Toward π-conjugated molecule bundles: Synthesis of a series of B,B′,B″-trianthryl-N,N′,N″-triarylborazines and the bundle effects on their properties

Article abstract of DOI:10.1021/ja0537171

As a prototype of a π-conjugated molecule bundled system, a series of B,B′,B″-trianthryl- N,N′,N″-triarylborazine derivatives bearing various p-substituted phenyl groups (p-R-C₆H₄: R = hexyl (1), i-Pr (2), CF₃ (3), Br (5))

Full text of DOI:10.1021/ja0537171

Published on Web 10/01/2005
Toward π-Conjugated Molecule Bundles: Synthesis of a
Series of B,B′,B′′-Trianthryl-N,N′,N′′-triarylborazines and the
Bundle Effects on Their Properties
Atsushi Wakamiya, Toshihisa Ide, and Shigehiro Yamaguchi*
Contribution from the Department of Chemistry, Graduate School of Science,
Nagoya UniVersity, Chikusa, Nagoya 464-8602, Japan
Received June 7, 2005; E-mail: yamaguchi@chem.nagoya-u.ac.jp
Abstract: As a prototype of a π-conjugated molecule bundled system, a series of B,B′,B′′-trianthryl- N,N′,N′′-
triarylborazine derivatives bearing various p-substituted phenyl groups (p-R-C6H4: R ) hexyl (1), i-Pr (2),
CF3 (3), Br (5)) as aryl groups was designed and synthesized. The crystal structure analysis of these
derivatives confirmed that the three anthryl and three phenyl groups are bundled up alternately in a C3
symmetrical gear-shaped fashion. On the basis of this structure, the trianthrylborazine derivatives form a
unique honeycomblike packing structure consisting of intermolecular π-stacking of the anthryl moieties.
Significant bundle effects were observed in the photophysical and electrochemical properties of these
compounds. In their fluorescence spectra, the trianthrylborazine derivatives (1-3) show intense emissions
around 390 nm, whose quantum yields (1, ΦF ) 0.62; 2, ΦF ) 0.59; 3, ΦF ) 0.63) are about twice high as
that of anthracene (ΦF ) 0.27). The cyclic voltammetry measurements show that the oxidation peak potential
can be tuned by varying the substituents on the phenyl moieties. Theoretical calculations (B3LYP/ 6-31G-
(d)) suggested that secondary through-bond/through-space interactions in the bundled structure play an
important role in the tuning of these properties. Facile structural derivatization at the 10-position of the
anthryl moieties of trianthrylborazine was conducted to demonstrate the utility of the borazine skeleton as
a core framework for new organic electronic materials.
Introduction
Progress in organic electronics and optoelectronics highly
relies on the creation of excellent new π-electron materials. One
possible direction in molecular designs is the construction of
cumulated π-conjugated systems in which multiple π-conjugated
frameworks are assembled three-dimensionally through covalent
bonding in a specific fashion. These systems are divided into
several types such as (a) spiro-type, (b) propeller-type, and (c)
double-decker-type (Figure 1), exemplified by spirofluorenes1-3
and spirobiphenalenes,4 metal-quinolinato complex such as
Alq3,5 and paracyclophane-based materials,6-9 respectively. In
these π-electron systems, spatial proximity or topology among
the π-conjugated moieties causes unique orbital interactions,
which make it possible to tune the electronic structures (types
(a)1-4 and (c)6-9). In addition, the rigid three-dimensional
(1) (a) Salbeck, J.; Yu, N.; Bauer, J.; Weisso¨rtel, F.; Bestgen, H. Synth. Met.
1997, 91, 209. (b) Salbeck, J.; Weisso¨rtel, F.; Bauer, J. Macromol. Symp.
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Chiang, H.-H.; Hsieh, P.-Y.; Wu, C.-C.; Chou, C. H.; Su, Y. O.; Lee, G.-
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Figure 1. Various types of cumulated π-conjugated systems.
skeletons favor the formation of well-oriented crystalline (type
(a)4) or stable amorphous (types (a)1-3 and (b)5) solid-state
structures.
We now focus our attention on another type of cumulated
system, that is, π-conjugated molecule bundles with a hexagonal
core, as shown in Figure 1d. In this system, six π-conjugated
9
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Wakamiya et al.
Scheme 1
frameworks are bundled up in parallel fashion. We envisioned
that the construction of this bundled structure would cause
certain through-bond and/or through-space interaction among
the π-conjugated frameworks, resulting in the appearance of
novel photophysical and electronic properties different from the
original properties of each π-conjugated framework. Here, we
employ borazine (B3N3) as the core skeleton. The use of
borazine allows us not only to achieve efficient synthesis, but
also to incorporate two kinds of π-conjugated frameworks, π1
and π2, alternately on the boron and nitrogen atoms, respectively,
as shown in Figure 1. Although benzene might be the primarily
conceivable candidate for the core skeleton,10 difficulty is often
encountered in the synthesis of such sterically congested
trigonally symmetric benzenes in terms of efficiency and
regioselectivity.10e The borazine skeleton has a definite advan-
tage over the benzene skeleton in this point. As a prototype of
the borazine-based bundle, we here report the synthesis and
properties of a series of B,B′,B′′-trianthryl-N,N′N′′-triarylbora-
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zines. Our interests in this paper are the elucidation of bundle
effects on the properties of these compounds as well as the
investigation of their potential utility as a key framework for
the creation of new organic electronic materials.
Results and Discussion
Synthesis of Trianthrylborazines. The trianthrylborazines
were synthesized using a one-pot procedure, as shown in
Scheme 1.11 The reaction of BCl3 with aniline derivatives
produced the corresponding B,B′,B′′-trichloro-N,N′,N′′-triarylbo-
razines, which were subsequently treated with 9-anthryllithium
to afford a series of trianthrylborazines bearing various p-
substituted phenyl groups (p-R-C6H4: R ) hexyl (1), i-Pr (2),
CF3 (3)) as the aryl groups on the nitrogen atoms. Although
the overall yield using this procedure was only moderate to
good, the procedure is essentially facile and allows us to
synthesize the bundled systems on a gram scale.
X-ray Crystal Structure Analysis. The crystal structures of
the series of trianthrylborazines were determined by X-ray
crystallography. As an example, the structure of the CF3-
substituted derivative 3 is shown in Figure 2. The crystal lattice
of 3 belongs to the trigonal R-3 space group, and this compound
has a 3-fold symmetry axis. The anthryl and phenyl groups are
arranged nearly orthogonally to the borazine plane, but the
dihedral angles between these planes and the borazine plane
deviate slightly from 90°, at 75.6° and 72.4°, respectively. As
a consequence, the six π-frameworks are arranged in propeller-
like fashion.
There are two notable features. (1) The nonbonded distances
between the ipso positions of the anthryl and phenyl groups
(11) For the synthesis of hexaphenylborazine: Groszos, S. J.; Stafiej, S. F. J.
Am. Chem. Soc. 1958, 80, 1357.
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A R T I C L E S
Table 1. Photophysical Data for a Series of
B,B′,B′′-Trianthrylborazine Derivatives
absorptiona
fluorescencea
b
compd.
λmax/nm (log
ꢀ)
λmax/nm (ΦF)
1
2
3
4
6
7
8
390 (4.41)
390 (4.43)
390 (4.45)
387 (4.49)
402 (4.58)
437 (4.60)
401 (4.66)
377 (3.77)
397 (0.62)
397 (0.59)
397 (0.63)
390 (0.38)
411 (0.80)c
466 (0.73)d
459 (0.36)c
380 (0.27)
anthracene
a In THF. b Determined with anthracene as a standard, unless otherwise
stated. c Determined with 9,10-diphenylanthracene as a standard. d Deter-
mined with perylene as a standard.
Chart 1. Structure of B,B′,B′′-Trianthryl-N,N′,N′′-tributylborazine 4
this two-dimensional network consists of offset face-to-face
intermolecular π-stacking between the anthryl moieties with a
cofacial π-π distance of about 3.45 Å. A similar packing
structure is also observed for 2, which indicates the generality
of this packing structure for these C3 symmetrical borazine
derivatives. However the honeycomb network of 2 is rather
loose compared to that of 3, due to the bulkier isopropyl groups
on the benzene rings (see Supporting Information).
Photophysical Properties. To investigate the effects of the
bundled structure on the compounds’ photophysical properties,
we obtained UV-vis absorption and fluorescence spectra for
compounds 1-3. The data are collected in Table 1 together
with the data for a parent anthracene and an N,N′,N′′-trialkyl
derivative 4 (Chart 1) for comparison.
In the UV-vis absorption spectra, all the trianthrylborazine
derivatives 1-4 have absorption maxima around 387-390 nm,
which are bathochromically shifted by about 10 nm from that
of anthracene (377 nm), mainly due to the inductive electronic
effect of the borazine moiety.
More significant differences were observed by comparing the
fluorescence spectra of anthracene, N,N′,N′′-trialkyl derivative
4, and N,N′,N′′-triaryl derivative 1. The emission maximum
shifts to longer wavelengths, in the order anthracene < 4 < 1,
by about 10-17 nm. Moreover, the fluorescence intensity
significantly increases in the same order, as shown in Figure 3.
In terms of the fluorescence quantum yield, more than a 2-fold
increment was observed between the parent anthracene (ΦF )
0.27) and the bundled molecule 1 (ΦF ) 0.62). This bundle
effect can be rationalized by considering that the sterically
congested bundled structure prevents conformational disorder
leading to nonradiative decay from the excited state.
Figure 2. (a) ORTEP drawing of 3 (R ) CF3). Thermal ellipsoids are
drawn at the 50% probability level. Hydrogen atoms and solvent molecules
are omitted for clarity. Selected bond lengths (Å) and angles (deg) are as
follows: N1-B1, 1.437(2); N1-B1*, 1.447(2); B1-C1, 1.581(3); N1-
C15, 1.447(2); B1-N1-B1*, 122.86(16); B1-N1-C15, 119.40(14); B1*-
N1-C15, 117.62(14); N1-B1-N1*, 117.14(14); N1-B1-C1, 123.39(15);
N1*-B1-C1, 119.45(15). (b) Packing structure of 3 (R ) CF3). In the
crystal structure of 3, solvent molecules of hexane and toluene were included
between the π-stacking network sheets. The inner space of each hexagonal
assembly is occupied by a disordered hexane molecule. Solvent molecules
and hydrogen atoms are omitted for clarity.
(C1-C15, C1*-C15) are rather shorter (3.00 and 2.90 Å) than
the sum of the van der Waals radii of two C sp2 atoms (3.45
Å), suggesting a possible through-space interaction between
them. (2) The structure of 3 serves as a hexagonal gear-shaped
motif, and in the crystal it forms a unique honeycomblike
packing structure, as shown in Figure 2b. It is noteworthy that
Cyclic Voltammetry Measurement. We also evaluated the
electrochemical properties of the synthesized compounds by
means of cyclic voltammetry. Their cyclic voltammograms are
shown in Figure 4, and the data are summarized in Table 2.
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Wakamiya et al.
alternately bundled phenyl and anthryl moieties, resulting in
the decrease in Epa from anthracene to 1. However, the CF3-
derivative 3 (+1.01 V) has a higher oxidation peak potential
than 1, indicating that the electronic structures can be tuned by
varying the p-substituents of the phenyl moieties on the nitrogen
atoms. This secondary perturbation may be beneficial to the
material designs, since the electronic fine-tuning of the material
is a key issue to fabricate high-performance multilayered
electronic devices, such as organic light-emitting diodes.
Theoretical Calculations. To obtain a deeper insight into
the bundle effects on the electronic structures, we conducted
DFT calculations at the B3LYP/6-31G(d) level of theory. The
calculated Kohn-Sham (KS) HOMO level of 1′ (R ) Me, a
model compound for 1: -4.98 eV) is slightly higher than those
of B,B′,B′′-trianthryl-N,N′,N′′-trimethylborazine 4′ (a model
compound for 4: -5.09 eV) and anthracene (-5.23 eV). In
addition, a comparison between 1′ and 3 (R ) CF3, -5.31 eV)
shows that the introduction of the electron-withdrawing CF3
group decreases the HOMO level by 0.33 eV compared to that
of 1′ (-4.98 eV). All these results are qualitatively in good
agreement with the aforementioned cyclic voltammetry results.
It is noteworthy that, while the HOMO of the trianthrylborazine
is mainly localized on the three anthracene moieties, it also
contains slight contributions from the B-N-B through-bond
interaction as well as the through-space interaction between
adjacent anthryl and phenyl moieties, as shown in Figure 5.
These secondary through-bond/through-space interactions play
an important role in the tuning of the electronic structures. In
fact, as shown by comparison of the HOMOs of 1′ and 3, the
extent of the contribution of the benzene moieties is significantly
decreased by the incorporation of the electron-withdrawing CF3
group.
Figure 3. Fluorescence spectra of 1, 4, and anthracene in THF: solid line,
1; dashed line, 4; dotted line, anthracene.
Structural Modification. One synthetic advantage of the
present trianthrylborazine systems is their facile structural
derivatization. In the one-pot synthesis of the trianthrylborazine
framework, the use of 10-bromo-9-anthryllithium, instead of
9-anthryllithium, gave tris(10-bromoanthryl)borazine 5, as
shown in Scheme 1. This compound can be used as a key
precursor for a variety of 10-substituted anthryl derivatives. For
example, as shown in Scheme 2, the trilithiation of 5 using
t-BuLi followed by treatment with electrophiles such as diiso-
propylsilyl chloride or dimesitylfluoroborane gave tris(diiso-
propylsilyl) derivative 6 and tris(dimesitylboryl) derivative 7,
respectively. In addition, after the transformation from 5 to the
corresponding trizinc species, the Negishi coupling reaction with
p-bromo(diphenylamino)benzene gave the triphenylamine-bound
derivative 8.
Figure 4. Cyclic voltammograms of anthracene, 4, 1, and 3 in CH2Cl2,
-
measured with Bu4N+ClO4 (0.1 M) as a supporting electrode at a scan
rate of 100 mV s-1
.
Table 2. Oxidation Potentialsa and KS HOMO Levelsb
c
Epa
(V)
KS HOMO
compd.
(eV)
anthracene
+0.99
+0.94
+0.85
+1.01
-5.23
-5.09d
-4.98e
-5.31
4
1
3
-
a In CH2Cl2 containing Bu4N+ClO4 (0.1 M) with a scan rate of 100
mV s-1 b Calculated at the B3LYP/6-31G(d) level of theory. c V vs Fc/
.
Fc+. d Calculated for the model compound 4′. e Calculated for the model
compound 1′ (R ) Me).
These extended bundle systems show some intriguing proper-
ties. The tris(diisopropylsilyl) derivative 6 shows a very intense
fluorescence maximum at 411 nm with a fluorescent quantum
yield of 0.80 (Figure 6). The higher quantum yield of 6
compared to that of 1 (ΦF ) 0.62) can be ascribed to the silyl
effect on the fluorescence of anthracene.12 The tris(dimesityl-
boryl)-substituted derivative 7 shows substantially red-shifted
absorption and fluorescence maxima at 438 and 466 nm,
respectively, due to the contribution of the vacant p-orbital of
the boryl groups.13b These values are slightly longer, even in
comparison with those of dimesityl(9-anthryl)borane13 (absorp-
Again, bundle effects are noticeable in the comparison between
anthracene, N,N′,N′′-trialkyl derivative 4, hexyl-substituted 1,
and CF3-substituted 3 with respect to the reversibility of the
redox process as well as oxidation potential. Thus, while the
parent anthracene only showed an irreversible one-electron
oxidation wave, all trianthrylborazines, 1, 3, and 4, exhibited
quasi-reversible one-electron oxidation waves, suggesting that
the radical cations produced thereby can be stabilized in the
trianthrylborazine structures. The oxidation peak potential (Epa)
gradually shifts to less positive potential in the order anthracene
(+0.99 V vs Fc/ Fc+) > 4 (+0.94 V) > 1 (+0.85 V). These
results demonstrate that there is an interaction between the
(12) Kyushin, S.; Ikarugi, M.; Goto, M.; Hiratsuka, H.; Matsumoto, H.
Organometallics 1996, 15, 1067.
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π
-Conjugated Molecule Bundles
A R T I C L E S
Scheme 2a
a Reagents and conditions: i, t-BuLi, THF; ii, Hi-Pr2SiCl or Mes2BF;
iii, ZnCl2(tmen); iv, ArBr, Pd(PPh3)4, THF.
Figure 6. Fluorescence spectra of 1 and 6-8 in THF: solid line, 1; long
dashed line, 6; short dashed line, 7; dotted line, 8.
Epc ) -2.29, -2.41, and -2.52 V (vs Fc/Fc+) in THF, as well
as a reversible oxidation wave with potential Epa ) +0.72 V in
CH2Cl2, as shown in Figure 7. The first reduction peak potential
(Epc1; -2.29 V) of 7 is comparable to that of Alq3 (-2.36 V),14,15
which indicates its potential as an electron-transporting material
for organic electroluminescence devices. In contrast, the ami-
nophenyl derivative 8 shows three oxidation waves with peak
potential Epa ) +0.60, +0.80, and +1.03 V (vs Fc/Fc+). All
these data demonstrate the considerable potential utility of
Figure 5. Pictorial presentation of KS HOMO of (a) 1′, (b) 3, and (c) 4′.
tion, λmax 420 nm; fluorescence λmax 455 nm). In addition, the
aminophenyl derivative 8 shows rather red-shifted emission at
459 nm, in comparison with that of the unsubstituted derivate
1, while its absorption maximum is only slightly longer than
that of 1. These results suggest a substantial contribution of the
aminophenyl group to the excited state.
Notably, in cyclic voltammetry, the boryl-substituted deriva-
tive 7 shows three reversible reduction waves with peak potential
(14) Sakamoto, Y.; Suzuki, T.; Miura, A.; Fujikawa, H.; Tokito, S.; Taga, Y. J.
Am. Chem. Soc. 2000, 122, 1832.
(15) Theoretical calculations at the B3LYP/6-31G(d) level of theory showed
that B,B′,B′′-tris(10-diphenylboryl-9-anthryl)-N,N′,N′′-tris(p-methylphenyl)-
borazine (a model for 7; KS LUMO, -1.74 eV) and Alq3 (KS LUMO,
-1.73 eV) have their LUMO at comparable energy level to each other.
(13) (a) Blount, J. F.; Finocchiaro, P.; Gust, D.; Mislow, K. J. Am. Chem. Soc.
1973, 95, 7019. (b) Yamaguchi, S.; Akiyama, S.; Tamao, K. J. Am. Chem.
Soc. 2000, 122, 6335.
9
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A R T I C L E S
Wakamiya et al.
using Kieselgel 60 (70-230 mesh; Merck). All experiments were
carried out under argon atmosphere.
Computational Method. All calculations were conducted using the
Gaussian 98 program.16
B,B′,B′′-Tri(9-anthryl)-N,N′,N′′-tris(p-hexylphenyl)borazine (1).
To a solution of BCl3 (1 M, 7.20 mL, 7.20 mmol) in hexane, a solution
of 4-hexylaniline (1.00 g, 5.65 mmol) in toluene (7.5 mL) was added
dropwise at 0 °C. The mixture was refluxed for 19 h to give a solution
containing N,N′,N′′-tris(4-hexylphenyl)-B,B′,B′′-trichloroborazine. This
solution was added to a THF solution (12 mL) of 9-lithioanthracene at
0 °C via cannula, which was prepared from 9-bromoanthracene (1.45
g, 5.65 mmol) with t-BuLi (1.47 M in pentane, 7.7 mL, 11.3 mmol) in
THF at -78 °C. The mixture was allowed to warm to room temperature
and was stirred for 20 h. After addition of 10 mL of water, the organic
layer was separated, and the aqueous layer was extracted three times
with CHCl3. The combined organic layer was dried over MgSO4, fil-
tered, and evaporated under reduced pressure. The mixture was purified
by a silica gel column chromatography (5:2 hexane/toluene, Rf ) 0.40)
to give 1.43 g (1.31 mmol) of 1 in 70% yield as yellow solids: mp
282-283 °C; 1H NMR (CDCl3) δ 8.44 (d, JHH ) 8.4 Hz, 6H), 7.96 (s,
3H), 7.70 (d, JHH ) 8.4 Hz, 6H), 7.59 (t, JHH ) 8.4 Hz, 6H), 7.32 (t,
JHH ) 8.4 Hz, 6H), 6.57 (d, JHH ) 8.4 Hz, 6H), 5.77 (d, JHH ) 8.4 Hz,
6H), 1.73 (t, JHH ) 7.2 Hz, 6H), 1.10-0.76 (m, 27 H), 0.52-0.45 (m,
6H); 13C NMR (CDCl3) δ 142.6, 143.7, 137.5 (br), 132.9, 130.5, 129.4,
128.5, 126.3, 126.2, 126.0, 124.3, 124.2, 34.2, 31.4, 30.2, 27.5, 22.4,
14.1; FAB MS m/z 1089 (M+). Anal. Calcd for C78H78B3N3: C, 85.96;
H, 7.21; N, 3.86. Found: C, 85.69; H, 7.16; N, 4.03.
Figure 7. Cyclic voltammograms of (a) 7 in CH2Cl2, (b) 7 in THF, and
-
(c) 8 in CH2Cl2, measured with Bu4N+ClO4 (0.1 M) as a supporting
electrolyte at a scan rate of 100 mVs-1
.
trianthrylborazine as a core framework for electronic device
applications.
Conclusion
We here disclosed a new molecular design for cumulative
π-electron systems, namely, π-conjugated molecule bundles
exploiting borazine as a hexagonal core skeleton. As a prototype,
a series of B,B′,B′′-trianthryl-N,N′,N′′-triarylborazines was
synthesized in a facile one-pot procedure. On the basis of their
C3 symmetrical gear-shaped molecular structures, these com-
pounds form characteristic two-dimensional honeycomblike
networks, which consist of offset face-to-face intermolecular
π-stacking of the anthracene moieties. These structures might
be suitable for achieving high carrier-transporting abilities; thus,
their application in this area is our next subject for investigation.
In addition, the elucidation of the properties of these compounds
demonstrates distinct bundle effects on their electronic structures
and thus on their photophysical and electrochemical properties,
such as the enhancement of fluorescence intensity and the
possibility of tuning oxidation potential. These results suggest
the great potential of this design in the creation of excellent
new π-electron materials. Expanding on this molecular design,
our current work involves the introduction of more extended
π-conjugated frameworks in place of the anthracenes.
B,B′,B′′-Tri(9-anthryl)-N,N′,N′′-tris(p-isopropylphenyl)bor-
azine (2). This compound was prepared essentially in the same manner
as described for 1 using 4-isopropylaniline as a starting material. The
purification by a silica gel column chromatography (3:2 hexane/toluene,
Rf ) 0.40) gave 4.85 g (5.03 mmol) of 2 in 52% yield as yellow
solids: mp > 300 °C; 1H NMR (CDCl3) δ 8.38 (d, JHH ) 8.4 Hz, 6H),
7.94 (s, 3H), 7.68 (d, JHH ) 8.4 Hz, 6H), 7.55 (t, JHH ) 8.4 Hz, 6H),
7.30 (t, JHH ) 8.4 Hz, 6H), 6.51 (d, JHH ) 8.4 Hz, 6H), 5.77 (d, JHH
) 8.4 Hz, 6H), 2.00 (sep, JHH ) 6.8 Hz, 3 H), 0.47 (d, JHH ) 6.8 Hz,
18H); 13C NMR (CDCl3) δ 143.9, 142.7, 133.0, 130.6, 129.5, 128.4,
126.4, 126.1, 124.3, 124.2, 123.8, 32.6, 23.2 (one peak for the carbon
atoms bonding to the boron atoms is not observed due to quadrupolar
relaxation); EI MS m/z 963 (M+). Anal. Calcd for C69H60B3N3: C,
86.00; H, 6.28; N, 4.36. Found: C, 85.81; H, 6.17; N, 4.43.
B,B′,B′′-Tri(9-anthryl)-N,N′,N′′-tris[p-(trifluoromethyl)phenyl]bor-
azine (3). This compound was prepared essentially in the same manner
as described for 1 using 4-trifluoromethylaniline as a starting material.
The purification by a silica gel column chromatography (3:2 hexane/
toluene, Rf ) 0.25) gave 3.52 g (3.38 mmol) of 3 in 33% yield as pale
1
yellow solids: mp > 300 °C; H NMR (CDCl3) δ 8.30 (d, JHH ) 8.4
Hz, 6H), 8.05 (s, 3H), 7.75 (d, JHH ) 8.4 Hz, 6H), 7.63 (t, JHH ) 8.4
Hz, 6H), 7.36 (t, JHH ) 8.4 Hz, 6H), 6.78 (d, JHH ) 8.4 Hz, 6H), 6.28
(d, JHH ) 8.4 Hz, 6H); 13C NMR (CDCl3) δ 147.9, 134.7 (br), 132.7,
130.5, 129.2, 128.0, 127.6, 126.7, 126.5, 125.4, 124.7, 124.6, 123.4
(q); EI MS m/z 1041 (M+). Anal. Calcd for C63H39B3F9N3: C, 72.66;
H, 3.77; N, 4.03. Found: C, 72.46; H, 3.80; N, 4.17.
Experimental Section
General Procedure. Melting points (mp) were measured on a
1
Yanaco MP-S3 instrument. H and 13C NMR spectra were measured
with a JEOL A-400 spectrometer in CDCl3 (400 MHz for 1H and 100
MHz for 13C). UV-vis absorption spectra and fluorescence spectra
measurements were performed at room temperature with a Shimadzu
UV-3150 spectrometer and a Hitachi F-4500 spectrometer, respectively,
in a degassed spectral grade THF. Cyclic voltammetry (CV) was
performed on an ALS/chi-617A electrochemical analyzer. The CV cell
consisted of a glassy carbon electrode, a Pt wire counter electrode,
and an Ag/AgNO3 reference electrode. The measurements were carried
out under argon atmosphere using CH2Cl2 or THF solutions of samples
with a concentration of 1 mM and 0.1 M tetrabutylammonium
perchlorate as a supporting electrolyte. The redox potentials were
calibrated with ferrocene as an internal standard. Thin-layer chroma-
tography (TLC) was performed on plates coated with 0.25-mm thick
silica gel 60F-254 (Merck). Column chromatography was performed
B,B′,B′′-Tri(9-anthryl)-N,N′,N′′-tributylborazine (4). This com-
pound was prepared essentially in the same manner as described for 1
using butylamine as a starting material. The purification by a silica gel
column chromatography (3:1 hexane/CHCl3, Rf ) 0.50) gave 0.717 g
(0.922 mmol) of 4 in 48% yield as colorless solids: mp > 300 °C; 1H
NMR (CDCl3) δ 8.40 (s, 3H), 8.24 (d, JHH ) 8.4 Hz, 6H), 8.00 (d, JHH
) 8.4 Hz, 6H), 7.60 (t, JHH ) 8.4 Hz, 6H), 7.47 (t, JHH ) 8.4 Hz, 6H),
2.62-2.58 (m, 6H), 0.85-0.77 (m, 6H), -0.13 (sex, JHH ) 7.2 Hz,
6H), -0.53 (t, JHH ) 7.4 Hz, 9H); 13C NMR (CDCl3) δ 133.5, 131.3,
129.1, 128.9, 126.6, 125.1, 125.0, 48.8, 35.6, 19.3, 12.1 (one peak for
(16) Frisch, M. J., et al. A. Gaussian 98, revision A.5; Gaussian, Inc.: Pittsburgh,
PA, 1998.
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Toward
π
-Conjugated Molecule Bundles
A R T I C L E S
the carbon atoms bonding to the boron atoms is not observed due to
quadrupolar relaxation); FAB MS m/z 778 (M+H+). Anal. Calcd for
C54H54B3N3: C, 83.42; H, 7.00; N, 5.40. Found: C, 83.64; H, 7.07; N,
5.41.
6.78 (s, 6H), 6.58 (d, JHH ) 8.4 Hz, 6H), 6.48 (s, 6H), 5.79 (d, JHH )
8.4 Hz, 6H), 2.21 (s, 18H), 2.03 (s, 18H), 1.80 (t, JHH ) 8.0 Hz, 6H),
1.15 (s, 18H), 1.15-1.03 (m, 6H), 1.01-0.97 (m, 6H), 0.92-0.88 (m,
6H), 0.83-0.78 (m, 6H), 0.76 (t, JHH ) 7.2 Hz, 9H); 13C NMR (CDCl3)
δ 145.6, 145.5, 142.6, 141.3, 141.1 (br), 140.3, 139.4, 137.8, 132.7,
132.4, 130.4, 128.8, 128.7, 128.5, 126.5, 125.9 (br), 124.2, 123.9, 34.7,
31.6, 30.6, 28.7, 23.3, 23.0, 22.5, 21.2, 14.1; MALDI-TOF MS m/z
1836 (M+). Anal. Calcd for C132H141B6N3: C, 86.43; H, 7.75; N, 2.29.
Found: C, 86.16; H, 7.75; N, 2.35.
B,B′,B′′-Tris(10-bromo-9-anthryl)-N,N′,N′′-tris(p-hexylphenyl)-
borazine derivative (5). To a solution of BCl3 (1 M, 21.7 mL, 21.7
mmol) in hexane, a solution of 4-hexylaniline (2.96 g, 16.7 mmol) in
toluene (20 mL) was added dropwise at 0 °C. After addition of the
solution of the aniline derivative, the mixture was refluxed for 15 h to
give a solution containing N,N′,N′′-tris(p-hexylphenyl)-B,B′,B′′-trichlo-
roborazine. This solution was added to a THF solution (65 mL) of
10-bromo-9-anthryllithium at 0 °C via cannula, which was prepared
from 9,10-dibromoanthracene (5.63 g, 16.8 mmol) with n-BuLi (1.60
M in hexane, 10.5 mL, 16.8 mmol) in THF at -78 °C. The mixture
was gradually warmed to room temperature and was stirred for 20 h.
After the addition of 50 mL of water, the organic layer was separated,
and the aqueous layer was extracted three times with CHCl3. The
combined organic layer was dried over MgSO4, filtered, and evaporated
under reduced pressure. The mixture was purified by a silica gel column
chromatography (5:1 hexane/toluene, Rf ) 0.20) to give 5.15 g (3.88
N,N′,N′′-Tris(p-hexylphenyl)-B,B′,B′′-tris{10-[p-(N,N-dipheny-
lamino)phenyl]-9-anthryl}borazine (8). To a solution of 5 (403 mg,
0.304 mmol) in THF (2 mL) cooled at -78 °C was added t-BuLi (1.47
M in pentane, 1.25 mL, 1.84 mmol) dropwise. After the mixture was
stirred at -78 °C for 1 h, ZnCl2(tmen) (230 mg, 0.91 mmol) (tmen:
N,N,N′,N′-tetramethylethylenediamine) was added to the mixture at 0
°C. The reaction mixture was stirred at 0 °C for additional 2 h.
p-Bromo(N,N′-diphenylamino)benzene (326 mg, 1.01 mmol) and Pd-
(PPh3)4 (35.5 mg, 0.0307 mmol) were added to the mixture under a
stream of argon gas. The reaction mixture was refluxed for 24 h. After
addition of 2 mL of water, the organic layer was separated, and the
aqueous layer was extracted with CHCl3 three times. The combined
organic layer was dried over MgSO4, filtered, and evaporated under
reduced pressure. The mixture was purified by a silica gel column
chromatography (3:2 hexane/toluene, Rf ) 0.25) to give 133 mg (0.073
mmol) of 8 in 24% yield as yellow solids: mp 184-186 °C; 1H NMR
(CDCl3) δ 8.48 (d, JHH ) 8.4 Hz, 6H), 7.58 (t, JHH ) 8.4 Hz, 6H),
1
mmol) of 5 in 70% yield as pale yellow solids: mp 186-188 °C; H
NMR (CDCl3) δ 8.40 (d, JHH ) 8.4 Hz, 6H), 8.26 (d, JHH ) 8.4 Hz,
6H), 7.63 (t, JHH ) 8.4 Hz, 6H), 7.45 (t, JHH ) 8.4 Hz, 6H), 6.48 (d,
JHH ) 8.4 Hz, 6H), 5.77 (d, JHH ) 8.4 Hz, 6H), 1.74 (t, JHH ) 7.2 Hz,
6H), 1.07-1.00 (m, 6H), 0.95-0.88 (m, 6H), 0.83-0.78 (m, 6H), 0.75
(t, JHH ) 7.2 Hz, 9 H), 0.56-0.48 (m, 6H); 13C NMR (CDCl3) δ 142.0,
138.5, 137.9 (br), 133.5, 129.6, 129.4, 128.0, 126.4, 126.2, 126.1, 124.7,
122.7, 34.2, 31.3, 30.3, 27.6, 22.4, 14.1. Anal. Calcd for C78H75B3-
Br3N3: C, 70.62; H, 5.70; N, 3.17. Found: C, 70.90; H, 5.75; N, 3.31.
7.51 (d, JHH ) 8.4 Hz, 6H), 7.25 (t, JHH ) 8.4 Hz, 6H), 7.24 (t, JHH
)
8.4 Hz, 12H), 7.17 (d, JHH ) 8.4 Hz, 12 H), 7.13 (d, JHH ) 8.4 Hz,
6H), 7.00 (t, JHH ) 8.4 Hz, 6H), 6.98 (d, JHH ) 8.4 Hz, 6H), 6.59 (d,
JHH ) 8.4 Hz, 6H), 5.81 (d, JHH ) 8.4 Hz, 6H), 1.75 (t, JHH ) 7.2 Hz,
6H), 1.00-0.94 (m, 6H), 0.90-0.80 (m, 12H), 0.65 (t, JHH ) 7.2 Hz,
9H), 0.63-0.58 (m, 6H); 13C NMR (CDCl3) δ 147.8, 146.6, 142.8,
137.8, 136.4, 133.1, 132.8, 132.1, 129.7, 129.2, 129.2, 127.1, 126.4,
126.0, 124.3, 124.2, 124.1, 123.1, 122.8, 34.5, 31.5, 30.8, 28.0, 22.3,
14.0 (one peak for the carbon atoms bonding to the boron atoms is not
observed due to quadrupolar relaxation); MALDI-TOF MS m/z 1819
(M+). Anal. Calcd for C132H117B3N6: C, 87.12; H, 6.48; N, 4.62.
Found: C, 87.11; H, 6.42; N, 4.59.
N,N′,N′′-Tris(p-hexylphenyl)-B,B′,B′′-tris(10-diisopropylsilyl-9-
anthryl)borazine (6). To a solution of 5 (401 mg, 0.303 mmol) in
THF (2 mL) cooled at -78 °C was added t-BuLi (1.47 M in pentane,
1.25 mL, 1.84 mmol) dropwise. After the mixture was stirred at -78
°C for 1 h, diisopropylsilyl chloride (150 mg, 1.00 mmol) was added
to the mixture at -30 °C. The reaction mixture was gradually warmed
to room temperature and stirred for 20 h. After addition of 1 M NaHCO3
aqueous solution, the organic layer was separated, and the aqueous layer
was extracted three times with CH2Cl2. The combined organic layer
was dried over MgSO4, filtered, and evaporated under reduced pressure.
The mixture was purified by a silica gel column chromatography (5:1
hexane/toluene, Rf ) 0.23) to give 199 mg (0.139 mmol) of 6 in 46%
X-ray Crystal Structure Analysis of Compound 2. Single crystals
of 2 suitable for X-ray crystal analysis were obtained by slow diffusion
of hexane into a solution of 2 in toluene. Intensity data were collected
at 100 K on a Bruker SMART APEX diffractometer with Mo KR
radiation (λ ) 0.71073 Å) and a graphite monochromator. A total of
15190 reflections were measured at a maximum 2θ angle of 50.0°, of
which 10215 were independent reflections (Rint ) 0.0226). The structure
was solved by direct methods (SHELXS-9717) and refined by the full-
matrix least-squares on F2 (SHELXL-9717). All non-hydrogen atoms
were refined anisotropically, and all hydrogen atoms were placed using
AFIX instructions. Two solvent molecules of toluene were included in
a lattice. The crystal data are as follows: C76H68B3N3; FW ) 1055.76,
crystal size 0.30 × 0.30 × 0.30 mm3, Triclinic, P-1, a ) 10.0274(9)
Å, b ) 15.5465(14) Å, c ) 20.3707(18) Å, R ) 69.938(2)°, â )
87.374(2)°, γ ) 83.796(2)°, V ) 2965.3(5) Å3, Z ) 2, Dc ) 1.182 g
cm-3. The refinement converged to R1 ) 0.0457, wR2 ) 0.0981 (I >
2σ(I)), GOF ) 0.899.
X-ray Crystal Structure Analysis of Compound 3. Single crystals
of 3 suitable for X-ray crystal analysis were obtained by slow diffusion
of hexane into a solution of 3 in toluene. Intensity data were collected
at 100 K on a Bruker SMART APEX diffractometer with Mo KR
radiation (λ ) 0.71073 Å) and a graphite monochromator. A total of
19059 reflections were measured at a maximum 2θ angle of 56.5°, of
which 4754 were independent reflections (Rint ) 0.1451). The structure
was solved by direct methods (SHELXS-9717) and refined by the full-
1
yield as colorless solids: mp 208-210 °C; H NMR (CDCl3) δ 8.46
(d, JHH ) 8.4 Hz, 6H), 8.24 (d, JHH ) 8.4 Hz, 6H), 7.55 (t, JHH ) 8.4
Hz, 6H), 7.31 (t, JHH ) 8.4 Hz, 6H), 6.51 (d, JHH ) 8.4 Hz, 6H), 5.73
(d, JHH ) 8.4 Hz, 6H), 4.63 (t, JHH ) 4.8 Hz, 3H), 1.62 (t, JHH ) 7.2
Hz, 6H), 1.47-1.40 (m, 6H), 1.13 (d, JHH ) 7.6 Hz, 18H), 1.06-1.04
(m, 3H), 1.04-1.01 (m, 6H), 0.92-0.88 (m, 6H), 0.77-0.72 (m, 3H),
0.74 (t, JHH ) 7.6 Hz, 9H), 0.63 (m, 6H), 0.56 (d, JHH ) 7.6 Hz, 18H);
13C NMR (CDCl3) δ 142.4, 140.8 (br), 137.9, 136.5, 132.4, 131.3, 130.6,
128.9, 126.3, 125.8, 124.1, 123.6, 34.4, 31.3, 30.4, 28.2, 22.3, 20.4,
19.4, 14.0, 13.5; FAB MS m/z 1432.44 (M+H+); HRMS calcd for
C96H121B3N3Si3, 1432.9186; found, 1432.9204.
N,N′,N′′-Tris(p-hexylphenyl)-B,B′,B′′-tris(10-dimesitylboryl-9-an-
thryl)borazine (7). To a solution of 5 (427 mg, 0.322 mmol) in THF
(3 mL) cooled at -78 °C was added t-BuLi (1.46 M in pentane, 1.35
mL, 1.97 mmol) dropwise. After the mixture was stirred at -78 °C
for 1 h, dimesitylfluoroborane (389 mg, 1.45 mmol) was added to the
mixture at -78 °C. The reaction mixture was gradually warmed to
room temperature and stirred for 27 h. After addition of 3 mL of water,
the organic layer was separated, and the aqueous layer was extracted
three times with CHCl3. The combined organic layer was dried over
MgSO4, filtered, and evaporated under reduced pressure. The mixture
was purified by a silica gel column chromatography (2:1 hexane/toluene,
Rf ) 0.30) to give 201 mg (0.109 mmol) of 7 in 34% yield as yellow
solids: mp > 300 °C; 1H NMR (CDCl3) δ 8.42 (d, JHH ) 8.4 Hz, 6H),
7.77(d, JHH ) 8.4 Hz, 6H), 7.45 (br, 6H), 7.05 (t, JHH ) 8.4 Hz, 6H),
(17) Sheldrick, G. M. SHELX-97, Program for the Refinement of Crystal
Structures; University of Gottingen: Gottingen, Germany, 1997.
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J. AM. CHEM. SOC. VOL. 127, NO. 42, 2005 14865

A R T I C L E S
Wakamiya et al.
matrix least-squares on F2 (SHELXL-9717). The CF3 group was dis-
ordered. Two sets of fluorines, that is, F1-F3 and F4-F6, were placed
and their occupancies were refined to be 0.60 and 0.40, respectively.
The disordered solvent molecules of nine toluenes and three hexanes
were included in a lattice. The toluene molecule (C22, C22*, C23, C23*,
C24, C24*, C25, C25*) sits on a 2-fold rotation axis. Thus, the
disordered methyl group of C25 was placed with fixed occupancy value
of 0.50. On the other hand, the hexane molecule (C26, C27, C28, C26*,
C27*, C28*) sits on a 3-fold rotation axis. The disordered carbons of
C26-C28 were placed with the fixed occupancy value of 0.33. All
non-hydrogen atoms were refined anisotropically. All hydrogen atoms,
except for those of disordered hexane (C26-C28), were placed using
AFIX instructions. The crystal data are as follows: C76.5H51B3F9N3;
FW ) 1215.63, crystal size 0.30 × 0.30 × 0.30 mm3, Trigonal, R-3,
a ) b ) 20.4905(10) Å, c ) 25.5846(17) Å, R ) γ ) 90°, â ) 120°,
V ) 9302.8(9) Å3, Z ) 6, Dc ) 1.302 g cm-3. The refinement converged
to R1 ) 0.0808, wR2 ) 0.2217 (I > 2σ(I)), GOF ) 1.071.
Acknowledgment. We thank Professor Koichi Komatsu of
Kyoto University for use of the X-ray diffractometer. This work
was supported by Grants-in-Aid (No.12CE2005 for Elements
Science, and No. 16750031) from the Ministry of Education,
Culture, Sports, Science, and Technology, Japan.
Supporting Information Available: X-ray structure of 2;
calculated molecular coordinates of 1′, 3, and 4′ at the B3LYP/
6-31G(d) level of theory (PDF). X-ray crystallographic files of
2 and 3 (CIF). This material is available free of charge via the
Internet at http://pubs.acs.org.
JA0537171
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14866 J. AM. CHEM. SOC. VOL. 127, NO. 42, 2005