77, 160;
S. Tokito, K. Noda, K. Shimada, S. Inoue, M. Kimura, Y. Sawaki
and Y. Taga, Thin Solid Films, 2000, 363, 290.
21 K. R. J. Thomas, J. T. Lin, Y.-T. Tao and C.-W. Ko, J. Am. Chem.
Soc., 2001, 123, 9404.
22 Y. Qiu, J. Qiao, Y. Gao, D. Zhang and L. Wang, Synth. Met.,
2002, 129, 25; S. Grigalevicius, G. Blazyls, J. Ostrauskaite,
J. V. Grazulevicius, V. Gaidelis, V. Jankauskas and
E. Montrimas, Synth. Met., 2002, 128, 127; T. Okamoto,
E. Terada, M. Kozaki, M. Uchida, S. Kikukawa and K. Okada,
Org. Lett., 2003, 5, 373.
23 K. Naito and A. Miura, J. Phys. Chem., 1993, 97, 6240.
24 S. A. VanSlyke, C.-H. Chen and C. W. Tang, Appl. Phys. Lett.,
1996, 69, 2160.
31 F.-I. Wu, R. Dodda, D. S. Reddy and C.-F. Shu, J. Mater. Chem.,
2002, 12, 2893.
32 A. Lutzen, F. Thiemann and S. Meyer, Synthesis, 2002, 2771.
33 C. Poriel, Y. Ferrand, P. Le Maux and G. Simmonneaux,
SYNLETT, 2003, 71.
34 C. D. Muller, A. Falcou, N. Reckefuss, M. Rojahn, V Wiederhin,
P. Rudati, H. Frohne, O. Nuyken, H. Becker and K. Meerholz,
Nature, 2003, 421, 829.
35 A possible IUPAC name of 5 is as follows, based on G. P. Moss,
Pure Appl. Chem., 1999, 71, 531, trispiro[10,15-dihydro-5H-
diindeno[1,2-a:19,29-c]fluorene-5,99:10,90:15,990-tri(9H-fluorene)].
In a recent CAS index name, the truxene part is 10,15-dihydro-5H-
tribenzo[a,f,k,]triindene.
36 For the structural interest, Professor G. Yamamoto et al. at Kitasato
University, Japan, prepared 5 independently, a part of their work
being presented at the 81st Annual meeting of the Chemical Society
of Japan in spring 2002. Until now we are not aware of the details.
37 J. Cymernan and W. F. Short, J. Chem. Soc., 1949, 703.
38 F. H. Case, J. Chem. Soc., 1943, 2137.
39 S. J. Branch, D. J. Byron, G. W. Gray, A. Ibbotson and
B. M. Worrall, J. Chem. Soc., 1964, 3279.
25 U. Scherf and E. J. W. List, Adv. Mater., 2002, 14, 477.
26 J. Husmann, Chem. Ber., 1889, 22, 2019.
40 T. Yamamoto, M. Nishiyama and Y. Koie, Tetrahedron Lett.,
1998, 39, 2367.
27 C. Lambert, G. Noll, E. Schmalzlin, K. Meerholz and C. Bauchle,
Chem.–Eur. J., 1998, 2129.
28 O. de Frutos, T. Granier, B. Gomez-Lor, J. Jimenez-Barbero,
A. Monge, E. Gutierrez-Puebla and A. M. Echavarren,
Chem.–Eur, J., 2002, 2879.
29 K. Jakob, M. Signalov, J. Y. Becker, A. Ellern and
V. Khadorkovsky, Eur. J. Org. Chem., 2000, 2047.
30 J. Pei, J. Ni, X.-H. Zhou, X.-Y. Cao and Y.-H. Lai, J. Org. Chem.,
2002, 67, 4924.
41 M. Brinkmann, G. Gadret, M. Muccini, C. Taliani, N. Masciocchi
and A. Sironi, J. Am. Chem. Soc., 2000, 122, 5147.
42 M. F. Semmelhack, J. S. Foos and S. Katz, J. Am. Chem. Soc.,
1973, 95, 7325.
43 W. Schmidt and E. Steckhan, Chem. Ber., 1980, 113, 577.
44 J. Pommerehne, H. Vestweber, W. Guss, R. F. Mahrt, H. Baessler,
M. Porsch and J. Daub, Adv. Mater., 1995, 7, 551; S. Janietz,
D. D. C. Bradley, M. Grell, C. Giebeler, M. Inbasekaran and
E. P. Woo, Appl. Phys. Lett., 1996, 73, 2453.
2398 | J. Mater. Chem., 2005, 15, 2393–2398
This journal is ß The Royal Society of Chemistry 2005