Locked planarity: A strategy for tailoring ladder-type π-conjugated anilido-pyridine boron difluorides

Article abstract of DOI:10.1021/jo402583y

A novel series of syn- and anti-ladder-type anilido-pyridine boron difluorides (APBDs) were synthesized by stepwise incorporation of boron into laddered ligands. The boron coordination-locked strategy endows the ladder-type APBDs with a stiff conformation

Full text of DOI:10.1021/jo402583y

Note
pubs.acs.org/joc
Locked Planarity: A Strategy for Tailoring Ladder-Type π‑Conjugated
Anilido−Pyridine Boron Difluorides
Qingshan Hao,† Shuai Yu,† Shayu Li,‡ Jinping Chen,*,† Yi Zeng,† Tianjun Yu,† Guoqiang Yang,*,‡
and Yi Li*,†
†Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese
Academy of Sciences, Beijing 100190, China
‡Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Photochemistry, Institute of Chemistry, Chinese
Academy of Sciences, Beijing 100190, China
S
* Supporting Information
ABSTRACT: A novel series of syn- and anti-ladder-type
anilido−pyridine boron difluorides (APBDs) were synthesized
by stepwise incorporation of boron into laddered ligands. The
boron coordination-locked strategy endows the ladder-type
APBDs with a stiff conformation, which results in a substantial
bathochromic shift of their absorption spectra and a narrowed
HOMO−LUMO energy gap, reinforcing the compounds for
potential applications in organic electronics.
rganic conjugated molecules have drawn increasing
attention because of their wide applications in electronic
(APBDs), which exhibit high emission quantum yields and
large Stokes shifts.47 Inspired by their research, we anticipated
that the construction of new ladder-type π-conjugated
structures based on anilido−pyridine skeletons may provide
molecules with the merits of both ladder-type molecules and
boron compounds, which will reinforce the compounds for
applications in material chemistry. Herein we report a series of
syn- and anti-ladder-type APBD dyes based on the pyrimidine−
carbazole and pyrazine−carbazole structures. The double-
coordination endows the ladder-type APBDs with a stiff planar
conformation, which allows effective π-delocalization.
The procedure for the synthesis of syn-ladder-type APBDs
based on pyrimidine−carbazole is shown in Scheme 1. 1-
Bromo-3,6-di-tert-butyl-9H-carbazole (1) was synthesized
according to a literature procedure.48 Borylation of 1 with
pinacolborane provided 3,6-di-tert-butyl-1-borylcarbazole 2 in
85% yield. The Suzuki−Miyuara coupling reaction of 2 with
4,6-dichloropyrimidine afforded the syn-laddered ligand 3 in
70% yield. Then, treatment of 3 with excess BF3·OEt2 furnished
the corresponding syn-ladder-type APBD 5 in 80% yield. The
1H NMR spectrum of 5 is simple, exhibiting two singlets at 9.87
and 8.62 ppm for the pyrimidine protons (Hp) along with three
singlets at 8.52, 8.13, and 8.09 ppm and two doublets at 7.84
and 7.66 ppm for the carbazole protons (Hc). It shows only one
characteristic peak in the 19F NMR spectrum, a doublet at
O
and optoelectronic devices, such as photovoltaic cells,1−3 light-
emitting diodes,4−7 and field-effect transistors.8−10 Among the
classes of conjugated molecules, ladder-type π-conjugated
molecules with fully ring-fused structures are particularly
attractive because the flat and rigid π-conjugated skeletons
endow the molecules with desired properties such as intense
luminescence, good thermal stability, and high carrier
mobility.11−17 Recently, it has been demonstrated that the
incorporation of boron into organic conjugated frameworks
offers considerable promise for the development of new
functional materials with outstanding photophysical and
electronic properties.18−24 The boron atom serves as a conduit
for the π-conjugated skeleton and substantially decreases
energy of the lowest unoccupied molecular orbital (LUMO),
which is essential for the performance of organic electronics
with high electron affinities and mobilities. Despite recent
advances, examples of the incorporation boron atoms into
ladder-type π-conjugated molecules are rare.25−29
Among boron compounds, BODIPYs have received much
interest in research areas such as labeling reagents,30−32
fluorescent switches,33−35 chemosensors,36−38 light-harvesting
systems,39−41 and dye-sensitized solar cells42−44 because of
their advantageous photophysical properties. The great
potential has motivated the search for new π-conjugated
bidentate ligands to provide boron compounds with promising
electronic and optical properties.45,46 Recently, Piers and co-
wokrers reported a series of anilido−pyridine boron difluorides
Received: November 22, 2013
© XXXX American Chemical Society
A
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Note
Scheme 1. Synthesis of the Ladder-Type Ligands and APBDs
−131.6 ppm, thereby reflecting its highly symmetric structure.
The parent ion peak of 5 was observed at m/z 730.5 (calcd for
C44H48B2F4N4 [M]+: 730.4) in its MALDI-TOF mass
spectrum. The high-resolution ESI-TOF mass spectrum of 5
displays only an ion peak for the ligand at m/z 657.3908 (calcd
for C44H50N4Na: 657.3933), which may be ascribed to the
deborylation of 5 during the measurement. The same
phenomenon was also observed for other prepared APBDs. It
is worth noting that the coordination of ligand 3 with BF3·OEt2
is a stepwise process. The monochelated ladder-type APBD 4
was obtained in 65% yield by reducing the amount of BF3·OEt2
All of the products were fully characterized by NMR
spectroscopy (1H, 13C, and 19F) and mass spectrometry.
Single crystals of syn-laddered ligand 3 suitable for X-ray
diffraction analysis were obtained by slow diffusion of methanol
vapor into a toluene solution of 3. The obtained structure is
depicted in Figure 1. Obviously, the mean planes of the two
1
to 3.0 equiv and the reaction time to 1 h. The H NMR
spectrum of 4 exhibits an unsymmetric structure with two
singlets at 10.73 and 9.57 ppm for the pyrimidine protons (Hp)
and complicated signals (about 10 groups) for the carbazole
protons (Hc). The 19F NMR spectrum exhibits a singlet at
−131.1 ppm. The parent ion peak of 4 was observed at m/z
682.5 (calcd for C44H49BF2N4 [M]+: 682.4) in its MALDI-TOF
mass spectrum.
Figure 1. X-ray crystal structure of 3: (a) top view; (b) side view. The
thermal ellipsoids are shown at the 50% probability level. tert-Butyl
groups, solvent molecules, and H atoms have been omitted for clarity.
The anti-ladder-type APBDs were obtained with a procedure
similar to that for the syn ones by using 2,5-dibromopyrazine
instead of 4,6-dichloropyrimidine. Treatment of 2 with 2,5-
dibromopyrazine in the presence of Pd(PPh3)4 as a catalyst
furnished the anti-laddered ligand 6 in 95% yield. The single
and double chelation of 6 with BF3·OEt2 afforded the desired
anti-ladder-type APBDs 7 and 8 in yields of 68% and 85%,
respectively, by control of the reaction conditions (Scheme 1).
carbazole rings and the pyrimidine ring take a nearly coplanar
conformation, as clearly shown in the side view. The pyrimidine
bridge is held to the neighboring carbazoles with a dihedral
angle of 9.7°. This orientation allows 3 to coordinate with
boron effectively to form the conjugated ladder-type APBDs.
The crystal structure is consistent with the results from the
NMR spectra, both of which indicate a symmetrical structure.
B
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The UV/vis absorption spectra of the ladder-type complexes
4, 5, 7, and 8, along with those of ligands 3 and 6, were
measured in THF and are shown in Figure 2. The syn ligand 3
Information). Compared with the reported carbazole−
pyridine-based APBD monomer (λmax = 510 nm, Φf =
62%),47 the decreased emission efficiency of the syn-laddered
APBD can be attributed to the enhanced conjugation, which
reduces the HOMO−LUMO energy gap and consequently
accelerates the nonradiative decays according to the energy gap
law. In the case of the anti-APBD ladders (7 and 8), no
fluorescence at longer wavelength was observed at room
temperature, suggesting that the nonradiative decays dominate
the photophysical processes of the excited states. A comparative
study suggests more effective electronic delocalization in the
anti framework than in the syn one. The spectra data for all of
the compounds are collected in Table 1.
The electrochemical properties of the laddered APBDs and
ligands were studied by cyclic voltammetry. All of the
compounds displayed reversible redox waves in CH2Cl2 (see
the Supporting Information). The coordination of the BF2
groups slightly changes the oxidation potential but increases the
reduction potential obviously for the laddered APBDs. The
energies of the HOMOs and LUMOs, together with the
HOMO−LUMO energy gaps, were estimated from the redox
potentials, as shown in Table 1. The subtle differences of the
oxidation potentials among the laddered compounds indicate
that the incorporation of boron has a negligible influence on
the HOMO energy. Thus, the gradual decrease in the
HOMO−LUMO gap upon boron chelation can be attributed
to the enhanced conjugation, which decreases the LUMO
energy significantly. The HOMO−LUMO gaps estimated from
absorption spectra onset are consistent with the electro-
chemical results (Table 1).
To obtain a better understanding of the photophysical and
electronic properties of the ladder-type APBDs, theoretical
calculations were performed using the Gaussian 09 suite of
programs. The HOMO and LUMO diagrams are shown in
Figure 3. It is noteworthy that the electron density of the
HOMO is predominantly distributed along the carbazole unit,
exhibiting the character of a carbazole π system, while the
electron density of the LUMO is considerably delocalized over
the pyrimidine or pyrazine group. Thus, the locations of the
HOMO and LUMO depict a perpendicular arrangement that
outlines the ladder structure of the APBDs. The theoretical
values determined for the frontier orbital energies are in
approximate agreement with the experimental data (Table 1).
The energy gap follows the trend 8 (1.58 eV) < 5 (2.07 eV) < 7
(2.41 eV) < 4 (2.73 eV) < 6 (3.22 eV) < 3 (3.93 eV). The anti-
laddered APBDs exhibit lower HOMO−LUMO energy gaps
Figure 2. UV/vis absorption spectra of the syn- and anti-ladder-type
APBDs and the corresponding ligands in THF.
exhibits two well-resolved absorption bands with maxima at 300
and 410 nm. The complexation of boron causes a broadening
and a significant bathochromic shift of the absorption spectra.
The absorption maximum shifts from 410 nm for ligand 3 to
493 and 586 nm for the mononuclear complex 4 and the
dinuclear complex 5, respectively. Apparently, the color of the
solutions changes from yellow for 3 to red for 4 and dark-green
for 5, as can be observed by the naked eye. In the case of the
anti ladders, the absorption spectra of 7 and 8 also exhibit
substantial bathochromic shifts and broadening because of the
complexation with boron, but the extinction coefficients
decrease compared with those of the plain ligand 6.
Furthermore, the extent of the bathochromic shift is enhanced
compared with the corresponding syn ladders, indicative of a
more effective electronic delocalization through the anti-
laddered framework. The narrowing of the HOMO−LUMO
gaps (2.76, 2.25, and 1.90 eV for 3, 4, and 5 and 2.67, 2.13, 1.59
eV for 6, 7, and 8, respectively) was estimated from the
absorption spectra onsets.
No fluorescence from ligand 3 was observed with excitation
at the maximal absorption wavelength of 410 nm under
ambient conditions. However, the syn-laddered APBD 4
exhibits a broad emission band with maximum at 567 nm
(Φf = 18%). The emission maximum of 5 shifts to 650 nm,
reaching into the near-infrared spectral region with a relatively
lower quantum yield (Φf = 6%) (see the Supporting
a
Table 1. Spectral and Electrochemical Data of the Ligands and Ladder-Type APBDs
3
4
5
6
7
8
λabs (nm)
10−4ε (M−1 cm−1
λem (nm)
Φf
410
3.48
no
493
586
424
5.44
no
500
2.97
no
620
0.76
no
)
5.50
567
4.27
645
no
0.18
1.02
−1.13
−3.47 [−2.75]
−5.62 [−5.48]
2.15 (2.25) [2.73]
0.06
1.09
−0.92
−3.68 [−3.65]
−5.69 [−5.72]
2.01 (1.90) [2.07]
no
no
no
Eox (V)
0.99
0.90
0.92
1.06
Ered (V)
−1.16
−1.17
−0.98
−0.64
b
ELUMO (eV)
−3.44 [−1.54]
−5.59 [−5.47]
2.15 (2.76) [3.93]
−3.43 [−1.85]
−5.50 [−5.08]
2.07 (2.67) [3.22]
−3.62 [−3.00]
−5.52 [−5.41]
1.90 (2.13) [2.41]
−3.96 [−4.11]
−5.66 [−5.70]
1.70 (1.59) [1.58]
b
EHOMO (eV)
c
Egap (eV)
a
b
+
The values in square brackets are theoretical results. Calculated from the empirical following formulas: ELUMO = −(Ered − EFc/Fc + 4.80 eV);
c
EHOMO = −(Eox − EFc/Fc + 4.80 eV). The measured value of EFc/Fc is 0.20 V vs Ag/Ag+. Egap = ELUMO − EHOMO. The values in parentheses were
estimated from absorption spectra onsets.
+
+
C
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Note
Figure 3. Frontier molecular orbital diagrams for 3−8 calculated using DFT.
with argon and then charged with pinacolborane (0.8 mL, 5.0 mmol,
5.0 equiv), Et3N (1.49 mL), and 1,4-dioxane (4 mL). The mixture was
stirred at reflux for 3 h under argon. After removal of solvents under
vacuum, the crude product was purified by column chromatography
on silica gel (CH2Cl2/petroleum ether = 1/4) and recrystallized from a
mixture of dichloromethane and petroleum ether to afford 2 (345 mg,
than the corresponding syn ones, suggesting enhanced
conjugation in the anti series. This is consistent with the
trend observed by the UV−vis absorption spectroscopy. Time-
dependent DFT calculations were also performed to under-
stand the absorption properties. The contribution of the
molecular orbitals involved in the UV−vis transitions was
determined on the basis of their oscillator strengths (f).
According to the calculated results, the lower-energy bands in
the absorption spectra show a preferential correspondence with
the HOMO → LUMO and HOMO−1 → LUMO transitions.
Overall, the theoretical calculations fully support the electro-
chemical and photophysical properties of these novel laddered
APBDs.
In summary, we have accomplished the synthesis of a series
of syn- and anti-ladder-type APBDs by a Suzuki−Miyaura
coupling reaction and stepwise incorporation with boron. The
single-crystal X-ray diffraction analysis of 3 unambiguously
confirmed the formation of the ladder structure. The UV/vis
absorption and fluorescence spectra indicate that there exists
effective π-delocalization in the ladder-type APBDs. The
electrochemical experiments as well as the theoretical
calculations revealed that the energy of the lowest unoccupied
molecular orbital is substantially decreased upon boron
chelation, which is essential for the performance of organic
electronic devices with high electron affinities and mobilities,
reinforcing a potential application of the APBDs in the area of
organic electronics.
1
85%) as a white solid. H NMR (400 MHz, CDCl3): δ 8.96 (s, 1H),
8.22 (d, J = 2.0 Hz, 1H), 8.08 (d, J = 1.6 Hz, 1H), 7.89 (d, J = 2.0 Hz,
1H), 7.47 (dd, J = 8.5, 1.9 Hz, 1H), 7.40 (d, J = 8.5 Hz, 1H), 1.50−
1.41 (m, 30H).
General Procedure for the Ligand Synthesis by Suzuki−
Miyaura Coupling Reaction. Compound 2 (3.0 equiv), the
dichloro- or dibromo-substituted bridge (1.0 equiv), Pd(PPh3)4 (0.1
equiv), Cs2CO3 (2.0 equiv), and CsF (2.0 equiv) were added to a
Schlenk flask, which was purged with argon and then charged with
dried toluene and DMF (2/1 v/v). The resulting mixture was degassed
thoroughly through three freeze−pump−thaw cycles and then stirred
at 90 °C for 12 h under argon. The reaction was quenched with water,
and the mixture was extracted with CH2Cl2. The organic layer was
dried over anhydrous sodium sulfate. After removal of the solvent
under vacuum, the residue was purified by column chromatography on
silica gel to afford the desired product.
syn-Laddered Ligand 3. Ligand 3 was prepared by the Suzuki−
Miyaura coupling reaction of 2 (121.6 mg, 0.3 mmol, 3.0 equiv) with
4,6-dichloropyrimidine (14.9 mg, 0.1 mmol, 1.0 equiv) according to
the general procedure and purified by column chromatography on
silica gel (CH2Cl2/petroleum ether = 1/2) and recrystallization from
n-hexane/CH2Cl2 (1/4) to afford 3 as a yellow solid (44.4 mg, 70%
1
yield). H NMR (400 MHz, CDCl3): δ 11.06 (s, 2H), 9.51 (s, 1H),
8.60 (s, 1H), 8.33 (d, J = 1.3 Hz, 2H), 8.21 (d, J = 1.4 Hz, 2H), 8.16
(s, 2H), 7.60−7.52 (m, 4H), 1.58 (s, 18H), 1.49 (s, 19H). 13C NMR
(100 MHz, CDCl3): δ 164.9, 158.0, 142.7, 141.9, 138.6, 138.0, 125.7,
124.5, 122.5, 121.1, 120.6, 117.3, 116.5, 111.1, 110.9, 35.1, 32.3. MS
(MALDI-TOF) m/z: calcd for C44H50N4, 634.4 [M]+; found, 634.4.
HR-MS (ESI-TOF) m/z: calcd for C44H50N4Na, 657.3933 [M + Na]+;
found, 657.3929 [M + Na]+.
EXPERIMENTAL SECTION
■
General Information. Reagents were used without further
purification, unless otherwise noted. 1, 4-Dioxane, toluene, and
DMF were dried with sodium or CaH2 and distilled under a N2
1
atmosphere. H NMR (400 MHz), 13C NMR (100 MHz), and 19F
anti-Laddered Ligand 6. Ligand 6 was prepared by the Suzuki−
Miyaura coupling reaction of 2 (121.6 mg, 0.3 mmol, 3.0 equiv) with
2,5-dibromopyrazine (23.8 mg, 0.1 mmol, 1.0 equiv) according to the
general procedure and purified by column chromatography on silica
gel (CH2Cl2/petroleum ether = 1/2) and recrystallization from n-
hexane/CH2Cl2 (1/4) to afford 6 as a yellow solid (60.3 mg, 95%
NMR (376 MHz) spectra were obtained from a spectrometer with
tetramethylsilane as an internal standard. Mass spectra were measured
by MALDI-TOF or high-resolution ESI-TOF experiments. Absorption
and emission spectra were recorded in a conventional quartz cell (10
mm light path) on a standard, commercial spectrometer. Fluorescence
quantum yields were determined with excitation at 500 nm using zinc
tetraphenylporphyrin (Zn-TPP) as a standard. X-ray data were taken
1
yield). H NMR (400 MHz, CDCl3): δ 10.87 (s, 2H), 9.55 (s, 2H),
́
8.26 (s, 2H), 8.17 (d, J = 17.3 Hz, 4H), 7.61−7.42 (m, 4H), 1.60 (m,
36H). 13C NMR (100 MHz, CDCl3): δ 150.1, 142.6, 142.1, 140.1,
138.5, 137.7, 125.4, 124.4, 122.8, 120.2, 119.0, 117.0, 116.5, 110.8,
35.1, 32.3. MS (MALDI-TOF) m/z: calcd for C44H50N4, 634.4 [M]+;
found, 634.4. HR-MS (ESI-TOF) m/z: calcd for C44H50N4Na,
657.3933 [M + Na]+; found, 657.3925 [M + Na]+.
General Procedure for the Synthesis of Ladder-Type APBDs.
The laddered ligand (3 or 6) (1.0 equiv) and toluene were added to a
three-neck flask, and then triethylamine (3.0 or 10.0 equiv) was added
to the reaction mixture. After the mixture was stirred at room
temperature for 15 min, BF3·OEt2 (3.0 or 10.0 equiv) was added
dropwise. The reaction mixture was stirred at 80 °C for 1 or 3 h under
argon and then cooled to room temperature. The reaction was
quenched with water, and the mixture was extracted with CH2Cl2. The
organic layer was washed with water and dried over anhydrous sodium
sulfate. After removal of the solvent under vacuum, the residue was
on a diffractometer with Mo Kα radiation (λ = 0.71073 Å). The redox
potentials of the compounds were determined by cyclic voltammetry
using glassy carbon as the working electrode, platinum as the counter
electrode, and nonaqueous Ag/Ag+ as the reference electrode in the
presence of 0.1 M Bu4NPF6 as the supporting electrolyte. The working
electrode was polished with a 0.05 μm alumina paste and washed with
water and acetone by sonication before use. The electrolyte solution
was purged with argon for 20 min before measurement.
1-Bromo-3,6-di-tert-butyl-9H-carbazole (1). Compound 1 was
synthesized according to the reported procedure.48 1H NMR (400
MHz, CDCl3): δ 8.06 (d, J = 1.6 Hz, 1H), 8.05 (s, 1H), 8.03 (d, J = 1.4
Hz, 1H), 7.61 (d, J = 1.5 Hz, 1H), 7.52 (dd, J = 8.6, 1.8 Hz, 1H), 7.40
(d, J = 8.5 Hz, 1H), 1.47 (d, J = 3.6 Hz, 18H).
1-Boryl-3,6-di-tert-butyl-9H-carbazole (2). Compound 1
(358.0 mg, 1.0 mmol, 1.0 equiv) and Pd(PPh3)2Cl2 (70.2 mg, 0.1
mmol, 0.1 equiv) were added to a Schlenk flask, which was purged
D
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The Journal of Organic Chemistry
Note
purified by column chromatography on silica gel to afford the desired
product.
crystallographic data for 3 have been deposited with the
Cambridge Crystallographic Data Centre as CCDC 952228.
syn-Ladder-Type APBD 4. APBD 4 was prepared by the reaction of
3 (63.5 mg, 0.1 mmol, 1.0 equiv), triethylamine (43 μL, 0.3 mmol, 3.0
equiv), and BF3·OEt2 (38 μL, 0.3 mmol, 3.0 equiv), upon stirring at 80
°C for 1 h according to the general procedure and purified by column
chromatography on silica gel (CH2Cl2/petroleum ether = 1/3) and
recrystallized from n-hexane/CH2Cl2 (1/4) to afford ladder-type
APBD 4 as an orange solid (44.4 mg, 65% yield). 1H NMR (400 MHz,
CDCl3): δ 10.73 (s, 1H), 9.57 (s, 1H), 8.62 (s, 1H), 8.34 (d, J = 11.7
Hz, 2H), 8.12 (s, 3H), 7.89 (s, 1H), 7.80 (d, J = 8.4 Hz, 1H), 7.62−
7.49 (m, 3H), 1.65−1.40 (m, 36H). 13C NMR (100 MHz, CDCl3): δ
166.0, 153.4, 138.4, 125.4, 125.2, 123.4, 121.9, 118.1, 116.7, 113.4,
111.0, 108.0, 35.2, 35.0, 32.5. 19F NMR (376 MHz, CDCl3): δ −133.1.
MS (MALDI-TOF) m/z: calcd for C44H49BF2N4, 682.4 [M]+; found,
682.5 [M]+. HR-MS (ESI-TOF) m/z: calcd for C44H50N4Na,
657.3933 [M − BF2 + Na]+; found, 657.3948.
AUTHOR INFORMATION
Corresponding Authors
*E-mail: yili@mail.ipc.ac.cn.
*E-mail: chenjp@mail.ipc.ac.cn.
*E-mail: gqyang@iccas.ac.cn.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Financial support by the National Natural Science Foundation
of China (Grants 21172229 and 21233011) and the National
Basic Research Program of China (Grants 2013CB834700,
2010CB934500, and 2013CB834505) is gratefully acknowl-
edged. J.C. thanks the Beijing Nova Program for financial
support.
syn-Ladder-Type APBD 5. APBD 5 was prepared by the reaction of
3 (63.5 mg, 0.1 mmol, 1.0 equiv), triethylamine (139 μL, 1.0 mmol,
10.0 equiv), and BF3·OEt2 (124 μL, 1.0 mmol, 10.0 equiv) upon
stirring at 80 °C for 3 h according to the general procedure and
purified by column chromatography on silica gel (CH2Cl2/petroleum
ether = 1/3) and recrystallized from n-hexane/CH2Cl2 (1/4) to afford
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ladder-type APBD 5 as a purple-black solid (58.4 mg, yield 80%). H
NMR (400 MHz, CDCl3): δ 9.87 (s, 1H), 8.62 (s, 1H), 8.52 (s, 2H),
8.13 (s, 2H), 8.09 (s, 2H), 7.84 (d, J = 8.4 Hz, 2H), 7.66 (d, J = 9.2
Hz, 2H), 1.59 (s, 19H), 1.48 (s, 18H). 13C NMR for 5 was unreadable
because of low solubility. 19F NMR (376 MHz, CDCl3): δ −131.6. MS
(MALDI-TOF) m/z: calcd for C44H48B2F4N4, 730.4 [M]+; found,
730.5 [M]+. HR-MS (ESI-TOF) m/z: calcd for C44H50N4Na,
657.3933 [M − 2(BF2) + Na]+; found, 657.3908.
anti-Ladder-Type APBD 7. APBD 7 was prepared by the reaction of
6 (63.5 mg, 0.1 mmol, 1.0 equiv), triethylamine (43 μL, 0.3 mmol, 3.0
equiv), and BF3·OEt2 (38 μL, 0.3 mmol, 3.0 equiv) upon stirring at 80
°C for 1 h according to the general procedure and purified by column
chromatography on silica gel (CH2Cl2/petroleum ether = 1/3) and
recrystallized from n-hexane/CH2Cl2 (1/4) to afford ladder-type
1
APBD 7 as a red solid (46.4 mg, yield 68%). H NMR (400 MHz,
(10) Murphy, A. R.; Frec
(11) Jacob, J.; Sax, S.; Piok, T.; List, E. J. W.; Grimsdale, A. C.;
́
het, J. M. J. Chem. Rev. 2007, 107, 1066.
CDCl3): δ 10.61 (s, 1H), 10.00 (s, 1H), 9.42 (s, 1H), 8.40 (s, 1H),
8.33 (s, 1H), 8.22 (s, 1H), 8.16 (s, 2H), 8.10 (s, 1H), 7.86 (d, J = 8.4
Hz, 1H), 7.65 (d, J = 8.6 Hz, 1H), 7.58 (d, J = 8.4 Hz, 1H), 7.50 (d, J
= 8.5 Hz, 1H), 1.53 (s, 36H). 13C NMR (100 MHz, CDCl3): δ 152.4,
144.1, 143.3, 142.8, 138.4, 137.1, 131.2, 125.9, 125.3, 124.8, 124.4,
123.5, 122.5, 120.8, 120.2, 117.5, 117.0, 116.6, 115.2, 113.5, 110.9,
108.5, 47.3, 35.4, 35.3, 32.3. 19F NMR (376 MHz, CDCl3): δ −133.1.
MS (MALDI-TOF) m/z: calcd for C44H49BF2N4, 682.4 [M]+; found,
682.4. HR-MS (ESI-TOF) m/z: calcd for C44H50N4Na, 657.3933 [M
− BF2 + Na]+; found, 657.3981.
Mullen, K. J. Am. Chem. Soc. 2004, 126, 6987.
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anti-Ladder-Type APBD 8. APBD 8 was prepared by the reaction of
3 (63.5 mg, 0.1 mmol, 1.0 equiv), triethylamine (139 μL, 1.0 mmol,
10.0 equiv), and BF3·OEt2 (124 μL, 1.0 mmol, 10.0 equiv) with
stirring at 80 °C for 3 h according to the general procedure and
purified by column chromatography on silica gel (CH2Cl2/petroleum
ether = 1/3) and recrystallized from n-hexane/CH2Cl2 to afford anti-
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Akcelrud, L.; Mullen, K.; Friend, R. H.; Wegner, G. Adv. Funct. Mater.
̈
2007, 17, 3231.
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1
ladder-type APBD 8 as a purple-black solid (62.1 mg, yield 85%). H
NMR (400 MHz, CDCl3): δ 9.80 (s, 2H), 8.47 (s, 2H), 8.16 (s, 2H),
8.09 (s, 2H), 7.84 (d, J = 8.6 Hz, 2H), 7.67 (d, J = 8.5 Hz, 2H), 1.60−
1.47 (m, 36H). 13C NMR for 8 was unreadable because of low
solubility. 19F NMR (376 MHz, CDCl3): δ −129.9. MS (MALDI-
TOF) m/z: calcd for C44H48B2F4N4, 730.4 [M]+; found, 730.5. HR-
MS (ESI-TOF) m/z: calcd for C44H50N4K, 673.3673 [M − 2(BF2) +
K]+; found, 673.3607.
9130.
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̈
ASSOCIATED CONTENT
■
S
* Supporting Information
NMR and MS spectra, fluorescence spectra, cyclic voltammetry,
atom coordinates and absolute energies from DFT calculations,
and the CIF file and crystal data for 3. This material is available
free of charge via the Internet at http://pubs.acs.org. The
S.; Yamaguchi, S. Organometallics 2011, 30, 3870.
E
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